Method for diagnosing energy transfer

Abstract

A method for performing a diagnostic test on a multilevel converter is provided. The method can comprise: selectively switching (S1) the at least one first module with the at least one second module into a series positive electrode or a series negative electrode; connecting (S2) at least one third module of the remaining modules to a series anode and / or a series cathode and / or to each other in parallel; and charging at least one first module from or discharging at least one or more of the remaining modules at a first predefined charging rate or a first predefined discharging rate (S3) until a first predefined criterion is reached. When a first predefined criterion is reached, the at least one first module N1 can be discharged relative to at least one or more of the remaining modules Nnd or charged relative to at least one or more of the remaining modules Nnd at a second predefined discharge rate or a second predefined charge rate, until a second predefined criterion is reached.

Description

Cross - reference to related applications

[0001] This application claims the priority of European Patent Application No. 23217308.8, filed on December 15, 2023, the entire disclosure of which is incorporated herein by reference. Technical field

[0002] The present invention relates to a method for diagnosing energy transfer between phases and / or modules of a multilevel converter. Background art

[0003] With the increasing integration of (renewable) energy sources and the need for grid stability, the demand for reliable and efficient energy storage solutions has grown significantly. In this context, the concept of battery - powered multilevel converters has emerged as a promising technology. Such systems combine the advantages of energy storage batteries with the flexibility and functionality of multilevel converters.

[0004] During normal operation, an AC battery operates by switching energy sources according to a dynamically defined schedule to generate an alternating voltage. Thus, the AC battery is sized such that it can continue to operate normally if one energy source or a module comprising multiple energy sources is cut off, i.e., bypassed. This allows the AC battery to continue operating in the event of a single energy source or module failure.

[0005] Furthermore, with regard to the AC battery, it is crucial to maintain a clear understanding of the health and / or performance of individual energy sources over time. To achieve this, a rigorous evaluation process is typically employed, involving a series of well - defined tests at fixed intervals throughout the device's life cycle. These evaluations are usually carried out once a year or at predefined time intervals, thus providing valuable insights into the condition and functionality of the device.

[0006] However, the challenge here is that these predefined test conditions rarely occur in the system's daily operating parameters. Therefore, during these evaluations, the entire AC battery must be taken offline temporarily, resulting in a significant loss of runtime.

[0007] In known prior art documents, during diagnostic testing, the energy released during diagnosis is often dissipated into the power grid. However, an advantage of the present application is that the energy in a system, such as a multilevel converter, can be kept without loss or with minimal energy loss. This means that the energy released from one module and / or phase is used to charge another module and / or phase. In addition, one or more of the modules and / or phases can return to the operating state within a short notice return time. Returning to the operating state does not require one or more of the modules and / or phases to be charged to a 100% charge state and can switch to the operating state at any available charge state.

[0008] This necessity emphasizes the delicate balance between ensuring the health of the AC battery and minimizing downtime, and is thus a crucial concern in the field of electrochemical technology. Summary of the Invention

[0009] Based on this, an object of the present invention is to provide an improved method for diagnosing energy exchange between modules of a multilevel converter.

[0010] The object of the present invention is achieved by a method for performing a diagnostic test on a multilevel converter.

[0011] Of course, the content of the present disclosure includes linguistically general rephrasing and / or similar substitutions of the corresponding terms within the scope of common linguistic practices, in particular the use of synonyms supported by generally recognized linguistic literature, without having to explicitly mention each change.

[0012] According to a first aspect, there is provided a method for performing a diagnostic test on a multilevel converter. The multilevel converter includes a plurality of modules, at least one of the plurality of modules having a preferably predefined charge state. Each of the plurality of modules includes a plurality of energy sources and a plurality of power converter modules. The method includes selectively switching at least one first module of the plurality of modules together with at least one second module of the plurality of modules to series positive or series negative; connecting at least one third module of the remaining modules of the plurality of modules in series positive and / or series negative and / or in parallel with each other; charging at least one first module from at least one or more of the remaining modules at a first predefined charging rate or discharging at least one first module to at least one or more of the remaining modules at a first predefined discharging rate until a first predefined criterion is reached, and, when the first predefined criterion is reached, discharging at least one first module relative to at least one or more of the remaining modules at a second predefined discharging rate or charging at least one first module from at least one or more of the remaining modules at a second predefined charging rate until a second predefined criterion is reached.

[0013] At least one of the plurality of modules has a predefined charge state. It should be understood that each module can have a different predefined charge state (varying from 0% SOC to 100% SOC). It should be understood that at least one of the plurality of modules can have a predefined voltage instead of a predefined charge state.

[0014] Here, "selectively switching at least one first module among the plurality of modules together with at least one second module among the plurality of modules to series positive or series negative" can also refer to preferably selectively switching at least one of the plurality of modules from a non-diagnostic state to a state different from the non-diagnostic state (such as a bypass state or a diagnostic state).

[0015] In one non-limiting example, at least one first module is switched to a diagnostic state. However, the "selective switching" of at least one first module does not necessarily mean that at least one first module has a different connection configuration from at least one second module among the plurality of modules. After switching at least one first module to a state different from the non-diagnostic (state), at least one first module can remain connected to at least one second module in series positive or series negative.

[0016] By preferably selectively switching at least one first module and at least one second module to series positive or series negative, at least one or more first modules can be in a state different from the non-diagnostic state. This means that several first modules can be in a diagnostic state, for example, which can accelerate the diagnostic test of the entire system of the multilevel converter.

[0017] At least one first module can be connected to one or several second modules in series positive or series negative to provide a potential difference between at least one first module and at least one second module. However, all the remaining modules, that is, the plurality of modules that are not at least the first module or at least the second module, such as at least one third module, can be connected in series positive and / or series negative and / or in parallel with at least another one of the remaining modules. It should be noted that if the number of the remaining modules is one, for example, there is only one third module, then this third module can be connected in parallel with at least one second module.

[0018] One mentionable advantage of the present disclosure is that the present disclosure provides the possibility of selectively switching a plurality of power converter modules and / or a plurality of energy sources relative to each other in varying ways. In addition, the method can perform at least one diagnostic test while other power converter modules and / or energy sources remain in operation. Therefore, the method eliminates the need to disconnect the entire system to perform at least one diagnostic test at the module or energy source level.

[0019] In the known prior art, the entire system is disconnected for a long period of time, such as several hours to several days, to perform at least one diagnostic test at the system level. During the diagnostic test, the entire system of the multilevel converter remains inoperative, making it impossible to store and / or deliver electrical energy to other devices. In the known prior art documents, the diagnostic cycle is a long period of time, and the diagnostic tests in the prior art are only performed when a multilevel converter defect occurs, or are only performed periodically at large time intervals between diagnostic tests (such as once a year or once every six months).

[0020] In the prior art documents, disconnecting the entire system of the multilevel converter for diagnostic tests causes inconvenience due to the rare opportunities for performing diagnostic tests on the multilevel converter, thereby increasing the risk of undetected multilevel converter defects.

