Author: baiyuzhan

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Repairing the Stubborn GF Fault in Yaskawa 616G3 55kW Frequency Converter

Repairing a frequency converter, especially one that reports a stubborn ground fault (GF), can be a challenging and frustrating task. Recently, I encountered such an issue with a Yaskawa 616G3 55kW frequency converter. Despite the common advice to replace the board, I delved deeper into the problem, determined to find a logical solution. This article outlines the step-by-step process I followed to diagnose and repair the GF fault without replacing any major components.

Initial Diagnosis and Background

The Yaskawa 616G3 frequency converter had been out of service for two to three years before it arrived at our repair department. Upon inspection, we found that two of the three-phase power input rectifier modules and two of the six inverter IGBT modules were damaged. The driver board had also suffered some component damage due to the module failure.

The GF fault typically indicates an issue with the drive circuit or the IGBT module itself, especially during the initial startup stage when the three-phase output voltage has not yet been established. Understanding the structure of the protection circuit helped narrow down the potential causes. The GF and OC (load-side short circuit) fault signals are fed directly to the CPU by the protection circuit of the driving circuit board.

Driver and Protection Circuits Inspection

The driver circuit of the Yaskawa frequency converter includes six pulse signals from the CPU, isolated and amplified by six TLP250 ICs, and sent to the IGBT modules. Additionally, six TLP750 ICs form a module fault protection circuit, reporting GF and OC signals to the CPU. There are also three 2501 optocouplers responsible for detecting fuse status.

After disconnecting the driver board and CPU motherboard, I replaced the damaged components in the power amplifier circuit. The switch power supply and motherboard appeared to be functioning correctly. I manually cleared other potential faults, such as overvoltage, undervoltage, overheating, and fan issues, to ensure the drive circuit could output normal excitation pulses.

Addressing the FU Fault

During the initial tests, the circuit reported an FU (fuse) fault. After inspecting the relevant optocoupler components and circuit components, I found that the copper foil strip of the N lead was broken due to mold. This caused the fuse detection circuit to assume the fuse was broken. I repaired the moldy copper foil strip and retested the circuit, which resolved the FU fault.

Further Investigation and Component Replacement

With the FU fault resolved, I pressed the RUN button on the operation panel and measured the six pulses output by the drive circuit, all of which were normal. However, the GF fault persisted. I re-inspected the driver board, measuring all circuit components and short-circuiting the GF fault feedback optocoupler, but the GF fault still tripped.

Further investigation revealed a poor contact between a diode in the IGBT voltage drop detection circuit and the copper foil strip. I also found that the positive voltage of the W-phase transistor driver pulse was low, indicating an issue with the driver IC. After replacing the faulty A3320 IC, the output pulse amplitude returned to normal.

The Stubborn GF Fault

Despite repairing the identified issues, the GF fault still occurred during startup. I used the fault zone cutting method to narrow down the fault range, eventually finding that the IGBT driver circuit (protection circuit) of the U-arm was prone to reporting the GF fault. A diode with a poor contact was identified and replaced.

However, even after these repairs, the GF fault persisted. I then conducted a series of tests, including short-circuiting the module detection circuit’s transistors to relieve the fault protection function. During these tests, I observed an abnormal phenomenon: the series-connected light bulb lit up with high brightness after the start signal was activated, indicating a potential issue with the IGBT modules or driving circuit.

Discovering the Common Cause

After ruling out issues with the driving circuit and modules, I focused on the common factors that could affect all six protection circuits. I noticed that the leads of the capacitor bank, which were longer due to the repair setup, could be introducing inductance into the circuit. This inductance could generate induced electromotive force and current, interfering with the module fault detection circuit.

To test this hypothesis, I formally installed the machine, limiting the lead inductance of the capacitor bank within the allowable value. After the installation, the Yaskawa frequency converter operated normally without tripping the stubborn GF fault.

Conclusion

Repairing the GF fault in the Yaskawa 616G3 55kW frequency converter was a challenging but rewarding experience. By thoroughly understanding the protection circuit and methodically diagnosing each potential issue, I was able to repair the machine without replacing any major components. The key to solving the stubborn GF fault was identifying the common cause—inductance in the capacitor bank leads—and addressing it through proper installation.

This case study highlights the importance of logical reasoning and thorough investigation in repairing electronic equipment. It also demonstrates that, with patience and persistence, even stubborn faults can be resolved without resorting to costly board replacements.

