阅读说明：本技术 一种改进的光伏发电系统mppt方法 (Improved MPPT method of photovoltaic power generation system ) 是由 李洁 魏登 李壮 李宁 于 2021-10-14 设计创作，主要内容包括：本发明公开了一种改进的光伏发电系统MPPT方法,具体包括如下步骤：步骤1,计算光伏板的输出功率P-(pv)以及变换器输入功率P-(L)；步骤2,对第一个周期t-(1)增加变换器输入功率；步骤3,每过周期t-(1)判断一次ΔP-(pv)(t-(1))/ΔV-(pv)(t-(1))的正负；步骤4,每过周期t-(2)判断一次ΔP-(pv)(t-(2))/ΔV-(pv)(t-(2))的正负；步骤5,将当前时刻的功率参考值P-(ref)(t)与变换器输入功率P-(L)作差,经过PI调节器转化为脉冲信号,驱动开关管IGBT的通断。本发明解决了现有直接功率控制的MPPT方法以及传统算法扰动速度和精度无法兼顾,稳态工作时会因振荡而损失能量,输出功率无法实现与负载功率的自平衡问题。(The invention discloses an improved MPPT method of a photovoltaic power generation system, which specifically comprises the following steps: step 1, calculating the output power P of the photovoltaic panel pv And converter input power P L (ii) a Step 2, aiming at the first period t 1 Increasing the converter input power; step 3, every passing period t 1 Determining the primary Δ P pv (t 1 )/ΔV pv (t 1 ) Positive and negative; step 4, every passing period t 2 Determining the primary Δ P pv (t 2 )/ΔV pv (t 2 ) Positive and negative; step 5, the power reference value P of the current moment is obtained ref (t) and converter input power P L And (4) making a difference, converting the difference into a pulse signal through a PI regulator, and driving the on-off of the IGBT. The invention solves the problems that the disturbance speed and precision of the traditional MPPT method for direct power control and the traditional algorithm cannot be considered at the same time, energy is lost due to oscillation during steady-state work, and self-balancing between output power and load power cannot be realized.)

1. An improved MPPT method of a photovoltaic power generation system is characterized in that: the method specifically comprises the following steps:

step 1, controlling the input power P of the converter_LRespectively collecting the output current I of the photovoltaic panel to be 0_pvThe current I flowing through the converter_LAnd the output voltage V of the photovoltaic panel_pvAnd calculating the output power P of the photovoltaic panel at the moment_pvAnd converter input power P_L；

Step 2, aiming at the first period t₁Increasing the converter input power;

step 3, starting from the second period, every period t₁Determining the primary Δ P_pv(t₁)/ΔV_pv(t₁) Positive and negative;

step 4, starting from the second period, every period t₂Determining the primary Δ P_pv(t₂)/ΔV_pv(t₂) Positive and negative;

step 5, the power reference value P of the current moment is obtained_ref(t) and converter input power P_LAnd (4) making a difference, converting the difference into a pulse signal through a PI regulator, and driving the on-off of the IGBT.

2. The improved MPPT method for photovoltaic power generation systems of claim 1, wherein: in the step 1, the output power P of the photovoltaic panel is calculated by adopting the following formula (1)_pvCalculating the input power P of the converter by using the following formula (2)_L：

P_pv＝V_pv·I_pv (1)；

P_L＝V_pv·I_L (2)。

3. The improved MPPT method for photovoltaic power generation systems of claim 2, wherein: in the step 2, a first period t₁After the input power of the converter is increased, the following formula (3) is satisfied:

P_L(t₁)＝P_L+P_up (3)。

4. the improved MPPT method for photovoltaic power generation systems of claim 3, wherein: in said step 3,. DELTA.P_pv(t₁)/ΔV_pv(t₁) The judgment process comprises the following steps:

when Δ P_pv(t₁)/ΔV_pv(t₁) When the value is more than or equal to 0, the operation is not performed;

when Δ P_pv(t₁)/ΔV_pv(t₁) When less than 0, then:

P_ref(t)＝P_L(t)+ln[1-ΔP_pv(t₁)/ΔV_pv(t₁)]P_up (4)。

5. the improved MPPT method for photovoltaic power generation systems of claim 3, wherein: in said step 4,. DELTA.P_pv(t₂)/ΔV_pv(t₂) The judging process is as follows:

when Δ P_pv(t₂)/ΔV_pv(t₂) When the ratio is greater than or equal to 0, then:

P_ref(t)＝P_L(t)-ln[1+ΔP_pv(t₂)/ΔV_pv(t₂)]P_down (5)；

when Δ P_pv(t₂)/ΔV_pv(t₂) If the value is less than 0, the operation is not performed.

