From the six PWM output terminals of the CPU to the intermediate buffer circuit, it is called the inverter pulse pre-stage circuit, and the driving circuit is called the inverter pulse post-stage circuit. Together, they are called the inverter pulse loop.
Fault status:
1. The start-up operation is normal, and the operation display panel shows a normal output frequency indication, but there is no three-phase output voltage;
2. Start-up operation is normal, and the operation display panel shows a normal output frequency indication, but the three-phase output voltage is unbalanced;
3. Pressing the start button immediately triggers an OC (Overclocking) fault.
4. OC (Overclocking) error during operation;
5. Normal operation under light load, but motor jumps or trips to overload under load.
Fault nature and troubleshooting approach (corresponding to the five fault states):
1. The following factors may be present: a) Loss of +5V power supply to the input side of the optocoupler in the drive circuit; b) Damage to the buffer in the pre-stage pulse circuit; c) Uncertainty in the relevant control signals of the CPU or damage to the relevant control pins; d) Malfunction of the fault protection circuit, causing the pulse pre-stage circuit to be locked by the fault signal.
One point that requires special attention here is that the pre-amplifier circuitry for the inverter pulse signal, such as tri-state triggers and buffer circuits, may be directly controlled by voltage and current detection and protection circuits. When the protection circuit malfunctions, it clamps and blocks the transmission of the six pulse signals. It is essential to understand that the fault protection circuit can independently participate in pulse transmission control. Although the failure rates caused by factors a and b are relatively low, the causes in factors c and d often constitute difficult-to-diagnose faults. If the troubleshooting approach doesn't reach these points, the repair process will be detours.
2. There are three possible causes: a) The optocoupler of the drive circuit is damaged and cannot transmit the inverter pulse signal normally; b) The internal resistance of the inverter module is increased, and the three upper arm IGBT modules have poor conduction. Therefore, the three drive circuits may not have IGBT voltage drop detection circuits, so they cannot report OC faults; c) The pulse preamplifier circuit or the CPU inverter pulse output pin is faulty, resulting in one or two inverter pulses being missing.
Don't just focus on the subsequent drive circuit; the problem could also be the lack of input drive circuitry for the inverter pulses in the preceding stage. In particular, keep in mind the possibility of a faulty module or increased internal resistance in the inverter module. Failing to consider factors like C can lead to complex and difficult-to-diagnose faults.
3. The following factors may be present: a) The downstream driver circuit itself is faulty; b) The power supply to the driver circuit has insufficient load-carrying capacity, such as a degraded filter capacitor or an inefficient rectifier diode (increased forward resistance and decreased reverse resistance); c) The inverter module is faulty. Dynamic and static testing (voltage testing) of the driver circuit may appear normal; however, the current output capability of the driver circuit should be tested. Factors b and c should be carefully considered.
4. Several factors may be involved: a) the load-carrying capacity of the drive circuit and the on-resistance detection of the inverter module; b) the three-phase output current detection circuit; c) the reference voltage circuit in the fault detection circuit; d) user load-related issues. Pay attention to the impact of factors b, c, and d. A faulty three-phase detection circuit itself, causing a shift in the operating point, may falsely report an OC fault; a deviation in the reference voltage in the fault detection circuit can lead to inaccurate current detection and false OC fault reports. If no problems are found during inspection, the cause needs to be investigated on-site, and load-related issues cannot be ruled out. Factors b and c may lead to more complex faults.
5. There are three possible causes: a) Insufficient current (power) output capacity of the drive circuit; b) Faulty inverter module with excessively high internal resistance; c) Problem with the load circuit, the motor is broken, not the inverter itself. Abnormal inverter operation does not always indicate an inverter problem. It is recommended that the user try replacing the motor. Factors b and c should be considered, and sometimes factors outside the inverter itself need to be taken into account.
