A New MPPT Method for Low-Power solar energy harvesting
A New MPPT Method for Low-Power
Solar Energy Harvesting Oscar López-Lape?a,Maria Teresa Penella,Student Member,IEEE,and
Manel Gasulla,Member,IEEE
Abstract—This paper describes a new maximum-power-point-tracking(MPPT)method focused on low-power(<1W)pho-tovoltaic(PV)panels.The static and dynamic performance is theoretically analyzed,and design criteria are provided.A pro-totype was implemented with a500-mW PV panel,a commer-cial boost converter,and low-power components for the MPPT https://www.wendangku.net/doc/654212478.html,boratory measurements were performed to assess the effectiveness of the proposed method.Tracking ef?ciency was higher than99.6%.The overall ef?ciency was higher than92%for a PV panel power higher than100mW.This is,in part,feasible due to the low power consumption of the MPPT controller,which was kept lower than350μW.The time response of the tracking circuit was tested to be around1s.Field measurements showed energy gains higher than10.3%with respect to a direct-coupled solution for an ambient temperature of26?C.Higher gains are expected for lower temperatures.
Index Terms—Energy harvesting,maximum power point track-ing(MPPT),solar cells,wireless sensor networks(WSNs).
I.I NTRODUCTION
L OW-POWER devices mainly use either primary or sec-ondary(rechargeable)batteries.Primary batteries are cheaper and are suitable whenever they survive the life cycle of the device.On the other hand,secondary batteries are used in mobile devices that must often be recharged from the mains,such as,for example,mobile phones.However,in some devices,such as the nodes of wireless sensor networks(WSNs), this solution is not practical.Energy harvesting constitutes a feasible alternative and has been proposed in order to power autonomous nodes using optical[1],[2],mechanical[3],or thermal energy[4]or even a combination of them[5].Among the ambient sources,optical(or solar)energy provides high power density,principally outdoors.
In order to extract the maximum power from a photovoltaic (PV)panel,several maximum-power-point-tracking(MPPT) methods have been proposed and used for high-power systems [6].Their application to low-power PV panels(<1W)has just
Manuscript received December31,2008;revised May8,2009,June29, 2009,September25,2009,and October26,2009;accepted November10, 2009.Date of publication December4,2009;date of current version August11,2010.This work was supported in part by the Spanish Ministry of Education and Science under Contract TEC2007-66331/MIC,by the European Regional Development Fund,and by the Spanish–Tunisian Cooperation Project (AECI–A/01218207).The work of M.T.Penella was supported by the Ministry of Education and Science of Spain under the FPU Program(AP2005-2508). The authors are with the Instrumentation,Sensors and Interfaces Group, Universitat Politècnica de Catalunya,08860Barcelona,Spain(e-mail:os-car@https://www.wendangku.net/doc/654212478.html,;mpenella@https://www.wendangku.net/doc/654212478.html,;manel.gasulla@https://www.wendangku.net/doc/654212478.html,).
Color version of one or more?gures in this paper are available online at https://www.wendangku.net/doc/654212478.html,.
Digital Object Identi?er
10.1109/TIE.2009.2037653
Fig.1.PFM technique for a boost regulator at light loads.
recently been proposed[7]–[10]and poses new challenges to
achieve a net power gain.In contrast to high-power applica-
tions,the power consumption of the MPPT control circuit can
contribute signi?cantly to the?nal power ef?ciency.This paper
proposes and implements a new MPPT method that is partic-
ularly suitable for these low-power source levels.The method
does not require complex operations and can be implemented
with low-power components.
II.B ACKGROUND
A.Energy Harvesting
The autonomous nodes of a WSN are composed of sensing,
processing,and communication stages.Power consumption
usually ranges from tens of milliwatts when fully active to
units of microwatts in sleep mode.When the power is pro-
vided by the environment[11],a transducer,e.g.,a PV panel,
converts ambient energy into electrical energy,with a given
ef?ciency.For perpetual operation,the harvested power must
be higher,in average,than the consumed power of the node.An
energy storage unit,e.g.,a rechargeable battery,must account
for the variability of the ambient energy.Finally,an energy-
conditioning block matches the transducer to the storage unit.
B.DC/DC Conversion and PFM Control
Direct-coupled solutions use a single diode to connect the PV
panel to the storage unit.More elaborated designs use instead
a dc/dc converter in order to work at the maximum power 0278-0046/$26.00?2010IEEE
Fig.2.PFM technique applied to the energy-conditioning block of solar energy harvesters.
point(MPP:I MPP,V MPP)and then increase the harvested
energy[12].
Switching converters are the most energy-ef?cient dc/dc reg-
ulators,and plenty of commercial off-the-shelf(COTS)compo-
nents are available.Pulse frequency modulation(PFM)control
techniques,which are based on a hysteresis control of the output
voltage,are used to achieve a low power consumption of the
converter and then a high ef?ciency with light loads[13].Fig.1
shows a schematic of a PFM boost regulator,together with
the temporal evolution of the output voltage(v o),the inductor
current(i L),and the control signal of the internal switch M1.
Switches M1and M2are off until v o falls below a low threshold
value(V ref?V TL).Then,the switches alternately activate in order to transfer electrical charge from the input to the output
until v o reaches a high threshold value(V ref+V TH),restarting
the process.For light loads,the inactive period increases,
which maintains a low overall power consumption and a high
ef?ciency.
We propose to use the same PFM technique,using COTS
components,in the energy-conditioning block of solar energy
harvesters(Fig.2).Now,an input capacitor(C in)is connected
in parallel with the PV panel,and an external hysteresis com-
parator is placed between the panel and the feedback(FB)
terminal of the dc/dc converter.First,during a time T charge,
switches M1and M2are off,and the current of the PV panel
(i s)charges C in until the voltage of the PV panel(v s)reaches
v m+V TH.Then,V FB toggles,and the converter switches M1
and M2alternately activate,during a time T disch,in order to
transfer charge from C in to the output until v s decreases to
v m?V TL,restarting the process.The voltage operating point of the PV panel is determined by v m.To reach the MPP,v m must be obtained from an MPPT controller.
In Figs.1and2,a boost converter has been shown for illustration,but the same concepts can be applied to buck or buck–boost converters.
C.Low-Power MPPT Methods
An MPPT controller that is suitable for low-power PV panels must have low power consumption.Then,low computation complexity and low-power components are preferred.
One of the simplest MPPT methods is the fractional open-circuit voltage(FOCV),which exploits the nearly linear re-lationship between the PV panel open-circuit voltage(V OC) and its voltage at the MPP(V MPP)under varying irradiance and temperature levels.However,this result is based on obser-vations and must be empirically determined for each speci?c type of PV panel[14].V OC is either measured periodically by momentarily opening the output of the PV panel,as that in[9], or by using a pilot cell(an additional PV panel of the same type in an OCV con?guration),as that in[8].
A more elaborated method is the perturb and observe(P&O) method,as that in[7].The basic idea is to slightly perturb the operating voltage of the PV panel and see how the power changes.If the power increases,the perturbation should be kept in the same direction;otherwise,it should be reversed. To compute power,current and voltage measurements must be usually performed.Overall,a true MPPT is achieved at the expense of increasing the circuit complexity and the power consumption with respect to the FOCV method.
Recently,a new low-complexity technique has been pro-posed[15].However,the method has only been tested in a (relatively high power)55-W PV panel and presents a poor tracking ef?ciency for low-power irradiation levels.
