Technical Post: Maintenance and Repair of IGBTs in Photovoltaic Inverters

IGBT is an insulated gate bipolar transistor, which is a semiconductor device composed of a bipolar transistor and an insulated gate field effect transistor. It has the advantages of high input impedance and low conduction voltage drop. The packaged IGBT module is also used in the UPS uninterruptible power supply in the inverter. Therefore, IGBT is very suitable for the conversion system that provides 600V and above DC voltage. Therefore, TGBT plays a vital role in the inverter.

Application of IGBT Modules in Inverters

The basic function of the IGBT module in the inverter is a high-speed contactless electronic switch.

By utilizing the switching principle of the IGBT module and giving appropriate on/off signals through the control circuit, the IGBT module converts DC into AC according to the control signal. After DC is converted into AC, the voltage will be reduced. For example, the 600V DC part of the inverter is converted into 270V or 315V AC part, and then boosted to 110kV through the box transformer, main transformer, etc. for transmission.

The IGBT module can also control the current by adjusting the pulse width of the control signal, and can also control the AC frequency, thereby controlling the output power of the inverter.

Daily inspection and maintenance of IGBT modules

According to the characteristics of IGBT modules and their applications in inverters, the following points should be achieved in daily inspection and maintenance:

1. During the on-site inspection of the inverter, pay attention to the DC and AC current and voltage values ​​on the LCD screen. The DC and AC voltage values ​​should not exceed the rated input and output values ​​of the inverter (generally the DC voltage does not exceed 900V), the maximum DC current value should not exceed 1000A, and the AC three-phase current value should be balanced, and the maximum difference between the three phases should not exceed 20A to prevent IGBT module failure due to overcurrent and overvoltage.

2. When inspecting the inside of the inverter, you should also pay attention to whether the IGBT module's auxiliary driver board, driver adapter board, and sampling line (board) plug are loose, and whether the running indicator light and fault indicator light indicate normal.

3. In addition to the above inspections, the temperature of the IGBT module should be measured regularly, and the operating temperature should generally not exceed 150°C.

IGBT module troubleshooting

1. Cause of failure: IGBT is often impacted by capacitive or inductive loads during use, and may be overloaded or even short-circuited, which may cause IGBT damage. The main reasons for damage to IGBT modules during use are as follows:

(1) Overcurrent damage

(2) Overvoltage damage and electrostatic damage

(3) Overheating damage

2. Fault phenomenon: First, the inverter will shut down. Secondly, the inverter will report overcurrent, overtemperature and other faults or no fault report.

3. Solution:

(1) Observe the appearance of the IGBT module to see if there is any damage (the red arrow in the figure indicates the observation point). If there is any damage, remove the corresponding module, replace it with a new one, and power it on again (Note: When removing a module, remove it together with the corresponding heat sink. When replacing a module, wear anti-static gloves and wipe and clean the module replacement area with alcohol).

(2) Damage to the IGBT module is usually accompanied by a breakdown failure of some of its protection capacitors (absorption capacitors) (the yellow arrow in the figure points to the absorption capacitor). These capacitors need to be inspected and replaced if damaged.

(3) If the inverter still cannot start normally after power is turned on again, the output voltage of its drive adapter board should be tested (the red arrow in the figure indicates the drive adapter board, which is normally powered by DC and outputs 15V).

(4) If the inverter still cannot start normally after replacing the corresponding drive adapter board, the IGBT drive board should be replaced (the yellow arrow in the figure indicates the drive board).

(5) If an over-temperature fault is reported, it is necessary to check the operation of the cooling fan (the green arrow in the figure points to the cooling fan). If the fan does not run, it is necessary to test the corresponding fan and connect the fan to a 220V AC power supply. If the fan does not rotate, replace the fan: If the fan runs normally, it is necessary to check the temperature controller and sampling line (board). If necessary, the corresponding sampling line (board) should be replaced.

(6) Inverter overcurrent may also cause damage to the DC fuse or AC fuse. After completing the above treatment, the DC fuse and AC fuse should be tested (the inverter should be shut down and the on/off test can be performed). If damaged, the corresponding fuse must be replaced (if the fuse is damaged, the inverter generally does not report a fault).