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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Troubleshooting Guide for CVF-G1 Switching Power Supplies in CONVO Frequency Converters

Title: Troubleshooting Guide for CVF-G1 Switching Power Supplies in CONVO Frequency Converters

Introduction:
We recently received three CVF-G1 frequency converters from Kangwo, all exhibiting identical issues: no output from the switching power supply and no screen display. Given that the power supply IC in these machines is a 3844B, and considering the rarity of this IC causing failures in multiple units simultaneously, we embarked on a troubleshooting journey focusing on the peripheral circuits.

Understanding the Switching Power Supply:
A typical switch-mode power supply comprises several key branches:

  1. Power-On Start Branch: This consists of a series of high-resistance resistors that, upon powering on, direct 500V DC to the 3844B power supply pin, initiating the switch tube’s starting voltage.
  2. Positive Feedback and Working Power Supply Branches: These are composed of feedback windings and rectifier filtering circuits, varying between machines in configuration.
  3. Voltage Stabilizing Branch: Powered by a secondary 5V supply, this branch compares 5V voltage changes against a reference, feeding back variables to the 3844B via an optocoupler. Notably, the CVF-G1 model feedback is derived from the primary side.

Conditions for Circuit Oscillation:
For the circuit to oscillate, the following must be met:

  1. The 500V power supply circuit must be functional, delivering DC voltage to the switch’s drain through the main winding.
  2. The power-on start branch must supply an adequate starting voltage (current).
  3. The positive feedback and working power supply branches must provide the necessary feedback voltage (current) and working power.
  4. The load side must be free of short circuits, as these prevent the establishment of sufficient feedback voltage, halting oscillation.

Troubleshooting Approach:
To pinpoint the fault, we began by isolating the voltage stabilizing branch to check if the circuit could oscillate without it. We ensured safety by implementing voltage reduction and disconnecting circuits susceptible to voltage damage. If the circuit oscillated, it suggested that the oscillation conditions were generally met, shifting our focus to the voltage stabilizing branch for further investigation. If not, the issue lay within the oscillation circuit itself.

Findings and Repairs:

  • Machine A: All four branches and 3844B peripherals checked out normal. Replacing the 3844B with a 3845B restored power output.
  • Machine B: Despite replacing the IC with a 3845B, oscillation failed to initiate. All branch components appeared normal. However, paralleling a 200k resistor with the existing 300k resistor in the power-on start branch resolved the issue, indicating a subtle performance shift in one or more components affecting electrical parameters.
  • Machine C: The fault was traced to the 3844B IC, and replacing it resolved the issue.

Analysis of Machine B’s Unique Fault:
Machine B’s fault was particularly intriguing. No obvious defective parts were found, yet it failed to oscillate until the starting branch’s resistance was adjusted. This suggests minor changes in component performance, such as reduced switching tube amplification, moisture-affected transformer Q values, increased 3844B output resistance, or slight variations in resistance/capacitance components. Identifying these precise causes can be challenging, but they all lead to one outcome: ineffective switch tube activation. Adjusting the starting branch’s resistance proved to be an effective solution, highlighting the importance of adequate starting current for circuit oscillation.

Conclusion and Recommendations:
Based on our experience, an efficient repair strategy for similar issues involves:

  1. Verifying the switch tube’s integrity and the general functionality of the four branches.
  2. Conducting a parallel resistance test on the starting branch.
  3. If unsuccessful, replacing the 3844B IC.
  4. If issues persist, conducting a thorough circuit inspection.

Often, issues are resolved during the initial tests, emphasizing the importance of a systematic approach to troubleshooting. Additionally, considering the role of starting current in circuit oscillation, adjusting the starting branch’s resistance may offer a simple yet effective solution in many cases.

