CN113708655B - Inverter switching tube fault tolerance control method based on self-adaptive SVPWM - Google Patents

Inverter switching tube fault tolerance control method based on self-adaptive SVPWM Download PDF

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CN113708655B
CN113708655B CN202111021371.4A CN202111021371A CN113708655B CN 113708655 B CN113708655 B CN 113708655B CN 202111021371 A CN202111021371 A CN 202111021371A CN 113708655 B CN113708655 B CN 113708655B
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CN113708655A (en
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朱琴跃
魏伟
谭喜堂
李爱华
李姚霖
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Tongji University
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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
    • H02M7/487—Neutral point clamped inverters
    • 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
    • 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
    • H02M7/53871—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 with automatic control of output voltage or current
    • H02M7/53875—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 with automatic control of output voltage or current with analogue control of three-phase output
    • 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
    • H02M7/539—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 with automatic control of output wave form or frequency
    • H02M7/5395—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 with automatic control of output wave form or frequency by pulse-width modulation

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Abstract

The invention relates to a fault tolerance control method for an inverter switching tube based on self-adaptive SVPWM, which comprises the following steps: 1) Based on a space voltage vector plane corresponding to the NPC five-level inverter, acquiring the number n of the space voltage vectors distributed by each node; 2) Acquiring a space voltage vector set S which can be continuously output by the NPC five-level inverter after a switching tube fails according to failure information n The method comprises the steps of carrying out a first treatment on the surface of the 3) According to the number n of space voltage vectors and the space voltage vector set S n Calculating the maximum linear modulation coefficient m after the fault occurs; 4) The amplitude of the target reference current is adjusted in real time according to the maximum linear modulation coefficient m, the difference between the actual current output and the reference current under fault is taken as a target control function, and a voltage vector sequence S meeting the minimum target control function is adaptively selected opt And then generates a PWM control signal at the next time. Compared with the prior art, the invention has the advantages of strong applicability, practicality, safety, low implementation difficulty and the like.

Description

Inverter switching tube fault tolerance control method based on self-adaptive SVPWM
Technical Field
The invention relates to the field of multi-level inverter control, in particular to an NPC five-level inverter switching tube fault tolerance control method based on self-adaptive SVPWM.
Background
The multi-level inverter has the advantages of reducing the withstand voltage value of the power device, reducing the output harmonic distortion rate, improving the output waveform quality and the like, and is widely applied to high-power occasions with medium and high voltage, so that the requirements on the safety and the reliability of the multi-level inverter are higher and higher. How to make a multilevel inverter adopt an effective fault-tolerant control method after a fault occurs is widely paid attention to the vast expert and scholars. At present, the main fault-tolerant control method can be divided into two main types of fault-tolerant control based on hardware topology reconstruction and software fault-tolerant control based on redundant space vectors.
For hardware fault-tolerant control, a variety of inverter fault-tolerant topologies have been proposed since the nineties of the last century, which can be broadly divided into switch-redundant fault-tolerant topologies, phase-redundant fault-tolerant topologies, and active neutral-point-clamped fault-tolerant topologies. This type of approach can be tolerant to multiple fault types, but can greatly increase hardware cost and complexity of control for a multilevel inverter due to the additional devices or bridge arms that it requires.
The basic idea of the software fault-tolerant control is to replace a space voltage vector which cannot be output by a redundant space voltage vector when a power device fails, so that the fault-tolerant control is performed. The method does not increase the volume of the system and the cost of the system, but needs to formulate different modulation strategies for different fault types, and needs to offline adjust vector action sequences according to the fault types and fault tolerance schemes, so that the calculated amount is complex, the response time of the system to fault tolerance control is delayed greatly, the control effect and the output performance of the system under the fault condition do not reach the expected requirements, and further research is needed.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a fault-tolerant control method for the switching tube fault of the inverter based on the adaptive SVPWM.
