Sensorless Maximum Power Control of a Stand-Alone Squirrel-Cage Induction Generator Driven by a Variable-Speed Wind Turbine

For the cost-effectiveness of variable-speed wind energy conversion systems (WECSs), it is extremely important to extract the maximum available power at different wind speeds within the normal operating range. Furthermore, reduction of the electric generator losses additionally contributes to the efficiency of the WECS, whereas reduction of the number of sensors is beneficial in terms of reliability and cost. This paper presents sensorless control of a stand-alone WECS comprising a squirrel-cage induction generator (IG) and a battery system. An indirect rotor-field-oriented control (IRFOC) algorithm including stray load and iron losses and online tuning of IG’s equivalent resistances and magnetising inductance is adopted for IG control to achieve high level of agreement with the actual machine. Fuzzy-logic-based optimisations of the wind turbine (WT) and IG are implemented to maximise the IG output power. The IG speed, which is required by the IRFOC algorithm, is estimated by using a model-reference-adaptive-system. The estimated IG speed is also utilised for online WT optimisation in combination with the IG torque obtained from the IRFOC equations. The performance of the proposed control strategy has been experimentally evaluated and compared with two competing sensorless control strategies for two 1.5 kW IGs of different efficiency class.