A Variable Voltage MPPT Control Method for Photovoltaic Generation System

Transcription

1 WSEAS TRANSACTIONS n CIRCUITS and SYSTEMS A Variable Vltage MPPT Cntrl Methd fr Phtvltaic Generatin System Liu Liqun Department f Electrical Engineering, Shanghai Jiatng University, Shanghai, 4, China; Department f electrnic and infrmatin Taiyuan University f Science & Technlgy, Taiyuan 34, Shanxi Prvince, China llqd4@163.cm Wang Zhixin Department f Electrical Engineering, Shanghai Jiatng University, Shanghai, 4, China; wangzxin@sjtu.edu.cn Abstract: - T increase the utput efficiency f a phtvltaic (PV) generatin system it is imprtant t have an efficient maximum pwer pint tracking (MPPT) technique. This paper describes the analysis, design and implementatin f an efficient tracking methd fr a stand-alne PV generatin system, which autmatically adjusts the reference f utput vltage t track the maximum pwer pint (MPP) by using the expiatry prgram. Cmpared with the cnventinal cnstant vltage (CV) methd, the prpsed apprach can effectively imprve the tracking speed and accuracy simultaneusly. Furthermre, an imprved cntrl system is designed fr the pulse-width-mdulatin (PWM) inverter t achieve the bjective f MPPT. Theretical analysis and principle f prpsed methd are presented and simulatin results are given t verify the validity f cntrl methd Key-Wrds: - Maximum pwer pint tracking (MPPT), Variable vltage, Pulse-width-mdulatin (PWM), Phtvltaic generatin system, Slar energy 1 Intrductin At present, renewable energy surces, i.e., slar energy, wind energy, bimass energy, etc., are regarded fr electrical pwer generate due t their sustainable characteristic and envirnmental friendly nature [1]. Researches f PV generatin systems are actively being regarded t mitigate envirnment issues such as the green huse effect and envirnment pllutin. The cnventinal PV generatin systems have tw big prblems that the efficiency f PV system is very lw, especially under lw irradiatin states and the utput available pwer f PV system is always changing with weather cnditins, i.e., the intensity f the slar radiatin (irradiatin) and ambient temperature [-4]. A typical PV installatin is cmpsed f: PV panels, regulatr, batteries and the inverter. The regulatr is the element which is cnnected between the PV panels and the batteries and its missin is t keep the batteries charged and avid their vercharge [5]. But a phtvltaic generate system still requires expensive initial investments. In rder t extract as much energy as pssible frm a PV system, it is imprtant t have an efficient Maximum Pwer Pint Tracking algrithm. In develping natins, the PV generate system is expected t play an imprtant rle in ttal electrical energy demand, and slar phtvltaic energy has gained a lt f attentin because it is renewable, friendly t the envirnment, and flexible fr installatin. And mre and mre specialist f China realized the fundamentality f PV generate systems. In rder t extract as much energy as pssible frm a PV system, it is imprtant t have an efficient Maximum Pwer Pint Tracking algrithm. Varius MPPT algrithms and cntrl methds fr PV generate system have been described in the literature [1-13], such as a cst-effective singlestage inverter with maximum pwer pint tracking (MPPT) in cmbinatin with ne-cycle cntrl (OCC) fr phtvltaic pwer generatin is prpsed in the literature[1]. The linearity methd is a nvel methd in rder t track the maximum pwer pint, the prprtinality cefficient f the predictin line is autmatically crrected using the hill-climbing methd when the panel temperature f ISSN: Issue 4, Vlume 8, April 9

2 WSEAS TRANSACTIONS n CIRCUITS and SYSTEMS the slar arrays is changed [-4]. The literature [5] presents a regulatr which can perate in the maximum pwer pint f PV arrays regardless f the meterlgical cnditins and the effects f them in the dispersin f the PV array characteristics. A cmparative study f the maximum pwer pint trackers using a switching-frequency mdulatin scheme (SFMS) fr phtvltaic panels is presented [6]. Methd f lcating the maximum pwer pint (MPP) is based n injecting a small-signal sinusidal perturbatin int the switching frequency f the cnverter and cmparing the ac cmpnent and the average value f the panel s terminal vltage. The incremental cnductance (IC) methd is prpsed in the literature [7], which is based n the Incremental Cnductance methd but des nt require any current sensing devices. The perturbatin and bservatin (PO) methd is well knwn as the hill-climbing methd, it has been widely used because f its simple feedback structure and fewer measured parameters. A digital hill-climbing cntrl strategy cmbined with a bidirectinal current mde pwer cell is presented which allws getting a regulated bus vltage tplgy [8]. The cnstant vltage (CV) and perturbatin and bservatin (PO) methd are very cmmn, a cst-effective tw-methd MPPT cntrl scheme is prpsed in this paper t track the maximum pwer pint (MPP) at bth lw and high irradiatin, by cmbining a Cnstant Vltage (CV) methd and a mdified PO algrithm [9]. The fuzzy methds are described in the literature [1-1] that fcus n the nnlinear characteristics f PV. A Rapid MPPT Algrithm Based n the Research f Slar Cell s Dide Factr and Reverse Saturatin Current are described in the literature [13], which described that hw t gain the actual Dide Factr and Reverse Saturatin Current f a slar cell and actual Maximum Pwer Pint (MPP), and the utput current is cntrlled in rder t track the actual MPP. Althugh, varius methds f MPPT cntrl have been prpsed in existing literature, but the pwer generate efficiency is relative lw, and the amunt f electric pwer generated by slar arrays is always changing with weather cnditins. Different slar panel have different dide factr (n) and reverse saturatin current (I). S they are impssible t quickly acquire the generate pwer at the maximum pwer pint (MPP). The essential reasn is the unknwn values f n and I. The theretical and simulative results shw that a piece f PV have same phtcurrent under different dide factr n and reverse saturatin current I and the weather cnditins are sameness cnditins. The cnclusin is very imprtant t acquire the actual dide factr and reverse saturatin current. In this paper, first, a piece f PV have same phtcurrent under different dide factr n and reverse saturatin current I cnditins is testified by using the theretical and simulative results, and the cnventinal cmbined perturb and bserve (PO) methd is used t acquire the actual n and I. Next, the linear relatinship between the ptimal utput vltage and the pen-circuit vltage is described in next sectin. Then, an expiatry prgram f reference vltage is applied t acquire the actual maximum pwer pint, and a rapid Variable Vltage maximum pwer pint tracking methd is described which is based n the actual n and I. Finally, a new prpsed duble-lp cntrl scheme and the Sepic cnverter are used t verify the crrectness and validity f MPPT algrithm, and the simulatin results shws that the prpsed MPPT cntrl methd imprve the tracking speed and accuracy fr PV generatin system during tracking curse. Principle analyzing and mdeling f PV.1 PV mdeling Fig.1, Equivalent circuit fr PV The literature [3-11] prpsed varius mdelling f PV. The utput current I and utput vltage V f PV is given by (1) and () using the symbls in Fig. 1, I = Iph Id Vd / Rsh (1) V = Vd RsI () qvd Id = I[exp( ) 1] nkt (3) where Iph is the phtcurrent (in amperes), I is the reverse saturatin current (in amperes), Id is the average current thrugh dide (in amperes), n is the dide factr, q is the electrn charge (in culmbs), 19 q = C, k is Bltzmann s 3 cnstant (in jules per Kelvin), k = J / K, and T is the PV panel temperature (in Kelvin). Rs ISSN: Issue 4, Vlume 8, April 9

