Cost-Effective Design of Inverter Output Filters for AC Drives

The paper deals with the minimization of output filter cost in inverter-fed AC drives. The LC Alter design is constrained by the total harmonic distortions of the stator voltage and inverter output current, the voltage drop in the filter inductor, and the system resonance frequency. The last constraint is important from the control point of view, because the vector control requires that the sampling frequency is sufficiently higher than the resonance frequency. The design takes into account the frequency dependence of the filter resistance and inductance due to the eddy currents in the laminated iron- core inductor. The design method is further enhanced by taking into account the inverter power stage cost as a function of the switching frequency. The design minimizes the total cost of the inverter and filter, and determines the optimal switching frequency. Simulations and experiments show that the filter designed according to the proposed design procedure fulfils the design constraints, and the speed-sensorless control works well with the cost-optimized filter.