Experimental evaluation of an isolated induction generator with voltage and frequency control

An approach to voltage and frequency control for an isolated induction generator (IG) is presented. In the developed approach, constant frequency control is achieved through kinetic energy control by a speed governor while constant voltage control is reached through reactive power control by a voltage-sourced inverter. In order to reach effective frequency control, the relative rotating speed, which is computed from the rate of change of voltage phase angle at generator terminal, is used to estimate the frequency. Constant voltage control is essential for the frequency control, since the random load fluctuation due to bus voltage variations can be eliminated. As a result, the real power unbalance of the IG is minimized and generator speed as well as mechanical power can be more effectively controlled by the frequency controller. The effectiveness of the proposed control strategy is demonstrated on a 3 kW experimental set up with an induction generator driven by a servomotor. Disturbances such as step changes in load and frequency reference setting have been considered. The experimental results show that satisfactory dynamic performance of the isolated IG can be achieved by the proposed frequency controller and voltage controller