Tag: VSD maintenance

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Maintenance ideas and methods for VFD switching power supply

The switching power supply circuit of VFD can be completely simplified into the circuit model shown in the diagram, and the key elements in the circuit are included. And any complex switching power supply, after removing the branches, will still have a backbone like the one shown in the picture. In fact, in maintenance, it is necessary to have the ability to simplify complex circuits, and to identify these main threads in the seemingly disorderly extension of circuits. To learn from the skilled chef of Jieniu, train yourself that there is no overall switch power circuit in front of your eyes, only the direction of the various parts and veins – oscillation circuit, voltage stabilization circuit, protection circuit, and load circuit, etc.

Take a look at how many veins there are in the circuit.

  1. 1.Oscillation circuit: The leakage source and R4 of the main windings N1 and Q1 of the switching transformer are the paths for the working current of the power supply; R1 provides starting current; The self powered windings N2, D1, and C1 form the power supply voltage for the oscillating chip. The normal operation of these three links is a prerequisite for the power supply to oscillate.

Of course, the 4-pin external timing components R2, C2, and PC1 chip itself of PC1 also constitute a part of the oscillation circuit.

  1. 2,.Voltage stabilizing circuit: The+5V power supply of N3, D3, C4, etc., and components such as R7-R10, PC3, R5, R6 constitute the voltage stabilizing control circuit.

Of course, the PC1 chip and peripheral components R3 and C3 on pins 1 and 2 are also part of the voltage stabilization circuit.

3.Protection circuit: The PC1 chip itself and the 3-pin peripheral component R4 form an overcurrent protection circuit; The parallel D2, R6, and C4 components on the N1 winding form the protection circuit of the IGBT; In essence, the voltage feedback signal of the voltage stabilizing circuit, the voltage stabilizing signal, can also be regarded as a voltage protection signal. However, the content of protecting the circuit is not limited to the protection circuit itself. The initiation and control of the protection circuit are often caused by abnormalities in the load circuit.

  1. 4.Load circuit: N3 and N4 secondary windings and subsequent circuits are all load circuits. The abnormality of the load circuit will involve the protection circuit and the voltage stabilizing circuit, causing the two circuits to make corresponding protection and adjustment actions.

The oscillation chip itself participates in and constitutes the first three circuits. If the chip is damaged, all three circuits will strike together. The maintenance of three or four circuits is carried out under the premise that the chip itself is normal. In addition, like playing chess, we should use a global perspective and systematic approach to diagnose faults, and see the essence through phenomena. If there is a stop vibration fault, it may not be caused by damage to the oscillation circuit components. It may be a voltage stabilization circuit fault or an abnormal load circuit, which causes the internal protection circuit of the chip to start controlling and stops the output of PWM pulses. It is not possible to completely isolate each circuit for maintenance, and the appearance of a faulty component may exhibit the effect of “pulling one engine and moving the whole body”.

The oscillation chip itself participates in and constitutes the first three circuits. If the chip is damaged, all three circuits will strike together. The maintenance of three or four circuits is carried out under the premise that the chip itself is normal. In addition, like playing chess, we should use a global perspective and systematic approach to diagnose faults, and see the essence through phenomena. If there is a stop vibration fault, it may not be caused by damage to the oscillation circuit components. It may be a voltage stabilization circuit fault or an abnormal load circuit, which causes the internal protection circuit of the chip to start controlling and stops the output of PWM pulses. It is not possible to completely isolate each circuit for maintenance, and the appearance of a faulty component may exhibit the effect of “pulling one engine and moving the whole body”.

Switching power supply circuits often exhibit the following three typical fault phenomena (combined with Figures 3 and 9):
A、 The secondary load supply voltage is 0V. After the frequency converter is powered on, there is no response, and there is no indication on the operation display panel. The measured voltage of 24V and 10V at the control terminal is 0V. If the charging resistance or pre charging circuit of the main circuit is intact, it can be determined that there is a switch power supply fault. The maintenance steps are as follows:

1.First, use the resistance measurement method to measure whether there is any breakdown or short circuit phenomenon in switch Q1, and whether there is an open circuit in the current sampling resistor R4. The easily damaged component of the circuit is the switch tube. When it is damaged, R4 will increase in resistance or open circuit due to impact. The G-pole series resistor and oscillation chip PC1 in Q1 are often damaged by strong electrical shocks and need to be replaced simultaneously; Check for short circuits in the load circuit and eliminate them.

2.If the damaged parts are replaced or there are short circuited components that have not been detected, a power on inspection can be conducted to further determine whether the fault is in the oscillation circuit or the voltage stabilizing circuit.

Inspection method:
a、 First, check if there is an open circuit in the starting resistor R1. After normal operation, use an 18V DC power supply to directly power on pins 7 and 5 of UC3844 to separately power on the oscillation circuit. Measure that pin 8 should have a 5V voltage output; The 6 pins should have a voltage output of about 1V. The oscillation circuit is basically normal, and the fault is in the voltage stabilizing circuit;
If the voltage output of pin 8 is 5V, but the voltage of pin 6 is 0V, check the external R and C timing components of pins 8 and 4, and the peripheral circuit of pin 6;
If the voltage measured on pins 8 and 6 is 0V, the UC3844 oscillation chip is broken and needs to be replaced.

b、 Power on UC3844 separately and short circuit the input side of PC2. If the circuit vibrates, it indicates that the fault is in the peripheral circuit of the input side of PC2; The circuit still does not vibrate, check the PC2 output side circuit.

