CN112731193B - NPC inverter multi-class fault diagnosis method based on sliding-mode observer - Google Patents

NPC inverter multi-class fault diagnosis method based on sliding-mode observer Download PDF

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CN112731193B
CN112731193B CN202011524499.8A CN202011524499A CN112731193B CN 112731193 B CN112731193 B CN 112731193B CN 202011524499 A CN202011524499 A CN 202011524499A CN 112731193 B CN112731193 B CN 112731193B
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current
bridge arm
power switch
current sensor
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CN112731193A (en
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许水清
王巨兴
黄文展
陶松兵
冯莉
马铭遥
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Hefei University of Technology
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Abstract

The invention provides an NPC inverter multi-class fault diagnosis method based on a sliding-mode observer, and relates to the technical field of fault diagnosis. According to the method, an improved sliding mode observer is used for establishing an accurate mathematical model, so that an observer system quickly enters a sliding mode motion state, buffeting of sliding mode motion is reduced, and the system stably runs in the sliding mode motion state; and constructing a residual error by utilizing the output of the sliding mode observer and the three-phase output current, calculating a residual error current mean value and combining the three-phase output current to realize fault diagnosis of a single switch tube and a current sensor. The method well overcomes the defects of slow approaching speed and more unstable and harmonic vibrations of the sliding mode motion of the common sliding mode observer, can carry out accurate and rapid fault diagnosis by analyzing the residual error, does not need to add an additional sensor, and reduces the cost of fault detection.

Description

NPC inverter multi-class fault diagnosis method based on sliding-mode observer
Technical Field
The invention relates to the technical field of fault diagnosis, in particular to an NPC inverter multi-class fault diagnosis method based on a sliding-mode observer.
Background
The gradual exhaustion of fossil energy brings about rapid development of the field of new energy power generation, and the inverter is taken as a core component in a new energy power generation system and has important functions of current transformation, frequency modulation, voltage regulation and the like in photovoltaic systems, wind power systems and other systems. The NPC inverter has the advantages of large output power, small output voltage and current harmonic, half-reduced voltage and switching loss borne by a switching device and the like, and is widely applied to a new energy power generation system. However, the NPC inverter includes a large number of power switching tubes and current sensors, and operates in a high salt spray, high temperature, high voltage and large current state for a long time, so the power switching tubes and the current sensors of the NPC inverter have high failure rate and low reliability. In order to ensure the safe and stable operation of the NPC inverter, the fault diagnosis of a power switch tube and a current sensor of the inverter is required to be rapid and high in reliability, and economic loss and safety accidents caused by the fact that the inverter operates for a long time under the condition that devices are damaged are avoided.
The faults of the power switching tube of the NPC inverter are divided into open-circuit faults and short-circuit faults. Short-circuit faults are difficult to diagnose because the short-circuit faults have the characteristics of large fault current, short time and the like, and the current treatment method is to add a quick fuse in a power switch tube to convert the power switch tube into the open-circuit faults. When the power switching devices have an open-circuit fault, the fault phenomenon is not easy to be perceived, and if a certain power switching device is in the open-circuit fault for a long time, overcurrent, heating and insulation damage can be caused to other power switching devices, so that the whole NPC inverter system is broken down. Meanwhile, the phenomenon of open-circuit fault of a single power switch tube is the most common phenomenon, so that the open-circuit fault diagnosis of the single power switch tube becomes especially important. The current sensor faults are classified into micro faults, offset faults, open-circuit faults and the like, wherein the open-circuit faults can cause the inverter control system not to acquire a reference current signal, so that the output current of the NPC inverter is seriously distorted, and further the whole inverter system is broken down, and therefore, the method is also particularly important for diagnosing the open-circuit faults of the current sensor.
Most of the existing inverter fault diagnosis technologies only aim at the fault of a power switching tube, and the technologies can be roughly divided into the following types:
1. the signal analysis method comprises a wavelet analysis method, a frequency spectrum analysis method and the like, and the method directly utilizes the time domain and frequency domain characteristics of the measurement signal to realize the detection and the positioning of the fault. However, such methods have long diagnostic periods and are difficult to classify and compare fault features, and are computationally intensive, often requiring the incorporation of other artificial intelligence algorithms.
