TWI653521B - A maximum power tracking algorithm - Google Patents

Abstract

A maximum power tracking algorithm is implemented using a control circuit. The maximum power tracking algorithm includes the following steps: measuring the output current value and output voltage value of two initial operating points of a solar power generation system to obtain (I ₁ , V ₁ ) and (I ₂ , V ₂ ); perform a simplified weighted least square method operation on the (I ₁ , V ₁ ) and (I ₂ , V ₂ ) to obtain an estimated illuminance value S _guess and An estimated temperature value T _guess , the simplified weighted least square method operation includes: ,and , Where Sf and Tf are preset illuminance values and temperature values, , , Where Isc, Is, q, K, A, and N are constants, , , ,as well as Calculate a maximum power point voltage value Vmpp according to the estimated illumination value Sguess, where ; And performing a disturbance observation method operation according to the maximum power point voltage value Vmpp to determine a voltage command.

Description

A Maximum Power Tracking Algorithm

The invention relates to a maximum power tracking method for a solar power generation system, in particular to an algorithm combining a simplified weighted least square method and a disturbance observation method to track the maximum power output point of a solar power generation system.

Since the Industrial Revolution, energy use has grown significantly. According to the distribution of global energy consumption in 2016, it is known that the current energy consumption is mainly fossil fuels and nuclear energy, with the proportion as high as 75.5%, and the second is renewable energy. However, due to the increasing demand for petroleum and fossil fuels, there has been a shortage. The carbon dioxide and methane produced by burning petroleum and fossil fuels have caused the greenhouse effect, which has caused global environmental changes and warming in recent years. In order to enable human beings to survive and develop on the earth, it has become a global consensus to use renewable energy sources that do not cause ecological warming and destruction. Solar energy is currently one of the most attractive renewable energy sources, mainly because it has abundant reserves and has a low negative impact on the environment when used. From 2009 to 2016, it can be seen that the average cost of power generation from renewable energy sources, the average cost of solar power generation is decreasing year by year. Therefore, how to develop and effectively use photovoltaic conversion equipment has become a very important subject for the development of solar power generation systems.

However, the current generation efficiency of commercial solar cells is only about 20%. Because the electrical characteristics of solar cells are non-linear and the non-linear curve has a maximum power point, and the electrical characteristics are easily affected by the illumination value and temperature, that is, the solar cells are at There is a maximum power output point under a certain fixed sunlight and temperature. Therefore, how to capture the maximum output power of solar cells to maximize the cost-effectiveness of solar cells is an important issue for the development of solar power systems, which makes the maximum power The tracking (Maximum Power Point Tracking, MPPT) algorithm plays a key role in high-efficiency solar power systems.

In order to obtain the maximum conversion power from the solar cell to optimize the photovoltaic conversion efficiency, the solar cell must be operated at the maximum power point. This operation method is called the maximum power tracking technology, and the related research of its algorithm can be divided into two major Focus:

1. When the system reaches the maximum power point, a transient tracking loss will occur. In order to strain the external environment and reduce the transient tracking loss, it is necessary for the maximum power tracking system to have an ideal transient response.

2. Even if the solar power generation system is in a steady state for a long time, in order to avoid a steady state loss when the operating point oscillates near the maximum power point in the steady state, how to increase the accuracy of the solar steady state is the solar maximum power tracking system Important topics that must be explored.

At present, the most commonly used maximum power tracking methods in commercial solar power generation systems are disturbance observation methods and incremental conductance methods. The disturbance observation method determines the control command value of the system based on the previous operating state and the power value obtained at the current operating point, while the incremental conductance method determines the control command value of the system with the power-voltage differential value.

When the value of the control variable is large, the time required for the system to track from steady state to another steady state is less, but at the steady state, the power loss caused by disturbance will become larger; on the other hand, the smaller The value of the control variable can improve the power loss caused by disturbance in the steady state, but the tracking speed will be slower. This phenomenon is generally called the tracking speed-tracking accuracy trade-off. Generally speaking, the maximum power tracking method using a fixed step for disturbance will be affected by this problem.

Some literatures point out that the traditional incremental conductance method is changed into a variable step type to determine the step size by the power change amount, the voltage change amount, the current change amount, and the scaling factor, and then the step size is corresponding to the current operating point. ; There are also literatures that use a set of proportional-integral controllers to improve the trade-off problem of the traditional fixed-step disturbance observation method, and use another set of proportional-integral controllers to determine the duty cycle to have a good transient and steady state. response. However, the use of two sets of proportional-integral controllers has a relatively large amount of calculation, which will increase the calculation load of the digital signal processor. In addition, based on the incremental conductance method, fuzzy control is applied to solar power generation systems.

However, there is still room for improvement in the tracking ability of the above method at the maximum power point, the accuracy at steady state, and whether the tracking rule can be implemented with a low-cost microcontroller. Therefore, a new maximum power tracking algorithm is urgently needed in the field. .

An object of the present invention is to disclose a maximum power tracking algorithm, which uses a simplified weighted least square method, which can estimate the illumination value quite accurately with only one estimation operation, and then obtain the maximum power point voltage. In order to achieve a simple operation and can be achieved with a low-cost microcontroller.

