Closed loop Control of grid Integrated High Frequency Linked Active Bridge Converter for multiple PV modules interfacing

Overview Background Topology Control Scheme Simulation Results OPAL-RT Results Conclusion & Future Scope Bibliography
Closed Loop Control of Grid Integrated High Frequency
Linked Active Bridge Converter for multiple PV module
interfacing
Perwez Alam
Supervised by: Mrs Anindita Jamatia
Assistant Professor
Department of Electrical Engineering
National Institute of Technology
Agartala
March 13, 2021
Perwez Alam NITA HFLAB Converter Topology March 13, 2021 1 / 45

Content
1 Overview
2 Background
3 Topology
4 Control Scheme
5 Simulation Results
6 OPAL-RT Results
7 Conclusion & Future Scope
8 Bibliography

Overview

Overview
Figure: Electricity demand increase with population
Figure: PV-grid integration
The demand for electricity is rising in the country with the increase in population.
Supplying adequate electricity to the people is a big challenge
Power coming out from renewable source (Solar energy) can not directly fed to the
convention grid.
Dual Active Bridge based converter topologies are the converter which become
the bridge for different voltage level.

Background

Topologies & its limitations for multiple PV interfacing
Central and string inverter
To provide galvanic isolation, a big LF transformer is used
Cascaded H- bridge Multi-Level inverter
ground leakage current flow through the modules’ parasitic capacitances.
Lack of isolation between PV modules and grid
Inter module current flow due to galvanic connection between the full-bridge cells
module-integrated micro inverters
dedicated micro inverter for each PV module can make it a more expensive
solution

Topology

DAB Based PV-Grid integration
Figure: DAB based PV-grid integration
Types of converter used
One boost converter
A Dual Active Bridge Converter
Grid connected inverter

Harmonic Modeling of DAB Converter
The harmonic switching function for square
wave can be represented by equation (1):
Sk (t) =
1
2
+
2
π
∞
X
n=0
sin([2n + 1]{ωs(t) − φk })
[2n + 1]
(1)
where, k = 1,2,3.. and φ is the phase shift
angle.
S11(t) =
1
2
+
2
π
∞
X
n=0
sin([2n + 1]{ωs(t) + φ})
[2n + 1]
(2)
S12(t) =
1
2
+
2
π
∞
X
n=0
sin([2n + 1]{ωs(t) + φ − π})
[2n + 1]
(3)
S21(t) =
1
2
+
2
π
∞
X
n=0
sin([2n + 1]{ωs(t)})
[2n + 1]
(4)
S22(t) =
1
2
+
2
π
∞
X
n=0
sin([2n + 1]{ωs(t) − π})
[2n + 1]
(5)
Figure: Basic Circuit diagram of DAB

Figure: Basic Circuit diagram of DAB
Vpri (t) = VC2
(t)

S11(t) − S12(t)

(6)
Vsec(t) = nVC2
(t)

S11(t) − S12(t)

(7)
VCD(t) = Vdc−bus(t)

S21(t) − S22(t)

(8)
By applying KVL in figure 5, equation can be written in loop as:
RLiL(t) + L
diL(t)
dt
= nVC2
(t)

S11(t) − S12(t)

− Vdc−bus(t)

S21(t) − S22(t)

(9)

Overview Background Topology Control Scheme Simulation Results OPAL-RT Results Conclusion Future Scope Bibliography
iL(t) =
4
π
∞
X
n=0
1
[2n + 1]
(
nVC2
| z[n] |
sin([2n + 1]ωs(t) + φ − φz [n])
−
Vdc−bus
| z[n] |
sin([2n + 1]ωs(t) − φz [n])
)
(10)
where, | z[n] |=
p
([2n + 1]ωsL2 + ([2n + 1]ωsL)2 and φz [n] = tan−1

[2n+1]ωsL
RL

i.e.
the magnitude and angle of the AC impedance between the bridges for each harmonic
frequency of interest.
By transformer turn ratio Ip(t) can be written as:
Ip(t) = niL(t) (11)

Current through capacitor C2 can be written by applying KCL at input node.
iC2
(t) = ib1(t) − iHB1(t)
C2
dVC2
(t)
dt
= iC2
(t) (12)
= ib1(t) −

niL(t){S11(t) − S12(t)}

= ib1(t) −
4
π
N
X
n=0
1
[2n + 1]
(
n2VC2
| z[n] |
sin([2n + 1]ωs(t) + φ − φz [n])
−
nVdc−bus
| z[n] |
sin([2n + 1]ωs(t) − φz [n])
)
∗
(
4
π
N
X
n=0
1
[2n + 1]
sin{[2n + 1]ωs(t) + φ}
)
(13)

