Cascade H-bridge converter power switch open-circuit fault diagnosis method

Abstract

The invention belongs to the technical field of power electronic equipment fault diagnosis, and particularly discloses a cascaded H-bridge converter power switch open-circuit fault diagnosis method, which is characterized in that a logic relationship between diagnosis signals is analyzed, an attenuation accelerated average model is established by using a detection result, and finally a fault device indication signal is obtained. And fault positioning of multiple switch tubes of multiple power units in the converter can be realized. By adopting the diagnosis method provided by the invention, the identification of the open-circuit fault of the multi-unit multi-power switch tube of the cascaded H-bridge converter can be effectively realized, meanwhile, the method does not need to carry out circuit modeling and only needs to carry out corresponding conversion on the voltage signal, and the diagnosis system is simple in design and high in universality.

Description

Technical Field

[0001] The invention belongs to the technical field of fault diagnosis of power electronic equipment, and relates to a method for diagnosing open-circuit faults of inverter power semiconductor devices based on rough set theory and a voltage average model, and in particular to a method for diagnosing open-circuit faults of power switches of cascaded H-bridge converters. Background Art

[0002] The cascade topology was first proposed by M. Marchesoni et al. at the 1988 PESC conference. In 1997, the application of cascaded H-bridge topology in power grids attracted attention, which led to its extensive research in the future. Figure 1 As shown. When multiple full-bridge units with independent DC power supplies are cascaded and the switch states of the four switch tubes of each unit are different, three different output voltages of +Ud, 0, and -Ud will be generated. Then the output voltages of N inverter units are superimposed to make the output level number 2N+1. Within a certain range, when the level number of the output voltage is higher, its waveform will be closer to a sine wave, the harmonic content in the output waveform will be lower, and the converter efficiency will be higher.

[0003] However, compared with traditional inverters, the more cascade units there are, the more switches there are. According to industrial statistics, power semiconductor switches are one of the most vulnerable components in power electronic systems, so their failure will pose a huge threat to the reliable operation of cascaded H-bridge converters. As a common manifestation of power semiconductor devices, open-circuit faults do not cause transient mutations in electrical quantities in a short period of time, so fault characteristics are difficult to identify. However, if they are not handled in a timely manner, open-circuit faults will cause inverter output distortion and increased electrical stress, causing secondary damage to other parts of the circuit, and ultimately leading to catastrophic failures. Therefore, designing a fast and reliable method for diagnosing open-circuit faults of power semiconductor switches is of great significance to ensuring the safe operation of converter systems. Nowadays, fault diagnosis methods for power semiconductor switches can be mainly divided into state feature-based diagnosis methods and data-driven diagnosis methods. The former predicts the state variables corresponding to different operating modes by establishing an analytical model of the converter, and analyzes the fault type and location by comparing with the state variables collected by the sensor, such as the average bridge arm voltage method and the grid-side voltage evaluation method. However, for large-capacity cascaded H-bridge converters, there are many internal power units and the modeling is complex, so the design of this type of diagnostic system is relatively difficult. The data-driven diagnostic method does not require a detailed analysis of the working mechanism or model of the converter. It extracts feature information from the collected data to evaluate whether the operating status of the system is normal, such as artificial neural networks (patent application number 201610438466.9), extreme learning machines, random forests, etc. Although this type of method can avoid the dependence of diagnostic accuracy on the system model, it has a large amount of calculations and high requirements on the system controller, making it difficult to apply to online real-time diagnosis.

[0004] In summary, the diagnostic method based on analytical model can perform well in terms of diagnostic accuracy and diagnostic speed, but it requires the establishment of accurate models and parameters of the inverter system, and it needs to be remodeled when applied to different topologies, so it has poor versatility. The data-driven method has lower requirements on the accuracy of circuit models and parameters, but it requires a lot of calculation and analysis of data, takes a long time to diagnose and occupies more computing resources, and is not suitable for online fault monitoring of inverter systems.

