Full Digital Control of an All-Si On-Board Charger Operating in Discontinuous Conduction Mode

• Main Authors: Davide Cittanti, Matteo Gregorio, Fabio Mandrile, Radu Bojoi
• Format: Article
• Language: English
• Published: MDPI AG 2021-01-01
• Series: Electronics
• Subjects: digital control; on-board charger (OBC); discontinuous conduction mode (DCM); power factor corrector (PFC); interleaved boost converter; isolated DC/DC
• Online Access: https://www.mdpi.com/2079-9292/10/2/203

This paper deals with the design, tuning and implementation of a digital controller for an all-Si electric vehicle (EV) on-board battery charger operated in discontinuous conduction mode (DCM). This charger consists of two cascaded conversion stages: a front-end power factor corrector (PFC) with two interleaved legs and an isolated phase-shifted full bridge DC/DC converter. Both stages operate in DCM over the complete battery charging power range, allowing lower inductance values for both the PFC and the DC/DC filtering elements. Moreover, DCM operation ensures a large reduction of the reverse-recovery losses in the power diodes, enabling the adoption of relatively cheap Si devices. The main goal of the work is to address the well-known DCM control challenges, leveraging a novel control strategy for both converter stages. This control scheme counteracts the DCM system non-linearities with a proper feed-forward contribution and an open-loop gain adjustment, ensuring consistent dynamical performance over the complete operating range. The designed controllers are tuned analytically, taking into account the delay components related to the digital implementation. Finally, the proposed control strategy is implemented on a single general purpose microcontroller unit (MCU) and its performance is experimentally validated on a <inline-formula><math display="inline"><semantics><mrow><mn>3</mn><mo>.</mo><mn>3</mn></mrow></semantics></math></inline-formula><inline-formula><math display="inline"><semantics><mi mathvariant="normal">k</mi></semantics></math></inline-formula><inline-formula><math display="inline"><semantics><mi mathvariant="normal">W</mi></semantics></math></inline-formula> battery charger prototype.