Category: Industrial control technology

Debugging, application, and maintenance techniques for industrial control products，Such as Variable speed driver(VSD),Variable frequency driver(VFD),Industrial touch screen,Programmable Logic Controller(PLC),Servo Driver,servo motor,servo amplifier,Servo Controller,etc.

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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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15kW WEICHI VSD fault repair due to lightning strike

Taking over a 15kW WEICHI frequency inverter, it was damaged by lightning strikes. The motherboard and driver board were both struck by lightning, but fortunately, the module and CPU were not damaged.

Inspection:

  1. Control terminal+10V voltage to 0, no output. This voltage is obtained by stabilizing the+15V of the switching power supply through the LM317 (eight pin SMT IC) circuit. At the moment, there is no LM317 SMT IC at hand, so a 100 Ω resistor and a 10V voltage regulator are used as substitutes for repair;
  2. The LF347 chip IC (four operational amplifier integrated circuit) in the voltage detection circuit is damaged, and the LM324 chip is directly used as a substitute. The functions of each pin are consistent;
  3. The SMT transistor for controlling the charging relay is damaged and replaced with a plastic sealed direct insertion transistor D887.
    All lightning faults have been repaired. The test run is normal.
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Test run failure of the CHRH-415AEE Rihong VSD

Repairing the Shanghai Rihong CHRH-415AEE 1.5kW machine, the user reported unstable output and motor jumping. The output module and output module are both normal. After cutting off the power supply to the inverter module, in order to check the quality of the inverter pulse conveying circuit (including the driving circuit), they were installed as a complete machine on the maintenance bench (without the machine cover installed) and powered on for inspection. The operation panel displays normally, but when starting the operation, it jumps E OH means overheating. The thermal signal output terminals of the short-circuit modules T1 and T2 are invalid. Disconnect the thermal signal terminal and connect the original wiring terminal to the potentiometer for voltage regulation. The test is also ineffective. Check the internal circuit diagram of the module. The terminal is only equipped with a thermistor (10k at zero degrees Celsius), which is connected to an external+5V resistor to divide the voltage and directly send the signal to the CPU. According to room temperature, this partial pressure point should be below 2.5V. The measured voltage is 2.3V, and the built-in thermal element and circuit should be normal.

Later, it was discovered by chance that a small square shielding iron sheet was wrapped around the back of the operation panel. When pressing the operation panel, one corner of this iron sheet touched the 41 pin of the CPU, which happened to be the input pin for the overheat signal. Therefore, pressing the button on the operation panel inputs a module overheating signal (disturbance generated) to the CPU, which is truly a coincidence.
A piece of cardboard is placed between the operation panel and the motherboard circuit, so that when operating the panel, it no longer jumps OH fault code. The fault was quickly identified as a faulty driver circuit, and the machine was repaired by replacing it with a driver IC.

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Several major causes of damage to the inverter output module of the VSD drive

A. Damage caused by abnormal load
Indeed, the protection circuit of the frequency converter is already quite complete. For the protection of expensive inverter modules, various inverter manufacturers have put a lot of effort into their protection circuits, from output current detection to IGBT voltage drop detection in the drive circuit, and strive to implement the fastest overload protection with the fastest strain rate! From voltage detection to current detection, from module temperature detection to phase loss output detection, there has not been a protection circuit for any particular electrical appliance yet. A frequency converter has been focused and invested in this approach. When salespeople talk about the performance of frequency converters, they must also mention the protection function of the frequency converter. They often unconsciously promise users that with the comprehensive protection function of the frequency converter, your motor will not be easily burned. This salesperson doesn’t know that this promise will bring him great passivity!

