CN111624514A

CN111624514A - Method for diagnosing short-circuit and open-circuit faults of switching tube of three-level rectifier

Info

Publication number: CN111624514A
Application number: CN202010629019.8A
Authority: CN
Inventors: 朱叶; 徐冰心; 丁宇劼; 张海龙; 王恩荣
Original assignee: Nanjing Normal University
Current assignee: Nanjing Normal University
Priority date: 2020-07-02
Filing date: 2020-07-02
Publication date: 2020-09-04
Anticipated expiration: 2040-07-02
Also published as: CN111624514B

Abstract

The invention discloses a method for diagnosing short-circuit and open-circuit faults of a switching tube of a three-level rectifier, which selects a switching state, a bridge arm phase voltage, the polarity of alternating-current side phase current and clamping diode current as fault characteristics, analyzes the short-circuit and open-circuit fault characteristics under different switching states based on a current circulation path, provides a fault diagnosis rule and realizes the short-circuit and open-circuit fault diagnosis of the switching tube of a diode neutral-point clamped (NPC) three-level rectifier. The method can simultaneously detect short-circuit and open-circuit faults, accurately position the fault position, realize quick diagnosis and have high reliability.

Description

Method for diagnosing short-circuit and open-circuit faults of switching tube of three-level rectifier

Technical Field

The invention belongs to the power electronic device fault diagnosis technology, and particularly relates to a method for diagnosing short-circuit and open-circuit faults of a switching tube of a three-level rectifier.

Background

Compared with the traditional two-level rectifier, the three-level rectifier has the advantages of low voltage stress of a power device, good waveform frequency spectrum, small voltage change rate, small waveform distortion and the like, and is widely applied to medium-voltage and high-power electric energy conversion and electric transmission occasions. The three-level rectifier has been developed to date, and a large number of topologies are generated, and the basic topologies of the three-level rectifier mainly include a midpoint clamping type, a cascade type, a flying capacitor type, and the like. Among them, the Neutral Point Clamped (NPC) rectifier has been widely used in practice because of its simple topology, relatively stable performance, and easy control of devices.

Despite significant technological advances in this area, semiconductors and their associated circuitry remain the primary cause of failure in industrial applications. According to the study, printed circuit boards resulted in about 26% of circuit equipment failures, while semiconductor and solder failures resulted in about 34% of power equipment failures. Power switch failures are typically caused by high thermal or electrical stress, which can lead to short circuit and open circuit failures. Failure of the gate driver or other control circuit is also a very important cause of converter failure, accounting for 53.1% of all converter failures. Such failures are typically caused by interruption of the Insulated Gate Bipolar Transistor (IGBT) activation signal, resulting in a permanent IGBT open failure. At present, current and voltage signals of a certain time are needed for detecting the open-circuit fault of the three-level rectifier, a large amount of mathematical processing is needed, the algorithm is complex, the training requirement on the algorithm is high, the method is not suitable for popularization and use, and no method can be used for simultaneously detecting the short-circuit fault and the open-circuit fault of the rectifier.

Disclosure of Invention

The purpose of the invention is as follows: in order to overcome the defects of the prior art, the invention provides a method for diagnosing the short-circuit and open-circuit faults of the switching tube of the three-level rectifier.

The technical scheme is as follows: a method for diagnosing short-circuit and open-circuit faults of a switching tube of a three-level rectifier comprises the following steps:

(1) detecting and collecting operation data of the diode neutral point clamped three-level rectifier circuit, wherein the operation data comprises a switching state, a bridge arm phase voltage, the polarity of an alternating current side phase current and a clamping diode current;

(2) the model of the diode neutral point clamping type three-level rectifier carries out fault classification according to the short circuit state and the open circuit state of a circuit, and the fault classification comprises the following three types:

a type: no switching device fails;

b type: only one switching device has a short-circuit fault;

class C: only one switching device has an open circuit fault;

(3) based on a current circulation path method, the NPC three-level rectifier circuit working in different switching states is subjected to fault characteristic analysis according to B-type short-circuit faults or C-type open-circuit faults respectively to obtain single-tube short-circuit fault or open-circuit diagnosis information, and the single-tube short-circuit fault or open-circuit diagnosis information is correspondingly input into a single-tube short-circuit fault diagnosis module or a single-tube open-circuit fault diagnosis module to carry out fault diagnosis and determine the fault type.