Technical Field

The invention belongs to the technical field of new energy power generation, and relates to an improved MPPT method of a photovoltaic power generation system.

Background

In recent years, the problems of energy shortage and environmental pollution are increasingly serious, and clean, efficient and environment-friendly energy is pursued in the market. Solar energy is a hotspot of new energy research due to the characteristics of wide distribution, easy acquisition, high cleaning efficiency, sustainability and the like.

The photovoltaic power generation system consists of a solar cell, a storage battery, a controller and an inverter and can convert solar energy into electric energy. The output of the solar cell panel has nonlinearity, and the P-V curve of the solar cell panel has unimodal characteristic. In order to obtain solar energy to the maximum, the solar panel is required to operate at the Maximum Power Point (MPP).

At present, the mainstream MPPT (maximum power point tracking) method mostly adopts a disturbance observation method (P & O), also called a mountain climbing method or a mountain climbing method, and a conductance increment method (INC) and some improved methods thereof (such as variable step length, zero oscillation, etc.). The two methods have simple and understandable principle and are convenient to realize. The method has the advantages of easy realization, moderate display precision and oscillation of the working point around the Maximum Power Point (MPP). However, the method is slow and not suitable for the condition of rapid change, and simultaneously the quality of grid-connected current is easily influenced.

These disadvantages are inherent in the algorithm itself and can only be improved but not eliminated. There are therefore other methods such as fuzzy logic, neural network algorithms, etc. which are very complex and therefore not much used.

Disclosure of Invention

The invention aims to provide an improved MPPT method of a photovoltaic power generation system, and solves the problems that the conventional MPPT method for direct power control and the disturbance speed and precision of a traditional algorithm cannot be considered at the same time, energy is lost due to oscillation during steady-state work, and self-balance between output power and load power cannot be realized.

The invention adopts the technical scheme that an improved MPPT method of a photovoltaic power generation system specifically comprises the following steps:

step 1, controlling the input power P of the converter_LRespectively collecting the output current I of the photovoltaic panel to be 0_pvThe current I flowing through the converter_LAnd the output voltage V of the photovoltaic panel_pvAnd calculating the output power P of the photovoltaic panel at the moment_pvAnd converter input power P_L；

Step 2, aiming at the first period t₁Increasing the converter input power;

step 3, starting from the second period, every period t₁Determining the primary Δ P_pv(t₁)/ΔV_pv(t₁) Positive and negative;

step 4, starting from the second period, every period t₂Determining the primary Δ P_pv(t₂)/ΔV_pv(t₂) Positive and negative;

step 5, the power reference value P of the current moment is obtained_ref(t) and converter input power P_LAnd (4) making a difference, converting the difference into a pulse signal through a PI regulator, and driving the on-off of the IGBT.

The invention is also characterized in that:

calculating the output power P of the photovoltaic panel by adopting the following formula (1)_pvCalculating the input power P of the converter by using the following formula (2)_L：

P_pv＝V_pv·I_pv (1)；

P_L＝V_pv·I_L (2)。

In step 2, the first period t₁After the input power of the converter is increased, the following formula (3) is satisfied:

P_L(t₁)＝P_L+P_up (3)。

in step 3,. DELTA.P_pv(t₁)/ΔV_pv(t₁) The judgment process comprises the following steps:

when Δ P_pv(t₁)/ΔV_pv(t₁) When the value is more than or equal to 0, the operation is not performed;

when Δ P_pv(t₁)/ΔV_pv(t₁) When less than 0, then:

P_ref(t)＝P_L(t)+ln[1-ΔP_pv(t₁)/ΔV_pv(t₁)]P_up (4)。

in step 4,. DELTA.P_pv(t₂)/ΔV_pv(t₂) The judging process is as follows:

when Δ P_pv(t₂)/ΔV_pv(t₂) When the ratio is greater than or equal to 0, then:

P_ref(t)＝P_L(t)-ln[1+ΔP_pv(t₂)/ΔV_pv(t₂)]P_down (5)；

when Δ P_pv(t₂)/ΔV_pv(t₂) If the value is less than 0, the operation is not performed.

