PV inverter is dedicated to the inverter in the field of solar photovoltaic power generation, which is an indispensable core component of the photovoltaic system.
Its biggest role is to convert the direct current generated by solar cells into alternating current energy that can be directly integrated into the grid and loaded through power electronic conversion technology.
In order to achieve the optimal way of solar conversion, this will inevitably require a variety of inverters, and this article will talk about central inverter.
This is due to the diversity of the buildings, which leads to the diversity of solar panel installations. At the same time, in order to maximize the conversion efficiency of solar energy, taking into account the appearance of the building.
1. Introduction of central inverter
The power of the central inverter equipment is between 50 kw and 630 kw, and the system topology adopts the first stage power electronics to convert direct current into alternating current, and the full bridge central inverter is converted. In the case of power frequency isolation transformers, the protection level is generally IP 20.
It is large in size and installed vertically indoors. In systems typically used in large-scale photovoltaic power plants (>10 kW), a large number of parallel PV strings are connected to the DC input of the same central inverter. The grid tie inverter 1000w mainly used in user side.
Generally, three-phase IGBT power modules are used for large power, and field-effect transistors are used for small power. At the same time, a DSP conversion controller is used to improve the quality of the generated energy so that it is very close to the sine wave current.
2. What are the classifications of inverters
In terms of product types, inverter products are mainly divided into four categories, namely:
250 KW-10 MW
Large-scale ground-mounted power station
1 MW-10 MW
Complex large-scale ground-mounted power station
1.5 KW-250 KW
Residential, commercial and industrial distributed and ground power station
Distributed and other small and medium-sized power station
3. Features of central inverter
Its biggest feature is the high power and low cost of the system. However, due to the fact that the output voltage and current of different PV strings are often not fully matched (especially when the PV strings are partially blocked due to clouds, shadows, stains, etc.).
The use of central inverter will lead to the reduction of the efficiency of the central inverter process and the reduction of household power energy. At the same time, the power generation reliability of the entire photovoltaic system, including distributed pv system is affected by the poor working condition of a certain photovoltaic unit.
Central inverter is generally used in large-scale power generation systems such as large-scale factories, desert power stations, and ground power stations with uniform sunlight. Unlike the inverter 3000w used in our home, the total power of the system is large, generally above megawatts.
5. Analysis of the advantages and disadvantages of central inverters
● Advantages of central inverter
- The number of central inverters is small, which is easy to manage.
- The number of components is small and the reliability is high.
- Low harmonic content, low DC component, high power quality.
- High integration, high power density, low cost.
- All kinds of protection functions are complete, and the power station has high safety.
- It has a power factor regulation function and a low voltage ride-through function, and the grid regulation is good.
● Disadvantages of central inverter
- Security issues
In the centralized solution, the DC combiner box is used, and there is a risk of continuous fire due to the built-in DC branch fuse. Because as long as there is light, the solar panels will be in working condition.
For distributed rooftop plants, it brings serious safety hazards. Not only will the economic benefits of the power station itself be affected, but more importantly, it will affect other equipment in the plant. Brings great losses.
- Subject to installation environment
Irregular roofs with a single 500 KW inverter cannot make full use of the roof area. Central inverter is often overloaded or lightly loaded, over-provisioned, and underloaded.
On rooftops facing multiple directions, panels are partially shaded to cause string inconsistencies, and single-channel MPPT leads to relatively low power generation. At the same time, the mismatch loss of each string will also lead to the loss of power generation.
- Difficult to maintain
Central inverter requires professional engineers to maintain, and the failure of a single inverter has a great impact on power generation.
At the same time, there are many types of spare parts, and fault location and repair take more than 3 days, which seriously affects the customer's power generation income. It is expensive to maintain and needs to be replaced regularly.
- Many supporting facilities
The central inverter system requires an central inverter room and corresponding civil works, as well as corresponding fans, air ducts, smoke sensors, temperature sensors and other equipment.
However, if a photovoltaic power station is installed on the roof of a traditional plant, it not only increases the complexity of construction, but also increases the initial investment and operation and maintenance costs.
- Affected by the weather
The MPPT voltage range of the central inverter is narrow, generally 450-820V, and the module configuration is not flexible.
In areas with a lot of fog on rainy days, power generation time is short. There is no redundancy in the centralized grid-connected inverter system, and if there is a failure, the entire system will stop generating electricity.
6. Functional characteristics of central photovoltaic power stations
Photovoltaic power generation is mainly composed of three parts: power generation unit, inverter and box transformer system, and central control system. The power generation unit is composed of photovoltaic modules, photovoltaic brackets and foundations.
The inverter and box substation system inverts and boosts the direct current emitted by the power generation unit and then transmits it to the central control system via cables.
The central control system collects the electrical energy of each power generation unit and outputs it stably to the power grid, so that the entire power generation process is completed.
The construction of centralized photovoltaic power stations has the characteristics of large footprint, short construction time, and concentrated capital investment, so it is necessary to pay attention to the site selection, the selection and inclination angle of photovoltaic modules of power generation units, and the selection of inverter systems in the construction process.
From photovoltaic power generation, it is necessary for central inverter. Under the dual pressure of energy tightening and energy conservation and emission reduction, solar energy resources, such as renewable clean energy, have become one of the most promising green energy sources.
Photovoltaic power generation has the characteristics of short construction periods, simple system structure, and relatively stable power generation, and has the potential for large-scale development.