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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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.