Does the motor really not burn when using a frequency converter? My answer is: compared to power supply, using a frequency converter makes it easier for the motor to burn, and the motor is prone to burning, making it easier for the inverter module of the frequency converter to be “reimbursed” together. The sensitive overcurrent protection circuit of the frequency converter is at a loss here and has no effect at all. This is a major external cause of damage to the frequency converter module. Listen to me explain the truth behind it.
A motor can operate at power frequency, although the operating current is slightly higher than the rated current, there is a certain temperature rise during long-term operation. This is a faulty motor that can indeed run before it burns out. But after connecting to the frequency converter, frequent overloads may occur, making it impossible to operate. It doesn’t matter yet.
A motor that can operate in power frequency mode and has been used normally by the user for many years. Please pay attention to the word “many years”. Users may think of saving electricity bills or need to undergo frequency conversion modifications due to process modifications. But after connecting to the frequency converter, there will be frequent OC faults, which is good. The protection has stopped and the module is not damaged. What’s scary is that the frequency converter didn’t immediately trip the OC fault, but was running for no reason – after only three or two days of operation, the module exploded and the motor burned out. The user relied on the salesperson: the quality of the frequency converter you installed is poor, burned my motor, you want to compensate my motor!
Prior to this, the motor seemed to have no problems and was running well. The operating current was measured because the load was relatively light, reaching half of the rated current; Tested three-phase power supply, 380V, balanced and stable. It really seems like the damage to the frequency converter, along with the damage to the motor.
If I were present, I would be fair and impartial: don’t blame the frequency converter, it’s because your motor is already “critically ill” and suddenly malfunctioned, accompanied by damage to the frequency converter!
A motor that has been in operation for many years, due to temperature rise and moisture, the insulation degree of the winding has greatly decreased, and even has obvious insulation defects, which are at the critical point of voltage breakdown. In the case of power supply at power frequency, the input voltage of the motor winding is a three-phase 50Hz sine wave voltage, and the induced voltage generated by the winding is also relatively low. The surge component in the circuit is small, and the decrease in the insulation degree of the motor may only bring about inconspicuous “leakage current”. However, the voltage breakdown phenomenon has not yet occurred between the turns and phases of the winding, and the motor is still “operating normally”. It should be said that as the degree of insulation aging deepens, even under power supply at power frequency, it is believed that in the near future, the motor will eventually burn out due to voltage breakdown between phases or windings caused by insulation aging. But the problem is, it hasn’t burned down yet.

After connecting to the frequency converter, the power supply conditions of the motor become “harsh”: the PWM waveform output by the frequency converter is actually a carrier voltage of several kHz or even more than ten kHz, and various components of harmonic voltage will also be generated in the motor winding power supply circuit. According to the characteristics of the inductor, the faster the change rate of the current flowing through the inductor, the higher the induced voltage of the inductor. The induced voltage of the motor winding has increased compared to the power frequency supply. Insulation defects that cannot be exposed during power supply at power frequency are caused by the inability to withstand the impact of induced voltage under high-frequency carriers, resulting in voltage breakdown between turns or phases of the winding. The sudden short circuit of the motor winding was caused by a phase to turn short circuit in the motor winding. During operation, the module exploded and the motor burned out.
In the initial stage of start-up, due to the low output frequency and voltage of the frequency converter, when there is a fault in the load motor, although it causes a large output current, this current is often within the rated value. The current detection circuit acts in a timely manner, and the frequency converter implements a protective shutdown action, so there is no risk of module damage. But if the three-phase output voltage and frequency reach high amplitudes under full speed (or near full speed) operation, if there is voltage breakdown phenomenon in the motor winding, it will instantly form a huge surge current. Before the current detection circuit acts, the inverter module cannot withstand it and will explode and be damaged.
From this, it can be seen that protective circuits are not omnipotent, and any protective circuit has its own weaknesses. The frequency converter is unable to effectively protect the motor winding from sudden voltage breakdown during full speed operation. Not only the frequency converter protection circuit, but any motor protector cannot effectively protect against such sudden faults. When such sudden faults occur, it can only be declared that the motor has indeed passed away.
This type of fault is a fatal blow to the inverter output module of the frequency converter and cannot be avoided.