[0021] In view of the prior art, the present disclosure can have the advantage that it makes it possible to keep the multilevel converter in normal operation while performing at least one diagnostic test on at least one of a plurality of power converter modules by switching at least one first module among the plurality of modules to be in series positive or series negative with at least one second module among the plurality of modules. The AC topology (topology, topological structure) of the multilevel converter enables this possibility, so that the plurality of power converter modules can be selectively switched relative to each other in different ways.

[0022] By preferably periodically performing diagnostic tests on the power converter module and / or the energy source, the method of the present invention helps to identify and correct potential problems early, thereby improving overall reliability and reducing the risk of unexpected failures. In addition, the method ensures that the multilevel converter operates optimally by monitoring and maintaining the health of its components. This in turn results in consistent and efficient performance. Although the diagnostic test requires a temporary switch of the module to one of a diagnostic state, a non-diagnostic state, or a bypass state, the ability to quickly detect and / or resolve problems can prevent greater, unplanned downtime in the future.

[0023] "Energy source" preferably refers to a single component or unit that stores and / or delivers electrical energy within the multilevel converter topology. These energy sources can include batteries, supercapacitors, photovoltaic cells, wind turbines, fuel cells, electric vehicles, chargers with at least one battery storage (device), flywheels (flywheel, inertial wheel), gravity-based storage, compressed air storage, or any other energy storage device capable of storing and delivering electricity.

[0024] "Power converter module" preferably refers to a module within a multilevel converter that facilitates the conversion and / or control of electrical power. It includes circuitry, such as switching elements (switching element, switching components), to manipulate the flow of electrical energy and regulate voltage and current levels.

[0025] "Switching element" is configured to selectively switch at least one first module among a plurality of modules with at least one second module among the plurality of modules into series positive or series negative. "Switching element" preferably refers to an electronic device used to control the flow of current within a power converter module, such as a transistor or thyristor. The switching element can be selectively opened or closed to initiate or interrupt a current path and facilitate the desired energy transfer or conversion.

[0026] Switching into series positive preferably means connecting at least one power converter module and / or energy source in series with at least one other in a positive configuration, potentially contributing to the generation of direct current (DC) or alternating current (AC) at the output of the multilevel converter.

[0027] Switching into series negative preferably means connecting the selected power converter module and / or energy source in series, but in a negative configuration, which can also be used for DC or AC generation.

[0028] Parallel switching preferably means connecting the selected module and / or energy source in parallel with at least one other power converter module and / or energy source, potentially affecting the output characteristics of the multilevel converter.

[0029] Bypass state preferably means switching the selected power converter module and / or energy source to deviate it from the normal operating path relative to at least one other power converter module and / or energy source. This can be used to isolate or protect the module / power supply or manage load distribution.

[0030] Off state preferably means partially or completely deactivating or shutting down the selected power converter module and / or energy source, thereby removing it from the multilevel converter to conserve energy or perform maintenance. Standby state preferably means transitioning the selected power converter module and / or energy source to a standby or low-power mode, preferably ready to be quickly activated when needed. Another diagnostic state preferably means that the non-diagnostic state can involve transitioning the selected power converter module and / or energy source to another form (potentially having different parameters and / or objectives from the initial diagnostic state) of diagnostic state or test.

[0031] By charging or discharging the module at a predefined charge or discharge rate and monitoring specific criteria, the method improves system performance by identifying any inefficiencies or anomalies that may exist in the system. Early detection of potential problems can also result in cost savings in terms of maintenance and repair. Additionally, it is possible to reduce the downtime of the system. In particular, using the proposed method, it is possible to avoid system shutdowns that may occur after a certain time (e.g., annually) for testing the system against warranty conditions. The method allows for the selective switching of power converter modules and energy sources, optimizing the use of available resources based on their conditions and performance. This can lead to better resource utilization and potentially extend the lifespan of these components.

[0032] It should be understood that the first predefined charge rate or the first predefined discharge rate is module-specific and can be different for each module in a diagnostic state. For example, the predefined charge rate of the first module is not necessarily equal to the predefined charge rate of the second module. Similarly, the first charge rate can be different from the discharge rate of the first or second module.

[0033] In other words, at least one first module under diagnosis can be charged or discharged with a predefined charge or discharge current that can be specifically set for performing diagnostic tests and is thus different from the charge or discharge current applied to the remaining modules in a normal or non-diagnostic state. The predefined charge or discharge current can be arbitrary and / or steady and / or variable and / or stepped and / or pulsating.

[0034] "Predefined charge or discharge rate" can refer to a specific and / or pre-set speed and / or rate at which at least one power converter module and / or at least one energy source is charged with electrical energy or releases the energy they store. The predefined charge or discharge rate can be pre-set and maintained consistent during the diagnostic test of the multilevel converter. It ensures that the charge or discharge process occurs at a known and controlled pace, enabling precise monitoring and evaluation. The predefined charge or discharge rate can include arbitrary and / or steady and / or variable and / or stepped and / or pulsating charge or discharge rates.

[0035] It is also possible to observe at least one power converter module and / or at least one energy source under diagnosis without being discharged or charged to collect data on at least one power converter module and / or at least one energy source during a rest period and / or before or after charging or discharging at least one power converter module and / or at least one energy source.

[0036] Note that data, particularly measurement data, can be collected from at least one of multiple power converter modules and / or at least one of multiple energy sources during diagnostics. Such collected measurement data can preferably be used to test at least one of multiple power converter modules and / or at least one of multiple energy sources, and / or can be stored. Optionally or additionally, the collected measurement data can be used to dynamically set the end conditions of diagnostic tests and / or for further manual and / or automated analysis. Over time, such analysis may also affect the operating conditions.

[0037] The measurement data can be, for example, at least one of voltage and / or current and / or temperature from at least one first module in a diagnostic state and their combinations. These measurement data can then be used to determine the health status and / or lifetime information or potential defects of the module.

[0038] In a non - limiting example, at least a first module among multiple modules is in a diagnostic state and is charging from an external energy source or discharging to an external load. In this case, the multilevel converter can be connected or connectable to the grid. In grid connecting (grid - connecting, grid - connected), the multilevel converter can operate in a so - called online mode. Only at least one of multiple power converter modules and / or at least one of multiple energy sources in a diagnostic state can discharge to an external load or be charged by an external energy storage or energy - providing source. At the same time, at least another in the first module can be connected to at least one of the remaining modules and / or at least one of multiple energy sources in series at least in positive and / or negative series forms and can discharge to the grid or be charged by the grid.

[0039] When at least one first module is in a diagnostic state, the remaining modules can be connected to at least one of multiple energy sources to generate direct current and / or alternating current at the output of the multilevel converter.

[0040] Specifically, this can be the case in the "offline mode", that is, when the multilevel converter is not connected to the grid. Thus, energy from at least another of multiple power converter modules and / or at least another of multiple energy sources (where at least another of multiple power converter modules and / or at least another of multiple energy sources can be connected to at least another of multiple power converter modules and / or at least another of multiple energy sources in series positive and / or series negative manners) can be charged from an external energy storage or discharged to an external energy storage, that is, a battery or BEV, where the external energy storage is electrically isolated from the grid. Additionally, an external load can be discharged.

