阅读说明：本技术 基于光伏组件电压实时计算比较的光伏阵列故障判别方法 (Photovoltaic array fault discrimination method based on real-time calculation and comparison of photovoltaic module voltage ) 是由 赵庆明 李伟 于 2021-09-24 设计创作，主要内容包括：本发明公开了一种基于光伏组件电压实时计算比较的光伏阵列故障判别方法,它包括：步骤1、利用光伏阵列运行在最大功率点的信息计算光伏阵列中所处位置的太阳实际辐照度G和温度T-(C)；步骤2、利用光伏组件在标准测试条件下的物理参数值计算在太阳实际辐照度G和温度T-(C)下的光伏组件实际物理参数值；步骤3、根据光伏阵列中组串电流计算相应的光伏组件电压；步骤4、根据光伏阵列组串实测电压值和计算电压值之差进行光伏阵列故障检测；解决了现有技术光伏阵列和组件的保护存在盲区,并且保护的灵敏性和可靠性都得不到保证等技术问题。(The invention discloses a photovoltaic array fault discrimination method based on real-time calculation and comparison of photovoltaic module voltage, which comprises the following steps: step 1, calculating the actual solar irradiance G and the temperature T of the position in the photovoltaic array by utilizing the information of the maximum power point of the photovoltaic array in operation C (ii) a Step 2, calculating actual solar irradiance G and temperature T by using physical parameter values of the photovoltaic module under standard test conditions C Actual physical parameter values of the photovoltaic module; step 3, calculating corresponding photovoltaic module voltage according to the string current in the photovoltaic array; step 4, detecting the faults of the photovoltaic array according to the difference between the actually measured voltage value and the calculated voltage value of the photovoltaic array string; the photovoltaic array and module protection device solves the technical problems that in the prior art, a blind area exists in photovoltaic array and module protection, and the sensitivity and reliability of protection cannot be guaranteed.)

1. A photovoltaic array fault discrimination method based on real-time calculation and comparison of photovoltaic module voltage comprises the following steps:

step 1, calculating the actual solar irradiance G and the temperature T of the position in the photovoltaic array by utilizing the information of the maximum power point of the photovoltaic array in operation_C；

Step 2, calculating actual solar irradiance G and temperature T by using physical parameter values of the photovoltaic module under standard test conditions_CLower photovoltaic moduleAn inter-physical parameter value;

step 3, calculating corresponding photovoltaic module voltage according to the string current in the photovoltaic array;

and 4, detecting the faults of the photovoltaic array according to the difference between the actually measured voltage value and the calculated voltage value of the photovoltaic array string.

2. The photovoltaic array fault discrimination method based on real-time calculation and comparison of photovoltaic module voltage according to claim 1, characterized in that: step 1, calculating the actual solar irradiance G and the temperature T of the position in the photovoltaic array by utilizing the information of the maximum power point of the photovoltaic array in operation_CThe method comprises the following steps:

obtaining the maximum value of the output power of the solar battery according to the MPPT algorithm of the photovoltaic inverter, namely P_mpp＝V_mppI_mpp，V_mppAnd I_mppRespectively corresponding voltage and current of the photovoltaic cell when the output power is maximum; under standard test conditions, i.e. irradiance of G_STC＝1000W/m²At a temperature of T_C,STCThe maximum output power of the photovoltaic cell under the spectral conditions of AM1.5, expressed as P, is 25 ℃_mpp,STC＝V_mpp,STCI_mpp,STCIn the formula V_mpp,STCAnd I_mpp,STCRespectively corresponding to the maximum power point under the standard test condition;

establishing the current I of the photovoltaic cell at the maximum power point_mppRelation to solar irradiance:

in the formula G and G_STCThe actual irradiance and the standard irradiance of the position of the photovoltaic array are respectively obtained by the formula (1):

solar irradiance G is calculated according to the current at the maximum power point of actual operation of the inverter, and the relation between the power and the temperature of the maximum power point of the photovoltaic cell is as follows:

gamma in the formula (3) is a temperature coefficient of the maximum power point, and the formula for calculating the temperature of the photovoltaic array obtained by the formula (3) is as follows:

calculating the actual irradiance G and the temperature T of the position where the photovoltaic array is located in real time according to the formulas (2) and (4)_C。

