A Soft Decoding Strategy for Resolvers Based on a Second-Order Phase-Locked Loop

Resolvers are extensively utilized in servo systems and electric vehicle (EV) due to their high reliability and robust environmental adaptability. To achieve low-cost, high-performance resolver-to-digital conversion, this paper presents a novel soft decoding strategy. The proposed strategy features a signal shaping stage, consisting of a high-pass filter (HPF) and automatic gain control (AGC), to effectively eliminate DC offsets and compensate for amplitude imbalances. Subsequently, a low-pass filter (LPF) is used to extract low-frequency quadrature signals. Finally, an improved phase-locked loop (PLL) estimates the rotor position from the demodulated sine and cosine signals. The effectiveness of the proposed approach is validated through both simulation and experiments. Experimental results on the STM32G431 platform demonstrate that the strategy achieves high accuracy, low cost, and strong dynamic tracking capability.