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Many people take ride quality for granted when they ride in an elevator. A smooth and responsive ride requires precise adjustment from all system components such as the controller, variable frequency drive, and brakes.

The variable frequency drive or VFD, can be a powerful adjustment tool for mechanics when properly applied. This article will specifically focus on software functions available in an elevator VFD for two main elevator adjustments; rollback and increased speed control response.

Elevator Car Rollback

Rollback can occur for a brief moment at the beginning of the ride when the brake lifts, a speed command has not yet been initiated, and the VFD has not built up enough holding torque to prevent the car from moving in the direction of weighting. This may be felt as a bump by passengers in the car during takeoff. Rollback is more noticeable on permanent magnet gearless motors than induction geared motors due to lower starting friction of gearless machines. Rollback can be diagnosed visually if the elevator controller is located in the machine room along with the motor. However, in machine room-less (MRL) applications, diagnosing rollback may be more difficult since the motor is out of sight. Inverter scoping software can aid in identifying and adjusting for rollback. Figure 1 below provides a visual representation of rollback using a four channel scope trace showing command speed (red), actual motor speed (blue), motor torque (green), and motor position (yellow).

Figure 1: Command speed (red), motor speed (blue), motor torque (green), motor position (yellow).

The motor position (yellow) starts to deviate from zero before the speed command is given, indicating the brake has lifted and not enough holding torque (green) is present to hold the car at zero speed. There are several torque bumps present in response to motor movement when the brake was lifted, which can cause a bump to be felt by passengers on takeoff.               

Adjusting for Rollback

There are several ways to adjust for rollback. For example, brake and speed command timing may be adjusted such that as the brake is lifting, the car begins to move. While this may reduce the affects of rollback, it doesn’t address the root cause and still doesn’t provide a smooth takeoff for passengers. Luckily, depending on VFD manufacture, software can be used to eliminate rollback.

Most elevator drive manufacturers have some method of providing a torque command, while under brake or immediately after the brake picks to eliminate rollback. The following paragraphs describe different methods of providing holding torque to prevent rollback.

Feedback Control Loop to Reduce Rollback

One method involves using a feedback control loop. A feedback control loop consisting of both a proportional and integral coefficient can be used to provide the motor with adequate holding torque, thus preventing rollback. When this method is used, movement of the car is necessary to make the function work properly. This may seem counterintuitive at first, but the movement is very small. This movement cannot be seen to the naked eye (as the sheave rotating) or felt by passengers riding in the car. Figure 2 below shows a scope trace of torque buildup in response to movement.


Figure 2: Properly adjusted pre-torque settings, without any rollback on scope trace. Command speed (red), motor speed (blue), motor torque (green), motor position (yellow).

Based on the amount of movement detected from the motor encoder, the drive will quickly ramp torque (green) to hold the motor at zero speed. This is done by adjusting the integral coefficient of the feedback control loop or ‘gain’. The integral response accumulates error, in this case, non-zero speed, over time. Higher integral gain values will ramp the torque faster to accommodate for the non-zero speed error until a steady state situation is reached (zero speed). All of this happens very quickly, within 0.3 – 0.5sec, meaning passengers do not feel anything. This method of providing torque when the brake lifts works very well for most elevator applications. However, its basic functionality, a PI feedback control loop, relies on error (motor movement) to function.

Using a Load Weigher to Reduce Rollback

Another method of providing torque involves using a load weigher. A load weighing device uses sensors to detect the amount of load in the car, and can provide a precise holding torque response based on different loading conditions. Depending on the type of load weigher used, it can connect directly to the VFD and transmit a torque command via an analog signal or it can be connected to the controller where further filtering can be applied and then a resulting torque command can be sent to the drive via serial communication.

Increased Speed Control Response

For most elevator applications, the standard proportional, integral, and derivative (PID) gains in the feedback control loop in a VFD provide adequate speed control response. However, for some high profile elevator applications (high end office buildings, apartment complexes, etc.), additional elevator ride quality adjustment tuning may be necessary to achieve the desired result, such as aggressive floor to floor times.

A traditional PID feedback control loop relies on feedback from the motor encoder to make speed control adjustments based on the difference between command speed and actual motor speed from the encoder. This difference is called error. The VFD’s response to this error is adjusted via proportional and integral speed control gains. While this method of speed control works well, it relies on the feedback from the motor encoder for speed control. For some high performance applications, traditional PI control may not provide the desired speed control response. For these types of applications, a more sophisticated speed control method can be used.

Feed Forward Torque Control (FFTC) can be used to provide added speed control response. FFTC reduces the dependence on speed feedback from the motor encoder by predicting what the system will do, based on the system inertia, and providing the required torque command based on that prediction. Figure 3 below provides block diagram of how FFTC works.


Figure 3: Feed forward torque control block diagram.

After the system inertia has been learned by the VFD, FFTC can be activated. By modeling the motor data, ysp, the system response, uff, with the system inertia, a prediction of the response can be made. A pre-correction is made before the motor encoder feedback is received, reducing the amount of error. This method of speed control provides a more accurate response with less reliance on the proportional and integral gains.

To show how effective FFTC can be, a detuned motor was set up in a controlled R&D lab setting, with low speed control gains and FFTC turned off. No additional adjustments were made to the motor. Figure 4 below shows a scope trace of the command speed (red), actual motor speed (blue), motor current (yellow), and motor torque (green) of a simulated elevator run.


Figure 4: Command speed (red), motor speed (blue), motor current (yellow), motor torque (green).

Significant amounts of undershoot and overshoot are present on both the acceleration and deceleration portions of the profile (circled). Additionally, these areas of undershoot and overshoot correspond to large torque bumps that can negatively impact ride quality.

Next, to show the impact of using FFTC, the system inertia was learned and FFTC was activated. The same run was performed and scoped below in Figure 5.


Figure 5: Command speed (red), motor speed (blue), motor current (yellow), motor torque (green).

Activating FFTC drastically reduces undershoot and overshoot that were present in the acceleration and deceleration portions of the profile. Also, the magnitude of the torque bumps are much smaller, with smoother torque transitions providing a much more comfortable ride for passengers. While this is an exaggerated case and done under lab conditions, it shows the basic principle and impact FFTC can have on elevator speed control.

Adjustments such as a low pass filter can be set to further improve ride quality. When the speed profile is generated externally by the controller, increasing the sample time of the low pass filter can help reduce any unwanted affects from discontinuous inflection points on the speed profile generated by the controller. Additionally, FFTC also features a gain value which can be used to strengthen or weaken the response of the feed forward torque command.

In general, activating FFTC makes the elevator system more responsive. The speed gains will have less effect and adequate speed control can be maintained over a wider range of gains. FFTC works well in applications featuring aggressive speed control profiles and applications exhibiting high starting friction, such as induction geared machines.

