阅读说明：本技术 提高光伏模拟器适应光伏逆变器追踪稳定性的方法及系统 (Method and system for improving tracking stability of photovoltaic simulator adaptive to photovoltaic inverter ) 是由 钟钢炜 赵涛 蔡振鸿 唐德平 于 2021-09-24 设计创作，主要内容包括：提高光伏模拟器适应光伏逆变器追踪稳定性的方法及系统,属于光伏逆变器测试技术领域,解决传统的在整个电压-电流特性曲线范围内将电流值设为基准值让光伏模拟器输出电流逐渐收敛至此电流值的方式而导致的逆变器追踪稳定性差的问题；本发明的技术方案将电压-电流特性曲线分为两个区域,即最大功率点右侧和最大功率点左侧,当运行点在不同的区域时,采用不同的控制模式,实现了光伏模拟器在电压-电流特性曲线的全范围都能够保证稳定工作,提高了光伏模拟器在模拟光伏组件电压-电流特性曲线的全范围段的输出稳定性,从而提高光伏逆变器的追踪稳定性。(A method and a system for improving tracking stability of a photovoltaic simulator adapted to a photovoltaic inverter belong to the technical field of photovoltaic inverter testing, and solve the problem of poor tracking stability of the inverter caused by the traditional mode that the current value is set as a reference value in the whole voltage-current characteristic curve range, and the current output by the photovoltaic simulator is gradually converged to the current value; according to the technical scheme, the voltage-current characteristic curve is divided into two areas, namely the right side of the maximum power point and the left side of the maximum power point, when the operation point is in different areas, different control modes are adopted, the photovoltaic simulator can guarantee stable operation in the whole range of the voltage-current characteristic curve, the output stability of the photovoltaic simulator in the whole range section of the voltage-current characteristic curve of the simulated photovoltaic module is improved, and therefore the tracking stability of the photovoltaic inverter is improved.)

1. The method for improving tracking stability of the photovoltaic simulator adaptive to the photovoltaic inverter is characterized by comprising the following steps of:

s1, according to the voltage V of the mpp point_mpMpp point current I_mpOpen circuit voltage V_ocShort-circuit current I_scCalculating a voltage-current characteristic curve simulating the characteristics of the photovoltaic module;

s2, measuring the output voltage and current value of the current working point of the photovoltaic simulator, and obtaining the output voltage V according to the measured output voltage_oJudging whether the current working point is positioned on the right side or the left side of the maximum power point, and correspondingly selecting a control mode as follows:

s21, if the current working point is located at the right side of the maximum power point, adopting a current voltage checking method, and according to the measured output current value I of the photovoltaic simulator₁Obtaining the corresponding voltage value V on the voltage-current characteristic curve₁At the moment, the control mode of the photovoltaic simulator is modified into a CV mode, and the given voltage value is modified into: v_n+k*(V₁-V_n)；

S22, if the current working point is located at the left side of the maximum power point, adopting a voltage and current checking method to check the current according to the measured output voltage value V of the photovoltaic simulator₂Obtaining the corresponding current value I on the voltage-current characteristic curve₂At the moment, the control mode of the photovoltaic simulator is modified into a CC mode,the given current value is modified as follows: i is_n+k*(I₂-I_n)；

Wherein k represents a convergence coefficient, V_nIndicating the present voltage set-point, V₁Indicating a desired voltage set-point, I_nIndicating the current set point, I₂Indicating the desired current setpoint, and k the convergence factor.

2. The method of claim 1, wherein the step S1 of calculating the voltage-current characteristic curve of the simulated photovoltaic module characteristic is as follows:

wherein, V_ocRepresents the open circuit voltage, I_scIndicating short-circuit current, V_mpRepresenting the mpp point voltage, I_mpRepresenting the mpp point current.

3. The method of claim 2, wherein the step S2 of determining whether the current operating point is located on the right side or the left side of the maximum power point is: if V_o＞V_mpThen, it indicates that the current working point is located at the maximum workRight side of rate point; if V_o＜V_mpIt indicates that the current operating point is located on the left side of the maximum power point.

