A Generalized Inverter Control Method for a Variable Speed Wind Power System Under Unbalanced Operating Conditions

This thesis presents a generalized control method for complete harmonic elimination and adjustable power factor of a grid side inverter under unbalanced operating conditions used in variable speed wind power systems. The theoretical analysis of the proposed control method is described and verified by simulation in Simulink®. Two types of traditional control methods are also explained and applied in the wind power system for comparison, which are the indirect current control in a-b-c reference frame and the active and reactive power control in d-q synchronous frame. This method is verified for the gird fault right-through operation as wel

Electromechanics of an Ocean Current Turbine

The development of a numeric simulation for predicting the performance of an Ocean Current Energy Conversion System is presented in this thesis along with a control system development using a PID controller for the achievement of specified rotational velocity set-points. In the beginning, this numeric model is implemented in MATLAB/Simulink® and it is used to predict the performance of a three phase squirrel single-cage type induction motor/generator in two different cases. The first case is a small 3 meter rotor diameter, 20 kW ocean current turbine with fixed pitch blades, and the second case a 20 meter, 720 kW ocean current turbine with variable pitch blades. Furthermore, the second case is also used for the development of a Voltage Source Variable Frequency Drive for the induction motor/generator. Comparison among the Variable Frequency Drive and a simplified model is applied. Finally, the simulation is also used to estimate the average electric power generation from the 720 kW Ocean Current Energy Conversion System which consists of an induction generator and an ocean current turbine connected with a shaft which modeled as a mechanical vibration system

Performance and Power Factor Improvement of Indirect Vector Controlled Cage Induction Generator in Wind Power Application

Wind energy is one of the most important and promising source of renewable energy all over the world, mainly because it is considered to be nonpolluting and economically viable. At the same time there has been a rapid development of related wind energy technology. The control and estimation of wind energy conversion system constitute a vast subject and are more complex than those of dc drives. Induction generators with cage type rotors have been used extensively in wind power generation systems for the variable speed applications in a wide power range. Generally, variable speed wind energy conversion system with Induction generators require both wide operating range of speed and fast torque response, regardless of any disturbances and uncertainties (turbine torque variation, parameters variation and un-modeled dynamics). This leads to more advanced control methods to meet the real demand. The recent advances in the area of field-oriented control along with the rapid development and cost reduction of power electronics devices and microprocessors have made variable speed wind energy conversion system an economical alternative for wind power applications. The complexity of wind energy conversion system increases substantially if high performances are demanded. The main reasons for this complexity are the need of variable frequency, harmonically optimum converter power supplies, the complex dynamics of ac machines, machine parameter variations etc. Various control techniques have been developed in the recent days for the control of cage induction generators. In this work a hybrid controller is developed for performance improvement of a cage induction generator used for wind power applications. The wind power generation system employs an indirect vector controlled cage induction machine as the generator. The induction generator system is evaluated separately with conventional PI-controllers, fuzzy controllers, self tuned fuzzy controllers and hybrid controllers and the performances are compared for each case. Power factor of the overall system is improved through control of grid side converter. Control circuits for PWM converter inverter system are also fabricated and tested

Višefazni sustav za pretvorbu energije vjetra zasnovan na matričnom pretvarač

Abstract: This paper presents a new variable speed wind energy conversion systems (WECS). It is based on a six-phase asymmetrical squirrel cage induction generator (SCIG) and a matrix converter (MC) as power electronic interface between six-phase SCIG and electrical network. The analysis employs a rotor flux vector control algorithm and a scalar strategy modulated MC to control the generator. Characteristics of MC are used for maximizing the power tracking control when different wind speeds and delivering powers to the grid are simultaneously considered. The MC provides sinusoidal input and output voltages and a unity power factor, but causes an asymmetry in the generator. A current control strategy including the method of suppressing imbalance caused by this asymmetry is discussed. Some numerical simulations are carried out showing the effectiveness of the proposed WECS topology.U ovom radu prikazan je novi sustav za pretvorbu energije vjetra s promjenjivom brzinom. Zasnovan je na šestofaznom asimetričnom kaveznom generatoru i matričnom pretvaraču koji je sučelje između generatora i elektroenergetske mreže. U analizi se koristi vektorsko upravljanje tokom u rotoru i skalarna strategija moduliranog matričnog pretvarača za upravljanje generatorom. Karakteristike matričnog pretvarača koriste se za maksimiziranje slijeđenja snage u slučajevima kada se istovremeno promatraju različite brzine vjetra i snage koja se daje u mrežu. Matrični pretvarač daje sinusni ulazni i izlazni napon te jedinični faktor snage, ali uzrokuje asimetriju u generatoru. Razmotrena je strategija upravljanja strujom koja uključuje metodu za smanjivanje neravnoteže koju uzrokuje asimetrija. Provedene su numeričke simulacije koje pokazuju efektivnost predložene topologije sustava za pretvorbu energije vjetra