As a supplier of frequency inverters, I often encounter questions from customers about the braking function of frequency inverters. Today, I’d like to delve into what the braking function of a frequency inverter is and how it works. Frequency Inverter
What is the Braking Function of a Frequency Inverter?
The braking function of a frequency inverter is a crucial feature designed to control the deceleration of an electric motor. In many industrial applications, motors need to stop quickly and precisely. For example, in conveyor systems, cranes, and elevators, sudden stops or rapid deceleration may be required for safety or operational efficiency. The braking function of the frequency inverter enables the motor to slow down or stop within a specified time frame, preventing over – running and ensuring smooth operation.
There are mainly two types of braking functions in frequency inverters: dynamic braking and regenerative braking.
Dynamic Braking
Dynamic braking is a common method used in frequency inverters. When the motor is in the process of deceleration, it acts as a generator, converting the mechanical energy of the rotating motor into electrical energy. In dynamic braking, this electrical energy is dissipated as heat through a braking resistor.
The principle behind dynamic braking is based on the fact that when the frequency inverter reduces the output frequency to the motor, the motor speed becomes higher than the synchronous speed corresponding to the new frequency. At this time, the motor operates in the generating mode, and the induced electromotive force (EMF) is generated. The braking resistor is connected to the DC bus of the frequency inverter. The electrical energy generated by the motor is then dissipated in the form of heat in the braking resistor, which in turn slows down the motor.
Dynamic braking is relatively simple and cost – effective. It is suitable for applications where the braking energy is not very large and the braking time does not need to be extremely short. For example, in some small – scale conveyor systems, dynamic braking can meet the requirements well.
Regenerative Braking
Regenerative braking is a more advanced and energy – efficient braking method. Similar to dynamic braking, when the motor decelerates, it also generates electrical energy. However, instead of dissipating this energy as heat, regenerative braking feeds the electrical energy back to the power grid.
The regenerative braking system in a frequency inverter consists of a rectifier, an inverter, and a control circuit. When the motor generates electrical energy during deceleration, the control circuit detects the DC bus voltage. If the voltage exceeds a certain threshold, the inverter is controlled to convert the DC power back into AC power with the same frequency and phase as the power grid, and then feed it back to the grid.
Regenerative braking is particularly suitable for applications with large braking energy, such as high – speed elevators and large – scale cranes. By feeding the energy back to the grid, it can save a significant amount of energy and reduce operating costs.
How Does the Braking Function Work?
Dynamic Braking Process
- Deceleration Command: When the frequency inverter receives a deceleration command, it starts to reduce the output frequency to the motor. As the frequency decreases, the synchronous speed of the motor also decreases.
- Generating Mode: Once the motor speed is higher than the new synchronous speed, the motor enters the generating mode. In this mode, the motor generates an induced EMF, and the current flows through the stator windings.
- Braking Resistor Activation: The electrical energy generated by the motor is transferred to the DC bus of the frequency inverter. When the DC bus voltage rises above a certain set value, the braking transistor in the frequency inverter is turned on, connecting the braking resistor to the DC bus. The electrical energy is then dissipated as heat in the braking resistor, and the motor slows down.
- Monitoring and Control: The frequency inverter continuously monitors the DC bus voltage. If the voltage drops below a certain value, the braking transistor is turned off to prevent over – dissipation of energy.
Regenerative Braking Process
- Deceleration Detection: Similar to dynamic braking, the frequency inverter first detects the deceleration command and starts to reduce the output frequency.
- Energy Generation: The motor enters the generating mode, generating electrical energy. The DC bus voltage starts to rise.
- Grid – Feed – Back Control: When the DC bus voltage exceeds the set threshold, the control circuit of the frequency inverter activates the regenerative braking function. The inverter converts the DC power on the bus into AC power with the appropriate frequency and phase.
- Energy Feed – Back: The converted AC power is then fed back to the power grid through the grid – connected circuit. The frequency inverter continuously monitors the grid voltage and current to ensure that the energy is fed back safely and efficiently.
Advantages of the Braking Function in Frequency Inverters
Safety
The braking function enhances the safety of the motor – driven equipment. In applications such as elevators and cranes, sudden stops are often required to prevent accidents. The braking function of the frequency inverter can ensure that the motor stops quickly and accurately, reducing the risk of collisions and other safety hazards.
Efficiency
As mentioned earlier, regenerative braking can save energy by feeding the braking energy back to the grid. This not only reduces the operating cost but also makes the system more environmentally friendly. Even in the case of dynamic braking, although the energy is dissipated as heat, it still allows for precise control of the motor’s deceleration, improving the overall efficiency of the system.
Precision
The braking function enables precise control of the motor’s deceleration time and stopping position. In industrial automation, this precision is crucial for ensuring the quality and accuracy of the production process. For example, in a robotic arm application, the ability to stop the motor precisely at a specific position is essential for performing tasks accurately.
Applications of the Braking Function
Industrial Conveyor Systems
In conveyor systems, the braking function is used to stop the conveyor belt quickly when there is a need to prevent material spillage or when maintenance is required. Dynamic braking is often used in small – to – medium – sized conveyor systems, while regenerative braking may be employed in large – scale conveyor systems to save energy.
Elevators
Elevators require precise control of the braking function to ensure smooth and safe operation. Regenerative braking is commonly used in modern elevators to recover the energy generated during the descent of the elevator car, reducing the overall energy consumption of the elevator system.
Cranes
Cranes need to stop quickly and precisely when lifting and moving heavy loads. The braking function of the frequency inverter allows for safe and efficient operation of the crane, preventing over – running and ensuring the stability of the load.
Why Choose Our Frequency Inverters for Braking Applications?
Our frequency inverters are designed with high – quality components and advanced control algorithms to ensure reliable and efficient braking performance. We offer both dynamic and regenerative braking options to meet the diverse needs of different applications.
Our R & D team is constantly working on improving the braking function of our frequency inverters. We use the latest technologies to enhance the energy – saving performance of regenerative braking and to optimize the heat – dissipation design of dynamic braking.
In addition, our frequency inverters are easy to install and operate. We provide comprehensive technical support and after – sales service to ensure that our customers can use our products with confidence.
Permanent Magnet Propulsion Motor If you are looking for a reliable frequency inverter with excellent braking function for your application, we would be more than happy to discuss your requirements. Whether you need a small – scale frequency inverter for a simple conveyor system or a large – scale one for a high – end industrial application, we have the right solution for you. Please feel free to contact us to start a procurement negotiation, and let us work together to find the best frequency inverter for your needs.
References
- "Power Electronics: Converters, Applications, and Design" by Ned Mohan, Tore M. Undeland, and William P. Robbins.
- "Electric Drives: Concepts, Applications, and Control" by Simon M. Dunn.
- Technical documentation of various frequency inverter manufacturers.
Ciitto servo Motor Co., Ltd.
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