13.56 MHz high power and high efficiency inverter for dynamic EV charging systems
A DISSERTATION SUBMITTED TO THE
GRADUATE SCHOOL OF ENGINEERING AND SCIENCE OF
SHIBAURA INSTITUTE OF TECHNOLOGY
by
NGUYEN KIEN TRUNG
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS
FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY
SEPTEMBER 2016
Abstract
Recently, Electric Vehicles (EVs) are a promising solution for reduc-
ing CO2 emission and air pollution in the big cities. However, until
now, the EVs have been not so attractive to consumers due to the
short running distance, long charging time and high battery cost. The
dynamic charging solution has been proposed to reduce the energy de-
pendence and battery cost of EVs. As the demand of that systems, a
13.56 MHz high power inverter with the eciency of over 95% is re-
quired. With the previous researches, there are three major research
challenges have been recorded. At very high switching frequency such
as 13.56 MHz, the in
uence of the parasitic elements in the circuit is
the rst challenge because it strongly a ect both of power and drive
circuit of the inverter. Consequently, the inverter may be damaged
or unstable. Secondly, the switching and gate drive power loss in the
inverter are also the challenge when it proportionally increase with
the switching frequency. At 13.56 MHz, it is dicult to obtain the
extremely high eciency such as 95%. Finally, the high output power
required is another challenge due to the low rate-parameters and the
challenges in the parallel connecting of the high speed switching de-
vices. To overcome these challenges, a number of the analyses and
proposed design are presented in this dissertation.
Firstly, the e ect of the parasitic elements in the high switch-
ing frequency half-bridge inverter is analyzed and evaluated in detail
based on the perspective of the ringing loop in the circuit. Based on
these, an optimized PCB design is proposed to minimize the parasitic
inductance in the ringing loop of the inverter. With the improved
PCB, the experiment results show that, the peak voltage and the am-
plitude of the ringing current in the circuit is reduced. However, the
ZVS condition and the stability of the inverter at high input voltage
condition are not achieved due to the high frequency ringing in the
circuit. Therefore, a ringing damping circuit is proposed. The high
stability and the low power loss on the proposed damping circuit is
the advantage to obtain high eciency of the inverter. In the ex-
periment results, the ringing current in the circuit is damped. A 1.2
kW output power is obtained with the eciency of 93.1%. This is an
improvement in the 13.56 MHz inverter. However, it does not meet
the required eciency of the inverter for the dynamic EV charging
systems due to limited switching speed of the silicon-MOSFET.
Secondly, to improve the eciency of the inverter, the GaN HEMT
device is used. In an experiment, the inverter using GaN HEMT
obtains the eciency of 97.5% which shows the potential to meet
the required eciency of the inverter for the dynamic EV charging
systems. However, the output power of the inverter is limited due to
the low rate current of the GaN HEMT. And the parallel connection
of GaN HEMT devices at 13.56 MHz is very dicult because of the
strong unbalance dynamic current distribution. Therefore, a design
using multiphase resonant inverter is proposed. The proposed module
design, the proposed power loss analysis method to obtain highest
eciency and the proposed drive circuit design have been addressed
in detail. In experiment, a 3 kW inverter with the eciency of 96.1%
is achieved that signicantly improves the eciency of 13.56 MHz
inverter. A 10 kW inverter with the eciency of over 95% will be
developed by following this proposed design in near future.
Finally, the 13.56 MHz high power inverter with the eciency of
over 95% can be realizable. However, the Class DE operation mode
which is used in multiphase resonant inverter requires exact parameter
of load, resonant circuit and several turning in the experiment process.
Therefore, it is still dicult to apply in the dynamic charging systems
where the parameters of the coupling system will always change in the
operation. The inverter behavior analysis and the further researches
to keep the soft switching condition in the operation with the dynamic
coupling system are necessary in the future work.
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