CN105045332B - A kind of MPPT control method being applicable to photovoltaic cell - Google Patents

Abstract

The present invention relates to a kind of MPPT control method being applicable to photovoltaic cell, use bilinear method of approximation and little step-length disturbance observational method to combine and carry out the MPPT tracking of photovoltaic cell, first set up two maximum power point voltages and ambient temperature according to photovoltaic cell equivalent model, near linear between intensity of sunshine, then according to the ambient temperature gathered, intensity of sunshine and two near linears determine maximum power point voltage, the pwm pulse signal driving switching device is generated by photovoltaic cell actual output voltage and maximum power point voltage difference after being regulated by PI again, photovoltaic cell is adjusted near maximum power point, disturbance observational method accurate tracking maximum power point finally by little step-length.The present invention has quick, efficient, the advantage of precise control, and algorithm is simple simultaneously, require low to controller, and Project Realization is convenient.

Description

A kind of MPPT control method being applicable to photovoltaic cell

Technical field

The present invention relates to solar photovoltaic technology field, especially relate to a kind of MPPT control being applicable to photovoltaic cell Method processed.

Background technology

Solar energy is the energy clean, pollution-free, that be available anywhere, and inexhaustible, nexhaustible.Fossil energy by Gradually today of shortage, solar energy becomes one of world new forms of energy doing one's utmost development.But solar-energy photo-voltaic cell is one Planting the power supply of extremely unstable, photoelectric transformation efficiency is low is its key factor developed of restriction.MPPT maximum power point tracking (Maxim Power Point Tracking, MPPT) proposition of technology, make the photoelectric transformation efficiency of solar-energy photo-voltaic cell greatly be carried High.

Conventional fixed voltage method principle is simple, be easily achieved, but control accuracy ratio is relatively low；Disturbance observational method has vibration The shortcoming that amplitude is big or tracking velocity is slow；Conductance increment rule is high to hardware requirement, needs high-speed a/d to sample；Fuzzy adaptive Answering method and neural network scheduling algorithm the most complicated, Practical Project realizes difficult；Simple straight-line approximation method excessively depends on itself Rely the equivalent model of photovoltaic cell, and partial straight lines approximate rele ignores the impact on equivalent model of temperature or intensity of sunshine, makes Become arithmetic accuracy the highest.

The most existing technology haves much room for improvement and develops.

Summary of the invention

The technical problem to be solved in the present invention is to propose a kind of MPPT control method with Project Realization feasibility, energy Follow the tracks of maximum power of photovoltaic cell point quickly, efficiently and accurately, thus improve the photoelectric transformation efficiency of photovoltaic cell.

For solving above-mentioned technical problem, the technical scheme that the present invention takes is as follows:

A kind of MPPT control method being applicable to photovoltaic cell, it is characterised in that: use bilinear method of approximation and little step-length Disturbance observational method combines and carries out the MPPT tracking of photovoltaic cell.First set up two peak powers according to photovoltaic cell equivalent model Near linear between point voltage and ambient temperature, intensity of sunshine, then according to ambient temperature, intensity of sunshine and two gathered Near linear determines maximum power point voltage, then is passed through PI by photovoltaic cell actual output voltage and maximum power point voltage difference Generate the pwm pulse signal driving switching device after regulation, photovoltaic cell is adjusted near maximum power point, finally by little The disturbance observational method accurate tracking maximum power point of step-length.

Further, comprise the following steps:

(1), according to the equivalent model of actually used photovoltaic cell, set up between maximum power point voltage and intensity of sunshine Near linear V '_mpp(S_i), and the near linear V between maximum power point voltage and temperature_mpp(T)。

(2), Real-time Collection photovoltaic cell output voltage V, output electric current I, and ambient temperature T, intensity of sunshine S_i。

(3), according to intensity of sunshine S_iWith straight line V '_mpp(S_i) determine maximum power point voltage V '_mpp。

(4), according to temperature T, maximum power point voltage V '_mppWith straight line V_mpp(T) maximum power point voltage V is determined_mpp。

(5), by voltage V and maximum power point voltage V_mppDifference generate drive switching device pwm pulse signal, directly To V=V_mpp。

(6), the regulation photovoltaic cell output voltage V of little step-length, make the output power from photovoltaic cells reach maximum power point.

