CN109525134B - Discontinuous PWM modulation method for diode clamping three-level inverter - Google Patents

Discontinuous PWM modulation method for diode clamping three-level inverter Download PDF

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CN109525134B
CN109525134B CN201811441250.3A CN201811441250A CN109525134B CN 109525134 B CN109525134 B CN 109525134B CN 201811441250 A CN201811441250 A CN 201811441250A CN 109525134 B CN109525134 B CN 109525134B
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action
small vector
output voltage
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CN109525134A (en
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吕佃顺
许洪华
王立鹏
黄志松
李利军
孙明丽
张雷
李海东
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Baoding Corona Control Equipment Co ltd
Corona Wind Energy Equipment Beijing Co ltd
Beijing Corona Science and Technology Co Ltd
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Baoding Corona Control Equipment Co ltd
Corona Wind Energy Equipment Beijing Co ltd
Beijing Corona Science and Technology Co 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
    • H02M7/487—Neutral point clamped inverters

Abstract

A discontinuous PWM modulation method of a diode clamping three-level inverter is characterized in that small vectors participating in output voltage synthesis do not have a redundant state, a switching sequence in one PWM period is of a 5-segment type, and midpoint voltage balance is controlled by adjusting action angle intervals of an upper small vector and a lower small vector. Selecting three space vectors participating in output voltage synthesis according to the sector cell number of the output voltage of the inverter, and acquiring a corresponding midpoint current flow direction symbol when a lower small vector acts from three-phase current of the inverter; and the midpoint voltage deviation multiplied by the midpoint current flow direction symbol enters the PI regulator for closed-loop control. The PI regulator outputs a small vector action angle interval regulating signal, and neutral point voltage balance control is realized by regulating the action angle interval of the upper small vector and the lower small vector. Compared with a common 7-segment continuous PWM method, the IGBT operating frequency is reduced by 28.6%, the purpose of reducing the switching loss is realized, and the requirement of midpoint voltage balance is met.

Description

Discontinuous PWM modulation method for diode clamping three-level inverter
Technical Field
The invention relates to a PWM (pulse-width modulation) method of a diode clamping three-level inverter.
Background
According to the electrical principle, three-phase inverters are classified into two-level inverters and multi-level inverters, wherein the most common inverter among the multi-level inverters is a diode-clamped three-level inverter. The diode clamping three-level inverter has the advantages of high energy conversion efficiency, relatively simple control, low du/dt and the like, and is widely applied to the fields of new energy power generation, motor dragging, pumped storage and the like. In any field, the energy conversion efficiency of the inverter is a great concern, and it is desirable to minimize the loss of the inverter.
The inverter loss is the largest in specific weight and is the switching loss of power electronic devices such as a MOSFET, an IGBT, an IGCT, and the like, the inverter generally adopts a PWM (pulse Width modulation) modulation method to realize the on-off control of the power electronic devices, the PWM modulation method is divided into a continuous PWM modulation method and a discontinuous PWM modulation method, wherein the discontinuous PWM modulation method can reduce the switching loss of the power electronic devices by reducing the number of switching actions within one PWM period.
Discontinuous PWM modulation methods have found wide application in two-level inverters. Document "three-phase inverter unified space vector PWM implementation method [ J ] (break bell, yinjin, etc., electrotechnical bulletin) discusses various discontinuous PWM modulation methods PWMMax, PWMMin, DPWM0, DPWM1, DPWM2, and DPWM3, and differences and connections between them, but only applies to two-level inverters. The document "control application of large-capacity multi-level converter principle" M "(li yong, xiao, etc., scientific press) discusses a continuous PWM modulation method of a diode-clamped three-level inverter, and indicates that midpoint voltage balance is the basis for stable operation of the diode-clamped three-level inverter.
Disclosure of Invention
The invention aims to overcome the defects of the existing PWM modulation method and provides a discontinuous PWM modulation method for a diode clamping three-level inverter. The invention can reduce the switching loss of the diode clamping three-level inverter and maintain the balance of the midpoint voltage.
The vector space of the diode clamping three-level inverter is divided into 6 sectors, each sector is divided into 6 cells, small vectors are divided into an upper small vector and a lower small vector according to the condition that the small vectors are connected with a positive bus and a negative bus in the action period, the upper small vector is a small vector connected between the positive bus and a 0 bus in the action process, and the lower small vector is a small vector connected between the 0 bus and the negative bus in the action process. And the balance control of the midpoint voltage is realized by adjusting the action angle interval of the upper small vector and the lower small vector in the PWM switching sequence. Compared with a common 7-segment continuous PWM method, the discontinuous PWM method has the advantages that small vectors participating in output voltage synthesis do not have a redundant state, the switching sequence in one PWM period is 5-segment, the switching frequency of a power electronic device can be reduced by 28.6 percent on the basis of the 7-segment continuous PWM method, the switching loss of an inverter is greatly reduced, and meanwhile midpoint voltage balance control can be realized.