= ib1(t) −
8
π2
N
X
n=0
1
[2n + 1]2
n2VC2
| z[n] |

cos{φz [n]}

−
8
π2
N
X
n=0
1
[2n + 1]2
nVdc−bus
| z[n] |

cos{[2n + 1]φ + φz [n]}

)
(14)
d4VC2
(t)
dt
= A4VC2
+ B4φ + C4ib1 (15)
A = −
8
C2π2
N
X
n=0
1
[2n + 1]2
n2
| z[n] |

cos{φz [n]}

(16a)
B = −
8
C2π2
N
X
n=0
1
[2n + 1]
nVdc−bus
| z[n] |

sin{[2n + 1]φo + φz [n]}

(16b)
C =
1
C2
(16c)

To develop the plant transfer function, laplace transform of the above equation (15) has
been carried out. Transfer function for the proposed converter
VC2
(s)
4φ(s)
can be written
while keeping the 4ib1 zero as (17b):
VC2
(s)
4φ(s)
=
B
S − A
(17a)
G(s) =
BTp
1 + STp
(17b)
where Tp is equal to −1
A
.

Control Scheme

Control scheme
Control
Grid Side Inverter Control
DAB Converter Input Voltage Control
MPP Voltage Control by Boost Converter

DC bus voltage control Inner loop Current control
Figure: Grid connected inverter

DC bus voltage control
Main function
To regulate the
SPWM inverter DC
bus voltage and
generate the
reference of grid
injected current
To administer the
power exchange
between Dc bus and
grid Figure: Block diagram of PI controller for dc bis voltage control

DC bus voltage control
Transfer functions
Hc(s) = Kp

1 +
KI
s

(18)
G1(s) =
G
1+sTd

1
Rf
1+sTs

1 + G
1+sTd

1
Rf
1+sTs
(19)
G2(s) = G1(s)

K
Cbuss

(20)
Figure: Block diagram of dc bus voltage controller

Inner Loop current control
Transfer functions
Hc(s) = Kp

1 +
KI
s

(21)
Ginv (s) =
G
1 + sTd

(22)
G1(s) =
G
1+sTd

1
Rf
1+sTs

1 + G
1+sTd

1
Rf
1+sTs
(23)
G1(s)Hc(s) = G1(s)Kp

1+
KI
s

(24)
Figure: Block diagram of inner current loop controller

DAB Converter Input Voltage Control
Figure: Phase shift angle control
Figure: block diagram of the VC2
voltage control

MPP Voltage Control by Boost Converter
Equations
Hc(s) =
Kp 1 + s
ωz

s 1 + s
ωp
(25)
Gb(s)Hc(s) =
−1
sC1
Kp 1 + s
ωz

s 1 + s
ωp

(26)
Figure: Boost converter control loop

DAB simulation Outputs
Figure: Simulation: PV output voltage and inductor current of boost converter

Figure: Simulation: DAB outputs results

Figure: Simulation: Input voltage control of DAB converter

Figure: Simulation: Grid output voltage
Figure: Simulation: Grid output voltage

Basic required features
Converter should have galvanic isolation
Independent MPPT for multiple PV module
interfacing
It should not allow flow of inter module
leakage current

Circuit Configuration
Types of converter used
Two PV connected
boost converter
A High Frequency
Linked Active Bridge
Converter
A grid connected
SPWM inverter
Figure: Complete system
Advantages
Independent MPPT control for Two PV modules
Only (n+1) H-bridge converter is required for n PV modules

Input Voltage Control Scheme
Figure: Phase shift angle control

Simulation Results

Simulation Results
Boost converter
specification
parameter value Unit
C1 C3 1000 µF
C1 C3 2000 µF
Fsb 10 KHz
Vpv1 30.7 V
VC2
40 V
Observation
Independent PV control
Boost converter input voltage
control
MPPT Control Figure: Simulation: PV output results

Simulation Results
HFLAB converter
specification
L 200 µH
Cdc−bus 1800 µF
Fs 20 KHz
Vdc−bus 200 V
HFLAB Topology
Output waveforms of HFLAB
converter
Validates the HFLAB
Topology
Figure: Simulation: a) Vsec (t), b) VCD(t) c) VL(t) and d) IL(t)

Simulation Results
Grid specification
Lf , Rf 15,
0.447
mH,
ohm
Vg 120 V
Fg 60 Hz
HFLAB Topology
Input DC voltage control
Impressive step response at
t=1.71 sec
Figure: Simulation: a) VC2
(t), b) VC4
(t) c) Vdc−bus(t) and d) IC2
(t)

