Regarding the issue of inverter overload

1. The meaning of inverter overload protection is that the current output by the inverter continuously exceeds the rated current, but has not yet reached the instantaneous overcurrent threshold; the duration is generally defined as 1 minute. For constant-torque frequency converters, the typical overload capacity is 150% for 1 minute, while for variable-torque frequency converters it is generally 110%–120% per minute. If the motor is compatible with the inverter, and since the motor has a higher overload capacity than the inverter, the overload in this case is referred to as an inverter overload; the current used for comparison is the inverter’s rated current ； If the motor’s rated current is lower than that of the inverter, and the motor’s nameplate data and protection settings are entered correctly, then this overload protection is often referred to as motor overload protection. Therefore, it is essential to distinguish the specific circumstances of the current protection. Since the overload point of the inverter is not far from its overcurrent point, these two types of protection often activate alternately. 　　 　　2. Since overload detection is based solely on current, it can occur during startup, shutdown, acceleration, deceleration, and constant-speed operation. Moreover, current is closely related to the slip of asynchronous motors; therefore, the following situations can be considered for analysis: A. Overload during startup often occurs in one of the following two scenarios: 1. The static torque of the load is high, and the inverter’s output at low frequencies is insufficient, resulting in stall or slow rotation. Possible reasons include poor torque output at low frequencies by the inverter; in this case, the startup frequency can be adjusted (within a limited range, usually up to 5 Hz), the torque can be increased, or a vector control inverter can be used. 2. The external motor is still rotating at high speed when attempting to start it; the solution is to use another starting method or to brake the motor first. 　　B. The main causes of acceleration/deceleration overload are: excessive changes in the slip between the stator and rotor. 1. Reduce the acceleration/deceleration time to lower the rate of change in the stator’s parameters. 2. Install a braking unit or adjust the braking efficiency. 3. In the case of vector-controlled inverters, the PID parameters of the speed control loop can be modified. C. Constant-speed overload: 1. If it’s a single-drive system and there are fluctuations in the load, checking the mechanical components is a good approach. 2. If it’s a multi-drive system, other mechanical components might be affecting the operation of this equipment; therefore, check the coordination and synchronization between various components in the system. D. Overload error when stopping: 1. The amount of DC braking applied is too high; reduce the braking current and duration.

Thank you, it’s very helpful. I’ll discuss it with my supervisor and the others :) If there are any things I’m not clear about, I’ll ask further questions