B、 Intermittent oscillation occurs in the switching power supply, where a “hiccup” or “squeaking” sound can be heard, or a “hiccup” sound cannot be heard, but when the display panel is operated, it lights up and turns off. This is a typical fault characteristic caused by abnormal load circuit, resulting in power overload and triggering overcurrent protection circuit action. The abnormal increase in load current causes a significant increase in the excitation current of the primary winding, forming a voltage signal of more than 1V at the current sampling resistor R4, which activates the internal current detection circuit of UC3844 and causes the circuit to stop vibrating; The overcurrent signal on R4 disappears, and the circuit starts vibrating again. This cycle repeats, causing intermittent oscillations in the power supply.

Inspection method:
a、 Measure the resistance values at both ends of the power supply circuit C4 and C5. If there is a short circuit, it may be due to a short circuit in the rectifier diodes D3 and D4; Observe the appearance of C4 and C5 for any bulging or liquid spraying, and remove them for inspection if necessary; There is no abnormality in the power supply circuit, which may be due to a short circuit fault component in the load circuit;
b、 Check the power supply circuit for any abnormalities, power on, and use the troubleshooting method to troubleshoot each power supply one by one. If the power supply terminal of the fan is unplugged, the switch power supply works normally, and the operation display panel displays normally, it indicates that the 24V cooling fan has been damaged; If the+5V power supply connector is unplugged or the power supply copper foil is cut off, and the switch power supply is working normally, it indicates that there are damaged components in the+5V load circuit.

C、 The supply voltage of the load circuit is too high or too low. The oscillation circuit of the switching power supply is normal, but the problem lies in the voltage stabilizing circuit.

The output voltage is too high, and the components of the voltage stabilizing circuit are damaged or inefficient, resulting in insufficient feedback voltage amplitude. Inspection method:
a、 Connect a 10k resistor in parallel to the output terminal of PC2, and the output voltage drops back. The output side voltage stabilizing circuit of PC2 is normal, and the fault lies in both the PC2 itself and the input side circuit;
b、 Parallel connection of a 500 Ω resistor on R7 results in a significant drop in output voltage. The optocoupler PC2 is in good condition, but the fault is low efficiency of PC3 or a change in the value of the external resistor component of PC3. On the contrary, it is PC2 defect.
If the load supply voltage is too low, there are three possible faults: 1. The load is too heavy, causing a decrease in output voltage; 2. Poor components of the voltage stabilizing circuit result in excessive voltage feedback signals; 3. The switch tube is inefficient, causing insufficient energy exchange in the circuit (switch transformer).

Inspection and repair methods:
a、 Remove the load circuits of the power supply branch one by one (note! Do not disconnect the load circuit by opening the power supply rectifier tube of that branch, especially the+5V power supply circuit with a voltage stabilizing feedback signal! The disappearance of the feedback voltage signal will cause abnormal increase in output voltage of each branch, and burn out large areas of the load circuit!) Determine whether the voltage drop is caused by excessive load; If the circuit returns to normal after cutting off a certain power supply, it indicates that the switching power supply itself is normal. Check the load circuit; Low output voltage, check the voltage stabilizing circuit.
b、 Check the resistance components R5-R10 of the voltage stabilizing circuit, and there is no change in value; Replace PC2 and PC3 one by one. If everything is normal, it indicates that the replacement components are inefficient and the internal resistance of conduction increases.
c、 If replacing PC2 and PC3 is ineffective, the fault may be low efficiency of the switch tube, or there may be problems with the switch and excitation circuit, which does not rule out the low efficiency of the internal output circuit of UC3844. Replace high-quality switch tubes and UC3844.

For general faults, the above troubleshooting methods are effective, but not necessarily 100% effective. If there are no abnormalities in the oscillation circuit, voltage stabilization circuit, or load circuit, but the circuit still has low output voltage, intermittent oscillation, or simply no response, this situation may occur. Don’t worry for now, let’s delve deeper into the cause of the circuit malfunction to help identify the faulty component as soon as possible. What other reasons can cause the circuit to not vibrate when the intermittent oscillation or stoppage of the circuit is not caused by the starting and stabilizing circuits?

(1) The R, D, and C circuits with parallel connection at both ends of the main winding N1 serve as a peak voltage absorption network, providing a discharge path for the magnetic field energy stored in the transformer during the switching period (reverse current channel of the switching tube), protecting the switching tube from overvoltage breakdown. When D2 or C4 experiences severe leakage or breakdown short circuit, the power supply is equivalent to adding a heavy load, causing the output voltage to drop significantly. U3844 lacks power supply, and the internal undervoltage protection circuit is activated, leading to intermittent oscillation of the circuit. Due to the parallel connection of components on the N1 winding, it is difficult to detect a short circuit and is often overlooked;
(2) Some switch mode power supplies have a protection circuit with an input power supply voltage (high voltage). Once the circuit itself malfunctions, the circuit will experience a false overvoltage protection action and the circuit will stop vibrating;
(3) Poor current sampling resistance, such as pin oxidation, carbonization, or increased resistance, can lead to an increase in voltage drop, resulting in false overcurrent protection and causing the circuit to enter an intermittent oscillation state;
(4) The rectifier diode D1 of the self powered winding is inefficient, and the forward conduction internal resistance increases, causing the circuit to fail to vibrate. Replacement testing is required;
(5) The quality factor of the switch transformer is reduced due to mold and moisture in the winding, and the original model transformer is used for replacement testing;
(6) The parameters of the R1 oscillation circuit vary, but no abnormalities are detected in the measurement, or the switching tube is inefficient. At this time, the circuit is checked and found to be normal, but it does not vibrate.

