Patent Description:
A photovoltaic power generation system is a power generation system in which solar energy is directly converted into electrical energy by using a photovoltaic module (Solar Cell Module), and includes a photovoltaic string, a battery, a controller, and a photovoltaic inverter. The photovoltaic string includes a plurality of photovoltaic modules that are combined in series or/and in parallel. The photovoltaic module is a smallest indivisible photovoltaic cell assembly that can independently provide a direct current output.

Currently, to detect the photovoltaic string to determine whether the photovoltaic string is defective or damaged, a photovoltaic system may perform IV curve scanning on the photovoltaic string on line. In addition, IV curve scanning can also help the photovoltaic system to learn of information such as a current power generation capability and working condition of the photovoltaic string. However, a light change exerts relatively large impact on an IV output feature of the photovoltaic string. If there is a light change in a process in which the photovoltaic system performs IV curve scanning on the photovoltaic string, an IV curve that is of the photovoltaic string and that is obtained through detection cannot accurately reflect the IV output feature of the photovoltaic string. <CIT> discloses an optimizer, a photovoltaic power generation system, and an IV curve scanning method for a photovoltaic module. The photovoltaic power generation system includes a plurality of photovoltaic modules, a plurality of optimizers, and an inverter. An input end of each optimizer is connected to at least one photovoltaic module, and output ends of the plurality of optimizers are connected in series to form a string and then connected to the inverter. The optimizer includes a conversion unit, and a control unit configured to control the conversion unit. The optimizer further includes an auxiliary power source, an energy storage unit, and a first unidirectional conduction unit that are connected between the conversion unit and the control unit. The control unit is configured to perform IV curve scanning for each voltage segment, where the voltage segments are obtained by segmenting a range of an output voltage of a photovoltaic module corresponding to the optimizer from an open-circuit voltage to a preset minimum voltage, and at least two voltage segments are obtained through division. In this application, costs and a volume of the optimizer can be reduced. <CIT> discloses an IV curve scan method for a photovoltaic module and an optimizer. The optimizer receives an IV curve scan signal and controls an output voltage of the photovoltaic module corresponding to the IV curve scan signal to change from an open-circuit voltage to a preset minimum voltage according to a preset rule, while photovoltaic module connected to another optimizer can still operate normally, so that the system can operate normally. Then the optimizer uploads IV curve data of the photovoltaic module corresponding to the IV curve scan signal, to complete an IV curve scan on a single photovoltaic module.

Embodiments of this application disclose a parametric curve scanning method for a photovoltaic string, a converter, and a photovoltaic power generation system, so that whether the currently obtained parametric curve is affected by a light change can be determined based on the obtained parametric curve, to determine whether the currently obtained parametric curve is valid, thereby improving parametric curve scanning reliability.

According to a first aspect, an embodiment of this application discloses a parametric curve scanning method for a photovoltaic string, including in particular: controlling an output voltage of the photovoltaic string to change from a first endpoint voltage of a first voltage range to a second endpoint voltage of the first voltage range, and obtaining a current parameter or a power parameter of the photovoltaic string in the process in which the output voltage of the photovoltaic string changes, to scan a first parametric curve;
controlling the output voltage of the photovoltaic string to change from a third endpoint voltage of a second voltage range to a fourth endpoint voltage of the second voltage range, and obtaining a current parameter or a power parameter of the photovoltaic string in the process in which the output voltage of the photovoltaic string changes, to scan a second parametric curve, where there is an intersection set between the first voltage range and the second voltage range.

The first voltage range is a voltage scanning range including a maximum output voltage and a minimum output voltage of the photovoltaic string in a process of scanning the first parametric curve. The second voltage range is a voltage scanning range including a maximum output voltage and a minimum output voltage of the photovoltaic string in a process of scanning the second parametric curve. For example, the maximum output voltage of the photovoltaic string may be an open-circuit voltage, and a minimum output voltage value may be <NUM> V.

According to the technical solution in the first aspect, parametric curve scanning is separately performed on the photovoltaic string in the first voltage range and the second voltage range, and there is an intersection set between the first voltage range and the second voltage range, so that the first parametric curve and the second parametric curve that are obtained include parts corresponding to a same voltage. However, currents corresponding to the same voltage are obtained at different time points, so that it can be determined, by comparing the currents corresponding to the same voltage part, whether the currently obtained parametric curve is affected by a light change, to further determine whether the currently obtained parametric curve is valid, thereby improving reliability of parametric curve scanning reliability. In addition, in this method, no test device needs to be additionally added, to effectively reduce a quantity of hardware devices that need to be provided, and reduce costs.

With reference to the first aspect, according to the invention, the first endpoint voltage is greater than the second endpoint voltage and the third endpoint voltage is less than the fourth endpoint voltage; or the first endpoint voltage is less than the second endpoint voltage and the third endpoint voltage is greater than the fourth endpoint voltage. In this case, a scanning endpoint of the first parametric curve is relatively close to a scanning startpoint of the second parametric curve. Therefore, a parametric curve scanning speed can be increased.

With reference to the first aspect, in a possible implementation, to improve comparison precision, the first endpoint voltage is equal to the fourth endpoint voltage, and/or the second endpoint voltage is equal to the third endpoint voltage.

With reference to the first aspect, in a possible implementation, to further improve comparison efficiency, data at two sampling points is completely the same, and a time-related waveform in the first voltage range is symmetrical to a time-related waveform in the second voltage range.

With reference to the first aspect, in a possible implementation, controlling an output voltage of the photovoltaic string to change from a first endpoint voltage of a first voltage range to a second endpoint voltage of the first voltage range according to a first preset rule; and controlling the output voltage of the photovoltaic string to change from a third endpoint voltage of a second voltage range to a fourth endpoint voltage of the second voltage range according to a second preset rule, and to improve comparison efficiency, the first preset rule is a rule in which a voltage drops by a fixed voltage difference and the second preset rule is a rule in which a voltage rises by a fixed voltage difference; or the first preset rule is a rule in which a voltage rises by a fixed voltage difference and the second preset rule is a rule in which a voltage drops by a fixed voltage difference.