其它由供电或负载方面引起的原因，如过、欠压、负载重、甚至堵转引起的过流等故障，在变频器的保护电路正常的前提下，是能有效保护模块安全的，模块的损坏机率将大为减小。在此不多讨论。
B、由变频器本身电路不良造成的模块损坏
1、 由驱动电路不良对模块会造成一级危害
由驱动电路的供电方式可知，一般由正、负两个电源供电。+15V电压提供IGBT管子的激励电压，使其开通。-5V提供IGBT管子的截止电压，使其可靠和快速的截止。当+15V电压不足或丢失时，相应的IGBT管子不能开通，若驱动电路的模块故障检测电路也能检测IGBT管子时，则变频器一投入运行信号，即可由模块故障检测电路报出OC信号，变频器实施保护停机动作，对模块几乎无危害性。
而万一-5V截止负压不足或丢失时（如同三相整流桥一样，我们可先把逆变输出电路看成一个逆变桥，则由IGBT管子组成了三个上桥臂和三个下桥臂，如U相上桥臂和U相下桥臂的IGBT管子。）， 当任一相的上（下）桥臂受激励而开通时，相应的下（上）桥臂IGBT管子则因截止负压的丢失，形成由IGBT管子的集-栅结电容对栅-射结电容的充电，导致管子的误导通，两管共通对直流电源形成了短路！其后果是：模块都炸飞了！
截止负压的丢失，一个是驱动IC损坏所造成；还有可能是驱动IC后级的功率推动级（通常由两级互补式电压跟随功率放大器组成）的下管损坏所造成；触发端子引线连接不良；再就是驱动电路的负供电支路不良或电源滤波电容失效。而一旦出现上述现象之一，必将对模块形成致命的打击！是无可挽回的。
2、脉冲传递通路不良，也将对模块形成威胁
由CPU输出的6路PWM逆变脉冲，常经六反相（同相）缓冲器，再送入驱动IC的输入脚，由CPU到驱动IC，再到逆变模块的触发端子，6路信号中只要有一路中断——
a、变频器有可能报出OC故障。逆变桥的下三桥臂IGBT管子，导通时的管压降是经模块故障检测电路检测处理的，而上三桥臂的IGBT管子，在小部分变频器中，有管压降检测，大部分变频器中，是省去了管压降检测电路的。当丢失激励脉冲的IGBT管子，恰好是有管压降检测电路的，则丢失激励脉冲后，检测电路会报出OC故障，变频器停机保护；
b、变频器有可能出现偏相运行。丢失激励脉冲的该路IGBT管子，正是没有管压降检测电路的管子，只有截止负压存在，能使其可靠截止。该相桥臂只有半波输出，导致变频器偏相运行，其后果是电机绕组中产生了直流成分，也形成较大的浪涌电流，从而造成模块的受冲击而损坏！但损坏机率较第一种原因为低。
若此路脉冲传递通路一直是断的，即使模块故障电路不能起到作用，但互感器等电流检测电路能起到作用，也是能起到保护作用的，但就怕这种传递通路因接触不良等故障原因，时通时断，甚至有随机性开断现象，电流检测电路莫名所以，来不及反应，而使变频器造成“断续偏相”输出，形成较大冲击电流而损坏模块。
而电机在此输出状态下会“跳动着”运行，发出“咯楞咯楞”的声音，发热量与损耗大幅度上升，也很容易损坏。
3、电流检测电路和模块温度检测电路失效或故障，对模块起不到有效地过流和过热保护作用，因而造成了模块的损坏。
4、主直流回路的储能电容容量容量下降或失容后，直流回路电压的脉动成分增加，在变频器启动后，在空载和空载时尚不明显，但在带载起动过程中，回路电压浪起涛涌，逆变模块炸裂损坏，保护电路对此也表现得无所适从。
对已经多年运行的变频器，在模块损坏后，不能忽略对直流回路的储能电容容量的检查。电容的完全失容很少碰到，但一旦碰上，在带载启动过程中，将造成逆变模块的损坏，那也是确定无疑的！
C、质量低劣、偷工减料的少部分国产变频器，模块极易损坏
这是国民劣根性的一种体现，民族之痒啊。不错，近几年变频器市场的竞争日趋激烈，变频器的利润空间也是越来越狭窄，但可以通过技术进步，提高生产力等方式来提高自身产品的竞争力。而采用以旧充新、以次充好、并用减小模块容量偷工减料的方式，来增加自己的市场占有率，实是不明智之举呀，纯属一个目光短浅的短期行为呀。
1、质量低劣、精制滥造，使得变频器故障保护电路的故障率上升，逆变模块因得不到保护电路的有效保护，从而使模块损坏的机率上升。
2、逆变模块的容量选取，一般应达到额定电流的2.5倍以上，才有长期安全运行的保障。如30kW变频器，额定电流为60A，模块应选用150A至200A的。用100A的则偏小。但部分生产厂商，竟敢用100A模块安装！更有甚者，还有用旧模块和次品模块的。此类变频器不但在运行中容易损坏模块，而且在启动过程中，模块常常炸裂！现场安装此类变频器的工作人员都害了怕，远远地用一支木棍来按压操作面板的启动按键。
容量偏小的模块，又要能勉强运行，模块超负荷工作，保护电路形成同虚设（按变频器的标注功率容量来保护而不是按模块的实际容量值来保护），模块不出现频繁炸毁，才真是不正常了。
这类机器，因价格低廉，初上市好像很“火”，但用不了多长时间，厂家也只有倒闭一途了。