(7), computing environment temperature T, intensity of sunshine S_iVariable quantity, if variable quantity is excessive, i.e. return step (3), again Determine maximum power point voltage V '_mppAnd V_mpp。

Further, near linear V '_mpp(S_i) form be V '_mpp=k_siS_i+ b, wherein coefficient k_siWith b by photovoltaic cell Equivalent model determine.

Further, near linear V_mpp(T) form is V_mpp=V '_mpp+k_T(25-T), wherein coefficient k_TBy photovoltaic cell Equivalent model determine, and with intensity of sunshine is relevant.

Described coefficient k_T, k_TForm be k_T=kS_i, wherein coefficient k is determined by the equivalent model of photovoltaic cell.

Further, photovoltaic cell output voltage V and maximum power point voltage V_mppDifference regulated by PI after generate and drive The pwm pulse signal of dynamic switching device so that photovoltaic cell output voltage V reaches V_mppTime the shortest, can reach 30ms with In.

Further, the step-length of disturbance observational method regulation photovoltaic cell output voltage V is smaller, less than 0.1V.

Further, after entering little step-length disturbance observational method step, monitoring of environmental temperature T, intensity of sunshine S simultaneously_iIf, Both variable quantities are excessive, be again through bilinear method of approximation estimated maximum power point voltage V_mpp。

Compared with prior art, beneficial effects of the present invention:

(1) bilinear method of approximation can accurately be followed the tracks of maximum power of photovoltaic cell point and be followed the change of ambient temperature, intensity of sunshine Change, and rapidly the output power from photovoltaic cells is adjusted near maximum power point, the tracking velocity overcoming general algorithm is slow, Adapt to the defect of environmental change difference.

(2) use of little step-length disturbance observational method avoids the defect that conventional disturbance observational method oscillation amplitude is big, also overcomes Simple straight-line approximation method excessively relies on the weakness of photovoltaic cell equivalent model.

(3) this algorithm quickly, efficiently, precise control, engineering realizability is strong, requires low to controller.

Accompanying drawing explanation

The software flow pattern of Fig. 1 present invention

During Fig. 2 T=25 DEG C, V_mpp-S_iCharacteristic curve and near linear

Fig. 3 S_i=100mW/cm²Time, V_mpp-T characteristic curve and near linear

Fig. 4 S_i=20mW/cm²、40mW/cm²、60mW/cm²、80mW/cm²、100mW/cm²Time, V_mpp-T characteristic curve

The hardware system block diagram that Fig. 5 present invention realizes

Detailed description of the invention

The present invention is described in detail with detailed description of the invention below in conjunction with the accompanying drawings.

Fig. 1 show a preferred embodiment of the invention, including step implemented as described below:

Step S1, equivalent model according to actually used photovoltaic cell, set up maximum power point voltage and intensity of sunshine S_i Between near linear V '_mpp(S_i), and the near linear V between maximum power point voltage and temperature T_mpp(T)。

Inference process is as follows:

The mathematic(al) representation of photovoltaic cell equivalent model is as follows:

$I=I_{\mathrm{ph}}-I_{\mathrm{sat}}[\exp \left(\frac{\mathrm{qV}}{\mathrm{kTA}}\right)-1]$

I_ph=[I_sso+K_i(T-T_r)]S_i/100

$I_{\mathrm{sat}}=I_{\mathrm{rr}}{\left[\frac{T}{T_r}\right]}^3\exp \left[\frac{q{E}_{\mathrm{Gap}}}{\mathrm{kA}}(\frac{1}{T_r}-\frac{1}{T})\right]$

In formula, I, V are photovoltaic cell output electric current and voltage respectively；I_phIt it is the electric current of photovoltaic cell generation；I_satIt is anti- To saturation current；Q is the quantity of electric charge of an electronics；K is Boltzmann constant；T is the temperature of photovoltaic cell；A is photovoltaic cell Ideality factor；I_ssoIt it is the short circuit current under standard conditions；K_iIt it is the short circuit current temperature coefficient of photovoltaic cell；T_rIt it is photovoltaic electric The reference temperature in pond；S_iIt it is intensity of sunshine；I_rrIt is that photovoltaic cell is in temperature T_rTime reverse saturation current；E_GapIt it is quasiconductor material Energy during band gap crossed over by material.