Another object of the present invention is to disclose a maximum power tracking algorithm, whose rise time and stabilization time in transient performance are better than the fixed-step perturbation observation method and the variable-step perturbation observation method of the conventional technology.

Another object of the present invention is to disclose a maximum power tracking algorithm. The average tracking power loss can be greatly reduced compared to the fixed step and perturbation observation methods of the variable step and the conventional method with good tracking efficiency. .

Yet another object of the present invention is to disclose a maximum power tracking algorithm that employs an appropriate estimation operation in conjunction with the disturbance observation method. The tracking results are compared with the fixed-step disturbance observation method and the variable-step disturbance observation method. Speed increased by 84.6% and 76% respectively, and tracking power loss also decreased by 68.48% and 47.5%, respectively.

In order to achieve the aforementioned purpose, a maximum power tracking algorithm is proposed, which is implemented using a control circuit. The maximum power tracking algorithm includes the following steps: measuring the output current values of two initial operating points of a solar power generation system and Output voltage values to obtain (I ₁ , V ₁ ) and (I ₂ , V ₂ ); perform a simplified weighted least square method operation on the (I ₁ , V ₁ ) and (I ₂ , V ₂ ) to obtain An estimated illuminance value S _guess and an estimated temperature value T _guess . The simplified weighted least square method operation includes:

,and

,

Where S _f and T _f are preset illuminance values and temperature values,

,

Where I _sc , I _s , q , K , A and N are constants,

, ,as well as ;

Calculate a maximum power point voltage value V _mpp according to the estimated illumination value S _guess , where ;as well as

A disturbance observation method operation is performed according to the maximum power point voltage value V _mpp to determine a voltage command.

In an embodiment, it further includes a power change threshold judgment step to re-perform the simplified weighted least square method operation when a power change is greater than a preset power change threshold to obtain a new said estimate. Measure illumination value S _guess .

In one embodiment, the preset power change threshold is 15W.

In one embodiment, the control circuit includes: a boost converter having an input terminal, a control terminal, and an output terminal. The input terminal is used for coupling with a solar cell system, and the control terminal is used for To receive a pulse width modulation signal, and the output terminal is used for coupling with a load; and a microcontroller is used to generate the voltage command and provide the pulse width modulation signal according to the voltage command.

In one embodiment, the microcontroller has a digital signal processor for performing an analog-to-digital conversion operation and a digital filtering operation on the current voltage and the current, respectively, and performing a proportional-integral operation according to the voltage command. A control operation and a pulse width modulation operation are performed to output the pulse width modulation signal.

In order to enable your reviewers to further understand the structure, characteristics, and purpose of the present invention, drawings and detailed descriptions of the preferred embodiments are attached below.

Please refer to FIG. 1, which illustrates a flowchart of steps in an embodiment of the maximum power tracking algorithm of the present invention.

As shown in the figure, the maximum power tracking algorithm of the present invention is implemented using a control circuit. The maximum power tracking algorithm includes the following steps: measuring the output current value and output of two initial operating points of a solar power generation system Voltage value to obtain (I ₁ , V ₁ ) and (I ₂ , V ₂ ); (step a);

Perform a simplified weighted least square method operation on the (I ₁ , V ₁ ) and (I ₂ , V ₂ ) to obtain an estimated illuminance value S _guess and an estimated temperature value T _guess . The Xiaoping method operations include:

,and

,

Where S _f and T _f are preset illuminance values and temperature values,

,

Where I _sc , I _s , q , K , A and N are constants, , , ,as well as ; (Step b);

Calculate a maximum power point voltage value V _mpp according to the estimated illumination value S _guess , where ; (Step c); and

A disturbance observation method is performed according to the maximum power point voltage value V _mpp to determine a voltage command (step d).

Please refer to FIG. 2, which illustrates a flowchart of steps in another embodiment of the maximum power tracking algorithm of the present invention.

As shown in the figure, it further includes a power change threshold judgment step to re-perform the simplified weighted least square method operation when a power change is greater than a preset power change threshold to obtain a new said estimate. Illumination value S _guess .

The preset power change threshold is, for example, but not limited to, 15W.

The Perturb and observe calculation is based on the curve characteristic of power versus voltage "curve rises when the maximum power is not reached, and decreases when the maximum power is exceeded". By slightly increasing or decreasing the voltage, and observing the output voltage and output power after the load changes, it is decided to generate a voltage command. This part is a conventional technology, and it will not be repeated here.

The following will explain the principle of the present invention:

Electrical characteristics of solar cells:

Please refer to FIG. 3, which shows a single diode equivalent circuit diagram of a solar cell.

As shown in the figure, the electrical characteristics of a solar cell are a non-linear power source, and its voltage and current exhibit an exponential relationship. Therefore, when the output voltage of a solar cell changes, its output current also changes accordingly. According to the equivalent circuit, it can be known that the relationship between the output voltage and the current of the solar cell is shown in equation (1).