3. The photovoltaic array fault discrimination method based on photovoltaic module voltage real-time calculation and comparison as claimed in claim 2, characterized in that: step 2, calculating the actual solar irradiance G and the actual solar temperature T by using the physical parameter values of the photovoltaic module under the standard test condition_CThe following method for the actual physical parameter values of the photovoltaic module comprises the following steps:

establishing an output current expression of the solar cell module:

wherein a is nN_skT_C/q；I₀Is a reverse saturation current; n is a diode influence factor; q is an electron charge constant value of 1.6x10^-19C; k is Boltzmann constant value of 1.23x10^-23J/K；T_CIs the temperature in degrees Kelvin; n is a radical of_sFor each lightThe number of photovoltaic cells in the photovoltaic module in series connection; at solar irradiance G and temperature T_CNext, a series resistor R is provided_sThe harmonic tube influence factor n remains constant, I_ph、I₀And R_shThe calculation formula of the parameters is as follows:

in the formula: alpha is alpha_ISCThe temperature coefficient of the short-circuit current of the photovoltaic module.

4. The photovoltaic array fault discrimination method based on real-time calculation and comparison of photovoltaic module voltage according to claim 3, characterized in that: step 3, the method for calculating the corresponding photovoltaic module voltage according to the string current in the photovoltaic array comprises the following steps: when the photovoltaic array fails, the voltage of the photovoltaic modules of the photovoltaic array failure string changes, and N is the number of the photovoltaic array string, I_PV1,…,I_PVNFor the output current of the corresponding string in the photovoltaic array, V_measureThe voltage between the positive electrode and the negative electrode measured for the photovoltaic array is also the voltage of each string; deriving a component voltage V in a photovoltaic string_pvThe analytic solution of (c) is:

i in the formula (10)_pvCalculating the voltage of the photovoltaic component of the corresponding photovoltaic array group string according to the formula (10) for the output current of the corresponding group string in the photovoltaic array, and obtaining the photovoltaic arrayThe voltage calculation formula of the corresponding string group is as follows:

V_Cal＝M·V_pv (11)

m in equation (11) is the number of photovoltaic modules in each string.

5. The photovoltaic array fault discrimination method based on real-time calculation and comparison of photovoltaic module voltage according to claim 1, characterized in that: step 4, the method for detecting the photovoltaic array fault according to the difference between the actually measured voltage value and the calculated voltage value of the photovoltaic array string comprises the following steps:

when a string in a photovoltaic array breaks down, the actually measured voltage and the calculated voltage of the photovoltaic string are different, and the calculation formula of the change between the two voltages is as follows:

wherein abs represents the absolute value, K_relFor a reliability coefficient, when the calculated voltage and the measured voltage criterion of a certain photovoltaic string in the photovoltaic array satisfy the formula (12), judging that the photovoltaic string is grounded or has a fault between strings; otherwise, judging that the photovoltaic array system is in a normal operation state.

6. The photovoltaic array fault discrimination method based on real-time calculation and comparison of photovoltaic module voltage according to claim 5, characterized in that: k_relThe value is less than 1.

7. The photovoltaic array fault discrimination method based on real-time calculation and comparison of photovoltaic module voltage according to claim 5, characterized in that: k_relThe value range is 0.5-0.8.

Technical Field

The invention belongs to the technical field of photovoltaic array fault diagnosis; in particular to a photovoltaic array fault discrimination method based on real-time calculation and comparison of photovoltaic module voltage.

Background

According to whether a direct current bus of a photovoltaic power station is grounded or not, the photovoltaic power station can be divided into a grounded photovoltaic system and an ungrounded photovoltaic system. The direct current bus negative pole of Ground connection type photovoltaic system passes through Ground Fault Detection and Isolation (GFDI) fuse device and links to each other with Ground, GFDI uses ordinary fuse to accomplish photovoltaic module's simple overcurrent protection usually, has the blind area to the protection of photovoltaic array and subassembly, and the sensitivity and the reliability of protection can not be guaranteed, receive the influence of fault location, when breaking down, the fault current that flows through photovoltaic array is often less than the fusing current of GFDI fuse far away, lead to the fuse unable action. The non-grounded photovoltaic system generally uses a Residual current detection device (RCDs) to collect a difference between direct current positive and negative bus currents of a photovoltaic power station as an action signal to control an inverter, so as to realize fault isolation of a photovoltaic array, and the protection performance of the RCDs is similar to that of GFDI and also has a protection blind area.

