10 common inverter failure and the solutions

The inverter is one of the core components of the home solar power system. It can not only convert DC power into AC power, but also feed back the operation of the entire system to the users. When some inverter failure occurs in the system, how to troubleshoot the causes and repair it in time? This article will give you an overall guide.

1. No display on the inverter screen

Under normal circumstances, the inverter is connected to DC power. After turning on the DC switch, wait for a few seconds, and the inverter display and indicator light will light up, showing the inverter model or initialization information. Description of inverter status indicator light :

Reasons and solutions for inverter failure of no display:

Reason 1: The DC switch is not turned off.

Solution: Check whether the DC switch of the inverter is in the "ON" position. If not, turn the switch to "ON". Note that the installation positions of the DC switches of inverters in different power segments are different.

Reason 2: The positive and negative poles of the PV input terminals are connected reversely. The positive pole of the photovoltaic module is connected to the negative pole of the inverter input, and the negative pole is connected to the positive pole of the inverter input. ​

Solution: Set the multimeter to the DC voltage range, connect the red test lead to the positive pole of the string, and the black test lead to the negative pole of the string. Measure the output voltage of the string. If the measured output voltage value is positive, the positive and negative poles of the string are correct; if the measured output voltage value is negative, the positive and negative poles of the string are wrong.

When the string output voltage is lower than the minimum input voltage of the inverter, there is no display on the inverter screen. To make sure, you can use a multimeter to measure the output voltage of the photovoltaic string to see whether the voltage reaches the minimum input voltage of the inverter.

Common causes and solutions for low DC input voltage: 

• Too few solar modules in series:

The open circuit voltage of the string should be much greater than the minimum input voltage of the inverter; if there are too few modules in series, the open circuit voltage of the string will be too low, resulting in no display on the inverter screen.

Solution: Increase the number of solar panels in series.

• Poor DC cable connector connection:

When there is an open circuit in the string input circuit, the cable is separated from the terminals, the positive and negative terminals are loose, etc., the string output voltage will be unstable or drop to 0, causing no display on the screen.

Solution: Check the connection status of each terminal of the photovoltaic module and find the inverter failure terminal.

• There are components in the string that are reversely connected:

In the same string, the negative pole (positive pole) of the previous component is connected to the positive pole of the next component, and finally a pair of positive and negative terminals are drawn out.

The theoretical open circuit voltage of the string is equal to the sum of the open-circuit voltages of each component. If the lighting conditions are good, the open-circuit voltage of the string is lower than the theoretical value, and the cables and terminals are connected normally, there may be components in the string that are reverse-connected.

Solution: Find the component that was reversed and rewire it.

• The intensity of sunlight is too weak:

When the intensity of sunlight is very weak, the string output voltage is too low, resulting in no display on the inverter screen.

Solution: Wait for the light to get stronger.

2. Inverter failure of over direct current injection (DCI High)

The DC component detection circuit inside the inverter samples the AC output, filters out the AC part, and then compares the DC part with the set value (rated current × 0.5%). If the set value is exceeded, the inverter reports inverter failure of DC overweight inverter failure.

Reason: A sudden change in DC input power may cause this inverter failure.

Solution: You can turn off the AC/DC switch, restart the inverter and try again. Check whether there are high-power electrical equipment near the photovoltaic power station. If there is, special processing can be performed by updating the software.

If there is no high-power electrical equipment near the power station, the inverter can be restarted several times. If the inverter still reports this inverter failure after updating the software or restarting the inverter, it is recommended to replace the inverter.

3. Bus voltage balance failure

When the difference between 1/2 of the BUS+, BUS- voltage and the BUS+, BUS- midpoint voltage exceeds the limit, the inverter will report a bus voltage balance inverter failure. ​

Solution:

Check whether the DC terminal is grounded (such as the cable is damaged, the connector is soaked in water, etc.), and correct it if necessary.

• Disconnect the AC and check whether the AC neutral line wiring (inverter output side, AC circuit breaker side) is in good contact, otherwise rewire it.

   

• If the equipment is more than 2 years old, you need to check whether the internal wiring of the inverter is poorly connected (the wiring is loose), and if so, re-insert the wiring or replace the wiring.

