The connection methods between photovoltaic power generation systems and the power grid can be divided into two categories: independent photovoltaic systems and grid-connected photovoltaic systems. After years of development, photovoltaic power generation is now a relatively mature and reliable technology, and has gradually developed from an independent system in the past to large-scale grid connection. However, the most significant disadvantage of photovoltaic power generation is its high cost. The current cost of producing electricity per kilowatt hour is about 20 times that of coal power and about 10 times that of wind power. According to the development roadmaps of the United States, Japan, and Europe, it is expected that with technological advancement, improvement in conversion efficiency, and expansion of market scale, the cost of photovoltaic power generation may be close to the current cost of wind power by around 2030. In short, the current cost of solar photovoltaic power generation is high, but it has a good industrialization foundation. It will have the technical, cost and environmental advantages to become a strategic energy source around 2030, and it can become an important source of energy supply around 2050.
Requirements: Voltage deviation: In order for the local AC load to work properly, the output voltage of the inverter in the photovoltaic system should match the grid. During normal operation, the allowable voltage deviation at the interface between the photovoltaic system and the power grid should comply with the regulations of GB/T12325. The allowable deviation of three-phase voltage is ±7% of the rated voltage, and the allowable deviation of single-phase voltage is +7% and -10% of the rated voltage. Frequency: When the photovoltaic system is connected to the grid, it should run synchronously with the grid. The rated frequency of the power grid is 50Hz. The allowable frequency deviation of the photovoltaic system after being connected to the grid should comply with the provisions of GB/T15945, that is, the deviation value is allowed to be ±0.5Hz.
Harmonics and Waveform Distortion Low harmonic levels in current and voltage are desirable; higher harmonics increase the potential for harmful effects on connected equipment. The permissible levels of harmonic voltages and currents depend on the characteristics of the distribution system, the type of supply, the connected loads/equipment, and the current regulations on the grid. The output of the photovoltaic system should have low current distortion to ensure that there is no adverse effect on other equipment connected to the grid. The total harmonic current should be less than 5% of the inverter's rated output. Each harmonic should be limited to the percentages listed in Table 1 and Table 2.