Simulation Analysis Of Control System Of Direct Driven Square Wave Permanent Synchronous Wind Generator

With the development of large power wind generation system, the directly connected driven structure is made up of wind turbine and Permanent Magnet Synchronous Generator (PMSG) are attracting increasing attention. Because the direct-drive permanent magnet synchronous wind generation system leaves out the gearbox that is easy to have malfunction, the structure improve the stability and reliability of whole generation system.Against the characteristic of function that the wind turbine tracks the maximum power point, a novel maximum power point tracking (MPPT) strategy for the varied speed constant frequency direct-drive permanent magnet synchronous generation system was proposed. The structure of main circuit is that the permanent magnet synchronous generator is connected to a fixed dc-link through a three-phase diode rectifier and the dc-dc converter, and the dc-link connected to the grid through a voltage resource inverter. The boost circuit and inverter were controlled individually in the paper, that is, the electromagnetic torque is controlled by regulating the boost circuit and the balance between the power output to grid and the output power from generator is maintained by controlling the inverter.The improved MPPT control strategy can obtain the maximum torque difference of turbine torque and electromagnetism torque to adjust turbine speed and track the optimal velocity promptly in this way. When wind speed decreases, the turbine speed should also be decreased to release kinetic energy simultaneously, and the vast majority energy will be transformed into electricity. So as to reduce the turbine speed and release the kinetic energy quickly, the system needs to enhance the electric energy output. It means that the electromagnetism torque is maintained onto a high value and does not decrease with turbine torque reducing, in order to obtain high slowdown acceleration and achieve the optimal operation status promptly. Similarly, when the wind speed increases, the generator maintains a relatively low electromagnetism torque. The electromagnetism torque does not increase with the turbine torque raising and the speedup acceleration should be high, thus the system can more quickly achieve the optimal operation status.The storage and filter capacitor between the boost circuit and power inverter plays a buffer role between the input energy from generator and the inverter output energy to the electricity grid. According to the electromagnetic torque signal in the way of MPPT control strategy, only by varying the switch duty cycle the rectifier output current can be controlled. The electromagnetic torque can be controlled to change rotor speed to track the optimal speed and capture the most energy. The active and reactive power of inverter output control is based upon the input power from boost circuit and the reactive power that grid needs wind generation system output. Simultaneously, considering the system loss and unbalance of instantaneous active power, the input power, the capacitor voltage and the grid current feedback loops are introduced in the control unity. To maintain capacitor voltage of DC bus bar constant and the system power dynamical equilibrium, the system continually regulates the output of active power of inverter to guarantee the quality of output power.