Analysis And Use Of Components For Grid-connected Photovoltaic Power Systems

Grid-connected photovoltaic power generation systems are processes that are powered by solar cells and grid-connected countercurrents. The PV grid-connected power system's are widely used in today's life. The conversion of light energy from PV grid-connected power systems into electrical energy, various advantages and functions are supported and researched by professionals and national governments, and our research direction also revolves around grid-connected countercurrents and PV cells. Their equipment has also been very hot on the market, and solar products are now popular with domestic users, so some basic concepts and principled knowledge are explained.

I. Grid-connected photovoltaic power generation systems

1. Grid-connected photovoltaic power generation system is the direct current generated by solar products through the grid-connected counter-current converter into alternating current and then directly connected to the public grid. Simply put, it is the conversion of light energy into electrical energy for the user's use.

　Because the electricity is fed directly into the grid, all batteries present in the PV stand-alone system are replaced by the grid-connected system, thus eliminating the need for batteries and thus reducing costs. However, the system requires a grid-connected counter-current converter to ensure that the power can meet the grid's frequency, frequency and other properties.

Strengths.

(1) The use of non-polluting, renewable solar power, but also fast to reduce non-renewable. The consumption of energy with limited resources, the emission of greenhouse gases and pollution gases at noon during the use process, in harmony with the ecological environment, is to promote the development of the road to sustainable development!

(2) The electricity generated is directly fed into the grid through the inverter, eliminating the need for a battery, which reduces the investment in construction by up to 35% to 45% compared to a PV stand-alone system, greatly reducing production costs. It can also remove the battery to avoid the secondary pollution of the battery, and can increase the service life and normal use time of the system.

(3) photovoltaic building integrated power generation system, due to small investment, fast construction, small footprint, making the building high technology content, enhance the building selling point

(4) Distributed construction, decentralised construction in the vicinity of various large and small places makes it convenient to enter the power grid, which is not only good for increasing the defence capability of the system and resisting natural disasters, but also good for load balancing of the power system and reducing the loss of lines.

(5) can play a peaking role. Grid-connected solar photovoltaic system is the key object of development and support of many developed countries, is the main development trend of solar power generation system, large market capacity, large development space.

2. Grid-connected inverters

There are several types of grid-connected inverters.

(1) Central inverters

(2) String inverters

(3) Module inverters

     The main circuit of the above several types of inverters are taken to control the circuit to reality then we can divide into two types of control: square wave and sine wave.

　　Inverter with square wave output: Most of the inverters with square wave output take pulse width modulated integrated circuits, such as TL494. The fact that the SG3525 integrated circuit is used to take power field effect tubes as switching power components can achieve a superb performance ratio for inverters, as the SG3525 is very effective in driving power field effect tubes and has internal reference sources and operational amplifiers and undervoltage protection, all with simple relative peripheral circuitry.

　　Inverter with sine wave output: schematic diagram of a sine wave inverter, with the difference between a square wave output and a sine wave output. The inverter with a square wave output is highly efficient, but for appliances designed for a sine wave power supply, it is not always easy to use, although it can be used for many appliances, some of them are not suitable, or the indicators of the appliances may change. An inverter with a sine wave output does not have this disadvantage, but has the disadvantage of low efficiency.

　　The principle of grid-connected inverters: we convert AC current into DC current is rectification, the circuit process to complete this rectification function we call rectifier circuit, the whole process of realising the rectifier circuit device we become rectifier. In contrast to it, the ability to convert DC current into AC current is the counter-current, the circuit process that completes the whole counter-current function we call the inverter circuit, the whole process of realising the inverter device we become the inverter.

Functions.

　　a.Automatic switch on/off: It enables the function of automatic switch on/off according to the sun's working hours.

　　b.Maximum power point tracking control: when the surface temperature of the PV module and the temperature of the sun exposure change, the voltage and current generated by the PV module also changes, it can track these changes to ensure maximum power output.

　　c. Prevention of the islanding effect: Passive detection determines whether islanding has occurred by detecting the grid, while active detection creates positive feedback by actively introducing small disturbances and using the cumulative effect to infer whether islanding has occurred. It is through this combination of passive and active detection methods that the anti-islanding effect control effect can be achieved.

　　d. Automatic voltage adjustment. In the event of excessive current backflowing through the grid, the voltage at the point of delivery rises due to the reverse transmission of power, potentially exceeding the operating range of the voltage. To maintain the normal operation of the grid, the grid-connected inverter has to be able to automatically prevent the voltage from rising.

　　Installation: If the inverter is centralised, install it near the electricity meter if there is one nearby. If the conditions and environment are suitable, it is also possible to install it near the PV terminal block, which greatly reduces the wear and tear on the wiring and equipment. Large central inverters are usually installed in an inverter box with other equipment (e.g. meters, circuit breakers, etc.). Decentralised inverters are increasingly being installed on rooftops, but experiments have found that they should be well protected from direct sunlight and rain as much as possible. When choosing an installation site, it is important to meet the temperature and humidity requirements recommended by the inverter manufacturer. The impact of the inverter's noise on the surrounding environment should also be taken into account.