Control of wind power systems imposing the current in the intermediate circuit of the converter at variable wind speed

Abstract

This paper presents a control method for a wind turbine with a synchronous generator with permanent magnet (SGPM), to achieve optimal function in the optimal energy field at variable wind speed. The wind speed and the angular speed of the SGPM impose the value of the generator load in the optimal energy area. Based on energy balances, done with speed and power measurements, the generator load is determined so that the system can be brought into the optimal energy area. The operation at maximum power of a wind turbine (WT) is analyzed by modifying the generators load, under the terms of a significant wind speed variation in time. The coordinates of the maximum power point (MPP) change in time being determined by the instantaneous values of the wind speed and the mechanical inertia, not in every case the wind turbine can be brought, in a timely manner, in the MPP area. The rapidity of the wind speed variation in time as well as the inertial value, are two fundamental elements upon which the operation in MPP depends. Prescribing the value of the DC current, Icc, from the intermediate converter circuit, a simple and useful control of the wind turbine system can be achieved. The control method that allows the WT to function in the optimal energy area is based on knowing the value of Icc, which is determinate from wind speed and the angular mechanical velocity (AMV).