Control algorithm design of auxiliary power unit in high-speed electric multiple unit

Control algorithm for the auxiliary power unit (APU) of CRH2 350 km/h electric multiple unit (EMU) is designed in this paper. The front stage of APU is a four-quadrant rectifier, and the latter is a three-phase voltage inverter. Double closed-loop control algorithm based on current decoupling is used for the four-quadrant rectifier. Double closed-loop control algorithm based on voltage and current decoupling is used for the three-phase voltage inverter. In order to suppress the large amount of output voltage harmonics due to the auxiliary rectifier applied as load, a repetitive control loop is added to the instantaneous voltage loop. In addition, a novel short-circuit current limiting control algorithm is designed for the three-phase inverter. The feasibility and effectiveness of the proposed controller is verified by simulation and experimental results of a 220kVA APU. The single-phase input power factor closely achieves one when fully loaded. The output voltage THD reduces significantly under rectifier load. APU could limit the short-circuit current properly, and quickly restore the rated output without protection action when short-circuit is removed.