An Approach to Suppress Low-frequency Oscillation by Combining Extended State Observer with Model Predictive Control of EMUs Rectifier

Recently, a phenomenon of low frequency oscillation (LFO) occurred in electrified railways, which exhibits a synchronous voltage oscillation of about 2-7 Hz between the traction network and electric multiple units (EMUs). To suppress the LFO, an improved predictive control method combining with extended state observer (ESO) is proposed. First, the changes of system parameters and the unmodeled item in vehicle mathematical model are extended to a new variable and then estimated to compensate the calculated control voltage in real time. Second, the control voltage calculated by the cost function is combined with the control voltage by estimated ESO. The observer stability is analyzed by obtaining the transfer function, and the appropriate gains of observer are chosen through the pole assignment technique. The control performance among the basic predictive, dq decoupling and the proposed control is compared, respectively. The system robustness when system parameters change is discussed in detail. To further verify the effectiveness of the proposed method, an integrated dSPACE semi-physical experimental platform is constructed. The simulation and experimental results show that the proposed method not only effectively suppresses LFO, but also accelerates the response speed of the traction line-side converter (LSC), and reduces the distortion of grid-side and vehicle-side currents, and overcomes the disadvantages of MPC and dq decoupling control under the mismatching of system parameters.