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Energy Procedia 88 (2016) 964 – 969
CUE2015-Applied Energy Symposium and Summit 2015: Low carbon cities and urban
energy systems
Research on control strategy of the bidirectional full-bridge
DC/DC converter used in electric vehicles
Zhifu Wang a,*, Yupu Wangb, Yinan Ronga, Zhi Lia
a. Collaborative Innovation Center of Electric Vehicles in Beijing, Beijing, 100081, China
b. China north vehicle research institute, Beijing, 100072, China
Abstract
This paper designed a DC/DC converter used in electric vehicles. The control strategy of phase shifted full-bridge
was used. The dynamic model of DC/DC controller was analyzed by using small signal analysis method. The ZVS
character and the power loss of the transformer were analyzed by simulation. Experimental results showed the
validity of the model and the effectiveness of the method.
Keywords: phase-shifted full-bridge; ZVS; vehicle power supply; DC/DC;electric vehicle
1. Introduction
The bidirectional DC/DC has been widely used in electric vehicles[1][2], and the control mothed of
DC/DC was gradually changing from hard switching control mode to soft switch control mode[3][4]. In
recent years, the soft switching technology of bidirectional DC/DC converter has been developed, and a
variety of soft switching topologies were proposed, such as resonant soft switching technology, quasi zero
voltage switching PWM technology, passive buffer, active buffer and active clamp, etc.. The switching
losses were reduced, which contributed to improve the operating frequency and reduce the volume of the
converter [5][6] .
Small signal analysis method was suitable for nonlinear system, By using the small signal analysis
method, the nonlinear DC/DC converter was converted into a linear mathematical model, which is the
basis of the closed-loop feedback control system[6].
2. Dynamic modeling of full-bridge DC/DC converter
2.1. Dynamic model of buck mode
* Corresponding author. Tel.: +86-10-68915202; fax: +86-10-68940589.
E-mail address: wangzhifu@bit.edu.cn.
1876-6102 © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/).
Peer-review under responsibility of the organizing committee of CUE 2015
doi:10.1016/j.egypro.2016.06.120
Zhifu Wang et al. / Energy Procedia 88 (2016) 964 – 969 965
The main idea of the small signal perturbation method is to bring a low frequency small signal
perturbation to one static operating point of the converter. When the perturbation is small enough, the
converter can be treated as a linear system around this static operating point. Assuming that the duty
cycle d(t)=D, the input voltage v1(t) =V1 and a low frequency perturbation was applied on d(t) and v1(t),
then
d (t ) D d (t ) (1)
v1 (t ) Ts
V1 v1 (t ) (2)
Each state variable and input current in the converter circuit would have a small change due to the
small signal perturbation. Assuming
iL (t ) Ts
I L iL (t ) (3)
v2 (t ) Ts
V2 v2 (t ) (4)
i p (t ) I p ip (t ) (5)
Ts
The low frequency signal component was much smaller than the direct current component, which
satisfied the assumption of small signal method. Then the switching cycle average equation of inductor
current could be shown as follows:
d[ I L iL (t )]
L n[V1 v1 (t )][ D d (t )] [V2 v2 (t )] (6)
dt
So
dI L di (t )
L L L [nDV1 V2 ] [nDv1 (t ) nV1d (t ) v2 (t )] nd (t )v2 (t ) (7)
dt dt
The direct current component and alternating current component on the either side of the formula (7)
were respectively equal, so:
dI
L L nDV1 V2 (8)
dt
di (t )
L L nDv1 (t ) nV1d (t ) v2 (t ) nd (t )v2 (t ) (9)
dt
Because of the steady state, the direct current component of the inductor current was 0, and the neglect
of the two order exchange in the alternating current component was available.
V2
nD (10)
V1
diL (t )
L nDv1 (t ) nV1d (t ) v2 (t ) (11)
dt
Then from the formulas above, we could get:
V2
IL (12)
R
dv2 (t ) v (t )
C iL (t ) 2 (13)
dt R
D
Ip IL (14)
n
D I
ip (t ) iL (t ) L d (t ) (15)
n n
The steady direct current model of converter was consisted of formula (10), (12) and (14). And the
966 Zhifu Wang et al. / Energy Procedia 88 (2016) 964 – 969
small signal alternating current model of the converter was consisted of formula (11), (13) and (15). The
small signal alternating current model was a second-order dynamic model of the CCM mode converter
circuit in time domain, which reflects the dynamic behavior of the converter in the static working point.
The model was the basis of the closed-loop feedback control system.