The aim of the invention can be achieved by the following technical scheme:
an inverter switching tube fault tolerance control method based on adaptive SVPWM comprises the following steps:
1) Based on a space voltage vector plane corresponding to the NPC five-level inverter, acquiring the number n of the space voltage vectors distributed by each node;
2) Acquiring a space voltage vector set S which can be continuously output by the NPC five-level inverter after a switching tube fails according to failure information n ；
3) According to the number n of space voltage vectors and the space voltage vector set S n Calculating the maximum linear modulation coefficient m after the fault occurs;
4) The amplitude of the target reference current is adjusted in real time according to the maximum linear modulation coefficient m, the difference between the actual current output and the reference current under fault is used as a target control function, and the current is controlled in spacePressure vector set S n In which a voltage vector sequence S satisfying a minimum of a target control function is adaptively selected opt And further generating a PWM control signal at the next moment, controlling the output of the NPC five-level inverter, and completing the whole fault tolerance process.
The step 1) specifically comprises the following steps:
101 For each node, a space voltage vector (S) with the smallest a-phase component a ，S b ，S c ) The alpha and beta components of continuous voltage variable under the two-phase static coordinate system are converted into the following components:
Figure BDA0003242078070000021
wherein U is dc Is the direct-current side voltage, U, of the NPC five-level inverter α 、U β Alpha and beta components of the continuous voltage variable, respectively;
102 U) to be U α 、U β Converting into an amplitude form to obtain a space voltage vector amplitude U and an included angle delta between the space voltage vector amplitude U and an alpha axis, wherein the space voltage vector amplitude U is as follows:
Figure BDA0003242078070000022
103 The number n of the space voltage vectors distributed by the node is calculated according to the space voltage vector amplitude U, and the method comprises the following steps:
Figure BDA0003242078070000023
where ceil () is a round-up function.
For space voltage vector (S a ，S b ，S c ) After determining the number n of space voltage vectors distributed by the node, a space voltage vector is obtained (S a ，S b ，S c ) Is:
(S a+1 ，S b+1 ，S c+1 )，(S a+2 ，S b+2 ，S c+2 )，…，(S a+n-1 ，S b+n-1 ，S c+n-1 )。
the step 2) specifically comprises the following steps:
201 Generating 5 of NPC five level topology under normal operation conditions 3 Space voltage vector (S) a ，S b ，S c ) A vector set S formed by the vector sets;
202 According to the input fault information matrix F, combining the loss condition of the level when different types of faults occur to different switching tubes to obtain a fault vector set S which cannot be normally output due to the influence of the fault tube under the set fault type f ；
203 Eliminating the fault vector set S from the vector set S f Obtaining a vector set S which can still continue to be output under the influence of a fault tube n 。
The fault information matrix F is a matrix of i rows and j columns, wherein i=1, 2,3, j=1, … and 8, each element in the matrix represents the state of each switching tube, 0 represents normal operation, 1 represents open-circuit fault, and 2 represents short-circuit fault.
The step 3) specifically comprises the following steps:
301 When the reference voltage vector is located in the x-th sector in the space vector plane, the maximum vector that the system can output in the x-th sector is (S) a0 ，S b0 ，S c0 )∈S n Calculating a maximum linear modulation coefficient m, and respectively drawing symmetrical hexagonal areas corresponding to the maximum linear modulation coefficient m in the changing process from large to small on a five-level space voltage vector plane;
302 Starting from the space voltage vector in the x-th sector which is smaller than the maximum vector which can be output, and selecting the space voltage vector in the vector set S n The remaining 5 vectors constituting the vertices of the hexagon are searched, which vectors have the same search priority when two hexagons composed of different vectors possess the same size of maximum linear modulation coefficient, if the vector set S n If the vector in the tree is unable to be output due to failure, searching the redundant vector, if the redundant vector is still available, the rootAnd calculating the maximum linear modulation coefficient m of the system after various faults according to the space voltage vector coordinate with the minimum a-phase component in the maximum space voltage vector in the x-th sector in real time.
In the step 301), the calculation formula of the maximum linear modulation coefficient m is:
Figure BDA0003242078070000031
wherein, N represents the level number which each phase can output when the system operates normally, and N takes a value of 5 for NPC five-level topology.
