CN117413458A

CN117413458A - Intelligent photovoltaic module controller and control method thereof

Info

Publication number: CN117413458A
Application number: CN202180098929.0A
Authority: CN
Inventors: 崔凤辰
Original assignee: Time Robotics Co ltd
Current assignee: Time Robotics Co ltd
Priority date: 2021-04-01
Filing date: 2021-08-30
Publication date: 2024-01-16
Also published as: KR102361318B1

Abstract

The present invention relates to a method for maximizing power generation efficiency by: an intelligent photovoltaic module controller for controlling a series/parallel connection to connect two photovoltaic modules in series or parallel is included in a photovoltaic power generation system, and the series/parallel connection is controlled according to a change in current flowing through an external connection terminal pair of the corresponding photovoltaic module controller or through a string of a plurality of controllers connected in series.

Description

Intelligent photovoltaic module controller and control method thereof

Technical Field

The present invention relates to an intelligent photovoltaic module controller capable of maximizing power generation efficiency of a photovoltaic power generation system by switching electrical connections between a plurality of photovoltaic modules arranged in the photovoltaic power generation system in response to a control signal, and a control method thereof.

Background

The basic unit of generating direct current from sunlight is called a battery, and a plurality of batteries are connected to form a module, which is one basic unit from which electric power is extracted. Generally, a photovoltaic power generation system includes one or more arrays of a plurality of photovoltaic modules connected in series and a power converter that converts Direct Current (DC) into DC power or alternating current (alternating current, AC) power. Fig. 1 is a schematic diagram of a conventional photovoltaic power system.

Photovoltaic modules are designed with multiple cells connected in series or parallel to produce the required amount of power. Under international standard test conditions (incident irradiance: 1,000w/m, solar cell temperature: 25 ℃, atmospheric mass: 1.5), the magnitude of open circuit voltage generated by an individual cell is about 0.5V to 0.6V, and the magnitude of short circuit current generated by the cell is about 8A, but the magnitude varies depending on the size and quality of the cell. The most important factors affecting the voltage-current characteristics of the power generated by the photovoltaic module are temperature and solar radiation. As the temperature increases, the voltage generated by the photovoltaic module decreases, while as the temperature decreases, the voltage increases. For example, in the case of silicon solar cells, it is known that the energy conversion efficiency decreases by about 0.4% for every 1 ℃ increase in temperature. If the surface temperature of the battery rises to 60 c to 70 c in summer, the power generation rate may be reduced due to the reduction of the voltage generated by each battery, although there is enough sunlight. For a given voltage, the current that the photovoltaic module is allowed to flow is proportional to solar radiation. That is, the current increases with increasing insolation. However, once the maximum current allowed to flow through the battery is reached, the current may not increase even if the sunlight increases. Thus, the desired maximum power is generated by allowing maximum current to flow through the battery at maximum voltage levels.

The photovoltaic module includes a plurality of cells connected in series. If a cell does not receive enough sunlight and the current through the cell decreases, the cell becomes a "bottleneck" and becomes the load for the other cells. If a current reduction occurs in any one of the plurality of batteries connected in series, this reduces the total current of a series of batteries connected in series, resulting in a significant reduction in power generation efficiency, and in severe cases, damage to the batteries due to the occurrence of hot spots. The heat generated by the failed battery may cause secondary failure of the entire module. To avoid these problems, the batteries may be divided into several groups to provide a bypass circuit (bypass circuit) that enables current to bypass the batteries in the group including the failed battery, and a reverse current protection diode may be provided to suppress reverse current generated due to voltage drop generated by the photovoltaic module.

Solar/temperature variation due to weather, shading, pollution, etc., or voltage-current fluctuation of the photovoltaic module due to occurrence of accidents or faults are important factors for reducing the photovoltaic power generation efficiency. The current-voltage relationship that allows maximum power to be generated is variable. Accordingly, various maximum power point tracking (maximum power point tracking, MPPT) control methods are known in the art to improve the overall power generation efficiency of a photovoltaic power generation system under varying conditions. For example, korean patent laid-open publication (KR) No. 10-2013-0025286 discloses a technique of controlling a power inverter to track a maximum power point.

However, even when the power converter is controlled to track the maximum power point, the operation of the power converter must be interrupted in the event that the voltage generated by the photovoltaic module array falls below the operating range of the power converter. When the energy conversion efficiency of the cells constituting the photovoltaic module is reduced due to a high temperature event or a decrease in solar radiation caused by a change in weather conditions, the under-voltage trip device (undervoltage trip device) of the power converter is operated for a certain period of time (e.g., 5 minutes) to protect the internal circuits thereof. Therefore, even under weather conditions suitable for power generation, power cannot be generated, resulting in a decrease in the overall energy efficiency of photovoltaic power generation, and damage to an overload internal circuit of the power converter or a reduction in the service life due to a surge (arc) or an arc (arc) that may occur during the operation of the under-voltage trip device. In this regard, korean patent laid-open publication (KR) No. 10-2011-0038975 discloses the following technology: the technology enables the main solar cell module and the auxiliary solar cell module to be connected in series or in parallel according to the total output voltage of the solar cell modules so that the total output voltage of the solar cell modules can be maintained within the normal operation range of the power converter (inverter). However, this technique has problems in that: a separate auxiliary battery or voltage booster is required and voltage support using such a device is only temporarily provided to prevent the power converter from stopping operation.

If the power generation rate of a certain photovoltaic module is reduced due to shading by clouds, cell surface contamination, malfunction, etc. and the photovoltaic module becomes a bottleneck restricting current flow, this may result in a reduction in the total current of the array of photovoltaic modules connected in series to the photovoltaic module and thus in a reduction in the overall power generation efficiency. In this case, even when the voltage of the array is temporarily increased, power loss generated by other normal photovoltaic modules is unavoidable. In this regard, korean patent registration (KR) No. 10-1743908 discloses the following management techniques: the management techniques allow the photovoltaic power generation system to operate efficiently and uninterruptedly by installing a sensor module and bypass circuit on each photovoltaic module to exclude (bypass) defective or faulty photovoltaic modules from the power generation circuit. In order to control this operation of bypassing defective or faulty photovoltaic modules, each photovoltaic module needs to be provided with a bypass switching circuit and a sensor for monitoring the condition (fault) of the photovoltaic module, which leads to an increase in cost and thus a decrease in the profitability of the photovoltaic power generation system. While the current produced by each photovoltaic module is sensitive to conditions such as weather, environmental changes, and faults, the same current (total current) will flow through each photovoltaic module connected in series on a string (string). Therefore, even when the current generated by a certain photovoltaic module decreases, it is difficult to determine which photovoltaic module causes a decrease in the total current. Furthermore, since the above conditions have relatively little effect on the voltage and the variation of the voltage does not necessarily lead to a reduction of the total current, monitoring the voltage generated by each photovoltaic module is insufficient to determine which photovoltaic module leads to a reduction of the total current.