Conclusion

The VFD is a powerful elevator ride quality adjustment tool that can provide solutions to two common elevator ride quality problems. Rollback can be eliminated using a PI control loop in the VFD. Additional tools such as load weighers can also be used to eliminate rollback. For highly dynamic elevator applications, FFTC can provide added response to achieve desired ride quality. Additional adjustments such as low pass filters and gains can fine tune the ride for the best possible passenger experience.

Interested in KEB’s automation technology? Contact a KEB engineer today to discuss your application.

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What are the most important factors when considering VFD Technology for Running High Speed Gearless Turbo Blowers? Here at KEB, we like difficult applications because this is where we excel and where our technology and application engineering differentiate us from our competitors.  These applications could require multiple axes of coordinated motion control or be located in challenging environmental conditions.  Operating a high speed motor/generator is one example of a difficult drive application.

KEB has many years of experience running High Speed Turbo Blowers

One high speed application that KEB has extensive experience in is running gearless turbo blowers.  This post gives an overview of KEB’s VFD offering and reasons why KEB is the partner of choice for turbo blower manufacturers worldwide.

High Speed VFDs

First off, what do we mean by “High Speed”?  The best definition is the one that is used by the US Department of Commerce. Outlined in regulation ECCN 3A225, drives operating 600Hz and above are considered high speed.

High speed applications are very demanding applications for VFDs.  They require extremely stable motor control algorithms with very fast control loops.  I use the analogy of skateboarding.  I am not very good at skateboarding, but I can stand still on one.  I can go forward slowly and still remain in control.  I can even correct from some small obstacles like a crack in the road or rough pavement.  This is comparable to normal low speed VFD applications where the drive can control the motor and correct from dynamic load requirements.

High speed applications allow less room for error

However, if you were to put me on a steep hill and I were to go very fast, the end result would not be good.  I would likely begin to lose control, then try to correct myself, overcorrect, and crash.  This is like a high speed motor application – there is less room for error on the control stability.  Any small load transient acts like the crack in the road or the rough pavement and can cause the control system to become unstable.

A company does not develop high speed motor control algorithms overnight.  KEB’s high speed drive products represent decades of motor control engineering. And that is evident in the over 100,000 high speed applications that are running in the field across a wide variety of power ranges and motor types. 

Dedicated High Speed Power Stages

The VFD power stages used in high speed applications are also unique, especially at high power (200Hp+).  The IGBTs must be capable of switching at a very high frequency – usually 8kHz or 16kHz.  The higher switching frequency causes more heating and the power stages must be designed specifically for that use. 

Air cooling these large IGBTs with high frequency can be challenging if not impossible.  So KEB also offers liquid-cooled drives which are particularly effective at cooling the large high speed VFDs.

KEB Liquid Cooled drives offer many advantages in High Speed motor applications
3C3 Protection for Corrosive Gases

Some high-speed blower applications in the wastewater industry are exposed to corrosive gases.  This is particularly true for high humidity environments where gases like chlorine, ammonia and hydrogen sulfide can corrode the drive’s components and connections.  Ultimately, this can lead to complete drive failure.  For these applications, KEB has developed a special protective board coating to address these conditions.  Specifically, this is designed to IEC/EN 60721-3-3 class 3C2.

Commercial Drives vs. R&D Drives

An important differentiator in this application is KEB’s large installed base and the fact that the product is part of our standard F5 and F6 product lines.  Some high speed drives being used are not really commercial products.  They are more like lab or R&D projects.  These have no UL certification, no documentation, etc.  KEB’s high speed drives are all UL listed, with up to date documentation which makes the final blower product easier to install and support.

Filter Technology

A critical part of KEB’s drive offering is our compliment filter technology.  KEB offers a variety of different filters that include Harmonic Filters, EMI filters, and Sinewave filters.  Harmonic filters can be used in Blower applications if IEEE 519 requirements need to be met. 

KEB Harmonic Filters reduce Power Distortion

Sinewave filters can be very advantageous to the motor-drive combination because they deliver a near perfect sinusouid waveform to the motor which reduces motor heating and ultimately allows the motor to output more usable power.

KEB Sine-wave filters provide a near-perfect waveform for High Speed motors
Conclusion

Because KEB has engineered both the filter and drive technology, we have become an important solution partner instead of a component supplier.  This is best shown by our ability to run powerful control simulations that approximate the performance of the filter VFD motor.  These simulations can be run very quickly compared to months of iterative testing.

Tap into KEB’s expertise – Contact an Engineer today

Do you have a high speed turbo or compressor application to discuss?  Speak with a KEB application engineer today to discuss.

Interested in KEB’s automation technology? Contact a KEB engineer today to discuss your application.

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KEB America by Carlton Stripe - 3w ago

This is how to quickly and effectively start-up an asynchronous induction motor using our F5 drive. Utilizing KEB’s programming software COMBIVIS 6, we can break down the programming process into 10 simple steps.

Specifically, we will be highlighting a KEB F5 startup in closed-loop control with encoder feedback.  The general process will be similar for other motors and control types.

What do I need to Get Started?

Closed-loop control with encoder feedback is a VFD control method that utilizes measured speed feedback through an encoder device.

In general, there are five main components that will be required for a KEB F5 startup using your particular motor. They are:

  1. Power Source (F5 has AC 1-phase, AC 3-phase, and DC input options)
  2. F5 Drive
  3. 3-phase AC motor (Either induction or PM synchronous)
  4. Encoder feedback system
  5. COMBIVIS 6 programming software to configure VFD

Once we connect our power and devices in their respective manner, we can startup COMBIVIS 6 and soon begin programming.

Before We Begin Connect the KEB F5 Drive to COMBIVIS 6 Software

One option to scan for a device is on the start page of COMBIVIS 6
You can also click the “Scan for Device” Icon after opening a new project in COMBIVIS 6

Before we can start programming, we first need to connect our drive to COMBIVIS 6 using the KEB USB-to-serial converter. We can then perform a device scan to locate the F5 drive.

Click the Start Search button to find the KEB F5 Drive

Once the F5 has been found, we can add the selected device to the COMBIVIS 6 project.

Once the F5 VFD is found, add the device to your project

Once added to the project, we can see all of the F5 drive parameters inside the “Device Parameters” tab.

All parameter groups are available for programming and monitoring

Now that all of our components are wired up and connected, we can dive into our 10 startup steps.

The 10 Steps to Starting a Motor

Unlike the S6 drive startup, the F5 drive does not have integrated programming wizards and programming is strictly parameter-based. Therefore, we are going to create a startup parameter list to show how to quickly and easily program and startup the drive. Just for reference, the parameter list we are going to create is in accordance with the F5 Application Manual, which is available to customers at no charge. Please visit www.keb.de/my-account/registration to register.