(1)

Among them, I _T is the output current of the solar cell, I _g is the photoelectric conversion current, I _S is the reverse saturation current of the diode, and q is the carrier charge amount ( ), R _S is the series equivalent resistance, V _T is the solar cell output voltage, and K is the Bozman constant ( ), A is the dielectric constant (between 1 and 2), T is the absolute temperature value, N is the number of solar modules in series, and R _P is the parallel equivalent resistance.

The relationship between the photoelectric conversion current I _g and the illuminance value is shown in equation (2).

(2)

Among them, S is the illuminance value, the unit is W / m ² , and I _SC is the short-circuit current of the solar cell.

In general, since the value of the parallel resistance of the solar cell is much larger than the value of the series resistance, Equation (1) and Equation (2) can be integrated into Equation (3).

(3)

In order to observe the influence on the output characteristic curve of the solar cell when the illuminance value and the ambient temperature value change, the equation (3) can be rewritten into the equation (4).

(4)

Please refer to FIGS. 4a and 4b together, wherein FIG. 4a shows the power-voltage curves of the solar cell under different illumination values; and FIG. 4b shows the current-voltage curves of the solar cell under different illumination values.

Among them, the ambient temperature value is fixed at 25 ° C, and the different illuminance values are 200W / m ² , 400W / m ² , 600W / m ² , 800W / m ² and 1000W / m ² , as shown in the figure. The value is drawn from equation (3) by five solar cell output curves, and the characteristic curve will change with the change of the illumination value.

It is known from equation (2) that when the solar illuminance value is increased, the output electric energy of the semiconductor is increased due to the increase of the incident light energy, and the photoelectric conversion current of the solar cell is also increased accordingly. It is known from equation (3) that the output current of the solar cell is almost directly proportional to the photoelectric conversion current, so when the illuminance value increases, the output current of the solar cell also increases. It is known from equation (4) that due to the natural logarithmic relationship, the output voltage of the solar cell changes only slightly when the illuminance value rises.

Please refer to FIGS. 5a and 5b together, wherein FIG. 5a shows the power-voltage curves of the solar cell at different temperature values; and FIG. 5b shows the current-voltage curves of the solar cell at different temperature values.

As shown in the figure, the output characteristic curve of the solar cell is also affected by the ambient temperature value. According to equation (3), when the ambient temperature value increases, the equivalent diode current decreases and the output current of the solar cell increases slightly. Equation (4) shows that the ambient temperature value is directly proportional to the output voltage of the solar cell, but the output current of the solar cell will also increase as the temperature value rises, and it will be affected much more than the output voltage. The output voltage has little effect. On the contrary, the attenuation of the series equivalent resistance across voltage increases due to the increase of the output current, which causes a significant drop in the output voltage of the solar cell, and its output power also decreases.

Hardware architecture of solar maximum power tracking system adopted by the present invention :

Please refer to FIG. 6, which illustrates a schematic diagram of a control system architecture adopted by the present invention.

As shown in the figure, the control system architecture adopted by the present invention includes a solar cell system 100, a boost converter 200, and a microcontroller 300.

The boost converter 200 has an input terminal, a control terminal, and an output terminal. The input terminal is used for coupling with the solar cell system 100. The control terminal is used for receiving a pulse width modulation signal. The output terminal is used for coupling with a load 400.

The micro-controller 300 has a digital signal processor for sampling, voltage-analog-to-digital conversion, and digital-filtering operations on the voltage and current output by the solar cell system 100, and then performing the maximum power tracking method to generate a The voltage command generates a duty cycle through a proportional-integral control operation and a pulse width modulation operation to control the boost converter 200 to achieve the purpose of maximum power tracking.

Among them, since the output voltage of the conventional solar cell system 100 is generally too low, the boost converter 200 is used to increase the output voltage of the solar cell system 100; the microcontroller 300 is, for example but not limited to, using a low voltage. Cost of a digital signal processor to implement.

Introduction to the weighted least square method of state estimation technology:

State Estimation estimates other unknown information by observing known information in the system. Its behavior is similar to using a filter to eliminate errors in the data. The most commonly used state estimation technology is Weighted Least Square (WLS) method, and this method is based on the system measurement and the numerical relationship between system state variables to perform state estimation, as follows:

First establish the relationship between the measured value and the state variable, as shown in equation (5).

(5)

Among them, z is the measured value vector, h (x) is the measured value function, x is the state variable, and n is the error vector of the measured value.

The weighted least square method is to find the state variables of the system by solving the minimum of equation (6).

(6)

Wherein, w _i is the i th weight measured values of weight, z _i is the i-th measured value, h _i is the relationship between the measured values of the i-th vector function, J (x) is the error measured values the relationship between the function of Function, zh (x) is the Residual Vector, W is the weight vector of the measured value, [] ^T table Transposed Matrix.

Differentiate the equation (6) and make it equal to zero to find the minimum value of the error function, as shown in equation (7).

(7)

Among them, H (x) is the Jacobian matrix of the weighted least square method, and h (x) is the measurement value function, as shown in equation (8).