3 WSEAS TRANSACTIONS n CIRCUITS and SYSTEMS stands fr the intrinsic series resistance f the PV, which is ideally zer. Rsh dentes the equivalent shunt resistance f the slar array, which is ideally infinity. In general, the utput current f PV is expressed by q V + RsI I = Iph I[exp{ ( V + RsI)} 1] (4) nkt Rsh Where the resistances Rs and Rsh can generally be neglected, and therefre, last term in (4) is generally drpped. q I = Iph I[exp{ ( V )} 1] (5) nkt When the circuit is pened, the utput current I =, and the pen-circuit vltagevc is expressed by nkt Iph nkt Iph Vc = V max = In( + 1) In( ) (6) q I q I If the circuit is shrted, the utput vltagev =, the average current thrugh dide Id is generally be neglected, and the shrt-circuit current Isc= I is expressed by using (7). The relatinship exists between shrt-circuit current Isc and phtcurrent Iph by using (8). RsI I = Iph (7) Rsh Rs I = Isc = Iph /(1 + ) Iph (8) Rsh Finally, the utput pwer P is expressed by (9) P = IV = ( Iph Id Vd / Rsh) V = ( Iph Id) V q (9) = ( Iph I{exp[ ( V )] 1}) V nkt nkt Vc = IphVc { In(1 + qvmppt ) q nkt qvmppt /( nkt) (1) nkt 1 qvmppt + ( ) In(1 + )} q Vmppt nkt Here P and V are the instantaneus utput pwer and utput vltage f PV, respectively. The steady-state f the maximum pwer pint (MPP) cntains P/ V =. The maximum pwer P max is expressed by (1). Here P max and Vmppt are the maximum utput pwer and ptimal utput vltage at the time, respectively. Isc= Isc(5 C, 1KW / m ) S /1 (11) Iph(5 C,1KW / m ) = Isc(5 C,1KW / m ) (1) (1 + Rs Rsh) Isc(5 C,1KW / m ) Iph = Iph(5 C,1KW / m ) [1 + Ki ( T Tr)] (13) (1 + Rs Rsh) Sj /1 Iph 1 S = (14) Iph(5 C,1 KW/ m ) [1 + Ki ( T Tr)] (1 + Rs Rsh) Output Pwer (W) Output Pwer (W) Output Vltage (V) Output Vltage (V) Fig. Calculated P-I characteristics and P max curve under the knwn n and I cnditins. The irradiatin S is 8W / m, and the temperature is changing frm 5 C t 75 C. The irradiatin is changing frm 1 W / m t 1KW / m at the temperature 45 C. Many parameters affect the utput pwer f PV generatin system, such as tw intrinsic resistances, ambient temperature, the slar irradiatin, the dide factr and the reverse saturatin current. Firstly, Rs is very small (mω), and Rsh is very large (in kω) in actual PV system, and the values f tw intrinsic resistances are the unknwn cnstants. Secndly, the utput pwer f PV is affected by the temperature and irradiatin. The shrt-circuit current Isc and the pen-circuit vltagevc f PV are always changing with the ambient temperature and slar irradiatin. If the temperature is changeable, the changing cefficient Kvf Vcis (.37.4%)/ C at slar panel temperature5c, the changing cefficient Ki f Isc is ( %) / C at slar panel temperature5 C, where, Tr are 5 C (in Kelvin). If the irradiatin is changeable, the shrt-circuit current Iscis expressed by using (11) at temperature 5 C. Here Isc( 5 C,1KW / m ) is the shrt-circuit current at slar ISSN: Issue 4, Vlume 8, April 9

