CN116961460B - Space vector pulse width modulation method and device based on virtual space vector - Google Patents
Space vector pulse width modulation method and device based on virtual space vector Download PDFInfo
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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
- H02M7/53—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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- 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
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Abstract
The invention discloses a space vector pulse width modulation method and equipment based on a virtual space vector, and relates to the field of control of power electronic converters. The method comprises the following steps: calculating a virtual small vector according to the vector sum of the positive small vector and the negative small vector; calculating a virtual middle vector according to the virtual space vector distribution coefficient and the positive small vector and the middle vector in two different directions; for any sector, according to different overmodulation of the reference voltage vector and the amplitude of the reference voltage vector, calculating the acting time of the basic vector by adopting a mode based on overmodulation compensation coefficient, amplitude phase hybrid compensation or amplitude phase simultaneous compensation, thereby carrying out space vector pulse width modulation according to the acting time of the basic vector. The invention can reduce output voltage harmonic wave and distortion.
Description
Technical Field
The invention relates to the field of control of power electronic converters, in particular to a space vector pulse width modulation method and equipment based on a virtual space vector.
Background
Compared with the traditional two-level inverter, the Neutral Point Clamped (NPC) three-level inverter has the advantages of more output level numbers, lower harmonic content of output voltage, lower voltage conversion rate, smaller electromagnetic interference, high output efficiency, smaller switching loss, common-mode voltage and neutral point potential being capable of being inhibited by the same algorithm and the like. Meanwhile, with the development of space vector pulse width modulation (Space Vector Pulse WidthModulator, SVPWM) technology, three-level converters gradually replace two-level converters as main topological structures, and meanwhile, the control strategy of the three-level converters has become a research hot spot of the current power electronic technology.
Compared with the traditional PWM modulation algorithm, the output voltage of the SVPWM technology is improved by about 15%, however, the SVPWM modulation technology has an overmodulation region, when the amplitude of the reference voltage exceeds a certain value, the voltage vector track synthesized by the basic vector is not circular any more, and the output voltage and current can generate distortion and harmonic waves and even pollute a power grid.
Most algorithmic studies have been limited to linear modulation regions with a modulation range of 90% before the nineties of the last century. In engineering application, in order to improve the utilization rate of the converter to the direct current bus, increase the output voltage amplitude of the inverter and improve the output torque of the motor and the low voltage applicability requirement of the converter, domestic and foreign scholars propose related SVPWM overmodulation algorithms, such as a dual-mode overmodulation algorithm and a single-mode overmodulation algorithm, and obtain certain results, however, the overmodulation strategies do not consider the influence on the midpoint potential.
The basic vector of the voltage vector of the composite three-level converter comprises a small vector, a middle vector and a large vector, wherein the small vector and the middle vector can generate midpoint current to cause charge and discharge of a direct current capacitor, so that midpoint potential fluctuation is caused to cause output voltage fluctuation and increase of harmonic components. The small vectors exist in pairs, the directions of midpoint currents generated by the positive small vector and the negative small vector are opposite, the influence on midpoint potential is opposite, and the influence can be eliminated by distributing the action time; the middle vector exists independently, so that the traditional algorithm is uncontrollable, and when the voltage vector synthesis is carried out in the overmodulation region, the proportion of the middle vector is larger, so that the phenomenon of the fluctuation of the midpoint potential is more obvious in the overmodulation region, fluctuation higher than output frequency can be generated, and the fluctuation and unbalance of the midpoint potential can cause a series of hazards, such as the increase of output voltage harmonic waves, the distortion of voltage, the pollution of a power grid, the shortening of the service time of a device, the breakdown of a power switch device and the like.
Disclosure of Invention
The embodiment of the invention provides a space vector pulse width modulation method and equipment based on a virtual space vector (NTV 2), which can reduce fluctuation and unbalance of midpoint potential and reduce output voltage harmonic waves and distortion.
