WO2024056155A1

WO2024056155A1 - Controller and method for controlling a power converter

Info

Publication number: WO2024056155A1
Application number: PCT/EP2022/075337
Authority: WO
Inventors: Emanuel VALLARELLA; Roland Huempfner; Zhaohui Wang
Original assignee: Huawei Technologies Duesseldorf Gmbh
Priority date: 2022-09-13
Filing date: 2022-09-13
Publication date: 2024-03-21

Abstract

The present disclosure relates to a controller (140) for controlling an operation of a power converter (120) to operate in an operation mode (151) for power conversion of a voltage (111) generated by a photovoltaic panel (110) or to operate in a diagnosis mode (152) for an inspection of the photovoltaic panel by setting the photovoltaic panel at a first operation point (201) for taking a first image of the photovoltaic panel or at a second operation point (202) for taking a second image of the photovoltaic panel, the controller comprising: an interface (150) configured to receive a mode selection signal (153), the mode selection signal indicating either the operation mode or the diagnosis mode of the power converter, wherein the controller is configured to set the power converter in the operation mode if the mode selection signal indicates the operation mode, or to set the power converter in the diagnosis mode, if the mode selection signal indicates the diagnosis mode.

Description

CONTROLLER AND METHOD FOR CONTROLLING A POWER CONVERTER

TECHNICAL FIELD

The present disclosure relates to the field of power converters for photovoltaic (PV) panels and inspection of PV panels by photoluminescence (PL) inspection techniques. In particular, the disclosure relates to a controller and corresponding method for controlling an operation of such power converter. More particular, the disclosure relates to a photoluminescence-enabled smart string inverter and a corresponding method.

BACKGROUND

Photovoltaic plants should have reliable and robust PV modules (also called PV panels) which are the components that transform sunlight into direct electrical current. Even though PV modules are steadily improved in terms of performance, materials, robustness and costs, there seems a need for investigation and inspection of already deployed PV modules in the field. In order to investigate the functioning of such PV modules, there exist many techniques that are able to determine the status of these components on physics-based approaches. One of these techniques is called Photoluminescence (PL) which is an inspection technique that applies sunlight as excitation source and inspects the normal operation principle of a PV module, namely that it creates charge carriers by irradiation with light.

Several research has been done on solutions to apply techniques for PL inspection. However, currently no fast, cost-effective, reliable and large-scale solutions are available. All the available solutions deploy either PSU units that are added to the circuits of the PV plant (thus costing time and effort) or deploy special electronics to each PV module (with their prohibitive costs) or deploy manual changes of operating points with manual pictures. These solutions seem less applicable for large-scale PV plants whose sizes might render these solutions not practical.

SUMMARY

This disclosure provides a solution for overcoming the manual, slow and inefficient inspection techniques for changing the operating point of a PV module (or PV string) for the PL inspection.

The foregoing and other objects are achieved by the features of the independent claims. Further implementation forms are apparent from the dependent claims, the description and the figures. This disclosure describes a novel technique for a fast, cost-effective, reliable and large-scale PL inspection.

The disclosure presents a solution how to fulfill the requirements to deploy the PL (Photoluminescence) inspection. The concept is based on controlling two predefined electrical operating points of the PV module (or PV string) with a configurable frequency via a dedicated communication channel (e.g., RS485). Accordingly, via the interface, the electrical points of the PV module (or PV string) are triggered, such that a specially designed camera can take according pictures of the PV modules.

For the mode selection only, the control can be performed from an external host system. During the sequence of the PL there is no further control necessary as the clocking between a “low current mode” (LC mode) and a “high current mode” (HC mode), which is done internally without direct communication with the image taking device. On the recorded picture(s) the mode in which it was taken is obviously recognizable. This simplifies the approach and supports a fast image taking. So, the communication is necessary to start/stop and define the operating condition (i.e., voltage/current references) of the test sequence. In general, the system can select in an autonomous way the references for HC mode, LC mode, as well as the test frequency, how long the system should stay on the HC and LC mode; all of the mentioned before can be pre-defined. For the control, only the start and stop is needed, while this can also be operated to PV array areas in an opposite behavior, which would lead to a constant power on the output side of the converter.

The disclosed method can be implemented in standard power converters and string inverters. It enables PL inspection and provides a user-friendly interface for the users/customers via newly developed dedicated registers, e.g., MODBUS registers, to freely operate the method and set the two predefined electrical operating points of interest.

According to the disclosure, an inverter-enabled cost-effective method is provided, that brings the PV string to two fixed electrical conditions.

The disclosed solution allows to temporarily switch-off the normal inverter MPPT (Maximum- power-point Tracking) operation for enabling switching between two voltage levels from two electrical points of the PV string:

- Open-circuit (OC) conditions

Mode "0”: Normal MPPT Inverter Mode;

- Maximum-power-point (MPP) condition or around this point Mode "1”: PL Mode. Accordingly, the MPPT operation is temporarily switched-off in the inverter and gives a string voltage reference to the MPPT controller following a pre-defined, independent timing.