Disclosure of Invention

Technical problem

The present invention is conceived to solve such problems in the art, and it is an object of the present invention to provide an intelligent photovoltaic module controller capable of switching electrical connection between photovoltaic modules to series or parallel connection, thereby ensuring more efficient and easier maintenance of photovoltaic power generation without detecting the voltage or current of the respective photovoltaic modules.

Another object of the present invention is to provide a control method of an intelligent photovoltaic module controller that enables photovoltaic modules to be electrically connected in series or parallel, ensuring more efficient and easier maintenance of photovoltaic power generation.

Technical solution

According to one aspect of the present invention, there is provided an intelligent photovoltaic module controller for switching electrical connections between photovoltaic modules each comprising a plurality of solar cells connected to each other. The intelligent photovoltaic module controller includes: a first pair of input terminals electrically connected to positive (+) and negative (-) terminals, respectively, of the first photovoltaic module; a second pair of input terminals electrically connected to the positive (+) terminal and the negative (-) terminal, respectively, of the second photovoltaic module; a pair of positive (+) and negative (-) external connection terminals electrically connected to the power converter or to another intelligent photovoltaic module controller in series; a series circuit connected between the first pair of input terminals, the second pair of input terminals, and the pair of external connection terminals such that one terminal of the first pair of input terminals is electrically connected to one terminal of the second pair of input terminals having an opposite polarity to the one terminal of the first pair of input terminals, and the other terminal of the first pair of input terminals and the other terminal of the second pair of input terminals are electrically connected to the positive (+) external connection terminal and the negative (-) external connection terminal, respectively; a parallel circuit connected between the first pair of input terminals, the second pair of input terminals, and the pair of external connection terminals such that positive (+) and negative (-) terminals of the first pair of input terminals are electrically connected to positive (+) and negative (-) terminals of the second pair of input terminals, respectively, which in turn are electrically connected to positive (+) and negative (-) external connection terminals, respectively; a switching circuit that performs a switching operation to connect a selected one of the series circuit and the parallel circuit between the first pair of input terminals, the second pair of input terminals, and the pair of external connection terminals; and a control unit that controls the switching circuit to perform switching between the series connection and the parallel connection, wherein when the electrical connection between the first photovoltaic module and the second photovoltaic module is switched from the series circuit to the parallel circuit, it is determined whether to switch the electrical connection between the first photovoltaic module and the second photovoltaic module back to the series circuit based on a change in current flowing through the pair of external connection terminals or through a string connected to the pair of external connection terminals due to switching to the parallel circuit.

The intelligent photovoltaic module controller may further include: and a current sensor detecting a magnitude of a current flowing through the pair of external connection terminals.

The intelligent photovoltaic module controller may further include: and a voltage sensor that detects a magnitude of a voltage applied between the pair of external connection terminals.

When the control unit controls the switching operation of the switching circuit such that the parallel circuit is connected between the first photovoltaic module and the second photovoltaic module, the control unit may compare the current magnitude detected by the current sensor with the current magnitude detected before the circuit is switched, and may independently control the switching operation of the switching circuit such that the first photovoltaic module and the second photovoltaic module are allowed to remain connected in parallel when the current magnitude measured after the switching to the parallel circuit is increased by a predetermined value or by more than a predetermined value compared with the current magnitude measured before the switching to the parallel circuit, and the first photovoltaic module and the second photovoltaic module are allowed to be connected back to the series circuit when the current magnitude measured after the switching to the parallel circuit is increased by less than the predetermined value compared with the current magnitude measured before the switching to the parallel circuit.

The control unit may control a switching operation of the switching circuit such that the first photovoltaic module and the second photovoltaic module are periodically connected to the parallel circuit at predetermined time intervals to check the power generation state.

The intelligent photovoltaic module controller may further include: and a communication unit which communicates with the power converter and has a unique identification code (identification code, ID), wherein when the communication unit receives the circuit control command, the control unit can control the switching operation of the switching circuit in response to the circuit control command.

The intelligent photovoltaic module controller may further include: and a power supply unit connected to the first and second pairs of input terminals to supply power required for operation of the internal components of the intelligent photovoltaic module controller.

The intelligent photovoltaic module controller may further include: and a reverse current prevention circuit connected to the pair of external connection terminals to prevent reverse current from flowing from the outside, the reverse current prevention circuit including a fuse or a positive temperature coefficient (positive temperature coefficient, PTC) thermistor to provide over-power protection due to a fault or accident.

According to another aspect of the present invention, there is provided a control method of an intelligent photovoltaic module controller for switching electrical connection between photovoltaic modules each including a plurality of solar cells connected to each other, wherein the intelligent photovoltaic module controller includes: a first pair of input terminals electrically connected to positive (+) and negative (-) terminals, respectively, of the first photovoltaic module; a second pair of input terminals electrically connected to the positive (+) terminal and the negative (-) terminal, respectively, of the second photovoltaic module; a pair of positive (+) and negative (-) external connection terminals electrically connected to the power converter or to another intelligent photovoltaic module controller in series; a series circuit connected between the first pair of input terminals, the second pair of input terminals, and the pair of external connection terminals such that one terminal of the first pair of input terminals is electrically connected to one terminal of the second pair of input terminals having an opposite polarity to the one terminal of the first pair of input terminals, and the other terminal of the first pair of input terminals and the other terminal of the second pair of input terminals are electrically connected to the positive (+) external connection terminal and the negative (-) external connection terminal, respectively; a parallel circuit connected between the first pair of input terminals, the second pair of input terminals, and the pair of external connection terminals such that positive (+) and negative (-) terminals of the first pair of input terminals are electrically connected to positive (+) and negative (-) terminals of the second pair of input terminals, respectively, which in turn are electrically connected to positive (+) and negative (-) external connection terminals, respectively; a switching circuit that performs a switching operation to connect a selected one of the series circuit and the parallel circuit between the first pair of input terminals, the second pair of input terminals, and the pair of external connection terminals; and a control unit that controls the switching circuit to perform switching between the series connection and the parallel connection. The method comprises the following steps: detecting a change in current flowing through the pair of external connection terminals when the switching circuit switches the electrical connection between the first photovoltaic module and the second photovoltaic module from the series circuit to the parallel circuit; and determining whether to connect the first photovoltaic module and the second photovoltaic module back to the series circuit based on the detected change in current.