The step 4) specifically comprises the following steps:
401 Sampling at k time to obtain three-phase output current i of NPC five-level inverter a (k)，i b (k) I c (k)；
402 Clark transformation is carried out on the three-phase output current to obtain controlled variables under a two-phase static coordinate system, and the following steps are provided:
Figure BDA0003242078070000041
wherein i is α (k)、i β (k) The current components of the alpha axis and the beta axis under a two-phase static coordinate system are respectively;
403 Obtaining a predicted value of the controlled variable at the moment k+1 according to a predicted model of the NPC five-level inverter;
404 The reference current value at time k+1 is calculated by the second-order Lagrangian extrapolation method, and then:
Figure BDA0003242078070000042
wherein,,
Figure BDA0003242078070000043
reference current values of the alpha axis and the beta axis at the time points k+1, k-1 and k-2 respectively;
405 The amplitude of the target reference current is adjusted in real time by the maximum linear modulation coefficient m, then:
Figure BDA0003242078070000044
wherein,,
Figure BDA0003242078070000045
respectively the amplitude values of the adjusted target reference currents;
406 Vector set S) n All the voltage vector states in the set are substituted into the cost function in sequence to calculate, and the space vector S which enables the cost function to be minimum is selected opt The method is applied to an NPC five-level inverter at the next moment, and square errors are selected as a cost function of a current tracking model, and the method comprises the following steps:
Figure BDA0003242078070000046
where g represents the square error.
In the step 403), the process of establishing the five-level inverter predictive control model specifically includes the following steps:
4031 Assuming that the three-phase output load of the NPC five-level inverter is a symmetrical resistive-inductive load, the relationship between the three-phase voltage and the current is obtained by kirchhoff voltage and current law, then:
Figure BDA0003242078070000047
wherein u is a (k)、u b (k)、u c (k) The three-phase output voltages are respectively three-phase output voltages, L is a load inductance, and R is a load resistance;
4032 Clark transformation to obtain an output model under a two-phase stationary alpha beta coordinate system, the following are:
Figure BDA0003242078070000051
wherein u is α (k)、u β (k) The output voltages of the alpha axis and the beta axis under a two-phase static coordinate system are respectively;
4033 Sampling forward difference method to discretize, transform and sort the continuous output model to obtain NPC five-level inverter discrete prediction model under two-phase static coordinate system, then:
Figure BDA0003242078070000052
Figure BDA0003242078070000053
wherein T is s For the sampling period, R is the load resistance and L is the load inductance.
The method is realized by an inverter switching tube fault tolerance control system, and the inverter switching tube fault tolerance control system comprises:
the space voltage vector redundancy calculation module: the method comprises the steps of calculating the number n of space voltage vectors distributed by each node based on a space voltage vector plane corresponding to an NPC five-level inverter;
the voltage vector set calculation module: space voltage vector set S capable of continuously outputting after fault is calculated according to fault information n ；
The maximum linear modulation coefficient calculation module: combining output results of the space voltage vector redundancy calculation module and the voltage vector set calculation module, and calculating a maximum linear modulation coefficient m of the system after the fault occurs;
a current tracking control module: the amplitude of the target reference current is regulated in real time through the output result of the maximum linear modulation coefficient calculation module, the difference between the actual current output and the reference current under fault is taken as a target control function, and a vector set S is obtained by the voltage vector set calculation module n In which a voltage vector sequence S satisfying a minimum of a target control function is adaptively selected opt And generating a PWM control signal at the next moment, and controlling the output of the NPC five-level inverter to complete the whole fault tolerance process.
Compared with the prior art, the invention has the following advantages:
1. the invention has simpler requirements on the control object, and the provided design method only requires to know the corresponding parameters of the controlled object, namely the five-level inverter, the fault information of the switching tube, the sampling current/voltage, the space voltage vector parameters and other information, so that the requirements on the object are greatly relaxed, and the applicability of the method is enhanced.
2. The invention fully considers the constraint condition of the NPC five-level inverter in practical application in the process of designing the control method, not only can effectively restrain output current harmonic waves, but also can carry out effective fault-tolerant control when the inverter has open circuit and short circuit faults, thereby improving the dynamic and steady-state performance of the inverter during operation and enhancing the practicability and safety.
3. When the method is used for compounding faults of different positions and types of the inverter, a corresponding PWM mapping table is not required to be established, the real-time delineation of the available space voltage vector set is carried out through the fault type, the corresponding modulation ratio is calculated, and a switching tube grid signal is generated by matching with a model predictive control algorithm, so that the implementation difficulty of the fault-tolerant control algorithm is reduced.
4. The invention solves the problem that the existing offline algorithm cannot tolerate unexpected faults through the self-adaptive SVPWM fault-tolerant control, has a certain degree of universality for open-circuit and short-circuit fault-tolerant control of the NPC five-level inverter switching tube, and is flexible to use.
