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This article was downloaded by: [Jawaharlal Nehru Technological University]On: 19 February 2015, At: 03:46Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registeredoffice: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
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Single-phase Phase-shift Full-bridge
Photovoltaic Inverter with IntegratedMagneticsYing Jiang
a , Fei Gao
a & Junmin Pan
a
a
Department of Electrical Engineering , Shanghai Jiao TongUniversity , Shanghai, P.R. China
Published online: 26 May 2010.
To cite this article: Ying Jiang , Fei Gao & Junmin Pan (2010) Single-phase Phase-shift Full-bridge
Photovoltaic Inverter with Integrated Magnetics, Electric Power Components and Systems, 38:7,
832-850, DOI: 10.1080/15325000903489751
To link to this article: http://dx.doi.org/10.1080/15325000903489751
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Electric Power Components and Systems, 38:832–850, 2010
Copyright © Taylor & Francis Group, LLC
ISSN: 1532-5008 print/1532-5016 online
DOI: 10.1080/15325000903489751
Single-phase Phase-shift Full-bridge PhotovoltaicInverter with Integrated Magnetics
YING JIANG,1 FEI GAO,1 and JUNMIN PAN1
1Department of Electrical Engineering, Shanghai Jiao Tong University,
Shanghai, P.R. China
Abstract A single-phase phase-shift full-bridge photovoltaic inverter with integrated
magnetics is proposed. In the DC/DC stage, the inductor and transformer are inte-
grated into one magnetic core; then the number of magnetic components is reduced,and soft switching is achieved by the integrated magnetics. First, the coupling co-efficients expression of integrated magnetics is analyzed; then, based on coupling
coefficients expression, the mode analysis is done. Second, a comparison is madeof the zero-voltage switching range when different coupling coefficients are adopted.
Also, the design of integrated magnetics is analyzed. In the DC/AC stage, an SPWM control is adopted, and the sinusoidal output voltage is achieved. The inverter achieves
high efficiency and compact structure. Finally a 100-W prototype inverter is made and the experimental results are given to verify the analysis.
Keywords integrated magnetics, coupling coefficient, phase-shift full-bridge circuit,photovoltaic inverter, zero-voltage switching range
1. Introduction
Single-phase photovoltaic (PV) systems are widely used in PV applications [1–7], which
include the possibility of easily enlarging the system and the opportunity to become a
“plug and-play” device. The PV inverter, which is the main component of a PV system,
always includes a DC/DC stage and a DC/AC stage, and the main challenge is that the
DC/DC stage has a high conversion ratio to lift the low input voltage from the PV panel
and high efficiency to reduce the cost.
A traditional phase-shift full-bridge (PSFB) circuit is usually used as a step-down
DC/DC converter due to its advantages such as simple structure and zero-voltage switch-ing (ZVS) [8–11]. However, when the PSFB converter is used as a step-up DC/DC stage
in a PV inverter, it has a problem with the leakage inductor that mainly comes from
the transformer primary winding achieving full ZVS operation. The methods in previous
literature [12, 13] that make the leakage inductor of the transformer a resonant inductor
are unsuitable for the DC/DC stage in a PV inverter. An external inductor can be added as
a resonant inductor to achieve the ZVS operation, but it increases the number of magnetic
components, thereby decreasing the power density.
Received 7 April 2009; accepted 15 November 2009.
Address correspondence to Dr. Ying Jiang and Prof. Junmin Pan, Department of ElectricalEngineering, Shanghai Jiao Tong University, Shanghai 200240, P.R. China. E-mail: [email protected], [email protected]
832
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Single-phase Phase-shift Full-bridge PV Inverter 833
In the modern power electronics industry, the demand for integrated magnetics has
become much stronger. The integrated magnetics appear in different forms such as
coupled inductors, integrated transformers (two or more transformers sharing a com-
mon magnetic core), and an integrated inductor and transformer [14–22]. By using
integrated magnetics, the number of magnetic components can be reduced, and a con-
trolled coupling between magnetic components is sometimes required to achieve special
functions such as removing current/voltage ripples or reducing voltage/current stress.