The reason for the third type of module damage should not have been a single cause. Hopefully, in the near future, the only reasons for module damage will be the first two.
For domestic frequency converters, sometimes it’s just a piece of mouse manure that spoils a pot of soup. Many frequency converters are also quite good, not inferior to foreign products, and they are of good quality and affordable.

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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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What should be done if the CONVO VSD is not connected to the motor and the frequency of the motor cannot be adjusted?

A 5.5kW Konwo frequency converter sent for repair, the customer said: there is output, but it cannot operate with load, the motor cannot rotate, and the operating frequency cannot be adjusted. Check the main circuit, rectifier and inverter circuits, all of which are normal. Power on, measure the three-phase output voltage without load and it is normal. Connect a 1.1kW no-load motor and start the frequency converter to run. The frequency cannot rise near one or two hertz, and the motor has a pause and produces a creaking sound. No overload or OC fault is reported. Stop and restart, still the same.
Disconnect the 550V DC power supply of the inverter module and send another 24V DC low-voltage power supply to check the driving circuit. Check the capacitors and other components of the driving circuit and driving power supply circuit, and they are all normal. The positive and negative pulse currents output by the three arm drive circuit on the inverter output have reached a certain amplitude, and there should be no problem driving the IGBT module; But when measuring the positive and negative pulse currents output by the three arm drive circuit, a module fault is reported. Analyze the reason, as the DC current range of the multimeter is directly short circuited to measure the triggering terminal, the internal resistance of the DC current range of the multimeter is small, which greatly lowers the positive excitation voltage output by the driving circuit, such as below 10V. This voltage cannot trigger the IGBT tube normally and reliably. Therefore, the module fault detection circuit detects the voltage drop of the IGBT tube and reports a fault in the OC module. The fault was actually caused by the measurement method. When the probe was connected in series with a resistance of more than ten ohms and the output current of the drive circuit was measured, the OC fault was not reported. Check the signal output circuit of the current transformer again, and it is also normal. During operation, no fault signal is reported.

I feel like there’s nowhere else to go and I can’t find the cause of the malfunction. Is the problem with the driver, module, current detection, or other circuits? The fault was not detected throughout the afternoon. For a moment, I felt a bit indifferent and worried.

  1. Does the CPU detect abnormal current during startup and take measures to slow down?
  2. Is the current limiting action made by the driving circuit due to abnormal driving or poor module performance?
    Under low-frequency operation, try to short-circuit the shunt resistors of the U, V, and W output circuits to make the CPU exit the frequency reduction and current limiting action, which is ineffective;
    Restoring the parameters to their factory values (suspecting that this operating mode may have been manually set) is invalid.
    Start the frequency converter and observe carefully: after the speed rises to 3Hz, it drops to 0Hz, and repeat this process. The motor stops running.
    After significantly increasing the acceleration time, it steadily increased to 3Hz and then decreased to 0Hz, indicating that there were no abnormalities in the driving and other circuits. This operating phenomenon should be formed based on the signal emitted by the CPU, which seems to act as a current limiting action based on the current signal.
    The self deceleration during the starting process is generally due to the following two reasons:
  1. During the startup process, the CPU detects a sharp increase in abnormal current values and performs immediate frequency reduction processing. When the current returns to within normal values, it then increases the frequency for operation;
  2. During the startup process, the CPU detects an abnormal drop in the DC voltage of the main circuit and performs immediate frequency reduction processing. When the voltage of the main circuit returns to within normal values, it then increases the frequency for operation;
    After the drive and current detection circuits have no issues, maintenance should be carried out from the perspective of voltage.
    The anomalies caused by voltage can also be divided into two aspects:
  3. Caused by abnormal DC voltage detection circuit in the circuit (drift of reference voltage, variation of sampling resistance, etc.). This signal causes the CPU to mistakenly assume that the voltage is too low, and therefore takes measures to reduce the output frequency to maintain a stable voltage;
  4. The abnormality of the main DC circuit causes a low voltage (loss of capacity of the energy storage capacitor, failure to close the charging short circuit contactor, etc.), which is detected by the detection circuit and causes the CPU to take a frequency reduction action during the startup process.
    Reinstall and power on the machine, and conduct a motor test. When powered on, no sound of the charging contactor closing was heard. Check that the contactor coil is AC 380V, taken from the R and S power supply incoming terminals. Loose coil lead terminals caused poor contact, and the contactor failed to engage. The large current during startup creates a significant voltage drop on the charging resistor. The sharp drop in the DC voltage of the main circuit is detected by the voltage detection circuit, prompting the CPU to issue a frequency reduction command.

