Papers by Author: Yuan Sheng Xiong

Abstract: Three-phase bidirectional AC/DC converter acts as a key part in DC microgrid. To improve the stability of DC bus voltage for the grid-connected mode in DC microgrid, a sliding mode or PI controller based on SVPWM modulator is designed for the bidirectional AC/DC converter in inverter mode. When the error between grid-connected current reference value and actual value is larger than the threshold value, the sliding mode controller is used. Otherwise, the PI controller is adopted. The great grid-connected current reference value fluctuation is simulated in PSIM software when the DC microgrid operates in the grid-connected inverter mode. The simulation results show that the gird-connected current actual value can fast track with the reference value. Then the dynamic response performance of DC bus voltage is improved.

Abstract: To improve the stability of DC bus voltage in DC microgrid, and reduce the impact on microgrid equipments by the DC bus voltage fluctuations, a supercapacitor energy storage (SCES) is designed to connect to the DC bus by the bi-directional converter. The controller is designed by the feedforward control and proportional method with the deadband. The great load disturbance is simulated in PSIM software when the DC microgrid operates in the grid-connected rectification mode. The simulation results show that SCES under the proposed control strategy can reduce the fluctuation range of the DC bus voltage in a wide range of load disturbances, and the dynamic response performance of DC bus voltage is improved.

Abstract: In order to maintain the maximum output power of the WGS (Wind generation system) for all wind speed conditions, a boost converter is used as the power interface between the WGS and DC microgrid. Traditional method is to directly measure the real-time output voltage and current of WGS by sensors. Considering the DC bus voltage is actually stable, the output voltage can be computed by the duty cycle of boost converter and the stable DC bus voltage. A MPPT method is proposed, which only measures the output current of WGS. The output scale power can be obtained by the output current and the duty cycle, and then the perturbation and observation method is executed. A number of voltage sensors and associated circuitry are cancelled. It reduces the interference and system cost and improves the system reliability. Simulation results with PSIM prove the validity of the proposed method.

Abstract: Single-state grid-connected photovoltaic (PV) system has only one stage of power conversion and the control objectives needed to be considered simultaneously include synchronization with the utility voltage, harmonics reduction for grid-connected current and etc. Then the complexity of control strategy is increased. To deal with the characteristics, sliding mode controller is used to achieve the synchronization between grid-connected current and grid voltage and to control the waveform of grid-connected current, and the slide surface is designed based on PI method. Σ−Δ modulator is proposed to achieve the fixed switching frequency. Simulation results show that the system has good performance and the system is feasible.