An Improved Hybrid Control Method for 400Hz Medium Frequency Inverter

The medium frequency inverter power supply (usually 400 Hz) can effectively reduce the size and weight of passive components. Therefore, it is widely used in airplanes, ships and other fields that require high power density. These fields usually have higher requirements on the quality of the output voltage waveform. For example, it is necessary to meet the voltage requirements of unbalanced or nonlinear loads and the smooth transition when the load changes suddenly. Compared with the line frequency inverter, the number of output pulses in one fundamental cycle of the medium frequency inverter (take 400 Hz as an example) is 1/8 of that. Under the same switching frequency, the number of switching in each fundamental wave cycle is reduced. Therefore, the sampling, calculation, filtering and sampling delay of the PWM in the digital control all affect the design of the controller. These cause the control of the system to be difficult. In this paper, a hybrid control is proposed. The method can ensure the high quality of the three-phase output voltage waveform of the inverter under unbalanced or nonlinear loads, and alleviate the voltage fluctuation when the load changes suddenly. The effectiveness of the method is verified by simulation.