The supplier of frequency converter braking unit reminds you that with the popularity of frequency converters, the use of braking units as one of the supporting equipment for frequency converters is also increasing.
1、 The main function of the braking unit
In certain applications, rapid deceleration is required. According to the principle of asynchronous motors, the greater the slip, the greater the torque. Similarly, the braking torque will increase with the increase of deceleration rate, greatly shortening the deceleration time of the system, accelerating energy feedback, and causing the DC bus voltage to rise rapidly. Therefore, the feedback energy must be quickly consumed to maintain the DC bus voltage below a certain safe range. The main function of the braking unit system is to quickly dissipate the energy (which is converted into thermal energy by the braking resistor). It effectively compensates for the disadvantages of slow braking speed and small braking torque (≤ 20% rated torque) of ordinary frequency converters, and is very suitable for situations where fast braking is required but the frequency is low.
2、 Advantages of braking unit
Due to the short-term operation of the braking unit, which means that the power on time is very short each time, the temperature rise during the power on time is far from stable; The interval time after each power on is longer, during which the temperature is sufficient to drop to the same level as the ambient temperature. Therefore, the rated power of the braking resistor will be greatly reduced, and the price will also decrease accordingly; In addition, due to the fact that there is only one IGBT and the braking time is in the millisecond range, the instantaneous performance indicators for power transistor turn-on and turn off are low, and even the turn off time is required to be as short as possible to reduce the turn off pulse voltage and protect the power transistor; The control mechanism is relatively simple and easy to implement. Due to the above advantages, it is widely used in potential energy loads such as cranes and in situations where rapid braking is required but for short-term work.
3、 The action process of the braking unit
1. When the electric motor decelerates under external force, it operates in a generating state, producing regenerative energy. The three-phase AC electromotive force generated by it is rectified by a three-phase fully controlled bridge composed of six inverter specific energy feedback units and freewheeling diodes in the inverter section of the inverter, which continuously increases the DC bus voltage inside the inverter.
2. When the DC voltage reaches a certain voltage (the starting voltage of the braking unit), the power switch tube of the braking unit opens and current flows through the braking resistor.
3. The braking resistor releases heat, absorbs regenerative energy, reduces motor speed, and lowers the DC bus voltage of the frequency converter.
4. Khi điện áp bus DC giảm xuống một mức điện áp nhất định (điện áp dừng của bộ hãm), transistor công suất của bộ hãm sẽ tắt. Lúc này, dòng điện hãm không chạy qua điện trở, và điện trở hãm sẽ tự tản nhiệt, làm giảm nhiệt độ của chính nó.
5. Khi điện áp của bus DC tăng trở lại để kích hoạt bộ phận phanh, bộ phận phanh sẽ lặp lại quá trình trên để cân bằng điện áp bus và đảm bảo hệ thống hoạt động bình thường.