Photovoltaic MPPT Research Based on Fuzzy-PID Dual-mode Control

Transcription

1 Internatial Cference Advances in Energy and Envirmental Science (ICAEES 2015) Photovoltaic MPP Research Based Fuzzy-PID Dual-mode Ctrol Fei Wang1, a* Xianxiang Li2,b 1 Foshan University, Foshan , China 2 Foshan University, Foshan , China a qdwf111@163.com Keywords: PID; MPP; Boost circuit; fuzzy ctrol. Abstract. his aer introduces the basic rincile of Boost circuit toology and hotovoltaic maximum ower oint tracking technology.according to the characteristics of hotovoltaic cells outut nlinearity, this aer designs a fuzzy-pid ctroller to track the maximum ower oint of PV cell. he ctroller can ctrol the voltage of hotovoltaic cells.by changing the duty ratio of the switch tube and then ctrol the outut ower of hotovoltaic cells.he simulati model is established in Simulink.he simulati results show that the ctroller can track maximum ower oint of hotovoltaic cell raidly and stably. Introducti he world's energy shortage and olluti roblems have become more and more serious. Develoment and utilizati of clean, renewable energy has attracted much attenti. Human beings must as so as ossible to seek a new alternative energy or renewable energy generati of natural energy. Research and ractice show that energy of the direct solar radiati to the earth is rich and and does not ollute the envirment. It is internatially recognized as the ideal alternative energy. Whether from the ecomic and social sustainable develoment, or from the earth ecological envirment for human survival level to look at, the develoment and utilizati of solar energy is of great strategic significance. he solar hotovoltaic ower generati is an imortant art of solar energy utilizati. Photovoltaic cells affected by sunlight intensity and envirmental temerature, the voltage will change and the outut ower will also change. he hotovoltaic cell is a kind of unstable energy. Under different illuminati and temerature cditis as far as ossible electrical energy outut, It has imortant significance to imrove the ower efficiency of solar cell. his aer resents a BOOS based circuit, It adots fuzzy-pid double model ctrol method to realize the solar maximum ower oint tracking. System model he mathematical model of hotovoltaic cells At resent, the use of solar battery in hotovoltaic system is mostly silic solar cell. Figure 1 is the equivalent circuit of hotovoltaic cells. he equivalent series resistance Rs of the ideal hotovoltaic battery is small, and the equivalent arallel resistance Rsh is very big. Usually for mocrystal line silic or olycrystalline silic hotovoltaic cell, they can be ignored. Fig. 1 Equivalent circuit of the hotovoltaic battery he authors - Published by Atlantis Press 648

2 Outut characteristic equati of hotovoltaic cells: q( V + IRS ) V + IRS I = I L I 0 ex AK 1 (1) Rsh Formula 1 is the most basic analytical exressis based hysical rinciles, It has been widely alied in solar cell theory analysis, It is difficult to identify the arameters in the exressi. solar cell model for Engineering usually requires several imortant technical arameters by suliers, such as I sc, V oc, I o,v o,p. he characteristics of reroducti can be in a certain recisi array, and can facilitate the comuter analysis. Outut characteristic equati of hotovoltaic cells: I V R C V OC I sc c 2 = 1 e 1 1 v + DI In the formula, RS is the series resistance of hotovoltaic cells, V oc is an oen circuit voltage, V m I m are voltage and current corresding to the maximum ower oint, α is temerature coefficient current changes (Ams/ O C) In reference to sunlight cditi, β is the temerature coefficient of the voltage change (V/ O C) In the reference temerature. PV cell characteristic I-V characteristic curve of solar cell is the most imortant asect to hotovoltaic system analysis.he I-V characteristics of hotovoltaic cell is the relatishi between the outut voltage and outut current of hotovoltaic cell in a certain intensity of sunlight and temerature. shown in Figure 2. I-V curves indicated that the hotovoltaic cell is not a cstant voltage source and it is not a cstant current source, It is a nlinear DC ower suly. Each oint the curve ly corresds with the outut ower of the hotovoltaic cell the oerating voltage. P m is the maximum ower outut of the hotovoltaic cell. U m and I m are voltage and current of solar cell at the maximum ower oint. At a certain temerature and sunlight intensity, the maximum ower oint of hotovoltaic cell is the ly e. hotovoltaic cell characteristics is shown in Figure 2. (2) Fig. 2 he volt amere characteristic curve of PV cells he main circuit of Boost he system uses Boost cverter, It is a kind of switching DC voltage boost circuit and can make the outut voltage higher than the inut voltage. It has the advantages of simle structure, high efficiency, small size advantages. As shown in Figure 3. Fig.3 oology of Boost circuit A large value of assuming inductance L, Boost circuits work in ctinuous current mode (CCM), he current is substantially cstant. he caacitor value C is great. V cducti time is, 649