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Repair Guide for INVT G9 Series Frequency Converter “Crash” Fault

Repair Guide for INVT G9 Series Frequency Converter “Crash” Fault

When dealing with a reported “crash” fault in an INVT G9 series frequency converter, a systematic approach to diagnosis and repair is crucial. This article outlines a step-by-step process based on user feedback, detailed inspection, and successful repair.

INVT INVERTER physical picture

User Feedback and Initial Observations

The user reported that the frequency converter was not operational at the time of the incident, but other machines on the same three-phase power supply experienced abnormalities, leading to a short circuit and tripping. Consequently, the power switch for the frequency converter also tripped. Upon attempting to reset the power switch, it was discovered that the operation panel was no longer displaying any information, prompting the need for repair.

Detailed Inspection and Fault Identification

Upon inspecting the frequency converter, an open circuit was found between the R, S, T terminals and the main DC circuit (P and N). Further disassembly revealed that the copper foil strip connecting to the module had been damaged by an arc. Testing confirmed a short circuit at the three-phase power supply terminal of the module.

Root Cause Analysis

The root cause of the malfunction was traced back to instantaneous short circuits and tripping of other load branches in the power supply, which induced abnormal voltage spikes in the three-phase power supply. These dangerous voltage levels caused the rectifier circuit in the frequency converter module to break down and short circuit. The resulting strong arc burned the copper foil strip and triggered the power switch to trip.

Repair Plan

INVT inverter drive board

Fortunately, the inverter part of the module was still functional, with no signs of bulging or deformation. Therefore, the decision was made to cut off the damaged rectification part of the module and install an additional three-phase rectification bridge. This low-cost repair plan allowed for the reuse of the original three-phase inverter circuit in the module.

Inspection and Troubleshooting

To prevent further abnormalities, the power supply to the inverter section of the module was cut off. A 500V DC voltage was applied from an external repair power supply, but the operation panel displayed “H.00,” and all operations were ineffective. Based on experience, this indicated that the module’s short circuit detection function had activated, causing the CPU to reject all operations.

Further inspection revealed that the overcurrent signals in the fault signal collection and processing circuit were all negative, whereas they should have been positive under normal conditions. Tracing the current detection circuit, it was found that an incorrect overcurrent signal was being output. By disconnecting the overcurrent fault signal, the operation panel’s parameter settings returned to normal, but the start/stop operation still had no response.

Additional Fault Signals and Resolution

Suspecting that there might be other fault signals causing the frequency converter to remain in protection mode, the voltage at the module’s thermal alarm terminal was measured and found to be 3V, lower than the normal 5V. It was hypothesized that the damaged rectification circuit might be outputting a thermal alarm signal. By cutting off the copper foil strip connected to the thermal alarm, the start/stop operation on the operation panel became effective.

Protection Sequence and Final Repairs

The protection sequence of the INVT G9/P9 frequency converter is designed to ensure safe operation. If a fault is detected in the power inverter output section during power-on detection, the SC – output short circuit fault code will be displayed, and all operations will be rejected. Similarly, if an overcurrent signal is detected, “H.00” will be displayed, and all operations will be halted. When a thermal alarm signal is detected, most operations can be performed, but the startup operation is rejected to prevent overheating.

To complete the repair, the damaged copper foil strip lead of the three-phase power supply was cut off, cleaned, and properly insulated. An external three-phase rectifier circuit was connected, and its DC output was introduced to the P and N terminals. Additionally, a thermal protection circuit was installed using a 60℃ normally closed thermal relay, which is connected in series with an NPN type transistor base to the 5V ground circuit. This ensures that the module does not overheat and burn, providing an additional layer of safety.

By following this structured approach, the INVT G9 series frequency converter was successfully repaired, restoring it to full functionality.

