Islanding effect of PV public power grid
The so-called islanding effect refers to a power generating device that is incorporated into a public power grid. In the case of a power outage galvanized c section, the power generating device cannot detect, or has no corresponding detection means, and still feeds power to the public power grid. Due to the potential danger of the islanding effect and the damage to equipment, social public works and power generation equipment owners have long been concerned about the anti-island control of photovoltaic grid-connected inverters. Therefore, the islanding effect must be prevented in the application of photovoltaic grid-connected power generation systems.
The principle of the islanding effect: In the circuit in which the capacitors are connected in series, only the two plates connected to the external circuit (note: not the plates of the same capacitor) have current flow (charge exchange), and the total charge of other plates is not Changed, so called an island. An island is an electrical phenomenon that occurs when a part of the grid is disconnected from the main grid, and this part of the grid is completely powered by the photovoltaic system. This is still a matter of debate on the topic of international PV grid-connected standardization, because the island will damage the safety of the public and power company maintenance personnel and the quality of the power supply. It may be damaged when the power switch is automatically or manually re-closed to the island grid. device. Therefore, the inverter usually has an islanding prevention device.
The islanding effect may adversely affect the entire distribution system equipment and the equipment at the customer premises:
1. Harm the life safety of power maintenance personnel; affect the protection switch operation procedure on the power distribution system; the unstable nature of the power supply voltage and frequency occurring in the island area will cause damage to the power equipment.
2. When the voltage phase is not synchronized when the power supply is restored, it will generate surge current, which may cause another trip or damage to the PV system, load and power supply system. The photovoltaic grid-connected power generation system will cause system three due to single-phase power supply. Under-phase power supply problem with phase load. It can be seen that as a safe and reliable grid-connected inverter device, the island effect must be detected in time, and the harm caused should be avoided.
The high resistance of the battery causes the PV component PID phenomenon:
First, the system design reason: the lightning protection grounding of the photovoltaic power station is realized by grounding the component frame at the edge of the square array, which causes a bias voltage to be formed between the single component and the frame. The higher the bias voltage of the component occurs, the PID phenomenon occurs. The more serious it is. For the P-type crystalline silicon component, the grounding of the negative pole of the inverter with the transformer eliminates the forward bias of the component frame relative to the cell, which effectively prevents the occurrence of the PID phenomenon, but the grounding of the negative pole of the inverter increases the corresponding system. Construction costs.
Second, the reason for the photovoltaic components: high temperature, high humidity environment, the leakage current is formed between the battery chip and the ground frame, and a leakage current channel is formed between the packaging material, the back plate, the glass and the frame. The use of a modified insulating film, ethylene vinyl acetate (EVA), is one of the ways to achieve component anti-PID, and the anti-PID performance of the components may vary under different EVA encapsulation films. In addition, the glass in the photovoltaic module is mainly calcium soda glass, and the influence of glass on the PID phenomenon of the photovoltaic module is still unclear.
The third reason is the battery piece: the uniformity of the cell sheet resistance, the thickness of the anti-reflection layer and the refractive index have different effects on the PID performance. In the above three aspects of causing the PID phenomenon, the component PID phenomenon caused by the component frame in the photovoltaic system and the potential difference inside the component is recognized by the industry, but in the component and the battery chip, the component generates the PID phenomenon. The mechanism is still unclear, and the corresponding measures to further improve the anti-PID performance of photovoltaic modules are still unclear.