[0005] It should be noted that the information disclosed in the above background technology section is only used to enhance the understanding of the background of the present invention, and therefore may include information that does not constitute the prior art known to ordinary technicians in the field. Summary of the invention

[0006] In view of the existing power electronic converter fault diagnosis methods, there are problems such as strong dependence on model and parameter accuracy or dependence on training sample quality, large amount of calculation, and slow diagnostic response. To this end, the present invention provides a cascade H-bridge converter power switch open circuit fault diagnosis method. The method uses rough set theory to analyze the voltage and current variables of the cascade H-bridge converter in normal and fault modes, and selects the simplest variable set that can represent all normal and fault operation modes as diagnostic variables. The detection signal of the switch tube open circuit fault is obtained by analyzing the logical relationship between the diagnostic variables, and then the attenuation accelerated average model of the detection signal is established to obtain the positioning result during the fault period. Compared with the traditional diagnostic method, the method can realize multi-unit multi-fault diagnosis in a very short time, and can accurately identify the tube fault in its full-bridge module, is not affected by the number of units and operating conditions, has good robustness, and can also be applied to other full-bridge converter topologies (such as dual active bridge converters), and has strong versatility.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] A method for diagnosing an open circuit fault of a power switch of a cascaded H-bridge converter comprises the following steps:

[0009] Step S1: Analyze the operation mode of any full-bridge power unit in the cascaded H-bridge converter in the four quadrants, obtain the mapping relationship between the switch state and the output voltage value, and analyze the voltage and current components that change in different modes;

[0010] Step S2: using rough set theory to select the simplest diagnostic variable set that characterizes all fault modes;

[0011] Step S3: deriving the logical relationship between the diagnostic signal and the detection result according to each fault mode;

[0012] Step S4: establishing a decay acceleration average model based on the detection results to obtain a fault indication signal;

[0013] Step S5: Determine the fault location according to the fault indication signal.

[0014] The following is a technical solution further defined in the present invention, defining the modulation wave polarity ρ v Equivalently represents the output voltage u m The polarity, ρ c Indicates the current i m The polarity of the output voltage u m The amplitude logic signals u1 and u2 are expressed as follows:

[0015]

[0016]

[0017] Among them, v c Indicates the modulation voltage of the converter, U ref Indicates the reference threshold.

[0018] The following is a technical solution further defined by the present invention, which establishes a state information base of the power unit operation mode, defines a condition attribute set CA and a decision set DA of the information base, simplifies the attributes, obtains a discrimination matrix of the system, calculates the disjunctive normal form of all attributes in each row of non-empty set elements, and simplifies the disjunctive normal form by conjunction operation:

[0019] DP(U)=(ρ c )∧(u1)∧(u2)∧(s1∨s2)∧(s3∨s4);

[0020] Rewrite it into disjunctive normal form:

[0021]

[0022] Among them, m1, m2, m3, and m4 represent the four conjunctions that make up DP(U);

[0023] Select the attributes in item m1 as diagnostic variables.

[0024] The following is a technical solution further defined by the present invention, analyzing the diagnostic variable (ρ c , u1, u2, s1, s3), the logical expression indicating the open circuit fault of the switch pair (T1, T4) or (T2, T3) is obtained:

[0025]

[0026] It is detected whether the two groups of tubes in the full-bridge unit have an open circuit fault, and the calculation result is the detection signal of the open circuit fault.

[0027] The following is a technical solution further defined by the present invention, which adds analysis of the freewheeling mode to obtain the logical expressions of each switch tube failure:

[0028]

[0029] In the formula, the detection signal F T1 ~F T4 Represents the fault status of each tube. A value of 1 indicates that the corresponding switch tube is faulty, and a value of 0 indicates that the switch tube is healthy.

[0030] The following is a technical solution further defined by the present invention, which establishes an attenuation accelerated average model and inputs a detection signal to finally obtain a fault indication signal. oThe attenuation acceleration average model corresponding to each fault indication signal is:

[0031]

[0032]

[0033] The fault indication signal (F U_m 、F T_D1 、F T_D2 、F T_D3 、F T_D4 ), the faulty switch is determined.

