CN107732966B - MPPT (maximum power point tracking) optimization control method for small wind driven generator based on duty ratio - Google Patents

MPPT (maximum power point tracking) optimization control method for small wind driven generator based on duty ratio Download PDF

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CN107732966B
CN107732966B CN201711076713.6A CN201711076713A CN107732966B CN 107732966 B CN107732966 B CN 107732966B CN 201711076713 A CN201711076713 A CN 201711076713A CN 107732966 B CN107732966 B CN 107732966B
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duty ratio
value
buck
boost converter
pwm signal
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CN107732966A (en
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胡海安
戴康
李富鹏
管宇翔
何艳明
薛陆清
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Suzhou Power Supply Co of State Grid Jiangsu Electric Power Co Ltd
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Suzhou Power Supply Co of State Grid Jiangsu Electric Power Co Ltd
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    • H02J3/386—
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05F—SYSTEMS FOR REGULATING ELECTRIC OR MAGNETIC VARIABLES
    • G05F1/00—Automatic systems in which deviations of an electric quantity from one or more predetermined values are detected at the output of the system and fed back to a device within the system to restore the detected quantity to its predetermined value or values, i.e. retroactive systems
    • G05F1/66—Regulating electric power
    • G05F1/67—Regulating electric power to the maximum power available from a generator, e.g. from solar cell
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/70—Wind energy
    • Y02E10/76—Power conversion electric or electronic aspects

Abstract

The invention relates to a duty ratio-based MPPT (maximum power point tracking) optimization control method for a small wind driven generator, which is applied to lifting connected with the small wind driven generatorIn the voltage converter, the first operation period of the small wind-driven generator is based onP‑DDetermining the tracking mode and step length based on the slope of the curveP‑DThe slope of the curve and the output power of the small wind driven generator determine the change direction of the duty ratio of the PWM signal of the buck-boost converter, finally the duty ratio of the PWM signal of the buck-boost converter in the next working period is obtained, and maximum power point tracking control is achieved. The wind energy tracking system has the advantages of high stability and high response speed of wind energy tracking, wide working wind speed range, capability of utilizing wind energy to the maximum extent, strong loading capacity and capability of tracking the maximum wind energy in a wider wind speed range.

Description

MPPT (maximum power point tracking) optimization control method for small wind driven generator based on duty ratio
Technical Field
The invention belongs to the field of new energy, and particularly relates to an MPPT control method used in small wind power generation equipment.
Background
At present, a 1-10 KW small wind driven generator is high in development speed, and the problem of electricity utilization in basic life of farmers, herders and fishermen without electricity or with less electricity is solved. However, the output of most of the existing small-sized wind driven generators directly charges the storage battery, so that the wind energy utilization coefficient is very low, generally about 0.3.
The output voltage, current and power of the small wind driven generator are affected by the change of wind conditions and loads, and in order to fully utilize the small wind driven generator to generate electricity, the maximum power of the small wind driven generator needs to be acquired in real time, the utilization efficiency of the small wind driven generator needs to be improved, and the maximum power point tracking control is carried out on the small wind driven generator. If the maximum power point tracking control of the wind driven generator is fully utilized, the annual energy production can be improved by about 20-30%.
Because the wind speed is random and intermittent and does not always run above the rated wind speed, most wind generators run below the rated wind speed, and therefore maximum power point tracking needs to be kept in a wider range, the utilization efficiency of the wind generators is improved, and more energy is obtained.
The maximum power tracking method of the small wind driven generator is multiple, different application methods have advantages and disadvantages in the actual use process, a wind measuring device is not needed based on a duty ratio disturbance observation method, the aerodynamic characteristics of a wind wheel are not needed to be known, the duty ratio is directly used as a control parameter, and the difficulty in designing a controller is reduced.
According to circuit theory, in a linear circuit, when the impedance of an external load is conjugated with the impedance of the internal resistance of a power supply, the maximum output power can be obtained, the whole system can be regarded as a linear circuit in a small time interval, and the function of a DC/DC conversion circuit in MPPT is essentially an impedance converter which plays a role of impedance conversion. That is, the input resistance of the chopper can be adjusted by adjusting the duty ratio D of the PWM signal to be equal to the change of the impedance of the wind turbine, so that the DC/DC conversion circuit and the load resistance can be regarded as an external resistive load, and the equivalent load resistance can be realized by adjusting the DC/DC converter, thereby realizing the matching of the input and output characteristics of the generator and the load impedance, and enabling the generator to operate at the optimal operating point, thereby controlling the rotation speed of the wind turbine and realizing the maximum power output, and the system structure diagram is shown in fig. 1.
