Year: 2024

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Global Variable Frequency Drive (VFD) repair center

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

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

European and American Brands

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

Japanese Brands:

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

Taiwanese Brands:

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

Chinese Mainland brands:

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

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

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

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

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

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Debugging of ABB VFD for ACS800 Enhancement

A. Motor Auto-tuning (Quick Debugging Steps)

  1. Power On: Ensure the system is powered on.
  2. Input Initialization:
    • Press PAR to select the language. Set 99.1 to ENGLISH.
    • Choose the application macro. Set 99.2 to CRANE.
    • Determine if parameters should be reset to factory defaults. Set 99.3 to YES or NO.
    • Select the motor control mode in 99.4: DTC (Direct Torque Control) or SCALAR.
    • Enter the rated voltage in 99.5 V.
    • Input the rated current in 99.6 A.
    • Specify the rated frequency in 99.7 HZ.
    • Set the motor’s rated speed in 99.8 RPM.
    • Define the motor’s rated power in 99.9 KW.
  3. Motor Identification Run:
    • Proceed to motor identification by selecting 99.10.
    • Generally, choose ID MAGN (the motor won’t rotate).
    • For STANDARD mode (motor rotates), the motor must be disconnected from the equipment.
    • In REDUCED identification mode (motor rotates), the motor remains connected.
    • After selecting the identification mode, a “WARNING” signal may appear.
    • Press the start button to begin motor identification. This process can be stopped at any time using the stop button.
    • Once the motor identification is complete, press RESET to enter actual signal display mode.
  4. Motor Direction Check: Verify the motor’s rotation direction using the control panel.
  5. Input Speed Limits and Acceleration/Deceleration Times: Enter the necessary parameters.

B. Parameter Configuration – Optimized for Google SEO

  1. Set parameter 10.1 to DI1 for brake acknowledgment digital input.
  2. Leave parameter 10.2 as NOT SEL for zero-position digital input.
  3. Parameter 10.3 remains NOT SEL for deceleration digital input.
  4. Parameter 10.4 is NOT SEL for rapid stop digital input.
  5. Parameter 10.5 is NOT SEL for power-on acknowledgment digital input.
  6. Keep parameter 10.6 as NOT SEL for synchronization request digital input.
  7. Set parameter 10.7 to EXT DI1.1 for chopper fault digital input.
  8. Configure parameter 10.8 to DI2 for the second speed level digital input.
  9. Set parameter 10.9 to DI5 for the third speed level digital input.
  10. Parameter 10.10 is set to DI6 for the fourth speed level digital input.
  11. Parameters 10.11 to 10.15 and 10.17, 10.18 remain NOT SEL.
  12. Set parameter 10.16 to DI-1L for fault reset digital input.
  13. Parameter group 13 deals with analog input signals. No need for modification.
  14. Set parameter 14.1 to BRAKE LIFT for relay output 1.
  15. Configure parameter 14.2 to WATCHDOG-N for relay output 2.
  16. Parameter 14.3 is set for relay output 3 to indicate a FAULT-N signal. When a fault occurs, the relay releases, and during power-on, the fault relay engages.
  17. Parameter group 15 covers analog output signals. No modifications required.
  18. Parameter group 16 deals with password settings. No need to change.
  19. Parameter group 20 defines limit values:
    • Parameter 20.1: Minimum speed for the operating range.
    • Parameter 20.2: Maximum speed for the operating range.
    • Parameter 20.3: Maximum output current.
    • Parameter 20.4: Maximum positive output torque.
    • Parameter 20.5: Maximum negative output torque.
    • Parameter 20.6: DC overvoltage controller.
    • Parameter 20.7: DC undervoltage controller.
    • Parameter 20.8: Minimum frequency for the operating range.
    • Parameter 20.9: Maximum frequency for the operating range.
    • Parameters 20.10 to 20.13 relate to analog inputs but are not detailed here.
  20. Parameter 21.1 is not to be changed.
  21. Set parameter 21.2 for the field excitation time, approximately 4 times the motor’s rated KW (in milliseconds).
  22. Parameter group 23 covers speed control gains, integral and derivative times, motor slip, etc. Generally left unchanged.
  23. Parameter group 24 deals with torque build-up time. Typically not modified.
  24. Parameter group 26 allows compensation voltage setting for the motor (only in SCALAR mode).
  25. Parameter group 27 configures the braking chopper:
    • Set parameter 27.1 to ON for brake chopper control.
    • Parameter 27.2 is set to FAULT to activate overload protection for the braking resistor.
    • Enter the actual value for the braking resistor in parameter 27.3.
    • Set the time constant for the braking resistor in parameter 27.4 to 300S.
    • Define the maximum continuous braking power for the resistor in parameter 27.5.
    • Set the control mode for the brake chopper control to AS GENERATOR in parameter 27.6.
  26. Parameter group 28 deals with motor modeling. Typically not modified.
  27. Parameter group 30 covers fault functions. Generally left unchanged.
  28. Parameter group 50 configures encoder values:
    • Set the number of encoder pulses in parameter 50.1.
    • Define the calculation method for encoder pulses in parameter 50.2.
    • Parameter 50.3 is set to FAULT for encoder fault action.
    • Set the encoder monitoring delay time in parameter 50.4 (avoid setting to 0).
    • Parameter 50.5 determines the encoder feedback usage, typically set to TRUE.
  29. Parameter group 60 handles the switch between local and external operation.
  30. Parameter groups 61 and 62 deal with speed monitoring. Generally not modified.
  31. Parameter group 63 covers torque monitoring. Typically left unchanged.
  32. Parameter group 64 is for crane mode:
    • Set parameter 64.1 to TRUE for STAND ALONE mode.
    • Parameter 64.10 is configured to STEPJOYST or STEPRADIO.
    • Parameters 64.13 to 64.16 define the speeds for the four speed levels (as a percentage of rated speed).
  33. Parameter group 65 deals with motor field current settings. Generally not modified.
  34. Parameter group 66 covers torque verification, typically left unchanged.
  35. Parameter group 67 configures brake control:
    • Set the brake application time to 0.5S in parameter 67.1.
    • Define the brake fault delay as 0.5S in parameter 67.2.
    • Parameters 67.3 to 67.10 are not detailed but can be set as needed.
  36. Parameter group 68 is for power optimization, typically not modified.
  37. Parameter group 69 defines the maximum speed and acceleration/deceleration times.
  38. Parameter group 98 activates optional modules.
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ACS800 Variable Speed Drive (VSD) Debugging Steps

