Frequency converter overvoltage generation and regenerative braking - News - Global IC Trade Starts Here.

Specializing in the production of LED chip LED LED lamp beads

Photocoupler

The overvoltage of the inverter refers to the voltage of the inverter exceeding the rated voltage due to various reasons, and is concentrated on the DC voltage of the DC bus of the inverter. During normal operation, the DC voltage of the inverter is the average value after three-phase full-wave rectification. If calculated with a line voltage of 380V, the average DC voltage Ud=1.35U line = 513V.

When an overvoltage occurs, the storage capacitor on the DC bus will be charged. When the voltage rises to about 700V, the inverter overvoltage protection action (depending on the model). There are two main causes of overvoltage: power supply overvoltage and regenerative overvoltage. The overvoltage of the power supply means that the DC bus voltage exceeds the rated value because the power supply voltage is too high. Most inverters now have an input voltage of up to 460V, so the overvoltage caused by the power supply is extremely rare.

The main issue discussed in this paper is the regenerative overvoltage. The main reason for generating regenerative overvoltage is as follows: When the large GD2 (flywheel torque) load decelerates, the deceleration time of the inverter is set too short; the motor is affected by external force (fan, drafting machine) or potential energy load (elevator, crane). For these reasons, the actual motor speed is higher than the command speed of the inverter, that is, the motor rotor speed exceeds the synchronous speed. At this time, the slip of the motor is negative, and the direction of the rotor winding cutting the rotating magnetic field is opposite to that of the motor state. The electromagnetic torque generated is a braking torque that hinders the direction of rotation. Therefore, the motor is actually in a power generation state, and the kinetic energy of the load is "regenerated" into electrical energy.

The regenerative energy charges the inverter DC storage capacitor through the freewheeling diode of the inverter, so that the DC bus voltage rises, which is the regenerative overvoltage. Since the torque generated during the process of regenerating the overvoltage is opposite to the original torque, it is the braking torque, so the process of regenerating the overvoltage is the process of regenerative braking. In other words, the regenerative energy is eliminated and the braking torque is increased. If the regenerative energy is not large, the inverter and the motor itself have 20% regenerative braking capacity, and this part of the electric energy will be consumed by the inverter and the motor. If this part of the energy exceeds the consumption capacity of the inverter and the motor, the capacitance of the DC link will be overcharged, and the overvoltage protection function of the inverter will operate to stop the operation. In order to avoid this situation, this part of the energy must be disposed of in time, and the braking torque is also increased, which is the purpose of regenerative braking.