4. Bus voltage is too high or bus hardware overvoltage fault

When the DC voltage input to the inverter exceeds the maximum DC input voltage of the inverter, the inverter reports inverter failure of an excessive bus voltage or inverter failure of bus hardware overvoltage.

Solution:

Check the DC input parameters displayed by the inverter, to see whether the DC input voltage is too high (at any time, the string open circuit voltage cannot exceed the maximum input voltage of the inverter), whether there are too many components in series, and if so, then shut down the inverter, reassemble the strings, reduce the number of components in series, and restart the inverter. If the inverter failure still occurs repeatedly, it is recommended to replace the inverter.

The following are some troubleshooting suggestions given by TYCORUN inverter for your reference.

5. Inverter failure of grid loss failure

When the inverter cannot detect the voltage on the AC side or the detected voltage value is too low, the inverter reports a inverter failure of grid loss failure. Common causes and solutions for grid loss faults reported by the inverter are as follows:

• Power grid outage:

Check whether the nearby electrical equipment can work. If the electrical equipment cannot work, it may be a power grid outage. Use an electric pen to test whether there is power at the incoming line on the grid side of the grid-connected box. If there is no power, it may be a power grid outage.

Solution: Wait for power to be restored.

• The grid side wire is disconnected:

If the AC wire is disconnected at any point from the inverter AC output terminal to the grid connection point, the inverter will report an inverter failure of grid loss.

Common causes and solutions for grid side line disconnection:

① Circuit breaker disconnection:

If the rated current of the selected circuit breaker is too small, when the inverter output current is too large, the circuit breaker will trip due to overheating, disconnecting the inverter from the grid, causing the inverter to report an inverter failure of grid loss.

② Overvoltage and undervoltage protector disconnects:

If the rated current of the overvoltage and undervoltage protector is too small, when the inverter output current is too large, check whether the specifications of the overvoltage and undervoltage protector meet the requirements (the rated current of the overvoltage and undervoltage protector should be equivalent to the rated current of the circuit breaker).

If the grid voltage exceeds the voltage protection range of the overvoltage and undervoltage protector, the overvoltage and undervoltage protector will disconnect, cutting off the connection between the inverter and the grid, causing the inverter to report an inverter failure of grid loss.

Solution: Find the reason why the grid voltage exceeds the voltage protection range of the over-voltage and under-voltage protector, and make corresponding rectifications.

③ Poor AC cable connection:

If the connection between the AC cable and the electrical components is poor (for example, the screws are not tightened or the cable is stripped too little), the AC cable may be disconnected, and the inverter cannot detect the voltage and will report an inverter failure of grid connection error.

Solution: Check the connection status of all cables from the inverter AC output end to the grid connection point (including the inverter AC terminals, AC cables in the grid box, and meter cables). If there is a poor connection, reconnect Connect and use a multimeter to measure whether the voltage of the inverter AC terminals is normal.

6. Repeat countdown or stop countdown

Under normal circumstances, the inverter is connected to DC power. If the DC switch is closed and the AC switch is closed, the inverter will count down from 60s and enter the self-test grid connection process.

After counting down for a period of time, abnormally, the inverter may start counting down from 60s again. This phenomenon is called repeated countdown. If the DC switch is closed and the AC switch is also closed, the inverter screen displays a countdown number that stops at 60 seconds, it is called stop countdown.

Reasons for repeated countdown:

Under conditions of low light, the DC input voltage is low and is near to the starting voltage of the inverter. After starting to connect to the grid, the DC input voltage is pulled down and is lower than the starting voltage, and the inverter stops connecting to the grid, and repeated countdown occurs.

Solution: Check the DC input voltage of the inverter. If the voltage value is close to the starting voltage, it is because the light is too weak, which is normal. Wait for the light to become stronger.

If the DC input voltage is much higher than the starting voltage, then inverter failure occurs to itself and needs to be repaired, in which situation it is recommended to replace the inverter. If the light is strong and the DC input voltage far exceeds the starting voltage, and the inverter reports an inverter failure of relay fault and repeats the countdown, following the inverter failure handling steps.