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Omron PLC Switch Power Supply: Understanding and Maintenance Guide

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

Internal physical diagram of Omron PLC

The Importance of Switch Power Supplies in Omron PLCs

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

Schematic diagram of Moron PLC switch power supply circuit

Common Faults in Omron PLC Switch Power Supplies

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

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

Diagnosing and Repairing Omron PLC Switch Power Supplies

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

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

Understanding the IC11 MIP0223SC Power Module

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

MIP0223SC Power Module Parameter Table

Conclusion

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

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Mitsubishi VSD F700-A700 Power Driver Board Circuit Diagram and MCU and Optocoupler Specification Confirmation

There is a separate MCU and six communication optocouplers OI1~OI6 on the power drive board of Mitsubishi F700 (F740, F720) and A700 (A740, A720) frequency converters. Their specifications look a bit mysterious and may cause confusion during maintenance. The relevant circuit diagram will be drawn below, and a simple functional analysis of the MCU and optocoupler will be conducted to reduce the difficulty of repairing and changing the frequency converter.

OI6:
Responsible for transmitting the operation and shutdown instructions of the motherboard MCU, with instructions in the form of 1 and 0 levels. The 19 pin of CON1 is a 5V high level, which is a running command. The output side of OI1 becomes 0V, and the local MCU can send 6 pulse signals such as U+~W – to the driving circuit; The 19 pin of CON1 is at 0V low voltage level, and the motherboard MCU sends a shutdown command (if it becomes low during operation, the OI1 output side becomes 5V, which is an overload fault shutdown command). The messenger of the motherboard MCU sends running and stopping commands to the local MCU in the form of DC
The 0 and 1 levels of opening and closing quantities.

OI2:
The serial data returned by the local MCU and motherboard MCU is in the form of rectangular wave pulses. Start working immediately after powering on.
The communicator between the local MCU and the motherboard MCU, signal direction: transmitted locally to the motherboard MCU.

OI5:
The communicator between the motherboard MCU and the local MCU, signal direction: The motherboard MCU issues instructions to the local MCU
MCU. The signal form is serial data, and the test is a rectangular pulse train. Start working immediately after powering on.

OI4:
The main board MCU sends switching instructions to the local MCU, and under normal conditions (running and stopping), the output terminal 6 pins are 0V. When it reaches 5V high level, an E7 code (meaning CPU error) is reported. Is its task to confirm the working status of the motherboard MCU?

OI3:
The communication personnel between the motherboard MCU and the local MCU, signal direction: The motherboard MCU issues instructions to the local MCU. The input signal is in the form of serial data (synchronous clock signal?), but due to the capacitance integration effect at pins 5 and 6, a triangular wave of 760kHz is measured. Start working immediately after powering on.

OI1:
The communication personnel between the local MCU and the motherboard MCU, signal direction: The local MCU reports the fault situation to the motherboard MCU. Signal form 0, 1 switch quantity DC voltage. The shutdown status between pins 5 and 6 of the output terminal is 0V, which changes to a high level of 5V after operation. When there is a fault, it changes to 0V and displays the alarm code EOC1.
As a module fault reporter, he reports the fault situation to the motherboard MCU.

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

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

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

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Simplified Debugging Guide for Siemens 400 Series (420/430/440) VFD Drives

Simplified Debugging Guide for Siemens 400 Series (420/430/440) VFD Drives

Debugging a Siemens 400 series Variable Frequency Drive (VFD), specifically models 420, 430, and 440, can initially seem daunting due to the multitude of parameters and unfamiliar symbols on the operation panel. However, with a structured approach, even newcomers can quickly master the basics and get these drives running efficiently. This guide will outline a straightforward method for debugging, focusing on essential functions like start/stop control and frequency adjustment, along with some tips for PID operation and parameter adjustment.

Terminal connections of the Siemens 400 Series (420/430/440) VFD Drives

Initial Setup and Terminal Connections

Before diving into the parameter settings, ensure that the terminal wires are properly connected. For basic operation, you’ll need to connect five wires:

  1. Start/Stop Switch: Connect between terminals 5 and 9.
  2. Potentiometer for Frequency Adjustment: Short-circuit terminals 2 and 4, then connect wires from terminals 1, 3, and 4 to the potentiometer, with terminal 3 connected to the center head.
Operation Panel

Understanding Operation Panel Keys

The operation panel of the Siemens VFD is equipped with several keys that serve different functions:

  • Start/Stop Keys: Marked as 1 and 0, these control the run and stop operations.
  • Parameter Adjustment Keys: The P key enters parameter adjustment mode, while the up and down arrows navigate through the parameters. The P key also confirms selections and writes values.
  • Data Display/Reset Key: Press for 2 seconds to view operating data. It also serves as a return key after parameter adjustment and a reset button for fault shutdown.
  • Control Mode Switch Keys: The “Hand” key enables operation via the panel, while the “Auto” key switches to terminal control.
Operation Panel Keys

Quick Start Guide for New Machines

For newly manufactured machines, you can bypass extensive parameter adjustments by understanding the basic button functions and ensuring correct terminal connections. However, for used machines, it’s often simplest to initialize all parameters to their factory settings:

  • Set P0010=30
  • Set P0970=1

After entering these values, the drive will reset, which may take about three minutes.