2. The data driving method comprises statistical analysis, artificial intelligence quantitative algorithm and the like, and the method carries out statistics and analysis on system operation data by using a basic mathematical theory and a method to realize fault diagnosis of the system. However, such methods require a large amount of data training, and the accuracy of the data determines the accuracy of fault detection, which is difficult to be applied to the inverter system.
3. The analytical model method comprises a parameter estimation method, a state estimation method and the like, and the method generates a residual error by comparing measurable information of a diagnosed object with system prior information expressed by a mathematical model, and analyzes and processes the residual error so as to realize the identification and the positioning of faults. However, the NPC inverter is a complex nonlinear system, and how to build an accurate mathematical model becomes a difficult point.
Disclosure of Invention
The objective of the present invention is to solve the above problems in the prior art, and specifically, an improved sliding mode observer is used to establish an accurate mathematical model, which includes the noise influence in the inverter system, an exponential function is used to replace the constant approach law in the general sliding mode observer, so that the observer system rapidly enters the sliding mode motion state, an arctangent function is used to replace the sign function in the conventional sliding mode observer, thereby reducing the buffeting of the sliding mode motion, and the system stably operates in the sliding mode motion state. And then, residual errors are constructed by utilizing the output of the sliding mode observer and the three-phase output current, the mean value of the residual errors is calculated, and the fault diagnosis of a single switch tube and the single current sensor is realized by combining the three-phase output current.
The invention aims to realize the method, and provides a NPC inverter multi-class fault diagnosis method based on a sliding-mode observer, wherein a topological structure of the NPC inverter related to the diagnosis method comprises a direct-current power supply, a main inverter circuit, three same current sensors, three same inductors, three same load resistors and a control module; the three current sensors are respectively marked as current sensors MaCurrent sensor MbAnd a current sensor McThe three same inductors are respectively marked as an inductor L1, an inductor L2 and an inductor L3, and the three same load resistors are marked as a load resistor R1, a load resistor R2 and a load resistor R3;
the main inverter circuit comprises two same supporting capacitors and three-phase bridge arms, the three-phase bridge arms are respectively marked as an a-phase bridge arm, a b-phase bridge arm and a c-phase bridge arm, each phase of bridge arm comprises 4 power switch tubes with reverse parallel diodes, namely the three-phase bridge arms totally comprise 12 power switch tubes with reverse parallel diodes, and the 12 diodes are respectively marked as VjnJ represents the phase of the bridge arm, j is a, b, C, n represents the serial number of the power switching tube, n is 1, 2, 3, 4, and the two same supporting capacitors are respectively marked as a supporting capacitor C1 and a supporting capacitor C2;
the above-mentionedThe supporting capacitor C1 and the supporting capacitor C2 are connected in series and then connected between a direct current positive bus P and a direct current negative bus Q of the direct current power supply, and a common node of the supporting capacitor C1 and the supporting capacitor C2 is marked as a point O; the a-phase bridge arm, the b-phase bridge arm and the c-phase bridge arm are mutually connected in parallel between a direct current positive bus P and a direct current negative bus Q, namely a power switch tube Va1、Vb1、Vc1The input end of the power switch is connected with a direct current positive bus P and a power switch tube V after being connected in parallela4、Vb4、Vc4The output ends of the two-way switch are connected in parallel and then connected with a direct current negative bus Q; in the a-phase arm, power switch tube Va1、Va2、Va3And Va4Sequentially connected in series, in a b-phase bridge arm, a power switch tube Vb1、Vb2、Vb3And Vb4Are sequentially connected in series, and in a c-phase bridge arm, a power switch tube Vc1、Vc2、Vc3And Vc4Sequentially connecting in series;
the switch tube Va2The output end of the current sensor M is connected in series in sequenceaAn inductor L1 connected with the input end of a load resistor R1, and a switching tube Vb2The output end of the current sensor M is connected in series in sequencebAn inductor L2 connected with the input end of a load resistor R2, and a switching tube Vc2The output end of the current sensor M is connected in series in sequencecThe inductor L3 is connected with the input end of the load resistor R3, and the output ends of the load resistor R1, the load resistor R2 and the load resistor R3 are connected in parallel and then grounded;