That means, the disclosure presents an inverter with a Photoluminescence (PL) interface, powered by a novel method, to control two predefined electrical operating points of the PV string at an adjustable frequency, via a communication channel.

This disclosure presents a commercially available photoluminescence-ready inverter version for which no additional hardware is needed and a specially designed camera may be used for capturing pictures of the PV string.

The PL operation, that powers the PL interface, can be activated and deactivated on command based on the user’s needs. A newly dedicated set of registers, e.g., MODBUS registers, may be used to easily control the PL operation from a user’s/customer’s perspective.

The PL operation can be replicated and applied to existing utility-scale inverters as they share the same architecture of DC/DC (booster) and DC/AC (inverter) converters.

The test conditions for the sequences can be selected via communication but can also be predefined as a default. The on/off triggering of a diagnostic mode can also be automatically triggered when the recording device is supporting corresponding light emitting frequency range of the PV panel.

The disclosed controller and method is applicable to all Smart String Inverters, power converters and power inverters, in particular to all inverters that share the same architecture which is made up of a double-stage architecture consisting of a DC/DC converter and a DC/AC converter. However, the disclosed controller and method is not limited to such structure of a two stage PV string inverter as primarily described herein. It will also work with a single stage inverter, i.e., no DC/DC, while the inverter is designed for a wide DC input voltage range.

In order to describe the solution presented hereinafter in detail, the following terms, abbreviations and notations will be used:

PV photovoltaic

EL electroluminescence

PL photoluminescence

Si silicon OC open-circuit

SC short-circuit

MPP Maximum Power Point

MPPT Maximum Power Point Tracking

PSU external power supplies l-V current-voltage curve

DC direct current

AC alternating current

In this disclosure, electrical grids are described. Such an electrical grid is an interconnected network for delivering or distributing electricity from producers to consumers. It may comprise generating stations that produce electric power, electrical substations for stepping electrical voltage up for transmission or down for distribution, high voltage transmission lines that carry power from distant sources to demand centers and distribution lines that connect individual customers.

The diagnosis method as presented in this disclosure is not really dependent on the availability of the grid, it can also be used in an off-grid system.

Power converters as described in this disclosure are applied for converting electric energy from one form to another, such as converting between DC and DC, e.g. between high or medium voltage DC and low voltage DC. Power converters can also change the voltage or frequency or some combination of these. Power converters are based on power electronics switches that can be actively controlled by applying ON/OFF logic (i.e., PWM operation, usually commanded by a closed loop control operation).

Maximum Power Point Tracking (MPPT) is described in this disclosure. MPPT is a technology used commonly with photovoltaic (PV) solar systems to maximize power extraction under all conditions. PV solar systems exist in many different configurations with regard to their relationship to inverter systems, external grids, battery banks, or other electrical loads. Regardless of the ultimate destination of the solar power, the central problem addressed by MPPT is that the efficiency of power transfer from the solar cell depends on the amount of sunlight falling on the solar panels, the temperature of the solar panel and the electrical characteristics of the load. As these conditions vary, the load characteristic that gives the highest power transfer efficiency changes. The efficiency of the system is optimized when the load characteristic changes to keep the power transfer at highest efficiency. This load characteristic is called the maximum power point (MPP). MPPT is the process of finding this point and keeping the load characteristic there. Electrical circuits can be designed to present arbitrary loads to the photovoltaic cells and then convert the voltage, current, or frequency to suit other devices or systems, and MPPT solves the problem of choosing the best load to be presented to the cells in order to get the most usable power out.

A controller or controlling device as described in this disclosure is any device that can be utilized for regulation of voltage, currents or powers of a power converter. A controller or controlling device can be a single micro-controller or processor or a multi-core processor or can include a set of micro-controllers or processors or can include means for controlling and/or processing. The controller can perform specific control tasks, for example controlling a converter, according to a software, hardware or firmware application.

According to a first aspect, the disclosure relates to a controller for controlling an operation of a power converter to operate in an operation mode for power conversion of a voltage generated by a photovoltaic panel or to operate in a diagnosis mode for an inspection of the photovoltaic panel by setting the photovoltaic panel at a first operation point for taking a first image of the photovoltaic panel or at a second operation point for taking a second image of the photovoltaic panel, the controller comprising: an interface configured to receive a mode selection signal, the mode selection signal indicating either the operation mode or the diagnosis mode of the power converter, wherein the controller is configured to set the power converter in the operation mode if the mode selection signal indicates the operation mode, or to set the power converter in the diagnosis mode, if the mode selection signal indicates the diagnosis mode.