Furthermore, 4 IGBT switching devices S connected in series for each phase bridge arm in B type_x1-S_x4The method comprises the following steps of:

(A101) switching device S for a-phase bridge arm_a1The short-circuit fault diagnosis process is as follows:

when the current on the a-phase cross current side is in the negative direction, the a-phase bridge arm is in an O state, if the clamping diode VD_a2When the current flowing in the upper circuit is not 0, the switching device S is judged_a1A short circuit occurs;

when the current on the cross current side of a is in the positive direction, if the clamping diode VD_a1Without current, clamping diode VD_a2Has current and a cross current side current is not equal to VD of the clamping diode_a2Upper current, determining the switching device S_a1A short circuit occurs;

(A102) switching device S for a-phase bridge arm_a4The short-circuit fault diagnosis process is as follows:

when the switching state of the a-phase bridge arm is in an O state and the current on the a-phase current-crossing side is in a positive direction, if the clamping diode VD_a1Is supplied with current, determines the switching device S_a4Short circuit failure;

when the current on the cross current side of a is in the negative direction, if the clamping diode VD_a1Upper current, VD_a2Has no current, and a intersects with the current on the current side and VD_a1When the currents are not equal, the switching device S is determined_a4Short circuit failure;

(A103) switching device S for a-phase bridge arm_a3The short-circuit fault diagnosis process is as follows:

when the a-phase bridge arm is in a P switch state, if the clamping diode VD_a2The current flowing in the upper circuit is not 0, and the switching device S is judged_a3Short-circuiting;

(A104) switching device S for a-phase bridge arm_a2The short-circuit fault diagnosis process is as follows:

when the switching state of the a-phase bridge arm is N, if the clamping diode VD_a1The current flowing in the upper circuit is not 0, and the switching device S is judged_a2Short-circuit failure occurs;

(B101) switching device S for b-phase bridge arm_b1The process of diagnosing the occurrence of the short-circuit fault is as follows:

when the current on the cross current side of the phase b is in the negative direction, the bridge arm of the phase b is in an O state, if the clamping diode VD is adopted_b2When the current flowing in the upper circuit is not 0, the switching device S is judged_b1A short circuit occurs;

when the current on the cross current side of the b is in the positive direction, if the clamping diode VD_b1Without current, clamping diode VD_b2Has current and b cross current side current is not equal to the clamp diode VD_b2Upper current, determining the switching device S_b1Short-circuit failure occurs;

(B102) switching device S for b-phase bridge arm_b4The short-circuit fault judgment process is as follows:

when the switching state of the b-phase bridge arm is in an O state and the current on the side of the b-phase cross current is in a positive direction, if the clamping diode VD_b1Is supplied with current, determines the switching device S_b4Short-circuiting;

when the current on the cross current side of b is in the negative direction, if the clamping diode VD_b1Upper current, VD_b2Has no current, and b intersects with VD_b1When the currents are not equal, the switching device S is determined_b4Short-circuiting;

(B103) switching device S for b-phase bridge arm_b3The short-circuit fault judgment process is as follows:

when the b-phase bridge arm is in a P switch state, if the clamping diode VD_b2The current flowing in the upper circuit is not 0, and the switching device S is judged_b3Short-circuiting;

(B104) switching device S for b-phase bridge arm_b2The short-circuit fault judgment process is as follows:

when the switching state of the b-phase bridge arm is N, if the clamping diode VD_b1The current flowing in the upper circuit is not 0, and the switching device S is judged_b2Short-circuit failure occurs;

(C101) switching device S for c-phase bridge arm_c1The short-circuit fault judgment process is as follows:

when the current on the cross current side of the c phase is in the negative direction, the c-phase bridge arm is in an O state, and the clamping diode VD_c2When the current flowing in the upper circuit is not 0, the switching device S is judged_c1A short circuit occurs;

when the current on the side of the c cross current is in the positive direction, if the clamping diode VD_c1Without current, clamping diode VD_c2Has current and c cross current side current is not equal to the clamp diode VD_c2Upper current, determining the switching device S_c1Short-circuit failure occurs;

(C102) switching device S_c4The short-circuit fault judgment process is as follows:

when the switching state of the c-phase bridge arm is in an O state and the current on the side of the c-phase current intersection is in the positive direction, if the clamping diode VD_c1Is supplied with current, determines the switching device S_c4Short-circuiting;

when the current on the side of the cross current is in the negative direction, if the clamping diode VD_c1Upper current, VD_c2C has no current, and c has a current crossing with VD_c1When the currents are not equal, the switching device S is determined_c4Short-circuiting;

(C103) switching device S_c3The short-circuit fault judgment process is as follows:

when the c-phase bridge arm is in a P switch state, if the clamping diode VD_c2The current flowing in the upper circuit is not 0, and the switching device S is judged_c3Short-circuiting;

(C104) switching device S_c2The short-circuit fault judgment process is as follows:

when the switching state of the c-phase bridge arm is N, if the clamping diode VD_c1The current flowing in the upper circuit is not 0, and the switching device S is judged_c2A short-circuit fault occurs.