4 WSEAS TRANSACTIONS n CIRCUITS and SYSTEMS panel temperature 5 C, and the irradiatin is 1KW / m. The relatinship exists between shrt-circuit current Isc(5 C,1KW / m ) and phtcurrent Iph( 5 C,1KW / m ) is expressed by using (1) at slar panel temperature 5 C, and the irradiatin is 1KW / m. The phtcurrent Iph is expressed by using (13) with the temperature and irradiatin changing. Thus, using (6) and (13), the pen-circuit vltagevc is evaluatin. Thirdly, the dide factr n and reverse saturatin current I affect the utput pwer. The n and I are the unknwn cnstant. Althugh different PVs have different n and I, a piece f PV s n and I is same. Nrmally, the n exists between 4 and 11, and the I exists between. μa and 5 μ A. If the value f n and I are knwn, the methd is easy t acquire a piece f PV s maximum utput pwer. The effect f n and I are analysed in this paper. The irradiatin S is expressed (14) as a functin f Iph.. Analyses f ptimal utput vltagevmppt Output Pwer (W) CV methd utput pwer Output Vltage (V) Fig.3 Draw a cmparisn between the utput pwer f CV methd and the actual P max curve at temperature C Fr example, the pen-circuit vltage Vc and shrt-circuit current Isc, which were measured at irradiatin 1KW/ m and temperature 5 C, are V and 3.8A, respectively. The changing cefficient Ki f Isc and the changing cefficient Kv f Vc were measured, are.1 and -.4, respectively. The dide factr n and reverse saturatin current I were suppsed, are 6 and 5μA, respectively. Fig. shws P V characteristics and curve f PV are calculated using abve values. Fig. shws the maximum pwer curve at different temperature and same irradiatin8 W / m, Fig. shws the maximum pwer curve at same temperature 45 C and different irradiatin. It is cnfirmed thrugh calculating results shwn in Fig. that prprtinal relatinships between the pen-circuit vltage and the ptimal utput vltage have been prpsed in sme literature. The prprtinality cefficient using K, K is the cefficient f the ptimum utput vltage and the pen-circuit vltage. K is expressed by using (15) at time n. In general, it is apprximate equal.76. Base n the cnclusin, the maximum pwer pint tracking is very easy under the knwn n and I cnditins. Vmppt ( n) / Vc( n) = K Analyses f maximum utput pwer The perturbatin and bservatin (PO) methd is well knwn as the hill-climbing methd, it has been widely used because f its simple feedback structure and fewer measured parameters. But the PO methd is nt aviding the pwer lss. The cnstant vltage (CV) methd is very cmmn, i.e. a cst-effective tw-methd MPPT cntrl scheme is prpsed in the literature [9] t track the maximum pwer pint (MPP) at bth lw and high irradiatin, by cmbining a Cnstant Vltage (CV) methd and a mdified PO algrithm. But the cnstant vltage (CV) methd is impssible t exact acquire the maximum pwer (MP) pint because f sme prblems is nt be reslved, i.e., the efficiency is very lw, and nly ne maximum pwer pint (MPP) is tracked in the whle tracking curse. Fig.3 shws the utput pwer f CV methd, and draws a cmparisn between the utput pwer f CV methd and the actual maximum pwer. As shwn in Fig.3, nly ne maximum pwer pint is tracked in the whle tracking curse. As a cnclusin, the CV methd is impssible t exact track the MPP. The reasn is nt knwn the pen-circuit vltage at that time. If the values f n and I are knwn, the pen-circuit vltage is easy gained by using (6). S the essential reasn is nt knwn the values f n and I. 3 The prpsed MPPT algrithms Base n abve data, n and I were suppsed, are 6 and 5 μa, respectively. The pen-circuit vltage is easy gained. The ptimal utput vltage is gained at that time. As shwn in Fig.4, the simulative and calculated results verified that the prpsed methd is mre efficiency than the CV methd. But Fig.4 shws an errr exists between the actual maximum pwer curve and the pwer curve at K =. 76under the knwn n and I cnditins. Fig. 4 shws the P I characteristics, and draws a cmparisn between the curve and the P max' curve at K =. 76 under same irradiatin 6W / m and varius temperature ISSN: Issue 4, Vlume 8, April 9

5 WSEAS TRANSACTIONS n CIRCUITS and SYSTEMS cnditins. Fig. 4 shws the P I characteristics, and draws a cmparisn between the curve and the P max' curve at K =. 76 under same temperature 3 Cand varius irradiatin cnditins. As shwn in Fig.4, the cefficient K is nt very accurate in the literature. The reasn is nt cnsider the effect f temperature and irradiatin and dide factr n and reverse saturatin current I. Output Pwer (W) Output Pwer (W) ' Output Vltage (V) ' Output Vltage (V) Fig.4 P I characteristics, and draws a cmparisn between the P max curve and the P max' curve at K =.76 under the knwn n and I cnditins. The irradiatin S is 6W / m, and the temperature is changing frm 5 C t 75 C. The irradiatin is changing frm 1 W / m t 1KW / m at the temperature. 3 C 3.1 Relatinship f n, I and Iph As mentin abve, Vc and Isc, which were measured at irradiatin 1KW/m and temperature 5 C, are V and 3.8A, respectively. Ki and Kv were measured, are.1 and -.4, respectively. Fig. 5 shws P I characteristics and P max curve f PV, the data are calculated by using abve values under the same n and different I cnditins. Fig.5 shws the maximum pwer curve at same irradiatin and different temperature, Fig.5 shws the maximum pwer curve at same temperature and different irradiatin. Output Pwer (W) Output Pwer (W) n=6,i=.3e-6,s=8 n=6,i=e-6,s= Output Current (A) n=4,i=3e-6,t=5 n=4,i=5e-6,t= Output Current (A) Fig.5 Calculated P-I characteristics and P max curve under the same n and different I cnditins. The irradiatin S s 8 i W / m, and the temperature is changing frm 5 C t 75 C. The irradiatin is changing frm 1W / m t 1KW / m at the temperature 5 C. When the slar irradiatin is steady, and the values is 8W / m, and the temperature is changing frm 5 C t 75 C, under same n and different I cnditins, Fig. 5 shws that the phtcurrent Iph is same under same temperature cnditins, and the utput pwer is increasing with the I decreasing frm 5 μ A t. μ A. When the temperature is steady and the values is 5 C, and the slar irradiatin is changing frm 1W / m t1 KW / m under same n and different I cnditins, Fig. 5 shws that the phtcurrent Iph is same under same irradiatin cnditins, and the utput pwer is increasing with the I decreasing frm 5 μ A t. μ A. ISSN: Issue 4, Vlume 8, April 9

