Photovoltaic maximum power control method combining cubic spline interpolation and improved PO

Abstract

The invention relates to a method combining cubic spline interpolation and improved Pamp. The invention aims to improve the energy conversion efficiency and the stability of a photovoltaic system. The method comprises the following steps: firstly, establishing a power-voltage (P-V) characteristic curve of a photovoltaic array by utilizing a cubic interpolation method, outputting a current duty ratio, and then utilizing an improved Pamp; an O algorithm accurately tracks the photovoltaic maximum power point, finally outputs the optimal duty ratio, and finally outputs the final duty ratio under the condition that the power of the global maximum power point meets the set restart condition, so that the photovoltaic array operates at the global maximum power point; the cubic spline interpolation method is introduced into the MPPT control link, the global maximum power position is rapidly tracked through a small number of sample points, and MPP tracking time is obviously shortened; at the same time, it is associated with improved Pamp; o, the tracking precision is improved, and power oscillation is eliminated; and finally, the power oscillation at the maximum power point is further eliminated while the relatively high tracking speed is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of renewable energy power generation, and specifically relates to a photovoltaic maximum power control method combining cubic spline interpolation and improved P&O. Background Art

[0002] With the continuous development of renewable energy, solar energy, as a clean and sustainable energy source, has received more and more attention. In photovoltaic power generation systems, changes in external environmental factors will affect the output power of photovoltaic systems, especially temperature and light intensity. Maximum Power Point Tracking (MPPT) technology is one of the key technologies to improve the efficiency of photovoltaic power generation systems. In order to ensure that photovoltaic power generation systems achieve optimal power output in complex environments, it is very important to study and optimize the maximum power point tracking strategy of photovoltaic cells.

[0003] Traditional MPPT algorithms mainly include the perturbation observation method and the conductance increment method. The perturbation observation method determines the operation by comparing the voltage and power changes through periodic perturbations, but power oscillations will occur near the maximum power point, and the perturbation step size needs to be reduced to reduce the fluctuations, which increases the response time. The conductance increment method improves the perturbation observation method and identifies the maximum power point through the conductance and current and voltage change rates, but it still cannot take into account both rapidity and stability, and has high hardware requirements, which increases costs.

[0004] In actual engineering applications, photovoltaic arrays are often affected by local shading, dust accumulation and other factors, resulting in multiple peaks in the output power-voltage (PU) characteristic curve. The traditional maximum power point tracking (MPPT) method is difficult to effectively track the global maximum power point under such conditions. The MPPT algorithm under local shadow conditions is mainly based on swarm intelligence optimization algorithms, such as particle swarm optimization (PSO) algorithm, cuckoo optimization (CSA) algorithm, sparrow optimization (SSA) algorithm, etc. Although the intelligent algorithm can track the global maximum power point in a complex environment, there is also power oscillation at the maximum power point, causing large system losses. In addition, the intelligent algorithm requires many parameter adjustments, and the speed and accuracy of tracking are greatly affected by the parameters, which is unstable. At the same time, some intelligent algorithms have defects such as unstable optimization ability, easy to fall into local extreme points, and slow response speed due to a large number of iterations. At the same time, the intelligent algorithm requires a relatively large number of iterations to converge, which is more complicated than the traditional algorithm. Summary of the invention

[0005] In view of the existing problems of the above MPPT control method, the present invention introduces a photovoltaic maximum power control method combining cubic spline interpolation and improved P&O. The cubic spline interpolation method can quickly locate the vicinity of the maximum power point, and the improved P&O algorithm can accurately track the maximum power point and ensure the power oscillation after stabilization, thereby improving the power generation efficiency.