[0034] Compared with the prior art, the present invention has the following technical effects:

[0035] The diagnostic method proposed in the present invention can effectively realize the identification of open-circuit faults of multiple units and multiple power switches of the cascaded H-bridge converter. At the same time, this method does not require circuit modeling, but only requires corresponding transformation of the voltage signal. The diagnostic system design is simple and has strong versatility. In addition, compared with the existing diagnostic methods, the fault diagnosis method proposed in the present invention does not rely on the system switching frequency and is suitable for different modulation strategies. In order to verify the performance of this method, the open-circuit faults of different power switches in the full-bridge unit of the converter are verified through simulation. The results show that the diagnostic method proposed in the present invention can achieve better diagnostic performance and effectively improve the reliability of the operation of the modular converter.

[0036] The present invention is further described below in conjunction with the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0038] Figure 1 It is a schematic diagram of the cascaded H-bridge topology;

[0039] Figure 2 is a flow chart of the method of the present invention;

[0040] Figure 3 It is a fault diagnosis circuit diagram of each power unit switch tube T1 to T4 of the present invention;

[0041] Figure 4 is the result diagram of the open circuit fault diagnosis of the switch device in the power unit, where: Figure 4 (a) is the open circuit fault of T1 tube. Figure 4(b) The T4 tube has an open circuit failure. DETAILED DESCRIPTION

[0042] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed below.

[0043] This embodiment designs a method for diagnosing open-circuit faults of power switches in cascaded H-bridge converters. By analyzing the logical relationship between diagnostic signals and using the detection results to establish an attenuation accelerated average model, a fault device indication signal is finally obtained, which can realize the fault location of multiple power units and multiple switches in the converter. The implementation process of this method is as follows: Figure 2 As shown, the specific steps are as follows:

[0044] (1) Analysis of power unit operation mode

[0045] By analyzing the voltage at the output end of the bridge arm u of any full-bridge power unit in the cascaded H-bridge converter in the four quadrants m and the output current i m Respectively satisfy: u m >0,i m >0;u m >0,i m <0;u m <0,i m >0;u m <0,i m <0) operation status, the switch status s can be obtained j and the output voltage u m Similarly, when the switch fails, the output voltage changes due to the forced transformation of the current path. Define the modulation wave polarity ρ v Equivalent representation u m The polarity, ρ c Indicates the current i m The polarity of the output voltage u m Amplitude logic signals u1, u2; v c Represents the modulation voltage of the converter, which is related to the output voltage u m The relationship in polarity is the same polarity, that is, v c The positive and negative of u m (That is, U in the expression m ) is the same in sign and negative, and the relationship between their values ​​can be expressed as That is, the output voltage um The average value within one switching cycle The modulation voltage v c , DC bus voltage U dc and carrier voltage v tri To indicate that v tri Usually the value is 1; U ref1 and U ref2 It represents the reference threshold value, which can be set within the given range according to the actual situation. The specific expression is as follows.

[0046]

[0047] Therefore, the variable characteristics of the power unit when operating in normal and fault modes are summarized in Table 1.

[0048] Table 1 Summary of state variables for normal and fault modes of power units

[0049]

[0050] (2) Diagnostic signal selection based on rough set theory

[0051] The table is processed using rough set theory to establish a state information base of the power unit operation mode, and the condition attribute set CA and decision set DA of the information base are defined according to Table 1, and Table 2 can be obtained.

[0052] Table 2 Power unit status information table

[0053]

[0054]

[0055] The indiscernible relations in Table 2 are studied and found, and the attributes are simplified to obtain the discernibility matrix of the system, as shown in Table 3.

[0056] Table 3 Discrimination matrix of different operation modes of power unit

[0057]

[0058] Find the disjunctive normal forms of all attributes in the non-empty set elements in each row of Table 3, and simplify these disjunctive normal forms by conjunction operation:

[0059] DP(U)=(ρ c )∧(u1)∧(u2)∧(s1∨s2)∧(s3∨s4) (6)

[0060] Finally, rewrite the above formula into the structure of disjunctive normal form.