Further, to the switching device S_a1-S_a4The steps for diagnosing the single-tube open-circuit fault characteristics are as follows:

(A201) switching device S for a-phase bridge arm_a1The single-tube open-circuit fault characteristic diagnosis method comprises the following steps:

when the a-phase load current is in a positive direction and the a-phase switch state is P, no fault occurs;

when the load current of the a-phase is in the negative direction and the switching state of the a-phase is P, if the load current flows through the clamping diode VD_a1Is not 0, and the voltage U_anIs not equal to U_dc1The AC side phase current is equal to the clamp diode VD_a1Upper current, determining the switching device S_a1An open circuit fault occurs;

(A202) switching device S for a-phase bridge arm_a4The single-tube open-circuit fault characteristic diagnosis method comprises the following steps:

when the a-phase switch state is N, the a-phase load current is in the positive direction, and if the a-phase load current flows through the clamping diode D_a2Is not 0 and phase voltage Uan is not equal to U_dc2Then, the switching device S is determined_a4Opening a circuit;

(A203) switching device S for a-phase bridge arm_a2The single-tube open-circuit fault characteristic diagnosis method comprises the following steps:

in the P state, i_a<At 0, if there is no current on the a phase, the clamping diode VD_a1The current at is also 0, and U_an<0, determination of the switching device S_a2Single tube open circuit failure;

in the O state, when i_a>When 0, the rectifier does not fail; when i is_a<At 0, the switch state is changed from O to N; the conditions for judging the fault at this time are as follows: ia<At 0, the clamping diode VD_a1No current above, phase voltage U_an<0；For distinguishing from short-circuit fault, time-alternating side phase current i different from short-circuit fault_aIs equal to the clamping diode VD_a1A current on the substrate;

(A204) switching device S for a-phase bridge arm_a3The single-tube open-circuit fault characteristic diagnosis method comprises the following steps:

if the fault occurs in the N state, i_a>At 0, there is no current on the a phase, the clamping diode VD_a2Upper current is 0, and U_an>0；

If the fault occurs in the O state, when i_a>At 0, the clamping diode VD_a2No current above, phase voltage U_an>0, time alternating side phase current i different from short-circuit fault_aIs equal to the clamping diode VD_a2A current on the substrate;

(B201) s for b-phase bridge arm_b1The single-tube open-circuit fault characteristic diagnosis process is as follows:

when the b-phase load current is in a positive direction and the b-phase switch state is P, no fault occurs;

when the b-phase load current is in the negative direction and the b-phase switch state is P, if a fault occurs, the fault flows through the clamping diode VD_b1Is not 0, and the voltage U_bnIs not equal to U_dc1. The phase current on the AC side is equal to the voltage of the clamping diode VD_b1Upper current, unlike a short circuit fault;

(B202) s for b-phase bridge arm_b4The single-tube open-circuit fault characteristic diagnosis process is as follows:

when the b-phase switch state is N, the b-phase load current is in the positive direction, and when the b-phase switch state is N, the b-phase load current flows through the clamping diode D_b2Is not 0 and phase voltage Ubn is not equal to U_dc2Then, the switching device S is determined_b4Open circuit failure;

(B203) s for b-phase bridge arm_b2The single-tube open-circuit fault characteristic diagnosis process is as follows:

when switching device S_b2When open-circuit fault occurs, the b-phase bridge arm only has N state and i_b>The O state at 0 is valid;

when a fault occurs in the P state, i_b<At 0, no current is in phase b, and the clamping diode VD_b1The current at is also 0, and U_bn<0；

If the fault occurs in the O state, when i_b>At 0, the rectifier will not fail. When i is_b<At 0, the switch state is changed from O to N; when i is_b<At 0, the clamping diode VD_b1No current above, phase voltage U_bn<0; decision switch device S_b4Open circuit failure;

