CN116298756A - Single switching tube fault diagnosis method for T-type three-level grid-connected inverter - Google Patents

Single switching tube fault diagnosis method for T-type three-level grid-connected inverter Download PDF

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CN116298756A
CN116298756A CN202310257250.2A CN202310257250A CN116298756A CN 116298756 A CN116298756 A CN 116298756A CN 202310257250 A CN202310257250 A CN 202310257250A CN 116298756 A CN116298756 A CN 116298756A
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switching tube
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张晓�
王强
董崇
陶泽
刘畅
吕柄欣
彭天然
江奕苇
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China University of Mining and Technology CUMT
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Abstract

The invention discloses a fault diagnosis method for a single switching tube of a T-shaped three-level grid-connected inverter, which aims at rapidly positioning a faulty switching tube in a faulty system of the inverter. Firstly, by analyzing the type of fault and the influence on the circuit after the fault, the upper switching tube is judged by the change of the output voltage of the inverter (S x1 ,S x2 (S) failure, or lower switching tube (S) x3 ,S x4 ,). And then judging whether the horizontal switching tube is in fault or the vertical switching tube is in fault by a method for judging neutral point current, so that a quick and accurate positioning effect is achieved. The method has the advantages of simple structure, small calculated amount and easy realization, is applied to the control system of the T-type three-level grid-connected inverter, and has the advantages of simplicity, convenience, rapidness and accurate positioning.

Description

Single switching tube fault diagnosis method for T-type three-level grid-connected inverter
Technical Field
The invention belongs to a T-type three-level inverter, and particularly relates to a fault diagnosis method for a single switching tube of a T-type three-level grid-connected inverter.
Background
Along with the increasing application of the T-type three-level inverter in industry, the control requirement on the T-type three-level inverter is correspondingly higher and higher, and the T-type three-level inverter mainly aims at two aspects: firstly, for tracking performance of reference current, the point is of great importance in industry, and good tracking performance can ensure better application effect of the inverter in industry. And secondly, balancing effect on the midpoint potential. For the above two aspects, a number of methods have been proposed by the former to improve the control effect. At present, a common control method for a T-type three-level inverter is SVPWM modulation, has a good control effect, but has the problems of poor dynamic response, complex control process and the like. In the last sixties, the use of the model predictive control (Moedl Predictive Control, MPC) in power electronics has become a research hotspot in recent years with the rapid development of microcontrollers.
Model predictive control (Moedl Predictive Control, MPC) is becoming increasingly interesting in the power electronics and motor drive fields and is becoming more and more widely used in industry, because of its simplicity in control methods, better control results, the possibility of implementing multivariable control, and the great advantages in handling complex constraint optimizations of nonlinear systems.
However, model predictive control has a number of drawbacks, such as too much dependence on parameters of the model, fixed inverter output voltage, too high switching frequency, difficult selection of weight coefficients, and excessive calculation amount, which affects the industry. The solution to these problems is very urgent, in which the switching devices of the circuit are easily damaged due to the excessively high switching frequency thereof, causing a short circuit of the circuit, or an open circuit. Because the damage of the short-circuit fault is great, when the short-circuit fault occurs, the circuit is generally cut off in time, so that the fault diagnosis and fault-tolerant control for the prediction of the T-shaped three-level inverter model mainly refers to the open-circuit fault. In order to ensure the normal operation of the T-type three-level grid-connected inverter when the switching device fails, the method is important to rapid fault diagnosis measures and corresponding fault-tolerant control methods.
Disclosure of Invention
Aiming at the improvement requirement of the prior art, the invention provides a fault diagnosis method for a T-type three-level grid-connected inverter. The method judges that the fault is an upper switch tube S through the research of fault types and the line voltage difference x1 ，S x2 Whether the fault is a lower switch tube S x3 ，S x4 Failure, finally judging that the current is vertical switching tube S through the change of neutral point current x1 ，S x4 Or a horizontal switch tube S x2 ，S x3 And (3) failure.