Parameter access level

PID Operation Adjustment (440 Model)

For PID control, you’ll need to configure specific parameters:

  • P2200=1: Enables PID function, disables conventional frequency settings.
  • P2253: Selects the PID setting signal source (e.g., P2253=755 for analog input 1).
  • P2264: Selects the PID feedback signal source.

Multi-machine operations, such as PID one variable frequency with three power frequencies, require detailed adjustments according to the manual.

Tips for Parameter Adjustment

  • To access PID parameters, set P003=3 for expert-level parameters.
  • Adjust P004 to change specific parameter settings, such as P004=10 for frequency setting values.
  • Define digital terminal functions with P700=2 for digital input control.

Shortcuts and Precautions

  • Fault Reset: Set a terminal to 12 for reverse operation and fault reset.
  • Fixed Frequency Operation: Set a terminal to 15 for multi-stage speed control. Adjust P1000=33 for analog signal plus fixed frequency.
  • V/F Curve Adjustment: Customize the V/F curve with P1300 based on the load type (e.g., constant torque, variable torque).
parameter level

Inertial (Free) Parking Control

For applications requiring inertial parking, set P701=1 for forward start/stop and P702=3 for inertial parking. Connect terminals 5 and 6 in parallel and control via terminal 9.

Special Considerations for High-Power Motors

When starting high-power motors, Siemens VFDs may output a certain excitation current to magnetize the stator winding before the motor starts. This is not a malfunction but a feature to reduce starting current.

Conclusion

By following this structured approach, even those new to Siemens 400 series VFDs can quickly become proficient in their operation and debugging. Remember to consult the manual for detailed parameter descriptions and always initialize parameters for used machines to ensure a smooth start. With a basic understanding of the operation panel, terminal connections, and key parameters, you’ll be well-equipped to handle a variety of applications and control requirements.

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Different scenarios of “GF” ground fault are reflected in the maintenance of Yaskawa 616G3 VSD drive

The power on display is normal. Start the operation, that is, jump “GF” fault, but it does not run or shows no signs of running. I quickly jumped over the ground fault. The “GF” fault at this time is equivalent to the “OC” fault of other frequency converters, and the fault is located in the inverter module or driving circuit. At the moment when the CPU sends the trigger pulse, it detects an abnormally large pressure drop in a certain IGBT tube and fails to open it normally during the arrival of the trigger pulse. In fact, during this time, the current transformer of the frequency converter did not detect the output current signal at all. At this point, the “GF” fault signal is fed back to the CPU by the module fault detection circuit of the driving circuit. (This fault action was determined by testing.)

Repair and inspection: Check the quality of the inverter block, especially the inspection of the trigger terminal cannot be ignored; Check the driving circuit, especially the filter capacitor of the driving power supply, and measure whether the driving voltage is normal, but whether there is a certain current driving ability.

  1. Jumping “GF” fault during operation is a fault reported by the current detection circuit. There are two aspects that need to be distinguished. On the one hand, it is a normal fault shutdown action, where the current transformer detects abnormal overcurrent and reports to the CPU to implement fault shutdown protection; On the one hand, the subsequent current signal processing circuit of the current transformer is faulty, such as the variable value of the resistor element, which causes the “GF” fault voltage setting point to drift, resulting in false alarm faults. The signal from the current transformer is processed through an operational amplifier, sent to the CPU for current display and fault alarm processing, and sent to a voltage comparator, reporting a “GF” fault. (Note: The subsequent circuit of this current transformer was not thoroughly investigated, but it was inferred from numerous fault phenomena and is for reference only.)
    Repair and inspection: When it is confirmed to be a false alarm fault, it is not necessarily necessary to replace the motherboard for repair. Detailed inspection of the current transformer and its subsequent circuits should be able to repair it.
  2. By the way, when an overcurrent fault is reported during operation for OL1, OL2, and OL3, it is detected by the current transformer and subsequent current signal processing circuit during operation. After sending the current signal to the CPU, it is judged, frequency reduced, and processed to report the overcurrent fault signal. For sudden abnormal overcurrent faults, module damage, or abnormal driving circuit faults, the driving circuit will directly feedback to the CPU, and the CPU will report an OC fault.

