450W Solar Battery Charging System Design

EE4504 – Design of Clean Energy
Report on: Design of 450W Solar Battery Charging System.
Prepared By:
Srinivasan Vivek (K1500002L)

Table of Content
Acknowledgement.....................................................................................................................ii
List of Figures ............................................................................................................................iii
Chapter 1....................................................................................................................................3
1.1 Objective ...........................................................................Error! Bookmark not defined.
1.2 Overall deisgn circuit........................................................................................................1
Chapter 2....................................................................................................................................2
2.1 Choosing the Solar Panel..................................................................................................2
2.2 Calculation for the PWL model ........................................................................................2
2.3 Solar Panel Circuit Model.................................................................................................4
2.4 Simulation Result..............................................................................................................5
2.5 Commercial Part...............................................................................................................6
Chapter 3....................................................................................................................................7
3.1 DC-DC converter...............................................................................................................7
3.2 DC-DC Sepic Converter.....................................................................................................9
3.3Calculations........................................................................................................................10
3.4 Simulation Result............................................................................................................11
3.5CommercialParts................................................................................................................11
Chapter4....................................................................................................................................13
4.1MPPT SYSTEM..................................................................................................................13
4.2 MPPT Controller.............................................................................................................13
4.3SimulationResult.................................................................................................................15
4.4 Commercial Part.............................................................................................................16
Chapter5....................................................................................................................................17
5.1BatteryCircuitModel...........................................................................................................17
5.2Calculation..........................................................................................................................18
5.3SimulationResult.................................................................................................................19
5.4Commercialpart..................................................................................................................19
Chapter 6..................................................................................................................................20
6.1 Conclusion......................................................................................................................20
References ...............................................................................................................................22

i
Abstract
The report will cover the utilization of solar cells and the power distribution generated from
solar cells. This includes the modeling a solar cell from scratch, studying and understanding
the V-I characteristic curve of the model in comparison with the commercial product.
Other areas like the SEPIC converter circuit, individual components of the DC-DC converter
will also be studied through calculation and simulation. Maximum power point tracking
circuit is also designed to improve the efficiency of the designed circuit.
Lastly, a battery model is built to complete the system.

ii
Acknowledgement
Would like to express our sincere gratitude to A/P Ali Iftekhar Maswood and A/P Luo Fang
Lin for their dedicated teaching and guidance in this module. This module has enriched us in
the knowledge of Solar Energy and the type of Conversion Technique that we can used to
conserve energy. This also mark an important episode in our commitment in global warming
as well as making use of such renewable energy collected from the natural resources and by
replenishing them naturally without causing harm to the environment.

iii
List of Figures
Figure 1 Overall Design Circuit Diagram .........................................Error! Bookmark not defined.
Figure 2 Chosen Solar Panel........................................................Error! Bookmark not defined.
Figure 3 PWL model and I-V curve..............................................Error! Bookmark not defined.
Figure 4 Solar Panel Equivalent ..................................................Error! Bookmark not defined.
Figure 5 450W Solar Panel Equivalent Circuit ............................Error! Bookmark not defined.
Figure 6 Simulated VI & Max Power Characteristic Curve.........................................................2
Figure 7 Buck Converter.............................................................................................................5
Figure 8 Boost Converter...........................................................................................................5
Figure 9 Buck Boost Converter ..................................................................................................5
Figure 10 Sepic DC-DC Converter with Resistor ........................................................................7
Figure 11 Result for the SEPIC DC-DC converter........................................................................8
Figure 12 DC-DC SEPIC Converter with MPPT............................................................................8
Figure 13 Description of MPPT System......................................................................................9
Figure 14 Truth table of XOR Gate..............................................Error! Bookmark not defined.
Figure 15 Simulation of MPPT Controller ................................................................................13
Figure 16 Battery Equivalent Circuit ........................................................................................14
Figure 17 Simulation result for Battery charging and Output power......................................15