the input end of the control module is respectively connected with a current sensor MaCurrent sensor MbCurrent sensor McThe output end of the control module is respectively connected with 12 power switch tubes Vjn；
The method for diagnosing the multiple types of faults comprises the following specific steps:
step 1, passing a current sensor MaCurrent sensor MbCurrent sensor McDetecting three-phase output current i of NPC invertera、ib、icSampling the voltage U of the DC power supplydc；
Step 2, the three-phase output current i detected in the step 1 is subjected toa、ib、icCoordinate transformation is carried out to obtain a two-phase output current alpha beta component i under a two-phase static coordinateα、iβAnd establishing a current state equation of the NPC inverter under a two-phase static coordinate system, wherein the expression is as follows:
Figure GDA0003357754040000041
wherein the content of the first and second substances,
Figure GDA0003357754040000042
for two-phase output current alpha beta component iα、iβA derivative of (a);
a is a matrix of coefficients 1 and,
Figure GDA0003357754040000043
wherein, R is the resistance values of three identical load resistors R1, R2 and R3, and L is the inductance values of three identical inductors L1, L2 and L3;
b is a matrix of coefficients 2 which are,
Figure GDA0003357754040000051
d is a second-order identity matrix,
Figure GDA0003357754040000052
f is a noise signal of the NPC inverter;
Sarepresenting the switching function of the a-phase bridge arm, SbRepresenting the b-phase bridge arm switching function, ScRepresenting c-phase bridge arm switching function, defining SjAs a function of the switching of the j-phase bridge arm and switching the power switch tube VjnIs noted as deltajn，
Figure GDA0003357754040000053
Wherein the symbol "-" represents a logical not;
step 3, building a novel sliding mode observer according to the current state equation of the NPC inverter obtained in the step 2 under the two-phase static coordinate system, wherein the expression of the novel sliding mode observer is as follows:
Figure GDA0003357754040000054
wherein the content of the first and second substances,
Figure GDA0003357754040000055
for two-phase output current alpha beta component iα、iβAn estimated value of (d);
Figure GDA0003357754040000056
for two-phase output current alpha beta component iα、iβIs estimated value of
Figure GDA0003357754040000057
A derivative of (a);
c is the coefficient matrix 3 and C is,
Figure GDA0003357754040000058
Figure GDA0003357754040000059
representing the output quantity of the novel sliding mode observer;
k1is an adjustable parameter 1, k1＞0；
k2Is an adjustable parameter 2, k2＞0；
s is the surface of the sliding form,
Figure GDA00033577540400000510
arctan () represents an arctangent function;
step 4, obtaining the output quantity of the novel sliding mode observer according to the step 3
Figure GDA00033577540400000511
Obtain three-phase output current ia、ib、icIs estimated value of
Figure GDA00033577540400000512
The expression is as follows:
Figure GDA0003357754040000061
step 5, outputting the three-phase output current ia、ib、icIs expressed as ijThree phases of output current ia、ib、icIs estimated value of
Figure GDA0003357754040000062
Is expressed as
Figure GDA0003357754040000063
Computing j-phase current residual rjAnd j-phase residual current mean value vjThe expressions are respectively:
Figure GDA0003357754040000064
Figure GDA0003357754040000065
wherein T represents the current period, T represents time, and d represents the differential;
definition of | vjL is vjCalculating absolute value | v of the mean value of the residual currents corresponding to the three phasesa|，|vb|，|vcI, then at va|，|vb|，|vcTaking the maximum value in | and marking the phase corresponding to the maximum value as an x phase;
the mean value of the residual current of the x phase is denoted as vxAnd marking the 4 power switch tubes of the bridge arm corresponding to the x as VxnAnd n is 1, 2, 3, 4, and the current sensor corresponding to x is denoted as MxX is equal toThe corresponding three-phase output current is marked as ix；
Step 6, defining x-phase fault detection characteristic quantity wxAnd making the following judgments:
|vx|≤|vF|，wxwhen the result is equal to 0, no fault occurs, and the diagnosis is finished;
|vx|＞|vF|，wx＝sign(vx) If a fault occurs, the step 7 is entered;
wherein v isFThe mean value of the residual currents due to the noise signal F of the NPC inverter,
Figure GDA0003357754040000066
Figure GDA0003357754040000067
sign () represents a sign function;
step 7, defining Z as the sum of three-phase output currents, and enabling Z to be equal to ia+ib+icDefining x-phase fault location characteristic quantity muxThe expression is as follows:
Figure GDA0003357754040000071
step 8, for the power switch tube VxnAnd a current sensor MxThe fault diagnosis of (2) is as follows:
if Z ≠ 0, then MxAn open circuit fault occurs;
if Z is 0 and w x1 and muxWhen 1, then Vx1An open circuit fault occurs;
if Z is 0 and w x1 and muxWhen the value is 0, then Vx2An open circuit fault occurs;
if Z is 0 and w x1 and muxWhen the value is 0, then Vx3An open circuit fault occurs;
if Z is 0 and w x1 and muxWhen 1 is not substituted, then Vx4An open circuit fault occurs.
