CN113472228B - Three-level midpoint potential balance control method and system based on voltage feedback - Google Patents

Three-level midpoint potential balance control method and system based on voltage feedback Download PDF

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CN113472228B
CN113472228B CN202110762138.5A CN202110762138A CN113472228B CN 113472228 B CN113472228 B CN 113472228B CN 202110762138 A CN202110762138 A CN 202110762138A CN 113472228 B CN113472228 B CN 113472228B
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sector
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voltage
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CN113472228A (en
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李建斌
贾连辉
孙志洪
张鹏
范波
李向春
谢彦昆
苏新波
李航
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China Railway Engineering Equipment Group Co Ltd CREG
China Railway Hi Tech Industry Corp Ltd
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China Railway Hi Tech Industry Corp Ltd
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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
    • 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

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Abstract

The invention provides a three-level midpoint potential balance control method and a three-level midpoint potential balance control system based on voltage feedback, which relate to the technical field of variable frequency speed regulation, and comprise the following steps: acquiring voltages at two ends of a capacitor of the NPC type three-level inverter and direct-current measurement voltages through a voltage sensor, and judging whether deviation occurs or not by comparing the voltages at two ends of the capacitor; in a space vector of the NPC type three-level inverter, dividing each large sector by taking an angular bisector as a boundary; controlling potential balance through a midpoint potential balance control strategy, wherein the control strategy comprises the following steps: selecting a small vector for balancing the midpoint potential according to the midpoint current and the unbalance coefficient; synthesizing a reference vector, and obtaining the action time of the vector in the current small sector according to the imbalance coefficient and the modulation degree; and setting a switching action sequence according to the switching action state and action time corresponding to the vector, and controlling the on-off of the inverter switch through the switching action sequence to control the potential balance.

Description

Three-level midpoint potential balance control method and system based on voltage feedback
Technical Field
The invention relates to the technical field of variable frequency speed regulation, in particular to a three-level midpoint potential balance control method and a three-level midpoint potential balance control system based on voltage feedback.
Background
The problem of unbalanced three-level midpoint potential can cause the problems of shortened service life of a switching device, distortion of voltage output waveform and the like due to different bearing voltages of the switching device, and when the traditional VSVPWM method is adopted, two paired small vector amplitudes which need to balance the midpoint potential are different in size, the switching loss of device action is high, and the system does not perform feedback closed-loop control on the midpoint potential. This approach to natural recovery process is typically slow when disturbances are generated and does not address the problem of offset accumulation errors due to the control strategy.
In view of the above, a technical solution for balancing and controlling the midpoint potential, which can overcome the above-mentioned drawbacks, is needed.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides a three-level midpoint potential balance control method and system based on voltage feedback. In the NPC type three-level midpoint potential balance control strategy of VSVPMs, the control algorithm is improved, the offset coefficient k and the modulation degree n of midpoint potential voltage are introduced into the algorithm, when the voltage is offset, the sector is partitioned when the midpoint potential is offset, and the sector is partitioned by judging kiaAnd iaThe magnitude comparison relationship between the vector and the switching sequence of the device is selected according to the magnitude comparison relationship between the vector and the switching sequence, and the switching sequence of the device is obtained according to the action time of each vector, so that the midpoint voltage deviation of VSVPWM in the process of generating disturbance is overcome, and the midpoint voltage of the system is quickly balanced.
In a first aspect of an embodiment of the present invention, a three-level midpoint potential balance control method based on voltage feedback is provided, where the method includes:
acquiring voltages at two ends of a capacitor of the NPC type three-level inverter and direct-current measurement voltages through a voltage sensor, and judging whether deviation occurs or not by comparing the voltages at two ends of the capacitor; when the deviation between the voltage at the two ends of the first capacitor and the voltage at the two ends of the second capacitor is larger than a preset value, the midpoint potential is unbalanced, and the deviation occurs;
in a space vector of the NPC type three-level inverter, dividing each large sector by taking an angular bisector as a boundary, wherein each divided large sector comprises three small sectors;
controlling potential balance through a midpoint potential balance control strategy; which comprises the following steps:
obtaining an unbalance coefficient according to the voltage at the two ends of the capacitor and the direct current measurement voltage;
when the reference vector is positioned in one of the small sectors, selecting a small vector for balancing the midpoint potential according to the midpoint current and the imbalance coefficient;
synthesizing a reference vector according to the small vector, obtaining a modulation degree according to the reference vector, and obtaining the action time of the vector in the current small sector according to the unbalance coefficient and the modulation degree;
and setting a switching action sequence according to the switching action state and action time corresponding to the vector, and controlling the on-off of the inverter switch through the switching action sequence to control the potential balance.