Reasons for stop countdown:

When the light is weak and the DC input voltage is greater than the starting voltage, the inverter starts to count down and enters the grid connection process. However, if the DC input power is insufficient, the inverter stops counting down and stays at the 60-second countdown. In this case, you need to wait for the light to become stronger.

When the lighting is good and the DC input voltage is greater than the starting voltage, the inverter will start counting down, enter the grid connection process, and boost the voltage. If the boost circuit is abnormal and the boost fails, the inverter will stop counting down and stay at countdown to 60 seconds. In this case, the inverter needs to be replaced.

7. Component-to-ground insulation failure (ISO)

During the self-test process before the inverter is connected to the grid, it is necessary to detect the insulation resistance of PV+ and PV- on the photovoltaic module side to the ground. If the impedance value is too low, the inverter must stop connecting to the grid and report an inverter failure if ISO error , otherwise there is a risk of electric shock.

Reason: The impedance value of one or more strings of PV+/PV- to the ground in the string input to the inverter is too low.

Solution: Find the string that caused inverter failure (PV+/PV- impedance value to ground is too low), find the corresponding cause and handle accordingly.

① Find the string that caused inverter failure. Disconnect the AC and DC inputs, remove all PV inputs, and measure the voltage of the positive/negative pole of each PV to ground. If the difference between the positive pole to ground voltage and the negative pole to ground voltage exceeds 70V, you can judge that the string is where inverter failure occurs.

If the string that caused inverter failure cannot be found by this method, connect only one PV to the inverter, close the AC and DC switch, and check whether the inverter will report this inverter failure again; then operate in sequence, pressing only one string each time to find the string that caused inverter failure.

② After finding the string that caused inverter failure, do the following inspection and processing: 

• Check whether there is water on the surface of the component, and if so, remove the water;
• Check whether the components are damaged and replace them if they are;
• Check whether the DC cable is damaged and connect it to the bracket. If it is, you can temporarily cover the damaged area with insulating tape and replace the cable later;
• Check whether the DC cable connector is tight or the connector is soaked in water. If so, tighten the connector or dry the connector and change the wiring position.

③ If the inverter failure is not eliminated after the second step, use an insulation resistance meter to measure the impedance of the positive and negative poles of each component of the string that caused inverter failure to ground (at least 100kΩ), find the component that caused inverter failure and replace it.

Notice:

• Before measuring the insulation resistance, use a multimeter to confirm that there is no short circuit between the positive and negative poles of the component to ground to avoid damage to the component due to insulation testing;
• Insulating gloves must be worn when testing insulation resistance;
• The handle of the insulation resistance meter should rotate at a constant speed of 2 revolutions/second;
• When measuring the insulation resistance between the positive electrode of the module and the metal frame, connect the red clip to the PV positive electrode and the black clip to the module frame;
• When measuring the insulation resistance between the negative electrode of the module and the metal frame, connect the black clip to the negative electrode of the PV and the red clip to the module frame.

8. Relay failure

When a photovoltaic power generation system fails, the inverter must actively isolate the grid from the inverter main circuit through a relay. Common causes and solutions for inverter failure of relay are as follows:

• Reason 1: The inverter falsely reported a inverter failure.

Solution: Restart the inverter several times. Disconnect the AC and DC of the inverter, wait for 5 minutes, and then close the DC and AC to see if the inverter failure is still reported; repeat several times.

• Reason 2: AC side phase line is short-circuited to ground.

Solution: Measure the phase-to-ground voltage. Use a multimeter to measure the voltage between the phase wire and the ground wire. If the voltage is lower than 100V, it can be judged that the phase wire is short-circuited to the ground. The ground wire can be temporarily removed to allow the inverter to continue working.

Then, the AC cable damage point or the phase wire can be searched for. Check the grounding point of the cable, and perform rectifications such as replacing the cable or rewiring.

9. Inverter failure of ground fault circuit interrupter (GFCI)

In order to avoid electric shock accidents, in any case when the inverter is connected to the AC power grid and the AC circuit breaker is closed, the inverter needs to monitor excessive continuous residual current and sudden changes in excessive residual current. When the residual current exceeds the limit, the inverter must stop generating electricity and disconnect from the grid.

