Variable Structure Observing Strategy Of DFIG Current Based On PSCAD Platform

Compared to onshore wind power, offshore wind power had greater potential with the advantage of high wind speed, low turbulence intensity, wind speed and direction stability, and do not take the land, less subject to environmental constraint. It is another important area in the development of wind power industry. But on the one hand, maritime operational difficulties resulting in significant increase in maintenance costs of offshore wind power systems, on the other hand, wind power system is difficult to be repaired in time after a failure under the constraints of marine environment and weather. It is resulting in a reduction of effective power generation time. The study on strategy of the observation of status and reconfiguration control for wind power system at sensor fault to achieve its uninterrupted operation during sensor failure will help to improve the reliability of offshore wind power system, reduce maintenance costs and increase the effective power generation time.Aiming at the deficiency of the existing design of the state observer for doubly fed wind power system, the theory of sliding mode variable structure control is introduced. The observation strategy of current status was studied with strong robustness of parameter and fast dynamic response. The mathematical model of DFIG was transformed to select the stator currents as state vectors by analyzing the machine model in synchronous coordinate. The sliding controller was designed to track stator current with regulating the bias of the estimated value of stator current. The high frequency distortion section of the output signal of controller was removed to obtain rotor current observation value with a low pass filter as the system entered the sliding mode. Similarly, the stator current can also be observed by controlling the rotor current to converge to the true value.The simulation model of DFIG vector control system was built in PSCAD/EMTDC simulation environment in order to verify the effectiveness of the observation strategy. The rotor-side converter applied stator flux oriented vector control technology. The grid side converter used grid voltage oriented vector control technology. And the output of the observer accessed to control system for implementing the control of feedback of double fed wind power system. The results of simulation shows that the changes in the current of DFIG can be quickly tracked by the method of observer estimation, and the influence of parameter errors was repressed on the accuracy of current observation. The reconfiguration control of wind power system can be realized at current sensor fault. The algorithm is simple, easy to implement and have strong robustness.