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ACEEE International Journal on Control System and Instrumentation, Vol. 1, No. 1, July 2010 Design of Soft Switching Conve...
ACEEE International Journal on Control System and Instrumentation, Vol. 1, No. 1, July 2010power point so that the overall...
ACEEE International Journal on Control System and Instrumentation, Vol. 1, No. 1, July 2010bus voltage. By monitoring the ...
ACEEE International Journal on Control System and Instrumentation, Vol. 1, No. 1, July 2010The insolation changes much mor...
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Design of Soft Switching Converter with Digital Signal Processor Based MPPT for Solar Hybrid Applications

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This paper is based on the design of soft
switching converter (ZVS-ZCS resonant action) with
digital signal processor (DSP) based maximum power
point tracking (MPPT) algorithm for solar hybrid
applications. The converter aims to get the regulated
output voltage from several power sources like wind
turbines, photovoltaic (PV) arrays and energy from these
sources are simultaneously transferred to the load. The
input stage circuits for different energy sources are put in
parallel using a coupled inductor and the converter to
prevent power coupling effect it acts in interleaving
operating mode. As the buck/boost converter input range
is restricted interleaved ZVS-ZCS converter with low
switching loss and conduction loss and efficiency of more
than 92% can be easily achieved. DSP based MPPT
algorithm adjusts solar array voltage (equal to battery
voltage) with a digital compensator technique and
discrete PI control to track the MPP with high tracking
efficiency. Hence the proposed work gives a novel idea in
the modern hybrid energy system.

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Transcript of "Design of Soft Switching Converter with Digital Signal Processor Based MPPT for Solar Hybrid Applications"

  1. 1. ACEEE International Journal on Control System and Instrumentation, Vol. 1, No. 1, July 2010 Design of Soft Switching Converter with Digital Signal Processor Based MPPT for Solar Hybrid Applications N.SenthilMurugan 1 , C.Sharmeela 2 , K.Saravanan3 1 Sri Venkateswara College of Engineering , Dept. of Electrical & Electronics Engineering, Sriperumbudur-602105, Tamilnadu, India. Email: nsm@svce.ac.in 2 Anna University, Department of Chemical Engineering, Chennai -25,Tamilnadu, India. 3 MNC- Power Electronics Division, Chennai, Tamilnadu, India. {Email: sharmeela20@yahoo.com, saravanank96@gmail.com}Abstract: This paper is based on the design of soft supplied by solar arrays depends upon the insolation,switching converter (ZVS-ZCS resonant action) with temperature and array voltage, its necessary to drawdigital signal processor (DSP) based maximum power the maximum power of the solar array. A DSP basedpoint tracking (MPPT) algorithm for solar hybrid simple MPPT algorithm that adjusts the solar array /applications. The converter aims to get the regulatedoutput voltage from several power sources like wind wind voltage with a discrete PI control to track theturbines, photovoltaic (PV) arrays and energy from these MPP for the converter system is used in this paper tosources are simultaneously transferred to the load. The achieve the maximum power transfer and highinput stage circuits for different energy sources are put in efficiency for the solar energy system. The trackingparallel using a coupled inductor and the converter to efficiencies are on firmed by simulations andprevent power coupling effect it acts in interleaving experimental results. If the solar energy systemoperating mode. As the buck/boost converter input range provides power to a load, the system often operatesis restricted interleaved ZVS-ZCS converter with low away from maximum power points of the solar array.switching loss and conduction loss and efficiency of more Fig.1 shows the solar array I-V characteristics and thethan 92% can be easily achieved. DSP based MPPTalgorithm adjusts solar array voltage (equal to battery load curve, together with constant power curves (P =voltage) with a digital compensator technique and VI = const). It is observed that the delivered outputdiscrete PI control to track the MPP with high tracking power, which is represented by the operating point 1, isefficiency. Hence the proposed work