Cause and treatment of inverter module damage of t

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The cause and treatment of the damage of the inverter module of the frequency converter

the damage of the inverter module of the frequency converter is mostly caused by the damage of the driving circuit, which leads to the conduction of two switching devices on one bridge arm at the same time. The damage of inverter power module of frequency converter is a common fault in other frequency conversion equipment, such as vector frequency converter or energy-saving frequency converter. To solve this problem, the inverter module can be replaced only after the root cause of the damage is found and the possibility of damage again is eliminated first, otherwise the new module replaced will be damaged again

I. judge that the inverter power modules mainly include IGBT, IPM, etc. check whether the appearance has been exploded and whether there are ablation marks between the terminal and the connected printed board. Use a multimeter to check whether C-E, G-C, G-E are connected, or use a multimeter to measure whether the resistance of P to u, V, W and N to u, V, W is inconsistent, and whether the resistance of each driving power device control pole to u, V, W, P, n is inconsistent, so as to judge which power device is damaged

II. Find out the cause of damage

⑴ the device itself is of poor quality

⑵ the external load has serious overcurrent and imbalance, a phase winding of the motor is short circuited to the ground, a phase winding is internally short circuited, the load machinery is stuck, interphase breakdown, and the output wire is short circuited or short circuited to the ground

⑶ capacitance is connected to the load, or the capacitance to the ground is too large due to improper wiring, so that the power tube has impulse current

⑷ the user's electric voltage is too high, or there is a strong instantaneous overvoltage, causing overvoltage damage

⑷ the overvoltage absorption circuit of the power switch tube in the machine is damaged, which makes it impossible to absorb the overvoltage effectively, so the basic requirement of IGBT for the compact style is that the two support end faces should be damaged in parallel with each other, as shown in the figure below

⑥ due to aging, the capacity of the filter capacitor decreases or the internal inductance becomes larger, and the overvoltage absorption capacity of the bus decreases, resulting in too high overvoltage on the bus and damaging the IGBT. During normal operation, the Overvoltage on the bus comes from the inductive energy storage of the bus circuit when the inverter switching device is switched off

⑺ the front stage photoelectric isolation device of IGBT or IPM power device also breaks down due to breakdown, or there is ignition breakdown due to dust and humidity on the isolation device of the printed board, resulting in IGBT and IPM damage

8 improper operation or defects in the product design software cause the upper and lower power switching devices to be turned on instantly at the same time under the conditions of interference and instability such as startup and shutdown

⑼ accidents such as lightning strike, water leakage intrusion of the house, entry of foreign matters, accidental touch of inspectors, etc

⑽ after maintenance, the filter capacitor was replaced. Because the quality of the capacitor was poor, or the line connected to the capacitor was longer than the original, the inductance increased, resulting in a significant increase in the amplitude of bus overvoltage

⑾ the front stage rectifier bridge is damaged, and IGBT and IPM are damaged because the front stage of the main power supply enters AC

⒁ repair and replace the power module, because there is no electrostatic protection measures, IGBT was damaged during welding operation. Or damage caused by short-term use due to poor heat dissipation, fastening, insulation, etc. during repair

⒀ IGBT is used in parallel, and the consistency of model and batch number is not considered during replacement, resulting in uneven current of each parallel element and damage

⒁ development of horizontal tensile testing machine inside the frequency converter. The protection circuit (overvoltage and overcurrent protection) has a component represented by the symbol HR damaged and lost its protection function

⒂ a group of power supplies inside the frequency converter, especially the + and - power supplies of the IGBT drive stage, are damaged, the output value is changed, or the insulation between the two groups of power supplies is broken down

III. replacement

the inverter module can be replaced only after the root cause of the damage is found and the possibility of damage again is eliminated first, otherwise the new module replaced will be damaged again

⑴ like insulated gate FET, IGBT should avoid electrostatic damage. The fundamental measure to prevent damage during assembly and welding is to connect all the machines to be repaired, IGBT modules, electric soldering irons, people, operation workbench pads, etc. with wires, so that the operation can be carried out under the same electric field potential, and it is better if all the connected common points can be grounded. In particular, the electric soldering iron head should not have a high potential of mains power, and the oscilloscope power supply should be isolated by a transformer with good isolation. Before using the IGBT module, keep the control electrode G and emitter e connected, and do not arbitrarily remove the anti-static protection G-E connection measures of the device before leaving the factory

⑵ apply thermal conductive silicone grease between the power module and the radiator to ensure that the coating thickness is 0.1 ~ 0.25mm, and the contact surface is more than 80%. The tightening torque is applied according to the size of the fastening screw (M4 13kg? Cm, M5 17kg? Cm, M6 22kg? Cm), so as to ensure good heat dissipation of the module

⑶ when the machine is disassembled, take notes of the disassembled parts, thread ends and parts. When reassembling, deal with the original 8. Circuit breaker Protector: protect the compressor and extend the service life. Various technical measures should not be simplified or omitted. For example, the input twisted pair, the resistance value of each electrode connection, insulation, absorption plate or absorption capacitance should be maintained as is; The drive printed board that has been repaired and welded should be cleaned and painted to prevent creepage, and the insulation should be reliable, not to mention less and wrong parts

⑷ parallel modules are required to have the same model and number. If the number cannot be consistent, ensure that all modules connected in parallel have the same performance

⑷ for the defects of copper parts caused by blasting machine, the burrs should be rounded and sanded to avoid damage again due to tip discharge caused by overvoltage

4. Power on after replacing the module

often after replacing the module, it burns out after being powered on. In order to prevent such accidents, generally, a resistor is connected in series in the DC main circuit of the frequency converter. The resistance value is 1.2k, and the power is more than 50W. Due to the current limiting effect of the resistor, even if the fault is started, the module will not be damaged. When no-load, the current flowing through the resistance is small, and the voltage drop is also small, so it can be used for no-load inspection. Generally, as long as the no-load operation is normal, it will be normal after removing the resistance

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