(B204) s for b-phase bridge arm_b3The single-tube open-circuit fault characteristic diagnosis process is as follows:

when switching device S_b3When open-circuit fault occurs, the b-phase bridge arm only has P state and i_b<The O state at 0 is valid;

if the fault occurs in the N state, i_b>At 0, no current is in phase b, and the clamping diode VD_b2Upper current is 0, and U_bn>0；

If the fault occurs in the O state, when i_b>At 0, the clamping diode VD_b2No current above, phase voltage U_bn>0, alternating side phase current i_bIs equal to the clamping diode VD_b2A current on the substrate;

(C201) s for c-phase bridge arm_c1The single-tube open-circuit fault characteristic diagnosis process is as follows:

when the c-phase load current is in a positive direction and the c-phase switch state is P, no fault occurs;

when the c-phase load current is in the negative direction and the c-phase switch state is P, if a fault occurs, the fault flows through the clamping diode VD_c1Is not 0, and the voltage U_cnIs not equal to U_dc1；

(C202) S for c-phase bridge arm_c4The single-tube open-circuit fault characteristic diagnosis process is as follows:

when switching device S_c4When an open-circuit fault occurs, the state of the switch of the c-phase bridge arm N is only influenced;

when the c-phase switch state is N, the c-phase load current is in the positive direction, and when the c-phase load current flows through the clamping diode D_c2Is not 0, and the phase voltage U_cnIs not equal to U_dc2Then, the switching device S is determined_c4Open circuit failure;

(C203) s for c-phase bridge arm_c2The single-tube open-circuit fault characteristic diagnosis process is as follows:

when switching device S_c2When open-circuit fault occurs, the c-phase bridge arm only has N state and i_c>The O state at 0 is valid. When a fault occurs in the P state, i_c<At 0, no current is on the c-phase, the clamping diode VD_c1The current at is also 0, and U_cn<0；

If the fault occurs in the O state, when i_c>At 0, the rectifier will not fail. When i is_c<At 0, the switch state is changed from O to N; when i is_c<When 0, if the clamping diode VD_c1No current above, phase voltage U_cn<0, determination of S_c2Single tube open circuit failure;

(C204) s for c-phase bridge arm_c3The single-tube open-circuit fault characteristic diagnosis process is as follows:

when switching device S_c3When open-circuit fault occurs, the c-phase bridge arm only has P state and i_c<The O state at 0 is valid;

if the fault occurs in the N state, i_c>At 0, no current is on the c-phase, the clamping diode VD_c2Upper current is 0, and U_cn>0；

If the fault occurs in the O state, when i_c>At 0, the clamping diode VD_c2No current above, phase voltage U_cn>0, time alternating side phase current i different from short-circuit fault_cIs equal to the clamping diode VD_c2The current in the capacitor.

Further, in the method, for the switching device S_a1-S_a4And fault output is always kept after the short circuit or open circuit fault of the single tube is judged.

Furthermore, the diagnostic failure categories in the method have 25 cases, wherein the A category is 1 category, the B category comprises 12 categories, and the C category comprises 12 categories.

Furthermore, the method is used for switching the tube S_a1-S_a4When a fault occurs, the fault diagnosis module outputs a high level.

Has the advantages that: compared with the prior art, the invention can simultaneously detect the short circuit or short circuit fault of a single switch tube. The method realizes the diagnosis of the open-circuit short-circuit fault of the switching tube of the NPC three-level rectifier by utilizing the switching state, the bridge arm phase voltage, the alternating current polarity and the clamping two-turn-off current. Compared with the fault diagnosis method based on the signals, the diagnosis method does not need to process the fault diagnosis signal, and the short-circuit and open-circuit faults can be directly identified according to the characteristics of the selected signals. Compared with the fault diagnosis method based on knowledge, the method can realize online diagnosis, does not need to learn and train a large amount of fault data, and greatly reduces the workload. In addition, the diagnosis method does not need to carry out complex algorithm operation, and has simple logic diagnosis thought, high diagnosis speed and high reliability.

