Unbalance and harmonic voltage compensation for a stand-alone variable speed constant frequency double-output induction generator supplying non-linear and unbalanced loads

This study presents an improved control algorithm for a stand-alone double-output induction machine-based variable speed constant frequency generator. The algorithm ensures sinusoidal load voltage and machine stator current for all types of loads such as balanced, unbalanced, linear and non-linear in any arbitrary combination. This is achieved by incorporating harmonic and unbalanced load compensation function to the stator side converter. Unlike other control strategies reported in the literature for this purpose, the proposed algorithm does not require extraction or compensation of individual harmonic/unbalance components of the load voltage/stator current. Harmonic compensation performance of the algorithm is thoroughly analysed theoretically and design guidelines provided. The experimental results obtained from a laboratory prototype demonstrate excellent load voltage regulation property during severe transient operating conditions. Total harmonic distortion and unbalance of the load voltage and stator current even with large unbalanced non-linear loads are also found to be much smaller compared with similar systems reported earlier in the literature.