5. The invention does not need to increase the number of other devices, does not increase the control cost, does not increase the volume of the system, has high cost performance, is easy to realize and convenient to apply, improves the utilization rate of the power devices, and has higher practical application value.
Drawings
FIG. 1 is a schematic diagram of signal transmission between the present invention and a controlled object.
Fig. 2 is a topology diagram of an NPC five-level inverter.
FIG. 3 is a block diagram of the system architecture of the present invention.
Fig. 4 is a schematic diagram of space voltage vector redundancy calculation.
FIG. 5 is a vector set S n A computational flow chart.
Fig. 6 shows different m and their corresponding hexagonal areas.
Fig. 7 is a block diagram of NPC five level inverter current tracking control.
FIG. 8 is S a1 And S is equal to b1 Three-phase output current waveform at open circuit fault.
FIG. 9 is S a1 And S is equal to b1 Three-phase output voltage waveform at open circuit fault.
FIG. 10 is S a1 And S is equal to a3 And outputting current waveforms by three phases when short circuit faults occur.
FIG. 11 is S a1 And S is equal to a3 And outputting a voltage waveform of three phases when a short circuit is fault.
Detailed Description
The invention will now be described in detail with reference to the drawings and specific examples.
Examples
The invention provides a fault tolerance control system and a control method for an NPC five-level inverter switching tube based on self-adaptive SVPWM, wherein the signal transmission condition among NPC five-level inverters is shown in figure 1, an NPC five-level inverter module is a controlled object, and the topological structure is shown in figure 2. The self-adaptive fault-tolerant control module contains a program for realizing a fault-tolerant control method, and fault-tolerant control is completed between the two modules by transmitting a sampling current/voltage value, fault information and a switching signal.
As shown in fig. 3, the fault-tolerant control system based on the adaptive SVPWM mainly includes a space voltage vector redundancy calculation module, a voltage vector set calculation module, a maximum linear modulation coefficient calculation module, and a current tracking control module. The space voltage vector redundancy calculation module calculates the number n of the space voltage vectors distributed by each node based on the space voltage vector plane corresponding to the NPC five-level inverter; the voltage vector set calculation module calculates the space voltage vector which can still be continuously output after the fault according to the fault informationSet S n The method comprises the steps of carrying out a first treatment on the surface of the The maximum linear modulation coefficient calculation module integrates the results of the two modules, and realizes the calculation of the maximum linear modulation coefficient m of the system after the system fails; the current tracking control module adjusts the amplitude of the target reference current in real time through the output result of the maximum linear modulation coefficient calculation module, takes the difference between the actual current output and the reference current under fault as a target control function, and obtains a vector set S by the voltage vector set calculation module n In which a voltage vector sequence S satisfying the minimum of the target control function is adaptively selected opt The PWM control signal at the next moment is generated to control the output of the NPC five-level inverter, so that the whole fault tolerance process is completed.
The invention provides a fault-tolerant control method based on a self-adaptive SVPWM fault-tolerant control system, which comprises the following steps:
(1) Establishing a space voltage vector redundancy calculation model
According to the basic principle of SVPWM modulation strategy, the side length of the space vector plane hexagon is 2U dc For a space voltage vector plane of five-level topology, each small triangle has a side length of U dc And/6, as shown in FIG. 4. For the space voltage vectors distributed on each node, the more the space voltage vectors are located on the inner side, the more the redundancy of the space voltage vectors is, so that the model is mainly based on the geometrical relationship of space vector planes and the basic principle of SVPWM, and the number of the space voltage vectors corresponding to each node is calculated on line.
The method specifically comprises the following substeps:
(101) For the space voltage vector with the smallest a-phase component on each node (S a ，S b ，S c ) It is converted into alpha and beta components of continuous voltage variable under two-phase static coordinate system by the formula (1), wherein U dc The dc side voltage of the NPC five-level inverter is:
Figure BDA0003242078070000071
(102) U is set to α 、U β Converting into a form of an amplitude angle to obtain a space voltage vector amplitude U and an angle delta between the space voltage vector amplitude U and an alpha axis, wherein the space voltage vector amplitude U and the angle delta are shown as a formula (2):
Figure BDA0003242078070000081
(103) As can be seen from fig. 4, for each space vector, the distance from U to zero vector determines the redundancy of the space voltage vector with respect to the size of each small triangle side, so after obtaining U, the number n of space voltage vectors distributed by the node can be obtained by using equation (3), where ceil () is an upward rounding function.
