CN100426175C - Mixed maximum power point-tracing control method of photovoltaic water-raising system - Google Patents

Abstract

A tracking and control method for the hybridded maximum power point of the photovoltaic pumping system. It contains: a, the check and choice logo, it will turn to the step b if it is ture, or it will turn to the step d. b, the output frequency of the inverter will be adjusted the running of the multiple criteria. C, the choice logo will become untrue and the reference voltage Verf=V (n), and the real running time of the normal voltage method, tCV, will be reset, and turn to the step a, or turn to the step a. d, the output frequency of the inverter will be adjusted by the running of the normal voltage method. e, To add a control cycle into the running time of the normal voltage method, tvc, the choice logo will be true if the tvc >= TVC and turn to the step a, or it will turn directly to the step a. it adjust the output frequency by the alternative running of multiple criteria and normal voltage, it can adjust the output frequency in time and control the DC voltage effectively and assure the stable running of the system, the system owns rapid and dynamic tracking characteristics, and a good stable characteristics by taking advantage of this method .

Description

The mixed maximum power point-tracing control method of photovoltaic water-raising system

Technical field

The present invention relates to the photovoltaic power generation technology field, particularly a kind of maximum power point tracing method that is applied in the independent photovoltaic water-raising system.

Background technology

The independent photovoltaic water-raising system has broad application prospects for ecological problems such as solving human livestock drinking water from far-off regions, agricultural and shelter-forest irrigation, also can be applicable to Urban Parks's water spray view etc., has therefore obtained paying attention to widely.The independent photovoltaic water-raising system is made up of three parts shown in Figure 9: the water pump of photovoltaic battery array, special converter and use threephase asynchronous.Based on the policy of electric power storage in photovoltaic water-raising system, do not dispose accumulator, the purpose that reach simplified system, reduces cost not as retaining.

Photovoltaic cell is a kind of non-linear power, and factors such as its output characteristics and structure, material, intensity of illumination and environment temperature are closely related.According to equivalent circuit and expression formula thereof, can obtain the family curve of output voltage shown in Figure 10, electric current and power.As shown in Figure 10, output power exists maximum value, i.e. a maximum power point.Output current-voltage characteristic then is the boundary with the maximum power point, and electric current keeps constant substantially in the zone in left side, is called the constant current district, and change in voltage is less in the zone on right side, is called areas of permanent pressure.

Special converter is used to control pump rotary speed, and its control circuit is core with MCU, must possess following two functions: invert function---the direct current of photovoltaic battery array output is transformed to the required alternating current of driving motor; MPPT maximum power point tracking (MPPT) function---according to intensity of illumination real-time regulated output frequency, guarantee that system works is at maximum power point.In the independent photovoltaic water-raising system of no storage battery, the required power of water pump is directly provided by photovoltaic cell, and the VD of photovoltaic battery array descends along with increasing of frequency converter output frequency.Therefore by regulating the output frequency of frequency converter, can control the working point of photovoltaic battery array.In areas of permanent pressure, increase output frequency, in the constant current district, reduce output frequency, can realize the tracking of maximum power point.

Maximum power point-tracing control method needs to satisfy the requirement of three aspects: tracking velocity, tracking accuracy and system stability to the operation characteristic decisive role of system.Classic methods based on single order extreme value discrimination principles, by detecting output voltage and electric current, is set up single criterion according to the output characteristics of photovoltaic cell, and there are non-pressure process, disturbance observation method (PAO) in the working point of regulating system and increase node-pair method (ICT) or the like.In system and grid-connected system that energy storage link (as accumulator) is arranged, do not exist because of output voltage and cross the low problem that causes the system-down protection, classic methods can satisfy the requirement of system to control characteristic substantially.But; in the independent photovoltaic water-raising system that the present invention uses; owing to there is not accumulator that DC voltage is played a supportive role; stability problem mainly is the voltage stable problem; the dynamic perfromance of control law is undesirable slightly; will cause the photovoltaic battery array output voltage sharply to descend; the frequency converter under-voltage protection; system is out of service; for example, when too high or intensity of illumination reduces rapidly when pump rotary speed, if can not turn down the output frequency of frequency converter in time; the voltage of photovoltaic battery array will descend rapidly, cause frequency converter under-voltage protection action.Therefore, the dynamic perfromance of controller is had higher requirement.Existing photovoltaic water-raising special converter product all adopts classical maximum power tracking method, and control characteristic is not ideal enough, remains further to be improved.

