CN111697539B

CN111697539B - Three-level ANPC inverter open-circuit fault tolerance method based on carrier modulation

Info

Publication number: CN111697539B
Application number: CN202010504136.1A
Authority: CN
Inventors: 赵鲁; 高瞻; 葛琼璇; 李耀华; 张波; 张树田; 郭科宇; 杨董
Original assignee: Institute of Electrical Engineering of CAS
Current assignee: Institute of Electrical Engineering of CAS
Priority date: 2020-06-05
Filing date: 2020-06-05
Publication date: 2022-05-24
Anticipated expiration: 2040-06-05
Also published as: CN111697539A

Abstract

A three-level ANPC inverter open-circuit fault tolerance method based on carrier modulation is disclosed. When the single-phase switching device has open-circuit fault, the fault-tolerant method firstly detects the current direction I of the fault phase_dir(ii) a Defining the maximum value and the minimum value of the three-phase sine wave as V respectively_maxAnd V_minZero sequence voltage of Z_sSaid fault tolerant method is in_dirWhen is 1 hour Z_s＝‑0.5×(V_max+V_min+1) in I_dir0 season Z_s＝‑0.5×(V_max+V_min-1) and by reacting Z_sInjecting a three-phase sine wave to obtain a three-phase modulation wave during open-circuit fault; comparing the three-phase modulation wave with a carrier wave to obtain a level state output by the three-level ANPC inverter; and determining switching signals of all switching devices of the three-level ANPC inverter according to the output level state and the type of the switching device with the open-circuit fault. The fault-tolerant method can realize the fault-tolerant operation of the three-level ANPC inverter when the single-phase switching devices generate open-circuit faults at most, can ensure that the fault phase outputs phase voltage normally, and is convenient to realize.

Description

Three-level ANPC inverter open-circuit fault tolerance method based on carrier modulation

Technical Field

The invention relates to a fault tolerance method, in particular to an open-circuit fault tolerance method for a three-level ANPC inverter.

Background

The traditional three-level Neutral Point Clamped (NPC) inverter has wide application in the field of medium-voltage high power, but the loss distribution of each switching device on the same bridge arm is not balanced. To address this problem, Bruckner, germany scholars, proposed a three-level Active NPC (ANPC) inverter as shown in fig. 1 by replacing the clamp diodes with controllable switching devices. The literature, "study of midpoint potential control strategy of three-level ANPC converter" (zhang bo. [ J ]. new electrical energy technology, 2016,35(8):1-7.) indicates that, compared with the traditional three-level NPC inverter, the three-level ANPC inverter has more switching states and midpoint current conduction paths, and can balance the loss of each switching device by reasonably utilizing the midpoint current conduction path, thereby improving the maximum switching frequency and the output power of the inverter. In addition, more midpoint current conducting paths provide the possibility of designing a new fault-tolerant method.

Fault tolerance is short for fault tolerance, and the literature, "diagnosis of fault and fault tolerance control research of three-level inverter" (royal [ D ]. jiangsu: university of mining china 2015.), indicates that fault tolerance control of the inverter means that when the inverter fails, the continuous, safe and reliable operation of the system is maintained on the premise that performance indexes are basically unchanged or slightly sacrificed within an acceptable range by reconstructing inverter topology, adjusting control strategy or combining the two in a mode of meeting performance indexes. In the document entitled "summary of fault-tolerant technology for multilevel voltage source inverter" (xushuai [ J ]. report of electrotechnical science 2015,30(21): 39-50), it is pointed out that the adoption of fault-tolerant technology is one of the main approaches for improving the reliability of an inverter system, and open-circuit faults are common faults of inverter switching devices, so that the research on the open-circuit fault-tolerant method of the three-level ANPC inverter has important application value.

In order to research the open-circuit fault tolerance method of the three-level ANPC inverter, a space vector corresponding to the three-level inverter is analyzed firstly. The level states of the three-level inverter from high to low output are defined as P, O, N, and the space vectors of the three-level inverter can be summarized in fig. 2. The space vectors shown in fig. 2 can be further classified into a large vector, a medium vector, a P-type small vector, an N-type small vector and a zero vector according to the magnitude, and the specific classification of the space vectors is shown in table 1. The P type small vector and the N type small vector at the same position, and the zero vector OOO, PPP and NNN are mutually redundant vector states.

For Open-circuit fault-tolerant control of a three-level inverter based on space vectors, the document Open-circuit fault diagnosis and fault-tolerant control for a grid-connected NPC inverter (u.m.choi. [ J ] IEEE transition on

TABLE 1 type of space vector for three-level inverter

Power Electronics,2016,31(10): 7234-. According to the method, the redundant space vector duty ratio is adjusted, and fault-tolerant operation can be realized without adding extra hardware equipment. However, the method needs to calculate the action time of the space vector, and the space vectors used in fault-tolerant operation are different according to different fault conditions, so that the implementation is complex.

Aiming at the open-circuit fault-tolerant control of a three-level inverter based on a carrier wave, an open-circuit fault-tolerant control method based on a carrier wave is proposed in the literature of Analysis and design of Active NPC (ANPC) inverters for fault-tolerant operation of high-Power electric drives (Jun Li [ J ]. IEEE transfer on Power Electronics,2012,27(2): 519) 533). The method does not need to calculate the action time of the space vector, and has the advantages of simple calculation and easy realization. However, under the action of the method, the phase voltage of the fault phase cannot be normally output, so that the three-phase voltage is not symmetrical, and the harmonic characteristics of the output current are adversely affected.

Disclosure of Invention

In order to overcome the defects of the traditional open-circuit fault tolerance method of the three-level ANPC inverter, the invention provides the open-circuit fault tolerance method of the three-level ANPC inverter based on carrier modulation, and the reliability of the three-level ANPC inverter can be improved. Compared with the traditional open-circuit fault-tolerant control method based on the space vector, the method realizes fault-tolerant operation directly according to the comparison result of the carrier wave and the modulation wave, does not need to calculate the action time of the space vector, and is very convenient for engineering realization. In addition, compared with the traditional open-circuit fault-tolerant control method based on the carrier wave, the method does not need to clamp the output level of the fault phase to O forcibly, and the three-phase voltage under the action of the method keeps symmetry, so that the method has better harmonic performance during fault-tolerant operation.