Disclosure of Invention

The technical problems to be solved by the invention are as follows: the photovoltaic array fault discrimination method based on the real-time calculation and comparison of the voltage of the photovoltaic module is provided, and the technical problems that in the prior art, a blind area exists in the protection of the photovoltaic array and the module, the sensitivity and the reliability of the protection cannot be guaranteed, and the like are solved.

The technical scheme of the invention is as follows:

a photovoltaic array fault discrimination method based on real-time calculation and comparison of photovoltaic module voltage,

it includes:

step 1, calculating the actual solar irradiance G and the temperature T of the position in the photovoltaic array by utilizing the information of the maximum power point of the photovoltaic array in operation_C；

Step 2, calculating actual solar irradiance G and temperature T by using physical parameter values of the photovoltaic module under standard test conditions_CActual physical parameter values of the photovoltaic module;

step 3, calculating corresponding photovoltaic module voltage according to the string current in the photovoltaic array;

and 4, detecting the faults of the photovoltaic array according to the difference between the actually measured voltage value and the calculated voltage value of the photovoltaic array string.

Step 1, calculating the actual solar irradiance G and the temperature T of the position in the photovoltaic array by utilizing the information of the maximum power point of the photovoltaic array in operation_CThe method comprises the following steps:

obtaining the maximum value of the output power of the solar battery according to the MPPT algorithm of the photovoltaic inverter, namely P_mpp＝V_mppI_mpp，V_mppAnd I_mppRespectively a photovoltaic cell inOutputting the voltage and current corresponding to the maximum power; under standard test conditions, i.e. irradiance of G_STC＝1000W/m²At a temperature of T_C,STCThe maximum output power of the photovoltaic cell under the spectral conditions of AM1.5, expressed as P, is 25 ℃_mpp,STC＝V_mpp,STCI_mpp,STCIn the formula V_mpp,STCAnd I_mpp,STCRespectively corresponding to the maximum power point under the standard test condition;

establishing the current I of the photovoltaic cell at the maximum power point_mppRelation to solar irradiance:

in the formula G and G_STCThe actual irradiance and the standard irradiance of the position of the photovoltaic array are respectively obtained by the formula (1):

solar irradiance G is calculated according to the current at the maximum power point of actual operation of the inverter, and the relation between the power and the temperature of the maximum power point of the photovoltaic cell is as follows:

gamma in the formula (3) is a temperature coefficient of the maximum power point, and the formula for calculating the temperature of the photovoltaic array obtained by the formula (3) is as follows:

calculating the actual irradiance G and the temperature T of the position where the photovoltaic array is located in real time according to the formulas (2) and (4)_C。

Step 2, utilizing physical parameters of the photovoltaic module under standard test conditionsThe values are calculated at the actual irradiance G and temperature T of the sun_CThe following method for the actual physical parameter values of the photovoltaic module comprises the following steps:

establishing an output current expression of the solar cell module:

wherein a is nN_skT_C/q；I₀Is a reverse saturation current; n is a diode influence factor; q is an electron charge constant value of 1.6x10^-19C; k is Boltzmann constant value of 1.23x10^-23J/K；T_CIs the temperature in degrees Kelvin; n is a radical of_sThe number of the photovoltaic cells in each photovoltaic module is in series connection; at solar irradiance G and temperature T_CNext, a series resistor R is provided_sThe harmonic tube influence factor n remains constant, I_ph、I₀And R_shThe calculation formula of the parameters is as follows:

in the formula: alpha is alpha_ISCThe temperature coefficient of the short-circuit current of the photovoltaic module.