Due to the randomness of wind speed and the uncertainty of some parameters, there is a problem of selecting the size of the adjustment step when adjusting the duty ratio D. If the step length is too large, the output power is at the maximum output power PmaxFluctuation near the point is increased, power loss is caused, wind energy conversion efficiency is reduced, and steady-state errors of the system are increased; if the step length is too small, the tracking time is prolonged, and the dynamic response speed of the system is influenced.
The MPPT control of the small wind driven generator actually adjusts the generator to reach the optimal rotating speed according to the change of the wind speed, and when the mechanical power input on the rotating shaft of the small wind driven generator is greater than the output power of the generator, the rotating speed of the generator is increased; otherwise, the rotation speed will decrease. Therefore, the power transmission relation between the small wind driven generator and the load can be adjusted by controlling the duty ratio of the trigger pulse of the DC/DC converter, so that the rotating speed control of the generator is realized, namely the duty ratio of the trigger pulse is increased, the electric power transmitted to the load is increased, the mechanical power input by the generator is smaller than the output electric power, and the rotating speed is reduced; conversely, if the duty ratio of the trigger pulse is reduced, the electric power transmitted to the load is also reduced, the mechanical power input by the generator is greater than the electric power output by the generator, and the rotating speed is increased. Therefore, the output electric power of the generator can be controlled by controlling the duty ratio of the PWM signal of the DC/DC converter, and the rotating speed of the generator can be further controlled.
Most DC/DC converters of the traditional wind power generation system adopt a Buck converter (Buck Chopper) or a Boost converter (Boost Chopper), and when the wind speed is low, the direct current voltage is low, so that the wind energy is not favorably utilized; when the wind speed is high, the direct current voltage is high, and the voltage reduction protection is not facilitated, so that the MPPT of the wind driven generator can work in a narrow range by the aid of the voltage increasing converter or the voltage reducing converter.
Therefore, the MPPT control method adopted by the existing small wind driven generator has the defects of narrow working range, poor stability and slow tracking response speed.
Disclosure of Invention
The invention aims to provide an MPPT (maximum power point tracking) optimization control method of a small-sized wind driven generator based on a duty ratio, which realizes better stability and higher response speed of wind energy tracking and can track in a wider wind speed range.
In order to achieve the purpose, the invention adopts the technical scheme that:
the MPPT optimization control method for the small wind driven generator based on the duty ratio is used for carrying out maximum power point tracking control on the small wind driven generator, is applied to a buck-boost converter connected with the small wind driven generator, and comprises the following steps in each working period of the small wind driven generator:
step 1: sampling the voltage U (k) and the current I (k) output by the kth working cycle of the small-sized wind driven generator, and then executing the step 2;
step 2: calculating a power value P (k) of the kth working period according to the voltage U (k) and the current I (k) output by the small wind driven generator sampled in the kth working period, and further calculating a power deviation value dP (k) between the power value P (k) of the kth working period and the power value P (k-1) of the kth working period; calculating a duty ratio deviation value dD (k) between the duty ratio D (k) of the PWM signal of the buck-boost converter in the k work period and the duty ratio D (k-1) of the PWM signal of the buck-boost converter in the k-1 work period, and then executing the step 3;
and step 3: obtaining a sampling value of a P-D curve slope corresponding to the kth working period according to the power deviation value dP (k) and the duty ratio deviation value dD (k) of the kth working periodAnd low-pass filtering the slope to obtain a filtered slope value
Figure BDA0001457948130000032
Then, executing the step 4;
and 4, step 4: comparing absolute values of the filtered slope values
Figure BDA0001457948130000033
And a scaling factor K, if
Figure BDA0001457948130000034
Step 5 is executed if
Figure BDA0001457948130000035
Then step 6 is executed;
and 5: determining to adopt a fixed step length adjusting mode, determining a step length value delta D (k) as a preset step length D, and then executing a step 7;