6 WSEAS TRANSACTIONS n CIRCUITS and SYSTEMS 3 5 n=8,i=e-6,s=6 3 5 n=6,i=e-6,s=6 Output Pwer (W) n=55,i=e-6,s=6 Output Pwer (W) n=7,i=e-6,s= Output Current (A) Output Current (A) 6 Output Pwer (W) 6 4 n=8,i=1e-6,t=35 n=6,i=1e-6,t=35 Output Pwer (W) n=45,i=.6e-6,t=45 n=6,i=1e-6,t= Output Current (A) Fig.6 Calculated P-I characteristics and P max curve under the different n and same I cnditins. The irradiatin S is 6W / m, and the temperature is changing frm 5 C t 75 C. The irradiatin is changing frm 1W / m t 1 KW / m at temperature 35 C. If the weather cnditins are same, Fig.7 shws that the utput phtcurrent Iph is same under different n and different I cnditins. If the irradiatin is 6W / m, and the temperature is increasing frm 5 C t 75 C, Fig. 7 shws that the phtcurrent Iph is same under different dide factr n and different reverse saturatin current I cnditins. If the temperature is 45 C, and the irradiatin is increasing frm 1 W / m t 1KW / m, Fig.7 shws that the phtcurrent Iph is same under different dide factr n and different reverse saturatin current I cnditins. A cnclusin is gained in this paper. If the weather cnditins are same, the utput phtcurrent Iph fr a piece PV is same under different n and different I cnditins, and the cnclusin is very imprtant t acquire the maximum pwer pint f PV system. Based n the cnclusin, a nvel methd was presented t acquire the actual n and I Output Current (A) Fig.7 Calculated P-I characteristics and P max curve under different n and I. If the irradiatin S is 6W / m, and the temperature is changing frm 5 C t 75 C. If the irradiatin is changing frm 1W / m t 1KW / m at 45 C. 3. Acquire the actual n and I Firstly, the n and I were suppsed, are 4 and 5 μa, respectively. The utput vltage V, the utput current I and temperature T f PV is detected by using the Hall Effect sensrs fr current and vltage and temperature sensr, respectively. Iph is given by using (5), and the assumptive maximum pwer pint was gained. Fig.8 shws the assumptive maximum pwer pint A f PV by using the assumptive n and I under steady weather cnditins. Secndly, Fig.8 shws the actual maximum pwer pint B by using PO methd at that time. The actual ptimal utput current Im ppt and ptimal utput vltage Vmppt is gained by using sensrs. Based n abve cnclusin, the phtcurrent Iph is same under same weather cnditins. The n is suppsed minimum and the I is suppsed maximum. The actual maximum pwer pint is mre than the assumptive maximum pwer. ISSN: Issue 4, Vlume 8, April 9

7 WSEAS TRANSACTIONS n CIRCUITS and SYSTEMS T gain the actual n and I, the dide factr shuld increase and the reverse saturatin current shuld decrease. Accrding t the increasing values f dide factr and decreasing reverse saturatin current I, the phtcurrent Iph and actual ptimal utput current Im ppt is u sed t calculate the assumptive ptimal utput vltage Vmppt 1 by using (5). Then, the errr between the actual ptimal utput vltage and assumptive ptimal utput vltage is Δ V, which can be expressedvmppt1 Vmppt. Once ΔV =, the dide factr n and reverse saturatin current I are actual value. Thus, the actual value f n and I was saved, and PO methd is stpped. Next, the prcess cited abve is cncretely explained by examples with number btained based n Fig.8. First, the utput vltage and utput current were measured at time n1, are 7.573V and.181a, respectively. In this case, the gen erated pw er P(n1 ) is w. The temperature T f slar penal is 5 C at time n1. Then, the dide factr n and reverse saturatin current I were suppsed, are 4 and 5 μa, respectively. The phtcurrent Iph =.66A is gained by using (5). The irradiatin S is 7W / m by using (14). The temperature and irradiatin are steady at enugh lng time. The calculated ptimal utput current and ptimal utput vltage were gained, are.389a and 6.74V, respectively. The calculated ptimal utput pwer P max' ( n1) is 15.56W > P(n1). Secnd, the PO methd is utilized t acquire the actual maximum pwer pint under same weather cnditins. The actual ptimal utput current Imppt ( n1) and ptimal utput vltage Vmppt (n1) were measured, are.385aand15.54v, respectively. Thus, the maximum utput p wer P max(n1 ) is 37.45W, and ( P max( n1) > '( n1)). Based n abve cnclusin, in rder t acquire the actual n and I f a piece f PV it is bligatry t increase the dide factr n and decrease the reverse saturatin current I. In this case, the actual phtcurrent Iph and the ptimal utput current Im ppt ( n1) were used t calculate the assumptive ptimal utput vltage Vmppt1 by using (5). Then, the difference Δ V between the actual ptimal utput vltage a nd assumptive ptimal utput vltage is calculated. If ΔV =, the actual value f the dide factr n and reverse saturatin current I is gained, are 7. and 5.45η A, respectively. The values f actual n and I were saved. Output Pwer (W) n=7.,i=5.45e-6,t=5 n=4,i=5e-6, T=5 A Output Vltage (V) Fig.8 Calculated the actual dide factr n and reverse saturatin current I by using the cmbined perturb and bserve (PO) methd. 3.3 The prpsed Variable Vltage MPPT algrithms Output Pwer (W) Output Pwer (W) Output Vltage (V) B n=7.,i=5.45e-6,t=75 n=7.,i=5.45e-6,t=-5 ' ' Output Vltage (V) Fig.9 P max curve and P max' curve under different temperature cnditins. The irradiatin is changing frm t 1W / m 1KW/ m at 75 C. The irradiatin is changing frm 1W / m t 1KW/ m at 5 C. As shwn in Fig.4, an errr exists between the ISSN: Issue 4, Vlume 8, April 9

