Performance improvement of shunt active power filter based on non-linear least-square approach

Nowadays, the shunt active power filters (SAPFs) have become a popular solution for power quality issues. A crucial issue in controlling the SAPFs which is highly correlated with their accuracy, flexibility and dynamic behavior, is generating the reference compensating current (RCC). The synchronous reference frame (SRF) approach is widely used for generating the RCC due to its simplicity and computation efficiency. However, the SRF approach needs precise information of the voltage phase which becomes a challenge under adverse grid conditions. A typical solution to answer this need is the application of advanced phase locked loops
(PLLs). The PLLs are closed-loop control systems that often have a response time more than two cycles of the nominal frequency. Besides, a special care should be paid in designing their control parameters to ensure their stable operation in all circumstances. This paper proposes an improved open loop strategy which is unconditionally stable and flexible. The proposed method which is based on non-linear least square (NLS) approach can extract the fundamental voltage and estimates its phase within only half cycle, even in the presence of odd harmonics and dc offset. The performance of the proposed method is verified under MATLAB/Simulink environment and validated experimentally and compared with advanced PLLs.