In the diode clamping three-level inverter, a power electronic device consists of 12 IGBTs and 6 clamping diodes, each bridge arm comprises 4 IGBTs and two clamping diodes, and the 4 IGBTs are sequentially defined as S from top to bottomx1、Sx2、Sx3、Sx4Wherein
Figure GDA0002556822540000021
Values represent A, B, C three phases respectively. In each bridge arm, the upper two IGBTSx1、Sx2Conducting represents state 2, two IGBTSs in betweenx2、Sx3Turn-on represents state 1, two IGBTSs belowx3、Sx4Conduction represents state 0. By switching variable Sa、Sb、ScRespectively representing the switching states of each bridge arm of the three-level inverter, and defining the switching state of each bridge arm of the three-level inverter as SaSbScThen, the three-level inverter has 27 switching states, and each switching state corresponds to 1 space vector, and has 27 space vectors. According to the difference of output voltage, there are three states of 0, 1 and 2, which are respectively corresponding to
Figure GDA0002556822540000022
Three voltage outputs, wherein UdcIs the dc bus voltage.
The entire vector space is divided into 6 sectors, each sector is divided into 6 cells, each cell is represented by (xy), x represents a sector number, y represents a cell number, for example, the (12) area represents the 1 st sector, 2 nd cell. Space vectors are classified into 4 types according to length: the vector comprises a zero vector, a small vector, a middle vector and a large vector, wherein the zero vector is positioned at the point 0, the small vector is positioned on a small vector circle in length, the middle vector is positioned on a middle vector circle in length, and the large vector is positioned on a large vector circle in length. The small vector has 1 redundant state and the zero vector has 2 redundant states. For the small vector with the redundancy state, if the small vector is connected between the positive bus and the 0 bus when acting, the small vector is defined as an upper small vector; if the small vector is connected between the 0 bus and the negative bus when acting, the lower small vector is defined. In the invention, the small vectors of each space position in the PWM switching sequence only contain 1, and the small vectors have no redundant state.
In different sector cells, the space vectors participating in output voltage synthesis are all 3 space vectors, and according to the action sequence of the space vectors, the three space vectors are respectively defined as V1、V2And VmThe action times respectively correspond to T1、T2、Tm. For cells 1 and 2, the small vector of phase lag corresponds to V1Small vectors with phase-leading correspond to V2Zero vector corresponds to Vm(ii) a For cells 3 and 4, the small vector of phase lag corresponds to V1Small vectors with phase-leading correspond to V2The medium vector corresponds to Vm(ii) a For cell 5, the small vector corresponds to V1Large vector corresponds to V2The medium vector corresponds to Vm(ii) a For cell 6, the large vector corresponds to V1Small vector is V2The medium vector corresponds to Vm。
The action time of each space vector participating in the synthesis of the output voltage is calculated as follows;
the space vector action time is classified according to different cells and divided into four working conditions, namely a 1 st cell, a 2 nd cell, a 3 rd cell, a 4 th cell, a 5 th cell and a 6 th cell.
1, 2 cells, V1、V2And VmThree space vector action times T1、T2、TmRespectively as follows:
Figure GDA0002556822540000031
in cells 3 and 4, V1、V2And VmThree space vector action times T1、T2、TmRespectively as follows:
Figure GDA0002556822540000032
at cell 5, V1、V2And VmThree space vector action times T1、T2、TmRespectively as follows:
Figure GDA0002556822540000033
at cell 6, V1、V2And VmThree space vector action times T1、T2、TmRespectively as follows:
Figure GDA0002556822540000034
the invention adjusts the action angle interval of the upper small vector and the lower small vector according to the action time of each space vector to control the midpoint voltage. The key factor influencing the midpoint voltage balance is midpoint current, and therefore the midpoint current condition under the action of small vectors participating in output voltage synthesis when different sectors and different cells are analyzed. Defining three-phase current of inverter as IabcWherein the phase A current is IaPhase B current is IbPhase C current is IcAt a midpoint current of Im. Three-phase current I of inverterabcAnd a midpoint current ImThe flow directions of (1) are all positive with outflow, and the correspondence relationship between the phase current and the midpoint current when the lower small vector acts is shown in table 1.
TABLE 1 correspondence between point current and phase current under small vector action
Figure GDA0002556822540000041
"100", "110", "010", "011", "001" and "101" in table 1 indicate the arm switching states S of the three-level inverteraSbSc0 represents the phase connection to the negative bus, 1 represents the phase connection to the 0 bus, and 2 represents the phase connection to the positive bus.