The invention has the beneficial effects that: compared with the traditional MPPT method for power control, the traditional algorithm has the output voltage V of the photovoltaic panel when the illumination changes_pvThe invention has the advantages of extremely low cost, too large loss and restarting requirement, and the output voltage V of the photovoltaic panel can not appear when illumination changes by redesigning the power reference value_pvThe method has the advantages of extremely low cost, no need of restarting, and reduced loss, and the logarithmic function of the invention is superior to the traditional power control algorithm in tracking speed and precision.

Drawings

FIG. 1 is a topological diagram of a solar photovoltaic power generation system in an embodiment of an improved MPPT method for a photovoltaic power generation system of the present invention;

FIG. 2 is a schematic flow chart of an MPPT control method of a photovoltaic power generation system according to the present invention;

3(a) -3 (d) are graphs illustrating the operation of the photovoltaic system in an MPPT method for an improved photovoltaic power generation system according to the present invention;

FIG. 4 is a graph comparing the theoretical maximum power point achieved by the MPPT method of an improved photovoltaic power generation system of the present invention with a conventional method;

FIG. 5 is a graph of photovoltaic panel power simulation in a conventional manner;

FIG. 6 is a diagram illustrating simulation of photovoltaic panel power in an MPPT method for an improved photovoltaic power generation system according to the present invention;

FIG. 7 is a simulation diagram of a conventional method in steady state;

fig. 8 is a simulation diagram of an improved MPPT method of a photovoltaic power generation system according to the present invention in a steady state.

Detailed Description

The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

FIG. 1 is a circuit diagram of a solar photovoltaic power generation system, the inventionDetailed description is made by using Sepic circuit; wherein L is₁、L₂Is an inductor, C₁、C₂Is a capacitor, R_LTo be a load, D₁Is a diode, the power P is shown in FIG. 1_LAnd P_CThe formula (1) is obviously established for the flow direction of (1).

P_pv＝P_L+P_C (1)；

The invention discloses an improved MPPT method of a photovoltaic power generation system, which specifically comprises the following steps:

step 1, controlling the input power P of the converter_LTo 0, collecting the output current I of the photovoltaic panel_pvInductor L₁Current I of_LAnd the output voltage V of the photovoltaic panel_pvAnd calculating the output power P of the photovoltaic panel at the moment_pvAnd converter input power P_L。

Wherein P is_pv＝V_pv·I_pv，P_L＝V_pv·I_L. As can be seen from FIG. 1, there is P_pv＝P_L+P_CWhen the system is stable, there is P_pv＝P_LSo that only the converter input power P needs to be controlled_L。

Step 2, the first period t₁Increasing converter input power to P_L(t₁)＝P_L+P_up(ii) a The converter power is increased in order to disturb the operating state of the system, so that the power value and the voltage value change. P_L(t₁) Is a period t₁Converter input power in;

step 3, starting from the second period, every period t₁Determination of Δ P_pv(t₁)/ΔV_pv(t₁) Positive and negative; if the current value is more than or equal to 0, the operation is not carried out; if less than 0, P_ref(t)＝P_L(t)+ln[1-ΔP_pv(t₁)/ΔV_pv(t₁)]P_upIn which P is_upIs a power up value. Delta P_pv(t₁) Is a period t₁Difference of output power of inner photovoltaic panel, Δ V_pv(t₁) Is a period t₁The difference of the output voltages of the inner photovoltaic panels.

Step 4, independently proceeding with step 3, without sequence relation, starting from the second period, every period t₂Determination of Δ P_pv(t₂)/ΔV_pv(t₂) Positive and negative; if not less than 0, P_ref(t)＝P_L(t)-ln[1+ΔP_pv(t₂)/ΔV_pv(t₂)]P_downIn which P is_downIs the power droop value; if the current value is less than 0, the operation is not carried out; delta P_pv(t₂) Is a period t₂Difference of output power of inner photovoltaic panel, Δ V_pv(t₂) Is a period t₂The difference in the output voltage of the photovoltaic panel.

