A fault data generation and acquisition method for a modular multilevel converter

Abstract

The application discloses a fault data generation and acquisition method of a modular multilevel converter, comprising the following steps: sam Each acquisition period T is divided into a fault period and a recovery period, wherein the length of the acquisition period is 3 base frequency periods; the starting point t0 of the acquisition period is the zero-crossing point at which the alternating current of the first base frequency period changes from negative to positive; the length of the fault period is 1 base frequency period T0, and the starting point t F Of the fault period is [t0, t0+T0]; in each acquisition period, the time period other than the fault period is the recovery period; in each fault period, a sub-module is randomly calibrated as a target sub-module, an open-circuit fault of the target sub-module is controlled, fault data is acquired, and the output voltage of the target sub-module is compensated through a redundant sub-module, so that the normal operation of the modular multilevel converter is avoided from being affected. The method provided by the application does not need any hardware introduction, can be widely applied to various voltage levels and power levels, does not affect the normal operation of the modular multilevel converter in the data acquisition process, does not damage the equipment, and can realize low-cost and high-reliable fault data acquisition.

Description

Technical Field

[0001] This invention belongs to the field of DC power transmission technology, and relates to the reliability of medium and high voltage power electronic converters, and in particular to a method for generating and collecting fault data for modular multilevel converters. Background Technology

[0002] Modular multilevel converter systems are large, containing numerous submodules, each with several power switching devices. Open-circuit faults in these power switching devices do not readily manifest as significant fault characteristics at the submodule level, making it difficult to quickly identify and bypass faulty submodules. Existing fault location methods are generally divided into two categories: hardware-based and software-based methods. Among these, software-based methods are widely popular due to their wide applicability, lack of need for additional hardware, and low cost.

[0003] Software-based fault location methods include model-based and data-based methods. Model-based methods require setting appropriate thresholds to determine the location of the faulty submodule by comparing the differences between relevant variables and reference values. However, since modular multilevel converters often face complex operating environments and various working conditions, threshold settings are difficult to fully meet the requirements for accurate and rapid fault location under different circumstances. Data-based fault location methods, through training on collected data, can automatically identify faulty submodules without setting thresholds, achieving rapid and accurate fault location. However, obtaining fault data is one of the bottlenecks hindering the widespread adoption of this method. The amount of fault data in actual engineering projects is limited, insufficient for data training; laboratory prototype simulations are prone to damage due to varying fault severity, significantly increasing costs; and the training results obtained from laboratory prototype simulations may not meet the operational requirements of actual engineering projects.

[0004] Currently, most methods for acquiring open-circuit fault data in modular multilevel converters are based on simulation models or small-power prototypes in laboratories. Existing methods may not meet the positioning requirements of actual engineering operations in complex scenarios and at multiple power levels. In addition, the fault data acquisition process for small-power prototypes is somewhat destructive and harmful to the prototypes. Under the requirement of acquiring large amounts of fault data, the cost of data generation and acquisition is high.

[0005] Therefore, it is necessary to explore more efficient, lower-cost, more reliable, and more adaptable methods for generating and acquiring fault data, so as to achieve accurate and rapid fault location based on data in modular multilevel converters and improve operational reliability. Summary of the Invention

[0006] The purpose of this invention is to provide a method for generating and acquiring fault data for modular multilevel converters. This method requires no hardware and can be widely applied to various voltage and power levels. The data acquisition process does not affect the normal operation of the modular multilevel converter and does not damage the equipment. It can achieve low-cost and highly reliable fault data acquisition.

[0007] To achieve the above objectives, the solution of the present invention is:

[0008] A method for generating and acquiring fault data of a modular multilevel converter, wherein the modular multilevel converter has a three-phase topology, each phase includes an upper bridge arm from the positive terminal to the connection point and a lower bridge arm from the connection point to the negative terminal. The upper bridge arm includes N sub-modules connected in series from the positive terminal to the connection point and a first inductor; the lower bridge arm includes N sub-modules connected in series from the negative terminal to the connection point and a second inductor. Each sub-module includes an upper transistor, a lower transistor, and a capacitor. The method includes...

[0009] Each acquisition cycle T sam It is divided into a fault cycle and a recovery cycle, wherein the duration of the acquisition cycle is T. sam =3T0, where T0 is one fundamental frequency cycle; the starting point t0 of the acquisition cycle is the zero-crossing point where the AC current changes from negative to positive in the first fundamental frequency cycle; the duration of the fault cycle is one fundamental frequency cycle T0, and its starting point t0 is... F [t0, t0+T0]; within each acquisition cycle, except for the fault cycle [t F ,t F Except for +t0], the remaining time periods are the recovery period;

[0010] During each fault cycle, a submodule is randomly selected as the target submodule and controlled to simulate an open-circuit fault in order to obtain fault data.

