Photovoltaic maximum power point tracking control method based on the zero-crossing of the product of the fluctuating power amplitude and phase

Abstract

The present invention relates to a photovoltaic maximum power point tracking control method based on the zero-crossing of the product of the amplitude and phase of the fluctuating power, belonging to the field of photovoltaic power generation control. In the prior art, the MPPT control of a photovoltaic power generation system can be simply divided into traditional algorithms and intelligent algorithms. However, it is difficult for the traditional perturbation observation method and conductance increment method to balance the tracking speed and tracking accuracy, and the intelligent algorithm has higher requirements for the hardware computing ability due to its complex control logic. The method described in the present invention makes the photovoltaic output power fluctuate by superimposing a sinusoidal ripple on the duty cycle, extracts the amplitude and phase of the fluctuating power by using a quadrature lock-in amplifier, and realizes the accurate tracking of the maximum power point through the product of the two. When the external environment changes, the method can also adaptively adjust to capture a new maximum power point. By using the method described in the present invention, good dynamic response and steady-state performance are achieved for both static environmental conditions and dynamic environmental conditions.

Description

Technical Field

[0001] The present invention belongs to the technical field of photovoltaic power generation control, and particularly relates to a photovoltaic maximum power point tracking control method for the zero-crossing of the product of the amplitude and phase of fluctuating power. Background Art

[0002] With the aggravation of climate problems and energy crises, the demand for renewable energy is increasing day by day, setting off a wave of clean energy reforms globally. The driving force of this clean energy revolution mainly comes from solar energy and wind energy. The reason why solar energy has become one of the most concerned clean energies is that it has the following advantages: environmentally friendly, non-fossil fuel, no noise pollution, and low maintenance cost. Converting solar energy into electric energy that is convenient to use and store is mainly achieved through photovoltaic cells. Factors such as atmospheric conditions, dust, temperature, cloud cover, and geographical location will all affect the output power of photovoltaic cells. In addition, the size of the load will also significantly affect the energy collection of photovoltaic cells. Because under certain illumination conditions, there is only a single load value that can make the photovoltaic cell output at the maximum power. That is, for a changing load, the output power of the photovoltaic cell has a maximum value and is affected by environmental factors. This makes it difficult to maintain the operation of the photovoltaic system at the maximum power point, which restricts the utilization of solar energy.

[0003] To achieve the maximum power output of photovoltaic cells, most current photovoltaic power generation systems connect photovoltaic cells to loads through DC converters, and dynamically adjust the equivalent resistance of the external circuit of photovoltaic cells by adjusting the duty cycle of the DC converter, thereby performing maximum power point tracking (MPPT) of photovoltaic cells. Many MPPT methods have been proposed in the past few years to solve the problem of photovoltaic power tracking. [Xiao Yiping, Zhao Yunfeng. A MPPT control method and system based on improved particle swarm optimization algorithm [P]. Hubei Province: CN115543004A, 2022-12-30.], this patent proposes a MPPT control method based on improved particle swarm optimization algorithm. Compared with the traditional particle swarm optimization algorithm, the improved algorithm effectively shortens the time of power fluctuation, but there is still a large power fluctuation in the initial stage of startup and when the environment suddenly changes. [Sun Shaohui, Wang Shi, Zheng Lixiang. MPPT power fast tracking algorithm [P]. Guangdong Province: CN115344078A, 2022-11-15.], this patent uses the least squares method to fit and track the maximum power point of photovoltaic. When starting for the first time and when the environment changes, the output power curve of the photovoltaic cell is fitted by scanning the voltage and current output by the photovoltaic cell. The principle of this method is relatively simple, but it requires loading and scanning every time the working point changes, and the relationship between the number of iterations and the tracking accuracy is not introduced in detail in the patent, nor is there any support from simulation and experimental results. [Wang Jianchun, Huang Bangfu, Fang Gang, Huang Min. Photovoltaic static and dynamic MPPT perturbation observation and identification method and photovoltaic array power generation system [P]. Anhui Province: CN114879806A, 2022-08-09.], this patent introduces a static and dynamic MPPT perturbation observation and identification method. Compared with the traditional perturbation observation method, it increases the adjustment of the perturbation direction in the unconventional perturbation state, but there is still a large power fluctuation in the steady state, and the unconventional perturbation state will prolong the tracking time. Summary of the Invention