In order to achieve the above purpose, the embodiment of the present invention adopts the following technical scheme:
in a first aspect, a space vector pulse width modulation method based on a virtual space vector is provided, including:
acquiring a space vector diagram corresponding to the voltage of the three-phase inverter circuit in one switching period; the space vector diagram comprises: six sectors;
calculating a virtual small vector according to the vector sum of the positive small vector and the negative small vector in the space vector diagram;
calculating a virtual middle vector according to the virtual space vector distribution coefficient, the positive small vectors in two different directions in the space vector diagram and the middle vector in the space vector diagram;
for any sector, if the reference voltage vector is in the overmodulation I region and the amplitude of the reference voltage vector is larger than a set value, calculating the acting time of the basic vector based on the overmodulation compensation coefficient; the base vector includes: virtual small vectors, virtual medium vectors and large vectors in the space vector diagram;
for any sector, if the reference voltage vector is in the overmodulation I region and the amplitude of the reference voltage vector is smaller than or equal to a set value, calculating the acting time of the basic vector based on an amplitude-phase hybrid compensation mode;
for any sector, if the reference voltage vector is in the overmodulation II area, calculating the acting time of the basic vector based on the mode of amplitude phase simultaneous compensation;
and in one switching period, performing space vector pulse width modulation according to the action time of the basic vector.
In a first possible implementation manner, with reference to the first aspect, calculating the acting time of the base vector based on the overmodulation compensation coefficient specifically includes:
if the motion track of the reference voltage vector in a certain sector is a nonlinear region, calculating the acting time of the basic vector according to the switching period, the acting time of the middle vector and the rotation angle;
if the motion track of the reference voltage vector in a certain sector is a linear region, the acting time of the basic vector is calculated according to the overmodulation compensation coefficient.
In a second possible implementation manner, with reference to the first aspect, the calculating the acting time of the basic vector based on the mode of amplitude phase hybrid compensation includes:
if the motion track of the reference voltage vector in a certain sector is a nonlinear region, calculating the acting time of the basic vector according to the switching period, the acting time of the middle vector and the rotation angle;
if the motion track of the reference voltage vector in a certain sector is a linear region, calculating the acting time of the basic vector according to the overmodulation compensation coefficient;
if the motion trail of the reference voltage vector in a certain sector is a linear compensation area, calculating the acting time of the basic vector by adopting an amplitude-phase hybrid compensation mode.
In a third possible implementation manner, with reference to the first possible implementation manner of the first aspect, when the amplitude of the reference voltage vector in the overmodulation I region is greater than a set value and the motion track of the reference voltage vector in a certain sector is a nonlinear region, a calculation formula of the acting time of the basic vector is as follows:
wherein,representing the time of action of the virtual vector; />Representing the time of action of the large vector; />Representing the time of action of the virtual small vector; t (T) S Representing a switching period; θ represents the rotation angle.
In a fourth possible implementation manner, with reference to the first possible implementation manner of the first aspect, when the amplitude of the reference voltage vector in the overmodulation I region is greater than a set value and the motion track of the reference voltage vector in a certain sector is a linear region, a calculation formula of the acting time of the basic vector is as follows:
wherein η represents an overmodulation compensation coefficient;representing the time of action of the vector in the virtual before compensation; />Representing the action time of the virtual small vector before compensation; />Indicating the time of action of the large vector before compensation.
In a fifth possible implementation manner, with reference to the second possible implementation manner of the first aspect, if the amplitude of the reference voltage vector in the overmodulation I region is less than or equal to a set value and the motion track of the reference voltage vector in a certain sector is a linear compensation region, the calculation formula of the acting time of the basic vector is:
in a sixth possible implementation manner, with reference to the first aspect, a calculation formula of the virtual small vector is:
wherein V 'is' S1 Representing a virtual small vector; v (V) S1+ Representing a positive small vector; v (V) S1- Representing a negative small vector.
In a seventh possible implementation manner, with reference to the first aspect, a calculation formula of the virtual middle vector is:
wherein V 'is' M Representing a virtual mid-vector; v (V) S1+ Representing a positive small vector in one direction; v (V) S2+ Representing a positive small vector in the other direction; v (V) M Representing a middle vector in the space vector diagram; ζ represents the virtual space vector allocation coefficient.
In an eighth possible implementation manner, with reference to the first aspect, the set value is 2/3.
