CN105071759A - Maximum power point tracking method of self-adaption variable step sizes with saturation constraint - Google Patents

Abstract

The invention discloses a maximum power point tracking method of self-adaption variable step sizes with saturation constraint. The method comprises steps of 1) establishing a photovoltaic cell model; 2) establishing a boost circuit model; 3) searching the maximum power point; and converting D into a PWM signal by use of pulse width modulation based on sawtooth wave carrier waves and allowing the PWM signal to pass through a triode in a PWM single control boost circuit. The PWM signal based on the sawtooth wave carrier waves is used for directly controlling duty ratio of the boost circuit to track the maximum power point in high efficiency; when the system environment changes suddenly, the control algorithm can reliably work so that the maximum power of the photovoltaic system can be rapidly tracked; according to the self-adaption variable step sizes of positions where the power point locates, the system is allowed to use the bigger step size to perform rapid tracking when being away from the MPP, so duty ratio near the MPP is reduced and vibration is avoided; and by adding the saturation constraint, invalid tracking caused by too big step size when the gradient value may be too big can be avoided.

Description

A kind of maximum power point tracing method of the Step-varied back propagation with saturated restriction

Technical field

The present invention relates to a kind of maximum power point tracing method of the Step-varied back propagation with saturated restriction, belong to control system technical field.

Background technology

Solar energy is the clean energy resource that can be recycled, and photovoltaic cell is the major way directly utilizing solar energy at present, and its power generation mode and conventional electric power generation pattern have the difference of essence.Photovoltaic generation has intermittent and instable feature, and the power output of photovoltaic cell is subject to the impact of intensity of illumination and ambient temperature.Thus, under the operating state of constantly change, the maximum power point adopting effective algorithm to trace into rapidly photovoltaic cell can improve the generating efficiency of photovoltaic module conscientiously.

MPPT maximum power point tracking MaximunPowerPointTracking (MPPT) controls to mainly contain the application of intelligent algorithm in tracing control such as determining voltage-tracing method (CVT), disturbance observation, conductance increment method and fuzzy control, artificial neural net, particle group optimizing.Intelligent algorithm is effective to the Nonlinear Processing of P-U curve, needs to carry out a large amount of calculating and process, so the processor of low cost can not adapt to requirement to data; Determining voltage-tracing method is not real MPPT maximum power point tracking in essence, and this tracking have ignored the impact of environment pair array output voltage, and thus just a kind of voltage stabilizing controls; Disturbance observation can produce vibration near maximum power point; And the step-length of conductance increment method and the selection of threshold value have difficulties.

Summary of the invention

In order to solve the problems of the technologies described above, the invention provides a kind of maximum power point tracing method of the Step-varied back propagation with saturated restriction.

In order to achieve the above object, the technical solution adopted in the present invention is:

A maximum power point tracing method for Step-varied back propagation with saturated restriction, comprises the following steps,

Step one, sets up photovoltaic cell model;

Photovoltaic cell model is,

$I=I_{sc\_new}-C_1{I}_{sc}\[\exp \left(\frac{U}{C_2{U}_{oc\_new}}\right)-1\]$

Wherein,

I is the instantaneous output current of photovoltaic cell;

U is the instantaneous output voltage of photovoltaic cell;

Parameter $C_1=(1-\frac{I_{m\_new}}{I_{sc\_new}})\exp (-\frac{U_{m\_new}}{C_2{U}_{oc\_new}});$

Parameter $C_2=(\frac{U_{m\_new}}{U_{sc\_new}}-1)/\ln (1-\frac{I_{m\_new}}{I_{Sc\_new}});$

U _{oc_new}＝U _oc(1-cT _new)ln(e+bG _new)；

$I_{sc\_new}=I_{sc}\frac{G}{G_{ref}}(1+{\mathrm{aT}}_{new});$

U _{m_new}＝U _m(1-cT _new)ln(e+bG _new)；

$I_{m\_new}=I_m\frac{G}{G_{ref}}\left(1+{\mathrm{aT}}_{new}\right);$

T _new＝T-T _ref；

$G_{new}=\frac{G}{G_{ref}}-1;$

U _{oc_new}, I _{sc_new}, U _{m_new}, I _{m_new}, T _new, T, G _new, G represents the open circuit voltage of photovoltaic cell under non-standard operating state, short circuit current, maximum power point voltage, maximum power point electric current respectively, ambient temperature and standard ambient temperature is poor, ambient temperature, intensity of illumination and standard light be according to intensity difference, intensity of illumination;