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Handling Method for SC Jumping Fault of GS Series INVT VSD

SC: Refers to a short circuit in the output load of the frequency converter. In the state of power outage, there is no short circuit between U, V, W and between U, V, W and DC P, N. To distinguish whether it is a current detection circuit fault on the CPU motherboard or a signal returned by the driving IC, short circuit the signal to the diode side of the optocoupler device with a wire, and operate the RUN key after power on. The output frequency displayed on the panel is normal. The SC signal is returned by the driving IC, and there are two reasons for the malfunction: first, the inverter module is damaged, and second, the driving IC itself is faulty.

After cutting off the power supply to the inverter module, the six pulse signals of the drive IC were checked again. It was found that the U-upper arm drive IC had input pulses but no output pulses (static negative pressure normal). After replacing the drive IC, the output was normal. The static negative pressure of the U lower arm drive IC is only a few tenths of a volt. After replacement, the fault still persists. After welding the 100 ohm resistor connected to the trigger end of the inverter module, the static negative pressure rises to the normal value. The forward resistance of the lower arm terminal of the module U is consistent with the resistance of other trigger terminals, but its reverse resistance is slightly smaller than that of other trigger terminals, indicating that the circuit inside the U-phase trigger terminal of the module is damaged!
This is a key point in checking module faults: the resistance of the main terminal cannot be roughly measured to be normal, which means that the module is good. It is not uncommon for the circuit inside the triggering terminal to be damaged, but it is more concealed! When the frequency converter reports an SC or OC fault and the main terminal of the detection module is normal, the inspection of the forward and reverse resistance of the triggering terminal should not be missed!
The damage of modules and the damage of driving ICs are usually related: when the U-phase main circuit is damaged, the upper and lower arm driving ICs of the U-phase are often also damaged by strong voltage shocks; When the driver IC of the phase is found to be damaged, it often hides the internal circuit damage of the triggering terminal of the phase. So one of the two is that a comprehensive inspection must be conducted. Of course, there are also cases where modules and driver ICs are damaged separately, but it is extremely rare.

During maintenance, another phenomenon of drive IC failure was also discovered in the low-power model of the Envision GS: when the frequency converter is powered on and there is an SC fault signal output, the CPU performs self check, reset, and reset, and after clearing, the panel only displays H:00, and all panel buttons fail to operate. When the corresponding optocoupler circuit is short circuited to eliminate the SC signal, all panel operations are normal. If the model detects an SC fault signal output when powered on, it may perform a “program lock” and refuse to operate! When this phenomenon occurs, the fault signal output circuit should be checked and corresponding measures should be taken to temporarily eliminate the fault signal, in order to facilitate operation and judgment, and thus solve the fault.

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Special situation of Alpha VFD tripping OC fault

Generally speaking, there are two sources of OC faults:

  1. When the operating current of the inverter module is too high, reaching more than three times the rated current, and the voltage drop of the IGBT tube rises to more than 7V, the driving IC returns an overload OC signal to notify the CPU and implement fast shutdown protection;
  2. After collecting a sharp increase in abnormal current from three current transformers at the output end of the frequency converter (some low-power models use two), a voltage comparator (or internal circuit of the CPU) outputs an OC signal to notify the CPU and implement fast shutdown protection.

Of course, when the driving IC or current sampling circuit is abnormal, the frequency converter will falsely report an OC fault.
Small power models often use a shunt resistor directly connected in series at the output end to collect current signals. After being amplified in the front stage, they are isolated by an optocoupler operational amplifier and transmitted to the CPU. The power supply of its preamplifier is taken from the floating power supply of the driving IC. In this way, when the module is damaged (or removed), the power supply branch connected to the inverter module is broken, causing the current sampling circuit to output the highest negative pressure. The CPU mistakenly believes that there is a large current signal and reports an OC fault. In this situation, the frequency converter trips the OC fault as soon as it is powered on, making it impossible to inspect whether the drive IC circuit can output six normal trigger pulses.
In addition, if the peripheral circuit of the driving IC is abnormal or damaged, it can also misreport OC faults. Therefore, during maintenance, it is necessary to distinguish whether it is a fault reported by the current sampling circuit or the driving IC, whether it is a circuit damage misreport or a module damage. Is there really an overcurrent fault? And take measures to clear the alarm status for easy maintenance.
But the OC jumping faults caused by the following reasons often go unnoticed. Overhaul an Alpha frequency converter. Due to damage to the main DC circuit voltage detection circuit, the voltage on terminal 8 was 0 (normally around 3V). The frequency converter experienced an undervoltage fault and could not be put into operation. When the terminal is artificially fed with a voltage of+5V, the frequency converter trips the OC fault when powered on. Through experiments, it has been proven that when the voltage is below 2.5V, an undervoltage fault code will trip, and when the voltage is above 3.8V, an OC fault will trip. Therefore, it is found that when the DC circuit voltage is too high or the DC detection circuit is abnormal, it is another reason for the frequency converter to trip the OC fault.

