CN110518820B - Fault-tolerant control method and system for open-circuit faults of T-type three-level inverter - Google Patents
Fault-tolerant control method and system for open-circuit faults of T-type three-level inverter Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/32—Means for protecting converters other than automatic disconnection
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/483—Converters with outputs that each can have more than two voltages levels
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
- H02M7/5387—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/32—Means for protecting converters other than automatic disconnection
- H02M1/325—Means for protecting converters other than automatic disconnection with means for allowing continuous operation despite a fault, i.e. fault tolerant converters
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Abstract
The invention discloses a method and a system for diagnosing open-circuit faults and carrying out fault-tolerant operation of a T-shaped three-level inverter, which comprise the steps of firstly adopting a 7-segment SVPWM modulation mode to control the operation of the T-shaped three-level inverter, sampling the midpoint voltage of the bridge arm output and the direct current side of the inverter to obtain a low-frequency voltage signal of the bridge arm output and carrying out coordinate transformation to obtain an equivalent output voltage vector track of the inverter, establishing a fault characteristic value truth table by calculating voltage vector tracks under different fault conditions and operating states, judging the current fault type of the system according to the characteristic value of the current system and the fault characteristic value truth table, finally switching a corresponding control scheme, and realizing the fault-tolerant operation of the T-shaped three-level inverter by utilizing a redundancy vector equivalent replacement method.
Description
Technical Field
The invention relates to the field of fault-tolerant control of T-type three-level inverters, in particular to a fault-tolerant control method and a fault-tolerant control system for open-circuit faults of a T-type three-level inverter.
Background
The T-type three-level inverter has fault-tolerant operation capability under certain fault conditions and has very wide application in the fields of power systems, aerospace, metallurgical mining industry, rail transit and the like. The requirements on the power supply continuity of the power supply in the occasions are high, and a long-time outage can cause great economic loss or accidents, so that the requirements on the long-time stable operation of the T-type three-level inverter are higher. Fault-tolerant operation of the inverter in the case of partial faults can greatly improve the power supply continuity of the system. The premise of the inverter to realize fault-tolerant operation is that the system diagnoses faults and rapidly realizes switching of control schemes. At present, the biggest problem of fault diagnosis research of the T-type three-level inverter is how to diagnose various types of faults rapidly and accurately, and meanwhile misdiagnosis caused by load change is reduced.
In ac speed regulation systems for industrial applications, most faults result from damage to the power devices. The device faults comprise short-circuit faults and open-circuit faults, the short-circuit faults exist for a short time, and the quick fuse can be implanted into a circuit to convert the short-circuit faults into open-circuit faults. When a single switching tube of the T-type three-level inverter has open faults, abnormal conditions such as distortion of output current and voltage waveforms, neutral point potential offset at the direct current side, heating of a power device and the like can occur. At present, three methods of expert system method, current detection method and voltage detection method are mainly developed in the IGBT open-circuit fault diagnosis method. Among them, the amperometric method is the most commonly used one. The traditional diagnosis method takes the waveform distortion of the output voltage and current when the inverter fails in an open circuit as the basis for judging the failure position, and the method can generate larger misdiagnosis when the load is switched or suddenly changed, and has more severe requirements on the load balance degree and the power factor.
Disclosure of Invention
The invention mainly aims to provide a method and a system for diagnosing and controlling open-circuit faults of a T-shaped three-level inverter, which can solve the problem that the diagnosis method of a fault-tolerant control system cannot be applied to various load sizes, load power factors and load unbalance degrees in the prior art.
The invention adopts the following technical scheme:
the fault-tolerant control method for the open-circuit fault of the T-type three-level inverter is characterized by comprising the following steps of:
step 1: the system adopts a 7-segment SVPWM modulation mode to control the operation of a T-type three-level inverter;
step 2: sampling bridge arm output and direct current side midpoint voltage of a T-shaped three-level inverter to obtain a low-frequency voltage signal of the T-shaped three-level inverter;
step 3: performing coordinate transformation on the low-frequency voltage signal to obtain an inverter equivalent output voltage vector track;
step 4: calculating voltage vector tracks under different fault conditions and running states, and establishing a fault characteristic value truth table;
step 5: judging the current fault type of the system according to the characteristic value of the current system and the fault characteristic value truth table;
step 6: and switching the corresponding control scheme according to the fault type to realize the fault-tolerant operation of the T-type three-level inverter.