Preferably, step 2 said two phase deliveryComponent i of the outgoing current α βα、iβThe transformation of (a) is as follows:
Figure GDA0003357754040000072
compared with the prior art, the invention has the beneficial effects that:
1. the novel sliding-mode observer is utilized to simultaneously realize the diagnosis of the fault of a single power switching tube and the fault of a current sensor;
2. the defects of slow approaching speed and serious slip form motion unstable resonance of a common slip form observer are well overcome;
3. the three-phase output current value and the three-phase output current construction residual error obtained by the current sensor are estimated based on the novel sliding mode observer, accurate and quick fault diagnosis can be carried out by analyzing the residual error, an additional sensor is not required to be added, and the cost of fault detection is reduced.
Drawings
FIG. 1 is a topology diagram of an NPC inverter in an embodiment of the present invention;
FIG. 2 is a flow chart of a multi-class fault diagnosis method of the NPC inverter based on the sliding-mode observer;
FIG. 3 shows a three-phase output current i according to an embodiment of the present inventiona、ib、icA simulated waveform diagram of (1);
FIG. 4 is a diagram illustrating an estimation of three-phase output current according to an embodiment of the present invention
Figure GDA0003357754040000081
A simulated waveform diagram of (1);
FIG. 5 shows the current residual r according to the embodiment of the present inventiona、rb、rcA simulated waveform diagram of (1);
FIG. 6 shows a residual current mean value v in an embodiment of the present inventiona、vb、vcA simulated waveform diagram of (1);
fig. 7 shows a fault detection result in the embodiment of the present invention.
Detailed Description
The technical solution of the present invention is further described in detail below with reference to the accompanying drawings.
Fig. 1 is a topology diagram of an NPC inverter in an embodiment of the invention. As shown in fig. 1, the topology of the NPC inverter according to the present invention includes a dc power supply, a main inverter circuit, three identical current sensors, three identical inductors, three identical load resistors, and a control module. The three current sensors are respectively marked as current sensors MaCurrent sensor MbAnd a current sensor McThe three same inductors are respectively denoted as an inductor L1, an inductor L2, and an inductor L3, and the three same load resistors are denoted as a load resistor R1, a load resistor R2, and a load resistor R3.
The main inverter circuit comprises two same supporting capacitors and three-phase bridge arms, the three-phase bridge arms are respectively marked as an a-phase bridge arm, a b-phase bridge arm and a c-phase bridge arm, each phase of bridge arm comprises 4 power switch tubes with reverse parallel diodes, namely the three-phase bridge arms totally comprise 12 power switch tubes with reverse parallel diodes, and the 12 diodes are respectively marked as VjnWhere j denotes a phase of the arm, j is a, b, C, n denotes a serial number of the power switching tube, n is 1, 2, 3, 4, and the two same support capacitors are respectively denoted as a support capacitor C1 and a support capacitor C2.
The support capacitor C1 and the support capacitor C2 are connected in series and then connected between a direct current positive bus P and a direct current negative bus Q of the direct current power supply, and a common node of the support capacitor C1 and the support capacitor C2 is marked as a point O. The a-phase bridge arm, the b-phase bridge arm and the c-phase bridge arm are mutually connected in parallel between a direct current positive bus P and a direct current negative bus Q, namely a power switch tube Va1、Vb1、Vc1The input end of the power switch is connected with a direct current positive bus P and a power switch tube V after being connected in parallela4、Vb4、Vc4The output ends of the three-phase alternating current transformer are connected in parallel and then connected with a direct current negative bus Q. In the a-phase arm, power switch tube Va1、Va2、Va3And Va4Sequentially connected in series, in a b-phase bridge arm, a power switch tube Vb1、Vb2、Vb3And Vb4Are sequentially connected in series, and in a c-phase bridge arm, a power switch tube Vc1、Vc2、Vc3And Vc4Are connected in series in sequence.
