Research on SVPWM strategy for three-phase four-leg Inverter using natural coordinate

Three-phase four-leg medium frequency inverter is gradually able to meet the needs of avionics and radar equipments on power supply, which can maintain a stable three-phase voltage output under unbalanced load. In order to study the capacity under unbalanced load of the inverter, the Space Vector Pulse-width Modulation (SVPWM) in natural coordinate is analyzed firstly, which reduces the complexity of coordinate transformation, vector selection and duty cycle calculation in α-β-γ coordinate, as well as facilitates the realization of digital control. By analyzing the average current model of the three-phase four-leg topology, the load current is sampled in real time and the reference voltage is calculated so that the inverter can adapt to various unbalanced loads, the PI controller is used to stabilize the output voltage. Simulation and experiments verify that the inverter can bear non-linear and unbalanced load, total harmonic distortion of the output voltage waveform is small.