In order to achieve the above purpose, the technical scheme adopted by the invention is as follows:
a fault diagnosis method for a single switching tube of a T-type three-level grid-connected inverter is characterized by comprising the following steps of: the method comprises the following steps:
step one: firstly, researching the fault type of a T-type three-level grid-connected inverter and the influence on a circuit after the fault occurs, and determining the change of the output voltage of the inverter and the change of neutral point current;
step two: judging whether the upper switching tube fails or the lower switching tube fails according to the change of the output voltage of the inverter;
step three: and judging whether the horizontal switching tube is in fault or the vertical switching tube is in fault according to the change of neutral point current, and finishing the accurate positioning of the fault switching tube.
Further, in the step one
The inverter output voltage formula is:
Figure BDA0004130093250000031
the neutral point current formula is:
Figure BDA0004130093250000032
further, the second step specifically includes:
and judging whether the fault device is an upper switching tube or a lower switching tube by using the voltage difference of an output line of the inverter according to the change of the output voltage of the inverter.
Further, the line voltage difference is defined as
Figure BDA0004130093250000033
Wherein,,
Figure BDA0004130093250000034
the reference value of the voltage of the output line of the inverter, U, is calculated by the switching state of MPC output under the normal state xy The actual inverter output line voltage calculated for the inverter output current measurement.
Further, when the voltage difference of the output line of the inverter is used for judging faults, an error threshold V needs to be added to the voltage difference of the output line th The values are:
Figure BDA0004130093250000035
further, the third step specifically includes:
and judging whether the fault device is a horizontal switching tube or a vertical switching tube by using the output current difference of the inverter according to the change of the neutral point current.
Further, the current difference is defined as
Figure BDA0004130093250000041
Wherein,,
Figure BDA0004130093250000042
neutral point current calculated from the switching state output at time k；i np To obtain U by measurement c2 -U c1 The resulting neutral point current.
Further, delay compensation is performed on model predictive control when the inverter output current difference is used for judging faults.
Compared with the prior art, the technical scheme designed by the invention has the following advantages compared with the prior art:
1. the invention judges whether the upper switch tube is in fault or the lower switch tube is in fault by the line voltage, thereby reducing the influence of common-mode voltage when judging by the phase voltage.
2. The invention judges whether the horizontal switching tube is in fault or the vertical switching tube is in fault through neutral point current, is easy to realize, does not need to add an additional sensor, reduces cost, and has high detection precision and high speed.
Drawings
FIG. 1 is a topology of a main circuit of a T-type three-level inverter;
FIG. 2 is S a2 I after failure>Current flow direction change diagram at 0;
FIG. 3 is S a2 I after failure<Current flow direction change diagram at 0;
FIG. 4 is a graph of the inverter output voltage vector after a horizontal switching tube failure;
FIG. 5 is S a1 I after failure>Current flow direction change diagram at 0;
FIG. 6 is S a1 I after failure<Current flow direction change diagram at 0;
FIG. 7 is a graph of the inverter output voltage vector after a vertical switching tube failure;
FIG. 8 is S a1 Line voltage change diagram after fault;
FIG. 9 is S a2 A neutral point current change map after failure.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be further described in detail with reference to the accompanying drawings and specific embodiments. The advantages and features of the present invention will become more apparent from the claims and the following detailed description. It should be noted that the specific examples are given here for the purpose of illustrating the present invention and are not to be construed as limiting the present invention. In addition, technical features of the embodiments of the present invention described below may be combined with each other as long as they do not collide with each other.
As shown in fig. 1, in the ABC three-phase static coordinate system, the voltage and the current in the mathematical model of the T-type three-level grid-connected inverter are both ac quantities, and have the characteristics of time variation, nonlinearity, strong coupling and the like.
The output voltage of the inverter is shown as (1)
Figure BDA0004130093250000051
In the formula, [ u ]]＝[u A ,u B ,u C ] T -three-phase inverter output voltage; [ e ]]＝[e A ,e B ,e C ] T -three-phase network side voltage; [ i ]]＝[i A ,i B ,i C ] T -three-phase inverter output current; r is an alternating current measuring resistor; L-AC side inductance; [ U ]]＝[U AO ,U BO ,U CO ] T -a voltage between the voltage and O-point; u (U) ON Is the voltage between the O-point and the neutral point on the net side.