In table 1, when the sector number x is 1, if the cell number y is 1, 3 or 5, the lower small vector 100 is applied to correspond to im＝iaIf the cell number is 2, 4 or 6, the lower small vector 110 is active and corresponds to im＝-ic(ii) a When the sector number x is 2, if the cell number y is 1, 3 or 5, the lower small vector 110 acts corresponding to im＝-icIf the cell number is 2, 4 or 6, the lower small vector 101 acts corresponding to im＝ib(ii) a When the sector number x is 3, if the cell number y is 1, 3 or 5, the lower small vector 010 acts corresponding to im＝ibIf the cell number is 2, 4 or 6, the lower small vector 011 acts corresponding to im＝-ia(ii) a When the sector number x is 4, if the cell number y is 1, 3 or 5, the lower small vector 011 acts corresponding to im＝-iaIf the cell number is 2, 4 or 6, the lower small vector 001 is acted on corresponding to im＝ic(ii) a When the sector number x is equal to 5, if the cell number y is equal to 1, 3 or 5, the lower small vector 001 is applied to correspond to im＝icIf the cell number is 2, 4 or 6, the lower small vector 101 acts corresponding to im＝-ib(ii) a When the sector number x is 6, if the cell number y is 1, 3 or 5, the lower small vector 101 acts corresponding to im＝-ibIf the cell number is 2, 4 or 6, thenSmall vector 100 acting on corresponding to im＝ia。
The invention is based on the midpoint current ImThe design midpoint voltage control method is as follows: will be negative DC bus voltage UdcNMinus the positive DC bus voltage UdcPTo obtain a midpoint voltage Uneut. Midpoint voltage UneutAnd the midpoint current flows to sign (I)m) The product of the two-dimensional vector and the phase difference enters a PI regulator to carry out closed-loop control, and the PI regulator outputs a small vector action angle interval regulating signal TPSmall vector action angle interval regulation signal TPThe regulation range is [ -1,1 [)]. Adjusting signal T with small vector action intervalPAnd adjusting the action angle interval of the upper small vector and the lower small vector. Three selected space vectors V1、V2、VmCalculated time of action T of three vectors1、T2、TmAnd small vector action angle interval signal T output by PI regulatorPAnd entering a switch sequence generation module, generating a PWM (pulse-width modulation) switch sequence required by the control of the IGBT of the inverter in the switch sequence generation module, controlling the on and off of the IGBT and realizing the neutral point voltage balance control.
Will inverter output voltage UαβThe corresponding vector space is divided into 360 degrees, and the small vectors participating in the output voltage synthesis in each angle interval are shown in table 2.
TABLE 2 Small vectors participating in output voltage synthesis in each angle interval
Angular interval (degree) Small vector
330-30*TP～30+30*TP Upper small vector 211
30+30*TP～90-30*TP Lower small vector 110
90-30*TP～150+30*TP Upper small vector 121
150+30*TP～210-30*TP Lower small vector 011
210-30*TP～270+30*TP Upper small vector 112
270+30*TP～330-30*TP Lower small vector 101
"211", "110", "121", "011", "112" and "101" in table 2 indicate the arm switching state S of the three-level inverteraSbSc0 represents the phase connection to the negative bus, 1 represents the phase connection to the 0 bus, and 2 represents the phase connection to the positive bus.
In table 2, the upper small vector 211 indicates that the two IGBTs on the a-phase arm of the three-phase inverter are turned on and connected to the positive bus
Figure GDA0002556822540000051
Corresponding to the switch state 2, the middle two IGBTs of the B-phase bridge arm are conducted and connected to the 0 bus, corresponding to the switch state 1, the middle two IGBTs of the C-phase bridge arm are conducted and connected to the 0 bus, and corresponding to the switch state 1; the lower small vector 110 indicates that two IGBTs in the middle of the A-phase bridge arm of the three-phase inverter are conducted and connected to the 0 bus corresponding to the switching state 1, two IGBTs in the middle of the B-phase bridge arm are conducted and connected to the 0 bus corresponding to the switching state 1, and two IGBTs under the C-phase bridge arm are conducted and connected to the negative bus corresponding to the switching state 1
Figure GDA0002556822540000061
For the switch state 0; the upper small vector 121 indicates that the middle two IGBTs of the A-phase bridge arm of the three-phase inverter are conducted and connected to the 0 bus, and the two IGBTs of the B-phase bridge arm are conducted and connected to the positive bus corresponding to the switching state 1
Figure GDA0002556822540000062
Corresponding to the switch state 2, the middle two IGBTs of the C-phase bridge arm are conducted and connected to the 0 bus, and corresponding to the switch state 1; the lower small vector 011 shows that two IGBTs below an A-phase bridge arm of the three-phase inverter are conducted and connected to a negative bus
Figure GDA0002556822540000063
Corresponding to a switch state 0, two IGBTs in the middle of a B-phase bridge arm are conducted and connected to a 0 positive bus, corresponding to a switch state 1, two IGBTs in the middle of a C-phase bridge arm are conducted and connected to the 0 positive bus, and corresponding to a switch state 1; the upper small vector 112 indicates that the middle two IGBTs of the A-phase bridge arm of the three-phase inverter are conducted and connected to the 0 bus corresponding to the switching state 1, the middle two IGBTs of the B-phase bridge arm are conducted and connected to the 0 bus corresponding to the switching state 1, and the upper two IGBTs of the C-phase bridge arm are conducted and connected to the positive bus corresponding to the switching state 1
Figure GDA0002556822540000064
Corresponding to switch state 2; the lower small vector 101 indicates that the middle two IGBTs of the A-phase bridge arm of the three-phase inverter are conducted and connected to the 0 bus, and the two IGBTs below the B-phase bridge arm are conducted and connected to the negative bus corresponding to the switching state 1
Figure GDA0002556822540000065
And corresponding to the switching state 0, the middle two IGBTs of the C-phase bridge arm are conducted and connected to the 0 bus, and corresponding to the switching state 1.