The step of determining whether to connect the first photovoltaic module and the second photovoltaic module back to the series circuit may comprise: allowing the first and second photovoltaic modules to remain connected to the parallel circuit when the magnitude of the current measured after switching to the parallel circuit increases by a predetermined value or by more than a predetermined value as compared to the magnitude of the current measured before switching to the parallel circuit; and connecting the first and second photovoltaic modules back to the series circuit when the magnitude of the current measured after switching to the parallel circuit increases by less than a predetermined value as compared to the magnitude of the current measured before switching to the parallel circuit.

The step of detecting a change in current may include detecting a change in current flowing through a string of the pair of external connection terminals connected to the intelligent photovoltaic module controller.

The method may further comprise: the switching operation of the switching circuit is controlled by the control unit of the power converter such that the first photovoltaic module and the second photovoltaic module are periodically connected to the parallel circuit at predetermined time intervals to check the power generation state.

The intelligent photovoltaic module controller may further include: and a communication unit which communicates with the power converter and has a unique identification code (ID), and when the communication unit receives the circuit control command, the control unit may control a switching operation of the switching circuit in response to the circuit control command.

The method may further comprise: communicating with at least two intelligent photovoltaic module controllers to remotely control the at least two intelligent photovoltaic module controllers, the at least two intelligent photovoltaic module controllers being mounted on a power converter and connected in series via a string of respective pairs of external connection terminals connected to the at least two intelligent photovoltaic module controllers, wherein the step of determining whether to connect a first photovoltaic module and a second photovoltaic module back to a series circuit may comprise: allowing the first and second photovoltaic modules to remain connected to the parallel circuit when the magnitude of the current measured after switching to the parallel circuit increases by a predetermined value or by more than a predetermined value as compared to the magnitude of the current measured before switching to the parallel circuit; and connecting the first and second photovoltaic modules back to the series circuit when the magnitude of the current measured after switching to the parallel circuit increases by less than a predetermined value as compared to the magnitude of the current measured before switching to the parallel circuit, and when the first and second photovoltaic modules are allowed to remain connected to the parallel circuit, identifying a corresponding intelligent photovoltaic module controller among the at least two intelligent photovoltaic module controllers by a unique identification code (ID) to provide information about the power generation state.

The detecting of the change in the current flowing through the pair of external connection terminals may include: a change in current flowing through a string of the at least two intelligent photovoltaic module controllers connected in series is detected by a sensor unit of the power converter to control each of the intelligent photovoltaic module controllers based on the change in current.

The power converter may notify an administrator at the remote location of the abnormal condition according to a predetermined condition, or may provide information in response to a query from the remote location.

Advantageous effects

The intelligent photovoltaic module controller according to the present invention can adaptively switch the electrical connection between the photovoltaic modules in series or in parallel to track the maximum power point in response to the magnitude of the voltage/current of a certain photovoltaic module being reduced due to various reasons such as weather changes, temperature, pollution and malfunction. The intelligent photovoltaic module controller may be used with an array of photovoltaic modules connected by a single string and may also be installed as an add-on to an existing photovoltaic power generation system.

According to the present invention, the connection between the photovoltaic modules can be switched in real time between series and parallel based on the detection and analysis of the voltage or current of each intelligent photovoltaic module controller, and problematic photovoltaic modules can be easily identified based on the measured voltage or current information to take necessary actions.

According to the present invention, by series/parallel switching of electrical connections between the photovoltaic modules, the power converter can continue to operate in the MPPT mode, thereby reducing the number of times the operation of the power converter is interrupted, and thus improving the power generation efficiency and preventing the reduction in the service life of the power converter and preventing the power converter from malfunctioning.

Drawings

The above and other aspects, features and advantages of the present invention will become apparent from the following detailed description of embodiments when taken in conjunction with the accompanying drawings in which:

fig. 1 is a schematic diagram of a conventional photovoltaic power system.

Fig. 2 is a diagram of a power converter controlling a smart photovoltaic module controller for series/parallel switching in accordance with the present invention.

Fig. 3 is a diagram of a smart photovoltaic module controller and power converter for series/parallel switching in accordance with the present invention.

Fig. 4 is a diagram illustrating one embodiment of a power converter controlling a smart photovoltaic module controller in accordance with the present invention.

Detailed Description

Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings. It is to be understood that the invention is not limited thereto and may be practiced in various ways. The following examples are presented in order to fully disclose the invention and provide a thorough understanding of the invention to those skilled in the art. It should be noted that throughout the specification, like components will be denoted by like reference numerals.

In other instances, well-known functions or constructions are not described in detail that may unnecessarily obscure the subject matter of the present invention. It will be appreciated that for convenience and clarity, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. However, it will be understood by those skilled in the art that the present invention may be practiced without these specific details.

Fig. 2 is a diagram of a power converter controlling a smart photovoltaic module controller according to the present invention, wherein the smart photovoltaic module controller can switch the electrical connection between two photovoltaic modules to a series or parallel connection. An intelligent photovoltaic module controller (100) according to one embodiment of the present invention includes: two pairs of input terminals electrically connected to pairs of positive (+) and negative (-) terminals of the two photovoltaic modules, respectively; and a pair of positive (+) and negative (-) external connection terminals electrically connected in series to an adjacent power converter or another intelligent photovoltaic controller. Respective pairs of external connection terminals of a plurality of intelligent photovoltaic module controllers (100) are connected in series to form a photovoltaic module array, wherein an output voltage of the array is equal to a sum of voltages across the respective pairs of external connection terminals of the plurality of photovoltaic module controllers.