Adding three phases to obtain formula (2)
Figure BDA0004130093250000061
By introducing the formula (2) into the formula (1)
Figure BDA0004130093250000062
From this, the output voltage of the inverter is related to the upper and lower capacitors on the dc side, and when the midpoint potential is balanced, the T-type three-level inverter has three operating states, and the corresponding switching function is defined as:
Figure BDA0004130093250000063
thus, the output voltage of each phase is
Figure BDA0004130093250000064
Wherein x is A, B, C
The inverter output voltage equation in the three-phase stationary coordinate system can be obtained as follows:
Figure BDA0004130093250000065
for neutral point currents there are:
i np ＝(S a2 -S a1 )i a +(S b2 -S b1 )i b +(S c2 -S c1 )i c (7)
wherein i is np Is the current flowing through the midpoint of the two capacitors. At the same time:
Figure BDA0004130093250000071
due to S x2 And S is equal to x3 (x.epsilon.a, b, c) faults are of substantially opposite influence, herein S being phase A a2 Failure is exemplified.
As shown in fig. 2, the T-type three-level inverter operates in the O-state when i a >0, as shown in the figure (a), in the normal state, the current flows as indicated by arrow a1 from S a2 And S is a3 Through the diode of (c); when S is a2 When a fault occurs, the current flows as indicated by arrow b1 from S a4 I.e. phase a changes from O to N state at this time.
As shown in FIG. 3, when ia<At 0, since current does not flow S when the A phase is operating in the O state a2 But flows through S a2 Is of (2)Tube, so when S a2 The failure has no effect, and the A-phase works in O state. The current flow is indicated by arrows a2, b 2.
Switch tube S a3 In case of failure, i a >No influence on the circuit when 0, when i a <At 0, the a phase changes from O state to P state.
As shown in FIG. 4, when the horizontal switching tube S of phase A a2 In case of failure, at i>The inverter output voltage in the case of 0 includes: OOO, OOP, OON, OPO, ONO, OPP, OPN, ONP, ONN, nine outputs cannot be normally output, at this time, the current distortion rate of the inverter output will rise, and the midpoint potential will be severely shifted.
Due to S x1 And S is equal to x4 The effect of faults is substantially opposite, herein S in phase A a1 As an example of the occurrence of a failure,
as shown in fig. 5, the T-type three-level inverter operates in the O-state when i a >In the normal state at 0, the current flows as indicated by arrow a3 from S a1 Flowing through; when S is a1 When a fault occurs, the current flows as indicated by arrow b3 from S a2 And S is a3 I.e. phase a changes from P to O state.
As shown in fig. 6, when i a <At 0, since current does not flow S when the A phase is operating in the O state a1 But flows through S a1 So when S a1 The failure has no effect, the A-phase is naturally operated in the P-state, and the current flows are shown by arrows a4 and b 4.
Switch tube S a4 In case of failure, i a >No influence on the circuit when 0, when i a <At 0, the a phase changes from the N state to the O state.
As shown in FIG. 7, when the vertical switching tube S of phase A a1 In case of failure, at i>The inverter output voltage in the case of 0 includes: PPP, PPO, POO, POP, PPN, PON, PNN, PNO, PNP, nine total are unable to output normally. At this time, the current distortion rate of the inverter output is increased, and the midpoint potential is severely deviated.
From the fault analysis, different switching devices damage the circuitThe influence is that, in particular, when S a1 /S a2 In case of failure, at i a >When 0, the output state is changed from P to O or from O to N, and when the output state is obtained according to the formula (3), U XO Drop, resulting in its output voltage U X Descending;
and when S a3 /S a4 In case of failure, at i a <When 0, the output state is changed from O to P or from N to O, and U is obtained according to (3) XO Drop, resulting in its output voltage U X Rising.
Therefore, the damaged device can be judged as S by the change of the actual measured value and the reference value of the output phase voltage a1 /S a2 Or S a3 /S a4 。
At the moment, the fault switching tube can be positioned only by judging whether the horizontal switching tube is faulty or the vertical switching tube is faulty.
From the above, S a1 Failure, when i a >When 0, the inverter output state is changed from the P state to the O state, and the current flowing from the P point to the load is changed from the neutral point to the load, and the inverter output state is obtained by the formula (7), and the neutral point current is increased;
when S is a2 In case of failure, i a >When 0, the output state of the inverter is changed from the O state to the N state, and the current flowing from the O point to the load is changed from the N point to the load, and the output state is obtained by the formula (7), and the current flowing from the neutral point is reduced;
equivalent S a3 In case of failure, i a <When 0, the output state of the inverter is changed from the O state to the P state, and the neutral point inflow current is reduced at the moment;
S a4 in case of failure, i a <At 0, the inverter output state is changed from the N state to the O state, and the neutral point inflow current increases at this time.
