Archive for the ‘Grid Connection’ Category

Inductor Go Round – Redux

Wednesday, May 9th, 2018

ELMG Redux from 2010

This post was originally published in 2010.  It is republished here because it looks like people are still doing the inductor-go-round.

So what is the inductor-go-round?  It is like a merry-go-round (carousel) except with inductors.  It can cost companies (or their startup backers) lots of time and money.  And usually when you are on the inductor-go-round it feels much like a carousel at a fair.  Round and round and sadly, not much progress.

Power Converters

Often the optimization of a power converter’s performance comes down to the optimization of the converter inductor. (It can also be optimization of the transformer but lets for the moment assume a non-isolated converter). For people with big and small inductors there is, it seems, an inductor go round.

What is a big inductor? At ELMG Electronics Design and Development we generally say that any inductor with mass more than 1 kg – and yes it says kilograms (1kg = 2.2 pounds) – is a big inductor. Some of you will say that until you have a 40kg inductor you don’t really have an inductor. Other inductors will be smaller.  I guess it is all a matter of what you are familiar with.

For the inductors for grid connected inverters people start with laminated iron or some other laminated material.  This is typically the  inexpensive choice.  Some others choose ferrite cores. Some start with another core material.

Air cored next

Then running first into core material problems they then move to air cored as the core is the cause of all the problems. They then either come up against either;

  • the magnetic field interference problem (the enclosure is now the core),
  • the fault rupture problems that occur with designing air cored mechanical restraints,
  • or the size constraint.


From here most people head to a modern core material such a powder core. These materials are not necessarily homogeneous and so they then realize that to get long life times requires careful consideration of the wear out mechanisms and to meet this requirement means using a quality core material vendor (See for a good first discussion on thermal aging). The lesson here is that not all core materials are the same.

Back again

At this point some people go back to iron or ferrite and others go to an alternative core material like an amorphous alloy. If they then cannot meet the price point then they may well go back to laminated iron.

At this stage the realization is that there is no magic answer. The optimization of power inductors becomes the requirement and there is usually a realization that the inductor vendors are not as able as they seem. In the defense of the inductor manufacturers it must be said that most power electronics companies struggle to correctly specify inductors.

Getting off the inductor go round means designing the inductor completely.

Advanced Digital Control Power Electronics Course

Wednesday, October 19th, 2016

Digital Control Power Electronics course – January 30 to February 2

The next Advanced Digital Control of Power Electronics training course is running in

Camarillo, California

January 30 to February 2

Registrations open now – click here or on the button below

Register now

Course outline is here.

Four days

The course has been expanded to four days and includes lab sessions each day to reinforce the learning on

  • Precision extension of Digital Modulators
  • Digital Loop closing
  • The effects of delay
  • Loop measurement using the control processor.

What people who have attended say about the course?

“Had very high expectations of this course. Hamish delivered. Excellent for power engineers who are starting digital power. Thanks for putting this on…I only regret it is a 3 day course. I could sit here for 3 more days”

“This course was full of critical material not found in the app notes.  Very enjoyable and well taught.”

“Good course. Hamish knows his material. I’ll be able to apply this coursework to my work.”


“I would highly recommend the ELMG digital control course to all power electronics engineers.  What makes this course particularly valuable is in the practical approach and relevance to the control of power electronics.  The topic of digital control is a very broad subject and hence the specific challenges and applicable tools are very different depending on the application details. Many digital control / DSP courses try to approach the topic from a very generic broad approach, treating all applications in the same way.  The classic approach involves starting from a conventional analog control model and then adding ADC and DAC blocks to change between the analog and digital domains with a digital controller replacing the traditional analog controller. The problem with this classic approach is that it is not a practical or applicable method for designing high bandwidth controllers for use for the control of power converters. The ELMG digital control course specifically focuses on the control of power electronics and hence the course only considers concepts and techniques that are applicable to the control of power electronics.  The course covers a wide range of digital control theory and introduces the power electronics engineer to all of the state of the art digital control concepts.  This course is a must for any power electronics engineer who is involved in the digital control of power converters.”

Michael Harrison – Director of Power Conversion, Enphase.

Register by clicking below

Register now


Free Webinar High Performance Digital Control on Zynq

Sunday, July 10th, 2016

If you have just sat down at your desk with a coffee, then put that aside for a minute and grab your diary.

Review your schedule for Tuesday 12th July 2016 and consider this stellar opportunity: on that day ELMG Digital Power will be hosting a FREE webinar on Digital Power using Xilinx Zynq SoC.

That’s right, from the comfort of your own desk you can join ELMG Digital Power (Members of the Xilinx Alliance Program) for their Zynq Digital Power Webinar and expand your knowledge and expertise by discovering:

* What is important in digital power, including numeric precision and latency
* How to design a compensator in the digital domain
* Why you would use a FPGA for digital power and why the Zynq SoC in particular
* Key issues in digital controllers in programmable logic, such as the serial-parallel trade-off, fixed or floating point,      choosing sample rates and what precision to use
* The building blocks for digital control and ELMG’s licensable IP cores
* IIR digital filter design (a case study) along with understanding the delta operator
* Using the ARM cores in the Zynq to your full advantage.

This webinar will be hosted and presented by Dr. Tim King, ELMG Digital Power’s Principal FPGA Engineer. Tim has considerable experience the design and implementation of varied digital control systems and IP for power electronics on FPGA platforms.

