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.
For calculating and designing of photovoltaic (PV) plant, it is necessary to choose the optimal tilt angle and azimuth orientation of solar panels which will largely determine the electricity output produced by future PV plant during an operational calendar period. However, in order to determine these angles experimentally by monitoring the PV plant electricity yield at different panel’s positions, it will take many years. Therefore, it is advisable to develop a theoretical model, which a priori calculates the optimal tilt and azimuth angles of panels amounted in fixed positions. This paper assumes the maximum of the total radiation arrival per unit area on the receiving surface over the calendar period of PV plant operation as an optimization criterion for these angles. The calculation scheme has been applied for the whole year, for four year seasons and for a whole year period except winter. In the developed optimization method, the initial data are the geographical coordinates of the PV plant, the hourly sums of direct and diffuse radiation on the horizontal plane, as well as the reflectivity of the earth's surface. These data obtained by averaging the long-term measurements of the main solar radiation components are experimental ones. The developed computational scheme is based on nonlinear equations for the optimal tilt angles of panels first obtained for anisotropic solar radiation models. This scheme allows us to calculate the optimal panel angles for any operational PV plant period and for any region for which experimental radiation data are available. As the examples, we have calculated the graphs of the average daily radiation arrival dependencies on the panel’s position angles and have determined the optimal fixed tilt and azimuth angles for six cities of Russia located in different climatic zones. The method allows us to evaluate the gain in the electricity yield of PV plant when choosing the optimum tilt angles and azimuth of the panels, and to a djust the tilt angles to the optimum values for each season if this is envisaged by the PV string design.
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