The supplier of the frequency converter braking unit reminds you that the method used for energy consumption braking is to install a braking unit component on the DC side of the frequency converter, which consumes the regenerated electrical energy on the power resistor to achieve braking. This is the most direct way to handle regenerative energy, which is to consume the regenerative energy through a dedicated energy consumption braking circuit on a resistor and convert it into thermal energy. Therefore, it is also known as resistance braking, which includes a braking unit and a braking resistor.
(1) Braking unit. The function of the braking unit is to connect the energy dissipation circuit when the voltage Ud of the DC circuit exceeds the specified limit (such as 660V or 710V), allowing the DC circuit to release energy in the form of thermal energy after passing through the braking resistor. The braking unit can be divided into two types: internal and external. The internal type is suitable for low-power general-purpose frequency converters, while the external type is suitable for high-power frequency converters or working conditions with special requirements for braking. In principle, there is no difference between the two. The braking unit serves as a "switch" to connect the braking resistor, including a power transistor, a voltage sampling comparison circuit, and a driving circuit.
(2) Braking resistor. Braking resistor is a carrier used to consume the regenerative energy of an electric motor in the form of thermal energy, including two important parameters: resistance value and power capacity. Generally, corrugated resistors and aluminum alloy resistors are more commonly used in engineering. Corrugated resistors use surface vertical corrugations to facilitate heat dissipation and reduce parasitic inductance. High flame retardant inorganic coatings are also selected to effectively protect the resistance wires from aging and extend their service life; Aluminum alloy resistors have better weather resistance and vibration resistance than traditional ceramic frame resistors, and are widely used in harsh industrial control environments with high requirements. They are easy to install tightly, easy to attach heat sinks, and have a beautiful appearance.
The process of energy consumption braking is: when the electric motor decelerates or reverses (including being dragged) under external force, the electric motor runs in a generating state, and the energy is fed back to the DC circuit, causing the bus voltage to rise; The braking unit samples the bus voltage. When the DC voltage reaches the conduction value set by the braking unit, the power switch tube of the braking unit conducts, and current flows through the braking resistor; The braking resistor converts electrical energy into thermal energy, reducing the speed of the motor and lowering the DC bus voltage; When the bus voltage drops to the cut-off value set by the braking unit, the switching power transistor of the braking unit is cut off, and no current flows through the braking resistor.