Two-stage Four-legged Matrix Converter

The two-stage matrix converter is a new type of the matrix converter based on three phase AC-DC-AC two-stage topological structure and have physical rectifer and inverter which is similar to the traditional three phase AC-DC-AC converter. For its functions with a two-way flow of energy, sinusoidal input and output current, and controllable input power factor, without intermediate energy storage capacitance,it is a potential matrix converter with good prospect.But in normal applications,there usually exsists three-phase unbalenced loads or demands three-phase four-wires system.Since the two-stage matrix converter cannot provide road for zero sequence current, it has been limited to apply to such situations.The two-stage four-leg matrix converter is derived from the traditional two-stage matrix converter by adding a neutral leg in the inverter stage.As the neutral leg in the two-stage four-leg matrix converter can provide the road for zero sequence current, therefore the two-stage four-leg matrix converter is very suitable in three-phase four-wires applications.The topology of the two-stage four-leg matrix and the modulation methods were studied at first in this paper,math model of the two-stage four-leg matrix converter based on average in switching periods was also built. The paper also analysed the influence of unbalenced loads to the input currents in steady state. The close-loop control strategy and the design of the repetitive controller for this system was presented,the results of numeric simulation based on Matlab simulink toolbox demenstrates the correctness and feasibility of the control strategy.The paper analysed the nolinear factors in practical two-stage four-leg matrix converter and proposed various compensation strategies. At last,the carrier modulation and control algorithm were implementated on a 10 KVA prototype,the results demenstrates the correctness and feasibility of the modulation strategy and the control algorithm.