Repair method:
Change the existing parameters and status of the circuit to expose the fault! Try reducing the resistance value of R1 (not less than 200k Ω) so that the circuit can vibrate. This method can also be used as one of the emergency repair methods. Invalid, replace switch tube, UC3844, switch transformer test.
The output voltage is always slightly higher or lower, and cannot reach the normal value. Unable to detect any abnormalities in the circuit or components, almost all components in the circuit were replaced. The output voltage value of the circuit is still in a “barely and barely” state, sometimes seeming to work “normally”, but it makes people feel uneasy, as if they are neurotic, and I don’t know when an “abnormal performance” will occur. Don’t give up, adjust the circuit parameters to make the output circuit reach its normal value and reach its working state, so that we can rest assured. There are several reasons for the variation of circuit parameters:

  1. a、 Transistors are inefficient, such as a decrease in the amplification factor of the transistor, an increase in the internal resistance of conduction, an increase in the forward resistance of the diode, and a decrease in the reverse resistance;
  2. b、 The related dielectric loss, frequency loss, etc. of capacitors that cannot be measured with a multimeter;
  3. c、 Aging and parameter drift of transistors and chip devices, such as decreased light transfer efficiency of optocouplers;
  4. d、 Inductive components, such as switch transformers, have reduced Q values, etc;
  5. e、 The resistance variation of resistive components is not significant.
  6. f、 There are several factors involved in the above 5 reasons, forming a “comprehensive effect”.
  7. The “current” state of a circuit formed by various reasons is a “pathological” state. Perhaps we need to change our maintenance approach. Traditional Chinese medicine has a “dialectical treatment” theory, and we also need to use it. The next prescription is not to target a specific component, but to “regulate” the entire circuit, making it from “pathological” to “normal”. Just like this, the illness was treated with confusion and confusion.
  8. Repair method (slight adjustment of component values):

(1) Low output voltage:
a、 Increase R5 or decrease R6 resistance value; b、 Reduce the resistance values of R7 and R8 or increase the resistance values of R9.
(2) High output voltage:
a、 Reduce R5 or increase R6 resistance value; b、 Increase the resistance values of R7 and R8 or decrease the resistance values of R9.
The purpose of the above adjustments is to thoroughly inspect the circuit and replace inefficient components before proceeding. The purpose is to adjust the relevant gain of the stabilizing feedback circuit, so that the pulse duty cycle of the oscillation chip output changes, the energy storage of the switching transformer changes, and the output voltage of the secondary winding reaches the normal value, and the circuit enters a new “normal balance” state.
Many seemingly irreparable and difficult faults were repaired with ease after adjusting one or two resistance values.

During maintenance, attention should be paid to the following issues: 1. During the inspection and repair process of the switching power supply, the power supply to the IGBT module of the three-phase output circuit should be cut off to prevent abnormal driving power supply and damage to the IGBT module; 2. When repairing faults with high output voltage, it is even more important to cut off the+5V power supply to the CPU motherboard to avoid abnormal or high voltage damage to the CPU, resulting in the CPU motherboard being scrapped. 3. Do not interrupt the voltage stabilizing circuit, as it will cause an abnormal increase in output voltage! 4. The diodes in switch mode power supply circuits, used for rectification and protection, are both high-speed diodes or Schottky diodes and cannot be replaced by ordinary IN4000 series rectifier diodes. 4. After the switch tube is damaged, it is best to replace it with the original model. With such a developed network, the source of goods is not a problem and can generally be purchased. Many things can be purchased at cheap prices on Taobao, pay attention to quality!

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Global Variable Frequency Drive (VFD) repair center

“Longi Electromechanical” has more than 20 years of experience in industrial control maintenance, and is one of the earliest companies engaged in VFD repair. Equipped with artificial intelligence AI maintenance instruments, it specializes in emergency repair of various equipment, with high technical efficiency. It has repaired more than 200,000 units of equipment, including ultrasonic, robot, charging pile, inverter,Variable Frequency Drive (VFD), touch screen, servo, intelligent instrument, industrial control machine, PLC and other products. General problems can be repaired on the same day. LONGI promises you that “if it can’t be repaired, we won’t charge you”. And it provides lifelong maintenance service and free technical consultation for inspection! For urgent repair consultation, please call the contact number or add WHATSAPP maintenance hotline: +8618028667265 Mr. Guo

From European and American brands to Japanese, Korean, and Taiwanese ones, until various domestic brands, we have repaired countless models and specifications of VFDs. In the process of serving our customers, we have continuously learned and accumulated maintenance experience to enhance our skills. We specialize not only in repairing VFDs but also in summarizing various maintenance experiences, elevating them to a theoretical level. We have published the book “VFD Maintenance Technology” and offered VFD maintenance training, thereby promoting the development of the VFD maintenance industry. Longi Electromechanical Company has repaired VFDs from the following brands:

European and American Brands

ABB drives, SEW drives, LUST VFD, LENZE VSD, Schneider drives, CT drives, KEB VSD, Siemens drives, Eurotherm VFD, G.E. VFD, VACON VSD, Danfoss VFD, SIEI VFD, AB VFD, Emerson VFD, ROBICON VFD, Ansaldo VFD, Bosch Rexroth VSD, etc.

