Synchronization and Control of Grid Connected Single-Phase Power Converter

The adoption of power converters has thrived in electric loads, distributed generation, utility, and electric vehicles for their role in efficient energy conversion. However, interfacing these nonlinear power electronics based devices to the power system has triggered a rise in the harmonic distortion level. Grid overvoltage is another issue attributable to the deepening penetration of distributed generation such as rooftop PV systems in the distribution network. To address these power quality concerns, power converters offer the most effective solution. One such application is the active power filter (APF) which can accomplish fast and flexible power quality compensation. Synchronization and control system remains an indispensable part for the effective operation of APF or any grid interfaced power quality compensator. The performance of APF essentially depends on the dynamics and accuracy of two subsystems: grid synchronization and the reference current extraction (RCE). The RCE is basis to the operation of APF and responsible for computing the compensation current. The aim is to extract the fundamental/harmonics component fast and accurately. Among numerous solutions, RCE based on dq/synchronous reference frame (SRF) transformation is advantageous for its simplicity, efficacy, and clarity in selective harmonic extraction. It necessitates orthogonal signal generation (OSG) unit and synchronization signal (from synchronization unit) both of which remain vital to its working. Deploying transfer delay (TD) as OSG in RCE application has been restrained by the deficiency of harmonic filtering and adversity in adapting to grid frequency. Synchronization is an act of acquiring details of the grid (phase, frequency, and amplitude), to assure the power converter works in harmony with the utility grid. Among several synchronization techniques, phase locked loop (PLL) based on OSG has been widely embraced for single-phase electric power applications. Despite offering a simpler implementation, transfer delay (TD) and all-pass filter (AF) built OSG-PLLs have found limited applications in literature. Two main challenges facing these PLLs are the degraded performance in abnormal grid voltage (i.e distortion and presence of dc offset) and adaption of OSG units to variations in grid frequency. In this dissertation, some contributions are made to TD-RCE and two state-of-the-art PLLs (belonging to family of OSG-PLL): transfer delay (TD) and all-pass filter (AF). This thesis demonstrates that through systematic and optimal design, TD-RCE can be competitive with other advanced methodologies reported in the literature. In this context, an enhanced TD-RCE is proposed with faster transient and higher steady state accuracy even in off-nominal frequency. Regarding TD-PLL, first, the use of arbitrary delay length to further enhance the dynamic performance is proposed via dual-loop PLL system. Secondly, to improve the accuracy of grid parameter estimation in abnormal grid scenarios, an efficient inloop filtering method with the least impact on PLL dynamics is presented. Concerning AF-PLL, first, four topologies of frequency-fixed AF-PLLs are developed to eliminate the frequency feedback loop (to OSG) to simplify the control and stability analysis. Secondly, to boost the filtering capability, an efficient integration of prefilter before the AF-PLL structure is recommended. Lastly, this thesis recommends an alternative solution to address the overvoltage problem in low voltage distribution systems. A typical response to mitigate the voltage rise problem involves reactive power control, which if inadequate, is followed by active power curtailment of distributed generation. Instead of having a separate power quality compensator (such as APF), the possibility of employing electric home appliances for ancillary services is recommended. However, in the current configuration, the grid support capabilities of residential electrical loads are sparse and limited. This thesis first formulates the required modification in appliance topology and control to enable wider reactive power support (RPS) capability. Then, the framework assisting the realization of RPS from electrical home appliances is devised. Finally, the financial benefit of this strategy is justified by economic assessment