[0006] The present invention is achieved in that:

[0007] A photovoltaic maximum power control method combining cubic spline interpolation and improved P&O is designed, which includes the following steps:

[0008] Step a: First, apply six duty cycles [d 1 ,d 2 ,d 3 ,d 4 ,d 5 ,d 6 ] and measure their voltage and current respectively;

[0009] Step b: Calculate the power of each of the six duty cycles and compare them to get the group of data with the largest power [d max ,P max ], and record d max Two adjacent duty cycles; step c, between two adjacent duty cycles to d max Between them, two auxiliary duty cycles are added and a set of duty cycles [d 1 ,d 2 ,d 3 ,d 4 ,d 5 ] The respective current and voltage values ​​and calculate the power;

[0010] Step d: A new set of data [v 1 ,p 1 ]、[v 2 ,p 2 ]、[v 3 ,p 3 ]、[v 4 ,p 4 ]、[v 5 ,p 5 ], the power-voltage (PV) characteristic curve at the maximum power is simulated by using the cubic spline interpolation method, and then the global maximum power point [v mpp ,p mpp ], using the formula to get d mpp ;

[0011] Step e: obtain d mppBring it into the improved P&O algorithm, compare the power changes before and after, make disturbances, and get the final output duty cycle;

[0012] Step f: determine whether the power at the global maximum power point meets the set restart condition. If |1-(v pv *i pv ) / P max |≥0.1, indicating that the external environment changes and the power changes greatly, then enter the global search mode and return to step a. If |1-(v pv *i pv ) / P max |<0.1, execute step g;

[0013] Step g: adjust PWM according to the final duty cycle, and then control the Boost circuit to achieve the operation of the photovoltaic array at the global maximum power point.

[0014] Specifically, the six duty cycles applied in step a are evenly distributed in the range of [0.15, 0.85], that is, the corresponding voltages are distributed from large to small.

[0015] Specifically, in step b, if d max If d is in the middle, max Denoted as d 3 , two adjacent duty cycles are denoted as d 1 and d 5 If d max is d 6 , then d max Denoted as d 4 , d 5 Take d 6 +0.05,d 2 =d 5 , d 1 =d 4 , in d 2 and d 4 Insert auxiliary duty cycle d 3 If d max is d 1 , then d max Denoted as d 2 , d 1 Take d 1 -0.05, d 4 =d 2 , d 5 =d 3 , in d 2 and d 4 Insert auxiliary duty cycle d 3 .

[0016] Specifically, in step c, the method of inserting the auxiliary duty cycle is: n=(d n-1 +d n+1 ) / 2+α, where α is a random value in (0,0.1).

[0017] Specifically, in step d, v 1 to v 5 Strictly satisfy the increasing or decreasing and interpolation every 0.01, where d is extracted mpp The formula is as follows:

[0018]

[0019] This formula is applicable to the case where the output end is a resistive load;

[0020]

[0021] This formula is applicable to the case where the output voltage is fixed.

[0022] Specifically, step e is as follows:

[0023] Measure the input voltage V K 、V K-1 、V K-2 , input current I K ,I K-1 ,I K-2 ,have:

[0024] P K =V K ×I K , P K-1 =V K-1 ×I K-1 , P K-2 =V K-2 ×I K-2 , ΔP K =P K -P K-1 , ΔP K-1 =P K-1 -P K-2 , ΔV K =V K -V K-1 .

[0025] When ΔP K >0, satisfying ΔV K >0, and ΔP K-1 >0,d * =d mpp -Δd, if ΔP is not satisfied K-1 >0,d * =d mpp ;

[0026] When ΔP K>0, does not satisfy ΔV K >0, and ΔP K-1 >0,d * =d mpp +Δd, if ΔP is not satisfied K-1 >0,d * =d mpp ;

[0027] When ΔP K ≤0, satisfying ΔV K >0, and ΔP K-1 >0,d * =d mpp +Δd, if ΔP is not satisfied K-1 >0,d * =d mpp ;

[0028] When ΔP K ≤0, does not satisfy ΔV K >0, and ΔP K-1 >0,d * =d mpp -Δd, if ΔP is not satisfied K-1 >0,d * =d mpp ;

[0029] Where Δd is the variable step size, and the update formula is as follows:

[0030]

[0031] Where S max The maximum step size coefficient can be set to 0.01.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1. The present invention proposes to use cubic spline interpolation to simulate the power-voltage (PV) characteristic curve of photovoltaic arrays. The function defined by this method is simple, smooth and accurate. Moreover, this method can quickly find GMPP under uniform illumination and partial shading conditions. Compared with intelligent algorithms, it is simpler and only requires a small number of sample points to quickly find the global optimal solution.

