A reliability improvement topology and method for a flexible dc converter

Abstract

The embodiment of the application provides a reliability improvement topology structure and method of a flexible direct current converter, and belongs to the technical field of power electronic conversion. The topology structure comprises: a basic unit array composed of N H-bridge units connected in series in three phases A, B and C, and a short-circuit switch is connected in parallel at the output side of each H-bridge unit; a redundant unit module comprising two redundant H-bridge units; a redundant switching switch group comprising three groups of switching switches; a redundant control switch network comprising two redundant control switches; a fault identification unit for identifying a fault phase and a fault module based on current and voltage similarity; and a controller for executing a "first isolation and then input" strategy, closing the short-circuit switch of the fault module first, then controlling the redundant switching switch and the redundant control switch to switch the redundant unit into the fault phase, and issuing a lock signal to the non-acting switch. Through the "3N+2" redundant topology, the similarity fault identification and the multi-scenario redundant access control, the full coverage fault tolerance of single module and multi-module faults is realized.

Description

Technical Field

[0001] This application relates to the field of power electronic conversion technology, and in particular to a reliability improvement topology and method for flexible DC-DC converters. Background Technology

[0002] A cascaded H-bridge converter is a multilevel converter. Its basic principle is to connect the outputs of multiple H-bridge units in series, and synthesize a multilevel stepped voltage by superimposing the PWM waveforms of each unit. It is mainly used in medium- and high-voltage, high-power applications. Its core advantages lie in its modular structure, ease of expansion, ability to achieve high-voltage output, and low harmonic content. Current methods involve connecting several H-bridge units in series with each phase in a three-phase system. Each unit employs a PWM control strategy with a different duty cycle to synthesize a phase voltage close to a sine wave.

[0003] However, existing technologies have the following drawbacks: traditional topology redundancy design is insufficient, it can only cope with single module failures, it cannot adapt to scenarios where multiple modules in the same phase fail simultaneously, and its fault tolerance is weak; the access logic between redundant modules and the basic part is simple, lacking a precise switching linkage mechanism, which is prone to malfunctions and access conflicts, resulting in output voltage distortion or equipment damage, affecting system stability; fault isolation relies on the action of a single short-circuit switch, without forming a coordinated timing control with redundant access, resulting in slow isolation speed and easy expansion of the fault range.

[0004] Therefore, how to improve the fault tolerance and system stability of cascaded H-bridge converters under multi-module failure scenarios has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] The main objective of this application is to propose a reliability improvement topology and method for flexible DC-DC converters to achieve fast, safe, and reliable redundant switching in multi-module failure scenarios.

[0006] To achieve the above objectives, one aspect of this application proposes a reliability enhancement topology for a flexible DC-DC converter, applied to a cascaded H-bridge converter, comprising: The basic unit array consists of N H-bridge units connected in series in three phases A, B, and C, with a short-circuit switch connected in parallel on the output side of each H-bridge unit for fault isolation. Redundant unit module, including first redundant H-bridge unit ( ) and the second redundant H-bridge unit ( The output side of the redundant unit module is connected in parallel to the three-phase main circuit through a redundant switching switch group; A redundant control switch network is connected between the redundant unit module and the redundant switching switch group, and is used to control the first redundant H-bridge unit or the second redundant H-bridge unit to switch to any fault phase; The fault identification unit is used to collect the grid-connected current of each phase and the DC-side capacitor voltage of each H-bridge unit, and to identify the faulty phase and faulty module based on current similarity and voltage similarity. The controller is connected to the short-circuit switch, the redundant switching switch, and the redundant control switch network, respectively. The controller is configured to: based on the identification result of the fault identification unit, execute a "first isolate, then engage" timing control strategy, that is, first close the short-circuit switch corresponding to the fault module to isolate the fault, then control the engaging and disengaging timing of the redundant control switch network and the redundant switching switch, switch the redundant H-bridge unit into the fault phase, and send a blocking signal to the non-operating switch.

[0007] In some embodiments, the redundant switching group includes: The first redundant switching group consists of a first switch connected in series between the first redundant H-bridge unit and phases A, B, and C. ), second switch ( ), third switch ( )constitute; The second redundant switching group consists of a fourth switch connected in series between the second redundant H-bridge unit and phases A, B, and C. ), the fifth switch ( ), the sixth switch ( )constitute; The third redundant switching group consists of a seventh switch connected in series between the redundant unit module and the three-phase main circuit. ), the eighth switch ( ), Ninth Switch ( ), the tenth switch ( ), Eleventh Switch ( ), the twelfth switch ( )constitute; The redundant control switch network includes a first redundant control switch connected to the first redundant H-bridge unit. ) and the second redundant control switch connected to the second redundant H-bridge unit ( ); Under normal operating conditions, all short-circuit switches remain open, and all redundant switching switches ( , , ) Remain in the closed state, all redundant control switches ( , Keep it disconnected.