The reason for taking many detours is that the machine only performed frequency reduction treatment when the voltage dropped, and did not report an undervoltage fault. In this case, other models often have reported undervoltage faults. Also due to the reason of no load, during frequency reduction processing, the voltage quickly rises and the frequency continues to rise. Then the voltage drops again, and the frequency converter reduces the frequency processing, allowing the voltage to rise again. This repeated process causes the frequency converter to increase speed, decrease to zero speed, pause and then increase speed again, and then decrease to zero speed. But it does not shut down and does not report any fault signals.
It’s a bit funny that such a simple fault should be thoroughly investigated on its normal circuit. Due to its failure to report fault codes, the inspection steps were somewhat bewildered.
This article is shared with everyone – when the charging contactor of the Kangwo inverter is in poor contact, it may be adjusted in a frequency reduction manner during the starting process in a light load state, without reporting an undervoltage fault signal and implementing shutdown protection. In the loaded starting state, the DC circuit should have a significant drop and should be able to report an undervoltage fault.
The frequency converter is an organic combination of software and hardware circuits, and the above fault phenomena are formed under the automatic control of software programs. If we only rely on the fixed thinking pattern formed by surface phenomena and past experience, without in-depth analysis and detailed observation, we would really treat this simple fault as a difficult one to repair.

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Solving Two Unusual Faults in AMB VSD: A Detailed Guide

When dealing with variable speed drives (VSDs), encountering unusual faults can be both perplexing and time-consuming. This article will delve into two unique faults encountered in an Anbang Xin AMB-G9/P9 22kW frequency converter and provide step-by-step solutions to resolve them.

Fault A: Mysterious “Fault Characters”

A user sent in a domestically produced frequency converter for repair, specifically an Anbang Xin AMB-G9/P9 22kW model. Upon initial inspection, the damaged module was removed, and the drive circuit was tested for normalcy. Upon powering on, the operation panel displayed an OC fault code. Once the short-circuit fault signal was addressed, the OC signal stabilized. However, when attempting to run the converter by pressing the RUN button, the charging relay momentarily disconnected, causing the panel indicator light to go out and the display screen to flash a series of unrecognizable “fault characters” not listed in the fault code table.

Diagnosis and Solution:
  1. Identify the Anomaly:
    • The output terminals of the three-phase output current detection signal were all at 0V, which is normal.
    • Occasionally, upon cycling the power, it was discovered that the “fault characters” were actually startup characters.
  2. Root Cause Analysis:
    • The malfunction indicated a possible short-circuit load on the switching power supply’s load side, particularly in the driving circuit.
    • When the startup signal was activated, the power supply voltage dropped significantly, causing the switching power supply to stop oscillating.
    • This voltage drop also released the charging relay due to insufficient suction voltage, prompting the CPU to believe it was being re-powered on and displaying startup characters.
  3. Circuit Inspection:
    • Examination of the driving circuit revealed that two power amplification tubes, connected in a push-pull configuration behind the driving IC, had sustained damage.
    • One transistor in both the upper and lower arm driving power amplifier circuits of the U-phase was damaged.
    • This damage caused an instantaneous short circuit to the driving power supply when pulse signals arrived, resulting in a momentary shutdown.
  4. Resolution:
    • Conduct a thorough inspection of the driver board before powering on after dismantling the module.
    • Replace the damaged transistors in the driving circuit to ensure proper pulse amplification and module driving.

Fault B: Unlisted Fault Characters Related to the Brake Circuit

After replacing the module, the converter was tested with a 24V DC power supply without connecting the 530V DC voltage of the DC circuit. Upon startup, the Br Tr FeiLuRe character appeared but could be reset with the reset button. However, disconnecting the 24V power supply resulted in the fault persisting and becoming unresettable.