Figure BDA0003242078070000082
(104) For space voltage vector (S a ，S b ，S c ) After the number n of space voltage vectors distributed by the node is determined, the method can obtain (S a ，S b ，S c ) Is: (S) a+1 ，S b+1 ，S c+1 )，(S a+2 ，S b+2 ，S c+2 )，…，(S a+n-1 ，S b+n-1 ，S c+n-1 ) The vector and its resulting redundant vector will be used as input to the calculation of the maximum linear modulation factor of the system after failure.
(2) Establishing a voltage vector set calculation model
The voltage vector set calculation module is used for 5 corresponding to NPC five-level topology 3 In the vector set S formed by the space voltage vectors, the vector set S which can still continue to be output under the fault type without being influenced by fault management is calculated in real time according to the fault information n 。
The method specifically comprises the following substeps:
(201) Generating 5 of NPC five level topology under normal operation condition 3 Space voltage vector (S) a ，S b ，S c ) Vector set of componentsS；
(202) According to the input fault information F, combining the loss condition of the level when different types of faults occur to different switching tubes to obtain a fault vector set S which cannot be normally output due to the influence of the fault tube under the fault type f . F is a matrix of i rows and j columns, wherein i=1, 2,3, j=1, …,8, each element in the matrix represents the state of each switching tube, 0 represents normal operation, 1 represents open-circuit fault, and 2 represents short-circuit fault;
(203) Subtracting the fault vector set S from the vector set S f Obtaining a vector set S which can still continue to be output under the influence of the fault tube n Vector set S n A computational flow diagram of (a) is shown in figure 5.
(3) Establishing a maximum linear modulation coefficient calculation model
The maximum linear modulation coefficient calculation model is a vector set S obtained by a voltage vector set calculation module n And (3) continuously changing the vector to the inner layer according to a pre-designed searching sequence by taking the vector with the maximum amplitude as the start, and finally calculating the maximum linear modulation coefficient of the system after the fault occurs on line.
The method specifically comprises the following substeps:
(301) When the reference voltage vector is located in the x-th sector in the space vector plane, the maximum vector that the system can output in the x-th sector is (S a0 ，S b0 ，S c0 ) Here (S) a0 ，S b0 ，S c0 )∈S n The maximum linear modulation factor m can be calculated according to equation (4) where N represents the number of levels that each phase of the system can output during normal operation, i.e., n=5 for NPC five-level topologies. According to the above calculation method, symmetrical hexagonal areas corresponding to the maximum linear modulation coefficient m in the changing process from large to small are respectively drawn on the five-level space voltage vector plane, as shown in fig. 6.
Figure BDA0003242078070000091
(302) Starting with a space voltage vector in the x-th sector that is smaller than the maximum vector that can be output, at S n The remaining 5 vectors that make up the vertices of the hexagon. It should be noted that for different vectors, the two hexagons they make up may have the same size of maximum linear modulation factor, when they have the same search priority.
Whereby from sector 1 to sector 6, from large vector to zero vector, are arranged in vector set S n And searching each vector in turn according to the priority order in the searching order of the medium priority from large to small. If the vector in the table cannot be output due to faults, the redundant vector obtained through the space voltage vector redundancy calculation module is required to be searched, if the redundant vector still can be output, the coordinates of the space voltage vector with the smallest a-phase component in the largest space voltage vector in the x-th sector are substituted into the formula (3), and the maximum linear modulation coefficient m of the system after various faults can be obtained in real time.
(4) Establishing a current tracking control model
The current tracking control model is based on the idea of modern model predictive control, and the actual three-phase output current and the target reference current are subjected to difference in each sampling moment when faults are acquired, so that a target control function, namely a cost function, is obtained, a voltage vector sequence meeting the minimum of the cost function is solved on line and acts on a controlled object at the next moment, namely the output performance of the system at the next moment is predicted by adopting the measured value of each moment, and the current tracking control under the fault condition is realized. The control flow of the current tracking control model is as shown in fig. 7, and mainly comprises the following steps:
(401) Three-phase output current i to inverter at time k a (k)，i b (k) I c (k) Sampling is performed.