In Table 2, the angle interval of the upper small vector 211 participating in the output voltage synthesis is 330-30 × TP～30+30*TPThe angle interval of action of the lower small vector 110 participating in the output voltage synthesis is 30+30 × TP～90-30*TPAngle interval of action of upper small vector 121 participating in output voltage synthesisIs 90-30 × TP～150+30*TPThe action angle interval of the lower small vector 011 participating in the output voltage synthesis is 150+30 × TP～210-30*TPThe action angle interval of the upper small vector 112 participating in the output voltage synthesis is 210-30 × TP～270+30*TPThe action angle interval of the lower small vector 101 participating in output voltage synthesis is 270+30 × TP～330-30*TP。
Thus, the small vector action angle interval adjusts the signal TPAnd adjusting the action angle interval of the upper small vector and the lower small vector according to the table 2, generating a PWM (pulse width modulation) switching sequence required by the control of the IGBT (insulated gate bipolar transistor) of the inverter in a switching sequence generation module, and controlling the on-off of the IGBT. T isPThe regulation range is [ -1,1 [)],30*TPThe adjustment of plus or minus 30 degrees in the small vector action angle interval can be realized. The action angle interval of the upper small vector and the lower small vector is adjusted, so that the accumulated action time of the upper small vector and the lower small vector is indirectly adjusted, and the balance control of the midpoint voltage is realized.
The switch sequence generation module has the specific functions of: combining three selected space vectors V participating in output voltage synthesis1、V2、VmAnd its corresponding action time T1、T2、TmWhen the last small vector is selected to participate in the output voltage synthesis in the 1 st, 3 rd and 5 th cells of the 1 st, 3 rd and 5 th sectors, the action sequence of the three space vectors in the 5-segment switch sequence is V2,Vm,V1,Vm,V2Each space vector has an action time of
Figure GDA0002556822540000071
When the lower small vector is selected to participate in the output voltage synthesis, the sequence of action of the three space vectors in the 5-segment switch sequence is V1,V2,Vm,V2,V1Each space vector has an action time of
Figure GDA0002556822540000072
When the 1 st, 3 rd and 5 th sectors 2, 4 th and 6 th cells select the upper small vector to participate in the output voltage synthesis, the action sequence of the three space vectors in the 5-segment switch sequence is Vm,V1,V2,V1,VmEach space vector has an action time of
Figure GDA0002556822540000073
When the lower small vector is selected to participate in the output voltage synthesis, the sequence of action of the three space vectors in the 5-segment switch sequence is V2,Vm,V1,Vm,V2Each space vector has an action time of
Figure GDA0002556822540000074
When the 1 st, 3 rd and 5 th cells of the 2 nd, 4 th and 6 th sectors select the upper small vector to participate in the output voltage synthesis, the action sequence of the three space vectors in the 5-segment switch sequence is Vm,V2,V1,V2,VmEach space vector has an action time of
Figure GDA0002556822540000075
When the lower small vector synthesis output voltage is selected, the sequence of action of three space vectors in the 5-segment switch sequence is V1,Vm,V2,Vm,V1Each space vector has an action time of
Figure GDA0002556822540000076
When the 2 nd, 4 th and 6 th sectors 2, 4 th and 6 th cells select the last small vector to participate in the output voltage synthesis, the action sequence of the three space vectors in the 5-segment switch sequence is V1,Vm,V2,Vm,V1Each space vector has an action time of
Figure GDA0002556822540000077
When the lower small vector is selected to participate in the output voltage synthesis, the sequence of action of the three space vectors in the 5-segment switch sequence is V2,V1,Vm,V1,V2Each space vector has an action time of
Figure GDA0002556822540000078
The switching sequence of the invention is 5-segment type, and small vectors do not existA redundant state.