The interface can be an electrical interface, for example, or a signal interface, or any kind of interface for providing the mode selection signal to the controller.

Such a controller provides the technical advantage that there is no need to use external components, added costly electronics and manual solutions for the PL analysis. The PL function can just be enabled to any power converter or power inverter via a simple software update. The interface allows a comfortable and easy setting of the controller between operation mode and diagnosis mode. Inspecting the PV modules will be cheaper and technically less complex.

In an exemplary implementation of the controller, the first operating point corresponds to a high current state of the photovoltaic panel and the second operating point corresponds to a low current state of the photovoltaic panel. This provides the advantage that the controller enables efficient switching between these two characteristic operating points of the photovoltaic panel in order to allow an efficient inspection of the PV panel, e.g., by using a camera.

The high current state of the photovoltaic panel, also referred to as HC operating point corresponds to a high current and low voltage of the photovoltaic panel, e.g., according to a maximum power point (MPP).

The low current state of the photovoltaic panel, also referred to as LC operating point corresponds to a low current and high voltage of the photovoltaic panel, e.g., according to an open circuit (OC) point.

The first operation point enables the photovoltaic panel to generate the first image, e.g., a background image. The second operation point enables the photovoltaic panel to generate the second image, e.g., an image containing a luminescence signal. A difference between the first image and the second image indicates an electrical characteristic of the photovoltaic panel that is suitable for the inspection, in particular optical inspection of the photovoltaic panel.

In an exemplary implementation of the controller, the controller further comprises: a reference signal interface configured to provide a first reference signal for controlling the first operation point of the photovoltaic panel and a second reference signal for controlling the second operation point of the photovoltaic panel.

This provides the advantage that the reference signal interface can be used for delivering the first and second reference signals simply and quickly with a low hardware complexity.

In an exemplary implementation of the controller, the first reference signal comprises a first current reference signal indicative of a first current reference value and a first voltage reference signal indicative of a first voltage reference value; and the second reference signal comprises a second current reference signal indicative of a second current reference value and a second voltage reference signal indicative of a second voltage reference value.

This provides the advantage that four signals corresponding to four reference values can be easily provided by the reference interface. By using these four reference values, the controller can temporarily switch-off the normal inverter’s MPPT operation to enable the switching between two voltage levels from two electrical points of the PV string. In an exemplary implementation of the controller, the reference signal interface is configured to switch between providing the first reference signal and the second reference signal.

This provides the advantage that an efficient and controlled switching between the two operating points can be easily implemented.

In an exemplary implementation of the controller, the reference signal interface is configured to receive a reference control signal, the reference control signal indicating either the provision of the first reference signal or the provision of the second reference signal, wherein the reference signal interface is configured to provide the first reference signal if the reference control signal indicates the provision of the first reference signal, or to provide the second reference signal if the reference control signal indicates the provision of the second reference signal.

This provides the advantage that the reference signal interface can be easily controlled by the reference control signal which can be provided from outside the controller or by a suitable PL method controlling the switching between the two operating points.

In an exemplary implementation of the controller, the reference control signal comprises a clock signal having a first state and a second state, wherein the first state indicates the provision of the first reference signal and the second state indicates the provision of the second reference signal.

This provides the advantage that the clock signal can be flexible designed in order to define the switching period between the first and second operating points.

In an exemplary implementation of the controller, a frequency, by which the clock signal switches between the first state and the second state is configurable.

This provides the advantage that the switching period between the first and second operating points can be easily designed by a respective frequency of the clock signal.

In an exemplary implementation of the controller, the frequency configuration of the clock signal is based on a photoluminescence control scheme for controlling a switching between the first operation point and the second operation point of the photovoltaic panel. This provides the advantage that the PL control scheme can efficiently control the operating states of the PV panels via frequency configuration of the clock signal for enabling high-quality optical inspection of the PV panels.

In an exemplary implementation of the controller, the controller comprises: a communication channel configured to receive the reference control signal.

This provides the advantage that the reference control signal can be easily provided to the controller from an external device by a communication channel, for example an external device on which the PL method is implemented.

In an exemplary implementation of the controller, the communication channel is further configured to receive the mode selection signal.

This provides the advantage that both signals can be efficiently provided by the same communication channel which reduces hardware costs and complexity.

In an exemplary implementation of the controller, the communication channel comprises an RS485 serial communication interface.

This provides the advantage that such a serial communication interface is a standard interface which can be easily implemented and integrated with the controller software.

In an exemplary implementation of the controller, the controller is configured to provide, in the diagnosis mode of the power converter, a current reference value for a current control stage of the controller, based on the first reference signal and the second reference signal.

This provides the advantage that the current reference value for the power converter which is used to perform the current control can be easily derived in the diagnosis mode.