When the single-phase switching device of the three-level ANPC inverter has an open-circuit fault, the three-level ANPC inverter open-circuit fault tolerance method based on carrier modulation firstly detects the current direction I of a fault phase_dir(ii) a Defining the maximum value of three-phase sine wave as V_maxMinimum value of V_minZero sequence voltage of Z_sThe fault-tolerant method of the invention is in_dirWhen is 1 hour Z_s＝-0.5×(V_max+V_min+1) in I _dir0 season Z_s＝-0.5×(V_max+V_min-1) and by applying a zero sequence voltage Z_sInjecting a three-phase sine wave to obtain a three-phase modulation wave during open-circuit fault; comparing the three-phase modulation wave with a carrier wave to obtain a level state output by the three-level ANPC inverter; and determining the switching signals of the switching devices of the three-level ANPC inverter according to the output level state and the type of the switching device with the open-circuit fault, thereby realizing the fault-tolerant operation of the three-level ANPC inverter.

The three-level ANPC inverter open-circuit fault tolerance method based on carrier modulation specifically comprises the following steps:

1. detecting fault phase current direction I_dir

Defining the current corresponding to the fault as I_xThe invention detects the fault phase current direction I_dirThe method comprises the following steps:

when I is_xWhen the temperature is more than or equal to 0, let I _dir1 is ═ 1; when I is_xWhen less than 0, let I_dir＝0。

2. Determining zero sequence voltage Z_s

Defining zero sequence voltage as Z_sThe invention is to Z _sThe determination method of (2) is as follows:

when I is_dirWhen 1, let Z_s＝-0.5×(V_max+V_min+ 1); when I is_dirWhen equal to 0, let Z_s＝-0.5×(V_max+V_min-1)。

In the above determination method, I_dirIs the direction of current flow of the faulted phase, Z_sIs zero sequence voltage, V_maxAnd V_minRepresenting the maximum and minimum values of the three-phase sine wave, respectively. Defining three-phase sine waves as V_a、V_bAnd V_cMaximum value V of three-phase sine wave_maxAnd the minimum value V of the three-phase sine wave_minThe judging method comprises the following steps:

when V is_a≥V_bAnd V is_a≥V_cWhen making V_max＝V_a(ii) a When V is_b≥V_aAnd V is_b≥V_cWhen making V_max＝V_b(ii) a When V is_c≥V_bAnd V is_c≥V_aWhen making V_max＝V_c；

When V is_a≤V_bAnd V is_a≤V_cWhen making V_min＝V_a(ii) a When V is_b≤V_aAnd V is_b≤V_cWhen making V_min＝V_b(ii) a When V is_c≤V_bAnd V is_c≤V_aWhen making V_min＝V_c。

3. Obtaining three-phase modulated wave in open-circuit fault

Defining three-phase modulated waves as V_am、V_bmAnd V_cmThe invention is realized by applying a zero sequence voltage Z_sThe method for injecting the three-phase sine wave to obtain the three-phase modulation wave during the open-circuit fault comprises the following steps:

in the formula (1), V_am、V_bmAnd V_cmRepresenting a three-phase modulated wave, V_a、V_bAnd V_cRepresenting a three-phase sine wave, Z_sFor zero sequence voltage, t is time, ω is angular frequency, a represents the amplitude of the sine wave, and the maximum value of a is limited to 0.577.

4. Obtaining the output level state of the three-level ANPC inverter

Defining three level states of the three-level ANPC inverter from high to low output as P, O and N respectively, the method for obtaining the output level state of the three-level ANPC inverter of the invention is as follows:

When V is_am≥V_c1When the output level state of the phase A is P; when V is_am≤V_c2When the output level state of the phase A is N; when V is_am＞V_c2And V is_am＜V_c1When the output level state of the phase A is O;

when V is_bm≥V_c1When the phase B output level state is P; when V is_bm≤V_c2When the current is in the second phase, the output level state of the B phase is N; when V is_bm＞V_c2And V is_bm＜V_c1When the phase B output level state is O;

when V is_cm≥V_c1When the output level state of the phase C is P; when V is_cm≤V_c2When the current is in the second phase, the output level state of the C phase is N; when V is_cm＞V_c2And V is_cm＜V_c1When the output level state of the phase C is O;

in the above output level state determining method, V_am、V_bmAnd V_cmRepresenting a three-phase modulated wave, V_c1And V_c2Representing two triangular carriers of the same amplitude, frequency and direction, where V_c1Representing a triangular carrier wave, V, of value between 0 and 1_c2Representative value is-1To a triangular carrier between 0.

5. Determining switching signals for switching devices of a three-level ANPC inverter

Defining six switching devices from top to bottom of each phase of the three-level ANPC inverter as S1, S2, S3, S4, S5 and S6, the method of determining the switching signals of the switching devices of the three-level ANPC inverter of the present invention is as follows:

when the output level state is P, the switching devices S1 and S3 are turned on, and S2, S4, S5 and S6 are turned off; when the output level state is N, the switching devices S4 and S6 are turned on, and S1, S2, S3 and S5 are turned off; when the output level state is O, the switching signals of the switching devices are respectively:

1) Aiming at the open-circuit fault of any one of the S1, S3, S4 and S6, the switching devices S2 and S5 are turned on, and the S1, S3, S4 and S6 are turned off;

2) aiming at the open-circuit fault of any one of the S1, S2, S5 and S6, the switching devices S3 and S4 are turned on, and the S1, S2, S5 and S6 are turned off;

3) for any switching device of S1, S2, S3 and S6 to generate open-circuit fault, I_dirWhen the signal value is 1, the switching devices S2 and S5 are turned on, and S1, S3, S4 and S6 are turned off; in I_dirWhen the signal value is 0, the switching devices S3 and S4 are turned on, and S1, S2, S5 and S6 are turned off;

4) open-circuit failure of any switching device among S1, S4, S5 and S6, and is shown in I_dirWhen the signal value is 1, the switching devices S3 and S4 are turned on, and S1, S2, S5 and S6 are turned off; in I_dirWhen the signal value is 0, the switching devices S2 and S5 are turned on, and S1, S3, S4 and S6 are turned off;

in the above switching signal determining method, I_dirRepresenting the direction of current flow for the failed phase.