(402) And (3) carrying out Clark conversion on the sampled current value through the formula (5) to obtain a controlled variable under a two-phase static coordinate system.
Figure BDA0003242078070000092
(403) Calculating the predicted value of the controlled variable at the moment k+1 according to a predicted model of the five-level inverter, wherein the process for establishing the predicted control model of the five-level inverter is as follows:
(4031) Assuming that the three-phase output load of the NPC five-level inverter is a symmetrical resistive-inductive load, the relation between the three-phase voltage and the three-phase current can be obtained by the kirchhoff voltage and the current law and is shown as a formula (6).
Figure BDA0003242078070000101
(4032) Clark transformation is carried out on the formula, and an output model under a two-phase static alpha beta coordinate system can be obtained and is shown as a formula (7).
Figure BDA0003242078070000102
(4033) And selecting a forward difference method to discretize the continuous model, wherein a forward difference calculation formula is shown in a formula (8), and converting and arranging the obtained NPC five-level inverter discrete prediction model under an alpha beta coordinate system according to the forward difference method is shown in a formula (9). Wherein T is s For the sampling period, R is the load resistance and L is the load inductance.
Figure BDA0003242078070000103
Figure BDA0003242078070000104
(404) The reference current value at the time k+1 is calculated by a second-order Lagrangian extrapolation method, and the expression is shown as a formula (10).
Figure BDA0003242078070000105
(405) And adjusting the amplitude of the target reference current in real time through the output result of the maximum linear modulation coefficient calculation model, as shown in the following formula (11).
Figure BDA0003242078070000106
(406) The vector set S is obtained by a voltage vector set calculation module n All the voltage vector states in the set are substituted into the cost function in sequence to calculate, and the space vector S which enables the cost function to be minimum is selected opt At the next moment, the method acts on the NPC five-level inverter, and the square error is selected as a basic form of a cost function of the current tracking model, as shown in a formula (12).
Figure BDA0003242078070000107
The effectiveness of the invention is illustrated by the simulation operation result when the NPC five-level inverter is connected with a three-phase resistance-inductance symmetrical load.
(501) Assume that the parameters are set as follows: the three-phase resistive load is a resistor r=10Ω, and an inductance l=10mh. DC side voltage U dc =1500v, divider capacitor C i =2.125 mF (i=1, 2,3, 4), the inverter parameters being the fundamental frequency f 1 =50 Hz, modulation ratio m=0.8, carrier frequency f c ＝1250Hz。
(502)S a1 And S is equal to b1 The output current and voltage simulation waveforms after the phase-to-phase open fault of the switching tube are shown in fig. 8 and 9 respectively. Because the fault-tolerant control method provided by the invention does not change the original topological structure of the NPC five-level inverter, the system is used for S x4 Open circuit faults occurring in the switching tube do not have fault tolerance capability. Therefore, the fault-tolerant control method provided by the invention does not contain S x4 The single-tube open-circuit fault, the single-phase double-tube open-circuit fault and the interphase double-tube open-circuit fault of the switching tube open-circuit fault have better fault tolerance.
(503)S a1 And S is equal to a3 The output current and voltage simulation waveforms after the switching tube has single-phase short circuit fault are respectively shown in figure 10. 11. While short-circuit faults of the same fault tube location and the same number of fault tubes have better fault tolerance relative to open-circuit faults from a fault tolerance perspective, they have a much more serious impact on the system than open-circuit faults. The fault-tolerant control method provided by the invention has better fault-tolerant capability for single-tube short-circuit faults and single-phase double-tube short-circuit faults, and for interphase double-tube short-circuit faults and more complex short-circuit fault types, the situation of the system after the fault becomes more complex, and the fault-tolerant control method only can carry out fault-tolerant control on the single-tube short-circuit faults and the single-phase double-tube short-circuit faults by combining an actual topological structure and a current circulation path when the system is subjected to fault-tolerant.