gives a novel idea in significantly smaller than the maximum output power,the modern hybrid energy system. which is represented by point 2. In order to ensure a maximum power transfer, DC/DC converters are usedIndex Terms -- Zero Voltage Switching (ZVS), Zero to adjust the voltage at the load to the value of Vr = √Current Switching (ZCS), Maximum power point (Pm.R), r – equivalent resistance of the load. In thetracking (MPPT), Solar Wind Hybrid systems (SWHS). districts where solar energy and wind energy are naturally complementary, the application of solar-wind I. INTRODUCTION hybrid generation systems (SWHS) can reduce the In late years, the problem of energy crunch is more storage capacity of batteries and the total cost of theand more aggravating. Very much exploitation and system compared with stand-alone PV or windresearch for new power energy are preceded around the generation system.[1][2]. This paper presents a cost-world. In particular, the solar energy attracts lots of effect controller system for 1kW to 5kW SWHS withattention. In recent years, the development of power low DC voltage input (18V DC or 48V DC) and highsemiconductor technology results in easier conversion output AC sine wave voltage (220V AC).between AC and DC. Therefore, the use of solarenergy is emphasized increasingly and regarded as animportant resource of power energy in the nextcentury. [1]The solar modules have a long lifetime (20years or more)and their best production efficiency isapproaching 20%. Solar energy can be utilized in two ways: solarheating/cooling and solar electricity. Some appliancescan be connected directly because they work on dc atthe system voltage. Solar arrays were developed for Fig. 1 The operation of the MPPTpower satellites in the space program. In high power This control system includes features like: 1) PWMapplications, parallel connected converters are often technique in charging control of batteries, which canused to provide electrical power. As the power make wind turbine and solar array operate at maximum 12© 2010 ACEEEDOI: 01.ijcsi.01.01.03
  2. 2. ACEEE International Journal on Control System and Instrumentation, Vol. 1, No. 1, July 2010power point so that the overall system efficiency can normally large air-gap, while the leakage inductancebe improved greatly. 2) Constant voltage and limited increases and magnetization inductance decreases. Thiscurrent two-loop control of battery charge, which can causes low power conversion efficiency. To overcomemake batteries in float charging state, enhance the such problems, a series resonant converter is widelycycle rate and prolong the life of the batteries. 3) used [4] However, the series resonant converter for theSPWM conversion with front-end high frequency DC- power supply generally operates with higher switchingDC modules in parallel and special DSP control frequency than resonant frequency to achieve softtechnique with high performance-cost, which can switching under continuous resonant current mode. Inaccomplish sine wave output voltage at the final stage this case, the main switches can achieve zero voltageto feed the grid with high reliability and high load switching (ZVS), but it has disadvantage that theefficiency. secondary side diode converter cannot achieve zero current switching. Furthermore, due to the higher switching frequency operation than resonant frequency, it has low voltage gain and high power loss since a large primary side circulating current flows [5]. Since the proposed power supply using LLC converter operates with lower switching frequency than the resonant frequency, it can achieve high voltage gain, which, in turn, offers low turns ratio for the Fig. 2 Proposed Hybrid system block diagram transformer and high efficiency due to discontinuous resonant current.Fig. 2 gives the introduction to overall hybrid systemwith soft switching converters and DSP based MPPT III. POWER MODULE IN PARALLELalgorithm implementation which is a novel idea in The DC-DC boost converter stage, used to convertmodern renewable energy system. The impact of air 18V DC or 48V DC to 350 DC, is designed as 1kWpollution and global climate change are becoming module that can dynamically adjust its output currentincreasingly important topics throughout the world and in terms of load current. In this way, 3kW and 5kWinternational organizations are fighting to reduce the system can be derived