N. Schinas^1,, A. Moullas¹

In this paper the voltage regulation of a grid bus is studied. The bus accepts real power from a wind park through a medium voltage cable. The changes of the wind speed result in large alterations in the exchange of real and reactive power between the cable and the grid. As a result, the voltage of the bus is not stable. The installation of a Static Var Compensator(SVC) is a rational choice for the stabilization of the voltage. The SVC needs a controller which according to the difference of the measured voltage from its nominal value, it defines the equivalent susceptance of the SVC. So, the right amount of reactive power between the grid and the SVC is achieved. Two design techniques for the controller are proposed, both based on the theory of optimal control. The full theory of the optimal control used in the design procedure, is given clearly. In the first place, the nonlinear model is linearized in two ways and then the mathematical principles of optimal control are applied. The second input of the linearized model, regarded as disturbance, has been taken into account in the design procedure. The proposed application of the optimal control theory has resulted in controllers that can be regarded approximately as PI controllers andso, their implementation is very easy. The whole nonlinear system has been simulated in SIMULINK so as the response of the proposed system to be judged. The results are satisfactory. Despite the large variations in the exchange of real and reactive power between the wind park and the grid, the variation of the grid voltage is under 1.5%.

optimal control, voltage regulation, wind turbine, FACTS