[0008] In some embodiments, the fault identification unit executes a fault identification algorithm based on the similarity of key electrical signals, including: Fault phase identification subunit, used to identify fault phases according to the formula Calculate the Euclidean distance of current energy between any two phases of the three phases A, B, and C, where L is the number of sampling points and E is the current energy; when the minimum Euclidean distance corresponds to a certain two phases and the difference in current energy between the two phases and the third phase exceeds a preset threshold, the third phase is determined to be a faulty phase; The fault module identification subunit is used to identify the faulty phase, taking the first H-bridge module as a reference, and then, according to the formula... Calculate the Euclidean distance of the capacitor voltage of each of the remaining H-bridge modules. When the distance exceeds the preset voltage threshold, the corresponding module is determined to be a faulty module, and further includes the logic for judging the fault of the reference module itself.

[0009] In some embodiments, the fault detection logic for the reference module itself includes: when the Euclidean distance of the capacitor voltages of all non-reference modules exceeds a threshold, calculating the pairwise Euclidean distance between all non-reference modules. If all If all values ​​are less than the preset value, it is determined that only the reference module is faulty; if there is a fault in one module and the other non-reference modules... If the increase is significant, it is determined that the module and the reference module are both faulty.

[0010] In some embodiments, the "isolate first, then activate" timing control strategy executed by the controller includes access logic for single-phase, single-module faults: When a fault is detected in a single module of phase A, first close the short-circuit switch of the corresponding module, and then connect the redundant part; if the switch... Disconnect, then switch First disconnect, then switch on. and switches Closing, opening and closing and switches Locked, all other switches remain unchanged; if switch Close, switch Disconnect, then switch First disconnect, then switch on. and switches Closing, opening and closing and switches Locked, all other switches remain unchanged; if the switch and switch All connections are closed, indicating a failure to isolate the fault. Immediate power outage and repair are required. When a fault is detected in a single module of phase B, first close the short-circuit switch of the corresponding module, and then connect the redundant part; if the switch... Disconnect, then switch First disconnect, then switch on. and switches Closing, opening and closing and switches Locked, all other switches remain unchanged; if the switch Close, switch Disconnect, then switch First disconnect, then switch on. and switches Closing, opening and closing and switches Locked, all other switches remain unchanged; if the switch and switch All connections are closed, indicating a failure to isolate the fault. Immediate power outage and repair are required. When a fault is detected in a single module of phase C, first close the short-circuit switch of the corresponding module, and then connect the redundant part; if the switch... Disconnect, then switch First disconnect, then switch on. and switches Closing, opening and closing and switches Locked, all other switches remain unchanged; if the switch Close, switch Disconnect, then switch First disconnect, then switch on. and switches Closing, opening and closing and switches Locked, all other switches remain unchanged; if the switch and switch All connections are closed, indicating a failure to isolate the fault. Power outage and repair are required immediately.

[0011] In some embodiments, the "isolate first, then activate" timing control strategy executed by the controller includes access logic for simultaneous faults in multiple modules within a single phase: When two modules in phase A fail simultaneously, first close the short-circuit switch of the corresponding module, then connect the redundant section; if the following conditions are met: switch and switch If both are off, then the switch and switch First disconnect, then switch on. ,switch ,switch ,switch Closing, opening and closing ,switch ,switch ,switch Locked, all other switches remain unchanged; if the condition is not met: switch and switch All connections are disconnected, fault isolation has failed, and immediate power outage and repair are required. When two modules in phase B fail simultaneously, first quickly close the short-circuit switch of the corresponding module, then connect the redundant section; if the following conditions are met: switch and switch If both are open, then the switch and switch First disconnect, then switch on. ,switch ,switch ,switch Close, switch ,switch ,switch ,switch Locked, all other switches remain unchanged; if the condition is not met: switch and switch All connections are disconnected, fault isolation has failed, and immediate power outage and repair are required. If two modules in phase C fail simultaneously, first quickly close the short-circuit switch of the corresponding module, then connect the redundant section; if the following conditions are met: switch and switch If both are open, then the switch and switch First disconnect, then switch on. ,switch ,switch ,switch Close, switch ,switch ,switch ,switch Locked, all other switches remain unchanged; if the condition is not met: switch and switch All connections were disconnected, indicating a failure to isolate the fault. Power outage and repairs are required immediately.

