Zero-Sequence Current Reduction Technique for Electrical Machine Emulators With DC Coupling by Regulating the SVM Zero States

In this article, a new zero-sequence current suppression technique for electrical machine emulators with reduced component count is proposed. The proposed control scheme is implemented by properly regulating the zero states in space vector modulation (SVM). It is well known that a machine emulator allows fast experimental validation of the control and design of a drive system without having a physical electrical machine, since the machine is replaced by another voltage-source converter and a three-phase inductor. However, in emulators with a coupled dc link, circulating zero-sequence current is freely developed creating additional load for the power switches. The currently available control methods require additional hardware common-mode filters to effectively reduce this current. Contrarily, the proposed SVM algorithm suppresses the zero-sequence current more effectively via direct compensation of common-mode voltage, and thus, no additional hardware filters are needed. Thus, an electrical machine emulator with less hardware requirements can be developed with the proposed control technique for being utilized in several laboratory test-bench applications. Experimental results on a 60-kW system validate the effectiveness of the proposed SVM algorithm, since the zero-sequence current amplitude has been measured to be 3.7% of the phase current or even less than this.