[0041] In one embodiment, when at least one first module is charged from at least one or more of the remaining modules at a first predefined charging rate or discharged to at least one or more of the remaining modules at a first predefined discharging rate until a first predefined criterion is reached, the at least one first module is in a diagnostic state for performing at least one diagnostic test.

[0042] In a further embodiment, when a second predefined criterion is reached, at least one first module is switched from the diagnostic state to a non-diagnostic state, wherein the at least one first module is connected in parallel with at least one or more of the remaining modules.

[0043] After the second predefined criterion is reached, the at least one first module can change from the diagnostic state to a non-diagnostic state or a bypass state or enter an operating state, or can be shut down, for example, due to safety issues.

[0044] "Predefined criterion" can represent a predefined condition or threshold that can be met or exceeded during the diagnostic state of a multilevel converter. Such a condition can serve as a critical point for evaluation, indicating when the charging or discharging process has progressed far enough to end the diagnostic state. Once the predefined criterion is met, it can trigger the transition of at least one power converter module and / or at least one energy source from the diagnostic state to the non-diagnostic state. Additionally, the predefined criterion can be a period of time after the charging / discharging has been completed and at least one power converter module and / or at least one energy source has stopped in the bypass state, to allow the at least one power converter module and / or at least one energy source to rest for a predefined time, particularly to collect the rest data of the at least one power converter module and / or at least one energy source.

[0045] For example, in the case of switching at least one first module from the diagnostic state to the non-diagnostic state, when the second predefined criterion is reached, the second predefined criterion can be a predefined value of SOC. For example, when at least the first module is charged or discharged to the predefined value of SOC, then at least the first module is switched to a state other than the diagnostic state.

[0046] In a non-limiting example, the first predefined criterion and the second predefined criterion are a predefined temperature and / or a predefined state of charge (SOC), and / or a predefined voltage, and / or a predefined time, and / or a predefined system control signal, and / or a predefined current, and / or a predefined temperature, and / or a predefined energy state, and / or a time available to perform a diagnostic test, and / or a predefined capacity throughput, and / or a predefined energy throughput and / or a predefined differential capacity (dQ / dV), and / or a predefined voltage-to-capacity ratio (predefined voltage change with respect to capacity) dV / dQ, and / or a predefined voltage-to-time ratio (predefined voltage change with respect to time) dV / dt, and / or a predefined current-to-time ratio (predefined current change with respect to time) dI / dt, and / or a predefined temperature-to-time ratio (predefined temperature change with respect to time) dT / dt, or a combination thereof.

[0047] A "non-diagnostic state" may refer to an operating mode of a multilevel converter and / or at least one power converter module and / or at least one energy source when not actively performing a diagnostic test or evaluation. In such a non-diagnostic state, the multilevel converter and / or at least one power converter module and / or at least one energy source may operate in its normal operating mode, and it may not actively charge or discharge at a predefined rate and may not monitor against predefined criteria. Once the predefined criteria are met, a transition from a diagnostic state to a non-diagnostic state may occur, meaning that the test or evaluation phase has been completed and normal operation can resume without diagnostic constraints.

[0048] It should be understood that, particularly before the predefined criteria are met, if at least one of the plurality of power converter modules and / or at least one of the plurality of energy sources has been at least partially and / or at least temporarily discharged in a diagnostic state, then at least one of the plurality of power converter modules and / or at least one of the plurality of energy sources may be recharged or discharged.

[0049] "Diagnostic state" preferably refers to the state of at least one of a plurality of power converter modules and / or at least one of a plurality of energy sources, in which the corresponding (one or more) modules and / or (one or more) energy sources can be used to run at least one diagnostic test to provide measurement data. The measurement data can be used to provide information about the state of at least one of a plurality of power converter modules and / or at least one of a plurality of energy sources, such as the health state and / or lifetime information or potential defects of the modules. The output of such a diagnostic test can be a voltage-capacity curve for at least one of a plurality of power converter modules and / or at least one of a plurality of energy sources. The voltage data for at least one of a plurality of power converter modules and / or at least one of a plurality of energy sources can be post-processed to generate at least one dQ / dV curve. The peaks of such dQ / dV curves can be isolated and compared with previous and / or historical test data. In the case where the energy source includes at least one lithium, sodium ion or any other suitable battery cell, the offset can indicate the amount of loss of lithium inventory (LLI) and / or loss of active material (LAM).

[0050] In a further embodiment, the method further includes continuing to perform at least one diagnostic test on at least one second module when a second predefined criterion is reached, wherein the second predefined criterion is the time available for performing at least one diagnostic test.

[0051] It should be understood that the available time for performing at least one diagnostic test on at least one first module can be checked before starting at least one diagnostic test on a multilevel converter. "Available time" preferably refers to the time period during which at least one diagnostic module can be disconnected for diagnostic testing. During this time period, at least one of the remaining modules in the plurality of modules can be configured to generate energy for the output of the multilevel converter. The available time can range from a few seconds to several hours or days. When the first diagnostic module is in a diagnostic test, the available time is checked again to perform at least a second diagnostic test on a second module in the plurality of modules. If the available time permits the performance of the second diagnostic test, at least one second module is switched to the diagnostic state. Subsequent modules after the second module are switched to the diagnostic state considering the available time. It should be noted that the first module, the second module and other modules are not necessarily selected for diagnostic testing in a serial or consecutive order. The second module and other modules can be selected for diagnostic testing based on other criteria, which will be explained below.

[0052] In the diagnostic state of at least one of a plurality of power converter modules and / or at least one of a plurality of energy sources, the power converter modules and / or energy sources not in the diagnostic state can be configured to generate an alternating current (AC) output to the power grid. At least one of the plurality of power converter modules and / or at least one of the plurality of energy sources in the diagnostic state can alternatively be configured to discharge a direct current output to a DC-based energy storage, such as a DC battery, e.g., an EV. This may require a separate current path into and out of the power converter module, which can be achieved via a specific switching configuration of the switch element(s), which can connect the diagnosed module and / or energy storage to a DC energy storage (such as the power grid) rather than the AC output.

[0053] It should be noted that if at least one of the plurality of power converter modules and / or at least one of the plurality of energy sources returns to the non-diagnostic state, at least one of the plurality of power converter modules and / or at least one of the plurality of energy sources can be incorporated back into the normal switching schedule of the multilevel converter. If the state of charge (SoC) of at least one of the plurality of power converter modules and / or at least one of the plurality of energy sources permits, at least one of the plurality of power converter modules and / or at least one of the plurality of energy sources can resume providing alternating current.

[0054] Furthermore, in particular, if the multilevel converter may not be connected to the power grid and thus operates in an offline mode, another one of at least one of the plurality of power converter modules and / or another one of at least one of the plurality of energy sources can charge or discharge at least one of the plurality of power converter modules and / or at least one of the plurality of energy sources in the diagnostic state to rebalance the SOC. Furthermore, it should be noted that at least one of the plurality of power converter modules and / or at least one of the plurality of energy sources present in the diagnostic mode can be charged from an external power source (such as a solar panel, a fuel cell, a battery electric vehicle (BEV), and / or any other suitable DC source), especially in direct current (DC) mode. It should be understood that such DC charging can include the use of another DC / DC converter.