I opened a blank parameter list and made visible only a few columns that we will need for our programming.

Blank parameter list showing useful data columns for this KEB F5 startup

The “Offline value” column represents the desired value we are writing in our program and the “Online value” column displays the active parameter value inside a connected KEB drive.

Prior to starting Step 1, we must ensure that the F5 drive is disabled or is in a “noP” state. Programming the F5 drive while the drive is enabled will cause erroneous drive behavior.

Ensure F5 drive is disabled before proceeding Step 1 – Control Type and Speed
Set control type and speed range

Starting with Step 1, we will set our Ud.02 control type to a value of “4: F5-M / 4000 rpm”. This sets the drive for operation of an asynchronous induction motor with a maximum attainable reference speed of 4000 RPM.

Step 2 – Enter Factory Settings
Load factory-default parameter settings

Step 2 of the parameter list sets the parameters inside the drive back to factory defaults using parameter Fr.01. This ensures we are starting our parameterization from scratch.

Step 3 – Configure Speed Control
Program for closed-loop control

Step 3 has us setting the drive into closed-loop control with encoder feedback.

Step 4 – Set Feedback Source
Setting feedback source to “Encoder 1”

In Step 4 we set the feedback source as encoder 1.

Step 5 – Set Encoder PPR Value
Set incremental encoder PPR

For our startup, we are using an incremental encoder, so we need to set the pulses per revolution, or PPR, in parameter Ec.01.

Step 6 – Enter Motor Rated Data
Enter motor rated data

For Step 6, we need to enter our motor rated data which is typically obtained from either the physical motor nameplate or a motor specification sheet.

We need the rated current, rated speed, rated voltage, rated power, rated power factor, and rated frequency of the induction motor. The resistance and inductance values found in parameters dr.06 – dr.10 will be computed automatically during the motor identification in Step 9.

Step 7 – Modify More Parameters
Optimize closed-loop operation through these parameters

For Step 7, we are going to modify a few parameters that are integral for successful operation in closed-loop control. These parameters turn on current decoupling, allow for motor model activation, and set proper flux control. These parameters are assigned in accordance with the F5 Application Manual.

Step 8 – Set Maximum Command Speed
Set desired maximum speed

In Step 8, we will set our maximum command speed for this startup.

Now that we have completed Step 8, we have completed our programming and we are now ready to download our parameter list into the F5 drive.

Download parameter list to F5 device

We can download the parameter list into the connected F5 drive by going to the green down arrow in the toolbar, which reads “download list to device”. Click “Yes”, to download. The list will download into the drive. The parameter download process then begins and writes the “Offline value” column into the “Online value” column.

Step 9 – Motor Identification
Motor Identification Online Wizard

Now that the drive has been programmed, we are able to move to Step 9, which is our motor identification. We can access the motor identification by first navigating to the drive tab, then going into the “Online Wizards”, and finally selecting “Motor ident.”

In box [1] there are no required changes since the drive has already been programmed and adjusted via the parameter list download. In box [2] we must confirm the rated nameplate data of our particular motor. Moving to box [3], we must first click the drop-down arrow next to “Start Identification.”

Motor Identification is possible WITH or WITHOUT motor rotation
Caution:

Selecting the “auto ident with move” option will cause the motor shaft to rotate. This identification mode should only be utilized under no-load conditions. If your motor is loaded or coupled to any other mechanical components, it is imperative to use “auto ident without move” for safe and successful motor identification.

After selecting “auto ident with move” in the case of this startup, you will be prompted to confirm the motor rated data once again. After that, another popup will appear asking to confirm the actual speed value source as encoder 1 – we will click OK.

Confirm speed source as encoder channel 1

During the identification process, the motor may rotate and also different audible noises of varying frequency may be heard which is normal during the identification process. The identification process may take anywhere from 30 seconds to a few minutes depending on the system. We will click “OK” to start the identification.

Set the ST / control release to begin the motor identification

Now we’ll set the ST / control release and begin the identification.

Open ST to complete the operation after the motor identification process is completed

Motor identification completed successfully

Step 10 – Test the Motor

Once the motor identification is complete, we can look back at the parameter list and see the inductance and resistance values have been modified real-time in the F5 drive due to the motor identification.

Results of motor identification are shown by inductance and resistance values

We are now ready to test our motor. For Step 10, we will use a potentiometer connected to an analog input which will allow us to adjust the speed control of the drive for this test. A COMBIVIS scope trace showing encoder speed and inverter status is shown below.

COMBIVIS scope trace of motor test
F5 Startup Conclusion

You have now quickly and effectively started a motor with a KEB F5 Drive.

You may have noticed that there are approximately 20 parameter groups within an F5 drive, many of which were skipped over or not used during this startup. There are many other important parameters that you would visit to complete the commissioning of your drive and motor for successful integration into your industrial machine.

If you are interested in visiting with KEB sales or engineering regarding your new application, please contact us using the form below.

Interested in KEB’s automation technology? Contact a KEB engineer today to discuss your application.

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When choosing a drive controller for highly automated, safety-oriented, process plant and machines, a number of factors should be considered, including functional safety, real time communications, ease of integration, feedback control and stability of the operating environment.

Minimizing production downtime is critical, as well as ensuring the safety and energy efficiency of machines and processes.

In applications such as material handling, textiles, woodworking, plastics, food and beverage processing, packaging, robotics and machine tools, processes are typically high speed with production plant, equipment and machines operating at high speeds, high reliability and in a stable operating environment. Minimizing production downtime is critical, as well as ensuring the safety and energy efficiency of machines and processes.

When selecting drive controllers for high speed, highly automated, safety-oriented applications, a number of important factors should be considered:1

#1 – Functional Safety

Machine and process safety is a major consideration when choosing a drive controller for your system. If you are designing a new production process or machine, it is important to consider the cost of safety. For example, could you purchase drive controllers with integrated functional safety? If so, this is likely to reduce the cost of installing separate protective devices, as well as their associated cabling and installation costs.

With drive-based safety, the safety functions are shifted into the drive platform. Some suppliers only provide drives with basic safety functions such as STO (Safe Torque Off). Other suppliers go much further providing modular, scalable functional safety from the basic STO to higher level encoder-based safety functions such as Safe Limited Speed, Safe Maximum Speed, Safe Speed Range, Safe Operating Stop, Safe Direction and Safe Emergency Limit. It is also extremely helpful and cost effective if the supplier provides its own software that enables faster parameter set up, configuration, analysis and parameterisation of key safety indicators and functions.

