Impact of Photovoltaic Generation in the System Stability: A Case Study with Nuwakot PV

Abstract

As innovation drives costs lower and begins to fulfill the promise of a clean energy future, renewable energy is rising. Renewable energy sources like PV and wind are taking on greater significance as a source of power as we discover more inventive and affordable ways to capture and store wind and alternative energies. Due to sunlight's accessibility, solar PV systems may be used practically anywhere in the world. Traditionally it was assumed that, the grid inertia is sufficiently high with some small variations with respect to time. But this is not valid for the power system with high Renewable Energy Sources (RES) shares composed of PV and wind generations. The increase in the generation of the inertia-less system can cause different synchronization and stability issues along with the implication over frequency dynamics. So, the size of PV system to be injected to the system should be studied. In this study, the simulation has been performed for the interconnected system encapsulating the Kathmandu valley, considering the scenario of injection of PV generation at Nuwakot. The load flow analysis before and after the placement of PV infers that the generation being placed away from the load center increases the overall network loss with minor change in the voltage at the nearby substations. The loss of the existing loss with 3.47%, with the placement of the PV at Nuwakot has increased to 3.97%. The transient analysis indicates that when the PV suddenly isolates from the INPS, the voltage of the terminal bus of Devighat substation drops down to 0.954pu from existing 1.008pu. For the higher value of generation considered, the impact on the frequency and voltage is severe however is within the limits for the case of Nuwakot PV. In case of the synchronous system, with the increase in the generation voltage, for certain generation limits, the stabilization time reduces and the transient response would be gradual. Finally, the small signal stability analysis with 0.1pu torque added in the generator at the Devighat confirms that the existing system is stable even due to the small disturbances. When the PV system was increased to 46MW capacity, the eigen value for the Mode 00046 and Mode 00047 was on the positive real axis with negative damping ratio indicating the system is unstable with some disturbances. However, the system with synchronous generator is stable at 46MW generation. This indicates that the size of inertia-less PV generation needs to be studied for the integration with the INPS and the stability with the synchronous machine is higher as compared to the PV generations.