First: Troubleshooting and maintenance of frequency converters
Shandong New Wind Optoelectronics Technology Development Co. Zhou Jasheng
1 Introduction
IBGT frequency converter governor, since the development of the development and put into the market since its superior speed performance, considerable energy savings has been accepted by the majority of motor users, is a large-scale sales to the community every year Large-scale sales to society, for electric power, building materials, petroleum, chemical industry, coal mining and other industries to provide quality services, its user base has been all over the production of all walks of life, become the majority of users of the favorite products.
Here the author combined with their own after-sales service work in the long-term experience of some common failures and methods of treatment, put forward to discuss with the majority of users and maintenance workers, with a view to using the product better, more practical customer service.
2 inverter operation fault code display fault
In the inverter manual, there is a specific column of the inverter fault code display fault, specifically as shown in Table 1.
Note: Table 1, Io, Vo are output rated current, input rated voltage; Vin is the input voltage.
These cases are analyzed.
Table 1 Fault code display fault
2.1 Short-circuit protection
If the frequency converter is running in the short-circuit protection, shutdown after the display of "0", that is, the frequency converter internal or external short-circuit factors. There are several reasons:
(1) Load short circuit
In this case, if the load is thrown off, that is, the frequency converter is disconnected from the load, open the frequency converter, the frequency converter should work normally. At this time we use megohmmeter (or shake table) to measure the motor insulation, the motor winding will be shorted to ground, or the motor line and terminal board insulation deterioration, at this time should check the motor and ancillary facilities.
(2) Inverter internal problems
If the above test after the load is no problem, the inverter open short circuit protection still occurs, this is the inverter internal problems, should be excluded. As shown in Figure 1.
Figure 1 Schematic diagram of the main circuit of the inverter
In the module of the inverter bridge, if a junction of the IGBT breaks down, it will form a short-circuit protection, and in serious cases, it can cause the bridge arm to break down, and even to send no power, and the circuit breaker in front of the bridge will trip. This situation is generally only allowed to send another power, so as not to expand the fault, resulting in greater losses, should contact the manufacturer for maintenance.
(3) Frequency converter internal interference or detection circuit has a problem
Some machine internal interference is also prone to cause such problems, at this time the frequency converter does not have too many problems, just uninterrupted, irregular short-circuit protection, the so-called misprotection, which is caused by interference.
Short-circuit protection of the inverter is generally from the main circuit of the positive and negative bus shunt sampling, with the current sensor by the main control board detection to the main control chip for protection, so any one of these links on the problem, may result in a fault shutdown.
For the interference problem, now low-voltage high-power and high-voltage inverter are added photoelectric isolation, but there is interference, mainly current sensor control line alignment unreasonable, the line can be a separate line, away from the power line, strong voltage, high-current line, and other electromagnetic radiation strong line, or shielded wire, to enhance the ability of anti-jamming, to avoid the occurrence of false protection.
For the detection circuit problems, generally the current sensor, sampling resistor or detection of the gate circuit problem. The current sensor should be detected by an oscilloscope, and its normal waveform should be as shown in Figure 2.
Figure 2 current sensor waveform if the waveform is not good or a messy waveform or even no waveform, that is, the current sensor has a problem, can be replaced with a new one. Sampling resistor problem, some machines used for a long time, its resistance will become large, or even broken, with a multimeter can be detected, should be replaced with the original resistance value or less small resistors.
For the detection of the gate circuit, should check the working point in the static state, if the state does not correspond to the replacement.
(4) parameter setting problems
For elevator class or other (such as wire drawing machine, submerged oil pumps, etc.) heavy load, need to set the low frequency compensation. If the low-frequency compensation setting is not reasonable, it is also easy to short-circuit protection. Generally low-frequency can start the load is appropriate, and the smaller the better, if too high, will not only cause short-circuit protection, but also after the start of the entire operation process current is too large, resulting in related failures, such as IGBT gate burnout, inverter temperature rise. Therefore, compensation should be added gradually, so that the load can just start normally as the best. As shown in Figure 3, V1 is the starting voltage, V0 is the rated output voltage.