[0012] In some embodiments, the "isolate first, then activate" timing control strategy executed by the controller includes access logic for simultaneous failures of multiple modules in different phases: When two faulty modules are on different phases, first close their short-circuit switches, then connect the redundant parts; if the following conditions are met: switch and switch If all switches are disconnected, the redundant switching switch of the faulty phase and its corresponding redundant module will disconnect first, followed by the closing of the redundant control switch of the faulty phase, and the locking of the redundant control switches of the non-faulty phases. The remaining switches will remain unchanged. If the condition is not met: the switches... and switch All connections were disconnected, indicating a failure to isolate the fault. Power outage and repairs are required immediately.

[0013] In some embodiments, the controller is further configured to: monitor the grid-connected current energy change and capacitor voltage waveform in real time during the redundant H-bridge unit access process, and confirm the successful redundant access when the three-phase current similarity and output voltage waveform distortion rate recover to within the preset normal threshold.

[0014] In some embodiments, the blocking signal has a higher priority than the action command, and is used to prevent redundant switching switches or redundant control switches of unselected phases from being turned on simultaneously due to malfunction during redundant access, thereby avoiding redundant access conflicts.

[0015] To achieve the above objectives, another aspect of this application proposes a method for improving the reliability of a flexible DC-DC converter based on the aforementioned topology, comprising the following steps: S1. Construct the flexible DC-DC converter topology as described in claim 1; S2. The fault identification unit collects electrical signals in real time and identifies faulty phases and faulty modules step by step based on current similarity and voltage similarity. S3. Based on the identification results, the controller generates and executes a "isolate first, then activate" timing control strategy, including: S31. Send a closing command to the short-circuit switch corresponding to the faulty module to isolate the fault; S32. Based on the fault type (single-phase single module, same-phase multiple modules, different-phase multiple modules), select the corresponding switching sequence of the redundant switching switch and the redundant control switch. S33. Send an action command to the selected switch, and at the same time send a high-priority blocking signal to other switches that may cause conflict, and switch the redundant H-bridge unit into the fault phase. S4. Monitor the system status after redundant access in real time and confirm that the system has returned to stable operation.

[0016] Compared with the prior art, this application has the following beneficial effects: (1) This application innovatively designs a “3N+2” redundant topology structure, that is, each phase has N basic units plus two common redundant units. Through the coordinated configuration of three sets of redundant switching switches and redundant control switches, the fault tolerance capability is improved, and the dual adaptation of single module faults and multi-module faults in the same phase is realized. (2) Optimize the switch linkage logic and access architecture, and design a combination configuration of three-phase output side dual switch group + redundant control switch + redundant unit side switch group to avoid redundant access conflicts; (3) The similarity-based fault identification algorithm is simple in principle, has low computational load, strong real-time performance, and includes the logic for judging faults of reference modules. It consumes less software resources and is easy to integrate. (4) Construct a blocking protection mechanism with higher priority than action commands to reduce the risk of switch malfunction and ensure system operation safety during multi-phase faults; (5) The system can maintain stable operation without shutdown, which significantly improves the power supply reliability and equipment availability in scenarios such as offshore wind power generation. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the following description is provided with accompanying drawings of the relevant technical solutions in the embodiments of this application or the prior art. It should be understood that the accompanying drawings described below are only for the purpose of clearly illustrating some embodiments of the technical solutions of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0018] Figure 1 The diagram shows the 3N+2 redundant topology of the flexible DC-DC converter provided in the embodiments of this application. Detailed Implementation

[0019] The embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. The step numbers in the following embodiments are set only for ease of explanation, and there is no limitation on the order between the steps. The execution order of each step in the embodiments can be adaptively adjusted according to the understanding of those skilled in the art.

[0020] In the description of this invention, it should be understood that the orientation descriptions, such as up, down, front, back, left, right, etc., are based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0021] In the description of this invention, "several" means one or more, "more than" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. The use of "first" and "second" in the description is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0022] Furthermore, in the description of this invention, unless otherwise stated, "multiple" means two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0023] In the description of this invention, unless otherwise explicitly defined, terms such as "set up," "install," and "connect" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this invention in conjunction with the specific content of the technical solution.

[0024] Before providing a detailed description of the embodiments of this application, some of the nouns and terms involved in the embodiments of this application will be explained first. The nouns and terms involved in the embodiments of this application are subject to the following interpretations.