In a second aspect, there is provided a space vector pulse width modulation apparatus based on a virtual space vector, comprising:
the space vector diagram acquisition unit is used for acquiring a space vector diagram corresponding to the voltage of the three-phase inverter circuit in one switching period; the space vector diagram comprises: six sectors;
a virtual small vector calculation unit for calculating a virtual small vector from the vector sum of the positive small vector and the negative small vector in the space vector diagram;
the virtual middle vector calculation unit is used for calculating a virtual middle vector according to the virtual space vector distribution coefficient, the positive small vectors in two different directions in the space vector diagram and the middle vector in the space vector diagram;
the first time calculation unit is used for calculating the acting time of the basic vector based on the overmodulation compensation coefficient if the reference voltage vector is in the overmodulation I area and the amplitude of the reference voltage vector is larger than a set value for any sector; the base vector includes: virtual small vectors, virtual medium vectors and large vectors in the space vector diagram;
the second time calculation unit is used for calculating the acting time of the basic vector based on the mode of amplitude-phase hybrid compensation if the reference voltage vector is in the overmodulation I area and the amplitude of the reference voltage vector is smaller than or equal to a set value for any sector;
the third time calculating unit is used for calculating the acting time of the basic vector based on the mode of amplitude phase simultaneous compensation if the reference voltage vector is in the overmodulation II area for any sector;
and the pulse width modulation unit is used for carrying out space vector pulse width modulation according to the action time of the basic vector in one switching period.
According to the specific embodiment provided by the invention, the invention discloses the following technical effects:
according to the embodiment of the invention, the original small vector in the space vector diagram is replaced by the calculated virtual small vector, so that the midpoint potential fluctuation caused by the original small vector is reduced; according to the virtual space vector distribution coefficient, the positive small vectors in two different directions and the original medium vector, the virtual medium vector replaces the original medium vector, the medium vector is reserved to participate in the synthesis of the reference voltage vector, the characteristics of the three-level converter are ensured, and the harmonic wave and distortion of the output voltage are reduced.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions of the prior art, the drawings that are needed in the embodiments will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a flowchart of a space vector pulse width modulation method based on a virtual space vector according to an embodiment of the present invention;
fig. 2 is a schematic diagram of a three-level inverter;
FIG. 3 is a raw space vector diagram of a three-level inverter;
FIG. 4 is a schematic diagram of the division of an area within a sector when the virtual vector allocation coefficient ζ > 2/3;
FIG. 5 is a schematic diagram of the division of an area within a sector with a virtual vector allocation coefficient ζ < 2/3;
FIG. 6 is a diagram of a motion trajectory with a virtual vector allocation coefficient ζ >2/3 and a reference voltage vector falling in an overmodulation I region;
FIG. 7 is a diagram of a motion trajectory with a virtual vector allocation coefficient ζ <2/3 and a reference voltage vector falling in an overmodulation I region;
FIG. 8 is a diagram of a motion trajectory for controlling a reference voltage vector in the overmodulation region II;
fig. 9 is a schematic structural diagram of a space vector pulse width modulation device based on a virtual space vector according to another embodiment of the present invention;
fig. 10 is a schematic structural diagram of a space vector pulse width modulation device based on a virtual space vector according to still another embodiment of the present invention.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The embodiment of the invention provides a space vector pulse width modulation method based on a virtual space vector, which is shown in fig. 1 and comprises the following steps:
s101, acquiring a space vector diagram corresponding to voltage of a three-phase inverter circuit in a switching period; the space vector diagram comprises: six sectors.
The output performance of the three-level inverter mainly depends on a modulation algorithm, and the SVPWM technology has the advantages of easy digital implementation, high voltage utilization rate, low harmonic content of output waveforms and the like, so that the switching state of the three-level inverter circuit can be illustrated by using a space vector diagram.
The space vector area is divided into six sectors including a first sector, a second sector, a third sector, a fourth sector, a fifth sector and a sixth sector in a counter-clockwise manner. Each sector is divided into five cells, and each sector comprises a zero vector; two small vectors, a virtual synthesized middle vector and two large vectors; each small vector comprises a positive small vector and a negative small vector.
S102, calculating a virtual small vector according to the vector sum of the positive small vector and the negative small vector in the space vector diagram.
The calculation formula of the virtual small vector is as follows:
wherein V 'is' S1 Representing a virtual small vector; v (V) S1+ Representing a positive small vector; v (V) S1- Representing a negative small vector.
The average value of the vector sum of the original positive small vector and the original negative small vector is adopted to replace the original small vector, so that the midpoint potential fluctuation caused by the original small vector is reduced.
S103, calculating a virtual middle vector according to the virtual space vector distribution coefficient, the positive small vectors in two different directions in the space vector diagram and the middle vector in the space vector diagram.
The calculation formula of the virtual middle vector is as follows:
wherein V 'is' M Representing a virtual mid-vector; v (V) S1+ Representing a positive small vector in one direction; v (V) S2+ Representing a positive small vector in the other direction; v (V) M Representing a middle vector in the space vector diagram; ζ represents the virtual space vector allocation coefficient.