Figure 3 Voltage curve of the starting process
(5) In the multi-unit parallel inverter, if a unit has a problem. It is bound to make the other units bear a large current, resulting in an imbalance of current between the units, and overcurrent or short-circuit protection. Therefore, for the parallel connection of multiple units of inverters, should first be measured in its average current, abnormalities should be found to find the cause, troubleshooting. The coefficient of equalization of the units should not be greater than 5%.
2.2 Overcurrent protection
Inverter overcurrent protection, the code shows "1", generally due to excessive load caused by the load current exceeds the rated current of 1.5 times the fault shutdown and protection. This is generally not harmful to the frequency converter, but long-term overload is likely to cause the frequency converter internal temperature rise, component aging or other corresponding failure.
Figure 4 sensor waveform
This protection is also caused by internal faults in the inverter, if the load is normal, the inverter is still overcurrent protection, generally caused by the detection circuit, similar to short-circuit faults, such as current sensors, sampling resistors, or detection circuits. The sensor waveform shown in Figure 4, the envelope is similar to a sine wave, if the waveform is not right or no waveform, that is, the sensor is damaged, should be replaced.
The detection circuit for overcurrent protection is an analog op amp circuit, shown in Figure 5.
Figure 5 overcurrent detection circuit
In the static state, the working voltage at point A should be 2.4V, if the voltage is not right, that is, the circuit has a problem, you should look for the cause to be eliminated. r4 is a sampling resistor, if there is a problem, you should also replace it.
Another cause of overcurrent protection is phase loss. When the inverter input phase is missing, it is bound to cause the bus voltage reduction, load current increase, cause protection. And when the output of the inverter is out of phase, is bound to make the motor of the other two phases of the current increase and cause overcurrent protection. So the input and output should be checked, troubleshooting.
2.3 Over- and under-voltage protection
Inverter over- and under-voltage protection, mostly due to fluctuations in the power grid caused by the power supply circuit in the frequency converter, if there is a large load of motors directly starting or stopping, caused by instantaneous wide fluctuations in the power grid that will cause the frequency converter over- and under-voltage protection, and can not work properly. This situation generally does not last too long, the power grid fluctuations can be normal operation. This situation can only be improved by increasing the capacity of the power supply transformer to improve the quality of the grid can be avoided.
When the grid works normally, that is, in the allowable fluctuation range (380V ± 20%), if the frequency converter still appear this protection, this is the frequency converter internal detection circuit failure. General over- and under-voltage protection detection circuit shown in Figure 6.
Figure 6 over- and under-voltage protection detection circuit
When W1 is not adjusted properly, it will make the over- and under-voltage protection range become narrower, and there is false protection. At this time, you can adjust the potentiometer, generally in the network power 380V, so that the inverter panel display value (running hold down the "〈"key〉with the actual value can be consistent. When the detection circuit is damaged, such as the rectifier bridge, filter capacitor or R1, W1 and R2 in any device problem, will also make the circuit work properly and out of control. If the machine R1 damage caused by open circuit, so that the circuit P point does not get the voltage, the chip that the detection is not right and under-voltage protection. P point of the working point of the range of 1.9 ~ 2.1V, which corresponds to the range of its voltage fluctuations.
For the hoist inverter, because of the pollution back to the grid, increase the isolation circuit, as shown in Figure 7.
Figure 7 Detection circuit for over- and under-voltage protection of hoist inverter
Sometimes improper regulation can also cause mis-protection, which should be carefully adjusted according to the fluctuation of the power grid. Because the hoist load in the operation of the power grid is fluctuating, in the lifting of heavy loads, the voltage drop (some can drop 20V), in the devolution back to the grid voltage rises, can be adjusted according to this change, generally increase W3, reduce W2, until it is suitable for in the steady state.
2.4 Temperature rise is too high protection
The temperature rise of the frequency converter is too high protection (panel display "5"), generally due to the frequency converter working environment temperature is too high caused by the working environment should be improved at this time, increase the surrounding air flow, so that it works within the specified temperature range.
Another reason is that the inverter itself cooling duct ventilation caused by poor, some of the working environment is poor, dust, dust is too much, resulting in cooling ducts blocked so that the fan does not pump into the cold air, so the user should be frequently cleaned up inside the inverter (generally once a week). There are also due to the poor quality of the fan during operation damage, this time should replace the fan.