In an exemplary implementation of the controller, the controller is configured to provide, in the diagnosis mode of the power converter, the current reference value based on a difference of the first voltage reference signal and the voltage generated by the photovoltaic panel or based on a difference of the second voltage reference signal and the voltage generated by the photovoltaic panel. This provides the advantage that the current reference value can be easily derived for each of the operating points of the PV panel.

In a specific implementation each point HC and LC is referred to by a preset voltage and current reference. However, in a general implementation, one point can be enough. For example, this one point can even be automatically chosen by the system itself. Note that the implementation suggested above provides only one way to optimize the transition from HC to LC point without restricting the manner this transition can be performed. It understands that a variety of different transition methods can be applied as well.

In an exemplary implementation of the controller, the controller is configured to provide, in the diagnosis mode of the power converter, the current reference value based on a control transfer function with respect to the first voltage reference signal, the second voltage reference signal and the voltage generated by the photovoltaic panel.

This provides the advantage that the current reference values can be easily derived based on the control transfer function.

In an exemplary implementation of the controller, the controller is configured to perform, in the operation mode of the power converter, voltage control based on Maximum Power Point Tracking.

This provides the advantage that the controller can efficiently switch between the operation mode, i.e., normal operation in which optimal voltage control can be performed based on MPPT and the diagnosis mode in which efficient inspection of the PV panels can be performed.

According to a second aspect, the disclosure relates to a method for controlling an operation of a power converter to operate in an operation mode for power conversion of a voltage generated by a photovoltaic panel or to operate in a diagnosis mode for an inspection of the photovoltaic panel by setting the photovoltaic panel at a first operation point for taking a first image of the photovoltaic panel or at a second operation point for taking a second image of the photovoltaic panel, the method comprising: receiving, by an interface, a mode selection signal, the mode selection signal indicating either the operation mode or the diagnosis mode of the power converter; and setting the power converter in the operation mode if the mode selection signal indicates the operation mode; or setting the power converter in the diagnosis mode if the mode selection signal indicates the diagnosis mode. As described above for the controller, the same technical advantages also apply for this method, i.e., there is no need to use external components, added costly electronics and manual solutions for the PL analysis. The PL function can just be enabled to any power converter or power inverter via a simple software update. The interface allows a comfortable and easy setting of the controller between operation mode and diagnosis mode. Inspecting the PV modules will be cheaper and technically less complex.

According to a third aspect, the disclosure relates to a computer program product including computer executable code or computer executable instructions that, when executed, causes at least one computer to execute the method according to the second aspect described above.

The computer program product may run on a controller for controlling the above-described power converter, e.g., a controller as shown in Figure 1.

According to a fourth aspect, the disclosure relates to a computer-readable medium, storing instructions that, when executed by a computer, cause the computer to execute the method according to the second aspect described above. Such a computer readable medium may be a non-transient readable storage medium. The instructions stored on the computer-readable medium may be executed by the controller as described in Figure 1 .

The solution described in this disclosure presents an inverter-integrated PL function to set the PV module (or PV string) at two predefined electrical operating points. These points are the requirement for the PL analysis. By using that inverter-integrated PL function there is no need to use external components, to add costly electronics and manual solutions for the PL analysis. The disclosed method works for all kind of inverter structures. The PL function can just be enabled via a simple software update of the controller software. The solution is almost at zero cost (i.e., technical complexity) and inspection of the PV modules will be cheaper compared to existing solutions.

In this disclosure reference is made to inverter and inverter solutions, referring in technical terms to DC/AC converter for the power electronics supporting the operation point HC - LC toggling. In general, the solution described in this disclosure is not restricted to such inverter or inverter solution. Instead of inverter or inverter solution, it understands that also a power converter or power converter solution can be applied, e.g., a power converter that can feed directly into DC, such as PV systems with DC coupled battery storage systems. BRIEF DESCRIPTION OF THE DRAWINGS

Further embodiments of the disclosure will be described with respect to the following figures, in which:

Figure 1 shows a block diagram illustrating an exemplary system architecture for power conversion based on PV modules by using a power converter 120 and a controller 140 according to the disclosure for controlling the power converter 120;

Figure 2 shows a performance diagram of a PV module showing the two operating points of the PV panels; and

Figure 3 shows a schematic diagram illustrating a method 300 for controlling an operation of a power converter according to the disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

In the following detailed description, reference is made to the accompanying drawings, which form a part thereof, and in which is shown by way of illustration specific aspects in which the disclosure may be practiced. It is understood that other aspects may be utilized and structural or logical changes may be made without departing from the scope of the present disclosure. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present disclosure is defined by the appended claims.

It is understood that comments made in connection with a described method may also hold true for a corresponding device or system configured to perform the method and vice versa. For example, if a specific method step is described, a corresponding device may include a unit to perform the described method step, even if such unit is not explicitly described or illustrated in the figures. Further, it is understood that the features of the various exemplary aspects described herein may be combined with each other, unless specifically noted otherwise.