The switch tube Va2The output end of the current sensor M is connected in series in sequenceaAn inductor L1 connected with the input end of a load resistor R1, and a switching tube Vb2The output end of the current sensor M is connected in series in sequencebAn inductor L2 connected with the input end of a load resistor R2, and a switching tube Vc2The output end of the current sensor M is connected in series in sequencecThe inductor L3 is connected with the input end of the load resistor R3, and the output ends of the load resistor R1, the load resistor R2 and the load resistor R3 are connected in parallel and then grounded.
The input end of the control module is respectively connected with a current sensor MaCurrent sensor MbCurrent sensor McThe output end of the control module is respectively connected with 12 power switch tubes Vjn. The output of the control module is a power switch tube VjnControl signals of, i.e. power switching tubes VjnOf the switching signal deltajn。
Fig. 2 is a flowchart of the multi-class fault diagnosis method of the NPC inverter based on the sliding-mode observer, and it can be seen from the diagram that the steps of the diagnosis method of the present invention are as follows:
step 1, passing a current sensor MaCurrent sensor MbCurrent sensor McDetecting three-phase output current i of NPC invertera、ib、icSampling the voltage U of the DC power supplydc. In this embodiment, Udc＝500V。
Step 2, the three-phase output current i detected in the step 1 is subjected toa、ib、icCoordinate transformation is carried out to obtain a two-phase output current alpha beta component i under a two-phase static coordinateα、iβAnd establishing a current state equation of the NPC inverter under the two-phase static coordinate system.
The two-phase output current α β component iα、iβThe transformation of (a) is as follows:
Figure GDA0003357754040000101
the expression of the current state equation of the NPC inverter in the two-phase static coordinate system is as follows:
Figure GDA0003357754040000102
wherein the content of the first and second substances,
Figure GDA0003357754040000103
for two-phase output current alpha beta component iα、iβA derivative of (a);
a is a matrix of coefficients 1 and,
Figure GDA0003357754040000104
wherein, R is the resistance values of three identical load resistors R1, R2 and R3, and L is the inductance values of three identical inductors L1, L2 and L3;
b is a matrix of coefficients 2 which are,
Figure GDA0003357754040000105
d is a second-order identity matrix,
Figure GDA0003357754040000106
f is a noise signal of the NPC inverter;
Sarepresenting the switching function of the a-phase bridge arm, SbRepresenting the b-phase bridge arm switching function, ScRepresenting c-phase bridge arm switching function, defining SjAs a function of the switching of the j-phase bridge arm and switching the power switch tube VjnIs noted as deltajn，
Figure GDA0003357754040000107
Wherein the symbol "-" represents a logical not.
In this embodiment, L is 0.08H, R is 10 Ω, k1＝50，k2Given F500.01 sin (100 tt).
Step 3, building a novel sliding mode observer according to the current state equation of the NPC inverter obtained in the step 2 under the two-phase static coordinate system, wherein the expression of the novel sliding mode observer is as follows:
Figure GDA0003357754040000111
wherein the content of the first and second substances,
Figure GDA0003357754040000112
for two-phase output current alpha beta component iα、iβAn estimated value of (d);
Figure GDA0003357754040000113
for two-phase output current alpha beta component iα、iβIs estimated value of
Figure GDA0003357754040000114
A derivative of (a);
c is the coefficient matrix 3 and C is,
Figure GDA0003357754040000115
Figure GDA0003357754040000116
representing the output quantity of the novel sliding mode observer;
k1is an adjustable parameter 1, k1＞0；
k2Is an adjustable parameter 2, k2＞0；
s is the surface of the sliding form,
Figure GDA0003357754040000117
arctan () represents an arctangent function.