The webinar, which includes a short Q&A session, will be held on Tuesday 12th July and is available globally. Just choose a time that best suits you from these three options:

1. July 12th 2016 – commencing at 4pm in Christchurch NZ. (This will be 2pm Sydney, 1pm Tokyo, and 9:30am Delhi)

Register for Asia-Pacific


2. July 12th 2016 – commencing at 9am London (10am Berlin)

Register for Europe


3. July 12th 2016 – commencing at 1pm San Francisco (3pm Houston, 4pm New York)

Register for USA

Spaces are limited.  

See you at the webinar



US Congress extends ITC for solar

Friday, December 18th, 2015

The US Congress looks to have agreed that the ITC tax credit for solar installations in the USA will be extended passed 31st December 2016.

While nothing is ever certain in politics or government, the stock markets have run up the stocks of the solar companies showing that there is some confidence that this will happen.

Contact us for digital control systems for your grid tied solar inverter.

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.



Intelligent Stacks need Digital Power Controllers – PCIM 2015 Highlights

Thursday, June 11th, 2015
Intelligent Stacks need Digital Power Controllers

Semikron Slimline SEMIKUBE










PCIM is the show where the large power electronics industry comes together to celebrate and show off.  Three big trends at PCIM in May 2015 are off the shelf IGBT stacks, mature inductors and intelligent IGBT power stacks.  No off the shelf controllers for these stacks were to be seen at the show.


By large converter I mean above 3kW.  PCIM Europe is in Nuremberg, Germany.  Other PCIM shows are in China and South America. When I attended this years PCIM show it was clear that three large trends are occurring in the power electronics market.  With the off the shelf converters and inductors now available it is clear that intelligent stacks need digital power controllers.

Three trends at PCIM

The PCIM show always has significant numbers of new products launched.  This year three trends were very clear.

IGBT Stacks

Firstly there are more and more ready made stacks available.  These are IGBT modules mounted on heatsinks with integrated gate drivers and DC bus capacitors.  In some products there are fans included as does Semkron’s SEMIKUBE SlimLine, while other vendors, like AgileSwitch and Infineon, have left the cooling to the user.  An interesting turn up is the Danfoss semiconductors stack that reportedly is a drop in replacement for the SkiiP product from Semikron.  This might be that this is the result of Danfoss buying Vacon.

Intelligent Stacks need Digital Controllers

Infineon’s MiPaqPro is a new Intellingent IGBT Stack










Semikron also showed a watercolled megawatt converter in a cabinet for large wind and solar applications.  They also had a really effective new parallel power converter system.  Both are very impressive and useful for large grid connected converters.

When the Semikron, Danfoss, AgileSwitch (AgileStack) and Infineon (MiPaqPro) products are stacked up (sorry for the pun) together is it clear that off the shelf power converter stacks and systems are here to stay as all these vendors are truly committed.  It also is clear that buying stacks off the shelf is going to be a valid solution instead of developing your own.  I am not sure what that means for those who are still doing converter development.  Time will tell.  Probably purchasing volume and management commitment to building converters will be the deciding factors internally in the product companies.  One colleague at the show thought that “If you stop developing your own converters you may as well just call it quits”.

Inductors are mature

I recall seven years ago struggling to find an inductor manufacturer that could design reasonable quality and that had a balance sheet that would pass any kind of financial stress test.  And now there are at least three inductor companies who do a good job technically and who do not present too large a financial risk.  Hoganas from Sweden have perhaps the strongest balance sheet of all the vendors at the show.  And their inductors are good.

Intelligent Stacks

Monitoring of the IGBT performance while the stack is running looks like a great feature.  Amantys had gate drives that did this.  That company went by the wayside when they folded at the beginning of the year. .  Two other vendors Infineon and AgileStack have created intelligent stacks and AgileSwitch are doing replacement gate drives for the Amantys part.  Contact Rob at AgileSwitch for their intelligent gate drives.

AgileSwitch - An Intelligent Stacks which needs a Digital Power Controllers

AgileSwitch Power Stack – Intelligence and robust implementation.










These intelligent stacks have microprocessors or FPGAs that can monitor the stack performance and provide data for controller to do condition monitoring and system performance analysis.  The Infineon MiPaqPro has a great water cooled heatsink plate that may become the new high performance low cost standard for heatsinks.  The monitoring for the IGBTs is in the stack and there was a fiber optic interface also.  Fiber optics are a good idea for monitoring as they provide great safety in the event of a fault or failure.  Fiber optic systems are also very robust in highly noisy EM environments.

The AgileSwitch stack is a great little converter.  It has integrated gate drives and has the ability to self monitor and provide digital output for status and current via a digital link.  This link is electrical.  AgileStack do not yet have a fiber optic link for their stack.  Their system is however very flexible and all the external signals are differential which gives higher noise immunity.

The AgileStack system can also come with inbuilt low inductance DC bus capacitors.  It looks to be a great solution.

All you need is a controller – Intelligent Stacks need Digital Power Controllers

The stacks at PCIM all need inductors and capacitors for the grid coupling filters.  There were lots of capacitor and inductor vendors at the show.  The stacks also need controllers to make them switch.  How this controller is implemented is not the concern of the stack manufacturer as all they need is the gate dive signals.  Ensuring that the gate drive signals make the converter do as required is the missing piece in the the three trends at PCIM.

It seems that power electronics companies can now purchase off the shelf power stacks.  By adding inductors and capacitors from other vendors the converter is almost complete.

Then the controller is required.  The stack manufacturers and the inductor manufacturers have solved two thirds of the power converter.  The controller is the missing part of the puzzle.  Get your digital power controller from ELMG Digital Power.

Get the ELMG Digital Power Controller Technology by clicking here