Frequency Adaptive CDSC-PLL Using Axis Drift Control Under Adverse Grid Condition

This paper presents a new technique to adapt the cascaded delayed signal cancellation phase-locked loop (CDSC-PLL) using a proposed axis drift control (ADC). When grid frequency changes, the estimated grid angle by PLL drifts with a residual error proportional to the frequency change value thus, the accuracy and performance of the conventional CDSC-PLL is deteriorated which can lead to malfunction of the connected applications. Accordingly, CDSC-PLL type has to be adaptable to frequency changes with high immunity to grid disturbances. Designing frequency adapted CDSC-PLL is complex and needs a dedicated design due to the high nonlinearity introduced by adaptive loops. The ADC is proposed as an online adaptive technique that contains a self-tuned DSC operator to mitigate the grid disturbances and a PI controller to perform the adaptation task. The proposed technique is mathematically analyzed and systematic tuning methods are presented. A new analysis for CDSC under off-nominal sample parameter is presented and verified. The robustness of proposed adaptive controller is investigated under parameters uncertainty and various grid disturbances. The proposed technique is numerically and experimentally verified.