The step adopts original small vectors (V) S1+ And V S2+ ) And vector of primitive vector (V M ) And replacing the original middle vector, keeping the middle vector to participate in the synthesis of the reference voltage vector, ensuring the characteristics of the three-level converter, and reducing the harmonic wave of the output voltage.
S104, for any sector, if the reference voltage vector is in the overmodulation I area and the amplitude of the reference voltage vector is larger than a set value, calculating the acting time of the basic vector based on the overmodulation compensation coefficient; the base vector includes: virtual small vectors, virtual medium vectors, and large vectors in the space vector diagram.
Firstly, introducing a modulation area of reference voltage, dividing the modulation area into a modulation I area and a modulation II area according to the value of a reference voltage modulation ratio M, and when M is 0.907< 0.9535, the reference voltage falls in the overmodulation I area; when M >0.9535, the reference voltage falls in the overmodulation II region.
S104, specifically comprising:
if the motion track of the reference voltage vector in a certain sector is a nonlinear region, calculating the acting time of the basic vector according to the switching period, the acting time of the middle vector and the rotation angle; if the motion track of the reference voltage vector in a certain sector is a linear region, the acting time of the basic vector is calculated according to the overmodulation compensation coefficient.
When the amplitude of the reference voltage vector in the overmodulation region I is larger than a set value and the motion track of the reference voltage vector in a certain sector is a nonlinear region, the calculation formula of the acting time of the basic vector is as follows:
wherein,representing the time of action of the virtual vector; />Representing the time of action of the large vector; />Representing the time of action of the virtual small vector; t (T) S Representing a switching period; θ represents the rotation angle.
When the amplitude of the reference voltage vector in the overmodulation region I is larger than a set value and the motion track of the reference voltage vector in a certain sector is a linear region, the calculation formula of the acting time of the basic vector is as follows:
wherein η represents an overmodulation compensation coefficient;representing the time of action of the vector in the virtual before compensation; />Representing the action time of the virtual small vector before compensation; />Indicating the time of action of the large vector before compensation.
It should be noted that T is the pre-compensation time, T' is the post-compensation time, i.e The time of action of each corresponding vector after overmodulation compensation is adopted, and space vector pulse width modulation is carried out according to the time of action, so that the characteristics of the three-level converter can be ensured, and the harmonic wave and distortion of output voltage can be reduced.
Further, the set value may be 2/3, for example.
S105, for any sector, if the reference voltage vector is in the overmodulation I region and the amplitude of the reference voltage vector is smaller than or equal to a set value, calculating the acting time of the basic vector based on an amplitude-phase hybrid compensation mode. The method specifically comprises the following steps:
if the motion track of the reference voltage vector in a certain sector is a nonlinear region, calculating the acting time of the basic vector according to the switching period, the acting time of the middle vector and the rotation angle; if the motion track of the reference voltage vector in a certain sector is a linear region, calculating the acting time of the basic vector according to the overmodulation compensation coefficient; if the motion trail of the reference voltage vector in a certain sector is a linear compensation area, calculating the acting time of the basic vector by adopting an amplitude-phase hybrid compensation mode.
If the reference voltage vector is in the overmodulation region I, the amplitude of the reference voltage vector is smaller than or equal to the set value, and the motion track of the reference voltage vector in a certain sector is a linear compensation region, the calculation formula of the acting time of the basic vector is as follows:
s106, for any sector, if the reference voltage vector is in the overmodulation II area, calculating the acting time of the basic vector based on the mode of amplitude phase simultaneous compensation.
S107, in a switching period, space vector pulse width modulation is carried out according to the action time of the basic vector.
The embodiment reduces the algorithm module of the controller, has simple control, does not increase a hardware structure, increases the modulation range, improves the utilization rate of the direct current bus, reduces the fluctuation and unbalance of the midpoint potential, and reduces the harmonic wave and distortion of the output voltage.
An example of a space vector pulse width modulation method based on virtual space vectors is given in further detail below in connection with fig. 2-8.
First, a three-level inverter will be described.