Step 3, the method for calculating the corresponding photovoltaic module voltage according to the string current in the photovoltaic array comprises the following steps: when the photovoltaic array fails, the voltage of the photovoltaic module of the photovoltaic array failure string changes, and N is set as the photovoltaic array stringNumber of (2), I_PV1,…,I_PVNFor the output current of the corresponding string in the photovoltaic array, V_measureThe voltage between the positive electrode and the negative electrode measured for the photovoltaic array is also the voltage of each string; deriving a component voltage V in a photovoltaic string_pvThe analytic solution of (c) is:

i in the formula (10)_pvFor the output current of the corresponding string in the photovoltaic array, calculating the voltage of the photovoltaic module of the corresponding string of the photovoltaic array according to the formula (10), and then calculating the voltage of the corresponding string of the photovoltaic array according to the formula:

V_Cal＝M·V_pv (11)

m in equation (11) is the number of photovoltaic modules in each string.

Step 4, the method for detecting the photovoltaic array fault according to the difference between the actually measured voltage value and the calculated voltage value of the photovoltaic array string comprises the following steps:

when a string in a photovoltaic array breaks down, the actually measured voltage and the calculated voltage of the photovoltaic string are different, and the calculation formula of the change between the two voltages is as follows:

wherein abs represents the absolute value, K_relFor a reliability coefficient, when the calculated voltage and the measured voltage criterion of a certain photovoltaic string in the photovoltaic array satisfy the formula (12), judging that the photovoltaic string is grounded or has a fault between strings; otherwise, judging that the photovoltaic array system is in a normal operation state.

K_relThe value is less than 1.

K_relThe value range is 0.5-0.8.

The invention has the beneficial effects that:

according to the invention, when a photovoltaic array fails, the voltage of a photovoltaic module of a photovoltaic array failure string changes, when the string in the photovoltaic array fails, the actually measured voltage and the calculated voltage of the photovoltaic string have obvious difference, and the calculation formula of the change between the two voltages is as follows:

K_relfor reliability reasons, the device can effectively detect faults when the strings of the photovoltaic array have minimum mismatch faults (i.e. string-to-string ground faults and string-to-string faults as shown in fig. 2), K_relGenerally, the value should be less than 1. When the calculated voltage and the measured voltage criterion of a certain photovoltaic group string in the photovoltaic array satisfy the formula (12), the photovoltaic group string can be judged to be grounded or have a fault between the group strings; otherwise, judging that the photovoltaic array system is in a normal operation state.

The invention can effectively identify the faults of the photovoltaic array under the condition of the minimum fault mismatching degree, thereby effectively solving the problems of fault identification blind area, identification precision, reliability and the like in the conventional protection scheme.

Drawings

FIG. 1 is a schematic diagram of an equivalent circuit of a solar cell in accordance with an embodiment of the present invention;

fig. 2 is a schematic view of a photovoltaic array failure according to an embodiment of the present invention.

Detailed Description

A photovoltaic array fault discrimination method based on real-time calculation and comparison of photovoltaic module voltage specifically comprises the following steps:

step (1) calculating solar irradiance and temperature at the photovoltaic array

The photovoltaic inverter adopts a Maximum Power Point Tracking (MPPT) algorithm so that the photovoltaic array always operates at a Maximum Power Point. The method comprises the steps of firstly, calculating solar irradiance and temperature of the position in the photovoltaic array by utilizing relevant information of the photovoltaic array running at the maximum power point. Fig. 1 is an equivalent circuit diagram of a solar cell.

In FIG. 1I_phIn order to generate the electric current for light,I_Dis a pn junction diffusion current, R, of a solar cell_shIs a parallel resistor, R_sIs a series resistance, V_pvAnd I_pvRespectively, the output voltage and current of the photovoltaic cell. The MPPT algorithm of the photovoltaic inverter makes the output power of the solar battery be maximum, namely P_mpp＝V_mppI_mppIn which V is_mppAnd I_mppRespectively, the voltage and the current corresponding to the photovoltaic cell when the output power is maximum. Under standard test conditions, i.e. irradiance of G_STC＝1000W/m²At a temperature of T_C,STCThe maximum output power expression of the photovoltaic cell under the spectral condition of AM1.5 is P at 25 DEG C_mpp,STC＝V_mpp,STCI_mpp,STCIn the formula V_mpp,STCAnd I_mpp,STCRespectively, the output voltage and the output current corresponding to the maximum power point under the standard test condition.

Current I of photovoltaic cell at Maximum Power Point (MPP)_mppThe relationship with solar irradiance is as follows.