With reference to the first aspect, in a possible implementation, the scanning method further includes: determining, based on the first parametric curve and the second parametric curve, whether the currently scanned parametric curve is affected by a light change.

With reference to the first aspect, in a possible implementation, the determining, based on the first parametric curve and the second parametric curve, whether the currently scanned parametric curve is affected by a light change includes: comparing the first parametric curve and the second parametric curve, to determine whether light intensity corresponding to the first parametric curve and light intensity corresponding to the second parametric curve change.

With reference to the first aspect, in a possible implementation, if an absolute value of a difference between the corresponding parameter values of a same voltage point that are on the first parametric curve and the second parametric curve is less than a preset threshold, determining that the currently scanned parametric curve is not affected by the light change.

With reference to the first aspect, in a possible implementation, to further improve precision of the obtained curve, the scanning method further includes: processing the first parametric curve and the second parametric curve when it is determined that the currently scanned curve is not affected by the light change, to obtain a final parametric curve.

With reference to the first aspect, in a possible implementation, an abnormal signal is sent when it is determined that the currently scanned curve is affected by the light change, to report, to a host computer, that current scanning fails. Therefore, the host computer may determine, based on feedback, whether to send a parametric curve scanning instruction again.

According to a non-claimed second aspect, an embodiment of this application discloses a converter, including an adjustment unit and an obtaining unit. The adjustment unit is configured to control an output voltage of the photovoltaic string to change from a first endpoint voltage of a first voltage range to a second endpoint voltage of the first voltage range. The obtaining unit is configured to obtain a current parameter and/or a power parameter of the photovoltaic string in the process in which the output voltage of the photovoltaic string changes, to scan a first parametric curve. The adjustment unit is further configured to control the output voltage of the photovoltaic string to change from a third endpoint voltage of a second voltage range to a fourth endpoint voltage of the second voltage range according to a second preset rule. The obtaining unit is further configured to obtain a current parameter and/or a power parameter of the photovoltaic string in the process in which the output voltage of the photovoltaic string changes, to scan a second parametric curve. There is an intersection set between the first voltage range and the second voltage range.

It can be understood that a voltage parameter is also obtained when the current parameter and/or the power parameter of the photovoltaic string is obtained in the process in which the output voltage of the photovoltaic string changes, to form a current-voltage (IV) curve or a power-voltage (PV) curve.

The first voltage range is a first voltage scanning range including a maximum output voltage and a minimum output voltage of the photovoltaic string in a process of scanning the first parametric curve. The second voltage range is a second voltage scanning range including a maximum output voltage and a minimum output voltage of the photovoltaic string in a process of scanning the second parametric curve. For example, the maximum output voltage of the photovoltaic string may be an open-circuit voltage, and a minimum output voltage value may be <NUM> V.

With reference to the second aspect, in a possible implementation, the first endpoint voltage is greater than the second endpoint voltage and the third endpoint voltage is less than the fourth endpoint voltage; or the first endpoint voltage is less than the second endpoint voltage and the third endpoint voltage is greater than the fourth endpoint voltage.

With reference to the second aspect, in a possible implementation, the first endpoint voltage is equal to the fourth endpoint voltage, and/or the second endpoint voltage is equal to the third endpoint voltage.

With reference to the second aspect, in a possible implementation, a time-related waveform in the first voltage range is symmetrical to a time-related waveform in the second voltage range.

With reference to the second aspect, in a possible implementation, the first preset rule is a rule in which a voltage drops by a fixed voltage difference and the second preset rule is a rule in which a voltage rises by a fixed voltage difference; or the first preset rule is a rule in which a voltage rises by a fixed voltage difference and the second preset rule is a rule in which a voltage drops by a fixed voltage difference.

With reference to the second aspect, in a possible implementation, the converter further includes a determining unit. The determining unit is configured to determine, based on the first parametric curve and the second parametric curve, whether the currently scanned parametric curve is affected by a light change.

With reference to the second aspect, in a possible implementation, the determining unit is configured to compare the first parametric curve and the second parametric curve, to determine whether light intensity corresponding to the first parametric curve and light intensity corresponding to the second parametric curve change.

With reference to the second aspect, in a possible implementation, the determining unit is configured to: when an absolute value of a difference between the corresponding parameter values of a same voltage point that are on the first parametric curve and the second parametric curve is less than a preset threshold, determine that the currently scanned parametric curve is not affected by the light change.

With reference to the second aspect, in a possible implementation, the converter further includes a processing unit. The processing unit is configured to process the first parametric curve and the second parametric curve when it is determined that the currently scanned curve is not affected by the light change, to obtain a final parametric curve.

With reference to the second aspect, in a possible implementation, the processing unit is further configured to send an abnormal signal when it is determined that the currently scanned curve is affected by the light change.

According to a third aspect, an embodiment of this application discloses a converter, in particular including a DC/DC circuit and a sampling circuit. The sampling circuit and the DC/DC circuit are electrically connected. The DC/DC circuit is configured to control an output voltage of the photovoltaic string to change from a first endpoint voltage of a first voltage range to a second endpoint voltage of the first voltage range. The sampling circuit is configured to obtain a current parameter and/or a power parameter of the photovoltaic string in the process in which the output voltage of the photovoltaic string changes, to scan a first parametric curve. The DC/DC circuit is further configured to control the output voltage of the photovoltaic string to change from a third endpoint voltage of a second voltage range to a fourth endpoint voltage of the second voltage range. The sampling circuit is further configured to obtain a current parameter and/or a power parameter of the photovoltaic string in the process in which the output voltage of the photovoltaic string changes, to scan a second parametric curve. There is an intersection set between the first voltage range and the second voltage range.

The first voltage range is a first voltage scanning range including a maximum output voltage and a minimum output voltage of the photovoltaic string in a process of scanning the first parametric curve. The second voltage range is a second voltage scanning range including a maximum output voltage and a minimum output voltage of the photovoltaic string in a process of scanning the second parametric curve. For example, the maximum output voltage of the photovoltaic string may be an open-circuit voltage, and a minimum output voltage value may be <NUM> V.