8 WSEAS TRANSACTIONS n CIRCUITS and SYSTEMS actual maximum pwer curve and the pwer curve at K =.76under the knwn n and I cnditins. The reasn is nt cnsider the effect f temperature and irradiatin and dide factr n and reverse saturatin current I. Theretical and simulatin results shw that the effect f temperature and irradiatin must be cnsidered. The reverse saturatin current I has an imprtant effect in rder t acquire the actual K. The effect f dide factr n is very small. In rder t acquire the actual K, the expiatins f the temperature, irradiatin and reverse saturatin current I are necessary. Output Pwer (W) Output Pwer (W) n=7.,i=5.45,s=1 ' Output Vltage (V) n=7.,i=5.45e-6,s=1 ' Output Vltage (V) Fig.1 P max curve and P max' curve under different irradiatin cnditins. The irradiatin S is1 W / m, and the temperature is changing frm 5 C t 75 C. The irradiatin S is 1W / m, and the temperature is changing frm 5 C t 75 C. Accrding t abve data, Fig.9 shws the actual maximum pwer P max curve and the P max' curve at K =.76 under different temperature cnditins. The simulatin results shw that an errr exists in tw curves. As shwn in Fig.9, the actual ptimal utput vltage cefficient K is less than.76. Fig.9 shws that the actual ptimal utput vltage cefficient K is mre than.76. In a wrd, the different temperatures have the different prprtinality cefficient K. S the effect f temperature must be cnsidered under different temperature in rder t acquire the actual maximum pwer pint. An expiatin f temperature is necessity. Fig.1 shws the actual maximum pwer P max curve and the P max' curve at K =. 76 under different irradiatin cnditins. The simulatin results shw that an errr exists in tw curves. Output Pwer (W) n=1,i=5.45e-6,t=45 n=7.,i=5.45e-6, T= Output Vltage (V) max P max' Fig.11 P curve and curve under different dide factr n cnditins. Output Pwer (W) n=6,i=.5e-6,t=45 n=6,i=5e-6,t= Output Vltage (V) Fig.1 P max curve and P max' curve under different reverse saturatin current I cnditins. As shwn in Fig.1, the effect is different under high irradiatin r lw irradiatin cnditins. The effect f irradiatin must be thught under different irradiatin cnditins. An expiatin f irradiatin is necessity in rder t gain the MPP. Fig.11 shws that the curves are apprximate parallel under the different dide factr n cnditins. The simulatin results shw the prprtinal relatinships between the actual maximum pwer and the calculative utput pwer is apprximate equal. The effect f dide factr n is very small. An expiatin f dide factr is nt necessity. Fig.1 shws that the errr between the P max curve and the P max' curve at K =.76is different under different reverse saturatin ISSN: Issue 4, Vlume 8, April 9

9 WSEAS TRANSACTIONS n CIRCUITS and SYSTEMS current I cnditins. The effect f I must be thught under different I cnditins. An expiatin f I is necessity. Using (14), the irradiatin can be gained at time m. Theretical and simulatin results shw that the expiatry cefficient ΔKsf irradiatin is expressed (16) as a functin f the irradiatin S. The expiatry cefficient Δ is.7m /W when the irradiatin S is less than 75W / m. Or else, the expiatry cefficient Δ1 is.1 m / W. The expiatry cefficient ΔKt f temperature is expressed (17) as a functin f the temperature T 1. The expiatry cefficient is a cnstant.31/ C under the temperature is less than 5 C. Or else, the expiatry cefficient is a cnstant.33/ C. Here, T1is the actual slar panel temperature. ( S 75 ) Δ1 S 75W/m ΔKs = (16) ( S 75 ) Δ S < 75 W / m ( T1 5).31 T1 5 C ΔKt = (17) ( T1 5).33 T1 > 5 C ((5e-4)-I).5+ 1e-4 5 I 4e- 6 (5e- 4).149 I 3e- 6 ((5e-4)-I).5+ 5e-5 5 I 1e- 6 (18) (5e- 4) ΔKI= ((1e-4)-I).33+ 5e-5 1 I 1e-6 (1e- 4) ((1e-5)-I) I 1e-6 (1e- 5) ((1e-6)-I) I>.e- 6 (1e- 6) Kp = ΔKs ΔKt + ΔKI (19) The expiatry cefficient ΔKI f reverse saturatin current I is expressed (18) as a functin f I. The expiatry cefficient is 1e 4/ μa frm.5 under the reverse saturatin current I is mre than.4ma cnditins. The expiatry cefficient is a cnstant.149 /μa under the I mre than.3ma and less than. 4mA cnditins. The expiatry cefficient is 5e 5/ μa frm.5 under the I is mre than.1ma and less than.3ma cnditins. The expiatry cefficient is 5 e 5/ μa frm.33 under the I is mre than 1 μa and less than.1ma cnditins. The expiatry cefficient is./ μa frm.5 under the I is mre than 1 μa and less than 1μA cnditins. Or else, the expiatry cefficient is.16/ μa frm.7 under the I is mre than.μa and less than 1 μa cnditins. Output Pwer (W) Output Pwer (W) Output Pwer (W) Output Pwer (W) 5 4 n=6,i=3e-6,s=8 3 1 n=1,i=4e-6,s= Output Vltage (V) n=7,i=9e-6,s=6 n=5,i=.9e-6,s= Output Vltage (V) n=7,i=3e-6,s=1 n=9,i=4e-6,s= Output Vltage (V) (c) n=7,i=.5e-6,s=1 n=45,i=6e-6,s= Output Vltage (V) (d) ISSN: Issue 4, Vlume 8, April 9

