Deep Learn about the important parameters of the inverter in one article
Composition of Inverter
Inversion is the opposite process to rectification, which is the process of converting DC power into AC power. Photovoltaic inverter refers to a circuit that completes the inverter function or a device that implements the inverter process.
The main components of the inverter:
- Shell and terminals: used for junction box protection
- Radiator: used for system heat dissipation of the inverter
- Display: inverter status and data
- Control board: the core component of the inverter, used for inverter Power control of the inverter and various algorithm control
- Power supply board: Internal power supply for the inverter
- Power board: The core component of the inverter, the main circuits are concentrated on the power board.
Classification of inverters
Divided by function: Grid-connected inverters and off-grid inverter
Divided by the frequency of output AC power: industrial frequency inverter (frequency: 50-60Hz), medium frequency inverter (frequency: 400-20kHz) and High frequency inverter (frequency: 20kHz-10MHz).
Divided according to the number of inverter output phases: single-phase inverter, three-phase inverter and multi-phase inverter.
Divided according to the access status of photovoltaic modules: centralized inverters, string inverters and micro (module) inverters.
Centralized inverter | |||
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Definition | A square array composed of multiple photovoltaic strings is centrally connected to a large inverter. | Based on the concept of modularity, each photovoltaic string in the photovoltaic array is input into an inverter, and multiple photovoltaic strings and inverters are combined together in a modular manner. | Each photovoltaic module corresponds to a micro-inverter, which has independent variable speed and MPPT functions and can be directly fixed behind the photovoltaic module. |
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Main parameters of the inverter
1. Technical parameters of DC input side
- Maximum allowable access to photovoltaic string power
The maximum allowable connected photovoltaic string power is the maximum DC connected photovoltaic string power allowed by the inverter.
- Rated DC power
The rated DC power is calculated based on the rated AC output power divided by the conversion efficiency, plus a certain margin.
- Maximum DC voltage
Taking the temperature coefficient into consideration, the maximum voltage of the connected photovoltaic string should be less than the maximum DC input voltage of the inverter.
- MPPT voltage range
The MPPT voltage of the photovoltaic string taking into account the temperature coefficient must be within the MPPT tracking range of the inverter. A wider MPPT voltage range enables more power generation.
- Starting voltage
When the starting voltage threshold is exceeded, the inverter starts to start, and when it is lower than the starting voltage threshold, the inverter shuts down.
- Maximum DC current
When selecting an inverter, focus on the maximum DC current parameter. Especially when connecting thin-film photovoltaic modules, it is necessary to ensure that the photovoltaic string current connected to each MPPT is less than the maximum DC current of the inverter.
- Number of input channels and MPPT channels
The number of input channels of the inverter refers to the number of DC input channels, while the number of MPPT channels refers to the number of maximum power point tracking channels. The number of input channels of the inverter is not equal to the number of MPPT channels. If the inverter has 6 DC inputs, the inputs of every three inverters are used as one MPPT input. The inputs of several photovoltaic groups under 1 MPPT need to be equal, and the inputs of photovoltaic strings under different MPPTs do not need to be equal.
2. Technical parameters of AC output side
- Maximum AC power
Maximum AC power refers to the maximum power that the inverter can emit. Generally speaking, inverters are named according to their AC output power, but they are also named according to their DC input rated power.
- Maximum AC current
The maximum AC current refers to the maximum current that the inverter can emit, which directly determines the cross-sectional area of the cable and the parameter specifications of the power distribution equipment. Generally speaking, the circuit breaker specifications should be selected to be 1.25 times the maximum AC current.
- Rated output
Rated output has two types: frequency output and voltage output. In China, the frequency output is generally power frequency 50Hz, and the deviation should be within +1% under normal working conditions. Voltage outputs include 230V, 400V, 480V, etc.
- power factor
In an AC circuit, the cosine of the phase difference ( Φ ) between voltage and current is called the power factor, represented by the symbol cosΦ. Numerically, power factor is the ratio of active power to apparent power, that is, cosΦ=P/S. The power factor of resistive loads such as incandescent light bulbs and resistance furnaces is 1, while the power factor of circuits with inductive loads is less than 1.
3. Efficiency
There are four commonly used efficiencies for inverters: maximum efficiency, European efficiency, MPPT efficiency and overall efficiency.
- Maximum efficiency:
refers to the maximum instantaneous conversion efficiency of the inverter.
- European efficiency:
It is the weight of different power points based on European lighting conditions at different DC input power points, such as 5%, 10%, 15%, 25%, 30%, 50%, and 100%. Used to estimate the overall efficiency of the inverter.
- MPPT efficiency:
refers to the accuracy of the inverter's maximum power point tracking.
- Overall machine efficiency:
refers to the product of European efficiency and MPPT efficiency under a certain DC voltage.
4. Function protection parameters
- Island protection
When the power grid loses voltage, the photovoltaic power generation system continues to supply power to a certain part of the power grid. The so-called islanding protection is to prevent this unplanned islanding effect from occurring and ensure the personal safety of grid operators and users. And reduce the occurrence of power distribution equipment and load failures.
- Input overvoltage protection
Input overvoltage protection means that when the DC input side voltage is higher than the maximum DC array access voltage allowed by the inverter, the inverter shall not start or stop.
- Output side overvoltage/undervoltage protection
Output side overvoltage/undervoltage protection means that when the output side voltage of the inverter is higher than the maximum allowable output voltage of the inverter or lower than the minimum allowable output voltage of the inverter, the inverter starts the protection state. The abnormal voltage response time on the AC side of the inverter must comply with the specific provisions of the grid connection standards.
5. inverter connection for home
Home inverter connection: The most important thing to consider is the re-removal and arrangement of wires.
- Find the closest position between the inverter and the meter box, and plan the layout of the wires in advance.
- After determining the location, the connection is relatively simple. You only need to follow the rules and connect the wires to the circuit breaker of the distribution box in sequence.
- The most time-consuming part of the connection process is the arrangement of the cables. For beauty and safety, the wires need to be hidden in the wire box.
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