Based on the principle, the method comprises the following specific steps:
step 1: according to the output voltage U of the inverterαβAcquiring a sector cell number (xy) of the inverter output voltage, wherein x is the sector number and y is the cell number;
step 2: selecting three space vectors V participating in output voltage synthesis according to the sector cell number (xy) acquired in the step 11、V2And VmCalculating three space vectors V1、V2And VmTime of action T1、T2、Tm. If the cell is the 1 st cell or the 2 nd cell, the formula (1) is adopted for calculation, if the cell is the 3 rd cell or the 4 th cell, the formula (2) is adopted for calculation, if the cell is the 5 th cell, the formula (3) is adopted for calculation, and if the cell is the 6 th cell, the formula (4) is adopted for calculation;
and step 3: collecting three-phase current IabcAccording to the sector number (xy) obtained in the step 1, a table 1 is looked up to obtain the corresponding midpoint current I under the action of the small vectormObtaining the corresponding midpoint current flow sign (I) when the lower small vector actsm)；
And 4, step 4: collecting positive voltage U of direct current busdcPAnd a negative voltage UdcNBy negative voltage UdcNMinus a positive voltage UdcPObtain the midpoint voltage Uneut(ii) a Will mid point voltage UneutAnd the midpoint current flows to sign (I)m) The product of the two is sent to a PI regulator for closed-loop control, and the PI regulator outputs a small vector action angle interval regulating signal TP，TPThe regulation range is [ -1,1 [)]，30*TPThe positive and negative 30-degree adjustment of the small vector action angle interval can be realized;
and 5: step 4, the output small vector action angle interval adjusting signal T is obtainedPAnd adjusting the action angle interval of the upper small vector and the lower small vector according to the table 2. Three space vectors V selected in step 21、V2、VmCalculated time of action T of three vectors1、T2、TmAnd the small vector action angle interval information output by the PI regulator in the step 4Number TPAnd entering a switch sequence generation module, generating a PWM (pulse-width modulation) switch sequence in the switch sequence generation module, and controlling the on and off of an IGBT (insulated gate bipolar translator) in the inverter to realize the balance control of the midpoint voltage.
The method has the advantages that the accumulated action time of the upper small vector and the lower small vector is adjusted by adjusting the action angle interval of the upper small vector and the lower small vector, the diode clamping three-level discontinuous PWM modulation method is realized, the action times of the power electronic device in one PWM period are reduced from 7 times in the common 7-segment continuous PWM modulation method to 5 times in the discontinuous PWM modulation method, the aim of reducing the switching loss of the inverter is realized, and meanwhile, the balance control of the midpoint voltage can be met. Compared with a common 7-segment continuous PWM method, the IGBT operating frequency is reduced by 28.6%, the purpose of reducing the switching loss is realized, and the requirement of midpoint voltage balance is met. The invention is especially suitable for the motor load with larger armature inductance.
Drawings
FIG. 1 is a diode clamped three level inverter topology;
FIG. 2 three-level inverter space vector partitioning;
figure 3 different cells V1、V2And VmThree spatial vector position definitions;
FIG. 4 adjustment signal T for small vector action angle intervalPAdjusting the corresponding relation of the action time of the upper and lower small vectors;
FIG. 5 is a 5-segment switching sequence and its activation time for different sectors and different cells;
fig. 6 is a block diagram of a discontinuous PWM modulation method for a diode clamped three-level inverter.
Detailed Description
The invention is further described below with reference to the accompanying drawings and the detailed description.
A diode clamped three level inverter topology is shown in fig. 1. The inverter collects positive and negative DC bus voltages, which are respectively marked as UdcPAnd UdcN(ii) a Collecting three-phase AC current, denoted as IabcWherein phase A, phase B and phase C respectively correspond to phase Ia、IbAnd Ic(ii) a Is aligned with the DC bus voltage UdcPAnd negative DC bus voltage UdcNSumming to obtain DC bus voltage Udc(ii) a Is aligned with the bus voltage UdcPAnd negative DC bus voltage UdcNMaking a difference to obtain a midpoint voltage deviation delta Uneut。
As shown in FIG. 1, the upper small vector 211 represents the two IGBTSs above the A-phase leg of the three-phase invertera1And Sa2Is conducted and connected to the positive bus
Figure GDA0002556822540000091
Two IGBTS in the middle of B phase bridge armb2、Sb3Conducted and connected to the 0 bus and the middle two IGBTS of the C-phase bridge armc2、Sc3And conducting and connecting to the 0 bus. The lower small vector 110 represents the middle two IGBTSs of the A-phase leg of the three-phase invertera2、Sa3Conducted and connected to the 0 bus and two IGBTS in the middle of the B-phase bridge armb2、Sb3Conducting, connecting to 0 positive bus, two IGBTS below C phase bridge armc3、Sc4Is conducted and connected to the negative bus
Figure GDA0002556822540000092
The upper small vector 121 represents the middle two IGBTSs of the A-phase leg of the three-phase invertera2、Sa3Conducted and connected to the 0 bus and two IGBTS on the B phase bridge armb1、Sb2Is conducted and connected to the positive bus
Figure GDA0002556822540000093
Two IGBTS in the middle of C phase bridge armc2、Sc3Conducting and connecting to the 0 bus; the lower small vector 011 represents two IGBTSs below the A-phase bridge arm of the three-phase invertera3、Sa4Is conducted and connected to the negative bus
Figure GDA0002556822540000094
Two IGBTS in the middle of B phase bridge armb2、Sb3Conducted and connected to the 0 bus and the middle two IGBTS of the C-phase bridge armc2、Sc3Conducting and connecting to the 0 bus. Upper small vector 112 denotes the middle two IGBTS of the A-phase bridge arm of the three-phase invertera2、Sa3Conducted and connected to the 0 bus and two IGBTS in the middle of the B-phase bridge armb2、Sb3Conducting, connecting to 0 bus, two IGBTS on C phase bridge armc1、Sc2Is conducted and connected to the positive bus
Figure GDA0002556822540000095
The lower small vector 101 represents the middle two IGBTSs of the A-phase leg of the three-phase invertera2、Sa3Conducted and connected to the 0 bus and two IGBTS below the B-phase bridge armb3、Sb4Is conducted and connected to the negative bus
Figure GDA0002556822540000096
Two IGBTS in the middle of C phase bridge armc2、Sc3And conducting and connecting to the 0 bus.