step 6: determining to adopt a variable step length adjusting mode, determining a step length value delta D (k) according to an adjusting coefficient L, and then executing a step 7;
and 7: comparing the absolute value | d of the duty deviation valueD (k) and a preset first positive threshold epsilon1If | dD (k) | > ε1Then step 8 is performed if | dD (k) | ≦ ε1If yes, executing step 13;
and 8: judging the slope value after filtering
Figure BDA0001457948130000036
If yes, executing step 9, otherwise executing step 10;
and step 9: calculating the duty ratio D (k +1) ═ D (k) of the PWM signal of the buck-boost converter in the k +1 th working period according to the duty ratio D (k) of the PWM signal of the buck-boost converter in the k th working period, and then executing step 18;
step 10: judging the slope value after filteringIf the value is greater than 0, executing a step 11, otherwise, executing a step 12;
step 11: calculating the duty ratio D (k +1) ═ D (k) + Δ D (k) of the PWM signal of the buck-boost converter in the k +1 th working period according to the duty ratio D (k) of the PWM signal of the buck-boost converter in the k-th working period and the step value Δ D (k) determined in step 5 or step 6, and then executing step 18;
step 12: calculating the duty ratio D (k +1) ═ D (k) - Δ D (k) of the PWM signal of the buck-boost converter in the k +1 th working period according to the duty ratio D (k) of the PWM signal of the buck-boost converter in the k-th working period and the step value Δ D (k) determined in the step 5 or the step 6, and then executing a step 18;
step 13: comparing the absolute value | dP (k) | of the power deviation value with a preset second positive number threshold epsilon2If | dP (k) | is less than or equal to epsilon2Then step 14 is performed if | dP (k) | > ε2Then, go to step 15;
step 14: calculating the duty ratio D (k +1) ═ D (k) of the PWM signal of the buck-boost converter in the k +1 th working period according to the duty ratio D (k) of the PWM signal of the buck-boost converter in the k th working period, and then executing step 18;
step 15: determining whether the power deviation value dP (k) is greater than a second positive threshold ε2If yes, executing step 16, otherwise, executing step 17;
step 16: calculating the duty ratio D (k +1) ═ D (k) + Δ D (k) of the PWM signal of the buck-boost converter in the k +1 th working period according to the duty ratio D (k) of the PWM signal of the buck-boost converter in the k-th working period and the step value Δ D (k) determined in step 5 or step 6, and then executing step 18;
and step 17: calculating the duty ratio D (k +1) ═ D (k) - Δ D (k) of the PWM signal of the buck-boost converter in the k +1 th working period according to the duty ratio D (k) of the PWM signal of the buck-boost converter in the k-th working period and the step value Δ D (k) determined in the step 5 or the step 6, and then executing a step 18;
step 18: outputting the voltage U (k) and the current I (k) of the small-sized wind driven generator in the k working period, the duty ratio D (k) of the PWM signal of the buck-boost converter and the filtered slope value
Figure BDA0001457948130000041
And assigning the duty ratio D (k +1) of the PWM signal of the buck-boost converter in the calculated (k +1) th work period for the calculation of the (k +1) th work period.
In step 2, dp (k) ═ P (k) — P (k-1), and dd (k) ═ D (k) — D (k-1).
In the step 3, the step of processing the image,
Figure BDA0001457948130000042
wherein, a is a filter coefficient,
Figure BDA0001457948130000043
is the filtered slope value in the k-1 th working cycle.
a＜＜1。
In the step 4, the value range of the scaling coefficient K is [0.9,1.1 ].
In the step 5, the preset step length D ═ Dmax，DmaxIs the maximum tracking step size.
In either said step 5 or said step 6,. DELTA.D (k). ltoreq.1.
In the step 6, the process is carried out,
in the step 7, the first positive threshold value ε1The value is 0.01.
In the step 13, the second positive threshold value ε2The value is 0.01.
Due to the application of the technical scheme, compared with the prior art, the invention has the following advantages: the invention provides an MPPT (maximum power point tracking) optimization control method of a small wind driven generator based on duty ratio, which realizes high stability and high response speed of wind energy tracking, adopts a Buck-Boost Chopper (Buck-Boost Chopper), can output voltage higher than or equal to direct current voltage at an input side, has large direct current voltage regulation range and wide working wind speed range, can utilize wind energy to the maximum extent, has strong load capacity, and can track the maximum wind energy in a wider wind speed range.