Non-pressure process is ignored the influence of factors such as solar irradiance, environment temperature to maximum power point voltage, approximate thinks that the voltage of maximum power point is constant under the different operating condition.In service when surveying voltage greater than setting maximum power point reference voltage V _RefThe time, increase output frequency; Otherwise, then reduce output frequency.Output frequency f is by formula (7) decision, and Δ f＞0 is the frequency modulation step-length in the formula.

$f\left(n\right)=\begin{array}{c}\left\{\begin{array}{cc}f(n-1)+\mathrm{\&Delta;f}& V\left(n\right)>V_{\mathrm{ref}}\\ f(n-1)& V\left(n\right)=V_{\mathrm{ref}}\\ f(n-1)-\mathrm{\&Delta;f}& V\left(n\right)<V_{\mathrm{ref}}\end{array}\right.\end{array}---\left(7\right)$

The direct Control work point voltage of non-pressure process, the good stability of system.But, its reference voltage V _RefChoose the characteristic that depends on photovoltaic battery array, all must be to each system according to the parameter tuning V of photovoltaic battery array _Ref, versatility is relatively poor.And experiment shows that environment temperature is bigger to the voltage influence of maximum power point, if V _RefInvariable, system may depart from maximum power point when actual motion, so should manage to adjust reference voltage in real time according to the running status of system.

The PAO method is one of method that is widely used.In photovoltaic water-raising system, the basic operation of PAO method is as follows: regulate output frequency by a small margin, detect the variation of the output power P that causes therefrom, determine the frequency adjustment direction in next cycle according to the change direction of output power.Promptly

f(n)＝f(n-1)+Δf(n) (8)

$\mathrm{\&Delta;f}\left(n\right)=\left\{\begin{array}{cc}\mathrm{\&Delta;f}(n-1)& P\left(n\right)\&GreaterEqual;P(n-1)\\ -\mathrm{\&Delta;f}(n-1)& P\left(n\right)<P(n-1)\end{array}\right.---\left(9\right)$

The PAO method have versatility good, can assurance under the more stable situation of solar irradiance system from advantages such as motion tracking maximum power points; Its shortcoming is the system dynamic characteristic when considering not that solar irradiance changes fast, may select wrong speed governing direction, causes no storage battery independent photovoltaic water-raising system frequently to stop and starting.For example, when solar irradiance reduces significantly, cause that the output power of system descends continuously, this moment, frequency converter should reduce output frequency in continuous a plurality of cycles, made system stability at new maximum power point.But; according to formula (9) control strategy; in the process that output power reduces continuously; Δ f (n)=-Δ f (n-1); therefore in the process that output power reduces continuously, frequency converter replaces small size frequency reducing and raising frequency in adjacent two control cycles, and the power demand of water pump surpasses the peak power of photovoltaic battery array; cause voltage sharply to reduce, system's under-voltage protection.