[0025] 1) Flexible DC-DC converter: A flexible DC-DC converter is a power electronic converter based on fully controllable switching devices IGBTs. By controlling the drive signals of each IGBT to adjust its switching timing, the required voltage and current waveforms can be obtained.

[0026] A cascaded H-bridge converter is a multilevel converter. Its basic principle is to connect the outputs of multiple H-bridge units in series, and synthesize a multilevel stepped voltage by superimposing the PWM waveforms of each unit. It is mainly used in medium- and high-voltage, high-power applications. Its core advantages lie in its modular structure, ease of expansion, ability to achieve high-voltage output, and low harmonic content. Current methods involve connecting several H-bridge units in series with each phase in a three-phase system. Each unit employs a PWM control strategy with a different duty cycle to synthesize a phase voltage close to a sine wave.

[0027] Traditional topologies suffer from insufficient redundancy, only capable of handling single-module failures and unable to adapt to simultaneous failures of multiple modules within the same phase, resulting in weak fault tolerance. Furthermore, the connection logic between redundant modules and the base is simple, lacking a precise switching linkage mechanism, making them prone to malfunctions and connection conflicts. This can lead to output voltage distortion or equipment damage, impacting system stability. Fault isolation relies on a single short-circuit switch action, failing to establish coordinated timing control with redundant connections, resulting in slow isolation speeds and a tendency for the fault range to expand. To address these issues, this application provides a 3N+2 redundant topology for a flexible DC-DC converter, employing different control strategies to handle various system operating states.

[0028] The solutions of the embodiments of this application will be described in detail below with reference to the accompanying drawings and specific application examples.

[0029] In this embodiment of the cascaded H-bridge converter, two redundant modules are introduced to address system instability issues arising from the failure of one or more H-bridge modules, and a robust control strategy is employed. The specific method is as follows: Step 1: Design a 3N+2 redundant topology for the flexible DC-DC converter. Figure 1 This diagram illustrates a 3N+2 redundant topology for a flexible DC-DC converter. Each phase consists of N H-bridge units connected in series as the basic component. The output of each H-bridge unit is connected in parallel to the main circuit via a shorting switch. The 3N+2 topology includes... A total of 3N short-circuit switches; two redundant H-bridge units are set at the end of the circuit and A total of eight redundant control switches are connected in parallel to the main circuit as redundant components, forming a 3N+2 redundant topology; the three phases A, B, and C are connected in series. There are six redundant switching switches in total. In case of a fault, they work in conjunction with the redundant control switches to form a control logic of "first fault identification, then fault isolation, and finally redundancy activation".

[0030] Step 2: Develop control strategies for normal operation. Under normal operating conditions, the short-circuit switch remains open; the eight redundant switching switches on the output side of the redundant section remain closed, and the six redundant control switches remain open. In this state, the redundant section is isolated and does not affect the output voltage during normal operation.

[0031] When any one of the three switches is closed, a blocking signal must be continuously sent to the other two switches simultaneously to prevent abnormal access of the redundant module in the event of a multi-phase fault. The switch that receives the blocking signal will not operate even if it receives an action signal. The three switches are similar to those above, thus ensuring the system functions properly.

[0032] Step 3: Develop a fault identification algorithm This embodiment employs a fault identification algorithm based on the similarity of key electrical signals to accurately determine the location of the faulty module from two dimensions: grid-connected current and capacitor voltage. The specific implementation is as follows: (1) Identifying faulty phases based on grid-connected current similarity Each phase at the output end is equipped with a current sensor with the same sampling frequency. When a fault occurs in a phase, the output current of that phase will produce a large waveform distortion, and the similarity with the current of a healthy phase will decrease significantly. Fault identification can be achieved through the sensor.

[0033] The energy of alternating current is shown in equation (1): 2 (1) In the formula, E For electric current energy, The number of sampling points per power frequency cycle. f c Sampling frequency, f For power grid frequency; i For grid current, ( It represents the ratio of the cumulative current in the current cycle to the number of current sampling points in one cycle.

[0034] The similarity of three-phase currents is measured using Euclidean distance, as shown in equation (2): (2) (3) In the formula, and They are respectively m Harmony n Phase current energy ( m,n= (A, B, C) It is the Euclidean distance between the energy of the two-phase currents. It is the difference in energy between the two-phase currents. From equation (2), we can see that... The closer the current is to 0, the more similar the two-phase currents are. Therefore, the fault current satisfies equation (4): (3-4) In the formula, The current fault threshold is generally selected based on the actual situation. Considering that two-phase faults may occur in reality, equation (4) needs to be improved. Due to the three-phase symmetry of the circuit, we can assume that phase A has a fault, and then determine the faulty phase A according to the following formula.

