Photovoltaic power generation is a technology that directly converts light energy into electrical energy using the photovoltaic effect at semiconductor interfaces. The key component of this technology is the solar cell. Solar cells are connected in series and then encapsulated for protection to form large-area solar cell modules. These modules, along with inverters, power controllers, and other components, constitute a photovoltaic power generation system. The advantages of solar photovoltaic power generation include less geographical limitation due to the abundance of sunlight; photovoltaic systems also offer advantages such as safety and reliability, no noise, low pollution, no need for fuel consumption or transmission lines, and short construction time.
A photovoltaic (PV) inverter, as an electronic product, is composed of numerous components. Inverters, also known as power conditioners, can be categorized into two types based on their application in PV power generation systems: stand-alone power supply inverters and grid-connected inverters. Based on waveform modulation methods, they can be classified as square wave inverters, stepped wave inverters, sine wave inverters, and combined three-phase inverters. For inverters used in grid-connected systems, they can be further classified based on whether they contain a transformer: transformer-type inverters and transformerless inverters.
As the monitoring center of the entire power station, the photovoltaic inverter connects to the DC modules upstream and the grid-connected equipment downstream. Essentially all power station parameters can be monitored through the inverter. Generally, as long as the inverter is in grid-connected mode and the power curve displayed on the monitoring screen shows a normal upward trend, it indicates that the power station is operating stably. If abnormalities occur, the health status of the power station's supporting equipment can be checked through the information fed back by the inverter. Below is a summary of common photovoltaic inverter fault causes and troubleshooting methods:
1. The photovoltaic inverter screen is not displaying anything.
Fault analysis: There is no DC input; the inverter LCD is powered by DC.
Possible reasons:
(1) Insufficient module voltage. The inverter's operating voltage is 100V to 500V. The inverter will not work if the voltage is below 100V. The module voltage is related to the solar irradiance.
(2) The PV input terminals are reversed. The PV terminals have positive and negative poles, which must correspond to each other and cannot be reversed with other groups.
(3) The DC switch is not closed.
(4) When components are connected in series, one of the connectors is not properly connected.
(5) A component is short-circuited, causing other components to also fail to work.
Solution: After use, measure the inverter's DC input voltage using a multimeter in voltage mode. When the voltage is normal, the total voltage is the sum of the voltages of all components. If there is no voltage, check the DC switch, terminals, cable connectors, and components one by one to ensure they are functioning correctly. If there are multiple components, connect and test them individually. If the inverter has been used for a period of time without a known cause, the problem lies in the inverter's hardware circuitry; contact the manufacturer's after-sales service.
2. The photovoltaic inverter is not connected to the grid, and the screen displays "mains power not connected".
Fault symptom: The inverter is not connected to the grid, and the screen displays "mains power not connected".
Fault analysis: The inverter is not connected to the power grid.
Possible reasons:
(1) The AC switch is not closed.
(2) The inverter's AC output terminal is not connected.
(3) When wiring, the upper row of inverter output terminals was loosened.
Solution: Use a multimeter in voltage mode to measure the AC output voltage of the inverter. Under normal circumstances, the output terminals should have 220V or 380V. If not, check in turn whether the wiring terminals are loose, whether the AC switch is closed, and whether the leakage protection switch is open.
3. The screen displays high PV voltage.
Fault Analysis: DC Voltage Overload Alarm
Possible cause: Too many components are connected in series, causing the voltage to exceed the inverter's voltage.
Solution: Due to the temperature characteristics of the components, the lower the temperature, the higher the voltage. The input voltage range for single-phase string inverters is 100-500V, and it is recommended that the voltage after stringing be between 350-400V. The input voltage range for three-phase string inverters is 250-800V, and it is recommended that the voltage after stringing be between 600-650V. Within this voltage range, the inverter efficiency is high, and it can generate electricity even when the irradiance is low in the morning and evening, without exceeding the inverter's voltage limit, triggering an alarm and causing shutdown.
4. The screen displays that the PV insulation resistance is too low.
Fault Analysis: The grounding insulation resistance of the photovoltaic system is less than 2 megohms.
Possible causes: Short circuits to ground or damaged insulation in the solar panels, junction boxes, DC cables, inverters, AC cables, or terminals. Loose PV terminals and AC wiring housings, leading to water ingress.
Solution: Disconnect the power grid and the inverter, check the resistance of each component's wires to ground in turn, find the problem point, and replace it.
5. Excessive leakage current in screen display output
Fault Analysis: Excessive Leakage Current
Solution: Remove the PV array input terminal and then check the external AC power grid. Disconnect both the DC and AC terminals and let the inverter power off for at least 30 minutes. If it can be restored on its own, continue using it. If it cannot be restored, contact after-sales technical engineers.
6. The screen displays that the mains voltage is out of range.
Fault Analysis: Grid voltage is too high. Increased grid impedance means the photovoltaic power generation at the user side cannot absorb the load. When transmitted, the excessive impedance causes the inverter output voltage to be too high, triggering inverter protection shutdown or derating operation.
Solution:
(1) Increase the size of the output cable, because the thicker the cable, the lower the impedance.
(2) The closer the inverter is to the grid connection point, the shorter the cable and the lower the impedance.
