Time and Frequency Domain Evaluation Method of Current Noise on the Power Line connected Multiple LED Bulbs

The electromagnetic noise generated from the inverter circuit in the LED lighting unit has become a problem influencing to the communication system. The purpose of this research is to examine the evaluation method under the condition of the multiple LED bulbs connected to power line. When the spike-shaped current waveforms generate by switching of inverter, the large amplitude noise at wide frequency band is observed. The current waveform converts to frequency spectrum by short time fast Fourier transform (STFT). Since the spike-shaped waveform diminishes over time, current noise amplitude at time zone during which noise is not generated is very small. The amplitude variation at the peak frequency is small. As the peak frequencies are estimated the power line resonance, current noise generated by spike-shaped noise does not decrease. On the other hand, at the 20 LED bulbs, the current waveform synthesized from each LED bulbs is non-periodic and nonuniform. The variation of amplitude is larger than that of one LED bulb due to distance between LISN to LED bulbs or individual specificity of each LED bulbs. The effective current variating to time is calculated. The maximum histogram at each frequency is coincided with effective current. These methods can be possible to evaluate the noise from the multiple LED bulb.