In this article, the PSFB circuit with integrated magnetics for the DC/DC stage in
a PV inverter is proposed. The external resonant inductor and transformer are integrated
into one magnetic core to reduce the number of magnetic components, and the coupling
between resonant inductor and transformer is designed to achieve ZVS operation. In the
DC/AC stage, a full-bridge circuit with classical sine pulse width modulation (SPWM)
control is adopted to give the sinusoidal output voltage.
The article first studies the DC/DC stage in detail. The external resonant inductor and
transformer are integrated into one magnetic core. The coupling coefficients expression
of integrated magnetics is analyzed, and then, according to the coupling coefficientsexpression, the operation and key features of the individual modes of the DC/DC stage
are discussed. Also, the analyses of the ZVS range when different coupling coefficients are
adopted and the design of integrated magnetics are achieved. Second, the DC/AC stage
with the classical SPWM control is introduced. Finally, the experimental results of a
100-W inverter with 50-Hz, 220-V AC output are provided to confirm the theoretical
analysis.
2. Main Circuit of Single-phase PV Inverter withIntegrated Magnetics
Figure 1 shows the single-phase PV system configuration. In Figure 1, the maximum
power point tracker (MPPT) circuit makes sure that the output of the PV panel operates
in the maximum power point, the battery is then charged and the PV inverter inverts
the low DC voltage ratios of the battery into the AC voltage of the load. This article
researches the PV inverter, which lifts the 43–53 V DC of the battery into 380 V DC
in the DC/DC stage and then generates 220 V AC in the DC/AC stage. Figure 2(a)
shows the single-phase PV inverter with discrete magnetic, and Figure 2(b) shows the
proposed single-phase PV inverter with integrated magnetics, where the inductor and
transformer are integrated into one magnetic core. In Figure 2(b), several assumptions
are made:
1. Switches S 1–4 and Q1–4 are ideal; S 1–4 includes parasitic capacitors (C oss1 DC oss2 D C oss3 D C oss4 D C oss ) and internal diodes (D1 D D2 D D3 D D4).
Figure 1. Single-phase PV system configuration.
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834 Y. Jiang et al.
Figure 2. (a) PV inverter with discrete magnetics and (b) proposed PV inverter with integrated
magnetics.
2. The transformer T winding is in the middle leg, and the inductor Lr winding
divided into two parts in left and right legs.
3. The input voltage V in is the output of the battery, V DC is the voltage of the DC/DC
stage,V o is the output of the PV inverter, and Ro is the AC load.
4. A voltage-doubler is ideal; rectifier capacitors C r1 and C r 2 are identical; each
voltage is V DC =2; and Dr1 and Dr 2 are rectifier diodes.
3. Operation Principle of DC/DC Stage withIntegrated Magnetics
3.1. Coupling Coefficients Expression of Integrated Magnetics
In order to analyze the operation of the DC/DC stage in a PV inverter, the expression of integrated magnetics should be achieved. Integrated magnetics are shown in Figure 3. In
Figure 3, transformer T includes primary side T P and secondary side T S in the middle
leg. LP and LS are self-inductors of T P andT S , and inductor Lr is divided into two
parts, Lr1 and Lr 2, which are in the left and right legs, respectively. <1, <2, and <3
are the magnetic resistances in the left, right, and middle leg, respectively. N P , N S ,
N Lr1, and N Lr2 are, respectively, the number of turns of T P winding, T S winding, Lr1
winding, and Lr 2 winding. T , Lr1, and Lr2 are, respectively, the fluxes generated by
the transformer winding, Lr1 winding, and Lr 2 winding. 1, 2, and c are the total
fluxes in the left, right, and middle leg, respectively. B1, B2, and Bc are the flux densities
in left, right, and middle leg, respectively. V
P , V
S , V
Lr1, and V
Lr 2 are, respectively, thevoltages of T P , T S , Lr1, and Lr 2. iP , iS , iLr1, and iLr2 are, respectively, the currents of
T P , T S , Lr1, and Lr 2. Based on the magnetic circuit in Figure 3(b), T , Lr1, and Lr2
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Single-phase Phase-shift Full-bridge PV Inverter 835
Figure 3. (a) Integrated magnetic and (b) magnetic circuit.