4. Improve photovoltaic simulator adaptation photovoltaic inverter and track system of stability, its characterized in that includes: the device comprises a voltage-current characteristic curve calculation module and a working point judgment and control mode selection module;

the voltage-current characteristic curve calculation module is used for calculating the voltage V according to the set mpp point_mpMpp point current I_mpOpen circuit voltage V_ocShort-circuit current I_scCalculating a voltage-current characteristic curve simulating the characteristics of the photovoltaic module;

the working point judging and control mode selecting module is used for measuring the output voltage and the current value of the current working point of the photovoltaic simulator and measuring the output voltage V according to the measured output voltage_oJudging whether the current working point is positioned on the right side or the left side of the maximum power point, and correspondingly selecting a control mode as follows:

if the current working point is positioned at the right side of the maximum power point, adopting a current voltage checking method to check the output current value I of the photovoltaic simulator according to the measured value₁Obtaining the corresponding voltage value V on the voltage-current characteristic curve₁At the moment, the control mode of the photovoltaic simulator is modified into a CV mode, and the given voltage value is modified into: v_n+k*(V₁-V_n)；

If the current working point is positioned on the left side of the maximum power point, a voltage and current checking method is adopted, and the output voltage value V of the photovoltaic simulator is measured₂Obtaining the corresponding current value I on the voltage-current characteristic curve₂At the moment, the control mode of the photovoltaic simulator is modified into a CC mode, and the current given value is modified into: i is_n+k*(I₂-I_n)；

Wherein k represents a convergence coefficient, V_nIndicating the present voltage set-point, V₁Indicating a desired voltage set-point, I_nIndicating the current set point, I₂Indicating the desired current setpoint, and k the convergence factor.

5. The system for improving tracking stability of a photovoltaic simulator adapted to a photovoltaic inverter according to claim 4, wherein the voltage-current characteristic curve calculating module calculates the voltage-current characteristic curve of the simulated photovoltaic module according to the following formula:

wherein, V_ocRepresents the open circuit voltage, I_scIndicating short-circuit current, V_mpRepresenting the mpp point voltage, I_mpRepresenting the mpp point current.

6. The system for improving tracking stability of a photovoltaic simulator adapted to a photovoltaic inverter according to claim 5, wherein the method for judging whether the current operating point is located on the right side or the left side of the maximum power point in the operating point judging and control mode selecting module comprises: if V_o＞V_mpIf so, indicating that the current working point is positioned on the right side of the maximum power point; if V_o＜V_mpIt indicates that the current operating point is located on the left side of the maximum power point.

Technical Field

The invention belongs to the technical field of photovoltaic inverter testing, and relates to a method and a system for improving tracking stability of a photovoltaic simulator for a photovoltaic inverter.

Background

During research, development, test and production test of the photovoltaic inverter, Maximum power point tracking (MPPT for short) performance of the photovoltaic inverter within a full voltage, current and power range needs to be tested. The photovoltaic module cannot be used for testing, the photovoltaic module can generate power under a sufficient light source, conditions cannot be met in an actual factory, and the photovoltaic module cannot test the performance of the inverter in the full voltage, current and power ranges in a short time, so that a photovoltaic simulator is required by a photovoltaic inverter manufacturer to test products. This requires that the photovoltaic simulator be able to accurately simulate the voltage-current characteristic curve of the photovoltaic module. Meanwhile, the photovoltaic simulator is required to be capable of being fast and stably adaptive to tracking of the photovoltaic inverter, the output of the photovoltaic simulator is required to be stable while the fast dynamic performance is guaranteed, and large voltage and current fluctuation cannot occur. The tracking judgment of the photovoltaic inverter is affected by large voltage and current fluctuation, so that the inverter cannot quickly and stably track to a Maximum Power Point (MPP). The literature "study of current-voltage characteristic curve of photovoltaic solar cell" published at 8 months in 2020 (university of south China, in splendid province) discloses test data based on Photovoltaic Solar Cells (PSC), and the method comprises the steps of performing least square fitting on a current-voltage (I-V) characteristic curve of the PSC by using an exponential function fitting method and a polynomial fitting method, and researching the influence of different methods on the fitting effect of the I-V curve by analyzing fitting errors. However, this document does not solve the above-mentioned problems.