LóPEZ-LAPE?A et al.:NEW MPPT METHOD FOR LOW-POWER SOLAR ENERGY HARVESTING
3131
Fig.3.Observation and hysteresis windows of the proposed MPPT method.
III.P ROPOSED MPPT M ETHOD
A.Theoretical Approach
A true MPPT method must measure the generated power of the PV panel and?nd and follow its maximal value.Here,we propose to use the circuit described in Fig.2in combination with a new proposed MPPT technique well suited for low-power PV panels.In order to achieve the MPP,the method nulls the difference of the panel average power in two consecutive time intervals(T1and T2)within T charge.As Fig.3shows,T1 and T2correspond to the lower and upper halves,respectively, of an observation voltage window(whose gap is2V h)centered on the operating voltage v m.As can be seen,the minimum voltage of the observation window is slightly higher than the minimum voltage of the hysteresis window to let the devices used in the MPPT controller(see Section III-B)to overcome the transient response produced by the fast discharge of C in.On the other hand,the upper limits of the hysteresis and observation windows match.For the sake of simplicity,we will assume in the rest of this paper that both windows match and that T charge≈T1+T2.
Referring to Fig.3,the period of v s is given by
T cycle=T charge+T disch.(1) As the converter is inactive during T charge,the output power of the PV panel(P s)is equal to the incoming power at C in; then,
P s=v s i s=v s C in dv s
dt
.(2)
The average power results in
P s=1
T
t0+T
t0
P s dt=
C in
T
v s(t0+T)
v s(t0)
v s dv s(3)
where t0and T are an arbitrary time instant and a time interval within T charge,respectively.Applying(3)into the calculation of the average power during T1and T2results in
P s1=C in
T1
v m
v m?V h
v s dv s=
C in V h
T1
v m?
V h
2
P s2=C in
T2
v m+V h
v m
v s dv s=
C in V h
T2
v m+
V h
2
.
(4)
Fig.4.Evaluation of the operating point(v m)with respect to the MPP
(V MPP).
From(4),the power difference is
ΔP s≡P s2?P s1=
C in V h
T2T1
v m(T1?T2)+
V h
2
(T1+T2)
.
(5)
The sign of(5)will indicate the position of the operating
voltage v m with respect to V MPP.Fig.4shows the characteristic
power pro?le versus the operating voltage of a generic PV
panel(P–V curve)and illustrates this concept.As can be seen,
whenever(5)is positive,v m On the other hand,whenever(5)is negative,v m>V MPP and should be decreased.The sign of(5)depends exclusively on the term within the parentheses.This term will be de?ned as L(v m) L(v m)≡v m(T1?T2)+ V h 2 (T1+T2).(6) An equilibrium point v m,eq will be achieved whenΔP s= 0,i.e., L(v m,eq)=v m,eq(T1?T2)+ V h 2 (T1+T2)=0(7) resulting in v m,eq=V MPP if V h V MPP. B.Implementation To implement the MPPT control law,we propose to calculate v m as the iterative sum of L(v m)in each new cycle v m(n)= 1 τINT n?1 i=1 ? ?? T1(i) v m(i)dt? T2(i) v m(i)dt + T1(i)+T2(i) V h 2 ·dt ? ??(8) where v m(n)is sampled at the end of each T charge,τINT is an integral constant,and n is the cycle number.As can be seen,the multiplication operations in(6)have been replaced by integral operators.This equivalence is based on the fact that V h is a constant and that the sampled v m has a constant value during T1and T2.Moreover,in contrast to other methods,the measurement of the current is not required.The value of v m will increase whenever v m(n) v m(n)>V MPP,thus tending to v m,eq≈V MPP. Fig.5shows the schematic diagram of the implemented MPPT https://www.wendangku.net/doc/654212478.html,parator CMP2toggles SW2at the instant 3132IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS,VOL.57,NO.9,SEPTEMBER 2010 Fig.5.Simpli?ed schematic of the energy conditioner with the proposed MPPT control circuit. Fig.6.Expected temporal evolution of v m ,v s ,and v INT ,for the case in which v m time v s crosses v m .Hysteresis comparator CMP 3activates the converter during T disch .This same comparator,together with CMP 1,enables SW 2and selects terminal 1of SW 1during T 1and T 2.The output signals of SW 1and SW 2are added and integrated,and the resulting output v INT is sampled at the end of T charge ,providing a new value of v m .Fig.6shows the expected temporal evolution of v m ,v s ,and v INT ,for the case in which v m IV .A NALYSIS In order to achieve an optimum design,the static and dy-namic MPPT performance will be theoretically analyzed.Static performance will be assessed by the overall power ef?ciency,which can be split up into three terms ηT ≡ηMPPT ·ηav ·ηc (9) where ηMPPT ≡(P s (v m ,eq )/P MPP ),ηav ≡(P s /P s (v m ,eq )),and ηc ≡(P out /P s );P MPP and P s (v m ,eq )are the PV power at the MPP and at v m ,eq ,respectively;P s and P out are the average po-wer at the input and output of the dc/dc converter,respectively.On the other hand,the dynamic performance will be assessed by the time constant of v m modeled as a ?rst-order time function.A.Ef?ciency of the MPPT Algorithm (ηMPPT ) The goal of the proposed MPPT controller is to achieve high tracking ef?ciency with low power consumption.The LóPEZ-LAPE?A et al.:NEW MPPT METHOD FOR LOW-POWER SOLAR ENERGY HARVESTING 3133 Fig.7.De?nition of the time intervals when the propagation delays of the comparators are taken into account. propagation delays of the comparators CMP 1–CMP 3(Fig.5) will affect the tracking ef?ciency.This is of particular relevance due to the design tradeoff between the power consumption and the propagation delay of COTS comparators.In the following,we analyze how these delays affect the tracking ef?ciency.Fig.7shows the observation window considering the propa-gation delays t pd1,t pd2,and t pd3introduced by CMP 1,CMP 2,and CMP 3,respectively. The relationship between the different time intervals is given by T 1,int =T 1,win ?t pd1+t pd2T 2,int =T 2,win ?t pd2+t pd3. (10) T 1,win and T 2,win are the ideal interval times de?ned by the observation window and provide the actual ΔP s through (5).T 1,int and T 2,int are the integration times of the MPPT circuit in Fig.5and determine v m ,eq through (7).Therefore,due to the propagation delays,ΔP s (v m ,eq )will not be zero,and conse-quently,v m ,eq will not reach the MPP at the equilibrium point,worsening the tracking ef?ciency.Even so,we still assume that the equilibrium point will be near the MPP. Substituting T 1and T 2in (7)by T 1,int and T 2,int and using (10),we obtain v m ,eq ((T 1,win ?t pd1+t pd2)?