The output power from photovoltaic cells P=VI, orderTry to achieve maximum power point voltage V_mpp:

$V_{\mathrm{mpp}}=\frac{\mathrm{kTA}}{q}\ln \left[\frac{I_{\mathrm{ph}}+I_{\mathrm{sat}}}{I_{\mathrm{sat}}+I_{\mathrm{sat}}q{V}_{\mathrm{mpp}}/\left(\mathrm{kTA}\right)}\right]$

Understand, temperature T and intensity of sunshine S_iChange directly influence V_mppNumerical value, and V_mppDirectly determine photovoltaic electric The maximum power point in pond.V_mppSolve and can be completed by Newton iteration method.

Fig. 2 be typical case photovoltaic cell Solarex MSX60 60W be 25 DEG C at T, S_iFrom 20mW/cm²Change to 100mW/ cm²Time, V_mppAnd S_iBetween relation curve, and with V '_mpp=k_siS_iThe straight line of+b formal approximation.It is found that two lines it Between error not over 0.4V.Coefficient k near linear_siCan obtain according to Fig. 2 with b.

Fig. 3 is that typical case photovoltaic cell Solarex MSX60 60W is at S_iFor 100mW/cm², T in time changing to 85 DEG C for 25 DEG C, V_mppAnd the relation curve between T, and use V_mpp=V '_mpp+k_T(25-T) straight line of formal approximation.It is found that two lines it Between error not over 0.1V.Now V ' near linear_mppIt is S in Fig. 2_iFor 100mW/cm²Time corresponding peak power Point voltage value.

Fig. 4 is that typical case photovoltaic cell Solarex MSX60 60W is at S_iIt is respectively 20mW/cm²、40mW/cm²、60mW/ cm², 80mW/cm²、100mW/cm², T in time changing to 85 DEG C for 25 DEG C, V_mppAnd the relation curve between T.Visible, S_iFor difference During value, V_mppVariable quantity is different.Therefore, k_TForm be k_T=kS_i, wherein coefficient k is determined by Fig. 4.

Step S2, Real-time Collection photovoltaic cell output voltage V, output electric current I, and ambient temperature T, intensity of sunshine S_i。 If scene is furnished with environment detector, then ambient temperature T, intensity of sunshine S_iData by environment detector by communications interface transmission to MPPT controller, reduces the hardware cost of the present invention.

Step S3, according to gather intensity of sunshine S_iWith near linear V '_mpp(S_i) determine current S_iTime maximum power point electricity Pressure V '_mppValue.

Step S4, temperature T according to gathering, maximum power point voltage V '_mppWith near linear V_mpp(T) current temperature is determined Maximum power point voltage V under degree, current intensity of sunshine_mpp。

Step S5, by voltage V and maximum power point voltage V_mppDifference generate drive switching device pwm pulse signal, Until V=V_mpp。

Fig. 5 is the hardware system block diagram that the present invention realizes, and DC-DC conversion section uses conventional BOOST boost chopper electricity Road.The voltage V gathered and maximum power point voltage V_mppDifference regulated by PI after generate pwm signal, to control power device The dutycycle of S thus reach dynamically to change the purpose of the external equivalent load of photovoltaic cell.

Step S6, the regulation photovoltaic cell output voltage V of little step-length, make the output power from photovoltaic cells reach peak power Point.

There is error due to photovoltaic cell equivalent model and bilinear approximation there is also error, cause peak power There is error in point voltage and maximum power point theoretical value and actual value, so observing photovoltaic cell is defeated by the disturbance of little step-length Go out power and be adjusted to real maximum power point.

