A Monitoring Method and System for T-Type Three-Level Converters Based on the Residual Method

Abstract

The present invention provides a monitoring method and system for a T-type three-level converter based on the residual method. First, the changes in the current path and voltage magnitude of the T-type three-level converter before and after a fault are analyzed; then, predictive control is used as the control framework to obtain the residuals between the predicted current and voltage values and the actual current and voltage values; finally, diode faults and switch faults are judged based on the current flow direction, switch states, and current and voltage residuals, so as to achieve rapid diagnosis and location of open-circuit faults of diodes and switch tubes. The present invention does not require additional hardware devices and does not require additional cost investment; it has a fast diagnosis speed and high accuracy; it realizes the detection of open-circuit faults of switch tubes and diodes in the entire converter system, and provides guidance for subsequent fault tolerance and maintenance work.

Description

Technical Field

[0001] The present invention belongs to the technical field of converter monitoring, and relates to a monitoring method and system for a T-type three-level converter based on the residual method. Background Art

[0002] The statements in this part only provide background technical information related to the present invention, and do not necessarily constitute prior art.

[0003] New energy grid connection, advanced electric drive control, microgrid operation control, and high-voltage direct-connected energy storage technology based on modern converter control have become the hotspots in the development of the energy industry. The health monitoring of converters is a necessary prerequisite for the highly reliable operation of power electronic systems and energy systems, and provides reliable guidance for fault-tolerant control and maintenance after faults.

[0004] However, it is understood that under the current mainstream control algorithm framework, the switching devices in the converter are generally in a high-frequency switching state and mostly operate in harsh environments such as overheating, mechanical or electromagnetic interference, and time-varying loads. The failure of power devices is an important cause of abnormal states of the converter. According to the existing converter fault research report, the failure of power devices accounts for 34% of the entire converter system faults. The faults of power devices mainly include short-circuit faults and open-circuit faults. Among them, short-circuit faults can develop into open-circuit faults through fuses, etc.; while the detection and fault-tolerant control technologies for open-circuit faults of two-level converters are relatively mature, but there are still major problems with the detection and fault-tolerant control technologies for three-level converters, and basically all focus only on the faults of controllable devices, and the fault diagnosis of freewheeling diodes is still in the initial exploration stage. Summary of the Invention

[0005] In order to solve the above problems, the present invention proposes a monitoring method and system for a T-type three-level converter based on the residual method. The present invention does not require additional hardware devices and does not require additional cost investment; it has a fast diagnosis speed and high accuracy; it realizes the detection of open-circuit faults of switching tubes and diodes in the entire converter system, and provides guidance for subsequent fault-tolerant and maintenance work.

[0006] According to some embodiments, the present invention adopts the following technical solutions:

[0007] A monitoring method for a T-type three-level converter based on the residual method, comprising the following steps:

[0008] Using a prediction model, predicting the corresponding current value and future DC bus voltage value at a future moment;

[0009] Calculating the voltage residual and current residual according to the predicted values;

[0010] If the absolute value of the current residual is greater than the set threshold, then judge the faulty phase according to the maximum value of the absolute value of the current residual;

[0011] Based on the comprehensive current direction, switch states, voltage residuals, and current residuals, diode faults and switch faults are judged.

[0012] As an alternative implementation, a prediction model is utilized to obtain a reference current according to measurement data and the DC bus voltage control loop, and predict the corresponding current values at future n time instants and the future DC bus voltage value;

[0013] By traversing the independent switch states, the optimal control vector for the next time instant is determined with the principle of minimizing the cost function.

[0014] As an alternative implementation, the phase where the maximum value of the absolute value of the current residual is located is the faulty phase.

