Multi-functional bi-directional converter device and control method for traction power supply systems in urban rail transit

Traditional bi-directional converters serve as the key equipment for traction power supply and regenerative braking energy utilization in urban rail transit. However, designing these devices that are compatible with dual-voltage systems—specifically at DC 1500 V and DC 3000 V—while incorporating the functions of reactive power compensation, harmonic control, and negative sequence compensation remains a technical challenge in the industry. For this purpose, the paper proposes a multi-functional bi-directional converter device and control method. Firstly it analyzes the deficiencies of traditional bi-directional converters in actual application conditions, regarding compatibility with voltage system modes and power quality issues. It presents the topological design of a new multi-mode bi-directional converter device, along with a comprehensive control strategy for scenarios where the device is connected in parallel with a rectifier unit or used in combination with the single-phase AC mode. The proposed strategy encompasses reactive power compensation, harmonic control, and negative sequence compensation. Subsequent analysis based on a system simulation model verifies the effectiveness of the proposed solution in improving power quality, and demonstrates its technical feasibility and engineering application value.