Drawings
FIG. 1 is a structure diagram of an MPPT system of a small wind driven generator.
Fig. 2 is a power-duty cycle diagram.
Fig. 3 is a flow chart of the MPPT optimization control method of the small-sized wind driven generator based on the duty ratio.
Detailed Description
The invention will be further described with reference to examples of embodiments shown in the drawings to which the invention is attached.
The first embodiment is as follows: a MPPT (maximum power point tracking) optimization control method of a small wind driven generator based on a duty ratio is applied to a DC/DC converter connected with the small wind driven generator, wherein the DC/DC converter adopts a Buck-boost converter (Buck-boost chopper).
The MPPT optimization control method of the small wind driven generator based on the duty ratio comprises the following steps: the following steps are performed in each working cycle of the small wind power generator:
step 1: sampling the output voltage U (k) and the current I (k) of the small-sized wind driven generator in the current kth work cycle by using a voltage sensor and a current sensor, and then executing the step 2.
Step 2: calculating a power value P (k) ═ U (k) × I (k) of a k-th working period according to the voltage U (k) and the current I (k) output by the small wind driven generator sampled in the k-th working period, calculating a power value P (k-1) ═ U (k-1) × I (k-1) of the k-1-th working period according to the voltage U (k-1) and the current I (k-1) output by the small wind driven generator sampled in the k-1-th working period, and further calculating a power dP (k) ═ P (k) × I (k-1) deviation value between the power value P (k) of the k-th working period and the power value P (k-1) of the k-1-th working period; and calculating a duty ratio deviation value dD (k) ═ D (k) -D (k-1) between the duty ratio D (k) of the PWM signal of the buck-boost converter in the k-th working period and the duty ratio D (k-1) of the PWM signal of the buck-boost converter in the k-1 working period, wherein the duty ratio D (k) of the PWM signal of the buck-boost converter in the k-th working period is calculated from the k-1 period and is assigned and stored in a register for calling, and then executing the step 3.
And step 3: obtaining a sampling value of a P-D curve slope corresponding to the kth working period according to the power deviation value dP (k) and the duty ratio deviation value dD (k)
Figure BDA0001457948130000061
And sampling value of P-D curve slope
Figure BDA0001457948130000062
Low pass filtering to obtain a filtered slope value
Figure BDA0001457948130000063
Wherein a is a filter coefficient, a < 1,
Figure BDA0001457948130000064
for the filtered slope value in the k-1 th duty cycle, noise, sharp glitches and ripples due to sampling and environmental changes can be filtered out using a low-pass filter, and then step 4 is performed.
And 4, step 4: comparing the absolute values of the filtered slope values
Figure BDA0001457948130000065
The value range of the scaling coefficient K is [0.9,1.1]]Generally, 1 is taken, so that the absolute value of the slope of the filtered P-D curve is
Figure BDA0001457948130000066
The result of the comparison with the scaling factor K serves as a trigger for the transition from a fixed step size to a variable step size. From FIG. 2 (wind speed V3)>Wind speed V2>Wind speed V1), the slope of the P-D curve varies with the distance from the power maximum point, the farther away from the power maximum point, the larger the absolute value of the filtered P-D curve slope, and the closer to the power maximum point, the smaller the absolute value of the filtered P-D curve slope. If it is
Figure BDA0001457948130000067
Step 5 is executed ifStep 6 is executed.
And 5: due to the absolute value of the slope of the filtered P-D curve
Figure BDA0001457948130000069
And the larger value indicates that the small wind driven generator is far away from the maximum power point, so that the fixed step adjustment mode is determined to obtain a faster dynamic response speed. Determining the step size Δ D (k) as a predetermined step size D, typically D ═ Dmax，DmaxFor the maximum tracking step, Δ D (k) ≦ 1, then step 7 is performed.
Step 6: due to the absolute value of the slope of the filtered P-D curve
Figure BDA00014579481300000610
And the smaller size indicates that the small-sized wind driven generator is near the maximum power point, so that the step-variable adjustment mode is determined to obtain smaller steady-state error. Determining a step value from the control factor L
Figure BDA0001457948130000071
The regulating coefficient L is generally [0.01,0.05 ]]A value within the range,. DELTA.D (k). ltoreq.1, is followed by step 7.