[0061]

[0062] Each conjunction in the above formula is referred to as the minimum term, which represents the minimum set of attributes required to classify the types in the information library. From formula (7), it can be seen that the fault diagnosis variables that can realize fault identification must include current polarity, output voltage and the drive signals of the two bridge arms. m1, m2, m3, and m4 respectively represent the four conjunctions that make up DP(U). Any conjunction guarantees the maximum simplification of attributes while ensuring the expression of knowledge in the information table, that is, the elements in any conjunction can be used to distinguish all decision attributes in the information library. The attributes in item m1 are selected as diagnostic variables.

[0063] (3) Logical analysis of diagnostic signals

[0064] Combined with Table 1, we analyze the diagnostic variable (ρ c , u1, u2, s1, s3), we can get the logical expression that can indicate the open circuit fault of switch pair (T1, T4) or (T2, T3)

[0065]

[0066] The above formula can be used to detect whether the two pairs of tubes in the full-bridge unit have an open circuit fault, and the calculation result is the detection signal of the open circuit fault. In order to further distinguish the location of the fault in the pair of tubes, it is necessary to further add the analysis of the freewheeling mode on the basis of formula (8) and formula (9), that is, to obtain the logical expression of each switch tube fault.

[0067]

[0068]

[0069] The calculation result in the above formula represents the fault status of each tube. If the value is 1, it means that the corresponding switch tube is faulty, and if it is 0, it means that the switch tube is healthy. Usually, the cascaded H-bridge converter adopts the nearest level (NLC) modulation strategy. The switching frequency of each unit is low. Therefore, the detection signal is obtained by high-frequency sampling and completing the logical calculation of each diagnostic signal in the digital controller. At the same time, it is also possible to build a hardware logic circuit and output the detection signal (F T1 ~F T4 ),like Figure 3 shown.

[0070] (4) Design of diagnostic rules and acquisition of fault indication signals

[0071] However, based on Figure 3The obtained detection signal still cannot accurately locate the fault. This is because the identification of the tube fault depends on the time occupied by the power unit freewheeling mode. When the cascaded H-bridge converter adopts the NLC strategy, the power units in different positions have different proportions of freewheeling mode time in a fundamental wave cycle. If the freewheeling mode is maintained for a very short time, it is difficult to determine the fault location based on the high level time proportion of the detection signal. In order to solve this problem, while eliminating the influence of noise, voltage overshoot and other factors on the diagnosis results, an attenuation accelerated average model is established and the detection signal is input to finally obtain a fault indication signal. In any fundamental wave period T o The attenuation acceleration average model corresponding to each fault indication signal is:

[0072]

[0073]

[0074] The fault indication signal (F U_m 、F T_D1 、F T_D2 、F T_D3 、F T_D4 ) Combined with the diagnostic rules in Table 4, the faulty switch can be determined.

[0075] Table 4 Power unit fault switch location rules (ξ2>ξ1)

[0076]

[0077] In order to verify the performance of the diagnosis method proposed in this patent, taking the N / 2th unit of phase A of the converter as an example (N=42), the diagnosis results of the T1 tube fault and the T4 tube fault in the unit are given, as shown in FIG. Figure 4 As shown in the figure, it can be seen from the diagnostic results that the continuous flow operation mode of this unit is relatively obvious, so F T1 and F T4 After being processed by the attenuation accelerated average model, the fault indication signal F T_D1 and F T_D4 The faulty switch can be directly located. At the same time, the difference in the fault characteristics of the pair of tubes is also reflected in the fault indication signal F U_m According to the change of the detection signal F T1 and F T4 It can be seen from the changes in that this method can realize fault detection in a very short time after the fault occurs, and the detection time is approximately the sampling time of the diagnostic signal; at the same time, based on the changes in the fault indication signal, the faulty switch tube can be located in approximately one power frequency cycle (20ms).

