CN114759816A - Control method for adjusting midpoint potential of common mode voltage in T-type three-level inverter - Google Patents

Control method for adjusting midpoint potential of common mode voltage in T-type three-level inverter Download PDF

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CN114759816A
CN114759816A CN202210347899.9A CN202210347899A CN114759816A CN 114759816 A CN114759816 A CN 114759816A CN 202210347899 A CN202210347899 A CN 202210347899A CN 114759816 A CN114759816 A CN 114759816A
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胡慧慧
吴明铂
臧泽田
赵仁德
董磊
王永军
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China University of Petroleum East China
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • H02M7/487—Neutral point clamped inverters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/12—Arrangements for reducing harmonics from ac input or output
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
    • H02M7/539—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters with automatic control of output wave form or frequency
    • H02M7/5395—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters with automatic control of output wave form or frequency by pulse-width modulation

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Abstract

The invention discloses a control method for adjusting the midpoint potential of common mode voltage in a T-type three-level inverter, which comprises the following steps: s1, defining a virtual basic vector which avoids participation of the positive vector; s2, according to the virtual basic vector, adopting a space vector pulse width modulation method, and adjusting the action time of the virtual basic vector according to the time correction factor, and carrying out balance control on the midpoint potential of common-mode voltage in the T-type three-level inverter; the invention adopts a space vector pulse width modulation method and adjusts the action time of the virtual basic vector according to the time correction factor to realize the control of the midpoint potential. Therefore, the cooperative inhibition of the midpoint potential and the common-mode voltage according to the correction factor is realized.