Japanese Brands:

Fuji INVERTER, Mitsubishi INVERTER, Yaskawa INVERTER, Omron INVERTER, Panasonic INVERTER, Toshiba INVERTER, Sumner INVERTER, Tooka INVERTER, Higashikawa INVERTER, Sanken INVERTER, Kasia INVERTER, Toyo INVERTER, Hitachi INVERTER, Meidensha INVERTER, etc.

Taiwanese Brands:

Oulin INVERTER, Delta INVERTER, Taian INVERTER, Teco INVERTER, Powtran INVERTER, Dongling INVERTER, Lijia INVERTER, Ningmao INVERTER, Sanji INVERTER, Hongquan INVERTER, Dongli INVERTER, Kaichi INVERTER, Shenghua INVERTER, Adlee INVERTER, Shihlin INVERTER, Teco INVERTER, Sanchuan INVERTER, Dongweiting INVERTER, Fuhua INVERTER, Taian INVERTER (note: Taian is repeated, possibly a mistake in the original list), Longxing INVERTER, Jiudesongyi INVERTER, Tend INVERTER, Chuangjie INVERTER, etc.

Chinese Mainland brands:

Senlan Inverter, Jialing Inverter, Yineng Inverter, Hailipu Inverter, Haili Inverter, Lebang Inverter, Xinnuo Inverter, Kemron Inverter, Alpha Inverter, Rifeng Inverter, Shidai Inverter, Bost Inverter, Gaobang Inverter, Kaituo Inverter, Sinus Inverter, Sepaxin Inverter, Huifeng Inverter, Saipu Inverter, Weier Inverter, Huawei Inverter, Ansheng Inverter, Anbangxin Inverter, Jiaxin Inverter, Ripu Inverter, Chint Inverter, Delixi Inverter, Sifang Inverter, Geli Te Inverter, Kangwo Inverter, Jina Inverter, Richuan Inverter, Weikeda Inverter, Oura Inverter, Sanjing Inverter, Jintian Inverter, Xilin Inverter, Delixi Inverter, Yingweiteng Inverter, Chunri Inverter, Xinjie, Kemron-Bong Inverter, Nihonye Inverter, Edison Inverter

Other brands:
Migao VFD, Rongqi VFD, Kaiqi VFD, Shiyunjie VFD, Huichuan VFD, Yuzhang VFD, Tianchong VFD, Rongshang Tongda VFD, LG VFD, Hyundai VFD, Daewoo VFD, Samsung VFD, etc.

Longi Electromechanical Company specializes in the maintenance of VFDs and strictly requires its engineers to followlow standard operating procedures. Upon receiving a unit, the engineers carefully inspect its exterior and clarify any fault conditions with the customer before beginning work. Any removed circuit boards are cleaned using ultrasonic cleaning equipment. Repaired circuit boards are coated with high-temperature and high-pressure-resistant insulating paint, dried in a drying machine, and then reinstalled in the VFD, with measures taken to prevent corrosion and interference.

The repaired VFD will undergo a simulated operation with load using a heavy-load test bench to avoid any potential issues that may arise under actual load conditions on site.

When it comes to VFD maintenance, most cases are related to the equipment on site. Sometimes a standalone unit may have been repaired, but it doesn’t work properly when installed on site. In some cases, the problem lies with the system rather than the VFD itself. For such issues, if the customer requests on-site service, we will do our utmost to resolve the problem for them. If the location is far away, such as in another province, we can use tools like video conferencing and phone calls to allow our engineers to remotely diagnose and resolve the on-site issues for the customer.

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Repair process of driving circuit for 22kW Delta frequency Inverter

After checking the drive circuit of the 22kW Delta VFD Drive and replacing it with a new module, the OC will jump upon startup. The module is newly replaced, and all six drive pulses are working properly. I don’t think it should be. Still checking the measurement, the six negative pressures driving the IC during shutdown are all normal, and the six excitation voltages are also normal after startup. It is necessary to first determine whether the fault is caused by the driver IC or the module.