The alternating current model was transformed into the s domain, and the transfer function of the s
domain was obtained
° sLiL ( s ) nDv1 ( s) nV1d ( s) v2 ( s)
°
° v2 ( s )
® sCv2 ( s ) iL ( s ) (16)
° R
° D IL
°¯i p ( s ) n iL ( s ) n d ( s )
The s domain small signal alternating current model was described by the output voltage v2 ( s) , input
voltage v1 ( s) and the control signal d ( s)
L
( LCs 2 s 1)v2 (s) nDv1 (s ) nV1d (s ) (17)
R
When the input voltage perturbation v1 ( s) was zero, the transfer function Gvd ( s) from the control signal
to output voltage in the CCM model was˖
v2 ( s) nV1
Gvd ( s) (18)
d ( s) L
LCs 2 s 1
R
When the input voltage perturbation d ( s) was zero, the transfer function GiL 1 ( s) from the input voltage
to output current in the CCM model was˖
iL ( s) nD( RCs 1)
GiL v ( s) (19)
v1 ( s) RLCs 2 Ls R
2.2. Dynamic model of buck mode
Just like above, the transfer function from the control signal to the output current and the transfer
function from input voltage to output current were as follows:
2
Cs
iL ( s) V2 R
Gid '( s) (20)
d (s) 1 D L (1 D) 2
LCs 2 s
R n '2
1
Cs
iL ( s ) R
Giv '( s ) (21)
v2 ( s) L (1 D) 2
LCs s
2
R n '2
3. Simulation of the DC/DC converter
Zhifu Wang et al. / Energy Procedia 88 (2016) 964 – 969 967
In this paper, the phase shifted full bridge ZVS control strategy used in Buck mode converter was
established. When the voltage closed-loop control was adopted, the input voltage was 350V, the load
resistance was 0.1 : , the resonant capacitor of the system was set to 3nF, and the resonant inductance
was the primary leakage inductance of the transformer, the experiment results were as follows.
Fig.1 ZVS of IGBT on leading-leg
It showed in the Fig.1 that the terminal about the IGBT has been clamp at zero voltage before the super
forearm power switch driving signal rises, namely the super forearm realized zero voltage turn-on when
the resonant inductance was only the leakage inductance of the transformer.
The power loss of the duty about the transformer primary side and secondary side voltage waveform
was shown in Fig.2. There was obvious duty ratio loss of the transformer due to the existence of the
resonant inductor. However, the original side voltage has a certain pressure drop due to the lack of energy
in the resonant inductor.
Fig.2 Transformer duty ratio loss condition
4. Experiment
4.1. The duty loss of transformer
The transformer voltage waveform was shown in Fig.3. The experimental results show that transformer
968 Zhifu Wang et al. / Energy Procedia 88 (2016) 964 – 969
duty cycle loss phenomenon was not very obvious. This was because the inductance of the inductor was
very small, only 0.7uH, so the duty cycle of the loss of the phenomenon is not serious, the converter
efficiency was not much.
Primary
voltage
Secondary
voltage
Fig.3 Transformer voltage waveforms
4.2. The implementation of power switch ZVS with super forearm arm
Experimental results of the zero voltage turn-on of the super forearm power switch were shown in Fig.
4. Experimental results show that when the source drain voltage drops to zero voltage, the gate source
voltage is started to rise from zero. This shows that the power switch of the super forearm was in zero
voltage condition. The power switch of the switch was zero, that is, the zero voltage conduction is
achieved by the super forearm.
Source-grid
voltage
source-drain
voltage
Fig.4 Source drain voltage and gate source voltage waveform of IGBT on leading-leg
5. Conclusions
In this paper, the dynamic model of DC/DC was analyzed by using small signal analysis method, and
the results of simulation and test show that the ZVS state of DC/DC converter was effective.
6. Acknowledgement
Zhifu Wang et al. / Energy Procedia 88 (2016) 964 – 969 969
The research work was supported by National Natural Science Foundation (51105032).
7. Reference
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current regulated(I)ütifcuit principle and control scheme[J]ˊTransactions of China Electrotechnical Societyˈ2006ˈ21(10)˖3l-
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[4] Wang Kunrong, Lee FC, Lai J. Operation Principle of Bi-directional Full-Bridge DC/DC Converters with Unified Soft-
Switching Scheme and Soft-Starting Capability [A]. IEEE APEC 2000[C]. New Orleans, LA, USA, 2000:111-118DŽ
[5] Yakushev V, Meleshin V, Fraidlin S. Full-Bridge Isolated Current Fed Converter with Active Clamp [A]. IEEE APEC 1999,
Dallas, TX, USA, 1999:560-566
[6] Hajime Shiji, Kazurou Harada. A Zero-Voltage-Switching Bidirectional Converter for PV Systems[J]. IEICE/IEEE
INTELEC’03, 2003:14-19
Biography
Zhifu Wang received the M.E. degree and the Ph.D. degree from the Beijing Institute
of Technology, Beijing, China, in 2003 and 2013, both in vehicle engineering. He is
currently an Associate Professor with the National Engineering Laboratory for Electric
Vehicles, Beijing Institute of Technology