Diagnosis and Solution:
  1. Initial Checks:
    • The fault code was checked, and the manufacturer indicated it was a brake circuit fault, which seemed unusual given that the external brake resistor circuit was not connected.
    • Internal brake components were measured and found to have no short circuits.
  2. Voltage Analysis:
    • Upon disconnecting the 24V power supply, a residual voltage of about 6V was found at the inverter power supply terminal.
    • This voltage entered the fault detection circuit, potentially triggering the Br Tr FeiLuRe fault signal.
  3. Circuit Examination:
    • The negative pressure and pulse positive voltage of the six drive circuits were normal.
    • With the guarantee of cut-off negative pressure, connecting the 530V DC voltage to the DC circuit should not damage the module.
  4. Testing and Resolution:
    • For safety, the original 75A quick release fuse was replaced with a 2A one.
    • Everything operated normally after this change, indicating that a faulty fuse or short-circuited brake control IGBT inside the module could generate the Br Tr FeiLuRe alarm.
    • The fault detection circuit likely reported an abnormal low voltage in the DC circuit to the CPU as a brake circuit fault.
  5. Final Considerations:
    • Defining the fault as a brake circuit issue may be misleading.
    • The occurrence of this fault prevented low-voltage power supply testing of the inverter circuits, increasing maintenance costs and complexity.

Conclusion

Encountering unusual faults in VSDs requires a systematic approach to diagnosis and resolution. By carefully examining circuit components, analyzing voltage anomalies, and conducting thorough testing, these complex issues can be resolved effectively. This case study highlights the importance of detailed inspection and the potential pitfalls of misdiagnosed faults, ultimately leading to successful repairs and improved understanding of VSD operation.

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Is a IGBT module with no measurement issues necessarily a good module?

This article only discusses the inverter module made of a single or double IGBT tube, as well as the methods for measuring and judging its quality. The IPM module is not within the scope of this article’s discussion.
Field effect transistors have the advantages of fast switching speed and voltage control, but they also have the disadvantages of large conduction voltage drop and small voltage and current capacity. However, bipolar devices have exactly the opposite characteristics, such as current control, small conduction and voltage drop, and large power capacity. The combination of the two is known as complementary advantages. The origin of IGBT tubes or IGBT modules is based on this. Structurally, similar to the familiar composite amplifier transistor, the output transistor is a PNP type transistor, while the excitation transistor is a field-effect transistor, and the drain current of the latter forms the base current of the former. The amplification ability is the product of two tubes.
The equivalent circuit and symbols of IGBT tubes are shown in the following figure:

The pin function diagram of commonly used IGBT single and double tube modules (CM200Y-24NF) is as follows:

Pin function diagram of FP24R12KE3 integrated module:

Before disassembling, a rough measurement of the quality of the module can be made to make a preliminary judgment. For example, terminals 4, 5, and 6 are the U, V, and W output terminals of the frequency converter, while terminals 22 and 24 are the P (+) and N (-) terminals of the internal DC main circuit of the frequency converter, respectively. After identifying these 5 terminals, measurements can be made using a digital or pointer type multimeter. U. The V and W terminals all have forward and reverse resistance to the P and N terminals. Under normal conditions of IGBT tubes, the resistance between tubes C and E is infinite. Only the forward and reverse resistance of the six diodes in parallel on the tube can be measured. If terminals 4, 5, and 6 are considered as three-phase AC input terminals, the six diodes are equivalent to a three-phase rectifier bridge circuit. The method of measuring and judging the three-phase rectifier bridge is sufficient.

A. Online measurement:
If the measurement of this three-phase rectifier bridge is abnormal, it indicates that the module is damaged;
It is normal to measure this three-phase rectifier bridge, but it cannot be determined whether the module is good. The main circuit board of the frequency converter should be opened for further measurement and verification. Measure whether the triggering terminal and internal circuit are normal. Due to the fact that a resistor of about 10k (3k in parallel for high-power models) is often connected in parallel on the trigger terminal, both the forward and reverse online resistances of the trigger terminal should be the resistance value of the parallel resistor. The resistance values of these 6 trigger terminals should be the same. If there is a difference in the forward and reverse resistance of a certain triggering terminal, or if there is a decrease in resistance, after ruling out the fault of the driving circuit, it indicates that the module has been damaged.
The resistance measurement of the triggering terminal is also normal, and in general, the module is considered to be basically good. But it seems too early to announce that the module is absolutely fine at this time. See later on.

