Objective The application of bi-directional converters in China’s urban rail transit is still in the promotion stage. Various metro companies have conducted beneficial explorations on the configuration schemes of bi-directional converters, and a widely recognized industry consensus has not yet been formed. In particular, cases using two bi-directional converters per traction substation are rare with no lines currently in operation in China, and the power supply reliability of bi-directional converters is slightly lower. Therefore, a systematic study on the application of bi-directional converters is required.

Method The application of bi-directional converters at home and abroad is investigated, and economic and technical comparisons of configuration schemes are conducted. Schemes for traction substation positioning, equipment capacity selection, main electrical wiring, and equipment layout under the condition of full bi-directional converters are studied, along with the characteristics of relay protection configuration and settings.

Result & Conclusion  With the promotion and application of bi-directional converters, their functional advantages and reliability are preliminarily verified. The configuration scheme for traction units is gradually transitioning from three sets to two sets, and specific configuration schemes can be selected based on project requirements. Through systematic optimization of main electrical wiring, equipment layout, and frame protection settings, the reliability of full bi-directional converter applications can be enhanced. It is recommended to adopt a scheme where two sets of bi-directional converters are respectively connected to two sections of the medium-voltage 35 kV busbars, thereby reducing the feedback of train braking energy to the 110 kV grid.