Variable frequency converters (VFC) are becoming more and more important elements of an energy-efficient electric motor-driven system (EMDS). They help to adjust the speed and torque of the motor output to the required load of the application and thus are a major source of energy savings. On the other hand, a variable speed-driven system adds more cost and complexity, and the converter causes additional losses both in its own electronics as well as in the driven motor. The losses of converters for electric motor-driven systems have never been systematically and independently verified, as there are no consensus test standards on the subject. Following the publication of IEC 61800-9-2, edition 1, 2017 (IEC 61800-9-2, edition 1: Adjustable speed electrical power drive systems – Part 9–2: Ecodesign for power drive systems, motor starters, power electronics and their driven applications – Energy efficiency indicators for power drive systems and motor starters, Geneva, Switzerland, 2017), the need for a more robust testing protocol and repeatable results of tests from independent laboratories emerged and was recognized both by 4E EMSA (IEA Technology Collaboration Programme on Energy Efficient End-Use Equipment (4E), Electric Motor Systems Annex (EMSA)) and IEC SC 22G WG18 (IEC, Subcommittee (SC) 22G for Adjustable speed electric drive systems incorporating semiconductor power converters, Working Group (WG) 18 for Energy efficiency of adjustable speed electric power drive systems).
Also, the move by the European Commission to introduce in 2019 Minimum Energy Performance Standards for converter losses in the draft for the revision of the Ecodesign regulation no. 640 for motors (European Commission (EC), Commission Regulation No. 640/2009 of 22 July 2009 implementing Directive 2005/32/EC of the European Parliament and of the Council with regard to ecodesign requirements for electric motors, Brussels, Belgium, 2009) stimulated the research effort. Four independent labs (CalTest/Australia; DTI/Denmark; BFH/Switzerland and Advanced Energy/USA) agreed to team up for this project, financed by the four respective governments. Phase 1 of the Round Robin project started by the end of 2017 through early 2019. The goal of the project was to define/refine a proposed test method, known as Uniform Testing Protocol (UTP) and a Standard Reporting Format (SRF). By testing a number of converters, the project expected to provide a first feedback on the validity of the reference losses of the IEC standard.
The phase 1 report of March 2019 (Agamloh E., Baghurst A., Brunner C.U., Nielsen S.B., Vezzini A., EMSA IEC WG 18, Round Robin of Converter Losses, Report of Results of Phase 1, Zurich, Switzerland, March 2019. Available at: www.motorsystems.org) [
8] shows the results of 58 tests on nine converters between 0.75 kW and 11 kW. It documents excellent agreement of the results for losses and efficiencies. Between the four laboratories a high level of repeatability was achieved, despite the fact that 24 different load motors were used in the tests. The newly defined UTP testing methodology includes the precise definition of the product under test and its auxiliaries (filters, cooling fan, etc.), the selection of the nominal output current (rated or adapted to motor), the status of the converter (out-of-the-box, no automatic self-test run), the type and size of cabling and the preferred characteristics of the load motor (size vs. converter, rated current, IE-class, pole number, etc.). After the completion of phase 1, the UTP was updated with lessons learned into a new version (UTP2). About 60 converters are planned to be tested in phase 2 (Nielsen SB, Vezzini A, Preliminary results from (RR’C) round robin for converter losses, phase 2, in EEMODS’19 conference proceedings, Tokyo, Japan, 2019) from 2019–2020 [
9]. With the updated UTP2, a sufficient quantitative data will be made available to WG 18 to revise the reference losses in IEC 61800-9-2, which are widely seen as too high. Eventually, also the efficiency classification can be revised in an edition 2 of the standard, which is planned for 2021 publication.