This suggests different treatments for undervoltage and overvoltage faults in other frequency converters. For undervoltage, after power on, it is detected and delayed for at least 5 seconds before reporting. Started 5 seconds ago and was able to run, but then experienced an undervoltage fault; For overvoltage faults, the fault will trip immediately after power on and operation is prohibited. It can be seen that designers attach greater importance to overvoltage faults than undervoltage faults. It can also be known that overvoltage faults pose greater harm to frequency converters than undervoltage faults do to frequency converters. And the handling of different fault alarms by designers can also be understood.

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Key Considerations for Selecting and Using Variable Frequency Drives (VFDs)

Variable Frequency Drives (VFDs), also known as frequency converters, are essential devices in modern industrial and commercial applications, providing precise control over motor speed and torque. However, their effective utilization requires a thorough understanding of their operational nuances and precautions. This article delves into the critical aspects of selecting and using VFDs to ensure optimal performance and longevity.

Operational Modes and Control Mechanisms

When integrating a VFD into your system, it’s crucial to understand its operational mode. Some VFDs cannot be directly controlled via the panel for start/stop operations. Instead, they require control terminals to be connected in either the forward or reverse direction. Essentially, the motor’s direction must be predetermined through these terminals before the panel can control the start/stop functions. This setup ensures seamless operational control and prevents any potential misdirections or malfunctions.

For applications involving pole-changing motors, it’s advisable to connect the VFD according to the high-speed connection method initially and then adjust the speed as required. If the motor needs to operate at lower speeds, a medium-speed connection can also be utilized. This flexibility allows for optimized performance across various speed ranges.

Voltage and Connection Considerations

Low-power motors with three-phase angle connections of 220V can be connected in a star configuration when using a VFD. This setup enables direct driving by a 380V VFD, maintaining the motor’s output power without the need to reduce the VFD’s output voltage. This approach is superior in terms of efficiency and performance.

In scenarios where the power supply capacity significantly exceeds the VFD’s capacity, harmonic components in the input current may increase. This can lead to increased losses and potential damage to rectifier diodes and capacitors. To mitigate these effects, installing input reactors is recommended. These devices improve the power factor, reduce the impact of three-phase current imbalance, and provide a degree of lightning protection.

Enhancing Performance and Reducing Interference

Installing an output reactor can further enhance the system’s performance by improving the current waveform, reducing motor operating noise, and boosting energy-saving effects. In cases where VFD-generated interference affects on-site instruments, lowering the carrier frequency can often resolve or mitigate the issue. For high-power motors, a moderate reduction in carrier frequency is advisable, particularly when starting difficulties arise. Adjusting the starting curve by shortening it and reducing the carrier frequency can facilitate smoother starts.

Motors with high operating inertia and specific stopping time requirements may need the addition of braking units and braking resistors. Proper adjustment of these parameters ensures smooth deceleration and stopping. When driving submersible pump motors, selecting a VFD with a higher power rating is recommended due to their larger rated current compared to ordinary motors.

Shutdown Methods and Torque Boosting

In constant pressure water supply systems using a single VFD, a deceleration shutdown method, akin to soft shutdown, can prevent the water hammer effect. However, in systems with one-to-several configurations or power frequency bypasses, a free shutdown method is preferable to avoid contactor tripping and potential damage to the VFD module from the motor’s back electromotive force.

Torque boosting parameters must be carefully set and tested. Excessive torque boosting at low frequencies can cause motor windings to become overexcited, leading to magnetic saturation and a significant torque reduction. This can result in the motor emitting a buzzing sound without rotating, accompanied by a substantial increase in output current, potentially triggering OC faults. Reducing the torque boosting parameter often resolves this issue.

Parameter Protection and Maintenance

If parameters cannot be modified, it may indicate that they are protected or restricted. In such cases, adjusting relevant parameters to disable protection or performing parameter initialization can be necessary. In dusty environments, regular cleaning and dust prevention measures are crucial to maintain VFD performance.

When wiring low-power VFDs (below 1kW), it’s vital to check the voltage level label on the nameplate to ensure correct connection. Misconnecting a 220V VFD to a three-phase 380V supply can cause immediate damage. Manufacturers should clearly mark terminal connections to prevent such mistakes.

The VFD’s power supply should be introduced using an air circuit breaker, with contactors used solely for protection, not for start/stop control. Using contactors for this purpose can shorten the lifespan of the VFD’s energy storage capacitor and impact the rectifier module.