I. Basic Local Control Process for ACS800 VSD

Ensure that the air switch is closed and the contactor is energized.
Press the LOC/REM key to switch to local control mode.
Press the FAR key to enter the parameter setting interface. Use the double arrow keys to navigate to the 99 parameter group, then use the single arrow keys to select item 04. Press ENTER to confirm. Here, you can choose between DTC mode (suitable for most cases) or SCALA mode. After selecting, press ENTER to save or ACT to exit.
Press the ACT key to return to the main operation interface.
Press the REF key, use the up/down arrow keys to input the desired parameter value, and then press ENTER to confirm.
Press the start key to begin operating the VSD.
To replace the displayed actual signal, follow these steps:
a. Press the ACT key to enter signal display mode.
b. Select the row you want to change and press ENTER.
c. Use the arrow keys to browse and select a new signal (such as actual motor speed – SPEED, transmission output frequency – FREQ, etc.).
d. Press ENTER to confirm the change or ACT to exit.

II. Data Upload and Download Operations

To upload set motor parameters to the CDP-312 panel:

Verify that item 98.02 is set to FIELDBUS and item 98.07 is set to ABB DRIVES.
Switch to local control mode (LOC).
Press the FUNC key to access the function menu.
Use the arrow keys to navigate to the UPLOAD function and press ENTER to execute the upload.
If you need to move the control panel, ensure it is in remote control mode first.
To download data from the control panel to the drive unit:

Connect the control panel containing the uploaded data.
Ensure you are currently in local control mode.
Press the FUNC key to access the function menu.
Navigate to the DOWNLOAD function and press ENTER to execute the download.
III. Achieving PLC and VSD PROFIBUS-DP Communication

After confirming that the communication module is installed and the DP network cable is correctly connected, follow these steps to set the parameters:

In local mode, use FAR and the arrow keys to enter parameter settings.
Set 98.02 to FIELDBUS to activate the RPBA-01 communication module.
Set 98.07 to ABB DRIVES to determine the communication protocol.
Configure items 10.01, 10.02, and 10.03 as needed to define the external control source.
Set 16.01 to YES to allow operation.
Select the fault reset signal source for 16.04.
From 11.01 to 11.08, set the source of the control word and given value.
In items 22.01 to 22.03, define acceleration/deceleration time and stop function.
For the 51 group of parameters, configure according to the fieldbus adapter module’s settings.
Adjust the actual signal transmission content in the 92 group as needed.
IV. Additional Parameter Setting Reference (Not Currently Used)

This section provides guidance on setting speed limits, protection functions, and parameter locking for future reference.