With reference to the third aspect, according to the invention, the first endpoint voltage is greater than the second endpoint voltage and the third endpoint voltage is less than the fourth endpoint voltage; or the first endpoint voltage is less than the second endpoint voltage and the third endpoint voltage is greater than the fourth endpoint voltage.

With reference to the third aspect, in a possible implementation, the first endpoint voltage is equal to the fourth endpoint voltage, and/or the second endpoint voltage is equal to the third endpoint voltage.

With reference to the third aspect, in a possible implementation, a time-related waveform in the first voltage range is symmetrical to a time-related waveform in the second voltage range.

With reference to the third aspect, in a possible implementation, wherein the DC/DC circuit, configured to control an output voltage of the photovoltaic string to change from a first endpoint voltage of a first voltage range to a second endpoint voltage of the first voltage range according to a first preset rule; and control the output voltage of the photovoltaic string to change from a third endpoint voltage of a second voltage range to a fourth endpoint voltage of the second voltage range according to a second preset rule; the first preset rule is a rule in which a voltage drops by a fixed voltage difference and the second preset rule is a rule in which a voltage rises by a fixed voltage difference; or the first preset rule is a rule in which a voltage rises by a fixed voltage difference and the second preset rule is a rule in which a voltage drops by a fixed voltage difference.

With reference to the third aspect, in a possible implementation, the converter further includes a controller, and the controller is separately electrically connected to the DC/DC circuit and the sampling circuit. The controller is configured to determine, based on the first parametric curve and the second parametric curve, whether the currently scanned parametric curve is affected by a light change.

With reference to the third aspect, in a possible implementation, the controller is configured to compare the first parametric curve and the second parametric curve, to determine whether light intensity corresponding to the first parametric curve and light intensity corresponding to the second parametric curve change.

With reference to the third aspect, in a possible implementation, the controller is configured to: when an absolute value of a difference between the corresponding parameter values of a same voltage point that are on the first parametric curve and the second parametric curve is less than a preset threshold, determine that the currently scanned parametric curve is not affected by the light change.

With reference to the third aspect, in a possible implementation, the controller is further configured to process the first parametric curve and the second parametric curve when it is determined that the currently scanned curve is not affected by the light change, to obtain a final parametric curve.

With reference to the third aspect, in a possible implementation, the controller is further configured to send an abnormal signal when it is determined that the currently scanned curve is affected by the light change.

According to a fourth aspect, an embodiment of this application discloses a photovoltaic power generation system, including a power grid and at least one photovoltaic string. The photovoltaic power generation system further includes the converter according to any one of the second aspect and the possible implementations of the second aspect; or the photovoltaic power generation system further includes the converter according to any one of the third aspect and the possible implementations of the third aspect. An input end of the converter is connected to the at least one photovoltaic string, and an output end of the converter is connected to the power grid.

According to a fifth aspect, an embodiment of this application discloses a computer-readable storage medium. The computer-readable storage medium stores a computer program, the computer program includes at least one segment of code, and the at least one segment of code may be executed by a computer, to control the computer to perform the method according to any one of the first aspect and the possible implementations of the first aspect.

This application provides a photovoltaic power generation system, a converter applied to the photovoltaic power generation system, and a parametric curve scanning method for a photovoltaic string. The parametric curve includes a current-voltage (Current Voltage, IV) curve or a power-voltage (Power Voltage, PV) curve. The converter may perform parametric curve scanning on at least one photovoltaic string connected to the converter, to detect whether the photovoltaic string is defective or damaged, and learn of a power generation capability of the current photovoltaic power generation system by using a scanned parametric curve. The following describes embodiments of this application with reference to accompanying drawings.

<FIG> is a schematic structural diagram of a photovoltaic power generation system <NUM> according to an embodiment of this application. As shown in <FIG>, the photovoltaic power generation system <NUM> includes a converter <NUM>, at least one photovoltaic string <NUM>, and a power grid <NUM>. The photovoltaic string <NUM> includes a plurality of photovoltaic modules <NUM> that are combined in series or/and in parallel. The photovoltaic module <NUM>, also referred to as a solar panel, is a core part of the photovoltaic power generation system, converts solar energy into electrical energy to provide a direct current output, and transmits the electrical energy to a battery for storage or to drive a load to work. Because an individual solar cell cannot be directly used as a power supply, several individual cells need to be connected in series or/and in parallel and tightly packaged into a module, and the module is a smallest indivisible photovoltaic cell assembly. "A and/or B" in this application means A and B, and A or B.

Certainly, in some embodiments, the photovoltaic string <NUM> may include only one photovoltaic module <NUM>.

The converter <NUM> is connected to at least one photovoltaic string <NUM>, to convert output power of the photovoltaic module <NUM> connected to the converter <NUM>. In this embodiment of this application, the converter <NUM> is a photovoltaic inverter, and may be further configured to: convert, into an alternating current, a direct current output by the at least one photovoltaic string <NUM>, and then output the alternating current to the power grid <NUM>. In another embodiment, the converter <NUM> may be an optimizer. The converter <NUM> is not limited herein, provided that the converter <NUM> can convert the output power of the photovoltaic module <NUM> connected to the converter <NUM>.

The power grid <NUM>, also referred to as an electrical grid, includes a substation for various voltages and a power transmission and distribution line in a power system (that is, includes a voltage transformation unit, a power transmission unit, and a power distribution unit), and is configured to: transmit and distribute electrical energy, and change a voltage.

It can be understood that the photovoltaic power generation system <NUM> may include a plurality of converters <NUM>, and an alternating current side of the converter <NUM> may be connected to a step-up transformer (not shown in the figure) and then connected to the power grid <NUM>. Specifically, a quantity of converters <NUM> included in the photovoltaic power generation system <NUM> and whether the alternating current side of the converter <NUM> is connected to the step-up transformer may be determined based on a specific application environment. This is not specifically limited herein.