[0035] (5) Then, by comparing the differences in current energy between the three phases, the final fault identification rule is obtained: (6) When the grid-connected current of phase A simultaneously satisfies equations (4) and (6), the faulty phase can be identified. Faults in phases B and C can be handled similarly. After identifying the faulty phase, the faulty module in that phase is immediately identified.

[0036] (2) Fault identification module based on capacitor voltage similarity Each H-bridge module has a voltage sensor with the same sampling frequency on its DC-side capacitor. When a module fails, the capacitor voltage of that module will produce a significant waveform distortion, and the similarity to the normal operating waveform will decrease significantly. Fault identification can be achieved through the sensor.

[0037] Each phase uses the first module as a reference and measures the similarity of capacitor voltages using Euclidean distance, as shown in the following formula: (7) In the formula, Indicates the first module and the second module. i The Euclidean distance between the modules, Indicates the first i The capacitor voltage of each module ( i =1,2,3,…,N). Typically, the first... i When a module fails, the following formula applies: (8) In the formula, The voltage fault threshold is generally selected based on the actual situation. Considering that the reference module may also fail in reality, a separate identification algorithm needs to be designed for it. Assuming that the first module fails, the remaining modules will all exhibit the situation described in equation (8); at this time, the similarity between each pair of the remaining modules is immediately calculated: (9) When the voltage similarity of the remaining modules is very close, it can be determined that only the first module is faulty; when the similarity of a certain module with the remaining modules (excluding the first module) is significantly lower than the similarity between the remaining modules, it can be determined that the module and the first module are faulty at the same time.

[0038] In summary, the similarity-based fault identification algorithm used in this embodiment can achieve rapid step-by-step identification from locating the faulty phase to locating the faulty module, and has wide application value.

[0039] Step 4: Develop a redundancy control strategy for single-phase, single-module failures. When a fault is detected in a single module of phase A, first quickly close the short-circuit switch of the corresponding module, and then connect the redundant parts. If Disconnect, then Disconnect first, then and closure, and Locked, all other switches remain unchanged; if closure, Disconnect, then Disconnect first, then and closure, and Locked, all other switches remain unchanged; if and All connections are closed, indicating a failure to isolate the fault. Power outage and repair are required immediately.

[0040] When a fault is detected in a single module of phase B, first quickly close the short-circuit switch of the corresponding module, and then connect the redundant parts. If Disconnect, then Disconnect first, then and closure, and Locked, all other switches remain unchanged; if closure, Disconnect, then Disconnect first, then and closure, and Locked, all other switches remain unchanged; if and All connections are closed, indicating a failure to isolate the fault. Power outage and repair are required immediately.

[0041] When a fault is detected in a single module of phase C, first quickly close the short-circuit switch of the corresponding module, and then connect the redundant parts. If Disconnect, then Disconnect first, then and closure, and Locked, all other switches remain unchanged; if closure, Disconnect, then Disconnect first, then and closure, and Locked, all other switches remain unchanged; if and All connections are closed, indicating a failure to isolate the fault. Power outage and repair are required immediately.

[0042] For example, when module A1 is identified as faulty, the system immediately initiates the single-phase, single-module fault redundancy access procedure. First, its short-circuit switch... The circuit closes quickly, isolating the faulty module from the main circuit. At this time, the eight redundant control switches of the redundant section remain closed, and the six redundant switching switches are all open.

[0043] when When disconnecting, first disconnect the redundant switching switch. Then close the redundant control switch. and Connect the redundant module R1 to the main circuit, and simultaneously send a signal to the switch. X 2 and Continuously send a lockout signal to prevent malfunction; the remaining switches remain unchanged. closure, When disconnecting, first disconnect the redundant switching switch. Then close the redundant control switch. and Connect the redundant module R2 to the A-phase main circuit, and simultaneously send... Y 2 and A continuous blocking signal is sent to prevent malfunction, while the remaining switches remain unchanged. During the connection process, the grid-connected current energy changes and capacitor voltage waveforms are monitored in real time to ensure that the three-phase current similarity and output voltage waveform distortion rate quickly return to normal thresholds after the redundant module is connected, allowing the system to maintain stable operation without shutdown.

[0044] Step 5: Develop a redundancy control strategy for when multiple modules fail simultaneously. When two modules in phase A fail simultaneously, first quickly close the short-circuit switch of the corresponding module, then connect the redundant section. If the condition " and "All disconnected", then and Disconnect first, then closure, Locked, all other switches remain unchanged; if the condition is not met... and "All disconnected", fault isolation failed, power outage and repair required immediately.

