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MINISTRY OF EDUCATION AND TRAINING HANOI UNIVERSITY OF SCIENCE AND TECHNOLOGY PAULINO VICTORINO RODRIGUES MUEBE STUDY AND DESIGN OF A SOLAR PV SYSTEM MASTER OF SCIENCE HANOI 2016 MINISTRY OF EDUCATION AND TRAINING HANOI UNIVERSITY OF SCIENCE AND TECHNOLOGY - PAULINO VICTORINO RODRIGUES MUEBE STUDY AND DESIGN OF A SOLAR PV SYSTEM CONTROL AND AUTOMATION MASTER THESIS IN SCIENCE SCIENTIFIC SUPERVISOR: ASSOC PROF TA CAO MINH, PhD HANOI 2016 Contents Declaration iii List of Figures iv List of Tables vii List of Acronyms viii Acknowledgement ix Dedication x ABSTRACT xi CHAPTER I - INTRODUCTION 1.1 Generalities 1.2 Renewable energy 1.2.1 The solar panel 1.2.2 Typical configuration of a PV system .10 1.2.3 Main applications 11 1.2.4 Configuration of a 150W PV stand-alone system .11 Conclusions of Chapter .11 CHAPTER II - SYSTEM SIZING 13 Conclusions of Chapter .16 CHAPTER III - SYSTEM CONTROL 18 3.1 Charge controller 18 3.1.1 Buck converter modelling 19 3.1.2 Charger modelling .21 3.2 Inverter Control 27 3.2.2 Current mode control modelling .35 i 3.2.3 3.3 PWM (Pulse Width Modulation) Technique 40 DC/AC Converter (Inverter) 40 3.3.1 Three level Carrier PWM (single pole) .41 3.3.2 Working principle of the inverter 43 3.3.3 Output Filter equations 47 3.3.4 Mathematic modelling .47 3.3.5 Power circuit calculation 50 3.3.6 Determination of Modulation index 51 Conclusions of Chapter .52 CHAPTER IV: SIMULATION RESULTS 54 4.1 Charge controller 54 4.2 DC-DC step up converter 59 4.3 The DC/AC Converter 60 Conclusions of Chapter .63 Conclusions and future scope of work 64 Bibliography 65 Apendix .68 ii Declaration I hereby declare that this master thesis is of my authorship and of the orientation of my supervisor The data and results presented in this thesis are honest and not yet published in any previous study All cited informations are appreciated in the reference list The Author _ iii List of Figures Figure 1.1 Equivalent circuit of a solar panel .5 Figure 1.2 Block diagram of a modern PV system Figure 1.3: Buck converter schematic [5] Figure 1.4: MPPT P&O method graph .7 Figure 1.5: P&O algorithm flowchart [6] Figure 1.6: Graph power versus Voltage in INC algorithm [7] Figure 1.7: INC algorithm flowchart Figure 1.8 : Typical configuration of a PV system [8] .10 Figure 1.9: Basic diagram of a stand-alone PV [8] 10 Figure 1.10: Basic diagram of a grid-tied system [8] .10 Figure 2.1: PV system project 13 Figure 3.1: Single solar array and single battery arrangement [10] 18 Figure 3.2: Operation of Buck converter at the MPPT [11] .19 Figure 3.3: Buck converter circuit [11] .20 Figure 3.4: Equivalent buck circuit in ON state [11] 20 Figure 3.5: Equivalent Buck converter in the OFF state [11] 21 Figure 3.6: Control structure of a constant power (CP) mode [10] 22 Figure 3.7: Power flow diagram of a CP mode .22 Figure 3.8: Control structure of a constant voltage (CV) mode [10] 23 Figure 3.9: Power flow diagram of a CV mode 23 Figure 3.10:Single battery dual-mode control structure 24 Figure 3.11: Averaged system model .24 Figure 3.12: MPPT control scheme [13] 26 Figure 3.13: Arduino of solar charge controller [14] 26 Figure 3.14: Inversion scheme 27 Figure 3.15: Push pull converter .28 Figure 3.16: Current wave forms of the push pull circuit 29 Figure 3.17: Proposed inverter overall structure circuit 30 iv Figure 3.18: Schematic of proposed inverter 30 Figure 3.19: Output wave form 31 Figure 3.20: Simplified circuit of block1 converter 31 Figure 3.21: Simplification of Fig 3.21 by transformer elimination 31 Figure 3.22: Switching network circuit .32 Figure 3.23: Simplified network with parasitic parts 32 Figure 3.24: Large signal model of switch network 33 Figure 3.25: Averaged dc and small signal model 33 Figure 3.26: Small signal model of the converter .34 Figure 3.27: Current mode controlled push pull converter .36 Figure 3.28: Control block diagram of the converter 36 Figure 3.29: Proposed voltage and current controller [18] .37 Figure 3.30 Matlab graphs for the inverter circuit 39 Figure 3.31 PWM graphs 40 Figure 3.32: Structure of the full bridge inverter 41 Figure 3.33: Output impedance of single phase inverter 41 Figure 3.34: Details of the three levels modulation applied to the single phase inverter [20] .43 Figure 3.35: Simplification of the single phase inverter 44 Figure 3.36: First stage of operation of the inverter 44 Figure 3.37: Second stage of operation of the inverter .45 Figure 3.38: Third stage of operation of the inverter 45 Figure 3.39: Fourth stage of operation of the inverter 46 Figure 3.40: Vab voltage and switching commands 46 Figure 3.41: Closed loop control diagram 47 Figure 3.42: Closed loop block diagram of the system 48 Figure 3.43: Vab during the positive half cycle 48 Figure 3.44: Sinusoidal PWM 51 Figure 4.1: First Stage of battery