Note: Before making any parameter changes, ensure you fully understand their impact and consult a professional if necessary.

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How to adjust the power rating of ABB’s ACS510/ACS550/ACS350/ACS355/ACH550 VFDs

With ABB’s ACS510/ACS550/ACS350/ACS355 VFDs, you can easily adjust the power rating through a straightforward process. Whether you want to upgrade a 1.1KW VFD to 5.5KW or vice versa, this flexibility allows you to set the power rating according to your needs. This feature is particularly useful when you have a limited number of VFD main boards, such as SMIO-01C, and need to adapt them to different power ranges. With this adjustment, you can ensure seamless operation even if a VFD in a different power range fails. These are not mentioned in the ABB AC drives PDF manual

  1. How to access and modify parameters:
    Open the parameter table, navigate to the deepest level of parameters, such as 0102, or any other displayed parameters. For example, if it says 9905, then hold the UP (arrow up), DOWN (arrow down), and RETURN (the button on the upper left next to LOC) buttons simultaneously for 3 seconds. You will notice a flash on the screen, and the top line of the screen should show “PARAMETERS+”.
  2. Expanding parameter groups:
    After that, exit and re-enter the parameter groups. Now, you will notice that the number of parameter groups has expanded from the original 99 to a maximum of 120. Navigate to parameter group 105.
  3. Modifying power capacity:
    To modify the relevant power capacity, follow these steps:
    • Find and modify parameter 10509. Change 105.09 to the desired current value and modify the corresponding power value accordingly (make sure it matches theVFD label. For example, if your inverter model is ACS510-01-017A-4, change it to 0174H; for ACS510-01-031A-4, change it to 0314H).
    • Set 10502 to 1 and confirm.
    • Set 10511 to 4012 and confirm.
    Please note that the order of modifications is crucial. If you make a mistake, you may need to start over.
  4. Verifying parameter changes:
    Finally, re-enter the parameter table and check if parameter 3304 (transmission capacity) has been correctly modified.
    To improve SEO performance, here are the optimized suggestions for the above text:

How to access and modify parameters:
Open the parameter table, navigate to the deepest level of parameters, such as 0102, or any other displayed parameters. For example, if it says 9905, then hold the UP (arrow up), DOWN (arrow down), and RETURN (the button on the upper left next to LOC) buttons simultaneously for 3 seconds. You will notice a flash on the screen, and the top line of the screen should show “PARAMETERS+”.

Expanding parameter groups:
After that, exit and re-enter the parameter groups. Now, you will notice that the number of parameter groups has expanded from the original 99 to a maximum of 120. Navigate to parameter group 105.

Modifying power capacity:
To modify the relevant power capacity, follow these steps:

Find and modify parameter 10509. Change 105.09 to the desired current value and modify the corresponding power value accordingly (make sure it matches the VFD label. For example, if your inverter model is ACS510-01-017A-4, change it to 0174H; for ACS510-01-031A-4, change it to 0314H).
Set 10502 to 1 and confirm.
Set 10511 to 4012 and confirm.
Please note that the order of modifications is crucial. If you make a mistake, you may need to start over.

Verifying parameter changes:
Finally, re-enter the parameter table and check if parameter 3304 (transmission capacity) has been correctly modified.

Just a reminder, the process of changing the power above has only been changed to the power of the ABB drive motherboard(SMIO-01C). The power of the drive board has not been changed, although it shows that it can be expanded. In fact, if the power of the power board has not been changed, the actual output power of the variable frequency drive (VFD) has not changed. At the same time, this method is only applicable to ACS510/ACS550/ACS350/ACS355/ACH550 VFDs and is not suitable for ACS800 series inverters. If you would like to know the power modification method for ACS800 inverters, please contact us directly.