Choosing a drive controller like the one inside a KEB S6 offers robust Functional Safety Features

In safety-oriented drive applications, it is important to adhere to the relevant safety standards. Some key questions may need to be asked here, including whether the safety functions of the drive can be used up to IEC 62061-SIL3 levels in accordance with IEC 61508? Or if the functional safety is controlled via FSoE (Fail Safe over EtherCAT)? FSoE will help to ensure interaction of the drive controllers with safety PLCs and safety I/Os. It may be possible to download encrypted data packets through machine controllers.

Full system safety solutions

FSoE allows all available safety functions to be controlled and secure measurement values (speed, position, etc.) and the switching state of the secure I/Os to be transmitted serially to the safety PLC. Limit values of all safety functions relevant to machine safety can be adapted to the application at any time via FSoE. The result is tremendous flexibility and a significant saving in controls and wiring.

#2 – Real-Time Communications

If machines or production processes are high speed, choosing a drive controller that provides real-time Ethernet-based communications interfaces is critical. These Ethernet-based interfaces typically include ETHERCAT, VARAN, PROFINET, POWERLINK and Ethernet/IP, allowing optimal motor control and communication with higher level controllers. It is important that these real-time Ethernet-based interfaces are built-in (i.e. fully integrated) to the drives and not simply provided as an add-on module, as these add-ons can create unwanted latency in networks. It is also worth checking whether other diagnostic and/or display interfaces are provided as standard with the drive, such as RS 232, RS 485 and CAN interfaces.

Drives that speaks multiple real-time communication languages can be very valuable to machine builders

What motor types will the drive need to control? Does the drive support specific motor types, just some, or all major technologies? Motors are available in a wide variety of designs, including synchronous, asynchronous, permanent magnet, synchronous reluctance, linear, high-torque and high speed motors. It is therefore important to consider which motor types your drive will need to support, including possible future requirements too. Some drives even provide built-in motor temperature monitoring and integrated brake transistor and brake control.

#3 – Ease of Integration

How easily the drive controllers are able to integrate with other control systems is also important. Part of this is ensuring that the drives provide the necessary real-time Ethernet-based communications interfaces. But it also means checking whether the supplier can provide a wide range of supporting control and automation products such as integrated HMIs, set up, analysis and configuration software, as well as drives accessories to ensure a stable operating environment for the drives, including EMC filters, harmonic filters, output chokes and high performance ferrite cores (see point 5 below.

Drive accessories like harmonic filters are often necessary in certain applications

The number of software packages should be kept to a minimum in order to minimize the cost of user software licenses, so look for a supplier that offers a comprehensive all-in-one software package for drives set up, configuration, functional safety and applications development, without ongoing/annual licenses or initial set up costs.

#4 – Feedback Control

In addition, you may need to consider whether the drive needs to support encoder feedback. Some suppliers now offer drives with two-channel multi-encoder interfaces that allows control of all encoder types such as Resolver, TTL, HTL, SinCos, SSi, EnDAT, Hiperface and BiSS.

Choosing a drive controller often requires support for encoder feedback
#5 – Stable Operating Environment

In many industrial environments, ensuring the stability of drive controllers is sometimes overlooked. However, an EMC-compliant assembly with efficient control cabinet and suppression system is the basis for safe operation of machines and equipment. When choosing a drive controller platform, it is therefore prudent to check what range of accessories the drives supplier can offer. While these accessories can be sourced from a Third Party supplier, it is better to deal with a single supplier that can provide everything, optimized to suit their own specific drives.

EMI can effect the stability of your VFD application Considering Drive Accessories

Check whether you require any of the following drives accessories:

Mains EMC filters – these reduce the cable-fed emission to the required limits of IEC 61800-3-C1/C2. Other variants may offer low leakage currents or the operation of special mains networks.

Mains chokes – reduce the input peak current draw and the mains distortion. By smoothing the input current draw, the lifetime of the drive is enhanced, particularly at constant high utilisation.

Output chokes and filters – these reduce the voltage and current stress of the motor winding.

Combi-filters (EMC/ Output choke) – these space-saving combinations consistently adapt and optimise the drive controller.

Sine-wave filters – protect the motor winding from voltage peaks and allow the use of long motor cables.

Harmonic filters – reduce the low frequency mains distortion on rectifier supplied devices. These harmonic filters allow easy integration to a switchgear layout.

Sine-wave EMC filters – allow operation of motors with long motor cables even without screening.

High performance ferrite cores – these reduce the values of du/dt’s also in the frequency range of the bearing currents.

Interested in KEB’s automation technology? Contact a KEB engineer today to discuss your application.

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The post 5 Factors to Consider When Choosing a Drive Controller for Highly Automated Machines appeared first on KEB America.

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Jonathan talks about the challenges of VFDs at High Altitudes

“My electrical enclosure and VFD will be installed at a high elevation – what precautions do I need to take?”  This is a question that customers ask from time to time.  Any VFD-operated equipment such as pumps, HVAC fans, chairlifts, and satellites that is installed in mountainous areas is affected by this.

There are two main challenges when operating VFDs at high altitudes – The reduced cooling capacity and creepage and clearance distances.  This post discusses the main considerations and options when using drives at high altitudes.

Challenge 1 – Thinner air and reduced cooling capability

Being from Minnesota, I have jokingly been called a “lowlander” by friends that live in Colorado.  My body reminds me of it when I go to the mountains and do any strenuous activity like hiking or skiing.  I feel the effects of the “thin air”.  At high altitudes there is less air pressure and less molecules in a given volume of air.

Air cooling is less effective at high altitudes

The lower air pressure has implications when it comes to cooling electronics.  During normal operation, the drive’s IGBTs will create heat as they turn on and off.  Most commercial VFDs use a fan to force air across a finned heatsink where the IGBTs are seated.   With less air pressure (molecules/volume of air) the cooling capacity of the surrounding air is decreased.

Optimize the Drive Operation

An engineer has several options to combat this.  First, they can optimize the drive operation in a way that reduces IGBT heating.  This could mean lowering the switching frequency of the IGBTs.  Or, possibly operating the motor intermittently or reducing peak loading. 

Derate the Drive

The altitude derate for drives typically takes the form of reduced amps output. Check with your specific VFD manufacturer, but most drives have a derate that looks similar to this:

The second common option is to derate the drive.  In other words, operate the drive below its normal ratings.  Adjusting operating parameters and derating the drive are the most commonly used options because they require no additional components or investments.

Sample drive derate due to elevation

 All listed drive ratings such as rated current and peak current are applicable up to a certain elevation like 1000m.  Above 1000m, there is a linear derate applied, in this case 1% per 100m.  Often times there is a “maximum altitude” listed that should not be exceeded (See Challenge 2 below).

Add Air Conditioning

Another option to offset the reduced cooling capacity would be to add an air conditioning unit in the enclosure that has the ability to sufficiently regulate the enclosure cabinet at the specified altitude.  This adds cost to the system but could be more cost effective instead of upsizing the drive to the next frame size.