For example, when two photovoltaic modules each having an output voltage of 40V are connected in series, the voltage across the pair of external connection terminals of the photovoltaic module controller in a steady state is 80V, and the output voltage of an array of 10 such photovoltaic module controllers connected in series is 800V. Since the photovoltaic module controllers are all connected in series, the same magnitude of current flows through each photovoltaic module in the array. Assuming that a current of 10A flows through each photovoltaic module in the array, the total power generated is 800v×10a=8000W. If the electrical connection between the two photovoltaic modules connected to each photovoltaic module controller is switched to a parallel connection, the output voltage of the array is 400V and the output current of the array is 20A. Thus, if there is no problem with any of the photovoltaic modules, then when the photovoltaic modules in the array are all connected in parallel, the total power produced is 400v×20a=8000W, which is equal to the total power produced above. However, if any of the photovoltaic module controllers connects two photovoltaic modules connected in series therewith, the total current of the array is limited to 10A, which corresponds to the current of one photovoltaic module.

The series/parallel switching circuit unit (120) includes: a series circuit, a parallel circuit, and a switching circuit that performs switching between the series circuit and the parallel circuit. The series circuit is connected between a first pair of input terminals, a second pair of input terminals, and the pair of external connection terminals of a photovoltaic module controller (100) connected to the two photovoltaic modules such that one terminal of the first pair of input terminals is electrically connected to one terminal of the second pair of input terminals having an opposite polarity to the one terminal of the first pair of input terminals, and the other terminal of the first pair of input terminals and the other terminal of the second pair of input terminals are electrically connected to a positive (+) external connection terminal and a negative (-) external connection terminal, respectively. The parallel circuit is connected between the first pair of input terminals, the second pair of input terminals, and the pair of external connection terminals such that the positive (+) terminal and the negative (-) terminal of the first pair of input terminals are electrically connected to the positive (+) terminal and the negative (-) terminal of the second pair of input terminals, respectively, which in turn are electrically connected to the positive (+) external connection terminal and the negative (-) external connection terminal, respectively. The switching circuit performs a switching operation in response to a signal from the control unit (130) to connect a selected one of the series circuit and the parallel circuit between the first pair of input terminals, the second pair of input terminals, and the pair of external connection terminals.

Based on monitoring the power generation state of the photovoltaic module by detecting the current or voltage across the pair of external connection terminals, the intelligent photovoltaic module controller may control a switching operation for switching between the series connection and the parallel connection. The control unit (130) may compare the magnitude of the current or voltage detected at the time of circuit switching with the magnitude of the current or voltage detected before circuit switching. The magnitude of the current or voltage detected prior to the circuit switching may be stored in the corresponding sensor for transmission to the control unit as required, or may be transmitted to and stored in the control unit. The control unit (130) may independently control a switching operation of the switching circuit for switching between the series connection and the parallel connection according to a predetermined condition, or may control the switching operation in response to a command from the power converter (200) when the intelligent photovoltaic module controller includes the communication unit (160). Since the total voltage of the array of photovoltaic modules needs to be higher than a predetermined minimum operating voltage of the power converter (200) in order to keep the power converter (200) running without interruption, each switching circuit connected to the parallel circuit can be controlled to be connected to the series circuit when the total voltage of the array falls below the predetermined minimum operating voltage due to the effects of sunrise, sunset, weather, etc.

A current sensor (140) detects a current flowing through the pair of external connection terminals. The current information detected when the switching circuit connects the parallel circuit between the two photovoltaic modules may be transmitted to the control unit to determine whether the switching circuit needs to perform switching to the series circuit or the parallel circuit, or the current information may be transmitted to the power converter via the communication unit. The power converter may control all intelligent photovoltaic module controllers connected thereto in common. The power converter and the intelligent photovoltaic module controller may communicate with each other through a wired or wireless network.

If one of the two photovoltaic modules connected to the photovoltaic module controller becomes problematic, this can significantly affect the magnitude of the current generated by the problematic photovoltaic module. Thus, when the two photovoltaic modules are connected to a parallel circuit, the magnitude of the current flowing through the pair of external connection terminals is measured to be compared with the magnitude of the current stored before the circuit switching. If the measured current magnitude is greater than the stored current magnitude, this indicates that there is a problem with the power generation state of the photovoltaic module. Even when some of the photovoltaic modules in the photovoltaic module array are connected to the parallel circuit, the maximum current flowing through other photovoltaic modules connected to the series circuit does not increase. Therefore, under normal conditions, even when one intelligent photovoltaic module controller performs switching from the series circuit to the parallel circuit, the total current flowing through the pair of external connection terminals does not increase. However, in the case where one of the two photovoltaic modules connected to the photovoltaic module controller becomes a bottleneck of current flow, switching the two photovoltaic modules to parallel connection may increase the total current flowing through the pair of external connection terminals. Thus, a decrease in the current produced by one photovoltaic module in an array of series-connected photovoltaic modules results in the magnitude of the total current of the array being limited to a small value, resulting in a loss of power produced due to the decrease in the total current even when the other photovoltaic modules are operating normally. Thus, when the magnitude of the current detected by the current sensor (140) after switching to the parallel circuit is greater than the magnitude of the current prior to circuit switching, the controllable switching circuit allows the two photovoltaic modules to remain connected in parallel, thereby preventing the total current of the array from being limited to a small value. Based on comparing the power loss caused by the reduction of the total voltage of the array caused by allowing the two photovoltaic modules to remain connected in parallel with the power loss caused by the case where the total current of the array is limited to a small value when the two photovoltaic modules are switched back to be connected in series and the current across the other photovoltaic modules that are operating normally is also limited accordingly, it can be determined whether to control the switching circuit to effect switching to the series circuit or to allow the two photovoltaic modules to remain connected in parallel.

Without comparing the current magnitudes before and after switching to the parallel connection, it is difficult to determine which photovoltaic module causes a current reduction when the photovoltaic modules in the array are connected to a series circuit. Therefore, the current value detected by the current sensor needs to be temporarily stored. The control unit (130) controls the switching circuit such that the two photovoltaic modules are periodically connected to the parallel circuit at predetermined time intervals, and the current sensor (140) detects a current flowing through the pair of external connection terminals of the intelligent photovoltaic module controller. Such circuit switching operations for checking the power generation status may be carried out independently by each intelligent photovoltaic module controller, or may be carried out sequentially by each photovoltaic module controller based on interactions with other photovoltaic module controllers or in response to commands from the power converter when the intelligent photovoltaic module includes a communication unit (160). Since typical commercially available photovoltaic modules are provided with a reverse current prevention circuit, a reverse current is not caused even if a voltage difference exists between the photovoltaic modules connected in parallel.