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The circuit principle and modification and exchange method of frequency inverter transformer

The current transformers used in frequency inverter circuits, except for a few early products that used traditional transformers wound with through core inductor coils, are often integrated sealed current transformers made of Hall elements and pre current detection circuits (let’s call them electronic current transformers) in mature circuits. They are divided into standard and non-standard types, and the standard type uses specialized molded products in the market. For example, a 10A/1V current transformer generates a 1V signal voltage output for every 10A current in the circuit. Non standard type, designed and customized by the frequency converter manufacturer, cannot be used interchangeably. When damaged, it is generally necessary to replace the same model product provided by the original manufacturer. Of course, with deeper maintenance efforts, different models of current transformers can also be used for emergency repair or improvement, and later replaced.
Electronic current transformers often use some type of sealant for curing, which can cause damage and cannot be restored once removed. What kind of circuits are inside and whether they can be repaired or replaced, causing a lot of speculation. When I was repairing a Fuji frequency inverter, I replaced it with the main board of the TECO frequency inverter. When it was necessary to adjust the A/V ratio of the electronic current transformer, it had to be adjusted by the internal circuit of the transformer. Only then did I make up my mind and use a knife, a saw, and a lot of effort to dissect and map the internal circuits of the current transformers of these three types of frequency inverters. It was hard won.

An electronic current transformer is actually a circuit for a current/voltage converter. The Taian 7.5kW inverter current transformer circuit has a certain representativeness. The main body of the current transformer is also a circular hollow magnetic ring. The U, V, and W output lines of the frequency inverter pass through the iron core magnetic ring as the primary winding (small power models usually pass through multiple turns), and the magnetic ring generates magnetic field lines that vary in density with the output current of the frequency inverter. This magnetic ring has a gap in which a Hall element with four lead terminals is embedded. Hall elements are packaged in sheet form, and the magnetic field lines of the magnetic ring pass through the packaging end face of the Hall element, which is also known as the magnetic field line collection area (or magnetic induction surface). Hall elements convert changes in magnetic field lines into induced voltage outputs. The circuit consists of Hall elements and a precision dual operational amplifier circuit 4570. A constant current of mA (about 3-5mA) level must be added to the operation of the Hall element, and 4570A should be connected as a constant current source output mode to provide the mA level constant current required for the normal operation of the Hall element (the working current of the Hall element in this circuit is about 5.77 mA), which should be added to pins 4 and 2 of the Hall element; The induced voltage that varies with the output current at pins 1 and 3 of the Hall element is applied to the input terminals 2 and 3 of 4570b. Three pins are embedded in the reference voltage (zero potential point), and the change in input voltage of two pins is amplified and output by one pin (current detection signal). Electronic current transformers often have four terminal components, with two terminals supplying power to internal amplifiers of+15V and -15V, the other two terminals serving as signal output terminals, one terminal grounded, and one terminal serving as signal OUT terminal+ In addition to providing power for the dual operational amplifier IC4570, 15V and -15V are further stabilized by 6V to form a zero potential point introduced into the three pins of 4570. When the frequency converter is in a shutdown state, the ground measurement OUT point should be 0V. During operation, it will output an AC signal voltage below 4V in proportion to the output current.

After the electronic current transformer is damaged, it outputs a higher positive or negative DC voltage during static state (when the frequency inverter is shut down), which is mostly due to damage to the internal operational amplifier. Power on self-test of the frequency inverter, which displays a fault code (sometimes without a code in the manual), the frequency inverter will refuse to start or even parameter operation!
The current transformer circuit of TECO 3.7kW frequency converter uses a programmable operational amplifier chip. I have not yet found the model of this chip, but through modification tests, some characteristics of the circuit have been identified. According to the experiment, pin 2 is the constant current power supply terminal, pins 3 and 4 are the input terminals of the differential amplifier, and pin 13 is the signal output terminal. When short circuiting the solder gaps of pins 11, 12, and 13 step by step, the amplification factor shows a decreasing trend; When opening the circuit step by step, the amplification factor increases. This can adjust the amplification factor of the chip, making it easier to match frequency converters with different power outputs. I successfully applied the current transformer to a 45kW Fuji frequency Inverter by taking corresponding measures.
The voltage detection and current detection signals of the frequency converter may be applied by the program to control the output three-phase voltage and current – when the detection signal changes, the output three-phase voltage and current also change accordingly. When repairing or modifying the original circuit, be careful not to change the original circuit parameters. It is still recommended to use original accessories to repair the frequency converter while maintaining the original circuit form.

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Brake unit circuit diagram and repair ideas

When the speed of the load motor exceeds the output speed of the frequency inverter due to inertia or some other reason, the motor enters the “dynamic” state from the “electric” state, causing the motor to temporarily become a generator. The reverse generated energy of a load motor, also known as regenerative energy.

