Design and Implementation of a PWM Solar Charge Controller

Desklib provides past papers and solved assignments for students. This project details the design of a PWM solar charge controller.

Roll No
3/22/2019
2019
Designing a PWM Solar Charge Controller

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Designing a PWM Solar Charge Controller
Table of Contents
1 Industrial Standard User’s Requirements Evaluation.......................................................4
1.1 Specialized User’s Requirements......................................................................................4
1.2 Prioritization of Specialized Requirements.......................................................................4
1.3 Final Specifications...........................................................................................................4
1.4 Gantt Chart as per Design Schedule.................................................................................5
1.4.1 Critical Path...............................................................................................................5
1.4.2 Planning Techniques..................................................................................................5
1.5 Design Methodology.........................................................................................................6
1.6 Benchmarking...................................................................................................................6
2 Initial Technical Solutions....................................................................................................7
2.1 Ideas Generation Process..................................................................................................7
2.1.1 ID1.............................................................................................................................7
2.1.2 ID2.............................................................................................................................8
2.2 Initial Designs Evaluation.................................................................................................8
2.3 Concept Selection.............................................................................................................9
2.4 Software and Hardware Standards to Make Design Choices...........................................9
2.5 Possible Improvements in Design.....................................................................................9
3 Industry-Standard Technical Design.................................................................................10
3.1 Final Design Elements....................................................................................................10
3.1.1 Configuration of Solar Charge Controller in Solar Panel System...........................10
3.2 Final Design Limitations.................................................................................................12
3.3 Roles of Specifications in Complete Design Process.....................................................12
3.4 Compliance, Risk, and Safety Management...................................................................12
3.4.1 Risks During Installation.........................................................................................12

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Designing a PWM Solar Charge Controller
3.4.2 Safety Management.................................................................................................13
3.5 Off Load Testing.............................................................................................................13
3.6 Effectiveness...................................................................................................................13
4 Presentation of Final Design...............................................................................................14
4.1 Customer Feedback.........................................................................................................15
4.2 Improvements in response to Customer’s Feedback.......................................................15
5 Conclusions and Recommendations...................................................................................15
Appendix 1: PWM Solar Charge Controller Design Schematics............................................16
Appendix 2: PCB Layout............................................................................................................17
Appendix 3: Arduino Code.........................................................................................................18
Appendix 4: Case Design (CAD Model)....................................................................................19
Appendix 5: Final Design 3D View............................................................................................20

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Designing a PWM Solar Charge Controller
List of Figures
Figure 1: Prioritization of User’s Requirements..............................................................................4
Figure 2: Critical Path Showing Design Schedule..........................................................................5
Figure 3: Planning Techniques........................................................................................................5
Figure 4: PWM Signal showing on CRO........................................................................................7
Figure 5: ID1 Schematics................................................................................................................8
Figure 6: ID2 Circuit Schematics....................................................................................................8
Figure 7: Selection of Final Design Concept...................................................................................9
Figure 8: Software and Hardware Choices......................................................................................9
Figure 9: Design Elements.............................................................................................................10
Figure 10: Working Diagram of Solar Charge Controller in Solar Panel System.........................11
Figure 11: Flow Diagram Showing Working of PWM Solar Charge Controller..........................11
Figure 12: Specs Role in Design Process......................................................................................12
Figure 13: Chart Showing I-V Characteristics..............................................................................14
Figure 14: Chart Showing P-V Characteristics.............................................................................14
Figure 15: Design Presentation......................................................................................................14
Figure 16: PWM Controller Behavior at 61.1 Hz Frequency........................................................15
List of Tables
Table 1: Final Requirements............................................................................................................4
Table 2: Comparison with Industrial Controllers............................................................................6
Table 3: Concept Screening Matrix.................................................................................................9
Table 4: Off Load Testing Data.....................................................................................................13
Table 5: Customer Assessment and Feedback...............................................................................15

