阅读说明：本技术 一种快速状态追踪的变步长mppt光伏发电稳定性控制方法 (Variable-step MPPT photovoltaic power generation stability control method for rapid state tracking ) 是由 郑含博 杜齐 胡永乐 郭文豪 覃团发 于 2021-08-31 设计创作，主要内容包括：本发明公开了一种快速状态追踪的变步长MPPT光伏发电稳定性控制方法,该方法首先通过变步长实现快速跟踪最大功率点,当确定到达稳态之后,停止人工扰动,实现无振荡稳定输出功率,从而减少因振荡造成的功率损耗,提高了整个系统的效率；当外界环境突变时,该算法运用三点测量法可以根据电压、电流值的突变检测出工作条件的变化,并重置参数,从而降低重新追踪最大功率点的时间,实现了在保持基本的扰动观察法简单以及便于实现的特点的同时,还能停止稳态振荡并具备良好的追踪速度的效果。(The invention discloses a variable-step MPPT photovoltaic power generation stability control method for rapid state tracking, which comprises the steps of firstly realizing rapid tracking of a maximum power point through variable step length, stopping manual disturbance after confirming to reach a steady state, and realizing stable output power without oscillation, thereby reducing power loss caused by oscillation and improving the efficiency of the whole system; when the external environment suddenly changes, the algorithm can detect the change of the working condition according to the sudden change of the voltage and the current value by using a three-point measurement method, and resets parameters, so that the time for tracking the maximum power point again is shortened, the characteristics of simplicity and convenience in implementation of a basic disturbance observation method are kept, and the effect of stopping steady-state oscillation and having good tracking speed is realized.)

1. A variable-step MPPT photovoltaic power generation stability control method capable of realizing rapid state tracking is characterized by comprising the following steps of: the method comprises the following steps:

s1, sampling the output voltage u (k) and the output current i (k) of the photovoltaic array in the k-th cycle for the operating photovoltaic array, and calculating the output power p (k) ═ u (k) × i (k) at that time; setting two variables m and n for changing the step length, and respectively setting the initial values as m-1 and n-1;

s2, sampling the sampling values of the (k-1) th period and the (k-2) th period for the photovoltaic array in operation, and performing difference with the data of the k-th period:

dU1＝U(k)-U(k-1)；

dU2＝U(k-1)-U(k-2)；

dI1＝I(k)-I(k-1)；

dI2＝I(k-1)-I(k-2)；

dP1＝P(k)-P(k-1)；

dP2＝P(k-1)-P(k-2)；

s3, determining whether | dP1/dU1| >0.98 × i (k) is true from the calculated value in S2:

if yes, making m ═ a, wherein a is a constant greater than 1;

if not, the value of m is not changed;

s4, judging whether | dP1/dU1| < ε 1 is true, wherein ε 1 is a constant greater than 0:

if yes, making m ═ b, wherein b is a constant less than 1;

if not, the value of m is not changed;

s5, judging whether | dP1/dU1| < ε 2 is established, wherein ε 2 is a constant greater than 0:

if yes, making n equal to 0;

if not, the value of n is unchanged;

s6, judging whether (dI1< epsilon 3) & (dI2> epsilon 4) is established, wherein epsilon 3 and epsilon 4 are constants larger than 0:

if yes, making m be a;

if not, the value of m is not changed;

s7, it is determined whether dP/dU is 0:

if yes, performing reassignment:

let U (k-2) ═ U (k-1), U (k-1) ═ U (k);

I(k-2)＝I(k-1)、I(k-1)＝I(k)；

P(k-2)＝P(k-1)、P(k-1)＝P(k)；

returning the data after the value assignment to the step S1;

if not, go to step S8;

s8, judging whether dP/dU >0 is satisfied:

if yes, return to step S1 by making Uref + Δ U m n;

if not, making Uref- Δ U m n, and returning to step S1;

where Δ U is the initial step size.

2. The method for controlling the stability of the MPPT photovoltaic power generation with the variable step size by the fast state tracking as claimed in claim 1, wherein: in step S3, the value of a is preset as needed to increase the step size.

3. The method for controlling the stability of the MPPT photovoltaic power generation with the variable step size by the fast state tracking as claimed in claim 1, wherein: in step S4, the value of ∈ 1 is preset as needed, and the preset value is set to a positive value approaching 0.