[0004] Aiming at the coupling problem of tracking speed and tracking accuracy commonly existing in the existing MPPT technologies, the purpose of the present invention is to balance the tracking speed and tracking accuracy of maximum power point tracking, and be able to adaptively adjust the working point according to environmental changes, thereby improving the utilization efficiency of photovoltaic energy.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is: a photovoltaic maximum power point tracking control method for the zero-crossing of the product of the amplitude and phase of the fluctuating power, including the following steps:

[0006] (1) Adopt the perturbation injection control method, and superimpose a sine perturbation with an amplitude of A m , and a frequency of f on the duty cycle to make the photovoltaic output power fluctuate;

[0007] (2) Extract the amplitude R(k) and phase θ(k) of the fluctuating photovoltaic output power, and calculate the product of the two, which is the amplitude-phase product APP of the fluctuating power;

[0008] (3) Perform Gaussian filtering on the amplitude-phase product of the fluctuating power calculated in step (2) to make the zero-crossing of the amplitude-phase product curve of the fluctuating power transition smoothly. To eliminate the zero-crossing delay of the amplitude-phase product of the fluctuating power caused by Gaussian filtering, a compensation amount C is designed v , and subtract the compensation amount from the amplitude-phase product of the fluctuating power to eliminate the zero-crossing delay;

[0009] (4) According to the functional relationship between the perturbation duty ratio and the fluctuating power, the relationship between the amplitude-phase product and the duty ratio can be obtained, so as to perform maximum power point tracking and capture. Compare the amplitude-phase product of the fluctuating power with the MPPT control target, and the error of the comparison outputs the duty ratio through a proportional-integral regulator, and then adjusts the tracking direction of the photovoltaic MPPT in real time until the stable MPPT control target is reached;

[0010] (5) When it is recognized that the maximum power point has changed, return to step (2) to re-perform maximum power point tracking;

[0011] Furthermore, the sinusoidal perturbation superimposed on the duty ratio in step (1) is continuously generated by the control program, without the assistance of additional equipment, and the perturbation amplitude A m is variable and is calculated according to the following formula:

[0012]

[0013] In the formula, V pv represents the output voltage of the photovoltaic cell, and I pv represents the output current of the photovoltaic cell.

[0014] Furthermore, in step (2), an orthogonal phase-locked amplifier is used to extract the amplitude R(k) and phase θ(k) of the fluctuating photovoltaic output power, and the calculation is carried out according to the following formula:

[0015]

[0016]

[0017] In the formula, y x (k) and y y (k) represent the in-phase component and the quadrature component of the output of the orthogonal phase-locked amplifier.

[0018] Furthermore, the Gaussian filtering compensation amount C described in step (3) v The calculation formula is as follows:

[0019]

[0020] Wherein, Gauss step represents the normalized Gaussian filtering coefficient, and APP π represents the amplitude of the photovoltaic power fluctuation when the phase is π, and this value can be output by the quadrature phase-locked amplifier. For a determined Gaussian kernel Gauss step is a determined value, and its calculation formula is as follows:

[0021]

[0022] Wherein, f(-n), f(0), f(n) represent the elements of the Gaussian kernel.

[0023] Furthermore, the functional relationship satisfied by the perturbation duty cycle and the fluctuating power in step (4) is different for Boost and Buck converters, but the power shows a trend of increasing first and then decreasing as the duty cycle increases, and the expression is as follows:

[0024]

[0025]

[0026] Wherein, P pv-Buck and P pv-Boost respectively represent the output powers when the photovoltaic cell is connected to Buck and Boost converters at the back, V pv represents the output voltage of the photovoltaic cell, R load represents the load resistance, d represents the duty cycle, and r represents the equivalent internal resistance of the photovoltaic cell.

[0027] Even further, the MPPT control target in step (4) is:

[0028] APP = R(k)×θ(k) = 0

[0029] Wherein, APP represents the amplitude-phase product of the fluctuating power, R(k) represents the amplitude of the fluctuating power, and θ(k) represents the phase of the fluctuating power relative to the reference signal.

[0030] The expression of the duty cycle output by the PI regulator is as follows:

[0031]

[0032] Wherein, K p and K i respectively represent the proportional coefficient and the integral coefficient of the PI regulator.

[0033] Even further, the relationship between the amplitude-phase product and the duty cycle in step (4) is described as:

[0034]

[0035] When the duty cycle is on the left side of the maximum power point, APP>0, and the duty cycle will increase until the MPPT stable condition APP = 0 is reached; when the duty cycle is on the left side of the maximum power point, APP<0, and the duty cycle will decrease until the MPPT stable condition APP = 0 is reached.