[0055] It may be preferred if a scheduler or controller of the multilevel converter controls and / or schedules and / or issues an instruction to discharge the electrical energy of at least one of the plurality of power converter modules and / or at least one of the plurality of energy sources to a plurality of other power converter modules and / or a plurality of other energy sources, e.g., to balance energy between different power converter modules and / or energy sources.

[0056] In a further embodiment, the method further includes selectively switching at least one second module of the plurality of modules from a non-diagnostic state to a diagnostic state, and connecting the at least one second module in series positive or series negative with at least one fourth module of the plurality of modules, wherein at least one or more of the remaining modules of the plurality of modules are connected in series positive and / or series negative and / or in parallel with each other.

[0057] In this embodiment, at least one second module is in a diagnostic state and is connected to at least one fourth module for generating a potential difference relative to the remaining non-diagnostic modules between the at least one second module and the at least one fourth module.

[0058] It should be noted that, in a non-limiting example, the fourth module may also be at least one first module previously used to perform the first diagnostic test, or may also be at least one third module connected in series positive and / or series negative and / or in parallel with other remaining modules during the first diagnostic test. It should be understood that this example applies to a system having at least four modules. However, in another non-limiting example where there are only three modules in the system, the fourth module is the first module previously used to perform the first diagnostic test.

[0059] In a further embodiment, the state of charge (SOC) of at least one first module increases during charging of the at least one first module, or the state of charge (SOC) of at least one first module decreases during discharging of the at least one first module, and the increase or decrease of the SOC of the at least one first module is equal to the difference between the maximum value of the SOC of the at least one first module and the initial value of the SOC, wherein the maximum value of the SOC is in the range from 0 to 100.

[0060] In a non-limiting example of this embodiment, the maximum value of the SOC is, for example, 100, and before performing the diagnostic test, the initial value of the SOC of at least one first module is 40. Therefore, the decrease in the SOC of at least one first module is equal to 60.

[0061] In a further embodiment, during charging or discharging of at least one first module, the state of charge (SOC) of at least one or more of the remaining modules decreases or increases, and the decrease or increase of the SOC of at least one or more of the remaining modules is equal to the increase or decrease of the SOC of at least one first module divided by the number of at least one or more of the remaining modules.

[0062] In a further embodiment, during charging or discharging of at least one first module, the capacity of at least one or more of the remaining modules is decreased or increased, where the decrease or increase in the capacity of at least one or more of the remaining modules is equal to the increase or decrease in the capacity of at least one first module divided by the number of at least one or more of the remaining modules.

[0063] In the current embodiment, the increase or decrease in the SOC of at least one first module is not necessarily divided by all the remaining modules, but only by the remaining modules in a non-diagnostic state. Some of the remaining modules can be in a bypass state or disconnected from the entire system.

[0064] In a further embodiment, during discharging or charging of at least one first module, the state of charge (SOC) of at least one first module is decreased or increased, where the decrease or increase in the SOC of at least one first module is equal to the SOC difference (delta SOC, ΔSOC) divided by the number of at least one or more of the remaining modules, where the SOC difference is the difference between the maximum value of the SOC and the minimum value of the SOC, and where the minimum value of the SOC is in the range from 0 to 100.

[0065] In a further embodiment, during discharging or charging of at least one first module, the corresponding state of charge (SOC) of at least one or more of the remaining modules is increased or decreased, where the increase or decrease in the corresponding SOC of at least one or more of the remaining modules is equal to the decrease or increase in the corresponding SOC of at least one first module multiplied by (number) 2, then divided by the difference between the number of at least one or more of the remaining modules and (number) 2 and divided by the difference between the number of at least one or more of the remaining modules and (number) 1.

[0066] In a further embodiment, during discharging or charging of at least one first module, the corresponding capacity of at least one or more of the remaining modules is increased or decreased, where the increase or decrease in the corresponding capacity of at least one or more of the remaining modules is equal to the decrease or increase in the corresponding capacity of at least one first module multiplied by the number 2, then divided by the difference between the number of at least one or more of the remaining modules and the number 2 and the difference between the number of at least one or more of the remaining modules and the number 1.

[0067] In a further embodiment, the method further comprises generating a first potential difference between at least one first module and at least one or more of the remaining modules by switching at least one first module to a series negative or series positive with respect to at least one or more of the remaining modules (wherein at least one or more of the remaining modules are switched to series negative or series positive with respect to each other), or further comprises generating a first potential difference between at least one first module and at least one or more of the remaining modules by preferably alternately switching at least one first module and at least one second module of a plurality of modules to series positive or series negative, wherein at least one or more of the remaining modules are switched to series negative or series positive or parallel.

[0068] In a further embodiment, the sum of the potential differences between at least one second module and at least one or more of the remaining modules is higher than the first potential difference.

[0069] In a non-limiting example of the present application, when at least one first module does not have a sufficient potential difference, if the sum of the potential differences between at least one second module and at least one or more of the remaining modules is higher than the first potential difference, then at least one first module can be connected to at least one of the remaining modules in a non-diagnostic state.

[0070] It should be understood that the remaining modules can be switched to series negative with at least one first module, or to series positive or parallel with respect to the remaining modules.

[0071] In a further embodiment, during charging or discharging of at least one first module, at least one or more of the remaining modules are connected in parallel with each other.

[0072] In a further embodiment, the method further comprises measuring at least the voltage and / or current and / or temperature of at least one first module by at least one measuring unit when at least one first module is being charged or discharged.

[0073] There may be more than one measurement sensor and / or measurement unit in a multilevel converter. Such measurement sensors and / or measurement units can be configured for current and / or temperature measurement. The multilevel converter can be equipped with multiple sensors for monitoring modules and / or energy sources and / or remaining energy sources during diagnosis.

[0074] In a further embodiment, the method further comprises determining the differential capacity dQ / dV of at least one first module by at least one measuring unit based at least on the measured voltage of at least one first module, or wherein the time pulse and / or C-Rate for charging or discharging at least one first module is different from another time pulse and / or another C-Rate for charging or discharging at least one second module.

[0075] "Time pulse" can be understood as a parameter for charging or discharging at least one of a plurality of power converter modules and / or at least one of a plurality of energy sources. The time pulse can be a measure for controlling the duration of charging and / or discharging.

[0076] "C-rate" can be understood as a parameter for charging or discharging at least one of a plurality of power converter modules and / or at least one of a plurality of energy sources. In battery technology, the C-rate is a measure of the charging and discharging rate relative to the battery capacity. It indicates how fast or slow the battery is charged or discharged.

[0077] In other words, the parameters (time pulse and / or C-rate) for charging or discharging at least one of a plurality of power converter modules and / or at least one of a plurality of energy sources in a diagnostic state are different from another time pulse and / or another C-rate for charging or discharging at least one of another plurality of power converter modules and / or at least one of another plurality of energy sources. This means that during the diagnostic state, different components within the multilevel converter may be affected by different time pulses and / or C-rates.

[0078] In a further embodiment, at least one first module is selected for performing at least one diagnostic test based on a third predefined criterion, wherein the third predefined criterion is at least one of the following: the position of at least one first module among a plurality of modules, a potential problem caused by a software controller, or a warning message from the software controller indicating the end of the warranty period of at least one first module.