1
Chapter 1
1.1 Objective
Design a solar panel that is able to charge up a 12-V Battery rated with 30 ampere-hour
(Ah). This will include the designing, developing and implementing a suitable DC-DC buck-
Boost converter to supply the battery load. Maximum PowerPoint Tracking (MPPT) will be
used to extract the maximum power from the solar panel. Apart from designing the circuits,
choice of material construction and sizing of the components will also be studied and
investigated in this project. PSIM software will be used as the simulator to study and
determine the response and behaviour of the circuit. Figure 1 in this chapter will
demonstrate the overall circuit for the design and in the later chapters will describe in
detail.
1.2 Overall Design Circuit
Figure 1: Overall Design Circuit Diagram

2
Chapter 2
2.1 Choosing the Solar Panel
To verify the proposed circuit module, we are choosing SSP150M solar panel and the
specification of the panel as below.
Figure 2: Chosen Solar Panel
Looking at the specification for 150W Sunshine Solar Panel, a total number of 3 solar
modules will be required to produce an output of 450W.
2.2 Calculation for the PWL model:
With the reference from the paper: “Improved Circuit Model of Photovoltaic Array” by
Mohamed Azab. We are going to calculate the four line segments from the I-V curve in
figure 2 with the following consideration.
- PV parameters at maximum power point (MPP): Vmax=18.10V and Imax=8.31A.
- Vertex points are located at: 0.9 MPP, MPP, and 1.1MPP.
- The model assumes that: Von1<Von2<Von3.
Figure 3: PWL model and I-V curve
The operation in each segment is explained as below:
Specification for 150W Sunshine Solar panel
Maximum Power (Pmax) 150W
Maximum Voltage (Vmax) 18.10V
Maximum Current (Imax) 8.31A
Open Circuit Voltage (Voc) 22.4V
Short Circuit Current (Isc) 8.66A

3
Segment 1: (VD < Von1)
Von1=0.9MPP=0.9*18.10=16.29V.
When the generated voltage is less than Von1 all the diodes are OFF, and no current flows
through the diode (ID1= ID2= ID3=0).
Thus, the current generated from PV flows through the load and only small portion can flow
through the shunt resistance Rsh, therefore the current is nearly constant in this segment.
Segment 2: (Von1 <= VD < Von2)
Diode D1 is ON.
Since, The PV current fails from 8.66A (Isc) to 8.31A (Imax), thus the current through diode D1
is:
ID1= 8.66-8.31=0.35A.
Ron1 is calculated from the following equation:
Ron1 = (Vmax – 0.9 Vmax) / ID1
= (18.10 – 16.29) / 0.35 = 5.171Ω.
Segment 3: (Von2 <= VD < Von3)
Diode D1 and D2 are ON.
The current through D1 is calculated as:
ID1 = (1.1 Vmax – 0.9 Vmax) / Ron1
= (19.91 – 16.29) / 5.171 = 0.7A.
Assume: Output Current (Io) = 70% of Imax.
Therefore, Io = 8.31 * 0.7
= 5.817A.
The current through diode D2 is:
ID2 = Isc – ID1 – Io

4
= 8.66 – 0.7 – 5.817 = 2.143 A
Ron2 is computed using the equation as shown:
Ron2 = (1.1Vmax – Vmax) / ID2
= (19.91 – 18.1) / 2.143 = 0.8446 Ω.
Segment 4: (Von3 <= VD <= VOC)
All Diodes are ON.
The PV load current is zero at open circuit point, the open circuit voltage is VOC=22.4V.
The current through D1 is calculated from the equation:
ID1 = (VOC – 1.1Vmax) / Ron1
= (22.4 – 19.91) / 5.171 = 0.4813 A
The current through diode D2 is
ID2 = (VOC – 1.1Vmax) / Ron2
= (22.4 – 19.91) / 0.8446 = 2.9484A
The current through diode D3 is:
ID3 = ISC – ID1 – ID2– Io
= 8.66 – 0.4813 – 2.9484 - 0 = 5.2303A
Therefore, R3 is calculated as:
Ron3 = (VOC – 1.1Vmax) / ID3
= (22.4 – 19.91) / 5.2303 = 0.476 Ω.
2.3 Solar Panel Circuit Model:
The voltage V1, V2 & V3 are selected as 16.29V, 18.10V and 19.91V respectively.
Assume, parallel resistor large as possible and shunt resistor small as possible.
Therefore, Rp=10KΩ and Rsh = 0.001 Ω.

