Final Report.docx

Middle East Technical University

2017/2018 Fall

Electrical and Electronics Engineering

12.01.2018

EE213 Electical Circuits Laboratory Term Project

SOLAR TRACKING SYSTEM

Final Report

Metehan DEMİRCİOĞLU - 2166213 Eren TURGUT - 2318459

Assistant: Baver Özceylan Thursday Afternoon

TABLE OF CONTENTS 1. Introduction 2. Project Design 2.1. Sensing Unit 2.2. Control Unit 2.2.1. Decision Subunit 2.2.2. Detection Subunit 2.2.3. Inverting Subunit 2.2.4. Inspection Subunit 2.2.5. Function Subunit 2.3. Angle Adjustment Unit 2.4. RGB LED Bonus Unit 3. Selection of Equipment 4. Cost Analysis 5. Power Analysis 6. Conclusion 7. References

1. Introduction In this project, we have designed an analog single-axis solar tracking system that can take three different angular positions. The purpose of this system is to increase the efficiency of solar panels. First of all, we have designed a sensing unit that contains three LDR’s to measure the light intensity. Then we have designed a control unit that compares the outputs of LDR’s in order to generate the PWM(Pulse Width Modulation) signal with a corresponding duty cycle for each angle. We also have designed a function subunit that generates the PWM signal to drive the servo motor. Finally, we have an angle adjustment unit that contains a servo motor to adjust the angle of the panel.

2. Project Design We have studied our design as different parts and brought them together as a final process. An overall block diagram of our design is shown in the Figure 1.

Figure 1: Overall block diagram of our design

2.1. Sensing Unit Our sensing unit contains three LDR’s(Light Dependent Resistors) to measure the light intensity for three different angles. We connected LDR’s and regular resistors as shown in the Figure 2. We used same regular resistors and same DC voltage inputs in order to compare the light intensities correctly. Resistance of the LDR is decreasing while the intensity of light is increasing. Therefore, the output of the LDR which receives more light has the highest voltage value.

Figure 2: Sensing unit containing 3 LDR’s Outputs from each part goes to the control unit to compare the light intensities. Sample outputs from sensing unit is shown in the Figure 3.

Figure 3: Sample outputs of sensing unit

2.2. Control Unit Our control unit contains five different subunits called decision, detection, inverting, inspection and function.

2.2.1. Decision Subunit Decision subunit’s purpose is to compare sensing unit outputs and determine which LDR receives the most light intensity. We achieved that by constructing a basic comparator and a non-inverting summing amplifier as shown in the Figure 4.

Figure 4: One of the three parts of decision subunit When output 1 has the biggest voltage value, we get 12V from both point A and point B as labeled in Figure 4. We aimed to get final output of approximately 12V as outputA from this subunit so we designed a non-inverting summing amplifier. Outputs are calculated by this equation:

𝑉𝑜𝑢𝑡 =

𝑉𝐴 +𝑉𝐵 3

. (1 +

𝑅9 𝑅10

)

(1)

We have divided total voltages of A and B by 3 because we have three 2.2K resistances as shown in the Figure 4. By this way, the non-inverting summing amplifier stays in linear region.

𝑉𝑜𝑢𝑡𝐴 =

12+12 3

. (1 +

10𝐾 22𝐾

) = 11.63𝑉

Likewise, when output 1 has the lowest voltage value, we get -12V from both point A and point B. When output 1 has the middle voltage value, we get 12V from point A and -12V from point B. Summing amplifier calculations are shown below:

𝑉𝑜𝑢𝑡𝐶 =

𝑉𝑜𝑢𝑡𝐵

−12−12 3

. (1 +

10𝐾 22𝐾

) = −11.63𝑉

12 − 12 10𝐾 = . (1 + ) = 0𝑉 3 22𝐾

We have three of this decision subunit for all the possibilities explained as shown in the Figure 5.

Figure 5: Decision subunit

Final output voltages of comparator part of the decision subunit are shown in the Figure 6. Outputs of the decision subunit goes to detection subunit and inverting subunit which we will be explained next.

Figure 6: Outputs of decision subunit

2.2.2. Detection Subunit We have designed the detection subunit in order to observe which LDR receives the highest light intensity. The conditions and corresponding colors are listed in the Table 1.

The detection subunit contains 6 diodes, 6 resistors and a cathode RGB LED as shown in the Figure 7.

Figure 7: Detection subunit

When outputA has the value of 11.63V and other outputs have 0V and -11.63V, only diodes labeled as D1 and D2 let the current flow to RGB LED, so we get yellow light as a result. We set the resistances of R2 and R3 as equal so that the current ratio is 1. Similarly, when outputB has the value of 11.63V, only diodes labeled as D4 and D5 let the current flow to RGB LED, so we get purple light as a result. Their current ratio is also 1. In the final case, when outputC has the value of 11.63V, only diodes labeled as D3 and D6 let the current flow to RGB LED, so we get orange light as a result. Their current ratio is 2. Sample currents for orange light as shown in the Figure 8.

Figure 8: Current flow for orange light

2.2.3. Inverting Subunit The purpose of the inverting subunit is to invert 11.63V to -11.63V and -11.63V to 11.63V. This invert is necessary to make sure which capacitor is working in the function subunit. Output of this subunit goes to inspection subunit and RGB LED bonus part. Our design of this subunit is shown in the Figure 9. We have three of this subunit for each decision subunit.

Figure 9: One of the three inverting subunit

Calculations for the output of this subunit are shown below:

𝑉𝑜𝑢𝑡 = −

𝑅1 𝑅2

. 𝑉𝑖𝑛

(2)

2.2.4. Inspection Subunit The purpose of the inspection subunit is to decide whether the function subunit should work or not. Design of this subunit is shown in Figure 10.

