CN104765403A - Chaos optimizing search based photovoltaic array maximum power point tracing method - Google Patents

Abstract

The invention discloses a method for tracking the maximum power point of a photovoltaic array based on chaotic optimization search, and calculates the output power of the photovoltaic array by sampling the DC voltage Vpv and current Ipv output by the photovoltaic array in real time , and the current maximum power value stored in the MPPT controller For comparison, if > , then put The value assigned to , the value of Vpv is assigned to the output voltage of the MPPT controller , otherwise, put value discarded, and value remains unchanged. Then, the output voltage of the MPPT controller The voltage Vpv output by the photovoltaic array is added to the adder, and the generated error voltage is added to the non-inverting terminal of the comparator through a proportional integral link and compared with the sawtooth wave voltage added to the inverting terminal of the comparator to change the voltage in the DC/DC converter. The duty cycle of the gate drive signal of the switching tube is used to adjust and control the parameters of the DC/DC conversion circuit to achieve maximum power tracking control with fast tracking speed and high control precision.

Description

Photovoltaic Array Maximum Power Point Tracking Method Based on Chaotic Optimal Search

The present invention is a divisional application with application number 2014101365845, application date April 8, 2014, and title of the invention "a method for tracking the maximum power point of a photovoltaic array based on chaotic optimization search".

technical field

The invention relates to a photovoltaic power generation system, in particular to a method for tracking the maximum power point of a photovoltaic array based on chaotic optimization search, using the MPPT method to improve the efficiency of the photovoltaic cell array in the process of photovoltaic power generation, so that the solar energy can be converted into Electric energy output belongs to the technical field of photovoltaic power generation.

Background technique

When the photovoltaic power generation system is working, under a certain temperature and sunlight intensity, the photovoltaic cell array has a unique maximum power point, but because the output characteristics of the photovoltaic cell The output voltage and current of the photovoltaic system will change greatly accordingly, which will make the output power unstable. If the change cannot be tracked in real time, the output efficiency of the photovoltaic system will be reduced. In addition, due to the complex nonlinear characteristics of the output characteristics of the photovoltaic cell array, it is difficult to accurately determine its mathematical model, and it is impossible to obtain the maximum power by analytical method. In order to maximize the output power of the photovoltaic array, it is necessary to use the corresponding control method to track and control the maximum power point of the photovoltaic cell array in real time to maximize the use of solar energy. This adjustment process to ensure the continuous output of the maximum power of the photovoltaic array is called maximum power. Point Tracking (MPPT).

At present, the common maximum power point tracking control methods include constant voltage control method, disturbance and observation method, incremental admittance method and single chaos search, etc., but different methods have different advantages and disadvantages in actual use. The constant voltage method is a simple maximum power point tracking method. Its advantages are simple control and easy implementation. However, when the temperature changes, the tracking efficiency of this tracking method is not high, and there is a serious power loss. Both the perturbation and observation method and the incremental admittance method will oscillate near the maximum power point, resulting in partial power loss. Although a single chaotic search method can accurately track the global maximum, if there are many local maxima densely around the global maximum, although the chaotic motion has ergodicity, it often takes a long time to jump out of the local maximum. time, and due to the randomness of chaotic motion, it is possible to jump far when approaching the global maximum value, resulting in a waste of optimization search time.

Contents of the invention

The problem to be solved in the present invention is to provide a method for tracking the maximum power point of photovoltaic arrays based on chaotic optimization search for the above deficiencies. Narrowing the search space of optimization variables enables the algorithm to converge to the global optimal solution faster and more accurately, so the search efficiency is greatly improved.

The technical solution adopted by the present invention to solve the above technical problems is: a method for tracking the maximum power point of a photovoltaic array based on chaotic optimization search, characterized in that: the tracking method includes the following steps:

Step 1), according to the requirements of the system, initialize the system parameters: chaotic variables The initial value of the initial value of 0.126; the initial value of the upper and lower boundary values c and d of the voltage search are c=0, d=90; the power of the secondary carrier α is 0.6, and β is 3; the current maximum power =0; Constant r =2.1; Number of main loops =0;

Step 2), let the initial value of the carrier iteration number k be 0, the number of cycles i=0, and then enter step 3);

Step 3), the initial value of the chaotic variable substitute Carry out iterative operation, and get the above formula substitute , to get the mppt controller output voltage ,make , then go to step 4);

Step 4), calculate the instantaneous output power of the photovoltaic array , then go to step 5);

Step 5), judge the instantaneous output power of the photovoltaic array Is it greater than the current maximum power value stored in the MPPT controller , if yes, go to step 7); if no, go to step 6);

Step 6), execute i=i+1, and then go to step 8);

Step 7), the photovoltaic array output instantaneous power The value of is assigned to the current maximum power value stored in the MPPT controller , the instantaneous voltage The value assigned to the output voltage of the MPPT controller , and then go to step 8);

Step 8), judging whether the number of cycles i is greater than 10 or whether the number of iterations k of the chaotic variable of a carrier is greater than 100, if so, enter step 9), if not, enter step 3);

Step 9), let the number of iterations of the chaotic variable of the secondary carrier The initial value is 0, the number of cycles i=0, and then enter step 10);