[0015] As an alternative implementation, the process of judging diode faults and switch faults based on the comprehensive current direction, switch states, voltage residuals, and current residuals includes:

[0016] If the current residual is greater than the set value, a P-state signal for a set control period is injected into the faulty phase. If the absolute value of the current residual is within the set range, it is considered that the first switch of the faulty phase is faulty. If it is not within the set range, an O-state signal for a set control period is injected into the faulty phase. If the absolute value of the current residual is within the set range, the second switch and the first anti-parallel diode in the middle of the faulty phase are faulty. Otherwise, the second anti-parallel diode is faulty.

[0017] As an alternative implementation, the process of judging diode faults and switch faults based on the comprehensive current direction, switch states, voltage residuals, and current residuals includes: If the current residual is less than or equal to the set value, an N-state signal for a set control period is injected into the faulty phase. If the absolute value of the current residual is within the set range, it is considered that the second switch of the faulty phase is faulty. If it is not within the set range, an O-state signal for a set control period is injected into the faulty phase. If the absolute value of the current residual is within the set range, the first switch and the second anti-parallel diode in the middle of the faulty phase are faulty. Otherwise, the second anti-parallel diode is faulty.

[0018] As a further aspect, the set range is (the first threshold, the second threshold), where the first threshold is greater than the set threshold, and the second threshold is greater than the first threshold.

[0019] As a further aspect, the determination process of the set threshold includes: performing average filtering processing on the calculation result of the current residual through injecting a control signal and the successive difference method to obtain a theoretical deviation growth rate, and according to the theoretical deviation growth rate, considering external interference and communication delay, adding a coefficient to revise the theoretical deviation growth rate.

[0020] A monitoring system for a T-type three-level converter based on the residual method, comprising:

[0021] A prediction module configured to use a prediction model to predict the corresponding current value and the future DC bus voltage value at a future moment;

[0022] A residual calculation module configured to calculate a voltage residual and a current residual according to the prediction values;

[0023] A fault judgment module configured to, if the absolute value of the current residual is greater than a set threshold, judge the faulty phase according to the maximum value of the absolute value of the current residual;

[0024] A fault location module configured to comprehensively judge diode faults and switch tube faults based on the current flow direction, switch states, voltage residuals, and current residuals.

[0025] A computer-readable storage medium storing multiple instructions suitable for being loaded and executed by a processor of a terminal device to perform the steps in the method.

[0026] A terminal device comprising a processor and a computer-readable storage medium, the processor being used to implement each instruction; the computer-readable storage medium being used to store multiple instructions suitable for being loaded and executed by the processor to perform the steps in the method.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] The present invention accurately and quickly monitors the health status of T-type commutation equipment in systems such as renewable energy power generation grid connection, microgrids, energy storage, and new energy electric vehicles, providing a new idea for detecting open-circuit faults of diodes and switch tubes in T-type converters. It can be combined with the fault-tolerant control technology of T-type commutation equipment to further improve the reliability of the equipment.

[0029] In addition, the invention is not only applicable to the fault detection of power devices in power electronic equipment, but can also be extended to the field of relay protection in the power grid. The residual of the predicted current or voltage and the actual current or voltage is used for fault detection as the trigger signal of the relay protection device. The application is relatively wide.

[0030] The present invention does not require adding additional hardware devices or additional cost investment; it has a fast diagnosis speed and high accuracy; it realizes the detection of open-circuit faults of switch tubes and diodes in the entire converter system and provides guidance for subsequent fault tolerance and maintenance work.

[0031] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following specifically gives preferred embodiments and, in conjunction with the accompanying drawings, makes a detailed description as follows. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The accompanying drawings forming a part of this invention are used to provide a further understanding of the invention. The schematic embodiments of the invention and their descriptions are used to explain the invention and do not unduly limit the invention.

[0033] Figure 1 is the topological structure diagram of the T-type three-level converter for this embodiment;

[0034] Figure 2 is the model predictive control flowchart of the T-type three-level converter for this embodiment;

[0035] Figure 3 is the current path diagram of the T-type three-level converter for this embodiment;

[0036] Figure 4 is the flowchart of the fault diagnosis method for this embodiment. Detailed Description of the Invention

[0037] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0038] It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which the present invention belongs.