Drawings

FIG. 1(a) is a schematic diagram of forward current when the switch state is 'P' in the embodiment;

FIG. 1(b) is a schematic diagram showing the flow of forward current when the switch state is 'O' in the embodiment;

FIG. 1(c) shows that when the bridge arm is in 'N' state, the forward current passes through S_x3And S_x4The current of (a); a schematic diagram;

FIG. 1(d) shows the case where the switch state is 'P' in the embodiment, the current passes through S from the positive pole of the DC side_x1，S_x2A current schematic of (a);

in the embodiment of FIG. 1(e), when the bridge arm is in the 'O' state, the current passes through the neutral point D from the DC side_x1，S_x2A schematic diagram of the path to the bridge arm termination point;

FIG. 1(f) shows the state of the switch at 'N' in the embodiment, D_x3And D_x4Providing a current path;

fig. 2(a) is a schematic diagram of a current flow path before a short-circuit fault occurs in the switching device when the current on the current-intersecting side is in a negative direction;

fig. 2(b) is a schematic diagram of a current flow path after a short-circuit fault occurs in the switching device when the current on the current-intersecting side of a is in a negative direction;

fig. 2(c) is a current flow path diagram before the switching device fails when the current on the cross current side a is in the positive direction;

fig. 2(d) is a current flow path diagram after the switching device has failed when the current on the cross current side of a is in the positive direction;

FIG. 3(a) is a switching device S_a3A schematic diagram of a current flow path before short circuit;

FIG. 3(b) is a switching device S_a3A schematic diagram of a current circulation path after short circuit;

FIG. 4 switching device S_a1Schematic diagram of current circulation path before and after open circuit.

Detailed Description

For the purpose of explaining the technical solution disclosed in the present invention in detail, the following description is further made with reference to the accompanying drawings and specific embodiments.

The invention provides a method for diagnosing short-circuit and open-circuit faults of a switching tube of a three-level rectifier, which specifically comprises the following steps:

(S1) the switching state, the bridge arm phase voltage, the polarity of the ac side current, and the clamp diode current of the diode NPC three-level rectifier circuit are selected as the fault characteristics. Each phase of the NPC three-level rectifier is formed by connecting 4 IGBT switching devices in series, each switching device is connected with 1 freewheeling diode in anti-parallel, and a three-phase bridge arm is connected with two capacitors C connected in series in parallel₁,C₂. Two IGBT switching devices in the middle of each phase are connected with two diodes connected in series in parallel, and the middle point of the two diodes connected in series is connected with two series capacitors C₁,C₂At the midpoint of (i.e. V)_dAt the voltage of/2, the middle points (a, b and C) of 4 series-connected IGBT switching devices of each phase are input and connected with a corresponding three-phase power supply, the alternating-current side phase current is the current output by the power supply of each phase, and the bridge arm phase voltage is the middle point (a, b and C) of each phase and 2 series-connected capacitors C₁，C₂The switching state is a driving signal for controlling the on and off of the 4 series-connected IGBT switching devices, and the NPC three-level rectifier has three switching states, which are P, O, N respectively. The P state is a driving signal for controlling the upper 2 IGBT switching devices of each phase to be switched on and the lower 2 IGBT switching devices of each phase to be switched off, and the O state is a driving signal for controlling the middle 2 IGBT switching devices of each phase to be switched onThe N state is a driving signal for controlling the lower 2 IGBT switching devices of each phase to be switched on and the upper two IGBT switching devices to be switched off.

(S2) a model of the NPC three-level rectifier is established, and fault classification is carried out according to actual operation single-tube open circuit and single-tube short circuit faults, wherein the three types of the faults are 25.

1) The first type: and (4) normally operating, and no switching device generates short-circuit open-circuit fault.

2) The second type: short-circuit fault occurs to only one switching device, namely, each phase bridge arm is provided with 4 IGBT switching devices (S) connected in series_x1-S_x4And short-circuit faults occur in any one of the switching tubes of i, b and c), and the number of the switching tubes is 12.

3) In the third category: only one switching device has open-circuit fault, namely 4 IGBT switching devices (S) connected in series in each phase bridge arm_x1-S_x4And the open-circuit fault occurs in any one of the switching tubes i, a, b and c), and the number of the switching tubes is 12.

(S3) in view of circuit symmetry, taking an A-phase bridge arm as an example, performing single-tube short-circuit fault characteristic analysis of the second type in the step (2) on four switching tubes working in a P, O, N state to obtain a single-tube short-circuit fault diagnosis basis, inputting the single-tube short-circuit fault diagnosis basis to a single-tube short-circuit fault diagnosis module for diagnosis, and diagnosing 13 types of first type and second type faults of the NPC three-level rectifier.