The intelligent photovoltaic module controller may also include a voltage sensor (150). When a first pair of input terminals and a second pair of input terminals of each photovoltaic module are connected to a series circuit, a voltage sensor (150) detects the magnitude of a voltage applied between the pair of external connection terminals. If the magnitude of the detected voltage is less than a predetermined value, this indicates that there is a problem with the power generation state of the photovoltaic module. When there is some difference in solar radiation between the photovoltaic modules, the magnitude of the generated voltage is low in sensitivity to the solar radiation compared to the magnitude of the generated current. If the magnitude of the detected voltage is very low, it is likely that the magnitude of the current is also reduced. Accordingly, the control unit (130) controls the switching circuit to connect the first and second pairs of input terminals to the parallel circuit, and the current sensor (140) detects the magnitude of the current flowing through the pair of external connection terminals. The control unit (130) controls the switching circuit to reconnect the first pair of input terminals and the second pair of input terminals to the series circuit if there is no significant difference in the magnitude of the current before and after switching to the parallel connection. When the output voltage of the array drops below the minimum voltage required for the power converter due to sunset or the like and the operation of the power converter is interrupted, the switching circuit of each intelligent photovoltaic module controller is stopped while being connected to the series circuit.

Based on monitoring the power generation state of the photovoltaic module by detecting the current or voltage across the pair of external connection terminals, the power converter controlling the intelligent photovoltaic module controller according to the present invention can control the switching operation for switching between the series connection and the parallel connection as needed. The control unit (220) may compare the magnitude of the current or voltage detected at the time of circuit switching with the magnitude of the current or voltage detected before circuit switching. The magnitude of the current or voltage detected before the circuit switching may be stored in the sensor unit (210) to be transmitted to the control unit (220) as needed, or may be transmitted to the control unit (220) and stored in the control unit (220). The control unit (220) may independently control a switching operation of the switching circuit for switching between the series connection and the parallel connection according to a predetermined condition, or may control the switching operation in response to a command from the power converter (200) when the intelligent photovoltaic module controller includes the communication unit (160). Since the total voltage of the array of photovoltaic modules needs to be higher than a predetermined minimum operating voltage of the power converter (200) in order to keep the power converter (200) running without interruption, each switching circuit connected to the parallel circuit can be controlled to be connected to the series circuit when the total voltage of the array falls below the predetermined minimum operating voltage due to the effects of sunrise, sunset, weather, etc.

A sensor unit (210) of the power converter (200) detects a current flowing through the pair of external connection terminals. The current information detected when the switching circuit connects a parallel circuit between the two photovoltaic modules may be transmitted to the control unit (220) to determine whether the switching circuit needs to perform switching to a series circuit or a parallel circuit, or the current information may be transmitted to the intelligent photovoltaic module controller via the communication unit (240). Although the communication unit (240) may be disposed in the power converter (including embedded in the power converter), it should be understood that the invention is not so limited and that the communication unit (240) may also be mounted in an intermediate location or a remote location of the photovoltaic module array separately. The communication unit (240) may communicate in common with all intelligent photovoltaic module controllers connected thereto. The power converter and the intelligent photovoltaic module controller may communicate with each other through a wired or wireless network.

If one of the two photovoltaic modules connected to the photovoltaic module controller becomes problematic, this can significantly affect the magnitude of the current generated by the problematic photovoltaic module. Thus, when the two photovoltaic modules are connected to a parallel circuit, the magnitude of the current flowing through the pair of external connection terminals is measured to be compared with the magnitude of the current stored before the circuit switching. If the measured current magnitude is greater than the stored current magnitude, this indicates that the power generation state of the photovoltaic module is problematic. Even when some of the photovoltaic modules in the photovoltaic module array are connected to the parallel circuit, the maximum current flowing through other photovoltaic modules connected to the series circuit does not increase. Therefore, under normal conditions, even when one intelligent photovoltaic module controller performs switching from the series circuit to the parallel circuit, the total current flowing through the pair of external connection terminals does not increase. However, in the case where one of the two photovoltaic modules connected to the photovoltaic module controller becomes a bottleneck of current flow, switching the two photovoltaic modules to parallel connection may increase the total current flowing through the pair of external connection terminals. Thus, a decrease in the current produced by one photovoltaic module in an array of series-connected photovoltaic modules results in the magnitude of the total current of the array being limited to a small value, resulting in a loss of power produced due to the decrease in the total current even when the other photovoltaic modules are operating normally. Thus, when the magnitude of the current detected by the sensor unit (210) after switching to the parallel circuit is greater than the magnitude of the current before circuit switching, the controllable switching circuit allows the two photovoltaic modules to remain connected in parallel, thereby preventing the total current of the array from being limited to a small value. Based on comparing the power loss caused by the reduction of the total voltage of the array caused by allowing the two photovoltaic modules to remain connected in parallel with the power loss caused by the case where the total current of the array is limited to a small value when the two photovoltaic modules are switched back to be connected in series and the current across the other photovoltaic modules that are operating normally is also limited accordingly, it can be determined whether to control the switching circuit to effect switching to the series circuit or to allow the two photovoltaic modules to remain connected in parallel.

Without comparing the current magnitudes before and after switching to the parallel connection, it is difficult to determine which photovoltaic module causes a current reduction when the photovoltaic modules in the array are connected to a series circuit. Therefore, the current value detected by the sensor unit (210) needs to be temporarily stored. The control unit (220) controls the switching circuit such that the two photovoltaic modules are periodically connected to the parallel circuit at predetermined time intervals, and the sensor unit (210) detects a current flowing through the pair of external connection terminals of each intelligent photovoltaic module controller. Such circuit switching operations for checking the power generation status may be carried out independently by each intelligent photovoltaic module controller, or may be carried out sequentially by each photovoltaic module controller based on interactions with other photovoltaic module controllers or in response to commands from the power converter (220) when the intelligent photovoltaic module includes a communication unit (160). Since typical commercially available photovoltaic modules are provided with a reverse current prevention circuit, a reverse current is not caused even if a voltage difference exists between the photovoltaic modules connected in parallel.

