Why do some frequency inverters use braking resistors while others do not? What is the function of an external braking resistor?
A frequency converter is an electric drive device that controls the speed and output torque of a motor by changing the power supply frequency. In some applications, frequency converters require braking resistors to achieve specific functions. However, not all frequency converters require braking resistors; this depends on the specific application requirements and design goals.
First, let's understand what a braking resistor is. A braking resistor is a type of load resistor that absorbs the back electromotive force generated by the motor during braking, converting electrical energy into heat energy for dissipation. Braking resistors serve two main functions: first, they help the motor stop quickly, preventing excessive speed caused by inertia; second, they convert electrical energy into heat energy, reducing energy feedback in the circuit and protecting the motor and inverter.
So why do some frequency converters use braking resistors while others don't? This involves differences in application requirements and design goals. In some applications, the motor needs to stop or decelerate quickly to achieve precise control. In this case, a braking resistor can provide additional power dissipation, helping the motor to stop rapidly. For example, machining, factory automation, and transportation often require motors to have the ability to stop quickly. In these situations, the frequency converter needs to be equipped with a braking resistor to achieve this function.
On the other hand, some applications do not require precise control of motor speed variations, or only simple start and stop control. In such cases, a braking resistor may not be necessary. For example, motors in some ventilation, pumping, and conveyor belt applications do not require frequent starts and stops, and their speed changes are relatively gradual, thus eliminating the need for a braking resistor to aid in control.
Furthermore, some frequency converters are designed to maximize energy efficiency and save energy. Braking resistors convert electrical energy into heat, resulting in energy waste. Therefore, in these design goals, it is important to avoid or minimize the use of braking resistors.
However, even if some frequency converters do not use built-in braking resistors, a similar function can still be achieved through external braking resistors. External braking resistors typically consist of additional circuitry and resistors, connected to the frequency converter, and implement braking functionality through programming and control signals. The function of an external braking resistor is similar to that of a built-in braking resistor, providing additional power dissipation and a fast stop function.
It is important to emphasize that whether a braking resistor is built-in or external, its selection and configuration must be based on actual application requirements and design goals. The size, power, and resistance value of the braking resistor must be selected according to the characteristics of the motor and operating conditions to ensure the normal operation and safety of the braking function.
In summary, whether a frequency converter needs a braking resistor depends on the specific application requirements and design goals. Braking resistors provide rapid stopping and power dissipation, helping to achieve precise motor control. However, not all applications require braking resistors, and in some design goals, energy saving and improved energy efficiency may lead to minimizing their use. Whether the braking resistor is built-in or external, it needs to be selected and configured according to the actual situation to meet application requirements and improve system performance.
