Abstruct-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 induction 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 magnitude, variable frequency voltage at the generator terminals is rectified and the dc power is transferred to the load through a PWM inverter. The objective is to track and extract maximum power from the wind energy system (WES) and transfer this power to the local isolated load. This 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 = (Pref -Po) and its rate of change e. These input signals are fuzzified, that is defined by a set of linguistic labels characterized by their membership functions predefined for each class. Using a set of 49 rules which relate the fuzzified input signals (e, 6) to the fuzzy controller output U , fuzzy set theory and associated fuzzy logic operations, the fuzzy controller's output is obtained. The fuzzy set describing the controller's output (in terms of linguistic labels) is defuzzified to obtain the actual analog (numerical) 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 experimentally verified on a scaled down laboratory prototype of the SAWECS. NOMENCLATUREVR VI ZDC dc link current. Po Rectifier output power. P, , , TG Efficiency of induction generator. rlR Efficiency of rectifier. W m ws i d s a l p v d s Minv vw Wind velocity. dc voltage at rectifier output. dc voltage at inverter input. Maximum output power of wind energy system. Rotor speed of induction generator. Synchronous speed of induction generator. d-axis component of stator current. q-axis component of stator current. d-axis component of stator voltage. Modulation index of PWM inverter.Radius and swept area of wind turbine. Tip speed ratio (A = R w T / V~) .Rotor speed of wind turbine. Average torque conversion coefficient. Average torque at wind turbine shaft. Average torque at induction generator shaft. Gear box ratio.

No abstract

No abstract

ABSTRACT:The paper presents a Rule based controller based on fuzzy set theory to control the output power of a PWM inverter in PhotoVoltaic Energy conversion interface scheme. The objective is to track and extract maximum available solar power from the PV array under varying solar irradiation levels. To achieve this the power error e = (Pref -Ppy) and the rate of change of this error e are used as the input signals to the rule-based fuzzy controller and the output signal is used to control the PWM inverter. The input signals are defined by a set of linguistic variables or labels characterised by their membership functions which are preassigned for each class. A fuzzy relation matrix relates the input signals (e, e) to the fuzzy controller output U and using Fuzzy set theory and associated fuzzy logic operations, the desired fuzzy controller output is obtained. The fuzzy output (in terms of linguistic variable or label) is defuzzified to obtain the actual numerical (analog) output signal of the controller. This output (analog) signal is then fed to the PWM inverter to control only the output voltage (output frequency being fixed at 60 Hz.) and hence power drawn from the PV array. The proposed rule based controller is simulated and the results are experimentally verified on a PV energy conversion scheme consisting of an emulated PV array and a Pulse width modulated Inverter and is found to give a good power tracking performance. I INTRODUCTION:Solar energy conversion/interface schemes using a photovoltaic solar array and line commutated/PWM inverter have been modelled, analyzed and implemented [1,2]. For a given solar insolation level and ambient temperature the voltage versus current and output power versus current characteristics are as shown in Fig: 1. It is seen that there is a particular operating point (Iopt Vopt) at which maximum output power Popt is obtained. Most of these schemes use a PID controller to track and extract maximum power under varying solar insolation levels. The conventional P D controller requires quite a bit of tuning to obtain a fast and dynamically acceptable response and are usually implemented using analog circuits which have the tendency to drift with age and temperature. This causes degradation of the system performance. In this paper a new type of controller using Fuzzy set theory is proposed. The rule based fuzzy controller to track and extract maximum power Popt from the solar m a y under varying conditions of solar irradiation, uses two real time measurements namely error e=(P, -PPJ and the rate of change of error e as the control input sign&. These input signals (e, e) are first expressed in terms of linguistic variables or labels such as LP (large positive), MP 762

Canada SELF EYCIIED POUER -INDUCIION e COHUERSIOH PRlnE IIOUER CEHLRIIOR L I N KAIlSTRACT: This paper presents the dynamic modelling of variable speed constant frequency [VSCF] wind energy conversion scheme [WECS], employing self excited induction generator, connected to the utility grid through an AC-DC-AC converter scheme with Uncontrolled rectilier and PWM inverter. The proposed scheme for regulating the flow of power through the link ensures reduced reactive power burden on the self excitation capacitor banks, reduced harmonic injection into the host power utility grid and efficient utili7ation of available wind energy. Modelling of the subsystems and simulation of the unified system with pulse width modulated [PWM] inverter control, to reduce harmonics iiijected into the utility grid are also presented. nt U T I L I T Y GRID I INTRODUCTION:Variable speed constant frequency [VSCF] wind energy conversion schemes generally use synchonous or wound rotor induction niachincs along with an asynchronous AC-DC-AC link, to obtain constant frequency power generation, even in presence of prime mover speed fluctuations. Further, on account of its simplicity, ease of implementation, and low cost, the self excited induction generator finds wide application in power generation using non-conventional energy sources such as wind [I-41. Due to the stochastic nature of wind, the speed fluctuation, in cases where wind turbine is used as a prime mover, is substantial. This has to be countered by constant speed gear train mechanism, mechanical pitch control and excitation control of synchronous generator, to ensure constant frequencyholtage power generation [SI. The constant speed gear train mechanism is complex and requires a lot of maintenance. On the other hand, an induction machine once synchronised with the utility grid will generate fixed frequency power, with speed variation of wind turbine, being countered by change in the machine slip (which in case of operation as a generator is negative). However, the terminal voltage will he fluctuating with the speed and requires a direct power conversion link (asynchronous link) as shown in Fig:l(a), to alleviate problems of voltage fluctuations, flickering and generation of harmonicshb-harmonics, associated with the pulsating torque, characteristic of wind turbine (prime mover) driving the induction generator which is directly interfaced to the utility grid [6]. Generally, the asynchronous DC link utilizes a phase controlled rectifier and line commutated inverter [5,7], as shown in Fig:l(b) which imposes certain restriction on the operating range based on i) KVAR requirement of Self excited Induction machine.0094-2898/91/0000/0033$01 .OO 0 1991 IEEE ii) Reactive power requirements of the controlled rectifier unit. iii) Reactive power to be supplied by host power system to the inverter stage. iv) Constraints imposed to ensure reliable commutation of inverter devices. v) Harmonics injected into the host power system grid. (b) Figure:l(a) DC power conversion link for variable speed pr...