Grounding, Lightning Protection, and Motor Compatibility

Signal shielding wires should be grounded at one end only to avoid circulating currents and interference. In lightning-prone areas, installing lightning arresters near the VFD’s incoming line and ensuring proper grounding is essential.

VFDs are designed based on the rated current of a four-pole motor. When used with motors with more poles, the VFD’s power capacity must be increased to accommodate the higher rated current.

Due to high-frequency leakage current in the VFD’s output circuit, both the motor and control cabinet casings must be reliably grounded. Standard circuit breakers with leakage protection should not be used as power switches for VFDs. If leakage protection is necessary, specialized switches for VFDs or isolation transformers should be used to prevent tripping.

Conclusion

In conclusion, selecting and using VFDs requires a comprehensive understanding of their operational characteristics and precautions. Proper connection, voltage management, interference reduction, parameter setting, and maintenance are critical for ensuring optimal performance, longevity, and safety. By adhering to these guidelines, industries can harness the full potential of VFDs, enhancing motor control, efficiency, and reliability in diverse applications.

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Exploring the Circuit Diagram and Maintenance Insights of the CONVO VSD Switch Power Supply

Exploring the Circuit Diagram and Maintenance Insights of the CONVO VSD Switch Power Supply

The CONVO VSD switch power supply, specifically designed for the GVF-G type drivers with a power rating of 5.5KW and version number 002-E-P00-01 8.6kVA 13A, presents an intriguing yet robust design in the realm of switch power supplies. Though it may not adhere to the most conventional designs, its performance in practical applications has proven to be reliable, with a notably low failure rate.

Schematic diagram of CONVO inverter switch power supply

Circuit Overview

At the heart of this power supply lies an input stage that receives approximately 550V DC voltage from the autonomous DC home energy storage capacitor. This voltage serves as the foundation for the entire circuit’s operation. The oscillation and driving mechanisms are managed by the widely-used 38440 power chip, which initiates its operation through the voltage and current supplied by components R40, R41, and Z8. While the exact stabilization value of Z8 has not been precisely measured, it is estimated to be around 13V. An LED indicator is conveniently integrated to signal the presence of power.

Once the 3844 chip initiates oscillation, it establishes a power supply voltage for its 7-pin through rectification and filtering circuits comprising D13, Dl4, C30, and C31, facilitated by the BT winding. This power supply not only fuels the chip but also plays a crucial role in output voltage sampling and feedback. The sampled voltage, after being divided by resistors R1 and R2, is fed back to the 2-pin of the 3844 chip. This feedback method, which indirectly samples the output voltage of each channel rather than directly from the transformer’s secondary power supply branch, offers a unique approach albeit with slightly lower control precision and response speed.

Secondary Power Supply Enhancements

To further enhance the power supply’s performance, the +18V and -18V outputs from the secondary winding are routed to the CPU motherboard. Here, they undergo voltage regulation through 7815 and 7915 stabilizers, respectively. Although this adds a layer of complexity to the circuit, it significantly improves the power supply’s stability and reliability. Additionally, the +8V power supply, once introduced to the motherboard, undergoes 7805 voltage regulation to serve as the CPU’s power source.

Current Sampling and Control

The switching tube’s current sampling is achieved through resistor R37, which is series-connected to the source of the K2225 switching tube. This sampled current is then sent to the 3-pin current detection terminal of the 3844 chip. The internal voltage amplifier’s feedback component, connected between the two pins, dictates the sampling voltage’s amplification rate. The 8-pin of the chip, known as the Vref terminal, outputs a stable 5V reference voltage during normal operation. This voltage provides a current path for the external R and C oscillation timing components connected to the 4-pin, ensuring the oscillation frequency’s stability.

The 6-pin of the 3844 chip serves as the pulse output or drive output terminal, introducing pulses to the gate of the K2225 switch through resistor R36. This meticulous control over the switching process is crucial for maintaining efficient and reliable power conversion.

Internal structure diagram of UC3844

24V Output and Fan Control

The 24V output power supply is versatile, providing both the control voltage for the frequency converter’s control terminal and powering two cooling fans. The fans’ operation modes are intelligently controlled by signals from the CPU motherboard, based on parameter settings. These modes typically include running upon power-on, running during operation, and running when the radiator temperature reaches a predefined threshold.

Maintenance Insights

When it comes to maintaining this power supply, several key points should be kept in mind. In the event of a breakdown-induced damage to the K2225 switch tube, a high voltage impulse can be introduced to the 3-pin of the 3844 chip, often leading to its simultaneous damage. Additionally, the R5 resistor may open or experience an increase in resistance value. Similarly, the current sampling resistor R37, connected to the source, is frequently found to be open. Therefore, a comprehensive inspection of these components is imperative before replacing the switch tube. As a direct replacement for the K2225, the K1317 tube can be used.

