One article to understand the inverter important parameters! Jan 23, 2024

The composition of the inverter

Inverter is the opposite of the process of rectification, is the process of converting direct current energy into alternating current energy. Photovoltaic inverter refers to the circuit that completes the inverter function or the device that realizes the inverter process.
The main components of the inverter:
Shell and terminal: used to protect junction boxes
Heat sink: Used to cool the inverter system
Display: Inverter status and data
Control board: the core component of the inverter, which is used for power control and various algorithm control of the inverter
Power supply board: Used for internal power supply of inverters
Power board: the core component of the inverter, and the main circuits are concentrated on the power board.

Classification of inverters

Divided by function: grid-connected inverter and off-grid inverter
According to the frequency of the output AC power: power frequency inverter (frequency: 50-60Hz), medium frequency inverter (frequency: 400-20kHz) and high frequency inverter (frequency: 20kHz-10MHz).
According to the number of inverter output phase: single-phase inverter, three-phase inverter and polyphase inverter.
According to the access of photovoltaic modules, it is divided into centralized inverters, series inverters and micro (modular) inverters.

The main parameters of the inverter

1. Technical specifications of the DC input side

(1) The maximum allowed access to photovoltaic series power
The maximum allowable access PV power is the maximum DC connection PV power allowed by the inverter.
(2) Rated DC power
The rated DC power is derived from the rated AC output power divided by the conversion efficiency, plus a certain margin.
(3) Maximum DC voltage
Under the premise of considering the temperature coefficient, the maximum voltage of the connected PV series is less than the maximum DC input voltage of the inverter.
(4)MPPT voltage range
Considering the temperature coefficient, the PV series MPPT voltage should be within the inverter MPPT tracking range. The wider MPPT voltage range enables more power generation.
(5) Starting voltage
When the starting voltage threshold is exceeded, the inverter starts, and when it is below the starting voltage threshold, the inverter shuts down.
(6) Maximum DC current
When selecting the inverter, it is necessary to focus on the maximum DC current parameter, especially when accessing the thin film photovoltaic module, to ensure that the photovoltaic series current of each MPPT access is less than the maximum DC current of the inverter.
(7) Number of routes and MPPT routes
The input path of the inverter refers to a direct current input, and the MPPT path refers to several maximum power point tracking, and the input path of the inverter is not equal to the number of MPPT routes.
If the converter has 6 DC inputs, the inputs of each of the three inverters are used as one MPPT input. The PV group input under one MPPT must be equal, and the PV group input under different MPPT can be unequal.

2. Technical specifications of the AC output side

(1)Maximum AC power
The maximum AC power is the maximum power that the inverter can emit. In general, the inverter is named according to the AC output power, but it is also named according to the rated power of the DC input.
(2)Maximum alternating current
The maximum AC current refers to the maximum current that can be emitted by the inverter, which directly determines the cross-sectional area of the cable and the parameters of the distribution equipment. Generally speaking, the specifications of the circuit breaker should be selected to 1.25 times the maximum AC current.
(3)Rated output
Rated output has two kinds of frequency output and voltage output. In China, the frequency output is generally 50Hz, and the deviation under normal working conditions should be within +1%. Voltage output 230V, 400V, 480V and so on.
(4)Power factor
In AC circuits, the cosine of the phase difference (Φ) between voltage and current is called the power factor and is represented by the symbol cosΦ. In numerical terms, the 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 bulbs and resistance furnaces is 1, and the circuit power factor of inductive loads is less than 1.

3. Efficiency
There are four kinds of efficiency commonly used in inverters: maximum efficiency, European efficiency, MPPT efficiency and machine efficiency.
Maximum efficiency: refers to the instantaneous maximum conversion efficiency of the inverter.
European efficiency: According to the lighting conditions in Europe, the weights of different power points at different DC input power points, such as 5%, 10%, 15%, 25%, 30%, 50%, 100%, are used to estimate the overall efficiency of the inverter.
MPPT efficiency: refers to the accuracy of the inverter maximum power point tracking.
Overall efficiency: refers to the product of European efficiency and MPPT efficiency at a certain DC voltage.

4. Function Protection parameters

  • Island protection
When the power grid is decompressed, the photovoltaic power generation system still maintains the situation of continuing to supply power to a certain part of the line of the decompressed power grid, the so-called island protection is to prevent this unplanned island effect, ensure the personal safety of grid operators and users, and reduce the occurrence of distribution equipment and load failures.
  • Input overvoltage protection
Input overvoltage protection: When the DC input voltage is higher than the maximum DC array access voltage allowed by the inverter, the inverter cannot start or stop.
  • Output side overvoltage/undervoltage protection
Output side overvoltage/undervoltage protection When the output side voltage of the inverter is higher than the maximum output voltage or lower than the minimum output voltage allowed by the inverter, the inverter starts the protection state. The abnormal voltage response time of the AC side of the inverter should conform to the specific provisions of the grid-connected standard.

Source: Photovoltaic power Knowledge Base

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