(T 2,win ?t pd2+t pd3)) +V h 2 ((T 1,win ?t pd1+t pd2)+(T 2,win ?t pd2+t pd3))=0.(11)Then,substituting T 1and T 2in (5)by T 1,win and T 2,win ,using (11),and considering V h v m ,eq ,we obtain ΔP s (v m ,eq )≈ C in V h T 1,win T 2,win v m ,eq (t pd1?2t pd2+t pd3). (12) We can then relate the slope of the P –V curve at the equilib-rium point with the propagation delays by dP s dv s v m ,eq ≈ΔP s V h v m ,eq V h V MPP ≈ t pd1?2t pd2+t pd3 C in V 2h P MPP I MPP (13) where we considered v m ,eq ≈V MPP and T 1,win ≈T 2,win ≈ T charge 2≈C in V h I MPP .(14) On the other hand,we can approximate P s around V MPP by a second-order Taylor polynomial P s (v s )≈P MPP +12d 2P s dv 2s V MPP (v s ?V MPP )2.(15)Derivating (15),we obtain v s ?V MPP = dP s /dv s |v s d 2P s /dv 2s |V MPP .(16) Then,substituting (15)at v s =v m ,eq in ηMPPT and using (13)and (16),we obtain ηMPPT ≈1+ t pd1?2t pd2+t pd3C in V h I MPP V h 2 2P MPP d 2P s dv 2s V MPP .(17) Notice that the second derivative of P s is negative and then ηMPPT <1.The tracking ef?ciency will tend to the unity with low and matched propagation delays and with higher values of V h .A higher value of the product C in V h also increases the tracking ef?ciency.This seems obvious from (14)since T charge increases and then the relative error contributed by the propagation delays diminishes. The adaptation of the method for high-power applications would require the selection of higher values of C in V h to main-tain a high tracking accuracy.An alternative is to use faster comparators that,obviously,will increase the power consump-tion of the MPPT controller.B.Averaging Ef?ciency (ηav ) The proposed MPPT method implies that P s ?uctuates around P s (v m ,eq )and,as a consequence,P s 1T T cycle P s dt ≈ T 1P s1+T 2P s2T 1+T 2= 2C in v m ,eq V h T 1+T 2 (18) and from (2),assuming that v m ,eq ≈V MPP , T 1+T 2= T 1+T 2 dτ= V MPP +V h V MPP ?V h v s C in P s dv s .(19) Using (15)and (19)in (18)and considering P s (v m ,eq )≈P MPP ,we arrive at ηav ≈1+161P MPP d 2P s dv 2s V MPP V 2h .(20)Then,a larger value of V h diminishes ηav because of the larger variations of P s around P s (v m ,eq ). 3134IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS,VOL.57,NO.9,SEPTEMBER2010 C.Ef?ciency of the Circuit(ηc) Considering the average circuit losses(P L),the average output power is given by P out=P s?P L(21) where P L accounts for the power losses of the dc/dc converter (P L,conv)and the MPPT control circuit(P L,MPPT). On the one hand,P L,conv can be expressed as P L,conv=P L,conv-o?T charge+P L,conv-on T disch T cycle (22) where P L,conv-on and P L,conv-o?are the power losses when the converter is active(T disch)and inactive(T charge), respectively. On the other hand,P L,MPPT can be expressed as[16] P L,MPPT=P L,MPPT-dc+ K T cycle (23) where P L,MPPT-dc accounts for the static power losses and the remaining term,where K is a constant,accounts for the increased switching activity of the MPPT controller as T cycle decreases. Considering that the power balance in the input capacitor during a whole cycle can be expressed as P disch T disch=P s T cycle(24) where P disch is the average power transferred from the capaci-tor to the converter during T disch,and using(18)and(21)–(23), we get ηc≈1? P L,conv-o?+P L,MPPT-dc P s + P L,conv-on?P L,conv-o? P disch + K(1?P s/P disch) 2·V MPP(C in V h) . (25) For low P s values,the contribution of the power losses of the MPPT control circuit(P L,MPPT)and the converter (P L,conv-o?)becomes signi?cant.Otherwise,for high P s val-ues,the ef?ciency of the converter(P L,conv-on)becomes dom-inant.On the other hand,for a given P s,ηc increases for larger values of the product C in V h. D.Dynamic Performance The dynamic response of v m can be described by a time continuous function if T cycle is short enough.Then, dv m dt ≈v m(n+1)?v m(n) T cycle .(26) From(5)and(8),we obtain v m(n+1)?v m(n)=T2(n)·T1(n) τINT C in ΔP s(v m(n)) V h (27) which,using(14)and(18),can be rewritten as v m(n+1)?v m(n)= T charge(n) 2τINT v m(n) ΔP s(v m(n)) P s(v m(n)) ≈T charge 2τINT V h v m 1 P s dP s dv s v m . (28) Substituting(28)into(26),we obtain dv m dt ≈V h 2τINT(1+T disch/T charge) v m 1 P s dP s dv s v m .(29) The lowest slope of P s will be in the neighborhood of the MPP, so we can assume that the interval of time required to reach the MPP is mainly due to the dynamic response in this region.In the neighborhood of the MPP,this dynamic can be approximated by a?rst-order Taylor polynomial around V MPP dv m dt ≈1 τ ·(V MPP?v m)(30) where,if T charge T disch, τ≈?2τINT V h V MPP 1 P MPP d2P s dv2s V MPP .(31) Note that T cycle does not appear in(31),and so,it will not determine the dynamic of v m.Nevertheless,T cycle determines the time discretizaton of v m(see Fig.6).Therefore,in order to keep T cycle short enough,it is required that T charge τ. V.S ELECTION OF P ARAMETERS This section describes the selection methodology of C in, V h,andτINT to reach maximum ef?ciency(ηT)with a given dynamic response.Speci?cally,we have selectedτ=1s. For the calculus,PV-power-related parameters,such as the second derivative of P s and P MPP,were estimated from the experimental P–V curve of the solar panel(see Section VII). The proposed MPPT method will be tested for a given range of the PV panel power and the corresponding I MPP.From Section VI,I MPP,min=3.7mA,and I MPP,max=141.4mA. A.First Step:Selection of C in V h From(14)and imposing T charge<τ/10,we get C in V h< I MPP,minτ/10 =185μC.