Meanwhile, the calculation amount and the actual measurement comparison are applied in the detection process, so that the delay compensation of the model predictive control is very important.
In combination, the fault point can be located according to the change of the output voltage of the inverter and the change of the neutral point current. The specific formula is determined as follows, taking a phase A fault as an example, and other two phases are similar to the phase A.
When S is a1 When a fault occurs, the P state of the A phase becomes the O state, and when S a2 When a fault occurs, the O state of the a phase becomes the N state. By S a1 The fault is exemplified by the fact that the change in the inverter output voltage is now obtained by equation (6).
Figure BDA0004130093250000091
Two algorithms of the inverter output voltage:
Figure BDA0004130093250000101
wherein,,
Figure BDA0004130093250000102
calculating the actual value of the output voltage of the inverter according to the actual current measured value;
Figure BDA0004130093250000103
and calculating an inverter output voltage reference value for the reference quantity predicted and output according to the model.
The amplitude of the phase voltage is continuously changed due to the influence of high-frequency common-mode voltage interference, so that the phase voltage is difficult to be used for fault diagnosis. The line voltage is used for the determination.
Figure BDA0004130093250000104
The line voltage difference is defined as
Figure BDA0004130093250000105
Wherein,,
Figure BDA0004130093250000106
the reference value of the voltage of the output line of the inverter, U, is calculated by the switching state of MPC output under the normal state xy The actual inverter output line voltage calculated for the inverter output current measurement.
If the circuit works normally, the delta U in the ideal state xy ＝0；
Is obtained by the formula (9) and the formula (10), when S a1 /S a2 When a fault occurs, the voltage difference of the line in the A phase P state is as follows:
Figure BDA0004130093250000111
similarly, when S a3 /S a4 When a fault occurs, the voltage difference of the line in the A phase P state is as follows:
Figure BDA0004130093250000112
in consideration of various relative errors, it is therefore necessary to add an error threshold V to the line voltage difference in judging whether or not a fault occurs th The value of which is obtained by experiment
Figure BDA0004130093250000113
Judging to be S by the calculated line voltage difference a1 /S a2 Or S a3 /S a4 And (3) failure.
Meanwhile, two calculation modes of neutral point current can be realized for the neutral point current formula (8);
Figure BDA0004130093250000114
wherein,,
Figure BDA0004130093250000121
the actual value of the neutral point current is calculated according to the actual direct-current side capacitor voltage;
i np ＝(S a2 -S a1 )i a +(S b2 -S b1 )i b +(S c2 -S c1 )i c
and calculating a neutral point current reference value for the switching state of the output according to the model prediction.
The current difference is defined as:
Figure BDA0004130093250000122
wherein,,
Figure BDA0004130093250000123
the neutral point current calculated according to equation (16) is the switching state output at time k. i.e np To obtain U by measurement c2 -U c1 The resulting neutral point current.
In a normal state, when the vertical switching tube fails, e.g. S a1 Failure, i a >At 0, the phase A P state is changed to the O state, and the neutral point current is increased, so i is obtained by measurement np Is greater than that obtained by calculation
Figure BDA0004130093250000124
And when S a2 In case of failure, i a >At 0, the phase A O state is changed to the N state, and the neutral point current is reduced, so i obtained by measurement np Is smaller than that obtained by calculation
Figure BDA0004130093250000125
Thereby determining S a1 Or S a2 Failure of S a3 /S a4, a And judging faults in the same way.
In summary, through two kinds of judgement, can pinpoint the switching device to the trouble, and control process is simpler than other methods, easily realizes.
As shown in fig. 8, a fault occurs at 0.1S, line a5 is an actual value of the inverter output line voltage calculated from the actual phase current measurement value, line b5 is a reference value of the inverter output line voltage calculated from the output switching state, and when operating in the normal state, the actual value is equal to the reference value, and when S a1 In the event of a fault, the actual value is smaller than the measured value. Equivalent S a2 When a fault occurs, the obtained actual value and the reference value are changed and S a1 The same applies. Similarly, lower switch tube S x3 ，S x4 Actual value and reference value change obtained during fault and upper switch tube S x1 ，S x2 The change at the time of failure is opposite.
