The Research On Three-Phase Four-Leg Inverter Based On 3D-SVM

Generally, the traditional three-phase three-leg inverters are used widely with three phase balanced loads. But, when the three phase loads are unbalanced or nonlinear, three phase voltage outputs can not be symmetrical. This paper presents a three-phase four-leg inverter. The three-phase four-leg inverter can supply a midpoint to the three phase unbalanced loads. It can control the zero sequence voltages and currents,so the three-phase four-leg inverter outputs three phase symmetrical voltages.Using symmetrical components, this paper analysises steady state of three-phase four-leg inverter. Three-dimensional space vector modulation scheme, that has high DC voltage utilization and can result in a low distortion, is proposed for three-phase four-leg inverter. The algorithm of three-dimensional space vector modulation is depict in detail.Then the mathematic model of three-phase four-leg inverter is established in two different coordinates. Based on comparison of three-phase four-leg inverter control strategies, this paper introduces a novel controller in three-phase four-leg inverter under clockwise and anti-clockwise rotating synchronous frame. The positive sequence, negative sequence and zero sequence components are controlled independently. The control strategy accomplishes the decoupling of the three-phase four- leg inverter. Using MATLAB software, the simulation of system control strategy validates consistency with theory analysis under open loop and closed loop. The control strategy is feasible.Finally, the experiments are completed using the TMS320LF2407 digital controller. The three-phase four-legg inverter can output three-phase balanced AC voltage under the unbalanced load conditions. The control strategy is verified.