Inverter function, classification and selection
Time:2024-01-19
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What is an inverter
An inverter is a device that converts direct current (battery, battery) into alternating current (usually 220V, 50Hz sine wave). It consists of an inverter bridge, control logic, and filtering circuit. Widely used in air conditioning, home theaters, electric grinding wheels, electric tools, computers, televisions, washing machines, range hoods, refrigerators, video recorders, massagers, fans, lighting, solar power generation, etc.
When driving a car to work or travel, an inverter can be connected to a battery to drive electrical appliances and various tools. The vehicle inverter output through the cigarette lighter has power specifications of 20W, 40W, 80W, 120W to 150W. A higher power inverter power supply needs to be connected to the battery through a connecting wire.
Connecting household appliances to the output of a power converter enables the use of various appliances in the car. The usable appliances include mobile phones, laptops, digital cameras, cameras, lighting fixtures, electric shavers, CD players, game consoles, handheld computers, electric tools, car refrigerators, and various travel, camping, medical emergency appliances.
The function of inverters
1. Maximum power tracking function ensures maximum output power
The current and voltage of solar panels vary with the intensity of solar radiation and the temperature of the solar cell components themselves, so the output power also varies. To ensure 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 inverter is designed for this characteristic.
MPPT tracking, also known as maximum power point tracking, is estimated to generate 50% more electricity in systems equipped with MPPT tracking compared to systems without MPPT tracking. So, if you want a photovoltaic system to generate more electricity, don‘t just look at solar panels. The amount of electricity generated by solar panels that can be effectively output ultimately depends on the inverter.
2. Anti standalone operation function to ensure the safety of the power grid
Many people install photovoltaic systems with the mentality that even if the power grid goes out, their homes can still be powered on. Little do they know that when the power grid goes out, their photovoltaic systems will also stop running. The reason for this phenomenon is that inverters are generally equipped with anti islanding devices. When the power grid voltage is 0, the inverter will stop working.
3. Automatically operate and shut down based on the output power of the solar panel
After sunrise in the morning, the intensity of solar radiation gradually increases, and the output of the solar cell also increases. When the output power required for inverter operation is reached, the inverter automatically starts running. After entering operation, the inverter constantly monitors the output of the solar cell module. As long as the output power of the solar cell module is greater than the output power required for inverter operation, the inverter will continue to operate; Until sunset, the inverter can operate even on cloudy and rainy days. When the output of the solar cell module decreases and the inverter output approaches 0, the inverter forms a standby state.
Classification of inverters
1. According to the nature of the source stream
Active inverter: It is an inverter that connects the current in the current circuit to the power grid on the AC side without directly connecting to the load.
Passive inverter: an inverter that directly connects the current in the current circuit to the load on the AC side without being connected to the grid (i.e., inverts DC power into AC power of a certain frequency or adjustable frequency to supply the load).
2. By grid connection type
It is divided into off grid inverters and grid connected inverters.
3. According to topological structure
Divided into two-level inverters, three-level inverters, and multi-level inverters.
4. By power level
Divided into high-power inverters, medium power inverters, and low-power inverters.
4、 How to choose a power inverter
1. Rated output voltage
Within the allowable fluctuation range of the specified input DC voltage, it represents the rated voltage value that the inverter should be able to output.
The stability and accuracy of the output rated voltage value are generally specified as follows: during steady-state operation, the voltage fluctuation range should have a limit, such as its deviation not exceeding ± 3% or ± 5% of the rated value. In dynamic situations with sudden load changes or other interference factors, the output voltage deviation should not exceed ± 8% or ± 10% of the rated value.
2. The imbalance of output voltage
Under normal working conditions, the three-phase voltage imbalance (ratio of reverse sequence component to positive sequence component) output by the inverter should not exceed a specified value, usually expressed in%, such as 5% or 8%.
3. The waveform distortion of the output voltage
When the output voltage of the inverter is sinusoidal, the maximum allowable waveform distortion (or harmonic content) should be specified. Usually expressed as the total waveform distortion of the output voltage, its value should not exceed 5% (single-phase output allows 10%).
4. Rated output frequency
The frequency of the inverter‘s output AC voltage should be a relatively stable value, usually 50Hz power frequency. Under normal working conditions, the deviation should be within ± 1%.
5. Load power factor
Characterize the ability of an inverter to carry inductive or capacitive loads. Under sine wave conditions, the load power factor is 0.7-0.9 (lagging), with a rated value of 0.9.
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Patrick Qi
Patrick Qi
Gitenno