(S4) performing single-tube open-circuit fault characteristic analysis of the second type in the step (2) on four switching tubes of the a-phase bridge arm in a P, O, N state to obtain a single-tube open-circuit fault diagnosis basis, inputting the single-tube open-circuit fault diagnosis basis to the single-tube open-circuit fault diagnosis module for diagnosis, and diagnosing a third type of faults of the NPC three-level rectifier under 12 conditions.

Specifically, fig. 1 shows a current flowing path of the three-phase NPC rectifier based on the switching states and a flowing direction of the phase current, each phase arm can output three switching states, ('P' and 'O' and 'N'), and the corresponding voltage is a voltage from an arm midpoint 'x (a, b, c)' to a neutral point 'N', as shown in fig. 1. The switch state 'P' expresses that the two switches S at the top of the bridge arm_x1And S_x2Are simultaneously conducted and bridge arm voltage V_xnIs + V_dc/2. The switch state 'O' means that the middle two switches S_x2And S_x3Are simultaneously conducted and have a voltage V_xnIs 0V. When the switch state is 'N', then the two lowest switches Sx3 and Sx4 are simultaneously turned on, and V is at this time_xnis-V_dc/2。

According to phase current i_xIn the direction of (1), each leg of the three-phase NPC rectifier has 6 current paths. FIG. 1(a) shows that when the switch state is 'P', a forward current flows through D_x2And D_x1Leading to the dc side anode. When the switching state is 'O', as shown in FIG. 1(b), a forward current flows through S_x3And D_x2Leading to the neutral point. In most cases, if the NPC rectifier operates well at unity power factor, the path of forward current flow is in the switching state of 'P' and 'O'. When the bridge arm is in 'N' state, the forward current passes through S as shown in FIG. 1(c)_x3And S_x4. There are three reverse current paths, corresponding to the current forward path, depending on the switching state, as shown in fig. 1 (d-f). When the switch state is 'P', the current passes through S from the positive pole of the direct current side_x1，S_x2. When the bridge arm is in an 'O' state, the current passes through D from a neutral point on the direct current side_x1，S_x2And flows to the bridge arm termination point. Finally, when the switch state is 'N', D_x3And D_x4Providing a current path.

The switching state, the bridge arm phase voltage, the alternating current side current and the clamping diode current of the NPC three-level rectifier are respectively extracted as fault characteristics, and short-circuit and open fault characteristics under different switching states are analyzed based on a current circulation path method. In view of the symmetry of the circuit, taking the a-phase bridge arm as an example, the single-tube short-circuit characteristics of 4 switching tubes of the a-phase bridge arm are analyzed.

(A) Short circuit fault

When a short-circuit fault occurs, three continuous switching devices of the same bridge arm are conducted at the same time at a certain moment, and at the moment, the bus capacitor C₁Or C₂Is shorted. The invention only considers the short-circuit fault of a single switch tube, so long as the short-circuit fault can be firstly detectedAnd accurately judging which switching tube has short-circuit fault, and only keeping outputting the first switching tube meeting the fault condition no matter whether other switching tubes meet the fault condition.

(101) Short circuit of external switching device

Firstly, a switching device S_a1The occurrence of a short-circuit fault is taken as an example. When the switching state of the a-phase bridge arm is P state or N state, the switching device S_a1The short circuit does not affect the rectifier output. Therefore, the operation conditions of the rectifier before and after the fault of the a-phase bridge arm in the O state need to be compared to judge whether the short-circuit fault occurs. When the current on the cross current side of a is in a negative direction, if a fault occurs, the switching device S_a1、S_a2、S_a3And a clamp diode VD_a2Torch C with DC bus₁The short-circuit, current flow paths before and after the fault are shown in fig. 2(a) and (b). The switching device S is obtained by comparing the difference of current circulation paths before and after the fault_a1The diagnosis basis of the short-circuit fault is as follows: when the a-phase bridge arm is in an O state, the a-phase load current is in a negative direction, and the clamping diode VD_a2When the current flowing upward is not 0, the switching device S is explained_a1A short circuit occurs.

When the current on the cross current side of a is in the positive direction, if a fault occurs, the switching element S_a1、S_a2、S_a3And a clamp diode VD_a2Will also connect the DC bus capacitor C₁The short circuit and the current flow paths before and after the fault are shown in fig. 2(c) and (d). Can obtain i_a>0-time switching device S_a1Basis of short-circuit failure: clamping diode VD_a1Without current, clamping diode VD_a2Has current and a cross current side current is not equal to VD of the clamping diode_a2At the time of the upper current, the switching device S is explained_a1A short-circuit fault occurs.

