Efficiency Optimization of Electric Drives with Full Variable Switching Frequency and Optimal Modulation Methods

In this paper, analysis and optimization of the efficiency of an electric drive with software control are discussed. The interaction between the electric machine and power electronics must be considered to increase the system efficiency with respect to the switching frequency or alternative modulation methods. The efficiency optimization is carried out considering various boundary conditions in the electric drive system such as voltage ripple and resonance effects in the high-voltage on-board network. The range of the electric vehicle can be extended by increasing the system efficiency. Or alternatively it is possible to save production costs per vehicle due to the lower battery capacity. At the same time, alternative modulation methods improve the continuous output power of the electric drive system. The losses in the inverter and the harmonic losses in the electric machine are calculated analytically. The analytical electric machine harmonic loss model is validated with finite element simulation for a fixed switching frequency. A system optimal switching frequency is measured and estimated for one operation point at a test bench and compared to the analytic calculated optimal switching frequency.