I _sc, U _oc, I _m, U _m, T _ref, G _refrepresent the short circuit current of photovoltaic cell under standard operating conditions, open circuit voltage, maximum power point electric current, maximum power point voltage, ambient temperature, intensity of illumination respectively; A, b, c are parameter, are the engineering experience values obtained according to the list of references published, represent the temperature difference and intensity of illumination difference to the impact of photovoltaic output voltage electric current;

Step 2, sets up booster circuit model;

Booster circuit model is,

U＝(1-D)u _dc

Wherein, D is the duty ratio of triode in booster circuit, 0≤D≤1; u _dcfor booster circuit instantaneous output voltage;

Step 3, search maximum power point;

Search strategy is:

When be positioned at maximum power point left, adopt the adaptive optimal gradient method computed duty cycle step-length of the saturated restriction of band, according to duty ratio step-length adjustment D, namely reduce D; Δ I is the difference between current between two steps, and Δ U is the voltage difference between two steps;

When be positioned at maximum power point;

When be positioned at maximum power point right, adopt the adaptive optimal gradient method computed duty cycle step-length of the saturated restriction of band, according to duty ratio step-length adjustment D, namely increase D;

The adaptive optimal gradient method of the saturated restriction of described band is using the linear scale function of P-U Optimal gradient as Step-varied back propagation size, and specific formula for calculation is,

$D_k=D_{k-1}\±\mathrm{\λ}\×\left|\frac{\mathrm{\Δ}P}{\mathrm{\Δ}U}\right|$

Wherein, λ is adaptation coefficient, is normal number;

Δ P is the difference power between two steps;

D _kfor the step-length after kth time adjustment;

D _k-1for the step-length after kth-1 adjustment;

When when being greater than the threshold value of definition, replace with the saturation value of definition

Step 4, adopts the pulse width modulation based on sawtooth waveforms carrier wave, converts D to pwm signal, controls the triode in booster circuit by pwm signal.

In photovoltaic system booster circuit, process D being converted to pwm signal is, is compared by the sawtooth waveforms of D value and codomain scope [0,1], when D is greater than sawtooth waveforms, exports 1, exports 0 when being less than sawtooth waveforms.

The beneficial effect that the present invention reaches: 1, the present invention adopts the pwm signal based on sawtooth waveforms carrier wave directly to control the duty ratio of booster circuit, to follow the tracks of maximum power point, tracking efficiency is high, when system environments is undergone mutation, control algolithm energy reliably working, traces into the maximum power point of photovoltaic system fast; 2, the present invention can position Step-varied back propagation residing for power points, make system following the tracks of fast by larger step-length away from during MPP, near MPP, reduce duty ratio step-length avoid concussion, add the excessive problem causing the excessive rear tracking of step-length to be lost efficacy of Grad that saturated restriction can be avoided occurring.

Accompanying drawing explanation

Fig. 1 is photovoltaic system structure chart.

Fig. 2 is flow chart of the present invention.

Fig. 3 is photovoltaic cell list diode equivalent circuit view.

Fig. 4 is typical photovoltaic output characteristic P-U curve.

Fig. 5 is the Step-varied back propagation conductance increment method flow chart being with saturated restriction.

Fig. 6 is that D turns PWM module design.

Fig. 7 is that sawtooth waveforms carrier wave produces pwm signal.

Fig. 8 is the output power from photovoltaic cells waveform under standard operating conditions.

Fig. 9 is illumination variation figure.

Figure 10 is temperature variation.

Figure 11 is the output power from photovoltaic cells waveform under light and temperature change.

Embodiment

Below in conjunction with accompanying drawing, the invention will be further described.Following examples only for technical scheme of the present invention is clearly described, and can not limit the scope of the invention with this.

In order to verify method of the present invention, shown in Fig. 1, design photovoltaic system, photovoltaic system is made up of photovoltaic cell, booster circuit (i.e. DC-DC circuit) and load.

As shown in Figure 2, a kind of maximum power point tracing method of the Step-varied back propagation with saturated restriction, comprises the following steps:

Step one, sets up photovoltaic cell model.