Furthermore, a sensor unit (210) of the power converter may detect the voltage. That is, when the first and second pairs of input terminals of each photovoltaic module are connected to the series circuit, the sensor unit (210) detects the magnitude of the voltage applied between the pair of external connection terminals. If the detected voltage magnitude is less than a predetermined value, this indicates that there is a problem with the power generation state of the photovoltaic module. When there is some difference in solar radiation between the photovoltaic modules, the magnitude of the generated voltage is low in sensitivity to the solar radiation compared to the magnitude of the generated current. If the magnitude of the detected voltage is very low, it is likely that the magnitude of the current is also reduced. Accordingly, the control unit (220) controls the switching circuit to connect the first and second pairs of input terminals to the parallel circuit, and the sensor unit (210) detects the magnitude of the current flowing through the pair of external connection terminals. The control unit (220) controls the switching circuit to reconnect the first pair of input terminals and the second pair of input terminals to the series circuit if there is no significant difference in the magnitude of the current before and after switching to the parallel connection. When the output voltage of the array drops below the minimum voltage required for the power converter due to sunset or the like and the operation of the power converter is interrupted, the switching circuit of each intelligent photovoltaic module controller is stopped while being connected to the series circuit.

The intelligent photovoltaic module controller (100) according to the present invention may include a communication unit (160) in communication with the power converter (200) and having a unique identification code (ID). The communication unit (160) transmits information about the magnitude of the voltage/current detected by the current sensor (140) or the voltage sensor (150), information about the state of the switching circuit, etc. to the power converter (200) controlling the total output power of the array, and may receive a series/parallel circuit control command.

As described above, a separate sensor unit (210) may be provided to the power converter (200) to detect the total current input to the photovoltaic module array of the power converter. In this case, the intelligent photovoltaic module controller may omit the current sensor (140) or the voltage sensor (150). Based on the change in current detected by the separate sensor unit (210), the power converter (200) may transmit a command to a communication unit of the photovoltaic module controller having a specific identification code (ID) to effectuate switching between the series circuit and the parallel circuit. Since the respective pairs of external connection terminals of the photovoltaic module controller are connected in series, the current flowing through each pair of external connection terminals is equal to the total current input to the array of power converters. Thus, the power converter (200) may transmit a command to the communication unit (160) of a particular photovoltaic module controller to connect two photovoltaic modules connected to the photovoltaic module controller to the parallel circuit, may detect a change in the total current of the array after performing a circuit switch, and may control whether to allow the two photovoltaic modules to remain connected to the parallel circuit based on the change. For example, if the total current increases after switching the switching circuit of a particular photovoltaic module controller to a parallel circuit, the power converter (200) allows the two photovoltaic modules connected to the photovoltaic module controller to remain connected in parallel based on determining that the two photovoltaic modules become bottlenecks for current flow. If the total current does not increase, the power converter (200) controls the photovoltaic module controller to switch the two photovoltaic modules back to a series connection. When the communication unit (160) of the photovoltaic module controller receives the circuit control command from the power converter (200), the control unit (130) may control the switching operation of the switching circuit in response to the control command from the power converter, instead of independently controlling the switching operation, even if the photovoltaic module controller includes the current sensor (140) and/or the voltage sensor (150).

The intelligent photovoltaic module controller according to the present invention may further include a power supply unit (170), the power supply unit (170) supplying power required for operation of internal components of the photovoltaic module controller using generated power supplied from the plurality of pairs of input terminals.

The external connection terminal according to the present invention may be connected to a reverse current prevention circuit that prevents reverse current from flowing from the outside, wherein the reverse current prevention circuit may include a fuse or a Positive Temperature Coefficient (PTC) thermistor to provide over-power protection due to a fault or accident.

According to one embodiment of the invention, the intelligent photovoltaic module controller may be configured such that the control unit (130) actively determines whether an abnormality is present in the photovoltaic module based on current and/or voltage information detected by the sensors (140, 150). More specifically, the control unit (130) of each intelligent photovoltaic module controller may allow two photovoltaic modules electrically connected to the intelligent photovoltaic module controller to be periodically connected in series at predetermined time intervals, and voltage/current information may be obtained by the sensors (140, 150) for comparison purposes. The magnitude of the current flowing through the pairs of external connection terminals when the two photovoltaic modules are connected to a series circuit is equal to the total current of the array. Thus, the magnitude of the current is stored as an initial current value. By comparing the initial current value with the magnitude of the current flowing through the pairs of external connection terminals when the two photovoltaic modules switch back to parallel connection, a change in current due to switching from series connection to parallel connection can be determined. The control unit (130) may independently control the operation of the switching circuit such that if the current value increases significantly after switching to the parallel connection, the two photovoltaic modules are kept connected in parallel, otherwise the two photovoltaic modules are switched back to the series connection. If the current flowing through the pair of external connection terminals does not increase after the switching circuit of a certain photovoltaic module controller switches two photovoltaic modules connected to the photovoltaic module to be connected in parallel, this indicates that the power generation state of the photovoltaic module connected to the photovoltaic module controller is not problematic. That is, by allowing each intelligent photovoltaic module controller to sequentially perform switching from a series circuit to a parallel circuit and checking the current value detected before and after switching, the power generation state of the photovoltaic module can be checked while minimizing the variation in the total output voltage of the array.

According to one embodiment of the invention, the power converter controlling the intelligent photovoltaic module controller may be configured such that the control unit (220) actively determines whether an abnormality is present in the photovoltaic module based on the current and/or voltage information detected by the sensor unit (210). More specifically, the control unit (220) may allow two photovoltaic modules electrically connected to each intelligent photovoltaic module controller to be periodically connected in series at predetermined time intervals, and voltage/current information may be obtained by the sensor unit (210) for comparison purposes. The magnitude of the current flowing through the pair of external connection terminals when the two photovoltaic modules are connected to a series circuit is equal to the total current of the array. Thus, the magnitude of the current is stored as an initial current value. By comparing the initial current value with the magnitude of the current flowing through the pair of external connection terminals when the two photovoltaic modules are switched back to the series connection, a change in current due to switching from the series connection to the parallel connection can be determined. The control unit (220) may independently control the operation of the switching circuit such that if the current value increases significantly after switching to the parallel connection, the two photovoltaic modules are kept connected in parallel, otherwise the two photovoltaic modules are switched back to the series connection. If the current flowing through the pair of external connection terminals does not increase after the switching circuit of a certain photovoltaic module controller switches two photovoltaic modules connected to the photovoltaic module to be connected in parallel, this indicates that the power generation state of the photovoltaic module connected to the photovoltaic module controller is not problematic. That is, by allowing each intelligent photovoltaic module controller to sequentially perform switching from a series circuit to a parallel circuit and checking the current value detected before and after switching, the power generation state of the photovoltaic module can be checked while minimizing the variation in the total output voltage of the array.