[0034] 2. The improved P&O photovoltaic maximum power control method proposed in the present invention introduces a new method to overcome the oscillation near the maximum power point when approaching the maximum power point, by testing the output power change in each cycle and comparing it with the array terminal power change in the previous cycle. If the array terminal power is observed to decrease after the previous cycle increases or in the opposite direction, the array terminal power is observed to increase after the previous cycle decreases; this means that we are at the peak of the power curve, so the duty cycle of the boost converter should remain the same as the previous cycle. This new method can improve the maximum power point drift problem of the traditional perturbation and observation method and eliminate oscillations.

[0035] 3. The present invention proposes a variable step size strategy while improving P&O, introduces an improved sigmiod function, and takes dP / dU as the independent variable; when dP / dU is zero, the step size can be guaranteed to be zero, further eliminating power oscillations, and when the operating voltage of the photovoltaic array is far away from the maximum power point voltage, the variable step size strategy proposed by the present invention can ensure the dynamic response speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 The present invention is a flow chart of a photovoltaic maximum power control method combining cubic spline interpolation and improved P&O.

[0037] Figure 2 It is the PV curve under partial shading.

[0038] Figure 3 It is a simulation power tracking diagram of the method of the present invention in a variable and complex environment. Specific implementation methods

[0040] In order to better reflect the advantages and innovations of the present invention and clearly demonstrate the technical solution of the present invention, the implementation methods of the present invention will be further described in detail below with reference to the accompanying drawings. Example 1

[0041] like Figure 1 As shown, the present invention provides a photovoltaic maximum power control method combining cubic spline interpolation and improved P&O, comprising the following steps:

[0042] Step a: First, apply six duty cycles [d 1 ,d 2 ,d 3 ,d 4 ,d 5 ,d 6 ] and measure their voltage and current respectively;

[0043] Step b: Calculate the power of each of the six duty cycles and compare them to get the group of data with the largest power [d max ,Pmax ], and record d max Two adjacent duty cycles; step c, between two adjacent duty cycles to d max Between them, two auxiliary duty cycles are added and a set of duty cycles [d 1 ,d 2 ,d 3 ,d 4 ,d 5 ] The respective current and voltage values ​​and calculate the power;

[0044] Step d: A new set of data [v 1 ,p 1 ]、[v 2 ,p 2 ]、[v 3 ,p 3 ]、[v 4 ,p 4 ]、[v 5 ,p 5 ], the power-voltage (PV) characteristic curve at the maximum power is simulated by using the cubic spline interpolation method, and then the global maximum power point [v mpp ,p mpp ], using the formula to get d mpp ;

[0045] Step e: obtain d mpp Bring it into the improved P&O algorithm, compare the power changes before and after, make disturbances, and get the final output duty cycle;

[0046] Step f: determine whether the power at the global maximum power point meets the set restart condition. If |1-(v pv *i pv ) / P max |≥0.1, indicating that the external environment changes and the power changes greatly, then enter the global search mode and return to step a. If |1-(v pv *i pv ) / P max |<0.1, execute step g;

[0047] Step g: adjust PWM according to the final duty cycle, and then control the Boost circuit to achieve the operation of the photovoltaic array at the global maximum power point.

[0048] Specifically, the six duty cycles applied in step a are evenly distributed in the range of [0.15, 0.85], that is, the corresponding voltages are distributed from large to small.

[0049] Specifically, in step b, if d max If d is in the middle, max Denoted as d 3, two adjacent duty cycles are denoted as d 1 and d 5 If d max is d 6 , then d max Denoted as d 4 , d 5 Take d 6 +0.05,d 2 =d 5 , d 1 =d 4 , in d 2 and d 4 Insert auxiliary duty cycle d 3 If d max is d 1 , then d max Denoted as d 2 , d 1 Take d 1 -0.05, d 4 =d 2 , d 5 =d 3 , in d 2 and d 4 Insert auxiliary duty cycle d 3 .