Photovoltaic cell list diode equivalent circuit according to Fig. 3, the instantaneous output current of photovoltaic cell is,

$I=I_{ph}-I_0\{\exp \[\frac{q(U+{\mathrm{IR}}_s)}{AKT}\]-1\}-\frac{U+{\mathrm{IR}}_s}{R_{sh}}$

Wherein,

U is the instantaneous output voltage of photovoltaic cell;

I _phfor photogenerated current, its value is proportional to the area of photovoltaic cell and the intensity of illumination of incident light;

I _dfor diode branch electric current;

I ₀for P-N junction effect reverse saturation current;

Q is electronics lotus (1.69 × 10 ^-19c);

A is PN junction conic constant;

K is Boltzmann constant (1.38 × 10 ^-23j/K);

T is absolute temperature;

R _s, R _shbe respectively photovoltaic cell equivalent series resistance, parallel resistance.

I in above-mentioned parameter ₀, A, R _s, R _shrelevant with ambient temperature, light intensity and operational environment, there is uncertainty.

Characterisitic parameter according to battery simplifies physical model, and obtaining photovoltaic cell model is,

$I=I_{sc\_new}-C_1{I}_{sc}\[\exp \left(\frac{U}{C_2{U}_{oc\_new}}\right)-1\]$

Wherein,

Parameter $C_1=(1-\frac{I_{m\_new}}{I_{sc\_new}})\exp (-\frac{U_{m\_new}}{C_2{U}_{oc\_new}});$

Parameter $C_2=(\frac{U_{m\_new}}{U_{sc\_new}}-1)/\ln (1-\frac{I_{m\_new}}{I_{Sc\_new}});$

U _{oc_new}＝U _oc(1-cT _new)ln(e+bG _new)；

$I_{sc\_new}=I_{sc}\frac{G}{G_{ref}}(1+{\mathrm{aT}}_{new});$

U _{m_new}＝U _m(1-cT _new)ln(e+bG _new)；

$I_{m\_new}=I_m\frac{G}{G_{ref}}\left(1+{\mathrm{aT}}_{new}\right);$

T _new＝T-T _ref；

$G_{new}=\frac{G}{G_{ref}}-1;$

U _{oc_new}, I _{sc_new}, U _{m_new}, I _{m_new}, T _new, T, G _new, G represents the open circuit voltage of photovoltaic cell under non-standard operating state, short circuit current, maximum power point voltage, maximum power point electric current respectively, ambient temperature and standard ambient temperature is poor, ambient temperature, intensity of illumination and standard light be according to intensity difference, intensity of illumination;

I _sc, U _oc, I _m, U _m, T _ref, G _refrepresent the short circuit current of photovoltaic cell under standard operating conditions, open circuit voltage, maximum power point electric current, maximum power point voltage, ambient temperature, intensity of illumination respectively; A, b, c are parameter, are the engineering experience values obtained according to the list of references published, represent the temperature difference and intensity of illumination difference to the impact of photovoltaic output voltage electric current; .

Step 2, sets up booster circuit model.

It is direct current that photovoltaic cell initially exports, but this direct current is affected by environment large and unstable, and booster circuit and switch DC booster circuit, its effect is that uncontrollable direct current is boosted into controlled direct current, namely realizes DC-DC and converts.

Boosting principle: in system shown in Figure 1 during charging process, triode S closes (triode ON), and triode plays wire and replaces, and photovoltaic cell is to inductance L _pVcharge, inductance L _pVstorage power, now diode prevents electric capacity C _dcdischarge over the ground, to electric capacity C _dcin reverse blocking state.Neglect the pressure drop on diode, electric capacity C _dcvoltage is approximately photovoltaic cell voltage; During discharge process, triode S disconnects (triode cut-off), inductance L _pVafterflow, i.e. inductance L _pVstart to electric capacity C _dccharging, makes electric capacity C _dcboth end voltage raises, and reaches the object higher than photovoltaic cell voltage.

Booster circuit model is,

U＝(1-D)u _dc

Wherein, D is the duty ratio of triode in booster circuit, 0≤D≤1; u _dcfor booster circuit instantaneous output voltage.

Step 3, search maximum power point.

