An Advanced RDC-Less System Independent of Motor Control PWM Frequency

In permanent magnet synchronous motors, a resolver to digital converter (RDC) is used to determine the position of a rotor with a resolver. Moreover, RDCs can be used to position rotors through resolver signals. However, such processes require significant costs and space. Recently, the motor control unit (MCU) has been required to implement RDC functions for cost reduction and functional safety. To implement the RDC function with the MCU, an excitation signal must be generated based on the pulse with modulation (PWM) signal. In this paper, with a single process core environment, the PWM frequency for motor control and the PWM frequency for generating the excitation signal are different. This study describes a demodulation method that enables accurate positioning of a rotor. The sampling time of the feedback signals is determined, and the rotor position is calculated through the second-order generalized integrator frequency locked loop technique. The rotor position information calculated from the proposed RDC-less system provides the same level of accuracy as that of a system with an RDC. The proposed method was verified through simulation and experiment. Moreover, this method can be applied to exclude RDCs from a single core system and process the resolver signal by the existing MCU.