A specific positioning through a change in neutral point current is required at this time.
As shown in fig. 9, line a6 is the actual value of the neutral point current calculated from the dc side upper and lower capacitance voltage measurement values, and line b6 is the neutral point current reference value calculated from the switching state. As can be seen from the figure, the actual value is equal to the reference value when operating in the normal state. When S is a1 When a fault occurs, obtaining that the actual value is larger than the reference value; when Sa2 fails, the actual value obtained is smaller than the reference value. Similarly, horizontal switch tube S x2 ，S x3 The actual value obtained in the fault is the same as the reference value; vertical switch tube S x1 ，S x4 The actual value obtained at the time of the fault is the same as the reference value.
In summary, the fault device can be accurately positioned through two judgments.
The technical research of the invention is sponsored by the innovation planning project of the university of Chinese mining research students.
It will be readily appreciated by those skilled in the art that the foregoing description is merely a preferred embodiment of the invention and is not intended to limit the invention, but any modifications, equivalents, improvements or alternatives falling within the spirit and principles of the invention are intended to be included within the scope of the invention.

Claims (8)

1. A fault diagnosis method for a single switching tube of a T-type three-level grid-connected inverter is characterized by comprising the following steps of: the method comprises the following steps:
step one: firstly, researching the fault type of a T-type three-level grid-connected inverter and the influence on a circuit after the fault occurs, and determining the change of the output voltage of the inverter and the change of neutral point current;
step two: judging whether the upper switching tube fails or the lower switching tube fails according to the change of the output voltage of the inverter;
step three: and judging whether the horizontal switching tube is in fault or the vertical switching tube is in fault according to the change of neutral point current, and finishing the accurate positioning of the fault switching tube.
2. The method for diagnosing the fault of the single switching tube of the T-type three-level grid-connected inverter according to claim 1, wherein the method comprises the following steps of: in the step one
The inverter output voltage formula is:
Figure QLYQS_1
the neutral point current formula is:
Figure QLYQS_2
3. the method for diagnosing the fault of the single switching tube of the T-type three-level grid-connected inverter according to claim 1, wherein the method comprises the following steps of: the second step specifically comprises the following steps:
and judging whether the fault device is an upper switching tube or a lower switching tube by using the voltage difference of an output line of the inverter according to the change of the output voltage of the inverter.
4. The method for diagnosing a single switching tube fault of a T-type three-level grid-connected inverter according to claim 3, wherein the method comprises the following steps of: the line voltage difference is defined as
Figure QLYQS_3
Wherein,,
Figure QLYQS_4
the reference value of the voltage of the output line of the inverter, U, is calculated by the switching state of MPC output under the normal state xy The actual inverter output line voltage calculated for the inverter output current measurement.
5. The method for diagnosing a single switching tube fault of a T-type three-level grid-connected inverter according to claim 3, wherein the method comprises the following steps of: when the voltage difference of the output line of the inverter is used for judging faults, an error threshold V is required to be added to the voltage difference of the output line th The values are:
Figure QLYQS_5
6. the method for diagnosing the fault of the single switching tube of the T-type three-level grid-connected inverter according to claim 1, wherein the method comprises the following steps of: the third step specifically comprises the following steps:
and judging whether the fault device is a horizontal switching tube or a vertical switching tube by using the output current difference of the inverter according to the change of the neutral point current.
7. The method for diagnosing the fault of the single switching tube of the T-type three-level grid-connected inverter according to claim 1, wherein the method comprises the following steps of: the current difference is defined as
Figure QLYQS_6
Wherein,,
Figure QLYQS_7
the neutral point current is calculated according to the switching state output at the moment k; i.e np To obtain U by measurement c2 -U c1 The resulting neutral point current.
8. The method for diagnosing the fault of the single switching tube of the T-type three-level grid-connected inverter according to claim 1, wherein the method comprises the following steps of: and performing delay compensation on model predictive control when the fault is judged by using the output current difference of the inverter.
CN202310257250.2A 2023-03-16 2023-03-16 Single switching tube fault diagnosis method for T-type three-level grid-connected inverter Pending CN116298756A (en)

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