10 WSEAS TRANSACTIONS n CIRCUITS and SYSTEMS Output Pwer (W) 1 n=7,i=.3e-6,t= n=5,i=7e-6,t=-5 4 reasnable under the I is mre than 1μA and different n and different T cnditins. Based n the results f Fig. 13, n matter hw the slar radiatin and slar panel temperature change, the maximum pwer pint is gained by using the integrated expiatry cefficient Kp. The maximum pwer pint is gained by using the integrated expiatin cefficient Kp n matter hw the values f n and I vary with varius PV. 1 3 Output Vltage (V) (e) 3.4 Flwchart f the prpsed MPPT algrithm 6 5 n=1,i=3e-6,t=-3 n=5,i=e-6,t=3 Output Pwer (W) C 1KW/ m Output Vltage (V) (f) Fig.13 The P max curve and P max' curve are simulated under different n and different I cnditins. The I is mre than 1 μ A. The I is less than 1 μ A. (c) The I is mre than 1 μ A, and the S less than 15 W / m. (d) The I is less than 1 μ A, and the S less than 15W / m. (e) The I less than 1 μ A, and the n and T are different. (f) The I mre than 1 μ A, and the n and T are different. The integrated expiatry cefficient Kp is expressed (19). Fig.13 shws the simulatin results under different n and different I cnditins. As shwn in Fig.13, the expiatry cefficient is reasnable under the I is mre than 1 μ A cnditins. Fig.13 shws that the expiatry cefficient is reasnable under the I is less than 1 μa cnditins. As shwn in Fig.13 (c), the expiatry cefficient is reasnable under the I is mre than 1 μa cnditins at lw irradiatin. As shwn in Fig.13 (d), the expiatry cefficient is reasnable under the I is less than 1 μa cnditins at lw irradiatin. Fig.13 (e) shws that the expiatin cefficient is reasnable under the I is less than 1μA and different n and different T cnditins. Fig.13 (f) shws that the expiatry cefficient is Fig.14 Flwchart f the prpsed MPPT algrithm The cntrl prcedure cited abve is summarized in the flw chart shwn in Fig.14. First, the pen-circuit vltagevc and shrt-circuit current Isc, which were measured at PV panel temperature and high irradiatin1kw / m, and m is defined zer. The changing cefficient Ki f Isc and cefficient Kvf Vc were measured, respectively. Secnd, The n and I are suppsed at start-up state. Third, the utput current I(n1) and the utput vltage V(n1) and the temperature T were detected by using sensrs at time n1. Then, the phtcurrent Iph(n1) and the irradiatin S(n1) and the pen-circuit vltage 5 C ISSN: Issue 4, Vlume 8, April 9

11 WSEAS TRANSACTIONS n CIRCUITS and SYSTEMS Vc(n1) were calculated by using the suppsed n and I. Next, the expiatry prgram f reference vltage is applied in rder t acquire the suppsed maximum pwer P max'. Cmpare m with 1, and if the value f m is less than 1, the value f m adds ne. The actual maximum pwer pint is gained by using the PO methd under same weather cnditins. The actual values f n and I are gained, and the values are saved, and the average values is calculated. Or else, the actual values f n and I were applied t acquire the maximum pwer at the time, and then the PO methd is stpped. The prpsed MPPT algrithm is high efficiency t track the maximum utput pwer f PV cmpare with the cnventinal CV methd. 4 Verificatin f the prpsed MPPT algrithm current-lp is used t inner-lp, and the vltage-lp is used t uter-lp. The ptimal utput vltage is calculated t act as the reference input by using DSP. The PI cntrller is used t imprve the input perfrmance f PWM. The utput f PWM is used t cntrl the switch frequency f MOSFET. The cntrl scheme is very easy t track the maximum pwer pint under varius weather cnditins, which is described t cmpare with the prpsed cntrl methd in next sectin. Output Pwer (W) Targeted Pwer: 46.4W Pwer Acquired by the cnverntinal MPPT Cntrl Targeted Pwer Fig.15 Blck diagram f series-cnnected lad cntrl fr PV generatin systems. Fig.15 shws the blck diagram f lad cntrl. The classical Sepic cnverter is used t track the maximum pwer pint. It cnsists f tw inductances, tw capacitrs, ne dide, ne MOSFET, the input PV and the lad resistance at the utput f the circuit [14]. The advantages f Sepic cnverter include the cntinuus input current and wide utput vltage range. Additinally, nt nly it can prvide islatin between the DC input and the DC lad, but als it can reduce the reverse-recvery lss and imprve the pwer efficiency [15]. Cmpared the cnventinal Buck r Bst cnverters, it allws a lw current ripple under lw level DC vltage cnditins [16]. The MOSFET switch is cntrlled by a multiple-lp cntrl scheme in rder t acquire the maximum pwer pint f PV. The multiple-lp cntrl scheme can ensure a line current wave-shaping and an apprpriate DC vltage. A cnventinal methd is used in the paper. The Output Pwer (w) Output Pwer (W) 3 1 Pwer Acquired by the cnverntinal MPPT Cntrl Targeted Pwer Pwer Acquired by the cnverntinal MPPT Cntrl Time (S) (c) ISSN: Issue 4, Vlume 8, April 9