(8)

Equation (7) is a non-linear equation that can be solved by iterative operations, and the jth iteration is shown in equation (9).

(9)

Among them, G (x) is the gain matrix of the system, as shown in equation (10).

(10)

The entire system can be iteratively calculated until ΔX ^j converges to less than a set value, where ΔX ^{j is} as shown in equation (11). .

(11)

The invention uses the measured output current values and output voltage values of the two initial operating points as system measurement values to perform calculations to obtain an estimated system state variable of the illuminance value and temperature value.

According to the relationship between the output voltage and current in equation (3), it can be known that the photoelectric conversion current is affected by the illuminance value, and the diode current is affected by the temperature value. In the present invention, the illuminance value and temperature value are used as system state variables. And by measuring the output voltage and output current at different operating points, the illuminance value and temperature value can be estimated. Rewrite equation (6) into equation (12), and find the minimum value to estimate the illuminance value and temperature value.

(12)

Among them, J (S, T) is the error function of the weighted least square method, Is the weight of the i-th measurement, and m is the total number of measurements. J (S, T ) is then differentiated and made equal to zero to solve, as shown in equation (13).

(13)

Among them, H is a Jacobian matrix, W is a weight vector of the measured value, and ΔI is a current error vector, as shown in Equation (14), Equation (15), and Equation (16), respectively.

(14)

(15)

(16)

The equation (3) is solved differentially, as shown in equation (17) and equation (18), respectively.

(17)

(18)

Equation (13) can be solved by an iterative operation. The jth iteration can be expressed as shown in equation (19).

(19)

Among them, the present invention completes the estimation by measuring the output current value and output voltage value of two initial operating points of a solar power generation system to obtain (I ₁ , V ₁ ) and (I ₂ , V ₂ ), where The Jacobian matrix Hj, weight vector Wj, and current error vector △ Ij are shown in Equation (20), Equation (21), and Equation (22), respectively, and then iterate until △ S and △ T converge to less than one. Up to the set value, the illuminance value and temperature value can be estimated.

(20)

(twenty one)

(twenty two)

Please refer to FIG. 4a and FIG. 7 together, wherein FIG. 4a shows the power-voltage curves of the solar cell under different illuminance values; and FIG. 7 shows the tracking diagram of the present invention.

It is known from FIG. 4a that the output power-voltage curves are different under different illuminance values, and the maximum power point voltages of solar cells are also different. As shown in FIG. 7, the present invention calculates the state estimation operation of a weighted least square method by measuring two different operating points (V ₁ and V ₂ ) in the solar power-voltage curve. An estimated illuminance value and temperature value, then jump the operating point voltage to the voltage near the maximum power point (point b in the figure) of the illuminance value and perform a perturbation observation method to achieve the effect of maximum power tracking.

Please refer to FIG. 8 and FIG. 9 together, wherein FIG. 8 shows an output power-voltage curve with an illuminance value of 100 W / m ² to 1000 W / m ² ; and FIG. 9 shows an illuminance value and a maximum power point voltage curve.

8, the illumination change value of 100W / m ^2, the maximum power point voltage of each are different from each luminance value, is the dot FIG maximum power point voltage of each of the illuminance values; FIG. 9 As shown in the figure, an SV _mpp curve is made by taking the illumination value as an independent variable and the maximum power point voltage as the strain number, as shown in equation (23).

V _mpp = 16.86 S ³ -37.97 S ² +32.76 S +55.76 (23)

Among them, V _mpp is the maximum power point voltage and S is the illuminance value. The graph shows that the curve is very close to the actual maximum power point voltage. Therefore, when the illuminance value is calculated, this value can be substituted to obtain the maximum value under the illuminance value. Power point voltage.

Reasons for the estimation operation of the present invention using a simplified weighted least square method:

When performing state estimation simulation, it was found that only one estimation operation was needed to accurately estimate the illuminance value. The simulation results are shown in Table 1. Among them, the initial illumination value is 800 W / m ² and the temperature value is 50˚C. In an ideal state, the illumination value is estimated to be 1000 W / m ² and the temperature value is 25˚C.

As can be seen from Table 1, four estimation calculations are required to accurately estimate the illuminance value and temperature value, but only one estimation calculation is performed. Although the temperature value is slightly different from the ideal state, it still can Accurately estimate the illuminance value.

Table 1         <TABLE border = "1" borderColor = "# 000000" width = "85%"> <TBODY> <tr> <td> Estimated times </ td> <td> 1 </ td> <td> 2 </ td> <td> 3 </ td> <td> 4 </ td> </ tr> <tr> <td> Estimated illumination value (W / m <sup> 2 </ sup>) </ td> < td> 1000 </ td> <td> 1000 </ td> <td> 1000 </ td> <td> 1000 </ td> </ tr> <tr> <td> Estimated temperature (˚C) < / td> <td> 19.98 </ td> <td> 24.8 </ td> <td> 24.99 </ td> <td> 25 </ td> </ tr> </ TBODY> </ TABLE>

Because the present invention is mainly related to estimating the illuminance value, the state estimation process of the weighted least square method is simplified, and only one estimation operation can be performed to accurately estimate the illuminance value and perform maximum power tracking.