[0036] Furthermore, the method for identifying the change of the maximum power point in step (5) is as follows:

[0037] When the system operates stably at the maximum power point, according to the control objective of MPPT, APP = 0 is satisfied. Changes in the environment will cause the power of the maximum power point to rise or fall, that is, a new maximum power point is generated. Since the duty cycle cannot change suddenly, if the new maximum power point shifts to the right, then APP>0 instantaneously during the environmental change, and the duty cycle will increase to match the new maximum power point. If the new maximum power point shifts to the left, then APP<0 instantaneously during the environmental change, and the duty cycle will decrease to match the new maximum power point.

[0038] The effects of the present invention are as follows: The present invention is directed to a photovoltaic power generation system composed of a photovoltaic cell, a DC-DC converter, and a load. By superimposing a sine ripple on the duty cycle to cause fluctuations in the photovoltaic output power, an orthogonal lock-in amplifier is used to extract the amplitude and phase of the fluctuating power, and the maximum power point is adaptively tracked and captured through the product of the two. At the same time, Gaussian filtering is used in this paper to solve the non-smooth problem of the amplitude-phase product curve, and a compensation method is proposed to eliminate the zero-crossing offset of the amplitude-phase product caused by Gaussian filtering. When the external environment changes, this method can adaptively adjust to track the new maximum power point. Using the method described in the present invention, good tracking speed and tracking accuracy are achieved for both static environment conditions and dynamic environment conditions. Description of the Drawings

[0039] Figure 1 Structure diagram of the photovoltaic power generation system;

[0040] Figure 2 Schematic diagram of the MPPT control method for the zero-crossing of the proposed fluctuating power amplitude-phase product;

[0041] Figure 3 Lock-in amplifier (a) Time-domain analysis (b) Frequency-domain analysis;

[0042] Figure 4 Schematic diagram of the proposed zero-crossing compensation method;

[0043] Figure 5 (a) Schematic diagram of the perturbed duty cycle and the fluctuating power (b) Relationship curve between the amplitude-phase product and the duty cycle;

[0044] Figure 6Schematic diagram of the tracking effect of the maximum power point;

[0045] Figure 7 Implementation results of the proposed MPPT control method at 100W;

[0046] Figure 8 Implementation results of the proposed MPPT control method at 1000W;

[0047] Figure 9 Experimental results of the proposed MPPT control method under enhanced light conditions;

[0048] Figure 10 Experimental results of the proposed MPPT control method under weakened light conditions;

[0049] Figure 11 Tracking efficiency of the proposed MPPT control method; Detailed implementation method

[0050] The present invention will be described in detail below in conjunction with the accompanying drawings and the detailed implementation method.

[0051] Figure 1 The following shows the structure diagram of the photovoltaic power generation system to which the proposed MPPT control method of the zero-crossing of the amplitude-phase product of the fluctuating power is applied. In the present invention, the Boost circuit is used for detailed description. In the figure, V pv represents the output voltage of the photovoltaic cell, I pv represents the output current of the photovoltaic cell, I0 represents the reverse saturation current of the photovoltaic array, R p represents the parallel equivalent resistance, R s represents the series equivalent resistance, R load represents the load resistance, L represents the inductor, Q1 and Q2 represent the switching tubes, C high and C low represent the high- and low-voltage side capacitors. The data shown in Table 1 and Table 2 are the experimental parameters involved in the description.

[0052] Table 1 Experimental parameters of the photovoltaic MPPT control with zero-crossing of the amplitude-phase product of the fluctuating power in a static environment

[0053]

[0054] Table 2 Experimental parameters of the photovoltaic MPPT control with zero-crossing of the amplitude-phase product of the fluctuating power in a dynamic environment

[0055]

[0056] For Figure 1 the system shown, the present invention provides a photovoltaic maximum power point tracking control method with zero-crossing of the amplitude-phase product of the fluctuating power, which specifically includes the following steps:

[0057] Step (1), Figure 1 In the system shown, the duty cycle of the Boost converter starts from the lower limit. After startup, a perturbation with a changing amplitude is superimposed on the duty cycle. The perturbation amplitude is the reciprocal of the photovoltaic output power, and the photovoltaic output power fluctuates accordingly. Among them, the perturbation amplitude A m is calculated according to the following formula:

[0058]

[0059] In the formula, V pv represents the output voltage of the photovoltaic cell, and I pv represents the output current of the photovoltaic cell.

