Generated by the grid connection of photovoltaic power generation systemsPower quality monitoringdeviceThe problems mainly include harmonics, voltage fluctuations, flicker, etc., which affect the characteristics of active and reactive power flow, frequency control, etc.

1. Due to factors such as weather, environmental temperature, and installation location of photovoltaic panels, the output power of photovoltaic power stations may vary, even exceeding 10% of the rated power, resulting in unstable power generation and affecting the harmonics fed into the power grid.

2. The grid connection of photovoltaic power plants requires the application of inverters, and the control technology of this product is closely related to the quality of photovoltaic power generation fed into the grid. Currently, using the capacity and power generation of the inverter, the manufacturer will set the power factor of the grid connected inverter to 0.99. However, as the installed capacity of photovoltaic power plants increases, the high power factor operation of inverters poses a threat to the stability of the grid due to the power fluctuation of photovoltaic power generation. When the active power remains unchanged, reactive power can hardly be adjusted, requiring additional reactive power to maintain voltage. In addition, when the inverter outputs a light load, the harmonics will significantly increase. When the rated output is below 10%, the total harmonic distortion rate of the current can even reach over 20%.

3. The variation of photovoltaic power generation with sunlight intensity has an impact on the load characteristics of the power grid. Its integration has changed the direction of power flow in the power grid and will have an impact on the planning, scheduling and operation of the existing power grid. Moreover, photovoltaic power generation units do not have scheduling automation functions, which increases the difficulty of grid control and scheduling operation. If a large number of photovoltaic power generation systems are connected to the power grid terminals, it will exacerbate voltage fluctuations and may cause frequent actions of voltage and reactive power regulation devices; If a high proportion of photovoltaic power generation systems are introduced, it will transform the distribution network from a traditional single source radial network to a dual or even multi terminal network, thereby changing the size and duration of fault currents and affecting the protection of the system.

Therefore, if online monitoring of power quality is required for photovoltaic grid connected power generation, the following conditions must be met:

Real time monitoring of all parameters of power quality; Capable of analyzing harmonics, inter harmonics, high order harmonics, and other functions; Real time alarm when power quality events occur; Data analysis function for power quality issues. Currently, in China, it is possible to meet the technical standards for grid connected photovoltaic power qualityOnline monitoring device for power qualityCombined with powerful backend software, it forms a power quality monitoring system for photovoltaic power generation grid connection.