A Robust Forward Compensated Type-2 PLL Without DC Phase Error During Frequency Ramp for Embedded Magnetic Encoder

To achieve high performance vector control of permanent magnet synchronous machine (PMSM), high precision rotor angle is essential. Compared with traditionally used angle feedback device, e.g., encoder and resolver, the embedded magnetic encoder achieves high precision angle estimation without extra space occupation by installing several linear Hall sensors into PMSM cavity to monitor the flux leakage and rotor angle. The conventional synchronous reference frame (SRF) phase-locked loop (PLL) can extract phase and frequency from three or two Hall signals simultaneously. Although the type-2 SRF-PLL shows good robust performance against parameter variation, phase error emerges when input frequency changes. More specifically, a dc phase error appears in type-2 SRF-PLL during speed ramp stage due to insufficient order. Increase of the loop order removes the dc phase error but leads to instability risk. In this letter, a novel forward compensation (FC) module is attached on type-2 SRF-PLL to achieve phase error-free when frequency changes, where the instability risk is avoided. The effectiveness of the proposed FC module is analytically and experimentally proved, where the phase error elimination, noise immunity, and dynamic response are evaluated.