Techniques for conditioning high-speed bit-stream signals for power electronic applications

The bit-stream technique, which uses one bit wide and low to high frequency digital signals to represent control values, is a new approach for designing controllers. A bit-stream signal can directly be used to control power electronics systems but its inherently high switching speeds may lead to excessive switching losses, which are a major concern for many potential power electronic applications. This paper therefore proposes three different conditioning techniques or modulators, which convert high speed bit-stream signals into relatively low speed bit-stream signals that are suitable for bit-stream control of power electronics systems. The performance of the proposed modulation techniques, namely standard fixed-frequency PWM, standard down-sampled bit-streams (SDBS) and hysteretically down-sampled bit-streams (HDBS), is investigated in detail, using low speed bit-stream signals generated by the modulators as gate drive signals for a single phase DC to AC inverter. Simulation results show that the HDBS approach offers spread spectrum operation, lower switching losses than PWM, and uses the fewest hardware resources. Experimental results confirm that the HDBS modulator operates as expected, and produces an output current with a lower THD than a conventional PWM design.