B. Offline measurement:

  1. This method is commonly used for measuring high-power single and dual modules, as well as newly purchased integrated modules.
    After disconnecting the single and double transistor modules from the circuit (or for newly purchased modules), the measurement field-effect transistor (MOSFET) method can be used for testing. There is a junction capacitance between the gate and cathode of MOSFET, which determines its extremely high input impedance and charge retention function. This feature can be effectively used to detect the quality of IGBT tubes.
    The method is to set the pointer type multimeter to x10k, connect the black meter to pole C, and the red meter to pole E. At this point, the measured resistance value is almost infinite; Set up the pen without moving, touch the C and G poles with your fingers and remove them, indicating a decrease in resistance from infinity to around 200k; After a few seconds or even longer, measure the resistance between C and E again (with the black probe still connected to the C pole), which can still protect the resistance of about 200k from changing; Set up the pen without moving, short circuit the G and E poles with your finger, and the resistance between the C and E poles will become close to infinity again.
    In fact, touching C and G with your finger charges the gate and anode capacitors. After removing your finger, there is no discharge circuit for the capacitor, so the charge on the capacitor can be maintained for a period of time. The charging voltage on this capacitor is a forward excitation voltage, causing slight conduction of the IGBT tube and reducing the resistance between C and E; When shorting G and E with your fingers for the second time, a discharge path for the capacitor is provided. As the charge is discharged, the excitation voltage of the IGBT disappears, the tube becomes cut off, and the resistance between C and E tends to infinity.
    Fingers are equivalent to a resistance of k Ω level, providing a path for charging and discharging gate cathode junction capacitors; Due to the high forward excitation voltage (above 10V) required for the conduction of IGBT tubes, the x10k range of the multimeter is used, and the internal battery power supply in this range is 9V or 12V to meet the amplitude of the IGBT tube excitation voltage.
    The measurement of trigger terminals can also be measured with a capacitance meter to increase the accuracy of judgment. Often, modules with high power capacity have slightly higher capacitance values between the two terminals.
  2. Below are the dual tube modules CM100DU-24H and SKM75GB128DE, as well as the integrated module FP24R12KE3, using an MF47C pointer multimeter, × Data measured at 10k levels:
    CM200Y-24NF module: main terminal C1, C2E1 E2 trigger terminal C1 E1 C2 E2; After triggering, the resistance for C and E is 250k;
    The measurement using a capacitance meter in the 200nF range is 36.7nF, and the reverse measurement (with the black pen connected to the G terminal and the red pen connected to the E terminal) is 50 nF.
    The main terminal of SKM75GB128DE is the same as above, and after triggering, the C and E resistances are 250k;
    Trigger terminal capacitance: Measure 4.1 nF forward and 12.3 nF backward.
    FP24R12KE3 integrated module, this method can also be used, with a C and E resistance of around 200k after triggering;
    Trigger terminal capacitance forward measurement 6.9 nF, reverse measurement 10.1 nF.

C. The power on measurement after online or offline measurement can finally determine the quality of the module:
Repair a 37kW Dongyuan frequency converter. Upon inspection, it was found that the inverter module was damaged, with model CM100DU-24H. After purchasing a module of the same type, I went through all the offline measurement procedures and confirmed that there were no issues with the module before installing it for testing. The three-phase output voltage is very unbalanced. After thoroughly checking the drive circuit to confirm that there are no faults, measure the zero line of the three-phase power supply from the U, V, and W outputs (using a pointer type multimeter in the DC 500V range). The DC components of the U and W phases are zero, while the V phase has a DC negative pressure of about 300V. From this, it can be concluded that the conduction of the V-phase lower tube is good, while the conduction of the upper tube is poor, resulting in a negative voltage output of V relative to the zero line. And the V-phase upper tube happens to be the newly replaced module. After purchasing another CM100DU-24H for replacement, the three-phase output is normal. The malfunction of the tube is that the internal MOSEFT tube is normal, so online or offline measurements are normal, while the internal output C and E poles have increased internal resistance due to conduction. It illustrates one thing that even after careful measurement, it cannot be 100% concluded that there is no problem with a good inverter module. The measurement and judgment ability of a multimeter is limited after all. Do not have preconceptions about the problems reflected after powering on the connected circuit, thinking that the module cannot be faulty, which can lead to false disconnection of the fault and lead to a detour in maintenance!