It is necessary to first test the load carrying capacity of the six drive ICs, that is, to measure the trigger current value of their output. Connect a 15 ohm resistor in series to the output terminal, and then connect a 15 ohm resistor in series to the probe to limit the circuit current to around 0.5A. After the start signal is activated, its current output capacity is measured, and it can still provide a dynamic current of about 150mA even when the original trigger circuit is connected normally. The driving circuit of the V-phase lower arm IGBT tube only outputs about 40mA of current, which obviously cannot meet the excitation requirements of the IGBT tube. The root cause of the OC fault lies in this!
There seems to be a misconception about the driving method of IGBT tubes, especially high-power IGBT tubes: IGBT tubes are voltage signal excitation devices, not current type excitation devices. The driving signal only needs to meet the voltage amplitude, without requiring too much current driving capability! I have previously analyzed that even IGBT tubes are essentially current driven devices!
The output signals of the driving ICs (PC929 and PC923) of the machine are amplified by a complementary voltage follower and then supplied to the triggering terminals of the module. The push-pull amplifier was originally a pair of field-effect transistors, but due to the lack of the original type of transistor on hand, it has now been replaced with transistor pairs D1899 and B1261. After modification testing, it should be able to meet the excitation requirements. Check the V-phase lower arm circuit. The resistance from pin 11 (pulse output pin) of PC929 to the subsequent power amplifier circuit was originally 100 ohms, but now it has changed to over 100k, causing D1899 to be unable to fully conduct and the output driving current to be too small. After replacing the resistor, the output current is normal. After replacing the power transistor, the base resistance was not measured, resulting in this phenomenon.
By the way, I measured the negative current supply capacity of the driving circuit when cutting off negative pressure output. The probe is still connected in series with a 15 ohm resistor, and each circuit is around 30mA.
This leads to the conclusion that measuring the output voltage of the driving IC is not as direct and effective as measuring its output current. And it can expose the root cause of the malfunction. When the internal resistance of the circuit output increases due to certain reasons, measuring the driving voltage is often normal, which masks the truth of insufficient driving current.

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Repair of EDS1000 ENC VFDV Misleading Current Fault

A ENC EDS1000 11kW Inverter will trip to constant speed overcurrent when accelerating to above 40Hz during operation. But in reality, the operating current is much lower than the rated current, and after switching to other frequency converters, the motor runs normally. Check that the six inverter pulse outputs of the driving circuit are all normal. It is determined that the current transformer circuit detection is abnormal. Check the current detection circuit. The output signal of the current transformer is divided by a 3-ohm resistor and a 30 ohm resistor before being supplied to the motherboard. Suspecting that the current transformer is a non-standard product, an external voltage divider network was connected for adjustment. The partial voltage value may not be accurate enough, causing the current sampling value to be too large and mistakenly skipping the current fault. Or there may be drift in the output value of the internal circuit of the current transformer, which can also cause a false skip current fault.

The simplest method is to adjust the external voltage divider network of the current transformer. Reduce the voltage divider resistance value below it to meet the requirements of the subsequent circuit input voltage range. If conditions permit, the panel current display value can be monitored during operation, and the voltage divider resistance value can be adjusted to match the operating current value with the displayed current value. Often in the maintenance department, it is not possible to connect the frequency converter to the rated load for operation. Therefore, first replace the lower resistor with a 100 Ω potentiometer, and then adjust it to the appropriate position during on-site installation and operation.

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Hitachi VFD drive L300P75kW , after repair, installation still jumps “fault”，How to solve ？

A Hitachi L300P75kW Inverter was installed and tested on site after repairing the module fault. When powered on and started, E16.4 or E16.2 jumps. The cause of the fault is a momentary open circuit in the power supply. Stop the machine and measure the three-phase 380V power input. All three phases have 380V and are quite balanced. During operation, when measuring the three-phase output circuit, there is an unstable voltage value in one phase, with fluctuations ranging from 280V to around 350V. The voltage detection circuit of this machine detects the input voltage of T and S phases in the input power supply. When the power grid pollution flash exceeds 15ms, it will protect and shut down. It was determined that the air switch supplying power to the frequency converter had poor contact with one phase, causing the frequency converter to trip E16.4 or E16.2 faults. Upon disassembly and inspection, it was confirmed that a set of contacts had been severely burned out.
Repair after replacing the power switch.

This fault is in a stationary state or a low current state, and due to the virtual connection of the air switch, the abnormal input voltage cannot be detected at all. Only visible when turned on. But due to the abnormal detection of the frequency Inverter, it immediately shuts down for protection. Sometimes, if there is no time to detect, the frequency converter has already stopped. So it’s not easy to detect. It took some effort.

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Exploring the Major Causes of Damage to Inverter Output Modules

Exploring the Major Causes of Damage to Inverter Output Modules

In variable speed drive (VSD) systems, damage to the inverter output module is an issue that cannot be ignored. This article delves into several primary reasons behind this failure, analyzing the underlying logic and mechanisms to provide valuable insights for relevant practitioners.

I. Damage Caused by Abnormal Loads

Despite the considerable sophistication of protective circuits in inverters, their protective capabilities may still be limited when faced with abnormal loads. Inverter manufacturers have invested significant effort in protecting inverter modules, employing various measures such as output current detection and IGBT voltage drop detection to achieve the fastest possible overload protection. However, when motors themselves have underlying issues like insulation aging or winding defects, even comprehensive protective functions of the inverter may not fully prevent module damage.

Especially in cases where motors have been operating for many years and their insulation has significantly degraded, connecting them to inverters may result in voltage breakdowns between windings due to high-frequency carrier voltages, leading to short-circuit currents that can instantly subject the inverter module to enormous shocks, causing damage. This type of module damage, triggered by internal motor faults, is difficult for inverter protective circuits to effectively prevent.

