MODERN TECHNICAL GRID CODES RE- QUIREMENTS FOR LARGE SCALE SO- LAR PV POWER PLANTS

Ahmed Darwish: Modern technical grid codes requirements for large scale solar PV power plants Master of Science Thesis, 63 pages Tampere University Master’s Degree Programme in Electrical Engineering November 2020 Transition into vast contribution of intermittent renewables such as photovoltaic (PV) systems in power production is escalating rapidly around the globe. This huge penetration level of PV technology as a distributed energy resource has started to impact the operation, stability, reliability and security of power grids. They can disrupt the grid voltage, frequency, protection devices, reliability and power quality. Consequently, Transmission System Operators (TSOs) in many countries have driven to develop new requirements and specifications for their connection grid codes of the PV power plants. This is to address the issues of stability and security in the power network. These grid codes requirements demand specific technical functions that shall be supplemented with the PV inverters to perform in the same manner of conventional based power plants during the steady state and dynamic operation of the power network. The main focus of this thesis is to draw a detailed comparison and analysis of the modern technical requirements and functions which are imposed in different international grid codes for interconnection of large scale PV power plants into their power networks. The comparison and analysis are implemented to identify the minimum technical requirements and functions which are required from PV power plants’ owners, and to define the expected future requirements which have to be considered in the future design of PV inverters. It is found from the comparison and analysis that the minimum modern technical requirements and functions of PV inverters in most of the grid codes are low voltage ride through (LVRT), reactive current support (RCS), voltage control and overfrequency regulation response. The LVRT requirement must be supplemented with RCS injection function to ride through the fault and remain connected to the grid during a limited period in case of voltage dip. The voltage control can be achieved with at least one mode of reactive power control mostly constant reactive power mode (Q (P)). The overfrequency response requirement can be established by active power curtailment (APC) function by decreasing the active power of the PV power plant gradually with a configured droop so as to avoid excessive generation at the PCC. Finally, the thesis also identifies the expected future technical requirements which shall be considered in the future design of the PV inverters to implement the same dynamic performance of the conventional synchronous power plants. These future requirements include high voltage ride through (HVRT), voltage control, underfrequency control response, virtual inertia capability (VIC), black start capability (BSC) and power oscillation damping (POD). The HVRT requirement must be supported with RCS absorption function during voltage swell. The voltage control requirement can also be implemented with constant voltage mode set point Q(V) or with power factor mode set point cos ɸ(P). During underfrequency disturbance, the active power reserve (APR) and ramp rate control (RRC) functions shall contribute to frequency regulation at the PCC. VIC, BSC and POD requirements are still not clearly stipulated in most of the grid codes. These future requirements still require more research and study to get the optimal design guidelines for the future PV inverters. Coordination between the countries by sharing resources, knowledge and experiences will be the main core to implement a global standard grid code that can harmonize these technical requirements to facilitate the integration of PV power plants and hence, support the PV owners to achieve the balance between the cost and the global standards and regulations.