4. The method for controlling the stability of the MPPT photovoltaic power generation with the variable step size by the fast state tracking as claimed in claim 1, wherein: in step S5, the value of ∈ 2 is preset as needed, and the preset value is set to a positive value approaching 0.

Technical Field

The invention belongs to the technical field of photovoltaic power generation, and particularly relates to a variable-step MPPT photovoltaic power generation stability control method for rapid state tracking.

Background

In recent years, clean energy has been receiving more and more attention from international society in order to cope with the problems of depletion of fossil energy, environmental pollution, climate change, and the like. Because solar energy has the advantages of large total energy, easy resource development, cleanness, no pollution and the like, the photovoltaic power generation technology is becoming the key point of research and utilization in various countries.

Since the output characteristics of the photovoltaic cell itself are affected by environmental conditions such as solar irradiance and temperature, and the current-voltage characteristic curve thereof is nonlinear; in order to improve the generating efficiency of the photovoltaic cell, a Maximum Power Point Tracking (MPPT) technology is introduced to enable the photovoltaic cell to obtain maximum power output; MPPT algorithms are various, and currently, disturbance observation (P & O) and conductance Increment (INC) are most widely used because they are simple and easy to implement, and can achieve tracking effect well. Because the conventional P & O and INC step lengths are fixed, it is not possible to both quickly track the maximum power point and maintain low oscillation at steady state. When the step length is too large, the steady-state oscillation is also large, the system stability is poor and energy loss is caused; when the step length is too small, the maximum power point tracking time is increased, and the tracking effect is poor. In addition, the two methods generate large fluctuation when the external environment is mutated, and the time for tracking the MPP again is long.

In order to improve the performance of a P & O algorithm and utilize solar energy resources with maximum efficiency, a variable-step MPPT photovoltaic power generation stability control method for fast state tracking is designed to solve the problems by starting from aspects of improving the speed of searching a maximum power point, reducing oscillation during system steady state and the like.

Disclosure of Invention

The invention aims to solve the technical problem of providing a variable-step MPPT photovoltaic power generation stability control method for rapid state tracking, and the method can stop steady-state oscillation and has good tracking speed while keeping the characteristics of simple basic disturbance observation method and convenient realization, reduces power loss caused by oscillation, improves the efficiency of the whole system, can reduce the time for re-tracking the maximum power point, and solves the problems that the prior art system has poor stability and poor tracking effect, cannot realize rapid tracking of the maximum power point and can keep low oscillation in a steady state.

In order to solve the technical problems, the technical scheme adopted by the invention is as follows:

a variable-step MPPT photovoltaic power generation stability control method capable of realizing rapid state tracking comprises the following steps:

s1, sampling the output voltage u (k) and the output current i (k) of the photovoltaic array in the k-th cycle for the operating photovoltaic array, and calculating the output power p (k) ═ u (k) × i (k) at that time; setting two variables m and n for changing the step length, and respectively setting the initial values as m-1 and n-1;

s2, sampling the sampling values of the (k-1) th period and the (k-2) th period for the photovoltaic array in operation, and performing difference with the data of the k-th period:

dU1＝U(k)-U(k-1)；

dU2＝U(k-1)-U(k-2)；

dI1＝I(k)-I(k-1)；

dI2＝I(k-1)-I(k-2)；

dP1＝P(k)-P(k-1)；

dP2＝P(k-1)-P(k-2)；

s3, determining whether | dP1/dU1| >0.98 × i (k) is true from the calculated value in S2:

if yes, making m ═ a, wherein a is a constant greater than 1;

if not, the value of m is not changed;

s4, judging whether | dP1/dU1| < ε 1 is true, wherein ε 1 is a constant greater than 0:

if yes, making m ═ b, wherein b is a constant less than 1;

if not, the value of m is not changed;

s5, judging whether | dP1/dU1| < ε 2 is established, wherein ε 2 is a constant greater than 0:

if yes, making n equal to 0;

if not, the value of n is unchanged;

s6, judging whether (dI1< epsilon 3) & (dI2> epsilon 4) is established, wherein epsilon 3 and epsilon 4 are constants larger than 0:

if yes, making m be a;

if not, the value of m is not changed;

s7, it is determined whether dP/dU is 0:

if yes, performing reassignment:

let U (k-2) ═ U (k-1), U (k-1) ═ U (k);

I(k-2)＝I(k-1)、I(k-1)＝I(k)；

P(k-2)＝P(k-1)、P(k-1)＝P(k)；

returning the data after the value assignment to the step S1;

if not, go to step S8;

s8, judging whether dP/dU >0 is satisfied:

if yes, return to step S1 by making Uref + Δ U m n;

if not, making Uref- Δ U m n, and returning to step S1;

where Δ U is the initial step size.