Conventionally, a voltage-current characteristic curve under specific conditions (irradiance, temperature, and fill factor) is generally drawn, then a current value to be reached corresponding to the voltage-current characteristic curve is obtained by measuring the output voltage of the photovoltaic simulator, and the current value is set as a reference value, so that the output current of the photovoltaic simulator gradually converges to the current value, thereby achieving the effect of simulating the voltage-current characteristic of the photovoltaic module. The output voltage of the photovoltaic simulator is measured to obtain a current value which is required to be achieved and corresponds to the output current of the photovoltaic simulator in a voltage-current characteristic curve, the current value is set as a reference value, and the output current of the photovoltaic simulator is gradually converged to the current value, so that no problem exists on the left side of a maximum power point.

Disclosure of Invention

The invention aims to provide a method and a system for improving tracking stability of a photovoltaic simulator adaptive to a photovoltaic inverter, and aims to solve the problem of poor tracking stability of the inverter caused by a traditional mode that a current value is set as a reference value in the whole voltage-current characteristic curve range, and the output current of the photovoltaic simulator is gradually converged to the current value.

The invention solves the technical problems through the following technical scheme:

the method for improving tracking stability of the photovoltaic simulator adaptive to the photovoltaic inverter comprises the following steps:

s1, according to the voltage V of the mpp point_mpMpp point current I_mpOpen circuit voltage V_ocShort-circuit current I_scCalculating a voltage-current characteristic curve simulating the characteristics of the photovoltaic module;

s2, measuring the output voltage and current value of the current working point of the photovoltaic simulator, and obtaining the output voltage V according to the measured output voltage_oJudging whether the current working point is positioned on the right side or the left side of the maximum power point, and correspondingly selecting a control mode as follows:

s21, if the current working point is located at the right side of the maximum power point, adopting a current voltage checking method, and according to the measured output current value I of the photovoltaic simulator₁Obtaining the corresponding voltage value V on the voltage-current characteristic curve₁At the moment, the control mode of the photovoltaic simulator is modified into a CV mode, and the given voltage value is modified into: v_n+k*(V₁-V_n)；

S22, if the current working point is at the maximumOn the left side of the power point, a voltage and current checking method is adopted, and the output voltage value V of the photovoltaic simulator is measured₂Obtaining the corresponding current value I on the voltage-current characteristic curve₂At the moment, the control mode of the photovoltaic simulator is modified into a CC mode, and the current given value is modified into: i is_n+k*(I₂-I_n)；

Wherein k represents a convergence coefficient, V_nIndicating the present voltage set-point, V₁Indicating a desired voltage set-point, I_nRepresenting the current set point, I₂Indicating the desired current setpoint, and k the convergence factor.

According to the technical scheme, the voltage-current characteristic curve is divided into two areas, namely the right side of the maximum power point and the left side of the maximum power point, when the operation point is in different areas, different control modes are adopted, the photovoltaic simulator can guarantee stable operation in the whole range of the voltage-current characteristic curve, the output stability of the photovoltaic simulator in the whole range section of the voltage-current characteristic curve of the simulated photovoltaic module is improved, and therefore the tracking stability of the photovoltaic inverter is improved.

As a further improvement of the technical solution of the present invention, the calculation formula for calculating the voltage-current characteristic curve of the simulated photovoltaic module characteristic in step S1 is as follows:

wherein, V_ocRepresents the open circuit voltage, I_scIndicating short-circuit current, V_mpRepresenting the mpp point voltage, I_mpRepresenting the mpp point current.

As a further improvement of the technical solution of the present invention, the method for determining whether the current operating point is located on the right side or the left side of the maximum power point in step S2 includes: if V_o＞V_mpIf so, indicating that the current working point is positioned on the right side of the maximum power point; if V_o＜V_mpIt indicates that the current operating point is located on the left side of the maximum power point.