In a second aspect of the embodiments of the present invention, a three-level midpoint potential balance control system based on voltage feedback is provided, the system including:
the judging module is used for acquiring the voltage at two ends of the capacitor of the NPC type three-level inverter and the direct current measurement voltage through the voltage sensor and judging whether the deviation occurs or not through comparing the voltages at two ends of the capacitor; when the deviation between the voltage at the two ends of the first capacitor and the voltage at the two ends of the second capacitor is larger than a preset value, the midpoint potential is unbalanced, and the deviation occurs;
the device comprises a dividing module, a judging module and a control module, wherein the dividing module is used for dividing each large sector in a space vector of the NPC type three-level inverter by taking an angular bisector as a boundary, and each divided large sector comprises three small sectors;
the potential balance control module is used for controlling potential balance through a midpoint potential balance control strategy; which comprises the following steps:
the unbalance coefficient calculation unit is used for obtaining an unbalance coefficient according to the voltage at the two ends of the capacitor and the direct current measurement voltage;
the small vector selection unit is used for selecting a small vector for balancing the midpoint potential according to the midpoint current and the unbalance coefficient when the reference vector is positioned in one of the small sectors;
the action time calculation unit is used for synthesizing a reference vector according to the small vector, obtaining a modulation degree according to the reference vector and obtaining the action time of the vector in the current small sector according to the unbalance coefficient and the modulation degree;
and the potential balance control unit is used for setting a switching action sequence according to the switching action state and the action time corresponding to the vector, controlling the on-off of the inverter switch through the switching action sequence and controlling the potential balance.
In a third aspect of the embodiments of the present invention, a computer device is provided, which includes a memory, a processor, and a computer program stored on the memory and executable on the processor, and the processor implements a three-level midpoint potential balance control method based on voltage feedback when executing the computer program.
In a fourth aspect of embodiments of the present invention, a computer-readable storage medium is provided, which stores a computer program that, when executed by a processor, implements a three-level midpoint potential balance control method based on voltage feedback.
The invention provides a three-level midpoint potential balance control method and system based on voltage feedback, which improve the NPC type three-level midpoint potential balance control strategy of VSVPWM, introduce a shift coefficient k and a modulation degree n of midpoint potential voltage into a control algorithm, partition a sector when the midpoint potential shifts when the voltage shifts, and judge kiaAnd iaThe magnitude comparison relation between the (midpoint current) is used for selecting a small vector suitable for potential balance control and calculating the action time of the small vector, and the switching sequence of the device is obtained according to the action time of each vector, so that the midpoint voltage deviation of VSVPWM in the disturbance generation process is overcome, and the midpoint voltage of the system is quickly balanced.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present application, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
Fig. 1 is a schematic flow chart of a three-level midpoint potential balance control method based on voltage feedback according to an embodiment of the present invention.
Fig. 2 is a space voltage vector diagram.
Fig. 3 is a voltage vector diagram for the I-th large sector.
Fig. 4 is a schematic diagram of an NPC type three-level midpoint potential balance control method based on voltage feedback vsvsvsvpm according to an embodiment of the present invention.
Fig. 5 is a schematic of a topology of an NPC type three-level inverter.
FIG. 6 is a schematic diagram of a three-level midpoint potential balance control system architecture based on voltage feedback according to an embodiment of the present invention.
Fig. 7 is a schematic structural diagram of a computer device according to an embodiment of the present invention.
Detailed Description
The principles and spirit of the present invention will be described with reference to a number of exemplary embodiments. It is understood that these embodiments are given solely for the purpose of enabling those skilled in the art to better understand and to practice the invention, and are not intended to limit the scope of the invention in any way. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.
As will be appreciated by one skilled in the art, embodiments of the present invention may be embodied as a system, apparatus, device, method, or computer program product. Accordingly, the present disclosure may be embodied in the form of: entirely hardware, entirely software (including firmware, resident software, micro-code, etc.), or a combination of hardware and software.
According to the embodiment of the invention, a three-level midpoint potential balance control method and a three-level midpoint potential balance control system based on voltage feedback are provided, and the invention relates to the technical field of variable frequency speed regulation.
The principles and spirit of the present invention are explained in detail below with reference to several representative embodiments of the invention.