[0011] Among them, during the fault cycle [t] F ,t F Within [+t0], the process of generating and collecting open-circuit fault data for the upper pipe is as follows:

[0012] Step a1, when the bridge arm current i xy When the value is greater than 0, the upper and lower switching signals of the target submodule are: T1 = S f T2 = S f '; where x is the phase of the bridge arm, x = a, b, c, y is the y-arm of phase x, y = p, n, p represents the upper bridge arm, and n represents the lower bridge arm; when S f When n = 0 or 1, xy =n xy0 , where n xy n is the actual command signal for the number of bridge arm submodules deployed. xy0The reference command signal generated for the corresponding number of bridge arm sub-modules to be deployed for bridge arm control; S f For the output command signal of the target submodule;

[0013] When the bridge arm current i xy When ≤0, the upper and lower switch signals of the target submodule are: T1=0, T2=S f ';When S f When n = 0, xy =n xy0 When S f When n = 1, xy =n xy0 +1;

[0014] Step a2, collect the fault cycle [t] respectively. F ,t F The bridge arm current i within +t0] xy Target submodule switch signal S f Target submodule capacitor voltage u Cf .

[0015] Among them, during the fault cycle [t] F ,t F Within [+t0], the process of generating and collecting open-circuit fault data for the lower pipe is as follows:

[0016] Step b1, when the bridge arm current i xy When ≤0, the upper and lower switch signals of the target submodule are: T1 = S f T2 = S f ';When S f When n = 0 or 1, xy =n xy0 ;

[0017] When the bridge arm current i xy When the value is greater than 0, the upper and lower switching signals of the target submodule are: T1 = S f, T2 = 0; when S f When n = 0, xy =n xy0 -1; when S f When n = 1, xy =n xy0 ;

[0018] Step b2, collect the fault cycle [t] respectively. F ,t F The bridge arm current i within +t0] xy Target submodule switch signal S f Target submodule capacitor voltage u Cf .

[0019] During the recovery period, the instruction for the number of bridge arm submodules to be deployed is always n. xy =n xy0 The switch command for the target submodule is always T1=S f T2 = S f '.

[0020] Each bridge arm takes turns collecting open circuit fault data for the upper and lower pipes, with a rotation cycle of no less than K0T0.

[0021] The starting point of the fault cycle is taken as t. F = t0 + k T0 / K0, where K0 is a positive integer and k = 1, 2, ..., K0.

[0022] The process involves randomly selecting a submodule as the target submodule and controlling it to simulate an open-circuit fault. This includes randomly selecting a submodule as the target submodule and controlling it to simulate an open-circuit fault in the upper tube when the bridge arm current is negative, while increasing the input of the bridge arm submodule to compensate for the output of the faulty submodule; and simulating an open-circuit fault in the lower tube when the bridge arm current is positive, while reducing the input of the bridge arm submodule to compensate for the output of the faulty submodule, in order to obtain fault data.

[0023] After adopting the above scheme, the present invention first sets a complete acquisition cycle, defining the fault cycle and recovery cycle within the acquisition cycle. Within different acquisition cycles, the fault cycle starts at different time points. Within the fault cycle, a target submodule is selected to simulate an open-circuit fault in the upper tube when the bridge arm current is negative, and the bridge arm submodule is increased to compensate for the faulty submodule output; when the bridge arm current is positive, a lower tube open-circuit fault is simulated, and the bridge arm submodule is reduced to compensate for the faulty submodule output; only one type of fault is simulated in each acquisition cycle. The present invention effectively solves the challenge of small and difficult-to-obtain fault data in actual engineering projects. It can obtain a large amount of fault data that conforms to actual operating conditions without affecting the normal operation of the modular multilevel converter, achieving high reliability, low cost, and high adaptability in fault data generation and acquisition. This is beneficial to improving the practicality, speed, and accuracy of data-based fault location methods. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the modular multilevel converter topology based on a half-bridge submodule used in this invention.

[0025] Among them, (a) is the overall topology diagram, and (b) is the structural diagram of each module;

[0026] Figure 2 This is a schematic diagram of the acquisition cycle in the modular multilevel converter fault data generation and acquisition method, and a flowchart of the acquisition cycle setting method and the fault cycle setting method.

[0027] Figure 3This refers to the sub-module switching principle of the modular multilevel converter bridge arm during the fault period and recovery period within the acquisition cycle;

[0028] Among them, (a) is the submodule switching method for simulating upper-side failure of submodule during the fault period, (b) is the submodule switching method for simulating lower-side failure of submodule during the fault period, and (c) is the submodule switching method during the recovery period. Detailed Implementation

[0029] The technical solution and beneficial effects of the present invention will be described in detail below with reference to the accompanying drawings.

