Research Of Doubly-Fed Induction Generator Control Strategy Under Power Grid Voltage Unbalance Situation

Large-scale application of wind power make on grid wind power systems must have faultride through ability. Power grid voltage unbalance is one of the most common faults， at thistime there is a negative sequence voltage component in the system. General doubly-fed inductionwind power generation system use PI controller and vector control in synchronous rotatingcoordinate system. When power grid contains a negative sequence voltage component， PIcontroller will result a shock. The shock of PI controller makes current has negative component，power and electromagnetic torque shock， which will damage the stability of motor and reducemotor life.According to the principle of superposition when power grid voltage unbalance system canbe treated as one positive sequence system plus one negative sequence system. The positivesequence system works in positive sequence synchronous rotating coordinate system， thenegative sequence system works in negative sequence synchronous rotating coordinate system，and both of them use PI controller and vector control. The sum of both system result is the givenof space vector pulse width modulation module.The reason of general control method works poorly when unbalance appears in system is PIcontroller can’t deal with ac signal. To solve this problem introduce a resonant to PI， which iscalled PIR controller will work in positive sequence synchronous rotating coordinate system， oruse a resonant to replace I in PI，which is called PR controller will work in two-phase stationarycoordinate system.Simulation results show all of three kinds of control strategies can achieve a good steadystate performance. The last two kinds of strategies achieve a better dynamic performance，which is useful when system needs a good dynamic performance.