Description

Control method for adjusting midpoint potential of common mode voltage in T-type three-level inverter
Technical Field
The invention relates to the field of power electronic control, in particular to a midpoint potential control method for regulating common-mode voltage in a T-type three-level inverter.
Background
The Neutral-point-clamped (npc) type three-level inverter mainly faces the problem of Neutral-point potential imbalance. The midpoint potential refers to the potential at the junction of the two capacitors on the dc side. In order to ensure the safe and reliable operation of the three-level inverter, two capacitors with the same capacitance value on the direct current side must be balanced and divided, otherwise, the neutral point potential is unbalanced, the service life of the capacitors is damaged, the voltage stress of a switching device is increased, the switching device can be directly damaged in severe cases, the output waveform of the inverter is distorted, the harmonic content is increased, and the load is damaged. Secondly, in the NPC inverter, the Common Mode Voltage (CMV) rejection is also an important issue, and a high CMV can cause a series of problems during the operation of the system. For example, a high CMV induces a shaft voltage with a high amplitude on the rotating shaft of the motor, thereby forming a shaft current, damaging the insulation, and shortening the service life of the motor; high frequency CMV can produce high frequency leakage currents that can cause significant electromagnetic interference to surrounding normally operating electrical equipment.
The existing common solutions mainly include two types, namely hardware improved topological structure and optimized software algorithm. Compared with a hardware method for improving a topological structure, the software optimization algorithm has the advantages of convenience in operation, simplicity in experiment, low cost and the like, and is favored by expert scholars. The corresponding software algorithm mainly comprises the following steps: virtual space vector, reasonably adjusting the acting time and sequence of small vectors, sliding mode control, zero sequence component injection and the like. Most of the research methods focus on one aspect of midpoint potential balance and common mode voltage suppression, and the research on the cooperative control of the midpoint potential balance and the common mode voltage suppression is less.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides the midpoint potential control method for regulating the common-mode voltage in the T-type three-level inverter, which solves the problem that only midpoint potential balance or common-mode voltage suppression is singly considered in the control of the existing T-type three-level inverter.
In order to achieve the purpose of the invention, the invention adopts the technical scheme that: a control method for adjusting the midpoint potential of common mode voltage in a T-type three-level inverter comprises the following steps:
s1, defining a virtual basic vector which avoids participation of the positive vector;
and S2, according to the virtual basic vector, adopting a space vector pulse width modulation method, and adjusting the action time of the virtual basic vector according to the time correction factor to perform balance control on the midpoint potential of the common-mode voltage in the T-type three-level inverter.
Further, the definition formula of the virtual basic vector in step S1 includes:
VN0＝VOOO
Figure BDA0003577697220000021
Figure BDA0003577697220000022
Figure BDA0003577697220000023
VNL1＝VPNN
VNL2＝VPPN
wherein, VN0Is a virtual basic zero vector, VNS1Is a first virtual basic small vector, VNS2Is a second virtual basic small vector, VNM1As virtual basic medium vectors, VNL1Is a first virtual basic large vector, VNL2Is a second virtual basic large vector, VOOOIs a zero vector V in OOO on-off stateOONIs a primitive negative small vector V in OON switching statesPOOIs a primary-negative base small vector V in the switching state of POOONOIs a primitive negative small vector V in OON switching statesOPOIs a proto-negative base in OPO switching statesThe smallest vector of this, VPONIs the original basic medium vector, V, in the PON switching stateOPNIs the original basic medium vector, V, in OPN switch statesPNOIs the original basic medium vector V in PNO switching statePNNIs the original basic large vector V in PNN switch statesPPNThe original basic large vector under the PPN switch states.
The beneficial effects of the above further scheme are: the virtual basic zero vector is the same as the original zero vector, the virtual basic large vector is the same as the original basic large vector, the virtual basic medium vector is synthesized by 3 original basic medium vectors, the virtual basic small vector is synthesized by an original negative basic small vector and two adjacent original negative basic small vectors, the participation of the positive vector is avoided, and the common-mode voltage generated during the action of the virtual basic small vector is UdcAnd/6, which is half of the original common mode voltage.
Further, the step S2 adjusts the acting time of the vector in the virtual basic according to the time correction factor by the following formula:
T′2＝fT2
wherein f is a time correction factor, T2Is a virtual basic medium vector primary action time, T'2And adjusting the action time of the vector in the virtual basic.
Further, the time correction factor is obtained by solving the following formula:
Figure BDA0003577697220000031
wherein f is a time correction factor, C is a capacitance value, and Δ U is a difference between two capacitance voltages, that is: midpoint potential, T2For the origin of the vector in the virtual base, ibIs the B-phase load current.
The beneficial effects of the above further scheme are: the virtual medium vector is synthesized by three adjacent medium vectors to form a virtual medium vector VNM1For example, VNM1From three basic voltage vectors VPON、VOPN、VPNOResultant, three basis vector generated midpoint potentialThe streams are each ib、ia、ic. Middle vector VPONAnd VPNOThe resulting midpoint currents add to-iaExactly with VOPNGenerated midpoint current iaThe moduli are equal but opposite in direction, and then a correction factor f is added above the action time of these three vectors, and the amount of charge at the midpoint is controlled by adjusting the correction factor, thereby suppressing fluctuations in the midpoint potential. Take the 4 th cell with the reference vector in the ith cell as an example, because the first large inter-cell virtual vector VNM1Sum voltage vector VPONAre aligned, so that the voltage vector VPONHas a time coefficient of (1+ f) and a voltage vector VOPN、VPNOThe time coefficient of (1-f) is set so that the direction and magnitude of the virtual vector are not affected no matter how the correction factor f changes.
In conclusion, the beneficial effects of the invention are as follows:
1. the invention defines a virtual basic vector for avoiding the participation of a positive vector, so that the common-mode voltage generated during the action of the virtual basic small vector is UdcAnd 6, the common mode voltage is half of the original common mode voltage, and the common mode voltage is reduced.
2. And a space vector pulse width modulation method is adopted, and the action time of the virtual basic vector is adjusted according to the time correction factor, so that the control of the midpoint potential is realized. Therefore, the cooperative inhibition of the midpoint potential and the common-mode voltage according to the correction factor is realized.
Drawings
FIG. 1 is a topology structure diagram of a T-type three-level inverter;
