Relevant Knowledge And Direction Guide Of Photovoltaic Inverter
- Photovoltaic inverter – the heart of photovoltaic power generation system
- The role of the photovoltaic inverter
- Types of photovoltaic inverter
- The power of the photovoltaic inverter will continue to increase
- Future photovoltaic inverter market demand
In the process of solar photovoltaic power generation, the power generated by the photovoltaic array is DC power, but many loads require AC power. The DC power supply system has great limitations. It is not easy to change the voltage, and the load application range is also limited. Except for special power loads, inverters are required to convert DC power into AC power.
The photovoltaic inverter is the heart of the solar photovoltaic power generation system. It converts the direct current generated by the photovoltaic power generation system into the alternating current required for life through power electronic conversion technology. It is one of the most important core components of photovoltaic power station.
Photovoltaic inverter – the heart of photovoltaic power generation system
The photovoltaic inverter is generally composed of a boost circuit and an inverter bridge circuit. The boost circuit boosts the DC voltage of the photovoltaic cell to the DC voltage required for inverter output control. The photovoltaic inverter bridge circuit converts the boosted DC voltage into an AC voltage of common frequency equivalently.
The principle of the inverter is to turn the DC input into an AC output by regularly turning the switching RMB components (IGBT, MOSFET, etc.) on and off (ON-OFF) at a high frequency.
MPPT technology is the core technology of photovoltaic inverter. MPPT is a maximum power point tracking system, which is an electrical system that enables photovoltaic cells to output more electrical energy by adjusting the working state of electrical modules. The amount of power generated by photovoltaic cells is affected by light intensity and external links, and its output power varies.
MPPT control detects the power generation voltage under conditions such as ambient temperature and light intensity in real time, tracks the highest voltage and current, and adjusts the equivalent resistance of the DC/DC conversion circuit, so that the photovoltaic cell can achieve maximum power output and improve charging efficiency. Therefore, MPPT is a key component that determines the power generation capacity of photovoltaic cells.
Photovoltaic inverter is in the downstream position in the photovoltaic industry chain. The photovoltaic industry chain can be divided into five links: silicon materials, silicon wafers, photovoltaic cells, photovoltaic modules, and photovoltaic systems. The upstream includes the production of high-purity polycrystalline silicon materials, the manufacture of monocrystalline silicon and polycrystalline silicon, and the production of silicon wafers.
The midstream includes photovoltaic cells, photovoltaic modules (glass, brackets, etc.) and other links. The downstream is the application side of photovoltaic power generation. The inverter industry is closely related to the development of downstream industries.
Photovoltaic inverter can convert the variable DC voltage generated by photovoltaic solar panels into AC frequency of mains power, which can be fed back to the commercial power transmission system, or It is used for the off-grid power grid, and the downstream industry has a greater traction and driving effect on the development of the inverter industry.
The role of the photovoltaic inverter
Photovoltaic inverter not only has DC-AC conversion functions, but also have active operation and shutdown functions, maximum power tracking MPPT functions, detection and control functions, grid detection and grid-connected functions, and zero (low) voltage ride-through functions.
- Active operation and shutdown function
After sunrise in the morning, the solar radiation intensity gradually increases, and the output of solar cells also increases accordingly. When the output power required by the inverter task is reached, the inverter will automatically start operation.
After entering the operation, the inverter will monitor the output of the solar cell components all the time, as long as the output power of the solar cell components is greater than the output power required by the inverter, the inverter will continue to run.
- Maximum power tracking MPPT function
When the sunshine intensity and ambient temperature change, the input power of photovoltaic modules presents a nonlinear change. The photovoltaic module is neither a constant voltage source nor a constant current source. Its power changes with the output voltage. Changes have nothing to do with load.
- Detection and control function
During normal power generation, the photovoltaic grid-connected power generation system is connected to the grid and transmits effective power to the grid. However, when the grid loses power, the photovoltaic grid-connected power generation system may continue to work, and local loads operate independently.
- Grid detection and grid-connected functions
Before the grid-connected inverter generates electricity, it needs to take power from the grid, detect the parameters of the grid’s power transmission voltage, frequency, phase sequence, etc., and then adjust the parameters of its own power generation. It is synchronized with the grid parameters and will be connected to the grid for power generation after completion.
- Zero (low) voltage ride-through function
When an accident or disturbance in the power system causes a voltage sag at the grid-connected point of the photovoltaic power station, within a certain voltage drop range and time interval, the photovoltaic power station can guarantee that it will not go off-grid continue to operate.