There is another situation is in the high-power inverter (especially multi-unit or high-voltage inverter), because the temperature sensor line is too long, close to the main circuit or electromagnetic induction strong place, resulting in interference, this time should be taken to anti-interference measures. Such as the use of relay isolation, or add filter capacitors. As shown in Figure 8.
Figure 8 anti-interference measures for high temperature rise protection
2.5 Electromagnetic interference is too strong
This situation inverter does not display fault code after shutdown, only the decimal point is lit. This is a more difficult to deal with the fault. Including after the shutdown display error, such as chaotic display, or run in the sudden crash, frequency display normal and no output, are due to inverter inside and outside electromagnetic interference is too strong.
This troubleshooting in addition to external factors, the frequency converter away from strong radiation sources of interference, the main thing is to enhance its own anti-interference ability. Especially for the main control board, in addition to taking the necessary shielding measures, to take the external isolation is particularly important.
First of all, the main control board should try to make the interface with the outside world using isolation measures. We use fiber optic transmission isolation in high voltage and low voltage high power inverter and elevator inverter, photoelectric isolation in the external sampling circuit (including short circuit protection, overcurrent protection, temperature protection and over- and under-voltage protection), PLC isolation in the elevator and the outside world interface circuit, these measures are effective in avoiding electromagnetic interference from the outside world, and have obtained good results in practical applications.
Another point is the control circuit of the frequency converter (main control board, sub-signal board and display board) in the application of digital circuits, such as 74HC14, 74HC00, 74HC373 and chip 89C51, 87C196, etc., should be particularly emphasized that each integrated block should be added decoupling capacitors, i.e., as shown in Figure 9.
Figure 9 decoupling capacitors of integrated circuits
Each integrated block of the power supply pin to control ground should be added 10μF/50V electrolytic capacitors and connected to 103 (0.01μF) ceramic capacitors, in order to reduce the power supply alignment of the interference. For the chip, the power supply and control ground should be added between the electrolytic capacitor 10μF / 50V and connected to 105 (1μF) monolithic capacitors, the effect will be a little better. I have some serious interference with the model for the above treatment, the effect is better.
These failures should gradually accumulate experience, and constantly seek solutions. Some machines have been used for too long, the circuit board filter capacitor capacity is not enough to cause poor filtering effect, resulting in the inverter dead or out of control, this situation is not very good to deal with, can be replaced with a new circuit board, the general problem can be solved.
3 Other faults of the inverter
In addition to the above fault code display of the inverter, there are some non-display faults of the inverter, now analyzed as follows for your reference.
3.1 Main circuit tripping
This fault is manifested in the frequency converter running process, there is a big sound (commonly known as "cannon"), or boot up the power supply can not be, the frequency converter control with the circuit breaker or air switch tripped. This situation is generally due to the main circuit (including rectifier module, electrolytic capacitors or inverter bridge) direct breakdown short-circuit caused by the breakdown of the instantaneous strong current caused by the module to blow up and produce a loud noise.
The cause of the damage to the module is multi-faceted, and it is not good to generalize. Now only on the author encountered a few types of cases to be listed.
(1) The damage to the rectifier module is mostly due to the pollution of the power grid. Because the inverter control circuit in the use of controllable rectifier (such as silicon controlled welding machine, locomotive charging bottles are controllable rectifier), so that the waveform of the grid is no longer the rule of sinusoidal, so that the rectifier module by the pollution of the grid and damage, which needs to enhance the power supply at the input side of the inverter absorption capacity. The circuit is also generally designed inside the inverter. However, with the deepening of the degree of grid pollution, the circuit should also be continuously improved to enhance the ability to absorb grid spike voltage.
(2) The damage to the electrolytic capacitors and IGBTs is mainly due to uneven voltage, which includes dynamic voltage equalization and static voltage equalization. In the use of long frequency converter, due to the capacity of some capacitors to reduce the entire capacitor group of uneven voltage, sharing the high voltage capacitor is sure to blow up.IGBT damage is mainly due to the bus spike bee voltage is too high and the buffer circuit to absorb the power caused by. In the IGBT on and off process, there is a very high rate of change of current, i.e., di/dt, and the voltage added to the IGBT that is:
U=L×di/dt
Which L is the bus inductance, when the bus design is unreasonable, resulting in high bus inductance, that is, it will make the module to bear the voltage is too high and breakdown, breakdown of the instantaneous high current caused by the module to explode, so reducing the bus inductance is the best way to reduce the bus inductance. So reduce the bus inductance is the key to make a good inverter. We improve the circuit using a wide copper structure has a better effect. The foreign multi-layer bus structure is worth learning.