Figure 1 shows a block diagram illustrating an exemplary system architecture 100 for power conversion based on PV modules 110 by using a power converter 120 and a controller 140 according to the disclosure for controlling the power converter 120.

In Figure 1 , a PL method is shown with respect to the overall structure of a power conversion system 100 based on PV modules 110.

The power conversion system 100 comprises a plurality of PV modules or PV panels 110 which provide electrical energy from solar energy. The PV panels 110 generate an actual string voltage 111 in the form of a DC voltage which is converted by the power converter 120 into AC power for supplying an electrical grid 130, i.e., an electrical power network. The power converter 120 is controlled by a controller 140. The power converter 120 comprises a sequential stage of a DC/DC converter 121 receiving the string voltage 111 of the PV panels 110 and a DC/AC converter 123 converting DC energy into AC energy for the electrical grid 130. A DC link 122 is arranged between the DC/DC converter 121 and the DC/AC converter 123 and filters 124 are arranged between the DC/AC converter 123 and the electrical grid 130.

The controller 140 controls the power converter 120 by corresponding control signals, e.g., PWM signals. The controller 140 comprises a first functional block 140a and a second functional block 140b.

As mentioned above, the solution described in this disclosure relates to an inverter’s or power converter’s 140 interface to control two predefined electrical operating points of the PV string with configurable frequency via a communication channel (e.g. RS485). This interface is powered by a novel method that triggers electrical points of the PV strings 110. This novel method is depicted in Figure 1 , and it can be seen how it interacts with the power converter, e.g., smart string inverter.

In the top of Figure 1 , the architecture of the power converter 120, which is based upon receiving the direct power from the PV modules or panels 110 and transforming this into alternating power for the electrical grid 130, is depicted. The disclosed PL method shown in the second functional block 140b of the controller 140 is then compared to the standard MPPT operation shown in the first functional block 140a of the controller 140.

A detailed explanation of the latter is presented in the following:

The power converter 120 uses the "MPPT operation” 141 (“Normal Mode” 151) to control the DC/DC converter 121 which is one of the first building block of the overall inverter or power converter 120 as shown in the top of Figure 1. This operation in the normal mode 151 is implemented by the first functional block 140a of the controller 140.

A novel method is disclosed in order to perform the PL diagnosis. This method is implemented by the second functional block 140b of the controller 140 as shown in Figure 1 when the power converter is in the “diagnosis mode” or “PL diagnosis” 152. The main idea behind this disclosure is the usage of this PL method to temporarily stop the "Normal Mode” 151 of the MPPT operation and give voltage and current references to the controller 140 in the PL diagnosis 152 mode. Once the "PL diagnosis” 152 is chosen over the "Normal Mode” 151 , four possible current and voltage references can be given to the controller 140 to achieve the two electrical operating points, as illustrated in Figure 2:

LC operating point 202

low-current and high-voltage (e.g., open-circuit (OC) point)

HC operating point 201

high-current and low-voltage (e.g., maximum power point (MPP) point).

Thus, the "PL diagnosis” mode 152 can be set according to these references that control the electrical operating points 201 , 202 of the PV module I PV string 110. Such references follow also a predefined and independent timing ("clock generation”).

Thanks to this PL mode 152, the PV module (or PV string) 110 can be set to the two specific operating points 201 , 202 for the PL analysis. Once such analysis is complete, the power converter 120 goes back to the "Normal mode” 151.

In the following, the functionality of the controller 140 is described in detail.

The controller 140 is used for controlling an operation of the power converter 120 to operate in an operation mode 151 (also called normal mode) for power conversion of a voltage 111 generated by a photovoltaic panel 110 or to operate in a diagnosis mode 152 (also called PL diagnosis) for an inspection of the photovoltaic panel 110 by setting the photovoltaic panel 110 at a first operation point 201 for taking a first image of the photovoltaic panel 110 or at a second operation point 202 for taking a second image of the photovoltaic panel 110, e.g., as shown in Figure 2.

The controller (140) comprises an interface 150 (or signal interface) configured to receive a mode selection signal 153. The mode selection signal 153 indicates either the operation mode 151 (i.e., normal mode) or the diagnosis mode 152 (i.e. PL diagnosis) of the power converter 120. The controller 140 is configured to set the power converter 120 in the operation mode 151 if the mode selection signal 153 indicates the operation mode 151 , or to set the power converter 120 in the diagnosis mode 152, if the mode selection signal indicates the diagnosis mode 152.

The interface 150 can be an electrical interface, for example, or a signal interface, or any kind of interface for providing the mode selection signal 153 to the controller 140. The first operating point 201 may correspond to a high current state of the photovoltaic panel 110, e.g., as illustrated in Figure 2. The second operating point 202 may correspond to a low current state of the photovoltaic panel 110, e.g., as illustrated in Figure 2.

