Upload
truongngoc
View
218
Download
1
Embed Size (px)
Citation preview
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
Low Cost MPPT Algorithms for PV Application: PV
Pumping Case Study
M. A. Elgendy, B. Zahawi and D. J. Atkinson
Presented by:
Bashar Zahawi
E-mail: [email protected]
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
Outline
Maximum power point tracking
Experimental system description
Directly Connected PV Pumping Systems
PV Pumping systems with MPPT
Constant Voltage MPPT Algorithm
Perturb and Observe (P&O) MPPT Algorithm
Incremental Conductance (INC) MPPT Algorithm
Conclusions
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
Introduction
Water pumping is probably one of the most
important applications of PV systems
Particularly in rural areas with no grid supply
Low power pumps ranging from 200W to 2kW
Most commonly used motor is the PM brushed dc
motor
Induction motors used for bore-hole and deep-well
pumping
The dc motor/pump set is connected directly to the
PV array in most commercial systems
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
Maximum Power Point Tracking
A PV array or generator will have one point on its
current/voltage characteristic that corresponds to
maximum power output
This is referred to as the maximum power point or MPP
Directly connected systems do not operate at the
MPP
Significant amounts of available energy are wasted
A pump controller (dc-dc converter) is required to
better match the PV generator to the motor/pump set
This is referred to as MPPT
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
1000 W/m2
400 W/m2
800 W/m2
600 W/m2
200 W/m2Maximum power line
PV array current-voltage curves
Mismatch between resistive load and PV Source; current–voltage curves
PV Array Current-Voltage Curves
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
Load line
Maximum power line
PV array current-voltage curves
Mismatch between resistive load and PV Source; power–voltage curves
PV Array Power-Voltage Curves
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
MPPT Circuit
V
Duty Ratio
S
PV
IPVVPV
VL
DSP, interface, and driver circuits
PV
generator CL
IPV IL
RL
L
C
Circuit diagram for PV system with MPPT control
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
MPPT Algorithms
Mapping or Model Based algorithms
A model of the system is developed to “map” the operating
characteristics and identify the MPP
Simple models are not very effective
More complex models require significant computational
resources and are site specific
Not suitable for commercial applications
Constant voltage algorithm
Hill climbing algorithms
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
Hill Climbing MPPT
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
Outline of Presentation
Experimental investigation of the performance of
Maximum power point tracking algorithms for
pumping applications
Constant Voltage Algorithm
Perturb and Observe (P&O) Algorithm
Incremental Conductance (INC) Algorithm
In each case, system performance is investigated
and the energy utilisation efficiency calculated
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
Experimental Set Up
Experimental investigation of the performance of
Maximum power point tracking algorithms for
pumping applications
Constant Voltage Algorithm
Perturb and Observe (P&O) Algorithm
Incremental Conductance (INC) Algorithm
In each case, system performance is investigated
and the energy utilisation efficiency calculated
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
Experimental Set Up
1080-Wp PV array facing south at a tilt angle of 54
w.r.t. the horizontal
Two parallel branches of 3 series connected 180-Wp solar
modules
Weather station installed at the same roof
Weather parameters were recorded at a 1 sec sampling rate
Solar irradiance was measured by a radiation sensor fixed
on a surface inclined at the same tilt angle
10-stage centrifugal surface pump driven by a
brushed PM dc motor
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
Experimental Set Up
Step-down dc-dc converter
470F link capacitance and 10kHz PWM frequency
Texas Instruments DSP based eZdsp kit used for
control and data acquisition
DSP used to provide flexibility
In a commercial product, a low cost microcontroller would
be more than adequate
Array installed on the roof of the New and
Renewable Energy Centre (NaREC) in
Northumberland.