It should be noted that in an embodiment, when the photovoltaic power generation system <NUM> includes a plurality of converters <NUM>, the plurality of converters <NUM> may communicate with each other through a communications bus. The communications bus may be an industry standard architecture (Industry Standard Architecture, ISA) bus, a peripheral component interconnect (Peripheral Component, PCI) bus, an extended industry standard architecture (Extended Industry Standard Architecture, EISA) bus, or the like. The bus may be classified into an address bus, a data bus, a control bus, and the like, for example, a bus <NUM>.

Further, in a specific implementation, the photovoltaic power generation system <NUM> may further include a host computer (not shown in the figure), configured to communicate with the converter <NUM>. The host computer may be an independent communications host, or may be a mobile terminal device. The host computer may communicate with the converter <NUM> through wireless communication (for example, Wi-Fi, Lora, or Zigbee) or PLC communication.

<FIG> is a diagram of a typical IV curve and PV curve of a photovoltaic string according to an embodiment of this application. As shown in <FIG>, a curve L1 is the IV curve of the string, and a curve L2 is the PV curve of the string. Voc is an open-circuit voltage of the photovoltaic string, and is defined as a string voltage corresponding to an output without load of the string. Vmpp is a maximum power point voltage of the string, and is defined as a string voltage corresponding to maximum output power of the string.

It can be seen from <FIG> that the photovoltaic string <NUM> has a feature in which the voltage decreases with an increase in a current. Therefore, there is an optimal working point at which the maximum power can be obtained. In addition, an output of the photovoltaic string <NUM> changes with solar radiation intensity and a temperature of the photovoltaic string <NUM>. Because the solar radiation intensity changes, the optimal working point is obviously changed. Relative to these changes, a working point of the photovoltaic string <NUM> is always at a maximum power point, and the photovoltaic power generation system <NUM> always obtains a maximum power output from the photovoltaic string <NUM>. Such control is maximum power tracking control. A most distinguishing feature of the converter <NUM> used in the photovoltaic power generation system <NUM> is that the converter <NUM> includes a maximum power point tracking (Maximum Power Point Tracking, MPPT) function.

<FIG> is a principle block diagram of a converter according to an embodiment of this application. In other words, the converter <NUM> in <FIG> may be implemented by using a structure in <FIG>. As shown in <FIG>, the converter <NUM> includes a DC/DC circuit <NUM>, a DC/AC circuit <NUM>, a sampling circuit <NUM>, a controller <NUM>, and a memory <NUM>. Functions of the DC/DC circuit <NUM>, the DC/AC circuit <NUM>, the sampling circuit <NUM>, the controller <NUM>, and the memory <NUM> may be implemented by using an integrated circuit. The DC-DC DC/DC circuit <NUM>, the DC-AC DC/AC circuit <NUM>, the sampling circuit <NUM>, the controller <NUM>, and the memory <NUM> are integrated on a PCB (Printed Circuit Board, printed circuit board). The printed circuit board, also referred to as a printed wire board, is an important electronic part, is a support of an electronic component, and is a carrier electrically connected to the electronic component.

In this embodiment of this application, the converter <NUM> includes at least one DC/DC circuit <NUM>. Each DC/DC circuit <NUM> is correspondingly connected to one photovoltaic string <NUM> that is used as an input end of the converter <NUM>. The DC/DC circuit <NUM> is configured to adjust an output voltage of the photovoltaic string <NUM>. In another embodiment, the converter <NUM> may include only one DC/DC circuit <NUM>, and the DC/DC circuit <NUM> is connected to at least one photovoltaic string <NUM>. In other words, the DC/DC circuit <NUM> has a plurality of input ends. In addition, in some embodiments, the DC/DC circuit <NUM> may be omitted. In this case, the photovoltaic string <NUM> needs to be connected to an input end of the DC/AC circuit <NUM>.

In a specific embodiment, the DC/DC circuit <NUM> may work in a power conversion mode, and is configured to: perform power conversion on direct-current electric energy of the photovoltaic string <NUM> at the input end, and then output the converted direct-current electric energy to an output end. Alternatively, the DC/DC circuit <NUM> may work in a pass-through mode, and directly connect the input end and the output end. In a specific actual application, the DC/DC circuit <NUM> may be set based on a specific application environment, for example, may be set to a buck circuit, a boost circuit, or a buck-boost circuit.

An input end of the DC/AC circuit <NUM> is electrically connected to the DC/DC circuit <NUM>, and an output end of the DC/AC circuit <NUM> is electrically connected to the power grid <NUM>, to convert direct-current electric energy into alternating-current electric energy, and input the alternating-current electric energy to the power grid <NUM>. It can be understood that in another embodiment, the DC/AC circuit <NUM> may be omitted. In other words, the converter <NUM> can include only the DC/DC circuit.

The sampling circuit <NUM> is electrically connected to the DC/DC circuit <NUM>, to detect an output voltage of each photovoltaic string <NUM> and a current corresponding to the output voltage. In a specific actual application, the sampling circuit <NUM> may include a sensor, for example, a current sensor.

The controller <NUM> is separately electrically connected to the DC/DC circuit <NUM>, the DC/AC circuit <NUM>, the sampling circuit <NUM>, and the memory <NUM>. The controller <NUM> is a part that can coordinate work of all parts based on a function requirement of an instruction, is a nerve center and a command center of a system, usually includes three parts: an instruction register IR (Instruction Register), a program counter PC (Program Counter), and an operation controller OC (Operation Controller), and plays an important role in coordinating ordered work of the entire system. The controller <NUM> herein may be one or more devices, circuits, and/or processing cores for processing data (for example, a computer program instruction).

In another embodiment, the controller <NUM> may be a processor or may be a collective term of a plurality of processing elements. For example, the processor <NUM> may be a general-purpose central processing unit (Central Processing Unit, CPU), or may be an application-specific integrated circuit (application-specific Integrated Circuit, ASIC), or one or more integrated circuits for controlling program execution of a solution of this application, for example, one or more microprocessors (Digital Signal Processor, DSP), or one or more field programmable gate arrays (Field Programmable Gate Array, FPGA). In a specific implementation, in an embodiment, the processor <NUM> may include one or more CPUs.