The simplified weighted least square method estimates the illuminance and temperature values as shown in equation (24), and the Jacobian matrix H _f and current error vector Δ I _f are as shown in equation (25) and equation (26), respectively. Among them, S _guess and T _guess are respectively the illuminance value and temperature value estimated by the state, and S _f and T _f are the illuminance value and temperature value of the first guess.

(twenty four)

(25)

(26)

This invention is related to Comparison of known technologies:

In the following, the maximum power tracking algorithm proposed by the present invention is compared with the fixed step perturbation observation method and the variable step perturbation observation method of the conventional technology to verify the feasibility and performance improvement of the present invention.

The control commands of each algorithm are updated with the maximum power tracking command every 0.2 seconds. The fixed-step perturbation observation method only tests the case where the average uniform illumination is 800W / m ² , and the present invention and the variable-step perturbation observation method It will be tested with increasing illumination changes.

In the present invention, two TYNS62610290 solar cell modules are connected in series as a system input source, and the solar cell specifications are shown in Table 2.

Table 2         <TABLE border = "1" borderColor = "# 000000" width = "85%"> <TBODY> <tr> <td> Maximum power <i> P <sub> mpp </ sub> </ i> </ td > <td> 290W </ td> <td> Open circuit voltage <i> V <sub> OC </ sub> </ i> </ td> <td> 39.54V </ td> <td> Short circuit current <i > I <sub> SC </ sub> </ i> </ td> <td> 9.41A </ td> </ tr> <tr> <td> Maximum power point voltage <i> V <sub> mpp < / sub> </ i> </ td> <td> 32.24V </ td> <td> Maximum power point current <i> I <sub> mpp </ sub> </ i> </ td> <td> 8.73A </ td> </ tr> <tr height = "0"> <td> </ td> <td> </ td> <td> </ td> <td> </ td> <td> < / td> <td> </ td> <td> </ td> <td> </ td> </ tr> </ TBODY> </ TABLE> After the solar cell module is connected in series, its corresponding experimental parameters The specifications are shown in Table 3.       

table 3         <TABLE border = "1" borderColor = "# 000000" width = "85%"> <TBODY> <tr> <td> Maximum power <i> P <sub> mpp </ sub> </ i> </ td > <td> 580W </ td> <td> Open circuit voltage <i> V <sub> OC </ sub> </ i> </ td> <td> 79.08V </ td> <td> Short circuit current <i > I <sub> SC </ sub> </ i> </ td> <td> 9.41A </ td> </ tr> <tr> <td> Maximum power point voltage <i> V <sub> mpp < / sub> </ i> </ td> <td> 64.48V </ td> <td> Maximum power point current <i> I <sub> mpp </ sub> </ i> </ td> <td> 8.73A </ td> </ tr> <tr height = "0"> <td> </ td> <td> </ td> <td> </ td> <td> </ td> <td> < / td> <td> </ td> <td> </ td> <td> </ td> </ tr> </ TBODY> </ TABLE>

( One ) The measurement results of the fixed-step perturbation observation method of the conventional technique:

Please refer to FIG. 10, which illustrates a waveform diagram of the measurement result of the fixed step perturbation observation method of the conventional technique.

Where the perturbation order is In the case of uniform illumination of 800W / m ² and temperature of 25 如图 C, as shown in the figure, the measured rise time is 3.9 seconds, the settling time is 4.8 seconds, the steady-state average power is 475.67 W, and the steady-state tracking power accuracy It is 97.97%, the tracking power loss is 4378.7 J, and the average tracking power loss is 89.02 W.

( 2. The measured results of the step-by-step perturbation observation method for the change of the conventional technology:

Please refer to FIG. 11a and FIG. 11b together, wherein FIG. 11a shows a waveform diagram of the measured result of uniform illumination of the step change disturbance observation method of the conventional technique, and FIG. 11b shows the step change disturbance observation of the conventional technique. Waveform diagram of the actual measurement results of the change in illumination.

This actual measurement is divided into two parts, the first part is the measurement of uniform illumination, and the second part is the measurement of varying illumination.

The measured part of the uniform illuminance is 800W / m ² and the temperature is 25˚C. Because the performance of the scale factor M is 0.65 is the best, so M is selected for the actual measurement. As shown in Figure 11a, the measured rise time is 2.5 seconds, the settling time is 3.2 seconds, the steady-state average power is 481.64W, the steady-state tracking power accuracy is 99.2%, the tracking power loss is 2967.32 J, and the average tracking power loss is 53.53 W.

The measured part of the illuminance changes, the illuminance changes from 300W / m ² to 800W / m ² , the temperature is 25˚C, and the scale factor M is set to 0.65 for actual measurement. As shown in Figure 11b, the best value of M at 800W / m ² is obtained. At 300W / m ² , the M value is too small, resulting in slow tracking speed and increased tracking power loss. After 800 W / m ² , the maximum power point can be quickly tracked. This also shows that it is difficult to select a scale factor for the variable step design.