And 7: comparing the absolute value | dD (k) | of the duty deviation value with a preset smaller first positive threshold epsilon1First positive threshold epsilon1The value is 0.01, if | dD (k) | > ε1If the power output of the small wind driven generator is possibly far away from the maximum power point and needs to be judged in detail, step 8 is executed, and if | dD (k) | is less than or equal to epsilon1If it is highly possible that the power output of the small-sized wind turbine is at the maximum power point, the detailed judgment needs to be continued, and step 13 is executed.
And 8: | dD (k) | > ε1Then, the slope value after filtering is judged
Figure BDA0001457948130000072
And if not, the power output of the small wind generator is far away from the maximum power point, and then the step 10 is executed.
And step 9:
Figure BDA0001457948130000073
to explain that the slope of the P-D curve is 0 and the maximum power point is tracked, the duty ratio D (k +1) ═ D (k) of the PWM signal of the buck-boost converter in the k +1 th duty cycle is calculated from the duty ratio D (k) of the PWM signal of the buck-boost converter in the k th duty cycle, and then step 18 is executed without duty ratio adjustment.
Step 10: when in use
Figure BDA0001457948130000074
Then, the slope value after filtering is judged
Figure BDA0001457948130000075
And judging whether the slope of the P-D curve is more than 0, if so, executing the step 11, and if not, executing the step 12.
Step 11:explaining that the slope of the P-D curve is greater than 0, the duty ratio of the small wind driven generator lags behind the duty ratio at the maximum power point, and the duty ratio of the small wind driven generator needs to be increased to track the maximum power, according to the duty ratio D (k) of the PWM signal of the buck-boost converter in the k-th working cycle and the step value Δ D (k) determined in step 5 or step 6, the duty ratio D (k +1) ═ D (k) + Δ D (k) to be adopted by the PWM signal of the buck-boost converter in the k + 1-th working cycle is calculated, and then step 18 is executed.
Step 12:
Figure BDA0001457948130000077
explaining that the slope of the P-D curve is less than 0, the duty ratio of the small wind driven generator exceeds the duty ratio at the maximum power point, and the duty ratio of the small wind driven generator needs to be reduced to track the maximum power, calculating the duty ratio D (k +1) ═ D (k) - Δ D (k) to be adopted by the PWM signal of the buck-boost converter in the k +1 th working period according to the duty ratio D (k) of the PWM signal of the buck-boost converter in the k th working period and the step value Δ D (k) determined in step 5 or step 6, and then executing step 18.
Step 13: epsilon is less than or equal to | dD (k) |1Then, the absolute value | dP (k) | of the power deviation value is compared with a preset smaller second positive threshold epsilon2Second positive threshold epsilon2The value is 0.01, if | dP (k) | is less than or equal to epsilon2If the power output of the small-sized wind driven generator is basically at the maximum power point, step 14 is executed, if | dP (k) | > epsilon2And it is stated that the power output of the small wind generator is far from the maximum power point, step 15 is performed.
