MAXIMUM POWER POINT TRACKER FOR SOLAR CHARGE CONTROLLER APPLICATIONS PRJ. NO. 64 STUDENT: GITONGA M. JAMES REG. NO. F17/2123/2004 SUPERVISOR: MR. C. OMBURA EXAMINER: MR. DHARMADHIKARY 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 renewable natural resource offering environmental friendly source of electricity. Conversion from solar to electrical energy is achieved by photovoltaic (PV) arrays. Since PV arrays are relatively expensive, it is desired to extract maximum power from them at any given time.
Introduction (cont.) Maximum Power Point Tracking (MPPT): Technique used in power electronics systems to obtain the maximum possible energy from energy such as solar, wind and tidal.. Its use is desired to compensate for the effect of temperature, ageing, variations in solar radiation (insolation), and load condition in a PV system. Implemented using simple and analog method - Ripple Correlation Control and Fixed 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 Panels Buck Converter Battery Sensors (V & I) Control Law PWM
PROCEDURE Voltage-Current characterization of PV array:
Buck converter A step down DC to DC converter. Procedure cont. + Vin - Buck Converter + Vout - Duty Cycle = V out = V in Vout Vin t on t on + t off
Procedure cont. Circuitry Implementation of a buck Converter C = L =
Procedure Cont.. Tabulation of Array voltage and subsequent Duty cycle and control voltage required for Fixed reference voltage law derivation PV array Voltage Required Control Required Duty Cycle Voltage 14 1 5 14.74 0.95 5.25 15.55 0.90 5.5 16.47 0.85 5.75 17.5 0.80 6 18.7 0.75 6.25 20 0.70 6.5 21.54 0.65 6.75 23.4 0.60 7 25.45 0.55 7.25
Procedure Cont Control law relates Control Voltage Panel Voltage Obtained using a linear approximation 8 7 6 Required Control voltage Versus PV. Voltage Control Voltage(Vc) 5 4 3 2 Ideal Linearized 1 0 0 5 10 15 20 25 30 PV Voltage (Vpv) Linearized equation Vc = 2.5 + 0.2Vpv
Procedure Cont Fixed reference voltage law derivation Circuit implementation V =15V
Procedure Cont Photovoltaic Array characterization For ripple Correlation Control law derivation Photovoltaic Array Characteristics Array Voltage Array Current(mA) Power(mW) 8.35 0.4 3.34 8.32 0.9 7.488 8.29 1.5 12.435 8.23 3 24.69 8.16 5.8 47.328 8.02 10.4 83.408 7.77 21.5 167.055 6.64 48.3 320.712 5.3 62.5 331.25 2.35 73.6 172.96 0.68 78.1 53.108 0.2 80 16
Procedure Cont 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. 350 300 dp/dt =0 Array Power 250 200 dp/dt > 0 dp/dt < 0 (mw) 150 100 50 0 0 1 2 3 4 5 6 7 8 9 Sgn Array Voltage (V)
Ripple correlation Control method (dv/dt) Procedure Cont circuitry implementation dp/dt
Procedure Cont Ripple correlation Control Conditions Comparator Output XOR output Switch Condition Effects Vpv dv/dt Xp Xv S V > 0 > 0 1 1 0 Opens Increases on V 0 0 0 0 0 Opens Increases V 1 0 1 Closes Decreases V 0 0 0 1 1 closes Decreases
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
RESULTS Panel 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 1 0.9 0.8 0.7 0.6 Duty Cycle 0.5 0.4 0.3 0.2 0.1 Practical Theoritical 0 0 5 10 15 20 25 Panel Voltage 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.
Prototype of the Designed Maximum Power Point Tracker
Questions
Testing of the designed MPPT
Square Wave generator
Effects of Temperature on Power
Solar panel equivalent circuit
Block of Fixed Reference Voltage Method
-Vpv Current Sensor
Analog Multiplier
Fixed reference Voltage Circuitry
Voltage Sensor
Differentiator
Complete Circuit Diagram
Observed waveform Vpv =18 volts, duty cycle =0.75 (theoretical 0.78)
Sawtooth waveform