12 WSEAS TRANSACTIONS n CIRCUITS and SYSTEMS Output Pwer (W) Targeted Pwer 1 Pwer Acquired by the cnverntinal MPPT Cntrl (d) Fig.16 The cnventinal cntrl scheme is respnded under varius lad resistance cnditins. The irradiatin is fixed. The disturbed signals exist. (c)the irradiatin is gradual increasing. (d)the irradiatin is wavy. If the lad resistance is varius, Fig.16 shws that the cnventinal cntrl scheme can nt track the pwer very well under the fixed irradiatin cnditins. Fig.16 shws that the cnventinal cntrl scheme is nt very feasible under the fixed irradiatin have the disturbed signals cnditins. Fig.16 (c) shws that the cnventinal cntrl scheme is relatively lw cnversin efficiency under the gradual increasing irradiatin have the disturbed signals cnditins. As shwn in the Fig.16 (d), the efficiency is lw at wavy irradiatin. Based n the results f Fig.16, n matter hw the disturbed signals are varius with the time, the utput efficiency f cnventinal MPPT cntrl scheme is nt mre than 85% under different lad resistance cnditins. utput pwer and the ptimal utput vltage are calculated t act as the reference input f cntrl. Fig.18 shws that the prpsed cntrl scheme is respnded under different irradiatin and resistances cnditins. Fig.18 shwn that the prpsed cntrl scheme can track the pwer very well under the fixed irradiatin cnditins. Fig.18 shws that the prpsed cntrl scheme is very feasible under the fixed irradiatin have the disturbed signals cnditins. As shwn in Fig.18 (c), the utput pwer f PV is increasing with the increase f irradiatin. Nt matter hw the disturbed signals are varius with time, the prpsed MPPT cntrl scheme can track the targeted pwer which is calculated by using DSP and the prpsed MPPT algrithm. Fig.18 (d) shw that the utput pwer is varius with the different f irradiatin under evil weather cnditins. Base n the results f Fig.18, the prpsed MPPT algrithm is very easy t rapid calculate the maximum pwer pint under smart varius weather cnditins. Base n the knwn n and I, the maximum pwer algrithm is very rapid t acquire the maximum pwer pint in the whle tracking curse by using the prpsed Sepic circuit. Output Pwer (W) Targeted Pwer: 46.4W Pwer Acquired by the Prpsed MPPT Cntrl Targeted Pwer Fig.17 Imprved blck diagram f series-cnnected lad cntrl fr PV generatin systems. As shwn in the Fig.17, a prpsed cntrl scheme is described in the paper. An easy imprvement is described in rder t acquire the higher efficiency than the cnventinal cntrl methd. The vltage-lp is used t inner-lp, and the pwer-lp is used t uter-lp. The maximum Output Pwer (W) 3 1 Pwer Acquired by the Prpsed MPPT Cntrl ISSN: Issue 4, Vlume 8, April 9

13 WSEAS TRANSACTIONS n CIRCUITS and SYSTEMS Output Pwer (W) Output Pwer (W) Targeted Pwer Pwer Acquired by the Prpsed MPPT Cntrl Targeted Pwer (c) Pwer Acquired by the Prpsed MPPT Cntrl (d) Fig.18 The prpsed cntrl scheme is respnded under varius irradiatin and the disturbed signals exist cnditins. The irradiatin is fixed. The disturbed signals exist. (c) The irradiatin is increasing with the time. (d) The irradiatin is wavy. As shwn in the Fig.19, the prpsed cntrl scheme is cmpared with the cnventinal cntrl methd under different irradiatin cnditins. Fig.19 shws that the utput efficiency f prpsed MPPT cntrl scheme is mre than the cnventinal cntrl scheme under different lad resistance and fixed irradiatin cnditins. Fig.19 shws that the utput efficiency f prpsed MPPT cntrl scheme is mre than the cnventinal cntrl scheme under the fixed irradiatin has the disturbed signals cnditins. As shwn in the Fig.19 (c), the utput efficiency f prpsed MPPT cntrl scheme is mre than the cnventinal cntrl scheme under the gradual increasing irradiatin has the disturbed signals cnditins. The same cnclusin can be gained frm the Fig.19 (d) under the wavy irradiatin cnditins. As shwn in the Fig.19, the prpsed MPPT algrithm is very easy t rapid calculate the maximum pwer pint under smart varius weather cnditins. The prpsed cntrl scheme has higher utput efficiency than the cnventinal cntrl scheme. S the prpsed variable vltage MPPT cntrl methd can acquire maximum available pwer frm PV generatin system with the changing f ambient weather at real time. The prpsed duble lp cntrl imprves the utput efficiency f traditinal cntrl methd. It is evident that the PV generatin system with variable vltage MPPT algrithm has a gd dynamic perfrmance du t the actual n and I is gained. Certainly, the aging and partial shading will change the utput characteristic f actual PV system, s it is essential t run the PO methd t gain the new actual n and I when the PV have been used a perid f time. The variable step size PO methd shuld be used t gain accurate n and I. And the incremental cnductance (IC) methd can be used t gain the actual n and I by intrducing the methd in abve sectin under steady weather cnditins. In the future, the intelligent thery shuld be used t imprve PI characteristic f cntrl scheme, i.e., the fuzzy thery, the immune thery, and the nerve net thery etc. And the intelligent MPPT cntrl methd is expected t imprve the utput efficiency f PV cmpare with traditinal cntrl methd. Output Pwer (W) Output Pwer (W) Targeted Pwer: 46.4W Pwer Acquired by the Prpsed MPPT Cntrl Pwer Acquired by the cnverntinal MPPT Cntrl Targeted Pwer Pwer Acquired by the Prpsed MPPT Cntrl Pwer Acquired by the cnverntinal MPPT Cntrl ISSN: Issue 4, Vlume 8, April 9

