Influence of the Control Strategy on the Efficiency of SynRM Based Small-Scale Wind Generators

Improvement of the energy efficiency of wind generation installations can significantly reduce their payback period, especially for small-scale wind turbines in regions where wind streams are highly unstable. Meanwhile, electric machines are still the main source of losses in such systems. The most effective Permanent Magnet Synchronous Motors (PMSMs) substantially depend on the availability and prices of rare-earth magnets, as well as proper thermal and flux operating conditions. A good alternative in terms of efficiency and reliability for PMSM can be a Synchronous Reluctance Motor (SynRM). However, high nonlinearity of SynRM's magnetic circuits hampers the improvement of the control performance, which can be crucial not only for accuracy of torque curve MPPT tracking, but also for the efficiency of the inverter-motor systems as a whole. This paper provides a description of the offline characterization procedure for SynRM motors and comparison of main control laws in terms of inverter-motor efficiency. The methods for calculation of maximum torque-per-ampere (MTPA), maximum torque-per-volt (MTPV), maximum power factor (MPF) and maximum torque-per-loss (MTPL) current trajectories are presented. Efficiency performance of the listed control techniques were tested and analyzed on a 4 kW REEL SynRM motor for application with a torque-curve MPPT regulator of a general small-scale wind turbine.