Similarly, the switching device S_a4The short-circuit fault judgment method comprises the following steps: when the switching state of the a-phase bridge arm is in an O state and the current on the a-phase current-crossing side is in a positive direction, if the clamping diode VD_a1Above, a current flows, illustrating the switching device S_a4And (4) short-circuiting. When the current on the cross current side of a is in the negative direction, the clamping diode VD_a1Upper current, VD_a2Has no current, and a intersects with the current on the current side and VD_a1The currents on are not equal.

(102) Internal switching device short circuit

Firstly, a switching device S_a3The occurrence of a short-circuit fault is taken as an example. Switching device S_a3The current flow paths before and after the short circuit are shown in fig. 3(a) and (b). When the switching state of the a-phase bridge arm is O state or N state, the switching device S_a3The short circuit does not affect the rectifier output. The operation conditions of the rectifier before and after the fault of the a-phase bridge arm in the P state are compared to judge whether the short circuit occurs. When the a-phase bridge arm is in a P switch state, if the clamping diode VD_a2The current flowing in the upper circuit is not 0, which indicates that the switching device S_a3And (4) short-circuiting.

Similarly, the switching device S_a2The short-circuit fault judgment method comprises the following steps: and when the switch state of the a-phase bridge arm is N. If the clamping diode VD_a1The current flowing in the upper circuit is not 0, indicating that the switching device S is_a2A short-circuit fault occurs.

In addition, all short-circuit faults are fault conditions which can occur at the moment of judging the occurrence of the faults, and fault conditions are overlapped with each other. When the switching tube has a fault, the fault diagnosis module outputs a high level. With S_a1For example, when a short-circuit fault occurs, except for the judgment of S_a1The module will output high level and judge S_a4The module of (2) will also output high level, but the judgement fault basis that every switch tube used all designs according to self parameter characteristics, when a certain switch tube broke down, must output corresponding high level at first, and the quantity of high level is also the most. Therefore, when the judgment conditions are coincident, the invention adopts a counting module to record the quantity of the high level output by each switching tube, and can make accurate judgment.

(B) Open circuit fault

(201) External switching device open circuit

Firstly, a switching device S_a1An open circuit fault occurs as an example. When the switching state of the a-phase bridge arm is N state or O state, the switching device S_a1Open circuit and non-rectifier outputAn influence is produced. Therefore, the operation conditions of the rectifier before and after the fault in the state of the a-phase bridge arm P need to be compared, and whether the open-circuit fault occurs or not is further judged. When the a-phase load current is positive and the a-phase switch state is P, the current passes through D_a2，D_a1And the current flows to the bus capacitor, so that no fault occurs. When the load current of the phase a is in a negative direction and the switching state of the phase a is P, if a fault occurs, the phase current of the phase a can only pass through the clamping diode VD from the midpoint n of the bus capacitor_a1Switching device S_a2To the ac side, which means that the switch state changes from P to O. I is_a>The 0, P-state pre-and post-fault current flow paths are shown in fig. 4, where the dashed lines represent the pre-fault current flow paths and the solid lines represent the post-fault current flow paths.

As can be seen from fig. 4, when the a-phase load current is in the negative direction and the a-phase switching state is P, the current flows through the clamp diode VD_a1Is not 0, and the voltage U_anIs not equal to U_dc1. In order to distinguish between open-circuit faults and short-circuit faults, a further criterion is applied here: i.e. i_a＝i_d1. When the above conditions are satisfied, the switching device S_a1An open circuit fault occurs.

Similarly, when switching device S_a4When an open-circuit fault occurs, the O switch state and the P switch state of the a-phase bridge arm are not influenced. Therefore, if the a-phase switch state is N, the a-phase load current is in the positive direction and flows through the clamping diode D_a2Is not 0, and the voltage U_anIs not equal to U_dc2Now, the switching device S is explained_a4And (4) opening the circuit. To differentiate between open and short faults, a condition may be imposed: i.e. i_a＝i_d2。