Step 10), the initial value of the chaotic variable substitute Carry out iterative operation, and get the above formula substitute

make , and then go to step 11);

Step 11), calculate , and then go to step 12);

Step 12), judge Is it greater than , if yes, that is, the real-time power is greater than the current preset maximum power, then go to step 14); if no, go to step 13);

Step 13), execute i=i+1, and then go to step 15);

Step 14), set the real-time power The value assigned to the output voltage of the MPPT controller , the voltage The value assigned to the output voltage of the MPPT controller , and then go to step 15);

Step 15), judging whether the secondary carrier cycle number i is greater than 10 or whether the chaotic variable iteration number k of the secondary carrier is greater than 100, if it enters step 16), if not, enters step 10);

Step 16), execute

, , that is, adjust the values of c and d to realize the reconstruction of the optimized variable value range, and then the number of main loops , and then go to step 17);

Step 17), determine the number of main loops Whether it is greater than 3, if yes, go to step 18); if not, go to step 2);

Step 18), output the maximum power value and the optimum output voltage of the mppt controller , and then go to step 19);

Step 19), the search ends.

The present invention adopts the above technical scheme, and compared with the prior art, has the following advantages:

(1) Using the combination of the primary carrier and the secondary carrier for iterative search can improve the tracking speed more than the traditional chaotic search method; (2) Due to the use of the secondary carrier method for search and further precise tracking control, the control accuracy is improved and the control accuracy is also improved. It solves the problem that the maximum power point tracking of the partially shaded photovoltaic system tends to fall into a local maximum; (3) the present invention can meet the needs of the maximum power tracking control of the photovoltaic power generation system, and can more effectively improve the tracking efficiency of the system.

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

Description of drawings

Fig. 1 is the structural diagram of control system in the embodiment of the present invention;

Fig. 2 is the flow chart of tracking method in the embodiment of the present invention;

In the figure,

1-PV Array is a photovoltaic array, 2-MPPT controller, 3-adder, 4-proportional integral circuit, 5-comparator, 6-DC/DC converter output capacitor, 7-freewheeling diode, 8-switch tube , 9-inductance, 10-filter capacitor.

Detailed ways

Embodiment, as shown in Figure 1, a kind of photovoltaic array maximum power point tracking method based on chaotic optimization search, Vpv is the real-time output voltage of photovoltaic array, Ipv is the real-time output current of photovoltaic array, is the instantaneous output power of the photovoltaic array, The current maximum power value of the PV array pre-stored for the MPPT controller, for with Corresponding to the optimal output voltage of the MPPT controller, [c, d] is the output voltage range of the photovoltaic array in the i-th iteration in the mppt process, c is the lower boundary, and d is the upper boundary. is the loop count of the main loop. is the chaotic variable of a carrier wave, is the instantaneous output voltage of the photovoltaic array during one carrier iteration,

MPPT controller 2 calculates the output power of the photovoltaic array by sampling the DC voltage Vpv and current Ipv output by the photovoltaic array 1 in real time , and the current maximum power value stored in the MPPT controller For comparison, if > , then put The value assigned to , the value of Vpv is assigned to the output voltage of the MPPT controller , otherwise, put value discarded, and value remains unchanged. Then, the output voltage of MPPT controller 2 The voltage Vpv output by the photovoltaic array is added to the adder, and the generated error voltage is added to the non-inverting terminal of the comparator 5 through the proportional integral link 4 and compared with the sawtooth wave voltage applied to the inverting terminal of the comparator 5 to change the DC/DC The duty cycle of the gate drive signal of the switching tube 8 in the converter is used to adjust and control the parameters of the DC/DC conversion circuit to achieve maximum power tracking control.

Primary Carrier Selection Logistic Mapping for Chaotic Optimal Search

(1)

Where k is the number of iterations of the chaotic variable, μ is a control parameter, when μ = 4, the chaotic variable generated by the Logistic mapping is in a complete chaotic state, and it is ergodic in the range of (0, 1).

The secondary carrier method of chaos optimization search is shown in formula (3), which can generate a chaotic variable with a large orbital probability density near a specified point.

(3).

In the formula is the maximum power point in the primary carrier search process The corresponding mppt controller output voltage, is the chaotic variable generated by formula (1), is another chaotic variable generated by formula (1), 0<α<1, β>1. When α is taken as a smaller value and β is taken as a larger value, the following can be obtained centered secondary carrier chaotic sequence , which can make the chaotic search have better ergodicity near the maximum power point. is the number of iterations of the secondary carrier.

As shown in FIG. 2 , for the basic control process of tracking the maximum power point, the process starts at step S101 . Then, in step S102, according to the requirements of the system, the system parameters are initialized: chaotic variables The initial value of 0.126; the initial value of the upper and lower boundary values c and d of the voltage search are c=0, d=90; the power of the secondary carrier α is 0.6, and β is 3; the current maximum power =0; Constant r =2.1; Number of main loops =0.