Choose Liquid Cooling

A final option is to not rely on air as the cooling medium.  It might be possible to use a liquid cooled VFD instead.  In this scenario, a fluid like water or glycol is cycled through the drives heatsink.  It should be noted that the pump and radiator will still need to be sized to handle the required heat dissipation at the target elevation.

F5 VFD with a liquid cooling option
Challenge 2 – Creepage and Clearance distances

The second challenge at high elevation is due to what’s called creepage and clearance distances.  During the design phase of the PCB, the conductors are separated from each other to ensure there is no arcing between the traces.  The distance of the dielectric material (PCB or air) insulates the conductors from each other.  The distance of separation on the PCB is referred to as the creepage distance.  The distance of separation through the air is called the clearance distance.

Trace distances on Printed Circuit Boards (PCBs) are a factor at high altitudes

In short, the dielectric properties of the air change with altitude – specifically the air at high altitude does not insulate as well as at sea level.  This has significant implications, especially for products involving high voltages like VFDs.

Increase Trace Distances on PCB

So why don’t designers just increase the distances between the traces on a PCB?  Because smaller is usually better for most industrial applications and drive manufactures are always trying to optimize designs and get more output from smaller sizes.  Unfortunately, this means there is no easy way to redesign the boards or modify a standard VFD in a way that is usable at very high elevations (e.g. 2000 meters and above). 

Pressurize the Enclosure

The only option above the maximum defined altitude is to pressurize the enclosure to a suitable level.

Creepage and clearance distances will become increasingly important as VFD manufactures move from the old UL 508C standards to the new harmonized UL 61800-5-1 standards.  UL 61800-5-1 has higher creepage and clearance distance requirements and more stringent investigation of the PCB design.  This likely means that drive manufacturers and users have less flexibility than before when applying drives at high elevations.  Often times a pressurized enclosure will be required to meet the standard.

Summary

The two main challenges when applying VFDs at high altitudes are reduced cooling capacity and creepage and clearance distances.  The reduced cooling can be addressed passively by adjusting the operating parameters or derating the drive.  However, additional equipment such as an A/C unit or pressurized cabinet might be needed depending on the application requirements.

Interested in KEB’s automation technology? Contact a KEB engineer today to discuss your application.

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Simplifying Communication

Robots are becoming part of our everyday lives, especially in the industrial space.  Leading automation component manufacturers are focused on developing interfaces that harmonize with current and future robotics technologies. At KEB, we’ve developed automation components for robotic systems with communication drivers that allow KEB C6 control products to easily communicate with robots and other intelligent industrial machines.

Figure 1: List of KEB Communication Drivers

This is a living list and new protocols are added as they are developed.  These libraries are all included with KEB’s programming software. Furthermore, KEB has collaborated with KUKA Robotics using their function module library “mxAutomation”.  This library is based on PLC open standards and allows programming, diagnosis or manual running of the KUKA robot via fieldbus modules of KEB’s C6 HMI-LC.  The library allows the HMI-LC to send commands while the motion control of the axes is handled by the robot itself.  The user can then view information such as the current position of the robot on the HMI-LC.  KEB also supports drivers for GE-Fanuc legacy robots.  This aids seamless integration with existing robots when adding new or replacing old control systems.

Add-Ons for Robot Functionality

Robotic arms are well-designed pieces of machinery, but there are certain situations where the functional part of the robot needs to be added to the arm to allow it to perform its required task.  Spindles are often added to give the operator full control over a tool.

During the design and programming phase, the robot’s controller’s capacity of handling the motion of the arm and the I/O can quickly reach its limits. When this is the case, adding a spindle axis to the robotic arm controller is an option, but in other cases, it is best to leave this to a separate dedicated control system.  A KEB spindle control system consists of a C6 Smart PLC, EtherCAT I/O, and a F6 EtherCAT VFD


Figure 2: KEB Component configuration created in Combivis Studio 6

This system comes at a much smaller investment compared to similar performance systems and, as mentioned earlier, the programming software is included in all of KEB’s libraries without additional charge.

When you are commissioning one part or control system in a very large group, having a startup technician on site can lead to a lot of downtime and unnecessary traveling costs.  KEB’s C6 Router allows you to log into a control system (or individual VFD) to view and change the program.  It creates a remote VPN connection that gives you the same control that you would have if you were hardwired into the machine via PC.

Safety for Robotic Systems

The workplace is a place for innovation and teamwork.  When it comes to teamwork with robots, KEB’s main concern is safety.  While robots are increasingly interacting with users, a robotics machine designer needs to ensure that this teamwork is safe.  A KEB safety system uses Safety Over EtherCAT (FSoE) to accomplish this. 

Figure 3: KEB S6 VFD and available safety functions

In the KEB system, a safety module within the VFD performs the safe motion functions such as Safe Limited Speed, Safe Limited Position and Safe Direction and receives commands and STO inputs over the EtherCAT bus from the safety PLC.  The safe motion feature within the safety modules in the VFD takes the load off of the safety PLC and allows it to process other signals coming from the safety I/O.

Integrated Axes

There is a lot to consider when designing a robotic system.  Generally when we think about robotics, we think of movement.  Sometimes what is overlooked are the static pieces of the assembly.  You will need to mount the robot on a fixture that works with system design and is strong enough to hold everything.  A robotic frame will typically be sourced from a company such as Vention (www.vention.io).  One of Vention’s possible modules includes a KEB P1 Brake assembly.  Their design team was able to design a housing that contains a KEB permanent magnet brake which is mounted between a motor and the load.  This brake module will allow the motor and load to spin freely when it is powered on, and hold it or slow it down and bring it to a stop when powered off.

Figure 4: KEB’s hub to inside style P1 brake

Another way KEB’s permanent magnet brakes are used in robotics is integrated into a joint.  The P1s are a great choice when a strong, compact, quality holding brake is needed.  Its design does not have any toothed or fingered connections to prevent backlash when closed or residual torque when opened. Whether you are a robot manufacturer, user or integrator contact us to find out how KEB automation components for robotic systems can seamlessly integrate with your application!

Interested in KEB’s automation technology? Contact a KEB engineer today to discuss your application.

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The post Automation Components for Robotic Systems appeared first on KEB America.

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Selecting the right technology for your application can improve component functionality and equipment performance. The different drive technologies featured in KEB drive products are designed to provide the best solution for the application. Our standard fan-cooled heatsinks are suitable for most applications. For Variable Frequency Drives (VFDs) that are used on machines with cooling pumps, the KEB Liquid Cooled VFDs are the most common option.  If environmental conditions are a concern, a push-through heatsink with oversized cooling fins might be a better option since forced air fans can become clogged with fibers (e.g. textile). Another option is the KEB cold plate or “flat back” heatsink.

