A Simple Power Transistor Voltage Drop Identification Technique for Motor Drives

The nonlinear characteristics of inverters, primarily caused by dead-time effects, non-ideal switching behaviors, and conduction voltage drops of power devices, critically impair the accuracy of motor parameter identification and control stability. This paper presents a power switch voltage drop identification method for inverters. By injecting multiple sets of DC reference voltages with varying magnitudes into the d-axis while applying zero voltage to the q-axis, the motor operates exclusively within a single sector under the specified DC reference voltage conditions. In this configuration, the resulting steady-state currents remain constant DC quantities. By measuring the steady-state line currents and converting them to phase currents, each pulse waveform segment within one switching cycle can be analyzed. This enables precise determination of the conduction voltage drops across power switches and freewheeling diodes under specific current conditions. After the insertion of a dead-time interval, the original seven-segment SVPWM will be transformed into thirteen segments within one cycle, six of which are dead-time intervals. By analyzing the conduction status of each segment's switching devices, the voltage drop across the inverter's transistors can be determined. By injecting different DC currents, the relationship between the transistor's voltage drop and the current can be obtained. Through segmented SVPWM waveform analysis incorporating dead-time insertion, the origins of deviations between reference voltages and actual output voltages are elucidated. Experimental validations confirm the theoretical findings. The proposed methodology provides critical data for inverter nonlinearity compensation, effectively enhancing motor control precision.