SOME OF THE POWER QUALITY PROBLEMS AND SOLUTIONS OF SMART GRID

Abstract

The implementation of smart grid technologies presents a myriad of advantages with significant implications for the efficiency and sustainability of power infrastructure. On the other hand, these smart grid technologies give rise to various power quality problems. However, providing the excellent power quality to the consumers is one of the main objectives of the smart grid. Unified power quality conditioners (UPQCs) are highly adaptable active power filters that can rectify a wide range of power quality problems. Existing literature indicates that when compensating for voltage sag for the critical loads, the magnitude of the source current in a traditional UPQC tends to increase compared to situations without voltage sag compensation. Because, the extra active power demanded by the load during voltage sag compensation is supplied by the source. This increase in source current consequently leads to a further escalation of the voltage sag experienced by the buses located behind the PCC. Similarly, the existing literature indicate that when compensating of voltage swell for the critical load, the magnitude of the source current in a traditional UPQC decreases compared to situations without voltage swell compensation. Because during voltage swell compensation, the UPQC feeds back the extra power to the supply system. This decrease in source current subsequently results in a further escalation of the voltage swell experienced by the buses located behind the PCC. Hence, in the present doctoral work, the battery integrated UPQC is developed to prevent any further escalation of the voltage sag or swell experienced by the buses located behind the PCC. In battery integrated UPQC, the battery is integrated into the dc-link capacitor of the traditional UPQC through bi-directional dc to dc converter. During voltage sag compensation, the additional active power required by the load is provided by the battery through the bi-directional dc to dc converter instead of being drawn from the source. Similarly, during voltage swell compensation, UPQC feeds the extra power to the battery through the bi-directional dc to dc converter instead of feeding back to the source. Hence the current drawn from the source will not be affected by the level of voltage sag or swell compensated by the battery integrated i UPQC. This eventually results in the prevention of further escalation of voltage sag or swell experienced by the buses located behind the PCC during voltage sag or swell compensation by the battery integrated UPQC. In addition, this thesis also presents the simple and cost-effective power reserve control strategy for the single stage photovoltaic (PV) systems. Ensuring power reserve control in a PV system without energy storage is of paramount importance for offering frequency regulation of ancillary service to the power grid. Traditional power reserve control algorithms use an additional dc to dc converter to maintain reserve power in PV arrays, leading to several limitations, including increased component count, reduced efficiency, diminished reliability, higher expenses, and larger physical dimensions. In this work, we have proposed a power reserve control strategy that eliminates the need for an extra dc to dc converter, thus addressing the aforementioned limitations prevalent in two stage systems. In this approach, the desired reserve power is achieved by directly setting the PV array voltage, which corresponds to the reserve power input command, as the dc link capacitor reference voltage. This PV array voltage is obtained from the predetermined power versus voltage characteristics and the open circuit voltage of the PV array. Furthermore, the proposed method is simple to implement since it involves fewer steps compared to existing power reserve control algorithms. Hence, the proposed algorithm provides a simple and cost-effective solution for providing the reserve power in a PV array.