can be represented as follows:
8̂̂̂ˆ̂̂̂<ˆ̂ˆ̂̂̂̂:
T D N P iP N S iS
<3 C <1==<2
D .N P iP N S iS /.<1 C <2/
<1<2 C <1<3 C <2<3
Lr1 D N Lr1iLr1
<1 C <2==<3
D N Lr1iLr1.<2 C <3/
<1<2 C <1<3 C <2<3
Lr2 D N Lr1iLr2
<2
C <1==
<3
D N Lr2 iLr2 .<1 C <3/
<1
<2
C <1
<3
C <2
<3
: (1)
According to Eq. (1), the expressions between the voltages V Lr1, V Lr2 , V P , andV S
and the fluxes in each leg 1, 2, and c can be represented as8̂̂ˆ̂̂̂̂̂ˆ̂̂̂̂<ˆ̂̂̂̂̂̂̂̂̂̂ˆ̂:
V Lr1 D N Lr1
d1
dt D N Lr1
d
dt
Lr1 T
<2
<1 C <2
C Lr 2
<3
<1 C <3
V Lr 2 D N Lr 2
d2
dt D N Lr2
d
dt
Lr 2 C T
<1
<1 C <2
C Lr1
<3
<2 C <3
V P
DN P
dc
dt DN P
d
dtT
Lr1
<2
<2 C <3 CLr2
<1
<1 C <3
V S D N S
dc
dtD N S
d
dt
T Lr1
<2
<2 C <3
C Lr2
<1
<1 C <3
: (2)
Since the voltage of Lr can be achieved as V Lr D V Lr1 CV Lr2 and iLr D iLr1 D iLr2 ,
then according to Eqs. (1) and (2), V Lr , V P , and V S can be represented as
0B@
V Lr
V P
V S
1CA D
0B@
Lr M PLr M SLr
M PLr LP
M PS
M SLr M PS LS
1CA
0
BBBBBB@
d iLr
dt
d iP
dtd iS
dt
1
CCCCCCA; (3)
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836 Y. Jiang et al.
where 8̂
ˆ̂̂̂̂̂̂̂̂̂̂̂̂̂̂ˆ̂̂̂̂̂<ˆ̂̂̂̂̂ˆ̂̂̂̂ˆ̂̂̂
ˆ̂̂̂̂̂̂:
M PLr D N P .N Lr2<1 N Lr1<2/
<1<2 C <1<3 C <1<3
;
M SLr D N S .N Lr1
<2
N Lr2
<1/
<1<2 C <1<3 C <1<3
LP DN 2P .<1 C <2/
<1<2 C <1<3 C <1<3
;
LS D N 2S .<1 C <2/
<1<2 C <1<3 C <1<3
Lr D N 2Lr1.<2 C <3/ C N 2Lr2 .<1 C <3/ C 2N Lr1N Lr2<3
<1<2 C <1<3 C <1<3
;
M PS
D N P N S .<1 C <2/
<1<2 C <1<3 C <1<3
: (4)
According to Eqs. (3) and (4), the coupling coefficients can be represented as
8̂̂̂ˆ̂̂̂̂̂ˆ̂̂̂̂ˆ̂̂ˆ̂̂<̂̂̂̂̂̂ˆ̂̂̂̂ˆ̂̂̂̂̂ˆ̂̂:
kPS D M PS p
LP LS
D 1
kLP D M PLrp
Lr LP
D N Lr2<1 N Lr1<2
q N 2
Lr1
.<
2
C <3/
CN 2
Lr2
.<
1
C <3/
C2N Lr1N Lr2
<3 .