Drawings

FIG. 1 is a schematic diagram of a main circuit of a three-level ANPC inverter;

FIG. 2 is a three-level inverter space vector diagram;

the a-phase output level condition when open circuit fault occurs at Sa1 or Sa2 of the three-level ANPC inverter of fig. 3a, 3b, wherein: FIG. 3a shows that the current direction is positive and phase A cannot output P level, and FIG. 3b shows that the current direction is negative and phase A can normally output P level;

In the case of open-circuit fault at Sa3 or Sa4 of the three-level ANPC inverter of fig. 4a and 4b, the a-phase output level condition is as follows: FIG. 4a shows that the A phase cannot output N level when the current direction is negative, and FIG. 4b shows that the A phase can normally output N level when the current direction is positive;

fig. 5a and 5b are schematic diagrams of space vector sequences OOO → OOP → POP → PPP and OOO → ONO → NNO → NNN based on the comparison between the modulated wave and the carrier wave, wherein: fig. 5a corresponds to a schematic diagram of space vector sequence OOO → OOP → POP → PPP obtained based on the comparison between modulated wave and carrier wave, and fig. 5b corresponds to a schematic diagram of space vector sequence OOO → ONO → NNO → NNN obtained based on the comparison between modulated wave and carrier wave;

when open circuit faults occur in Sa1, Sa3, Sa4 and Sa6 of the three-level ANPC inverters in fig. 6a and 6b, current flow paths corresponding to the O level are provided, wherein: FIG. 6a corresponds to a current flow path with a positive current direction, and FIG. 6b corresponds to a current flow path with a negative current direction;

when open circuit faults occur in Sa1, Sa2, Sa5 and Sa6 of the three-level ANPC inverters in fig. 7a and 7b, current flow paths corresponding to the O level are provided, wherein: FIG. 7a corresponds to a current flow path with a positive current direction, and FIG. 7b corresponds to a current flow path with a negative current direction;

When open faults occur at Sa1, Sa2, Sa3 and Sa6 of the three-level ANPC inverters in fig. 8a and 8b, current circulation paths corresponding to the O level are provided, wherein: FIG. 8a corresponds to a current flow path with a positive current direction, and FIG. 8b corresponds to a current flow path with a negative current direction;

when open circuit faults occur in Sa1, Sa4, Sa5 and Sa6 of the three-level ANPC inverters in fig. 9a and 9b, current flow paths corresponding to the O level are provided, wherein: FIG. 9a corresponds to a current flow path with a positive current direction, and FIG. 9b corresponds to a current flow path with a negative current direction;

FIG. 10 is a flowchart illustrating an embodiment of a three-level ANPC inverter open-circuit fault tolerance method based on carrier modulation according to the present invention;

simulation results of the phase-a switching devices Sa1, Sa3, Sa4, Sa6 in the embodiments of fig. 11a, 11b, 11c, 11d, and 11e when open-circuit fault occurs and the fault-tolerant method is not used, wherein: fig. 11a shows a phase voltage a, a phase voltage B and three-phase currents, fig. 11B shows phase voltage and line voltage fundamental wave amplitudes at the time of no fault, fig. 11c shows phase voltage and line voltage fundamental wave amplitudes at the time of open circuit fault, fig. 11d shows three-phase currents THD at the time of no fault, and fig. 11e shows three-phase currents THD at the time of open circuit fault;

simulation results of the phase-a switching devices Sa1, Sa3, Sa4 and Sa6 in the embodiments of fig. 12a, 12b, 12c and 12d when open-circuit faults occur and the conventional open-circuit fault tolerance control method based on carrier waves is used, wherein: fig. 12a shows a phase voltage a, a phase voltage B and three-phase currents, fig. 12B shows fundamental amplitude values of the phase voltage and the line voltage at the time of an open-circuit fault, fig. 12c shows a three-phase current THD at the time of an open-circuit fault, and fig. 12d shows a midpoint voltage deviation value at the time of an open-circuit fault;

Simulation results of the phase-a switching devices Sa1, Sa3, Sa4 and Sa6 in the embodiments of fig. 13a, 13b, 13c, 13d and 13e when open circuit faults occur and the fault-tolerant method of the present invention is used, wherein: fig. 13a shows a-phase voltage, and three-phase currents, fig. 13B shows fundamental amplitudes of the phase voltage and the line voltage at the time of an open fault, fig. 13c shows a three-phase current THD at the time of an open fault, fig. 13d shows a midpoint voltage deviation value at the time of an open fault, and fig. 13e shows a-phase voltage, an a-phase current, an a-phase modulation wave, and a carrier wave at the time of an open fault;

simulation results of the phase-a switching devices Sa1, Sa4, Sa5 and Sa6 in the embodiments of fig. 14a and 14b when an open fault occurs, wherein: fig. 14a shows a-phase voltage, B-phase voltage and three-phase current when Sa1, Sa4, Sa5 and Sa6 have open circuit faults and the fault-tolerant method is not used, and fig. 14B shows a-phase voltage, line voltage and three-phase current when Sa1, Sa4, Sa5 and Sa6 have open circuit faults and the fault-tolerant method of the invention is used;

simulation results of the phase-a switching devices Sa1, Sa2, Sa5 and Sa6 in the embodiments of fig. 15a and 15b when an open fault occurs, wherein: fig. 15a shows the a-phase voltage, the B-phase voltage and the three-phase current when Sa1, Sa2, Sa5 and Sa6 have open circuit faults and the fault-tolerant method is not used, and fig. 15B shows the a-phase voltage, the three-phase current and the midpoint voltage deviation value when Sa1, Sa2, Sa5 and Sa6 have open circuit faults and the fault-tolerant method is used;