Step 14: calculating a duty ratio D (k +1) ═ D (k) which is required to be adopted by the PWM signal of the buck-boost converter in the k +1 th working period according to the duty ratio D (k) of the PWM signal of the buck-boost converter in the k-th working period, not adjusting the duty ratio, and then executing the step 18;
step 15: determining whether the power deviation value dP (k) is greater than a second positive threshold value epsilon2Namely, when the power is not changed or is slightly changed, the distance of the current output power tracking maximum power point is judged, if yes, the step 16 is executed, and if not, the step 17 is executed;
step 16: dP (k) > ε2When the duty ratio is unchanged or slightly changed, the power is increased, the duty ratio of the small wind driven generator lags behind the duty ratio at the maximum power point, and the duty ratio of the small wind driven generator needs to be increased to track the maximum power, then the duty ratio D (k +1) ═ D (k) + Δ D (k) to be adopted by the PWM signal of the buck-boost converter in the k +1 th working period is calculated according to the duty ratio D (k) of the PWM signal of the buck-boost converter in the k th working period and the step value Δ D (k) determined in step 5 or step 6, and then step 18 is executed;
and step 17: dP (k) < -epsilon2When the duty ratio is not changed or slightly changed, the power is reduced, the duty ratio of the small wind driven generator exceeds the duty ratio at the maximum power point, the duty ratio of the small wind driven generator needs to be reduced to track the maximum power, the duty ratio D (k) of the PWM signal of the buck-boost converter in the k-th working period and the step length value delta D (k) determined in the step 5 or the step 6 are calculated to obtain the duty ratio D (k +1) ═ D (k) -delta D (k) adopted by the PWM signal of the buck-boost converter in the k + 1-th working period, and then the step 18 is executed;
step 18: the output voltage U (k) and the current I (k) of the small and medium sized wind driven generator in the current working period, the duty ratio D (k) of the PWM signal of the buck-boost converter and the filtered slope value
Figure BDA0001457948130000081
And assigning the calculated duty ratio D (k +1) of the PWM signal of the buck-boost converter in the (k +1) th working cycle and storing the duty ratio D (k +1) in a register for the next working cycle, namely assigning U (k-1) in the register to be the kth working cycle U (k), assigning I (k-1) to be the kth working cycle I (k), assigning D (k-1) to be the kth working cycle D (k), and assigning D (k-1) to be the kth working cycle D (k)
Figure BDA0001457948130000091
Assigned to the kth duty cycleAssigning D (k) to the calculated (k +1) th work cycle D (k +1), and utilizing U (k-1), I (k-1), D (k) in the (k +1) th work cycle,
Figure BDA0001457948130000093
And new sampled U (k), I (k) are calculated.
The above embodiments are merely illustrative of the technical ideas and features of the present invention, and the purpose thereof is to enable those skilled in the art to understand the contents of the present invention and implement the present invention, and not to limit the protection scope of the present invention. All equivalent changes and modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.

Claims (10)

1. A MPPT optimization control method of a small wind driven generator based on duty ratio is used for carrying out maximum power point tracking control on the small wind driven generator and is characterized in that: the MPPT optimization control method based on the duty ratio is applied to a buck-boost converter connected with a small wind driven generator, and the following steps are executed in each working cycle of the small wind driven generator:
step 1: sampling the voltage U (k) and the current I (k) output by the kth working cycle of the small-sized wind driven generator, and then executing the step 2;
step 2: calculating a power value P (k) of the kth working period according to the voltage U (k) and the current I (k) output by the small wind driven generator sampled in the kth working period, and further calculating a power deviation value dP (k) between the power value P (k) of the kth working period and the power value P (k-1) of the kth working period; calculating a duty ratio deviation value dD (k) between the duty ratio D (k) of the PWM signal of the buck-boost converter in the k work period and the duty ratio D (k-1) of the PWM signal of the buck-boost converter in the k-1 work period, and then executing the step 3;
and step 3: the power deviation value dP (k) and the duty cycle according to the k-th duty cycleObtaining the sampling value of the slope of the P-D curve corresponding to the kth working period by the deviation value dD (k)
Figure FDA0002303912420000011
And low-pass filtering the slope to obtain a filtered slope valueThen, executing the step 4;
and 4, step 4: comparing absolute values of the filtered slope values
Figure FDA0002303912420000013
And a scaling factor K, if
Figure FDA0002303912420000014
Step 5 is executed if
Figure FDA0002303912420000015
Then step 6 is executed;
and 5: determining to adopt a fixed step length adjusting mode, determining a step length value delta D (k) as a preset step length D, and then executing a step 7;