<1
C <2/
kLS D M SLrp
Lr LS
D N Lr1<2 N Lr2<1q N 2Lr1.<2 C <3/ C N 2Lr2 .<1 C <3/ C 2N Lr1N Lr2<3
.<1 C <2/
; (5)
where kLP , kLS ; and kPS are the coupling coefficients between Lr and T P , Lr and T S ,
and T P and T S , respectively.
In this article, in order to design conveniently, the air gaps of the EE magnetic core
are the same. Then <1 D <2 D 2<3 D 2<0, where <0 is the gap magnetic resistance of middle leg. Therefore, the Eq. (5) can be simplified as
8̂̂̂ˆ̂̂̂̂<̂ˆ̂̂̂̂̂
ˆ̂̂:
kPS D 1
kLP D N Lr2 N Lr1q
3N 2Lr1 C 3N 2Lr2 C 2N Lr1N Lr 2
kLS D N Lr1 N Lr2
q 3N 2Lr1 C 3N 2Lr2 C 2N Lr1N Lr2
: (6)
According to Eq. (6), kLS D kLP can be obtained, and k D kLS D kLP can be
defined, then coupling coefficient k can be adjusted by N Lr1 and N Lr2. According to the
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Single-phase Phase-shift Full-bridge PV Inverter 837
different values of k, the coupling method of integrated magnetics can be divided into
two kinds: 0 k 1 and 1 k 0.
Based on Eqs. (3) and (6), the coupling coefficients expression of integrated
magnetics can be represented as
0B@
V Lr
V P
V S
1CA D
0B@
Lr kp
Lr LP kp
Lr LS
kp
Lr LP LP p LP LS
kp
Lr LS p LP LS LS
1CA
0BBBBBB@
d iLr
dt
d iP
dt
d iS
dt
1CCCCCCA
: (7)
Therefore, the coupling coefficients expression of integrated magnetics is achieved as in
Eq. (7), where LP , LS , and Lr can be adjusted by the number of turns and air gaps, as
shown in Eq. (4), and k can be adjusted by N Lr1 and N Lr2, as shown in Eq. (6).
3.2. Mode Analysis of DC/DC Stage with Integrated Magnetics
According to the coupling coefficients expression of integrated magnetics in Eq. (7), the
mode analysis of the DC/DC stage can be done. The operating waveforms of the DC/DC
stage in the steady state are shown in Figure 4; each switching period is subdivided into
six modes, and their topological states are shown in Figure 5.
Mode 1 .t0 t t1/. The input power is transferred to the secondary side through S 1and S 4. Dr1 is turned on, and C r1 is charged by iDr1.t/ and iDr1.t/ D iS .t/. Therefore,
Figure 4. Operating waveforms of the DC/DC stage.
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F i g u
r e
5 . E q u i v a l e n t c i r c u i t s o f t h e p r
o p o s e d c o n v e r t e r f o r m o d e a n a l y s i s : ( a ) M o d e 1 ,
( b ) M o d e 2 ,
( c ) M o d e 3 ,
( d ) M o d e 4 ,
( e ) M o d e 5 , a n
d ( f ) M o d e 6 .
838
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Single-phase Phase-shift Full-bridge PV Inverter 839
voltage V DC =2 is reflected on the secondary side of T , that is, V S D V DC =2. Lr is
in series with the transformer primary side, that is, iP .t/ D iLr .t/ and V Lr C V P D V in.