The memory <NUM> may be a read-only memory (read-only memory, ROM) or another type of static storage device that can store static information and instructions, or a random access memory (random access memory, RAM) or another type of dynamic storage device that can store information and instructions, or may be an electrically erasable programmable read-only memory (Electrically Erasable Programmable Read-Only Memory, EEPROM), a compact disc read-only memory (Compact Disc Read-Only Memory, CD-ROM) or another compact disc storage, an optical disc storage (including a compressed optical disc, a laser disc, an optical disc, a digital versatile disc, a Blu-ray disc, and the like), a disk storage medium or another magnetic storage device, or any other medium that can be used to carry or store expected program code in a form of an instruction or a data structure and that can be accessed by a computer. However, the memory is not limited thereto. The memory <NUM> may exist independently. The memory <NUM> may alternatively be integrated with the controller <NUM>. The memory <NUM> may be configured to store data such as a current, a voltage, and power of the photovoltaic string <NUM>.

In this embodiment of this application, the memory <NUM> is further configured to store application code for execution of the solution of this application, and the execution is controlled by the controller <NUM>. In other words, the controller <NUM> is configured to execute the application code stored in the memory <NUM>.

It can be understood that the structure illustrated in this embodiment of this application constitutes no specific limitation on the converter <NUM>. In some other embodiments of this application, the converter <NUM> may include more or fewer parts than those shown in the figure, or combine some parts, or split some parts, or have different part arrangements. The parts shown in the figure may be implemented by using hardware, software, or a combination of software and hardware.

In this embodiment of this application, the converter <NUM> may be further configured to perform IV curve scanning on the photovoltaic string <NUM> connected to the converter <NUM>, to detect whether the photovoltaic string <NUM> connected to the converter <NUM> is defective or damaged. In addition, an IV curve can also be used to indicate information such as a current power generation capability and working condition of the photovoltaic string <NUM>. However, a light change exerts relatively large impact on an IV output feature of the photovoltaic string. If there is a light change in a process in which the photovoltaic system performs IV curve scanning on the photovoltaic string, an IV curve that is of the photovoltaic string and that is obtained through detection cannot accurately reflect the IV output feature of the photovoltaic string.

To determine whether the currently scanned IV curve is valid and affected by the light change, an embodiment of this application further discloses a parametric curve scanning method for a photovoltaic string. This method is applied to the converter <NUM>. The parametric curve includes one of a current-voltage IV curve or a power-voltage PV curve. In the embodiments of this application, the IV curve is used as an example for description.

<FIG> is a flowchart of an IV curve scanning method for a photovoltaic string according to an embodiment of this application. As shown in <FIG>, the IV curve scanning method for the photovoltaic string includes the following steps.

Step S11: Control an output voltage of the photovoltaic string to change from a first endpoint voltage of a first voltage range to a second endpoint voltage of the first voltage range according to a first preset rule, and sample an output current of the photovoltaic string in the process in which the output voltage of the photovoltaic string changes, to obtain a first IV curve.

The first voltage range is a voltage scanning range including a maximum output voltage and a minimum output voltage of the photovoltaic string in a process of scanning the first IV curve. For example, the maximum output voltage of the photovoltaic string may be an open-circuit voltage, and a minimum output voltage value may be <NUM> V.

In an implementation, the first preset rule is at least one of a rule in which a voltage drops by a fixed voltage difference or a rule in which a voltage drops by a changeable voltage difference. In a specific actual application, a preset rule in which the converter <NUM> controls an output voltage of the photovoltaic string <NUM> to change from an open-circuit voltage to a preset minimum value may be that the output voltage gradually decreases by a fixed voltage difference (for example, <NUM> V), or gradually decreases according to the rule in which a voltage drops by a changeable voltage difference. The rule in which a voltage drops by a changeable voltage difference specifically means that the voltage drops relatively fast near the open-circuit voltage of the photovoltaic string or the preset minimum value, and drops relatively slow in a middle part. In another implementation, the first preset rule may be another rule that can be used to implement a voltage change. This is not specifically limited herein.

Step S12: Control the output voltage of the photovoltaic string to change from a third endpoint voltage of a second voltage range to a fourth endpoint voltage of the second voltage range according to a second preset rule, and sample an output current of the photovoltaic string in the process in which the output voltage of the photovoltaic string changes, to obtain a second IV curve, where there is an intersection set between the first voltage range and the second voltage range.

The second voltage range is a voltage scanning range including a maximum output voltage and a minimum output voltage of the photovoltaic string in a process of scanning the second IV curve. For example, the maximum output voltage of the photovoltaic string may be an open-circuit voltage, and a minimum output voltage may be <NUM> V The second preset rule is similar to the first preset rule.

The steps of the method shown in <FIG> may be specifically implemented by the converter <NUM> shown in <FIG>. For example, both step S11 and step S12 may be implemented by the DC/DC circuit <NUM> and the sampling circuit <NUM>. For example, the DC/DC circuit <NUM> actively adjusts input power corresponding to the photovoltaic string <NUM>, to further control the output voltage of the photovoltaic string <NUM> to change to a corresponding endpoint voltage.

In the IV curve scanning method for the photovoltaic string disclosed in this embodiment of this application, IV curve scanning is separately performed on the photovoltaic string in the first voltage range and the second voltage range, and there is an intersection set between the first voltage range and the second voltage range, so that the first IV curve and the second IV curve that are obtained include parts corresponding to a same voltage. However, currents corresponding to the same voltage are obtained at different time points, so that it can be determined, by comparing the currents corresponding to the same voltage part, whether the currently obtained IV curve is affected by light, to further determine whether the currently obtained IV curve is valid, thereby improving scanning reliability. In addition, in this method, no test device needs to be additionally added, to effectively reduce a quantity of hardware devices that need to be provided, and reduce curve scanning costs.