Simulation results when open faults occur in phase-a switching devices Sa1, Sa2, Sa3 and Sa6 in the embodiments of fig. 16a and 16b, wherein: fig. 16a shows a-phase voltage, B-phase voltage and three-phase current when Sa1, Sa2, Sa3 and Sa6 have open circuit faults and the fault-tolerant method is not used, and fig. 16B shows a-phase voltage, a-phase modulation wave, carrier wave and three-phase current when Sa1, Sa2, Sa3 and Sa6 have open circuit faults and the fault-tolerant method of the invention is used;

Detailed Description

The invention is further described with reference to the following figures and detailed description.

When the single-phase switching device has open-circuit fault, the three-level ANPC inverter open-circuit fault tolerance method based on carrier modulation firstly detects the current direction I of the fault phase_dir(ii) a Defining the maximum value and the minimum value of the three-phase sine wave as V respectively_maxAnd V_minZero sequence voltage of Z_sThe fault-tolerant method of the invention is in_dirWhen is 1 hour Z_s＝-0.5×(V_max+V_min+1) in I _dir0 season Z_s＝-0.5×(V_max+V_min-1) and by reacting Z_sInjecting a three-phase sine wave to obtain a three-phase modulation wave during open-circuit fault; comparing the three-phase modulation wave with a carrier wave to obtain a level state output by the three-level ANPC inverter; and determining the switching signals of the switching devices of the three-level ANPC inverter according to the output level state and the type of the switching device with the open-circuit fault, thereby realizing the fault-tolerant operation of the three-level ANPC inverter.

1. detecting the fault phase current direction I_dir

The current corresponding to the fault is defined as Ix, and the method for detecting the fault phase current direction Idir comprises the following steps:

when Ix is more than or equal to 0, making Idir equal to 1; when Ix is less than 0, let Idir equal 0.

The current direction flowing out of the midpoint is defined to be positive, and the invention needs to detectPhase current direction I for fault detection_dirThe reason for (a) is as follows:

taking phase a as an example, if the switching device Sa1 or Sa2 in fig. 1 has an open fault, when the phase a current direction is positive, as shown in fig. 3a, current cannot flow through the switching devices Sa1 and Sa2, and it cannot output the P level; and when the a-phase current direction is negative, as shown in fig. 3b, a current may flow through the anti-parallel diodes of the switching devices Sa1 and Sa2, thereby outputting a P level. Therefore, when the switching device S1 or S2 of the three-level ANPC inverter has an open-circuit fault, the corresponding current direction is required to be negative when the fault phase outputs the P level so that the fault phase can normally output the P level.

If the switching device Sa3 or Sa4 in fig. 1 has an open fault, when the a-phase current direction is negative, as shown in fig. 4a, current cannot flow through the switching devices Sa3 and Sa4, which cannot output N level; and when the a-phase current direction is positive, as shown in fig. 4b, a current may flow through the anti-parallel diodes of the switching devices Sa3 and Sa4, thereby outputting an N level. Therefore, when the switching device S3 or S4 of the three-level ANPC inverter has an open-circuit fault, the corresponding current direction is required to be positive when the fault phase outputs the N level in order that the fault phase can normally output the N level.

In order to enable the phase voltage of the fault phase to normally output three level states when an open-circuit fault occurs, it is necessary to ensure that the corresponding current direction is negative when the fault phase outputs a P level and positive when the fault phase outputs an N level. Therefore, the present invention requires first detecting the current direction of the failed phase.

2. Determining zero sequence voltage Z_s

On the basis of detecting the phase current direction of the fault, the invention also needs to determine the level state of the output of the fault phase. The invention realizes fault-tolerant control based on carrier modulation, and the output level state of the inverter is determined according to the comparison result of the three-phase modulation wave and the carrier. Since the modulation wave is obtained by injecting the zero-sequence voltage into the sine wave, the expression of the zero-sequence voltage needs to be further analyzed.

In order to ensure that the fault phase can normally output the P level when the open-circuit fault occurs, the P level output by the fault phase is ensuredThe corresponding current direction is negative. I.e. to ensure that the fault phase output level state is O or P level when the current direction is negative. When the reference voltage is in the phase angle region of 0 ° to 30 ° shown in fig. 2, the space vector sequence with the output level state of O or P level corresponds to OOO → OOP → POP → PPP, where OOO and PPP are redundant zero vectors and have the same action time. Let the sampling period be t _sThe action time of OOO and PPP in a single sampling period is t₁OOP action time of t₂POP action time is t₃. The method is obtained by the area equivalent principle of the modulated wave:

in the formula (2), V_am、V_bmAnd V_cmRespectively representing A-phase modulated wave, B-phase modulated wave and C-phase modulated wave, V_a、V_bAnd V_cRespectively an A-phase sine wave, a B-phase sine wave and a C-phase sine wave, Z_sIs a zero sequence voltage.

Based on the comparison between the modulated wave and the carrier, a space vector sequence OOO → OOP → POP → PPP is obtained as shown in fig. 5 a.

As can be seen from fig. 5 a:

when formula (3) is substituted for formula (2), it is possible to obtain:

Z_s＝-0.5×(V_c+V_b-1) (4)

according to FIG. 5a, for the space vector sequence OOO → OOP → POP → PPP, the maximum modulation wave is V_cmMinimum modulation wave is V_bmCorresponding to a maximum sine wave of V_cMinimum sine wave is V_bThen, equation (4) can be expressed as:

Z_s＝-0.5×(V_max+V_min-1) (5)

in the formula (5), V_maxRepresenting the maximum value of a three-phase sine wave, V_minRepresentative of threeThe minimum of the phase sine wave. The same applies to equation (5) in the remaining phase angle region of fig. 2.