In step S103, the initial value of the number of carrier iterations k is 0, the number of cycles i=0, and then enter step S104;

In step S104, the initial value of the chaotic variable substitute Carry out iterative operation, and get the above formula substitute , to get the mppt controller output voltage ,make , and then enter step S105;

In step S105, calculate the instantaneous output power of the photovoltaic array , and then enter step S106;

In step S106, judge the output instantaneous power of photovoltaic array Is it greater than the current maximum power value stored in the MPPT controller , if yes, that is, the real-time power is greater than the current preset maximum power, then enter step S108; if no, then enter step S107;

In step S107, execute i=i+1, and then enter step S109;

In step S108, the photovoltaic array output instantaneous power The value of is assigned to the current maximum power value stored in the MPPT controller , the instantaneous voltage The value assigned to the output voltage of the MPPT controller , and then enter step S109;

In step S109, it is judged whether the number of cycles i is greater than 10 or whether the number of iterations k of the chaotic variable of a carrier is greater than 100, if it enters step S110, if not, enters step S104;

In step S110, the number of iterations of the chaotic variable of the secondary carrier The initial value is 0, the number of cycles i=0, and then enter step S111;

In step S111, the initial value of the chaotic variable substitute Carry out iterative operation, and get the above formula substitute

when when odd

make , and then enter step S112;

In step S112, calculate , and then enter step S113;

In step S113, it is judged that Is it greater than , if yes, that is, the real-time power is greater than the current preset maximum power, then enter step S115; if no, then enter step S114;

In step S114, execute i=i+1, and then enter step S116;

In step S115, the real-time power The value assigned to the output voltage of the MPPT controller , the voltage The value assigned to the output voltage of the MPPT controller , and then enter step S116;

In step S116, it is judged whether the number of cycles i of the secondary carrier is greater than 10 or whether the number of iterations k of the chaotic variable of the secondary carrier is greater than 100, if it is entered into step S117, if not, it is entered into step S111;

In step S117, execute ,

, that is, adjust the values of c and d to realize the reconstruction of the optimized variable value range, and then the number of main loops , and then enter step S118;

In step S118, determine the number of main loops Whether it is greater than 3, if yes, then enter step S119; if no, then enter step S103;

In step S119, output the maximum power value and the optimum output voltage of the mppt controller , and then enter step S120;

In step S120, the search ends.

After testing, the tracking speed and control precision are high.

Those skilled in the art should realize that the above-mentioned specific embodiments are only exemplary, and are intended to enable those skilled in the art to better understand the content of the present invention, and should not be construed as limiting the protection scope of the present invention. The improvements made in the technical solution of the invention all fall into the protection scope of the present invention.

Claims (1)

1. The photovoltaic array maximum power point tracking method based on chaos optimization search, is characterized in that: described tracking method comprises the following steps: Step 1), according to the requirements of the system, initialize the system parameters: chaotic variables The initial value of the initial value of 0.126; the initial value of the upper and lower boundary values c and d of the voltage search are c=0, d=90; the power of the secondary carrier α is 0.6, and β is 3; the current maximum power =0; Constant r =2.1; Number of main loops =0; Step 2), let the initial value of the carrier iteration number k be 0, the number of cycles i=0, and then enter step 3); Step 3), the initial value of the chaotic variable substitute Carry out iterative operation, and get the above formula substitute , to get the mppt controller output voltage ,make , then go to step 4); Step 4), calculate the instantaneous output power of the photovoltaic array , then go to step 5); Step 5), judge the instantaneous output power of the photovoltaic array Is it greater than the current maximum power value stored in the MPPT controller , if yes, go to step 7); if no, go to step 6); Step 6), execute i=i+1, and then go to step 8); Step 7), the photovoltaic array output instantaneous power The value of is assigned to the current maximum power value stored in the MPPT controller , the instantaneous voltage The value assigned to the output voltage of the MPPT controller , and then go to step 8); Step 8), judging whether the number of cycles i is greater than 10 or whether the number of iterations k of the chaotic variable of a carrier is greater than 100, if so, enter step 9), if not, enter step 3); Step 9), let the number of iterations of the chaotic variable of the secondary carrier The initial value is 0, the number of cycles i=0, and then enter step 10); Step 10), the initial value of the chaotic variable substitute Carry out iterative operation, and get the above formula substitute make , and then go to step 11); Step 11), calculate , and then go to step 12); Step 12), judge Is it greater than , if yes, that is, the real-time power is greater than the current preset maximum power, then go to step 14); if no, go to step 13); Step 13), execute i=i+1, and then go to step 15); Step 14), set the real-time power The value assigned to the output voltage of the MPPT controller , the voltage The value assigned to the output voltage of the MPPT controller , and then go to step 15); Step 15), judging whether the secondary carrier cycle number i is greater than 10 or whether the chaotic variable iteration number k of the secondary carrier is greater than 100, if it enters step 16), if not, enters step 10); Step 16), execute , , that is, adjust the values of c and d to realize the reconstruction of the optimized variable value range, and then the number of main loops , and then go to step 17); Step 17), determine the number of main loops Whether it is greater than 3, if yes, go to step 18); if not, go to step 2); Step 18), output the maximum power value and the optimum output voltage of the mppt controller , and then go to step 19); Step 19), the search ends.