Preferably, the step 1 specifically includes the following steps:
step 1.1: obtaining a phase voltage output equation according to a three-phase T-shaped three-level inverter topological circuit:
in which X is { A, B, C }, S A1 =1 indicates that the a-phase No. 1 tube is on, S A1 =0 indicates that phase a, no. 1 tube is off, u dc Representing the DC side bus voltage of the T-type three-level inverter;
step 1.2: calculating a three-phase voltage vector space distribution equation output by the T-shaped three-level inverter:
wherein S is A ,S B ,S C ∈{1,0,-1}，S A Taking 1 to represent A phase to output high level u dc With/2, 0 representing the output intermediate level, -1 representing the output low level-u dc /2；
Step 1.3: drawing an output voltage vector distribution map of the three-level inverter according to a three-phase voltage vector space distribution equation;
step 1.4: calculating the current reference voltage vector V ref In the interval of the voltage vector distribution diagram;
step 1.5: SVPWM modulation is performed according to V ref The sector in which it is located calculates the vector order and the time of action within the switching cycle.
Preferably, in the step 1.5, according to V ref The vector sequence and the acting time in the switching period of the sector calculation comprise: when each vector is switched in a switching period, only one phase of bridge arm is ensured to be switched in state, and each phase is switched in one period only twice; the short vectors with negative polarity are used as a first vector and a last vector in a switching period, so that the switching state of at most one bridge arm is ensured when small sectors are switched; positive and negative short vectors within each large sector for midpoint potentialThe offset effects cancel each other.
Preferably, in the step 2, the bridge arm output of the T-type three-level inverter and the dc side midpoint voltage pass through a low-pass filter to obtain the low-frequency voltage signal.
Preferably, in the step 3, the coordinate transformation is a Clark transformation, and the formula is:
u α 、u β the components of the voltage vector in the alpha-axis direction and the beta-axis direction, u AO 、u BO 、u CO Is the voltage between three points of the three-phase bridge arm output end A, B, C of the T-type three-level inverter and the midpoint O of the direct current side.
Preferably, the step 4 specifically includes:
step 4.1: calculating current paths under various open-circuit faults, and analyzing the change rule of phase voltage under each open-circuit fault;
step 4.2: modifying an inverter output voltage vector distribution diagram according to a change rule of phase voltages;
step 4.3: according to the sequence and time of vector action in each small sector, calculating an equivalent voltage vector in each switching period under the current fault type, and drawing a corresponding distortion track;
the equivalent vector calculation equation under the fault condition is:
v in cal To distort the voltage vector, V ref For reference voltage vector V k An offset vector, η, for the kth fault switch state in the cycle k The duty ratio of the k-th fault switch state in the period is given by k which is 1 to 7;
s44: and drawing distortion tracks corresponding to various fault conditions under various modulation conditions, extracting characteristic values of the tracks, including the degree of distortion and the direction of distortion, and obtaining a fault characteristic value truth table.
Preferably, the step 5 specifically includes: calculating the current characteristic values A and theta of the system, wherein A and theta are the modes and phase angles of the average voltage vector respectively;
the calculation formula of A is as follows:
the calculation formula of θ is:
n is the sampling times of the T-type three-level inverter system in one power frequency period.
Preferably, the step 6 specifically includes:
step 6.1: calculating the residual effective voltage vector of the T-type three-level inverter under the current fault according to the fault type;
step 6.2: judging whether the T-type three-level inverter has fault-tolerant operation capacity or not according to the obtained residual effective voltage vector;
step 6.3: calculating the failure condition of a switching state in a switching period, and drawing an effective output voltage vector range diagram of the current inverter; if the effective output voltage vector range is reduced and the modulation degree is more than 0.5, the modulation degree is forcedly adjusted to be within the effective output voltage vector range, and derating fault-tolerant operation is performed; if the effective output voltage vector range is unchanged, full fault-tolerant operation can be performed;
step 6.4: the vector sequence and switching time in the switching period are adjusted by the method of equivalent vector replacement.
A fault-tolerant control system for open-circuit faults of a T-type three-level inverter is characterized in that: the fault-tolerant control method for realizing the open-circuit fault of the T-type three-level inverter comprises a direct current source, the T-type three-level inverter, a load, a controller and a fault feature extraction module; the direct current source is connected with the T-shaped three-level inverter for supplying power, and the load is connected with the T-shaped three-level inverter; the fault characteristic extraction module is connected with the T-shaped three-level inverter so as to read fault signals; the controller is connected with the fault feature extraction module and the T-type three-level inverter to realize fault diagnosis and fault-tolerant control of the T-type three-level inverter according to fault types.
