Posts Tagged ‘Power Electronics’

Three Day Digital Control Course August 22-24 California

Friday, July 22nd, 2016

The ELMG Digital Power Electronics Control Course

Three days of focused unique training in digital control of power electronics!

Our Digital Power Electronics Control Course overs the essential knowledge and know-how for engineers to implement digital power electronic control!

Come to the Three Day Digital Control Course in Camarillo, California August 22-24, 2016.  Register here.

How did the course came about?

Essentially the course came about because we were asked by one of our customer’s to provide one. The story is we were in the middle of a “fix up” job where the power supply had shown some control instability at its final release testing. The testing that showed the problem was passing a short circuit test of parallel connected power supplies. When the short circuit was removed the supplies came out of current limit, however they did not come out of the limit at exactly the same time. This created an oscillation where individual power supplies came out of current limit and then returned to current limit.  It was possible for the oscillation to continue indefinitely.  This was an unacceptable and embarrassing problem.

Six months of expertise in a three day course

During the six month project to rework the control code we spent lots of time teaching the team about the underlying issues that had been missed when the controller had been designed, coded and tested.  And part way through the “fix-up” the R and D manager suggested we could put a course together covering all that the team needed to know.

And so the digital control course was born

The first course covered exactly what we had discovered during the fix up job.  This included lots of digital expertise targeted for power electronics.  The areas we covered were diverse from;

  • Numeric precision loss in filters
  • Improvement of modulation spectral performance
  • Stability
  • The effect of numeric precision on stability
  • Best filter forms
  • Direct digital control design
  • Linearising control loops

What is covered in our course?

The course was created at the request of a Power Electronics Research  and Development manager.  He asked that we make it specific his team’s needs.  And this is why the course has the unique structure that it has.  We have been through the pain and heartbreak of having digital control development go wrong and have seen clearly where the repeated problems lie; our course addresses those areas.

Digital PWM and VPO modulators

One of the big differences between digital power electronics control and conventional analog control is the timer precision in digital modulators. This difference can be corrected or made negligible and in some cases can be made an advantage.  Spectral control in digital modulators is a focus area in the course as it is so effective.

Digital Precision in control blocks

It is possible to use a digital system and adjust the coefficients of the filters so that small inputs result in no output from the filter. Such scaling issues often lead to a loss of precision in the digital control system. The resulting slip-strike behavior can create limit cycle oscillations in the power converter output.

Direct Digital design of controllers

The “design then translation” approach of taking analog controllers to digital form can be avoided by using the direct digital design approach. This simple but powerful method of digital control loop design is covered in the course.

Converter non-linearity correction

Certain converter topologies are non-linear either in the control input to the output or the conversion ration.  Dealing with the converter non-linearity to achieve high bandwidth is key to stable parallel connected converters.


The course covers the fundamentals of stability from a physical basis with a focus on measurements of power converter transfers.  This along with a simple framework for managing margins and robustness is an integral part of the course.

Why we offer the course?

Understanding and implementing digital control of power electronics offers great advantages for configuration and flexibility. However, this is not without road blocks and issues that need to be designed around. This course provides the know how to get digital control working robustly and reliably.

How do I get on the course?

The course is next being run in Camarillo, California USA August 22-24.  To register for the course, click and visit the information page here. Press the ‘Register’ button on the page and this will take you to the shopping cart for the course. Complete the purchase to register for the course.

Next course

The next course is being held August 22-24 in Camarillo, California, USA.



There are several hotels a short distance from the Ridley Engineering Design Center. The prices below reflect their current prices for August 2016. The last hotel listed is a nice beachfront resort if you do not mind the 25-minute commute to the office. Regardless of your selection, we recommend arriving on Sunday evening and departing Wednesday evening or Thursday.


Best Western Inn

295 E Daily Drive, Camarillo

0.3 mi.



Residence Inn by Marriott

2912 Petit Street, Camarillo

2.8 mi.



Courtyard by Marriott

4994 Verdugo Way, Camarillo

4.3 mi.



Hampton Inn & Suites

50 W Daily Drive, Camarillo

1.1   mi.



Hilton Garden Inn

200 Solar Dr., Oxnard

5.6 mi.



Embassy Suites Mandalay Beach Resort

2101 Mandalay Beach Rd., Oxnard

15.4 mi.



Travelling to the course


Airports: There are three options for airports. Bob Hope Airport in Burbank will be the least congested and is serviced by American, United, Delta, Southwest and JetBlue:

Bob Hope Airport (BUR)

Los Angeles International Airport (LAX)

Santa Barbara Airport (SBA)

Shuttle: The Roadrunner Shuttle is a Camarillo-based service that provides door-to-door service from the airport.