The ICT method is applied to photovoltaic water-raising system, by detecting the output voltage V (n) and the electric current I (n) of photovoltaic battery array, the output voltage V (n-1) of calculating and last control cycle and electric current l's (n-1) is poor, Δ V (n)=V (n)-V (n-1), Δ I (n)=I (n)-I (n-1), can controlled rule as follows:

$f\left(n\right)=\left\{\begin{array}{cc}f(n-1)& I\left(n\right)/V\left(n\right)+\mathrm{\&Delta;I}\left(n\right)/\mathrm{\&Delta;V}\left(n\right)=0\left(\mathrm{MPP}\right)\\ f(n-1)-\mathrm{\&Delta;f}& I\left(n\right)/V\left(n\right)+\mathrm{\&Delta;I}\left(n\right)/\mathrm{\&Delta;V}\left(n\right)>0\\ f(n-1)+\mathrm{\&Delta;f}& I\left(n\right)/V\left(n\right)+\mathrm{\&Delta;I}\left(n\right)/\mathrm{\&Delta;V}\left(n\right)<0\end{array}\right.---\left(10\right)$

Can guarantee system works on the ICT law theory in maximum power point, and the dynamic perfromance of system is made moderate progress.But the criterion I/V+ Δ I/ Δ V that contains division arithmetic is not suitable for adopting the photovoltaic water-raising control system of fixed point MCU.Because in digital control system, feedback quantity I, V obtain after the A/D conversion by the testing circuit signal is carried out, and scope and precision in order to guarantee to detect, and the size of the A/D conversion value of rated voltage and electric current is more approaching usually.Therefore, in the normal regulating scope of photovoltaic water-raising control system, the result of calculation of I/V is often less than 1, and the result of calculation of Δ I/ Δ V also often drops in (1,1) scope.Because fixed point MCU only possesses the ability of handling integer, absolute value all is used as 0 processing less than 1 result of calculation, causing and incite somebody to action | all working point in I/V+ Δ I/ Δ V|＜1 all is judged as maximum power point, causes system may be trapped in continuous firing on the non-maximum power point.In addition, when solar irradiance increased fast, system should increase frequently, improves output power.But make Δ I＞0, Δ V＞0 because irradiance strengthens, formula (10) is counter does frequency reducing control, causes output frequency on the low side in short-term, has influenced the MPPT maximum power point tracking effect.

Summary of the invention

First purpose of the present invention provides a kind of maximum power point-tracing control method of photovoltaic water-raising system, and this tracking and controlling method can be applied to adopt the photovoltaic water-raising system of fixed point MCU, and has the Fast Dynamic tracking characteristics.

Second purpose of the present invention is the mixed maximum power point-tracing control method that a kind of photovoltaic water-raising system further is provided, this tracking and controlling method can be applied to adopt the photovoltaic water-raising system of fixed point MCU, make system both have the Fast Dynamic tracking characteristics, have good stable again.

For realizing above-mentioned first purpose, the maximum power point-tracing control method of photovoltaic water-raising system of the present invention is a kind of multicriterion method, it is in each control cycle TC, by detecting the output voltage V (n) and the output current I (n) of photovoltaic battery array, calculate output power P (n)=V (n) I (n), and with last control cycle to dependent variable relatively, Δ P (n)=P (n)-P (n-1), Δ V (n)=V (n)-V (n-1), Δ I (n)=I (n)-I (n-1), directly with Δ P, the symbol of Δ V and Δ I is a criterion, according to multicriterion method logic as shown in table 1, the working point of regulating system.

Table 1 multicriterion method logic

This method specifically may further comprise the steps:

Output voltage V (n), the output current I (n) of the MCU sampling photovoltaic battery array in the system, calculate output power P (n), use described output voltage V (n), output current I (n) and output power P (n) to deduct output voltage V (n-1), output current I (n-1) and output power P (n-1) in the control cycle respectively, draw voltage difference delta V, difference between current Δ I and difference power Δ P, according to the positive and negative of described voltage difference delta V, difference between current Δ I and difference power Δ P and whether be zero, one of selecting type (1)-(3) respectively

F (n)=f (n-1)+Δ f Δ P＜0 and Δ V＞0, or Δ P＞0 and Δ I 〉=0........................ (1)

f(n)＝f(n-1) ΔP＝0 ........................(2)

F (n)=f (n-1)-Δ f Δ P＜0 and Δ V≤0, or Δ P＞0 and Δ I＜0 ... ... ... ... (3)

The output frequency f (n) of inverter in the regulating system, Δ f is the frequency modulation step-length in the formula, Δ f＞0, f (n-1) is the output frequency of inverter in the last control cycle.

