Overvoltage fault when the inverter decelerates
Overvoltage fault when the inverter decelerates
The most common time for a VFD overvoltage fault to occur is during deceleration. Sometimes the braking torque request exceeds the drive braking circuit capacity. Other times the deceleration is too fast for its load and the inertia from the load is faster than the specified frequency. If a stop is encountered during deceleration, the load rotates faster than the specified frequency and the motor regenerates power back to the drive. The motor load then becomes a generator. This power is fed back into the driver and stored on the DC bus. Extending the deceleration time is one way to solve the VFD overvoltage fault during deceleration.
If extended deceleration time does not resolve the VFD overvoltage fault, dynamic braking may be required to dissipate the excess energy. A dynamic brake is a resistive device that takes energy from the bus and burns it off as heat. The only other solution is to reduce the inertia of the motor load. How you do this depends on your application. A constant overhaul load can be a good application for a regenerative drive, where energy is removed by converting it to heat instead of dynamic brakes, the regenerative unit returns the energy to the utility line, and may even reduce your energy bill.
VFD overvoltage faults during acceleration are uncommon, but have been known to occur for extended periods of time under high inertia loads. A flywheel is a common high inertia application that can accelerate in time. During acceleration, these types of loads can actually accelerate faster than an electric motor due to inertia, and the load becomes regenerative. To address overvoltage during acceleration, try reducing the acceleration time. Some experimentation and fine-tuning is usually required before the technician is satisfied with the results and commits to speeding up the time setting.