from the 1kW system with thecarbon emissions produced by fossil fuel. [3] Energy parallel operation of multi independent modules inconservation has become a priority. Table. I give, using 1kW. These multiple independent power modules canhybrid systems how C0 2 emissions reduced drastically. be paralleled such that each module supplies only itsOver a five year operating period, correspondingapproximately to the life duration of the Ni-Cd batteryand of the gen set in such a hybrid application, thereduction in the C02 emission for a 2 kW mobile sitewith this hybrid power system will be higher than 200tons. This 200 tons should be compared with aboutonly 2.7 tons of equivalent C0 2. The addition of a windturbine or possibly solar panels will emphasize thisreduction in C02 with an increase in cycling time. TABLE. I EXAMPLE OF CO2 SAVINGS WITH HYBRID AND GEN SET Fig. 3 Simplified circuit of proposed ZVS-ZCS boost converter Operational 2.5 KW 6 KW 12 KW 24 KW Details System System System System TABLE. II Daily SPECIFICATION OF HALF BRIDGE CONVERTER Generator 8.25h 9h 9h 11.75h Operation Daily Battery 15.75h 15h 15h 12.25h Operation CO2 savings 58 Tons 56 Tons 58 42 Tons Per year TonsII. SOFT SWITCHING CONVERTER OPERATION In this paper, a hybrid power generation system proportionate share to total-load current. This sharingusing soft switching technique is proposed as shown in is accomplished by controlling each module’s powerFig 3. The proposed system consists of a ZVS-ZCS stage with a command generated from a voltageboost converter, a half-bridge LLC resonant converter feedback amplifier whose reference can beand transformer. However, since the transformer has independently adjusted in response to a common-share- 13© 2010 ACEEEDOI: 01.ijcsi.01.01.03
  3. 3. ACEEE International Journal on Control System and Instrumentation, Vol. 1, No. 1, July 2010bus voltage. By monitoring the current from each where Kp, is the proportional gain, and K i, is themodule, the current share bus circuitry determines integralgain.Rearranging equation in finite-which paralleled module would normally have the difference formhighest output current and with the designation of this [Y(n+l)-Y(n)]/ T = Ki,U(n)+Kp[U(n+1) - U( n)/ T]unit as the master, adjusts all the other modules to where T is the sampling time .increase their output current to within 2.5% of that of Taking the Z-transform of equation yieldsthe master. The 1kW DC-DC stage with load sharingcontroller UC3907 and PWM controller SG3525 is Y(Z) / U(Z) =Kp+KiT / Z-1shown in Fig.4 Equation can be expressed in state variable form as X(n+1)= AX(n)+BU(n) Y(n) = Cx(n)+Du(n) where A=l , B=KiT, C=l , D=Kp, and X(n) is the state variable. Fig. 7 shows the block diagram of the compensator for digital implementation. Fig. 4 Inverter stage and controller in Hybrid system Fig.7 Implementation of the digital compensator A. DSP Algorithm Fig. 8 shows the simplified MPPT control block diagram. In Fig. 8, D(j), V ref(j) and vcell(j) are respectively the converter switching duty ratio, the Fig. 5 Block diagram of inverter stage demanded cell voltage and the actual cell voltage in the jth MPPT controller cycle, where j = k, k+1. The MPPT IV. MPPT CONTROL OF SWHS controller calculates the new cell voltage set point based on the converter switching duty ratios and the The basic block diagram of the MPPT control is measured cell voltages in the past and at present. Theshown inFig. 6. The proposed control consists of Proportional-Integral (PI) controller forces the celltwo loops, the maximum power point tracking loop voltage to follow the demanded cell voltage signal. Inis used to set a corresponding ‘Vref’ to the charger the practical design of the control software, theinput, the regulating voltage loop is used to regulate threshold ε j (j = 1,2,3 ), which is a small positivethe solar array output voltage according to ‘Vref’ number close to zero, is used to determine whether thewhich is set in the MPPT loop.The functions of the MPP has been reached and CV is used as a positivetwo loops are performed by a DSP based controller. increment in the demanded cell voltage. The variable δThe controller senses the solar array urrent and j ( j = 1, 2, 3 ) can be defined as:voltage to calculate the solar array output power, δ1 = V cell(k+1)-V cell(k)power slope and ‘Vref’ for maximum power control δ2 = D(k+1)-D(k) δ3 = D(k+1)+V cell(k+1) δ 2 / δ 