What are the types of solar inverters?
As the core equipment of PV power generation system, the role of inverter is to convert the variable DC voltage generated by PV modules into utility frequency AC power, which is one of the important system balances in PV array system. At present, the common inverters on the market are mainly centralized inverters, string inverters and micro inverters, and we will compare and analyze these three types of inverters below.
Centralized inverter technology is a number of parallel PV strings connected to the DC input of the same centralized inverter, generally using three-phase IGBT power modules for high power and field-effect transistors for lower power, while using DSP conversion controllers to improve the quality of the output power, making it very close to sinusoidal current, generally used in large PV power plant systems larger than 10KW.
Centralized inverters are generally used in large power generation systems such as large plants with uniform sunlight, desert power stations, ground power stations, etc. The total system power is large, generally above megawatt level.
The main advantages are：
- Small number of inverters for easy management.
- low number of inverter components and high reliability.
3、Less harmonic content, less DC component, high power quality.
- high integration of inverters, high power density and low cost.
5、Inverter various protection functions are complete, the power station security is high.
6、With power factor adjustment function and low voltage ride-through function, the grid is well regulated.
The main disadvantages are：
- high failure rate of DC sink, which affects the whole system.
2, centralized inverter MPPT voltage range is narrow, generally 450-820V, inflexible component configuration, short power generation time in rainy days and foggy ministry areas.
- Difficulties in the installation and deployment of inverter rooms and the need for dedicated rooms and equipment.
4、The inverter itself consumes power and the ventilation and heat dissipation of the room consumes power, and the system maintenance is relatively complicated.
- In a centralized grid-connected inverter system, the module square arrives at the inverter after two convergences, and the inverter maximum power tracking function (MPPT) cannot monitor the operation of every module, so it is impossible to make every module in the best working point, and when one module fails or is shaded, it will affect the power generation efficiency of the whole system.
6、No redundancy capability in the centralized grid-connected inverter system, if there is a fault shutdown, the whole system will stop generating electricity.
String inverter is based on the modular concept, each PV string (1-5kw) through an inverter with maximum power peak tracking at the DC side and parallel grid connection at the AC side, has become the most popular inverter in the international market now.
String inverters are mainly used for small and medium-sized rooftop photovoltaic power generation systems, small ground power plants.
The main advantages are：
1, string inverter adopts modular design, each PV string corresponds to an inverter, the DC side has the maximum power tracking function, and the AC side is connected to the grid in parallel, the advantage of which is that it is not affected by module differences between strings, and shadow shading, and at the same time reduces the mismatch between the best working point of PV modules and the inverter, which maximizes the power generation.
2, string inverter MPPT voltage range is wide, generally 250-800V, component configuration is more flexible, long power generation time in rainy days, foggy part of the area.
3、The string-type grid-connected inverter is small in size and light in weight, and it is very convenient to carry and install. It does not need professional tools and equipment, and it does not need a special distribution room, which can simplify the construction and reduce the area in various applications, and the DC line connection does not need DC sink box and DC distribution cabinet, etc. String type also has the advantages of low self-consumption, low fault impact, easy replacement and maintenance.
The main disadvantages are:
1, more electronic components, power devices and signal circuits on the same board, the difficulty of design and manufacturing, slightly less reliable.
2、Small electrical gap of power devices, not suitable for high altitude areas, outdoor type installation, wind and sunlight will easily lead to the aging of the shell and heat sink.
3, without isolation transformer design, electrical safety is slightly poor, not suitable for thin film module negative grounding system, DC component is large, the impact on the grid is large.
- When multiple inverters are connected in parallel, the total harmonics are high, and the THDI of a single inverter can be controlled to more than 2%, but if more than 40 inverters are connected in parallel, the total harmonics will be iterated, and it is difficult to suppress them.
- the number of inverters will increase the total failure rate and make system monitoring difficult.
- no DC circuit breaker and AC circuit breaker, no DC fuse, which cannot be easily disconnected when the system fails.
7、Single inverter can realize zero-voltage ride-through function, but when multiple machines are connected in parallel, it is difficult to realize zero-voltage ride-through function, reactive power regulation, active power regulation and other functions.
Microinverters have the advantage over central inverters by being able to achieve maximum power point tracking at the panel level. This allows the overall output power to be maximized by optimizing the output power of each module.
The main advantages are:
1、When one or even more modules fail, the system can still continue to provide power to the grid, with high availability; multiple redundant modules are optional to improve system reliability.
2, flexible configuration, in the home market can be installed in accordance with the user’s financial resources photovoltaic cell size.
3, effectively reduce the impact of shadows caused by local shading on the output power.
- No high voltage electricity, safer, easier and faster installation, low maintenance and installation costs, and less dependence on installation service providers.
5、Improve the power generation of each inverter power module and track the maximum power. Due to the tracking of the maximum power point of a single module, the power generation of PV system can be greatly improved by 25%.
The main disadvantages are:
- micro-inverter applications are generally suitable for rooftop homes and applications are restricted.
- The cost of micro-inverters is higher than that of both central inverters and string inverters.
Through comparative analysis, string inverters occupy more advantages than central inverters and micro inverters in terms of failure rate, system safety and operation and maintenance costs, and the system reliability is better, which can ensure long-term safe and reliable operation of power plants.
Foshan Sunpv Technology Co., Ltd. specializes in the manufacture of solar micro inverters, solar power optimizers and rapid shutdown. Our factory has over 10 years of experience in manufacturing precision electrical products. Our high quality solar related products are sold well in many countries around the world. We have certifications from various countries and are committed to providing our customers with the highest quality products and services! We warmly welcome new energy companies from all over the world to establish long-term cooperation with us!
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