Fig. 1 is a schematic flow chart of a three-level midpoint potential balance control method based on voltage feedback according to an embodiment of the present invention. As shown in fig. 1, the method includes:
step S101, collecting voltages at two ends of a capacitor of the NPC type three-level inverter and direct current measurement voltages through a voltage sensor, and judging whether deviation occurs or not by comparing the voltages at two ends of the capacitor; when the deviation between the voltage at the two ends of the first capacitor and the voltage at the two ends of the second capacitor is larger than a preset value, the midpoint potential is unbalanced, and the deviation occurs;
step S102, dividing each large sector in a space vector of the NPC type three-level inverter by taking an angular bisector as a boundary, wherein each divided large sector comprises three small sectors;
step S103, controlling potential balance through a midpoint potential balance control strategy; which comprises the following steps:
step S1031, obtaining an imbalance coefficient according to the voltage at the two ends of the capacitor and the direct current measurement voltage;
step S1032, when the reference vector is located in one of the small sectors, selecting a small vector for balancing the midpoint potential according to the midpoint current and the imbalance coefficient;
step S1033, synthesizing a reference vector according to the small vector, obtaining a modulation degree according to the reference vector, and obtaining the action time of the vector in the current small sector according to the imbalance coefficient and the modulation degree;
and S1034, setting a switching action sequence according to the switching action state and action time corresponding to the vector, and controlling the on-off of the inverter switch through the switching action sequence to control the potential balance.
In order to explain the above three-level midpoint potential balance control method based on voltage feedback more clearly, the following is a detailed description with reference to each step.
Referring to fig. 2, a space voltage vector diagram is shown.
Referring to fig. 3, a voltage vector diagram for the I-th large sector is shown.
As shown in fig. 2 and 3, the analysis is performed by taking the I-th large sector as an example, when the midpoint potential is unbalanced and offset occurs, and the reference amount is located in the I-th large sector, the potential balance control is performed by the midpoint potential balance control strategy, and the other large sectors are performed in the same manner according to the I-th large sector.
The neutral point potential balance control strategy comprises the following steps:
and S1, calculating the unbalance coefficient.
According to the voltage at two ends of the capacitor and the direct current voltage, obtaining an unbalance coefficient, wherein the calculation formula of the unbalance coefficient is as follows:
Figure BDA0003149402100000051
wherein k is an imbalance coefficient; u shapeC1Is the voltage across the first capacitor; u shapeDCIs the dc side voltage.
S2, selecting a small vector.
When the reference vector is positioned in one of the small sectors, selecting a small vector for balancing the midpoint potential according to the midpoint current and the imbalance coefficient; wherein the content of the first and second substances,
as shown in FIG. 3, when the reference vector is located in the first small sector (A sector) of the I-th large sector, if 1 < k < 2 and Ia< 0, or 0 < k < 1 and ia> 0, selecting a small vector V1P(ii) a If 1 < k < 2 and ia> 0, or 0 < k < 1 and ia< 0, select the small vector V1N；
Wherein, V1PIs a po vector; v1NIs an onn vector.
S3, the action time of each vector is calculated.
Synthesizing a reference vector according to the small vector, obtaining a modulation degree according to the reference vector, and obtaining the action time of the vector in the current small sector according to the unbalance coefficient and the modulation degree; wherein the content of the first and second substances,
the analysis using sector A as an example can be divided into the following two cases (ki)a＞ia、kia＜ia)：
When kia＞iaThen, the vector V is selected1N、V0And V1' Synthesis Vref，VrefThe expression of (a) is:
Figure BDA0003149402100000052
wherein, VrefIs a reference vector; v0Ooo; v' is a resultant vector, V ═ V1+V2+V8)/3；V1Is a po, an on vector; v2The vector is ppo and oon; v8Is a pon vector; t is t0、t1、t2Are respectively a vector V0、V1NThe action time of V';
the modulation degree is:
Figure BDA0003149402100000061
wherein n is a modulation degree;
the action time of the vector in the current small sector is:
Figure BDA0003149402100000062
wherein θ is VrefThe spatial position angle of (a);
when kia＞iaWhen t is0< 0, reference vector VrefCan not use V0Is synthesized by using V7Alternative V0Synthesis of VrefAfter substitution VrefThe synthetic expression relationship is as follows:
Figure BDA0003149402100000063
wherein, V7Is a pnn vector; t is t3Is a V7The action time of (c);
the action time of the vector in the current small sector is:
Figure BDA0003149402100000064
when kia＜iaWhen selecting V1P、V0And V1' Synthesis Vref，VrefThe expression of (a) is:
Figure BDA0003149402100000065
the action time of the vector in the current small sector is:
Figure BDA0003149402100000066
when kia＜iaWhen t is0< 0, reference vector VrefCan not use V0Is synthesized by using V7Alternative V0Synthesis of VrefAfter substitution VrefThe synthetic expression relationship is as follows:
Figure BDA0003149402100000071
the action time of the vector in the current small sector is:
Figure BDA0003149402100000072
when V isrefWhen located in the second small sector (B sector), the same method is performed according to the first small sector (a sector); wherein the content of the first and second substances,
from the analysis, a vector V is obtained0、V9And V1The influence on the center potential is 0, vector V2NThe current flowing through the midpoint is icVector V2PThe current flowing through the midpoint is-ic，V2NAnd V2PThe influence on the midpoint potential is opposite;
according to kicAnd icThe small vector V is selected according to the size comparison relationship between the small vectors2NOr V2PTo carry out VrefAnd obtaining the action time of the vector in the current small sector.
