Intergration of large Photovoltanic distributed generation into grid and the effect on power quality (Modelling Nigerian low voltage distribution Grid system 415V)

Abstract

The integration of photovoltaic distributed generation (PV-DG) system is on the increase virtually every day all over the globe, as a result of its contributions to long term energy security, environmental quality, economic competitiveness and extension of energy access to new consumers. Even though the benefits that come with PV-DG are enormous, integration to grid and power quality issues are also of major disquiet. This is largely due to the variability and volatility characteristic of the sun, and the connection of power electronics equipment (Inverters) to the grid, which contributes some percentage of harmonics to the grid network. The integration of PV-DG to an existing grid at steady state was studied and the impact on the stability of the Grid frequency, Voltage regulation, Reactive power fluctuation and Harmonics were studied. Comparisons was made on the power quality of the grid without the integration of PV-DG and with the integration of PV-DG at different penetration levels (0%, 20%, 40%, 60% and 80%) with the help of a simulation software. The study shows that the integration of PV-DG sources does not add to the grid inertia, because the components used do not have moving parts like the synchronous generators and turbines in convention power generation, which makes the frequency of the grid susceptible to instability at high penetration level. It was also discovered that there is need for auxiliary component to stabilize the variation in the voltage characteristic of the grid which is as a result of the intermittent nature of the sun. The study also reveals that the incessant switching off and on of Voltage-controlled Capacitor banks (VCCB’s) and Load Tap Changers (LTC’s) and line Voltage Regulators (VRs) lead to fluctuation of reactive power flow. The presence of harmonics was also observed, which originated from the inverter. The observation made in modern inverters is that, switching frequencies occasionally trigger resonances in the main distribution system. This produces non-harmonic frequency signals

VI usually at the 35th harmonic and higher, affecting clocks and other circuitry that rely on a clean voltage zero crossing. With proper auxiliaries in place and the right proportion of PV-DG penetration, virtually most of the challenges that comes with the integration of PV-DG to the grid system can be solve, thereby improving the power quality of the grid.