kW Converters ‑ High Frequency Medium Power Isolated Converters

This project targeting the medium power level converters (few kW) at high frequency, based on the expertise in the existing research carried out in power electronics group. Together with industrial partners such as SAAB anew, more effective high frequency kW converters will be developed.

Background

The complexity in the power grid as a result of household micro-power generation and the introduction of electrical vehicles (EVs) is strongly increasing the need for the light weight and efficient power conversion in the few kW range. There is a consensus in the electrical automotive industry nowadays that the charging system will be divided into a DC fast charging (off board) and an on-vehicle single phase AC over-night charger. The battery side of the vehicle is a high voltage DC source and needs appropriate isolation for safety which demands the isolated converters. This is because a fault can easily be detected and the system can be turned off nicely and quietly instead of a short circuit that will lead damages and possibly even explosion in the battery. The large amount of batteries in the electrical vehicles are expected to be connected to the grid so that the energy can be fed back to the grid for power levelling and reduce the required peak power generations in the morning and evening hours. The batteries can be charged during night time where the overall energy consumption is the least. In order to accomplish such a scenario the on-board converters must be of bidirectional type so that it can also deliver the energy back to the grid instead of using separate converters for this task. The project will get specifications from Volvo cars AB ensuring that relevant and complete designs are carried out and they will also participate actively within the project contributing with their expertise in the application requirements.

The introduction of new semiconductor devices in Silicon-Carbide and Gallium-Nitride opens new possibilities in increasing the switching frequency for high power levels and hence will be utilized in the project. In order to successfully demonstrate high frequency kW converters, further research must be conducted in four different areas:

1. Transformers
2. Converter topologies
3. EMI filters
4. Converter control

Mid Sweden University have in a few years reached the research front in high frequency magnetics and converters for power transfer applications in the power levels of 50-100W. This project targeting the medium power level converters (few kW) at high frequency, based on the expertise in the existing research carried out in power electronics group at Mid Sweden University.

At high power the energy in the electromagnetic interference also increases and will be a major challenge to restrict this to the allowed limits. SAAB EMC Services has a very solid knowledge in the area of EMC since 1970 and will contribute in the EMC design issues. EG electronics (or ETAL Group AB) have a strong position in magnetic components that are of most importance in both the converter and the EMC filter, especially at higher frequencies than normal where off-the-shelf components often are insufficient. A consequence of increasing the switching frequency above 150 kHz is that not only the harmonics but also the fundamental frequency containing much more energy must be filtered by the line filter. This might result in that the reduction of size achieved in the switching circuit is cancelled by the increased complexity in the input EMI filter. Well above 150 kHz, it would thus be more attractive increasing the frequency further as the input filter that occupies a significant part of the volume can in such cases be reduced in dimensions due to the smaller circuit elements required.

Goal

The goal with the project is to reach the research front at medium power applications but also to advance these further enabling more compact, high power density and integrated power converters for medium power applications. By participating in the project, the industrial partners get an early access to future converter technology and can prepare for expected customer needs of the future.

The project aim is to develop technology for coming generation of energy efficient high frequency medium power (kW) converters.

• Transformer
  • Develop transformer technology for next generation high frequency medium power applications.
  • Targeted transformer efficiency is >98% at the specified power level
• Isolated power converter
  • Develop necessary power electronics modules for Power Converter
  • Power Factor Correction unit
  • Targeted PF > 0.98, THD : < 5% from 50% load to full load
  • Targeted AC/DC Converter efficiency >95% including active PFC
  • Targeted DC/DC Converter efficiency >97%
  • Both PFC and converter will be designed to meet the EMC compliance.
• EMI filter for converter and PFC
  • Demonstrator Converter
• Design a full demonstrator converter for a medium power high frequency converter