When V isrefWhen located in the third small sector (C sector), reference vector VrefThe synthesis relationship is as follows:
Figure BDA0003149402100000073
wherein, V9Is a ppn vector;
t5is a vector V9The action time of (c);
when kia＞iaWhen, VxGet V1PThe action time of the vector in the current small sector is:
Figure BDA0003149402100000074
when kia＜iaWhen, VxGet V1NThe action time of the vector in the current small sector is:
Figure BDA0003149402100000081
and S4, controlling the action of the inverter switching device according to the corresponding switching sequence obtained by the action time.
In the NPC type three-level midpoint potential balance control strategy of VSVPMs, the control algorithm is improved, the offset coefficient k and the modulation degree n of midpoint potential voltage are introduced into the algorithm, when the voltage is offset, the sector is partitioned when the midpoint potential is offset, and the sector is partitioned by judging kiaAnd iaThe magnitude comparison relationship between the vector and the switching sequence of the device is selected according to the magnitude comparison relationship between the vector and the switching sequence, and the switching sequence of the device is obtained according to the action time of each vector, so that the midpoint voltage deviation of VSVPWM in the process of generating disturbance is overcome, and the midpoint voltage of the system is quickly balanced.
It should be noted that although the operations of the method of the present invention have been described in the above embodiments and the accompanying drawings in a particular order, this does not require or imply that these operations must be performed in this particular order or that all of the illustrated operations must be performed to achieve desirable results. Additionally or alternatively, certain steps may be omitted, multiple steps combined into one step execution, and/or one step broken down into multiple step executions.
For a clearer explanation of the above three-level midpoint potential balance control method based on voltage feedback, a specific embodiment is described below, however, it should be noted that the embodiment is only for better explaining the present invention, and should not be construed as an undue limitation to the present invention.
Referring to fig. 4, a schematic diagram of an NPC type three-level midpoint potential balance control method based on voltage feedback vsvsvpms according to an embodiment of the invention is shown. As shown in fig. 4, the method includes:
s401, judging whether the midpoint potential is shifted:
the topological structure of the NPC type three-level inverter is shown in fig. 5, and the voltage across the capacitor of the NPC type three-level inverter is acquired by a voltage sensor: u shapeC1Is a capacitor C1Voltage of UC2Is a capacitor C2Voltage of UDCIs a direct current side voltage; and comparing the voltages at the two ends of the capacitor, and judging whether the midpoint potential deviates.
S402, sector division:
taking the space vector diagram of fig. 2 as an example, 3 small sectors are divided for each large sector (I, II, III, IV, V, VI) by using an angular bisector as a boundary.
The schematic diagram of the division of the ith large sector is shown in fig. 3, which includes A, B, C three sectors (small sectors), and the other 5 large sectors are divided and analyzed according to the mode of the ith large sector.
Defining a reference vector as Vref＝|VrefL (cos theta + j sin theta), theta is VrefJ is a reference coefficient.
When V isrefWhen the potential of the midpoint is balanced when k is 1, the reference vector composition relation is as follows:
Figure BDA0003149402100000091
wherein the content of the first and second substances,
Figure BDA0003149402100000092
TSis a sampling control period.
Thus, the action time of each vector is:
Figure BDA0003149402100000093
voltage vector V0，V7And V1' without influencing the midpoint potential, then V1NHas a midpoint current of ia，V1PHas a midpoint current of-ia,V1NAnd V1PThe effect on the midpoint current is opposite.
S403, selecting a proper small vector:
when C is present1Voltage and C of2The voltage deviation is large, when the output of the midpoint potential is unbalanced, the unbalanced coefficient is k,
Figure BDA0003149402100000094
the degree of modulation n is such that,
Figure BDA0003149402100000095
according to the unbalance degree k of the midpoint potential and the midpoint current iaThe relationship between them is chosen to favour balancing the small vector of midpoint potentials, iaThe current is a midpoint current, wherein the direction of the current flowing into the midpoint is a positive direction, and the direction of the current flowing out of the midpoint is a negative direction. The selection table is shown in table 1:
TABLE 1 Small vector selection Table to facilitate Balancing midpoint potentials
1＜k＜2 0＜k＜1
ia＜0 V1P V1N
ia＞0 V1N V1P
Different small vectors are selected according to table 1.