[0050] Specifically, in step c, the method of inserting the auxiliary duty cycle is: n =(d n-1 +d n+1 ) / 2+α, where α is a random value in (0,0.1).

[0051] Specifically, in step d, v 1 to v 5 Strictly satisfy the increasing or decreasing and interpolation every 0.01. mpp The formula is as follows:

[0052]

[0053] This formula is applicable to the case where the output end is a resistive load;

[0054]

[0055] This formula is applicable to the case where the output voltage is fixed.

[0056] Specifically, step e is as follows:

[0057] Measure the input voltage V K 、V K-1 、V K-2 , input current I K ,I K-1 ,IK-2 ,have:

[0058] P K =V K ×I K , P K-1 =V K-1 ×I K-1 , P K-2 =V K-2 ×I K-2 , ΔP K =P K -P K-1 , ΔP K-1 =P K-1 -P K-2 , ΔV K =V K -V K-1 .

[0059] Compared with the traditional perturbation and observation method, the improved P&O algorithm is as follows:

[0060] When ΔP K >0, satisfying ΔV K >0, and ΔP K-1 >0,d * =d mpp -Δd, if ΔP is not satisfied K-1 >0,d * =d mpp ;

[0061] When ΔP K >0, does not satisfy ΔV K >0, and ΔP K-1 >0,d * =d mpp +Δd, if ΔP is not satisfied K-1 >0,d * =d mpp ;

[0062] When ΔP K ≤0, satisfying ΔV K >0, and ΔP K-1 >0,d * =d mpp +Δd, if ΔP is not satisfied K-1 >0,d * =d mpp ;

[0063] When ΔP K ≤0, does not satisfy ΔV K >0, and ΔP K-1 >0,d * =d mpp -Δd, if ΔP is not satisfiedK-1 >0,d * =d mpp ;

[0064] Where Δd is the variable step size, and the update formula is as follows:

[0065]

[0066] Where S max The maximum step size coefficient is set to 0.01.

[0067] In this example, the illumination distribution of each photovoltaic module under different environments is shown in Table 1. A photovoltaic system simulation model is built in the Matlab / Simulink environment. The photovoltaic module is under working condition 1 for 0 to 2 seconds, working condition 2 for 2 to 4 seconds, working condition 3 for 4 to 6 seconds, and working condition 4 to 8 seconds. The simulation results are shown in Table 1. Figure 3 shown.

[0068] Table 1. Light distribution of each photovoltaic module under different environments

[0069]

[0070] It can be seen that the photovoltaic maximum power control method provided by the present invention, which combines cubic spline interpolation and improved disturbance observation method, can quickly locate the global maximum power point through several sample data under the set sampling time of 0.05s, and then use the improved P&O algorithm to accurately track the photovoltaic maximum power point to ensure that the output has no oscillation. This method can quickly and accurately track the maximum power point under complex shading conditions, without oscillation when stable, and improve the efficiency of photovoltaic power generation.

[0071] It should be understood that the above description of the preferred embodiment is relatively detailed and cannot be regarded as limiting the scope of patent protection of the present invention. Under the enlightenment of the present invention, ordinary technicians in this field can also make substitutions or modifications without departing from the scope of protection of the claims of the present invention, which all fall within the scope of protection of the present invention. The scope of protection requested for the present invention shall be based on the attached claims.

