Simulation Analysis Of Grid-connected Inverter Control Strategy Of Direct-driven Wind Power System

Nowadays, the industry is rapidly developing and the energy consumption is increasing.As a kind of clean and renewable energy, the wind power has attracted every county’sattention. Wind power technology is the most direct use and the most effective transformationfor the rich wind power resources. At present, the wind turbine system with a permanentmagnet synchronous generator (PMSG) has become the hot spot in the world wide researchbecause of its unique advantage. The converter is the core technology of the wind powersystem. In this paper, the structure, the control theory and the operation characteristic of thedirect driving wind power grid inverter have been studied by the theoretical analysis and thesimulation.Firstly, this paper briefly introduced the working principle of the direct-driven windpower system with full power and back to back double PWM converters, and emphasized theimportance of the grid inverter. According to the working principle, the mathematical modelsof the grid-connected inverter were established in the three-phase static coordinate system,two phase static coordination system and two phase rotation coordination system respectively.Then a feed forward decoupling double closed loop control strategy was proposed, and thecalculation method of control parameters was deduced. Furthermore, the analysis and theresearch have been conducted on the principle and realization method of the space vectorpulse width modulation (SVPWM) method.Secondly, some work has been done to the Low voltage ride through capability ofD-PMSG, especial to the three-phase symmetrical fault of gird voltage. This paper designed anew protection circuit of DC side, which used super capacitor as the energy storage device,and presented the simplified model of the super capacitor and the control method of thebi-directional DC-DC converter. In order to meet the requirement on the reactive power in thewind power station, this paper proposed the reactive power compensation control strategy.Finally, the dynamic performance of the grid inverter for the PMSG was simulated withdifferent control methods during the normal working and symmetrical dip for the networkvoltage respectively. The results have indicated that the current change of grid converter andchange of direct bus have important influences on dynamic response of PMSGsystem. It can make the grid current track the network voltage and synchronize successfullyby using the double closed loop control strategy and adjusting the control parameters, and italso makes DC side voltage steady; when the grid voltage drop deeply, the reactive powercompensation control strategy and the DC side protection circuit, not only make DC sidevoltage more stable, but also provide the reactive power for the wind farms.