(3) The parameter setting is unreasonable. Especially in the large inertia load, such as centrifugal fans, centrifugal mixers, etc., due to the inverter frequency drop time is too short, resulting in the shutdown process of motor power generation and make the bus voltage rise, more than the limit of the module can withstand and blow up. This situation should try to make the decline time put long, generally not less than 300s, or in the main circuit to increase the relief circuit, the use of energy-consuming resistors to release the energy. As shown in Figure 10.
Figure 10 Wiring diagram of energy-dissipating resistor
R is the energy-dissipating resistor. When the bus voltage is too high, the A tube conducts, so that the bus voltage drops, and then turns off after normal. This stabilizes the bus voltage and ensures the safety of the main device.
(4) Of course, there are many other reasons for module blow-up. Such as the main control chip disorder, signal interference caused by the upper and lower bridge arm straight-through, etc. are prone to cause module cracking, absorption circuit is also a direct cause of the situation should be treated differently, in order to make the inverter better.
3.2 Delay resistor burnout
This is mainly due to the delay control circuit problems.
(1) In the inverter delay circuit, most of the thyristor (thyristor) circuit, when it does not conduct or poor performance, it can cause the delay resistor burned. This is mainly caused by the boot moment.
(2) In the process of frequency converter operation, when the control circuit problems, some due to the main circuit module breakdown, resulting in a drop in the control circuit voltage, so that the delay thyristor control circuit works abnormally, the thyristor cutoff so that the time-delay resistor burned out. There are also problems with the control transformer power supply circuit, so that the main control board to lose voltage instantly caused by the thyristor work abnormally and make the delay resistor burned out.
3.3 Only frequency and no output
This failure is generally the IGBT drive circuit controlled by the switching power supply circuit, when the switching power supply or its drive power excitation circuit failure, that is, this problem will occur. As shown in Figure 11.
Figure 11 switching power supply and its driving circuit block diagram
In the wind inverter, the switching power supply is generally selected 30 ~ 35V, ± 15V or ± 12V, power excitation of the output for the one side of the wave, the amplitude of ± 35V, the frequency of about 7kHz. Detection of these voltage values, with an oscilloscope to measure the output of the power excitation can be identified, as shown in Figure 12. However, the replacement of this part of the device should be adjusted so that the driver board voltage in line with the specified value (+15V, -10V) is appropriate.
Figure 12 Output waveform of power excitation stage
3.4 No display on the panel after power supply
This is mainly a common fault of elevator type inverter, so the power supply used for the main control board of this type of frequency converter is a switching power supply, when it is damaged, it will make the main control board is not normal and no display.
This power supply is mostly caused by damage to its internal fuse. Because of the moment of power supply switching power supply by the impact of a large, resulting in an instantaneous fuse, can be replaced with a suitable fuse to solve the problem. Some of its varistor damage, can be replaced with a new switching power supply.
3.5 Frequency does not rise
That is, after the start of the inverter only in the "2.00" Hz run without rising, which is mainly due to the external control voltage is not normal. The external control voltage of the inverter is introduced through the 16-pin terminal of the main control board, if the external control voltage is not normal, or the internal op-amp of the 16-pin is out of order, it will cause the fault, as shown in Figure 13.
Figure 13 frequency adjustment circuit
Then please check the frequency adjustment potential W2 (3.9K), measure the 16-pin 0-5V voltage, and then detect the op-amp circuit C point is working properly. If the 16-pin voltage is normal, and no output at point C, generally due to the operating voltage of the op-amp is not normal, you should check whether the supply voltage is normal or whether the op-amp is damaged.
4 Conclusion
There are a lot of faults in the inverter, just like the maintenance of other electrical appliances, there are a lot of unexpected problems, we need to seriously analyze, figure out the principle of operation, and gradually deepen its circuitry in order to grasp the essence of the fast and accurate handling of the problem, so as to faster and better service to the user.