charging (MPPT) 55 v Figure 4.2: MPPT charge controller graphs 56 Figure 4.3: Charge controller without MPPT 56 Figure 4.4: Connection in parallel of two solar panels in PSIM .57 Figure 4.5: First stage of charging 58 Figure 4.6: Second stage of charging 58 Figure 4.7: Third stage of charging 59 Figure 4.8: DC-DC push pull circuit 60 Figure 4.9: Voltage and current graphs of the push pull converter 60 Figure 4.10: Power circuit 61 Figure 4.11 carrier PWM circuit .61 Figure 4.12: The inverter circuit .62 Figure 4.14 Voltage at A-B terminals of the inverter .63 Figure 4.15: RMS output Inverter current (in blue) and voltage (in red) graphs 63 vi List of Tables Table 1: Loads vs watt hours/day consumption 11 Table 2: Total energy demand/day 13 Table 3: Inverter specifications 28 Table 4: Output filter specifications 51 Table 5: Specification for the inverter project 61 vii List of Acronyms DC - Direct current AC - Alternative current PWM - Pulse Width Modulation MPP - Maximum power point MPPT- Maximum power point tracker Cin/Ci - input capacitor Cout/Co - output capacitor Lf - filter inductor Vin - input voltage Vout - output voltage D - duty cycle Fsw - switching frequency Fc - cutoff frequency Voc- open circuit voltage Isc - short circuit current viii Figure 4.1: First Stage of battery charging (MPPT) 55 Figure 4.2: MPPT charge controller graphs The following graphs show the input and output power of the system without the MPPT Here is possible to see that response of the system is too slow and also the track is not performed as fast as can be seen in the above graph Figure 4.3: Charge controller without MPPT In the following figure it’s presented the way were connected the solar panels in parallel 56 Figure 4.4: Connection in parallel of two solar panels in PSIM The total system must match 150W Thus, were connected two solar panels of 80W each (figure 4.4) in parallel The voltage of each solar panel is around 18V and the current is 4.85A As they are in parallel the total current will be the double of 4.85, i.e around 9A The voltage still 18V, so to charge a parallel of batteries is necessary a buck converter as a power interface between the solar array and the battery bank The incident values of temperature and irradiance are 25o C that can vary 10 and 400-1000 w/m2 respectively The control strategy used in the circuit was the P&O algorithm and the wave forms can be seen in the following figures: As the correct battery charging is performed in three stages, the first stage (Bulk) will be done by the MPPT strategy were, is driven to the battery the maximum current (constant) and the voltage (increasing) until reach around 80% of the total capacity of the battery; 57 Figure 4.5: First stage of charging The second stage (Absorption), the voltage is kept constant at a certain value and the current decreases slowly This stage lasts for the next 20% of the total battery capacity Figure 4.6: Second stage of charging The last stage is the Float where the current decreases to around 1% of the total capacity of the battery and the voltage is kept constant at a value lower than the Bulk stage’s voltage and upper than the battery nominal voltage 58 Figure 4.7: Third stage of charging 4.2 DC-DC step up converter As it said in the previous chapter, the DC-DC converter is a push pull circuit with a power transformer center tapped This circuit will have 12V DC input and around 400V DC output The MOSFET will be driven by a PWM technique with the carrier frequency of 100 kHz As known the modulation index is responsible of the determination of where: is the modulation index, VM is the amplitude of the reference signal and VC is the amplitude of the carrier signal Generally, for the modulation index, the voltage VC is kept constant and the adjustment of the modulation index is done by varying the VM The variation of changes the pulse width and controls the effective signal in the output of the inverter In this circuit VM must be 220V rms, so we choose 250V for the carrier signal, thus the modulation index is 0.88, which satisfies the condition The following figures show us the DC-DC push pull converter structure (figure 4.8), and voltage and current graphs of the push pull (figure 4.9) 59 Figure 4.8: DC-DC push pull circuit The following pictures show the graphs of the output voltage and current of the push pull circuit converter, where is possible to see the desired signal boosted to 400V and that it stable at about ms Is also possible to see that the current is set at around 12A Figure 4.9: Voltage and current graphs of the push pull converter 4.3 The DC/AC Converter To prove the studies we propose the project for the inverter with the following specifications: 60 Parameters Nominal Value Input Voltage 400V Effective output Voltage 220V Output power 150W Output frequency 50Hz Switching frequency 35kHz Inductor