14 WSEAS TRANSACTIONS n CIRCUITS and SYSTEMS Output Pwer (W) Output Pwer (W) Targeted Pwer Pwer Acquired by the 1 Prpsed MPPT Cntrl Pwer Acquired by the cnverntinal MPPT Cntrl Time (S) (c) Targeted Pwer Pwer Acquired by the Prpsed MPPT Cntrl 1 Pwer Acquired by the cnverntinal MPPT Cntrl (d) Fig.19 Draw a cmparisn between the prpsed cntrl scheme and the cnventinal cntrl methd under different irradiatin cnditins. The irradiatin is fixed. The disturbed signals exist. (c) The irradiatin is increasing with the time. (d) The irradiatin is wavy. 5 Cnclusin A nvel MPPT cntrl methd was prpsed in this paper. A new methd f acquire the actual n and I are prpsed by using the PO methd. The expiatry prgram f reference vltage is applied t acquire the actual maximum pwer pint. The crrectness and validity f expiatry cefficients is verified thrugh simulatin under varius weather cnditins. In rder t acquire the maximum pwer, the PO methd is applied t acquire the actual n and I, but it is nt applied t acquire the MPP during tracking curse, the lss f energy f PV is very small, and the utput efficiency f prpsed MPPT algrithm is mre than 99%. Next, the prpsed PI cntrl scheme f MPPT and the Sepic circuit are used t track the maximum pwer pint by cntrlling the switch frequency f MOSFET. The prpsed cntrl scheme has mve efficiency than the cnventinal cntrl scheme. ACKNOWLEDGMENT THIS PROJECT WAS GRANTED FINANCIAL SUPPORT FROM CHINESE POSTDOCTORAL RESEARCH FOUNDATION (NO: 8R14134), SHANGHAI BAI YU LAN SCIENTICE AND TECHONLGY FOUNDATION (NO: 7B73), AND CHINA EDUCATION MINISTRY RESEARCH FOUNDATION (NO: 7118), SCIENCE RESEARCH AND DEVELOPMENT PROGRAM OF SHANXI PROVINCE (NO: 8116), YOUTH SCIENCE RESEARCH FOUNDATION OF SHANXI PROVINCE (NO: 91). References: [1] Yang Chen, Keyue Ma Smedley. A Cst- Effective Single-Stage Inverter with Maximum Pwer Pint Tracking. IEEE Transactins n Pwer Electrnics, 4, 19(5): [] Muth, N, Inue, T. A cntrlling methd fr charging phtvltaic generatin pwer btained by a MPPT cntrl methd t series cnnected ultraelectric duble layer capacitrs. In: Industry Applicatins Cnference, 39th IAS Annual Meeting, Cnference Recrd f the 4 IEEE. 4: [3] N. Muth, M. Ohn, T. Inue. A Methd fr MPPT Cntrl While Searching fr Parameters Crrespnding t Weather Cnditins fr PV Generate Systems. Industrial Electrnics, IEEE Transactins, 6, 53(4): [4] N. Muth, M. Ohn, T. Inue. A Cntrl Methd t Charge Series-Cnnected Ultraelectric Duble-Layer Capacitrs Suitable fr Phtvltaic Generate Systems Cmbining MPPT Cntrl Methd. IEEE Transactins n Industrial Electrnics, 7, 54(1): [5] Arias, J, Linera, F.F, Martin-Rams, J, Pernia, A.M, Cambrner, J. A mdular PV regulatr based n micrcntrller with maximum pwer pint tracking. Industry Applicatins, 39th IAS Annual Meeting, Cnference Recrd f IEEE, 4, : [6] K. K. Tse, Billy M. T. H, Henry Shu-Hung Chung. A Cmparative Study f Maximum-Pwer-Pint Trackers fr Phtvltaic Panels Using Switching- Frequency Mdulatin Scheme. IEEE Transactins n Industrial Electrnics, 4, 51(): [7] Peter Wlfs, Quan Li. A Current-Sensr-Free Incremental Cnductance Single Cell MPPT fr ISSN: Issue 4, Vlume 8, April 9

15 WSEAS TRANSACTIONS n CIRCUITS and SYSTEMS High Perfrmance Vehicle Slar Arrays. In: Pwer Electrnics Specialists Cnference PESC '6, 37th IEEE, 6: 1 7. [8] W.J.A.Teulings, J.C.Marpinard, A.Capel, D.O Sullivan. A new maximum pwer pint tracking system. In: Pwer Electrnics Specialists Cnference PESC '93 Recrd, 4th Annual IEEE, 1993: [9] C. Drfte, U. Brup, F. Blaabjerg. A cmbined tw-methd MPPT cntrl scheme fr grid-cnnected phtvltaic systems. In: Pwer Electrnics and Applicatins, Eurpean Cnference, 5: 1-1. [1] M. Gdy Simes, N. N. Franceschetti, M. Friedhfer. A fuzzy lgic based phtvltaic peak pwer tracking cntrller. In: Industrial Electrnics Prceedings ISIE '98, IEEE Internatinal Sympsium 1: [11] Tsai-Fu Wu, Chien-Hsuan Chang, Yu-Kai Chen. A fuzzy-lgic-cntrlled single-stage cnverter fr PV-pwered lighting systems applicatins. IEEE Trans. Ind. Electrn,, 47(): [1] Ji, Changan, Zhang, Xiubin, Zeng, Guhui, He, Bin, Zhu, Xuelian, The study f the applicatin based n fuzzy cntrl fr hybrid phtvltaic-wind renewable energy surces. WSEAS Transactins n Circuits and Systems, Vl.5, NO.1, January, 6, pp [13] Liu, Li-qun, Wang Zhi-xin, A Rapid MPPT Algrithm Based n the Research f Slar Cell s Dide Factr and Reverse Saturatin Current. WSEAS Transactins n Systems, 8, 7(5): [14] A. Hren; P. Slibar, Full rder dynamic mdel f SEPIC cnverter. Industrial Electrnics, ISIE 5. Prceedings f the IEEE Internatinal Sympsium, 5 (): [15] J.-M. Kwn, W.-Y. Chi, J.-J. Lee, E.-H. Kim, B.-H. Kwn, Cntinuus-cnductin-mde SEPIC cnverter with lw reverse-recvery lss fr pwer factr crrectin, Electric Pwer Applicatins, IEE Prceedings, 6, 153(5): [16] H.Y. Kanaan, K. Al-Haddad, F. Fnaiech, Switching-functin-based mdeling and cntrl f a SEPIC pwer factr crrectin circuit perating in cntinuus and discntinuus current mdes, Industrial Technlgy, IEEE ICIT '4. 4, 1: ISSN: Issue 4, Vlume 8, April 9