Which products are affected?
8200 motec 0.55 kW to 2.2 kW
How is the reaction?
During acceleration phase the motor current increases strongly. When Imax is reached the internal current controller of the 8200 motec lowers the output frequency. This procedure is so quick that the motor switches to generator operation and regenerates energy to the drive controller. The generator energy power is so high that the overvoltage trip is set to the frequency inverter, which then sets pulse inhibit. This is enabled by the very small DC bus capacity in spite of the internal brake resistor. After the DC bus voltage has decreased the frequency inverter reaccelerates the motor at its current limit. This causes a prolongation of the driving cycle.
When does the problem occur?
Applications with high dynamic acceleration procedures (very short acceleration ramp)
Possible diagnostics?
Make an oscilloscope trace of the motor current
Short-term measures / recommendations?
- In order to avoid the quick decreasing of the output frequency the ramp function generator of the set value is stopped (C0410.5 = 203) when the Imax limit is reached. This avoids that the motor is set to generator operation, and this measure avoids the overvoltage trip.
- Additionally, the current controller must be adapted to the dynamic and real machine conditions by decreasing of the integral action time (C0078) and increasing of the proportional part (C0077). Attention: Due to the quick current controller the system can oscillate. In this case an inverter with DC bus capacity should be applied (8200 motec M4, or 8200 vector). The DC bus serves as an energy store and attenuation element and decreases oscillations, the current controller can be set more slowly.
- Another measure to improve the operational safety is a prolonged acceleration time to a value, where the current controller does not need to intervene.