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Designing a PWM Solar Charge Controller
1 Industrial Standard User’s Requirements Evaluation
1.1 Specialized User’s Requirements
 Integral Display
 PWM Solar Charge Controller
 Lighting control function.
 Fully programmable.
 Data Logging
 Reverse Current Protection
 Three-stage battery charging.
1.2 Prioritization of Specialized Requirements
Keeping in view of CE Marking and UL Listings for the solar charge controller, user’s
requirements can be prioritized in order to define project scope. This prioritization is being done
through story mapping shown below;
Figure 1: Prioritization of User’s Requirements
1.3 Final Specifications
Analyzing user’s requirements in terms of prioritization of user’s requirements and standard
requirements, we are able to specify final requirements for the design to get started. These are
being discussed in the table below; (Pathare et al, 2017).
Table 1: Final Requirements
Nominal Operating Voltage 12V
Battery Voltage Range 10 – 35V
Voltage Accuracy <=0.1% +/- 50mV
Maximum Battery Current 15A
Load Current Rating 15A or 30A
LED Indications yes
Data Logging
PWM Solar Charge Controller
Reverse Current Protection
Fully programmable.
Integral Display
Three stage battery charging
Lighting control function

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Designing a PWM Solar Charge Controller
Transient Surge Protection 1500 watts
Operating Temperature -40℃ to +60℃
Meter Operating Temperature -20℃ to +60℃
Storage Humidity -40℃ to +80℃
Humidity 100% non-condensing
Resolution 52.1 mm x 53.3 mm
1.4 Gantt Chart as per Design Schedule
1.4.1 Critical Path
Figure 2: Critical Path Showing Design Schedule
1.4.2 Planning Techniques
There are 3 main planning techniques that can be adopted while designing a full compliance
product;
1. Requirement analysis leading towards specification analysis, concept development and
then final designing.
2. After requirement analysis, concept development and evaluation and then final designing.
3. Specification analysis following requirement analysis and directing towards the final
design.
In all of the above ways, the first one is more considerable to provide durability and flexibility to
the final design. Planning techniques are being shown below;

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Designing a PWM Solar Charge Controller
Figure 3: Planning Techniques
1.5 Design Methodology
After finalizing design specifications, initial designing will be carried out. Initially, we will
simulate the solar charge controller circuit and will make it on a breadboard for onboard testing.
This initial troubleshooting will clarify the design limitations like what to add and avoid in
further designing. Then final design elements will be taken under considerations. After
purchasing elements, basic charge controller setup will be designed and simulated. Once its
output characteristics being tested on-load and off-load, we will lead towards PCB designing and
hence prototyping of our final design. After prototyping, a case will be designed for the charge
controller to be placed in.
1.6 Benchmarking
The final specifications of our product in contrast to the industrially available similar products
can be seen in the table below;
Table 2: Comparison with Industrial Controllers
PWM Solar Charge Controllers
Specifications Arduino Based
Controller (under
Progress)
LS0512E LS0512R LS0510E %age
Difference
Nominal System
Voltage
12V 12V 12V 12V 0
Max. Battery
Voltage
35V 16V 16V 16V 19
Battery Current 15A max 5A 5A 10A 5
LED Indications yes yes yes Yes 0
Operating -20℃ to +60℃ -35℃ to +55℃ -35℃ to +55℃ -35℃ to +55℃ 10

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Designing a PWM Solar Charge Controller
Temperature
Humidity 100% non-
condensing
≤ 95% N.C 10% - 90% ≤ 95% N.C 5
Dimensions 52.1 x 53.3 mm 92.8x65x20.2 mm 97x66x25 mm 101.2x67x21.8
mm
Large
difference
2 Initial Technical Solutions
2.1 Ideas Generation Process
There are four main functions of the solar charge controller;
 It charges the battery when needed.
 Detects and gives an indication when the battery is fully charged.
 It cuts offload from supply when battery voltages are at a certain minimum level.
 It also cuts offload when an overload occurs.
Keeping in view of above functions, we prepared two initial designs leading towards the final
design. Both of them are PWM charge controllers, but one is being tested for low voltages and
the other one is being tested with PIC microcontroller. Each of them is discussed below; (Rayhan
et al, 2016).
2.1.1 ID1
The solar charge controller is the heart of any solar panel system. The first prototype was being
designed using Arduino for 5W solar panel with Voc=10V to have an idea about its design and
to let it lead us towards our final design. A voltage divider is designed in a way to provide an
output voltage of less than 5V. power is being stored in 5.5Ah battery. For voltage sensing, we
used R1=10K, R2=4.7K, and hence sensed both battery and panel
voltages. So this solar panel was being tested for 6V battery, 5W/6V
solar panel. For high voltages, voltage divider resistors need to be
changed. PWM enables the digital output to provide a range of
different power levels just like analogue output. Frequency = 90Hz,
Duty Cycle = 90%. Attached are the PWM testing results of the test
setup. Breadboard testing is being shown in the diagram below; Figure 4: PWM Signal
showing on CRO