Step S7, computing environment temperature T, intensity of sunshine S_iVariable quantity, if variable quantity is excessive, i.e. return step S3, weight New estimated maximum power point voltage V '_mppAnd V_mpp。

The disturbance of little step-length is observed when adjusting maximum power point, also needs real-time monitoring of environmental temperature T, intensity of sunshine S_iChange Change amount, if variable quantity is excessive, needs to re-evaluate maximum power point voltage V ' by bilinear method of approximation_mppAnd V_mpp。

The foregoing is only presently preferred embodiments of the present invention, not in order to limit the present invention, all essences in the present invention Any amendment, equivalent and the improvement etc. made within god and principle, should be included within the scope of the present invention.

Claims (5)

1. the MPPT control method being applicable to photovoltaic cell, it is characterised in that: use bilinear method of approximation and little step-length to disturb Dynamic observational method combines and carries out the MPPT tracking of photovoltaic cell；First set up two maximum power points according to photovoltaic cell equivalent model Near linear between voltage and ambient temperature, intensity of sunshine, then near according to ambient temperature, intensity of sunshine and two gathered Determine maximum power point voltage like straight line, then adjusted by PI by photovoltaic cell actual output voltage and maximum power point voltage difference Generate the pwm pulse signal driving switching device after joint, photovoltaic cell is adjusted near maximum power point, finally by small step Long disturbance observational method accurate tracking maximum power point, comprises the following steps:

(1) according to the equivalent model of actually used photovoltaic cell, the approximation between maximum power point voltage and intensity of sunshine is set up Straight line V '_mpp(S_i), and the near linear V between maximum power point voltage and ambient temperature_mpp(T), wherein, near linear V′_mpp(S_i) form be V '_mpp=k_siS_i+ b, wherein coefficient k_siDetermine by the equivalent model of photovoltaic cell with b；Near linear V_mpp(T) form is V_mpp=V '_mpp+k_T(25-T), wherein coefficient k_TDetermined by the equivalent model of photovoltaic cell, and with day Relevant according to intensity；

(2) Real-time Collection photovoltaic cell output voltage V, output electric current I, and ambient temperature T, intensity of sunshine S_i；

(3) according to intensity of sunshine S_iWith straight line V '_mpp(S_i) determine maximum power point voltage V '_mpp；

(4) according to temperature T, maximum power point voltage V '_mppWith straight line V_mpp(T) maximum power point voltage V is determined_mpp；

(5) by voltage V and maximum power point voltage V_mppDifference generate the pwm pulse signal driving switching device, until V= V_mpp；

(6) the regulation photovoltaic cell output voltage V of little step-length, makes the output power from photovoltaic cells reach maximum power point；

(7) computing environment temperature T, intensity of sunshine S_iVariable quantity, if variable quantity is excessive, i.e. returns step (3), redefine High-power point voltage V '_mppAnd V_mpp。

The MPPT control method being applicable to photovoltaic cell the most according to claim 1, it is characterised in that k_TForm be k_T =kS_i, wherein coefficient k is determined by the equivalent model of photovoltaic cell.

A kind of MPPT control method being applicable to photovoltaic cell the most according to claim 1, it is characterised in that photovoltaic cell Output voltage V and maximum power point voltage V_mppDifference regulated by PI after generate drive switching device pwm pulse signal, Photovoltaic cell output voltage V is made to reach V_mppTime the shortest, within 30ms being reached.

A kind of MPPT control method being applicable to photovoltaic cell the most according to claim 1, it is characterised in that disturbance is observed The step-length of method regulation photovoltaic cell output voltage V is smaller, less than 0.1V.

A kind of MPPT control method being applicable to photovoltaic cell the most according to claim 1, it is characterised in that enter small step After long disturbance observational method step, monitoring of environmental temperature T, intensity of sunshine S simultaneously_iIf both variable quantities are excessive, again through double directly Line method of approximation estimated maximum power point voltage V_mpp。