For realizing second purpose of the invention described above, the present invention further provides a kind of mixed maximum power point-tracing control method of photovoltaic water-raising system, this tracking and controlling method is by alternate run multicriterion method and non-pressure process, regulate output frequency, the multicriterion method performance period is (in referring to once replace, the time of operation multicriterion method) be shorter than 1 second, energy real-time follow-up maximum power point, and be next non-pressure process performance period T _CV(in referring to once replace, the time of operation non-pressure process) provides best reference voltage V _Ref, this method may further comprise the steps:

Each control cycle T of MCU in a, the system _CCheck the logical value of selecting sign k, if true, go to step b operation multicriterion method, otherwise go to steps d operation non-pressure process;

B, described multicriterion method comprise, output voltage V of photovoltaic battery array (n) and output current I (n) in the sampling system, calculate output power P (n), use described output voltage V (n), output current I (n) and output power P (n) to deduct output voltage V (n-1), output current I (n-1) and output power P (n-1) in the control cycle respectively, draw voltage difference delta V, difference between current Δ I and difference power Δ P, according to the positive and negative of described voltage difference delta V, difference between current Δ I and difference power Δ P and whether be zero, one of selecting type (1)-(3) respectively

F (n)=f (n-1)+Δ f Δ P＜0 and Δ V＞0, or Δ P＞0 and Δ I 〉=0........................ (1)

f(n)＝f(n-1) ΔP＝0 ........................(2)

F (n)=f (n-1)-Δ f Δ P＜0 and Δ V≤0, or Δ P＞0 and Δ I＜0........................ (3)

The output frequency f (n) of inverter in the regulating system, Δ f is the frequency modulation step-length in the formula, Δ f＞0, f (n-1) is the output frequency of inverter in the last control cycle;

C, if last time frequency modulation and frequency modulation last time were frequency modulation in the same way not, then make the logical value of selecting sign k be vacation, reference voltage V _Ref=V (n), non-pressure process actual execution time t _CVZero clearing goes to step a; Otherwise directly go to step a;

D, described non-pressure process comprise that the output voltage V of photovoltaic battery array (n) in the sampling system is with reference voltage V _RefRelatively, according to one of result's difference selecting type (4)-(6) of comparing

f(n)＝f(n-1)+Δf V(n)＞V _ref........................(4)

f(n)＝f(n-1) V(n)＝V _ref........................(5)

f(n)＝f(n-1)-Δf V(n)＜V _ref........................(6)

The output frequency f (n) of inverter in the regulating system, Δ f is the frequency modulation step-length in the formula, Δ f＞0, f (n-1) is the output frequency of inverter in the last control cycle;

E, make non-pressure process actual execution time t _CVAdd a control cycle T _C, again with non-pressure process performance period T _CVRelatively, work as t _CV〉=T _CVThe time, then make the logical value of selecting sign k for true, go to step a; Otherwise directly go to step a.

When MCU operation non-pressure process, the reference voltage V of employing _RefDescribed reference voltage V is provided by multicriterion method tracking Control module _RefWhen equaling in the multicriterion method to occur not in the same way frequency modulation, the output voltage V (n) of the photovoltaic battery array that current control cycle detects.

Whether multicriterion method of the present invention is according to the positive and negative of voltage difference delta V, difference between current Δ I and difference power Δ P and be zero, control effect and intensity of illumination variation that output frequency is regulated are differentiated simultaneously, it is the tracker state, and then determine the output frequency of following one-period, real-time follow-up maximum power point by corresponding computing.Owing to can differentiate simultaneously control effect and intensity of illumination variation that output frequency is regulated, the dynamic tracking characteristic of system is improved.In addition, it does not have division arithmetic, can be applied to adopt the photovoltaic water-raising system of fixed point MCU.