[0079] In a further embodiment, wherein the multilevel converter includes at least two electrical phases, the first electrical phase includes at least one of a plurality of power converter modules and / or at least one of a plurality of energy sources, the second electrical phase includes at least one of another plurality of power converter modules and / or at least one of another plurality of energy sources, wherein the method further includes: charging the electrical energy stored in at least one of a plurality of power converter modules and / or at least one of a plurality of energy sources in the first phase from at least one of another plurality of power converter modules and / or at least one of another plurality of energy sources in the second phase or discharging the electrical energy stored in at least one of a plurality of power converter modules and / or at least one of a plurality of energy sources in the first phase to at least one of another plurality of power converter modules and / or at least one of another plurality of energy sources in the second phase.

[0080] The multilevel converter includes at least two "electrical phases". These two electrical phases can represent different parts and / or sections of the multilevel converter. The first phase can include certain "power converter modules" and / or "energy sources", while the second phase can include different "power converter modules" and / or "energy sources". These two phases can be connected to the corresponding phases of the power grid. The multilevel converter can include more than two phases. In particular, the multilevel converter can include three or more phases. These phases can be connected to a common star point and / or a delta connection. During the diagnostic state, there may be an action of "charging or discharging" the electrical energy stored in the "power converter modules" and / or "energy sources" of the first phase from or to at least one "power converter module" and / or at least one "energy source" of the second phase. Therefore, according to this embodiment, energy transfer may occur between the phases. The discharged energy can thus be guided and / or transferred to the "power converter modules" and / or "energy sources" of the second phase.

[0081] In a further embodiment, the method further includes controlling the effective current through a pulse width modulation controller on each of the plurality of modules such that the time pulse and / or C-rate for charging or discharging at least one first module remains constant or varies according to the needs of the diagnostic test (in particular by applying a series of pulses, etc.).

[0082] It should be understood that the pulse width modulation controller is a programmed multilevel controller adapted to control the effective current of a plurality of modules. As described above, in order to cause discharge from, for example, a plurality of remaining modules, a potential difference must be generated between the plurality of remaining modules and at least one first module. In a non-limiting example, the remaining modules or at least the first module can use a pulse width modulation controller to control the effective current. There is no resistive load between the plurality of modules, so the pulse width modulation controller allows avoiding current spikes and extremely high currents due to a low-resistance path. Current spikes and extremely high currents can damage the modules of the multilevel controller and other electronic components.

[0083] In a further embodiment, the first predefined criterion and the second predefined criterion are respective state of charge (SOC), where the first predefined criterion and the second predefined criterion are in the range of 0 to 100, preferably in the range of 10 SOC to 90 SOC.

[0084] There may be more than one predefined criterion or threshold. There may be predefined criteria with different weights. The predefined criteria can be used as criteria for initiating the diagnostic state. Therefore, at least one predefined criterion can be used as a trigger to switch the corresponding power converter module and / or energy source to the diagnostic state.

[0085] In a non - limiting example, different criteria have different weights or importance for initiating and ending a diagnostic state. In this non - limiting example, the more important weights in decreasing order are first the SOC limit, voltage limit, time limit, temperature limit, current limit, and finally the storage limit of the diagnostic module. However, other weights and "weight" orders can also be used.

[0086] In a non - limiting example, when a first predefined criterion is reached, a time interval is provided before discharging or charging at least one first module at a second predefined discharge rate or a second predefined charge rate, where the time interval is in the range of 1 second to 10 hours, preferably in the range of 10 seconds to 6 hours.

[0087] In a further embodiment, the method further includes re - balancing the SOCs of a plurality of modules, where at least one first module is connected in series to the negative electrode, and at least one or more of the remaining modules are connected in series to the positive electrode and / or in series to the negative electrode and / or in parallel with each other.

[0088] The re - balancing of the SOC or charge re - balancing refers to the process of equalizing or adjusting the charge levels of a plurality of power converter modules and / or a plurality of energy sources. After being diagnosed, this re - balancing and / or equalizing of the energy between the power converter modules and / or energy sources can be controlled by the controller or scheduler of a multilevel converter. The re - balancing and / or equalizing can be performed until the power converter modules and / or energy sources that have been diagnosed can have the same energy as their adjacent and / or neighboring power converter modules and / or energy sources.

[0089] In a further embodiment, the SOC of at least one first module after charging is the sum of the corresponding SOCs of the remaining modules, where, after charging, the SOC of at least one first module is less than or equal to 100%.

[0090] In a further embodiment, the minimum value of the SOC of at least one first module before charging is equal to or higher than the sum of the differences between the initial SOC of each remaining module and the SOC value of 100% before charging at least one first module.

[0091] In a further embodiment, the minimum value of the SOC of at least one first module before discharging is equal to or higher than the initial SOC of at least one first module, where the initial SOC is the SOC value before starting the diagnostic test.

[0092] In a further embodiment, the re - balancing of the SOCs of a plurality of modules includes charging or discharging at least one first module to a first final SOC, where the first final SOC is the difference between the maximum SOC and the minimum SOC divided by the number of the remaining modules.

[0093] In a further embodiment, the rebalancing of the SOC of the plurality of modules comprises charging or discharging at least one of the remaining modules to a second final value of the SOC, where the second final value of the SOC is equal to the first final value of the SOC multiplied by the sum of the number of at least one first module and the number 1, divided by the difference between the number of the remaining modules and the number 1.

[0094] All aspects and embodiments described above can be combined by those skilled in the art as needed.

[0095] In the present context, "a" should not necessarily be construed as strictly limited to only one element. On the contrary, a plurality of elements can also be provided, such as two, three or more. Any other numbers used herein should not be construed as meaning that the number of elements is strictly limited to the stated number. On the contrary, unless otherwise indicated to the contrary, fluctuations in quantity are possible.

[0096] Further possible embodiments of the present invention also include combinations of any features or embodiments not explicitly mentioned above or below with respect to the exemplary embodiments. In this case, those skilled in the art will also add the various aspects as improvements or supplementary content to the corresponding basic form of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0097] Figure 1 A flowchart showing a method for performing a diagnostic test on a multilevel converter according to an embodiment of the present invention;

[0098] Figure 2 Showing an improvement of a multilevel converter configured for grid connection; and

[0099] Figure 3 Showing another schematic improvement of a multilevel converter having a first topology. DETAILED DESCRIPTION

[0100] Unless otherwise indicated, in the drawings, identical or functionally identical elements are given the same reference numerals. It should also be noted that the illustrations in the drawings are not necessarily to scale.

[0101] Figure 1 A flowchart showing a method for diagnosing the energy transfer between phases and / or modules of a multilevel converter. A method for controlling a multilevel converter 200 including a plurality of modules N. The plurality of modules N each include a plurality of energy sources 2600 and a plurality of power converter modules 204. Each power converter module 204 includes at least two switching elements 2800 (see Figures 2 to 3 ). At least one of the plurality of modules N has a preferably predefined state of charge (SOC).

[0102] The method includes: in step S1, selectively switching at least one first module N1 among a plurality of modules N and at least one second module N2 among the plurality of modules N into series positive or series negative.