Photovoltaic system exports along with intensity of illumination and ambient temperature change, and typical photovoltaic output characteristic P-U curve as shown in Figure 4.

The essence of conductance increment method search maximum power point (MPP) MaximumPowerPoint is the working point that search meets dP/dU=0, and be usually similar to Δ P/ Δ U=0 in digital control algorithm, wherein Δ U is decided by step-length, because so namely maximum power point needs to meet condition.Δ I is the difference between current between two steps, and Δ U is the voltage difference between two steps, and Δ P is the difference power between two steps.

In photovoltaic system, working control object is the switching tube duty ratio of booster circuit, and when booster circuit instantaneous output voltage is constant, U and D is inverse change, and increasing U needs to reduce D.

Search strategy is:

When be positioned at maximum power point left, according to duty ratio step-length adjustment D, namely reduce D;

When be positioned at maximum power point;

When be positioned at maximum power point right, according to duty ratio step-length adjustment D, namely increase D.

Step-length due to duty ratio is chosen and can be produced larger impact to search efficiency and effect, if fixed too little of step-length, the process of systematic search MPP can be made very long; And if fixed too large of step-length, when searching near MPP, can reforming phenomena be there is again.Therefore the adaptive optimal gradient method of the saturated restriction of band is adopted here, adaptive optimal gradient method with saturated restriction is using the linear scale function of P-U Optimal gradient as Step-varied back propagation size, main thought be positive gradient direction by choosing target function (i.e. power) as the direction of search often walking iteration, the maximum of Step wise approximation power.

Adopt the adaptive optimal gradient method computed duty cycle step-length detailed process of the saturated restriction of band as shown in Figure 5,

The formula of summing up is,

$D_k=D_{k-1}\±\mathrm{\λ}\×\left|\frac{\mathrm{\Δ}P}{\mathrm{\Δ}U}\right|$

Wherein, λ is adaptation coefficient, is normal number;

D _kfor the step-length after kth time adjustment;

D _k-1for the step-length after kth-1 adjustment;

When when being greater than the threshold value of definition, replace with the saturation value of definition

When and when near MPP point time, can diminish, step-length reduce after can near maximum power point precise search, to avoid oscillation on large scale.This algorithm according to the position Automatic adjusument duty ratio step-length of power points, can take into account search speed and search quality simultaneously.

Step 4, adopts the pulse width modulation based on sawtooth waveforms carrier wave, converts D to pwm signal, controls the triode in booster circuit by pwm signal.

Here changed by a modular converter, concrete structure as shown in Figure 6.As shown in Figure 7, the sawtooth waveforms of D value and codomain scope [0,1] compares by this module, when D is greater than sawtooth waveforms, exports 1, exports 0 when being less than sawtooth waveforms.

In order to further illustrate this law method, following parameter is arranged to photovoltaic system in Fig. 1, specifically as shown in Table 1.

Table one photovoltaic system parameter list

When intensity of illumination is 1000W/m ², when ambient temperature is 25 DEG C, the output power from photovoltaic cells as shown in Figure 8.Photovoltaic cell DC output power searches maximum power point after 0.06s, and stable operation.Explanation said method is effective.

Change the output analysis of intensity of illumination and ambient temperature as shown in Fig. 9,10 and 11.Consider that intensity of illumination in actual photovoltaic system operation and ambient temperature can change at any time, in the time simulating 0.6 second, Spline smoothing several times occurs, record the output power from photovoltaic cells.From power output waveform, find that a Spline smoothing often occurs in illumination, just can follow the tracks of the maximum power point of battery through the time of 2 ~ 3 cycles, illustrate that said method can reliably working.

In sum, said method directly adopts the pwm signal based on sawtooth waveforms carrier wave to control the duty ratio of booster circuit, to follow the tracks of maximum power point, tracking efficiency is high, when system environments is undergone mutation, control algolithm energy reliably working, traces into the maximum power point of photovoltaic system fast; Simultaneously said method can position Step-varied back propagation residing for power points, make system following the tracks of fast by larger step-length away from during MPP, near MPP, reduce duty ratio step-length avoid concussion, add the excessive problem causing the excessive rear tracking of step-length to be lost efficacy of Grad that saturated restriction can be avoided occurring.