When conducting maintenance or emergency response, take 5V voltage from the 8 pins of the wiring block CN1 and fix a 3V voltage with a divider resistor. This will facilitate maintenance or emergency operation of the frequency converter.

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A Hidden Cause of Alpha Inverter OC Fault Tripping and Shutdown

During the maintenance of the Alpha low-power inverter, it was discovered that the inverter has a common problem – it is prone to OC failure. It manifests as: often jumping faults during start and stop operations, but sometimes also jumping faults during operation; Sometimes it inexplicably improves and can run for varying lengths of time. When I thought there was no problem, I started to frequently skip OC faults again; When measuring the output voltage of U, V, and W with a probe under no load, it is prone to tripping faults. However, after connecting the motor, it starts running and does not jump again. After a while, the OC fault still jumps when connecting the motor.

The handling of such faults is quite tricky, and it is possible that the fault has been eliminated during the testing process, resulting in no evidence for investigation. Even when testing the hardware circuit (protection circuit) during frequent malfunctions, I couldn’t find any problems and couldn’t figure out the root cause of the problem. This problem puzzled me for over two months.
The hardware protection circuit is mainly completed by two LM393 dual operational amplifier circuits, U22 and U24. The signal is then inverted by a first stage inverter and sent to pin 16 of the CPU. U22 and U24 jointly input two output current signals, one overload OC signal returned by the inverter drive IC, and one DC voltage detection signal, which are respectively added to the input terminals of four operational amplifiers. After open-loop amplification processing (the operational amplifier circuit is actually used as a switch circuit here), Four fault signals were connected in parallel, and after undergoing a first level of phase inversion processing, they were sent to pin 16 of the CPU. I first cut off the overload OC signal returned by the inverter drive IC, and then cut off the “total” fault signal of the inverter output, but both were ineffective, and the fault phenomenon still persists. Is there another way to string in OC signals elsewhere? Impossible!
There may be some inexplicable interference in the circuit, but the source and cause of the interference are difficult to identify. We racked our brains and exhausted all means to install capacitor and resistor filtering elements in the fault signal circuit to improve the anti-interference performance of the circuit, but to no avail. Could it be that during the loading and unloading process of the inverter drive module during the start/stop moment, the fluctuation of CPU power supply caused the malfunction? The measured CPU power supply is 4.98V, which is very stable and meets the requirements.
Without any reason, I had a sudden inspiration and adjusted 4.98V to 5.02V. After conducting a start/stop test, the fault was surprisingly eliminated!
Analyze and speculate the cause of the malfunction as follows: the setting of the static voltage working point outside or inside the CPU is improper or too low, which is exactly at the critical point of signal interference level, making it easy to experience random OC faults that are confusing. After slightly increasing its 5V power supply, the voltage value at its operating point also increases accordingly, avoiding the critical point of interference level, and the frequency converter changes from “neural” to “normal”.