[0103] The method includes: in step S2, connecting at least one third module N3 among the remaining modules Nnd of the plurality of modules N into series positive and / or series negative and / or in parallel with another one of the remaining modules.

[0104] The method includes: in step S3, charging at least one first module N1 from at least one or more of the remaining modules Nnd at a first predefined charging rate or discharging at least one first module N1 to at least one or more of the remaining modules Nnd at a first predefined discharging rate until a first predefined criterion is reached.

[0105] The method includes: in step S4, when the first predefined criterion is reached, discharging at least one first module N1 to at least one or more of the remaining modules Nnd at a second predefined discharging rate or charging at least one first module N1 from at least one or more of the remaining modules Nnd at a second predefined charging rate until a second predefined criterion is reached.

[0106] Figure 2 An improvement of a multilevel converter 200 configured for grid connection is shown. For example, in Figure 2 , two multilevel converters 200 are shown, both including the same or similar topologies. In this example, the corresponding multilevel converter 200 includes three phases, each phase including five power converter modules 204 and corresponding energy sources 2600. The three phases of each multilevel converter 200 are respectively represented by numbers 1, 2, and 3. The corresponding multilevel converter 200 includes grid terminal connectors 206 (preferably, phase-independent) arranged on each of the phases 1, 2, and 3.

[0107] The corresponding grid terminal connectors 206 can be configured to connect the corresponding phases 1, 2, and 3 of the corresponding multilevel converter 200 to the corresponding grid phases a, b, and c of the grid 208. The grid terminal connectors 206 can be contactors or another type of switching element. The corresponding multilevel converter 200 can include interphase connectors 210 on the grid connection side of the corresponding multilevel converter 200. The interphase connectors 210 are preferably arranged between phase 1 and phase 2, and between phase 2 and phase 3. Of course, in other improvements, the interphase connectors 210 can also be arranged between phase 1 and phase 3.

[0108] The phase - to - phase connector 210 can be a contactor or another switching element. The phase - to - phase connector 210 can be configured to connect phase 1 to phase 2 and / or phase 2 to phase 3 to each other. In addition, the respective multilevel converter 200 can include a common star - point connector 212. The star - point connector 212 can be arranged on the side of the common star - point 214 of the respective multilevel converter 200. Preferably, the star - point connector 212 is arranged between phase 1 and phase 2, and between phase 2 and phase 3.

[0109] The star - point connector 212 can be configured to connect the three phases 1, 2, 3 to the common star - point 214. In this case, the phase - to - phase connector 210 preferably remains open (disconnected). By selectively closing the phase - to - phase connector 210 and / or the star - point connector 212, at least two of the three phases 1, 2, 3 can be connected at least temporarily in series (positive and / or negative) and / or in parallel with each other. The left - handed multilevel converter 200 is shown connected to the grid and thus has a closed grid connector 206.

[0110] In addition, the left - handed multilevel converter 200 is shown as having a closed star - point connector. The right - handed multilevel converter 200 is shown without a grid connection and thus has an open grid connector 206. In addition, the right - handed multilevel converter 200 is shown as having an open star - point connector. Both multilevel converters 200 are shown as having open phase - to - phase connectors.

[0111] In addition, according to Figure 2 , for each multilevel converter 200, a power - converter module 204 in a diagnostic state is shown and indicated by 204D. According to the invention, energy transfer between the diagnosed power - converter module 204D and an adjacent power - converter module 204 is possible and is indicated by the respective arrows.

[0112] Figure 3 A schematic improvement of the multilevel converter 200 with an exemplary topology is shown. It should be specifically noted that this is only one possible configuration. Many other topologies of the multilevel converter 200 can be used. In particular, Figure 3 A potential switching setting for the multilevel converter 200 is shown. The multilevel converter 200 exemplarily includes at least two power - converter modules 204, which can be similar to Figure 2Those power converter modules shown in . In addition, the multilevel converter 200 further includes at least two energy sources 2600, with at least one of the energy sources 2600 being included in each power converter module 204. Each of the at least two energy sources 2600 includes at least one battery cell and / or at least one capacitor and / or at least one photovoltaic panel. The power converter module 204 is configured to selectively switch at least one energy source 2600 of the corresponding module in series positive or series negative or in parallel with respect to another energy source 2600 at least temporarily to generate a controllable alternating current or direct current at the output of the multilevel converter 200. The power converter module 204 exemplarily includes four switching elements 2800. In other topologies, different numbers of switching elements 2800 can be used. Each module string 2802, 2804 of the exemplary multilevel converter 200 is arranged with two corresponding switching elements 2800 in a series connection. Between each of the two switching elements 2800 of each string 2802, 2804, corresponding other terminal connections 2806, 2808 are provided. The terminal connections 2806, 2808 can be used to modularly connect multiple power converter modules 204 and / or the corresponding modules and / or the corresponding multilevel converter 200 together.

[0113] In a first aspect of the present invention, only one first module N1 is in a diagnostic state. In this aspect of the present invention, at least a second module N2 is connected in series positive or series negative with the first module N1 to generate a sufficient potential difference to drive a current. In a second aspect of the present invention, at least two of the plurality of modules N are in a diagnostic state simultaneously. In this aspect of the present invention, at least two first modules N1 are in a diagnostic state capable of generating a sufficient potential difference. Then, the remaining modules Nnd among the N (modules) are connected in series positive and / or series negative and / or in parallel with each other. The remaining modules Nnd are the remaining modules among the plurality of modules N after the first module N1 and the second module N2 are connected.

[0114] In a first aspect of the present invention, if needed, the remaining modules Nnd can still be used to generate AC power for the power grid. The first module N1 is selected for performing at least one diagnostic test based on a third predefined criterion, where the third predefined criterion is at least one of the following: the position of at least one first module N1 among the plurality of modules N, a potential problem caused by a software controller, or a warning message from the software controller indicating the end of the warranty period of at least one first module N1. The first module N1 is selected as the diagnostic module, denoted by the superscript "diag" in the equation.

[0115] The predefined charge state (SOC) at which the diagnostic test is started on the first module N1 is A predefined state of charge (SOC) is selected based on a combination of the required tests and / or the available time. Each module in a diagnostic test can have a different predefined state of charge (SOC). The increase in SOC during charging of the first module N1 is calculated as follows:

[0116] where, is the initial value of the SOC of the first module N1 at time t = 0 before the start of the first diagnostic test, and is the starting value of the SOC. The maximum value of the SOC of the first module N1 that can be reached during charging of the first module N1 (e.g., the diagnostic module) is not higher than the sum of the SOCs of the remaining modules Nnd (e.g., non-diagnostic modules). The maximum value of the SOC is in the range of 0 to 100%. During discharge of the first module N1 under a diagnostic test, the minimum value of the SOC of the first module N1 is equal to or higher than the initial value of the SOC of the first module N1.

[0117] The first module N1 and the second module N2 are connected in series positive or series positive. The first module N1 can be connected to one or more second modules N2. For example, if the output energy, output voltage, or output power required to be output from the system (i.e., the multilevel converter) is generated by at least N - 1 modules, then during energy release from the system, only one second module can be connected in series positive or series negative. In this case, it is necessary to minimize the difference between the SOC values of the remaining modules.

