energy storage system

The most complete energy storage inverter knowledge guide

The most complete energy storage inverter knowledge guide
This article mainly introduces the functions of inverters, classification and other knowledge of energy storage inverters.
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    As one of the core equipment of the photovoltaic power generation system, benefiting from the rapid development of the global photovoltaic industry, the energy storage inverter industry has maintained rapid growth in recent years. This article mainly introduces the functions of inverters, classification and other knowledge of energy storage inverters.

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    1. What is an inverter?

    Inverter is a converter that can convert direct current (battery, storage battery, etc.) into constant frequency and constant voltage or frequency modulation and voltage modulation alternating current

    2. The composition of the inverter

    The inverter is composed of semiconductor power devices and control circuits. At present, with the development of microelectronics technology and global energy storage, the emergence of new high-power semiconductor devices and drive control circuits has been promoted. Now photovoltaic and energy storage inverters Various advanced and easy-to-control high-power devices such as insulated gate transistors (IGBTs), power field effect transistors (MOS-FETs), MOS controller thyristors (GTOs) and intelligent power modules are mostly used.

    3. What is the function of the inverter?

    • Maximum power tracking function to ensure maximum output power

    For example, the current and voltage of the solar panel change with the intensity of solar radiation and the temperature of the solar cell module itself, so the output power will also change. In order to ensure the maximum output power, it is necessary to obtain the maximum output power of the solar panel as much as possible. The MPPT tracking function of the energy storage inverter is designed for this characteristic.

    • Anti-alone operation function to ensure the safety of the power grid

    Now the energy storage inverter is generally equipped with an anti-islanding device. When the grid voltage is 0, the inverter will stop working.

    • Automatic operation and shutdown according to the output power of solar panels

    When the output of the solar battery reaches the output power required by the energy storage inverter, the inverter will automatically start running. After starting to run, 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 energy storage inverter, the inverter will continue to run; The inverter can also operate on rainy days. When the output of the solar cell module becomes smaller and the output of the energy storage inverter is close to 0, the energy storage inverter will form a standby state.

    Inverters play an important role in storing energy

    4. What types of common inverters are there?

    4.1 Photovoltaic Inverter

    The main function of the photovoltaic inverter is to invert the direct current transformed by solar energy into alternating current through photovoltaic equipment, which can be used by loads or integrated into the grid or stored. Can be divided into the following categories:

    1. Centralized: the scope of application is large-scale ground power stations, distributed industrial and commercial photovoltaics, and the general output power is greater than 250KW.
    2. String type: the scope of application is large-scale ground power stations, distributed industrial and commercial photovoltaics (general output power less than 250KW), household photovoltaics (general output power less than or equal to 10KW).
    3. Micro-inverter: the scope of application is distributed photovoltaic (general output power is less than or equal to 5KW, three-phase), household photovoltaic (general output power is less than or equal to 2KW)

    Various types of inverters for different needs

    4.2 Energy storage inverter

    The main function of energy storage is to control the charging and discharging of the battery. The direct current generated by photovoltaic power generation is converted into alternating current through the inverter, and the alternating current is converted into direct current through the energy storage converter for charging.

    When this part of electric energy is needed, then It is necessary to convert the DC power in the battery into AC power (generally 220V, 50HZ) through the energy storage converter for load use or into the grid. Can be divided into the following categories:

    1. Large storage: ground power station, independent energy storage power station, the general output power is greater than 250KW
    2. Industrial and commercial storage: general output power is less than or equal to 250KW
    3. Household storage: general output power is less than or equal to 10KW
    4. Traditional energy storage converters: mainly use the AC coupling scheme, and the application scenarios are mainly large storage
    5. Hybrid: mainly adopts the DC coupling solution, and the application scenario is mainly household storage
    6. All-in-one machine: energy storage converter + battery pack, the products are mainly Tesla, Ephase

    4.3 Functional differences

    In fact, the biggest difference between the two is that the photovoltaic inverter can only convert direct current into alternating current in one direction, while the energy storage converter is bidirectional, with energy control in both directions of charging and discharging. To sum up, the energy storage inverter has the following advantages:

    • The self-use rate of traditional photovoltaic inverters is only 20%, while the self-use rate of energy storage inverters is as high as 80%
    • When the mains fails, the grid-connected inverter is paralyzed, but the energy storage inverter can still work efficiently
    • Under the background of continuous reduction of subsidies for grid-connected power generation, the income of energy storage inverters is higher than that of photovoltaic inverters
    • Photovoltaic inverters can only generate electricity during the day, and the power generation will be affected by the weather, which has unforeseen problems, while energy storage inverters can perfectly solve the existing problems of photovoltaic inverters

    The difference between photovoltaic inverter and energy storage inverter

    5. How to choose an energy storage inverter?

    5.1 Rated output voltage

    Within the allowable fluctuation range of the specified input DC voltage, it indicates the rated voltage value that the inverter should be able to output.

    The stable accuracy of the output rated voltage value is generally stipulated as follows: in the steady state operation, the voltage fluctuation range should have a limit, for example, the deviation should not exceed ±3% or ±5% of the rated value. In the case of sudden load changes or other disturbance factors, the output voltage deviation should not exceed ±8% or ±10% of the rated value.

    5.2 Unbalance of output voltage

    Under normal working conditions, the unbalance degree of the three-phase voltage output by the inverter (the ratio of the reverse sequence component to the positive sequence component) should not exceed a specified value, generally expressed in %, such as 5% or 8%.

    5.3 Waveform distortion of output voltage

    When the inverter output voltage is sinusoidal, the maximum allowable waveform distortion (or harmonic content) should be specified. It is usually expressed by the total waveform distortion of the output voltage, and its value should not exceed 5% (10% is allowed for single-phase output).

    5.4 Rated output frequency

    The frequency of the AC voltage output by the inverter should be a relatively stable value, usually the power frequency 50Hz. Under normal working conditions, the deviation should be within ±1%.

    5.5 load power factor

    Characterize the ability of the inverter with inductive load or capacitive load. Under the condition of sine wave, the load power factor is 0.7~0.9 (lag), and the rated value is 0.9.

    6.Summary

    As one of the core equipment of the photovoltaic power generation system, benefiting from the rapid development of the global photovoltaic industry and lithium-ion battery energy storage, the energy storage inverter industry has maintained rapid growth in recent years. Therefore, it is very useful to understand the energy storage inverter and choose according to the demand when needed. 

    Energy storage inverter industry maintains rapid growth

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