In conclusion, the CONVO VSD switch power supply, despite its unconventional design, offers a reliable and efficient solution for GVF-G type drivers. Its robust performance in practical applications, coupled with thoughtful design features and straightforward maintenance protocols, makes it a valuable asset in any frequency converter system. By understanding its circuit diagram and adhering to best maintenance practices, one can ensure the longevity and reliability of this power supply in various industrial and commercial applications.

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What happens to the VSD drive when the no-load current is greater than the load current?

Cause: A cement plant user sent a 75kW micro energy WIN-G9 frequency converter for repair. The cause of the malfunction was that during operation, the frequency converter suddenly caught fire and emitted smoke, causing it to shut down. Upon inspection, the power input circuit of the machine is a three-phase half controlled bridge. Using its controllable rectification principle, the DC main circuit energy storage capacitor is “soft charged”, eliminating the commonly used charging contactor for low-power frequency converters. In fact, the semi controlled bridge here is equivalent to a contactless soft switch. Upon inspection, it was found that there were obvious signs of arc flashover and burning on the terminals of one of the thyristor modules, but the measurement did not indicate a short circuit. During disassembly, it was found that the fixing nut was easily removed, and the cause of the flashover seems to be due to loose connection screws, causing poor contact. This module is a combination of a diode and a unidirectional thyristor. Further check the control board and inverter main circuit, and there are no abnormalities. After removing the module, the remaining two phase half control bridges were used as power inputs. After being powered on, a 2.2kW low-power three-phase motor was tested and there were no issues. After replacing it with a new module of the same model, it was installed on site.

To be cautious, first adjust the operating frequency to 5Hz, and the frequency converter is loaded with a fan. First, disconnect the motor connector and let the motor run at no load. This trial run was a shock! When the frequency is below 5Hz, the no-load operating current is 45A. Although it feels slightly higher, it may be caused by the repair of the motor winding or the adjustment of the parameters of the frequency converter, such as the starting curve or torque compensation, which was not taken into consideration. When the speed was increased to 10Hz, both the current displayed on the frequency converter panel and the output current measured with a clamp meter reached 100A! And the oscillation amplitude of the output current is very large, but when measuring the three-phase output voltage, it is about 70V, balanced and stable. Disconnect the motor connection wire and power on to measure the output of the frequency converter. The output voltage is 70V at 10Hz, 150V at 20Hz, and 250V at 35Hz. As the operating frequency increases, it reaches 400V at 50Hz. During this process, the balance of measuring the three-phase output voltage is very good. The V/F curve output by the frequency converter conforms to the quadratic load torque characteristics. No problem. The output voltage is balanced and stable, while excessive output current and severe current fluctuations are clearly caused by abnormal loads. This is a conclusion drawn from conventional judgment.
Discuss with the relevant technical personnel of the factory, attempting to identify the reasons for the motor and mechanical aspects. For example, whether the motor is newly repaired or whether the winding is poorly wound; Check for wear and unstable operation of bearings; Is there any looseness or non concentricity in the connecting shaft; The wind blades have deformation, etc. Restore the wiring of the original power frequency starting cabinet, compare the power frequency starting motors, and eliminate the above doubts one by one. According to on-site observations, the motor and connected loads are in good condition, and there is almost no electrical and mechanical noise during operation. The no-load current under full speed operation is only less than 35A, with three-phase balance and no fluctuation! There is no problem with the motor and load, and the problem is still with the frequency converter.
So where is the fault location of the frequency converter? It’s a bit scratching my head. Is the current detection inaccurate, causing erroneous output? The current value displayed on the observation panel is close to the value measured by the clamp ammeter, and there should be no problem. Is there still a problem with the CPU motherboard and the output driver waveform incorrect? It doesn’t make sense. All digital circuits, why is the waveform incorrect?
Fortunately, there is another inverter of the same model and power not far from here on site, carrying the same load. That’s great. This has brought great convenience to comparative experiments. The factory was eager to start the machine and provided active cooperation. Swapping the current transformers of two frequency converters is ineffective; Swapping the CPU motherboards of two machines is invalid. Retrieve the DC voltage display of the main circuit, which is 550V, and there is no problem with the voltage sampling circuit. I can no longer figure out which circuit the problem lies in. When the comparison machine is under load, the operating current is 75A at 10Hz. When it reaches 35Hz or above, the operating current only reaches 100A, which is smaller than the current of this motor with no load. The no-load current is much higher than the load current, so there must be a problem with the frequency converter.

