Suppression of First Side-Band Switching Harmonics Using DC-DC converters with an Advanced Modulation Scheme

The common DC bus concept has become an attractive solution for future aircraft electrical power systems. This paper considers the case where a battery connected DC-DC converter and a permanent magnet generator connected AC-DC converter are supplying a common dc bus. Applying a proper modulation scheme for DC-DC converters, suppression of the first-band harmonics (fc±3f0) from the AC-DC converter can be achieved. The proposed harmonic suppression scheme essentially uses the fact that two sinusoidal waveforms with phase shift of π will counteract to each other. For an aircraft engine driving generator, the fundamental frequency f0 is time-varying and dependent on aircraft engine speeds. This time-varying f0 is normally derived with a resolver and some measurement error is expected. To ensure the effectiveness of the proposed harmonic suppression scheme, an enhanced pulse width modulation (PWM) compensation scheme has been proposed and implemented every fundamental cycle when the rotor position is detected a zero crossing. The effectiveness of the proposed suppression scheme is validated by experimental results with selected fc-3f0 component for one DC-DC converter.