<FIG> is a flowchart of an IV curve scanning method for a photovoltaic string according to another embodiment of this application. A difference from <FIG> is that the IV curve scanning method in this implementation further includes the following steps.

Step S13: Determine whether an IV curve scanning instruction is received. If the IV curve scanning instruction is received, step S11 is performed; or if the IV curve scanning instruction is not received, step S13 continues to be performed.

The converter <NUM> is initially in a normal on-grid state. Therefore, only when the converter <NUM> receives an IV curve scanning instruction sent by a host computer, the converter <NUM> can determine that an IV curve scanning task that needs to be performed. In other words, in this implementation, step S13 further needs to be performed before step S11 is performed.

Step S14: Determine, based on the first IV curve and the second IV curve, whether the currently scanned IV curve is affected by a light change. If the currently scanned IV curve is not affected by the light change, step S15 is performed; or if the currently scanned IV curve is affected by the light change, step S16 is performed.

In this embodiment of this application, the first IV curve and the second IV curve may be compared, to determine whether the currently scanned IV curve is affected by the light change. For example, the controller <NUM> compares the first parametric curve and the second parametric curve, to determine whether light intensity corresponding to the first IV curve and light intensity corresponding to the second IV curve change. Specifically, if an absolute value of a difference between current values corresponding to a same voltage point that are on the first IV curve and the second IV curve is less than a preset threshold, the controller <NUM> determines that the current IV curve is not affected by light, in other words, the currently obtained IV curve is valid.

It should be noted that in an ideal environment, a same output voltage of a photovoltaic string <NUM> corresponds to a same current if light intensity does not change. However, in an actual use process, there may be a slight error between two sampled currents corresponding to a same voltage due to sampling precision, or although light may slightly change in a process of sampling the two currents, it may be considered that there is no light change. Therefore, provided that an absolute value of a difference between the two sampled currents corresponding to the same voltage falls within an allowable range, it can be determined that the currently obtained IV curve is not affected by the light change. The preset threshold may be determined based on an actual application. This is not limited herein.

Step S15: Process the first IV curve and the second IV curve, to obtain a final IV curve.

When it is determined that the first IV curve and the second IV curve that are currently obtained are not affected by the light change, it indicates that both the first IV curve and the second IV curve are valid. However, to further improve precision of the obtained curves, the first IV curve and the second IV curve may be comprehensively processed. For example, an average current of currents corresponding to a same voltage point is obtained, and then the final IV curve is obtained and sent to the host computer.

When it is determined that the first IV curve and the second IV curve that are currently obtained are affected by the light change, it indicates that the first IV curve and the second IV curve are invalid. Therefore, the abnormal signal is sent to the host computer, to indicate that current scanning fails. Therefore, the host computer may determine, based on feedback, whether to send a parametric curve scanning instruction again.

In an implementation, the first endpoint voltage is greater than the second endpoint voltage. To be specific, the first endpoint voltage is an upper limit voltage of the first voltage range, and the second endpoint voltage is a lower limit voltage of the first voltage range. The third endpoint voltage is less than the fourth endpoint voltage. To be specific, the third endpoint voltage is a lower limit voltage of the second voltage range, and the fourth endpoint voltage is an upper limit voltage of the second voltage range. In other words, the output voltage of the photovoltaic string <NUM> is first controlled to change from the upper limit voltage of the first voltage range to the lower limit voltage of the first voltage range according to the first preset rule, to scan the first IV curve; and then the output voltage of the photovoltaic string <NUM> is controlled to change from the lower limit voltage of the second voltage range to the upper limit voltage of the second voltage range according to the second preset rule, to scan the second IV curve. In this way, a scanning endpoint of the first IV curve is relatively close to a scanning startpoint of the second IV curve. Therefore, an IV curve scanning speed can be increased.

Specifically, to present a complete output feature of the photovoltaic string, the upper limit voltage of the first voltage range is set to be less than or equal to the open-circuit voltage Voc of the string and greater than a maximum power point voltage Vmpp of the string. In an actual application, the upper limit voltage of the first voltage range may be close to and slightly less than the open-circuit voltage of the string. The lower limit voltage of the first voltage range is set to be greater than or equal to zero and less than the maximum power point voltage Vmpp of the string. In an actual application, the lower limit voltage of the first voltage range may be close to and slightly greater than zero.

Similarly, the upper limit voltage of the second voltage range is set to be less than or equal to the open-circuit voltage Voc of the string and greater than the maximum power point voltage Vmpp of the string. In an actual application, the upper limit voltage of the second voltage range may be close to and slightly less than the open-circuit voltage of the string. The lower limit voltage of the second voltage range is set to be greater than or equal to zero and less than the maximum power point voltage Vmpp of the string. In an actual application, the lower limit voltage of the second voltage range may be close to and slightly greater than zero.

The upper limit voltage of the second voltage range may be equal to the upper limit voltage of the first voltage range, or may be unequal to the upper limit voltage of the first voltage range. The lower limit voltage of the second voltage range may be equal to the lower limit voltage of the first voltage range, or may be unequal to the lower limit voltage of the first voltage range.

In an implementation, to improve comparison precision, the upper limit voltage of the first voltage range is equal to the upper limit voltage of the second voltage range, and the lower limit voltage of the first voltage range is equal to the lower limit voltage of the second voltage range. In other words, the first voltage range and the second voltage range completely coincide.

Further, in a specific implementation, to facilitate comparison between the first IV curve and the second IV curve and improve comparison efficiency, the first preset rule and the second preset rule each are a rule in which a voltage changes by a fixed voltage difference. In this embodiment of this application, the first preset rule is a rule in which a voltage drops by a fixed voltage difference, and the second preset rule is a rule in which a voltage rises by a fixed voltage difference. For example, <NUM> sampling points may be selected in each of the first voltage range and the second voltage range. The upper limit voltage of the first voltage range is the open-circuit voltage Voc of the photovoltaic string <NUM>, and the lower limit voltage of the first voltage range is <NUM> V Therefore, the <NUM> sampling points in the first voltage range are respectively U1 = Voc, U2 = (<NUM>/<NUM>) x Voc, U3 = (<NUM>/<NUM>) x Voc,. , U31 = (<NUM>/<NUM>) x Voc, and U32 = <NUM>. Similarly, the <NUM> sampling points in the second voltage range are respectively U1 = <NUM>, U2 = (<NUM>/<NUM>) x Voc, U3 = (<NUM>/<NUM>) x Voc,. , U31 = (<NUM>/<NUM>) x Voc, and U32 = Voc. In this case, the sampling points in the first voltage range are exactly the same as the sampling points in the second voltage range, so that a calculation amount is reduced, and a comparison speed is improved.