This article is just in the author's maintenance experience, on the basis of some of the common failures of the inverter analysis to explore, in the work of the need to continue to analyze, summarize, and accumulate some of the common maintenance techniques for the user to solve the problem. Also make our products in the application process of continuous improvement, sublimation, make it do better, more comprehensive, more perfect service to the majority of users, try to less problems, no problems, problems can be solved in a timely manner, which is exactly where our expectations.
The control circuit of the frequency converter and the analysis of several common failures
1 Introduction
With the increasingly widespread application of frequency converters in industrial production, understanding the structure of the frequency converter, the electrical characteristics of the main devices and the role of some commonly used parameters, as well as their common failures is increasingly showing its importance.
2 Inverter control circuit
To the asynchronous motor power supply (voltage, frequency adjustable) of the main circuit to provide control signals of the circuit, known as the control circuit, shown in Figure 1. The control circuit consists of the following circuits: an arithmetic circuit for frequency and voltage, a voltage and current detection circuit for the main circuit, a speed detection circuit for the motor, a drive circuit that amplifies the control signals of the arithmetic circuit, and protection circuits for the inverter and motor.
Inside the dotted line of FIG. 1, there is no speed detection circuit for open-loop control. With the addition of a speed detection circuit to the control circuit, i.e., the addition of a speed command, the speed of the asynchronous motor can be controlled more accurately for closed-loop control.
1) The arithmetic circuit compares the external speed and torque commands with the current and voltage signals of the detection circuit to determine the output voltage and frequency of the inverter.
2)Voltage and current detection circuit
Isolated from the main circuit potential to detect voltage and current.
3)Driving circuit
The circuit to drive the main circuit device, which is isolated from the control circuit to make the main circuit device on and off.
4)I/0 input and output circuits
For better human-computer interaction in the inverter, the inverter has a variety of input signals (e.g., running, multi-speed operation, etc.) signals, and a variety of internal parameters of the output (e.g., current, frequency, protection action drive, etc.) signals.
5)Speed Detection Circuit
The speed signal from the speed detector (TG, PLG, etc.) mounted on the asynchronous motor shaft is sent to the operation circuit, and the motor is operated according to the instruction and operation at the instructed speed.
6)Protection circuit
The main circuit voltage and current are detected, and when an abnormality such as overload or overvoltage occurs, the inverter is stopped or the voltage and current are suppressed in order to prevent damage to the inverter and the asynchronous motor.
The protection circuit in the inverter control circuit can be divided into inverter protection and asynchronous motor protection, and the protection functions are as follows
(1) Inverter protection
①Instantaneous overcurrent protection Due to the short-circuiting of the load side of the inverter current, etc., the current flowing through the inverter device reaches an abnormal value (exceeding the permissible value), then it will instantaneously stop the operation of the inverter and cut off the current. When the output current of the converter reaches an abnormal value, the inverter operation is also stopped.
Related images of this topic are as follows:
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Figure 1
②Overload protection
The output current of the inverter is more than the rated value, and it continues to circulate for more than the specified time. devices, wires, etc. from being damaged, operation must be stopped. Proper protection requires inverse time characteristics, using thermal relays or electronic thermal protection (using electronic circuits). Overloading is caused by excessive GD2 (inertia) of the load or motor blockage due to excessive load.
③Regenerative overvoltage protection
Using an inverter is a rapid deceleration of the motor, due to the regenerative power of the DC circuit voltage will rise, sometimes exceeding the permissible value. It is possible to prevent overvoltage by stopping inverter operation or stopping rapid deceleration.
4 Instantaneous power failure protection
For instantaneous power failure within a few milliseconds, the control circuit works normally. However, if the instantaneous power failure reaches more than 10ms, usually not only the control circuit operates incorrectly, but also the main circuit can not supply power, so the inverter stops running after detection.
5 Ground overcurrent protection
When the load of the inverter is grounded, in order to protect the inverter, it is sometimes necessary to have ground overcurrent protection. But in order to ensure personal safety, it is necessary to install earth leakage circuit breaker.
6 Cooling fan abnormality
In devices with cooling fans, the temperature inside the device rises when the fan is abnormal, so a fan thermal relay or a device heat sink temperature sensor is used to stop the inverter after detecting the abnormality. This can be omitted if the temperature rise is small and does not interfere with operation.