When the machine leaves the factory, if the CPU power supply adjustment value is slightly higher, the machine can run normally for a long time. If the adjustment value is slightly lower, or if there is a slight decrease in 5V due to some reason (such as component variation, temperature drift, etc.) during use, frequent OC tripping faults may occur. Adjusting the 5V power supply can easily solve the problem while ensuring that there are no issues with the hardware protection circuit. If it is not due to an accidental factor, then the depth of the concealment of this fault makes it difficult to “adjust” it properly.

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Repairing Two Delta VFD-A Frequency Converters: A Detailed Guide

In the realm of industrial equipment maintenance, frequency converters play a crucial role in controlling motor speed and efficiency. Recently, I encountered two Delta VFD-A frequency converters that required extensive repairs due to severe damage in their output modules and driving circuits. This article documents the step-by-step process of diagnosing, repairing, and testing these converters, highlighting key lessons learned.

Initial Inspection and Diagnosis

Upon receiving the two converters, a thorough inspection revealed significant damage: the output modules were compromised, and the driving circuits were in poor condition. Specifically, the T250V driving integrated circuits were either exploded or short-circuited to the power supply ground. Additionally, filtering capacitors had leaked, voltage regulator tubes were broken, resistors were open or had increased resistance, and the circuit boards were carbonized.

Further inspection of one converter revealed a broken arm in the three-phase rectifier bridge, along with a damaged charging current limiting resistor. The charging resistor was short-circuited, and the relay contacts were stuck, leading to severe damage. Several signal introduction resistors on the input side of the driving integrated circuit were also open, indicating that the CPU had likely suffered a strong electrical shock.

Circuit Analysis and Component Replacement

With the main circuit and driver circuit diagrams in hand, I began a comprehensive inspection. Using a small knife, I scraped off the carbonized parts of the circuit board and removed all damaged components. After ensuring there were no short circuits in the main circuit, I powered on the converter for a preliminary inspection. The display was normal, indicating that the switch power supply and control section were functioning.

An oscilloscope measurement of the six driver inputs (trigger signals from the CPU) revealed a peak voltage of 1.5V and a carrier frequency of 10kHz, which varied with frequency and pulse width. This confirmed that, apart from the damaged inverter and drive circuits, all other circuits were operational. The CPU’s three-phase pulse output terminal had withstood the electrical shock remarkably well.

I immediately procured the necessary replacement parts and began the repair process. Over 30 components in the driver circuit were replaced, and I tested the static DC voltage of each pin of the driver integrated circuit upon powering on. All measurements were within normal ranges. An oscilloscope was then used to measure the output waveforms of each integrated circuit, which were also within normal limits. With these repairs complete, I proceeded to weld the inverter output module.

Testing and Further Issues

Upon powering on the repaired converter for testing, I noticed a three-phase imbalance using a multimeter. Switching to the DC 500V range revealed no DC component between V and W, but there was DC voltage between U and V, as well as U and W. This indicated an issue with the U-phase output.

Further inspection revealed that the voltage regulator diode DD11 in the EU circuit’s triggered power supply was damaged. After replacing it with a regular component (the original SMD component had weak bonding), I accidentally desoldered it during the installation of the inverter module. This caused the triggering end of the upper transistor in the U-phase to be forced to a low level, resulting in only the negative half-wave output of the lower transistor being conductive.

I re-soldered DD11 and tested the machine again. The three-phase output was balanced, and there was no DC component. A 5.5kW submersible pump was connected for further testing, and both startup and operation were normal. The first frequency converter was successfully repaired.

Lessons Learned and Second Converter Repair

When repairing the second converter, I followed the same cleaning and repair steps as the first. However, after welding the inverter module and connecting three light bulbs for testing, I encountered a problem. Upon momentarily short-circuiting the control terminals DCM and FWD to initiate forward starting, I heard a “snap” sound – the newly replaced inverter output module had instantly exploded and damaged.