Bob Hope Burbank Airport (BUR) via US 101

Los Angeles International Airport (LAX) via US 101

Los Angeles International Airport (LAX) via Pacific Coast Highway (PCH)

Santa Barbara Airport (SBA) via US 101

About the presenter

3 Day Digital Control Course

Dr. Hamish Laird

Dr. Hamish Laird is a well regarded digital power electronics control engineer, researcher, lecturer and teacher.  Hamish is Chief Technology Officer at ELMG Digital Pwoer and holds a visiting academic position at the University of Canterbury in Christchurch, New Zealand.

During his career Dr Laird has worked on the control for;

  • High Voltage Direct Current Transmission
  • Reactive Power Compensators
  • AC and DC Motor Drives
  • DC to DC converters including LLC and phase shifted bridges
  • Medium and low voltage AC motor starters

Dr. Laird has worked for;

  • Alstom Grid (GEC Alsthom)
  • Eurotherm Drives
  • University of Canterbury
  • Aucom

Through ELMG Digital Power Dr. Laird  has provided advice, services and products to;

  • ABB
  • Enphase
  • Comsys
  • Evashred
  • TNEI
  • Eaton

Dr Laird says

“In designing and presenting the course we aim to have engineers able to use digital control in power electronics to achieve robust and reliable results.  See you in Camarillo”.


How to Register

Click here to register.  

P.S. Please note that the ELMG Digital Power course is being hosted at the Ridley Engineering Centre in Camarillo, California.  Ridley Engineering are processing all course registrations viatheir webstore.  Click here to register.  

APEC Presentation Slide Correction for b1 Coefficient

Wednesday, July 20th, 2016

At APEC this year we presented High Performance Digital Control of Power Electronics.  We then made the slides available and repeated the presentation as two webinars.

Click here to download the slides if you do not have them already


Thanks to some good attention by a person who worked through the controller example,  we have noticed an error in one of the coefficients on the slide as shown below.

The correct value for the b1 coefficient is 0.00625.

Thanks to the helpful person who found this.

APEC Presentation slide correction for b1 coefficient

APEC Presentation slide correction for b1 coefficient






Congratulations to Dr. Rabia Nazir on completing her PhD in fractional delays in repetitive control

Friday, December 18th, 2015

Over the last two years ELMG Digital Power CTO, Dr. Hamish Laird, has helped supervise (the now Dr.) Rabia Nazir in the pursuit of her Doctoral studies.

Hamish Laird says

“The research that Rabia has completed in the area of fractional delays in recursive filters for current control in grid tied inverters gives great control tools in the implementation of control for GTIs in grids where the AC system frequency is varying. It is always great to help with PhD research as I learn so much so thanks to Rabia for letting me help.”

Congratulations to Dr. Rabia Nazir on her successful oral defense of here work.  Dr Laird again

“It was fantastic to attend Rabia’s defense.  I am so proud of and pleased with the work she did in analysing, simulating and building power converter hardware to show her findings. It was a great learning experience for me.”

Recently (now Dr.) Rabia Nazir presented a paper at a conference in Sicily on the use of Taylor Series expansion based fractional delay filters for recursive control of grid inverter currents.

Contact us for a copy of the paper.



Digital Power Electronics Control Group on LinkedIn

Wednesday, February 25th, 2015

We have started a group where we can share questions and discuss Digital Power Electronics Control on LinkedIn.

The group’s name is Digital Power Electronics Control.

The link to the group is

Look out for the group identified with the z-transform image like that shown above.

Recent Group Discussions

Recent discussions have included one on the effects of precision limits for PWM timers

Another thread covers how to get started in Digital Control of Power electronics.

There are some well known and expert members in the group who share experience and insight.

The group is private to prevent the spam that has been increasing on Linkedin so please ask to join.

Where to begin with digital control

The discussion on where to begin with digital control is an ongoing and popular thread.  The thread has 49 replies from group members offering advice on what is important in digital control of power electronics

Slip Strike

Another discussion covering a very specific issue is on handling slip-strike problems.  Slip strike is what happens where the system output gets “stuck” and then suddenly moves.  This typically happens in mechanical or hydraulic systems where the friction coefficient falls as movement begins.  A relatively simple solution is to use a high derivative gain to reduce the effect.  Other solutions include linearising the system to allow higher controller gains and higher bandwidth.

Choosing the control processor

The discussion on choosing the processor for digital control is also still popular.  This covers which is the best micro controller or processor for digital control of power electronics.  This is an ongoing and recurring theme as more people  use digital control for their power electronics.  Other subjects in the thread include

  • analogue to digital converter choice
  • aperture time
  • settling time and
  • how to design a digital loop compensator

Numeric precision and the effect of limited PWM timer bit limits are also mentioned.