The expression of integrated magnetics can be represented as
V in
V DC =2
!D
Lr C LP 2kp Lr LP kp Lr LS p LP LS
kp
Lr LS p
LP LS LS
!0BB@d iP
dt
d iS
dt
1CCA : (8)
According to Eq. (8), the primary current iP .t/ can be achieved as
iP .t/ D iP .t0 / C LS V in C .kp
Lr LS p
LP LS /V DC =2
.1 k2/LS Lr
.t t0/: (9)
Mode 2 .t1
t
t2/. When S 1 is turned off, C oss1 and C oss3 are charged and discharged
by resonance with Lr , respectively, that is, V Lr C V P D vcoss3. The expression of integrated magnetics iP .t/ and the voltage of C oss1 and C oss3 can be represented as
follows:
vcoss3
V DC =2
!D
Lr C LP 2kp
Lr LP kp
Lr LS p
LP LS
kp
Lr LS p
LP LS LS
!0BB@d iP
dt
d iS
dt
1CCA ; (10)
8̂̂<̂̂:
iP .t/ D iP .t1/ cos !.t t1/
vcoss1.t/ D iP .t1/ Z sin !.t t1/
vcoss3.t/ D V in iP .t1/ Z sin !.t t1/
; (11)
where 8̂̂̂<̂ˆˆ̂̂:
! D 1p 2C oss .1 k2/Lr
Z Ds
.1 k2/Lr
2C oss
: (12)
Mode 3 .t2 t t3/. The voltage of C oss3 is discharged to zero, the anti-paralleled diode
D3 of switch S 3 is turned on naturally, that is, V Lr C V P D 0; S 3 can then be turned on
to achieve ZVS. The expression of integrated magnetics and iP .t/ can be represented as
follows:
0
V DC =2
!D
Lr C LP 2kp
Lr LP kp
Lr LS p
LP LS
kp
Lr LS p
LP LS LS
!0BB@d iP
dt
d iS
dt
1CCA ; (13)
iP .t/ D iP .t2/ C
kp Lr LS p LP LS
V DC =2
.1 k2/LS Lr
.t t2/: (14)
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840 Y. Jiang et al.
Mode 4 .t3 t t4/. S 4 is turned off, C oss2 and C oss4 are discharged and charged by
resonance with Lr , respectively, that is, V Lr CV P D vcoss4.The expression of integrated
magnetics iP .t/ and the voltage of C oss2 and C oss4 can be represented as follows:
vcoss4
V DC =2
!D
Lr C LP 2kp Lr LP kp Lr LS p LP LS
kp
Lr LS p
LP LS LS
!0BB@d i
P dt
d iS
dt
1CCA ; (15)
8̂̂<ˆ̂:
iP .t/ D iP .t3/ cos !.t t3/
vcoss4.t/ D iP .t3/ Z sin !.t t3/
vcoss2.t/ D V in iP .t3 / Z sin !.t t3/
; (16)
where ! and Z are the same as in Eq. (12).
Mode 5 .t4 t t5/. The voltage of C oss2 is discharged to zero, the anti-paralleled
diode D2 of switch S 2 is turned on naturally, that is, V Lr C V P D V in. S 2 can then
be turned on to achieve ZVS. The expression of integrated magnetics and iP .t/ can be
represented as follows:
V in
V DC =2
!D
Lr C LP 2kp
Lr LP kp
Lr LS p
LP LS
kp
Lr LS p
LP LS LS
!0
BB@
d iP
dt
d iS
dt
1
CCA; (17)
iP .t/ D iP .t4/ C LS V in C .kp
Lr LS p
LP LS /V DC =2
.1 k2/LS Lr
.t t4/: (18)
Mode 6 .t5 t t6/. The primary current iP .t/ goes though S 2 and S 3, C r 2 is charged
by iDr 2.t/; therefore, the voltage V DC =2 is reflected on the secondary side of T , and the
analysis is similar that of Mode 1. From Mode 6, another circle is begun that is similar
to Modes 1 to 5, analyzed above.
When integrated magnetics are adopted, according to the mode analysis, it can be
seen that primary current iP .t/ is influenced by coupling coefficient k. Therefore, k canbe designed to meet the demand for the ZVS range.
