RESOURCES

Non−Isolated AC/DC Power Supply


Executive Summary

Electrical equipment is oftentimes well insulated from both earth ground and personnel. In such instances Galvanic Isolation from utility power might not be required. Under such conditions a simplified power converter topology can be employed, providing improved efficiency, power density and cost.


A power source well suited for providing DC power to electrical loads such as Isolated DC/DC converters, electric heaters, magnet coils, battery chargers, or others is proposed. The output of this supply can be either fixed or variable, providing good versatility. If coupled with isolated, unregulated DC/DC converters, the resultant power system is extremely efficient and compact. Likewise, for loads requiring variable DC power, excellent output dynamic range and control precision are available.

Input harmonic currents are well controlled, providing far superior performance as compared to traditional thyristor phase-regulated topologies.

Introduction

This paper reviews power topologies for generating high power DC from 3-phase power sources. A conventional liquid cooled isolated 54V output is reviewed as a benchmark, and a novel direct, non-isolated, high frequency switch mode circuit is compared at both the 54VDC and 380VDC bus levels.


The proposed topology has the advantage of maintaining its DC output relatively close to earth ground, minimizing the isolation required of connected equipment. This is in contrast with the conventional case, where the rectified output presents a voltage of similar magnitude as the input power line to appear from output to earth ground.


With the proposed topology, common-mode induced noise on follow-on stages is significantly reduced, and conductor to earth insulation spacing also benefits from a corresponding reduction (with proper redundant protection built in for safety). In addition, while the voltage rating of power semiconductors needs to be 1200V on a bulk rectified 480 VAC line, the topology presented herein can be safely implemented, maintaining the same margins, with conventional 600V semiconductors.

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