Use of passive filters to minimise harmonics generated by solar photovoltaic systems and non-linear loads use of passive filters to minimise harmonics generated by solar photovoltaic systems and non-linear loads

Abstract

Solar photovoltaic (PV) technology is increasingly gaining attention in South Africa due to its low maintenance and operating costs, as well as its ability to address power outages. However, both grid-tied solar PV systems and non-linear loads introduce harmonic currents into the grid, which can significantly impact power quality. These harmonics lead to distortions in the voltage and current waveforms of the grid network. However, regardless of the harmonics introduced into the grid network, a weak grid network can also adversely affect the performance of grid-tied solar PV systems. Many studies have examined the power quality issues of these solar PV systems without accounting for the negative effects of a weak grid-network itself. The strength of a grid network can vary based on the geographical area and the point of common coupling (PCC) where the renewable energy system connects to the grid. The grid's strength is determined by its source impedance, which encompasses all the equipment involved in power transmission, including transmission cables, transformers, and other components. The purpose of this dissertation is to design and implement four-star branch RCL passive filter that will eliminate harmonics generated by PV grid-tied system and nonlinear loads in a weak or good grid-network. Furthermore, the effects of a weak grid network have been examined to ensure that the designed filter effectively minimizes total harmonic distortion (THD) within the system, because of non-linear load, solar PV and weak grid-network. A power simulation (PSIM) software has been used to model a grid-tied solar PV network supplying nonlinear loads in order to analyse the harmonics, as well as designing the proposed RCL passive filter. Fast Fourier Transform (FFT) and THD functions of the software are used as a baseline parameter to analyse the simulation results. The study's findings showed that by integrating a weak grid-network with a solar PV system supplying non-linear loads can lead to increased THD in both current and voltage waveforms, compared to a strong grid-network. It is of great significance to analyse the quality of a grid network before designing a passive filter to be used to mitigate the harmonics injected by a power generation system. In this study, the designed filter has proved to effectively reduce the THD injected by a combination of solar PV system, weak grid-network and non-linear loads, using four branch RLC filter connected to a three-phase four-wire inverter, using PSIM simulator/software. The results showed that the designed filter managed to drastically reduce the %THD of both current and voltage waveforms from 91.5 % to 3.6 % and from 38% to 5.7%, respectively. Under a strong grid-network, the %THD were reduced from 41.7 % to 2.7 % and from 10 % to 3.7 % THD, respectively. For both cases, the minimum allowable limit set by IEEE standards for low voltage system (<1 kV) was met. The designed filter proved to successfully mitigate the harmonics from the worst-case scenario (strong grid-network) to a more favourable one (strong grid-network).