[0045] When two modules in phase B fail simultaneously, first quickly close the short-circuit switch of the corresponding module, then connect the redundant section. If the condition " and "All disconnected", then and Disconnect first, then closure, Locked, all other switches remain unchanged; if the condition is not met... and "All disconnected", fault isolation failed, power outage and repair required immediately.

[0046] If two modules in phase C fail simultaneously, first quickly close the short-circuit switch of the corresponding module, then connect the redundant section. If the condition "" is met... and "All disconnected", then and Disconnect first, then closure, Locked, all other switches remain unchanged; if the condition is not met... and "All disconnected", fault isolation failed, power outage and repair required immediately.

[0047] For example, when identification modules A1 and A2 fail simultaneously, the system immediately initiates the single-phase multi-module fault redundancy access procedure. First, its short-circuit switch... The circuit closes quickly, isolating the faulty module from the main circuit. At this time, the eight redundant control switches of the redundant section remain closed, and the six redundant switching switches are all open.

[0048] When the condition is met and When all are disconnected, first disconnect the redundant switching switch. and Then close the redundant control switch. , and , This connects redundant modules R1 and R2 to the A-phase main circuit, and simultaneously sends signals to the switch. A continuous blocking signal is sent to prevent malfunction, while the remaining switches remain unchanged. During the connection process, the grid-connected current energy changes and capacitor voltage waveforms are monitored in real time to ensure that the three-phase current similarity and output voltage waveform distortion rate quickly return to normal thresholds after the redundant module is connected.

[0049] When two faulty modules are on different phases, first quickly close their short-circuit switches, then connect the redundant section. If the condition " and If all are disconnected, the redundant switching switches of the faulty phase and its corresponding redundant module will disconnect first, followed by the closing of the redundant control switch of the faulty phase, the locking of the redundant control switches of the non-faulty phases, and the remaining switches will remain unchanged; if the condition is not met, and "All disconnected", fault isolation failed, power outage and repair required immediately.

[0050] For example, when identification modules A1 and B1 fail simultaneously, the system immediately initiates a two-phase multi-module fault redundancy access procedure. First, its short-circuit switch... The circuit closes quickly, isolating the faulty module from the main circuit. At this time, the eight redundant control switches of the redundant section remain closed, and the six redundant switching switches are all open.

[0051] When the condition is met and When all are disconnected, first disconnect the redundant switching switch. and Then close the redundant control switch. , and Y 2. This connects redundant modules R1 and R2 to the A and B phase main circuits respectively, and simultaneously sends signals to the switch. A continuous blocking signal is sent to prevent malfunction, while the remaining switches remain unchanged. During the connection process, the grid-connected current energy changes and capacitor voltage waveforms are monitored in real time to ensure that the three-phase current similarity and output voltage waveform distortion rate quickly return to normal thresholds after the redundant module is connected.

[0052] In summary, compared with the prior art, this application has at least the following advantages and beneficial effects: 1) This application adopts a "3N+2" redundant structure design to form a dual-redundant backup architecture, and formulates a similarity-based fault identification algorithm to achieve dual adaptation to single-module faults and multi-module faults. Among them, the similarity-based fault identification algorithm has a simple principle, low computational load, strong real-time performance, low software resource consumption, and is easy to integrate.

[0053] 2) This application incorporates a short-circuit switch in parallel within each H-bridge unit, and all switches in the redundant section are equipped with interlocking mechanisms and switching sequences to prevent malfunctions. Furthermore, the switch linkage logic and access architecture have been optimized, designing a combined configuration of dual switches on the three-phase output side plus redundant control switches to effectively avoid redundant access conflicts.

[0054] 3) This application proposes a control strategy for rapid isolation of faulty modules and rapid connection of redundant parts, following the timing principle of "isolation first, then activation," applicable to various fault conditions. In addition, a lockout protection mechanism with higher priority than action commands is constructed to reduce the risk of switch malfunctions and ensure system operational safety during multi-phase faults.

[0055] In the foregoing description of this specification, references to terms such as "one embodiment," "another embodiment," or "some embodiments" indicate that a specific feature, structure, material, or characteristic described in connection with an embodiment or example is included in at least one embodiment or example of the present invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0056] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

[0057] The above is a detailed description of the preferred embodiments of the present invention. However, the present invention is not limited to the above embodiments. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention. All such equivalent modifications or substitutions are included within the scope defined by the claims of this application.