Its mixed maximum power point-tracing control method is regulated output frequency by alternate run multicriterion method and non-pressure process, and wherein the multicriterion method performance period is shorter than 1 second, energy real-time follow-up maximum power point, and be next non-pressure process performance period T _CVBest reference voltage level is provided.And the direct Control work point voltage of non-pressure process, the stability problem of resolution system preferably.The quick tracking characteristics of multicriterion method is combined with the good stability of non-pressure process, can in time adjust output frequency, effectively control DC voltage, guarantee system stable operation, make system both have the Fast Dynamic tracking characteristics, have good stable again.

Description of drawings

Fig. 1 is the system chart of the embodiment of the invention 1 photovoltaic water-raising system;

Fig. 2 is the process flow diagram of its multicriterion method;

Fig. 3 a, b are the experimental result of embodiment 1 photovoltaic water-raising system with multicriterion method tracking characteristics, and wherein, Fig. 3 a is the intensity of illumination curve, and Fig. 3 b is corresponding output power curve;

Fig. 4 is the process flow diagram of the mixed maximum power point-tracing control method of the embodiment of the invention 2 photovoltaic water-raising systems employing;

Fig. 5 is the process flow diagram of non-pressure process among Fig. 4;

Fig. 6 a, b be embodiment 2 photovoltaic water-raising systems under fine condition, the curve map of output power and output voltage;

Fig. 7 a, b be embodiment 2 photovoltaic water-raising systems under cloudy condition, the curve map of output power and output voltage;

Fig. 8 a, b be embodiment 2 photovoltaic water-raising systems under cloudy condition, the curve map of output power and output voltage;

Fig. 9 is the basic structure of independent photovoltaic water-raising system;

Figure 10 is photovoltaic battery array P-V (I-V) family curve.

Embodiment

Be described further below in conjunction with accompanying drawing.

Embodiment 1:

As shown in Figure 1, this photovoltaic water-raising system comprises photovoltaic battery array 1, water pump 5 and inverter 4, output terminal water pump 5 power ends of inverter 4, the input end of inverter 4 is connected to photovoltaic battery array 1 output terminal, photovoltaic battery array 1 output loop is provided with inrush current prevention circuit 2 and flat wave circuit 3, also comprises:

MCU 11, and there are multicriterion method tracking Control module and non-pressure process tracking Control module in MCU inside, are used for the alternately maximum power point of this photovoltaic water-raising system of tracking Control;

Voltage detection module 7, its input end is connected in the output terminal of photovoltaic battery array 1, and its output terminal is connected to the input end of MCU11, is used to detect the output voltage V (n) of photovoltaic battery array 1;

First current detection module 6, its input end is connected in the output terminal of photovoltaic battery array 1, and its output terminal is connected to another input end of MCU 11, is used to detect the output current I (n) of photovoltaic battery array 1;

PWM driver module 9, its input end are connected in MCU 11 output ports, and its output terminal is connected to the control end of inverter 4, are used to drive inverter;

Described MCU alternate run multicriterion method tracking Control module and non-pressure process tracking Control module, the output voltage V (n) and the output current I (n) of sampling photovoltaic battery array, calculate, and determine output frequency f (n) according to corresponding criterion and formula, PWM driver module and inverter are moved with output frequency f (n).

Two input ends that also comprise second current detection module, 10, the second current detection modules 10 are respectively to the biphase current sampling of water pump 5, and its output terminal is connected to the respective input of MCU 11, is used to monitor the working current of water pump 5.

Fault-signal module 8, the operation conditions of monitoring inverter 4 also feeds back to MCU 11.

In the present embodiment, the peak power 2200W of photovoltaic battery array 1, maximum power point voltage 350V, electric current 6.28A.

