Modulated Model Predictive Control for Multilevel Cascaded H-Bridge Converter-Based Static Synchronous Compensator

The model predictive control (MPC) methods show certain limits when applied to the multilevel converters, such as unfixed switching frequency, large computation burden, and complex weighting factors selection. This paper proposes a novel modulated model predictive control (M2PC) method for cascaded H-bridge (CHB) converter based static synchronous compensator (STATCOM). Instead of multi-targets integration and weighting factors design, the proposed method disintegrates the voltage balancing control process from the cost function. The evaluated control sets for output current control is decided by the search step and the search range in each period. By properly design and selection of the adaptive search step for the output voltage references under α-β coordinate, the search range can be reduced, which greatly reduces the number of evaluated control sets in each control period. Therefore, the dynamic of output characteristics and the low prediction computation burden of the MPC method are guaranteed simultaneously. In addition, with the simple and independent integration of the capacitor voltage balancing control, the proposed method can be easily applied in the CHB converter based STATCOM application. Furthermore, this paper provides a delay compensation for the prediction process. Simulation and experimental results verify the effectiveness of the proposed method.