Control Strategy of Subway Bidirectional Converter for Suppressing Grid Background Harmonics

Objective The nonlinear power equipment in subway traction power supply systems causes distortions in grid voltage during operation, leading to large grid background harmonics, which will affect the grid-connected current quality of subway bidirectional converter. Therefore, it is necessary to study the control strategy of subway bidirectional converter to suppress the grid background harmonics. Method To effectively suppress the grid background harmonics, the suppression of the most common 5th, 7th, 11th and 13th harmonics in the grid is taken as the research target, and the unified transfer functions of power current and harmonic current loops under the α and β axes are established; in view of the problem of system instability caused by the small phase margin of PR（proportional resonance） controller for harmonic suppression, a zero-pole cancellation method is used to transform the PR controller into VR（vector resonance）, improving the system phase margin; and the tuning method of PI（proportional integral） controller and VR controller parameters for the power current loop is proposed. Result ＆ Conclusion The correctness and effectiveness of the control strategy and parameter setting method are verified through the RTDS（real-time digital simulation） test platform, achieving the purpose of effectively suppressing the grid background harmonics.