Analysis of Monitoring Data on the Operation of Pv-Inverters Connected to Distribution Network

Abstract

The article deals with the problems of the PV plants operation in the low voltage network (LVN), namely the influence of PV generation on bus voltages and stability of network, as well as disconnecting the inverters from network in order to avoid overvoltages. The operating of PV inverter tied to LVN is considered on the framework of the reduced two-bus equivalent circuit. One bus of this circuit describes the inverter which is connected to the step-up transformer via short line and second one is the equivalent representation of LVN. The reduced two-bus circuit in contrast to the multi-bus schemes has exact solutions for power flows between PV plant and network. The analytical solutions obtained for this model allows us to determine the voltage stability region, the disconnecting conditions from the network (islanding), the dependence of the bus voltages on the levels of generation and load. On the base of this model, the monitoring data for power and output voltages of three-phase Growatt 30 kW inverter were analyzed. The inverter is tied to LVN by a relatively short line segment with known parameters which is typical for private and small industrial photovoltaic systems. The stable operation of PV plant in the network depends on the ratio of generation and consumption levels at the bus on the plant side, as well as on the capacity of the connecting line. Under analyzing of an overvoltage in the inverter bus appearing due to large solar radiation, one should take into account the limited inverter’s possibility to reduce the output power by changing the operating point on the curve “voltagepower”. The article performs the optimization calculations which determine the parameters characterizing the inverter and line capacity. The developed method for analyzing monitoring data of modern inverters can be a useful tool in solving problems of PV plant equipment diagnostics, as well as of predicting the electricity amount supplied to the network.