Performance evaluation of doubly-fed twin stator induction machine drive with voltage and current space vector control schemes

The doubly-fed twin stator induction machine (DFTSIM) is of interest as an adjustable speed drive (ASD) and a variable speed generator (VSG), as it combines the advantages of a brushless drive with the potential for high-voltage, high-power and limited speed range applications. Previous work on the DFTSIM (or its equivalent brushless doubly-fed machine) has considered steady state performance with open loop control or dynamic performance with closed loop control, but has not considered an overall performance evaluation with an appropriate closed loop speed control. The comparative dynamic and steady state performance of a laboratory DFTSIM drive using 'voltage space vector control' and 'current space vector control' schemes is discussed. While the magnitude of the control winding voltage (or current) space vector is dynamically controlled to obtain the desired torque in a speed control loop, its position is regulated to operate the machine in synchronous mode. Results show that the maximum efficiency for the voltage space vector control is slightly higher than that for the current space vector control scheme, but the current space vector control offers better dynamic response and minimum converter voltampere requirement. Although the reduction in the converter VA rating with the DFTSIM drive is similar to that achievable with a slip power recovery drive, the brushless DFTSIM drive has a greater potential for applications requiring high reliability and low maintenance. Further, the DFTSIM is a viable alternative in the context of nonconventional power generation such as wind and small hydro.