An Improved Phase-shifted Carrier-based Modulation and Loss Distribution Analysis for MMC Using Full Bridge Sub-modules

Modular multilevel converter (MMC) is considered as one of the most promising and suitable converters in the high power applications. It is usually composited by a large number of half bridge or full bridge sub-modules (SMs). Right now MMC with half bridge SMs is the common choice and its modulation strategies have been researched on a lot. For MMC with full bridge SMs which is rarely focused on, it has shown the specific advantage of blocking DC fault and ride-through capability. This advantage make it more competitive in HVDC application because the DC-side short-circuit fault is very serious and the DC circuit breaker is not sufficiently mature and cost-effective. Conventionally, its modulation strategy can be similar as MMC using half bridge SMs, in which two states are used for one SM, inserted or bypassed. However, a full bridge SM has four switches and there are some redundancy switching states. An improved phase-shifted carrier-based modulation is proposed in this paper which makes each SM's loss evenly distributed in the two legs. Considering different power factors, the loss distribution is analyzed and compared with conventional modulation strategies based on the simulation in Matlab/Simulink, which verifies the effectiveness of the proposed modulation scheme.