(32) BecauseηT increases for a higher C in V h,we will select a value near the upper bound.We selected speci?cally C in V h= 100μC.On the other hand,(32)denotes the tradeoff between the speed of the dynamic response and the overall ef?ciency. The lower is the selectedτ,the lower will be C in V h and the resultingηT. LóPEZ-LAPE?A et al.:NEW MPPT METHOD FOR LOW-POWER SOLAR ENERGY HARVESTING 3135 Fig.8.Ef?ciencies versus V h. B.Second Step:Selection of V h Once the product C in V h is?xed,we observe thatηc does not depend on the value of V h.On the other hand,ηMPPT increases with an increase of V h,andηav decreases with an increase of V h.Therefore,the maximum of the productηMPPT·ηav will lead to an optimum value of V h.Fig.8shows these ef?ciencies in the worst case scenario and shows the existence of a max- imum around100mV.Therefore,we selected V h=100mV. For(17),considering the information provided in the datasheets of the comparators,we used t pd1?2t pd2+t pd3=5μs. C.Third Step:Determination of C in andτINT From the previous selected values,we obtain C in=1mF. Finally,from(31),we obtainτINT=88ms. VI.M ATERIALS AND M ETHODS A prototype of the proposed energy conditioner was im- plemented in order to be tested with a500-mW(I sc= 160mA,V OC=4.6V)PV panel(MSX-005,Solarex).The energy-conditioning circuit(Fig.5)was implemented with COTS components.For the dc/dc conversion,we used a MAX1675boost converter(PFM control with a current limit of0.5A),a22-μH inductor,and a low-equivalent- series-resistance(ESR)1-mF tantalum input capacitor(C in). LTC1440and LTC1441comparators were used to implement CMP1,CMP2,and CMP3.They provide low power(2.1μA) with a propagation delay of12μs.Low-power op amps,such as the OPA2369and the MAX9910,were used to obtain the limits of the observation window and to amplify the input voltage v s.An OPA2369,together with the analog switch TS5A2066, was used to implement the low-power sample-and-hold.The overall control circuit was powered from the output of the boost converter. Laboratory measurements were performed to assess the static and dynamic performance of the proposed energy conditioner. In order to achieve reproducible results,the PV panel and the battery in Fig.5were substituted by a PV array simulator and a voltage source,respectively.As commercial PV simulators are not suitable for the intended low power(<1W),we implemented an ad hoc solution connecting a current source (GS610,Yokogawa)in parallel with the PV panel,which was coated with an opaque cover.In this way,the short-circuit current(I sc)of the PV panel was adjusted by the current source. First,the PV simulator was characterized.Experimental I–V curves were obtained by changing the current source from5to 158mA in9-mA steps.For each current value,the PV output voltage was biased from0.1to5V with the voltage source. The output voltages and currents of the PV simulator were measured,and power values were calculated.To obtain the I–V and P–V curves,we used a cubic spline interpolation. A curve joining all the MPPs was also generated.Therefore, a correspondence was established between each generated I sc and the resulting P MPP.The limit values for P MPP(and I MPP) were8.2mW(3.7mA)and545.9mW(141.4mA). The generated P–V curves were used to determine the performance of the circuit prototype.Ef?ciencies were obtained against the whole range of P MPP and for different output voltages.First,ηMPPT was calculated by comparing the actual PV panel power P s(v m,eq)with P MPP for each generated I sc of the current source.P s(v m,eq)was estimated by measuring the average PV panel voltage and obtaining the corresponding power from the experimental P–V curve.Then,the overall ef?-ciencyηT was calculated by dividing the average output power (P out)by P MPP.P out was estimated from the measurement of the average output voltage and current.A low-ESR100-mF supercapacitor was added at the output of the circuit in order to obtain a quasi-dc output current and then achieve a proper measurement of the power ef?ciency[17].Finally,the dynamic performance of the MPPT method was assessed by program-ming step current changes with the current source and recording the resulting signals with an oscilloscope. Field measurements were also carried out to compare the proposed solution with a direct-coupled solution.This one used a low-turn-on-voltage Schottky diode(BAT47)to improve its ef?ciency.In order to avoid differences in using two PV panels,both circuits were connected alternatively through a reed relay to a single500-mW PV panel.Once the PV panel was connected to any of the two circuits,a30-s delay interval lets the circuit reach the steady state before starting to record the power during1min.The MPPT circuit had three AA NiMH batteries connected in series at its output,which assured that the output voltage of the boost converter was always higher than V MPP for any irradiance level.On the other hand,the direct-coupled circuit had two AA NiMH batteries connected in series at its output,in order to work near the MPP. VII.E XPERIMENTAL R ESULTS https://www.wendangku.net/doc/654212478.html,boratory Measurements Fig.9shows a set of measured I–V curves and the corre-sponding P–V curves of the PV simulator at24?C.The same graph also represents a curve joining the MPPs.As can be seen, V MPP increases for higher I sc values. Fig.10shows how the measured power consumption(at5V) of the MPPT control circuit increases with the input PV power. Higher PV power means a larger I sc and then a lower T cycle. Therefore,the experimental results agreed with(23). Fig.11showsηMPPT.As can be seen,ηMPPT>99.6%for the whole power range,which states the effectiveness of the proposed MPPT method and agrees with the corresponding graph in Fig.8for V h=100mV.Minor deviations can be observed when changing the output voltage from5to4V. On the other hand,ηav was estimated from(20)to be higher 3136IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS,VOL.57,NO.9,SEPTEMBER 2010 Fig.9.I –V and P –V curves of the PV simulator at 24?C.A curve joining the MPPs is also shown. Fig.10.Power consumption (at 5V)of the MPPT circuit versus the pro-grammed P MPP . Fig.11.ηMPPT versus the programmed P MPP . Fig.12.