1 When | δ1 | > ε1, the MPPT controller can be simplified as: V ref(k+1) = Vref (k) + Cv, δ3 > ε3 V ref(k+1) = Vref (k), |δ3 | > ε3 Fig.6 Basic block diagram of the control loop V ref(k+1) = Vref (k) - Cv, δ3 < -ε3 When | δ1 | < ε1, the MPPT controller can beThe equation can be expressed as the following simplified as: V ref(k+1) = Vref (k) + Cv, δ2 > ε2 Vref(k+1) = Vref(k) ± C V ref(k+1) = Vref (k), |δ2 | < ε2C is the amount of disturbance and the sign of C is V ref(k+1) = Vref (k) - Cv, δ2 < -ε2determined by the power slope. In the voltage loop,the PI compensator is used to make the systemstable.Therefore, the discretization of thecompensator transfer function is required for systemimplementation.The transfer function of a traditionalcompensator is Y(S) / U(S) = Kp + Ki / S Fig. 8 Simplified MPPT control block diagram 14© 2010 ACEEEDOI: 01.ijcsi.01.01.03
  4. 4. ACEEE International Journal on Control System and Instrumentation, Vol. 1, No. 1, July 2010The insolation changes much more rapidly than thetemperature does. As the cell MPP voltages only varyslightly under different insolation levels, the PIcontroller runs at a much faster frequency than theMPPT to force the cell voltage to follow the demandedvoltage. The MPPT controller executes once every 16PI control cycles. The PI and the MPPT controllers inFig. 9 are implemented by the digital signal processor,which is designed for 1.8V minimum supply voltage. Fig. 12 Efficiency characteristics of the proposed hybrid systemAs the cell voltage may fall below 1.8 V under rapidinsolation changes, the switching control signals for theMPPT converter will be suspended by the software CONCLUSIONonce the under voltage happens to allow the cell The design of novel soft switching converter withvoltage to recover and the digital signal processor to digital signal processor based maximum power pointfunction properly. tracking algorithm for solar wind hybrid applications is presented in this paper. The novelty in the proposed circuit is the method of generation of the auxiliary voltage needed to reset the ZVS circuit including the advantages of both ZVS and ZCS resonant action. The method of analysis is outlined for a boost converter with coupled inductor. Simulation results are presented Fig. 9 MPPT device circuit diagram for a 33W, 400 kHz boost converter. In this paper, a simple MPPT algorithm based on a DSP is presented to V. PSPICE SIMULATION deliver the highest possible power to the load from the solar arrays DC-DC converter were used in the solarThe Figure 10 represents the simulated boost converter wind hybrid energy system to investigate thewith coupled inductor using PSpice. Simulated results performance of the converters. The simulated resultsof the 33 W, 400 kHz boost converter with auxiliary show excellent performance (efficiencies over 92% forswitch are presented in this section. The 33 W 400kHz ZVS-ZCS converters) and further analysis can be doneboost converter with auxiliary switch is simulated in on improving the converter efficiency with high powerPSpice environment. rating in MW to electrify rural areas. REFERENCES 1.Youjie Ma, Deshu Cheng and Xuesung Zhou, “ Hybrid Modeling & Simulation for boost converter in Photo Voltaic system”, IEEE Computer Society International Conference on Information and Computer Science, January 2009, pp. 85-87. 2.S.M.Mousavi, S.H Fathi, “Energy Management of Wind/PV Fig. 10 Simulated boost converters with coupled inductor and battery hybrid system”, IEEE Proceedings on Industrial Electronics, August 2009, pp. 630-633 3.Joel Brunarie, George Myerscough, “Delivering CostThe main switch is turned on with a delay of 0.3 µs Savings & Environmental Benefits with hybrid power”,after the auxiliary switch is turned on. IEEE Transactions on Industrial Electronics, January 2008, pp. 1203-1212. VI. SIMULATION INPUT/OUTPUT 4. M. Z. Youssef, H. Pinheiro, and Praveen K. Jain, “Analysis and Modeling of a Self-Sustained Oscillation WAVEFORMS Analytical Technique,” Proceedings of the IEEE International Energy and Telecommunications Conference, INTELEC, Oct. 2003.pp.282-289 5. Laszlo Huber, Kevin Hsu and Milan M. Jovanovic, “1.8-MHz, 48-V resonant VRM: Analysis, Design and Performance Evaluation” IEEE transactions on Power Electronics Vol. 21 No 1,January 2006. pp. 79-88 Fig. 11 Output DC 15© 2010 ACEEEDOI: 01.ijcsi.01.01.03

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