3.3. Comparison of ZVS Range with Different Coupling Coefficient
In order to analyze the ZVS range, the waveform of primary current iP is analyzed. In
Figure 3, compared with Mode 3 (t2 t t3) and Mode 5 (t4 t t5), the charging and
discharging time of primary current iP in Mode 2 (t1 t t2) and Mode 4 (t3 t t4)
are much shorter and can be omitted. Therefore, the waveform of primary current iP is
simplified, as shown in Figure 6. In order to analyze conveniently, the primary current
iP .t/ can be represented as
iP .t/ D A C B.k/t: (19)
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Single-phase Phase-shift Full-bridge PV Inverter 841
Figure 6. Waveform of primary current.
According to Eqs. (9), (14), and (18), the slope of iP .t/ is B.k/, shown in Table 1,
and it can be seen that B.k/ is influenced by k. When t0 t t1, jB.k/0k1j jB.k/1k0j, it means that iP .t/0k1 increases more rapidly than iP .t/1k0 ; the av-
erage current I av.0k1/ is larger than I av.1k0/, and, based on the power conservation,
average current I av can be represented as
I av D V 2oV inRo
D V 2 DC
2V inRo
: (20)
Therefore, when 0 k 1, the PV inverter can transmit more power and lift higher
voltage, that is, V DC.0k1/ V DC .1k0/.
When t1
t
t3
, j
B.k/0k1j j
B.k/1k0j
, it means that iP
.t/0k1
decreases
more slowly than iP .t/1k0 , and since the anti-paralleled diode of the leading switch
is on, the ZVS of the leading switch is achieved. When t3 t T , the anti-paralleled
diode of the lagging switch is on, and the ZVS of lagging switch is achieved; since
jB.k/0k1j jB.k/1k0j, iP .t/0k1 decreases more slowly than iP .t/1k0 , and
the ZVS range (0 k 1) for the lagging switch is wider than the ZVS range (1 k 0).
3.4. Design of Integrated Magnetics
The flux distribution is shown in Figure 7. When t0
t
t5, the secondary side of
the transformer connects with C r1, meaning that voltage V DC =2 is reflected on thesecondary side. It can then be obtained that
V S D V P
N S
N P
D V DC
2 D N S
dc
dt ; t0 t t5: (21)
Therefore, the maximum flux density of the middle leg Bc;max can be obtained by
Bc;max D c;max
Ac
D V DC
4Ac N S
T; (22)
where T
D t
5 t
0,
c;max is the maximum value of
c, A
c is the cross-section area of the middle leg, and Ac and N s are selected to make sure that Bc is not more than Bc;max
to prevent magnetic saturation.
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T a b l e 1
C o m p a r i s o n o f t h e s l o p e B . k / o f p r i m a r y c u r r e n t
B . k
/ 0 k 1
B . k / 1 k 0
C o m p a r i s o n
t 0 t
t 1
L s V i n
C . j k j p L r L
S
p L P L S / V D C = 2
. 1 k
2 / L s L R
L S V i n C . j k j p L r L S
p L P L S / V D C = 2
. 1 k 2 / L s L R
j B . k / 0 k 1 j
j B . k / 1 k 0 j
t 1 t
t 3
. p L P L S
j k j p L
r L S / V D C = 2
. 1 k 2 / L s L R
. p
L P
L S
C j k j p L r L S V D C = 2
. 1 k 2 / L s L R
j B . k / 0 k 1 j
j B . k / 1 k 0 j
t 3 t
T
L s V i n
C . p L P
L s
j k j p L r L s V D C = 2
. 1 k 2 / L s L R
L s V i n C . p L P L S
C j k j p L r L S /
V D C = 2
. 1 k 2 / L s L R
j B . k / 0 k 1 j
j B . k / 1 k 0 j
842
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Single-phase Phase-shift Full-bridge PV Inverter 843
Figure 7. Flux distribution.
