Side effects in low-speed AC drives

Contemporary converter-fed AC machines are being increasingly applied in low-speed industrial applications. This is a demanding task for AC drives with respect to the power topology and the applied control. The side effects inherent in all categories of AC drives have a significant influence on low-speed performance. This paper discusses some of these effects such as the influence of the voltage drop over semiconductor switches, the DC offset in the system and the system asymmetries. Their common feature is that at near zero rotor speeds, assuming the closed-loop control of the machine, they might cause instabilities in the system thus worsening its dynamical behavior. Suitable examples are presented and analyzed to give the proper proportion of the problem. Also, troubleshooting hints and suggestions helpful to its solution are given.