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
Experimental System
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
Experimental System
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
Experimental System
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
Experimental System
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
SS
1080 WpPV Array
DSP Based MPPT
PWMiPV
vPVvPV
CL470µF
iPV
Step Down DC-DC Converter
Motor-Pump Set
III
B
J
ai aL
aR
be
eT PT
SelectorSwitch
va
Equivalent circuit of the PV pumping system setup
Circuit Diagram
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
Mismatch between motor-pump load and PV generator when pump is
connected directly to PV array; current-voltage curves
System Description
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
System Description
Mismatch between motor-pump load and PV generator when pump is
connected directly to PV array; power-voltage curves
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
0
20
40
60
80
100
120
140
160
180
200
220
0 1 2 3 4 5
Time (sec)
Voltage (
V)
0
1
2
3
4
5
6
7
Curr
ent
(A)
Array/Motor Current
Array/Motor Voltage
ψ = 736 W/m2, TC = 22.1 ºC
Experimental results showing array/motor voltage and current waveforms
Directly Connected DC PV pumping system
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
0
50
100
150
200
250
300
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
Time (sec)
Speed (
rad/s
ec)
0
10
20
30
40
50
60
Flo
w R
ate
(l/m
in)
Motor Speed Flow Rate
ψ = 736 W/m2, TC = 22.1 ºC
Motor speed and flow rate waveforms
Directly Connected DC PV pumping system
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
Influence of solar irradiance and cell temperature on MPP location
Directly Connected DC PV pumping system
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
Influence of solar irradiance and cell temperature on the energy utilization
Directly Connected DC PV pumping system
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
Experimental system performance under slow changing irradiance
Directly Connected DC PV pumping system
62.7%
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
Experimental system performance under rapidly changing irradiance
Directly Connected DC PV pumping system
51.3%
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
Outline
• Introduction
• System Description
• Directly Connected PV Pumping Systems
• PV Pumping systems with MPPT
– Constant Voltage MPPT Algorithm
– Perturb and Observe (P&O) MPPT Algorithm
– Incremental Conductance (INC) MPPT Algorithm
• Conclusions
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
Constant Voltage MPPT Algorithm
Block Diagram of Constant Voltage MPPT Algorithm
• The system performance is affected by:
– Vref
– KP and KI
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
Influence of solar irradiance and cell temperature on the energy utilization
Constant Voltage MPPT Algorithm
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
ψ=8625W/m2 and TC=28.6˚C
Experimental results showing array voltage, current, and power waveforms
Constant Voltage MPPT Algorithm
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
Experimental performance at nearly constant irradiance
Constant Voltage MPPT Algorithm
91.3%
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
Experimental performance at rapidly changing irradiance
Constant Voltage MPPT Algorithm
91.1%
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
Conclusions I
Directly connected PV pumping systems eliminate
the use of power electronics converters but suffer
from low energy utilization efficiency.
Simple constant voltage MPPT algorithm offers
significantly higher energy utilization efficiencies
(about 91%).
For more significant improvements in energy
utilization, more efficient MPPT control algorithms
that take into account the effects of insolation and
temperature variations on the MPP voltage would be
required.
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
Outline
• Introduction
• System Description
• Directly Connected PV Pumping Systems
• PV Pumping systems with MPPT
– Constant Voltage MPPT Algorithm
– Perturb and Observe (P&O) MPPT Algorithm
– Incremental Conductance (INC) MPPT Algorithm
• Conclusions
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
Perturb and Observe MPPT Algorithm
Flowchart of P&O MPPT Algorithm
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
Reference voltage control
Direct duty ratio control
+-
PI
Controller
PV
System
MPPT
Control
d
PVv
PVv
PVv
PVi PVi
refv
PV
System
MPPT
Control
d
PVvPVv
PVi PVi
Block diagram of MPPT with reference voltage control
Block diagram of MPPT with direct duty ratio control
Perturb and Observe MPPT Algorithm
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
System performance is affected by:
Step Size (Δd or ΔVref)
Perturbation Frequency (fMPPT)
Perturb and Observe MPPT Algorithm
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
