Exceeding the Physical Limits of Power Electronics by Inverter Cumulation
Final Report Abstract
In this project, a new high-power rating and high-dynamic response power electronics system based on the concept of inverter cumulation has been investigated. This high performance system extends the physical limitation of current topologies based on single type market-available power electronics devices. Thus, it serves as an effective means of PHiL systems which have higher requirements for its power convention system. The core idea of the inverter cumulation is that by magnetically coupling different and identical inverters, the final cumulation system accumulates the power and dynamics characteristics from various subunits. The method of magnetic coupling (magnetic-series coupling of IGBT and MOSFET inverters) has demonstrated its superior characteristics compared to the conventional power units of a PHiL systems (e.g. grid emulators). One high power IGBT inverter is magnetically coupled with another high switching frequency MOSFET inverter. The two inverters operate with totally different characteristics (power, DC-link voltage, switching frequency, fundamental voltage and frequency). Because of the different power rating of the two inverters, it is very critical to ensure the safe operating condition of the smaller power rating sides. The original topology neglected the effect of the high-amplitude switching components from the IGBT inverter, which caused a fatal problem to the MOSFET inverter as a result of its rectifying and recharging working mode. After the first unsuccessful attempt, the researcher realized that the switching components at the output terminal of the IGBT inverter have to be filtered out. The next key issue of the project is the low pass output filter design and its control. There are mainly three types of filters: L, LC and LCL filter. Due to the limited filtering effect of the first order L-filter, LC and LCL filters are the two reasonable choices of most industrial applications. The output of the LC filter is the capacitor voltage. On the other side, the inductor current serves as the output variable of the LCL filter. Choosing a type of filter is determined by the desired output signal. The proposed inverter system is supposed to emulate the behavior of the power grid, therefore the voltage signals generation is the main task. In this case, it performs like a programmable voltage source, thus an LC filter is the right choice. On the other hand, LCL filter is suitable for a system working as a current source. Three different strategies including the conventional synchronous-frame PI controller, the popular stationary-frame resonant controller and the state space feedback controller are investigated and implemented. The prototype of the proposed inverter cumulation system was built. By emulating not only the normal operation but also the typical fault of the power grid it demonstrates its high performance as a PHiL grid emulator.
Publications
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“Development of a power-hardware-in-theloop application — Power grid emulator by using voltage source inverter cumulation”, 2015 IEEE Applied Power Electronics Conference and Exposition (APEC), Charlotte, NC, 2015
G. Si, J. Cordier and R. Kennel
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G. Si and R. Kennel, “Comparative study of PI controller and quadratic optimal regulator applied for a converter based PHiL grid emulator”, 2016 IEEE 8th International Power Electronics and Motion Control Conference (IPEMC-ECCE Asia), Hefei, 2016
G. Si and R. Kennel
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“Extending the Power Capability With Dynamic Performance of a Power-Hardware-in-the-Loop Application — Power Grid Emulator Using Inverter Cumulation”, Industry Applications, IEEE Transactions on, vol. 52, no. 4, pp. 3193-3202, July-Aug. 2016
G. Si, J. Cordier and R. M. Kennel
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“Switch Mode Converter Based High Performance Power-Hardware-in-the-Loop Grid Emulator”, 2nd IEEE Southern Power Electronics Conference (SPEC 2016), Auckland, New Zealand, 2016
G. Si and R. Kennel