As can be seen from the above description of the present invention, compared with the prior art, the present invention has the following advantages:
the method adopts an open circuit fault diagnosis strategy based on equivalent voltage vector track prediction, and can adapt to the changes of load size, power factor and unbalance degree. The system dynamically adjusts the threshold value according to the modulation degree, well realizes the accurate positioning of the open-circuit point of the T-shaped three-level inverter, and realizes the fault-tolerant operation of the system through vector equivalent replacement.
Drawings
FIG. 1 is a schematic diagram of an open-circuit fault diagnosis and fault-tolerant control system of a T-type three-level inverter based on equivalent voltage vector characteristics in the invention;
FIG. 2 is a graph showing the output voltage vector of the T-type three-level inverter according to the present invention;
FIG. 3 is a schematic diagram of large sector judgment in SVPWM modulation according to the present invention;
FIG. 4 is a schematic diagram of small sector judgment in SVPWM modulation according to the present invention;
FIG. 5 is a diagram showing a three-phase switching state change of an inverter in a switching cycle according to the present invention;
FIG. 6 is a schematic diagram of a connection between a T-type three-level inverter and a fault feature extraction module according to the present invention;
FIG. 7 is a circuit diagram of a fault signature extraction module according to the present invention;
fig. 8 is a current path of the inverter in a normal operation state according to the present invention;
FIG. 9 is a current path condition of an inverter in the case of an open circuit fault in the present invention;
FIG. 10 is a graph of output voltage vector distortion in the event of an open circuit fault in the present invention;
FIG. 11 is a graph of the vector locus of the equivalent output voltage in the event of an open circuit fault in the present invention;
FIG. 12 is a graph of effective voltage vectors for an inverter requiring derated fault tolerant operation under open circuit failure in accordance with the present invention;
FIG. 13 is a graph of effective voltage vectors for an inverter capable of full fault tolerant operation under open circuit failure in accordance with the present invention;
FIG. 14 is a diagram illustrating the adjustment of the switching state during a switching cycle for fault tolerant control in accordance with the present invention;
the invention is further described in detail below with reference to the drawings and the specific examples.
Detailed Description
The invention is further described below by means of specific embodiments.
Referring to fig. 1, the invention provides a system for diagnosing open-circuit faults and controlling fault tolerance of a T-type three-level inverter, which comprises a direct current source, a T-type three-level inverter circuit, a load, a controller and a fault feature extraction module, wherein the direct current source, the T-type three-level inverter circuit and the load are main working parts of the system. The controller is connected with the T-shaped three-level inverter circuit to realize control, and the fault characteristic extraction module is connected with the T-shaped three-level inverter circuit to realize fault signal reading. The controller is connected with the fault feature extraction module to realize the processing of fault signals, namely the fault diagnosis, and finally the fault tolerance control of the controller to the T-type three-level inverter circuit is realized.
The system adopts a fault-tolerant control method of the open-circuit fault of the T-shaped three-level inverter, and comprises the following steps:
step 1: the system adopts a 7-segment SVPWM modulation mode to control the operation of a T-type three-level inverter, and specifically comprises the following steps:
step 1.1: obtaining a phase voltage output equation according to a three-phase T-shaped three-level inverter topological circuit:
in which X is { A, B, C }, S A1 =1 indicates that the a-phase No. 1 tube is on, S A1 =0 indicates that phase a, no. 1 tube is off, u dc Representing the dc side bus voltage of the T-type three-level inverter.
Step 1.2: calculating a three-phase voltage vector space distribution equation output by the T-shaped three-level inverter:
wherein S is A ,S B ,S C ∈{1,0,-1}，S A Taking 1 to represent A phase to output high level u dc With/2, 0 representing the output intermediate level, -1 representing the output low level-u dc /2。
Step 1.3: and drawing an output voltage vector distribution diagram of the three-level inverter according to the three-phase voltage vector space distribution equation.
As shown in fig. 2, the voltage vector distribution range is a regular hexagon, which includes six short vectors, each corresponding to 2 switching states, six medium vectors, each corresponding to 1 switching state, six long vectors, each corresponding to 1 switching state, one zero vector, and each corresponding to 3 switching states.
