In the frequency converter, motor fast braking or accurate stopping, generally using power braking and regenerative braking. For the power braking mode, the braking torque required by the system is below 20% of the rated torque of the motor and the braking is not fast, there is no need for external braking resistor, and only the internal active loss of the motor can make the DC side voltage limit below the action value of the over-voltage protection. On the contrary, it is necessary to select a braking resistor to dissipate this part of the energy regenerated by the motor. In order to realize electrical braking, the DC side of the inverter must be equipped with a voltage detection circuit to detect the voltage of the capacitor in order to realize energy braking. Braking resistors are widely used in various electronic products.
When braking with external braking resistor, the external resistor should be able to absorb 80% of the electrical energy transformed by the load potential energy, of which 20% can be consumed through the motor in the form of heat dissipation, at this time the value of the braking resistor becomes smaller, whether the motor is repeatedly decelerated, the selection of braking resistor rated power is different. When non-repeated deceleration, the braking resistor of the intermittent time (T-tS) > 600s. Usually use the continuous duty resistor, when the intermittent braking, the resistor’s permissible power will increase the application of the correct choice of the braking unit resistor can shorten the free stopping time of the large inertia loads to achieve rapid stopping or accurate stopping; can also be in the bit energy loads are lowered to achieve regenerative operation.
Some customers’ electrolysis workshop multifunctional unit design did not consider adding inverter braking resistor, resulting in long free stopping time and long skidding distance of the big car, which exists a hidden danger of production and operation; it is difficult to realize accurate positioning of tool trolleys and aluminum trolleys, which affects the operation efficiency. After the installation of braking resistors, the above problems are solved. However, it should be noted that, in the selection of braking resistor, not only to consider the requirements of each manufacturer’s inverter braking resistor selection, but also according to the user’s control requirements and the use of different environments, it must be through the speed, torque and other measurements, and then calculate the correct selection of braking resistor, in order to achieve the user’s control requirements.
