When dealing with a faulty inverter, the first step is usually to check the rectifier bridge and IGBT module using a multimeter before powering it on. Ensure that there's no visible damage or burning on the circuit board. The process involves using an analog multimeter set to the 1KΩ range. Connect the black probe to the negative DC terminal of the inverter and measure the resistance between the red probe and each of the three-phase input and output terminals. The resistance should be around 5K–10KΩ, and all three readings should be similar. The output resistance may be slightly lower, but there should be no charging or discharging behavior. Then, reverse the probes—connect the red probe to the positive DC terminal and the black probe to the three-phase input and output. Again, the resistance should fall within the same range, with consistent values across all phases. If any deviation is found, it may indicate a damaged module. In such cases, avoid powering the inverter, especially if the rectifier bridge is damaged or the board shows signs of burning, as this could cause further damage.
If the initial tests show no issues, proceed to power on the inverter. For example, if the display shows [F231] or [F002] (on MM3 inverters), the problem might be related to the power supply board or the main control board. Try replacing the main control board first. If the issue persists, it’s likely the power supply board is at fault. On MM4 inverters, if the panel shows no display and the green light doesn’t turn on while the yellow light flashes rapidly, the issue may lie with the switching power supply. Check the rectifier diodes for breakdown or open circuits. This type of failure is often due to low diode voltage ratings or excessive power supply ripple.
Occasionally, error codes like [F0022, F0001, A0501] may appear on MM4 inverters. These can sometimes be resolved by checking connectors, as loose connections are a common cause. In some cases, faulty RC components or poor soldering on the board can also lead to these issues. If the panel displays [-----], it’s typically a main control board issue. Replacing the board is often the solution, though some problems may originate from the power board as well.
For example, a MM440-200kW inverter used in a cement plant experienced frequent [F0001] alarms due to high load inertia. After adjusting motor parameters and ensuring proper vector control settings, the issue was resolved. However, later, the inverter began displaying [-----], which turned out to be caused by a damaged main control board. Poor installation practices, such as not separating strong and weak electrical lines or improper grounding, led to I/O port damage. Replacing the main control board fixed the problem.
If the inverter powers on normally but shows overcurrent during operation ([F0001] on MM4 or [F002] on MM3), it often indicates a damaged IGBT module or a faulty drive board. Before re-powering, replace the IGBT module and inspect the drive section carefully. Otherwise, repeated overloads or voltage fluctuations can cause the IGBT to fail again.
Some less common but instructive faults include: An MM3-30KW inverter that would shut down unexpectedly. After careful observation, it was found that the main contactor wasn’t properly connected, leading to intermittent power loss. Another MM4-22KW inverter displayed [P----] when the fan was connected, indicating a power supply issue. Replacing a leaking filter capacitor on the power board resolved the problem. In a steel plant, a 75kW MM440 inverter showed erratic current readings. After replacing the current detection unit on the drive board, the issue was resolved.
In summary, while major components like IGBT modules can cause failures, many issues stem from simpler problems such as faulty capacitors, poor soldering, or incorrect parameter settings. With the right tools and knowledge, most of these can be addressed without replacing entire boards. However, in some cases, swapping out the main control or power board may be the fastest and most effective solution.
The On-grid system is connected with utility grid and this system would work only if the grid is available. In case of a power cut, the system will not work and hence the On-grid system is also termed as a Grid-tied system. Grid is required since the inverter needs to be provided a reference voltage and the inverter needs to sync with the grid in order to export energy back into the grid.
On grid systems make sense for locations with no daytime power cut or with less than 2 hrs of daytime power cut. This type of system is apt for reducing your electricity bills since it is cheaper than a Battery based system and there is no recurring cost of replacement of panels.
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