<FIG> is a diagram of an IV scanning waveform of a photovoltaic string according to an embodiment of this application. To further improve comparison efficiency, data at two sampling points is completely the same. As shown in <FIG>, a time-related waveform F1 in the first voltage range is symmetrical to a time-related waveform F2 in the second voltage range. Herein, a1 is the upper limit voltage of the first voltage range, b1 is the lower limit voltage of the first voltage range, c1 is the lower limit voltage of the second voltage range, and d1 is the upper limit voltage of the second voltage range.

In another implementation, the first endpoint voltage is less than the second endpoint voltage. To be specific, the first endpoint voltage is the lower limit voltage of the first voltage range, and the second endpoint voltage is the upper limit voltage of the first voltage range. The third endpoint voltage is greater than the fourth endpoint voltage. To be specific, the third endpoint voltage is the upper limit voltage of the second voltage range, and the fourth endpoint voltage is the lower limit voltage of the second voltage range. In other words, the output voltage of the photovoltaic string <NUM> is first controlled to change from the lower limit voltage of the first voltage range to the upper limit voltage of the first voltage range according to the first preset rule, to scan the first IV curve; and then the output voltage of the photovoltaic string <NUM> is controlled to change from the upper limit voltage of the second voltage range to the lower limit voltage of the second voltage range according to the second preset rule, to scan the second IV curve. Other details are the same as or similar to those in the foregoing embodiments, and are not described herein again.

An IV scanning waveform in this implementation of this application is shown in <FIG>. A time-related waveform F3 in the first voltage range is symmetrical to a time-related waveform F4 in the second voltage range. Herein, a2 is the lower limit voltage of the first voltage range, b2 is the upper limit voltage of the first voltage range, c2 is the upper limit voltage of the second voltage range, and d2 is the lower limit voltage of the second voltage range.

<FIG> is a diagram of a function module of a converter according to an non-claimed embodiment of this application. In this embodiment, a converter <NUM> is presented in a form of a function unit. The "unit" herein may be an application-specific integrated circuit, a controller and a memory that execute one or more software or firmware programs, an integrated logic circuit, and/or another device that can provide the foregoing function. In a simple embodiment, a person skilled in the art may figure out that the converter <NUM> may be in a form shown in <FIG>. Specifically, as shown in <FIG>, the converter <NUM> includes an adjustment unit <NUM>, an obtaining unit <NUM>, a determining unit <NUM>, and a processing unit <NUM>.

The adjustment unit <NUM> is configured to control an output voltage of the photovoltaic string to change from a first endpoint voltage of a first voltage range to a second endpoint voltage of the first voltage range according to a first preset rule. The obtaining unit <NUM> is configured to obtain a current of the photovoltaic string in the process in which the output voltage change of the photovoltaic string changes, to scan a first IV curve.

The adjustment unit <NUM> is further configured to control the output voltage of the photovoltaic string to change from a third endpoint voltage of a second voltage range to a fourth endpoint voltage of the second voltage range according to a second preset rule. The obtaining unit <NUM> is further configured to obtain a current of the photovoltaic string in the process in which the output voltage of the photovoltaic string changes, to scan the second IV curve.

The determining unit <NUM> is configured to determine, based on the first IV curve and the second IV curve, whether the currently scanned parametric curve is affected by a light change. Specifically, the determining unit <NUM> is configured to: when an absolute value of a difference between the corresponding parameter values of a same voltage point that are on the first IV curve and the second IV curve is less than a preset threshold, determine that the currently scanned IV curve is not affected by the light change.

The processing unit <NUM> is configured to process the first IV curve and the second IV curve when it is determined that the currently scanned curve is not affected by the light change, to obtain a final IV curve. The processing unit <NUM> is further configured to send an abnormal signal when it is determined that the currently scanned curve is affected by the light change.

In a specific implementation, for example, the adjustment unit <NUM> may be implemented by a DC/DC circuit <NUM>. The obtaining unit <NUM> may be implemented by a sampling circuit <NUM>, and the determining unit <NUM> and the processing unit <NUM> may be implemented by a controller <NUM>.

An embodiment of this application further provides a computer storage medium, configured to store computer software instructions used by the converter shown in <FIG>. The computer software instructions include a program designed for performing the foregoing method embodiment. The stored program is executed, to implement IV curve scanning on a photovoltaic string, and further determine whether an IV curve is affected by the light change.

It may be clearly understood by a person skilled in the art that, for the purpose of convenient and brief description, for a detailed working process of the foregoing apparatuses and units, reference may be to a corresponding process in the foregoing method embodiments, and details are not described herein again.

The integrated unit may be implemented in a form of hardware, or may be implemented in a form of hardware in addition to a software function unit.

Further embodiments of the present invention are provided in the following. It should be noted that the numbering used in the following section does not necessarily need to comply with the numbering used in the previous sections.

Embodiment <NUM>. A parametric curve scanning method for a photovoltaic string, applied to a photovoltaic power generation system, wherein the photovoltaic power generation system comprises a converter and at least one photovoltaic string connected to the converter, and the scanning method comprises:.

Embodiment <NUM>. The scanning method according to embodiment <NUM>, wherein the first endpoint voltage is greater than the second endpoint voltage and the third endpoint voltage is less than the fourth endpoint voltage; or the first endpoint voltage is less than the second endpoint voltage and the third endpoint voltage is greater than the fourth endpoint voltage.