( C) The measured results of the present invention:

Please refer to FIG. 12a to FIG. 12c together, where FIG. 12a is a waveform diagram of the measured result of uniform illumination of the present invention, and FIG. 12b is a waveform diagram of the measured result of variation of illumination of 300W / m ² to 800W / m ^{2 of the} present invention. 12c shows a waveform diagram of the actual measurement result of the change of the illuminance from 800 W / m ² to 100 W / m ² according to the present invention.

This actual measurement is also divided into two parts, the first part is the measurement of uniform illumination, and the second part is the measurement of varying illumination.

The measured part of the uniform illuminance is 800W / m ² and the temperature is 25˚C. As shown in Figure 12a, the measured rise time is 0.6 seconds, the settling time is 0.8 seconds, the steady-state average power is 481.25 W, the steady-state tracking power accuracy is 99.12%, the tracking power loss is 696.16 J, and the average tracking power loss is 28.06. W.

The measured part of the illuminance is changed from 300W / m ² to 800W / m ² and the temperature is 25 2C. The results are shown in Figure 12b. The illuminance is changed from 800W / m ² to 100W / m ² and the temperature is 25. When ˚C is measured from high illuminance to low illuminance, the results are shown in Figure 12c. It can be seen that after the illuminance changes, it only needs to measure two operating points to jump back to the vicinity of the maximum power point for disturbance, which is consistent with the theoretical derivation.

( 4. Comparison and analysis:

In the following, the simulation and measured results of each maximum power algorithm are compared, and the results of each maximum power algorithm are listed in Tables 4 to 6. From the table, it can be seen that the simulation results and measured errors of the tracking method are not the same. Large, it can verify the correctness of the proposed tracking method.

Table 4         <TABLE border = "1" borderColor = "# 000000" width = "85%"> <TBODY> <tr> <td> Fixed-step perturbation observation method </ td> <td> Simulation results </ td> < td> Experimental results </ td> </ tr> <tr> <td> Rise time </ td> <td> 3.8 seconds </ td> <td> 3.9 seconds </ td> </ tr> <tr> < td> settling time </ td> <td> 5 seconds </ td> <td> 4.8 seconds </ td> </ tr> <tr> <td> steady state average power </ td> <td> 464.59 W < / td> <td> 475.67 W </ td> </ tr> <tr> <td> Steady-state tracking accuracy </ td> <td> 98.12% </ td> <td> 97.97% </ td> < / tr> <tr> <td> Tracking power loss </ td> <td> 4277.4 J </ td> <td> 4378.7 J </ td> </ tr> <tr> <td> Tracking power loss averagely </ td> td> <td> 81.71 W </ td> <td> 89.02 W </ td> </ tr> </ TBODY> </ TABLE>

table 5         <TABLE border = "1" borderColor = "# 000000" width = "85%"> <TBODY> <tr> <td> Variable step-type disturbance observation method </ td> <td> Simulation results </ td> < td> Experimental results </ td> </ tr> <tr> <td> Rise time </ td> <td> 2.4 seconds </ td> <td> 2.5 seconds </ td> </ tr> <tr> < td> settling time </ td> <td> 3 seconds </ td> <td> 3.2 seconds </ td> </ tr> <tr> <td> steady state average power </ td> <td> 473.41 W < / td> <td> 481.64 W </ td> </ tr> <tr> <td> Steady-state tracking accuracy </ td> <td> 99.98% </ td> <td> 99.2% </ td> < / tr> <tr> <td> Tracking power loss </ td> <td> 2577.4 J </ td> <td> 2967.32 J </ td> </ tr> <tr> <td> Tracking power loss averagely </ td> td> <td> 51.15 W </ td> <td> 53.53 W </ td> </ tr> </ TBODY> </ TABLE>

Table 6         <TABLE border = "1" borderColor = "# 000000" width = "85%"> <TBODY> <tr> <td> The invention </ td> <td> Simulation results </ td> <td> Experimental results < / td> </ tr> <tr> <td> Rise time </ td> <td> 0.6 seconds </ td> <td> 0.6 seconds </ td> </ tr> <tr> <td> Stabilization time < / td> <td> 1 second </ td> <td> 0.8 seconds </ td> </ tr> <tr> <td> Steady state average power </ td> <td> 472.88 W </ td> <td > 481.25 W </ td> </ tr> <tr> <td> Steady-state tracking accuracy </ td> <td> 99.87% </ td> <td> 99.12% </ td> </ tr> <tr > <td> Tracking power loss </ td> <td> 848.7 J </ td> <td> 1403.3 J </ td> </ tr> <tr> <td> Average tracking power loss </ td> <td> 16.97 W </ td> <td> 28.06 W </ td> </ tr> </ TBODY> </ TABLE>

From the actual measurement results, it can be known that the fixed-step disturbance observation method cannot meet the trade-off problem of rise time and steady-state tracking accuracy at the same time because of the fixed step. Therefore, the fixed-step disturbance observation method has a rise time and a stable time. And steady-state tracking accuracy are inferior to the other two; while the variable-step perturbation observation method successfully overcomes the trade-off problem of the fixed-step perturbation observation method, it also generates the design problem of the scale factor M, which is too large. The value will cause the system to be unstable. Conversely, too small a design value will also cause the transient response to be too slow, and the ideal value of the scale factor M is different under different illumination levels. Designing a pair of different solar cells, the ideal value of the scale factor M can only be applied to a specific solar cell curve, increasing the design difficulty; and the maximum power tracking algorithm of the present invention can solve the problems of the above two algorithms, although Only specific curves can be applied, but the transient and steady state performance is good, so the best performance improvement is obtained.