The diode clamping three-level inverter adopts a vector control method, and a vector control module shown as 10 in figure 1 outputs an inverter output voltage Uαβ. The control block diagram of the present invention is shown in fig. 6.
As shown in fig. 6, the present invention comprises the following steps:
step 1: inverter output voltage U output by vector control module 100 in FIG. 6αβAnd acquiring the sector cell number (xy) of the current voltage, as shown by 110 in fig. 6, wherein x is the sector number and y is the cell number. The specific method comprises the following steps: output voltage U required for inverterαβIn the alpha and beta axis components UαAnd UβCalculating the arc tangent to obtain a space vector space angle theta, and dividing the space vector space angle theta by 60 to obtain a sector number; the 1 st, 3 rd and 5 th cells are obtained when the remainder is less than 30 degrees, and the 2 nd, 4 th and 6 th cells are obtained when the remainder is more than or equal to 30 degrees; and then subdividing, wherein the vector length is the 1 st cell or the 2 nd cell at the inner side of the two small vector connecting lines, the vector length is the 3 rd cell or the 4 th cell between the two small vector connecting lines and the small vector and medium vector connecting lines, and the vector length is the 5 th cell or the 6 th cell at the outer side of the small vector and medium vector connecting lines, as shown in fig. 2.
Step 2: according toThe sector cell number (xy), obtained in part 110 in step 1, selects three space vectors involved in the output voltage synthesis, as shown at 120 in fig. 6. The three space vectors include V1、V2And VmThree space vectors V in different cells1、V2And VmThe method for defining (1) is shown in fig. 3, and the specific method for selecting the space vector participating in the output voltage synthesis is as follows: for cells 1 and 2, the small vector of the phase lag is V1The small vector of the phase lead is V2Zero vector is Vm(ii) a For cells 3 and 4, the small vector of the phase lag is V1The small vector of the phase lead is V2The middle vector is Vm(ii) a For cell 5, the small vector is V1Large vector is V2The middle vector is Vm(ii) a For cell 6, the large vector is V1Small vector is V2The middle vector is Vm. Calculating the acting time T of three space vectors according to the sector cell number acquired by the part 110 in the step 11、T2、TmAs shown at 130 in fig. 6. The calculation method specifically comprises the following steps: if the cell is the 1 st cell or the 2 nd cell, the formula (1) is adopted for calculation, if the cell is the 3 rd cell or the 4 th cell, the formula (2) is adopted for calculation, if the cell is the 5 th cell, the formula (3) is adopted for calculation, and if the cell is the 6 th cell, the formula (4) is adopted for calculation;
and step 3: three-phase current I of acquisition inverterabcLooking up table 1 to obtain the corresponding midpoint current I under the action of the lower small vector according to the sector cell number (xy) obtained from part 110 in FIG. 6mTo find the midpoint current flow sign (I)m) As shown at 150 in fig. 6;
and 4, step 4: collecting positive voltage U of direct current busdcPAnd a negative voltage UdcN，UdcNMinus UdcPObtain the midpoint voltage Uneut(ii) a Midpoint voltage UneutMultiplied by the midpoint current flow sign (I)m) The closed-loop control is carried out through a PI regulator, and the PI regulator outputs a small vector action angle interval regulating signal T P160 in FIG. 6, TPThe regulation range is [ -1,1 [)]；
And 5: using the step 4 outputSmall vector action angle interval regulation signal TPAnd adjusting the action angle interval of the upper small vector and the lower small vector according to the table 2. Three space vectors V selected in step 21、V2、VmCalculated time of action T of three vectors1、T2、TmAnd the small vector action angle interval signal T output in the step 4PAnd entering a switching sequence generation module, generating a PWM switching sequence in the switching sequence generation module, controlling the on and off of an IGBT in the inverter, and realizing the balance control of the midpoint voltage, such as 170 in fig. 5. The specific method comprises the following steps: the action angle interval of the upper small vector 211 participating in the output voltage synthesis is 330-30TP～30+30*TPThe angle interval of action of the lower small vector 110 participating in the output voltage synthesis is 30+30 × TP～90-30*TPThe action angle interval of the upper small vector 121 participating in the output voltage synthesis is 90-30 × TP～150+30*TPThe action angle interval of the lower small vector 011 participating in the output voltage synthesis is 150+30 × TP～210-30*TPThe angle interval of the small vector 112 participating in the output voltage synthesis is 210-30 × TP～270+30*TPThe action angle interval of the lower small vector 101 participating in output voltage synthesis is 270+30 × TP～330-30*TPAs shown in fig. 4. Wherein, TPFor the small vector action time regulating signal output by the PI regulator in the closed-loop control of the midpoint voltage, the regulating range is [ -1,1]，30*TPThe adjustment of plus or minus 30 degrees in the small vector action angle interval can be realized. According to the sector cell number (xy) obtained in step 1, the switching sequence generation module 170 shown in fig. 6 generates a PWM switching sequence to control the on and off of the IGBT device in the inverter. The 5-segment switching sequence in different sector cells is shown in fig. 5, when the 1 st, 3 rd and 5 th sectors are in the 1 st, 3 rd and 5 th cells, the selected upper small vector participates in the output voltage synthesis, and the action sequence of three space vectors in the 5-segment switching sequence is V2,Vm,V1,Vm,V2Each space vector has an action time of