[0060] Step (2), the fluctuating photovoltaic power is used as the input of the phase-locked amplifier. Taking a given reference signal as the standard, the fluctuating power passes through the phase-locked amplifier to output the amplitude R(k) and phase θ(k) of the fluctuating power. The product of the two is the amplitude-phase product APP. Figure 3 Analyzed from the frequency domain perspective, the photovoltaic power P pv contains a DC component and multiple harmonic components. The phase-locked amplifier first suppresses the components with frequencies different from the reference signal to prevent them from affecting the output result. Then, the extracted signal is mixed with the reference signal for demodulation into a DC signal and a double-frequency AC signal. The demodulated DC signal contains the amplitude and phase information of the input signal. Finally, the double-frequency signal is filtered out by a low-pass filter. In the figure, T s represents the sampling period, T MPPT represents the MPPT control period, f c represents the reference signal frequency, and P pv (ω), R(ω) and REF(ω) respectively represent the frequency-domain expressions of the time-domain signals photovoltaic power P pv , the amplitude R(k) of the photovoltaic power fluctuation, and the reference signal REF. The expressions for the amplitude R(k) and phase θ(k) of the fluctuating power output by the phase-locked amplifier are as follows:

[0061]

[0062]

[0063] Step (3), perform Gaussian filtering on the amplitude-phase product of the fluctuating power calculated in step (2). Then design the compensation amount Cv, and subtract the compensation amount from the amplitude-phase product of the fluctuating power to eliminate the zero-crossing delay.

[0064] In step (4), according to the functional relationship between the perturbation duty cycle and the fluctuating power, the relationship between the amplitude-phase product and the duty cycle can be obtained, so as to perform maximum power point tracking and capture. Then, the amplitude-phase product of the fluctuating power is compared with the MPPT control target, and the error of the comparison outputs the duty cycle through a proportional-integral regulator to adjust the tracking direction of the photovoltaic MPPT in real time until the stable MPPT control target is reached.

[0065] In step (5), when it is recognized that the maximum power point changes, return to step (2) to re-perform maximum power point tracking.

[0066] In step (3), Figure 4 shows the Gaussian filtering and compensation process of the amplitude-phase product. The amplitude-phase product after Gaussian filtering can be expressed as:

[0067]

[0068] In the formula, f(-n), f(0), f(n) represent the elements of the Gaussian kernel. The smoothing effect of the Gaussian filter is affected by the selection of the standard deviation and the Gaussian kernel. The larger the standard deviation and the Gaussian kernel, the better the smoothing effect on the signal, but the more serious the signal lag. The APP curve after Gaussian filtering is as shown by the dotted line in Figure 4 The purpose of smoothing the amplitude-phase product in the method proposed in the present invention is to accurately capture the zero-crossing point, and only the change trend is required for the part outside the zero-crossing point. Based on this, the present invention designs a zero-crossing compensation method to eliminate the delay caused by Gaussian filtering. The APP curve after compensation is as shown by the dot-dashed line in Figure 3 The proposed method eliminates the delayed zero-crossing point by shifting the amplitude-phase product curve after Gaussian filtering downward by the compensation amount C v The compensation amount C v is calculated according to the following formula:

[0069]

[0070] where Gauss step represents the normalized Gaussian filtering coefficient, and APP π represents point a in Figure 3 . The Gaussian filtering of point a gives point b. Taking the Gaussian filtering with a Gaussian kernel of size 3 and a standard deviation of 1 as an example, substituting it into the g(k) expression, the Gaussian kernel is calculated as f(3) = [0.2419, 0.3989, 0.2419]. For the sampling data on both sides of point a, it is known as π and -π respectively. Thus, the filtered data group at the zero-crossing point is [π, π, -π], and then the normalized Gaussian filtering coefficient Gauss step = 0.726 can be obtained.

[0071] In step (4), the functional relationship between the perturbation duty cycle and the fluctuating power for the Boost converter is expressed as follows:

[0072]

[0073] In the formula, P pv-Boost represents the output power of the photovoltaic cell, V pv represents the output voltage of the photovoltaic cell, R load represents the load resistance, d represents the duty cycle, and r represents the equivalent internal resistance of the photovoltaic cell. Figure 5 (a) shows the relationship curve between the perturbation duty cycle and the fluctuating power. It can be seen from the figure that the photovoltaic power first increases and then decreases with the increase of the duty cycle. Therefore, a sinusoidal ripple can be injected at the reference duty cycle. When the reference duty cycle is on the left side of the MPP, the photovoltaic power will generate fluctuations with the same frequency and phase as the injected ripple signal. When the reference duty cycle is on the right side of the MPP, the photovoltaic power will generate fluctuations with the same frequency but opposite phase as the injected ripple signal. When the reference duty cycle is at the MPP, the photovoltaic power will generate small fluctuations at double frequency.