As shown in Table 7, in the transient performance, the rise time of the present invention is 3.3 seconds faster than the fixed-step perturbation observation method, and 1.9 seconds faster than the variable-step perturbation observation method; the stabilization time is compared to the fixed The stepwise disturbance observation method is 4 seconds faster and 2.4 seconds faster than the variable stepwise disturbance observation method. It has the best transient response among the three methods.

Table 7         <TABLE border = "1" borderColor = "# 000000" width = "85%"> <TBODY> <tr> <td> </ td> <td> Fixed-step perturbation observation method </ td> <td> Variable step type perturbation observation method </ td> <td> The present invention </ td> </ tr> <tr> <td> Rise time </ td> <td> 3.9 seconds </ td> <td> 2.5 seconds </ td> <td> 0.6 seconds </ td> </ tr> <tr> <td> Stabilization time </ td> <td> 4.8 seconds </ td> <td> 3.2 seconds </ td> <td> 0.8 second </ td> </ tr> </ TBODY> </ TABLE>

As shown in Table 8, in the steady-state part, the fixed-step disturbance observation method will oscillate near the maximum power point after entering the steady-state. Its average steady-state power is only 475.67 W, and the steady-state tracking accuracy is 97.97%; The variable step type perturbation observation method adds a variable step, and no oscillation occurs at the maximum power point, so the steady-state tracking accuracy is increased to 99.2%; the maximum power tracking algorithm of the present invention is the perturbation observation method at the end, although it is Perturbation of 1V will still oscillate near the maximum power point, so the steady-state tracking accuracy is 99.12%, which is only 0.08% less than the variable-step perturbation observation method. Therefore, the proposed method still has a good steady-state response.

Table 8         <TABLE border = "1" borderColor = "# 000000" width = "85%"> <TBODY> <tr> <td> </ td> <td> Fixed-step perturbation observation method </ td> <td> Variable step type perturbation observation method </ td> <td> The present invention </ td> </ tr> <tr> <td> Steady state average power </ td> <td> 475.67 W </ td> <td> 481.64 W </ td> <td> 481.25 W </ td> </ tr> <tr> <td> Steady-state tracking accuracy </ td> <td> 97.97% </ td> <td> 99.2% </ td> <td> 99.12% </ td> </ tr> </ TBODY> </ TABLE>

As shown in Table 9, in the tracking power loss part, because the step design of the fixed step disturbance observation method must consider the trade-off between transient and steady state response performance, the average tracking power loss is more, and the variable step disturbance The observation method has better transient response and steady-state response, so its average tracking power loss is reduced by 39.8% compared with the fixed-step perturbation observation method; and the maximum power tracking algorithm of the present invention has good transient and stability. The average tracking power loss is the lowest of the three methods, which is 68.48% lower than the fixed-step disturbance observation method and 47.5% lower than the variable-step disturbance observation method. Therefore, the overall performance is the best.

Table 9         <TABLE border = "1" borderColor = "# 000000" width = "85%"> <TBODY> <tr> <td> </ td> <td> Fixed-step perturbation observation method </ td> <td> Variable step-type disturbance observation method </ td> <td> The present invention </ td> </ tr> <tr> <td> Tracking power loss </ td> <td> 4378.7 J </ td> <td> 2967.32 J </ td> <td> 1403.3 J </ td> </ tr> <tr> <td> Average tracking power loss </ td> <td> 89.02 W </ td> <td> 53.53 W </ td> <td> 28.06 W </ td> </ tr> </ TBODY> </ TABLE>

In summary, the experimental results confirm that compared with the fixed-step disturbance observation method and the variable-step disturbance observation method, the tracking speed of the present invention is increased by 84.6% and 76% respectively; in addition, the tracking power loss is also reduced by 68.48 % And 47.5%.

With the design disclosed above, the present invention has the following advantages:

1. The maximum power tracking algorithm disclosed in the present invention adopts a simplified weighted least square method, which can accurately estimate the illuminance value only after one estimation operation, and then obtain the maximum power point voltage to achieve a The operation is simple and can be achieved by a low-cost microcontroller.

2. The maximum power tracking algorithm disclosed in the present invention has a significantly shorter rise time and stable time in the transient performance than the fixed-step perturbation observation method and the variable-step perturbation observation method of the conventional technology. Transient response.

3. The maximum power tracking algorithm disclosed in the present invention has a significantly reduced average tracking power loss compared with the fixed-step perturbation observation method and the variable-step perturbation observation method of the conventional technology, and has good tracking efficiency.

