Abstract
The phase angle, frequency, and amplitude of grid voltage are the crucial information for the control and grid synchronization of grid-connected power electronic systems utilized in distributed generators. The conventional approach for the estimation of phase angle, frequency, and amplitude is to explore phase-locked loop techniques. In theory, synchronous reference frame (SRF) phase-locked loop (PLL) and enhanced phase-locked loop (EPLL) are the most conventional and widely used in power engineering applications because of their simple structure and robust features for digital implementation. With the proliferation of power electronic loads in the power grid, the grid voltage has unbalances and harmonic distortions. Under these severe conditions of the grid voltage, the bandwidth of the PLLs has to compromise between filtering capability and dynamic responses. The PLL dynamic performance can be improved by using in-loop filter or pre-filter. This thesis proposes novel filtering techniques based on multiple delayed signal cancellation (MDSC). These filtering techniques can be utilized for extracting (i) fundamental frequency positive sequence (FFPS) component of the grid voltage in stationary reference frame, (ii) dc component of the grid voltage in the synchronous reference frame, and (iii) selected harmonic component in single phase applications. The proposed MDSC filters have more flexibility to configure the lowest undesired harmonics and hence they can have less delay time when compared to the cascaded delayed signal cancellation (CDSC) filters for the same harmonic elimination capability. These filters can have combined advantages of both CDSC filters and moving average filters (MAFs) in their recursive implementations. For example, similar to CDSC filters, the MDSC filters can have more flexibility to configure the delay time introduced by the filters. In addition, similar to MAFs, the MDSC filters can provide less computational burden. In this thesis, advanced PLLs based on MDSC filters are proposed. They are (i) pre-filtered direct-form MDSC filters based three-phase SRF-PLL, (ii) recursive-form MDSC filters based three-phase SRF-PLLs, (iii) in-loop MDSC filters based three-phase enhanced PLL, and (iv) single-phase MDSC filters based enhanced PLL. Experimental verifications demonstrate the effectiveness of the proposed PLLs and provide good dynamic responses when compared to the recent advanced PLLs.