适用于输入输出频率接近或相同的组合式模块化多电平矩阵变换器拓扑OA

The modular multilevel matrix converter(M3C)is a topology that directly implements AC-AC conversion and has advantages such as easy scalability,bidirectional energy flow,and modularity.It has broad application prospects in pumped-storage power plants,wind power plants,and motor drives.Since the M3C operates between two AC systems at different frequencies,its arm power contains a beat-frequency component determined by the difference between the input and output frequencies.When the input and output frequencies are close or equal,this beat-frequency power component manifests as low-frequency pulsations or even DC components,resulting in significant low-frequency fluctuations or DC offsets in the arm submodule capacitor voltages.In severe cases,it can cause the system to malfunction. Existing approaches primarily suppress capacitor-voltage fluctuations in submodules by injecting circulating current or by simultaneously injecting circulating current and common-mode voltages.These approaches come at the cost of increased voltage and current stresses on the converter,leading to higher losses.Therefore,this paper proposes a novel topology combining an M3C with a cascaded H-bridge.This configuration effectively reduces capacitor voltage fluctuations in submodules when input and output frequencies are close or equal,without increasing voltage and current stresses on the bridge arms.It retains the advantages of conventional M3C,such as modular design flexibility,low output harmonics,and scalability.First,a mathematical model of the combined M3C is established,and its operating principle is explained.Then,the mechanism of voltage fluctuations in M3C bridge-arm capacitors is analyzed,and a control method is proposed that uses a cascaded H-bridge to provide reactive power to the load,thereby reducing capacitor voltage fluctuations.Compared with conventional methods,the combined M3C achieves a smaller range of capacitor-voltage fluctuations while avoiding the injection of common-mode voltage or circulating currents.Additionally,the device costs,power loss,and current THD are lower than those of conventional methods.Finally,the feasibility and effectiveness of the proposed topology and its control strategy are verified through simulation and experiments. The main conclusions are as follows.(1)A mathematical model of the combined M3C topology is established,and its working principle is explained.In addition,the capacitor voltage fluctuations in the M3C bridge arms are analyzed.(2)A method with a cascaded H-bridge for capacitive compensation is proposed,where the load's reactive power is supplied by the cascaded H-bridge,thereby reducing capacitor voltage fluctuations in the M3C bridge arm submodules.(3)Compared to conventional methods,this approach does not need to inject common-mode voltage and circulating currents,reducing voltage and current stress on the bridge arms.Additionally,it minimizes fluctuations in arm capacitor voltages and reduces device costs and power losses.Finally,simulations and experiments validate the proposed topology and control strategy.