Research on On-Line Modeling of High Frequency Impedance of Motor

The high-frequency parasitic parameters of the motor are an important part of the noise path of the motor drive system. This article mainly establishes the high-frequency impedance model of the motor in the off-line or static state. However, the high-frequency impedance of the motor in the working state is different from that in the static state. The difference between the motor impedance on the static and working state is analyzed. This article considers that the motor differential mode (DM) impedance is different at different angles of the rotating shaft on the working state and establishes a stepwise simulation model by measuring the motor DM impedance at different rotation angles. This model cannot only simulate the time-varying impedance characteristics of the motor in the actual working state, but also eliminate the noise simulation error caused by the time-varying circuit model of the motor. This article also proposes a high-frequency signal injection method to extract the common mode (CM) impedance of the motor on-line. This method increases the high-frequency components of the CM voltage and the CM current in the motor by injecting high-frequency signals, so as to obtain the CM impedance of the motor on the working state. It does not require some high-precision and high-bandwidth non-contact isolation probes, which greatly reduces the equipment and cost requirements. Finally, the simulation noise of motor impedance in the static state, the simulation noise of motor impedance in the working state, and the measured noise are compared. Experiments prove that the amplitude difference between the simulated noise of the motor impedance on the working state and the measured noise is no more than 6 dB<middle dot>mu V.