High-Precision Resolver-to-Digital Conversion via Composite PLL with Noise Reduction

In high-precision servo systems, phase-locked loops (PLLs) with feedforward compensation can simultaneously ensure dynamic performance and steady-state accuracy in extracting the information of angular position and speed from sinusoidal signals. However, these composite PLLs cannot effectively suppress the effect of measurement noise on the estimated speed, and the estimation accuracy may be seriously deteriorated. In this article, a noise reduction composite PLL (NR-CPLL) is proposed for resolver-to-digital converters (RDCs) to prevent the measurement noise from polluting the estimated speed with higher comprehensive accuracy. The proposed method consists of two tracking loops. The main loop adopts a noise reduction PLL (NRPLL) to track the angular position in resolver signals and output angular speed with enhanced noise immunity and high steady-state accuracy. The secondary loop adopts an angle-tracking observer (ATO) to generate feedforward speed since it can effectively suppress measurement noise in estimating speed. Thus, the proposed method combines the advantages of NRPLL and ATO in noise reduction and can also improve dynamic performance and steady-state accuracy by using feedforward. Simulation and experimental results demonstrate the effectiveness of the proposed method.