Research On Parallel Control Strategy Of T-type Three-level Inverters Base On Master-slave Control

With the rapid development of science and technology, the power supply technology has been developed rapidly. The uninterruptible power supply system with the core of the inverter is more and more widely used in the fields of banking, military, medical, aerospace and so on.T-type three-level inverter with low harmonic content, the system efficiency advantages and so on. However, the capacity of a single T-type three-level inverter is limited, which cannot meet the requirements of high reliability, large capacity and modularity. Therefore, the parallel operation of T-type three-level inverters is today's mainstream device. But the parallel T-type three-level inverter will produce zero-sequence circulating current (ZSCC). ZSCC will make the current serious distortion, increase the loss and reduce the efficiency of the system,Therefore, it is necessary to effectively suppress the ZSCC between parallel T-type three-level inverters.In this paper, the operating principle of T-type three-level inverter topology is analyzed,and the mathematical model is established to determine the voltage and current double closed loop control strategy of T-type three-level inverter. Based on the analysis of the causes about the neutral point voltage deviation of the T-type three-level inverter, the neutral point voltage deviation feedback control method is studied. At the same time, the modulation strategy of improving voltage utilization is discussed. On the basis of the research of single inverter operation control strategy, the loop condition of ZSCC of two T-type three-level inverters in parallel has been analyzed, and the mathematical model of ZSCC has been established. There are odd times of 150Hz components in ZSCC through the analysis of the ZSCC. Then, the feed forward control strategy based on proportional integral and resonant controller is used to suppress the ZSCC. At the same time, the master-slave control strategy based on redundant logic is adopted for the parallel system of two T-type three-level inverters, and uninterruptible power supply function of the parallel inverter system can be effectively improved.Finally, the system simulation model is verified by PSIM software. ARM (STM32F407ZG)is used as the core of digital control, and the experimental platform of the parallel system of T-type three-level inverters has been built. The simulation and experimental results verify the feasibility and rationality of the control strategy used in this paper.