Types of photovoltaic inverter
According to the technical route of photovoltaic inverters, photovoltaic inverter can be divided into large-scale centralized photovoltaic inverter, string photovoltaic inverter, distributed photovoltaic inverter, and micro-inverter.
- Large-scale centralized photovoltaic inverter
A large-scale centralized photovoltaic inverter is a power electronic device that aggregates the direct current generated by photovoltaic modules into a large direct current power and then converts it into alternating current.
Therefore, the power of this type of photovoltaic inverter is relatively large, and a centralized inverter of more than 500KW is generally used. It is usually suitable for large-scale ground photovoltaic power plants, agricultural photovoltaic complementary photovoltaic power plants, water surface photovoltaic power plants, etc.
- String photovoltaic inverter
The string photovoltaic inverter is a power electronic device that directly converts the direct current generated by a small single RMB photovoltaic module into alternating current. Therefore, the power of string photovoltaic inverter is relatively small, and generally photovoltaic inverter with power below 50kW are called string photovoltaic inverter.
String photovoltaic inverters are mainly used in small-scale power stations, such as household distributed power generation, small and medium-sized industrial and commercial rooftop power stations, etc., but they have also been used in some large ground power stations in recent years.
- Distributed photovoltaic inverter
The distributed inverter technology combines the centralized inverter advantages of large-scale centralized photovoltaic inverters and the decentralized MPPT tracking advantages of string photovoltaic inverters to achieve the low cost of centralized inverters.
A single component tracking transformation, suitable for household photovoltaic systems. The micro-inverter tracks the maximum power peak value of each photovoltaic module separately, and then connects it to the AC grid after inversion. The single capacity of micro-inverter is generally below 1kW.
The power of the photovoltaic inverter will continue to increase
The cost reduction of photovoltaic power generation systems is still the general trend. Higher power components can reduce the cost per watt. In order to adapt to the trend of large-scale components, the power and current of photovoltaic inverters have been further increased. In order to increase the power of modules and reduce the cost per watt, modules are developing in larger sizes. Silicon wafer size has reached 166mm (M6), 210mm (G12) and so on.
Since 2019, high-power modules based on large-size silicon wafers have become the mainstream trend in the photovoltaic industry, and various module manufacturers have launched 182mm and 210mm modules. According to the data, the combined proportion of 182mm and 210mm silicon wafers will increase rapidly from 4.5% in 2020 to 45% in 2021, and its proportion will continue to expand rapidly in the future.
In order to adapt to high-current components, the photovoltaic inverter current needs to support up to 20A/string, and at the same time, it has the ability to shut down at the component level. In the past few years, the module current has generally been maintained at around 10-13A.
Taking into account factors such as double-sided coefficient and radiation enhancement, the current of mainstream inverters on the market is 15A/string. For high-current components, the inverter current needs to support up to 20A/string. If the 15A/string inverter is still used, it will lead to severe DC power limitation. At the same time, as the component current and the number of inverter strings increase, the risk of inverter failure and fire will also increase.
Future photovoltaic inverter market demand
Demand for newly installed photovoltaic capacity in the world. Driven by the goal of “carbon neutrality”, according to forecasts, the world’s newly installed photovoltaic capacity is expected to increase from 170GW in 2021 to 330GW in 2025.
The demand for installed capacity of energy storage inverters brought about by the outbreak of energy storage. Due to the rapid development of scenery, the demand for energy storage facilities has accelerated. Among them, the inverter used for energy storage is similar to the photovoltaic grid-connected inverter technology, and the energy storage inverter brings incremental business to related inverter companies.
The service life of the inverter is limited by the power electronic devices, and the general service life is about ten years before it needs to be replaced. As the core component of photovoltaic power generation, the performance and quality of the inverter are crucial to the quality of power generation.
Generally speaking, the service life of traditional string photovoltaic inverter is about ten years, and the service life of large-scale ground power stations is about 20 years, which means that the inverter needs to be replaced when the life of the power station is half.
According to estimates, the world inverter market space will be 54.3 billion in 2021 and 136.7 billion in 2025. By 2025, new photovoltaic installed capacity will be 330GW, stock replacement will be 49GW, and energy storage installed capacity will be 80GW, corresponding to 178GW of centralized inverters, 174GW of string inverters, 28GW of micro-inverters, and 80GW of energy storage inverters. The space is 136.7 billion RMB.