In the new type of sliding-mode observer,
Figure GDA0003357754040000118
so that the system has good dynamic response, arctan (k), when far away from the sliding mode surface2s) the system can effectively restrain buffeting when moving on the sliding mode surface, so that the estimated state quantity can track the state quantity more quickly and accurately.
Step 4, obtaining the output quantity of the novel sliding mode observer according to the step 3
Figure GDA0003357754040000119
Obtain three-phase output current ia、ib、icIs estimated value of
Figure GDA00033577540400001110
The expression is as follows:
Figure GDA00033577540400001111
step 5, outputting the three-phase output current ia、ib、icIs expressed as ijThree phases of output current ia、ib、icIs estimated value of
Figure GDA00033577540400001112
Is expressed as
Figure GDA00033577540400001113
Computing j-phase current residual rjAnd j-phase residual current mean value vjThe expressions are respectively:
Figure GDA0003357754040000121
Figure GDA0003357754040000122
where T denotes the current period, T denotes time, and d denotes differentiation.
Definition of | vjIs |vjCalculating absolute value | v of the mean value of the residual currents corresponding to the three phasesa|，|vb|，|vcI, then at va|，|vb|，|vcTaking the maximum value in |, and marking the phase corresponding to the maximum value as the x phase.
The mean value of the residual current of the x phase is denoted as vxAnd marking the 4 power switch tubes of the bridge arm corresponding to the x as VxnAnd n is 1, 2, 3, 4, and the current sensor corresponding to x is denoted as MxLet x correspond to three-phase output current as ix。
Step 6, defining x-phase fault detection characteristic quantity wxAnd making the following judgments:
|vx|≤|vF|，wxwhen the result is equal to 0, no fault occurs, and the diagnosis is finished;
|vx|＞|vF|，wx＝sign(vx) If a failure occurs, the process proceeds to step 7.
Wherein v isFThe mean value of the residual currents due to the noise signal F of the NPC inverter,
Figure GDA0003357754040000123
Figure GDA0003357754040000124
sign () represents a sign function.
Step 7, defining Z as the sum of three-phase output currents, and enabling Z to be equal to ia+ib+icDefining x-phase fault location characteristic quantity muxThe expression is as follows:
Figure GDA0003357754040000125
step 8, for the power switch tube VxnAnd a current sensor MxThe fault diagnosis of (2) is as follows:
if Z ≠ 0, then MxAn open circuit fault occurs;
if Z is 0 and w x1 and muxWhen 1, then Vx1An open circuit fault occurs;
if Z is 0 and w x1 and muxWhen the value is 0, then Vx2An open circuit fault occurs;
if Z is 0 and w x1 and muxWhen the value is 0, then Vx3An open circuit fault occurs;
if Z is 0 and w x1 and muxWhen 1 is not substituted, then Vx4An open circuit fault occurs.
The invention was verified by simulation.
FIG. 3 is a diagram of a current sensor M according to an embodiment of the present inventiona、Mb、McObtained three-phase output current i of NPC invertera、ib、icIt can be seen from the simulation waveform diagram of (1), after 0.062 seconds, the three-phase output current ia、ib、icA large change occurs iaThe upper half of the waveform of (1) is partially lostb、icThe waveform of (a) slightly changes.
FIG. 4 shows the output of the sliding mode observer in the normal state
Figure GDA0003357754040000132
Obtaining estimated value of three-phase output current by Clarke inverse transformation
Figure GDA0003357754040000131
The simulation oscillogram of (2) can be seen, and the estimated value of the three-phase output current is smoother.
FIG. 5 shows the three-phase current residual ra、rb、rcThe simulation oscillogram of (1) can be seen, the three-phase current residual error ra、rb、rcNear zero before 0.062 seconds and r after 0.062 secondsaBecomes a positive value of periodic variation of amplitude, rb、rcBecome negative with periodic changes in amplitude.
FIG. 6 shows the mean value v of the three-phase residual currenta、vb、vcThe simulation waveform of (2) shows the absolute value | v of the mean value of the residual current of the a-phaseaI.e., maximum, so phase a is defined as phase x.
