A hybrid inverter system for medium voltage applications using a low voltage auxiliary CSI

Abstract

Abstract-Hybrid converters consist of a main inverter processing the bulk of the power with poor waveform performance and a fast and versatile auxiliary inverter to correct the distortion. In this paper, the main converter is a medium voltage NPC inverter and the auxiliary inverter is a low-voltage and low-current rated current source inverter (CSI), with series capacitor being used to minimize the CSI voltage stress. The result is a high output current quality which is obtained with a very low switching stress in the main converter and a very small added installed power (<4%) in the CSI. This paper expands this concept by investigating the hybridization of a medium voltage inverter with an existing LCL filter and investigates the additional challenges related to resonances and proposes a solution for stabile operation.

Harmonic Analysis and Mitigation of Low-Frequency Switching Voltage Source Inverter With Auxiliary VSI

“…Unlike the harmonic current introduced by the grid side harmonic voltage, the switching harmonics is introduced by the switch mode voltage source at the converter side. To realize (9), there are two options, which are given by (12) and (13)…”

“…However, this kind of power conversion faces several shortcomings: 1) the LCC can not operate without the APF due to the high magnitude of the low order harmonics, 2) the performance of the APF is dependent on the gridimpedance [11]. Other hybrid power conversion systems consisting of a high-power VSI with low pulse-ratio and a low-power Current Source Inverter (CSI) with high switching frequency have also been proposed and investigated [13]- [17]. The challenge for switching harmonic filtering of the high power VSI with a common VSI based APF is that its current control bandwidth should be much higher than the traditional APFs.…”