S404, calculating the acting time of each vector:
the situation in the analysis table when the reference vector is in sector a of the modified vsvsvsvsvsvpm modulation vector synthesis diagram (fig. 3) can be generalized to two categories to calculate the action time of each vector:
class 1: when kia＞iaThen, the vector V is selected1N、V0And V1' Synthesis Vref，VrefThe expression of (a) is:
Figure BDA0003149402100000101
v' is a resultant vector, V ═ V1+V2+V8)/3；
The action time can be obtained by the formula:
Figure BDA0003149402100000102
wherein if t0If < 0, it means that the modulation degree is relatively large, the reference vector VrefCan not use V0Is synthesized by using V7Alternative V0Synthesis of VrefAfter substitution VrefThe synthetic expression relationship is as follows:
Figure BDA0003149402100000103
the action time of each vector is obtained by the following formula:
Figure BDA0003149402100000104
class 2: when kia＜iaWhen selecting V1P、V0And V1' Synthesis of Vref，VrefThe expression of (a) is:
Figure BDA0003149402100000105
the action time can be obtained by the formula:
Figure BDA0003149402100000106
if t0If < 0, it means that the modulation degree is relatively large, the reference vector VrefCan not use V0Is synthesized by using V7Alternative V0Synthesis of VrefAfter substitution VrefThe synthetic expression relationship is as follows:
Figure BDA0003149402100000111
the action time of each vector is obtained by the following formula:
Figure BDA0003149402100000112
when V isrefWhen located in sector B, the vector V can be known according to analysis0、V9And V1The influence on the center potential is 0, vector V2NThe current flowing through the midpoint is icVector V2PThe current flowing through the midpoint is-ic，V2NAnd V2PThe influence on the center potential is opposite;
according to kicAnd icThe size contrast relation between the two vectors is selected to obtain a small vector V2NOr V2PTo carry out VrefAnd obtaining the action time of the vector in the current small sector. This situation is similar to that in the a sector.
When V isrefWhen the vector is located in the C sector, and the midpoint potential is not shifted by k equal to 1, the vector V7，V9And V1' action has no influence on the midpoint potential, VrefDoes not affect the midpoint potential, then VrefThe synthesis relationship is as follows:
Figure BDA0003149402100000113
the action time can be obtained by the formula:
Figure BDA0003149402100000114
when the midpoint potential is unbalanced, the situation is similar to that in sector A, then reference vector VrefThe synthesis relationship is as follows:
Figure BDA0003149402100000115
v in the formulaxIs a variable vector and represents two cases, (1) when kia＜iaWhen, VxGet V1P. (2) When kia＞iaWhen, VxGet V1N。
The action time of each vector obtained from the above formula is:
when kia＜iaWhen, VxGet V1PThe action time of the vector in the current small sector is:
Figure BDA0003149402100000121
when kia＞iaWhen, VxGet V1NThe action time of the vector in the current small sector is:
Figure BDA0003149402100000122
s405, selecting a switch sequence order:
and selecting a proper switching action sequence according to the light-on action state and action time corresponding to the vector, and controlling the on-off of the inverter switch through a switching sequence.
The switching operation sequence based on the voltage feedback vsvsvpm three-level NPC type neutral point potential balance control is shown in table 2:
TABLE 2 VSVPWM switching sequences based on midpoint potential voltage feedback
Figure BDA0003149402100000123
When V isrefIn sector B, the switching vector sequence of the device can be analyzed as in sector a.
When V isrefIn sector C, the switching vector sequence of the device is:
(1,1,0)→(1,1,-1)→(1,0,-1)→(1,-1,-1)→(0,-1,-1)→(1,-1,-1)→(1,0,-1)→(1,1,-1)→(1,1,0)。
aiming at the problems of high switching loss, no voltage feedback and the like caused by different magnitudes of paired small vectors when the midpoint voltage in the VSVPWM method is unbalanced, the invention can overcome the defects that the midpoint voltage deviation is processed when the VSVPWM method is disturbed, and a feedback control scheme is used for realizing accurate control so that the midpoint voltage is quickly balanced.
Having described the method of an exemplary embodiment of the present invention, a three-level midpoint potential balance control system based on voltage feedback of an exemplary embodiment of the present invention will be described with reference to fig. 6.
