Frequency Division Multiplexing Process for Motor Drive Data Acquisition Using Higher Resolver Excitation Frequency and Notch Filter for Angle Estimation

High-performance three-phase motor drives require accurate and robust acquisition of angular position and stator currents. A resolver sensor is widely used for angle measurement in harsh environmental conditions. This sensor receives a sinusoidal excitation signal and produces two amplitude-modulated outputs. Frequency division multiplexing is a useful alternative to simplify the data acquisition system (DAQ) to acquire the signals from stator current sensors and the resolver angular position sensor: a current signal and a resolver output are combined to produce a signal sent to the DAQ. In most cases, the sinusoidal excitation signal of the resolver is less than the switching frequency of the motor drive inverter. As a result, current signals may produce a significant interference in the angle estimation when the frequency of the resolver excitation signal is low. This paper describes an improved multiplexing approach where the resolver excitation frequency is 1.5 times the inverter switching frequency. Thus, the spectra of the resolver outputs and the stator currents are located further from each other, reducing the angle estimation interference. Synchronous sampling allows for the recovery of the current signals. A notch filter is added to an angle tracking observer to reduce even further this interference. Three different tests considering different operation conditions were performed. The proposed angle estimation method has less root mean square error in the angle estimation than other approaches (e.g., without using a notch filter or using a low resolver excitation frequency). Besides, the proposed multiplexing strategy allows recovering the fundamental component of the current signals.