Research On Transient Characteristic Of Grid-connected Photovaltaic Power System And Its Impact On Distribution Network

The rapid development of photovoltaic(PV) power generation system brings a positive impact on the energy crisis and environmental protection, at the same time it brings new challenges for the construction of “One Strength, Three Qualities” grid. The mass accession of PV power to the distribution system will change the network topology, affect voltages distribution, produce harmonic and interfere relay protection, which will influence the scheduling and the reliable operation with high-quality of the network. This paper aims to study the principle, composition and control of PV power system transient, as well as the effect of accession of PV power to the distribution system.The crucial part of the PV research is the PV power generation system. In this paper, the PV array, DC-DC circuit, three-phase inverter, PWM control algorithm and the theory and control method of AC filter are mentioned. Also, the operation mode and process of the whole PV system is analyzed to provide fundamental basis for the simulation test.Based on the PSCAD/EMTDC platform, the PV array, DC-DC circuit, three-phase inverter and AC filter are built and the control circuit with MPPT and inverter control algorithm are designed. Then a detailed 50 Hz grid-connected PV system model is complete. All the output physical quantities of this model are analyzed, the simulation results indicate that this PV system model meet the grid-connecting demand and can simulate the grid-connected PV system operation and control accurately. This paper also researches the transient performances of the PV system when the illumination intensity is changed or a fault disturbance is set.PV system which connected to distribution network mainly affects the quality of electric energy and the system protection. Based on an actual distribution network, this paper first simulates and analyzes the voltages distribution of each node and the total harmonic distortion(THD) variation when PV connection point or PV output power changed. Second, the influence to distribution network protection caused by PV is discussed through the simulation results of the feeder and adjacent feeders referenced to the aspects below: the reliability and sensitivity of overcurrent protection and whether the protection is malfunction or refused action. Last, this paper disposes all the data and diagrams, discovers and concludes the detailed influence to the quality of electric energy and the protection of the distribution network when PV systems connected.