In order to enable the fault phase to normally output the N level when the open circuit fault occurs, it is required to ensure that the corresponding current direction is positive when the fault phase outputs the N level. I.e. to ensure that the fault phase output level state is O or N level when the current direction is positive. When the reference voltage is in the phase angle region of 0 ° to 30 ° in fig. 2, the space vector sequence with the output level state of O or N level corresponds to OOO → ONO → NNO → NNN, where OOO and NNN correspond to redundant zero vectors and both have the same action time. Let the sampling period be t _sBoth OOO and NNN have time during a single sampling period₁ONO action time of time₂NNO action time is time₃. The method is obtained by the area equivalent principle of the modulated wave:

the schematic diagram of the space vector sequence OOO → ONO → NNO → NNN obtained based on the comparison between the modulated wave and the carrier wave is shown in fig. 5 b.

From fig. 5b it can be seen that:

when formula (7) is substituted for formula (6), it is possible to obtain:

Z_s＝-0.5×(V_c+V_b+1) (8)

according to FIG. 5b, for the space vector sequence OOO → ONO → NNO → NNN, the maximum modulation wave is V_cmMinimum modulation wave is V_bmCorresponding to a maximum sine wave of V_cMinimum sine wave is V_bThen, equation (8) can be expressed as:

Z_s＝-0.5×(V_max+V_min+1) (9)

in the formula (9), V_maxRepresenting the maximum value of a three-phase sine wave, V_minRepresenting the minimum of a three-phase sine wave. The formula (9) is the same in the remaining phase angle region of FIG. 2The method is also applicable.

To summarize the above conclusion, when the current direction is negative, the corresponding zero sequence voltage is-0.5 × (V) so that the fault phase can normally output P level when the open circuit fault occurs_max+V_min-1); in order to ensure that the fault phase can normally output N level when an open-circuit fault occurs, the current direction is required to be positive, and the corresponding zero-sequence voltage is-0.5 x (V)_max+V_min+1). Defining the fault phase current direction as I_dirZero sequence voltage of Z_sThen, there are:

when I is_dirWhen 1, let Z_s＝-0.5×(V_max+V_min+ 1); when I is _dirWhen equal to 0, let Z_s＝-0.5×(V_max+V_min-1)。

Further, when the modulation ratio is lower than 0.5, the space vector sequence outputting only the O and P levels and the space vector sequence outputting only the O and N levels can accurately synthesize the reference voltage. The modulation ratio of 0.5 corresponds to the amplitude of the three-phase sine wave being 0.577, so that the maximum amplitude of the three-phase sine wave needs to be limited to 0.577 in order to realize the open-circuit fault tolerance method of the present invention.

3. Obtaining three-phase modulated wave in open-circuit fault

On the basis of obtaining the zero sequence voltage expression, the three-phase modulation wave expression during open-circuit fault is obtained by injecting the zero sequence voltage into the three-phase sine wave.

4. Obtaining the output level state of the three-level ANPC inverter

On the basis of obtaining the expression of the three-phase modulation wave, the invention further formulates a comparison rule of the modulation wave and the carrier wave, and obtains the output level state of the three-level ANPC inverter according to the comparison result of the three-phase modulation wave and the carrier wave.

The switching signals of the switching devices of the three-level ANPC inverter are determined according to the output level state and the type of the switching device with the open-circuit fault. Defining six switching devices from top to bottom of each phase of the three-level ANPC inverter as S1, S2, S3, S4, S5 and S6, the principle of determining the switching signals of the switching devices of the three-level ANPC inverter according to the present invention is as follows:

According to the three-level ANPC inverter, the P level is output when the current direction is negative, and the N level is output when the current direction is positive, so that P, O and N three level states can be normally output by a fault phase when the three-level ANPC inverter has an open-circuit fault.

As can be seen from fig. 3b, when the current direction is negative, a current flows through the anti-parallel diodes of the switching devices Sa1, Sa3, thereby outputting a P level. Therefore, when the output level state is P, the switching devices S1 and S3 are turned on, and S2, S4, S5, and S6 are turned off.

As can be seen from fig. 4b, when the current direction is positive, a current flows through the anti-parallel diodes of the switching devices Sa4, Sa6, thereby outputting an N level. Therefore, when the output level state is N, the switching devices S4 and S6 are turned on, and S1, S2, S3, and S5 are turned off.

When the output level state is O, respectively analyzing according to the type of the switching device with the open-circuit fault:

for the open-circuit fault of any switching device in S1, S3, S4, S6, taking phase a as an example, when the phase a current direction is positive, as shown in fig. 6a, the midpoint current flows through the anti-parallel diode of Sa4 and Sa5, thereby outputting O level; and when the a-phase current direction is negative, as shown in fig. 6b, the midpoint current flows through the anti-parallel diode of Sa3 and Sa2, thereby outputting the O level. Therefore, when any of the switching devices S1, S3, S4, and S6 has an open-circuit fault, the switching devices S2 and S5 are turned on, and the switching devices S1, S3, S4, and S6 are turned off, so that the fault phase of the three-level ANPC can normally output an O level.

For the open-circuit fault of any switching device in S1, S2, S5, S6, taking phase a as an example, when the phase a current direction is positive, as shown in fig. 7a, the midpoint current flows through the anti-parallel diode of Sa2 and Sa3, thereby outputting the O level; and when the a-phase current direction is negative, as shown in fig. 7b, the midpoint current flows through the anti-parallel diode of Sa5 and Sa4, thereby outputting the O level. Therefore, when any of the switching devices S1, S2, S5, and S6 has an open-circuit fault, the switching devices S3 and S4 are turned on, and the switching devices S1, S2, S5, and S6 are turned off, so that the fault phase of the three-level ANPC can normally output an O level.

