The object of overcurrent protection in the inverter mainly refers to the overcurrent detection value (about 200% of the rated current) with a sudden change in nature, the peak value of the current exceeds the overcurrent detection value, the inverter displays OC to indicate the overcurrent, due to the poor overload capacity of the inverter parts, so the overcurrent protection of the frequency converter is a crucial part.
First, the cause of overcurrent fault analysis of inverter
Overcurrent fault can be divided into acceleration, deceleration, constant speed overcurrent. It may be caused by the acceleration and deceleration time of the frequency converter is too short, the load has a sudden change, the load distribution is uneven, the output is short-circuited and other reasons. At this time, generally through the extension of acceleration and deceleration time, reduce the sudden change of the load, plus energy braking components, load distribution design, check the line and so on to solve the problem. If disconnecting the load frequency converter or overcurrent fault, the inverter inverter circuit is bad, need to replace the frequency converter. According to the inverter display, you can find the reasons from the following aspects:
(1) overcurrent in work, i.e., overcurrent in the dragging system in the working process. The causes are roughly as follows:
First, the motor meets the impact load or the structure of the motor "stuck" phenomenon, causing a sudden increase in motor current;
Second, the output side of the inverter short circuit, such as the output to the motor between the connecting wires short-circuit, or motor internal short-circuit, etc., grounding (motor burnout, insulation degradation, cable damage caused by contact, grounding, etc.)
Third, the inverter itself is not working properly, such as inverter bridge in the same bridge arm of the two inverter pieces in the constant alternation of the work process is abnormal. For example, the ambient temperature is too high, or the aging of the inverter components themselves, so that the parameters of the inverter change, resulting in the alternation process, a device has been on, while the other device has not yet had time to turn off, resulting in the same bridge arm of the upper and lower two devices of the "through", so that the positive and negative DC voltage is in a short-circuit state between the positive and negative. The positive and negative terminals of the DC voltage are in a short-circuit state.
(2) Over-current during speed-up and speed-down: When the inertia of the load is large, and the speed-up time or speed-down time is set too short, it will also cause over-current. In the process of speed up, the frequency converter operating frequency rises too fast, the synchronous speed of the motor rises rapidly, and the rotor speed of the motor due to the load inertia and can not keep up, the result is that the speed current is too large; in the process of speed reduction, the speed reduction time is too short, the synchronous speed drops rapidly, and the motor rotor due to the inertia of the load, but still maintains a higher rotational speed, which can also make the rotor windings cut the speed of the magnet wire is too large to produce overcurrent. Too large and produce overcurrent.
Second, the frequency converter overcurrent fault processing methods
(1) when starting a speed trip, this is a very serious phenomenon of overcurrent, the main check:
A work machinery is not stuck;
B there is no short circuit on the load side, use megohmmeter to check whether there is no short circuit to the ground; l there is no damage to the power module of the inverter;
C motor starting torque is too small, the drag system can not turn up.
(2) If the motor does not trip immediately when starting, but trips during operation, mainly check:
l Ramp-up time setting is too short, lengthen the acceleration time; l Deceleration time setting is too short, lengthen the deceleration time;
The torque compensation (u/f ratio) is set too large, causing excessive no-load current at low frequency;
The electronic thermal relay is improperly calibrated, and the operation current is set too small, causing the inverter to operate incorrectly.
Finally remind, if the above methods can not solve the problem, it is the inverter hardware circuit is bad, usually drive circuit or module problems, replace the optocoupler or IGBT most can solve the problem.