Multiple Control Method for Bidirectional Subway Substation Based on Sag Characteristics

With the development of the economy and society, traffic congestion and environmental pollution in large and medium-sized cities in China are becoming increasingly serious, which has had a huge impact on the quality of life of urban residents. The development of urban rail transit such as subways and light rail has become an effective measure to alleviate this problem. The operation of subway trains has the characteristics of short distance between stations, high running speed, frequent starting, and braking. Currently, most of the energy treatment methods for regenerative braking in urban rail transit are consumed through braking resistors, resulting in serious energy waste. Therefore, improving the utilization rate of regenerative braking energy is of great significance for the energy-saving operation of rail transit. The use of a bidirectional substation scheme, which replaces a regular 24-pulse rectifier with a four-quadrant PWM converter, can invert regenerative braking energy back into the power grid, and the four-quadrant converter also has the characteristic of controllable output voltage. However, currently, bidirectional substations use constant voltage or quasi-constant voltage control, and the advantages of controllable output voltage have not been fully explored. This article studies a three-level four-quadrant converter for bidirectional substations and its control method for parallel operation. For subway lines using bidirectional substations, a control method is proposed to change the output external characteristic slope of the substation in real time based on train power and position. This method can improve the power interaction performance between trains and reduce the electrical energy of the substation's inverter return network.