Causes Of Phase Loss in Frequency Converter

Inverter phase loss typically manifests as input phase loss (power supply side) or output phase loss (motor side). Depending on the location of the fault, the causes can be categorized as follows:

I. Input Phase Loss (Power Supply Side Phase Loss)

Main Causes:

1. External Power Supply Issues:
* Power Line Fault: Phase loss in the upstream power supply line, unstable voltage, or voltage spikes.
* Front-End Component Fault: Poor contact, looseness, or even damage to the circuit breaker, fuse, AC contactor, or terminals at the input end.
* Misuse of Single-Phase Power: The inverter, which should be connected to a three-phase power supply, is mistakenly connected to a single-phase power supply.

2. Internal Inverter Issues:
* Rectifier Bridge Damage: A diode in the rectifier bridge is broken down or open-circuited.
* Aging Filter Capacitor: The DC bus filter capacitor is aged or has insufficient capacity, leading to excessive voltage ripple and triggering phase loss protection.

II. Output Phase Loss (Motor-Side Phase Loss)

Main Causes:
1. External Wiring and Motor:

Output Line Breakage: There is an open circuit or poor contact in the cable or terminals between the inverter output and the motor.

Motor Winding Burnout: One or more phases of the motor winding have an open circuit or short circuit.

Load Mismatch: When the inverter power is much greater than the motor power, the inverter may not be able to detect the normal output current due to the insufficient no-load current of the motor, resulting in a false phase loss report.

2. Internal Inverter Issues:

IGBT Module Damage: Damage to the IGBT (Insulated Gate Bipolar Transistor) module, a core component of the inverter section, prevents that phase from outputting properly.

Drive Circuit Failure: An abnormality occurs in the signal amplification circuit driving the IGBT. For example, damage to components such as optocouplers, drive transistors, Zener diodes, and capacitors can prevent the IGBT from functioning correctly.

III. Detection Circuit Failures (General)

Current/Voltage Detection Abnormalities: A fault occurs in the inverter's internal current or voltage detection circuit itself. For example, damage to components such as Hall effect sensors, voltage divider resistors, and operational amplifier circuits can lead to false alarms for phase loss.

IV. Other Common Causes

1. Incorrect Inverter Parameter Settings: Some brands can disable phase loss detection. If mistakenly set to "single-phase power supply" but actually connected to three phases, a false alarm will occur; or the "motor rated current" may be set too low, leading to false alarms for phase loss under light load.

2. Environmental Factors: Humidity can cause terminal oxidation and corrosion; dust accumulation on the detection circuit board can cause signal abnormalities.