The implementation of the three-level midpoint potential balance control system based on voltage feedback can refer to the implementation of the above method, and repeated details are not repeated. The term "module" or "unit" used hereinafter may be a combination of software and/or hardware that implements a predetermined function. Although the means described in the embodiments below are preferably implemented in software, an implementation in hardware, or a combination of software and hardware is also possible and contemplated.
Based on the same inventive concept, the invention also provides a three-level midpoint potential balance control system based on voltage feedback, as shown in fig. 6, the system comprises:
the judging module 610 is configured to acquire voltages at two ends of a capacitor of the NPC type three-level inverter and a direct current measurement voltage through a voltage sensor, and judge whether an offset occurs by comparing the voltages at two ends of the capacitor; when the deviation between the voltage at the two ends of the first capacitor and the voltage at the two ends of the second capacitor is larger than a preset value, the midpoint potential is unbalanced, and the deviation occurs;
a dividing module 620, configured to divide each large sector in a space vector of the NPC three-level inverter by taking an angular bisector as a boundary, where each large sector after division includes three small sectors;
a potential balance control module 630, configured to control potential balance through a midpoint potential balance control strategy; which comprises the following steps:
the imbalance coefficient calculating unit 631 is configured to obtain an imbalance coefficient according to the voltage at the two ends of the capacitor and the dc measurement voltage;
a small vector selection unit 632 configured to select a small vector for balancing the midpoint potential according to the midpoint current and the imbalance coefficient when the reference vector is located in one of the small sectors;
the action time calculation unit 633 is used for synthesizing a reference vector according to the small vector, obtaining a modulation degree according to the reference vector, and obtaining the action time of the vector in the current small sector according to the imbalance coefficient and the modulation degree;
and a potential balance control unit 634 for setting a switching action sequence according to the switching action state and action time corresponding to the vector, controlling the on/off of the inverter switch through the switching action sequence, and controlling the potential balance.
It should be noted that although several modules of the three-level midpoint potential balance control system based on voltage feedback are mentioned in the above detailed description, such division is merely exemplary and not mandatory. Indeed, the features and functionality of two or more of the modules described above may be embodied in one module according to embodiments of the invention. Conversely, the features and functions of one module described above may be further divided into embodiments by a plurality of modules.
Based on the aforementioned inventive concept, as shown in fig. 7, the present invention further provides a computer device 700, which includes a memory 710, a processor 720, and a computer program 730 stored in the memory 710 and executable on the processor 720, wherein the processor 720 implements the aforementioned three-level midpoint potential balance control method based on voltage feedback when executing the computer program 730.
Based on the foregoing inventive concept, the present invention provides a computer-readable storage medium storing a computer program which, when executed by a processor, implements the foregoing three-level midpoint potential balance control method based on voltage feedback.
The invention provides a three-level midpoint potential balance control method and a three-level midpoint potential balance control system based on voltage feedback, which improve the NPC type three-level midpoint potential balance control strategy of VSVPWM, introduce a shift coefficient k and a modulation degree n of midpoint potential voltage into a control algorithm, partition a sector when the midpoint potential shifts when the voltage shifts,by making a decision kiaAnd iaThe magnitude comparison relation between the midpoint currents is used for selecting small vectors suitable for potential balance control and calculating the action time of the small vectors, the switching sequence of the device is obtained according to the action time of each vector, the midpoint voltage deviation of VSVPWM in the disturbance generation process is overcome, and the midpoint voltage of the system is quickly balanced.