In FIG. 2, P, O, N respectively represent the output high level u of the bridge arm dc Zero point level 0, low level-u dc /2，
The short vectors are divided into positive polarity short vectors, under the action of which the midpoint potential on the direct current side rises, and negative polarity short vectors, under the action of which the midpoint potential on the direct current side falls.
Step 1.4: calculating the current reference voltage vector V ref In the interval of the voltage vector distribution diagram.
As shown in fig. 3, the sector is divided into a large sector at intervals of 60 ° in the counterclockwise direction, and is sequentially defined as an I-th sector to a VI-th sector; as shown in fig. 4, the sector I is divided into six small sectors 1 to 6, and the other sectors are divided in the same way; calculating a reference voltage vector V ref And judges its large sector and small sector.
Step 1.5: SVPWM modulation is carried out, rootAccording to V ref The sector in which it is located calculates the vector order and the time of action within the switching cycle.
In step 1.5, according to V ref The vector sequence and the acting time in the switching period of the sector calculation comprise: when each vector is switched in a switching period, only one phase of bridge arm is ensured to be switched in state, and each phase is switched in one period only twice; the short vectors with negative polarity are used as a first vector and a last vector in a switching period, so that the switching state of at most one bridge arm is ensured when small sectors are switched; the offset effects of the positive and negative short vectors in each large sector on the midpoint potential cancel each other out.
The vector state order of each sector is arranged according to the vector arrangement rule as follows:
as shown in fig. 5, according to the vector calculation method, a waveform diagram of the three-phase switching state in one of the periods is obtained.
Step 2: and sampling bridge arm output and direct current side midpoint voltage of the T-shaped three-level inverter to obtain a low-frequency voltage signal of the T-shaped three-level inverter. As shown in fig. 6, a connection diagram of a fault feature extraction module and a T-type three-level inverter system is shown, wherein the T-type three-level inverter is composed of 12 IGBTs and two dc side capacitors C1 and C2, the fault feature extraction module comprises a sampling circuit and a conditioning circuit, and samples and processes a voltage u between three points of a three-phase bridge arm output terminal A, B, C of the T-type three-level inverter and a midpoint O of the dc side AO 、u BO 、u CO . The three-phase circuit is identical, and an a-phase circuit is taken as an example for explanation, and as shown in fig. 7, a fault characteristic extraction module circuit diagram can sample discrete voltage signals between three A, B, C points and a direct-current side midpoint O, and extract effective signals for fault diagnosis from the discrete voltage signals. By sampling electricityThe sampled voltage signal u AO 、u BO 、u CO The low-frequency voltage signal u is obtained through the processing of the conditioning circuit AO1 、u BO1 、u CO1 。
In particular, in FIG. 7Sampling circuitThe voltage sensor LV25-P is used as a core for collecting the voltage signal u of the T-shaped three-level inverter AO And reduce the same to-3V to 3V. Wherein, one end of the limiting resistor R11 and R21 is connected with one input end of the voltage sensor, and the other end is connected with the T-shaped three-level inverter. The voltage sensor LV25-P, the sampling resistor R31, the filter capacitor C11, the resistor R11 and the resistor R21 form a sampling circuit.
Conditioning circuitThe operational amplifier TL082 is used as a core for further processing the signal obtained by the sampling circuit to obtain a voltage signal which can be read by the controller. The circuit specifically comprises two parts, and the bias of signals is realized by the circuit consisting of the resistors R41, R51, R61, the capacitor C21 and the operational amplifier U11A, namely, a pre-stage signal of-3V to 3V is processed into a signal of 0 to 3V; the circuit composed of the resistor R71, the capacitor C31, the diodes D11 and D21 and the operational amplifier U11B realizes low-pass filtering of signals, removes higher-frequency components in the signals, and finally obtains low-frequency signals U AO1 。
Step 3: and performing coordinate transformation on the low-frequency voltage signal to obtain an inverter equivalent output voltage vector track. I.e. a low frequency voltage signal u AO1 、u BO1 、u CO1 Clark conversion is carried out to obtain a voltage vector u inv And obtaining a corresponding voltage vector track in an alpha-beta coordinate system, wherein a Clark coordinate transformation formula is as follows:
the coefficient 2/3 corresponds to the coordinate transformation of the equal amplitude variation, u α 、u β U respectively inv Components in the alpha-axis direction and the beta-axis direction.
