Digital Multi-Loop Control of a 3-Level Rectifier for Electric Vehicle Ultra-Fast Battery Chargers

Abstract

This paper proposes a digital multi-loop control strategy for a 3-level unidirectional rectifier specifically targeted to electric vehicle (EV) ultra-fast charging applications. The basic operation of a 3-level rectifier is described and the state-space model of the complete system is explained, with particular focus on the mid-point current generation process. By means of an appropriate modeling of the delays and the discretization introduced by the digital control implementation, four controllers (i.e. dq-currents, DC-link voltage and mid-point voltage balancing loops) are analytically designed in the continuous time domain with conventional techniques. Ultimately, the proposed controller design procedure is tested on a 50 kW, 20kHzT-type rectifier, both in simulation and hardware-in-the-loop (HIL) environments, verifying the dynamical performance of all control loops.