Method for operating a frequency converter circuit
View Patent ↗A frequency converter circuit has at least two outputs that are respectively connected to a load, in particular an induction coil. A first output is operated at a first switching frequency and a second output is simultaneously operated at a second switching frequency that is different from the first, in such a way that noise having a frequency generated by the superposition of the first switching frequency and the second switching frequency is produced. The frequency converter circuit is operated in such a way that the frequency of the noise is lower than a first cutoff frequency and/or is higher than a second cutoff frequency.
1. A method of operating a frequency converter circuit having at least two outputs respectively connected to a load, the method which comprises:
operating a first output at a first switching frequency and simultaneously operating a second output at a second switching frequency different from the first switching frequency to produce noise having a frequency generated by a superposition of the first switching frequency and the second switching frequency;
operating the converter circuit to set the first switching frequency and the second switching frequency such that the frequency of the noise is lower than a first cut-off frequency or higher than a second cut-off frequency, the second cut-off frequency being higher than the first cut-off frequency; and
regulating an electrical power of at least one of the first and second outputs by adjusting the switching frequency and the relative switch-on time.
2. The method according to claim 1 , wherein the load is an induction coil.
3. The method according to claim 1 , which comprises determining the first cut-off frequency and/or the second cut-off frequency in dependence on a level of the noise.
4. The method of claim 3 , further comprising the step of estimating a level of the noise using the first and second switching frequencies of the first and second outputs and the electrical power supplied to the loads.
5. The method according to claim 1 , which comprises determining the first cut-off frequency and/or the second cut-off frequency in dependence on a total electrical power of the outputs.
6. The method according to claim 1 , which comprises setting the first cut-off frequency at 2 kilohertz and/or setting the second cut-off frequency at 14 kilohertz.
7. The method of claim 1 , wherein:
the first switching frequency is determined according to the required electrical power;
the relative switch-on time of 0.5 is used for the first output; and
the electrical power of the second load is adjusted using the relative switch-on time and the second switching frequency, and taking into account the first and second cut-off frequencies.
8. The method of claim 1 , wherein the frequency of the noise corresponds to a difference between the second switching frequency and the first switching frequency.