3 Inductance L stored energy is U PV I l. When the V is in off state, U PV and L together charge to caacitor C, and rovide energy to the load RL, V off time is off, During this eriod, the inductance U U I. When the circuit is in a steady job, a eriod inductance energy energy released is ( o v ) l off absorti and release of energy are equal. U I = U U I PV l he duty ratio: ( o v ) l off D = = + So he relatishi of outut voltage and the duty cycle: + off 1 U o = U v = U v 1 D off off Based the formula 4, the outut voltage of the hotovoltaic cell is roortial to the duty cycle. Design of the ctroller (3) (4) Design of PID ctroller he ctrol algorithms of digital PID ctroller : k d u( k) = K e ( k) + e ( j) + ( ek ( ) e( k 1 )) (5) i j= 0 In order to facilitate the comuter rogram, the above formula becomes Formula 6: u k ( k) K ek ( ) + K e( j) + K [ ek ( ) ek ( 1) ] = d (6) i j= 0 e( k) In the formula is inut of the digital PID ctroller; e( j) ( k) is the deviati of k samling time; u is the K oint samling outut of digital PID ctroller; is the samling eriod, Ki is the integral coefficient, K i = K ; K d is the differential coefficient, K = d d K i ; Incremental digital PID ctrol algorithm: u ( k) = u( k) u( k 1) = K [ e( k) e( k 1) ] + K e( k) + K [ e( k) 2e( k 1) + e( k 2) ] i d (7) he ctrol variable of digital PID ctroller is the duty ratio of D and the deviati signal is P, it can find the maximum ower oint according to figure 2 and figure 3, he relatishi between D and P : ⑴If U ( k) > 0 and P > 0, At this oint in the left side of the maximum ower oint, the duty ratio should ctinue to increase,hat is D > 0; If U ( k) > 0 and P < 0, At this oint in the right side of the maximum ower oint, the duty ratio should be reduced,hat is D < 0; ⑵If U ( k) < 0and P > 0, At this oint in the right side of the maximum ower oint, the duty ratio should ctinue to reduce,hat is D < 0; If U ( k) < 0and P < 0, At this oint in the left side of the maximum ower oint, the duty ratio should be increased, hat is D > 0; According to the above analysis, When U ( k) > 0 the outut ower and duty cycle the same directi change, When U ( k) < 0 he outut ower and duty cycle reverse directi change, incremental digital PID ctroller can be designed According to the U ( k) situati: If U ( k) > 0, then D( k) = D( k) D( k 1) = K [ P( k) P( k 1) ] + Ki P( k) + Kd [ P( k) 2 P ( k 1) + P( k 2) ] (8) if U ( k) < 0, then D( k) = D( k) D( k 1) = { K [ P( k) P( k 1) ] + Ki P( k) + Kd [ P( k) 2 P( k 1) + P( k 2) ]} (9) 650

4 PID Matlab simulati model was set u as shown in figure 4. he two unit delay module are resectively outut ower P and outut voltage V of a samling eriod of delay. Fig.4 PID ctroller simulati model Design of MPP fuzzy ctroller Inut and outut of fuzzy ctroller We can see from Figure 2, the outut voltage changes of hotovoltaic cells, can make the maximum outut ower of hotovoltaic cells formula (3) shows that the Boost circuit in ctinuous current mode (CCM) work, the outut voltage is roortial to the duty cycle. he inut variables of fuzzy ctroller can chose ower variable ΔP and voltage variable ΔU. Outut duty is ratio D. he outut voltage of hotovoltaic cell change by ctrolling the duty ratio, he maximum outut ower oints of hotovoltaic cells can be found. Fuzzy subset and domain of inut and outut variables he actual value of voltage variati Eu (n) and the ower variati E (n) and the duty ratio of ste size Ed (n) Resectively using the quantizati factor are maed to fuzzy set theory domain Eu E and Ed.Eu, E and Ed are defined as 5 fuzzy subsets Negative big (NB), negative small (NS), zero (Z), Positive small(ps),positive big(pb)were used to exress. hat is: Eu={NB, NS,Z,PS, PB} E={NB, NS,Z,PS, PB} Ed={NB, NS,Z,PS, PB} Fuzzy set theory domain Eu E and Ed use the discrete digital collecti, hat is: Eu={-6,-5,-4,-3,-2,-1,0,+1,+2,+3,+4,+5,+6} E={-6,-5,-4,-3,-2,-1,0,+1,+2,+3,+4,+5,+6} Ed={-6,-5,-4,-3,-2,-1,0,+1,+2,+3,+4,+5,+6} Membershi functi In the fuzzy ctrol rules, language variable value of Ev, E and Ed are NB, NM, NS, Z, PS, PM and PB, heir membershi functis are triangular wave, and each variable width range is equal heir membershi functi as shown in Figure 5 Fig.5 Membershi functi Fuzzy decisi table According to the relatishi between outut ower P of hotovoltaic cells and outut voltage U and and the relatishi between outut ower P of hotovoltaic cells and duty ratio D, we can get the following rinciles: If U increases and P increases, Pmax is the left of MPP, the duty is increased, If U increases and P reduces, Pmax is the right of MPP, the duty is reduced, 651