5
Figure 4 Solar Panel Equivalent
After evaluating all the parameters, we can then group 3 x solar panel in series so, that we
could achieve the overall output power about 450W. which as shown in Figure 5 below.
Figure 5 450W Solar Panel Equivalent Circuit
2.4 Simulation Result
Figure 6 Simulated VI & Max Power Characteristic Curve

6
The maximum power from the 3 x 150W solar panel is 448W at the point, where the voltage
is 53.92V and the current is 8.32A. As, we know the output voltage and current of the solar
panel may vary according to the sun light. So, in order to charge the 12V30AH battery, we
need to maintain the voltage and current at the same time, we need to get the maximum
power from the solar panel. So, we will be using buck-boost converter with MPPT
technique.
2.5 Commercial Part
Sunshine Solar Panels 150W 12V Monocrystalline
Specifications
 Product Code. SSP150M
 Max Power. 150W ± 3%
 Max Power Voltage. 18.10V
 Max Power Current. 8.31A
 Open Circuit Voltage. 22.40V
 Short Circuit Current. 8.66A
 Normal Operating Cell Temp. -45 to 80°C
 Max System Voltage. DC1000V
 Weight. 11.2Kgs
 Dimensions. 669 x 1470 x 35mm
PRODUCT CODE: SSP150M
 Price: $396
Part Number Description Manufacturer Price per
Part
Parts needed Total cost Remarks
SSP150M 150W solar
panel
Sunshine 396$ 03 1188$ 3 panel
will be
connect
in series

7
Chapter 3
3.1 DC-DC converter
DC–DC converter consists of passive store devices together with switches that simplify the
unregulated DC input voltages conversion to a regulated DC output voltage level. This
converter can be categorised by two topologies which are isolated and non-isolated where
these topologies will provide the characteristics of each converter and its output level. DC-
DC converters are designed to equip with LC filter to reduce the ripple content in output
voltage and current. From the ripple characteristics, the converters are classified to operate
in two distinct modes which are: continuous conduction mode (CCM) or Discontinuous
Conduction Mode (DCM) where the load current drops to zero between the switching
cycles. The common isolated topologies are fly back, forward, push-pull and bridge
configurations. While for non-isolated converter are buck, boost and buck-boost which are
widely used in industrial DC motor drives as the configuration could provide smooth
acceleration, high efficiency and fast dynamics.
Buck Converter
Figure 7 Buck Converter
This converter compromises of two energy storing elements and two switches. Buck
converter produces an output voltage that is lower than its input voltage. This converter is
also known as step down converter.

8
Boost Converter
Figure 8 Boost Converter
This converter produce output voltage that is greater than its input voltage. The inductor
and switch positions are interchanged compared to buck converters. This converter is also
known as step-up converter.
Buck-Boost Converter
Figure 9 Buck Boost Converter
This converter is a combination of the said two converters and it depends on the switching
duty cycle D, buck-boost converters are able to produce an output voltage magnitude that is
either greater or less than its input voltage. The output voltage produced is in opposite
polarity than its input voltage. In this design, DC-DC converters are used to transfer energy
from a solar cell to charge the battery where fixed DC output voltage and continuous load
current can be obtained.