ηT versus the programmed P MPP . than 99.8%.This value,together with the value of ηMPPT ,states that ηT ,shown in Fig.12,is mainly due to ηc (not represented).These results agreed with (25),which includes the power consumption of the MPPT control circuit and the dc/dc converter. Fig.13.Transient response of v m to step changes of the programmed P MPP value. Fig.14.MPPT startup process when P MPP was changed from 0to 8.2mW. Fig.13shows the dynamic response of v m to step changes of the programmed P MPP value.The time constant (τ)was around 1s,as stated in Section V. Fig.14shows the startup transient of v INT ,v m ,and v s when P MPP was changed from 0to 8.2mW.For this test,the input capacitor (C in )was discharged,and the circuitry was powered from the circuit output voltage (5V)some seconds prior to the zero time value of the graph.The power change was produced around t ≈1s.As can be seen,v m and v s fast catch v INT ,which is initially settled to an internal 1.2-V reference value.Then,the circuit behaves as a ?rst-order system,and v m tends to the corresponding V MPP value.The graph inset shows with more detail the temporal evolution of the three represented signals. B.Field Measurements Fig.15shows the power delivered to the batteries during one sunny day for both the proposed MPPT circuit and the direct-coupled solution.The maximum ambient temperature and irradiance over a horizontal surface were 26?C and LóPEZ-LAPE?A et al.:NEW MPPT METHOD FOR LOW-POWER SOLAR ENERGY HARVESTING 3137 Fig.15.Power delivered to the batteries during one day. 800W/m2,respectively.The sudden increase of the incoming power around14:30indicates the incidence of the direct sun over the PV panel.The results show that the total energy collected by the MPPT circuit was10.3%higher,even though the measured ef?ciency for the direct-coupled circuit was close to85%at high-irradiance conditions. As can be seen in the inset in Fig.15,even at low-irradiance conditions,from8:00to14:30,the power delivered by the proposed MPPT circuit was higher or equal to the power delivered by the direct-coupled solution.First,the MPPT circuit started to charge its batteries before the direct-coupled circuit. This circuit could not charge the batteries until the open-circuit voltage of the PV panel(OCV PV)was higher than its battery voltage(≈2.4V),whereas the MPPT-based circuit could start to charge from a lower OCV PV,corresponding to the startup voltage of the MAX1675(1.1V).As the irradiance increased, the operating point of the PV panel for the direct-coupled circuit approached to its MPP.As a consequence,its ef?ciency increased to a similar value to that of the MPPT circuit from 9:30to13:00,which is mainly limited by the power loss of the https://www.wendangku.net/doc/654212478.html,ter,the ef?ciency of the MPPT rose up as the PV power increased(Fig.12),delivering again a higher power to the batteries than the direct-coupled circuit. We also veri?ed that the MPPT circuit outperformed the direct-coupled solution for other weather conditions, e.g., cloudy days. The MPP voltage of the PV panel increases for a decrease in temperature(?16mV/?C).Therefore,it is expected that, with cold weather,e.g.,in winter,the ef?ciency of the direct-coupled solution will decrease,whereas the MPPT circuit will still maintain a high ef?ciency.Then,higher energy gains are expected. VIII.C ONCLUSION A new MPPT method that is suitable for low-power PV panels has been proposed and tested.The MPPT controller is used as an external control loop of a PFM dc/dc converter placed between the PV panel and the load.In contrast to other true MPPT controllers,such as the P&O method,the current has not to be measured,and no multiplier operator has to be used to calculate the power.Therefore,the control circuit is simpler,and its consumption is lower than using those conven-tional techniques.Consequently,a high energy ef?ciency can be achieved even for low-power sources. The static and dynamic performance of the proposed MPPT method has been theoretically analyzed,and design criteria have been provided.The static performance is assessed through the power ef?ciency.The analysis demonstrates that a high tracking accuracy can be achieved even using low-power com-parators whenever their propagation delays are matched or the charge cycle is long enough.The dynamic performance is assessed by the time response of the tracking voltage,which can be approximated by a?rst-order linear function. A prototype MPPT circuit has been implemented using a commercial PFM dc/dc boost converter and low-power compo-nents for the MPPT https://www.wendangku.net/doc/654212478.html,boratory measurements have been carried out using a custom PV array simulator in order to assess the static and dynamic performance.The tracking ef?ciency is higher than99.6%.The overall ef?ciency is higher than92%for a PV panel power over100mW.This is,in part,feasible due to the low power consumption of the MPPT controller,which is kept lower than350μW.The time response of the tracking circuit was tested to be around1s.Field measurements have also been performed in order to compare the proposed solution with a direct-coupled circuit.Energy gains that are higher than10.3%have been achieved for an ambient temperature of26?C.Higher gains are expected for lower temperatures. 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[16]L.Benini and G.De Micheli,Dynamic Power Management.Design Tech-niques and CAD Tools .Norwell,MA:Kluwer,1998. [17]J.Naik,Performing Accurate PFM Mode Ef?ciency Measurements, Apr.2006.[Online].Available:https://www.wendangku.net/doc/654212478.html,/lit/an/slva236/ slva236.pdf Oscar López-Lape?a received the M.S.degree in physics and the M.S.degree in electronics engineer-ing from the Universitat de Barcelona,Barcelona,Spain,in 1994and 1996,respectively,and the Ph.D.degree in electronics engineering from the Univer-sitat Politècnica de Catalunya (UPC),Barcelona,in 2000. Since 2002,he has been an Associate Profes-sor at UPC.His current research interests include low-power converters,control theory,and energy harvesting. Maria Teresa Penella (S’07)received the B.Sc.and M.Sc.degrees in telecommunication from the Uni-versitat Politècnica de Catalunya (UPC),Barcelona,Spain,in 2003and 2005,respectively,where she is currently working toward the Ph.D.degree. In 2007,she was with the Electronics Labora-tory,Ecole Polytechnique Fédérale de Lausanne,Lausanne,Switzerland.She is currently an Assistant Professor at UPC.Her research interests include energy harvesting,energy and power conditioning,storage elements,and wireless sensor networks. Manel Gasulla (S’97–M’01)received the M.Eng.and Ph.D.degrees in telecommunication from the Universitat Politècnica de Catalunya (UPC),Barcelona,Spain,in 1992and 1999,respectively.Since 1993,he has been with UPC,where he is currently an Associate Professor,engaged in teach-ing on analog electronics and electronic instrumen-tation.In 2001–2002,he was a Visiting Postdoctoral Fellow at the Electronic Instrumentation Laboratory,Delft University of Technology,Delft,The Nether-lands.His research interests include capacitive sen-sors,sensor interfaces,wireless sensor networks,and energy-harvesting circuits and methods for low-power autonomous sensors. (一) 假定你是红星中学初三学生李华。