FIG. 2 is a spatial vector diagram;
FIG. 3 is a flow chart of a method for controlling the midpoint potential of the common mode voltage in a T-type three-level inverter;
FIG. 4 is a virtual space vector partition diagram;
FIG. 5 is a graph of vector action time and output sequence;
FIG. 6 is a graph showing the comparison result of midpoint potential simulation;
FIG. 7 is a graph of simulation comparison results of common mode voltages;
fig. 8 is a waveform of the midpoint potential when the initial deviation is 10V.
Detailed Description
The following description of the embodiments of the present invention is provided to facilitate the understanding of the present invention by those skilled in the art, but it should be understood that the present invention is not limited to the scope of the embodiments, and it will be apparent to those skilled in the art that various changes may be made without departing from the spirit and scope of the invention as defined and defined by the appended claims, and all changes that can be made by the invention using the inventive concept are intended to be protected.
The topology of a T-type three-level inverter is shown in fig. 1. It mainly comprises 12 Insulated Gate Bipolar Transistors (IGBT), each phase comprises 4 switching devices IGBT, Sm2And Sm3Connecting the midpoint and the load to form a bidirectional switch, Sm1And Sm4And the positive and negative electrodes are respectively connected with the voltage of the direct current side bus, wherein m is a phase, b and c (one phase in the three phases). U shapedcIs a DC bus voltage ia、ib、icFor loading three-phase currents, C1And C2Is a DC side capacitor ic1And ic2Is the capacitive current. The T-type three-level inverter can output P, O, N three level states, so that the three phases are 3 in total327 switch states correspond to 27 elementary space vectors, as shown in fig. 2. According to the magnitude of the module value of the space vector, the space vector is divided into four vectors, namely a large vector, a medium vector, a small vector and a zero vector.
As shown in fig. 3, a midpoint potential control method for regulating common mode voltage in a T-type three-level inverter includes the following steps:
s1, defining a virtual basic vector which avoids participation of the positive vector;
and S2, according to the virtual basic vector, adopting a space vector pulse width modulation method, and adjusting the action time of the virtual basic vector according to the time correction factor to perform balance control on the midpoint potential of the common-mode voltage in the T-type three-level inverter.
When defining the virtual basic vector, the space vector diagram is divided into six large intervals at intervals of 60 °, as shown in fig. 4, and the virtual vector is redefined by taking the ith large interval as an example, as follows:
VN0＝VOOO
Figure BDA0003577697220000051
Figure BDA0003577697220000052
Figure BDA0003577697220000053
VNL1＝VPNN
VNL2＝VPPN
wherein, VN0Is a virtual basic zero vector, VNS1Is a first virtual basic small vector, VNS2Is a second virtual basic small vector, VNM1As virtual basic medium vectors, VNL1Is a first virtual basic large vector, VNL2Is a second virtual basic large vector, VOOOIs a zero vector V in OOO switching statesOONIs a primitive negative small vector V in OON switching statesPOOIs a primary-negative base small vector V in the switching state of POOONOIs a primitive negative small vector V in OON switching statesOPOIs an original negative base small vector in OPO switching state, VPONIs the original basic medium vector, V, in the PON switching stateOPNIs the original basic medium vector, V, in OPN switch statesPNOIs the original basic medium vector V in PNO switching statesPNNIs the original basic large vector V in PNN switch statesPPNThe original basic large vector under the PPN switch states.
The step S2 adjusts the acting time of the vector in the virtual basic according to the time correction factor by the following formula:
T′2＝fT2
wherein f is a time correctionFactor, T2Is a virtual basic medium vector original action time, T'2And adjusting the action time of the vector in the virtual basic.
The time correction factor is solved by the following formula:
Figure BDA0003577697220000061
wherein f is a time correction factor, C is a capacitance value, and Δ U is a difference between two capacitance voltages, that is: midpoint potential, T2For the origin of the vector in the virtual basis, ibIs a B-phase load current; since the on-time of the vector is unlikely to be negative, the absolute value of the correction factor f cannot be greater than 1. When the correction factor is too large, the effect of the vector effect is impaired, resulting in distortion of the output voltage waveform. When the correction factor is too small, the correction factor does not play a role in correcting the midpoint potential.
The calculation process of the time correction factor is as follows:
the problem of midpoint potential fluctuation is reflected in the voltage inequality of two capacitors at the DC side
Figure BDA0003577697220000071
Where U is the voltage and Q is the amount of charge.
The fluctuation of the midpoint potential is that the charge at the midpoint is not equal to 0. Therefore, holding the electric charge at the midpoint to 0 can suppress fluctuation of the midpoint potential and also correct the shift of the midpoint potential.
Midpoint charge quantity delta Q flowing out in one switching period*Comprises the following steps:
Figure BDA0003577697220000072
wherein ia、ib、icIs a three-phase load current, and ia+ib+ic＝0；
The midpoint charge amount Δ Q*The simplification is as follows:
Figure BDA0003577697220000073
the charge amount measured in one cycle varies as: Δ Q ═ Q2-Q2＝C(UC2-UC1) Is ═ C Δ U, where UC1、UC2Voltages, Q, of two capacitors on the DC side, respectively2And Q1The charge amounts of the two capacitors on the dc side are respectively. When the variation of the charge in the period is offset with the charge allowance in the previous period, the effect of balancing the midpoint potential is realized, and the method comprises the following steps: delta Q*+ Δ Q ═ 0, simultaneous
Figure BDA0003577697220000074
And ia+ib+icIs equal to 0, calculated to obtain
Figure BDA0003577697220000075
Table 1 shows the time correction factor f for each large interval:
TABLE 1
Figure BDA0003577697220000076
Taking the 4 th cell with the reference vector in the ith cell as an example, the output sequence and action time of the basic vector are changed as shown in fig. 5. After the limitation of the above condition, the obtained correction factor is substituted into the corresponding action time of the vector, thereby controlling the balance of the midpoint potential.
As shown in fig. 6(a), the midpoint potential obtained by using the conventional virtual space vector algorithm fluctuates stably in stages, but gradually shifts with time and is unstable. As shown in FIG. 6(b), the midpoint potential does not shift with the increase of time by using the method of the present invention, and is always stabilized within + -0.5V, which has a good effect of suppressing the fluctuation of the midpoint potential. FIG. 7(b) shows that the common mode voltage obtained by the method of the present invention has a magnitude of Udc100V, compared with the common-mode voltage U obtained by the traditional virtual space vector algorithmdcAnd/3 is reduced by half when the voltage is 200V. FIG. 8 shows, assuming initialThe voltage values of the two capacitors on the direct current side are respectively set to be 305V and 295V, the initial deviation of the midpoint potential is 10V, and the method provided by the invention realizes the control of the midpoint potential balance within about 0.03 s.