The high current state of the photovoltaic panel, also referred to as HC operating point corresponds to a high current and low voltage of the photovoltaic panel 110, e.g., according to a maximum power point MPP.

The low current state of the photovoltaic panel 110, also referred to as LC operating point corresponds to a low current and high voltage of the photovoltaic panel 110, e.g., according to an open circuit (OC) point.

The controller 140 further comprises a reference signal interface 156 configured to provide a first reference signal 154a, 154b for controlling the first operation point 201 of the photovoltaic panel 110 and a second reference signal 155a, 155b for controlling the second operation point 202 of the photovoltaic panel 110.

The first operation point 201 enables the photovoltaic panel 110 to generate the first image, e.g., a background image, e.g., as described below with respect to Figure 2. The second operation point 202 enables the photovoltaic panel 110 to generate the second image, e.g., an image containing a luminescence signal, e.g., as described below with respect to Figure 2. A difference between the first image and the second image indicates an electrical characteristic of the photovoltaic panel 110 that is suitable for the inspection, in particular optical inspection of the photovoltaic panel 110.

The first reference signal 154a, 154b may comprise a first current reference signal 154a indicative of a first current reference value and a first voltage reference signal 154b indicative of a first voltage reference value.

The second reference signal 155a, 155b may comprise a second current reference signal 155a indicative of a second current reference value and a second voltage reference signal 155b indicative of a second voltage reference value.

The reference signal interface 156 may be configured to switch between providing the first reference signal 154a, 154b and the second reference signal 155a, 155b. The above-described examples refer to a voltage and current reference for each point. In another example, the system can work either with a voltage or a current reference on each of the operating points HC and LC, which may also be chosen from automatically derived references. As already described above, each point HC and LC can be referred to by a preset voltage and current reference. Automatically derived references are easy to implement while direct references offer more flexibility.

Note that the implementation suggested above provides only one way to optimize the transition from HC to LC point without restricting the manner this transition can be performed. It understands that a variety of different transition methods can be applied as well.

The reference signal interface 156 may be configured to receive a reference control signal 159 which indicates either the provision of the first reference signal 154a, 154b or the provision of the second reference signal 155a, 155b.

The reference signal interface 156 may be configured to provide the first reference signal 154a, 154b if the reference control signal 159 indicates the provision of the first reference signal 154a, 154b, or to provide the second reference signal 155a, 155b if the reference control signal 159 indicates the provision of the second reference signal 155a, 155b.

The reference control signal 159 may comprise, for example, a clock signal having a first state and a second state, wherein the first state indicates the provision of the first reference signal 154a, 154b and the second state indicates the provision of the second reference signal 155a, 155b.

As already described above, the system can work either with a voltage or a current reference on each of the operating points HC and LC, which may also be chosen from automatically derived references. Each point HC and LC can be referred to by a preset voltage and current reference. This does not exclude an operation of the system where only one reference per point can be used or the references can be selected in an automatic way.

A frequency by which the clock signal switches between the first state and the second state may be configurable.

The frequency configuration of the clock signal may be based on a photoluminescence control scheme for controlling a switching between the first operation point 201 and the second operation point 202 of the photovoltaic panel 110. By that photoluminescence control scheme, a PL method can control the switching between the first reference signal and the second reference signal.

The controller 140 may comprise a communication channel configured to receive the reference control signal 159.

The communication channel may be further configured to also receive the mode selection signal 153 for switching between the operation mode 151 and the diagnosis mode 152.

In an exemplary implementation, the communication channel may comprise or may be implemented as an RS485 serial communication interface.

The controller 140 may be configured to provide, in the diagnosis mode 152 of the power converter 120, a current reference value 143 for a current control stage 145 of the controller 140, based on the first reference signal 154a, 154b and the second reference signal 155a, 155b as shown in the second functional block 140b of the controller 140.

The controller 140 may be configured to provide, in the diagnosis mode 152 of the power converter 120, the current reference value 143 based on a difference of the first voltage reference signal 154b and the voltage 111 generated by the photovoltaic panel 110 or based on a difference of the second voltage reference signal 155b and the voltage 111 generated by the photovoltaic panel 110.

The controller 140 may be configured to provide, in the diagnosis mode 152 of the power converter 120, the current reference value 143 based on a control transfer function 157 with respect to the first voltage reference signal 154b, the second voltage reference signal 155b and the voltage 111 generated by the photovoltaic panel 110.

The controller 140 may be configured to perform, in the operation mode 151 of the power converter 120, voltage control 142 based on Maximum Power Point Tracking 141.

Figure 2 shows a performance diagram 200 of a PV module showing the two operating points 201 , 202 of the PV panels 110.