Frequency converter 4 rated power 1500W, the highest output frequency 50Hz.Water pump 5 adopts specified incoming frequency 50Hz, power 1500W, flow/lift 14 (m ³/ h)/the three-phase 220V submersible pump of 20m.MCU 11 adopts 16 fixed point MCU, implements the control of inversion control and MPPT maximum power point tracking simultaneously; The MPPT maximum power point tracking controlling unit detects input current and DC voltage by 10 A/D converters, calculates the output frequency of determining frequency converter, control cycle T according to selected method _CBe 20 milliseconds, control cycle T _CCan be set to tens of milliseconds.

Embodiment 1 photovoltaic water-raising system adopts the maximum power point of multicriterion method tracking control system, and it is at each control cycle T _CIn, by detecting the output voltage V (n) and the output current I (n) of photovoltaic battery array 1, calculate output power P (n)=V (n) I (n), and with last control cycle to dependent variable relatively, Δ P (n)=P (n)-P (n-1), Δ V (n)=V (n)-V (n-1), Δ I (n)=I (n)-I (n-1), directly the symbol with Δ P, Δ V and Δ I is a criterion, according to multicriterion method logic as shown in table 1, the working point of regulating system.

Table 1 multicriterion method logic

With reference to Fig. 2, this multicriterion method may further comprise the steps:

Output voltage V (n), the output current I (n) of the MCU 11 sampling photovoltaic battery arrays 1 in the system;

Calculate output power P (n);

Use described output voltage V (n), output current I (n) and output power P (n) to deduct output voltage V (n-1), output current I (n-1) and output power P (n-1) in the control cycle respectively, draw voltage difference delta V, difference between current Δ I and difference power Δ P;

According to the positive and negative of described voltage difference delta V, difference between current Δ I and difference power Δ P and whether be zero, regulate the output frequency f (n) of frequency converter 4, if Δ P=0, promptly P (n)=P (n-1) then makes output frequency f (n)=f (n-1),

If Δ P＜0 and Δ V＞0 then make output frequency f (n)=f (n-1)+Δ f,

If Δ P＜0 and Δ V≤0 then make output frequency f (n)=f (n-1)-Δ f,

If Δ P＞0 and Δ I 〉=0 then make output frequency f (n)=f (n-1)+Δ f,

If Δ P＞0 and Δ I＜0 then make output frequency f (n)=f (n-1)-Δ f, Δ f is the frequency modulation step-length in the formula, Δ f＞0, and f (n-1) is the output frequency of inverter 4 in the last control cycle.

As shown in table 1, whether this method is by judging the positive and negative of voltage difference delta V, difference between current Δ I and difference power Δ P and being zero, control effect and intensity of illumination variation that output frequency is regulated are differentiated simultaneously, it is the tracker state, and then determine the frequency f (n) of following one-period, thereby in time adjust output frequency by corresponding computing.It does not have division arithmetic, and the dynamic tracking characteristic of system improves.

Contrast and experiment shows, when intensity of illumination changes fast, adopts the frequent stoppage protection of system of PAO method and ICT method, and the system of employing present embodiment method then can respond fast, stable operation.Fig. 3 a, b are for confirming the experimental result of this multicriterion method tracking characteristics, and wherein, Fig. 3 a is the intensity of illumination curve, and Fig. 3 b is corresponding output power curve.As can be seen, output power curve and intensity of illumination curve are very identical, show that system has outstanding tracking characteristics.

Embodiment 2:

The system of embodiment 2 photovoltaic water-raising systems constitutes identical with embodiment 1, difference is: embodiment 2 photovoltaic water-raising systems adopt mixed maximum power point-tracing control method to come the tracking Control maximum power point, with reference to Fig. 4, this mixed maximum power point-tracing control method alternate run multicriterion method and non-pressure process, regulate the output frequency of frequency converter, the multicriterion method performance period is shorter than 1 second, the real-time follow-up maximum power point, and be next non-pressure process performance period T _CV(about 10 seconds) provide best reference voltage level, specifically may further comprise the steps:

Each control cycle T of MCU11 in a, the system _CCheck the logical value of selecting sign k, if true (being k=1) goes to step b, otherwise go to steps d;