During the trial operation, I occasionally measured the three-phase output current of the inverter using a current clamp meter, and even discovered an incredible phenomenon! The input and output currents of this frequency converter are completely disproportionate, with a difference of more than 10 times!
When outputting a 40A current, the input current is a few amperes, which is almost undetectable; When outputting 100A current, the input current is only below 8A! Strange, it doesn’t comply with the law of conservation of energy. Where did the 100A output current come from?! It’s like an airtight water pipe, where 1 cubic meter of water enters and 10 cubic meters of water flows out. The water inside the pipe cannot come out.
We all know that in general, the input current of the frequency converter is always smaller than the output current. The reason is that the energy storage capacitor in the DC circuit acts as if a reactive power compensation cabinet is installed at the motor end. When the frequency converter is unloaded or lightly loaded, a portion of the current is provided by the energy storage capacitor to the load, reducing the current absorbed by the frequency converter from the grid. As the load increases, the input current of the frequency converter increases proportionally. When the rated load is applied, the input current and output current of the frequency converter should be close to equal. When outputting 40A, the input is only a few amperes; When outputting 100A, the input current has reached 70A; When the output current reaches 140A, the input current has also reached this value. Under normal circumstances, there may be a difference in input and output currents, but there will not be an extremely significant difference as mentioned above. The huge difference made me doubt whether the measuring instrument was broken. After changing the watch and retesting, the same result was still obtained.
There’s no way out. Consult the manufacturer. Due to the urgent need to solve the problem and find the answer, it’s not worth considering whether long-distance phone calls are expensive at this time. The technical personnel from the frequency converter manufacturer replied that this model of frequency converter is the earliest produced frequency converter, and there are problems with slightly higher no-load current and current fluctuations, but it is a normal phenomenon and does not affect its use. After being loaded, the current will stabilize. It is best to connect a motor of the same power for testing to see if there is a problem with the motor or load. Problems with motor bearings. If all motor and load issues are eliminated, as long as the three-phase voltage output of the frequency converter is balanced and the output current does not exceed the rated current of the frequency converter, can the machine be tested under no load or on load. Can’t it break down. As for the proportion of input and output currents, it is difficult to have a fixed proportion due to different load conditions. It’s not proportional. Don’t get entangled with the issue of proportion.
Think about it too. As long as the output three-phase voltage is balanced and does not exceed the rated current, can the load test be conducted. Can’t the frequency converter break down. Perhaps after being loaded, there will be no significant fluctuations in the output current. Maybe it’s normal.
We had to conduct a load test and a miracle occurred (which was surprising): when operating at 10 Hz and outputting a current of 40A, the output current was only 7 out of 8 amperes. When operating at 30 Hz, the output current is 60A and the input current is 25A; When operating at 40 Hz, when outputting a current of 100A, the input current is 70 amperes. The operating current has decreased and the fluctuation has decreased, and it is basically stable. The three-phase voltage and three-phase current are both balanced and relatively stable. The problem was inexplicably solved.
Thank you to the manufacturer’s technical personnel for their guidance: why not try the machine on load. But due to encountering this situation for the first time, abnormal current occurs at no load, and it is not dare to increase to full speed for operation. I’m even more afraid to carry it. I always want to find out the reason before loading. I always thought this was an abnormality with the frequency converter.
After the frequency converter was put into operation and returned from the site, I am still pondering this issue.
Remembering the problem of high zero line current in a power plant during maintenance, caused by harmonic components in the transmission line. It’s harmonic current. Is there also a significant harmonic component in the output circuit of the frequency converter during no-load or light load operation? Where does this harmonic component come from? Is the measured result true?

The analysis shows that there are significant harmonic components in the output current during no-load operation. There may be two reasons for the high harmonic current: 1. The output PWM wave of the inverter is not ideal enough, and the modulation method is not optimal. The software control concept has not been optimized (the new machine must have been improved); 2. When unloaded, it is equivalent to a serious mismatch between the power supply capacity and the load capacity. The power supply capacity is much larger than the frequency converter capacity, which is also a major reason for the generation of harmonic currents. When running on load, the capacity matching situation improves, and the harmonic components are greatly reduced. The combination of these two reasons has stumped me, an old electrician. For me, during the test drive, I made an empirical mistake. I was bound by the ratio of input and output currents and almost surrendered.