Upon investigation, I realized that I had forgotten to solder two output pulse introduction resistors on the back of the circuit board. This oversight caused the inverter module to be damaged due to the instantaneous and painless reverse output. It is crucial to thoroughly check all trigger terminal connections before conducting power tests to avoid such costly mistakes.

Mechanism of Damage

The damage to the inverter module was caused by short-circuit breakdown and explosion, resulting from overcurrent rather than overvoltage. Even when unloaded, the simultaneous conduction of two IGBT tubes in the inverter circuit can lead to a short circuit and subsequent module damage. This highlights the importance of ensuring that all trigger terminal leads are securely connected before powering on the converter.

Conclusion

Repairing these two Delta VFD-A frequency converters was a challenging but rewarding experience. It underscored the importance of thorough inspections, meticulous repairs, and rigorous testing. By documenting this process, I hope to provide valuable insights for others facing similar repair challenges in the future.

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n-depth Analysis and Maintenance Guide for Mitsubishi F1S Switching Power Supply

In-depth Analysis and Maintenance Guide for Mitsubishi F1S Switching Power Supply

In the field of modern industrial automation, the application of Mitsubishi PLCs (Programmable Logic Controllers) is extensive. As a critical component of PLCs, the stability and reliability of the switching power supply directly determine the operating efficiency of the entire system. This article takes the Mitsubishi F1S switching power supply as an example, deeply analyzing its circuit structure, working principle, and maintenance methods. The aim is to provide readers with a comprehensive and practical technical guide.

I. Overview of Circuit Structure

The Mitsubishi F1S switching power supply board is designed intricately, featuring two relatively independent 24V output structures (although somewhat isolated by L2, they can still be considered as two separate outputs). These two outputs not only provide stable 5V power supply for the PLC motherboard but also offer DC24V external control power for external measurement instruments and other devices. The power board is tightly connected to the motherboard through copper needle-shaped rigid wires, ensuring stable signal transmission.

II. Detailed Explanation of Working Principle

  1. Input Filtering and Protection: After entering the power board through the L and N terminals of the PLC, the industrial frequency 220V power first passes through a bidirectional low-pass filter network composed of C1, C2, C4, and L1. This design effectively filters out high-frequency interference and improves the purity of the power supply. Meanwhile, the bidirectional filters L1 and L2 further isolate high-frequency interference pulses from both inside and outside the power supply, ensuring stable system operation. F1 serves as an overload protection fast-acting fuse, while TH1 acts as a temperature fuse, together constituting a dual protection mechanism for the power supply.
  2. Rectification and Oscillation: The filtered AC power passes through F1 and TH1 into the full-wave rectification circuit, where it is rectified to obtain a direct current voltage of approximately 280V. This voltage is sent to the oscillation and voltage-stabilizing circuit centered on STRG6551. STRG6551 is a power oscillation module with an integrated switching tube. Its 4 and 3 pins are the power supply terminals, while 1 and 2 pins are internally connected to the source and drain of the power switching tube. Additionally, pin 2 provides negative feedback for the switching operating current. Pin 5 is the feedback voltage input terminal, used to regulate the stability of the output voltage.
  3. Voltage Stabilization and Protection: The voltage induced by the secondary winding of the switching transformer TB1 undergoes rectification and filtering before serving as the working power for the PLC. To maintain voltage stability, the system employs an output voltage sampling circuit composed of R9, IC2, PC1, and other components. When the voltage changes, this change is converted into a variation in the input current on the PC1 optocoupler device, which is then fed into pin 5 of STRG6551 through R4. The comparison amplification circuit inside STRG6551 adjusts the conduction/cutoff time of the switching tube, i.e., controls the duty cycle of the oscillation frequency, to achieve stable output voltage.

Furthermore, the system boasts a comprehensive protection mechanism. When an abnormal load causes a sharp increase in current, the voltage variation across the sampling resistor R2 is introduced into pin 5 of STRG6551, reducing the output voltage to decrease the load current. When the voltage or current anomaly reaches a certain threshold, STRG6551 disconnects the driving circuit of the switching tube, causing the circuit to oscillate and protecting the subsequent circuit from damage.