[0039] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular forms are also intended to include the plural forms. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0040] Embodiment 1

[0041] A monitoring method for a T-type three-level converter based on residuals is provided. First, the changes in the current path and voltage magnitude of the T-type three-level converter before and after a fault are analyzed; then, predictive control is used as the control framework to obtain the residuals between the predicted current and voltage values and the actual current and voltage values; finally, diode faults and switch faults are judged based on the current flow direction, switch state, and current and voltage residuals, realizing the rapid diagnosis and location of open-circuit faults of diodes and switches.

[0042] The key solutions of the method will be described in detail below in conjunction with the accompanying drawings.

[0043] As Figure 1 shown, the T-type three-level PWM rectifier is taken as an example for elaboration.

[0044] The TTL converter topology is asFigure 1 As shown, the converter includes two capacitors and a three-phase circuit, with each phase containing four IGBTs ( , where , the same below) and four anti-parallel diodes ( ). Each phase is connected to the DC-side capacitor ( ), and and are the upper and lower capacitor voltages of the DC bus respectively. In addition, the converter system also includes a three-phase AC voltage source ( ), a filter resistor ( ) and an inductor ( ). and represent the three-phase output voltage and current of the converter.

[0045] By controlling the conduction states of the IGBTs, the three-level converter can output three levels: high level (P), zero level (O), and low level (N), with corresponding voltage values of , 0, - respectively.

[0046] (1)

[0047] Since the same bridge arm consists of two groups of switch tubes with complementary states, the rectifier switch state can be defined as:

[0048] (2)

[0049] Model predictive control is based on vector control, and its basic idea is rolling optimization. It can, according to the measured data, obtain the reference current and from the DC bus voltage control loop and predict the states corresponding to the entire control system at the next n moments (future current values , and the future DC bus voltage value ).

[0050] The MPC algorithm can be selected for prediction, and the flowchart is as shown in Figure 2 , which will not be elaborated here.

[0051] Or other existing prediction algorithms can be used.

[0052] (3)

[0053] (4)

[0054] Traverse 27 independent switch states and determine the optimal control vector for the next moment based on the principle of minimizing the cost function.

[0055] (5)

[0056] wherein is the sampling period, is the weighting coefficient, which is generally set by experience.

[0057] Figure 3 respectively show the current paths corresponding to the switch states P(a, d), O(b, d), and N(c, e) under the normal operation of the converter (it is stipulated that the current directions corresponding to a, b, and c are negative directions, and the current directions corresponding to d, e, and f are positive directions). Assume that the three-phase of the T-type three-level converter is symmetrical, and in each phase, therefore, only the fault conditions of phase A are analyzed.

[0058] Let the voltage residual , wherein is the measured voltage value at time k, is the predicted voltage value at time k. The following analyzes the three switch states of P, O, and N respectively:

[0059] When the switch state is P and the current direction is negative, if has an open-circuit fault at this time, the current path of phase A will change from (a) to (b). At this time, the voltage predicted by the controller through the switch signal is , while the actually measured voltage is , and thus the voltage residual is ; when the current direction is positive, if has an open-circuit fault at this time, the current path of phase A will change from (d) to an open state. At this time, the predicted voltage is , but the measured voltage is uncertain, and the voltage residual is uncertain.

[0060] When the switch state is O and the current direction is negative, if has an open-circuit fault at this time, the current path of phase A will change from (b) to (c). At this time, the predicted voltage is 0, but the measured voltage is , then the voltage residual is . When the current direction is positive, if has an open-circuit fault at this time, the current path of phase A will change from (e) to (d). At this time, the predicted voltage is 0, but the measured voltage is , then the voltage residual is .

