Inverter overcurrent protection reason

In the inverter, the object of overcurrent protection mainly refers to the case where the peak value of the current has a sudden change exceeding the allowable value of the inverter.

Due to the poor overload capability of the inverter device, the overcurrent protection of the inverter is a crucial part. So far, it has been developed very well.

1. Overcurrent in operation, that is, the electric drive system has an overcurrent during the working process. The reasons are mainly from the following aspects:

(1) The motor encounters an impact load, or the drive mechanism is "stuck", causing a sudden increase in the motor current.

(2) The output side of the inverter is short-circuited, such as a short circuit between the output terminals and the motor, or a short circuit inside the motor.

(3) The inverter itself is not working properly. For example, two inverter devices of the same bridge arm in the inverter bridge are abnormal during the continuous alternating conduction. For example, due to the high ambient temperature or the aging of the inverter device itself, the parameters of the inverter device are changed, resulting in one device being turned on during the alternation process, and the other device being turned off in the future, causing the same The "straight through" between the upper and lower devices of the bridge arm causes the short-circuit state between the positive and negative terminals of the DC voltage.

Figure speed up and down speed too fast

a) The speed is too fast b) The speed is too fast

2. Overcurrent in speed up

When the inertia of the load is large and the speed up time is set too short, an overcurrent will occur. This is because the speed up time is too short, which means that during the speed increase process, the operating frequency of the inverter rises too fast, the synchronous speed n0 of the motor rises rapidly, and the speed nM of the motor rotor is not due to the large inertia of the load. Going up, causing the rotor winding to cut the magnetic lines of force too fast (equal to the slip is too large), the result is that the rising speed current is too large, as shown in Figure a.

3. Overcurrent in speed reduction

When the inertia of the load is large and the deceleration time is set too short, it will also cause an overcurrent. Because the speed reduction time is too short, the synchronous speed decreases rapidly, and the rotor of the motor maintains a high speed due to the inertia of the load. This also causes the rotor winding to cut the magnetic lines too fast and generate an overcurrent, as shown in Figure b. Show.