[0078] It should be noted that the three-phase cascade H-bridge converter mentioned in the present invention is not limited to Figure 1The converter topology shown may also be other single-phase or multi-phase converters including full-bridge units. The rough set information library, signal logic operation method and decay acceleration average model involved in the present invention are not limited to the diagnosis system design of the open-circuit fault of four power switch tubes in the full-bridge unit, but may also be the diagnosis system design of the open-circuit fault of a single or multiple power switch tubes in other converter topologies.

[0079] The above is only a preferred embodiment of the present invention, and does not limit the present invention in any form. Any technician familiar with the art can make many possible changes and modifications to the technical solution of the present invention by using the above disclosed methods and technical contents without departing from the scope of the technical solution of the present invention, or modify it into an equivalent embodiment of equivalent changes. Therefore, all equivalent changes made according to the shape, structure and principle of the present invention without departing from the content of the technical solution of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for diagnosing open circuit faults of power switches of cascaded H-bridge converters, characterized in that: The following steps are involved: Step S1: Analyze the operation mode of any full-bridge power unit in the cascaded H-bridge converter in the four quadrants, obtain the mapping relationship between the switch state and the output voltage value, and analyze the voltage and current components that change in different modes; Step S2: using rough set theory to select the simplest diagnostic variable set that characterizes all fault modes; Step S3: deriving the logical relationship between the diagnostic signal and the detection result according to each fault mode; Step S4: establishing a decay acceleration average model based on the detection results to obtain a fault indication signal; Step S5: Determine the fault location according to the fault indication signal.

2. A method for diagnosing an open circuit fault of a power switch of a cascaded H-bridge converter as claimed in claim 1, characterized in that: Define the modulation wave polarity ρ v Equivalently represents the output voltage u m The polarity, ρ c Indicates the current i m The polarity of the output voltage u m The amplitude logic signals u1 and u2 are expressed as follows: Among them, v c Indicates the modulation voltage of the converter, U ref Indicates the reference threshold.

3. A method for diagnosing an open circuit fault of a power switch of a cascaded H-bridge converter as claimed in claim 2, characterized in that: Establish a state information base of the power unit operation mode, define the condition attribute set CA and decision set DA of the information base, simplify the attributes, obtain the system's discernibility matrix, calculate the disjunctive normal form of all attributes in each row of non-empty set elements, and simplify the disjunctive normal form by conjunction operation: DP(U)=(ρ c )∧(u1)∧(u2)∧(s1∨s2)∧(s3∨s4); Rewrite it into disjunctive normal form: Among them, m1, m2, m3, and m4 represent the four conjunctions that make up DP(U); Select the attributes in item m1 as diagnostic variables.

4. A method for diagnosing an open circuit fault of a power switch of a cascaded H-bridge converter as claimed in claim 3, characterized in that: By analyzing the logical relationship of the diagnostic variables (ρc, u1, u2, s1, s3) in item m1, the logical expression indicating the open circuit fault of the switch pair (T1, T4) or (T2, T3) is obtained: It is detected whether the two groups of tubes in the full-bridge unit have an open circuit fault, and the calculation result is the detection signal of the open circuit fault.

5. A method for diagnosing open circuit faults of power switches of cascaded H-bridge converters as claimed in claim 4, characterized in that: Add analysis of the freewheeling mode and obtain the logical expressions of each switch failure: In the formula, the detection signal F T1 ~F T4 Represents the fault status of each tube. A value of 1 indicates that the corresponding switch tube is faulty, and a value of 0 indicates that the switch tube is healthy.

6. A method for diagnosing open circuit faults of power switches of cascaded H-bridge converters as claimed in claim 1, characterized in that: Establish the attenuation accelerated average model and input the detection signal, and finally obtain the fault indication signal. o The attenuation acceleration average model corresponding to each fault indication signal is: The fault indication signal (F U_m 、F T_D1 、F T_D2 、F T_D3 、F T_D4 ), the faulty switch is determined.

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