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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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Two “strange” faults of AMB VSD,How to solve it?

A. Strange “fault characters”
The user sent a domestically produced frequency converter for repair, which is an Anbang Xin AMB-G9/P9 22kW frequency converter. According to convention, first remove the damaged module and power on to check if the drive circuit is normal; Power on, the operation panel displays OC fault codes; After the short-circuit fault signal returns to the optocoupler, the OC signal will no longer jump. When operating the RUN button on the control panel, the charging relay momentarily disconnects (with a click), the panel indicator light also goes out, and the display screen flashes, displaying a string of “fault characters” that cannot be found in the fault code table. Suspect that there are still other fault signals present. The output terminals of the three-phase output current detection signal are all 0V, normal. For other signals, without surveying the circuit, it is difficult to quickly identify their origins.

Occasionally, when turning off the power and then on again, it is discovered that the so-called “fault characters” mentioned above are actually startup characters! The essence of the malfunction is that there may be a short-circuit load on the load side of the switching power supply, especially in the driving circuit. When the startup signal is activated, the power supply voltage is pulled to an extremely low level, and even the switching power supply will stop vibrating due to this. Except for the charging relay being released due to insufficient suction voltage, the CPU determines that it is re powered on and displays the startup character! In fact, it is a process that is equivalent to turning on power again.
Check the driving circuit. There are two power amplification tubes connected in a push-pull form behind the driving IC, which are used to amplify the pulse output by the driving IC and then drive the inverter module. The upper and lower arm driving power amplifier circuits of the U-phase both have a transistor damaged due to module damage and impact. When there is no triggering pulse, a single transistor breakdown short circuit does not form a short circuit to the driving power supply. The arrival of pulse signals caused an instantaneous short circuit to the driving power supply due to the conduction of good and bad transistors, resulting in a momentary shutdown of the switch and power outage. The starting signal was also interrupted due to power outage, and the short circuit state of the power amplifier to the transistor after driving the IC was also relieved due to power outage. Then the CPU determines that the frequency converter is being powered on again, so the operation panel displays the power on character.
After dismantling the module, I was eager to power on and check the quality of the drive circuit, but I did not measure and judge the circuit in detail, so I wasted some time on this startup character. After dismantling the module, a thorough inspection should be conducted before powering on the driver board.

B. Fault characters that are also not present in the alarm code table
This Anbang Xin frequency converter is also quite unique. After installing the new module, the 530V DC voltage of the DC circuit is not connected first, and a 24V DC power supply is added for testing. After startup, the Br Tr FeiLuRe character jumps again, but can be reset by pressing the reset button; If the 24V power supply is disconnected, this fault still occurs but cannot be reset. Check the fault code for this item, consult the manufacturer, and answer that it is a brake circuit fault, feeling a bit out of place. The external circuit of the terminal is not connected to the brake resistor, and there is no short circuit in the brake components inside the measured terminal. It is possible that after the power supply of the inverter is shut down, the control power supply (the power supply of the switching power supply) may be connected in series, causing the detection circuit to return a fault signal.

After shutting down the 24V power supply, there is still a voltage of about 6V at the inverter power supply terminal. This voltage enters the fault detection circuit through certain links, reaching the alarm level of Br Tr FeiLuRe or acting as a Br Tr FeiLuRe fault signal. Isn’t it?
The negative pressure and pulse positive voltage of the six drive circuits are normal, especially with the guarantee of cut-off negative pressure. After the 530V DC voltage is sent to the DC circuit, there is at most an output phase failure, but it is impossible to damage the module. For safety reasons, replace the original 75A quick release fuse with a 2A one and try it directly on. Everything is normal.
It can be seen that if the 75A quick release fuse is broken or the IGBT tube of the brake control inside the module is short circuited (which may cause voltage drop in the DC circuit), an alarm signal of Br Tr FeiLuRe may be generated. The source of this signal may be reported to the CPU by the fault detection circuit after detecting an abnormal low voltage in the DC circuit. But is it not appropriate to define it as a fault in the brake circuit?
However, the occurrence of “faults” makes it impossible to implement the method of detecting inverter circuits in low-voltage power supply. It also caused some setbacks in the maintenance cost.

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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.

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Analysis of PLC-Based Variable Frequency Constant Pressure Water Supply System with One-to-Two Drive

Introduction

Variable frequency constant pressure water supply systems are essential for maintaining stable water pressure in pipeline networks. This article delves into a specific system configuration that employs a Programmable Logic Controller (PLC) and a frequency converter to control two water pumps in a one-to-two drive setup. The system ensures continuous and stable water supply by automatically adjusting the pump operations based on pipeline pressure.

Mitsubishi PLC Constant Pressure Water Supply Circuit Diagram

System Overview

The system primarily consists of a frequency converter, a PLC, and two water pumps. The control mechanism leverages the PID (Proportional-Integral-Derivative) and other related functions of the frequency converter, in conjunction with the PLC, to achieve automatic constant pressure water supply. Additionally, the system is equipped with an automatic/manual switching function, allowing manual control of the water pumps in case of a frequency converter fault.