Thus, when a plurality of photovoltaic modules are provided, a plurality of intelligent photovoltaic module controllers may be provided, wherein each intelligent photovoltaic module controller switches the electrical connection of two photovoltaic modules connected thereto between a series connection and a parallel connection. Since each intelligent photovoltaic module controller has a unique identification code (ID), it is sufficient to easily identify which intelligent photovoltaic module controller is in an abnormal state and to check only whether there is a problem with two photovoltaic modules connected to the corresponding intelligent photovoltaic module controller among the plurality of intelligent photovoltaic module controllers.

According to the invention, a plurality of intelligent photovoltaic module controllers may be connected in series via a string (190) to deliver power generated by each photovoltaic module to a power converter, and the plurality of intelligent photovoltaic module controllers may each independently control series/parallel switching based on information detected by a current sensor (140) and/or a voltage sensor (150). Thus, the intelligent photovoltaic module controller can be applied to the photovoltaic module of the existing photovoltaic power generation system without a separate control device. The number of intelligent photovoltaic module controllers connected to the string (190) may vary depending on the total voltage demand. In addition, the number of photovoltaic modules connected to one intelligent photovoltaic module controller may be appropriately set depending on the installation environment or the capacity of the entire power generation system.

According to the invention, by performing real-time adaptive control on series/parallel switching of photovoltaic modules, a power converter controlling an intelligent photovoltaic module controller can prevent bottlenecks of current flow caused by faults of some photovoltaic modules, environments thereof and the like. Furthermore, when the generated total voltage falls below the minimum voltage required by the power converter, the power converter may be prevented from stopping operation by switching the photovoltaic modules from a parallel connection to a series connection. Although greatly affected by environmental changes such as sunrise, sunset, and cloud cover, the total voltage generated normally varies little. However, when the generated total voltage suddenly drops below the minimum voltage required by the power converter, the control unit (220) may control the switching circuit such that the two photovoltaic modules connected in parallel due to the variation are connected in series regardless of the variation of the current.

The power converter (200) according to the present invention can provide information so that an administrator can easily judge whether there is an abnormality in the photovoltaic module (110) belonging to each intelligent photovoltaic module controller (100) through remote monitoring. As such, when an abnormal condition is detected in any of the intelligent photovoltaic module controllers, a quick response including repairing the failed photovoltaic module may be made, thereby ensuring more efficient power generation and easier system management. The power converter (200) may notify an administrator at the remote location of the abnormal situation via the wireless network according to a predetermined condition, or may provide information in response to a query from the remote location. Further, the power converter (200) may transmit a control command to the intelligent photovoltaic module controller to check a power generation state and to effectuate switching between the series circuit and the parallel circuit based on the power generation state. The power converter (200) may include a sensor unit (210) that detects a total current flowing through the string (190). In this case, since the power converter (200) transmits a control command to the communication unit of the intelligent photovoltaic module based on detecting a change in total current caused by circuit switching performed by the intelligent photovoltaic module controller, the controller operating in response to the control command from the power converter (200) may omit the current sensor (140) and/or the voltage sensor (150).

Fig. 4 is a diagram illustrating one embodiment of a power converter controlling a smart photovoltaic module controller in accordance with the present invention. Referring to fig. 4, 10 intelligent photovoltaic module controllers and 20 photovoltaic modules (maximum voltage 40V, maximum current 10A) were installed on each string. When the photovoltaic modules are all connected in series, the total voltage across the string (190) is 800V, the current is 10A, and the total power is 8kW in steady state. When all of the photovoltaic modules are connected in parallel, the total voltage across the string (190) is 400V, the current is 20A, and the total power is 8kW (if only some of the photovoltaic modules are connected in parallel, the total current can be limited to 10A instead of 20A). If the current of one of the series-connected photovoltaic modules drops to 1A due to the external environment, the total current may be limited to 1A, resulting in a significant loss of the generated power. Here, when the intelligent photovoltaic module controller (100) connects an abnormal photovoltaic module to a normal photovoltaic module in parallel, the total current can be prevented from being limited to 1A. In conventional photovoltaic power generation facilities, such an active response cannot be made because the photovoltaic modules are always connected in series.

The number of intelligent photovoltaic module controllers (100) for series/parallel switching, the number of photovoltaic modules connected to each photovoltaic module controller, and the capacity of the power converter depending thereon may vary depending on the choice of the manufacturer or user, and thus are not particularly limited in the present invention.

Although a few embodiments have been described herein, those skilled in the art will appreciate that various other modifications and applications can be made without departing from the spirit and scope of the invention. Such modifications and applications are to be construed as falling within the scope of the invention, which is defined by the appended claims.

Claims

1. An intelligent photovoltaic module controller for switching electrical connections between photovoltaic modules, the photovoltaic modules each including a plurality of solar cells connected to one another, the intelligent photovoltaic module controller comprising:

a first pair of input terminals electrically connected to positive (+) and negative (-) terminals, respectively, of the first photovoltaic module;

a second pair of input terminals electrically connected to the positive (+) terminal and the negative (-) terminal, respectively, of the second photovoltaic module;

a pair of positive (+) and negative (-) external connection terminals electrically connected to the power converter or to another intelligent photovoltaic module controller in series;

a series circuit connected between the first pair of input terminals, the second pair of input terminals, and the pair of external connection terminals such that one terminal of the first pair of input terminals is electrically connected to one terminal of the second pair of input terminals having an opposite polarity to the one terminal of the first pair of input terminals, and the other terminal of the first pair of input terminals and the other terminal of the second pair of input terminals are electrically connected to the positive (+) external connection terminal and the negative (-) external connection terminal, respectively;

A parallel circuit connected between the first pair of input terminals, the second pair of input terminals, and the pair of external connection terminals such that positive (+) and negative (-) terminals of the first pair of input terminals are electrically connected to positive (+) and negative (-) terminals of the second pair of input terminals, respectively, which in turn are electrically connected to the positive (+) and negative (-) external connection terminals, respectively;

a switching circuit that performs a switching operation to connect a selected one of the series circuit and the parallel circuit between the first pair of input terminals, the second pair of input terminals, and the pair of external connection terminals; and

a control unit for controlling the switching circuit to switch between the series connection and the parallel connection,

wherein when the electrical connection between the first photovoltaic module and the second photovoltaic module is switched from the series circuit to the parallel circuit, it is determined whether to switch the electrical connection between the first photovoltaic module and the second photovoltaic module back to the series circuit based on a change in current flowing through the pair of external connection terminals or through a string connected to the pair of external connection terminals due to the switching to the parallel circuit.