012345678
Curr
ent
(A)
0 5 10 15 20 25 300
200
400
600
800
1000
Time (sec)
Pow
er
(W)
Vref
=10V, fMPPT
=1Hz
0
40
80
120
160
200
Voltge (
V)
=857.1W/m2, T
c=27.9
oC
Measured Array Current
Calculated MPP Current
Measured Array Power
Calculated Maximum Power
Measured Array Voltage
Calculated MPP Voltage
Three-level operation with reference voltage perturbation
P&O Algorithm Parameters
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
0 20 40 60 80 100 120 140 160 180 2000
100
200
300
400
500
600
700
800
900
1000
Array Voltage (V)
Arr
ay P
ow
er
(W)
A
B
CD
O
=857.1W/m2, Tc=27.9oC
Behavior with reference voltage perturbation in thee-level operation
P&O Algorithm Parameters
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
0
40
80
120
160
200
Voltage (
V)
=946.3W/m2, T
c=43
oC
0
2
4
6
8C
urr
ent
(A)
0200400600800
1000
Pow
er
(W)
0 5 10 15 20 25 300
20
40
60
80
100
Time (sec)
Duty
Ratio (
%)
d=5%, fMPPT
=1Hz
Measured Array Voltage
Calculated MPP Voltage
Measured Array Current
Calculated MPP Current
Measured Array Power
Calculated Maximum Power
Duty Ratio
Optimum Duty Ratio
Three-level operation with direct duty ratio perturbation
P&O Algorithm Parameters
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
0
40
80
120
160
200
=973.2W/m2, T
c=42.5
oC
d=2%, fMPPT
=1Hz
Vo
lta
ge (
V)
Measured Array Voltage
Calculated MPP Voltage
0 5 10 15 20 25 300
40
80
120
160
200
Time (sec)
Vo
lta
ge(V
)
=860.1W/m2, T
c=31.8
oC
d=2%, fMPPT
=10Hz
Measured Array Voltage
Calculated MPP Voltage
The effect of algorithm parameters on the array voltage; P&O MPPT
algorithm with direct duty ratio perturbation
Effect of P&O Algorithm Parameters
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
0
40
80
120
160
200
=760.3W/m2, T
c=26
oC V
ref=2V, f
MPPT=1Hz
Vo
lta
ge (
V)
Measured Array Voltage
Calculated MPP Voltage
0 5 10 15 20 25 300
40
80
120
160
200
=938.6W/m2, T
c=27.6
oC
Vref
=2V, fMPPT
=10Hz
Time (sec)
Vo
lta
ge (
V)
Measured Array Voltage
Calculated MPP Voltage
Experimental results showing the effect of algorithm parameters on the
array voltage; P&O MPPT algorithm with reference voltage perturbation
P&O Algorithm Parameters
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
100
120
140
160
Arr
ay V
olta
ge (
V)
=889.1W/m2, T
c=41.3
oC
2
4
6
8
Arr
ay C
urr
ent
(A)
d=5%, fMPPT
=4Hz
0 1 2 3 4 5 6 755
65
75
85
95
Time (sec)
Du
ty R
atio
(%
)
Confusion due to system
dynamics
Confusion due to branch
disconnection
Experimental results showing the system responses to a PV array
branch disconnection (Δd=5%, fMPPT=4Hz)
P&O Algorithm Parameters
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
Energy Utilization with P&O Algorithm
0
200
400
600
800
1000
1200
So
lar
Irra
dia
nce
(W
/m2)
0
40
80
120
160
200
Arr
ay V
olta
ge (
V)
Vref
=2V, fMPPT
=5Hz
0 200 400 600 800 1000 1200012345678
Time (sec)
Arr
ay C
urr
ent
(A)
Experimental system performance under slow changing irradiance; P&O
algorithm with reference voltage perturbation (ΔV=2V and fMPPT=5Hz)
97.2%
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
Energy Utilization with P&O Algorithm
0
200
400
600
800
1000
1200
Sola
r Ir
radia
nce (
W/m
2)
0
40
80
120
160
200
Arr
ay V
oltage (
V)
Vref
=5V, fMPPT
=5Hz
0 200 400 600 800 1000 12000
5
10
Time (sec)
Arr
ay C
urr
ent
(A)
Experimental system performance under rapidly changing irradiance;
P&O algorithm with reference voltage perturbation
97%
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
Energy Utilization with P&O Algorithm
0
200
400
600
800
1000
1200
So
lar
Irra
dia
nce
(W
/m2)
0
50
100
150
200
Arr
ay V
olta
ge
(V
)
0 200 400 600 800 1000 12000
2
4
6
8
Time (sec)
Arr
ay C
urr
en
t (A
)
d=2%, fMPPT
=10Hz
200 400 600 800 1000150
160
170
Experimental system performance under slow changing irradiance;
direct duty ratio perturbation
99%
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
Energy Utilization with P&O Algorithm
0
200
400
600
800
1000
1200
Sola
r Ir
radia
nce (
W/m
2)
0
50
100
150
200
Arr
ay V
oltage (
V)
d=2%, fMPPT
=10Hz
0 200 400 600 800 1000 12000
2
4
6
8
Time (sec)
Arr
ay C
urr
ent
(A)
Experimental system performance under rapidly changing irradiance;
direct duty ratio perturbation
97.9%
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
Conclusions II
The P&O MPPT algorithm is a simple algorithm that
does not require previous knowledge of the PV
generator characteristics or the measurement of
solar intensity and cell temperature.
Two approaches for implementing the P&O
algorithm have been investigated; reference voltage
perturbation and direct duty ratio perturbation.
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
Conclusions II
With reference voltage perturbation, the system has a faster
transient response to irradiance and temperature
transients.
However, stability is lost if the MPPT algorithm is operated at
high perturbation rates or if low pass filters are used to reject
noise from the array current and voltage feedback signals.
