Uncertainty of the wind results in a fluctuating power output of wind turbine generators, and consequently, causes adverse impacts on the stability of system frequency and voltage. To smooth such power fluctuation, this study proposes a power quality control strategy based on a three-level hierarchical structure for windbattery energy storage hybrid power system, including grid demand calculating level, energy management level and voltage-source converters control level. The advantage of the control strategy is that the state of charge of a battery energy storage system is regulated within proper range and the voltage at the point of common coupling is kept stable while smoothing wind power. Effectiveness of the proposed method is validated by MATLAB/SIMULINK simulations and experiments.

To suppress zero-sequence circulating current in parallel operating inverters with common DC power supply, this paper proposes a new strategy based on Dual-carrier SVPWM and proportional resonant (PR) control, which use two opposite active vectors instead of zero vectors to suppress the higher frequency circulating current and reduces the lower frequency circulating current by means of zero-sequence circulating current closed-loop control based on PR controller. It has the advantages of high-efficiency usage of DC voltage, needless carrier synchronization and eliminating the circulating current. Simulation experiments verify the strategy's effectiveness in the two parallel inverters.