你的美国朋友Jim在给你的邮件中提到他对中国新近出现的一种共享单车“mobike”很感兴趣，并请你做个简要介绍。请你给Jim回信，内容包括： 1. 这种单车的使用方法(如：APP查看车辆、扫码开锁等); 2. 这种单车的优势; 3. 你对这种单车的看法。 注意：1. 词数不少于80; 2. 开头和结尾已给出，不计入总词数。 提示词：智能手机smartphone, 二维码the QR code 参考范文 Dear Jim, I’m writing to tell you more about the new form of sharing bike mobike mentioned in your latest letter. It’s very convenient to use if you have a smartphone. What you do is find a nearest mobikethrough the APP, scan the QR code on the bike, and enjoy your trip. Compared to other forms of sharing bike, the greatest advantage of mobike is that you can easily find one and never worry about where to park it. It is becoming a new trend as a means of transportation, which relieves the traffic pressure and does good to the environment as well. Hope to ride a mobike with you in China. Yours, Li Hua (二) 最近很多大城市都投放了共享单车(shared bikes)，比如摩拜单车(Mobike)、Ofo共享单车等。由于它们方便停放，骑车也能起到锻炼身体的作用，作为代步工具很受大家欢迎。但是，各地也出现了很多毁车现象，比如刮掉车上的二维码(QR code)、上私锁等。 你对这种现象怎么看?你对共享单车公司有什么建议吗?写一篇符合逻辑的英语短文，80词左右。 参考词汇：bike-sharing companies 共享单车公司，Mobike 和Ofo 是两家共享单车公司，convenience 方便，register登记 参考范文 The shared bikes like Mobike and Ofo bring great convenience to people. You needn’t lock them by simply using your smart phone. They can take you where the subway and bus don’t go. And they can be left anywhere in public for the next user. However, bad things happen. Some people damage the QR code on the bike, or use their own lock, which causes trouble to other users. In my opinion, it’s difficult to turn these people’s ideas in a short time. Therefore, bike-sharing companies like Mobike and Ofo need to do something. For example, those who damage the bike should pay for their actions. Also, because people use their real name toregister as a user, it’s a good way to connect to one’s personal credit. In the end, what I want to say is to take good care of public services. (三) 共享单车(bicycle sharing)已成为时下最热的话题之一，请你就这一话题写一篇短文。内容须包括三方面：1. 共享单车蓬勃发展，成为社会热潮;2. 共享单车带来便利，但也存在问题;3. 我对解决问题的建议。 参考范文 Bicycle Sharing With the development of technology, bicycle sharing comes into people's lives. It becomes more and more popular and much news reported it. At the same time, we should see that there are some problems caused by bicycle sharing. On one side, bicycle sharing makes it very convenient of people traveling. You can find a bicycle anywhere at any time when you want to go out for a cycling, and the price of one trip is very low. It can save time for people. On the other side, its management is not perfect. Even kids can open the lock and ride the bicycle, there is no doubt that such behavior is very dangerous. 介绍北京的英语作文(2) AsBeijinghasbeenconfirmedhomecityofOlympics2008,the spiritofgreenOlympics,scientificOlympicsandhumanizedOlymp icwillsurelybringmoreandmorechangestoBeijing,promotethed evelopmentofsportsandOlympicsinChinaaswellasintheworld,a ndstrengthenthefriendlycommunicationsbetweenChineseandf oreignpeople. 篇六：Beijing BeijingisthecapitalofPeoplesRepublicofChinaandthenation scentreforpolitics,economyandculture.Itenjoysalongandrichhis tory.Therearenumerousheritagesitesandwonderfulexamplesof ancientarchitecture,suchastheworld-famousGreatWall,theTem pleofHeavenandtheForbiddenCity. Besidessightseeingplaces,therearemanydeliciousfoodsuch asPekingducksandBeijingsnacks.Beijingisreallyagoodplacetotr avel. 篇七：Beijing AsthecaptainofChina，Beijinghasbeenthemostpopularcityofchina。SomoreandmorepeoplewanttovisitBeijing. [标签:标题] 篇一：关于汽车的英语作文 好的 Nowadays, with the rapid improvement of people’s living standards, cars have become an indispensable part of people's lives,so that more and more people have a car of their own, especially in cities. It brings some benefits for us but also causes many problems at the same time. For one thing,there’s no doubt that cars provide much convenience for people to go where they want to quickly and easily. Especially on weekday,driving a car can save a lot of time for us to go to work.When some places are too far away from our home, driving our own car is also convenient, we can go wherever we want. However,for another, too many cars will lead to the pressure of public transport, a series of problems will appear.First of all,it will bring about more air pollution,a large amount of polluted air given off by cars do great harm to our health.What’s more, as the existing roads are not so wide for the increasing number of cars,undoubtedly,traffic jams will become more and more serious. Last but not least, cars also place burden on the public facilities in providing more parking lots. As far as I am concerned,everything has its advantages and disadvantages. It’s high time that effective action must be token to limit the ever growing number of cars, the government should take measures to control the air pollution from the cars. Some roads should be widened and more new roads should be constructed. Only in this way，will people benefit from the popularity of cars. 坏的 Nowadays, with the rapid improvement of people's living standards, cars have become an indispensable part of people's lives,so that more and more people have a car of their own, especially in cities.It brings some benefit for us but also causes many problems at the same time. For one thing,it's no doubt that that cars provide much convenience for people to go where they want to quickly and easily. Especially on weekday,driving a car can save a lot of time for us to go to work.When some places are too far away from our home, driving our own car is also convenient, we can go wherever we want. However,for another, too many cars will lead to the pressure of public transport, a series of problems will appear.First of all,it will bring about more air pollution,a large amount of polluted air given off by cars do great harm to our health .What's more, as the existing roads are not so wide for the increasing number of cars,undoubtedly,traffic jams will become more and more serious. Last but not least, cars also place burden on the public facilities in providing more parking lots. As far as I am concerned,everything has its advantages and disadvantages. It's high time that effective action must be token to limit the ever growing number of cars, the government should take measures to control the air pollution from the cars. Some roads should be widened and more new roads should be constructed. Only in this way,will people benefit from the popularity of cars. 