Step 4: and calculating voltage vector tracks under different fault conditions and running states, and establishing a fault characteristic value truth table. The method specifically comprises the following steps:
step 4.1: and calculating current paths under various open-circuit faults, and analyzing the change rule of the phase voltage under each open-circuit fault. Fig. 8 shows a current path in a normal working state of one phase bridge arm, fig. 9 shows a current path in various open-circuit fault conditions, and a change rule of phase voltage in each fault is analyzed.
Step 4.2: modifying the inverter output voltage vector distribution according to the change of the phase voltage, as shown in FIG. 10 as S A1 The voltage vector distortion condition in the open fault condition, wherein the switch state with box label is the distorted switch state.
Step 4.3: according to the sequence and time of vector action in each small sector, calculating equivalent voltage vector in each switching period under the current fault type, drawing a corresponding distortion track,
the equivalent vector calculation equation under the fault condition is:
v in cal To distort the voltage vector, V ref For reference voltage vector V k An offset vector, η, for the kth fault switch state in the cycle k The active time duty cycle for the kth fault switch state in the cycle. The T-type three-level inverter adopts seven-segment SVPWM modulation, and k takes the value of 1 to 7.
Step 4.4: drawing distortion tracks corresponding to various fault conditions under the condition of each modulation degree m, extracting characteristic values of each track, including the degree of distortion and the direction of distortion, and obtaining a fault characteristic value truth table. The modulation m is the amount for determining the output voltage in the output process of the T-type three-level inverter.
As shown in fig. 11, m=0.8, s A1 The equivalent voltage equivalent vector track during open circuit fault has the distortion track equation as follows:
step 5: and judging the current fault type of the system according to the characteristic value of the current system and the fault characteristic value truth table. Calculating n sampling values u in each power frequency period α 、u β Average value sigma u of (1) α /n、Σu β And/n, calculating a module A and a phase angle theta of the average voltage vector, wherein A and theta are taken as two characteristic values of fault diagnosis.
The calculation formula of the characteristic value A is as follows:
the calculation formula of the characteristic value theta is as follows:
step 6: and switching the corresponding control scheme according to the fault type to realize the fault-tolerant operation of the T-type three-level inverter. The method comprises the following steps:
step 6.1: and calculating the residual effective voltage vector of the T-type three-level inverter under the current fault according to the fault diagnosis result.
When an open circuit fault occurs, part of the switch states fail, wherein a short vector and a zero vector respectively correspond to two switch states and three switch states, a medium vector and a long vector only correspond to one switch state, and if each vector has no effective switch state, the vector fails.
Step 6.2: and judging whether the T-type three-level inverter has fault-tolerant operation capability according to the residual effective voltage vector under the obtained fault.
The basic conditions of the system with fault-tolerant operation capability are as follows:
1. the remaining effective voltage vector region contains a zero vector, and the zero vector is located inside the effective region;
2. the balance of the neutral point potential on the direct current side can be realized by the residual effective short vector.
Step 6.3: and calculating the failure condition of the switch state in the switch period, and drawing the effective output voltage vector range diagram of the current inverter.
As shown in fig. 12, if the effective output voltage vector range is reduced and the modulation m >0.5, then m is forcibly adjusted to be within the effective output voltage vector range, and derating fault-tolerant operation is performed.
As shown in fig. 13, if the effective output voltage vector range is unchanged, full fault tolerant operation is enabled.
Step 6.4: as shown in fig. 14, the vector order and switching time in the switching period are adjusted by the equivalent vector replacement method.
The foregoing is merely illustrative of specific embodiments of the present invention, but the design concept of the present invention is not limited thereto, and any insubstantial modification of the present invention by using the design concept shall fall within the scope of the present invention.