For the open-circuit fault of any switching device in S1, S2, S3, S6, taking phase a as an example, when the phase a current direction is positive, as shown in fig. 8a, the midpoint current flows through the anti-parallel diode of Sa4 and Sa5, thereby outputting the O level; on the other hand, when the a-phase current direction is negative, as shown in fig. 8b, the midpoint current flows through the anti-parallel diode of Sa5 and Sa4, thereby outputting the O level. Therefore, when any of the switching devices S1, S2, S3, and S6 has an open-circuit fault, the switching devices S2 and S5 are turned on and S1, S3, S4, and S6 are turned off when the fault phase current direction is positive, so that the fault phase of the three-level ANPC can normally output an O level; when the fault phase current direction is negative, the switching devices S3 and S4 are turned on, and S1, S2, S5, and S6 are turned off, so that the fault phase of the three-level ANPC can normally output the O level.

For the open-circuit fault of any switching device in S1, S4, S5, S6, taking phase a as an example, when the phase a current direction is positive, as shown in fig. 9a, a midpoint current flows through the anti-parallel diode of Sa2 and Sa3, so that an O level is output; and when the a-phase current direction is negative, as shown in fig. 9b, the midpoint current flows through the anti-parallel diode of Sa3 and Sa2, thereby outputting an O level. Therefore, when any of the switching devices S1, S4, S5, and S6 has an open-circuit fault, the switching devices S3 and S4 are turned on and S1, S2, S5, and S6 are turned off when the fault phase current direction is positive, so that the fault phase of the three-level ANPC can normally output an O level; when the fault phase current direction is negative, the switching devices S2 and S5 are turned on, and S1, S3, S4, and S6 are turned off, so that the fault phase of the three-level ANPC can normally output the O level.

Through the analysis of the switching signals of the switching devices, fault-tolerant control of the open-circuit fault of the three-level ANPC inverter can be realized based on carrier modulation.

The specific implementation flow of the three-level ANPC inverter open-circuit fault tolerance method based on carrier modulation according to the present invention is shown in fig. 10.

The fault-tolerant method for the open-circuit fault of the three-level ANPC inverter based on the carrier modulation can realize the fault-tolerant operation of the three-level ANPC inverter when the open-circuit fault occurs to at most four switching devices in a single phase at the same time, and improves the reliability of the three-level ANPC inverter. Compared with the traditional open-circuit fault-tolerant control method based on the space vector, the method realizes fault-tolerant operation directly according to the comparison result of the carrier wave and the modulating wave, does not need to calculate the action time of the space vector, and is very convenient for engineering realization; compared with the traditional open-circuit fault-tolerant control method based on the carrier wave, the method does not need to clamp the output level of the fault phase to the O level forcibly, and the three-phase voltage under the action of the fault phase keeps symmetrical, so that the method has better harmonic performance during fault-tolerant operation.

The following examples are provided to illustrate the effects of the present invention.

According to the embodiment of the invention, a three-level ANPC inverter model is established by means of PSIM software, and the effectiveness of the three-level ANPC inverter open-circuit fault tolerance method based on carrier modulation is verified by utilizing simulation. The simulation conditions of the embodiment are as follows: the simulation step size is 4us, the direct current side voltage is 2000V, the carrier ratio is 15, the modulation ratio is 0.4, the fundamental frequency is 50Hz, the output load is a resistance-inductance load, and the open-circuit fault occurs to the A-phase switching device when the set time is 0.1 s.

Fig. 11a, 11b, 11c, 11d, and 11e are simulation results of the phase-a switching devices Sa1, Sa3, Sa4, and Sa6 in the embodiment when an open circuit fault occurs and a fault tolerance method is not used, where: fig. 11a shows a phase voltage, a phase voltage B, and three-phase currents, fig. 11B shows fundamental amplitude values of the phase voltage and the line voltage in the case of no fault, fig. 11c shows fundamental amplitude values of the phase voltage and the line voltage in the case of open-circuit fault, fig. 11d shows three-phase currents THD in the case of no fault, and fig. 11e shows three-phase currents THD in the case of open-circuit fault. Analyzing fig. 11a, when open circuit faults occur at Sa1, Sa3, Sa4, and Sa6, if the fault-tolerant method is not used, the a-phase cannot normally output P, O, N level, the three-phase voltages lose symmetry, the phase of the B-phase and C-phase currents changes, and the a-phase current cannot normally output. Compared with fig. 11b and fig. 11c, in the absence of a fault, the amplitude of the fundamental wave of the phase voltage and the amplitude of the fundamental wave of the line voltage of the three phases are the same, and when open-circuit faults occur at Sa1, Sa3, Sa4 and Sa6 and a fault-tolerant method is not used, the amplitude of the fundamental wave of the phase voltage and the amplitude of the fundamental wave of the line voltage of the three phases are inconsistent, and the symmetry of the three phases is lost. As can be seen from fig. 11d and 11e, the THD of the three-phase currents is the same when there is no fault, and when open-circuit faults occur at Sa1, Sa3, Sa4, Sa6 and the fault-tolerant method is not used, the THD of the three-phase currents is not consistent and the a-phase current distortion is serious.

Fig. 12a, 12b, 12c, and 12d are simulation results of the a-phase switching devices Sa1, Sa3, Sa4, and Sa6 in the embodiment when open circuit faults occur and the conventional carrier-based open circuit fault tolerant control method is used, where: fig. 12a shows a phase voltage, a phase voltage B, and three-phase currents, fig. 12B shows fundamental amplitudes of the phase voltage and the line voltage at the time of an open fault, fig. 12c shows a three-phase current THD at the time of an open fault, and fig. 12d shows a midpoint voltage deviation value at the time of an open fault. Analyzing fig. 12a, when an open-circuit fault occurs at Sa1, Sa3, Sa4, Sa6, under the action of the conventional open-circuit fault tolerance control method based on carrier, the a-phase voltage is forcibly clamped to the O level, which results in that the symmetry of the three-phase voltage is lost, but the three-phase current remains symmetrical and can be normally output. Fig. 12B shows that under the action of the traditional open-circuit fault-tolerant control method based on carrier waves, the amplitude of phase voltage fundamental waves of the phase A and the phase B is different, but the amplitude of the line voltage between the phase A and the phase B is consistent with that of the line voltage fundamental waves between the phase B and the phase C, so that three-phase currents can be kept symmetrical. Comparing fig. 12c and fig. 11d, although the conventional open-circuit fault-tolerant control method based on carrier wave enables the fault phase current to be outputted normally, the THD of the fault phase current is increased significantly, and the current THD of the non-fault phase is also increased compared with the case without fault. As can be seen from fig. 12d, under the effect of the conventional open-circuit fault-tolerant control method based on carrier, the midpoint voltage deviation value reaches more than 30V.

