Enhanced Harmonic Current Injecting Method for Impedance Scanning Field Tests of Electric Railway Systems

The equivalent input impedance of power system usually needs to be obtained by an impedance scanning test in practical applications, i.e., a harmonic generator is utilized to emit fully controllable disturbing signals, and response is recorded to calculate the input impedance. However, in those high voltage application scenarios, the leakage inductance of a boosting transformer of the harmonic generator will reduce the harmonic current generation capacity heavily. This paper proposes an enhanced harmonic current injecting method based on the virtual impedance methodology for impedance tests in the traction power supply system (TPSS) of electric railways. By impedance shaping, converters of the harmonic generator can be regarded as a virtual capacitance. Its capacitive reactance can offset partial inductive leakage reactance of the boosting transformer at high frequencies. With this proposed method, a larger harmonic current can be injected into the TPSS under test at 25kV high voltage level more easily. Simulation results and experimental results based on StarSim Hardware-in-the-loop (HIL) platform confirm the effectiveness of the proposed method. The results show that the injected harmonic current at 2600 Hz at 25kV was increased by 133%.