As mentioned above, the PL techniques exploits the luminescence signal created by recombination of carriers in the silicon (Si). In Si, an indirect semiconductor, the share of radiative band-to-band recombination is low compared to other recombination processes. Nevertheless, if triggered, enough light is emitted to create an image about the conductive properties of solar cells made of Si. The latter gives knowledge about the performance and reliability of the solar cells (which make up a PV module).

Thus, the PL methodology works by setting the PV module or PV panels 110 as shown in Figure 1 at two different operating points 201 , 202 as can be seen in Figure 2, thus having two different images that can be taken each at their specific operating points. In fact, when a PV module, such as the PV panels 110 shown in Figure 1 , is in open-circuit (OC) conditions (this operating point 202 is also called low-current (LC) state) and irradiated, it creates carriers which cannot participate in any current. Therefore, when they recombine, the result is a luminescence signal.

In short-circuit or maximum-power-point (SC or MPP) conditions (this operating point 201 is also called high-current (HC) state) instead, no recombination occurs, and a background image is generated instead of the luminescence signal. This background image can then be subtracted from the image containing the luminescence signal.

By correspondingly changing the operating points 201 , 202 of the PV panels (or PV string) 110 to point "HC” (high-current) 201 and point "LC” (low-current) 202 and vice versa (as seen in Figure 2), the different pictures can be taken, e.g., by using a specifically designed camera.

Figure 3 shows a schematic diagram illustrating a method 300 for controlling an operation of a power converter according to the disclosure, e.g., the power converter 120 shown in Figure 1.

The method 300 can be used for controlling an operation of a power converter 120 to operate in an operation mode 151 for power conversion of a voltage 111 generated by a photovoltaic panel 110 or to operate in a diagnosis mode 152 for an inspection of the photovoltaic panel 110 by setting the photovoltaic panel 110 at a first operation point 201 (see Figure 2) for taking a first image of the photovoltaic panel 110 or at a second operation point 202 for taking a second image of the photovoltaic panel 110, e.g., as described above with respect to Figure 1.

The method 300 comprises: receiving 301 , by an interface 150, a mode selection signal 153, the mode selection signal 153 indicating either the operation mode 151 or the diagnosis mode 152 of the power converter 120, e.g., as described above with respect to Figure 1. The method 300 comprises: setting 302 the power converter 120 in the operation mode 151 if the mode selection signal 153 indicates the operation mode 151 ; or setting the power converter 120 in the diagnosis mode 152 if the mode selection signal 153 indicates the diagnosis mode 152, e.g., as described above with respect to Figure 1.

The method 300 can be performed by a computer program product including computer executable code or computer executable instructions that, when executed, causes at least one computer to execute the method 300.

The computer program product may run on a controller for controlling the above-described power converter 120, e.g., a controller 140 as shown in Figure 1.

While a particular feature or aspect of the disclosure may have been disclosed with respect to only one of several implementations, such feature or aspect may be combined with one or more other features or aspects of the other implementations as may be desired and advantageous for any given or particular application. Furthermore, to the extent that the terms "include", "have", "with", or other variants thereof are used in either the detailed description or the claims, such terms are intended to be inclusive in a manner similar to the term "comprise". Also, the terms "exemplary", "for example" and "e.g." are merely meant as an example, rather than the best or optimal. The terms “coupled” and “connected”, along with derivatives may have been used. It should be understood that these terms may have been used to indicate that two elements cooperate or interact with each other regardless whether they are in direct physical or electrical contact, or they are not in direct contact with each other.

Although specific aspects have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific aspects shown and described without departing from the scope of the present disclosure. This application is intended to cover any adaptations or variations of the specific aspects discussed herein.

Although the elements in the following claims are recited in a particular sequence with corresponding labeling, unless the claim recitations otherwise imply a particular sequence for implementing some or all of those elements, those elements are not necessarily intended to be limited to being implemented in that particular sequence.

Many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the above teachings. Of course, those skilled in the art readily recognize that there are numerous applications of the disclosure beyond those described herein. While the present disclosure has been described with reference to one or more particular embodiments, those skilled in the art recognize that many changes may be made thereto without departing from the scope of the present disclosure. It is therefore to be understood that within the scope of the appended claims and their equivalents, the disclosure may be practiced otherwise than as specifically described herein.

The project leading to this application has received funding from the European Union’s Horizon

2020 research and innovation programme EU H2020 TRUST-PV [September 2020 - August 2024] under grant agreement No. 952957.