Embodiment <NUM>. The scanning method according to embodiment <NUM>, wherein the first endpoint voltage is equal to the fourth endpoint voltage, and/or the second endpoint voltage is equal to the third endpoint voltage.

Embodiment <NUM>. The scanning method according to embodiment <NUM>, wherein a time-related waveform in the first voltage range is symmetrical to a time-related waveform in the second voltage range.

Embodiment <NUM>. The scanning method according to embodiment <NUM>, wherein the first preset rule is a rule in which a voltage drops by a fixed voltage difference and the second preset rule is a rule in which a voltage rises by a fixed voltage difference; or the first preset rule is a rule in which a voltage rises by a fixed voltage difference and the second preset rule is a rule in which a voltage drops by a fixed voltage difference.

Embodiment <NUM>. The scanning method according to any one of embodiments <NUM> to <NUM>, wherein the scanning method further comprises:
determining, based on the first parametric curve and the second parametric curve, whether the currently scanned parametric curve is affected by a light change.

Embodiment <NUM>. The scanning method according to embodiment <NUM>, wherein the determining, based on the first parametric curve and the second parametric curve, whether the currently scanned parametric curve is affected by a light change comprises:
comparing the first parametric curve and the second parametric curve, to determine whether light intensity corresponding to the first parametric curve and light intensity corresponding to the second parametric curve change.

Embodiment <NUM>. The scanning method according to embodiment <NUM> or <NUM>, wherein the scanning method further comprises:
if an absolute value of a difference between the corresponding parameter values of a same voltage point that are on the first parametric curve and the second parametric curve is less than a preset threshold, determining that the currently scanned parametric curve is not affected by the light change.

Embodiment <NUM>. A converter, comprising:.

Embodiment <NUM>. The converter according to embodiment <NUM>, wherein the first endpoint voltage is greater than the second endpoint voltage and the third endpoint voltage is less than the fourth endpoint voltage; or the first endpoint voltage is less than the second endpoint voltage and the third endpoint voltage is greater than the fourth endpoint voltage.

Embodiment <NUM>. The converter according to embodiment <NUM>, wherein the first endpoint voltage is equal to the fourth endpoint voltage, and/or the second endpoint voltage is equal to the third endpoint voltage.

Embodiment <NUM>. The converter according to embodiment <NUM>, wherein a time-related waveform in the first voltage range is symmetrical to a time-related waveform in the second voltage range.

Embodiment <NUM>. The converter according to embodiment <NUM>, wherein the first preset rule is a rule in which a voltage drops by a fixed voltage difference and the second preset rule is a rule in which a voltage rises by a fixed voltage difference; or the first preset rule is a rule in which a voltage rises by a fixed voltage difference and the second preset rule is a rule in which a voltage drops by a fixed voltage difference.

Embodiment <NUM>. The converter according to any one of embodiments <NUM> to <NUM>, wherein the converter further comprises a controller, the controller is separately electrically connected to the sampling circuit and the DC/DC circuit, and the controller is configured to determine, based on the first parametric curve and the second parametric curve, whether the currently scanned parametric curve is affected by a light change.

Embodiment <NUM>. The converter according to embodiment <NUM>, wherein the controller is configured to compare the first parametric curve and the second parametric curve, to determine whether light intensity corresponding to the first parametric curve and light intensity corresponding to the second parametric curve change.

Embodiment <NUM>. The converter according to embodiment <NUM> or <NUM>, wherein the controller is configured to: when an absolute value of a difference between the corresponding parameter values of a same voltage point that are on the first parametric curve and the second parametric curve is less than a preset threshold, determine that the currently scanned parametric curve is not affected by the light change.

Embodiment <NUM>. A photovoltaic power generation system, comprising a power grid and at least one photovoltaic string, wherein the photovoltaic power generation system further comprises the converter according to any one of embodiments <NUM> to <NUM>, an input end of the converter is connected to the at least one photovoltaic string, and an output end of the converter is connected to the power grid.

The embodiments in this specification are all described in a progressive manner, for same or similar parts in the embodiments, reference may be made to these embodiments, and each embodiment focuses on a difference from other embodiments. The method disclosed in the embodiments corresponds to the apparatus disclosed in the embodiments, and therefore is described relatively briefly. For related parts, reference may be made to descriptions of the apparatus.

It should be noted that, for brief description, the foregoing method embodiments are represented as a series of actions. However, a person skilled in the art should appreciate that this application is not limited to the described order of the actions, because according to this application, some steps may be performed in other orders or simultaneously.

A sequence of the steps of the method in the embodiments of this application may be adjusted, combined, or removed based on an actual requirement.

Implementations of this application may be randomly combined, to achieve different technical effects.

Claim 1:
A parametric curve scanning method for a photovoltaic string (<NUM>), applied to a photovoltaic power generation system (<NUM>), wherein the photovoltaic power generation system (<NUM>) comprises a converter (<NUM>) and at least one photovoltaic string (<NUM>) connected to the converter (<NUM>), and the scanning method comprises:
controlling an output voltage of the photovoltaic string (<NUM>) to change from a first endpoint voltage of a first voltage range to a second endpoint voltage of the first voltage range, and obtaining a current parameter or a power parameter of the photovoltaic string (<NUM>) in the process in which the output voltage of the photovoltaic string (<NUM>) changes, to scan a first parametric curve; and
controlling the output voltage of the photovoltaic string (<NUM>) to change from a third endpoint voltage of a second voltage range to a fourth endpoint voltage of the second voltage range, and obtaining a current parameter or a power parameter of the photovoltaic string (<NUM>) in the process in which the output voltage of the photovoltaic string (<NUM>) changes, to scan a second parametric curve, wherein there is an intersection set between the first voltage range and the second voltage range,
characterized in that the scanning method further comprises: the first endpoint voltage is greater than the second endpoint voltage and the third endpoint voltage is less than the fourth endpoint voltage; or the first endpoint voltage is less than the second endpoint voltage and the third endpoint voltage is greater than the fourth endpoint voltage.