5 If U reduces and P increases, Pmax is the right of MPP, the duty is reduced, If U reduces and P reduces, Pmax is the left of MPP, the duty is increased, he obtained fuzzy ctrol rule table as shown in able 1 ab.1 Fuzzy ctrol rule table V P NB NS Z PS PB NB PB PM PS NM NB NS PM PS PS NS NM Z PS PS Z NS NS PS NM NS NS PS PM PB NB NM NS PM PB Matlab simulati model is established According to the mathematical model of PV array and fuzzy ctrol rule table, shown in Figure 6. he two unit delay module are resectively outut ower P and outut voltage V of a samling eriod of delay results of simulati analysis Fig.6 Model of simulati ctrol System uses simulink module in matlab to establish the model of PV array and uses the Fuzzy Logic module to establish the fuzzy inferential ctrol system. Photovoltaic cell arameter setting: he short-circuit current I sc = 4. 5A, oen circuit voltage V oc = 42V, hotovoltaic cell series resistance R s = 0. 1Ω, In a hotovoltaic cell reference temerature, taking the temerature coefficient of current change (Ams/ o c) α = I sc, voltage variati coefficient(v/ o c) β = 0.005V oc, he outut voltage corresding to the maximum ower oint is V m = 34V and the outut current is I m = 3. 5A. he grah 7~9 are simulati results of the voltage outut of hotovoltaic cells, the current and ower outut of hotovoltaic cells in the standard cditis of temerature, sunshine intensity in the secd secds from the 600W/m 2 suddenly increased to 1000W/m2, the fourth secds from the 1000W/m 2 suddenly reduced to 800W/m 2. he figure 7 is the outut voltage curve of PV cell, figure 8 is the current outut curves of hotovoltaic cells, figure 9 is the outut ower curve. Fig.7 voltage outut curve 652

6 Fig.8 outut current curve Fig. 9 ower outut curve he initial cditis are zero, aearance of the 600 W/m 2 light suddenly, the ctroller can track maximum ower oint raidly and no shocks near the maximum ower oint. hen the maximum ower outut of hotovoltaic cells is about 61.8W, the outut voltage is about 30.6V, the outut current is about 2.0A. By the time of the secd secds, the light intensity suddenly increased from 600W/m 2 to 1000 W/m 2, after about 100ms or so, the fuzzy ctroller with a fast resse to quickly find the maximum ower oint. hen the maximum ower outut of hotovoltaic cells is about 121.6W, the outut voltage is about 35.8V, the outut current is about 3.4A. When the time of the fourth secds, the light intensity from the 1000W/m 2 suddenly droed to 800W/m 2, the fuzzy ctroller find the maximum ower oint quickly. hen the maximum ower outut of hotovoltaic cells is about 90.7W, the outut voltage is about 34.9V, the outut current is about 2.6A. From the simulati results, the fuzzy ctroller of sudden changes in the envirment can quickly find the maximum ower outut oint. After the fuzzy ctroller find the maximum ower oint, the PID ctroller can make the PV cells at maximum ower oint. Cclusi As hotovoltaic cells are more sensitive to sunlight intensity, using the fuzzy -PID double mode ctroller to ctrol the boost circuit, realize the PV maximum ower oint tracking. he simulati results show that fuzzy ctrollers can find the maximum ower oint raidly when the change of light intensity, PID ctroller can achieve high recisi ctrol after the fuzzy ctroller to find the maximum ower oint. References [1] S. Yuvarajan, Dachuan Yu, Shanguang Xu, A novel ower cverter for hotovoltaic alicatis, J. Power Sources135 (1-2) (2004) [2] Z.d. Zhg, H.b Huo,. X.j Zhu,. G.y. Cao, Y Ren, Adative maximum ower oint tracking -ctrol of fuel cell ower lants, J. Power Sources, 176 (1) (2008) [3] Ibrahim, H.E.-S.A. Houssiny, F.F. El-Din, H.M.Z. El-Shibini, M.A, Microcomuter ctrolled buck regulator for maximum ower ointtracker for DC uming system oerates from hotovoltaic system, Proceedings of the IEEE Internatial Cference Fuzzy Systems FUZZ IEEE 99, 1 (1999)

7 [4] Loes Luiz A.C., Lienhardt Anne-Marie, A simlified nlinear ower sourcefor simulating PV anels. In: Proc. IEEE ower electrics secialist cf; [5] Enslin Johan HR, Wolf Mario S, Snyman Dani el B, Swiegers Wernher. Integrated hotovoltaic maximum ower oint tracking cverter. IEEE rans Industrial Electrics December 1997;44: [6] Radziemska E, Klugmann E. Photovoltaic maximum ower oint varying with illuminati and temerature. J. Solar Energy Eng. February 2006;128(1):