When an electromagnetic heating controller is faced with an overvoltage problem, its countermeasures vary depending on the cause of the overvoltage. For energy-dissipating electromagnetic heating equipment, the method is to connect a braking resistor in parallel in the DC circuit of the electromagnetic heater. By detecting the DC bus voltage, we are able to control the on/off of the power tube. When the DC bus voltage rises to about 700V, the power tube is turned on, and the regenerative energy is introduced into the resistor and dissipated in the form of thermal energy, so as to prevent the DC voltage from continuing to rise.
For the electromagnetic heater with energy regenerative type, the electromagnetic heating on the grid side is reversible. When renewable energy is generated, reversible electromagnetic heating feeds the renewable energy back to the grid, so that the renewable energy can be fully utilized. However, this method requires high stability of the power supply. In the event of a sudden power outage, inverter subversion will occur.
For solenoid heaters with parallel DC bus absorption type, we use a multi-click drive system. In this system, each motor requires an electromagnetic heating device, multiple electromagnetic heaters share a grid-side electromagnetic heating controller, and all inverter parts are connected to a common DC bus. In this system, there are often one or several motors in the normal working braking state, and the motor in the braking state is dragged by other motors to generate regenerative energy. This energy is absorbed by the electric motor via the parallel DC bus. In the case of incomplete absorption, it is consumed by a common braking resistor.
DC bus overvoltage mainly occurs when the AC motor is in a braking state. At this time, the motor end is in the generator state, and its energy is sent to the DC wood wire on the input side of the inverter through the two tubes connected in parallel with the switching device of the inverter bridge, so that the energy storage capacitor connected to the bus is charged, resulting in the voltage on the DC bus rising. Generally speaking, electromagnetic heaters are equipped with DC bus overvoltage inducing units to prevent the overvoltage protection of electromagnetic heating equipment from shutting down. If the machine is shut down due to overvoltage protection, it is necessary to check whether the wiring of the unit caused by overvoltage is correct, whether the switching device is damaged, and whether the setting value of overvoltage protection is appropriate.