[0118] In this case, when fewer than N - 1 modules are required to generate energy and / or voltage and / or power from the system, then more than one second module N2 and the first module N1 can be connected in series positive or series negative.

[0119] In the first step of the method, the first module N1 can be charged or discharged. In the case of discharging the first module N1, the minimum SOC is equal to or higher than the sum of the difference between 100% of the SOC value and the initial SOC of each remaining module Nnd before charging the first module N1.

[0120] At the end of the diagnostic test, the charge from the first module N1 is discharged to the remaining modules Nnd. The final value of the SOC at the end of the diagnostic test is equal to or higher than the critical value of the SOC. The critical value of the SOC is the minimum possible value of the SOC of the first module N1, after discharging the first module N1 to the remaining modules Nnd, to charge all the remaining modules to a value of 100% of the SOC. For this purpose, at the end of the diagnostic test, the final value of the SOC must be equal to or higher than the minimum possible value of the SOC of the first module N1 (the critical value of the SOC).

[0121] During charging or discharging of the first module N1, the N-N1 modules (also referred to as the remaining modules) are connected in series positive, series negative, or in parallel with each other to another one of the remaining modules Nnd. At least two of the remaining modules Nnd are connected in parallel with each other to generate a sufficient potential difference with respect to the diagnostic module.

[0122] In one non-limiting example, all the remaining modules are connected in parallel with respect to each other. This configuration with parallel connections results in a minimum SOC variation between the non-diagnostic modules (remaining modules Nnd). Assuming all modules have the same nominal capacity (in Ah), the SOC drop of each remaining module Nnd is defined as follows:

[0123] where, is the starting SOC of the diagnostic module, is the initial SOC of the diagnostic module at time t = 0. If the nominal capacities of the modules are not equal, the SOC level of each module is unique, and the equation is

[0124] Capacity can be converted to SOC via the following For each module, where the nominal capacity is the reference value. The pulse width modulation controller is configured to control the current of all the multiple modules N. It should be noted, of course, that each module can be controlled individually. The pulse width modulation controller controls the effective current such that the time pulse and / or C-rate for charging or discharging the first module N1 remains constant or varies according to the requirements of the diagnostic test, particularly by applying a series of pulses, etc.

[0125] The time pulse can be a measure of the duration for controlling charging and / or discharging. “C-Rate” can be understood as a parameter for charging or discharging at least one of the multiple power converter modules and / or at least one of the multiple energy sources.

[0126] Assuming all modules have equal nominal capacity, after charging of the first module N1, the value of the SOC indicated by each remaining module Nnd at t = 1 is determined by the following equation:

[0127] It should be noted that the SOC value of the remaining module Nnd can be unique for each j = 1..N - 1 module and does not have to be equal to the SOC value of the first module N1 where the superscript j represents the remaining module Nnd. If the modules have different nominal capacities, the equation is

[0128] After charging the first module N1 and collecting measurement data during the charging of the first module N1, the first module N1 starts diagnostic discharging. The remaining modules Nnd are reconfigured in series positive and / or series negative and / or in parallel with each other to minimize the imbalance between the remaining modules Nnd. In one example, the first module N1 and the second module N2 (i = 1) are connected in series negative or series positive. In a non-limiting example, the remaining modules Nnd (j = 1..N-1, j ≠ i) are connected in parallel with each other. The reduction in the SOC value in the first module N1 is equal to:

[0129] Assuming that modules N1 and N2 have the same nominal capacity, the reduction in the SOC value of the second module N2 connected in series negative or series positive with the first module Nnd (t = 1 in the following equation) is equal to:

[0130] If the nominal capacities of N1 and N2 are not equal, the equation is:

[0131] For modules with equal nominal capacities, the increase in the SOC of the remaining modules j = 1..N-1, j ≠ i is equal to:

[0132] For modules with unequal nominal capacities, the formula is

[0133] When a second predefined criterion is reached, at least one first module N1 switches from the diagnostic state to the non-diagnostic state. Then, at least one first module N1 is connected in parallel with at least one or more of the remaining modules (such as the second module N2). The method further continues to perform at least one diagnostic test on a second module N2.

[0134] The last module among the multiple modules N is in the diagnostic state. When the SOC value of the last module i = N-1 after discharging is equal to the stop value of the SOC the diagnostic test stops. This means that at the desired value of the SOC (stop value), the discharging will stop and the diagnostic test of the entire system will stop. After the diagnostic test stops, a time interval can be provided. The time interval is provided before discharging or charging at least one first module N1 at a second predefined discharging rate or a second predefined charging rate, where the time interval ranges from 1 second to 10 hours, preferably from 10 seconds to 6 hours.

[0135] The method further includes the step of rebalancing the SOCs of a plurality of modules N, wherein a first module N1 is connected in series to the negative pole, and at least one or more of the remaining modules Nnd are connected in series to the positive pole and / or in series to the negative pole and / or in parallel with each other.

[0136] In a non-limiting example, during the rebalancing of the SOC, the first module N1 is switched to be in series with the negative pole, and the remaining modules Nnd are connected in series with the negative pole or in series with the positive pole or in parallel with each other. The increase in the value of the SOC of the first module N1 is determined by the following formula:

[0137] If all the modules have equal nominal capacities and preferably are at the same SOC, the decrease in the value of the SOC of each of the remaining modules Nnd is determined by the following formula:

[0138] For modules with unequal nominal capacities, the equation is:

[0139] It should be noted that at the end of the diagnostic test, the SOC values of the remaining modules are not necessarily equal. After completing the diagnostic test on at least one first module N1, the system can be reconnected to the power grid or used for any other function, such as a further diagnostic test, connected to an energy generation source, or can remain inactive.

[0140] In a second aspect of the present invention, more than one first module N1 from a plurality of modules N can be in a diagnostic state simultaneously. Typically, in the second aspect of the present invention, a short return of the multilevel converter is not required to generate AC power to the power grid or receive AC power from the power grid. In this case, energy is only exchanged between the modules within one phase 1, 2, 3. However, the modules across phases 1, 2, 3 can be connected as diagnostic or non-diagnostic modules.

[0141] Diagnostic modules (i.e., first modules N1) can be selected to perform at least one diagnostic test based on a third predefined criterion. The third predefined criterion is at least one of the following: the position of at least one first module among the plurality of modules, potential problems proposed by the software controller, or a warning message from the software controller indicating the end of the warranty period of at least one first module. There are at least two diagnostic modules N1 denoted by superscript i in the equation. In a non-limiting example, each first module N1 in a diagnostic state can have its own diagnostic start SOC value.

[0142] At least two first modules N1 are performing diagnostic tests. It should be understood that the same equation applies to the charging or discharging of at least two first modules N1.

