maximum power point tracker for solar...
TRANSCRIPT
MAXIMUM POWER POINT TRACKER FOR SOLAR CHARGE CONTROLLER APPLICATIONS
STUDENT: GITONGA M. JAMES
REG. NO. F17/2123/2004
SUPERVISOR: MR. C. OMBURA
EXAMINER: MR. DHARMADHIKARY
PRJ. NO. 64
2009
OUTLINE
• PROJECT OBJECTIVES• INTRODUCTION• METHODOLOGY• PROCEDURE• RESULTS• DISCUSSION• CONCLUSION• QUESTIONS
PROJECT OBJECTIVES
• To design a High efficient Maximum Power Point Tracker
• To Implement the design • Test the working of the Design
INTRODUCTION
• Solar energy is a clean, free and renewablenatural resource offering environmentalfriendly source of electricity.
• Conversion from solar to electrical energy isachieved by photovoltaic (PV) arrays.
• Since PV arrays are relatively expensive, it isdesired to extract maximum power fromthem at any given time.
Introduction (cont.)
• Maximum Power Point Tracking (MPPT):
– Technique used in power electronics systems toobtain the maximum possible energy fromenergy such as solar, wind and tidal..
– Its use is desired to compensate for the effect oftemperature, ageing, variations in solar radiation(insolation), and load condition in a PV system.
• Implemented using simple and analogmethod - Ripple Correlation Control andFixed reference voltage Method.
METHODOLOGY• To achieve the MPPT:
– Characterization of solar panels.
– Development of a mathematical relation to control the output Voltage of a buck converter.
– System modelling using Multisim 10.0 and Proteous 7.0 Professional.
– Practical implementation of the system.
Methodology (cont.)
Block diagram of the MPPT system:
Solar Solar PanelsPanels
Buck Buck ConverterConverter BatteryBattery
SensorsSensors(V & I)(V & I)
Control Control LawLaw PWM PWM
Procedure cont….
• Buck converter– A step down DC to DC converter.
VinVoutCycleDuty =
Buck Buck ConverterConverter
+
Vin
-
+
Vout
- V out = Vin tonton + toff
Tabulation of Array voltage and subsequent Duty cycle and control voltage required for Fixed reference voltage law derivation
PV array VoltageRequired Duty Cycle
Required Control Voltage
14 1 514.74 0.95 5.2515.55 0.90 5.516.47 0.85 5.7517.5 0.80 618.7 0.75 6.2520 0.70 6.521.54 0.65 6.7523.4 0.60 725.45 0.55 7.25
Procedure Cont…..
Procedure Cont…• Control law relates Control Voltage Panel Voltage
• Obtained using a linear approximation
0
1
2
3
4
5
6
7
8
0 5 10 15 20 25 30
Control Voltage(Vc)
PV Voltage (Vpv)
Required Control voltage Versus PV. Voltage
Ideal
Linearized
Linearized equation Vc = 2.5 + 0.2Vpv
Photovoltaic Array Characteristics
Array Voltage Array Current(mA) Power(mW)8.35 0.4 3.348.32 0.9 7.4888.29 1.5 12.4358.23 3 24.698.16 5.8 47.3288.02 10.4 83.4087.77 21.5 167.0556.64 48.3 320.7125.3 62.5 331.25
2.35 73.6 172.960.68 78.1 53.1080.2 80 16
Photovoltaic Array characterization For ripple Correlation Control law derivation
Procedure Cont…
Procedure Cont……
0
50
100
150
200
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300
350
0 1 2 3 4 5 6 7 8 9
Array Power (mW)
Array Voltage (V)
dP/dt > 0
dP/dt =0
dP/dt < 0
• Control law relating sign of differential of Voltage (dv/dt) to sign of product of differential of power and voltage (dp/dt) (Utilizing non-linear dynamics of a Switch mode dc converter to derive RCC law.
Sgn
Ripple correlation ControlConditions Comparator
Output XOR
output Switch
Condition Effects on Vpv
dv/dt Xp Xv S
V > 0 > 0 1 1 0 Opens Increases
V 0 0 0 0 0 Opens Increases
V 1 0 1 Closes Decreases
V 0 0 0 1 1 closes Decreases
Procedure Cont……
Procedure (cont.)
• Important Sections in the control unit (MPPT):– Current sensor: I to V Converter– Voltage sensor – Control circuit - circuit implementation of the
control law– Pulse Width Modulator (PWM)- adjusts the
duty cycle– Square wave generator– Sawtooth Wave Generator
RESULTSPanel Voltage (Vpv) V
Observed Duty Cycle
Theoretical Duty Cycle
Tracking Error
16 0.85 0.88 3.41%
18 0.75 0.78 3.85%
20 0.69 0.70 1.43%
23 0.58 0.61 4.92%
Average tracking efficiency = 100 - (3.41+3.85+1.43+4.92)/4= 96%
Results cont..• Comparison of theoretical and Practical results
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 5 10 15 20 25
DutyCycle
Panel Voltage
Practical
Theoritical
Average tracking efficiency =96%
DISCUSSION
• Maximum power points obtained using the control law were very close to theoretical values.
• Results obtained from the tests were as expected.
• The designed MPPT is not dependent on the converter used, making it flexible and adaptable to other dc-dc switching topologies.
• Divergence occurred for higher values of insolation and Low insolation levels.
CONCLUSIONS
• System is able to track maximum power at different insolation levels.
• Variations between theoretical and experimental data is due to:– Linear approximation of duty cycle
• Validation of the control laws through a simple and analog MPPT.
RECOMMENDATIONS
• Implementation of the designed MPPT using Microcontrollers
• Research on integrating the MPPT discussed in this paper with Wind power
• Research on ways of integrating the designed MPPT to dynamic systems such as solar powered vehicles.