Inverter pulse circuit fault detection - Solutions - Huaqiang Electronic Network

Brand AVX TPSE226M035R0125 Low impedance tantalum capacitor AVX 22

Filter 18.432M

The inverter pulse circuit consists of two main parts: the pre-stage and post-stage circuits. The pre-stage circuit is responsible for receiving six PWM signals from the CPU and passing them to the buffer stage, while the post-stage circuit, known as the drive circuit, amplifies and sends these signals to the inverter module. Together, they form the complete inverter pulse system.

Common Fault Symptoms:

• Normal startup with frequency display, but no three-phase output voltage.
• Normal startup and frequency display, but unbalanced three-phase output voltage.
• OC fault appears when the start button is pressed.
• OC fault occurs during operation.
• Light load operates normally, but under full load, the motor jumps or triggers an OC fault.

Root Causes and Troubleshooting Ideas:

1. No Output Voltage: Possible causes include loss of +5V power supply to the optocoupler on the driver side, damage to the pre-stage buffer circuit, unstable control signals from the CPU, or a malfunctioning protection circuit that locks out the pulse signal. It's important to note that the pre-stage circuit may be directly controlled by the protection system. If this fails, it can block all six pulse signals, leading to a complete failure. This type of issue is often tricky because it involves multiple layers of the system.

2. Unbalanced Three-Phase Output: This could be due to a faulty optocoupler in the drive circuit, increased internal resistance in the inverter module, or a defect in the pre-stage circuit or CPU output pin. In some cases, one or two pulses might be missing, which leads to uneven voltage distribution. It’s essential to check both the pre-stage and drive circuits thoroughly.

3. OC Fault During Start: This may be caused by a poor drive circuit itself, insufficient power supply capacity (such as a degraded filter capacitor or inefficient rectifier diode), or a defective inverter module. Even if the static voltage checks out, the dynamic current output capability of the drive circuit should be tested to ensure it can handle the load.

4. False OC Faults During Operation: Issues may stem from the drive circuit's load capacity, the conduction resistance detection of the inverter module, the three-phase current detection circuit, or the reference voltage in the fault detection system. Additionally, user-related factors like improper load settings can also trigger false OC faults. These are complex issues that require careful diagnosis of the entire system.

5. Motor Jumps or OC Fault Under Load: This could be due to insufficient drive circuit current output, high internal resistance in the inverter module, or a problem with the load circuit itself. Sometimes, the issue isn’t with the inverter at all, but with the motor or wiring. It’s recommended to test with a different motor to rule out external factors before assuming the inverter is faulty.

In summary, diagnosing inverter pulse circuit issues requires a systematic approach. Understanding how each component interacts is key to identifying the root cause. Always consider both electrical and mechanical factors, and don’t overlook the possibility that the problem lies outside the inverter itself.