A chemical fiber filament drawing production line is composed of three drafting machines, each driven by separate motors. The first roller motor has a power of 22KW, 4-pole, with a worm reducer and a speed ratio of 25:1; the second roller motor is 37KW, 4-pole, with a worm reducer and a speed ratio of 16:1; the third roller motor is 45KW, cylindrical gear reduction with a speed ratio of 6:1. These motors are powered by Huawei TD2000-22KW, IHF37K, and IHF45K inverters. The three inverters are controlled proportionally based on the draft ratio and speed ratio. The process involves winding the tow on the first, second, and third rolls, with the inverter controlling the speed differences between the rolls to achieve the desired drafting.
Initially, when the system was running with a low draft ratio, everything operated smoothly. However, after some time, due to process adjustments, the draft ratio and total denier of the tow increased. This led to higher drag forces on the rolls, especially between the first and second rolls, which account for about 70% of the total draft ratio. As a result, the first inverter started displaying SC (overvoltage prevention), and occasionally, the second inverter also showed E006 (overvoltage). The problem arose because the first and second roller motors were operating in a regenerative state, generating braking energy that the inverters could not handle effectively.
When the inverters detect overvoltage, they automatically increase the output frequency to prevent tripping, which leads to an increase in motor speed. However, this approach wasn’t sufficient to manage the high levels of regenerative energy. Therefore, the main issue was ensuring that the first and second roller motors had enough braking torque to maintain control during the drafting process.
Increasing the inverter and motor capacity would have been one solution, but it was not cost-effective. Instead, external brake units were added to both the first and second inverters. Two sets of Huawei TDB-4C01-0300 brake components were installed and tested. After implementation, the braking performance was significantly improved, confirming our analysis. The system has been running smoothly for nearly a year without any overvoltage issues.
This case highlights the importance of addressing overvoltage caused by regenerative braking. Several methods were explored, including DC bus absorption and energy feedback. Through practical application examples, the effectiveness of regenerative braking was demonstrated. The results clearly show that implementing proper regenerative braking systems is the most efficient way to prevent overvoltage and ensure stable operation of the system.
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