9
3.2 DC-DC Sepic Converter
Figure 10 Sepic DC-DC Converter with Resistor
The Single-Ended Primary-Inductance Converter (SEPIC) is a DC/DC-converter topology that
provides a positive regulated output voltage from an input voltage that varies from above to
below the output voltage. Similar to buck-boost converter, SEPIC converter has an addition
pair of energy storage devices in inductor and capacitor and the main storage device in this
topology is also the capacitor.
The output voltage can be regulated by controlling the duty cycle of the switch and the duty
cycle presents the ratio of the ON and OFF period for a switch in one cycle. It also allows
regulation of the input voltage through controlling the duty cycle. SEPICs are useful in
applications in which a battery voltage can be above and below that of the regulator’s
intended output for example, a single lithium ion battery typically discharges from 4.2V to
3V and if other components require 3.3v then the SEPIC would be effective. SEPIC converter
can be operating in two modes which are continuous-conduction and discontinuous
conduction. In continuous conduction mode, the current through the inductor never falls to
zero while in discontinuous conduction mode, the current through the inductor allow to fall
to zero. The voltage drop and switching time of diode is critical to SEPIC’s reliability and
efficiency. The diode’s switching time needs to be extremely fast in order to not generate
high voltage spikes across the inductors, which could damage to the component. The
resistances in the inductors and the capacitors also play a major role to SEPIC’s efficiency
sosss
ssssss

10
and ripple. Inductors with lower series resistance allow less energy to be dissipated as heat,
resulting in greater efficiency. Capacitors with low equivalent series resistance should also
be used to minimize ripple and heat build-up.
3.3 Calculations
Consider,
Ripple is 5%, Frequency is 20KHz, L1 = L2, and C1 = C2.
- Input current, Ii = I for Pmax = 8.34A.
- Input voltage, Vi = V for Pmax = 53.95V.
Required,
- Output current, Io = 30A.
- Output voltage, V0 = 12V.
Calculations for computing Duty cycle:
𝑽𝟎=(𝑽𝒊*𝑫)/(𝟏−𝑫)
12/53.95 = D/(1-D)
D = 0.222/1.222
D = 0.182.
Calculations for computing inductor value:
𝐿1=(𝑉𝑖*𝐷*T)/Δ𝑖𝐿1
Δ𝑖𝐿1 = 5% of Input current, Vi=53.95, T=1/20000, D=0.182.
L1 = (53.95*0.182)/(20000*0.05*8.34)
= 1.177mH
Since, L1 = L2 = 1.177mH.
Calculations for computing capacitor value:
𝐶1= (𝐼𝑜*𝐷*T)/Δ𝑣𝐶1
= (30 x 0.182 x 2 x 10-5) / 0.6

11
= 455uF
Since, C1 = C2 = 455uF.
Figure 11 Result for the SEPIC DC-DC converter
3.5 Commercial Parts
MOSFET

12
CAPACITOR (C1 & C2)
INDUCTOR 1 (L1)
INDUCTOR 2 (L2)
Part
Parts
needed
Total
cost
Remarks
IXTP28P065T-
ND
MOSFET P-channel
65V 28A to 220A
IXYS 2.79$ 01 2.79$ -
604D451F075
HP7
Capacitor, 450uF
with maximum
voltage is 75V.
Sprague 44.32$ 02 88.64$ For C1 and C2
Inductor with
maximum DC
current is 5A and
Inductance value
30mH.
Hammond 24.50$ 02 49$ For L1, we
required 15mH
so need to
connect the 2
pieces in parallel
RLB9012-
122KL
Inductor with
1.2mH
BOURNS 0.612$ 01 0.612$ For L2.