In conclusion, the invention designs an inverter switching tube fault tolerance control method based on self-adaptive SVPWM aiming at the open-circuit and short-circuit faults of an NPC five-level inverter power switching tube. When the composite faults of different positions and types are faced, a corresponding PWM mapping table is not required to be established, the available space voltage vector set is selected in real time through the fault type, the corresponding modulation ratio is calculated, and a model predictive control algorithm is matched to generate a switching signal. The invention reduces the implementation difficulty of the fault-tolerant control algorithm, solves the problem that the existing offline algorithm cannot tolerate unexpected faults, and improves the fault-tolerant capability of the NPC five-level inverter to complex faults.

Claims (6)

1. An inverter switching tube fault tolerance control method based on self-adaptive SVPWM is characterized by comprising the following steps:
1) Based on a space voltage vector plane corresponding to the NPC five-level inverter, acquiring the number n of the space voltage vectors distributed by each node;
2) Acquiring a space voltage vector set S which can be continuously output by the NPC five-level inverter after a switching tube fails according to failure information n ；
3) According to the number n of space voltage vectors and the space voltage vector set S n Calculating maximum linearity after failureA modulation factor m;
4) The amplitude of the target reference current is adjusted in real time according to the maximum linear modulation coefficient m, the difference between the actual current output and the reference current under fault is taken as a target control function, and the target control function is implemented in a space voltage vector set S n In which a voltage vector sequence S satisfying a minimum of a target control function is adaptively selected opt Generating a PWM control signal at the next moment, controlling the output of the NPC five-level inverter, and completing the whole fault tolerance process;
the step 3) specifically comprises the following steps:
301 When the reference voltage vector is located in the x-th sector in the space vector plane, the maximum vector that the system can output in the x-th sector is (S) a0 ,S b0 ,S c0 )∈S n Calculating a maximum linear modulation coefficient m, and respectively drawing symmetrical hexagonal areas corresponding to the maximum linear modulation coefficient m in the changing process from large to small on a five-level space voltage vector plane;
302 Starting from the space voltage vector in the x-th sector which is smaller than the maximum vector which can be output, and selecting the space voltage vector in the vector set S n The remaining 5 vectors constituting the vertices of the hexagon are searched, which vectors have the same search priority when two hexagons composed of different vectors possess the same size of maximum linear modulation coefficient, if the vector set S n If the redundant vector still can be output, calculating the maximum linear modulation coefficient m of the system after various faults according to the space voltage vector coordinate with the minimum a-phase component in the maximum space voltage vector in the x-th sector in real time;
in the step 301), the calculation formula of the maximum linear modulation coefficient m is:
Figure FDA0004094943090000011
n represents the level number which can be output by each phase during normal operation of the system, and for NPC five-level topology, the value of N is 5;
the step 4) specifically comprises the following steps:
401 Sampling at k time to obtain three-phase output current i of NPC five-level inverter a (k)，i b (k) I c (k)；
402 Clark transformation is carried out on the three-phase output current to obtain controlled variables under a two-phase static coordinate system, and the following steps are provided:
Figure FDA0004094943090000021
wherein i is α (k)、i β (k) The current components of the alpha axis and the beta axis under a two-phase static coordinate system are respectively;
403 Obtaining a predicted value of the controlled variable at the moment k+1 according to a predicted model of the NPC five-level inverter;
404 The reference current value at time k+1 is calculated by the second-order Lagrangian extrapolation method, and then:
Figure FDA0004094943090000022
wherein,,
Figure FDA0004094943090000023
reference current values of the alpha axis and the beta axis at the time points k+1, k-1 and k-2 respectively;
405 The amplitude of the target reference current is adjusted in real time by the maximum linear modulation coefficient m, then:
Figure FDA0004094943090000024
wherein,,
Figure FDA0004094943090000025
respectively the amplitude values of the adjusted target reference currents;
406 Vector set S) n All of (3)The voltage vector states are sequentially substituted into the cost function to calculate, and a space vector S which enables the cost function to be minimum is selected opt The method is applied to an NPC five-level inverter at the next moment, and square errors are selected as a cost function of a current tracking model, and the method comprises the following steps:
Figure FDA0004094943090000026
wherein g represents a square error;
in the step 403), the process of establishing the five-level inverter predictive control model specifically includes the following steps:
4031 Assuming that the three-phase output load of the NPC five-level inverter is a symmetrical resistive-inductive load, the relationship between the three-phase voltage and the current is obtained by kirchhoff voltage and current law, then:
Figure FDA0004094943090000027
wherein u is a (k)、u b (k)、u c (k) The three-phase output voltages are respectively three-phase output voltages, L is a load inductance, and R is a load resistance;
4032 Clark transformation to obtain an output model under a two-phase stationary alpha beta coordinate system, the following are:
Figure FDA0004094943090000031
wherein u is α (k)、u β (k) The output voltages of the alpha axis and the beta axis under a two-phase static coordinate system are respectively;
4033 Sampling forward difference method to discretize, transform and sort the continuous output model to obtain NPC five-level inverter discrete prediction model under two-phase static coordinate system, then:
Figure FDA0004094943090000032
Figure FDA0004094943090000033
wherein T is s For the sampling period, R is the load resistance and L is the load inductance.