[0143] At least two first modules N1 are connected in series positive and / or series negative and / or in parallel with each other. The SOC added to at least two first modules N1 is determined by the following formula:

[0144] The remaining modules Nnd are connected in series positive and / or series negative and / or in parallel with each other such that the potential difference of the remaining modules Nnd is higher than the potential difference of at least two first modules N1. Assuming that the remaining modules have the same nominal capacity, the SOC loss from each remaining module is:

[0145] If the nominal capacities are not equal, the equation is:

[0146] It can be converted into the SOC level for each module as described above. Step 3 – Diagnostic discharge

[0147] At least two first modules N1 are connected in series positive and / or series negative and / or in parallel with each other such that the combined potential difference of the first modules N1 is greater than the combined potential difference of the remaining modules Nnd. In one example, a time interval can be provided between the preparatory charging step and the start of the diagnostic discharge. The discharge of the SOC lost from each of at least two first modules N1 during the diagnostic discharge is equal to:

[0148] If the remaining modules have equal nominal capacities, the capacity obtained by the remaining modules Nnd is represented by SOC and is calculated by the following formula:

[0149] If the remaining modules do not have equal nominal capacities, the equation (equal) is:

[0150] Similar to the first aspect of the present invention, one of the last steps of the method is to rebalance all modules N to the final value of SOC. The final value of SOC is not necessarily equal to the initial SOC value at t = 0. The SOC value added to at least two first modules N1 (whose position in the system is represented by i) is:

[0151] For modules with equal nominal capacities, the capacity loss Nnd from the remaining modules is equal to:

[0152] For modules with unequal nominal capacities, the equation is: List of reference signs 1 - First electrical phase 2 - Second electrical phase 3 - Third electrical phase 200 - Multilevel converter 204 - Multiple power converter modules 206 - Grid terminal connector 208 - Power grid 210 - Interphase connector 212 - Star point connector 214 - Common star point 402 - Measuring unit 2600 - Multiple energy sources 2800 - Switching element 2802 - Module string 2804 - Module string 2806 - Terminal connection 2808 - Terminal connection a - Grid phase b - Grid phase c - Grid phase N - Multiple modules N1 - First diagnostic module N2 - Second module N3 - Third module Nnd - Other non - diagnostic modules S1 - Step "Selectively switch" S2 - Step "Selectively switch" S3 - Step "Charge or discharge at least one first module" S4 - Step "Discharge or charge at least one first module when a first predefined criterion is reached"

Claims

1. A method for performing a diagnostic test on a multi-level converter, the multi-level converter comprising a plurality of modules, at least one of the plurality of modules having a preferably predefined state of charge SOC, wherein each of the plurality of modules comprises a plurality of energy sources and a plurality of power converter modules, the method comprising: Selectively switching at least one first module among the plurality of modules and at least one second module among the plurality of modules to be connected in series with positive electrodes or in series with negative electrodes; Connecting at least one third module of the remaining modules of the plurality of modules in series with positive electrodes and / or in series with negative electrodes and / or in parallel with each other; charging the at least one first module from at least one or more of the remaining modules at a first predefined charging rate or discharging the at least one first module to at least one or more of the remaining modules at a first predefined discharging rate until a first predefined criterion is met; and When the first predefined criterion is reached, the at least one first module is discharged to at least one or more of the remaining modules at a second predefined discharge rate or is charged from at least one or more of the remaining modules at a second predefined charge rate until the second predefined criterion is reached.

2. The method according to claim 1, wherein: The at least one first module is in a diagnostic state for performing at least one diagnostic test when the at least one first module is charged from at least one or more of the remaining modules at the first predefined charge rate or discharged to at least one or more of the remaining modules at the first predefined discharge rate until a first predefined criterion is reached, Wherein, when the second predefined criterion is reached, the at least one first module is switched from the diagnostic state to a non-diagnostic state, wherein the at least one first module is connected in parallel with at least one or more modules of the remaining modules. 3 . The method of claim 2 , further comprising continuing to perform the at least one diagnostic test on the at least one second module when the second predefined criterion is reached, wherein the second predefined criterion is a time available to perform the at least one diagnostic test.

4. The method according to claim 3 further comprises selectively switching at least one second module among the plurality of modules from a non-diagnostic state to a diagnostic state, and connecting the at least one second module with at least one fourth module among the plurality of modules in a series positive connection or a series negative connection, wherein at least one or more of the remaining modules among the plurality of modules are connected in a series positive connection and / or a series negative connection and / or in parallel with each other.

5. The method according to claim 1, further comprising: A first potential difference is generated between the at least one first module and at least one or more of the remaining modules by switching at least one or more of the remaining modules that are switched to series negative poles or series positive poles relative to each other to series positive poles or series negative poles, or a first potential difference is generated between the at least one first module and at least one or more of the remaining modules that are switched to series negative poles or series positive poles or parallel by switching the at least one first module to series positive poles or series negative poles relative to at least one second module of the plurality of modules, The sum of the potential differences between the at least one second module and at least one or more of the remaining modules is higher than the first potential difference.

6. The method according to claim 1, further comprising measuring at least a voltage and / or a current and / or a temperature of the at least one first module by at least one measuring unit when the at least one first module is charged or discharged, wherein: The method further comprises determining, by the at least one measuring unit, a differential capacity dQ / dV of the at least one first module based at least on a measured voltage of the at least one first module, or wherein a time pulse and / or a C-rate for charging or discharging the at least one first module is different from another time pulse and / or another C-rate for charging or discharging the at least one second module, and The active current is controlled by a pulse width modulation controller on each of the plurality of modules so that the time pulse and / or C-rate for charging or discharging the at least one first module remains constant or is varied by applying a series of pulses as required for diagnostic testing.

7. The method according to claim 1, wherein: The multi-level converter includes at least two electrical phases, the first electrical phase includes at least one of the multiple power converter modules and / or at least one of the multiple energy sources, and the second electrical phase includes at least another of the multiple power converter modules and / or at least another of the multiple energy sources, wherein the method further includes: charging the electrical energy stored in at least one of the multiple power converter modules and / or at least one of the multiple energy sources of the first phase from at least another of the multiple power converter modules and / or at least another of the multiple energy sources of the second phase, or discharging the electrical energy stored in at least one of the multiple power converter modules and / or at least one of the multiple energy sources of the first phase to at least another of the multiple power converter modules and / or at least another of the multiple energy sources of the second phase.

8. The method according to claim 1, wherein: The first predefined criterion and the second predefined criterion are respective states of charge SOC, wherein the first predefined criterion and the second predefined criterion are within a range from 0% to 100% SOC.

9. The method according to claim 1, further comprising rebalancing the SOCs of the plurality of modules, wherein the at least one first module is connected in series with negative electrodes, and at least one or more of the remaining modules are connected in series with positive electrodes and / or in series with negative electrodes and / or in parallel with each other, wherein the rebalancing of the SOCs of the plurality of modules comprises charging or discharging the at least one first module to a first final SOC, wherein the first final SOC is a difference between a maximum SOC and a minimum SOC divided by the number of the remaining modules.

10. The method according to claim 1, wherein: The minimum value of the SOC of the at least one first module before charging is equal to or higher than the sum of the differences between the 100% SOC value of the at least one first module before charging and the initial SOC of each of the remaining modules, and The minimum value of the SOC of the at least one first module before discharge is equal to or higher than an initial SOC of the at least one first module, wherein the initial SOC is an SOC value before starting a diagnostic test.

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