Research On Control Strategy Of Dual-PWM Converter For Direct-driven Wind Turbine

In recent years, along with the decreasing of conventional reserves and more serious of environment pollution, it has become the primary mission for all countries to find a new kind of renewable and clean energy. Among many different kinds of new energy, the wind energy attracts many researchers’attention around the world with some key competitive advantages:low cost and non-pollution.Direct-driven permanent magnet wind power generator is one of the most promising wind power generation systems. As a key component in grid interconnection of wind farms, full power converter control is particularly important. With the increasing capacity of wind power generators, control accuracy and stability is under higher requirement. This article focus on dual-PWM converter of direct-driven permanent magnet wind power generation system, the control strategy of converter system is mainly researched. The main achievements of the paper are as following:The current development situation of wind power generation is analyzed. And the converter topologies and control technology development of direct-driven wind turbine is introduced. Based on the wind turbine system operation mechanism, mathematical models of wind speed, wind turbine, permanent magnet synchronous generator (PMSG) and dual-PWM converter are built. Then the control strategies of generator-side and grid-side converter are analyzed. It lays the foundation for simulation model in the following research.The whole wind turbine system simulation model is established based on Matlab/Simulink. To track the maximum power point of wind power under rated wind speed, for higher efficiency of the wind power generation, rotor flux-orientation vector control method is applied to generator-side converter control. At the same time, when wind speed and external circumstances change, the voltage orientation control strategy is used to the grid-side in order to keep the voltage stability of the DC side capacitance and realize the decoupling control of active power and reactive power.The change of wind speed over time is random and non-deterministic, and the wind power generation system is non-linear and strong coupling, it is difficult for traditional PI controller to obtain good control results. To obtain good dynamic performance, the fuzzy self-tuning PI controller is adopted in the speed closed-loop, PI controller is adopted in the current closed-loop. The similar double-closed-loop is selected in grid-side control strategy, and the fuzzy self-tuning PI controller is adopted in the voltage closed-loop, PI controller is adopted in the current closed-loop. Simulation results show that its control effect is much better than that of conventional PI controller.The PI parameters cannot fully adjust to the change of operating conditions. Thus, the traditional PI control and fuzzy control are combined for variable PI parameters. But the design of fuzzy controller has no classic and systematic method of guidance, and the control effect is sensitive to the parameters changes. To solve the problem, the Particle Swarm Optimization (PSO) is applied to optimize the parameters of fuzzy controller. And the simulation results show PSO high efficiency for solving such optimization problems.