How to reduce the interference of switching power supply to the power grid
1. Reduce voltage overshoot. Reducing the voltage overshoot not only prevents the tube from being exposed to excessive voltage, but also reduces high frequency noise to the grid. Selecting a diode with a small reverse recovery current, such as a silicon carbide diode, is also a viable method of reducing the intensity of the interference source. Although adjusting the edge of the trigger pulse and increasing the resistance of the gate can reduce the dv/dt, this will increase the switching loss and reduce the efficiency of the entire device. It is necessary to comprehensively consider the trade-offs of various properties of the switching power supply.
2. Improve the modulation method. The frequency-invariant modulation is changed to random modulation, frequency conversion modulation, and so-called “∑ △” modulation and so on. The interference low frequency band generated by the fixed frequency modulation pulse is mainly the harmonic interference of the modulation frequency, the low frequency interference is mainly concentrated on each harmonic point, and the low frequency interference generated by random modulation and other methods is dispersed in a certain frequency band. Therefore, the adoption of the above measures is conducive to the switching power supply through the test of the spectral characteristics of electromagnetic interference, so that it meets the electromagnetic standards of the power supply.
3. Increase the input filter. The two methods (1) and (2) are mainly to reduce the intensity of the interference source, while increasing the filter is to change the characteristics of the coupling channel. The added common-mode filter can reduce the interference of the switching power supply to the power grid. If no input filter is added, the power supply’s interference to the power grid will greatly exceed the corresponding standard. After adding the input filter, the interference of the power supply to the power grid will meet the corresponding standards. When taking measurements into account, the low-frequency interference of the switching power supply to the power grid is mainly harmonics of integral multiples of the switching frequency, so the frequency band resolution of the frequency sweeping instrument is 200 Hz, and the frequency band resolution in the frequency band of 150 kHz to 30 MHz is 9 kHz. The use of shielding measures can also reduce the interference of the switching power supply to the power grid.
The power supply is qualified through electromagnetic compatibility testing and meets the requirements of the standard. It is two different issues whether switching power supply will cause non-permissible interference during use. The use of standard power supplies or improper handling may also cause serious interference during use. Moreover, the switching power supply is not only a power supply device but also a noise generating device. It is connected to the disturbed element via a coupling channel. Obviously, the characteristics of the coupling channel do not cooperate well with the characteristics of the disturbed element and cause serious interference. It is possible that the phenomenon that the entire system is unstable due to the parallel power supply of the switching power supply is also present.