What is the islanding effect in a PV system?

The islanding effect refers to the grid-connected photovoltaic power generation system when the power grid suddenly loses voltage.

An effect that still maintains the state of supply to adjacent lines in the grid. Photovoltaic power station refers to a photovoltaic power generation system that is connected to the power grid and transmits power to the power grid, which is a green energy encouraged by the state.

Project. It can be divided into grid-connected power generation systems with and without batteries. Solar power generation is divided into solar thermal power generation and photovoltaic power generation. Solar power generation usually refers to solar photovoltaic power generation.

Because islanding can compromise the safety of the public and utility maintenance personnel and the quality of power supply, there is a risk of damage to equipment when automatically or manually reclosing the power switch to re-supply power to the islanded grid. So, the inverter.

It is usually equipped with an anti-islanding device. Passive techniques (detecting changes in voltage and frequency in the grid) are not sufficient for islanding prevention in both energizing and re-energizing situations under well-balanced load conditions, so it is necessary to combine active techniques, which are based on the shift of the sample frequency, impedance monitoring of the flowing current, phase jumps and harmonics.

The monitoring, positive feedback method, or the controller on the basis of unstable currents and phases.

In electronic circuits, islanding is a phenomenon in which there is a current path in an area of the circuit but no current actually flows. In the communication network, the coverage of wireless mobile base stations may exist as a phenomenon.

Any power generation device connected to the public transmission grid as long as it is not the main energy source side of the public transmission grid has an islanding effect, such as diesel generator sets, if connected to the grid, there is also an islanding effect. In electronic circuits, islanding is a phenomenon in which there is a current path in an area of the circuit but no current actually flows. In the communication network, the coverage of wireless mobile base stations may exist as a phenomenon.

The islanding effect is a problem of base station coverage, when the base station is covered by special terrain such as large water surface or mountainous areas, due to the reflection of water surface or mountain peaks, the base station appears at a great distance on the basis of the original coverage area unchanged"Enclaves", but the adjacent base station with the handover relationship cannot be covered due to the blocking of the terrain, which is caused"Enclaves"There is no handover relationship with adjacent base stations"Enclaves"Thus becomes an island when the phone is occupied on"Enclaves"When the signal in the coverage area is in the coverage area, it is easy to cause the call to drop due to the lack of switching relationship.

To solve the islanding effect, firstly, we should adopt methods such as adjusting engineering parameters to reduce the reflection and refraction of mountains and buildings on the isolated island, control the wireless signal in the coverage area of the community, eliminate or reduce the wireless signal in the isolated area, and reduce the interference of the isolated area to other cells. However, sometimes because of the complex wireless environment, sometimes the signal in the isolated area cannot be completely eliminated, so the frequency or code resource allocation can be adjusted to reduce the interference to other cells, and the neighbor relationship can be equipped according to the road test situation to make the handover normal.

At present, in China, solar photovoltaic grid-connected power generation has been included in the scope of key support under the great attention of the first. The photovoltaic grid-connected power generation system belongs to the distributed power supply system. When the power supply is interrupted due to electrical faults, misoperation or natural factors, the individual photovoltaic grid-connected power generation systems are still in operation and are connected to the local load in an independent state, a phenomenon known as the island effect.

From the perspective of electricity safety and electricity quality, the island situation is not allowed. Therefore, the photovoltaic grid-connected power generation system should have the ability to detect the islanding state and quickly and effectively stop the grid-connected operation.

In a circuit in which a capacitor is connected in series, only two plates connected to the outer circuit (note: plates that are not the same capacitor) have current flow (charge exchange), and the total charge of the other plates is constant, so it is called islanding. Islanding is an electrical phenomenon that occurs when a part of the grid is disconnected from the main grid, which is powered entirely by photovoltaic systems.

With the further widespread application of photovoltaic grid-connected power generation systems, when multiple photovoltaic inverters are connected to the grid at the same time, the output of different inverters changes very largely, resulting in the failure of the above methods.

Any power generation device connected to the public transmission grid as long as it is not the main energy source side of the public transmission grid, there is an island effect, not only for photovoltaic power generation, such as diesel generator sets, if connected to the grid, there is also an island effect.

That's right, if there is no mains, the photovoltaic will also be powered off.

Under the action of the electric field of the p-n junction, the holes flow from the n-region to the p-region, and the electrons flow from the p-region to the n-region, and the current is formed after the circuit is turned on. This is how photoelectric effect solar cells work. The photovoltaic effect refers to the phenomenon in which light causes a potential difference between an inhomogeneous semiconductor or between a semiconductor and a metal bond.

It is first of all the process of converting photons (light waves) into electrons and light energy into electrical energy; Secondly, there is the process of forming a voltage. With voltage, it's like building a dam, and if the two are connected, a loop of current will be formed.

When the p-n junction is exposed to light, both the intrinsic and non-intrinsic absorption of photons by the sample will produce photogenerated carriers (electron-hole pairs). However, only a few carriers excited by intrinsic absorption can cause the photovoltaic effect. Due to the photogenerated holes generated in the p-region and the photogenerated electrons produced in the n-region, they are all blocked by the potential barrier and cannot pass through.

Only photogenerated electrons in the p-region and photogenerated holes in the n-region and electron-hole pairs (few sons) in the junction can drift through the junction under the action of the built-in electric field when they diffuse near the junction electric field. The photogenerated electrons are pulled towards the n-region, and the photogenerated holes are pulled towards the p-region, i.e., the electron-hole pairs are separated by the built-in electric field. This results in photogenerated electron accumulation near the n-region boundary and photogenerated hole accumulation near the p-region boundary.

They generate a photogenerated electric field in the opposite direction to the built-in electric field of the thermally equilibrium p-n junction, pointing from the p-region to the n-region. This electric field lowers the potential barrier, and its reduction is the photogenerated potential difference, which is positive at the p end and negative at the n end, at this time, the Fermi energy level is separated, so the voltage drop is generated, and the electrodes are added on both sides of the silicon wafer and connected to the voltmeter. For crystalline silicon solar cells, the typical value of the open-circuit voltage is:

The more electron-hole pairs are created in the interfacial layer by illumination, the greater the current. The more light energy absorbed by the interfacial layer, the larger the area of the interfacial layer, i.e., the cell, and the greater the current formed in the solar cell.

In fact, not all of the photogenerated carriers produced contribute to the photogenerated current. Let the diffusion distance of the hole in the n-region be lp during the lifetime p, and the diffusion distance of the electrons in the p-region during the lifetime n is much greater than the width of the p-n junction itself. Therefore, it can be assumed that the photogenerated carriers generated within the average diffusion distance l near the junction contribute to the photocurrent.

The electron-hole pairs generated by the electron-hole pairs with a position more than L from the junction region will be recombined during the diffusion process, and will not contribute to the photoelectric effect of the p-n junction.