Fig. 13a, 13b, 13c, 13d, and 13e are simulation results of the open-circuit faults of the phase-a switching devices Sa1, Sa3, Sa4, and Sa6 in the embodiment and when the fault-tolerant method of the present invention is used, where: fig. 13a shows a phase voltage, and a three-phase current, fig. 13B shows fundamental amplitudes of the phase voltage and the line voltage at the time of an open fault, fig. 13c shows a three-phase current THD at the time of an open fault, fig. 13d shows a midpoint voltage deviation value at the time of an open fault, and fig. 13e shows an a-phase voltage, an a-phase current, an a-phase modulation wave, and a carrier wave at the time of an open fault. Analyzing fig. 13a, when an open-circuit fault occurs at Sa1, Sa3, Sa4, Sa6, the phase voltage of the fault phase may output P, O, N level normally under the action of the fault-tolerant method of the present invention, and the phase voltages and currents of the three phases remain symmetrical. Fig. 13B shows that under the action of the fault-tolerant method, the phase voltage fundamental wave amplitudes of the phase a and the phase B are the same, so that the fault-tolerant method overcomes the defect of asymmetric three-phase voltage of the traditional open-circuit fault-tolerant control method based on the carrier wave. Comparing fig. 13c and 12c, the THD of the failed phase current does not increase significantly under the fault tolerant method of the present invention. Compared with the traditional open-circuit fault tolerance control method based on the carrier wave, the three-phase current THD value of the fault tolerance method is low, so that the output current of the three-level ANPC inverter has better harmonic performance. Compared with the traditional open-circuit fault tolerance control method based on the carrier wave, the fault tolerance method has smaller midpoint voltage deviation value under the action of the fault tolerance method, so that the fault tolerance method has better midpoint voltage balance capability. As can be seen from fig. 13e, the fault-tolerant method of the present invention outputs the N and O levels in the positive half cycle of the fault phase current and outputs the P and O levels in the negative half cycle of the fault phase current, so that the fault phase can normally output P, O, N three level states. In addition, the fault-tolerant method of the invention realizes modulation directly according to the comparison result of the modulation wave and the carrier wave, and has simple calculation and easy engineering realization.

Fig. 14a and 14b are simulation results of open circuit faults of the phase-a switching devices Sa1, Sa4, Sa5, and Sa6 in the embodiment, where: fig. 14a shows the a-phase voltage, the B-phase voltage and the three-phase current when Sa1, Sa4, Sa5 and Sa6 have open circuit faults and the fault-tolerant method is not used, and fig. 14B shows the a-phase voltage, the line voltage and the three-phase current when Sa1, Sa4, Sa5 and Sa6 have open circuit faults and the fault-tolerant method of the invention is used. Analyzing fig. 14a, when open circuit faults occur at Sa1, Sa4, Sa5, and Sa6, if the fault-tolerant method is not used, the a-phase cannot normally output P, O, N level, the three-phase voltages lose symmetry, the phase of the B-phase and C-phase currents change, and the a-phase current cannot normally output. Fig. 14b shows that when open-circuit faults occur at Sa1, Sa4, Sa5 and Sa6, the phase voltage of the fault phase can output P, O, N level normally under the fault-tolerant method of the present invention, the currents of the three phases remain symmetrical and the line voltage is not distorted.

Fig. 15a and 15b are simulation results of open circuit faults of the phase-a switching devices Sa1, Sa2, Sa5 and Sa6 in the embodiment, in which: fig. 15a shows the a-phase voltage, the B-phase voltage and the three-phase current when the open-circuit faults occur at Sa1, Sa2, Sa5 and Sa6 and the fault-tolerant method is not used, and fig. 15B shows the a-phase voltage, the three-phase current and the midpoint voltage deviation value when the open-circuit faults occur at Sa1, Sa2, Sa5 and Sa6 and the fault-tolerant method is used. Analyzing fig. 15a, when open circuit faults occur at Sa1, Sa2, Sa5, and Sa6, if the fault-tolerant method is not used, the a-phase cannot normally output P, O, N level, the three-phase voltages lose symmetry, the phase of the B-phase and C-phase currents changes, and the a-phase current cannot normally output. As can be seen from fig. 15b, when an open-circuit fault occurs at Sa1, Sa2, Sa5, Sa6, the phase voltage of the fault phase can output P, O, N level normally under the fault-tolerant method of the present invention, the three-phase current remains symmetrical, and the midpoint voltage deviation value is only 1% of the bus voltage.