II. Damage Caused by Inverter Circuit Issues

  1. Drive Circuit Failures
    The drive circuit is a crucial component of the inverter module, typically supplied by both positive and negative power sources. When the +15V voltage is insufficient or lost, the IGBT cannot be turned on. If the drive circuit’s fault detection function is working properly, the inverter will report an OC signal and shut down for protection. However, if the -5V off-voltage is insufficient or lost, it may cause the IGBT to mistakenly turn on, creating a short circuit that can deal a fatal blow to the module.
  2. Poor Pulse Transmission Path
    The PWM inversion pulses output by the CPU pass through a buffer before being sent to the drive IC and then to the trigger terminals of the inverter module. Any interruption in this transmission path can cause the inverter to report an OC fault or operate in an unbalanced phase. Unbalanced phase operation generates DC components and surge currents, which can impact the module and increase the risk of damage.
  3. Failure of Detection Circuits
    Current detection circuits and module temperature detection circuits are important barriers for protecting the inverter module. If these circuits fail or malfunction, they will be unable to effectively monitor overcurrent and overheating conditions in the module, thereby losing their protective function.
  4. Decrease in Energy Storage Capacitor Capacity
    A decrease in the capacity of the energy storage capacitor in the main DC circuit increases the pulsating components of the DC circuit voltage. During loaded startup, this can cause the inverter module to withstand excessive voltage shocks, leading to damage.

III. Damage Caused by Product Quality Issues

In the market, some domestically produced inverters are criticized for their poor quality and shoddy workmanship. These inverters have obvious deficiencies in the design of protective circuits and the selection of inverter module capacities, making the modules prone to damage. For example, using small-capacity modules, old or defective modules, and ineffective protective circuits significantly increase the risk of module damage.

Conclusion

In summary, the damage to inverter output modules is a result of multiple factors working together. To reduce the risk of module damage, we should approach the issue from multiple angles: strengthen motor maintenance and inspection to ensure motors are in good condition; optimize inverter design to improve the reliability and response speed of protective circuits; and, when choosing inverters, consumers should prioritize product quality and after-sales service to avoid purchasing inferior products. Only in this way can we more effectively protect the safe operation of inverter output modules and extend the lifespan of inverters.

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Siemens MM430 VSD 7.5kW power supply hiccup fault

Repair an imported Siemens 7.5kW frequency converter due to power supply hiccup fault, with no display on the operation panel. Due to its special installation structure, the machine is surrounded by three circuit boards and a heat dissipation plate in a square shape, with an embedded shell. When repairing, it is necessary to disconnect the circuit board and lay the entire circuit flat on the workbench, such as unfolding a roll of ancient bamboo slips, in order to facilitate maintenance. Moreover, the circuit board is a four layer board, making circuit maintenance difficult.

Starting from the switch power supply circuit, first use the elimination method to cut off the load circuit one by one. If it still cannot vibrate well, it indicates that hiccups are not caused by excessive load. There are no abnormalities in the oscillation and voltage stabilization circuits. Finally, it was found that two 200V voltage stabilizing tubes in the cut-off shunt circuit of the switch tube were damaged due to breakdown. We purchased 110V voltage stabilizing tubes from the market and replaced them with four to repair them. A typical shunt (also known as anti peak voltage absorption) circuit uses a diode connected in series with a resistance capacitance parallel circuit, and then connected in parallel with the primary winding of a switching transformer. The diode connection method is similar to the freewheeling diode connection method of a typical coil circuit. Its function is to quickly release the electrical energy of the primary winding circuit during the period when the switching transistor is approaching cutoff, so that the switching transistor can cut off more quickly. But the circuit consists of two 200V voltage regulators connected in series from the P+end, followed by two thermistors with resistance values of 360k each, connected in series to the drain of the switching tube. The circuit is also connected in parallel to the primary winding. When the switch tube tends to cut off, the sharp decrease in current in the primary winding causes a sharp increase in the back electromotive force of the winding. When it is superimposed with the power supply voltage and exceeds the P+voltage by 400V, this protective circuit breaks down and conducts, releasing this energy back to the power supply. When the back electromotive force energy is small, the current flowing through the two thermistors is small, their temperature rise is also small, their resistance value is large, and the release of energy is also slow. When the back electromotive force energy is large, as the discharge current increases, the resistance temperature rises, the resistance value decreases, and the energy discharge is accelerated. Think about it, this circuit is connected in series with a thermistor, it’s really interesting. Adding a thermistor and a peak voltage absorption circuit with voltage stabilizing diodes to the primary winding of the switch transformer may only be done by Siemens frequency converters. I have also encountered this type of circuit form for the first time.

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Repairing the Stubborn GF Fault in Yaskawa 616G3 55kW Frequency Converter

Repairing a frequency converter, especially one that reports a stubborn ground fault (GF), can be a challenging and frustrating task. Recently, I encountered such an issue with a Yaskawa 616G3 55kW frequency converter. Despite the common advice to replace the board, I delved deeper into the problem, determined to find a logical solution. This article outlines the step-by-step process I followed to diagnose and repair the GF fault without replacing any major components.

Initial Diagnosis and Background

The Yaskawa 616G3 frequency converter had been out of service for two to three years before it arrived at our repair department. Upon inspection, we found that two of the three-phase power input rectifier modules and two of the six inverter IGBT modules were damaged. The driver board had also suffered some component damage due to the module failure.

