The Control And Design Of Three-Phase Four-Leg Inverter

The science and technology of the modern world is developing by leaps and bounds. Thus the power quality of grids have been influenced by the mounting number of asymmetric loads. Recently, the three-phase four-leg inverter which adds a bridge to three-phase three-bridge inverter has been researched because of the merit of the compacter structure, smaller bulk and higher efficiency, which has brought vigor into the power system with broad application prospects. Of course, the control method for three-phase four-leg inverter becomes much more complex and difficult to achieve. Therefore, the work in this paper is divided into the following major parts:Firstly, based onγcomponent control in three-dimensional space vector, the working principle of the three-phase four-leg inverter is analyzed, and a new controller is proposed. The comparison of output voltage vectors among linear, non-linear, balanced and unbalanced loads shows that theγcomponent is the key influencing factor on the unbalance of three-phase output voltage, and thus the load imbalance canbe compensated completely in order to controlγcomponent.Secondly, another new control method is proposed based on positive feedback of current control and three-dimensional space vector modulation. Through analysing the four-leg inverter system, three-phase unbalanced current is introduced based on the three-phase voltage feedback control. Forthermore, the amount of imbalance is increased through positive feedback in order to control the balanceness of three-phase output voltage more quickly and accurately.Thirdly, a dynamic reference voltage hysteretic control scheme is presented, through theoretical analysis of electric circuit. Dynamic reference voltage of the fourth bridge is achieved to make the control scheme more flexibility and adjustability. The proposed method is effective to implement output regulation of the inverter.Finally, the system simulation model is built using MATLAB/Simulink to prove the proposed method and the simulation results consistent with the theoretical analysis. Furthermore, a 300W/50Hz three-phase four-leg inverter is built under the digital signal processor (TMS320F2812 DSP). The experiment results show validate the feasibility of the proposed method.