2. The fault-tolerant control method of inverter switching tube based on adaptive SVPWM according to claim 1, wherein said step 1) specifically comprises the steps of:
101 For each node, a space voltage vector (S) with the smallest a-phase component a ,S b ,S c ) The alpha and beta components of continuous voltage variable under the two-phase static coordinate system are converted into the following components:
Figure FDA0004094943090000034
wherein U is dc Is the direct-current side voltage, U, of the NPC five-level inverter α 、U β Alpha and beta components of the continuous voltage variable, respectively;
102 U) to be U α 、U β Converting into an amplitude form to obtain a space voltage vector amplitude U and an included angle delta between the space voltage vector amplitude U and an alpha axis, wherein the space voltage vector amplitude U is as follows:
Figure FDA0004094943090000035
103 The number n of the space voltage vectors distributed by the node is calculated according to the space voltage vector amplitude U, and the method comprises the following steps:
Figure FDA0004094943090000036
where ceil () is a round-up function.
3. An inverter switching tube fault-tolerant control method based on adaptive SVPWM according to claim 2, characterized in that for the space voltage vector (S a ,S b ,S c ) After determining the number n of space voltage vectors distributed by the node, a space voltage vector is obtained (S a ,S b ,S c ) Is:
(S a+1 ,S b+1 ,S c+1 )，(S a+2 ,S b+2 ,S c+2 )，…，(S a+n-1 ,S b+n-1 ,S c+n-1 )。
4. the fault-tolerant control method of inverter switching tube based on adaptive SVPWM according to claim 1, wherein said step 2) specifically comprises the steps of:
201 Generating 5 of NPC five level topology under normal operation conditions 3 Space voltage vector (S) a ,S b ,S c ) A vector set S formed by the vector sets;
202 According to the input fault information matrix F, combining the loss condition of the level when different types of faults occur to different switching tubes to obtain a fault vector set S which cannot be normally output due to the influence of the fault tube under the set fault type f ；
203 Eliminating the fault vector set S from the vector set S f Obtaining a vector set S which can still continue to be output under the influence of a fault tube b 。
5. The fault-tolerant control method for switching tube faults of an inverter based on adaptive SVPWM according to claim 4, wherein the fault information matrix F is a matrix of i rows and j columns, wherein i=1, 2,3, j=1, …,8, each element in the matrix represents the state of each switching tube, 0 represents normal operation, 1 represents open circuit fault, and 2 represents short circuit fault.
6. The adaptive SVPWM-based fault-tolerant control method for an inverter switching tube according to claim 1, wherein the method is implemented by an inverter switching tube fault-tolerant control system, the inverter switching tube fault-tolerant control system comprising:
the space voltage vector redundancy calculation module: the method comprises the steps of calculating the number n of space voltage vectors distributed by each node based on a space voltage vector plane corresponding to an NPC five-level inverter;
the voltage vector set calculation module: space voltage vector set S capable of continuously outputting after fault is calculated according to fault information n ；
The maximum linear modulation coefficient calculation module: combining output results of the space voltage vector redundancy calculation module and the voltage vector set calculation module, and calculating a maximum linear modulation coefficient m of the system after the fault occurs;
a current tracking control module: the amplitude of the target reference current is regulated in real time through the output result of the maximum linear modulation coefficient calculation module, the difference between the actual current output and the reference current under fault is taken as a target control function, and a vector set S is obtained by the voltage vector set calculation module n In which a voltage vector sequence S satisfying a minimum of a target control function is adaptively selected opt And generating a PWM control signal at the next moment, and controlling the output of the NPC five-level inverter to complete the whole fault tolerance process.
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