Preferably, in step S3, the value of a is preset as needed to increase the step size, so as to achieve the purpose of quickly finding the maximum power point.

Preferably, in step S4, the value of ∈ 1 is preset as needed, and the preset value is set to a positive value approaching 0, which means that the operating point is closer to the maximum power point at this time, and the value b can reduce the step size, so as to achieve the purpose of more accurately searching the maximum power point and reducing the oscillation.

Preferably, in step S5, the value of ∈ 2 is preset as needed, the preset value is set to a positive value approaching 0, which means that the operating point is already approximated to the maximum power point, and the value of n is 0 to achieve the purpose of stopping the artificial disturbance.

Preferably, in step S6, it is able to detect whether the external environment has a sudden change by setting the values of ∈ 3 and ∈ 4, and if the environment has a sudden change, the maximum power point is quickly found again by changing the value of m with a large step.

Preferably, in step S8, Δ U is an initial step size, and the step size can be changed by changing the values of m and n.

The invention has the beneficial effects that:

the invention adopts a three-section self-adaptive variable-step method, the tracking speed is greatly accelerated by adopting a large step at the beginning, the original step transition is adopted in the middle period, and the purpose of more accurately searching the maximum power point and reducing the oscillation is realized by adopting a small step in the later period. Stopping artificial disturbance after finding the maximum power point, and eliminating steady-state oscillation;

2, measuring current values of three continuous working points by adopting a three-point measuring method, calculating two current difference values dI1 and dI2, detecting whether the external environment has sudden change or not by utilizing the two current difference values dI1 and dI2, and quickly tracking the maximum power point again when the external environment has sudden change;

3, the invention verifies the reliability of the performance through a simulation test and improves the generating efficiency of the photovoltaic cell.

Drawings

FIG. 1 is a graph of the I-U characteristics of a photovoltaic cell of the present invention;

FIG. 2 is a graph of the P-U characteristics of a photovoltaic cell of the present invention;

FIG. 3 is a flow chart of an improved P & O algorithm of the present invention;

FIG. 4 is a simulation model diagram of a light storage hybrid system according to an embodiment of the present invention;

FIG. 5 is a graph comparing output power of a conventional P & O algorithm and a modified P & O algorithm according to an embodiment of the present invention;

fig. 6 is a SOC variation diagram of the energy storage battery according to the embodiment of the invention.

Detailed Description

Example 1:

as shown in fig. 1-2, under the same illumination and temperature conditions, the P-U curve of the photovoltaic cell is similar to a parabola, and the theoretical output voltage and output current of the photovoltaic cell can be the case of any point on the I-U characteristic curve, and the actual output value thereof depends on the case of external load impedance; the maximum power point tracking technology is to adjust the resistance value of an external equivalent resistor through a control algorithm and an external circuit under different environments so as to change the output voltage and the output current of a photovoltaic cell, so that the photovoltaic cell continuously keeps the maximum power output, and the power generation efficiency of the photovoltaic cell is improved.

As shown in fig. 3, a method for controlling the stability of MPPT photovoltaic power generation with a fast state tracking variable step size includes the following steps:

s1, sampling the output voltage u (k) and the output current i (k) of the photovoltaic array in the k-th cycle for the operating photovoltaic array, and calculating the output power p (k) ═ u (k) × i (k) at that time; setting two variables m and n for changing the step length, and respectively setting the initial values as m-1 and n-1;

s2, sampling the sampling values of the (k-1) th period and the (k-2) th period for the photovoltaic array in operation, and performing difference with the data of the k-th period:

dU1＝U(k)-U(k-1)；

dU2＝U(k-1)-U(k-2)；

dI1＝I(k)-I(k-1)；

dI2＝I(k-1)-I(k-2)；

dP1＝P(k)-P(k-1)；

dP2＝P(k-1)-P(k-2)；

s3, determining whether | dP1/dU1| >0.98 × i (k) is true from the calculated value in S2:

if yes, making m ═ a, wherein a is a constant greater than 1;