篇二：雅思作文高分范文：私家车的利与弊 智课网IELTS备考资料 雅思作文高分范文：私家车的利与弊 课下作业(三十二) 、选择题 1．哲学基本问题又称哲学的根本问题、哲学的最高问题。这一问题包括( ) ①物质和意识的辩证关系问题 ②思维和存在何者是本原的问题 ③思维和存在有没有同一性的问题 ④唯物主义和唯心主义关系问题 A ．①② B ．②③ C .③④ D .①③ 解析：选 B 。哲学基本问题包括两个方面的内容：一是思维和存在何者是本原的问题；二是思维和存在有没有同一性的问题，②③入选。 2. 唯物主义是哲学上两个敌对的基本派别之一，是同唯心主义相对立的思想体系。划分唯物 主义和唯心主义的唯一标准是( ) A .物质和意识的关系问题 B .客观与主观的关系问题 C .思维和存在何者是本原的问题 D ?思维和存在有没有同一性的问题 解析：选C。对思维和存在何者是本原问题的不同回答，是划分唯物主义和唯心主义的唯一 标准， C 入选。 3. “二月春分八月秋分昼夜不长不短；三年一闰五年再闰阴阳无差无错。”这副对联从一个侧面反映了( ) ①思维和存在具有同一性 ②认识与自然的吻合具有必然性 ③认识以实证和猜测为基础 ④意识活动具有主动创造性 A .①③ B .②④ C .①④ D .②③ 解析：选C o材料反映人们可以认识和把握自然界的运动规律,说明思维和存在具有同一性 反映了意识活动具有主动创造性，①④符合题意；认识与自然的吻合不具有必然性，②错误；实践是认识的基础，③错误。 4 .(2019河南中原名校联考)“为天地立心，为生民立命，为往圣继绝学，为万世开太平”是北宋张载的名言。由于其言简意宏，一直被人们传颂不衰。下列观点符合“为天地立心”的 是( ) ①形存则神存，形谢则神灭②吾心即是宇宙，宇宙即是吾心 ③思维着的精神是地球上最 美的花朵④“天不生仲尼，万古长如夜” A ．①② B ．①③ C .③④ D .②④ 解析：选C。“为天地立心”的意思是为天地确立一种核心价值理念，强调精神的作用，③ ④强调思维着的精神的作用，符合题意；①强调物质决定意识，②片面夸大意识的作用，均不合题意。 5.有位生物学学者认为，唯有生物学才能带领人类探究物种本源、生从何来死往何方等问题，他确信构成生物的眼见为实的物质比辩证唯物主义判断猜想的物质还正确。这种认识( ) ①没弄清辩证唯物主义的物质概念与构成生物的物质之间的关系 ②坚持了唯物主义根本方向，但属于古代朴素唯物主义的思想 ③犯了近代形而上学唯物主义错误，具有机械性、形而上学性 ④是在自然科学基础上对辩证唯物主义和历史唯物主义的发展 A .①② B .①③ C .②③ D .③④ 解析：选B。材料中的生物学学者没有看到哲学对具体科学的意义，认为哲学中的物质是猜 想的，没有看到哲学中的物质与自然科学中的物质是共性与个性的关系，因而具有机械性、 形而上学性，①③正确，②④错误。 6.18世纪法国哲学家丹尼斯狄德罗认为：“自然界由数目无穷、性质不同的异质元素构成。” 这种观点( ) ①承认世界的物质性，但把物质归结为自然科学意义上的元素②建立在自然科学成就的基 础上，丰富和发展了唯物主义③坚持物质第一性，但对物质的认识没有科学依据④认为世界是物质的，正确揭示了物质世界的基本规律 A .①② B .③④ C .①③ D .②④ 解析：选A。“狄德罗认为：‘自然界由数目无穷、性质不同的异质元素构成。'” 这种观点承认世界的物质性，但把物质归结为自然科学意义上的元素，①正确；狄德罗生活在18世纪，其观点建立在自然科学成就的基础上，丰富和发展了唯物主义，属于近代形而上学唯物主义，②入选；③④ 说法错误。 7 ?“宇宙创造过程中，上帝没有位置……没有必要借助上帝来为宇宙按下启动键”。这是斯 温馨提示： 此套题为Word版，请按住Ctrl,滑动鼠标滚轴，调节合适的观看比例，答案解析附后。 课后巩固作业（十九） (30分钟50分) 一、选择题(每题4分，共16分) 1.下列试验中，是古典概型的是( ) (A)发射一颗卫星能否成功 (B)从高一(18)班60名同学中任选一人测量其身高 (C)抛掷一枚骰子，出现1点或2点 (D)射击选手射击一次，恰中靶心 2.(2011·温州高一检测)抛掷两个骰子,则两个骰子点数之和大于4的概率为 ( ) (A)13 18 (B)8 9 (C)7 12 (D)5 6 3.从{1,2,3,4,5}中随机选取一个数为a，从{1,2,3}中随机选取一个数为b，则 b>a的概率是( ) (A)4 5 (B)3 5 (C) 2 5 (D)1 5 4.用1，2，3，4这四个数字，组成比2 000大且无重复数字的四位数的概率是 ( ) (A)1 4 (B)1 2 (C)3 4 (D)1 3 二、填空题(每题4分，共8分) 5.(2011·江苏高考)从1，2，3，4这四个数中一次随机取两个数，则其中一个 数是另一个的两倍的概率是_____. 6.(2011·永定高二检测)扔两枚骰子出现的点数为m,n，以(m,n)为坐标的点出现在x2+y2=16内的概率为_____. 三、解答题(每题8分，共16分) 7.一个袋中装有四个形状大小完全相同的球，球的编号分别为1，2，3，4. (1)从袋中随机抽取两个球，求取出的球的编号之和不大于4的概率； (2)先从袋中随机取一个球，该球的编号为m，将球放回袋中，然后再从袋中随机取一个球，该球的编号为n，求n 介绍北京的英语作文1篇 篇一MyFamily Ilovemyfamily,becauseIhaveahappyfamily. MyfatherisanEnglishteacher.HisnameisJacky.Heisthirty-eight.Helikesplay ingbasketball.What’smymotherjop?Issheateacher?Yes,you’reright!Mymotherisverykindandnice,sheisthirty-seven.Mymotherisalways laboriouswork.Ilovemyparents! OnStaurdayandSunday,Ioftengotothelibraryandplaythepiano,Myfathergot oplaybasketball.Sometimes,wewatchTVandlistentomusicathome. Ilovemyfamily.BecauseI’mveryhappytolivewithmyparentstogether! 篇二MyFamily MyFamily Everyonehasafamily.Weliveinitandfeelverywarm.Therearethreepersonsin myfamily,mymother,fatherandI.Welivetogetherveryhappilyandtherearema nyinterestingstoriesaboutmyfamily. Myfatherisahard-workingman.Heworksasadoctor.Healwaystrieshisbesttoh elpevery,patientandmakepatientscomfortable.Butsonetimesheworkssohard thathecan”trememberthedate. 人教版二年级下册语文 每课作业 HEN system office room 【HEN16H-HENS2AHENS8Q8-HENH1688】 1、找春天 一、看拼音写词语。 tuō xiàjiědònɡxī shuǐmián yī tàn tóu yáo tóu?yě huā duǒcánɡ 二、按课文内容填空。 1、春天来了！我们几个孩子，_______棉袄，________家门，________田野，去_______春天。春天像个___________，遮遮掩掩，躲躲藏藏。我们________地找啊，找啊。 2、春天来了！我们______到了她，我们______到了她，我们______到了她，我们______到了她。她在柳枝上_________，在风筝尾巴上_________；她在喜鹊、杜鹃__________，在桃花、杏花__________…… 三、填空。 藏藏丁丁遮遮 慌慌清清摇摇 四、照样子写词语。 遮掩遮遮掩掩认真 开心（） （）（） 五、在正确读音下面画横线。 1、我家院子里有几（jǐ jī）只小鸡，这些小鸡真可爱！ 2、我家的客厅里的茶几（jǐ jī）上有两杯水。 ★照样子，写句子。 小草从地下探出头来，那是春天的眉毛吧？ ，是 2、古诗两首 一、看拼音写词语。 Wèi lái zhuī gǎn shūdiàn kūhuáng guāng róng yěcài zhù sù gāo shāo 二、抄写古诗《草》 题目： 作者：三、比一比，组词语。 未（）烧（）枯（）徐（） 末（）浇（）姑（）除（） ★这两首诗都是描写季景色的。 ★《草》是朝大诗人写的，诗中“， 。”句最为有名，它描写了草顽强的生命力。诗中还有一对反义词，分别是________和________。★《宿新市徐公店》描写了种景物，分别是 。诗中最有意思的一句 是、 。 3、笋芽儿 一、拼一拼，写一写。 shì jiè sǔn yá hūhuàn shān gāng hōng dòng 二、读一读，并照样子，写一写。 啊，多么明亮、多么美丽的世界呀！ 三、按课文内容填空。 1、笋芽儿被叫醒了。她（）眼睛，（）懒腰，（）四周一片漆黑，撒娇地说：“是谁在叫我呀” 2、春雨姑娘（）着她，（）着她。太阳公公（）着她，（）着她。笋芽儿脱下一件件衣服，长成了一株（）的竹子。她站在山冈上，（）地喊着：“我长大啦！”四、比一比，再组词。 岗（）界（）笋（）牙（）喊 （）呼（） 刚（）介（）笛（）芽（）减 （）乎（） 部编版三年级语文下册同步练习 20. 肥皂泡 一、看拼音写词语。 féi zào cháng láng mù wǎn tòu míng jiāo ruǎn yǎng tóu yí chuàn fēi yuè yīng ér xī wàng 二、给下列加点字选择正确的读音，打“√”。 1、几个同学散．（sǎn sàn）漫得在操场上散．（sǎn sàn）步。 2、若用扇．(shān shàn)子在下面轻轻地扇．(shān shàn)送,有时它能飞得很高很高。 三、比一比，再组词。 皂（）透（）婴（）娇（）希（） 泉（）诱（）耍（）骄（）杀（） 四、照样子，完成练习。 例：无声地散裂无声地（）无声地（） 例：轻轻地扇轻轻地（）轻轻地（） 例：颤巍巍（ABB式）（）（）（）（） 五、我会查字典，给加点字选择正确的解释。 “仰”字按部首查字法应先查（）部，再查（）画。按音序查字法应先查大写字母（），再查音节（）。“仰”字在字典里的解释有：①脸向上，与“俯”相对；②敬慕；③依赖；给下列加点字选择正确的解释，填序号。 仰．起头（）久仰．大名（）仰．仗（） 六、择合适的词语填空。（填序号） ①颤巍巍②软悠悠③轻飘飘④慢腾腾 1.不知为什么，我这几天头晕眼花，走起路来感觉________的。 2.轻轻地一提，那轻圆的球儿便从管上落了下来，_______地在空中飘游。 3.他做事总是像老牛拉破车，_______的。 4.有时吹得太大了，扇得太急了，这脆薄的球，会扯成长圆的形式，______的，光影零乱。 七、按要求完成句子练习。 1. 把句子写具体。 ①薄球就散裂了。___________________________________________________________ ②浮光在球面上乱转。______________________________________________________ 2.我把用剩的碎肥皂放在一只小木碗里。（改为“被”字句） ____________________________________________________________________________ 3.小时候，我喜欢玩吹泡泡、滚铁环、西瓜等游戏。（修改病句） ___________________________________________________________________________ 七、阅读课文片段,完成练习 方法是把用剩的碎肥皂放在一只小木碗里，加上点水，（），使它融化，然后 ．．用一 支竹笔的套管，蘸上那黏稠的肥皂水，（）地吹起，吹起一个（）的网球大小 的泡儿，再．（）地一提，那轻圆的球儿，便从管上落了下来，（）地在空中飘游。若用扇子在下面（）地扇送，有时它能飞得很高很高。 1.根据课文内容填空。 2.这是写（）肥皂泡和（）肥皂泡的过程。 3.用“”画出做肥皂水方法的句子。 4.用“先……然后……再……”说一说吹肥皂泡的过程。 . 八、快乐阅读。 种一片树叶 冰心 埋下一片树叶，固执地相信它终会长成一棵参天大树。这便是儿时最美的梦。 我4岁那年的秋天，枯黄的叶子从高高的树枝上飘落，正在院中玩耍的我俯身拾起一片， 觉得很美。玩赏了半天，我忽发一个奇怪的想法：这个曾经是树伯伯身上一部分的叶，把它 种进土里之后，必定可以长出一棵同样的大树! 于是我捡了许多片叶子，虔诚地跪在地上挖了个小坑，把树叶全埋到了土里。就像妈妈 生下了我，我也会渐渐长大—样，我坚定地相信我的梦马上可以实现。 我天天蹲在种树叶的地方等待我的大树，直到大雪纷飞。我想叶子大概怕冷，所以不敢 出来，等明年开春，一定会长得更好!