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Maintenance and Fault Shielding Tips for Senlan Inverter SB40-S11-11KW Drive Circuit

Maintenance and Fault Shielding Tips for Senlan Inverter SB40-S11-11KW Drive Circuit

When dealing with the repair of a Senlan SB40-S11-11KW frequency converter, it’s crucial to approach the process methodically to identify and resolve issues effectively. This article provides detailed insights and step-by-step guidance on troubleshooting and maintaining the drive circuit of this specific inverter model.

Initial Diagnosis

Upon inspecting a faulty Senlan SB40-S11-11KW frequency converter, you may encounter damage to the output terminals U and P+ of the module due to a breakdown. To begin the diagnostic process:

  1. Remove the Damaged Module:
    Carefully remove the damaged module from the circuit.
  2. Separate Circuit Board Testing:
    Power on the circuit board independently to check for any abnormalities in the drive circuit. If an “OLE” fault appears, refer to the manual, which indicates an external alarm signal.
  3. Short Circuit Control Terminal:
    Short circuit the control terminal Thr to CM. If the power-on display returns to normal but an “FL” fault code appears when pressing the run button, this indicates a module failure.

Drive Circuit Analysis

The drive board is a complex circuit board with over twenty integrated blocks. To understand the fault:

  1. Examine Optocouplers:
    Observe the six optocouplers on the back of the board, which are likely returning the “FL” fault to the CPU. These optocouplers’ outputs are typically parallel.
  2. Short Circuit Optocoupler Inputs:
    Short circuit all the input sides of the optocouplers and power on the board. If the “FL” fault does not appear, this indicates that the fault lies in the drive signals.
  3. Check Drive Power Supplies:
    Measure the voltages on the trigger terminals of the IGBT modules. The drive power supplies for the U, V, and W IGBT tubes should be output by a switching power supply on the motherboard at 12V, then oscillated and inverted by an NE555 chip. A cylindrical sealed transformer extracts voltage from the secondary three windings and rectifies it to form three independent driving power supplies. Ensure all three power supplies are functioning.

Identifying the Issue

If there is no voltage on the trigger terminal of the module, it suggests a deeper issue:

  1. No Static Negative Pressure or Excitation Positive Voltage:
    The absence of both static negative pressure and excitation positive voltage during operation indicates a problem in the drive circuit’s protection mechanism.
  2. Protection Circuit Activation:
    The large circuit board likely has a protection mechanism that detected an abnormally large “IGBT conduction voltage drop” due to the removed module. This activated the protection circuit, cutting off the signal on the module trigger terminal.

Bypassing Protection to Test

To test the drive circuit without the protection interference:

  1. Artificially Create IGBT Conduction:
    Connect the upper three channels of the triggering terminal with the U, V, and W terminals directly. Connect the lower three channels to the N-point, artificially short-circuiting the lower three IGBT tubes.
  2. Release Optocoupler Short Circuits:
    Release the short circuits on the corresponding three optocouplers reporting the “FL” fault.
  3. Power On and Test:
    Power on the circuit and start the operation. If the “FL” fault is no longer reported and the trigger terminals of the lower three arms have normal pulse voltage output, this indicates the drive circuit is functioning correctly.
  4. Repeat for Upper Arms:
    Connect the upper three circuits of the trigger terminal to the U, V, and W terminals and to point P+. Artificially short-circuit the upper three IGBT tubes and test for normal pulse voltage output.

Conclusion and Repair

If both the upper and lower arms of the module have normal pulse voltage outputs, this confirms that the entire drive circuit and operation control are functioning correctly. You can then proceed with replacing the module.

Final Thoughts

  • No Cut-Off Negative Pressure:
    In the shutdown state, the triggering terminal voltage should be zero. This is normal and indicates proper operation of the cut-off mechanism.
  • Successful Repair:
    After replacing the module, the frequency converter should be fully repaired and ready for use.

By following these logical and structured steps, you can effectively troubleshoot and repair the drive circuit of the Senlan SB40-S11-11KW frequency converter. Remember, a methodical approach and understanding of the circuit’s protection mechanisms are key to successful maintenance and repair.