[0030] Figure 1 It is a classic modular multilevel converter with a three-phase topology, combined with Figure 1 As shown in (a), each phase includes a symmetrically arranged upper bridge arm and a lower bridge arm. The upper bridge arm includes N half-bridge sub-modules connected in series from the positive terminal to the midpoint and an inductor L. S The lower bridge arm comprises N half-bridge sub-modules connected in series from the negative terminal to the midpoint, and an inductor L. S The phase voltage of this phase is U. dc The phase current is I dc Let the voltage at the upper bridge arm be u. ap The bridge arm current is i ap The voltage at the lower bridge arm is u an The bridge arm current is i an ;like Figure 1 (b) shows the circuit structure diagram of the half-bridge module, which includes an upper transistor, a lower transistor, and a capacitor C. The switching signal of the upper transistor is denoted as T1, and the switching signal of the lower transistor is denoted as T2.

[0031] Figure 2 This is a schematic diagram of the acquisition cycle in the modular multilevel converter fault data generation and acquisition method.

[0032] like Figure 2 As shown in Figure ②, during normal operation of the modular multilevel converter, fault data can be actively generated and collected based on control capabilities without affecting normal operation; a complete cycle for generating and collecting fault data is the collection cycle T. sam .

[0033] like Figure 2 As shown in ③, the acquisition period consists of three adjacent fundamental frequency periods with a duration of T. sam =3T0, where T0 is one fundamental frequency cycle, with a value of 1 / f0, and f0 is the fundamental frequency of the AC output voltage. The starting point t0 of the acquisition cycle is the zero-crossing point where the AC current changes from negative to positive in the first fundamental frequency cycle. One acquisition cycle includes a fault cycle and a recovery cycle. The fault cycle lasts for one fundamental frequency cycle. Within each acquisition cycle, except for the fault cycle [t...]... F,t F Except for +t0], the remaining time periods are the recovery period.

[0034] like Figure 2 As shown in ④ and ⑤, the starting point t of the fault cycle F The range of variation is [t0, t0+T0], and the value is t. F = t0 + kT0 / K0. K0 is a positive integer, with a value range of [30, 50]. k = 1, 2, ..., K0.

[0035] like Figure 2 As shown in ①, each bridge arm takes turns collecting open circuit fault data of the upper and lower pipes of the submodule, and the rotation cycle is no less than K0T0.

[0036] Figure 3 This refers to the submodule switching principle of the modular multilevel converter bridge arm during fault and recovery cycles within the acquisition period. In each acquisition cycle, a target submodule is randomly selected, and fault data is generated from this submodule. The output command signal S of the target submodule... f Generated by the bridge arm control signal, S f = 0 or 1.

[0037] like Figure 3 As shown in (a), the fault cycle [t] F ,t F Within +t0], the process by which the modular multilevel converter actively generates and acquires open-circuit fault data for the upper tube of the submodule is as follows:

[0038] Step 1: When the bridge arm current i xy When the value is greater than 0, the upper and lower switching signals of the target submodule are: T1 = S f T2 = S f '; where x is the phase of the bridge arm, x = a, b, c, y is the y-arm of phase x, y = p, n, where p represents the upper bridge arm and n represents the lower bridge arm. When S f When n = 0 or 1, xy =n xy0 , where n xy n is the actual command signal for the number of bridge arm submodules deployed. xy0 This is a reference command signal generated for the corresponding number of bridge arm sub-modules to be activated in the bridge arm control. When the bridge arm current i... xy When ≤0, the upper and lower switch signals of the target submodule are: T1=0, T2=S f ';When S f When n = 0, xy =n xy0 When S f When n = 1, xy =n xy0 +1.

[0039] Step 2: Collect the fault cycle [t] separately. F ,t F The bridge arm current i within +t0] xy Target submodule switch signal S f Target submodule capacitor voltage u Cf .

[0040] like Figure 3 As shown in (b), the fault cycle [t] F ,t F Within +t0], the process by which the modular multilevel converter actively generates open-circuit fault data for the lower tube of a submodule is as follows:

[0041] Step 1: When the bridge arm current i xy When ≤0, the upper and lower switch signals of the target submodule are: T1 = S f T2 = S f '。 When S f When n = 0 or 1, xy =n xy0 When the bridge arm current i xy When the value is greater than 0, the upper and lower switching signals of the target submodule are: T1 = S f, T2 = 0; when S f When n = 0, xy =n xy0 -1; when S f When n = 1, xy =n xy0 .

[0042] Step 2: Collect the fault cycle [t] separately. F ,t F The bridge arm current i within +t0] xy Target submodule switch signal S f Target submodule capacitor voltage u Cf .

