Twenty-seven level co-phase traction power supply system

For the sake of eliminating the power quality problems including negative-sequence and reactive power currents at the electric railway traction power supply system, a new type of co-phase traction power supply system (CTPSS) is proposed, which is composed of V/v traction transformers and the new multilevel power quality conditioner (MPQC) based on voltage source and current source in series. The voltage source adopts hybrid cascaded 27 level converter, and the fundamental component of its output voltage has the same frequency, the same phase and the near equal RMS value with the fundamental voltage of traction transformer secondary winding, so that there is the low level voltage in the current sources. The current source adopts the single phase three-level converter, and realizes reactive power and negative-sequence compensation by tracking the compensation current reference signal. The voltage source bears the main power of the system, and its switching frequency is low, so the power transfer efficiency of the system is high. The switching frequency of current source is high, so the system has good dynamic and steady-state response performance. This paper analyzes the system structure and its equivalent circuit, compensation current detection method and control strategy. Simulations are supplied to show that the studied scheme is valid and practicable.