III. Maintenance Methods and Practices

Faced with potential faults in the Mitsubishi F1S switching power supply, reasonable troubleshooting steps and scientific maintenance methods are crucial for improving maintenance efficiency. Here are some common maintenance methods:

  1. Routine Inspection: First, check whether the F1 and TH1 fuses are blown. If they are blown and there are no abnormal short-circuit points in the switching tube and load circuit, replacing the fuses generally resolves the issue. If the power still does not oscillate after replacing the fuses, further investigation is needed.
  2. Identify Fault Circuits: Disconnect the PLC motherboard, use a voltage regulator to adjust the input voltage to below AC100V, and connect a dummy load (such as a 100Ω 5W resistor). Short-circuit pins 1 and 2 of the PC1 optocoupler to make the voltage feedback signal zero. Power on and observe the power output. If there is output but not at a stable voltage, the fault lies in the voltage-stabilizing circuit; if there is no output, the fault is in the oscillation circuit.

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Principle of Frequency Converter (VFD)

A frequency converter, as the name suggests, is a device that can change the frequency. It is just an AC power supply that can adjust the frequency and voltage output, mainly used for speed regulation of asynchronous motors. Before the emergence of frequency converters, asynchronous motor speed regulation was very troublesome because the speed and torque were not in a straight line, such as using a slip head for speed regulation or simply reducing voltage for speed regulation, which had unsatisfactory results. According to the speed formula of a three-phase asynchronous motor, the speed n=60 * f/p (1-s), where p is the logarithm of poles, s is the slip rate, and f is the frequency of the power supply. As long as a frequency controllable AC power supply can be output, the speed of the three-phase asynchronous motor can be smoothly changed, which is the fundamental principle of frequency converter operation.

However, the three-phase AC power supply provided by power plants is a sine wave with a difference of 120 ° and a frequency of 50Hz. Before the invention of power electronic devices, it was almost impossible to change the frequency of this power supply. Therefore, the invention of AC motors has been almost 100 years without a good speed control device.

Later, high-power devices such as thyristors, GTR transistors, and IGBT transistors were invented at the end of the last century, and the embedded technology of single-chip microcontrollers became increasingly mature. People found the basic method for asynchronous motor speed regulation. That is to first rectify the three-phase AC voltage into fluctuating DC through diodes or thyristors, and then use capacitors to filter and stabilize it into stable DC. Six IGBT tubes are used to form an inverter circuit. The microcontroller uses PWM chopping to output a series of variable pulse width square waves, which are used to simulate the equivalent effect of variable frequency AC and achieve the goal of controlling motor speed.

It can be imagined that any curve can use many straight line segments to segment and simulate links. The more straight line segments used for simulation, the more accurate the curve can be described. This is actually the concept of calculus in mathematics.

Although a sine wave may seem complex, it can also be simulated and equivalent using many square waves. If a square wave with equal amplitude and variable width is output, and the area of the square wave is equal to the corresponding sine wave area, its effect will be equivalent to the working effect of the sine wave. By controlling the working cycle, the frequency of the output power can be changed, which is called PWM control, Because IGBT switches can achieve very high-speed switching functions, such as having a frequency of tens of K, the output square waves are sufficient, and the simulated sine wave effect is relatively good.

However, changing the frequency of the motor light is not enough, and the voltage should also be adjusted accordingly, otherwise it may cause the motor to work abnormally, such as severe heating and burning. The main reason is that the iron core of the motor is nonlinear, requiring that the voltage also changes when the power frequency changes, in order to control the main magnetic flux to remain constant.
Because: main magnetic flux ≈ motor voltage ÷ (4.44 * frequency * number of electronic winding turns)
Therefore, during frequency modulation, the motor voltage should also change with the frequency, so that the main magnetic flux can remain unchanged and avoid magnetic flux saturation or working in a weak magnetic state.