current ripple 15% Capacitor voltage ripple 1% Modulator pick Voltage 3,11V Table 5: Specification for the inverter project The used circuits are presented in the figure 4.10 and figure 4.11 which represents the power circuit and the switching circuit Figure 4.10: Power circuit Figure 4.11: carrier PWM circuit 61 Figure 4.12: The inverter circuit As the desired output voltage in rms (figure 4.14) is 220V and the power can’t exceed the 150W, we present the inverter circuit (figure 4.12) and the output values of voltage and current In Blue is the current (around 0.7A) and Red is the voltage (around 220V) RMS The voltage in a-b terminals is 400 V as can be seen in the graphs of figure 4.13 62 Figure 4.13: Voltage at A-B terminals of the inverter Figure 4.14: RMS output Inverter current (in blue) and voltage (in red) graphs Conclusions of Chapter In this chapter was simulated the entire system, partially, and presented the results At the last were simulated the entire system to see the behavior of the voltage and current in RMS values Here were concluded that the goals were met The voltage in the output of the system is 220V rms, was also possible to prove the efficiency of the MPPT algorithm as well as the charging of the battery Were implemented two different kinds of modulations – the PWM (for the battery charger and push pull) and the SPWM (for the inverter) 63 Conclusions and future scope of work This study presents in a simple way the design of a 150W PV System to apply in a small house with few appliances and low consumption It models each component and simulates the system using Psim software Inside the study is possible to see the design and calculation of the rated value of the PV system units (PV Array, charge controller and inverter) for a load home The control aspects were considered by using a PI controller and the results were presented in graphs All the calculations done are also presented and the goals of the study were met This work was done with the main propose of understanding how to design a solar PV system, so were considered the small power to easy manipulate the calculations and simulation The future scope is to design bigger system (more than 2kw) and connect it to the grid The control aspects for the inversion circuit can be done by the use of a PID controller which can give more robustness and stability to the system under load varying 64 Bibliography [1] [Online] Available : http://americanhistory.si.edu/lighting/19thcent/consq19.htm [Accessed 2016, July] [2] M MOUZINHO and D NANDJA (2004), "Literacy in Mozambique: Education for all challenges," UNESCO, Maputo [3] [Online] Available: http://www.khayapower.co.za/about-us/the-energy- situation [Accessed 2016, March] [4] [Online] Available: https://en.wikipedia.org/wiki/Renewable_energy [Accessed 2016, January] [5] [Online] Available: http://www.allaboutcircuits.com/technical- articles/utilization-of-simple-converters-circuits/ [Accessed 2016, May] [6] [Online] Available: https://www.researchgate.net/figure/259479658_fig7_Figure-212-Flowchartof-PO-MPPT-Algorithm [Accessed 2016 May] [7] R Srushti CHAFLE and Uttam B VAIDYA (2013), "Incremental Conductance MPPT Technique for PV system," vol 2, no [8] [Online] Available: 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Carlos, 66 Thesis [25] MARTY BROWN (2001), Power Supply Cookbook, 2nd ed Boston, United States of America: Newnes [26] SEDDIK BACHA, LULIAN MUNTEANU, and ANTONETA LULIANA BRATCU (2014), Power Electronics Converters and Control with case studies, Springer, Ed London [27] MUHAMMAD RASHID (2001), Power Electronics Handbook Florida, United States of America: Academic Press [28] [Online] Available: http://www.khayapower.co.za/about-us/the-energy- situation/ [ Accessed 2016, July] 67 Appendix Matlab Program file for PI compensator type II %push pull converter clear all; Vg=12; HO=2/400; %H(O)=Vfb/Vout Vm=3; %Vm is the amplitude of sawtooth waveform in TL494 TO=Vg*HO/Vm; R=1041.26; L=6.33e-6; C=10e-6; rc=0.06; r=0.06; RB1=1036; RB2=518; D=30/100; VI=12; w0=sqrt((R+r)/(L*C*(R+rc))); Q=sqrt(L*C*(R+r)*(R+rc))/(L+C*R*(r+rc)); k2=VI*(R/R+r); wZ=1/(rc*C); s=tf('s'); T=(k2*((1+s/wZ)/(1+(s/(Q*w0))+(s^2/w0^2)))); % push pull conv TF without controller bode(T); hold all; % PI controller model %voltage controller model R1=1036; %controller parameter R2=654.75; %controller parameter C1=12.15e-6;%controller parameter C2=24.32e-6;%controller parameter RP1=345.33; s=tf('s'); GcV=-((1/(C1*(R1+RP1)))*((s+(1/(R2*C2)))/(s*(s+((C1+C2)/(R2*C1*C2)))))); % controller TF bode(GcV); hold all; %open loop control include of controller GO=T*GcV; bode(GO); %current controller model 68 R3=1e3; R4=158.1; C3=10e-6; GcI=-(R3+(1/(s*C3)))/R4; bode(GcI); hold all; KB=RB1/(RB1+RB2); pi=3.14; Vm=3; fsw=100e3; Gm=(pi^2*fsw^2)/(Vm*s*(s+((pi^2*fsw)/2))); Ti=KB*GcV*GcI*Gm*T; bode(Ti); hold all; grid on; 69