A Minimum DC-Link Capacitance Estimation and Robust Voltage Control for an N-Phase Interleaved Boost Converter Supplying a Traction Inverter

There is a growing demand for high-power-density powertrains in electric and hybrid vehicles to increase the space available for passengers and/or other high-technology electronics. The dc-link capacitor bank occupies a large volume in traction inverters, so minimizing the needed capacitance reduces system volume. Thus, in this paper a numerical method is proposed to estimate the minimum required dc-link capacitor value. Then a novel control strategy, which integrates the current loop with an energy loop, is proposed for the interleaved boost dc-dc converter supplying a traction inverter. The impacts that the inductor value and control settling time of the dc-dc converter have upon the system stability are analyzed. The feasibility and effectiveness of the proposed controller are validated through experimental studies using a three-phase boost-interleaved dc-dc converter connected to a three-phase inverter.

I. Introduction

The dc-link capacitor bank occupies a large volume in power electronic systems of the electric vehicles; sometimes it is more than 40% of the traction inverter [1]. Hence, the volume of the dc-link capacitor greatly affects the system power density. Most of the existing work on dc-link capacitance minimization follows either one of two major approaches, i.e., in the first one, the capacitor minimization is realized using the system controller [2]-[5]; in the second one, the required capacitance is minimized by matching the switching algorithm of the dc-dc converter and the inverter; and the interaction between them [6]–[7]. In all cases, a highly-robust control system becomes extremely important as the capacitor value is decreased towards its stability limit. Closed-loop control methodology for a three-phase back-to-back ac-dc-ac converter was proposed in [5], in which the dc-link capacitor reduction was realized by balancing the power generation and consumption. An optimization method to determine the minimum current through the dc-link capacitor when the switching frequency of the dc-dc converter and the inverter are equal is explored in [6]. But, using a look-up table in every cycle makes the control system complicated. Furthermore, higher switching frequencies for the dc-dc converter could shrink the passives leading to higher power density. Most of these references, however, do not provide a formal methodology for calculating the minimum dc-link capacitor value.