Claims (4)

1. A control method for adjusting the midpoint potential of common mode voltage in a T-type three-level inverter is characterized by comprising the following steps:
s1, defining a virtual basic vector which avoids participation of the positive vector;
and S2, according to the virtual basic vector, adopting a space vector pulse width modulation method, and adjusting the action time of the virtual basic vector according to the time correction factor to perform balance control on the midpoint potential of common mode voltage in the T-type three-level inverter.
2. The method as claimed in claim 1, wherein the definition of the virtual basic vector in step S1 includes:
VN0＝VOOO
Figure FDA0003577697210000011
Figure FDA0003577697210000012
Figure FDA0003577697210000013
VNL1＝VPNN
VNL2＝VPPN
wherein, VN0Is a virtual basic zero vector, VNS1Is a first virtual basic small vector, VNS2Is a second virtual basic small vector, VNM1As virtual basic medium vectors, VNL1Is a first virtual basic large vector, VNL2Is a second virtual basic large vector, VOOOIs a zero vector V in OOO switching statesOONIs original negative basic small vector V of OON switch statesPOOIs a primary-negative base small vector V in the switching state of POOONOIs original negative basic small vector V of OON switch statesOPOIs an original negative basic small vector, V, of OPO switching statesPONIs the original basic medium vector V in the PON kind switch stateOPNIs the original basic medium vector, V, in OPN switch statesPNOIs the original basic medium vector V in PNO switching statesPNNIs the original basic large vector V in PNN switch statesPPNThe original basic large vector under the PPN switch states.
3. The method as claimed in claim 2, wherein the step S2 is performed by adjusting the acting time of the vector in the virtual basic medium according to the time correction factor as follows:
T′2＝fT2
wherein f is a time correction factor, T2Is a virtual basic medium vector original action time, T'2And adjusting the action time of the vector in the virtual basic.
4. The method of claim 3, wherein the time correction factor is obtained by solving the following equation:
Figure FDA0003577697210000021
wherein f is a time correction factor, C is a capacitance value, and Δ U is a voltage difference between two capacitors, that is: midpoint potential, T2For the origin of the vector in the virtual base, ibIs the B-phase load current.
CN202210347899.9A 2022-04-01 2022-04-01 Control method for adjusting midpoint potential of common mode voltage in T-type three-level inverter Pending CN114759816A (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115549505A (en) * 2022-11-30 2022-12-30 成都希望电子研究所有限公司 Midpoint potential and common-mode voltage cooperative control method of three-level NPC inverter
CN116032144A (en) * 2023-03-29 2023-04-28 成都希望电子研究所有限公司 Synchronous overmodulation algorithm for cooperative control of harmonic wave and midpoint potential

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115549505A (en) * 2022-11-30 2022-12-30 成都希望电子研究所有限公司 Midpoint potential and common-mode voltage cooperative control method of three-level NPC inverter
CN116032144A (en) * 2023-03-29 2023-04-28 成都希望电子研究所有限公司 Synchronous overmodulation algorithm for cooperative control of harmonic wave and midpoint potential

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