FIG. 7 is a diagram of the results of the fault detection, as can be seen, at time 0.062 seconds, waChanges from 0 to 1, so 0.062 second a phase of a certain power switch tube or current sensor MaWhen an open-circuit fault occurs and the sum Z of the three-phase output currents is 0, a certain power switch tube v can be determinedanOpen circuit fault occurs, and the characteristic quantity mu is positioned because of the fault at the time of 0.062 secondaTo 1, a specific diagnostic method w according to the inventiona＝1，Z＝0，μaPower switch tube v at 0.062 second moment is judged as 1a1An open circuit fault occurs.

Claims (2)

1. A NPC inverter multi-class fault diagnosis method based on a sliding-mode observer is disclosed, wherein a topological structure of the NPC inverter related to the diagnosis method comprises a direct-current power supply, a main inverter circuit, three same current sensors, three same inductors, three same load resistors and a control module; the three current sensors are respectively marked as current sensors MaCurrent sensor MbAnd a current sensor McThe three same inductors are respectively marked as an inductor L1, an inductor L2 and an inductor L3, and the three same load resistors are marked as a load resistor R1, a load resistor R2 and a load resistor R3;
the main inverter circuit comprises two same supporting capacitors and three-phase bridge arms, the three-phase bridge arms are respectively marked as an a-phase bridge arm, a b-phase bridge arm and a c-phase bridge arm, each phase of bridge arm comprises 4 power switch tubes with reverse parallel diodes, namely the three-phase bridge arms totally comprise 12 power switch tubes with reverse parallel diodes, and the 12 diodes are respectively marked as VjnJ represents the phase of the bridge arm, j is a, b, C, n represents the serial number of the power switching tube, n is 1, 2, 3, 4, and the two same supporting capacitors are respectively marked as a supporting capacitor C1 and a supporting capacitor C2;
the supporting capacitor C1 and the supporting capacitor C2 are connected in series and then connected between a direct current positive bus P and a direct current negative bus Q of a direct current power supply, and a common node of the supporting capacitor C1 and the supporting capacitor C2 is marked as a point O; the a-phase bridge arm, the b-phase bridge arm and the c-phase bridge arm are mutually connected in parallel between a direct current positive bus P and a direct current negative bus Q, namely the power switchPipe Va1、Vb1、Vc1The input end of the power switch is connected with a direct current positive bus P and a power switch tube V after being connected in parallela4、Vb4、Vc4The output ends of the two-way switch are connected in parallel and then connected with a direct current negative bus Q; in the a-phase arm, power switch tube Va1、Va2、Va3And Va4Sequentially connected in series, in a b-phase bridge arm, a power switch tube Vb1、Vb2、Vb3And Vb4Are sequentially connected in series, and in a c-phase bridge arm, a power switch tube Vc1、Vc2、Vc3And Vc4Sequentially connecting in series;
the switch tube Va2The output end of the current sensor M is connected in series in sequenceaAn inductor L1 connected with the input end of a load resistor R1, and a switching tube Vb2The output end of the current sensor M is connected in series in sequencebAn inductor L2 connected with the input end of a load resistor R2, and a switching tube Vc2The output end of the current sensor M is connected in series in sequencecThe inductor L3 is connected with the input end of the load resistor R3, and the output ends of the load resistor R1, the load resistor R2 and the load resistor R3 are connected in parallel and then grounded;
the input end of the control module is respectively connected with a current sensor MaCurrent sensor MbCurrent sensor McThe output end of the control module is respectively connected with 12 power switch tubes Vjn；
The method is characterized by comprising the following specific steps:
step 1, passing a current sensor MaCurrent sensor MbCurrent sensor McDetecting three-phase output current i of NPC invertera、ib、icSampling the voltage U of the DC power supplydc；
Step 2, the three-phase output current i detected in the step 1 is subjected toa、ib、icCoordinate transformation is carried out to obtain a two-phase output current alpha beta component i under a two-phase static coordinateα、iβAnd establishing a current state equation of the NPC inverter under a two-phase static coordinate system, wherein the expression is as follows:
Figure FDA0003357754030000021
wherein the content of the first and second substances,
