Inverter is an organic combination of power electronics technology and computer technology. With the development of frequency conversion technology, AC motor can be comparable to DC motor in speed control performance, so that the application scope of frequency converter is expanding, and the design is reasonable and the installation is correct. Based on the characteristics of the inverter, it is very important to strengthen the maintenance and repair work of the inverter system.
First, the matters needing attention
When maintaining or repairing, be sure to check the voltage of the link to the safe value when contacting the conductive parts and components of the inverter after a power outage, and to discharge the good habits of static electricity on the body to avoid personal injury. Equipment damage.
Second, maintenance
Doing a good job of maintenance can promptly discover hidden troubles during the normal operation of the inverter system, and effectively extend the frequency converter and normal working hours. Maintenance work can be divided into routine maintenance and regular maintenance.
1, routine maintenance
1) Whether the power supply voltage of the inverter is normal;
2) Whether the temperature and humidity of the inverter environment are normal;
3) Is the temperature of the radiator normal?
(The values in the above items are based on the technical data provided in the manual of the inverter.)
4) Whether the sound of the cooling fan in the inverter is normal;
5) Whether the high power resistor on the control board in the inverter is discolored;
6) Whether the inverter’s outgoing cable and motor’s safety condition are affected by external unfavorable factors.
2, regular maintenance
a) Remove dust from circuit boards and heat sinks;
b) Remove the lead wire from the inverter and check the insulation resistance of the lead wire and the motor (The output voltage of the inverter is a modulated pulse train, especially IGBT is used as the reverse side switching element. The switching frequency is high, and the value of du/dt is relatively large. , has a greater influence on the insulation of the motor);
c) Check for possible screws and connectors;
d) Replace the cooling fan that has failed to run but whose continuous operation time has exceeded the design value according to the specifications in the manual of the inverter.
Third, maintenance
Doing a good job of maintenance can not only reduce the company’s maintenance costs, but also through the maintenance of a detailed understanding of the inverter internal circuit structure, and accumulate experience. Improve the ability to judge faults and shorten inverter downtime. Inverter faults are generally caused by incorrect parameter settings or wiring errors (such faults usually appear in the commissioning phase), damage to the inverter hardware, damage to the external components of the inverter, and so on. The following is a brief introduction to the method of judging the fault of the inverter in connection with the maintenance example of the original AEG inverter of our company.
Maintenance example:
Example 1
Model: Maxiverter-170/380 (without brake unit)
Symptom: When the motor is controlled to decelerate from higher speed to zero when debugging
Processing process: When the motor is decelerating, the feedback energy will increase the voltage of intermediate DC link (abbreviated as the link, the same below) when the motor is decelerating. The resistance is consumed in the form of heat energy through the resistance connected across the link capacitor. Drop it. Since the limit value of the link voltage of this type of inverter can be adjusted as required, and when the link voltage rises to the limit value during deceleration, the magnitude of the feedback current can be limited to reduce the braking intensity to ensure that the link voltage does not exceed the limit value. . Through the PC inspection, the brake current limit is set to 100%, the link voltage limit is set to 115%, the link voltage has risen to the limit during deceleration, and the feedback current is small, due to large feedback energy The power of the resistance across the link capacitor is limited, causing the link voltage to quickly rise to the limit, and the brake torque is too small to stall. After several adjustments, the frequency converter deceleration function is normal after setting the braking current limit value to 67%.
Example 2
Model Number: Multiverter 178/225-400
Symptom: No display after the power is turned on
Processing procedure: Measure the normal voltage of the incoming power board, indicating that the power board is faulty. In the absence of spare parts, the power board is repaired at the component level based on the schematic circuit diagram. The power supply board is operated by two switches of the red main circuit of the control signal generated by the PWM controller SG3526N. The various power supplies required by the frequency converter are obtained through the switching transformer and each rectifier circuit. It was found through inspection that one output of the four-way differential voltage comparator LP339 is high, causing an effect transistor connected to the power pin of the SG3526N to stop, and the SG3526N cannot generate a control signal. After checking that there is no fault in the LP339 peripheral circuit, replace the LP339 and the inverter is normal.
Case 3
Model Number: Multiverter 78/102-400
Fault phenomenon: “overcurrent” fault is displayed during operation
Process: The inverter cannot reset the fault after “overcurrent” tripping. Check the inverter’s inverter-side components, cables, and electric motors for power failure. No problems are found. After the power transmission, the fault still exists. At this time, the inverter link is in contact. The device does not work, indicating that the fault is in the inspection circuit or its subsequent circuit, measuring the current feedback signal test terminal, in which the V-phase voltage value is 7.68V, which is much larger than the 2.5V that the inverter allows to pass the maximum current, while the other two phases of the current The feedback voltage is 0V. After replacing the V-phase current transformer, the inverter is normal. Since then, there has been an example of the same fault as this fault phenomenon, which has been checked as an operational amplifier TL04BC associated with the corresponding phase current transformer is damaged.
Case 4
Model Number: Multiverter 122/150-400
Fault phenomenon: Fault display “short circuit Uce”
Processing procedure: Fault help message on the inverter manual Note: Its Uce is too high to trigger this fault when the IGBT is turned on. When the Uce value of the IGBT with short-circuit protection is greater than the threshold value, a fault signal is output, and the IGBT is protected by blocking the pole pulse in a certain manner. Over current and short circuit will cause Uce of the IGBT to be too high. After inspection, it was found that the C and E poles of an IGBT had been broken down. In operation, due to its own causes of IGBT elements, overvoltage, overcurrent, and poor performance of IGBT driving circuits, IGBTs work in the amplifying area and cannot be protected, so that excessive tube consumption may cause IGBT breakdown. After confirming that the IGBT drive circuit, field cable and motor are normal, replace the damaged IGBT and the inverter is normal.
Example Five
Model Number: Multiverter 22/27-400
Symptom: The motor is overheated.
Processing process: If the temperature measuring element PTC embedded in the controlled motor is connected with the terminal X15:3/4 on the main board A10 of the frequency converter, the temperature of the motor can be monitored. There is no PTC element on this controlled motor and X15:3/4 has been short-circuited, indicating that the fault is on the A10 on the motherboard. Upon inspection, it was found that a 100 M chip resistor in the temperature detection circuit was opened, resulting in a change in the voltage division ratio of the detection circuit, which caused the protection circuit to malfunction. After replacing the resistor, the inverter is normal.
Fourth, summary
Based on the accumulated experience of inverter maintenance, the fault can be roughly divided into the following categories:
1) The link undervoltage is caused by the damage of the components on the rectifier side and the inverter side, and the action or overcurrent fault of the protection device on the line side of the inverter.
2) Ground fault or overcurrent fault caused by the fault of the inverter output cable and motor;
3) Failure of the components in the detection circuit leads to a fault corresponding to the detected object;
4) If the motor insulation is damaged many times, consider installing a filter on the output side of the inverter to limit the value of du/dt or increase the insulation level of the motor.
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