A RULE-BASED FUZZY-LOGIC CONTROLLER FOR A PWM INVERTER IN A STAND-ALONE WIND ENERGY-CONVERSION SCHEME

The paper presents a rule-based fuzzy logic controller to control the output power of a pulse width modulated (PWM) inverter used in a stand alone wind energy conversion scheme (SAWECS). The self-excited induct ion generator used in SAWECS has the inherent problem of fluctuations in the magnitude and frequency of its terminal voltage with changes in wind velocity and load. To overcome this drawback the variable magnit ude, variable frequency voltage at the generator terminals is rectifie d and the de power is transferred to the load through a PWM inverter. The objective is to track and extract maximum power from the wind ener gy system (WES) and transfer this power to the local isolated load. Th is is achieved by using the fuzzy logic controller which regulates the modulation index of the PWM inverter based on the input signals: the power error e = (P-ref - P-o) and its rate of change over dot e. These input signals are fuzzified, that is defined by a set of linguistic l abels characterized by their membership functions predefined for each class. Using a set of 49 rules which relate the fuzzified input signal s (e.overdot e) to the fuzzy controller output U, fuzzy set theory and associated fuzzy logic operations, the fuzzy controller's output is o btained. The fuzzy set describing the controller's output (in terms of linguistic labels) is defuzzified to obtain the actual analog (numeri cal) output signal which is then used to control the PWM inverter and ensure complete utilization of the available wind energy. The proposed rule-based fuzzy logic controller is simulated and the results are ex perimentally verified on a scaled down laboratory prototype of the SAW ECS.