我依旧固执地坚守着自己的梦，直到燕子衔泥，杨树吐 汽车的重要性《英语作文》 The automobile has become one of the most important means/ways of transportation in the world since it was invented. The automobile has completely changed the lifestyles of almost all the people in the world. In the past, animals like horses and camels were used for traveling and transporting goods. Automobiles are more comfortable and faster. Automobiles have also made it possible for us to transport large quantities of goods and people at the same time. Besides, the invention of the automobile has provided jobs for millions of people all over the world. 翻译： 汽车已经成为世界上最重要的交通工具之一，因为它是发明的。汽车已经完全改变了世界上几乎所有的人的生活方式。 在过去，像马和骆驼的动物被用来运送货物。汽车更舒适，更快速。汽车也使我们能够在同一时间运送大量货物和人。 此外，汽车的发明为全世界上百万的人提供了工作。 三一文库（https://www.wendangku.net/doc/654212478.html,） 〔我想去北京英语作文〕 我想去北京的英语作文如何写？那么，下面是小编给大家整理收集的我想去北京英语作文，供大家阅读参考。 我想去北京英语作文1 I’d like to go to a beautiful place. I think it would be Beijing. Beijing is not only our capital city, but also a famous city with long history and wonderful culture. Beijing is also China’s political and cultural center. There’re many old places of great interest, such as the Great Wall, the Summer Palace, the Forbidden City, the Temple of Heaven, and Tiananmen Square. Once you see Tiananmen Square, you will think of Beijing. It has been the symbol of Beijing since 1949. 我想去北京英语作文2 I went to Beijing more than eight times. Beijing is the capital of China. It’s a big city. I am very familiar with Beijing. It takes an hour and forty minutes from Nantong to Beijing by plane. There are many tall buildings in Beijing. It’s a modern city. My family visited the Great Wall, the Summer 必修2 Unit 1 课下作业（一~三） 课下作业（一）考点过关针对练 Ⅰ.单词拼写 1．Jim insisted that the book Mr.Black referred to was worth (值得的) reading. 2．She took one look at the horse and her heart sank (下沉)． 3．It was not until he removed (摘掉) his sunglasses that I recognized him. 4．I'll be waiting for you at the entrance (入口) to Guangzhou station. 5．The coal industry is now barely half its former (以前的) size. 6．The door opened and in came a troop of children in all sorts of fancy (奇特的) dresses. 7．Some animals are hunted illegally, so they become rare (珍贵的；稀有的)． 8．To make my room look nicer, I had the walls decorated (装饰) with paper cuts last year. Ⅱ.语境语法填空 1．?Having_removed (remove) from his hometown to the city, Zhang Qiang didn't know what ?to_do (do) at first.Under the guidance of his friend Li Ping, he made ?a fortune by doing business.He launched a campaign which ?was_designed (design) to help those in need in return ?for the society.He has done so much for the poor in his community that we can't think ?highly (high) of him enough. 2．As is known to all, cultural relics belong ?to human beings rather than individuals, so they are well worth ?protecting (protect)．However, some people are in search ?of them and take possession of them illegally.Some of them have been damaged while only a few survive.Therefore, every one of us should make all efforts to protect them from ?being_destroyed (destroy)．There is no doubt ?that it is our duty to protect cultural relics. 3．The old piano I bought years ago took up too much room, so ?by the light of the room, I ?took (take) it apart.I sold it to a waste recycling center at a low price. Ⅲ.语境改错 1．文中共有3处错误，每句中最多有两处，请找出并改正。 After removed dirt from the vase, the expert was amazed to find that it survived the Tang Dynasty.The vase was so amazingly designed that it was very worth buying at such a reasonable price. 答案：第一句：removed→removing; survived后加from 第二句：very→well 2．文中共有3处错误，每句中最多有两处，请找出并改正。 汽车英文演讲稿 篇一：汽车英语演讲稿 Good morning everyone ,today, the topic of my lecture（演讲） is “Do you love automobiles（'tmbilz）”. before I start my speech ,I want to ask a question,did there anybody present had seen the movie”the Fast and the Furious['fjrs]”.There are many cars of different styles in the movie,for example ,when you see the movie,you can find roadsters（跑车） just like Porsche（保时捷） GT3,sports utility (通用的）vehicles （车）SUV such as Volkswagen ['f:lks,va:gn]Touareg ['twɑ:reɡ](大众途锐）,even armored cars ,all of them are so powerful and beautiful. When I was a child,I dreamed I can have a car like FORD GT 40,this racing bike（跑车） is amazing and fantastic,but as time goes on ,my hobby is changing,now my favorite car is Jeep Rubicon,this is a car I really want ,it’s dynamic performance（性能） and off-road （越野） performance is top-ranking（一流的） ,which other ordinary SUV is unable to compare; the shape and color of this car is magnificent (华丽的） [mg'nfs()nt],and it’s gear-shift system（齿轮转 小学一年级介绍北京的英语作文 Beijing is an ancient city with a long history. Back in 3000 years ago in Zhou dynasty, Beijing, which was called Ji at the moment, had been named capital of Yan. Thereafter, Liao, Jin, Yuan, Ming and Qing dynasty all made Beijing their capital. Therefore, Beijing was famous for "Capital of a thousand years". The long history leaves Beijing precious cultural treasure. Winding for several kilometers in Beijing area, the Great Wall is the only man-made structure that could been seen in the space. The Summer Palace is a classic composition of ancient royal gardens, and the Forbidden City is the largest royal palaces in the world. Tiantan is where the emperor used to fete their ancestors, and also the soul of Chinese ancient constructions. The four sites above has been confirmed world cultural heritage by UNESCO. However, the best representatives for Beijing are the vanishing Hutongs and square courtyards. Through hundreds of years, they have become symbol of Beijing's life. Tian'anmen square being still brilliant today with cloverleaf junctions and skyscrapers everywhere, the old-timey scene and modern culture are combined to present a brand new visage of Beijing. As Beijing has been confirmed home city of Olympics 2008, the spirit of "green Olympics, scientific Olympics and humanized Olympic" will surely bring more and more changes to Beijing, promote the development of sports and Olympics in China as well as in the world, and strengthen the friendly communications between Chinese and foreign people. 北京是一个有着悠久历史的古城。 早在 3000 年前的周朝,北京,这叫霁,被命 名为首都燕。此后,辽、金、元、明、清都是北京首都。因此,北京著名的一千年 的“资本”。 悠久的历史使北京宝贵的文化瑰宝。绕组在北京地区几公里,长城是唯一的 人造结构,可以在空间。 颐和园是古代皇家园林的经典组合,和故宫是世界上最大 的皇家宫殿。 天坛是皇帝用来祭祀他们的祖先的地方,也是中国古代建筑的灵魂。 上面的四个网站已经确认被联合国教科文组织世界文化遗产。然而,北京最好的 代表是消失的胡同和广场庭院。数百年来,他们已经成为北京的生活的象征。天 安门广场到处都在今天依然灿烂的蝶式路口和摩天大楼的,古色古香的场景和现 代文化相结合,提出一个全新的北京的面貌。 随着北京 2008 年奥运会已被证实的家乡,精神的“绿色奥运、科技奥英语作文关于共享单车的篇精编
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