Fig. 16a and 16b are simulation results of open circuit faults of the phase-a switching devices Sa1, Sa2, Sa3 and Sa6 in the embodiment, in which: fig. 16a shows the a-phase voltage, the B-phase voltage and the three-phase current when the open circuit fault occurs at Sa1, Sa2, Sa3 and Sa6 and the fault-tolerant method is not used, and fig. 16B shows the a-phase voltage, the a-phase modulation wave, the carrier wave and the three-phase current when the open circuit fault occurs at Sa1, Sa2, Sa3 and Sa6 and the fault-tolerant method is used. Analyzing fig. 16a, when open circuit faults occur at Sa1, Sa2, Sa3, and Sa6, if the fault-tolerant method is not used, the a-phase cannot normally output P, O, N level, the three-phase voltages lose symmetry, the phase of the B-phase and C-phase currents changes, and the a-phase current cannot normally output. As can be seen from fig. 15b, when an open circuit fault occurs at Sa1, Sa2, Sa3, Sa6, the fault-tolerant method of the present invention outputs N and O levels in the positive half cycle of the fault phase current, and outputs P and O levels in the negative half cycle of the fault phase current, so that the fault phase can normally output P, O, N three level states, and the three-phase currents are kept symmetrical. In addition, the fault-tolerant method of the invention realizes modulation directly according to the comparison result of the modulation wave and the carrier wave, and has simple calculation and easy engineering realization.

As shown in fig. 11a, 11b, 11c, 11d, 11e to 16a, and 16b, the results of the embodiment verify the effectiveness of the open-circuit fault tolerance method for the three-level ANPC inverter based on carrier modulation according to the present invention. The fault-tolerant method can realize the fault-tolerant operation of the three-level ANPC inverter when the single-phase at most four switching devices simultaneously generate open-circuit faults, and improves the reliability of the three-level ANPC inverter. Compared with the traditional open-circuit fault-tolerant control method based on the space vector, the fault-tolerant method of the invention directly realizes modulation according to the comparison result of the carrier wave and the modulation wave, and has simple calculation and easy realization; compared with the traditional open-circuit fault tolerance control method based on the carrier wave, the fault tolerance method does not need to clamp the output level of the fault phase to the O level forcibly, the three-phase voltage and the three-phase current are kept symmetrical under the action of the fault tolerance method, the midpoint voltage deviation value and the three-phase current THD value are small, and therefore the fault tolerance method has good harmonic performance during fault tolerance operation.

Claims

1. The three-level ANPC inverter open-circuit fault tolerance method based on carrier modulation is characterized in that when an open-circuit fault occurs in a single-phase switching device of the three-level ANPC inverter, the fault tolerance method firstly detects the current direction I of a fault phase_dir(ii) a Defining the maximum value of three-phase sine wave as V_maxMinimum value of three-phase sine wave is V_minZero sequence voltage of Z_s(ii) a The fault tolerant method is in_dirWhen is 1 hour Z_s＝-0.5×(V_max+V_min+1) in I_dir0 season Z_s＝-0.5×(V_max+V_min-1) and by applying a zero sequence voltage Z_sInjecting a three-phase sine wave to obtain a three-phase modulation wave during open-circuit fault; comparing the three-phase modulation wave with a carrier wave to obtain a level state output by the three-level ANPC inverter; determining a switching signal of each switching device of the three-level ANPC inverter according to the output level state and the type of the switching device with the open-circuit fault, thereby realizing the fault-tolerant operation of the three-level ANPC inverter;

defining the current corresponding to the fault as I_xDetecting the fault phase current direction I_dirThe method comprises the following steps:

when I is_xWhen the temperature is more than or equal to 0, let I_dir1 is ═ 1; when I is_xWhen less than 0, let I_dir＝0。

2. The carrier modulation based three-level ANPC inverter open-circuit fault tolerance method of claim 1, wherein the zero sequence voltage Z is zero _sThe determination method of (2) is as follows:

when I_dirWhen 1, let Z_s＝-0.5×(V_max+V_min+ 1); when I_dirWhen equal to 0, let Z_s＝-0.5×(V_max+V_min-1)；

In the above determination method, I_dirIs the direction of current flow of the faulted phase, Z_sIs zero sequence voltage, V_maxRepresenting the maximum value of a three-phase sine wave, V_minRepresents the minimum of a three-phase sine wave;

defining three-phase sine waves as V_a、V_bAnd V_cMaximum value V of three-phase sine wave_maxAnd the minimum value V of the three-phase sine wave_minThe judging method comprises the following steps:

3. The carrier modulation based three-level ANPC inverter open-circuit fault tolerance method of claim 1, wherein three-phase modulation waves are defined as V respectively_am、V_bmAnd V_cmThe method for injecting the zero sequence voltage into the three-phase sine wave to obtain the three-phase modulation wave during the open-circuit fault comprises the following steps:

in the above formula, V_am、V_bmAnd V_cmRepresenting a three-phase modulated wave, V_a、V_bAnd V_cRepresenting a three-phase sine wave, Z_sFor zero sequence voltage, t is time, ω is angular frequency, a represents the amplitude of the sine wave, and the maximum value of a is limited to 0.577.

4. The carrier modulation based three-level ANPC inverter open-circuit fault tolerance method of claim 1, wherein the three level states defining the high-to-low output of the three-level ANPC inverter are P, O and N, respectively, and the method of obtaining the output level states of the three-level ANPC inverter is as follows:

When V is_am≥V_c1When the output level state of the A phase is P; when V is_am≤V_c2When the output level state of the A phase is N; when V is_am＞V_c2And V is_am＜V_c1When the output level state of the phase A is O;

in the above output level state determining method, V_am、V_bmAnd V_cmRepresenting a three-phase modulated wave, V_c1And V_c2Representing two triangular carriers of the same amplitude, frequency and direction, where V_c1Representing a triangular carrier wave, V, of value between 0 and 1_c2Representing a triangular carrier with values between-1 and 0.

5. The carrier modulation based three-level ANPC inverter open-circuit fault tolerance method of claim 1, wherein the six switching devices from top to bottom per phase of the three-level ANPC inverter are defined as S1, S2, S3, S4, S5, and S6, respectively, and the method of determining the switching signals of the switching devices of the three-level ANPC inverter is as follows:

3) for any switching device of S1, S2, S3 and S6 to generate open-circuit fault, I_dirWhen the current value is 1, the switching devices S2 and S5 are turned on, and S1, S3, S4 and S6 are turned off; in I_dirWhen the signal value is 0, the switching devices S3 and S4 are turned on, and S1, S2, S5 and S6 are turned off;