As will be appreciated by one skilled in the art, embodiments of the present invention may be provided as a method, system, or computer program product. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present invention is described with reference to flowchart illustrations and/or block diagrams of methods and computer program products according to embodiments of the invention. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
Finally, it should be noted that: the above-mentioned embodiments are only specific embodiments of the present invention, which are used for illustrating the technical solutions of the present invention and not for limiting the same, and the protection scope of the present invention is not limited thereto, although the present invention is described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: any person skilled in the art can modify or easily conceive the technical solutions described in the foregoing embodiments or equivalent substitutes for some technical features within the technical scope of the present disclosure; such modifications, changes or substitutions do not depart from the spirit and scope of the embodiments of the present invention, and they should be construed as being included therein. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims (8)

1. A three-level midpoint potential balance control method based on voltage feedback is characterized by comprising the following steps:
acquiring voltages at two ends of a capacitor of the NPC type three-level inverter and direct-current measurement voltages through a voltage sensor, and judging whether deviation occurs or not by comparing the voltages at two ends of the capacitor; when the deviation between the voltage at the two ends of the first capacitor and the voltage at the two ends of the second capacitor is larger than a preset value, the midpoint potential is unbalanced, and the deviation occurs;
in a space vector of the NPC type three-level inverter, dividing each large sector by taking an angular bisector as a boundary, wherein each divided large sector comprises three small sectors;
controlling potential balance through a midpoint potential balance control strategy; which comprises the following steps:
obtaining an unbalance coefficient according to the voltage at the two ends of the capacitor and the direct current measurement voltage;
when the reference vector is positioned in one of the small sectors, selecting a small vector for balancing the midpoint potential according to the midpoint current and the imbalance coefficient;
synthesizing a reference vector according to the small vector, obtaining a modulation degree according to the reference vector, and obtaining the action time of the vector in the current small sector according to the unbalance coefficient and the modulation degree;
setting a switching action sequence according to the switching action state and action time corresponding to the vector, and controlling the on-off of the inverter switch through the switching action sequence to control the potential balance;
the method comprises the following steps of analyzing by taking an I-th large sector as an example, carrying out potential balance control by a midpoint potential balance control strategy when midpoint potential is unbalanced and offset occurs and a reference vector is positioned in the I-th large sector, and executing other large sectors according to the I-th large sector in the same method;
in the neutral point potential balance control strategy, the calculation method of the action time of the vector in the current small sector comprises the following steps:
when V isrefA first small sector located in the I-th large sector, and kia＞iaThen, the vector V is selected1N、V0And V1' Synthesis Vref，VrefThe expression of (a) is:
Figure FDA0003550908120000011
wherein, VrefIs a reference vector; v0Ooo; v1Is a composite vector, V1'＝(V1+V2+V8)/3；V1Is a po, an on vector; v2The vector is ppo and oon; v8Is a pon vector; t is t0、t1、t2Are respectively a vector V0、V1NThe action time of V';
the modulation degree is:
Figure FDA0003550908120000021
wherein n is a modulation degree; u shapeDCIs a direct current side voltage;
the action time of the vector in the current small sector is:
Figure FDA0003550908120000022
wherein θ is VrefThe spatial position angle of (a);
when kia＜iaWhen selecting V1P、V0And V1' Synthesis Vref，VrefThe expression of (a) is:
Figure FDA0003550908120000023
wherein k is an imbalance coefficient; i.e. iaIs the midpoint current; v1PIs a po vector;
the action time of the vector in the current small sector is:
Figure FDA0003550908120000024
when V isrefWhen located in the third cell sector, the reference vector VrefThe synthesis relationship is as follows:
Figure FDA0003550908120000025
wherein, V9Is a ppn vector; v1NIs an onn vector; v7Is a pnn vector; t is t3Is a V7The action time of (c); t is t5Is a vector V9The action time of (c);
when kia＜iaWhen, VxGet V1PThe action time of the vector in the current small sector is:
Figure FDA0003550908120000031
when kia＞iaWhen, VxGet V1NThe action time of the vector in the current small sector is:
Figure FDA0003550908120000032
2. the voltage feedback-based three-level midpoint potential balance control method according to claim 1, wherein the midpoint potential balance control strategy comprises:
according to the voltage at two ends of the capacitor and the direct current voltage, obtaining an unbalance coefficient, wherein the calculation formula of the unbalance coefficient is as follows:
Figure FDA0003550908120000033
wherein k is an imbalance coefficient; u shapeC1Is the voltage across the first capacitor; u shapeDCIs the dc side voltage.
3. The voltage feedback-based three-level midpoint potential balance control method according to claim 2, wherein the midpoint potential balance control strategy further comprises:
when the reference vector is positioned in one of the small sectors, selecting a small vector for balancing the midpoint potential according to the midpoint current and the imbalance coefficient; wherein the content of the first and second substances,
when the reference vector is located in the first small sector of the I big sector, if 1 < k < 2 and Ia< 0, or 0 < k < 1 and ia> 0, selecting a small vector V1P(ii) a If 1 < k < 2 and ia> 0, or 0 < k < 1 and ia< 0, select the small vectorV1N；
Wherein, V1PIs a po vector; v1NIs an onn vector.