KEB’s cold plate (flat back) VFDs for compact heatsink design

This post describes the cooling plate heatsink and when it might be the preferred technical solution for an application.

Finned Heatsink (Fan-cooled)

Most commercial VFDs use a finned heatsink made out of casted or machined aluminum.  Fans push air across the large surface area of the heatsink and the heat is dissipated into the electrical cabinet. There are a few disadvantages to air-cooled drives:

Example of air cooled VFD heatsink
  1. The fans and heatsink fins add depth to the drive profile – A machine designer might prefer a drive with small depth if they are limited on panel options (e.g. explosion proof enclosure) or they need it to optimize the packaging.  If a machine builder wants a drive with the shortest depth possible, then there are better options.
  2. Air-cooled VFDs dissipate heat into the electrical enclosure – This means that the enclosure needs to be oversized to handle the extra heat.  This could lead to a larger than necessary and more costly enclosure and less than optimal packaging in the machine.
  3. Fans commonly fail and will likely need to be replaced at some point – Drive fans are typically one of the first VFD components to fail and this can happen within five years or less.  Fans that operate continuously (24/7 duty) in hot and dusty environments will be particularly susceptible to premature failure. 
  4. Fans add noise – This is usually a small factor, but the drive fans can be quite loud, especially for higher power applications.  If noise mitigation is a goal, then this could be an important point.
Cold Plate VFDs

An alternative to air-cooled drives would be to use a drive with a flat machined heatsink surface. These are often called cold plate drives or flat back drives. The machined surface of the drive is meant to be installed on a cooling plate and the heat is transferred through conduction.

Cold plate VFDs take up less space

This type of cooling provides a number of technical advantages:

  1. The heat from the drive’s insulated-gate bipolar transistor (IGBT) is more efficiently transferred via conduction rather than convection.  This means that the cold plate VFD can be used in applications that might not have been possible with an air-cooled drive (e.g. high-speed applications requiring high frequency switching).
  2. The VFD heat is transferred to the cooling plate and outside the drive cabinet.  This results in less heat dissipation inside the panel, meaning the overall enclosure size can be reduced.  This results in a smaller enclosure and better overall packaging for the machine.


The Cold Plate VFD is ideal for applications requiring small electrical enclosures

Relatively few drive manufacturers offer cold plate VFDs.  Among those manufacturers, the offering is limited in size – usually to 10Hp or less.  The KEB cold plate offering extends up to the R-Housing frame (F5 series) – or 125Hp  in the 480V class.  Finally, the cold plate option is also available for large multi-axis applications with our H6 drive.

Conclusion

KEB’s cold plate option for KEB VFDs might be interesting to machine builders looking to shrink the size of the drive panel and reduce their machine footprint.  It is also a good option for environments where there might be contaminants in the air like fibers or dust that could cause fans or A/C units to prematurely fail. KEB offers the cold plate heatsink option across a number of different drive models up to 125Hp.

Any other advantages to using a cold-plate design?  Can you see it working in your application? 

Interested in KEB’s automation technology? Contact a KEB engineer today to discuss your application.

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Another interesting function built into KEB drives such as the F5, is our UPS Function.  In short, the UPS Function allows the VFD to operate with a lower input voltage than would typically be used in normal operation.  This function is often used in emergency modes where a machine designer wants to operate the VFD with a battery or Uninterruptable Power Supply (UPS).

Suppliers like APC by Schneider Electric make UPS for industrial systems

This post describes the basics of KEB’s UPS Drive Function and where it might be used.

Drive Protection Parameters

All commercial drives are going to have some sort of protection parameters that are used to protect the system.  Some protection parameters like the motor temp sensor or motor overload counter are intended to protect non-VFD components like a motor.

Drives also have a number of protection parameters that are intended to protect the VFD. Protection parameters typically function as either warnings or faults. Warnings are used to alert a user or controller that some protection value is approaching a trip or fault level.  When a warning is tripped, the machine will typically run at a lower speed or duty until the warning clears to an acceptable level.

The protection parameter values used in warnings are usually going to be adjustable in order to give an engineer maximum flexibility. Example warning parameters might relate to motor temperature, drive heat sink temperature, or motor overload counters.

Protection parameters typically function as either warnings or faults. 

Undervoltage and Overvoltage Levels

There are also some hard-coded protection parameters that cannot be adjusted by a user.  Exceeding these values will result in a drive fault and a machine shutdown.  These values represent the extreme operating points and exceeding these values could result in catastrophic failure of the VFD.  Example hard-coded protection parameters include current overloads, phase imbalance detection, maximum heat sink temperatures, and undervoltage and overvoltage levels.

As it relates to the UPS Function, let’s take a look at the underpotential level of the KEB F5 480V drive.  As a quick reminder, the drive’s DC bus level will be:

The KEB F5 480V drives use the following values as thresholds before the drive will fault with over/under voltage faults:

Mode of OperationE.UP LevelE.OP Level
Normal240 V800 V
UPS Function200 V800 V

Applying too much voltage can damage components.  Applying too little voltage doesn’t in itself damage components but likely indicates that there is a problem with the drive’s incoming power supply like a brownout or phase loss which could be problematic.  Also, with reduced input voltage, the motor performance would likely be affected as the motor torque and speed would suffer, possibly resulting in loss of control.

Emergency Mode

Many machines or installations must plan for the event that there is a loss of power.  What will happen if my building loses power?  Will the machine safely come to a stop or will it crash to the floor?  Will anyone get hurt as a result?

A common desire for machine builders in the event of loss of power, is to bring the machine to a known position/state in a controlled manner.  Once in the safe position, the machine is shut down until the incoming power is restored or fixed. 

Machine builders can often times plan for a loss of power event by using a short-term power supply like a battery pack or UPS.

These supplies are not intended to run the VFD for long periods of time.  Rather, they are just meant to temporarily control the motor and bring the machine to a safe place where it is then shut down.

The problem is that many drives have this underpotential level hard-coded into the drive because it is a critical protection parameter.  This gives an engineer little flexibility unless they use a temporary power supply with a relatively large DC bus and 3 phase output. 

KEB’s UPS Function

KEB’s 400V class drives have a feature called the UPS Function that reduces the E.UP (Error UnderPotential) level.  One of the drive’s digital inputs is programmed with the UPS function.  When the digital input is activated, the KEB drive: resets an E.UP fault, allows for a single phase connection (UPS) and lowers the E.UP level to around 180VDC

Mode of OperationE.UP LevelE.OP Level
UPS Function216 V800 V

Additionally, with the flexible programming of KEB drives, separate speed and torque limits can be programmed that will help to make sure the DC bus voltage does not sag and trip an undervoltage fault.

Do you use UPS or batteries with your VFDs?  I’d be interested to hear if you use this function or would find it useful.

