A novel Multilevel Power Quality Compensator for electrified railway

Connected to high-voltage power system directly, electrified railway is a particular user to power system, and its loads have the characteristics such as non-liner, asymmetry and volatility and so on. Researched on Chunshen traction substation which belongs to Shanghai-Hangzhou electrified railway, and accorded to the requirements and characteristics of comprehensive management to harmonics, reactive power and negative sequence currents in electrified railway, this paper proposes a novel Multilevel Power Quality Compensator (MPQC). This novel MPQC is composed of two single-phase cascaded inverters by sharing the DC capacitors. Each cascaded inverter is made of two cascaded H-bridge inverters and the ratio of the DC voltage is 3:1, then, connects to traction power system via grid-transformer. By analyzing the working principle of the MPQC, researching the multilevel direct pulse width modulation (MDPWM) method, this work presented multilevel inverter control strategy based on energy balance. Simulation and Experimental results proved this novel MQPC was reliable, could compensate the both feeders in traction power system simultaneously, and also could manage the power quality of the electrified railway comprehensively to achieve satisfactory compensation effects.