4. The maximum power tracking algorithm disclosed in the present invention adopts appropriate estimation operation and disturbance observation method. Compared with the fixed-step disturbance observation method and the variable-step disturbance observation method, the tracking speed is increased by 84.6, respectively. % And 76%, the tracking power loss also decreased by 68.48% and 47.5%.

What is disclosed in this case is a preferred embodiment. For example, those who have partial changes or modifications that are derived from the technical ideas of this case and are easily inferred by those skilled in the art, do not depart from the scope of patent rights in this case.

To sum up, regardless of the purpose, method and effect, this case is showing its technical characteristics that are quite different from the conventional ones, and its first invention is practical, and it is also in line with the patent requirements of the invention. Granting patents at an early date will benefit society and feel good.

100‧‧‧solar battery system

200‧‧‧Boost Converter

300‧‧‧Microcontroller

400‧‧‧ load

Step a‧‧‧Measure the output current value and output voltage value of two initial operating points of a solar power generation system to obtain (I ₁ , V ₁ ) and (I ₂ , V ₂ )

Step b‧‧‧ performs a simplified weighted least square method operation on the (I ₁ , V ₁ ) and (I ₂ , V ₂ ) to obtain an estimated illuminance value S _guess and an estimated temperature value T _guess

Step c‧‧‧ calculate a maximum power point voltage value V _mpp according to the estimated illumination value S _guess

Step d‧‧‧ performs a disturbance observation method operation according to the maximum power point voltage value V _mpp to determine a voltage command

FIG. 1 is a flowchart of steps in an embodiment of a maximum power tracking algorithm of the present invention. FIG. 2 is a flowchart illustrating steps of another embodiment of the maximum power tracking algorithm of the present invention. FIG. 3 shows a single diode equivalent circuit diagram of a solar cell. FIG. 4a shows the power-voltage curve of the solar cell under different illumination values. FIG. 4b shows the current-voltage curve of the solar cell under different illumination values. FIG. 5a shows the power-voltage curves of the solar cell at different temperature values. FIG. 5b shows the current-voltage curves of the solar cell at different temperature values. FIG. 6 is a schematic diagram of a control system architecture adopted by the present invention. FIG. 7 illustrates a tracking diagram of the present invention. FIG. 8 illustrates output power-voltage curves with illuminance values from 100 W / m ² to 1000 W / m ² . FIG. 9 shows the curve of the illuminance value and the maximum power point voltage. FIG. 10 is a waveform diagram of actual measurement results of the fixed-step disturbance observation method of the conventional technique. FIG. 11 a is a waveform diagram showing the measurement results of the general uniform illumination of the step-by-step disturbance observation method of the conventional technique. FIG. 11b is a waveform diagram of the actual measurement results of the illuminance of the step change perturbation observation method in the conventional technique. FIG. 12a is a waveform diagram showing a measurement result of uniform illumination of the present invention. FIG. 12b is a waveform diagram of the actual measurement result of the variation of the illumination intensity from 300 W / m ² to 800 W / m ² according to the present invention. FIG. 12c is a waveform diagram of the actual measurement result of changing the illuminance from 800 W / m ² to 100 W / m ² according to the present invention.

Claims (5)

A maximum power tracking algorithm is implemented using a control circuit. The maximum power tracking algorithm includes the following steps: Measure the output current value and output voltage value of two initial operating points of a solar power generation system to obtain (I1, V1) and (I2, V2); performing a simplified weighted least square method operation on the (I1, V1) and (I2, V2) to obtain an estimated illuminance value Sguess and an estimated temperature value Tguess, the simplification Type weighted least square method operations include: ,and , Where Sf and Tf are preset illuminance values and temperature values, , , Where Isc, Is, q, K, A, and N are constants, , , ,as well as ; Calculate a maximum power point voltage value Vmpp according to the estimated illumination value Sguess, where ; And performing a disturbance observation method operation according to the maximum power point voltage value Vmpp to determine a voltage command. The maximum power tracking algorithm described in item 1 of the scope of patent application, further comprising a power change threshold judgment step to re-perform the simplified weighted minimum flat when a power change is greater than a preset power change threshold. The method operates to obtain a new estimated illumination value Sguess. According to the maximum power tracking algorithm described in item 2 of the patent application scope, the preset power change threshold is 15W. The maximum power tracking algorithm according to item 1 of the patent application scope, wherein the control circuit includes: a boost converter having an input terminal, a control terminal, and an output terminal, and the input terminal is used for connection with a solar energy The battery system is coupled, the control terminal is used for receiving a pulse width modulation signal, and the output terminal is used for coupling with a load; and a microcontroller is used for generating the voltage command and providing according to the voltage command The pulse width modulation signal. The maximum power tracking algorithm as described in item 4 of the scope of patent application, wherein the microcontroller has a digital signal processor for performing an analog-to-digital conversion operation and a digital filtering operation on the current voltage and the current, respectively. And execute a proportional-integral control operation and a pulse width modulation operation according to the voltage command to output the pulse width modulation signal.