(202) Internal switching device open circuit

When switching device S_a2In the event of an open-circuit fault, the current cannot flow from the switching device S_a2Flows upwards, so that the a-phase arm i_a<P switch state loss at 0, i_a<O-switch state loss at 0. The a-phase bridge arm only has N state and i_a>The O state at 0 is valid. When a fault occurs in the P state, i_a<At 0, there is no current on the a phase, the clamping diode VD_a1Current atIs 0, and U_an<0. If the fault occurs in the O state, when i_a>At 0, current passes through S_a3、D_a2The rectifier will not fail. When i is_a<When 0, the current path changes, and the current can only pass through D from the midpoint n of the direct current bus_a4And D_a3To the ac side. This means that the switch state is changed from O to N. The conditions for judging the fault at this time are as follows: i.e. i_a<At 0, the clamping diode VD_a1No current above, phase voltage U_an<0. To distinguish from a short-circuit fault, a judgment condition is added: i.e. i_aIs equal to i_da1。

Similarly, when switching device S_a3When open-circuit fault occurs, a phase bridge arm i_a>N loss of switching state at 0, i_a>O-switch state loss at 0. The a-phase bridge arm only has P state and i_a<The O state at 0 is valid. Thus, if a fault occurs in the N state, i_a>At 0, there is no current on the a phase, the clamping diode VD_a2Upper current is 0, and U_an>0. If the fault occurs in the O state, when i_a>At 0, the clamping diode VD_a2No current above, phase voltage U_an>0, to distinguish from a short-circuit fault, a judgment condition is added: i.e. i_aIs equal to i_d2。

The method can effectively diagnose open circuit and short circuit faults in the rectifier, has simple operation, quick diagnosis, reliable result and lower hardware cost, can be applied to application occasions with different power grades, and has bright characteristics and popularization.

Claims

1. A method for diagnosing short-circuit and open-circuit faults of a switching tube of a three-level rectifier is characterized by comprising the following steps: the method comprises the following steps:

a type: no switching device fails;

b type: only one switching device has a short-circuit fault;

class C: only one switching device has an open circuit fault;

2. The method of diagnosing short and open switching tube faults in a three-level rectifier according to claim 1, wherein: for IGBT switching device S with 4 bridge arms in series connection in each phase in B type_x1-S_x4The method comprises the following steps of:

when a.C. currentThe side current is in negative direction if the clamping diode VD_a1Upper current, VD_a2Has no current, and a intersects with the current on the current side and VD_a1When the currents are not equal, the switching device S is determined_a4Short circuit failure;

(C104) switch with a switch bodyDevice S_c2The short-circuit fault judgment process is as follows:

3. The method of diagnosing an open-circuit fault in a switching tube of a three-level rectifier according to claim 1, wherein: to the switching device S_a1-S_a4The steps for diagnosing the single-tube open-circuit fault characteristics are as follows:

in the O state, when i_a>When 0, the rectifier does not fail; when i is_a<At 0, the switch state is changed from O to N; the conditions for judging the fault at this time are as follows: ia<At 0, the clamping diode VD_a1No current above, phase voltage U_an<0; for distinguishing from short-circuit fault, time-alternating side phase current i different from short-circuit fault_aIs equal to the clamping diode VD_a1A current on the substrate;

when the b-phase load current is in the negative direction and the b-phase switch state is P, if a fault occurs, the fault flows through the clamping diode VD_b1Is not 0, and the voltage U_bnIs not equal to U_dc1(ii) a At this time, the phase current on the AC side is equal to the voltage of the clamping diode VD_b1Upper current, unlike a short circuit fault;

when a fault occurs in the P state, i_b<At 0, no current flows in phase bClamping diode VD_b1The current at is also 0, and U_bn<0；

If the fault occurs in the O state, when i_c>When 0, the rectifier does not fail; when i is_c<At 0, the switch state is changed from O to N; when i is_c<When 0, if the clamping diode VD_c1No current above, phase voltage U_cn<0, determination of S_c2Single tube open circuit failure;

4. The method of diagnosing short and open switching tube faults in a three-level rectifier according to claim 1, wherein: in the method for the switching device S_a1-S_a4And fault output is always kept after the short circuit or open circuit fault of the single tube is judged.

5. The method of diagnosing short and open switching tube faults in a three-level rectifier according to claim 1, wherein: the diagnostic fault category in the method has 25 cases, wherein the A category is 1 category, the B category comprises 12 categories, and the C category comprises 12 categories.

6. The method of diagnosing short and open switching tube faults in a three-level rectifier according to claim 1, wherein: in the method, when the switch tube S is switched on and off_a1-S_a4When a fault occurs, the fault diagnosis module outputs a high level.