The GF fault typically indicates an issue with the drive circuit or the IGBT module itself, especially during the initial startup stage when the three-phase output voltage has not yet been established. Understanding the structure of the protection circuit helped narrow down the potential causes. The GF and OC (load-side short circuit) fault signals are fed directly to the CPU by the protection circuit of the driving circuit board.

Driver and Protection Circuits Inspection

The driver circuit of the Yaskawa frequency converter includes six pulse signals from the CPU, isolated and amplified by six TLP250 ICs, and sent to the IGBT modules. Additionally, six TLP750 ICs form a module fault protection circuit, reporting GF and OC signals to the CPU. There are also three 2501 optocouplers responsible for detecting fuse status.

After disconnecting the driver board and CPU motherboard, I replaced the damaged components in the power amplifier circuit. The switch power supply and motherboard appeared to be functioning correctly. I manually cleared other potential faults, such as overvoltage, undervoltage, overheating, and fan issues, to ensure the drive circuit could output normal excitation pulses.

Addressing the FU Fault

During the initial tests, the circuit reported an FU (fuse) fault. After inspecting the relevant optocoupler components and circuit components, I found that the copper foil strip of the N lead was broken due to mold. This caused the fuse detection circuit to assume the fuse was broken. I repaired the moldy copper foil strip and retested the circuit, which resolved the FU fault.

Further Investigation and Component Replacement

With the FU fault resolved, I pressed the RUN button on the operation panel and measured the six pulses output by the drive circuit, all of which were normal. However, the GF fault persisted. I re-inspected the driver board, measuring all circuit components and short-circuiting the GF fault feedback optocoupler, but the GF fault still tripped.

Further investigation revealed a poor contact between a diode in the IGBT voltage drop detection circuit and the copper foil strip. I also found that the positive voltage of the W-phase transistor driver pulse was low, indicating an issue with the driver IC. After replacing the faulty A3320 IC, the output pulse amplitude returned to normal.

The Stubborn GF Fault

Despite repairing the identified issues, the GF fault still occurred during startup. I used the fault zone cutting method to narrow down the fault range, eventually finding that the IGBT driver circuit (protection circuit) of the U-arm was prone to reporting the GF fault. A diode with a poor contact was identified and replaced.

However, even after these repairs, the GF fault persisted. I then conducted a series of tests, including short-circuiting the module detection circuit’s transistors to relieve the fault protection function. During these tests, I observed an abnormal phenomenon: the series-connected light bulb lit up with high brightness after the start signal was activated, indicating a potential issue with the IGBT modules or driving circuit.

Discovering the Common Cause

After ruling out issues with the driving circuit and modules, I focused on the common factors that could affect all six protection circuits. I noticed that the leads of the capacitor bank, which were longer due to the repair setup, could be introducing inductance into the circuit. This inductance could generate induced electromotive force and current, interfering with the module fault detection circuit.

To test this hypothesis, I formally installed the machine, limiting the lead inductance of the capacitor bank within the allowable value. After the installation, the Yaskawa frequency converter operated normally without tripping the stubborn GF fault.

Conclusion

Repairing the GF fault in the Yaskawa 616G3 55kW frequency converter was a challenging but rewarding experience. By thoroughly understanding the protection circuit and methodically diagnosing each potential issue, I was able to repair the machine without replacing any major components. The key to solving the stubborn GF fault was identifying the common cause—inductance in the capacitor bank leads—and addressing it through proper installation.

This case study highlights the importance of logical reasoning and thorough investigation in repairing electronic equipment. It also demonstrates that, with patience and persistence, even stubborn faults can be resolved without resorting to costly board replacements.

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Mitsubishi VSD F700-A700 Power Driver Board Circuit Diagram and MCU and Optocoupler Specification Confirmation

There is a separate MCU and six communication optocouplers OI1~OI6 on the power drive board of Mitsubishi F700 (F740, F720) and A700 (A740, A720) frequency converters. Their specifications look a bit mysterious and may cause confusion during maintenance. The relevant circuit diagram will be drawn below, and a simple functional analysis of the MCU and optocoupler will be conducted to reduce the difficulty of repairing and changing the frequency converter.

OI6:
Responsible for transmitting the operation and shutdown instructions of the motherboard MCU, with instructions in the form of 1 and 0 levels. The 19 pin of CON1 is a 5V high level, which is a running command. The output side of OI1 becomes 0V, and the local MCU can send 6 pulse signals such as U+~W – to the driving circuit; The 19 pin of CON1 is at 0V low voltage level, and the motherboard MCU sends a shutdown command (if it becomes low during operation, the OI1 output side becomes 5V, which is an overload fault shutdown command). The messenger of the motherboard MCU sends running and stopping commands to the local MCU in the form of DC
The 0 and 1 levels of opening and closing quantities.

OI2:
The serial data returned by the local MCU and motherboard MCU is in the form of rectangular wave pulses. Start working immediately after powering on.
The communicator between the local MCU and the motherboard MCU, signal direction: transmitted locally to the motherboard MCU.

OI5:
The communicator between the motherboard MCU and the local MCU, signal direction: The motherboard MCU issues instructions to the local MCU
MCU. The signal form is serial data, and the test is a rectangular pulse train. Start working immediately after powering on.

