Generalized Method for Designing Nonisolated Safety Standard Compliant Onboard Chargers for Electric Vehicles

Galvanic isolation, characterized by the inclusion of a transformer as a conversion stage, is the most commonly used method to eliminate hazardous common-mode (CM) current in grid tied converters. However, this solution tends to harm system efficiency and power density, while increasing costs. This issue is of particular importance for electric vehicle, where the industry is devoting significant resources to improve vehicle power density, cost, and range. This paper proposes a general, systematic method to design nonisolated converters with near zero CM currents. Several options of connection structure are provided, and two converters are designed to elucidate the method. Simulations are performed to demonstrate the CM performance improvement delivered by the proposed solution.