Claims (2)
1. The fault-tolerant control method for the open-circuit fault of the T-type three-level inverter is characterized by comprising the following steps of:
step 1: the system adopts a 7-segment SVPWM modulation mode to control the operation of a T-type three-level inverter; the method specifically comprises the following steps:
step 1.1: obtaining a phase voltage output equation according to a three-phase T-shaped three-level inverter topological circuit:
in which X is { A, B, C }, S A1 =1 indicates that the a-phase No. 1 tube is on, S A1 =0 indicates that phase a, no. 1 tube is off, u dc Representing the DC side bus voltage of the T-type three-level inverter;
step 1.2: calculating a three-phase voltage vector space distribution equation output by the T-shaped three-level inverter:
wherein S is A ,S B ,S C ∈{1,0,-1}，S A Taking 1 to represent A phase to output high level u dc With/2, 0 representing the output intermediate level, -1 representing the output low level-u dc /2；
Step 1.3: drawing an output voltage vector distribution map of the three-level inverter according to a three-phase voltage vector space distribution equation;
step 1.4: calculating the current reference voltage vector V ref In the interval of the voltage vector distribution diagram;
step 1.5: SVPWM modulation is performed according to V ref The sector calculates the vector sequence and the acting time in the switching period, which comprises the following steps: when each vector is switched in a switching period, only one phase of bridge arm is ensured to be switched in state, and each phase is switched in one period only twice; the short vectors with negative polarity are used as a first vector and a last vector in a switching period, so that the switching state of at most one bridge arm is ensured when small sectors are switched; the offset effect of positive and negative short vectors in each large sector on the midpoint potential is mutually counteracted;
step 2: the bridge arm output of the sampling T-shaped three-level inverter and the midpoint voltage of the direct current side pass through a low-pass filter to obtain a low-frequency voltage signal;
step 3: performing coordinate transformation on the low-frequency voltage signal to obtain an inverter equivalent output voltage vector track; the coordinate transformation is Clark transformation, and the formula is as follows:
u α 、u β the components of the voltage vector in the alpha-axis direction and the beta-axis direction, u AO 、u BO 、u CO Is a T-shaped three-level inverter with three points A, B, C at the output end of a three-phase bridge armVoltage between the direct current side midpoints O;
step 4: calculating voltage vector tracks under different fault conditions and running states, and establishing a fault characteristic value truth table, wherein the method specifically comprises the following steps of:
step 4.1: calculating current paths under various open-circuit faults, and analyzing the change rule of phase voltage under each open-circuit fault;
step 4.2: modifying an inverter output voltage vector distribution diagram according to a change rule of phase voltages;
step 4.3: according to the sequence and time of vector action in each small sector, calculating an equivalent voltage vector in each switching period under the current fault type, and drawing a corresponding distortion track;
the equivalent vector calculation equation under the fault condition is:
v in cal To distort the voltage vector, V ref For reference voltage vector V k An offset vector, η, for the kth fault switch state in the cycle k The duty ratio of the k-th fault switch state in the period is given by k which is 1 to 7;
s44: drawing distortion tracks corresponding to various fault conditions under various modulation conditions, extracting characteristic values of the tracks, including the degree of distortion and the direction of distortion, and obtaining a fault characteristic value truth table;
step 5: judging the current fault type of the system according to the characteristic value of the current system and a fault characteristic value truth table, wherein the method specifically comprises the following steps: calculating the current characteristic values A and theta of the system, wherein A and theta are the modes and phase angles of the average voltage vector respectively;
the calculation formula of A is as follows:
the calculation formula of θ is:
n is the sampling times of the T-type three-level inverter system in a power frequency period;
step 6: according to the fault type, the corresponding control scheme is switched to realize the fault-tolerant operation of the T-type three-level inverter, and the method specifically comprises the following steps:
step 6.1: calculating the residual effective voltage vector of the T-type three-level inverter under the current fault according to the fault type;
step 6.2: judging whether the T-type three-level inverter has fault-tolerant operation capacity or not according to the obtained residual effective voltage vector;
step 6.3: calculating the failure condition of a switching state in a switching period, and drawing an effective output voltage vector range diagram of the current inverter; if the effective output voltage vector range is reduced and the modulation degree is more than 0.5, the modulation degree is forcedly adjusted to be within the effective output voltage vector range, and derating fault-tolerant operation is performed; if the effective output voltage vector range is unchanged, full fault-tolerant operation can be performed;
step 6.4: the vector sequence and switching time in the switching period are adjusted by the method of equivalent vector replacement.
2. A fault-tolerant control system for open-circuit faults of a T-type three-level inverter is characterized in that: the fault-tolerant control method for realizing the open-circuit fault of the T-type three-level inverter according to claim 1, comprising a direct current source, the T-type three-level inverter, a load, a controller and a fault feature extraction module; the direct current source is connected with the T-shaped three-level inverter for supplying power, and the load is connected with the T-shaped three-level inverter; the fault characteristic extraction module is connected with the T-shaped three-level inverter so as to read fault signals; the controller is connected with the fault feature extraction module and the T-type three-level inverter to realize fault diagnosis and fault-tolerant control of the T-type three-level inverter according to fault types.
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| CN113746107B (en) * | 2021-08-09 | 2023-06-06 | 电子科技大学 | Grid-connected inverter fault-tolerant control method based on sequence model predictive control |
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