Yanyan Shi

Robust model predictive current control strategy for three-phase voltage source PWM rectifiers

ABSTRACT Traditional model predictive control (MPC) strategy is highly dependent on the model and has poor robustness. To solve the problems, this paper proposes a robust model predictive current control strategy based on a disturbance observer. According to the current predictive model of three-phase voltage source PWM rectifiers (VSR), voltage vectors were selected by minimizing current errors in a fixed time interval. The operating procedure of the MPC scheme and the cause of errors were analysed when errors existed in the model. A disturbance observer was employed to eliminate the disturbance generated by model parameters mismatch via feed-forward compensation, which strengthened the robustness of the control system. To solve the problem caused by filter delay in MPC control, an improved compensation algorithm for the observer was presented. Simulation and experimental results indicate that the proposed robust model predictive current control scheme presents a better dynamic response and has stronger robustness compared with the traditional MPC.

Design and optimization of hybrid resonant loops for efficient wireless power transfer

Summary Frequency splitting, caused by magnetic overcoupling, is a great challenge in resonant wireless power transfer, which leads to decrease of transfer efficiency. In this paper, to avoid the frequency splitting, a new design of hybrid resonant loops with an inner coil positioned in the transmitter is proposed for efficient power transfer. It is shown to suppress dramatic variation of mutual inductance when the distance between transmitter and receiver decreases. Analytical expressions of the mutual inductance and the transfer efficiency for the proposed resonant wireless power transfer system are calculated. To obtain a relatively uniform mutual inductance with respect to the distance, the proposed resonant loops are optimized. Simulation and experiments are also performed to validate the effectiveness of the proposed resonant loops in eliminating the frequency splitting. The transfer efficiency remains higher than 80% when the transfer distance decreases below a critical value where frequency splitting occurs for conventional resonant loops. Furthermore, lateral and angular misalignments between the resonant loops are also considered and investigated. The results indicate that the proposed resonant loops are also applicable in suppressing the frequency splitting even in case of misalignments.

Current predictive control of three-phase voltage source PWM rectifiers under unbalanced grid voltage conditions

To improve the performance of three-phase voltage source pulse-width modulated (PWM) rectifiers (VSR) under unbalanced grid voltage conditions, a fixed-frequency current predictive control (CPC) strategy is presented. Instantaneous power of the three-phase VSR is analysed in a two-phase stationary frame. The calculation method for the reference current is improved to achieve the power stability at the AC side of the rectifier. Based on the current predictive model, the optimal duration of the voltage vectors is computed under the restricted condition of minimizing current error at α- and β-axes in fixed intervals. The control system is free of synchronous rotation coordinate transformation, and avoids positive and negative sequence decomposition, which simplifies the calculation. The simulation and experimental results show that the proposed control strategy is able to eliminate the AC current distortion effectively and depress DC link voltage fluctuation under unbalanced grid voltage. Furthermore, the control strategy has faster dynamic response ability, enhancing the control performance of the three-phase VSR system.

Synchronous Flux Weakening Control With Flux Linkage Prediction for Doubly-Fed Wind Power Generation Systems

Under grid-voltage dips, there exist dc and negative sequence components in the stator and rotor flux of doubly-fed induction generator (DFIG). As a result, higher transient overcurrent is generated in the rotor. To enhance the low-voltage ride-through (LVRT) ability of the DFIG, a synchronous flux weaken control strategy with flux linkage prediction is proposed to suppress the transient overcurrent. In the proposed control strategy, the deadbeat predictive control is used to realize rapid synchronization and weak interaction between the stator and rotor flux by flux linkage prediction under grid-voltage dips. A series of research is carried out on a typical 1.5-MW DFIG system, and comparisons are made with the LVRT control strategy based on proportional-resonant (PR) controller to validate the proposed control strategy. The results indicate that the proposed control strategy is effective in suppressing overcurrent in the stator and rotor and reducing oscillations in torque, which largely improves the performance of the DFIG during grid-voltage dips.