Some special machinery, such as mining elevators, winches, high-speed elevators, etc., when the electric motor decelerates, brakes, or lowers a heavy load (ordinary large inertia loads, deceleration and parking process), due to the potential energy and potential energy of the mechanical system, the actual speed of the frequency inverter can exceed the given speed of the frequency inverter. The phase of the induced current in the motor winding is ahead of the induced voltage, resulting in capacitive current, The diodes connected in parallel at both ends of the IGBT in the inverter circuit of the frequency converter and the energy storage capacitors in the DC circuit precisely provide a path for this capacitive current. The electric motor generates excitation electromotive force due to capacitive excitation current, which self excites and generates electricity, returning energy to the power supply. This is the process by which an electric motor converts mechanical potential energy into electrical energy and feeds it back to the power grid.

This regenerative energy is rectified by diodes parallel to the inverter circuit of the frequency inverter and fed into the DC circuit of the frequency converter, causing the voltage of the DC circuit to rise from around 530V to 600-700V or even higher. Especially during the process of decelerating and stopping under high inertia loads, it occurs more frequently. This sharp increase in voltage may cause significant voltage and current surges or even damage to the energy storage capacitor and inverter module of the inverter main circuit. Therefore, the braking unit and braking resistor (also known as the braking unit and braking resistor) are often essential components or preferred auxiliary components of the frequency converter. In low-power frequency converters, the braking unit is often integrated into the power module, and the braking resistor is also installed inside the body. But for high-power frequency converters, braking units and braking resistors are selected according to the load operation situation. The CDBR-4030C braking unit is one of the auxiliary configurations of the frequency inverter.

Regardless of the specific circuit, we can first imagine it from the control principle. The so-called braking unit is an electronic switch (IGBT module) that, when turned on, connects the braking resistor (RB) to the DC circuit of the frequency inverter to quickly consume the reverse power generation energy of the motor (converted into heat and dissipated in the ambient air), in order to maintain the voltage of the DC circuit within the allowable value. There is a DC voltage detection circuit that outputs a brake action signal to control the on and off of electronic switches. In terms of performance, when the DC circuit voltage of the frequency converter rises to a certain value (such as 660V or 680V), the switch is turned on to connect the braking resistor RB to the circuit until the voltage drops below 620V (or 620V), and then the switch is turned off, which is also feasible. Anyway, the braking unit has RB’s current limiting function and there is no risk of burning out. If its performance is further optimized, a voltage/frequency (or voltage/pulse width) conversion circuit will be controlled by a voltage detection circuit to control the on/off of the IGBT module in the braking unit. When the voltage of the DC circuit is high, the working frequency of the braking unit is high or the conduction cycle is long. When the voltage is low, the opposite is true. This type of pulse braking has much better performance than direct on/off braking. In addition, with the overcurrent protection and heat dissipation treatment of the IGBT module, this should be a high-performance braking unit circuit.

The CDBR-4030C braking unit is not very optimized in terms of structure and performance, but the actual application effect is still acceptable. The internal electronic switch is a dual tube IGBT module, and the gate and emitter of the upper tube are not used for short circuiting. Only the lower tube is used, which is somewhat wasteful. A single tube IGBT module can be used. The protective circuit is a combination of electronic circuits and mechanical trip circuits. The manufacturer has modified the internal structure of the QF0 air circuit breaker, changing it from leakage trip to trip when the module overheats. Temperature detection and action control are composed of a temperature relay, Q4, and KA1. When the module temperature rises to 75 º C, KA1 action triggers a trip, QF1 trips, and the power supply of the braking unit is turned off, thereby protecting the IGBT module from being burned out due to overcurrent or overheating to a certain extent.
The power supply of the detection circuit (as shown in the figure below) is obtained by reducing the power resistance, stabilizing the voltage with a voltage regulator, and filtering the capacitor, providing a 15V DC power supply.
The faults of the braking unit mainly occur in the control power supply circuit, manifested as open circuit of the step-down resistor, breakdown of the voltage regulator, etc; In addition, due to the introduction of 530V DC high voltage in the DC circuit of the frequency converter, the insulation of the circuit board decreases due to moisture, resulting in high voltage discharge and burning of copper foil strips in large areas of the circuit, as well as short circuits in the integrated blocks of the control circuit. Due to the fact that all circuit boards are coated with black protective paint, the connection and direction of the copper foil strips cannot be clearly seen, which also brings some inconvenience to maintenance.

