Development of a real-time testbed for renewable energy integration studies

Abstract

Joining the global energy movement, South Africa has, in recent, years seen a steady increase in the number of grid-connected renewables. This follows an interest to include renewable energy in its generation mix as early as 1998, supported by initiatives such as the updated 2030 IRP (Integrated Resource Plan) today. South Africa’s electrical energy demand is, however, still predominantly supplied by coal, which the 2030 IRP plans to change through a significant increase in the amount of grid-connected renewables, to the extent where renewable generation is set to almost match that of coal by 2030. Such a shift from synchronous inertia-providing fossil-fuel generation, to largely asynchronously natured renewables, is bound to bring about significant changes to South Africa’s electrical grid, and consequently, new challenges given South Africa’s still-limited renewable-generation experience. These challenges largely relate to grid stability and supply reliability concerns, noted by studies of countries with similar renewable-integration goals. It is often also observed that these effects tend to be more prominent for weaker grids, raising concerns over the effect South Africa’s planned renewable integration could have, given the ongoing struggle to supply the current electrical demand reliably. Perspective is, however, provided by the motivation behind South Africa’s integration goals which, contrary to displacing fossil-fuel generation, is intended in South Africa as a means of adding much-needed grid-connected generation capacity. This places immense pressure on the success of South Africa’s renewable-generation integration goals, necessitating comprehensive integration studies to determine grid-connected RPP (Renewable Power Plant) behaviour if this desired outcome is to be achieved. From what is known, no tailored South African simulation tools promoting RPP grid-integration behavioural studies yet existed for South Africa. The aim of the research is therefore to develop a tailored South African real-time RPP grid-integration behavioural studies testbed, promoting the necessary renewable-integration studies needed in support of the successful integration of South Africa’s renewable-integration goals. This work follows the development of the real-time testbed, which first sees the implementation of a MATLAB live script to select RPP grid-code requirements, according to which simulated RPPs are operated. MATLAB Simulink is then used to develop the testbed’s main circuit sections, which incorporate a means of importing external grid data to allow simplified recreation of test conditions. The testbed furthermore includes a voltage- and frequency-validation subsystem, responsible for active grid-code compliance monitoring and RPP control, allowing the strains imposed by grid-code requirements on RPPs to be studied. The MATLAB-developed testbed is then integrated with RT-LAB of OPAL-RT, adhering to the necessary real-time execution requirements, allowing the model to be simulated in real-time. To assess the accuracy and success of the developed testbed, while showing its worth as an RPP grid-integration behavioural studies tool, a testing procedure was developed involving high- and low-voltage and frequency, short-circuit, and real-world data simulations, operating the test RPP within its continuous, fault ride-through, and trip regions of operation. Results produced support the selected simulation data-import method as an effective and efficient means of replaying and recreating simulation conditions. Results furthermore support the testbed’s ability to assess and track POC conditions effectively, operating the RPP in line with voltage- and frequency grid-code requirements. Finally, results support the testbed’s design as an effective tool for assessing RPP response and behaviour in line with grid-code requirements, allowing the support abilities of the RPP, its limitations, and grid-code-imposed strains to become apparent. Then, through the design and testing of the developed testbed, the research achieved its goal of developing a real-time tailored South African RPP grid-integration behavioural studies tool, in support of the renewable grid-integration studies needed for the successful integration of South Africa’s renewable-integration goals.