Measuring the power conversion losses in voltage source inverters

The power losses in a voltage source inverter (VSI) are the sum of the additional constant power losses of the local power supply, the inverter circuits as well as the main power conversion losses. Power conversion losses consist of the power losses on switches (e.g. static power losses on the resistances of the switches in the “on state” and the dynamic switching power losses), the power losses on the serial resistances of the filter inductor winding together with the resistances of all of the serial inverter connections and the power losses of the filter coil, which are dependent on the material of the filter coil core. All of these power conversion losses can be presented as losses on the one equivalent serial resistance that is connected serially with the filter coil. This nonlinear (depending on the load and the switching frequency) serial equivalent resistance Rse can be calculated from the parameters of the maximum point of the measured magnitude Bode plot of the control transfer function of the inverter. The paper presents the concept of measuring the Bode plots of the control transfer function in order to get the serial equivalent resistance and to calculate the power conversion losses of an experimental model and discusses the accuracy of the results.