In Mode 1 (t0 t t1) and the former mode (t 00 t t0) before Mode 1,
8̂̂<ˆ̂:
V Lr D V in C V P D N Lr1
d1
dtC N Lr 2
d2
dt; t 00 t t0
V Lr D V in V P D N Lr1
d1
dt C N Lr2
d2
dt ; t0 t t1
: (23)
At t1, the maximum value of 1 is achieved. According to Eqs. (20) and (22) and
2 D 1 C c , the maximum flux density of the left leg B1;max can be obtained as
B1;max D 1;max
A1
D 1A1.N Lr1 C N Lr 2/
V in C V DC N P V DC N Lr2
2N S
Don1
C
V in V DC N P C V DC N Lr2
2N S
Don2
; (24)
where Don1T D t0 t 00, and Don2T D t1 t0, 1;max is the maximum value of 1; A1 is
the cross-section area of the left leg.
At t0, the maximum value of 2 is achieved, and the maximum flux density of left
leg B2;max can be obtained as
B2;max D 1.t0/ C c;max
A2
D 1
A2.N Lr1 C N Lr2 /
V in C V DC N P V DC N Lr 2
2N S
Don1 C V DC
4A2N S
T: (25)
For the EE magnetic core, Ac D 2A1 D 2A2. Therefore, the magnetic core of
integrated magnetics can be selected according to Eqs. (22), (24), and (25) to prevent
magnetic saturation.
Based on the formula in Eq. (4),
s LS
LP
Ds
N 2S
N 2P
D N T ; (26)
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844 Y. Jiang et al.
where N T is transformer turns ratio, and N T can be selected approximately according to
the demand conversional ratio. Then according to Eqs. (4) and (23), LS and LP can be
achieved.
According to the ZVS range (shown in Figure 6),
I P .t3/.1 k2/Lr
V in C .1=nT kp
Lr =LS /V DC =2D T t3 D tZV S ; (27)
where I P .t3/ is the average current of iP .t/ when t3 t T . Then, according to
Eq. (27), Lr can be selected to meet the demand for ZVS range tZV S .
4. DC/AC Stage
The waveforms of the DC/AC stage are shown in Figure 8. Q1 and Q2 are controlled by
a high-frequency SPWM signal, and Q3 and Q4 are controlled by a line frequency square
wave signal. Filtered by the LC circuit, the V DC and the output V o can be represented as
follows:
V o D mV DC sin !t; (28)
where m is the modulation ratio ! D 2f (f D 50 Hz).
5. Experimental Results
The parameters of integrated magnetics are shown as follows: A ferrite EE42/21/20 core
(PHILIPS Company, Holland) is selected, air gaps with 0.3 mm are placed in three legs,the cross-section area of the center leg is 233 mm 2, N P D 13, N S D 58, N Lr1 D 6,
N Lr2 D 0, Lr D 14 uH, Lp D 148 uH, Ls D 2:9 mH, and k D 0:445. Voltage-doubler
capacitors are 0.1 uF, filter circuit parameters of the DC/AC stage are Lf D 1 mH and
C f D 100 uF, the input voltage of the battery is 43 V DC–53 V DC, and the controller
is the DSP2812 (TI Company, USA). Based on the designed parameters, a 100-kHz,
Figure 8. Operating waveforms of the DC/AC stage.
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Single-phase Phase-shift Full-bridge PV Inverter 845
100-W inverter with 50-Hz, 220-V AC output is constructed. When Don2 D 0:7, the
input voltage of the battery is 48 V DC.
The key experimental waveforms of the DC/DC stage are shown in Figures 9(a)–
9(e). Figure 9(a) shows the waveforms of V AB . When the input power is transmitted in
the inverter, V AB
is 48 V; when the anti-parallel diode of the leading switch is on, V ABbecomes zero, and the leading switches can achieve ZVS. Figures 9(b) and 9(c) show
the waveforms of primary current iP and the lagging switch voltage. It can be seen that
primary current iP is continuous, and the lagging switch can achieve ZVS. When gate
signalV GS is on, the voltage of switch V DS has already been zero, and the lagging switch
then achieves ZVS. Figures 9(d) and 9(e) show the waveforms of V S and voltages V C r1
and V C r 2 of voltage-doubler capacitors C r1 and C r 2. When V C r1 is charged, V S equates
to V C r1, and when V C r 2 is charged, V S equates to V C r 2. Since V DC D V C r1 C V C r 2,
the output voltage V DC doubled the V S , and then V DC D 190 V DC C 190 V DC D380 V DC.