Figure 10: Inspection subunit As we explained in the inverting subunit, we now have respectively -11.63V, 0V and 11.63V as inputs of this subunit. We based on the working principle of diodes when we designed this subunit. When we have -11.63V as input, current will not flow through the diode, so our function subunit can work properly in range of -6V and 6V. However, when we have 0V and 11.63V as input, diode will allow the current flow to function subunit and capacitor will be disrupted. Output of this subunit is shown in Figure 11.

Figure 11: Output of the inspection subunit

2.2.5. Function Subunit The purpose of the function subunit is to generate the Pulse Width Modulation(PWM) to drive the servo motor. We achieved this by constructing negative resistance converters that generate square wave outputs as shown in Figures 12,13 and 14. We let our capacitor charge and discharge through two parallel resistors and oppositely connected diodes. By doing so, we can control the output period Ton (4) and Toff (5) to achieve necessary duty cycle (3). Ron and Roff resistance values are approximated in schematics. Their final values were determined in experiments. Duty cycle,D, is calculated by this equations:

𝐷=

𝑇𝑜𝑛

(3)

𝑇

𝑇𝑂𝑁 = 2. 𝑅𝑃𝑜𝑡𝐴 . 𝐶. ln(

1+𝜆 1−𝜆

𝑇𝑂𝐹𝐹 = 2. 𝑅𝑃𝑜𝑡𝐵 . 𝐶. ln(

Where

𝜆=

𝑅1 𝑅1 +𝑅2

𝑇 = 𝑇𝑂𝑁 + 𝑇𝑂𝐹𝐹

)

1+𝜆 1−𝜆

)

(4)

(5)

(6)

(7)

Operation of the servo motor and why we need the specific duty cycles will be explained in the 2.3. angle adjustment unit part.

Figure 12: Function subunit to adjust servo motor to 30°

Figure 13: Function subunit to adjust servo motor to 90°

Figure 14: Function subunit to adjust servo motor to 150°

The purpose of the diodes D18, D2, D14 as labeled in Figures 12,13 and 14 is to make our signal start from 0V. The other purpose of these diodes is to prevent the current flow from disrupted function subunits whose op-amps are in -saturation region to angle adjustment unit. Our PWM signals with necessary duty cycles are shown in Figures 15,16 and 17.

Figure 15: PWM signal for 30°

Figure 16: PWM signal for 90°

Figure 17: PWM signal for 150°

2.3. Angle Adjustment Unit Servo motors are simply connected by three wires: power, ground and signal. Power and ground signals are connected to DC power supply [1]. However, the signal line is connected to our function subunit which generates a PWM signal to drive the motor. We adjust the width length i.e. the duty cycle of the PWM signal to control the angular position of our servo motor. Servo motors also require a PWM signal with 20ms period and a pulse width between 1-2ms [2]. Servo motor stays at 0° with 1ms pulse width while it moves to 90° position with 1.5ms pulse width and 180° position with 2ms pulse width. We want our panels to be at 30°, 90° and 150° angular positions so we need pulse widths 1.16ms, 1.5ms and 1.83ms respectively. This is why we generated PWM signals with specific duty cycles.

2.4. RGB LED Bonus Unit We designed this bonus part the same as detection subunit. The conditions and corresponding colors are listed in Table 2. Table 2: Conditions and Procedures for State A,B and C

We have same input points with inverted inputs. In this case, LDR which has lowest light intensity has 11.63 V output. Like in the detection subunit, the current only flow through to RGB LED when output is 11.63V. The position of diodes and the resistors are the same because the colors are same when A has biggest and lowest output.

Finally, Figure 18 shows our final design with all units together.

Figure 18: Solar tracking system project design with all units.

3. Selection of Equipment In this project, we have used the circuit components that we have learned in EE213 laboratory such as resistors, capacitors, operational amplifiers, diodes, potentiometers and LDR’s. We have also used a servo motor to adjust our panel to an angular position. Additionally, we have used RGB LEDS to determine the intensity of the light.

4. Cost Analysis Table 3 shows our equipments and how much money we spent. Table 3: Equipments and their costs Component(s) Bread Board LDR(10mm) RGB(Cathode) Operational Amplifier(LM741) Male/Male Jumper Wires Resistances(1k,2.2k,3.3k,10k,22k) Potentiometer Diodes(1N5819) Capacitors(1uF) Servo Motor

Quantity 4 3 2 15 1 50 6 21 3 1

Unit Price(TL) 7,2 1,3 0,5 0,75 4,40 0,02 0,65 0,2 0,6 11 Total Price

5. Power Analysis Table 4 shows our power consumptions for different angles. Table 4: Power consumptions Angle(°) 150

90

30

Voltage(V) 6 12 -12 6 12 -12 6 12 -12

Current(mA) 5 46 23 5 42 23 5 39 23

Power(mW) 30 552 -276 30 504 -276 30 468 -276

Total Price(TL) 28,8 3,9 1 11,25 4,40 1 3,9 4,2 1,8 11 71,25TL

6. Conclusion In this project design we tried to use circuit components that we have learned in sensors to measure the light intensities for each angle. Then we designed the control unit to compare the measured light intensities and generate a PWM signal to drive the motor. By doing these designs, we practiced what we have learned from EE213 laboratory and put them into use. We also learned the use of PWM signals and how to generate them for different duty cycles. Finally, all of our designs and calculations are based on the Kirchoffs current and voltage laws.

7. References [1] Mike. (2012, March 4). Pure Analog Servo Control [Online]. Available: http://www.nlvocables.com/blog/?p=368

[2] Pinckney, N. (2006). Pulse-width modulation for microcontroller servo control. IEEE potentials, 25(1), 27-29.