Figure GDA0002556822540000111
Selecting a lower small vector to participate in outputtingWhen the voltages are synthesized, the sequence of action of three space vectors in the 5-segment switching sequence is V1,V2,Vm,V2,V1Each space vector has an action time of
Figure GDA0002556822540000112
When the 1 st, 3 rd and 5 th sectors 2, 4 th and 6 th cells select the upper small vector to participate in the output voltage synthesis, the action sequence of the three space vectors in the 5-segment switch sequence is Vm,V1,V2,V1,VmEach space vector has an action time of
Figure GDA0002556822540000113
When the lower small vector is selected to participate in the output voltage synthesis, the sequence of action of the three space vectors in the 5-segment switch sequence is V2,Vm,V1,Vm,V2Each space vector has an action time of
Figure GDA0002556822540000114
When the 1 st, 3 rd and 5 th cells of the 2 nd, 4 th and 6 th sectors select the upper small vector to participate in the output voltage synthesis, the action sequence of the three space vectors in the 5-segment switch sequence is Vm,V2,V1,V2,VmEach space vector has an action time of
Figure GDA0002556822540000121
When the lower small vector synthesis output voltage is selected, the sequence of action of three space vectors in the 5-segment switch sequence is V1,Vm,V2,Vm,V1Each space vector has an action time of
Figure GDA0002556822540000122
When the 2 nd, 4 th and 6 th sectors 2, 4 th and 6 th cells select the last small vector to participate in the output voltage synthesis, the action sequence of the three space vectors in the 5-segment switch sequence is V1,Vm,V2,Vm,V1Each space vector has an action time of
Figure GDA0002556822540000123
When the lower small vector is selected to participate in the output voltage synthesis, the sequence of action of the three space vectors in the 5-segment switch sequence is V2,V1,Vm,V1,V2Each space vector has an action time of
Figure GDA0002556822540000124

Claims (3)

1. A discontinuous PWM modulation method of a diode clamping three-level inverter divides the vector space of the diode clamping three-level inverter into 6 sectors, each sector is subdivided into 6 cells, and the method is characterized in that: the modulation method divides the small vectors into an upper small vector and a lower small vector according to the condition that the small vectors are connected with a positive bus and a negative bus in an action period, wherein the upper small vector is the small vector connected between the positive bus and a 0 bus in action, and the lower small vector is the small vector connected between the 0 bus and a negative bus in action; the switching sequence in one PWM period is in a 5-segment type, the balance control of the midpoint voltage is realized by adjusting the action angle interval of the upper small vector and the lower small vector, and the small vectors participating in the synthesis of the output voltage have no redundant state;
the modulation method comprises the following steps:
step 1: according to the output voltage U of the inverterαβAcquiring a sector cell number (xy) of the inverter output voltage;
step 2: selecting three space vectors V participating in output voltage synthesis according to the sector cell number (xy) acquired in the step 11、V2And VmCalculating three space vectors V1、V2And VmTime of action T1、T2、Tm；
And step 3: three-phase current I of acquisition inverterabcAccording to the sector number (xy) obtained in the step 1, the corresponding midpoint current I under the action of the lower small vector is obtainedmObtaining the corresponding midpoint current flow sign (I) when the lower small vector actsm)；
And 4, step 4: collecting positive voltage U of direct current busdcPAnd a negative voltage UdcNNegative voltage UdcNMinus a positive voltage UdcPObtain the midpoint voltage Uneut(ii) a Midpoint voltage UneutMultiplied by the midpoint current flow sign (I)m) The product enters a PI regulator for closed-loop control; the output of the PI regulator is a small vector action angle interval regulating signal TP，TPThe adjusting range is [ -1,1 [)]；
And 5: regulating signal T in angle interval by adopting small vector action output in step 4PAdjusting the action angle interval of the upper small vector and the lower small vector; three space vectors V selected in step 21、V2、VmCalculated three vector action times T1、T2、TmAnd step 4, outputting a small vector action angle interval adjusting signal TPAnd entering a switch sequence generation module, generating a PWM (pulse-width modulation) switch sequence in the switch sequence generation module, and controlling the on and off of an IGBT (insulated gate bipolar translator) in the inverter to realize the balance control of the midpoint voltage.