• Solution for GFCI equipment failure:

The main reason why the inverter reports GFCI equipment failure is the inverter failure of itself. You can turn off the AC and DC switches, wait for 5 minutes, then close the DC and AC switches to check whether the inverter failure occurs again, and repeat if the inverter failure still occurs several times, please contact after-sales personnel for help.

Note: If the photovoltaic power generation system has improper lightning protection measures, lightning strikes will cause the inverter to report a GFCI equipment failure.

• Solution for GFCI failure:

The main reason why the inverter reports a GFCI failure is generally that the leakage current of the photovoltaic power generation system exceeds the protection limit.

Processing steps:

① Turn off the AC and DC switches, check whether the ground wire of the AC output end of the inverter is firm, whether the AC wiring is correct and firm, and whether there is too much exposed copper. If it is found that the wiring is wrong, the wiring is not firm, or there is too much exposed copper, perform the corresponding rectification.

② Check whether the ground wire connection in the grid-connected box is correct and firm, whether the AC wiring is correct and firm, whether there is too much exposed copper, and whether the ground wire of the grid-connected box is correct and firm. If these inverter failure are found, make corresponding rectifications.

③ Check whether the surge protector in the grid-connected box is damaged or has leakage. If you cannot determine whether the surge protector is damaged or has leakage, you can disconnect the surge protector and try to connect to the grid again.

10. AC overvoltage fault

According to safety regulations, the grid-connected inverter must work within the specified grid voltage range, and can detect and synchronize with the grid voltage in real time. If the voltage value exceeds the safety regulations, the inverter must stop working and synchronize with the grid voltage. The power grid is disconnected to ensure the safety of equipment and operators.

Reasons:

• The safety regulations is unsuitable:

Check whether the safety regulations of the inverter are suitable and select the appropriate safety regulations according to the actual situation of the local power grid.

• The grid voltage is too high:

When the inverter is connected to the grid, use a multimeter to measure the actual voltage at the output end of the inverter. If the actual voltage does not exceed the safety overvoltage protection value, the inverter has an internal fault; if the actual voltage exceeds the safety overvoltage protection value, If the voltage protection value is too high, you need to determine the reason why the AC side voltage of the inverter is too high.

Reasons why the AC side voltage of the inverter is too high:

① The cable between the inverter and the grid connection point is too thin, too long, entangled, or the cable material is unqualified, causing the voltage on the AC side of the inverter to rise (ΔU increases). When the AC voltage exceeds the voltage protection range set by safety regulations, the inverter reports a grid overvoltage fault.

Solution: Choose AC cables with appropriate specifications and wire diameters to connect to the grid to reduce wire losses; choose the nearest point to connect to the grid to shorten the distance from the inverter to the grid connection point and reduce wire losses. Note: If the neutral line of the inverter is not connected or has poor contact, it may cause the inverter to report an AC overvoltage fault.

② Due to the local grid connection conditions of the photovoltaic power station, multiple single-phase inverters are connected to the same live line, and the grid's accommodation capacity is insufficient, causing the grid voltage to rise too high, and the inverter reports a grid overvoltage inverter failure.

Solution: Choose multi-point grid connection and allocate multiple inverters to the three phases of the power grid, or increase the proportion of power generation for self-use to reduce the loss of electric energy during transmission.

③ The installed capacity of the photovoltaic system is too large and the load absorption capacity of the grid is insufficient, causing the grid voltage to rise too high and the inverter reports an inverter failure of grid overvoltage.

Solution:

• Increase the proportion of self-use;
• Power grid transformation involves widening transmission lines and increasing transformer capacity (for a photovoltaic power generation system that uses a dedicated transformer to connect to the grid, the ratio of the installed capacity of the power station to the transformer capacity is 1:1;
• For a photovoltaic power generation system that uses a non-dedicated transformer to connect to the grid, the installed capacity of the power station is the transformer capacity 25-50%);
• Energy storage systems can be used to store electrical energy that cannot be consumed.

The above is a guide to common inverter failure and the solutions. You can also click to check the top 10 solar inverters.

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