Claims

1. A reliability-enhancing topology for a flexible DC-DC converter, applied to a cascaded H-bridge converter, characterized in that, include: The basic unit array consists of N H-bridge units connected in series in three phases A, B, and C, with a short-circuit switch connected in parallel on the output side of each H-bridge unit for fault isolation. The redundant unit module includes a first redundant H-bridge unit and a second redundant H-bridge unit. The output side of the redundant unit module is connected in parallel to the three-phase main circuit through a redundant switching switch group. A redundant control switch network is connected between the redundant unit module and the redundant switching switch group, and is used to control the first redundant H-bridge unit or the second redundant H-bridge unit to switch to any fault phase; The fault identification unit is used to collect the grid-connected current of each phase and the DC-side capacitor voltage of each H-bridge unit, and to identify the faulty phase and faulty module based on current similarity and voltage similarity. The controller is connected to the short-circuit switch, the redundant switching switch, and the redundant control switch network, respectively. The controller is configured to: based on the identification result of the fault identification unit, execute a "first isolate, then engage" timing control strategy, that is, first close the short-circuit switch corresponding to the fault module to isolate the fault, then control the engaging and disengaging timing of the redundant control switch network and the redundant switching switch, switch the redundant H-bridge unit into the fault phase, and send a blocking signal to the non-operating switch.

2. The reliability enhancement topology of the flexible DC-DC converter according to claim 1, characterized in that, The redundant switching group includes: The first redundant switching group consists of a first switch connected in series between the first redundant H-bridge unit and phases A, B, and C. ), second switch ( ), third switch ( )constitute; The second redundant switching group consists of a fourth switch connected in series between the second redundant H-bridge unit and phases A, B, and C. ), the fifth switch ( ), Sixth Switch ( )constitute; The third redundant switching group consists of a seventh switch connected in series between the redundant unit module and the three-phase main circuit. ), the eighth switch ( ), Ninth Switch ( ), the tenth switch ( ), Eleventh Switch ( ), the twelfth switch ( )constitute; The redundant control switch network includes a first redundant control switch connected to the first redundant H-bridge unit. ) and the second redundant control switch connected to the second redundant H-bridge unit ( ); Under normal operating conditions, all short-circuit switches remain open, and all redundant switching switches ( , , ) Remain in the closed state, all redundant control switches ( , Keep it disconnected.

3. The reliability enhancement topology of the flexible DC-DC converter according to claim 1, characterized in that, The fault identification unit executes a fault identification algorithm based on the similarity of key electrical signals, including: The fault phase identification subunit is used to identify the fault phase according to the formula. Calculate the Euclidean distance of current energy between any two phases of the three phases A, B, and C, where L is the number of sampling points and E is the current energy; when the minimum Euclidean distance corresponds to a certain two phases and the difference in current energy between the two phases and the third phase exceeds a preset threshold, the third phase is determined to be a faulty phase; The fault module identification subunit is used to identify the faulty phase, taking the first H-bridge module as a reference, and then, according to the formula... Calculate the Euclidean distance of the capacitor voltage of each of the remaining H-bridge modules. When the distance exceeds the preset voltage threshold, the corresponding module is determined to be a faulty module, and further includes the logic for judging the fault of the reference module itself.

4. The reliability enhancement topology of the flexible DC-DC converter according to claim 3, characterized in that, The logic for determining faults in the reference module itself includes: when the Euclidean distance of the capacitor voltages of all non-reference modules exceeds a threshold, calculating the pairwise Euclidean distance between all non-reference modules. If all If all values ​​are less than the preset value, it is determined that only the reference module is faulty; if there is a fault in one module and the other non-reference modules... If the increase is significant, it is determined that the module and the reference module are both faulty.

5. The reliability enhancement topology of the flexible DC-DC converter according to claim 2, characterized in that, The "isolate first, then activate" timing control strategy executed by the controller includes access logic for single-phase, single-module faults: When a fault is detected in a single module of phase A, first close the short-circuit switch of the corresponding module, and then connect the redundant part; if the switch... Disconnect, then switch First disconnect, then switch on. and switches Closing, opening and closing and switches Locked, all other switches remain unchanged; if the switch Close, switch Disconnect, then switch First disconnect, then switch on. and switches Closing, opening and closing and switches Locked, all other switches remain unchanged; if the switch and switch All connections are closed, indicating a failure to isolate the fault. Immediate power outage and repair are required. When a fault is detected in a single module of phase B, first close the short-circuit switch of the corresponding module, and then connect the redundant part; if the switch... Disconnect, then switch First disconnect, then switch on. and switches Closing, opening and closing and switches Locked, all other switches remain unchanged; if the switch Close, switch Disconnect, then switch First disconnect, then switch on. and switches Closing, opening and closing and switches Locked, all other switches remain unchanged; if the switch and switch All connections are closed, indicating a failure to isolate the fault. Immediate power outage and repair are required. When a fault is detected in a single module of phase C, first close the short-circuit switch of the corresponding module, and then connect the redundant part; if the switch... Disconnect, then switch First disconnect, then switch on. and switches Closing, opening and closing and switches Locked, all other switches remain unchanged; if the switch Close, switch Disconnect, then switch First disconnect, then switch on. and switches Closing, opening and closing and switches Locked, all other switches remain unchanged; if the switch and switch All connections are closed, indicating a failure to isolate the fault. Power outage and repair are required immediately.

