There are so many ways to mitigate the harmonic, but no any solution to solve all the problems. Different power supply, different load, need we offer the best solution to mitigate the harmonic.
The table below compare of THDi of various harmonic mitigate technologies before.
| Six pulse vfd
no reactor/choke |
Six pulsed vfd
Low DC bus capacitor |
Six pulse vfd+5% reactor/choke | 3 phase vfd active front end drive | Six pulse vfd+passive filter | Multipulse vfd | |
| Typical THDi | 90--120% | 35--40% | 35--45% | 3--5% | 5--10% | 12 pulse:10--12%
18 pulse: 5--6% |
| Pros | Simple and low cost solution, acceptable for installations with low quantities of small drives | Simple and low cost solution that result in some mitigate of current harmonics | Standard solution in HVAC applications | Best harmonic performance of any of the solutions.
Ability to boost output voltage during low-line conditions. Unity fundamental power factor. Can provide regenerative braking |
Assuming physical space is available, a passive harmonic filter can be added after the drive is installed, if harmonics are determined to be a problem. | Traditional harmonic mitigate method. |
| Cons | High harmonic content, not recommended for installations with higher quantities of drives. | Higher voltage distortion, more than the six pulse vfd with 5% reactor/choke. | Systems with a large quantity or large sizes of drives, may require additional harmonic mitigation. | The drive itself generates slightly more heat than a standard six pulse drive with reactor. | Leading power factor at light loads unless the filter’s capacitors are switched out
of the circuit. Risk of resonances between the filter capacitors and other capacitors in the system. |
Optimal harmonic performance requires perfectly balanced AC power feed with little background distortion.
Very difficult to retrofit in the field. |
With the continuous development of IGBT power technology, the new three-level active filter has been widely promoted and used in the market. APF acquires the current signal in real time through an external current transformer, and separates the harmonic part through the internal detection circuit, and generates a compensation current with the opposite phase of the harmonics in the system through the IGBT power converter to realize the function of filtering out harmonic.
The output compensation current of APF varies accurately according to the dynamic harmonics of the system, so there will be no compensation problem. In addition, APF has overload protection function. When the harmonic of the system is larger than the filter capacity, the device can automatically limit the output of 100% rated capacity without overload.
Post time: Nov-24-2023