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Analysis of IGBT Module and Driver Faults in Variable Frequency Drive Repairs

Analysis of IGBT Module and Driver Faults in Variable Frequency Drive Repairs

In the field of industrial automation, variable frequency drives (VFDs), as key equipment for motor speed control, are crucial for stable operation. However, due to the complex and varied working environments, faults in the IGBT modules and drive circuits within VFDs occasionally occur, causing significant impacts on production. This article delves into the identification, analysis, and handling processes of IGBT module and driver faults through three practical repair cases, aiming to provide valuable references for relevant technicians.

Case 1: Phase Deviation Fault in Dongyuan 7300PA3.7kW VFD
Fault Phenomenon: After powering on, a Dongyuan 7300PA3.7kW VFD had outputs on all U, V, and W phases, but with severe phase deviation.

Fault Diagnosis: Initially suspected as a drive circuit abnormality or IGBT module damage. Measurements revealed an open circuit in the upper arm diode of the U-phase in the inverter circuit. Typically, the IGBT transistor paralleled with this diode was also burnt due to short-circuit current, and the paralleled diode was damaged by the impact.

Repair Process:

  1. After removing the damaged SPIi12E IGBT module, clear all the module pins and prepare to test the six drive circuits.
  2. Upon powering on, the VFD immediately reported an overheating fault, with the CPU locking the drive pulse output, preventing drive circuit quality detection.
  3. Two terminals labeled T1 and T2 on the circuit board, suspected as internal overheating alarm outputs of the module, were observed. By connecting a 5V power supply through a resistor, the other end grounded. When these terminals were left open, the T1 terminal output a high-level module overheating signal through a pull-up resistor, triggering protective shutdown.
  4. After short-circuiting the T1 and T2 terminals, powering on no longer resulted in protective shutdown. It was found that the U-phase upper arm IGBT drive circuit had no trigger pulse output. After replacing the drive circuit IC/PC923, the six-pulse output returned to normal.
  5. A new IGBT inverter module was installed, the short-circuit wire between T1 and T2 was removed, and the VFD operated normally after powering on.
    Experience Summary: When an IGBT tube is damaged, the corresponding drive IC is often damaged by the impact as well. Before replacing the new module, be sure to check the drive IC in the same branch to avoid damaging the new module again due to drive circuit abnormalities.

Case 2: Repair of Lightning-Damaged Alpha 18.5kW VFD
Fault Phenomenon: An Alpha 18.5kW VFD was damaged by lightning, with the CPU motherboard reporting a 2501 error and panel operations failing.

Fault Diagnosis: Lightning caused damage to the CPU and surrounding communication circuits.

Repair Process:

  1. Temporarily ignoring the CPU motherboard issue, repair the drive board first. It was found that six A316J chips were responsible for six drive pulse outputs, with three upper arm pulse drive circuits damaged.
  2. As an alternative, three A316J chips (for three-phase lower arm drives) were used as three-phase OC signal alarm outputs, and the remaining three were replaced with 3120 (identical to PL250V) to drive the optocoupler ICs.
  3. The new ICs were adapted and soldered, and the input circuit was adjusted to ensure normal operation of the new ICs.
  4. After replacing the new CPU motherboard, the static output voltage and dynamic pulse output of the six drive circuits were tested and found to be normal.
  5. The damaged IGBT module was replaced, and the VFD resumed normal operation.

Case 3: Repair of Phase Deviation in a 7.5kW VFD
Fault Phenomenon: A user reported that a 7.5kW VFD had output but could not operate normally, with phase deviation present.

Fault Diagnosis: It was found that one of the six drive circuits was abnormal, with the drive IC model being PC929 (or A4503?). Measurements showed no pulse output at the input and output terminals of the drive IC.

Repair Process:

  1. Suspecting a fault in the CPU’s internal pin circuit, the input terminal of the PC929 was disconnected, and it was found that the voltage at the CPU’s pulse output terminal increased. However, when the drive IC was connected, the voltage dropped to nearly 0V.
  2. It was analyzed that the CPU directly drove the photoconductive tube, and long-term high-current output led to aging faults in the output stage. It was decided to enhance the signal voltage through an external amplification circuit.
  3. An amplification circuit was constructed using two NPN-type transistors and resistors to amplify the CPU’s pulse signal before inputting it to the drive IC.
  4. After powering on, the six-pulse output was normal, and the inverter module was powered on, with normal three-phase voltage output.
    Experience Summary: For aging faults in the CPU’s output stage, amplifying the signal voltage through an external circuit is an effective repair method, which not only saves repair costs but also shortens repair time.

In summary, IGBT module and driver faults are common challenges in VFD repairs. Through meticulous fault diagnosis, reasonable repair strategies, and innovative repair methods, these issues can be effectively resolved, ensuring the stable operation of VFDs. It is hoped that the sharing in this article can provide valuable references and insights for technicians.