2. The diode-clamped three-level inverter discontinuous PWM modulation method according to claim 1, characterized in that: the selection method of the 5-segment PWM switching sequence and the action sequence of three space vectors are as follows:
three space vectors participating in output voltage synthesis are defined as V respectively1、V2And VmFor cells 1 and 2, the small vector of phase lag corresponds to V1Small vectors with phase-leading correspond to V2Zero vector corresponds to Vm(ii) a For cells 3 and 4, the small vector of phase lag corresponds to V1Small vectors with phase-leading correspond to V2The medium vector corresponds to Vm(ii) a For cell 5, the small vector corresponds to V1Large vector corresponds to V2The medium vector corresponds to Vm(ii) a For cell 6, the large vector corresponds to V1Small vector corresponds to V2The medium vector corresponds to Vm(ii) a Three space vectors V1、V2And VmThe action times are respectively T1、T2、Tm(ii) a Combining three selected space vectors V participating in output voltage synthesis1、V2、VmAnd its corresponding action time T1、T2、TmWhen the last small vector is selected to participate in the output voltage synthesis in the 1 st, 3 rd and 5 th cells of the 1 st, 3 rd and 5 th sectors, the action sequence of the three space vectors in the 5-segment switch sequence is V2,Vm,V1,Vm,V2Each space vector has an action time of
Figure FDA0002556822530000021
When the lower small vector is selected to participate in the output voltage synthesis, the sequence of action of the three space vectors in the 5-segment switch sequence is V1,V2,Vm,V2,V1Each space vector has an action time of
Figure FDA0002556822530000022
When the 1 st, 3 rd and 5 th sectors 2, 4 th and 6 th cells select the upper small vector to participate in the output voltage synthesis, the action sequence of the three space vectors in the 5-segment switch sequence is Vm,V1,V2,V1,VmEach space vector has an action time of
Figure FDA0002556822530000023
When the lower small vector is selected to participate in the output voltage synthesis, the sequence of action of the three space vectors in the 5-segment switch sequence is V2,Vm,V1,Vm,V2Each space vector has an action time of
Figure FDA0002556822530000024
When the 1 st, 3 rd and 5 th cells of the 2 nd, 4 th and 6 th sectors select the upper small vector to participate in the output voltage synthesis, the action sequence of the three space vectors in the 5-segment switch sequence is Vm,V2,V1,V2,VmEach space vector has an action time of
Figure FDA0002556822530000025
When the lower small vector synthesis output voltage is selected, the sequence of action of three space vectors in the 5-segment switch sequence is V1,Vm,V2,Vm,V1Each space vector has an action time of
Figure FDA0002556822530000026
When the 2 nd, 4 th and 6 th sectors 2, 4 th and 6 th cells select the last small vector to participate in the output voltage synthesis, the action sequence of the three space vectors in the 5-segment switch sequence is V1,Vm,V2,Vm,V1Each space vector has an action time of
Figure FDA0002556822530000027
When the lower small vector is selected to participate in the output voltage synthesis, the sequence of action of the three space vectors in the 5-segment switch sequence is V2,V1,Vm,V1,V2Each space vector has an action time of
Figure FDA0002556822530000028
3. The diode-clamped three-level inverter discontinuous PWM modulation method according to claim 1, characterized in that: the method for realizing the balance control of the midpoint voltage by adjusting the action angle interval of the upper small vector and the lower small vector comprises the following steps:
the action angle interval of the upper small vector 211 participating in the output voltage synthesis is 330-30TP～30+30*TPThe angle interval of action of the lower small vector 110 participating in the output voltage synthesis is 30+30 × TP～90-30*TPThe action angle interval of the upper small vector 121 participating in the output voltage synthesis is 90-30 × TP～150+30*TPThe action angle interval of the lower small vector 011 participating in the output voltage synthesis is 150+30 × TP～210-30*TPThe action angle interval of the upper small vector 112 participating in the output voltage synthesis is 210-30 × TP～270+30*TPThe action angle interval of the lower small vector 101 participating in output voltage synthesis is 270+30 × TP～330-30*TP(ii) a Wherein T isPThe small vector action angle interval adjusting signal output by the PI regulator for the closed-loop control of the midpoint voltage has the adjusting range of [ -1,1]，30*TPThe positive and negative 30-degree adjustment of the small vector action angle interval can be realized.
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