engleski

Rotor flux estimation for speed sensorless induction generator used in wind power application

This paper compares two methods for rotor flux estimation for sensorless vector control of squirrel-cage induction generator in wind turbine application. Both methods are based on the integration of the back electromotive force (back- EMF) of stator based on the measured voltages and currents. Estimation of rotor flux based on the integration of back-EMF without feedback leads to estimation error. Implementation of an integrator for motor flux estimation is a very demanding task. Since it is difficult to avoid the measurements offset and DC component in the back- EMF a pure integrator goes into limit, and furthermore have initial value problems. To solve the problems, in first method the pure integrator is replaced by a low-pass filter (LPF). The second method has a quadrature detector to detect the orthogonality between the estimated flux and back- EMF, and a PI controller to generate an appropriate compensation feedback level. Both methods are implemented into digital control system and verified on the laboratory model. The experimental setup consists of a squirrel cage induction generator and the permanent magnet motor used as wind turbine emulator. Induction generator is connected to grid via back-to-back-converter controlled by digital control system, while permanent magnet motor is driven by industrial frequency converter. Experimental tests carried out on a induction generator connected to grid demonstrate advantages and disadvantages of both methods.

Induction generator; Flux estimation; Wind power application

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