[0074] Furthermore, the relationship between the amplitude-phase product and the duty cycle in step (4) is as Figure 5 (b) shows. As the duty cycle increases, the amplitude-phase product monotonically decreases and is 0 at the MPP. Therefore, the MPPT control objective described in step (4) is:

[0075] APP = R(k)×θ(k) = 0

[0076] The expression of the duty cycle output by the PI regulator is:

[0077]

[0078] In the formula, K p and K i represent the proportional coefficient and the integral coefficient of the PI regulator respectively. The relationship between the amplitude-phase product and the duty cycle is as Figure 5 (b) shows. As the duty cycle increases, the amplitude-phase product (APP) shows a monotonically decreasing trend, and the operating point corresponding to the zero-crossing point is the photovoltaic MPP to be tracked.

[0079] Figure 6It shows the process of the described MPPT control method for tracking the maximum power point and the way to cope with environmental changes. In the figure, a1-a4, b1-b4, c1, and c2 represent the operating points of the photovoltaic power generation system. MPP1 represents the maximum power point under strong light, and MPP2 represents the maximum power point under weak light. When the photovoltaic power generation system operates at the operating points a1-a4, the duty ratio of the DC converter is on the left side of the MPP duty ratio. At this time, APP>0, and the duty ratio will increase. The operating points a1 and a2 gradually approach MPP1, and a3 and a4 gradually approach MPP2 until the MPPT stable condition APP = 0 is reached. When the photovoltaic power generation system operates at the operating points b1-b4, the duty ratio of the DC converter is on the right side of the MPP duty ratio. At this time, APP<0, and the duty ratio will decrease. The operating points b1 and b2 gradually approach MPP1, and b3 and b4 gradually approach MPP2 until the MPPT stable condition APP = 0 is reached. For the working conditions where the external environment changes.

[0080] In step (5), the method for identifying the change of the maximum power point is as follows: If the photovoltaic power generation system is operating stably at MPP1 under strong light conditions and encounters a decrease in light intensity. Since the duty ratio of the DC converter cannot change suddenly, the operating point of the photovoltaic power generation system will change from MPP1 to c2. At this time, the MPPT stable condition APP = 0 is broken, and the APP corresponding to the c2 point is >0, and the duty ratio will increase, and finally reach the stable condition at MPP2. If the photovoltaic power generation system is operating stably at MPP2 under weak light conditions and encounters an increase in light intensity. Since the duty ratio of the DC converter cannot change suddenly, the operating point of the photovoltaic power generation system will change from MPP2 to c1. At this time, the MPPT stable condition APP = 0 is broken, and the APP corresponding to the c1 point is <0, and the duty ratio will decrease, and finally reach the stable condition at MPP1.

[0081] Finally, the experimental effect of the method used in the present invention is referred to Figures 7 to 10 , Figure 7 and Figure 8 The working condition data of Figure 9 and Figure 10 correspond to Table 1, Figure 11 and the working condition data of

[0082] The present invention can be implemented in other specific forms without departing from its spirit or essential characteristics. The described embodiments are considered to be illustrative rather than restrictive in all respects. For example:

[0083] 1) The topology of the selected DC-DC converter;

[0084] 2) The selected Gaussian kernel size and the position of the photovoltaic operating point under environmental changes;

[0085] 3) The selection of various photovoltaic parameters in the experiment, etc.

[0086] Therefore, the scope of the present invention is indicated by the appended claims rather than the above description. All changes that fall within the meaning and scope of equivalent technical solutions of the claims are included in its scope.