In order to compare the ZVS range when different magnetics are adopted in the
DC/DC stage, the experimental waveforms of iP are shown in Figures 10(a) and 10(b).The input voltage, magnetic core EE42/21/20, N P and N S , air gaps, and load are
unchanged as above except for N Lr1 and N Lr2. In Figure 10(a), N Lr1 D N Lr 2 D 0,
meaning the Lr winding is not placed. It is obvious that only the leakage inductance
of the transformer is not enough to achieve soft switching, causing the oscillation of iP ;
the leading switch and lagging switch both operate in hard switching. Therefore, it is
necessary to add an external inductor to achieve ZVS. In Figure 10(b), N Lr1 D 0 and
N Lr2 D 6, k D 0:474; it can be seen that primary current iP is near discontinuous,
and it is difficult to achieve the ZVS of lagging switch. On the other hand, the change
of the slope of iP agrees well with the theoretical analysis, which is shown in Table 1,
and the average current of iP .t/0k1 (Figure 9(b)) is larger than that of iP .t/1k0
(Figure 10(b)). Therefore, when 0 k 1, the PV inverter can transmit more power,
the output voltage is higher, which means that the conversional ratio of the DC/DC stage
is higher.
The key experimental waveforms of the DC/AC stage are shown in Figures 11(a)–
11(c). Figure 11(a) shows the driving singles for Q1 and Q2 and the SPWM control,
where a frequency of 20 kHz is adopted. Figure 11(b) shows the driving singles for Q3
and Q4 and the square wave control, where a frequency of 50 Hz is adopted. Figure 11(c)
shows a 220-V AC output V o, and at a rated condition, the total harmonic distortion
(THD) is 5%. A comparison of the conversional ratio of the DC/DC stage (V DC =V in)
and the efficiency of the proposed inverter is shown in Figure 12. It can be seen that
when 0 k 1, the conversional ratio of the DC/DC stage (V DC = V in) and the efficiencyare higher, and the efficiency is about 87% at a rated condition.
6. Conclusion
A single-phase PSFB PV inverter with integrated magnetics is proposed. In the DC/DC
stage, integrated magnetics is adopted due to the following reasons: (1) since the external
inductor and transformer are integrated into one magnetic core, the number of magnetic
components is reduced; (2) when the coupling coefficient k is selected as 0 k 1,
the wider ZVS range and the higher conversional ratio of the DC/DC stage (V DC =V in)
are achieved. In the DC/AC stage, SPWM control is adopted and the AC output isachieved. The experimental results of a 100-W prototype inverter have been presented.
The efficiency of the proposed inverter obtained is about 87% at a rated condition.
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846 Y. Jiang et al.
(a)
(b)
(c)
Figure 9. Experimental waveforms of DC/DC stage: (a) V AB , (b) iP , (c) lagging switch, (d) V S ,
and (e) voltage-doubler. (continued )
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Single-phase Phase-shift Full-bridge PV Inverter 847
(d)
(e)
Figure 9. (Continued ).
Figure 10. Experimental waveforms of ip: (a) without Lr winding and (b) k D 0:474.
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848 Y. Jiang et al.
(a)
(b)
(c)
Figure 11. Experimental waveforms of DC/AC stage: (a) driving singles for Q1 and Q2,
(b) driving singles for Q3 and Q4, and (c) output voltage V o.
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Single-phase Phase-shift Full-bridge PV Inverter 849
Figure 12. Comparison of conversional ratio of DC/DC stage (V DC =V in) and efficiency: (a) con-
versional ratio of DC/DC stage (V DC =V in) and (b) efficiency.
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