Figure FDA0003357754030000022
for two-phase output current alpha beta component iα、iβA derivative of (a);
a is a matrix of coefficients 1 and,
Figure FDA0003357754030000023
wherein, R is the resistance values of three identical load resistors R1, R2 and R3, and L is the inductance values of three identical inductors L1, L2 and L3;
b is a matrix of coefficients 2 which are,
Figure FDA0003357754030000024
d is a second-order identity matrix,
Figure FDA0003357754030000025
f is a noise signal of the NPC inverter;
Sarepresenting the switching function of the a-phase bridge arm, SbRepresenting the b-phase bridge arm switching function, ScRepresenting c-phase bridge arm switching function, defining SjAs a function of the switching of the j-phase bridge arm and switching the power switch tube VjnIs noted as deltajn，
Figure FDA0003357754030000031
Wherein the symbol "-" represents a logical not;
step 3, building a novel sliding mode observer according to the current state equation of the NPC inverter obtained in the step 2 under the two-phase static coordinate system, wherein the expression of the novel sliding mode observer is as follows:
Figure FDA0003357754030000032
wherein the content of the first and second substances,
Figure FDA0003357754030000033
for two-phase output current alpha beta component iα、iβAn estimated value of (d);
Figure FDA0003357754030000034
for two-phase output current alpha beta component iα、iβIs estimated value of
Figure FDA0003357754030000035
A derivative of (a);
c is the coefficient matrix 3 and C is,
Figure FDA0003357754030000036
Figure FDA0003357754030000037
representing the output quantity of the novel sliding mode observer;
k1is an adjustable parameter 1, k1＞0；
k2Is an adjustable parameter 2, k2＞0；
s is the surface of the sliding form,
Figure FDA0003357754030000038
arctan () represents an arctangent function;
step 4, obtaining the output quantity of the novel sliding mode observer according to the step 3
Figure FDA0003357754030000039
Obtain three-phase output current ia、ib、icIs estimated value of
Figure FDA00033577540300000310
The expression is as follows:
Figure FDA00033577540300000311
step 5, outputting the three-phase output current ia、ib、icIs expressed as ijThree phases of output current ia、ib、icIs estimated value of
Figure FDA00033577540300000312
Is expressed as
Figure FDA00033577540300000313
Computing j-phase current residual rjAnd j-phase residual current mean value vjThe expressions are respectively:
Figure FDA0003357754030000041
Figure FDA0003357754030000042
wherein T represents the current period, T represents time, and d represents the differential;
definition of | vjL is vjCalculating absolute value | v of the mean value of the residual currents corresponding to the three phasesa|，|vb|，|vcI, then at va|，|vb|，|vcTaking the maximum value in | and marking the phase corresponding to the maximum value as an x phase;
the mean value of the residual current of the x phase is denoted as vxAnd marking the 4 power switch tubes of the bridge arm corresponding to the x as VxnAnd n is 1, 2, 3, 4, and the current sensor corresponding to x is denoted as MxOutputs the three phases of x corresponding to each otherStream is denoted as ix；
Step 6, defining x-phase fault detection characteristic quantity wxAnd making the following judgments:
|vx|≤|vF|，wxwhen the result is equal to 0, no fault occurs, and the diagnosis is finished;
|vx|＞|vF|，wx＝sign(vx) If a fault occurs, the step 7 is entered;
wherein v isFThe mean value of the residual currents due to the noise signal F of the NPC inverter,
Figure FDA0003357754030000043
Figure FDA0003357754030000044
sign () represents a sign function;
step 7, defining Z as the sum of three-phase output currents, and enabling Z to be equal to ia+ib+icDefining x-phase fault location characteristic quantity muxThe expression is as follows:
Figure FDA0003357754030000045
step 8, for the power switch tube VxnAnd a current sensor MxThe fault diagnosis of (2) is as follows:
if Z ≠ 0, then MxAn open circuit fault occurs;
if Z is 0 and wx1 and muxWhen 1, then Vx1An open circuit fault occurs;
if Z is 0 and wx1 and muxWhen the value is 0, then Vx2An open circuit fault occurs;
if Z is 0 and wx1 and muxWhen the value is 0, then Vx3An open circuit fault occurs;
if Z is 0 and wx1 and muxWhen 1 is not substituted, then Vx4An open circuit fault occurs.
2. The NPC inverter multi-class fault diagnosis method based on the sliding-mode observer according to claim 1, characterized in that the two-phase output current α β component i in the step 2α、iβThe transformation of (a) is as follows:
Figure FDA0003357754030000051
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