[0043] like Figure 3 As shown in (c), during the recovery period, the instruction for the number of bridge arm submodules deployed is always n. xy =n xy0 The switch command for the target submodule is always T1=S f T2 = S f '.

[0044] It should be noted that the above are merely illustrative examples of embodiments of the present invention. The data generation and acquisition method proposed in this invention can be applied to modular multilevel converters based on any sub-module, as well as any power electronic converter based on multiple cascaded identical modules.

[0045] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0046] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for generating and acquiring fault data in a modular multilevel converter, wherein the modular multilevel converter has a three-phase topology, and each phase includes an upper bridge arm from the positive terminal to the connection point and a lower bridge arm from the connection point to the negative terminal, wherein... The upper bridge arm comprises N sub-modules connected in series from the positive terminal to the connection point and a first inductor; the lower bridge arm comprises N sub-modules connected in series from the negative terminal to the connection point and a second inductor; each sub-module includes an upper transistor, a lower transistor, and a capacitor; the method is characterized by including, Each acquisition cycle T sam It is divided into a fault cycle and a recovery cycle, wherein the duration of the acquisition cycle is T. sam =3T0, where T0 is one fundamental frequency cycle; the starting point t0 of the acquisition cycle is the zero-crossing point where the AC current changes from negative to positive in the first fundamental frequency cycle; the duration of the fault cycle is one fundamental frequency cycle T0, and its starting point t0 is... F [t0, t0+ T0]; within each acquisition cycle, except for the fault cycle [t F , t F Except for +T0], all other time periods are recovery periods; During each fault cycle, a submodule is randomly selected as the target submodule and controlled to simulate an open circuit fault in order to obtain fault data. The process involves randomly selecting a submodule as the target submodule and controlling it to simulate an open-circuit fault. This includes randomly selecting a submodule as the target submodule and controlling it to simulate an open-circuit fault in the upper tube when the bridge arm current is negative, while increasing the input of the bridge arm submodule to compensate for the output of the faulty submodule; and simulating an open-circuit fault in the lower tube when the bridge arm current is positive, while reducing the input of the bridge arm submodule to compensate for the output of the faulty submodule, in order to obtain fault data.

2. The method as described in claim 1, characterized in that: During the fault cycle [t] F , t F Within +T0], the process of generating and collecting open-circuit fault data for the upper pipe is as follows: Step a1, when the bridge arm current i xy When the value is greater than 0, the upper and lower transistor switching signals of the target submodule are: T1=S f T2=S f '; where x is the phase of the bridge arm, x=a, b, c, y is the y-arm of phase x, y=p, n, p represents the upper bridge arm, n represents the lower bridge arm; when S f When n = 0 or 1, xy =n xy0 , where n xy n is the actual command signal for the number of bridge arm submodules deployed. xy0 The reference command signal generated for the corresponding number of bridge arm sub-modules to be deployed for bridge arm control; S f For the output command signal of the target submodule; When the bridge arm current i xy When ≤0, the upper and lower switching signals of the target submodule are: T1=0, T2= S f ';When S f When n = 0, xy =n xy0 When S f When n = 1, n xy =n xy0 +1; Step a2, collect the fault cycle [t] respectively. F , t F The bridge arm current i within +T0] xy Target submodule switch signal S f Target submodule capacitor voltage u Cf .

3. The method as described in claim 1, characterized in that: During the fault cycle [t] F , t F Within [+T0], the process of generating and collecting open-circuit fault data for the lower pipe is as follows: Step b1, when the bridge arm current i xy When ≤0, the upper and lower switch signals of the target submodule are: T1 = S f T2=S f ';When S f When n = 0 or 1, xy =n xy0 ; When the bridge arm current i xy When the value is greater than 0, the upper and lower transistor switching signals of the target submodule are: T1 = S f, T2=0; when S f When n = 0, xy =n xy0 -1; when S f When n = 1, n xy =n xy0 ; Step b2, collect the fault cycle [t] respectively. F , t F The bridge arm current i within +T0] xy Target submodule switch signal S f Target submodule capacitor voltage u Cf .

4. The method as described in claim 1, characterized in that: During the recovery period, the command for the number of bridge arm submodules deployed is always n. xy =n xy0 The switch command for the target submodule is always T1 = S. f T2 = S f '.

5. The method as described in claim 1, characterized in that: Each bridge arm takes turns collecting open circuit fault data for the upper and lower pipes, with a rotation cycle of no less than K0T0.

6. The method as described in claim 1, characterized in that: The starting point of the fault cycle is t. F =t0+ k T0 / K0, where K0 is a positive integer and k=1,2, …, K0.

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