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
Conclusions II
• Direct duty ratio control offers better stability characteristics
and higher energy utilization efficiency at a slower transient
response and worse performance at rapidly changing
irradiance.
• Noise has significant impact on the algorithm
performance, especially with low step sizes where
the system response to noise is comparable to that
of MPPT perturbations.
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
Outline
• Introduction
• System Description
• Directly Connected PV Pumping Systems
• PV Pumping systems with MPPT
– Constant Voltage MPPT Algorithm
– Perturb and Observe (P&O) MPPT Algorithm
– Incremental Conductance (INC) MPPT Algorithm
• Conclusions
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
0 50 100 150 200 250 3000
200
400
600
800
1000
Voltage (V)
Po
wer
(W)
1000 W/m2, 60C
0dV
dP
0dV
dP
0dV
dP
Power-Voltage Curve of a PV Generator
Incremental Conductance MPPT Algorithm
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
0 50 100 150 200 250 3000
200
400
600
800
1000
Voltage (V)
Po
wer
(W)
1000 W/m2, 60C
0dV
dP
0dV
dP
0dV
dP
Power-Voltage Curve of a PV Generator
Incremental Conductance MPPT Algorithm
V
I
dV
dI
V
I
dV
dI
V
I
dV
dI
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
Reference voltage for the array output voltage
Converter duty ratio
+-
PI
Controller
PV
System
MPPT
Control
d
PVv
PVv
PVv
PVi PVi
refv
PV
System
MPPT
Control
d
PVvPVv
PVi PVi
Block diagram of MPPT with reference voltage control
Block diagram of MPPT with direct duty ratio control
Incremental Conductance MPPT Algorithm
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
The system performance is affected by:
Step Size (Δd or ΔVref)
Perturbation Frequency (fMPPT)
Incremental Conductance MPPT Algorithm
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
Three-level operation with reference voltage perturbation
INC Algorithm Parameters
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
Three-level operation with direct duty ratio perturbation
INC Algorithm Parameters
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
The effect of algorithm parameters on the array voltage; INC MPPT
algorithm with direct duty ratio perturbation
INC Algorithm Parameters
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
The effect of algorithm parameters on the array voltage; INC MPPT
algorithm with reference voltage perturbation
INC Algorithm Parameters
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
The effect of noise on the decision of the INC algorithm; reference
voltage perturbation
INC Algorithm Parameters
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
Experimental results showing the system responses to a PV array
branch disconnection (Δd=2%, fMPPT=10Hz)
INC Algorithm Parameters
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
Energy Utilization with INC Algorithm
Experimental system performance under slow changing irradiance;
reference voltage perturbation (ΔV=2V and fMPPT=5Hz)
97.6% ΔVref=5V and fMPPT=5Hz
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
Energy Utilization with INC Algorithm
Experimental system performance under rapidly changing irradiance;
reference voltage perturbation
94.9% ΔVref=5V and fMPPT=5Hz
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
Energy Utilization with INC Algorithm
Experimental system performance under slow changing irradiance;
direct duty ratio perturbation
98.5% Δd=2% and fMPPT=10Hz
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
Energy Utilization with INC Algorithm
Experimental system performance under rapidly changing irradiance;
direct duty ratio perturbation
96.8% Δd=2% and fMPPT=10Hz
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
The INC algorithm is less confused by noise and system
dynamics compared to the P&O algorithm. However, contrary
to general perceptions, it was found to exhibit worse confusion
than the P&O algorithm in rapidly changing weather
conditions.
Both algorithms offer high energy utilization
efficiencies of up to 99% depending on weather
conditions. The efficiency is marginally lower for
rapidly changing irradiance due to the energy loss
during the confusion and recovery periods.
Conclusions III
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
M. A. Elgendy, B. Zahawi and D. J. Atkinson,
“Comparison of Directly Connected and Constant
Voltage Controlled Photovoltaic Pumping Systems,”
IEEE Transactions on Sustainable Energy, Vol. 1, No.
3, pp. 184-192, Oct. 2010
M. A. Elgendy, B. Zahawi and D. J. Atkinson,
“Assessment of Perturb and Observe MPPT
Algorithm Implementation Techniques for PV
Pumping Applications,” IEEE Transactions on
Sustainable Energy, Vol. 3, No. 1, pp. 21-33, Jan. 2012
More Details
31 Jan 2012NEWCASTLE UNIVERSITY
Power Electronics, Drives and Machines Research Group
Thank you
Bashar Zahawi
E-mail: [email protected]