OI4:
The main board MCU sends switching instructions to the local MCU, and under normal conditions (running and stopping), the output terminal 6 pins are 0V. When it reaches 5V high level, an E7 code (meaning CPU error) is reported. Is its task to confirm the working status of the motherboard MCU?

OI3:
The communication personnel between the motherboard MCU and the local MCU, signal direction: The motherboard MCU issues instructions to the local MCU. The input signal is in the form of serial data (synchronous clock signal?), but due to the capacitance integration effect at pins 5 and 6, a triangular wave of 760kHz is measured. Start working immediately after powering on.

OI1:
The communication personnel between the local MCU and the motherboard MCU, signal direction: The local MCU reports the fault situation to the motherboard MCU. Signal form 0, 1 switch quantity DC voltage. The shutdown status between pins 5 and 6 of the output terminal is 0V, which changes to a high level of 5V after operation. When there is a fault, it changes to 0V and displays the alarm code EOC1.
As a module fault reporter, he reports the fault situation to the motherboard MCU.

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Exploring the Circuit Diagram and Maintenance Insights of the CONVO VSD Switch Power Supply

Exploring the Circuit Diagram and Maintenance Insights of the CONVO VSD Switch Power Supply

The CONVO VSD switch power supply, specifically designed for the GVF-G type drivers with a power rating of 5.5KW and version number 002-E-P00-01 8.6kVA 13A, presents an intriguing yet robust design in the realm of switch power supplies. Though it may not adhere to the most conventional designs, its performance in practical applications has proven to be reliable, with a notably low failure rate.

Schematic diagram of CONVO inverter switch power supply

Circuit Overview

At the heart of this power supply lies an input stage that receives approximately 550V DC voltage from the autonomous DC home energy storage capacitor. This voltage serves as the foundation for the entire circuit’s operation. The oscillation and driving mechanisms are managed by the widely-used 38440 power chip, which initiates its operation through the voltage and current supplied by components R40, R41, and Z8. While the exact stabilization value of Z8 has not been precisely measured, it is estimated to be around 13V. An LED indicator is conveniently integrated to signal the presence of power.

Once the 3844 chip initiates oscillation, it establishes a power supply voltage for its 7-pin through rectification and filtering circuits comprising D13, Dl4, C30, and C31, facilitated by the BT winding. This power supply not only fuels the chip but also plays a crucial role in output voltage sampling and feedback. The sampled voltage, after being divided by resistors R1 and R2, is fed back to the 2-pin of the 3844 chip. This feedback method, which indirectly samples the output voltage of each channel rather than directly from the transformer’s secondary power supply branch, offers a unique approach albeit with slightly lower control precision and response speed.

Secondary Power Supply Enhancements

To further enhance the power supply’s performance, the +18V and -18V outputs from the secondary winding are routed to the CPU motherboard. Here, they undergo voltage regulation through 7815 and 7915 stabilizers, respectively. Although this adds a layer of complexity to the circuit, it significantly improves the power supply’s stability and reliability. Additionally, the +8V power supply, once introduced to the motherboard, undergoes 7805 voltage regulation to serve as the CPU’s power source.

Current Sampling and Control

The switching tube’s current sampling is achieved through resistor R37, which is series-connected to the source of the K2225 switching tube. This sampled current is then sent to the 3-pin current detection terminal of the 3844 chip. The internal voltage amplifier’s feedback component, connected between the two pins, dictates the sampling voltage’s amplification rate. The 8-pin of the chip, known as the Vref terminal, outputs a stable 5V reference voltage during normal operation. This voltage provides a current path for the external R and C oscillation timing components connected to the 4-pin, ensuring the oscillation frequency’s stability.

The 6-pin of the 3844 chip serves as the pulse output or drive output terminal, introducing pulses to the gate of the K2225 switch through resistor R36. This meticulous control over the switching process is crucial for maintaining efficient and reliable power conversion.

Internal structure diagram of UC3844

24V Output and Fan Control

The 24V output power supply is versatile, providing both the control voltage for the frequency converter’s control terminal and powering two cooling fans. The fans’ operation modes are intelligently controlled by signals from the CPU motherboard, based on parameter settings. These modes typically include running upon power-on, running during operation, and running when the radiator temperature reaches a predefined threshold.

Maintenance Insights

When it comes to maintaining this power supply, several key points should be kept in mind. In the event of a breakdown-induced damage to the K2225 switch tube, a high voltage impulse can be introduced to the 3-pin of the 3844 chip, often leading to its simultaneous damage. Additionally, the R5 resistor may open or experience an increase in resistance value. Similarly, the current sampling resistor R37, connected to the source, is frequently found to be open. Therefore, a comprehensive inspection of these components is imperative before replacing the switch tube. As a direct replacement for the K2225, the K1317 tube can be used.

In conclusion, the CONVO VSD switch power supply, despite its unconventional design, offers a reliable and efficient solution for GVF-G type drivers. Its robust performance in practical applications, coupled with thoughtful design features and straightforward maintenance protocols, makes it a valuable asset in any frequency converter system. By understanding its circuit diagram and adhering to best maintenance practices, one can ensure the longevity and reliability of this power supply in various industrial and commercial applications.