Energy Management of Fast-Charger Systems for Electric Vehicles - Experimental investigation of power flow steering using bidirectional three-phase three-port converters

Student thesis: Doctoral Thesis

Abstract

Energy Management of Fast-Charger Systems for Electric Vehicles
Experimental investigation of power flow steering using bidirectional three-phase
three-port converters
Conventional utility grid networks are normally designed to support loads with
specific power demand patterns. Loads that require substantial energy in a short
time interval, as in the case of electric vehicle fast-charge systems, result in high
peak power demand. Specifically, a substantial number of electric vehicles con-
nected to the grid could produce a pulsating load that leads to voltage flicker,
affecting the distribution transformers. As a result, fast-charger systems will af-
fect the quality of supply voltage, and necessary actions, such as deploying static
var compensators and local energy storage, need to be undertaken.
This thesis presents a possible solution to enhance utility grid performance
when unconventional loads are connected to the public network. The topology
shows a combination of dc-link and magnetic-coupling structures, which allows the
interconnection of multiple sources, storage devices, and loads without the penalty
of extra conversion. The proposed general topology shows several possibilities
to construct a multiport converter for particular applications and, due to its
flexibility in structure, provides a solution to integrate a diverse class of sources
and loads. In addition, the control and energy management of the converter can be
implemented by a single processor. The centralized control eliminates complicated
communication structures that would be necessary in the conventional topology
based on separate conversion stages.
Specifically, this thesis studies the integration of electric vehicle fast-charge sys-
tems in the public network. The solution is based on the implementation of an
extra stationary source next to the facilities of the utility grid. Therefore, elec-
tric vehicles can be charged using energy simultaneously from two different power
sources, i.e., the utility grid and the stationary storage source. To implement
such a system, this thesis proposes, analyzes, designs, and verifies a three-port
converter. The proposed converter connects the three ports through a common
high-frequency transformer. Between each port and the high-frequency trans-
former, bidirectional dc/dc and ac/ac power converters are used to control the
energy flow in fast-charger systems. An innovative direct ac/ac converter is devel-
oped to connect the utility grid (low-frequency) to the high-frequency transformer,
avoiding additional conversions, as normally implemented in conventional ac/ac
converters.
The advantages of the proposed topology are the possibility of bidirectional
energy management in more than two ports, improvement of the power quality,
peak-shaving capability, and direct ac/ac conversion. Furthermore, the proposed
multiport technology could be implemented in future power systems, where in-
terfacing of various energy sources will be a must. An ideal multi-input power
supply could accommodate a variety of sources and combine their advantages.
With multiple inputs, the diversified energy sources increase reliability and uti-
lization.
To validate the theoretical study, a 40 kW prototype was built to connect the
vehicle battery, the utility grid, and the stationary storage battery. Experimental
results prove the capability of the multiport converter to control the power flow
between these ports, with an efficiency of 93%.
Date of Award22 Mar 2013
Original languageEnglish
SupervisorPhilippe Lataire (Jury) & Elena Lomonova (Promotor)

Keywords

  • Sustainable mobility
  • electric vehicles
  • power electronics

Cite this

'