Interested in KEB’s automation technology? Contact a KEB engineer today to discuss your application.

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The electrification of city transit and school buses continues to grow rapidly! This creates a lot of positive press for municipalities, providing further support for electric vehicle applications.  This success in EV advancement is paving the way for the next round of viable municipal vehicle applications, particularly waste trucks and street sweepers.  Even if the powertrain remains a combustion engine, there is the opportunity to electrify the auxiliary pumps, compressors, and condensers with electric motors and inverters as part of a hybrid design.

Street Sweepers and Waste trucks

Waste and recycling trucks are a good candidate as electric municipal vehicles due to regenerative braking from frequent stops. For example, street sweepers, typically have a set route where charging stops can be planned.  What differentiates waste trucks and sweepers from vehicles like buses is that they do more than just drive around, they also do work. 

The additional challenge of electrifying these municipal vehicles is the extra auxiliary components doing work added on to the base vehicle.  The typical auxiliaries in the base vehicle are the steering pump, air compressor, and optionally the air conditioning condenser.  Each of these electric motors requires its own control and as more auxiliaries are added on to municipal vehicle applications to support other functions, there is increased importance for auxiliary control system design considerations.

What differentiates waste trucks and sweepers from buses is that they do more than just drive around, they also do work.

What additional auxiliaries can be electrified?

For both waste truck and sweeper applications, there are a variety of vehicle types so the number of added electric auxiliaries depends on system design options. 

For waste and recycling trucks, one design option is to replace the transmission-driven PTO powering the hydraulic system with an electric motor.  A second option would be to replace the hydraulic system with electric motors for the pickup arm, compactor, and ejector.  

For sweepers, the electrified auxiliaries can include the vacuum fan and pumps for the hydraulic motors operating the brushes and broom.  A second option would be to replace the hydraulic motors with electric motors. 

What are the benefits of electrifying auxiliaries? Less weight and hydraulic fluid

In both applications, there is the opportunity to replace the hazardous hydraulic oil with an environmentally-friendly electric solution.  This additionally eliminates the weight of the large hydraulic fluid reservoir and reduces the power draw from the battery or engine powering the hydraulic system.

Speed, torque and positioning benefits

A second benefit is that inverters can provide speed, torque and position control of motors to optimally control all of these auxiliaries based on their function. 

For example, an inverter monitoring the torque of a waste truck auger can detect a jam and automatically reverse speed to clear the jam.  Advanced inverter sensorless control algorithms utilizing a model of the learned motor characteristics not only provides precise closed-loop performance without encoder feedback, but operate motors with power efficiency by adjusting current and voltage output based on actual load conditions (as opposed to on/off control).

What are inverter considerations for electrification options?

What is unique with the waste truck and sweeper applications is the possible number of electrified auxiliaries, which can range from 2 – 8 motors.  Likewise, the power requirements can range from 3kW – 10kW+.  A design that pieces everything together can pose significant development challenges and long-term operational reliability risks.  On the other hand, designing with a ‘system’ viewpoint ensures an efficient design which can easily be applied or scaled to multiple applications in additional to providing excellent operational performance.  Below are some key considerations when selecting auxiliary inverters for these applications:

Multi-Axis Inverter:  Scalable and Modular Design

At the end of the day, this undoubtedly should be the #1 consideration…especially as the number of electrified auxiliaries increase.

Customize outputs based on electric vehicle requirements
A Multi-axis Solution

A multi-axis solution has independently controlled inverter output stages for each auxiliary motor all contained in single housing with one high voltage DC input supply to the system, one set of cooling connections (preferred is a IP6k9k/IP67 housing with liquid cooling), and one set of control connections.

  • This allows optimal motor control and efficient operation for each motor compared to one large inverter supplying multiple auxiliary motors through a junction box of on/off switching contacts.
  • This eliminates the cost and complexity of redundant parallel power, cooling, and control connections of distributed stand-alone inverters for each auxiliary.
A Scalable Solution

A scalable solution maintains the same mutli-axis system architecture as additional inverter outputs are added to a unit. 

  • As inverter outputs are added, the marginal cost of each additional output will decrease, making a scalable multi-axis solution increasingly cost efficient.
  • Implementing additional auxiliaries is simplified with consistent development approach.
A Modular Solution

A modular solution allows multiple power options for each inverter output stage.

  • Offers full flexibility to mix and match power ratings for each inverter output independently
  • Allows optimal sizing for each auxiliary based on rated motor data
  • Motor cable gauge sizing can be optimized for each auxiliary motor
EMC Design and EMI Filtering

With ever more electronics being utilized in electric vehicles, electromagnetic compatibility (EMC) is critical.  EMC design ensures electrical devices do not negatively affect the operation of each other by both containing and protecting against radiated and conducted electromagnetic interference (EMI). 

Failure to properly control EMI can result in vehicle CAN communication disruptions, devices not operating properly, and even potential damage to devices from power or voltage spikes.  Auxiliary inverters with integrated DC chokes and EMC type standard approvals such as ECE R10 (E1) and CISPR 25 are two important considerations to keep in mind to ensure reliable operation within the electrical environment. 

Sensorless Motor Control

If one of the purposes of electrifying auxiliaries is to increase efficiency, then an inverter with sensorless motor control is important.  Compared with open loop volts/hertz operation, sensorless control provides more efficient operation with less motor losses as well as dynamic response to loading conditions which manages power consumption. 

Advantages of sensorless motor control in electric municipal vehicles

Sensorless control can also be used with permanent magnet motors, which are more efficient than induction motors, and additionally eliminate the need for a motor encoder.  In fact, sensorless motor control should perform better than closed loop operation since it uses the motor characteristics to operate the motor.  In this regard, one thing to consider in an auxiliary inverter is the availability of a built-in learn function for determining the motor characteristics. 

Since the motor data needed for sensorless control (resistances, inductances, EMF constant) is typically not listed on the motor nameplate, an easy-to-use learn function will take the guesswork out of working with different motors and provide quick start-up between start and finish.

KEB T6 Auxiliary Inverter

Given the large number of auxiliaries that can potentially be electrified on electric or hybrid waste truck and sweeper applications and the wide variety of each vehicle type, the KEB T6 Auxiliary Inverter provides highly flexible and competent solution. 

Ideal for Commercial Vehicles

The T6 is a multi-axis inverter specifically designed for commercial vehicle applications which can be scaled from 1 to 6 inverter outputs in a single system housing, has three modular power options (7.5 kW, 15 kW, 30 kW) for each inverter output, and integrated DC choke filtering with ECE R10 and CISPR type standard approvals for EMC. 