if not, the value of m is not changed;

s4, judging whether | dP1/dU1| < ε 1 is true, wherein ε 1 is a constant greater than 0:

if yes, making m ═ b, wherein b is a constant less than 1;

if not, the value of m is not changed;

s5, judging whether | dP1/dU1| < ε 2 is established, wherein ε 2 is a constant greater than 0:

if yes, making n equal to 0;

if not, the value of n is unchanged;

s6, judging whether (dI1< epsilon 3) & (dI2> epsilon 4) is established, wherein epsilon 3 and epsilon 4 are constants larger than 0:

if yes, making m be a;

if not, the value of m is not changed;

s7, it is determined whether dP/dU is 0:

if yes, performing reassignment:

let U (k-2) ═ U (k-1), U (k-1) ═ U (k);

I(k-2)＝I(k-1)、I(k-1)＝I(k)；

P(k-2)＝P(k-1)、P(k-1)＝P(k)；

returning the data after the value assignment to the step S1;

if not, go to step S8;

s8, judging whether dP/dU >0 is satisfied:

if yes, return to step S1 by making Uref + Δ U m n;

if not, making Uref- Δ U m n, and returning to step S1;

where Δ U is the initial step size.

Preferably, in step S3, the value of a is preset as needed to increase the step size, so as to achieve the purpose of quickly finding the maximum power point.

Preferably, in step S4, the value of ∈ 1 is preset as needed, and the preset value is set to a positive value approaching 0, which means that the operating point is closer to the maximum power point at this time, and the value b can reduce the step size, so as to achieve the purpose of more accurately searching the maximum power point and reducing the oscillation.

Preferably, in step S5, the value of ∈ 2 is preset as needed, the preset value is set to a positive value approaching 0, which means that the operating point is already approximated to the maximum power point, and the value of n is 0 to achieve the purpose of stopping the artificial disturbance.

Preferably, in step S6, it is able to detect whether the external environment has a sudden change by setting the values of ∈ 3 and ∈ 4, and if the environment has a sudden change, the maximum power point is quickly found again by changing the value of m with a large step.

Preferably, in step S8, Δ U is an initial step size, and the step size can be changed by changing the values of m and n.

Example 2:

as shown in fig. 4, the model mainly comprises a photovoltaic array, a Boost converter, a load, an energy storage lithium battery and an MPPT controller; in the simulation process, the set temperature is 25 ℃ and the illumination intensity is 800W/m at the beginning²From 800W/m at 1s²Jump to 1kW/m²To explore the larger magnitude of illumination changes, from 1kW/m at 2s²The transition is 400W/m²。

As shown in fig. 5, compared with the conventional P & O algorithm, the improved P & O algorithm adopted in the present invention can track the maximum power point more quickly, and basically has no oscillation in a steady state, and the output power is also improved more, and through calculation, the improvement efficiency can reach 0.39% at most, and the improvement effect is more significant as the illumination intensity increases.

As shown in fig. 6, it can be seen from the graph that the SOC of the energy storage battery increases from the initial 45% to 45.0042% (at 1 s) approximately linearly, then increases to 45.0113% (at 2 s) with a larger slope approximately linearly, and finally decreases to 45.0093% (at 3 s) approximately linearly; the cause of this change was analyzed as follows:

because when the illumination intensity is 800W/m²And 1000W/m²During the process, the generating power of the photovoltaic array is greater than the power consumption of the load, so the residual electric energy can be used for charging the energy storage battery, the curve is in an ascending trend, and the greater the illumination intensity is, the greater the generating power is, the faster the charging rate is, and the greater the slope of the curve is. However, when the illumination intensity is 400W/m²When the output power of the photovoltaic array is not enough to supply power to the load alone, the energy storage battery supplies power to the load at the same time, so the SOC of the energy storage battery is reduced between 2s and 3 s. In addition, when the illumination intensity is not changed, the output power of the photovoltaic array is constant in a steady state, so that the SOC change condition of the energy storage battery is close to linearity.

The above-described embodiments are merely preferred embodiments of the present invention, and should not be construed as limiting the present invention, and features in the embodiments and examples in the present application may be arbitrarily combined with each other without conflict. The protection scope of the present invention is defined by the claims, and includes equivalents of technical features of the claims. I.e., equivalent alterations and modifications within the scope hereof, are also intended to be within the scope of the invention.