The above is only the preferred embodiment of the present invention; it should be pointed out that for those skilled in the art, under the prerequisite not departing from the technology of the present invention principle; can also make some improvement and distortion, these improve and distortion also should be considered as protection scope of the present invention.

Claims (2)

1. be with a maximum power point tracing method for the Step-varied back propagation of saturated restriction, it is characterized in that: comprise the following steps,

Step one, sets up photovoltaic cell model;

Photovoltaic cell model is,

$I=I_{sc\_new}-C_1{I}_{sc}\[\exp \left(\frac{U}{C_2{U}_{oc\_new}}\right)-1\]$

Wherein,

I is the instantaneous output current of photovoltaic cell;

U is the instantaneous output voltage of photovoltaic cell;

Parameter $C_1=(1-\frac{I_{m\_new}}{I_{sc\_new}})\exp (-\frac{U_{m\_new}}{C_2{U}_{oc\_new}});$

Parameter $C_2=(\frac{U_{m\_new}}{U_{sc\_new}}-1)/\ln (1-\frac{I_{m\_new}}{I_{Sc\_new}});$

U _{oc_new}＝U _oc(1-cT _new)ln(e+bG _new)；

$I_{sc\_new}=I_{sc}\frac{G}{G_{ref}}(1+{\mathrm{aT}}_{new});$

U _{m_new}＝U _m(1-cT _new)ln(e+bG _new)；

$I_{m\_new}=I_m\frac{G}{G_{ref}}\left(1+{\mathrm{aT}}_{new}\right);$

T _new＝T-T _ref；

$G_{new}=\frac{G}{G_{ref}}-1;$

U _{oc_new}, I _{sc_new}, U _{m_new}, I _{m_new}, T _new, T, G _new, G represents the open circuit voltage of photovoltaic cell under non-standard operating state, short circuit current, maximum power point voltage, maximum power point electric current respectively, ambient temperature and standard ambient temperature is poor, ambient temperature, intensity of illumination and standard light be according to intensity difference, intensity of illumination;

I _sc, U _oc, I _m, U _m, T _ref, G _refrepresent the short circuit current of photovoltaic cell under standard operating conditions, open circuit voltage, maximum power point electric current, maximum power point voltage, ambient temperature, intensity of illumination respectively; A, b, c are parameter, are the engineering experience values obtained according to the list of references published, represent the temperature difference and intensity of illumination difference to the impact of photovoltaic output voltage electric current;

Step 2, sets up booster circuit model;

Booster circuit model is,

U＝(1-D)u _dc

Wherein, D is the duty ratio of triode in booster circuit, 0≤D≤1; u _dcfor booster circuit instantaneous output voltage;

Step 3, search maximum power point;

Search strategy is:

When be positioned at maximum power point left, adopt the adaptive optimal gradient method computed duty cycle step-length of the saturated restriction of band, according to duty ratio step-length adjustment D, namely reduce D; Δ I is the difference between current between two steps, and Δ U is the voltage difference between two steps;

When be positioned at maximum power point;

When be positioned at maximum power point right, adopt the adaptive optimal gradient method computed duty cycle step-length of the saturated restriction of band, according to duty ratio step-length adjustment D, namely increase D;

The adaptive optimal gradient method of the saturated restriction of described band is using the linear scale function of P-U Optimal gradient as Step-varied back propagation size, and specific formula for calculation is,

$D_k=D_{k-1}\±\mathrm{\λ}\×\left|\frac{\mathrm{\Δ}P}{\mathrm{\Δ}U}\right|$

Wherein, λ is adaptation coefficient, is normal number;

Δ P is the difference power between two steps;

D _kfor the step-length after kth time adjustment;

D _k-1for the step-length after kth-1 adjustment;

When when being greater than the threshold value of definition, replace with the saturation value of definition

Step 4, adopts the pulse width modulation based on sawtooth waveforms carrier wave, converts D to pwm signal, controls the triode in booster circuit by pwm signal.

2. be with a maximum power point tracing method for the Step-varied back propagation of saturated restriction, it is characterized in that: in photovoltaic system booster circuit, process D being converted to pwm signal is,

The sawtooth waveforms of D value and codomain scope [0,1] is compared, when D is greater than sawtooth waveforms, exports 1, when being less than sawtooth waveforms, export 0.