Filter parameter optimization design of single-phase LCL-type three-level rectifier equipped in train for high-speed-railway harmonic resonance suppression

Nowadays high-frequency resonances occur frequently and severely disrupt the normal operation of high-speed railways in China. The excitation prerequisite of high-frequency harmonic resonance is that the frequency of harmonic components, introduced by grid-side traction ac-dc converter in trains, matches with the inherent resonance frequency of traction power supply system. In order to eliminate high-frequency harmonic resonance, a single-phase three-level neutral-point-clamped (NPC) voltage source rectifier(VSR) applied in china railway high-speed 2(CRH2) with LCL-filter is more suitable due to its better attenuation characteristics on high frequencies. However, the parameters design for LCL-filter is more complicated, due to the inhibiting effect of the high-frequency harmonic current. Meanwhile the number of filter parameters increases from one to three compared with the L-filter. Therefore, parameters of LCL-filter should be treated carefully to gain good performance. Firstly, this paper discusses the single-phase LCL-type three-level rectifier topology. And then the total filter inductance expression of rectifier is deduced, and the relationships between inductance ratio, filter capacitor and resonant frequency, harmonic attenuation ratio are discussed. In addition, in order to neutralize the resonance introduced by LCL-filter, a new passive damping method is adopted due to its simplicity and reliability. Then, the parameter impacts of the LCL-filter are intuitively drawn on graphs by theoretical derivation. Also a simple engineering design criterion is reported to find the optimized parameters of LCL-filter. Finally, feasibility and effectiveness of the optimized parameter scheme of LCL-filter are verified by hardware-in-loop (HIL) experimental results.