Multirate Digital Signal Processing and Noise Suppression for Dual Active Bridge DC-DC Converters in a Power Electronic Traction Transformer

Power electronic traction transformer (PETT) is a single-phase ac-dc conversional system, which is made up of a cascaded H-bridge converter and output-parallel dc-dc converters, such as dual active bridge dc-dc (DAB) converters. As the voltage fluctuation of the dc output voltage of DAB converters is very small and the gain cross-over frequency of the open-loop transfer function of DAB converters is generally high, the DAB closed-loop control system is very sensitive to the influence of noises. The typical noises include the equivalent noise due to the conflict of controller interrupts, the noise due to the mismatch of sampling frequency and switching frequency (which is denoted as switching noise), the noise due to the second-order voltage ripple in the dc input side, the noise due to the quantization process of the analog-to-digital converter (which is denoted as quantization noise), and the noise due to the measuring error of transducers and conditioning circuits (which is denoted as measurement noise). The generation mechanism of these noises and their impacts on the DAB converters are analyzed. On the basis, the corresponding noise suppression schemes are presented, especially for the switching noise, quantization noise, and measurement noise. Besides, the mathematical models toward the sampling and the phase-shift modulation under multirate circumstance are derived, and the multirate digital control strategy of the PETT is proposed. Finally, based on a five-cell PETT laboratory prototype with a rated power of 30 kW, further research is carried out and the experiment results all verify the effectiveness of the proposed algorithms.