Control Process

The control process of the system is as follows:

  1. Initial Start-Up: When the pipeline pressure drops below the set value, the frequency converter starts the first pump (#1 pump).
  2. Full Speed Operation: After running at full speed for a predetermined period, if the pipeline pressure still does not reach the set value, the PLC switches the #1 pump from frequency conversion to power frequency operation.
  3. Second Pump Activation: The frequency converter then starts the second pump (#2 pump), adjusting its speed based on the pipeline pressure to maintain constant pressure.
  4. Pump Switching: As water demand decreases and pipeline pressure increases, if the #2 pump’s speed drops to zero but the pipeline pressure remains high, the PLC stops the #1 pump operating at power frequency, allowing the #2 pump to maintain constant pressure.
  5. Cycle Continuation: When the pipeline pressure drops again, the #2 pump is switched to power frequency operation, and the frequency converter starts the #1 pump, adjusting its speed to maintain constant pressure. This cycle continues indefinitely.

Frequency Converter Settings

For the system to function correctly, the frequency converter must be configured with specific parameters:

  • Start/Stop Control: Set to operate on external terminals.
  • Parking Mode: Configured for free parking to avoid impact during frequency conversion/power frequency switching.
  • PID Mode: Enabled, with the pressure setting value entered via the AUX terminal and the feedback signal entering via the VIN terminal.
  • Control Terminals: Configured to output contact actions for frequency conversion faults, zero speed, and full speed.
Mitsubishi PLC Constant Pressure Water Supply Program Diagram 1
Mitsubishi PLC Constant Pressure Water Supply Program Diagram 2
Mitsubishi PLC Constant Pressure Water Supply Program Diagram 3
Mitsubishi PLC Constant Pressure Water Supply Program Diagram 4

PLC Control Wiring and Program

The PLC control wiring diagram shows the integration of fault signals from the water pumps and frequency converter, summarized through relay KA2. The manual/automatic switching is controlled by relay KA1, while the frequency conversion/power frequency operation is interlocked via contactor contacts for enhanced safety.

The PLC program is straightforward, consisting of four main steps (S20 to S23) that form a complete cycle. The switching time between frequency conversion and power frequency is adjustable via two potentiometers (D8030 and D8031) connected to the FX1S type PLC.

The program utilizes step instructions combined with set and reset commands. Step control begins with the STL instruction, and upon completion of all steps, a RET instruction returns the program to the starting step (S0). The SET command energizes the coil, while the RST command de-energizes it. The ZRST command is used for batch resetting multiple coils.

Technological Advancements and Alternative Solutions

As technology progresses, frequency converters are becoming more advanced, with some models capable of one-to-three or even one-to-six configurations. Automated instruments can also perform the PID function, allowing the frequency converter to work passively. In some setups, the frequency converter drives only one pump in a fixed manner, with the second pump directly switched to power frequency when needed. This approach, combined with timely pressure regulation by the frequency converter, results in more stable pipeline pressure.

Conclusion

The PLC-based variable frequency constant pressure water supply system with a one-to-two drive is a reliable and efficient solution for maintaining stable water pressure in pipeline networks. By leveraging the capabilities of PLCs and frequency converters, the system automatically adjusts pump operations to meet changing water demands. As technology continues to evolve, alternative solutions and configurations will emerge, offering even greater flexibility and efficiency in water supply management.

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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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Omron PLC Switch Power Supply: Understanding and Maintenance Guide

Omron, a leading Japanese brand in the field of Programmable Logic Controllers (PLCs), holds a significant market share in mainland China. Given its widespread application in industrial control systems, understanding the maintenance of Omron PLCs, particularly their switching power supplies, is crucial for ensuring operational efficiency and minimizing downtime. This article delves into the maintenance process of Omron PLC switch power supplies, focusing on common faults, diagnosis, and repair methods.

Internal physical diagram of Omron PLC

The Importance of Switch Power Supplies in Omron PLCs

The switch power supply is a critical component of any PLC, including Omron models. It converts the incoming AC power into the DC voltage required to operate the PLC’s internal circuitry. A faulty power supply can lead to a variety of issues, ranging from the PLC not powering on at all to intermittent operation and potential damage to other components.

Schematic diagram of Moron PLC switch power supply circuit

Common Faults in Omron PLC Switch Power Supplies

One of the most common issues encountered with Omron PLCs not displaying after being powered on is a faulty switch power supply. Fortunately, these power supplies are often relatively simple in design, making them easier to diagnose and repair. Based on extensive repair experience, there are three primary components that commonly fail:

  1. F11 Fuse: This fuse is designed to protect the circuit from overcurrent situations. If the fuse blows, it indicates that there has been an excessive current draw, possibly due to a short circuit or component failure.
  2. IC11 Power Module: The power module is the heart of the switch power supply, responsible for converting AC to DC. It can fail due to age, overheating, or surge currents.
  3. C12 Electrolytic Capacitor: Often overlooked, the C12 capacitor plays a crucial role in stabilizing the power supply. Over time, the electrolyte inside the capacitor can evaporate, leading to a loss of capacity. This loss of capacity can cause surge currents that the power module cannot handle, leading to its failure.

