AbstractsEngineering

Modelling, Control and Performance of Large-Scale Grid-Connected Solar Photovoltaic Power Plants Under Static and Dynamic Conditions Considering No Energy Storage

by Mitra Mirhosseini




Institution: University of New South Wales
Department: Electrical Engineering & Telecommunications
Year: 2015
Keywords: Reactive power support; Photovoltaic systems; Grid-connected photovoltaic power plants (GCPPPs) are affected by grid requirements and affect the system by different control strategies. The GCPPP should support the system based on the grid code requirements including FRT capability, reactive power injection during voltage sags and power quality. From the GCPPP side, the main reasons for inverter disconnection are: loss of synchronization, excessive ac currents, excessive dc voltage, and voltage rise in non-faulty phases under unbalanced voltage sags due to the reactive current injection. The thesis deals with large-scale GCPPPs studies covering both static and dynamic aspects. The focus on the static studies is to support the grid voltages by the capability of the inverter to inject reactive currents. Four different methods based on the grid codes are designed and applied to a 10-MVA GCPPP. Considering dynamic studies, different control strategies are proposed to address the mentioned problems for inverter disconnection. The solutions are offered for three main controller strategies: controlling only the positive-sequence, controlling positive- and negativesequences and individual control of the phase currents. Dealing with the positive-sequence control of the currents, inverter disconnection issues are addressed for single-stage dc-ac and two-stage dc-dc-ac conversions by applying a current limiter and using an advanced phase-locked-loop (PLL). The difference in these two conversions is the protection of the dc voltage from overvoltage. While the dc voltage in the single-stage conversion is self-protected, three different methods are proposed to control the dc voltage in the two-stage conversion under voltage sag conditions. Limitations on using PI controllers in the current loops are demonstrated when controlling both positive- and negative-sequences of the grid currents. An alternative method based on resonant controllers is proposed with the capability to operate without a PLL for grid synchronization. The individual control of the phases is proposed, allowing the injection of a different reactive current to each phase. This prevents from overvoltage in the non-faulty phases during unbalanced voltage sags. For this control strategy a frequency-adaptive PLL is also designed that enables the extraction of the individual phase angles. Finally, the results confirm the viability of the proposed solutions using both simulation and experiments
Record ID: 1064433
Full text PDF: http://handle.unsw.edu.au/1959.4/54318


Abstract

Grid-connected photovoltaic power plants (GCPPPs) are affected by grid requirements and affect the system by different control strategies. The GCPPP should support the system based on the grid code requirements including FRT capability, reactive power injection during voltage sags and power quality. From the GCPPP side, the main reasons for inverter disconnection are: loss of synchronization, excessive ac currents, excessive dc voltage, and voltage rise in non-faulty phases under unbalanced voltage sags due to the reactive current injection. The thesis deals with large-scale GCPPPs studies covering both static and dynamic aspects. The focus on the static studies is to support the grid voltages by the capability of the inverter to inject reactive currents. Four different methods based on the grid codes are designed and applied to a 10-MVA GCPPP. Considering dynamic studies, different control strategies are proposed to address the mentioned problems for inverter disconnection. The solutions are offered for three main controller strategies: controlling only the positive-sequence, controlling positive- and negative sequences and individual control of the phase currents. Dealing with the positive-sequence control of the currents, inverter disconnection issues are addressed for single-stage dc-ac and two-stage dc-dc-ac conversions by applying a current limiter and using an advanced phase-locked-loop (PLL). The difference in these two conversions is the protection of the dc voltage from overvoltage. While the dc voltage in the single-stage conversion is self-protected, three different methods are proposed to control the dc voltage in the two-stage conversion under voltage sag conditions. Limitations on using PI controllers in the current loops are demonstrated when controlling both positive- and negative-sequences of the grid currents. An alternative method based on resonant controllers is proposed with the capability to operate without a PLL for grid synchronization. The individual control of the phases is proposed, allowing the injection of a different reactive current to each phase. This prevents from overvoltage in the non-faulty phases during unbalanced voltage sags. For this control strategy a frequency-adaptive PLL is also designed that enables the extraction of the individual phase angles. Finally, the results confirm the viability of the proposed solutions using both simulation and experiments.