In the formula (1), each photovoltaic module gives a corresponding V by a manufacturer when leaving a factory_mpp,STCAnd I_mpp,STCValues G and G_STCThe actual irradiance and the standard irradiance of the position of the photovoltaic array are respectively. From equation (1) it follows:

as can be seen from equation (2), the solar irradiance G can be calculated from the current at the maximum power point where the inverter actually operates. The relationship between power and temperature at the maximum power point of the photovoltaic cell is shown as follows:

in the formula (3), γ is a temperature coefficient of the maximum power point, which is given by the photovoltaic module at the time of factory shipment, and the formula for calculating the temperature of the photovoltaic array can be derived from the formula (3) as follows:

from the above, the actual irradiance G and the temperature T of the photovoltaic array can be calculated in real time according to the formulas (2) and (4)_C。

Step (2) calculating physical parameter values of the photovoltaic module in actual operation

Calculating the solar irradiance G and the temperature T by using the physical parameter values of the photovoltaic module under the Standard Test Condition (STC), which are obtained by testing the photovoltaic module when the photovoltaic module leaves factory_CAnd (5) actual physical parameter values of the photovoltaic modules. As can be seen from fig. 1, the output current of the solar cell module can be represented as:

in the above formula, a ═ nN_skT_C/q；I₀Is a reverse saturation current; n is a diode influence factor; q is an electron charge constant of 1.6x10^-19C; k is Boltzmann's constant, 1.23x10^-23J/K；T_CIs the temperature in degrees Kelvin; n is a radical of_sThe number of the photovoltaic cells in each photovoltaic module in series connection is the same as the above parameters. At solar irradiance G and temperature T_CHereinafter, the series resistance R can be generally considered_sThe harmonic tube influence factor n remains constant, I_ph、I₀And R_shThe calculation formula of the related parameters is as follows:

wherein α in the formula (7)_ISCThe temperature coefficient of the short-circuit current of the photovoltaic module is actually measured and given by a manufacturer when the photovoltaic module leaves a factory.

And (3) calculating corresponding photovoltaic module voltage according to the string current in the photovoltaic array.

Failure of the pv array as shown in fig. 2, LG1, LL1 and LL2 in fig. 2 represent a single string ground, a single string inter-string failure and a two string inter-string failure, respectively, and it can be seen from fig. 2 that when the pv array fails, the pv module voltage of the failed string of the pv array will change.

In FIG. 2, N is the number of photovoltaic array strings, I_PV1,…,I_PVNFor the output current of the corresponding string in the photovoltaic array, V_measureThe measured voltage between the positive and negative electrodes for the photovoltaic array is also the voltage for each string. The formula corresponding to the photovoltaic module physical model is shown as formula (5), and since in the actual physical model, R is generally_shIs large, approximately 500 to 1000 ohms, and is thus in formula (5)Is small and can be omitted, so that the component voltage V in the photovoltaic string can be derived_pvThe analytic solution of (c) is:

i in the formula (10)_pvI.e., the output current of the corresponding string in the photovoltaic array of fig. 2, the light of the corresponding string of photovoltaic arrays can be calculated according to equation (10)The voltage of the voltage component. And the voltage calculation formula of the corresponding group string of the photovoltaic array is as follows:

V_Cal＝M·V_pv (11)

m in equation (11) is the number of photovoltaic modules in each string, and M is 5 for the photovoltaic array shown in fig. 2.

Step (4) photovoltaic array fault detection method according to difference between actually measured voltage value and calculated voltage value of photovoltaic array string

According to the analysis, when the string in the photovoltaic array breaks down, the actually measured voltage and the calculated voltage of the photovoltaic string have obvious difference, and the calculation formula of the change between the two voltages is as follows:

in the above formula, abs represents the absolute value, K_relFor reliability reasons, the device can effectively detect faults when the strings of the photovoltaic array have minimum mismatch faults (i.e. string-to-string ground faults and string-to-string faults as shown in fig. 2), K_relGenerally, the value should be less than 1. Optimum K_relThe value range is 0.5-0.8.

When the calculated voltage and the measured voltage criterion of a certain photovoltaic group string in the photovoltaic array satisfy the formula (12), the photovoltaic group string can be judged to be grounded or have a fault between the group strings; otherwise, the photovoltaic array system is judged to be in a normal operation state, and the protection device continues to perform the fault monitoring function.