13
Chapter 4
4.1MPPT SYSTEM
Solar cells must be operated at their maximum power point (MPP) in order to achieve
optimised performance. The maximum power point varies with illumination, radiation,
temperature and other effects that produce non-linear output efficiency. Hence, a
maximum power point tracker (MPPT) system is used to vary the operating point so that the
solar cells are able to deliver maximum power achievable. A single MPPT system usually
consists of a controller and a dc-dc converter connected between the solar panels and
battery. In this design, a Sepic converter is used as the dc-dc converter. Figure 12 shows the
overall MPPT system inside this design.
Figure 12 DC-DC SEPIC Converter with MPPT
4.2 MPPT Controller
In this simulation design, the controller consists of components that vary with that of actual
components found in the market. This is due to the simplicity that is given in the simulation
software. The components in the simulation include a multiplier, differentiators, an XOR
logic gate and a D flip-flop as shown in Figure 17.

14
Figure 13 Description of MPPT System
The multiplier is used to calculate the power of the solar cells by multiplying the voltage and
current signals from the solar cells itself. In this design, a voltage and current sensor is used
to sense the incoming signals and is then passed through the multiplier. The power signal,
derived from the multiplier, and the voltage signal will then go through separate
differentiators. If the power is increasing, the differentiator would output a negative value
and if the power is decreasing, the differentiator would out put a positive value. Similarly,
the voltage signal is passed through the same process.
From the circuit referred in Figure 14, the outputs of differentiators’ dV/dt and dP/dt were
fed into a comparator. The comparators operate in such a way that it compares both the
differentiated signals with respect to ground, and switches the output to indicate which is
larger. The comparator would output a positive ‘1’ value if the differentiated value is
positive and output a zero if the differentiated value is negative, smaller than ground. Once
both outputs of the comparators have been generated, the signals will then be fed to an
XOR Logic Gate. The truth table of an XOR gate referred to the circuit in figure below.

15
Figure 14 Truth table of XOR Gate
The output signal of the XOR Logic gate is often undesirable to be fed to the gate driver of
the transistor due to its high frequency switching which is unsuitable for the DC-DC
converter. Hence, a D Flip-Flop is used as a device to send the signal to the gate driver with
its input signal received from the XOR Logic gate to prevent the high frequency switching
from happening. A D Flip-Flop is also considered in this design due to its simplicity.
Figure 15 Simulation of MPPT Controller

16
From the results we obtained, we can conclude the power across the load resistor is
approximately 425W. Hence, it can be deduce that the MPPT controller is working correctly.
4.4 Commercial Part.
Part
30amppt-OLD 30A 12/24V
MPPT charge
controller
TRACER 141$ 01 141$ -

17
Chapter5
5.1Battery Circuit Model
There are various existing designs to model a battery. In this system design, to design a 12V
30AH battery, we are incorporating Z.M. Salameh’s battery model design which takes into
account the dynamics during the charging and discharging phase. Figure 16, shows the
schematic of the model of the battery.
Figure 16 Battery Equivalent Circuit
Co = Overvoltage capacitance
Cbatt = Battery capacity
Roc = Charge overvoltage resistance
Rod = Discharge overvoltage resistance
Ric = Internal resistance for charge
Rid = Internal resistance for discharge
Rsd = Self-discharge resistance
All these parameters mentioned above are needed to be evaluated. However, only some of
these parameters which include the Cbatt and Rsd can be calculated while the rest can only be
estimated due to lack of some features in the datasheet. While the parameters of the Cbatt
and Rsd is calculated using the battery voltage and capacity.

18
5.2 Calculation
Assume, Co = 200F
Roc = 0.1Ω
Rod = 0.1Ω
Ric = 8.9mΩ
Rid = 8.9mΩ
Need to calculate, Rsd and Cbatt
Amount of total charge in 12V30AH battery is:
Q = 30A X 3600
= 108000 coulombs
Therfore, Cbatt = Q/V
= 108000/12
= 9000F
The state of charge of the battery is expected to be at 83% in 6months at a 20°C. Hence, the
charge expired in due 6 months is:
Q (discharge) = 108000 x 0.17
=18360 coulombs
The current flowing through the resistor Rsd, is then calculated using the following:
Current flowing through Irsd = 18360/ (6 x 30 x 24 x 60 x 60)
= 1.180 x 10-3
A
The voltage terminal at full charge is determined to be 14.5V as stated in the datasheet.
Therefore, the self-discharge resistance Rsd is then calculated to be:
Rsd = V/Isd
= 14.5/1.180 x 10-3
= 12.288KΩ.

