Multi-rate Finite Control Set Model Predictive Control with Reduced Circulating Currents for Parallel Dual-Converter-Fed PMSM Drive

In the field of electrical drives, finite control set model predictive control (FCS-MPC) scheme is widely used due to its fast-dynamic response and superior ability to handle nonlinear constraints. However, the typical practical switching frequency of FCS-MPC is relatively lower than its sampling frequency, which limits the improvement of power density and efficiency. This problem becomes more pronounced when implementing FCS-MPC to parallel-connected converters, where the heavy calculation burden imposes limitations on employing high sampling frequency. As a result, large circulating currents are inevitable. To effectively suppress the circulating current, an improved multi-rate FCS-MPC scheme is proposed, where the reduction of circulating current is realized with two aspects. First, the control set is modified by categorizing the control variables into two groups, hence the regulation of circulating current is decoupled from the motor-side variables, resulting in improved precision and effectiveness of circulating current control. In addition, exhaustive enumeration of all possible switching states is also avoided. Second, multi-rate technique is integrated, where multiple control cycles are inserted within one sampling interval. Experimental results verify the effectiveness of the proposed scheme.