"The Power Electronics, Machines and Drives (PEMD) community gathered at Austin Court, Birmingham on 1st December 2015 for a one day seminar “Passive Components for Power Electronics” organised by the IET PEMD TPN with the support of the EPSRC Centre for Power Electronics. Over 70 attended with a good balance between academia and industry.
Passive components typically account for around 50% of the volume and weight of a power electronic converter, and with faster switching speeds and operating frequencies their design is critical to optimised solutions. Their importance has been recognised by the EPSRC Centre for Power Electronics, which has a dedicated theme to components.
This seminar brought together academics and industrialists with both component and systems interests. Mark Johnson, Director of the EPSRC Centre Chaired the event.
Phil Mellor (University of Bristol) who is driving the EPSRC PE Centre Components theme, opened the day with an overview of the activities within the theme and highlighting the challenges and opportunities. The drive towards higher power density and higher switching frequency are placing ever greater demands on passive components. Achieving EMI compliance and acceptable reliability are often limiting factors. It was evident from this talk that switching the latest wide band gap (WNG) power semiconductors as fast as possible is often not desirable, yet big benefits can result from their use at more modest switching frequencies. EMI compliance and short switching times can be achieved by controlling the switching profile at points of voltage deflection, and Phil showed some interesting work being undertaken in the Centre on gate drives incorporating chip based “intelligence” to modify effective gate drive resistance through the switching profile. Design tools were emphasised as key to optimised design. A very key message was that the way forward towards design optimisation must be based on a clear understanding of the fundamentals.
Pete James (Lyra Electronics) looked at the role and design of passives in a resonant converter intended for automotive (and other) application. Pete gave a very helpful introduction to resonant converter design, highlighting the critical role and characteristics of the passive components. A key observation was the difficulty in getting suppliers to specify critical parameters such as leakage inductance and manufacturing spread. Non-the-less, Pete described 12kW converter designs with 98/99% efficiency (at rated output).
Nick Simpson (University of Bristol) introduced the “multi-physics” design approach - coupled design tools – circuit design, electromagnetic design and thermal design, and how to design such tools to ensure designs emerge in the operators lifetime. Nick gave some very valuable advice on how to judge acceptable accuracy. This valuable work is ongoing.
Andrew Forsyth (University of Manchester) looked at the application of power dense inductors with WBG devices. The talk was referenced to a DC-DC converter design switching at 75kHz (which exposed some inductors in the design to 150kHz switching!). Thin film inductors were used with nano-crystaline cores – which proved to be a good technical solution for high frequency, high current DC inductors but at high cost. Andrew highlighted how in the process of the high frequency work his team had questioned and then disproved some “rules of thumb” relating to loss – Again fundamental understanding is critical for optimised design. This understanding extends to the critical area of thermal management, critical to size reduction.
Martyn Williamson and Richard Kenney (Siemens Limited) introduced us to some hard learnt lessons on the design of input EMI filters and DC link capacitors in industrial drives. Passive components are often constrained by the materials available. Input filters, invariably containing metalised film capacitors, have been shrinking in size as film thickness has been reduced. Martyn described the delight when in 2005 5mm polypropylene film was introduced, and the dismay as they started to see problems, particularly in humid conditions. Richard talked about the design criteria for DC link capacitors and the need to understand the rated voltage and temperature with respect to lifetime – Operate at rated Temperature and rated voltage and your capacitor will last only 4 months!!! Richard described how lifetimes of 10 years can be achieved.
Mark Timothy (GE Grid Solutions) introduced the audience to HVDC saturable reactor designs. It was interesting to see the design approach for reactors operating at currents around 5kA, 200 kg in weight and the size of a large suitcase. The designs are clearly well established and work well, but Mark highlighted the need for better theoretical models.
Mark Johnson wrapped up the meeting with a few observations:
- Passive components clearly remain the pinch point in the design of weight and volume optimised power electronic equipment.
- More work is needed on the fundamental, underpinning theoretical models for passive components.
And a challenge:
“Where are the step changes”
Answers please on the blog at IET Power Electronics, Machines & Drives.
Bill Drury
Chairman, PEMD TPN
w.drury@btinternet.com"
Presentations from the day are now available to view online via IET.tv.