Partially Signed Binary Voltage Control of Hybrid Modular Multilevel Converter

Abstract

This article proposes the partially signed binary voltage control (PSBVC) method for a hybrid modular multilevel converter (MMC) (HMMC), which has a mixture of half-bridge submodules (SMs) (HB-SMs) and full-bridge SMs (FB-SMs). With the proposed PSBVC method, the HMMC can generate a large number of voltage levels with much fewer SMs than the MMC and enhanced MMC (EMMC) by having different voltages for each FB-SM. That is, all HB-SMs have the same voltage and their sum in an arm is the same as the dc-link voltage. On the contrary, the voltages of FB-SM are sequentially decreased by half from HB-SM voltage. As the voltage level becomes more sophisticated, the circulating current decreases effectively because the voltages of HB-SMs are tightly regulated. As the result, the HMMC with the proposed PSBVC method is superior in not only harmonic performance but also circulating current. To verify the effectiveness of the HMMC with the proposed PSBVC method, its controller is firstly designed by the electromagnetic transients program (EMTP). Then, it is experimentally verified with the hardware prototype of HMMC. Finally, the main advantages of HMMC with the proposed PSBVC method are emphasized by comparing it with MMC and EMMC in detail.