2. The intelligent photovoltaic module controller of claim 1, further comprising:

and a current sensor detecting a magnitude of a current flowing through the pair of external connection terminals.

3. The intelligent photovoltaic module controller of claim 1, further comprising:

and a voltage sensor that detects a magnitude of a voltage applied between the pair of external connection terminals.

4. The intelligent photovoltaic module controller according to claim 2, wherein when the control unit controls the switching operation of the switching circuit such that the parallel circuit is connected between the first photovoltaic module and the second photovoltaic module, the control unit compares a current magnitude detected by the current sensor with a current magnitude detected before switching to the parallel circuit, and independently controls the switching operation of the switching circuit such that the first photovoltaic module and the second photovoltaic module are allowed to remain connected in parallel when the current magnitude measured after switching to the parallel circuit is increased by a predetermined value or more than the predetermined value compared to the current magnitude measured before switching to the parallel circuit, and when the current magnitude measured after switching to the parallel circuit is increased by less than the predetermined value compared to the current magnitude measured before switching to the parallel circuit, the first photovoltaic module and the second photovoltaic module are allowed to be connected back to the series circuit.

5. The intelligent photovoltaic module controller according to claim 2, wherein the control unit controls the switching operation of the switching circuit such that the first photovoltaic module and the second photovoltaic module are periodically connected to the parallel circuit at predetermined time intervals to check a power generation state.

6. The intelligent photovoltaic module controller of claim 1, further comprising:

a communication unit in communication with the power converter and having a unique identification code (ID),

wherein when the communication unit receives a circuit control command, the control unit controls a switching operation of the switching circuit in response to the circuit control command.

7. The intelligent photovoltaic module controller of claim 1, further comprising:

and a power supply unit connected to the first and second pairs of input terminals to supply power required for operation of internal components of the intelligent photovoltaic module controller.

8. The intelligent photovoltaic module controller of claim 1, further comprising:

and a reverse current prevention circuit connected to the pair of external connection terminals to prevent reverse current from flowing from the outside, the reverse current prevention circuit including a fuse or a positive temperature coefficient thermistor to provide over-power protection due to a fault or accident.

9. A control method of an intelligent photovoltaic module controller for switching electrical connections between photovoltaic modules each comprising a plurality of solar cells connected to each other, wherein the intelligent photovoltaic module controller comprises:

the method comprises the following steps:

detecting a change in current flowing through the pair of external connection terminals when the switching circuit switches an electrical connection between the first photovoltaic module and the second photovoltaic module from the series circuit to the parallel circuit; and

it is determined whether to connect the first and second photovoltaic modules back to the series circuit based on the detected change in the current.

10. The control method of an intelligent photovoltaic module controller according to claim 9, wherein the step of determining whether to connect the first photovoltaic module and the second photovoltaic module back to the series circuit comprises:

allowing the first and second photovoltaic modules to remain connected to the parallel circuit when a magnitude of the current measured after switching to the parallel circuit is increased by a predetermined value or by more than the predetermined value compared to a magnitude of the current measured before switching to the parallel circuit; and

the first and second photovoltaic modules are connected back to the series circuit when the magnitude of the current measured after switching to the parallel circuit increases by less than the predetermined value compared to the magnitude of the current measured before switching to the parallel circuit.

11. The control method of the intelligent photovoltaic module controller according to claim 9, wherein the step of detecting a change in current includes detecting a change in current flowing through a string of the pair of external connection terminals connected to the intelligent photovoltaic module controller.

12. The control method of an intelligent photovoltaic module controller according to claim 9, further comprising:

The switching operation of the switching circuit is controlled by a control unit of the power converter such that the first photovoltaic module and the second photovoltaic module are periodically connected to the parallel circuit at predetermined time intervals to check a power generation state.

13. The control method of the intelligent photovoltaic module controller according to claim 9, wherein:

the intelligent photovoltaic module controller further comprises: a communication unit communicating with the power converter and having a unique identification code (ID); and is also provided with

When the communication unit receives a circuit control command, the control unit controls a switching operation of the switching circuit in response to the circuit control command.

14. The control method of an intelligent photovoltaic module controller according to claim 13, further comprising:

communicate with at least two intelligent photovoltaic module controllers for remotely controlling the at least two intelligent photovoltaic module controllers, the at least two intelligent photovoltaic module controllers being mounted on the power converter and connected in series via strings connected to respective pairs of external connection terminals of the at least two intelligent photovoltaic module controllers,

wherein the step of determining whether to connect the first photovoltaic module and the second photovoltaic module back to the series circuit comprises: allowing the first and second photovoltaic modules to remain connected to the parallel circuit when a magnitude of the current measured after switching to the parallel circuit is increased by a predetermined value or by more than the predetermined value compared to a magnitude of the current measured before switching to the parallel circuit; and connecting the first and second photovoltaic modules back to the series circuit when the magnitude of the current measured after switching to the parallel circuit increases by less than the predetermined value as compared to the magnitude of the current measured before switching to the parallel circuit, and

When the first and second photovoltaic modules are allowed to remain connected to the parallel circuit, corresponding ones of the at least two intelligent photovoltaic module controllers are identified by the unique identification code (ID) to provide information about a power generation state.

15. The control method of a smart photovoltaic module controller according to claim 14, wherein the step of detecting a change in current flowing through the pair of external connection terminals comprises: a change in current flowing through the string connecting the at least two intelligent photovoltaic module controllers in series is detected by a sensor unit of the power converter to control each of the intelligent photovoltaic module controllers based on the change in current.

16. The control method of a smart photovoltaic module controller according to claim 14, wherein the power converter notifies an administrator at a remote location of an abnormal situation according to a predetermined condition or provides information in response to a query from the remote location.