[0061] When the switch state is N and the current direction is negative, if has an open-circuit fault at this time, the current path of phase A will change from (c) to an open state. At this time, the predicted voltage is , while the actually measured voltage is uncertain, and thus the voltage residual is uncertain; when the current direction is positive, if an open - circuit fault occurs, the current path of phase A will change from (f) to (e). At this time, the predicted voltage is , but the measured voltage is 0, then the voltage residual is .

[0062] Since adding voltage sensors will increase the economic cost of the entire system, and the existing equipment can measure the grid - side current, and the current residual can change with the change of the voltage residual. Therefore, using formula (6), the voltage residual is replaced by the current residual , and then the open - circuit fault diagnosis of the diodes and switches of the T - type converter is realized:

[0063] (6)

[0064] To reduce the influence of parameter errors, modulation delay, etc. on the residual calculation results during the actual application process, the calculation results of the current residual are averaged and filtered by injecting a control signal and the successive difference method, and the deviation growth rate is obtained as follows:

[0065] , (7)

[0066] , (8)

[0067] In the formula, is the cumulative value of the current residual at time k, is the number of delay periods, is the deviation growth rate after average filtering processing.

[0068] The theoretical deviation threshold is here, but considering external interference and communication delay, etc. in practice, three thresholds ( , , ) are set, and cooperating with the above - mentioned threshold can complete the above - mentioned open - circuit fault diagnosis.

[0069] For the T - type three - level converter topology, the open - circuit fault diagnosis table is shown in Table 1, and the entire diagnosis process is as Figure 4 shown, that is, it includes the following steps:

[0070] Using the prediction model, predict the corresponding current value and the future DC bus voltage value at a future time;

[0071] According to the predicted values, calculate the voltage residual and the current residual;

[0072] If the absolute value of the current residual is greater than the set threshold, the faulty phase is judged according to the maximum value of the absolute value of the current residual.

[0073] Based on the comprehensive consideration of the current flow direction, switch status, voltage residual and current residual, diode faults and switch tube faults are judged.

[0074] Table 1 Open-circuit Fault Diagnosis Table of T-Type Three-Level Converter

[0075]

[0076] Those skilled in the art should understand that the embodiments of the present invention can be provided as a method, a system, or a computer program product. Therefore, the present invention can be implemented in the form of an all-hardware embodiment, an all-software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present invention can be implemented in the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk memory, CD-ROM, optical memory, etc.) containing computer-usable program code.

[0077] The present invention is described with reference to the flowcharts and / or block diagrams of methods, apparatuses (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram can be realized by computer program instructions, and the combination of processes and / or blocks in the flowchart and / or block diagram can also be realized by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing devices generate means for realizing the functions specified in one Figure 1 one process or multiple processes and / or blocks Figure 1 one block or multiple blocks.

[0078] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer-readable memory generate a manufactured article including instruction means, and the instruction means realizes the functions specified in one Figure 1 one process or multiple processes and / or blocks Figure 1 one block or multiple blocks.

[0079] These computer program instructions can also be loaded onto a computer or other programmable data processing device, so that a series of operation steps are executed on the computer or other programmable device to generate a computer-implemented process. Thus, the instructions executed on the computer or other programmable device provide means for realizing the functions specified in one Figure 1 one process or multiple processes and / or blocks Figure 1Steps of the functions specified in one or more boxes.

[0080] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, various changes and modifications can be made to the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

[0081] Although the specific implementation manners of the present invention are described above in conjunction with the accompanying drawings, it is not a limitation on the protection scope of the present invention. Those skilled in the art should understand that based on the technical solutions of the present invention, various modifications or deformations that can be made without creative efforts by those skilled in the art are still within the protection scope of the present invention.