Claims

CLAIMS:

1. A controller (140) for controlling an operation of a power converter (120) to operate in an operation mode (151) for power conversion of a voltage (111) generated by a photovoltaic panel (110) or to operate in a diagnosis mode (152) for an inspection of the photovoltaic panel (110) by setting the photovoltaic panel (110) at a first operation point (201) for taking a first image of the photovoltaic panel (110) or at a second operation point (202) for taking a second image of the photovoltaic panel (110), the controller (140) comprising: an interface (150) configured to receive a mode selection signal (153), the mode selection signal (153) indicating either the operation mode (151) or the diagnosis mode (152) of the power converter (120), wherein the controller (140) is configured to set the power converter (120) in the operation mode (151) if the mode selection signal (153) indicates the operation mode (151), or to set the power converter (120) in the diagnosis mode (152), if the mode selection signal indicates the diagnosis mode (152).

2. The controller (140) of claim 1, wherein the first operating point (201) corresponds to a high current state of the photovoltaic panel (110) and the second operating point (202) corresponds to a low current state of the photovoltaic panel (110).

3. The controller (140) of claim 1 or 2, further comprising: a reference signal interface (156) configured to provide a first reference signal (154a, 154b) for controlling the first operation point (201 ) of the photovoltaic panel (110) and a second reference signal (155a, 155b) for controlling the second operation point (202) of the photovoltaic panel (110).

4. The controller (140) of claim 3, wherein the first reference signal (154a, 154b) comprises a first current reference signal (154a) indicative of a first current reference value and a first voltage reference signal (154b) indicative of a first voltage reference value; and wherein the second reference signal (155a, 155b) comprises a second current reference signal (155a) indicative of a second current reference value and a second voltage reference signal (155b) indicative of a second voltage reference value.

5. The controller (140) of claim 4, wherein the reference signal interface (156) is configured to switch between providing the first reference signal (154a, 154b) and the second reference signal (155a, 155b).

6. The controller (140) of claim 5, wherein the reference signal interface (156) is configured to receive a reference control signal (159), the reference control signal (159) indicating either the provision of the first reference signal (154a, 154b) or the provision of the second reference signal (155a, 155b), wherein the reference signal interface (156) is configured to provide the first reference signal (154a, 154b) if the reference control signal (159) indicates the provision of the first reference signal (154a, 154b), or to provide the second reference signal (155a, 155b) if the reference control signal (159) indicates the provision of the second reference signal (155a, 155b).

7. The controller (140) of claim 6, wherein the reference control signal (159) comprises a clock signal having a first state and a second state, wherein the first state indicates the provision of the first reference signal (154a, 154b) and the second state indicates the provision of the second reference signal (155a, 155b).

8. The controller (140) of claim 7, wherein a frequency by which the clock signal switches between the first state and the second state is configurable.

9. The controller (140) of claim 8, wherein the frequency configuration of the clock signal is based on a photoluminescence control scheme for controlling a switching between the first operation point (201) and the second operation point (202) of the photovoltaic panel (110).

10. The controller (140) of any of claims 6 to 9, comprising: a communication channel configured to receive the reference control signal (159).

11. The controller (140) of claim 10, wherein the communication channel is further configured to receive the mode selection signal (153).

12. The controller (140) of claim 10 or 11 , wherein the communication channel comprises an RS485 serial communication interface.

13. The controller (140) of any of claims 4 to 12, configured to provide, in the diagnosis mode (152) of the power converter (120), a current reference value (143) for a current control stage (145) of the controller (140), based on the first reference signal (154a, 154b) and the second reference signal (155a, 155b).

14. The controller (140) of claim 13, configured to provide, in the diagnosis mode (152) of the power converter (120), the current reference value (143) based on a difference of the first voltage reference signal (154b) and the voltage (111) generated by the photovoltaic panel (110) or based on a difference of the second voltage reference signal (155b) and the voltage (111) generated by the photovoltaic panel (110).

15. The controller (140) of claim 13 or 14, configured to provide, in the diagnosis mode (152) of the power converter (120), the current reference value (143) based on a control transfer function (157) with respect to the first voltage reference signal (154b), the second voltage reference signal (155b) and the voltage (111) generated by the photovoltaic panel (110).

16. The controller (140) of any of the preceding claims, configured to perform, in the operation mode (151) of the power converter (120), voltage control (142) based on Maximum Power Point Tracking (141).

17. A method (300) for controlling an operation of a power converter (120) to operate in an operation mode (151) for power conversion of a voltage (111) generated by a photovoltaic panel (110) or to operate in a diagnosis mode (152) for an inspection of the photovoltaic panel (110) by setting the photovoltaic panel (110) at a first operation point (201) for taking a first image of the photovoltaic panel (110) or at a second operation point (202) for taking a second image of the photovoltaic panel (110), the method (300) comprising: receiving, by an interface (150), a mode selection signal (153), the mode selection signal (153) indicating either the operation mode (151) or the diagnosis mode (152) of the power converter (120); and setting the power converter (120) in the operation mode (151) if the mode selection signal (153) indicates the operation mode (151); or setting the power converter (120) in the diagnosis mode (152) if the mode selection signal (153) indicates the diagnosis mode (152).