Improve photovoltaic simulator adaptation photovoltaic inverter and track system of stability, include: the device comprises a voltage-current characteristic curve calculation module and a working point judgment and control mode selection module;

the voltage-current characteristic curve calculation module is used for calculating the voltage V according to the set mpp point_mpMpp point current I_mpOpen circuit voltage V_ocShort-circuit current I_scCalculating a voltage-current characteristic curve simulating the characteristics of the photovoltaic module;

the working point judging and control mode selecting module is used for measuring the output voltage and the current value of the current working point of the photovoltaic simulator and measuring the output voltage V according to the measured output voltage_oJudging whether the current working point is positioned on the right side or the left side of the maximum power point, and correspondingly selecting a control mode as follows:

if the current working point is positioned at the right side of the maximum power point, adopting a current voltage checking method to check the output current value I of the photovoltaic simulator according to the measured value₁Obtaining the corresponding voltage value V on the voltage-current characteristic curve₁At the moment, the control mode of the photovoltaic simulator is modified into a CV mode, and the given voltage value is modified into: v_n+k*(V₁-V_n)；

If the current working point is positioned on the left side of the maximum power point, a voltage and current checking method is adopted, and the output voltage value V of the photovoltaic simulator is measured₂Obtaining the corresponding current value I on the voltage-current characteristic curve₂At the moment, the control mode of the photovoltaic simulator is adoptedModified to CC mode, current set point is modified to: i is_n+k*(I₂-I_n)；

Wherein k represents a convergence coefficient, V_nIndicating the present voltage set-point, V₁Indicating a desired voltage set-point, I_nRepresenting the current set point, I₂Indicating the desired current setpoint, and k the convergence factor.

As a further improvement of the technical solution of the present invention, a calculation formula for calculating a voltage-current characteristic curve of the simulated photovoltaic module characteristic in the voltage-current characteristic curve calculation module is as follows:

wherein, V_ocRepresents the open circuit voltage, I_scIndicating short-circuit current, V_mpRepresenting the mpp point voltage, I_mpRepresenting the mpp point current.

As a further improvement of the technical solution of the present invention, the method for determining whether the current operating point is located on the right side or the left side of the maximum power point in the operating point determination and control mode selection module is as follows: if V_o＞V_mpIf so, indicating that the current working point is positioned on the right side of the maximum power point; if V_o＜V_mpIt indicates that the current operating point is located on the left side of the maximum power point.

The invention has the advantages that:

according to the technical scheme, the voltage-current characteristic curve is divided into two areas, namely the right side of the maximum power point and the left side of the maximum power point, when the operation point is in different areas, different control modes are adopted, the photovoltaic simulator can guarantee stable operation in the whole range of the voltage-current characteristic curve, the output stability of the photovoltaic simulator in the whole range section of the voltage-current characteristic curve of the simulated photovoltaic module is improved, and therefore the tracking stability of the photovoltaic inverter is improved.

Drawings

Fig. 1 is a flowchart of a method for improving tracking stability of a photovoltaic simulator in response to a photovoltaic inverter according to a first embodiment of the present invention;

fig. 2 is a voltage-current characteristic simulation curve of the photovoltaic module characteristic under the set condition parameters according to the first embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The technical scheme of the invention is further described by combining the drawings and the specific embodiments in the specification:

example one

As shown in fig. 1, a method for improving tracking stability of a photovoltaic simulator for a photovoltaic inverter includes the following steps:

(a) a voltage-current characteristic curve which can simulate the characteristics of the photovoltaic module is calculated according to set condition parameters (mpp point voltage, mpp point current, open-circuit voltage and short-circuit current) and is shown in fig. 2, and the specific calculation formula is as follows:

wherein, V_ocRepresents the open circuit voltage, I_scIndicating short-circuit current, V_mpRepresenting the mpp point voltage, I_mpRepresenting the mpp point current.