B, operation multicriterion method, the output frequency f (n) of adjusting frequency converter 4;

C, if last time frequency modulation and frequency modulation last time for not in the same way frequency modulation (for example: when last time being not frequency conversion or frequency reducing, be raising frequency last time; Perhaps ought last time be not frequency conversion or raising frequency, and last time be frequency reducing), then make the logical value of selecting sign k be false (being k=0), reference voltage V _Ref=V (n), non-pressure process actual execution time t _CVZero clearing goes to step a; Otherwise directly go to step a;

D, operation non-pressure process, the output frequency f (n) of adjusting frequency converter 4, wherein, the reference voltage V that adopts in the non-pressure process _RefBe reference voltage V described in the step c _Ref=V (n);

E, make non-pressure process actual execution time t _CVAdd a control cycle T _C, again with non-pressure process performance period T _CVRelatively, work as t _CV〉=T _CVThe time, then make the logical value of selecting sign k for true, go to step a; Otherwise directly go to step a.

In the practical application, non-pressure process performance period T _CVCan be set to 5～20S, time constant can be 10～30ms.

With reference to Fig. 2, MCU 11 operation multicriterion methods, the process of regulating frequency converter 4 output frequency f (n) may further comprise the steps:

Output voltage V (n), the output current I (n) of the MCU 11 sampling photovoltaic battery arrays 1 in the system;

Calculate output power P (n);

Use described output voltage V (n), output current I (n) and output power P (n) to deduct output voltage V (n-1), output current I (n-1) and output power P (n-1) in the control cycle respectively, draw voltage difference delta V, difference between current Δ I and difference power Δ P;

According to the positive and negative of described voltage difference delta V, difference between current Δ I and difference power Δ P and whether be zero, determine output frequency f (n), if Δ P=0, promptly P (n)=P (n-1) then makes output frequency f (n)=f (n-1),

If Δ P＜0 and Δ V＞0 then make output frequency f (n)=f (n-1)+Δ f,

If Δ P＜0 and Δ V≤0 then make output frequency f (n)=f (n-1)-Δ f,

If Δ P＞0 and Δ I 〉=0 then make output frequency f (n)=f (n-1)+Δ f,

If Δ P＞0 and Δ I＜0 then make output frequency f (n)=f (n-1)-Δ f, Δ f is the frequency modulation step-length in the formula, Δ f＞0, and f (n-1) is the output frequency of inverter in the last control cycle.

With reference to Fig. 5, MCU 11 operation non-pressure processs, the process of regulating frequency converter 4 output frequency f (n) may further comprise the steps:

The output voltage V of photovoltaic battery array 1 (n) in the sampling system,

With output voltage V (n) and reference voltage V _RefRelatively, if V (n)=V _Ref, then make output frequency f (n)=f (n-1),

If V (n)＞V _Ref, then make output frequency f (n)=f (n-1)+Δ f,

If V (n)＜V _Ref, then making output frequency f (n)=f (n-1)-Δ f, Δ f is the frequency modulation step-length in the formula, Δ f＞0, f (n-1) is the output frequency of inverter in the last control cycle.

Fig. 6-Fig. 8 is for adopting the experimental result of mixed maximum power point tracking Control; all performance is good under different weather conditions; especially when intensity of illumination changes fast; as shown in Figure 7; adopt the system of mixed maximum power point-tracing control method then can in time adjust output frequency; effectively the control DC voltage guarantees system stable operation, and adopts the system of classical maximum power point-tracing control method system often to be arranged because of under-voltage protection phenomenon out of service.