Claims

1. A monitoring method for a T-type three-level converter based on the residual method, characterized in that Including the following steps: Using a prediction model, predict the corresponding current value and future DC bus voltage value at a future moment; According to the predicted values, calculate the voltage residual and current residual; If the absolute value of the current residual is greater than the set threshold, then based on the maximum value of the absolute value of the current residual, determine the faulty phase; Comprehensively considering the current flow direction, switch state, voltage residual and current residual, determine diode faults and switch tube faults. The process includes: If the current residual is greater than the set value, inject a P-state signal with a set control period into the faulty phase. If the absolute value of the current residual is within the set range, it is considered that the first switch tube of the faulty phase is faulty. If it is not within the set range, inject an O-state signal with a set control period into the faulty phase. If the absolute value of the current residual is within the set range, the second switch tube and the first anti-parallel diode in the middle of the faulty phase are faulty, otherwise the second anti-parallel diode is faulty.

2. The monitoring method of a T-type three-level converter based on the residual method according to claim 1, characterized in that Using a prediction model, based on measurement data and the DC bus voltage control loop, a reference current is obtained to predict the current values corresponding to future n time instants and the future DC bus voltage value; By traversing the independent switch states, determine the optimal control vector at the next moment with the principle of minimizing the cost function.

3. The monitoring method of a T-type three-level converter based on the residual method according to claim 1, characterized in that, The phase where the maximum value of the absolute value of the current residual is located is the faulty phase.

4. A monitoring method for a T-type three-level converter based on the residual method according to claim 1, characterized in that, The process of comprehensively considering the current flow direction, switch state, voltage residual and current residual to determine diode faults and switch tube faults includes: If the current residual is less than or equal to the set value, inject an N-state signal with a set control period into the faulty phase. If the absolute value of the current residual is within the set range, it is considered that the second switch tube of the faulty phase is faulty. If it is not within the set range, inject an O-state signal with a set control period into the faulty phase. If the absolute value of the current residual is within the set range, the first switch tube and the second anti-parallel diode in the middle of the faulty phase are faulty, otherwise the second anti-parallel diode is faulty.

5. A monitoring method for a T-type three-level converter based on the residual method according to claim 1 or 4, characterized in that The set range is greater than the first threshold and less than the second threshold, where the first threshold is greater than the set threshold and the second threshold is greater than the first threshold.

6. A monitoring method for a T-type three-level converter based on the residual method according to claim 1 or 4, characterized in that, The determination process of the set threshold includes: performing average filtering processing on the calculation result of the current residual through injecting a control signal and the method of successive differences to obtain the theoretical deviation growth rate. According to the theoretical deviation growth rate, considering external interference and communication delay, add a coefficient to revise the theoretical deviation growth rate.

7. A T-type three-level converter monitoring system based on the residual method, characterized by including: A prediction module configured to use a prediction model to predict the corresponding current value and future DC bus voltage value at a future moment; A residual calculation module configured to calculate the voltage residual and current residual according to the predicted values; A fault judgment module configured to, if the absolute value of the current residual is greater than the set threshold, determine the faulty phase based on the maximum value of the absolute value of the current residual; A fault location module configured to comprehensively consider the current flow direction, switch state, voltage residual and current residual to determine diode faults and switch tube faults. The process includes: If the current residual is greater than the set value, a P-state signal with a set control period is injected into the faulty phase. If the absolute value of the current residual is within the set range, it is considered that the first switching tube of the faulty phase is faulty. If it is not within the set range, an O-state signal with a set control period is injected into the faulty phase. If the absolute value of the current residual is within the set range, the second switching tube and the first anti-parallel diode in the middle path of the faulty phase are faulty. Otherwise, the second anti-parallel diode is faulty.

8. A computer-readable storage medium, characterized in that, Among them, multiple instructions are stored, and the instructions are adapted to be loaded and executed by the processor of the terminal device for the steps in the method described in any one of claims 1-6.

9. A terminal device, characterized in that, It includes a processor and a computer-readable storage medium. The processor is used to implement each instruction; the computer-readable storage medium is used to store multiple instructions, and the instructions are adapted to be loaded and executed by the processor for the steps in the method described in any one of claims 1-6.

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