According to the formula, a V-I table can be established, the precision of the V-I table can be determined according to actual requirements, 128 points are taken as an example, the point to be explained is that the V-I table is divided by voltage, and the V-I table is as follows:

TABLE 1V-I TABLE

Similarly, an I-V table is established, the I-V table is divided by current, and the I-V table is as follows:

TABLE 2I-V TABLE

(b) Measuring the output voltage and current value of the photovoltaic simulator;

(c) based on the measured voltage value V_oAnd judging whether the working point is positioned on the right side or the left side of the maximum power point, wherein the judgment method comprises the following steps:

if V_o＞V_mpif the working point is located on the right side of the maximum power point, the working point is indicated;

if V_o＜V_mpif the working point is located on the left side of the maximum power point, the working point is indicated;

(d1) if it is to the right of the maximum power point, as shown by the point (V) in FIG. 2_n,I₁) Then, a current voltage checking method is adopted, an I-V table is checked according to the measured output current value I1 of the photovoltaic simulator, and the voltage value V which should be reached on the voltage-current characteristic curve is obtained₁；

The right side of the maximum power point is characterized in that: the voltage interval is very small, and the current interval is very large, and the characteristic is particularly prominent particularly when the Fill Factor (FF) is large. At the moment, a table looking-up mode of looking up the voltage by current and a CV control mode are adopted, even if slight fluctuation exists in the output current, the voltage value obtained by looking up the table does not have large change, and the voltage given value of the photovoltaic simulator does not have large fluctuation, so that the output voltage of the photovoltaic simulator can be more stable, and the stable tracking of the photovoltaic inverter is facilitated.

(d2) If it is to the left of the maximum power point, as shown by point (V) in FIG. 2₂,I_n) Then, a voltage and current checking method is adopted, and the output voltage value V of the photovoltaic simulator is measured according to the measured value₂Looking up the V-I table to find the current value I to be reached on the voltage-current characteristic curve₂；

The characteristics on the left side of the maximum power point are as follows: the voltage interval is large, the current interval is small, and the characteristic is particularly prominent when a Fill Factor (FF) is large. At the moment, a table checking mode of checking the current by using the voltage and a CC control mode are adopted, even if slight fluctuation exists in the output voltage, the current value obtained by table checking does not have large change, and then the current set value of the photovoltaic simulator does not have large fluctuation, so that the output current of the photovoltaic simulator can be more stable, and the stable tracking of the photovoltaic inverter is facilitated.

(el) modifying the control mode of the photovoltaic simulator into a CV modelFormula (constant voltage control), the voltage set point is modified to: v_n+k*(V₁-V_n) Where k denotes the convergence coefficient, V_nIndicating the present voltage set-point, V₁Indicating a desired voltage setpoint; the k value can be adjusted according to the actual measurement effect, the convergence is faster when k is larger, and otherwise, the convergence is slower;

(e2) the control mode of the photovoltaic simulator is modified into a CC mode (constant current control), and the given current value is modified into: i is_n+k*(I₂-I_n) Where k denotes the convergence coefficient, I_nIndicating the current set point, I₂Indicating a desired current setpoint; the k value can be adjusted according to the actual measurement effect, the convergence is faster when k is larger, and otherwise, the convergence is slower;

(f) and (e) re-executing from the step (b) until the step (e) is executed.

When the control mode is switched from voltage checking current to current checking voltage or from current checking voltage to voltage checking current, the switching of loop control, namely the switching between CV mode and CC mode, is involved. This requires smooth switching of the two loops in control, which otherwise would cause power jump at the switching time and affect normal tracking of the inverter; when the loop switching is adopted, the minimum value output by the current two outer loops is immediately taken as the initial value given by the inner loop, so that the smooth switching between the two loops can be effectively ensured. Because the switching between the CV mode and the CC mode can occur near the mpp point, when the inverter tracks to the vicinity of the mpp point, the switching back and forth is easy, so that the inverter can not stably work at the mpp point, hysteresis control is added, namely, a hysteresis band is arranged near the mpp point, and the switching back and forth of the two modes can be effectively prevented.

According to the technical scheme, the voltage-current characteristic curve is divided into two areas, namely the right side of the maximum power point and the left side of the maximum power point, when the operation point is in different areas, different table look-up modes (current look-up according to voltage or voltage look-up according to current) and control modes (CV mode or CC mode) are adopted, so that the photovoltaic simulator can guarantee stable operation in the whole range of the voltage-current characteristic curve, the output stability of the photovoltaic simulator in the whole range section of the voltage-current characteristic curve of the simulated photovoltaic module is improved, and the tracking stability of the photovoltaic inverter is improved.

The above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; such modifications and substitutions do not depart from the spirit and scope of the corresponding technical solutions.