19
Figure 17 Simulation result for Battery charging and Output power
Figure 17, shows the voltage, current and output power at terminal. It can be seen that the
voltage is increasing while the current is decreasing gradually. This shows that the battery is
charging and the output power from the converter is 443.5W which is the maximum power
taking from the 450W solar panel.
5.4 Commercial part
Part
EVX12300 12V 30AH
AGM battery
CSB 74.99$ 01 74.99$ -

20
Chapter 6
6.1 Conclusion
In the chapter 2, we do model for the 150W solar panel and then three 150W panel
connected in series to get the output power of 450W and also the model V-I curve match
with the practical solar panel curve. All the results are verified by PSIM. The maximum
power we got, 448W.
In chapter 3, we design the DC-DC sepic converter by calculating the values for inductor,
capacitor and duty cycle to get the output voltage 12V, and the output current 30A with 5%
ripple. In order, to take the maximum power from the solar panel, in the chapter 4, we do
the maximum power point tracking circuit by sensing the output voltage and output current
from the solar panel. The MPPT circuit drives the MOSFET switch by ON and OFF to get the
maximum output power from the panel. From our design, we got the simulation result with
maximum power from the solar panel is 425W.
In chapter 5, we model the 12V 30AH lead acid battery and the output of the solar panel
with DC-DC converter and MPPT is given to the designed battery model. We got the
simulation result where the voltage is increasing and the current is decreasing which shows
the battery is charging. We able to get the final maximum output power is 443.5W
We able to find all the commercial components for the designed circuit, and it show the
circuit which we designed is physically feasible. Below, is the list of commercial components:
Part
Number
Description Manufacturer Price per
Part
Parts
needed
Total
cost
Remarks
SSP150M 150W solar panel Sunshine 396$ 03 1188$ 3 panel will be
connect in series
IXTP28P065
T-ND
MOSFET P-channel
65V 28A to 220A
IXYS 2.79$ 01 2.79$ -
604D451F07
5HP7
Capacitor, 450uF
with maximum
voltage is 75V.
Sprague 44.32$ 02 88.64$ For C1 and C2
Inductor with Hammond 24.50$ 02 49$ For L1, we required

21
maximum DC current
is 5A and Inductance
value 30mH.
15mH so need to
connect the 2 pieces
in parallel
RLB9012-
122KL
Inductor with 1.2mH BOURNS 0.612$ 01 0.612$ For L2.
30amppt-
OLD
30A 12/24V MPPT
charge controller
TRACER 141$ 01 141$ -
EVX12300 12V 30AH AGM
battery
CSB 74.99$ 01 74.99$ -
The total cost to build the designed model is $1545.

22
References
1. Azab, M. (2009). Improved circuit model of photovoltaic array. International journal
of electrical power and energy systems engineering, 2(3), 185-188.
2. Falin, J. (2008). Designing DC/DC converters based on SEPIC topology.Analog
Applications, 19-20.
3. http://pveducation.org/pvcdrom/solar-cell-operation/short-circuit-current.
Retrieved 14th
April, 2016.
4. http://us.sunpowercorp.com/solar-resources/performance-reliability/solar-
efficiency/. Retrieved 14th
April, 2016.
5. http://www.qrg.northwestern.edu/projects/vss/docs/power/1-what-are-solar-
panels.html. Retrieved 14th
April, 2016.
6. NTU EEE, EE4504 Lecture notes
7. Salameh, Z. M., Casacca, M. A., & Lynch, W. A. (1992). A mathematical model for
lead-acid batteries. Energy Conversion, IEEE Transactions on,7(1), 93-98.

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