step 6: determining to adopt a variable step length adjusting mode, determining a step length value delta D (k) according to an adjusting coefficient L, and then executing a step 7;
and 7: comparing the absolute value | dD (k) | of the duty deviation value with a preset first positive number threshold epsilon1If | dD (k) | > ε1Then step 8 is performed if | dD (k) | ≦ ε1If yes, executing step 13;
and 8: judging the slope value after filtering
Figure FDA0002303912420000016
If yes, executing step 9, otherwise executing step 10;
and step 9: calculating the duty ratio D (k +1) ═ D (k) of the PWM signal of the buck-boost converter in the k +1 th working period according to the duty ratio D (k) of the PWM signal of the buck-boost converter in the k th working period, and then executing step 18;
step 10: judging the slope value after filtering
Figure FDA0002303912420000021
If the value is greater than 0, executing a step 11, otherwise, executing a step 12;
step 11: calculating the duty ratio D (k +1) ═ D (k) + Δ D (k) of the PWM signal of the buck-boost converter in the k +1 th working period according to the duty ratio D (k) of the PWM signal of the buck-boost converter in the k-th working period and the step value Δ D (k) determined in step 5 or step 6, and then executing step 18;
step 12: calculating the duty ratio D (k +1) ═ D (k) - Δ D (k) of the PWM signal of the buck-boost converter in the k +1 th working period according to the duty ratio D (k) of the PWM signal of the buck-boost converter in the k-th working period and the step value Δ D (k) determined in the step 5 or the step 6, and then executing a step 18;
step 13: comparing the absolute value | dP (k) | of the power deviation value with a preset second positive number threshold epsilon2If | dP (k) | is less than or equal to epsilon2Then step 14 is performed if | dP (k) | > ε2Then, go to step 15;
step 14: calculating the duty ratio D (k +1) ═ D (k) of the PWM signal of the buck-boost converter in the k +1 th working period according to the duty ratio D (k) of the PWM signal of the buck-boost converter in the k th working period, and then executing step 18;
step 15: determining whether the power deviation value dP (k) is greater than a second positive threshold ε2If yes, executing step 16, otherwise, executing step 17;
step 16: calculating the duty ratio D (k +1) ═ D (k) + Δ D (k) of the PWM signal of the buck-boost converter in the k +1 th working period according to the duty ratio D (k) of the PWM signal of the buck-boost converter in the k-th working period and the step value Δ D (k) determined in step 5 or step 6, and then executing step 18;
and step 17: calculating the duty ratio D (k +1) ═ D (k) - Δ D (k) of the PWM signal of the buck-boost converter in the k +1 th working period according to the duty ratio D (k) of the PWM signal of the buck-boost converter in the k-th working period and the step value Δ D (k) determined in the step 5 or the step 6, and then executing a step 18;
step 18: outputting the voltage U (k) and the current I (k) of the small-sized wind driven generator in the k working period, the duty ratio D (k) of the PWM signal of the buck-boost converter and the filtered slope value
Figure FDA0002303912420000022
And the duty ratio D (k +1) of the PWM signal of the buck-boost converter in the k +1 working period is calculated to be assigned, U (k-1) ═ U (k), I (k-1) ═ I (k), D (k-1) ═ D (k), D (k) ═ D (k +1),
Figure FDA0002303912420000031
for use in the k +1 th said duty cycle calculation.
2. The duty cycle based MPPT optimal control method for small wind power generator according to claim 1, wherein: in step 2, dp (k) ═ P (k) — P (k-1), and dd (k) ═ D (k) — D (k-1).
3. The duty cycle based MPPT optimal control method for small wind power generator according to claim 1, wherein: in the step 3, the step of processing the image,
Figure FDA0002303912420000032
wherein, a is a filter coefficient,
Figure FDA0002303912420000033
is the filtered slope value in the k-1 th working cycle.
4. The duty cycle based MPPT optimal control method for small-sized wind driven generators according to claim 3, characterized in that: a < 1.
5. The duty cycle based MPPT optimal control method for small wind power generator according to claim 1, wherein: in the step 4, the value range of the scaling coefficient K is [0.9,1.1 ].
6. The duty cycle based MPPT optimal control method for small wind power generator according to claim 1, wherein: in the step 5, the preset step length D ═ Dmax，DmaxIs the maximum tracking step size.
7. The duty cycle based MPPT optimal control method for small wind power generator according to claim 1, wherein: in either said step 5 or said step 6,. DELTA.D (k). ltoreq.1.
8. The duty cycle based MPPT optimal control method for small wind power generator according to claim 1, wherein: in the step 6, the process is carried out,
Figure FDA0002303912420000034
9. the duty cycle based MPPT optimal control method for small wind power generator according to claim 1, wherein: in the step 7, the first positive threshold value ε1The value is 0.01.
10. The duty cycle based MPPT optimal control method for small wind power generator according to claim 1, wherein: in the step 13, the second positive threshold value ε2The value is 0.01.
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