The circuit consists of an LM393 integrated operational amplifier, a CD4081BE four input and gate circuit, and a 7555 (NE555) time base circuit. The control principle is briefly described as follows:

The DC circuit voltage of the frequency converter introduced by the P and N terminals is divided by the R1 to R7 resistor network and input to the 2 pins of LM339. The 3 pins of LM339 are connected to the set voltage after further voltage stabilization and RP1 adjustment through 15V control power supply. This voltage value is the set voltage of the braking action point. LED1 also serves as a power indicator light. As LM393 is an open collector output operational amplifier circuit, the output terminals of the two amplifiers are connected with pull-up resistors R13 and R14 to provide high-level output during braking action. The first stage amplification circuit is a hysteresis voltage comparator (sometimes also known as a hysteresis comparator), where D1 and R10 are connected to form a positive feedback circuit, providing a certain hysteresis voltage to make the set point voltage fluctuate with the output, avoiding frequent output fluctuations caused by comparing at one point. The second stage amplifier is a typical voltage comparator connection. In essence, the operational amplifier is used here as a switching circuit, without a linear amplification link, but as a switching output. The two-stage amplification circuit forms a phase inversion process for the signal, so that when the output voltage is higher than the set voltage, the circuit has a high-level output.
When LM393 is static, it is a high level output. This high level is superimposed on pin 3 of LM393 through D1 and R10, which “boosts” the voltage value of the braking action set point. When the input voltage of pin 2 (such as 660V DC circuit voltage between P and N) is higher than the voltage of pin 3, pin 1 changes from high level to low level; After the second stage of phase inversion processing, output a high-level signal to pin 1 of CD4081BE. Meanwhile, due to the low level of pin 1 of LM393, pin 3 also dropped from the raised voltage value to the set value. In this way, when the braking unit acts and connects the braking resistor between P and N, the voltage of P and N starts to fall from 660V and continues to fall until the voltage of pin 2 (580V between P and N) is lower than the set voltage value of pin 3. The circuit flips and the braking signal stops outputting, avoiding the unstable output caused by frequent circuit actions at 660V voltage.

The time base circuit 7555 is connected to a typical multi harmonic oscillator and outputs a pulse frequency voltage with a fixed duty cycle. In the LM393 voltage sampling circuit, the braking action signal is output – pin 1 of CD4081BE is a high level, and the high-level component of the rectangular pulse voltage output by the time base circuit 7555 is combined with the high-level signal of LM393, causing pin 3 of CD4081BE to generate a positive voltage pulse output. This pulse is then processed by the master/slave conversion switch, the second stage, and the gate switch circuit. After power amplification by Q1 and Q2 complementary voltage followers, it drives the electronic switch IGBT module.

When the master/slave control switch is turned to the upper end, this machine acts as the master, implements braking action, and transmits braking commands to other slaves through terminals OUT+and OUT -; When the master/slave control switch is turned to the lower end, this machine acts as a slave and receives braking signals from the main unit through terminals IN+and IN -. The signal is input into pin 6 of CD4081BE through optocoupler U5, and braking action is carried out based on the signal from the main unit.
The part of the circuit marked “What is the intention of this circuit” on the blueprint, let’s start from the circuit itself and try to understand the designer’s original intention. If my analysis is incorrect, I hope readers can correct it. Under normal conditions, when implementing a braking action, it can be seen that the braking signal output by U2 is a rectangular pulse sequence signal (this signal is added to pin 1 of U4), and the signal added to pin 2 of U4 through a step-down resistor at the PB terminal is exactly an inverted rectangular pulse sequence signal. At any moment, one of pins 1 and 2 of U4 is always a high level. For the “high out of low” characteristic of the OR gate, pin 3 of U4 always outputs a low level, Q3 is in the cut-off state, and the circuit implements normal braking action; Assuming that the output module has been continuously connected or has been broken down, the signal from the PB terminal to pin 2 of U4 is a DC low level, which is in phase or phase with the pulse signal from pin 1, resulting in an output of “two low and one high”. By driving Q3 through U8, the output signal of pin 3 of U2 is short circuited to ground, causing pin 8 of U2 to also be at a low level until pins 1 and 2 of U4 are completely locked to ground (low) level, and Q3 continues to enter a fully conductive state, completely blocking the braking signal output by U2. Power must be cut off to lift this blockade. But this protective blockade seems powerless and beyond the reach of the module itself in transient overcurrent conditions or faults in the Q1 and Q2 drive circuits themselves.