Claims (4)

1, the mixed maximum power point-tracing control method of photovoltaic water-raising system is characterized in that may further comprise the steps:

Each control cycle T of MCU in a, the system _CCheck the logical value of selecting sign k, if true, go to step b operation multicriterion method, otherwise go to steps d operation non-pressure process;

B, described multicriterion method comprise, output voltage V of photovoltaic battery array (n) and output current I (n) in the sampling system, calculate output power P (n), use described output voltage V (n), output current I (n) and output power P (n) to deduct output voltage V (n-1), output current I (n-1) and output power P (n-1) in the control cycle respectively, draw voltage difference delta V, difference between current Δ I and difference power Δ P, according to the positive and negative of described voltage difference delta V, difference between current Δ I and difference power Δ P and whether be zero, one of selecting type (1)-(3) respectively

F (n)=f (n-1)+Δ f Δ P＜0 and Δ V＞0, or Δ P＞0 and Δ I 〉=0 ... ... ... ... (1)

f(n)＝f(n-1) ΔP＝0 ........................(2)

F (n)=f (n-1)-Δ f Δ P＜0 and Δ V≤0, or Δ P＞0 and Δ I＜0........................ (3)

The output frequency f (n) of inverter in the regulating system, Δ f is the frequency modulation step-length in the formula, Δ f＞0, f (n-1) is the output frequency of inverter in the last control cycle;

C, if last time frequency modulation and frequency modulation last time were frequency modulation in the same way not, then make the logical value of selecting sign k be vacation, reference voltage V _Ref=V (n), non-pressure process actual execution time t _CVZero clearing goes to step a; Otherwise directly go to step a;

D, described non-pressure process comprise that the output voltage V of photovoltaic battery array (n) in the sampling system is with reference voltage V _RefRelatively, according to one of result's difference selecting type (4)-(6) of comparing

f(n)＝f(n-1)+Δf V(n)＞V _ref........................(4)

f(n)＝f(n-1) V(n)＝V _ref........................(5)

f(n)＝f(n-1)-Δf V(n)＜V _ref........................(6)

The output frequency f (n) of inverter in the regulating system, Δ f is the frequency modulation step-length in the formula, Δ f＞0, f (n-1) is the output frequency of inverter in the last control cycle;

E, make non-pressure process actual execution time t _CVAdd a control cycle T _C, again with non-pressure process performance period T _CVRelatively, work as t _CV〉=T _CVThe time, then make the logical value of selecting sign k for true, go to step a; Otherwise directly go to step a.

2, the mixed maximum power point-tracing control method of photovoltaic water-raising system according to claim 1 is characterized in that: in steps d, and described non-pressure process performance period T _CVBe 5～20S, control cycle T _C10～30ms.

3, the mixed maximum power point-tracing control method of photovoltaic water-raising system according to claim 1 is characterized in that: when MCU operation non-pressure process, and the reference voltage V of employing _RefDescribed reference voltage V is provided by multicriterion method tracking Control module _RefWhen equaling in the multicriterion method to occur not in the same way frequency modulation, the output voltage V (n) of the photovoltaic battery array that current control cycle detects.

4, the multicriterion maximum power point-tracing control method of photovoltaic water-raising system is characterized in that may further comprise the steps:

Output voltage V (n), the output current I (n) of the MCU sampling photovoltaic battery array in the system, calculate output power P (n), use described output voltage V (n), output current I (n) and output power P (n) to deduct output voltage V (n-1), output current I (n-1) and output power P (n-1) in the control cycle respectively, draw voltage difference delta V, difference between current Δ I and difference power Δ P, according to the positive and negative of described voltage difference delta V, difference between current Δ I and difference power Δ P and whether be zero, one of selecting type (1)-(3) respectively

F (n)=f (n-1)+Δ f Δ P＜0 and Δ V＞0, or Δ P＞0 and Δ I 〉=0 ... ... ... ... (1)

f(n)＝f(n-1) ΔP＝0 ........................(2)

F (n)=f (n-1)-Δ f Δ P＜0 and Δ V≤0, or Δ P＞0 and Δ I＜0 ... ... ... ... (3)

The output frequency f (n) of inverter in the regulating system, Δ f is the frequency modulation step-length in the formula, Δ f＞0, f (n-1) is the output frequency of inverter in the last control cycle.

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