Papers by Author: Qing Song Liu

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.

Abstract: This study adopted a simulated evolutionary optimization algorithm, ant colony optimization algorithm to find the optimal unit commitment operation. The concepts such as status, strategy, and path, etc. were introduced to devise the optimization of unit commitment operation by ant colony optimization algorithm mode, so that the optimal unit commitment operation could be found by ant colony optimization algorithm. To cope with different constraints by additional penalties and restrict the statuses not satisfying the constraints by tabu table, the retrieval of ant colony optimization algorithm could always be performed in feasible region and the retrieval process of the algorithm was effectively conducted. It is feasible and efficient to find the optimal unit commitment operation by ant colony optimization algorithm, which was proved by stimulation.