Join the community

We look forward to seeing you there.

Come and join the community at the Digital Power Electronics Control group on LinkedIn.

Download the report ‘Your Digital Power Future – Roadblocks to Avoid’ to learn about the three key issues to watch out for in the Digital Control of Power electronics.

Download report now

Is the Little Box Challenge something you are up for?

Thursday, August 7th, 2014


Google are always shaking things up.  And they are shaking the digital power electronics and low power loss converter space with this competition.

For those of you who don’t know, the Little Box Challenge is a competition where you can win $1 Million USD for creating a 2kVA inverter with a power density of 50W per cubic inch.  For those not familiar with this unit I calculate this to be 3.4 kW per liter.  Other specifications are around efficiency, AC voltage and current THD  and noise,  and the DC side current ripple.  The inverter is a single phase device.

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This is an interesting challenge. It is also put together and presented in an interesting way. The marketing website has pictures of hybrid cars, laptops and washing machines.  The inverters in these are three phase inverters. The fan in your laptop is driven by a three phase inverter as is the motor in your hard drive.   Plugin hybrid car AC to DC converters for battery charging are single phase but they are probably not inverters and in a strange juxtaposition, there is a picture of a hairdryer.   Then I realised I had misunderstood.   The inverter is to power the appliances and charge the electric vehicle.

When you read on it becomes clear that the the little box challenge technical problem is single phase and more to do with solar inverters or probably standby inverters for your household single phase loads.  Sorry to those at Google for misunderstanding the picture.

The minimum efficiency is do-able now with silicon and/or SiC.  I have an in-production 2.88 kW isolated digitally controlled AC to DC converter that I had downstairs  on my desk now.  It is more efficient by some distance than the minimum efficiency required in the contest.  It has SiC diodes in the PFC stage.  Aside from that it is all silicon.  And it is from six years ago.   Just measuring it now and it is 10 inches by 1 and 5/8 inches by 4 and 3/4 inches for a total volume of 77.1875 cubic inches.  This gives 37 W /cubic inch so it is in the ballpark.  All of you who do this stuff know that to get to 50W per cubic inch will take some effort. Having said that looking in my power supply there is some air space.

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The Littlebox requires a a DC side ripple current that is quite low. I haven’t worked out the 120Hz filtering volume needed to do this with capacitors but am assuming the volume will be significant.  By adding the DC side ripple requirement the challenge becomes really quite different and is more about energy storage replacement or the equivalent of valley filling. The solution to that might be some sort of integrated reasonable switching frequency active filter on the DC side that only operates at certain conditions so the 20% current ripple can be met. Perhaps the active filter could gyrate the storage capacitor. Or maybe some sort of pulse number increase like the old HVDC ripple current re-injection schemes.  I might dig a few of those papers out to see what use they’d be.

The AC side specification doesn’t seem too harsh.  A good inverter feedforward lineariser for PWM precision, dead-time and minimum pulse width with a good repetitive or resonant notch filter based current controller will meet this THD and noise requirement.  It’d be good to know the measuring instruments noise measurement approach.  The magnetising current of the transformer is supplied by the inverter so this will mean that getting both the current THD and the voltage THD below a certain limit may not be actually possible.  This will depend on the transformer magnetising characterisitcs.

It is possible that you will be able to meet the power density with the minimum efficiency as the cooling might be OK. That said the description of the testing doesn’t cover exhaust air temperatures as would a UL standard. There may be room for that kind of really high temperature exhaust air that UL are always so troubled by.  It might be that the contest rules need to be tightened on this.

For those of you considering this from outside the US make sure you get some US fuses as the UL and IEC definition of the current is significantly different. Maybe a part number specification for the fuse for the testing would be useful. US fuses will be hard to buy outside the US in any case.

It’d also be good to get some idea of what the transformer in the test is so any EMC filter design can be optimised for that transformer.

The solution to the DC ripple current was solved by Tesla (Nikola – not the car company) back when he was doing his thing. It is three phase AC systems where balanced three phase currents give constant power flow and so constant DC side current.  If only we had three phase appliances.

Unfortunately most of the people who legitimately have a good shot at meeting this challenge will not be allowed to as they are already doing this type of stuff for a job and so will not be able to meet the disclosure requirements in the terms and conditions.

Other issues might be getting your gear into the US.

For power density trends, analysis and a good commentary on the current state of power converter density take a look at

The paper presents data that shows that the switching frequencies that maximise power density are surprisingly low.

Maybe Professor Kolar and his team at ETH will have a go at the little box challenge.

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