Simulation Results
Figure: Simulation: Grid dq-axis voltage Figure: Simulation: Decoupled dq-axis grid current
Inner loop current control
Impressive response of inner loop current control
Vector control in decoupled current mode

Simulation Results
Figure: Simulation: a) Vdc−bus(t), b) Vgrid (t) and c)
Igrid (t)
Grid current injection
No effect of irradiance change on dc
bus controller
Unity power factor power transfer from
PV module to grid
Figure: Simulation: Harmonic spectrum of grid current
Grid current injection
only 1.45% THD is found in FFT
analysis

OPAL-RT Results

OPAL-RT Results
Figure: OPAL-RT: boost converter inductor current
Boost current
8 A average current from boost
(=IMPP )
Figure: OPAL-RT: a) Vsec (t) b) VCD(t) and c) iL(t)
HFLAB Topology
Output waveforms of HFLAB converter
Validates the HFLAB Topology

OPAL-RT Results
Figure: OPAL-RT: HFLAB Converter dc voltage
HFLAB Topology
Input Voltage control of HFLAB
converter
Validates the HFLAB Topology
Figure: OPAL-RT: a) grid voltage and b) current
HFLAB Topology
Output waveforms of grid current
Validates unit power factor

Conclusion Future Scope

Conclusion
For PV-grid integration, vector control scheme has been implemented for grid
connected converter.
The phase shift angle modulation control technique has been proposed for
controlling the HFLAB input voltages.
Slope compensation current control for boost converter along with perturb and
observe method (MPPT) has implemented.

Future Scope
The proposed HFLAB converter has only implemented in MATLAB and OPAL-RT
simulator. Further, it can be implemented in hardware.
The dc bus voltage control implemented only by PI controller. Other type of
controller can be adopted for better and fast results.
For grid integration L-type filter is used. Further, a combination of inductor and
capacitor can be implemented for better output.
Perturb and observe algorithm has implemented for MPPT. The main problem with
P O is oscillation around the operating point. This can be resolve by other
MPPT algorithm.

Bibliography

Bibliography
1 S. Chakraborty and S. Chattopadhyay. A dual-active-bridge-based highfrequency
isolated inverter for interfacing multiple pv modules with distributed mppt. In 2018
IEEE Applied Power Electronics Conference and Exposition (APEC), pages
3256–3263, March 2018.
2 Shiladri Chakraborty and Souvik Chattopadhyay. A dual-active-bridge-based
high-frequency isolated inverter for interfacing multiple pv modules with distributed
mppt. In 2018 IEEE Applied Power Electronics Conference and Exposition
(APEC), pages 3256–3263. IEEE, 2018.
3 Aditi Chatterjee and Kanungo Barada Mohanty. Current control strategies for
single phase grid integrated inverters for photovoltaic applications-a review.
volume 92, pages 554–569, 2018.
4 K. Suryanarayana I. J. Prasuna, M. S. Kavya and B. R. Shrinivasa Rao. Digital
peak current mode control of boost converter. pages 1–6, 2014.
5 R. Ghosh J. Prasad, T. Bhavsar and G. Narayanan. Vector control of threephase
ac/dc front-end converter. volume 33, pages 591–613, 2008.
6 S. Kouro, J. I. Leon, D. Vinnikov, and L. G. Franquelo. Grid-connected photovoltaic
systems: An overview of recent research and emerging pv converter technology.
IEEE Industrial Electronics Magazine, 9(1):47–61, March 2015.

Bibliography
7 D. Segaran, B. P. McGrath, and D. G. Holmes. Adaptive dynamic control of a
bi-directional dc-dc converter. In 2010 IEEE Energy Conversion Congress and
Exposition, pages 1442–1449, Sep. 2010.
8 D Segaran, DG Holmes, and BP McGrath. Comparative analysis of singleand
three-phase dual active bridge bidirectional dc-dc converters. Australian Journal
of Electrical and Electronics Engineering, 6(3):329–337, 2009.
9 Yushan Li, Kevin R Vannorsdel, Art J Zirger, Mark Norris, and Dragan Maksimovic.
Current mode control for boost converters with constant power loads. IEEE
Transactions on Circuits and Systems I: Regular Papers, 59(1):198–206, 2012.
10 Allan Taylor, Guanliang Liu, Hua Bai, Alan Brown, Philip Mike Johnson, and Matt
McAmmond. Multiple-phase-shift control for a dual active bridge to secure
zero-voltage switching and enhance light-load performance. IEEE Transactions on
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Ozpineci. Modular cascaded h-bridge multilevel pv inverter with distributed mppt
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Closed loop Control of grid Integrated High Frequency Linked Active Bridge Converter for multiple PV modules interfacing

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