Step 5, the power reference value P of the current moment is obtained_ref(t) and converter input power P_LAnd (4) making a difference, converting the difference into a pulse signal through a PI regulator, and driving the on-off of the IGBT.

ΔP_pv(t)＝P_pv(t)-P_pv(t-1)；

Wherein, is Δ V_pvAnd (t) is the difference of the output voltages of the photovoltaic panels at the current time t.

P_pv(t) is the output power of the photovoltaic panel at the current moment t;

P_pv(t-1) is the output power of the photovoltaic panel at the time t-1;

ΔV_pv(t)＝V_pv(t)-V_pv(t-1)；

ΔV_pv(t) is the difference of the output voltage of the photovoltaic panel at the current time t;

V_pv(t) is the output voltage of the photovoltaic panel at the current moment t;

V_pv(t-1) is the output voltage of the photovoltaic panel at the time t-1;

in step 3, the determination of Δ P_pv(t)/ΔV_pvThe sign of (t) indicates whether the working point is located in the left half plane or the right half plane, and according to the theory of fig. 3(a), 3(b), 3(c) and 3(d), when the working point is located in the right half plane, the power reference value should be adjusted up, and when the working point is located in the left half plane, the power reference value should be adjusted down.

FIG. 3(a) is a graph of the operating characteristics of a photovoltaic system operating in the left plane of the characteristic with increasing converter power;

FIG. 3(b) is a graph of the photovoltaic system operating in the left plane of the characteristic curve with reduced converter power;

FIG. 3(c) is a graph of the photovoltaic system operating in the right plane of the characteristic curve with increasing converter power;

FIG. 3(d) is a diagram of the photovoltaic system operating in the right plane of the characteristic curve with reduced converter power;

from fig. 3(a), when the stable operating point is to the left of the maximum power point, P is increased_L，P_pvDoes not change instantaneously in order to satisfy formula P_pv＝P_L+P_C，P_CDecrease of V_CDecrease, resulting in the runaway of the circuit, where V_CThe voltage at the two ends of the capacitor is the output voltage of the photovoltaic panel; according to fig. 3(b), when the stable operating point is to the left of the maximum power point, P is decreased_L，P_pvDoes not change instantaneously in order to satisfy formula P_pv＝P_L+P_C，P_CEnlargement, V_CIncreasing, and stabilizing to the right of the maximum power point; according to fig. 3(c), when the stable operating point is to the right of the maximum power point, P is increased_L，P_pvDoes not change instantaneously in order to satisfy formula P_pv＝P_L+P_C，P_CDecrease of V_CDecreasing, and then increasing the power value; according to fig. 3(d), when the stable operating point is to the right of the maximum power point, P is decreased_L，P_pvDoes not change instantaneously in order to satisfy formula P_pv＝P_L+P_C，P_CIncrease of V_CIncreasing, when the power value decreases;

FIG. 4 illustrates the speed at which the maximum power point is reached and the fluctuation range of steady-state oscillations of the method of the present invention and conventional power control, according to which it is shown that during the near open start phase, dP/dV ≦ -1, fast tracking, fast approaching the maximum power point, slows down, and enters the left half plane for slower exceeding the maximum power point.

FIGS. 5-6 are simulation graphs of the photovoltaic panel with parameters of the photovoltaic panel according to the present invention and the conventional methodV_oc＝20V，V_mpp＝17V，I_sc＝3A，I_mpp2.94 under illumination of 1000W/m²The maximum power at 25 ℃ was 49.98W. The illumination intensity of the simulation is 800-500-800W/m²At a temperature of 25 ℃ wherein P_up＝2，P_down＝0.3，t₁＝0.003s，t₂It can be seen that fig. 6 reaches the maximum power point through 0.6s, and fig. 5 reaches the maximum power point through 1.4s, i.e. the method has faster tracking speed compared to the conventional algorithm.

Fig. 7-8 are steady-state power waveforms at time 0.8s to 0.9s, and it can be seen that fig. 8 has smaller oscillation and fluctuation range and lower power loss compared with fig. 7. The tracking speed and the steady-state oscillation error are better than those of the traditional power algorithm.