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Testing Method for Offline Operation of Mitsubishi MR-J3 Servo Driver Maintenance Board

When repairing Mitsubishi servo drives, encountering damaged modules is common. After repairing such modules, it’s crucial to test the drive board’s output function offline before reinstallation. This article provides a detailed guide for testing a repaired Mitsubishi MR-J3-350A/3.5KW servo module.

Mitsubishi Servo MR-J3 Circuit Board Maintenance Test Diagram

Preparation for Offline Testing:

  1. Power Connection: Connect 300V DC voltage to power boards P2 and N to avoid E9 fault after power-on.
  2. Module Pad Hole Shielding:
    • Connect the 10 pins of the module pad hole to N.
    • Connect pad holes U, V, W to N to prevent AL24 fault.
    • Connect pad holes EV, EU, EW (upper axle drive trigger) to N.

Parameter Setting Before Running:

  1. Change PA01: Set PA01 to 0002.
  2. Change PD01: Set PD01 to 0000.
  3. Power Board Connection: Connect P and D on the power board.
  4. Additional Power Board Connections: Connect L1 to L11 and L2 to L12 on the power board.
    • If PD parameters are not visible, change PA19 to 000C and power on again.
Mitsubishi servo MR-J3 drive circuit actual pulse state

Testing Process:

  • After following the above steps, power on and run the servo to test its 6-way waveform.
  • During parameter waveform testing, manually rotate the motor shaft to observe changes in pulse width and phase in the waveform. Note that this machine does not have a static cut-off negative voltage.

By following this comprehensive guide, you can effectively test the offline operation of a repaired Mitsubishi MR-J3 servo driver maintenance board, ensuring its functionality before reinstallation.

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Method of changing IP and station name using BOP panel for Siemens VSD G120 series

The Siemens G120 series frequency converters basically support communication control, such as Profibus and profinet protocols. When it comes to modifying addresses and station names, they are usually rewritten using software such as TIA and STARTER, or modified through the super panel IOP-2. However, the manual does not mention how to modify these parameters through the BOP panel. After practical exploration, I found that the BOP panel can also modify these parameters, The method is as follows:

1、 The G120C PN type frequency converter uses profinet communication, but it can be started, stopped, and adjusted using the manual function (HAND/AUTO) of the panel, which can directly determine the quality of the frequency converter without passing through the network.

3、 P3 is set to 4 first, and the station name P8920 can also be configured using a simple panel like BOP-2, but the following cannot be configured:
P8921—— r8931 IP Address
P8922—— r8932 Default gateway
P8923- r8933 subnet mask
P8924—— r8934 DHPC mode

4、 In practical use, it was found that as long as the station name P8920 (with a total of 240 subscripts, corresponding to a maximum of 240 values) is set, such as IND [000], IND [001], IND [002]… IND [239] is actually an ASII value, it can be connected to the profinet. The P8921-P8924 on the top should not be ignored, and the upper level should have the opportunity to assign them additional values.

5、 Method for changing P8920 parameters in BOP-2
A. P8920=0, all its subscripts ind [000] [001] [002] until the corresponding value of [239] must be set to 0. Remember to press the OK key every time you modify one;
B. P8925=3, press the OK key to delete all IP configurations;
C. Power off the frequency converter for at least 20 seconds;
D. Power on again and re-enter the corresponding station name value (ASII) in P8920, [000] – [239], usually using 8.
E. P8925=2, power off for more than 20 seconds;

6、 BOP-2 can directly upload data other than the station name P8920-P892, such as motor current and power, and then download it to a new frequency converter. However, the parameters of P8920 can only be manually inputted according to the above process. Remember to set p971=1 after debugging and save the parameters (automatically changing to 0 after successful saving), otherwise the parameters will be lost after power outage.