Research On Low-frequency Oscillation Of Four-quadrant Converter In High-speed Trains

In high-speed trains, single-phase four quadrant converter(4Q) has advantages of energy bi-directional flow, high power factor and low AC current harmonic. However, with the rapid development of high-speed railway and the use of new AC-DC-AC drive electric locomotives and CRHs, the high frequency resonance or low frequency oscillation problems caused by the vehicle-grid parameters mismatch have occurred. But the low frequency oscillation accidents which have occurred frequently in China and have a certain influence on the safety of railway operation.Based on the oscillation characteristics, traction power supply system is simplified as the thevenin equivalent model. The equivalent model of the coupling system is built between traction power supply system and multiple trains running at the same time, in which 4Q is controlled by transient current method. With the small signal model, the phenomenon that system stability is worse with trains increasing is explained based on the stability criterion.The damping ratio and oscillation frequency of multiple trains system are analyzed, and after that, the relation between oscillation and control parameters of 4Q is analyzed quantitatively. What’s more, the oscillation amplitude and oscillation frequency are analyzed and the saturation nonlinear characteristics are analyzed with Hopf bifurcation theory. Meanwhile, the effect factors of oscillation frequency are studied through the analysis of CRH5 test in QingDao.Based on the analysis results, the active damping compensation control strategy is put forward. The frequency domain analysis comparison shows that low pass filtering feedback compensation method can guarantee the stability of more trains running, and the dynamic effect is better among the suppressing measures including adjusting control parameters, adding proportional feedback damping compensation and adding low pass filtering feedback compensation link. The limitation on the train number is analyzed considering the condition of system circuit itself.Finally, the result of theoretical analysis is validated on experiments platform.