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Designing a PWM Solar Charge Controller
Figure 5: ID1 Schematics
Observing pulse width modulation in line with frequency selection, frequency needs to be
standardized.
2.1.2 ID2
The second prototype is being developed using PIC 16F876A microcontroller. This prototype is
being tested for 12V, 80Ah battery and 12V solar panel with no discharging below 80%. The
circuit schematics are shown below;
Figure 6: ID2 Circuit Schematics
2.2 Initial Designs Evaluation
Initial Designs are being evaluated according to the IEC 62509 standard certifications. Each
parameter is given a rating “+” if its performance is better than the reference parameter.
However, if the parameter’s performance is not good as compare to the reference design
requirement, it is given a rating as “-“. In ID1, voltage is not stabilized and frequency also needs
to be changed. In ID2, PIC microcontroller is not based on the latest technology and takes time
to operate. This must be replaced with Arduino or any other latest technology. The concept
screening matrix is shown below;

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Designing a PWM Solar Charge Controller
Table 3: Concept Screening Matrix
Photovoltaic Generator
Charging of a Battery
Load
Control
Protection
Functions
Voltage
Sensing
Voltage
Stabilization
ID1 + - + - -
ID2 + + - + -
2.3 Concept Selection
Observing tested results, and above the screening matrix, it’s been clear that the ID2 design is
more suitable but we need to update the microcontroller and some filtering capacitors for voltage
stabilization. Also, ID2 design is being burned out one time during testing, so for protection, we
need to place fuses in it.
Figure 7: Selection of Final Design Concept
2.4 Software and Hardware Standards to Make Design Choices
Figure 8: Software and Hardware Choices
2.5 Possible Improvements in Design
In case of overload, when the load comes to its normal value, the controller should turn
the load on after a specified time limit around 10~20 minutes.
There must be displayed indications for charging current levels.
Overcurrent and underrated current must also be displayed in design
Battery charging should also be displayed

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Designing a PWM Solar Charge Controller
Battery low voltage and high voltage protection must also be known through 0the proper
display.
A controller may restart charging itself after some time of being overpowered by a solar
panel.
3 Industry-Standard Technical Design
3.1 Final Design Elements
After conceptual modelling, screening, and evaluation, we came up to conclude the following
elements as final design components;
Figure 9: Design Elements
3.1.1 A configuration of Solar Charge Controller in Solar Panel System
Battery group voltages must match the solar panel voltages. Solar panels’ power is being decided
according to load power and sunshine per day. Solar panels should generate power more than the
load power and must have some power reserved. For the 12v system, solar panels should have
Voc = 22~50V. Power cables must be integrated according to the allowed voltage drop and
voltage/current ratings of the system. Keeping in view of these considerations, final design
schematics of the solar charge controller is being shown in the appendix. And an operational
diagram of the solar module along with the solar charge controller integration is being shown
below; (LokeshReddy et al, 2017).

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Designing a PWM Solar Charge Controller
Figure 10: Working Diagram of Solar Charge Controller in Solar Panel System
When solar panel generates power, a microcontroller (Arduino in our case) takes input pulse at
its analogue pin and converts that to digital input while sensing voltage levels. If the voltage
level increases the rated voltage which is being coded in Arduino, Arduino will sense voltage
and decrease pulse width, hence the controller will stop charging the battery. And if voltage
levels are according to rated voltages, then pulse width will be maintained. This process is being
shown in the flow diagram below;
Figure 11: Flow Diagram Showing Working of PWM Solar Charge Controller