Modeling and Control Method to Suppress Common-Mode Resonance Circulating Current for High-Power Parallel Three-Level Inverters System With Improved LCL Filter

Abstract

In parallel three-level inverters, to eliminate the undesired internal common-mode (CM) resonance circulating currents (ICMRCCs) and external CM resonance circulating currents (ECMRCCs) introduced by the improved <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> , the inverter-side CM current feedback (ICMCF) control is presented. However, since the switching frequency of the inverters is generally low in high-power applications to reduce power loss, the stability of the ICMCF control will be threatened by the delays of digital controller. In this case, the existing methods are not capable of ICMRCC and ECMRCC suppression any more. To deal with the situation, an improved CM resonance circulating current control method for high-power parallel inverters is proposed. First, the model of ICMCF with control delay is established. Second, the influences of control delay with different sampling modes on the stability of CM current control are investigated. Based on this, the allowable range of control delays and sampling frequency to keep the system stable is analyzed and deduced. Third, the multisampling mode is further extended to CM current control in the parallel inverters. The analysis results show that the stability margin and control bandwidth of the ICMCF control are significantly improved. Finally, the theoretical analysis and proposed control method are verified by simulation and experiment.