A method to improve the transient response of dq-frame cascaded delayed-signal-cancellation PLL

The cascaded delayed signal cancellation (CDSC) based PLL in dq rotate frame (dqCDSC-PLL) can totally eliminate the disturbances of phase error. However, its open-loop bandwidth is significantly affected after incorporating CDSC into the PLL structure, so the transient response performance of three dqCDSC-PLLs are deteriorated. This paper proposes an improved dqCDSC-PLL by cascading a digital filter based phase-lead compensator into CDSC-based PLL to improve the dynamic response without sacrificing the stability. The filter shows flat gain in the passband, which can compensate the phase delay induced by CDSC and simultaneously maintain the attenuation of the notch point. The improved dqCDSC-PLLs significantly increases the open-loop bandwidth and enhances the dynamic performance. Besides, in order to further minimize the undesirable steady-state error, the frequency adaptive control was adopted without using any additional circuits. In order to verify the effectiveness of the proposed method, the simulation based on Matlab/Simulink is carried out for various conditions. Furthermore, experimental results for typical scenarios are provided, which highlight the advantage of the improved dqCDSC-PLL in terms of the dynamic performance.