Active du/dt filtering for variable-speed AC drives

Cable reflection phenomenon in inverter-fed electric drives and typical solutions to the problem are presented in brief. Application of a new active du/dt filtering method based on a low-loss LC circuit and active control to eliminate the motor overvoltages is discussed in this paper. Active du/dt basic principles are presented along with experimental results to verify the potential of the concept. The main benefits of the method are the controllability of the output voltage du/dt within certain limits, considerably smaller inductances in the filter circuit resulting in a smaller physical component size, price, and excellent filtering performance. Moreover, no additional components are required, because the active control of the filter circuit takes place in the process of the upper-level PWM modulation using the same power switches as the inverter output stage. Further, the active du/dt method will benefit from the development of semiconductor power switch modules, as new technologies and materials emerge, since the method requires additional switching in the output stage of the inverter and generation of narrow voltage pulses.