4. The voltage feedback-based three-level midpoint potential balance control method according to claim 3, wherein the midpoint potential balance control strategy further comprises:
when kia＞iaWhen t is0< 0, reference vector VrefCan not use V0Is synthesized by using V7Alternative V0Synthesis of VrefAfter substitution VrefThe synthetic expression relationship is as follows:
Figure FDA0003550908120000034
wherein, V7Is a pnn vector; t is t3Is a V7The action time of (c);
the action time of the vector in the current small sector is:
Figure FDA0003550908120000041
when kia＜iaWhen t is0< 0, reference vector VrefCan not use V0Is synthesized by using V7Alternative V0Synthesis of VrefAfter substitution VrefThe synthetic expression relationship is as follows:
Figure FDA0003550908120000042
the action time of the vector in the current small sector is:
Figure FDA0003550908120000043
5. the voltage feedback-based three-level midpoint potential balance control method according to claim 4, wherein the midpoint potential balance control strategy further comprises:
when V isrefWhen located in the second cell sector, the method is executed according to the first cell sector in the same way; wherein the content of the first and second substances,
from the analysis, a vector V is obtained0、V9And V1The influence on the center potential is 0, vector V2NThe current flowing through the midpoint is icVector V2PThe current flowing through the midpoint is-ic，V2NAnd V2PThe influence on the midpoint potential is opposite;
according to kicAnd icThe small vector V is selected according to the size comparison relationship between the small vectors2NOr V2PTo carry out VrefAnd obtaining the action time of the vector in the current small sector.
6. A three-level midpoint potential balance control system based on voltage feedback, the system comprising:
the judging module is used for acquiring the voltage at two ends of the capacitor of the NPC type three-level inverter and the direct current measurement voltage through the voltage sensor and judging whether the deviation occurs or not through comparing the voltages at two ends of the capacitor; when the deviation between the voltage at the two ends of the first capacitor and the voltage at the two ends of the second capacitor is larger than a preset value, the midpoint potential is unbalanced, and the deviation occurs;
the device comprises a dividing module, a judging module and a control module, wherein the dividing module is used for dividing each large sector in a space vector of the NPC type three-level inverter by taking an angular bisector as a boundary, and each divided large sector comprises three small sectors;
the potential balance control module is used for controlling potential balance through a midpoint potential balance control strategy; which comprises the following steps:
the unbalance coefficient calculation unit is used for obtaining an unbalance coefficient according to the voltage at the two ends of the capacitor and the direct current measurement voltage;
the small vector selection unit is used for selecting a small vector for balancing the midpoint potential according to the midpoint current and the unbalance coefficient when the reference vector is positioned in one of the small sectors;
the action time calculation unit is used for synthesizing a reference vector according to the small vector, obtaining a modulation degree according to the reference vector and obtaining the action time of the vector in the current small sector according to the unbalance coefficient and the modulation degree;
the potential balance control unit is used for setting a switching action sequence according to the switching action state and action time corresponding to the vector, controlling the on-off of the inverter switch through the switching action sequence and controlling the potential balance;
the method comprises the following steps of analyzing by taking an I-th large sector as an example, carrying out potential balance control by a midpoint potential balance control strategy when midpoint potential is unbalanced and offset occurs and a reference vector is positioned in the I-th large sector, and executing other large sectors according to the I-th large sector in the same method;
in the neutral point potential balance control strategy, the calculation method of the action time of the vector in the current small sector comprises the following steps:
when V isrefA first small sector located in the I-th large sector, and kia＞iaThen, the vector V is selected1N、V0And V1' Synthesis Vref，VrefThe expression of (a) is:
Figure FDA0003550908120000051
wherein, VrefIs a reference vector; v0Ooo; v1Is a composite vector, V1'＝(V1+V2+V8)/3；V1Is a po, an on vector; v2The vector is ppo and oon; v8Is a pon vector; t is t0、t1、t2Are respectively a vector V0、V1NThe action time of V';
the modulation degree is:
Figure FDA0003550908120000052
wherein n is a modulation degree; u shapeDCIs a direct current side voltage;
the action time of the vector in the current small sector is:
Figure FDA0003550908120000061
wherein θ is VrefThe spatial position angle of (a);
when kia＜iaWhen selecting V1P、V0And V1' Synthesis of Vref，VrefThe expression of (a) is:
Figure FDA0003550908120000062
wherein k is an imbalance coefficient; i.e. iaIs the midpoint current; v1PIs a po vector;
the action time of the vector in the current small sector is:
Figure FDA0003550908120000063
when V isrefWhen located in the third cell sector, the reference vector VrefThe synthesis relationship is as follows:
Figure FDA0003550908120000064
wherein, V9Is a ppn vector; v1NIs an onn vector; v7Is a pnn vector; t is t3Is a V7The action time of (c); t is t5Is a vector V9The action time of (c);
when kia＜iaWhen, VxGet V1PThe action time of the vector in the current small sector is:
Figure FDA0003550908120000065
when kia＞iaWhen, VxGet V1NThe action time of the vector in the current small sector is:
Figure FDA0003550908120000071
7. a computer device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, wherein the processor implements the method of any one of claims 1 to 5 when executing the computer program.
8. A computer-readable storage medium, characterized in that the computer-readable storage medium stores a computer program which, when executed by a processor, implements the method of any of claims 1 to 5.
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