Other T6 features

From an operational standpoint, the T6 can sensorlessly control induction, permanent magnet (surface mount and internal), and switch reluctance motors and has a motor learn function for automatic characterization of the motor.  In addition, the T6 programming environment includes startup wizards which can be used to start from default to spinning the motor in only a matter of minutes.

The T6 Auxiliary Inverter offers many benefits to vehicle manufacturers
Conclusion

For municipal waste or recycling trucks and street sweepers, there is a wide variety of vehicle types and electrification of these vehicles can include 2 – 8 auxiliaries with a range of power ratings and potentially various motor types.  Therefore, it is important to select a solution which is flexible, reliable and efficient.  A multi-axis auxiliary inverter which is scalable and modular, includes EMI filtering, and has sensorless motor control would be the optimal solution for these applications.

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Once upon a time, just about everything in a vehicle was mechanical, most notably the combustion engine which provided power to other subsystems such as pumps for power steering and compressors for air conditioning.  But as technology progressed and fuel consumption and emission standards became more stringent, electric components started to take over.  A prime example of this has been the use of computer-controlled fuel injection systems replacing carburetors. 

Fast forward to the present where all-electric vehicles are rapidly on the rise with batteries replacing fuel systems, inverter-driven electric motors replacing the engine and auxiliaries such as pumps and compressors, and an ever-important vehicle control unit controlling it all.  But, to make this new electrically-dense environment work properly, it is increasingly important to consider EMI and EMC in the design and layout of these systems.

What is EMI and what are its effects?

EMI is electromagnetic interference.  There are two primary types of EMI, radiated and conducted. 


Radiated and conducted emissions can cause interference

Radiated emissions (also known RFI, radio frequency interference) are associated with the magnetic field generated by current flowing through a wire.  Like radio waves, radiated emissions can transcend space and be picked up by other devices in proximity.  The effect is that radiated emissions can induce fields which can disrupt communication signals and/or negatively affect the operation of the receiving devices themselves.  Of particular concern would be the critical vehicle control unit and CAN bus communication.  Additionally, this can also limit options to the spatial outlay of components.

Conducted emissions, on the other hand, travel along a path such as a as wire or plane connecting devices.  These emissions include transient current and voltage from high frequency switching devices, such as the pulse-width modulation of inverters, coupled through parasitic impedances.  The effect is that with a path to travel back to the DC grid, these conducted emissions can excite system resonance points.  This can lead to voltage or power peaks which may cause damage or lead to reduced lifetime of other DC-connected devices.  Conducted emissions are of particular concern since the primary electric vehicle components including the inverters, electric motors and power supply are all interconnected as a path for conducted emissions.

What is EMC and why is it important?

EMC is electromagnetic compatibility. That is, all devices in an electrical environment should not adversely affect the operation of others. It is the golden rule of electronics playing nice in the sandbox. This applies to all electronic devices and is important because the ultimate goal is the reliable operation of the system as a whole. To ensure this, there are international standards and type approvals for components to ensure EMC homologation requirements are met. Therefore, it is important to select components meeting EMC type standards such as ECE-R10 and CISPR 25.

…all devices in an electrical environment should not adversely affect the operation of others.  It is the golden rule of electronics playing nice in the sandbox…Therefore, it is important to select components meeting EMC type standards such as ECE-R10 and CISPR 25.

How can EMI be mitigated?

Although EMC applies to all devices in a system, power electronics with high frequency transistor switching such as inverters for the propulsion traction motor and auxiliaries are the primary producers of EMI in electric vehicle applications. 

A good EMI mitigation solution goes both ways though…keeping internally generated noise in and keeping externally generated noise out…and techniques may depend on the source and type of emission.

DC Filtering – A DC choke is a good option for mitigating conducted emissions generated from inverters.  A DC choke allows low frequency DC voltages and currents to pass through.  This keeps in noise generated by the device from going out to the DC grid.  Blocking the harmful high frequency and leakage currents prevents harmful or disruptive effects to other devices connected on the grid.  Additionally, the choke blocks noise from coming into the device from other external noise sources.

Shielded Motor Cables – The motor cables carrying high frequency switching power from an inverter to a motor present a ripe source for transmitting radiated emissions.  This noise can possibly affect any device in the vicinity of the cable run, particularly other power cables or low voltage communication signal cables running closely in parallel.  Braided shielding around the power conductors acts as a net to capture and provide a low-resistance path to ground for the radiated electromagnetic emissions generated by the current in the conductor.  Likewise, it also acts as a barrier to reflect any external emissions from being received.  There are many other considerations in selecting motor cables, but shielding is only effective as its weakest link so shielded connectors and cable clamping also need consideration.


Shielded VFD cables like this example from Balden

Unshielded motor cables, on the other hand, can wreak havoc on low signal vehicle communication signals and networks such as the CAN bus.  Additionally, unshielded motor cables can limit the distance between inverter and motor putting.  This puts additionally constraints on device layout such as needed to distributing auxiliary inverters, which adds additional cabling costs and design complexity.

What to look for in auxiliary inverter design?

EMC design should be a priority and not an afterthought.  Without proper electromagnetic compatibility in vehicle electric systems, it is not a matter of “if” EMI issues will arise but “when”… and can result troubleshooting headaches to resolve and costly redesigns to root out.  Therefore, it is important to consider EMC at the design stage and likewise select system components which share this philosophy.   

KEB is a company experienced in the design of inverters and filter solutions for a variety of specialized and high-tech applications across several industries.  With this experience in mind, the T6 inverter was specifically designed for controlling the auxiliary motors (pumps, compressors, e-PTO, etc.) in commercial electric and hybrid vehicles and providing EMC solutions has been part of the design process from the start. 


KEB’s testing chamber for EMC considerations for Electric Vehicle applications

Each T6 auxiliary inverter has an internally integrated DC common-mode EMC filter as standard design and the T6 meets CE, ECE R10 (E1) and CISPR 25 type standards for EMC and emissions as well as meeting even more stringent OEM standards which can be tested in-house.  KEB also sources high-quality DC and motor cables and connectors, providing customers a ready-made solution. 

In addition, the motor cables are tested and approved with the T6 for lengths up to 30 meters.  This allows users to leverage the benefits of a central, multi-axis auxiliary inverter with a single DC input, coolant connection, and CAN ID as opposed to individually distributed auxiliary inverters with parallel connections which add to system cost, design complexity, and makes electromagnetic compatibility of multiple devices more difficult to integrate into the system.  The KEB T6 auxiliary inverter provides an integrated system solution which is scalable from 1 – 6 inverter outputs in a single housing with three modular power stage options (7.5 kW, 15 kW, 30 kW) for each output.  With this flexibility and EMC design, the T6 provides a reliable solution for a variety of EMC considerations in Electric Vehicle applications. Commercial electric vehicles such as transit buses, heavy-duty trucks, and refuse collection vehicles.

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