Claims

1. A photovoltaic maximum power point tracking control method based on the zero-crossing of the amplitude-phase product of fluctuating power, characterized in that: (1) Adopt the disturbance injection control method to superimpose a sine disturbance with an amplitude of A on the duty cycle m , with a frequency of f, to cause fluctuations in the photovoltaic output power; (2) Extract the amplitude R(k) and phase θ(k) of the fluctuating photovoltaic output power, and calculate the product of the two, which is the amplitude-phase product APP of the fluctuating power; (3) Perform Gaussian filtering on the product of the amplitude and phase of the fluctuating power calculated in step (2) to make the zero-crossing of the product curve of the amplitude and phase of the fluctuating power have a smooth transition, and calculate the Gaussian filtering compensation amount C v , and apply it to the product of the amplitude and phase of the fluctuating power to eliminate the zero-crossing delay of the product of the amplitude and phase of the fluctuating power caused by Gaussian filtering; (4) According to the functional relationship between the perturbation duty ratio and the fluctuating power, the relationship between the amplitude-phase product and the duty ratio can be obtained, so as to perform maximum power point tracking and capture. Compare the amplitude-phase product of the fluctuating power with the maximum power point tracking control target. The error of the comparison outputs the duty ratio through a proportional-integral regulator, and then adjusts the tracking direction of the photovoltaic maximum power point in real time until the stable maximum power point is reached; (5) When it is recognized that a new maximum power point is generated due to a change in the external environment, return to step (2) to re-perform maximum power point tracking.

2. The photovoltaic maximum power point tracking control method with zero-crossing of the product of the amplitude and phase of the fluctuating power as described in claim 1, characterized in that: The sine perturbation superimposed on the duty cycle in step (1) is continuously generated by the control program without the assistance of additional equipment, and the perturbation amplitude A m is variable, and its calculation formula is as follows: Wherein, V pv represents the output voltage of the photovoltaic cell, and I pv represents the output current of the photovoltaic cell.

3. A photovoltaic maximum power point tracking control method for the zero-crossing of the product of the amplitude and phase of the fluctuating power as described in claim 1, characterized in that: In the above step (2), the extraction of the amplitude R and phase θ of the fluctuating photovoltaic output power is realized by an orthogonal phase-locked amplifier, and the calculation formula is as follows: where y x (k) and y y (k) represent the output of the quadrature lock-in amplifier.

4. A photovoltaic maximum power point tracking control method with zero crossing of the product of the amplitude and phase of the fluctuating power as described in claim 1, characterized in that: The Gaussian filtering compensation amount C described in step (3) v The calculation formula is as follows: where, Gauss step represents the normalized Gaussian filtering coefficient, APP π represents the fluctuation amplitude of the photovoltaic power when the phase is π, and this value can be output by an orthogonal phase-locked amplifier. For a determined Gaussian kernel Gauss step is a determined value, and its calculation formula is as follows: Where f(-n), f(0), f(n) represent the elements of the Gaussian kernel.

5. The photovoltaic maximum power point tracking control method with zero crossing of the product of the amplitude and phase of the fluctuating power as described in claim 1, wherein: The functional relationship between the perturbation duty ratio and the fluctuating power described in step (4) is applicable to both Boost and Buck converters, and the expression is as follows: Wherein, P pv-Buck and P pv-Boost respectively represent the output powers when a Buck converter and a Boost converter are connected behind a photovoltaic cell, V pv represents the output voltage of the photovoltaic cell, R load represents the load resistance, d represents the duty cycle, and r represents the equivalent internal resistance of the photovoltaic cell.

6. The photovoltaic maximum power point tracking control method with zero crossing of the product of the amplitude and phase of the fluctuating power as described in claim 1, characterized in that: The maximum power point tracking control target described in step (4) is: APP = R(k) × θ(k) = 0 The duty ratio expression output by the proportional-integral regulator is as follows: Where K p and K i represent the proportional coefficient and integral coefficient of the proportional-integral regulator, respectively.

7. A photovoltaic maximum power point tracking control method with zero crossing of the product of the amplitude and phase of the fluctuating power as described in claim 1, characterized in that: The relationship between the amplitude-phase product and the duty ratio described in step (4) is: When the duty ratio is on the left side of the maximum power point, APP > 0, and the duty ratio will increase until the stable condition of maximum power point tracking APP = 0 is reached; when the duty ratio is on the right side of the maximum power point, APP < 0, and the duty ratio will decrease until the stable condition of maximum power point tracking APP = 0 is reached.

8. A photovoltaic maximum power point tracking control method with zero crossing of the product of the amplitude and phase of the fluctuating power as described in claim 1, characterized in that: The method for recognizing that the external environment has changed described in step (5) is as follows: When the system is operating stably at the maximum power point, according to the control target of maximum power point tracking, APP = 0 is satisfied. A change in the environment will cause the power of the maximum power point to rise or fall, that is, a new maximum power point is generated. Since the duty ratio cannot change suddenly, if the new maximum power point moves to the right, then APP > 0 instantaneously during the environmental change, and the duty ratio will increase to match the new maximum power point; if the new maximum power point moves to the left, then APP < 0 instantaneously during the environmental change, and the duty ratio will decrease to match the new maximum power point.

Images