Diagnosing and Repairing Omron PLC Switch Power Supplies

When faced with a non-responsive Omron PLC, the first step is to check the switch power supply. Here’s a step-by-step guide to diagnosing and repairing common faults:

  1. Visual Inspection: Start by visually inspecting the power supply for any signs of damage or burnout. Check the fuse (F11) to see if it has blown.
  2. Measure Component Values:
    • Fuse (F11): Use a multimeter to check for continuity. If the fuse is open (no continuity), it needs to be replaced.
    • Power Module (IC11): Measure the voltage across the module’s input and output terminals. If the module is faulty, you may find abnormal voltage readings or no voltage at all.
    • Electrolytic Capacitor (C12): This is where many technicians make a mistake. Even if the capacitor looks normal and shows no signs of short-circuiting when measured in-circuit, it may have lost significant capacity. Remove the capacitor and measure its capacitance. A healthy capacitor should have a value close to its rated capacity. If it’s significantly lower, replace it.
  3. Repair and Replacement:
    • Replace any blown fuses (F11) with a fuse of the same rating.
    • If the power module (IC11) is faulty, replace it with an exact match. Ensure that the new module’s specifications (such as voltage, current, and frequency) match the original.
    • When replacing the electrolytic capacitor (C12), choose a high-quality replacement with the same or higher capacitance and voltage rating. Be sure to install it away from heat sources to prevent future capacity loss.
  4. Testing: After making repairs, test the power supply without load first. If it powers on without issue, gradually add load to ensure stability. Listen for any abnormal sounds, such as a “snap,” which may indicate a component failure.
Internal schematic diagram of MIP0223SC power module

Understanding the IC11 MIP0223SC Power Module

To effectively maintain the switch power supply, it’s essential to understand the key components, especially the IC11 MIP0223SC power module. While a detailed understanding of all the parameters and unit circuits is not necessary, familiarity with the module’s basic functions and pin connections is crucial. Refer to the schematic data table for key parameters such as power supply voltage, oscillation frequency, working current, and power capacity. This information will guide you in troubleshooting and ensuring compatibility when replacing components.

MIP0223SC Power Module Parameter Table

Conclusion

Maintaining Omron PLC switch power supplies doesn’t have to be a daunting task. By understanding the common faults, performing thorough diagnostics, and using high-quality replacement components, you can keep your PLCs running smoothly and minimize downtime. Remember, the key to successful maintenance is not just replacing faulty parts but also identifying the root causes of failures, such as the loss of capacity in electrolytic capacitors, and addressing them proactively. With this guide, you’ll be well-equipped to handle any issues that arise with Omron PLC switch power supplies, ensuring the reliability and longevity of your industrial control systems.

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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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How to handle the password lock of VFD-E Delta VFD converter?

I helped a friend debug a Delta VFD-E frequency converter on site, but due to a damaged panel, I couldn’t operate it after purchasing a panel provided by a friend. This friend went to the site and adjusted it all morning, but the frequency converter still couldn’t run. When I arrived at the site, I found that the parameters couldn’t be changed. The machine parameters 00.08 and 00.09 are for protecting password input and protection password setting, respectively. When the 00.09 parameter is assigned a value of 1, it indicates that the parameter has been locked by divisor. The correct password needs to be entered from parameter 0.08. After the value in parameter 00.09 becomes 0, all parameters can be operated. However, before changing the panel, the machine is said to be functional. In theory, You can use it by replacing the good panel. It’s impossible to set the password on your own after replacing the panel. Someone must have accidentally changed the 00.08 parameter! I don’t know the password! The factory personnel called to inquire about multiple people, but I’m not sure if there’s anything else they can do. Should we withdraw now? The machine is not running yet. It cannot be produced. We need to try to make the machine run. Although the parameters cannot be modified, they can be called up for monitoring. Therefore, we can call up parameters 02-00 and 02-21, which are frequency commands and operation commands. Both parameters have a value of 1, which is controlled by terminal start/stop and external potentiometer. The start/stop of the machine was originally wired through terminals, and a torsion switch has been connected to terminals M11 and DCM for starting, Stop the control. Find a 1k potentiometer, connect terminals+10VAV1 and ACM, power on and test the machine. The machine is running! The manufacturer’s personnel are very happy and eager to ship. The operators also feel that using a potentiometer for speed regulation is even more convenient than panel speed regulation.

After multiple efforts, we finally obtained the super password for this frequency converter. Parameter 008 is a password item, and entering the 8333 super password can unlock it. If you encounter similar problems in the future, you can unlock it through the super password and then operate it without changing the control method to complete the task.