6. The reliability enhancement topology of the flexible DC-DC converter according to claim 2, characterized in that, The "isolate first, then activate" timing control strategy executed by the controller includes access logic for simultaneous faults in multiple modules within a single phase: When two modules in phase A fail simultaneously, first close the short-circuit switch of the corresponding module, then connect the redundant section; if the following conditions are met: switch and switch If both are off, then the switch and switch First disconnect, then switch on. ,switch ,switch ,switch Closing, opening and closing ,switch ,switch ,switch Locked, all other switches remain unchanged; if the condition is not met: switch and switch All connections are disconnected, fault isolation has failed, and immediate power outage and repair are required. When two modules in phase B fail simultaneously, first quickly close the short-circuit switch of the corresponding module, then connect the redundant section; if the following conditions are met: switch and switch If both are open, then the switch and switch First disconnect, then switch on. ,switch ,switch ,switch Close, switch ,switch ,switch ,switch Locked, all other switches remain unchanged; if the condition is not met: switch and switch All connections are disconnected, fault isolation has failed, and immediate power outage and repair are required. If two modules in phase C fail simultaneously, first quickly close the short-circuit switch of the corresponding module, then connect the redundant section; if the following conditions are met: switch and switch If both are open, then the switch and switch First disconnect, then switch on. ,switch ,switch ,switch Close, switch ,switch ,switch ,switch Locked, all other switches remain unchanged; if the condition is not met: switch and switch All connections were disconnected, indicating a failure to isolate the fault. Power outage and repairs are required immediately.

7. The reliability enhancement topology of the flexible DC-DC converter according to claim 2, characterized in that, The "isolate first, then activate" timing control strategy executed by the controller includes access logic for simultaneous faults in multiple modules across different phases: When two faulty modules are on different phases, first close their short-circuit switches, then connect the redundant parts; if the following conditions are met: switch and switch If all switches are disconnected, the redundant switching switch of the faulty phase and its corresponding redundant module will disconnect first, followed by the closing of the redundant control switch of the faulty phase, and the locking of the redundant control switches of the non-faulty phases. The remaining switches will remain unchanged. If the condition is not met: the switches... and switch All connections were disconnected, indicating a failure to isolate the fault. Power outage and repairs are required immediately.

8. The reliability enhancement topology of the flexible DC-DC converter according to claim 1, characterized in that, The controller is also configured to: monitor the grid-connected current energy change and capacitor voltage waveform in real time during the redundant H-bridge unit access process, and confirm the successful redundant access when the three-phase current similarity and output voltage waveform distortion rate return to the preset normal threshold.

9. The reliability enhancement topology of the flexible DC-DC converter according to claim 1, characterized in that, The blocking signal has a higher priority than the action command and is used to prevent redundant switching switches or redundant control switches of unselected phases from being turned on simultaneously due to malfunction during redundant access, thereby avoiding redundant access conflicts.

10. A method for improving the reliability of a flexible DC-DC converter based on the topology of any one of claims 1-9, characterized in that, Includes the following steps: S1. Construct the flexible DC-DC converter topology as described in claim 1; S2. The fault identification unit collects electrical signals in real time and identifies faulty phases and faulty modules step by step based on current similarity and voltage similarity. S3. Based on the identification results, the controller generates and executes a "isolate first, then activate" timing control strategy, including: S31. Send a closing command to the short-circuit switch corresponding to the faulty module to isolate the fault; S32. Select the switching sequence of the corresponding redundant switching switch and redundant control switch according to the fault type; S33. Send an action command to the selected switch, and at the same time send a high-priority blocking signal to other switches that may cause conflict, and switch the redundant H-bridge unit into the fault phase. S4. Monitor the system status after redundant access in real time and confirm that the system has returned to stable operation.

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