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What is the working principle of a grid-connected photovoltaic inverter? What are the functions of a grid-connected inverter?

2026-04-06 06:32:18 · · #1

Grid-connected photovoltaic (PV) inverters are essential components in PV power generation systems. They are specialized inverters primarily used in solar PV power generation, converting the alternating current (AC) generated by solar panels into AC power that can be directly fed into the grid using power electronic conversion technology. Let's learn about the working principle of PV grid-connected inverters and their role in PV power generation systems.

I. Working Principle of Photovoltaic Grid-Connected Inverters

When the public power grid experiences a power outage, the grid side is essentially in a short-circuit state. In this situation, the inverter operating in parallel with the grid will automatically protect itself from overload. When the microprocessor detects an overload, in addition to blocking the SPWM signal, it will also disconnect the circuit breaker connected to the grid. If the solar panel array has energy output at this time, the inverter will operate in standalone mode. Standalone operation is relatively simple, essentially a negative feedback state of the AC voltage. The microprocessor detects the inverter's output voltage and compares it with a reference voltage (typically 220V), then controls the PWM output duty cycle to achieve both inversion and voltage regulation.

Of course, standalone operation requires the solar array to provide sufficient power at the time. If the load is too large or sunlight conditions are poor, the inverter will not be able to output enough power, causing the terminal voltage of the solar array to drop, which in turn lowers the output AC voltage and triggers a low-voltage protection state. When the grid restores power, it will automatically switch to feedback mode.

II. The Role of Photovoltaic Grid-Connected Inverters

Inverters not only have DC-AC conversion capabilities, but also the ability to maximize solar cell performance and provide system fault protection. These can be summarized as follows: automatic operation and shutdown functions, maximum power point tracking control, anti-isolation operation function (for grid-connected systems), automatic voltage regulation function (for grid-connected systems), DC detection function (for grid-connected systems), and DC grounding detection function (for grid-connected systems).

1. Automatic start and stop function

After sunrise, as solar radiation intensifies, the output of the solar cells increases accordingly. Once the output power required for the inverter to operate is reached, the inverter automatically begins operation. Once operational, the inverter continuously monitors the output of the solar cell modules. As long as the output power of the solar cell modules exceeds the inverter's required output power, the inverter continues to operate until sunset, even on cloudy or rainy days. When the output of the solar cell modules decreases and the inverter output approaches zero, the inverter enters standby mode.

2. Maximum Power Point Tracking (MPPT) function

The output of a solar cell module varies with the intensity of solar radiation and the module's own temperature (chip temperature). Furthermore, because the voltage of a solar cell module decreases as current increases, there exists an optimal operating point where maximum power can be obtained. Since solar radiation intensity is variable, the optimal operating point also changes. To keep the solar cell module's operating point at its maximum power point relative to these changes, ensuring the system consistently draws maximum power from the module, is called maximum power point tracking (MPPT) control. A key feature of inverters used in solar power systems is the inclusion of MPPT functionality.

3. Power grid detection and grid connection function

Before a grid-connected inverter can generate electricity, it needs to draw power from the grid, detect parameters such as voltage, frequency, and phase sequence of the power supplied by the grid, and then adjust its own power generation parameters to be synchronized with the grid's electrical parameters. Only after this is completed can it be connected to the grid to generate electricity.

4. Zero (low) voltage ride-through capability

When a power system accident or disturbance causes a voltage dip at the grid connection point of a photovoltaic power station, the photovoltaic power station can ensure continuous operation without disconnecting from the grid within a certain voltage drop range and time interval.

5. Detection and control of the island effect

During normal power generation, grid-connected photovoltaic (PV) systems are connected to the main power grid, supplying active power to the grid. However, when the grid loses power, the PV system may continue to operate independently of the local load; this phenomenon is known as islanding. Islanding in inverters poses significant safety hazards to personnel, grid operation, and the inverter itself. Therefore, grid connection standards stipulate that PV grid-connected inverters must have islanding detection and control functions.

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