Claims

1. A photovoltaic maximum power control method combining cubic spline interpolation and improved P&O, characterized in that: The following steps are involved: Step a: First, apply six duty cycles [d 1 ,d 2 ,d 3 ,d 4 ,d 5 ,d 6 ] and measure their voltage and current respectively; Step b: Calculate the power of each of the six duty cycles and compare them to get the group of data with the largest power [d max ,P max ], and record d max Two adjacent duty cycles; Step c: between two adjacent duty cycles to d max Add two auxiliary duty cycles, record the current and voltage values ​​of a set of duty cycles [d1, d2, d3, d4, d5] and calculate the power; Step d: A new set of data [v1, p1], [v2, p2], [v3, p3], [v4, p4], [v5, p5] is obtained. The power-voltage (PV) characteristic curve at the maximum power is simulated by using the cubic spline interpolation method, and then the global maximum power point [v mpp ,p mpp ], and use the formula to get d mpp ; Step e: obtain d mpp Bring it into the improved P&O algorithm, compare the power changes before and after, and perform disturbance to obtain the final output duty cycle; Step f: determine whether the power at the global maximum power point meets the set restart condition. If |1-(v pv *i pv ) / P max |≥0.1, indicating that the external environment changes and the power changes greatly, then enter the global search mode and return to step a. If |1-(v pv *i pv ) / P max |<0.1, execute step g; Step g: adjust PWM according to the final duty cycle, and then control the Boost circuit to achieve the operation of the photovoltaic array at the global maximum power point.

2. A photovoltaic maximum power control method combining cubic spline interpolation and improved P&O, characterized in that: The six duty cycles applied in step a are evenly distributed in the range of [0.15, 0.85], that is, the corresponding voltages are distributed from large to small.

3. A photovoltaic maximum power control method combining cubic spline interpolation and improved P&O, characterized in that: In step b, if d max If d is in the middle, max It is recorded as d3, and the two adjacent duty cycles are recorded as d1 and d5; if d max is d 6 , then d max Recorded as d4, d5 takes d 6 +0.05, d2 = d 5 , d1=d 4 , insert auxiliary duty cycle d3 between d2 and d4; if d max is d 1 , then d max Recorded as d2, d1 takes d 1 -0.05, d4 = d 2 , d5=d 3 , insert auxiliary duty cycle D3 between D2 and D4.

4. A photovoltaic maximum power control method combining cubic spline interpolation and improved P&O, characterized in that: In step c, the method of inserting the auxiliary duty cycle is as follows: n =(d n-1 +d n+1 ) / 2+α, where α is a random value in (0,0.1).

5. A photovoltaic maximum power control method combining cubic spline interpolation and improved P&O, characterized in that: In step d, v1 to v5 strictly satisfy increasing or decreasing and interpolation every 0.01, where d is extracted mpp The formula is as follows: This formula is applicable to the case where the output end is a resistive load; This formula is applicable to the case where the output voltage is fixed.

6. A photovoltaic maximum power control method combining cubic spline interpolation and improved P&O, characterized in that: Step e is as follows: Measure the input voltage V K 、V K-1 、V K-2 , input current I K ,I K-1 ,I K-2 ,have: P K =V K ×I K ,P K-1 =V K-1 ×I K-1 ,P K-2 =V K-2 ×I K-2 ,ΔP K =P K -P K-1 ,ΔP K-1 =P K-1 -P K-2 ,ΔV K =V K -V K-1 Compared with the traditional perturbation and observation method, the improved P&O algorithm is as follows: When ΔP K >0, satisfying ΔV K >0, and ΔP K-1 >0,d * =d mpp -Δd, if ΔP is not satisfied K-1 >0,d * =d mpp ; When ΔP K >0, does not satisfy ΔV K >0, and ΔP K-1 >0,d * =d mpp +Δd, if ΔP is not satisfied K-1 >0,d * =d mpp ; When ΔP K ≤0, satisfying ΔV K >0, and ΔP K-1 >0,d * =d mpp +Δd, if ΔP is not satisfied K-1 >0,d * =d mpp ; When ΔP K ≤0, does not satisfy ΔV K >0, and ΔP K-1 >0,d * =d mpp -Δd, if ΔP is not satisfied K-1 >0d * =d mpp ; Where Δd is the variable step size, and the update formula is as follows: Where S max The maximum step size coefficient can be set to 0.01.

Images