Referring to fig. 2, the three-level inverter has three ABC-phase bridge arms, and the main loop of each bridge arm is formed by four controllable power switching tube IGBTs, and by changing that the four IGBTs are in different on-off states, each bridge arm can be made to work in the following three states:
(1) 0-namely zero level, the bridge arm outputs 0 level at the moment, the switching tubes are respectively 0110,1 from top to bottom to be turned off, and 0 is turned on;
(2) n-i.e. low (negative) level, the arm outputting-V at this time dc Level/2, switch tube state 0011, V respectively dc The direct-current side voltage is output by the converter;
(3) p-i.e. high (positive) level, the arm outputting V at this time dc And the level/2, and the switch tube states are 1100 respectively.
Therefore, 000 indicates that the working states of the three bridge arms of ABC are all in a 0 level state, and similarly PPN indicates A, B phase high level and C phase low level.
Meanwhile, 000/NNN/PPP corresponds to a vector space 0 vector, PPN/PNN corresponds to a vector space large vector.
Taking phase A as an example, as shown in FIG. 2, the phase A has four controllable power switching tubes, respectively S A1 ，S A2 ，S A3 And S is A4 . The working state of the phase A is three: p high level, 0 zero level, N low level correspond to the switching tube respectively: P-S A1 ，S A2 Conduction, S A3 ，S A4 Turning off; 0-S A2 ，S A3 Conduction, S A1 ，S A4 Turning off; N-S A1 ，S A2 Turn off, S A3 ，S A4 Conducting.
The original space vector diagram of the three-level inverter is shown in fig. 3. The original space vector diagram is divided into 6 large sectors, and the states of voltage vectors (small vector, medium vector and large vector) corresponding to each sector are shown in table 1.
TABLE 1 Voltage vector State Table
The present example includes the following steps for a space vector pulse width modulation process based on a virtual space vector:
(1) Fig. 4 and fig. 5 correspond to the schematic area division diagrams of the motion track of the reference voltage vector in the first sector under two typical virtual vector distribution coefficients, and the mid-point potential balance is realized by redefining the virtual middle vector and the small vector, and the three-level characteristic is reserved, so that the harmonic wave is reduced.
As shown in fig. 4 and 5, the original small vector is replaced by the average of the sum of the original positive and negative small vectors:
compared with the traditional SVPWM modulation algorithm, positive and negative small vectors in the same direction exist simultaneously in the PWM modulation process, so that midpoint currents caused by the occurrence of the positive and negative small vectors are mutually offset in a period, and further the fluctuation problem of midpoint potential caused by the small vectors is suppressed.
The original vector is replaced by the sum of the original vector and the original small vectors in different directions:
the original negative small vectors in two different directions generate midpoint current vectors of different two phase currents when participating in modulation, and the directions of the synthesized equivalent current vectors in the period are opposite to the directions of the midpoint current vectors generated by the original middle vectors, so that the midpoint current generated by the original middle vectors is counteracted to a certain extent, and further the fluctuation problem of midpoint potential caused by the middle vectors is restrained.
When the virtual middle vector is synthesized, the original middle vector is reserved, so that the three-level characteristic of the converter is reserved, and no harmonic wave is introduced.
Introducing a virtual vector distribution coefficient, dynamically adjusting the proportion of the original middle vector and the original positive and negative small vectors in the synthesized virtual vector according to the change of the reference voltage vector, and further inhibiting the fluctuation of the midpoint potential.
(2) Fig. 6 and 7 are motion trajectories of reference voltage vectors in an overmodulation region I based on virtual vector space coordinates, and fig. 8 is a motion trajectory of reference voltage vectors in an overmodulation region II based on virtual vector space coordinates, wherein the overmodulation region I adopts a mode of mixed compensation of voltage vector amplitude and phase, and the overmodulation region II adopts a mode of simultaneous compensation of voltage vector amplitude and phase.
In fig. 6 and 7, θ' is the reference voltage vector V ref The specific physical meaning of the boundary angle between the nonlinear zone BC segment and the linear zone OA, OD is that O is taken as the center of a circle, |V ref And I is the angle at the intersection of the circle of radius and the triangle AOD. θ1' is the reference voltage vector V ref Falls in the overmodulation I region and the virtual vector distribution coefficient xi<At 2/3, the boundary angle between the nonlinear zone BC segment and the linear zone BB ', CC ' has the same physical meaning as theta '. θ2' is the reference voltage vector V ref Falls in the overmodulation I region and the virtual vector distribution coefficient xi<2/3, the boundary angle between the linear region BB ', CC' and the linear compensation region OA ', OD' has the specific physical meaning of taking O as the center of a circle, |V ref And I is the angle at the intersection of the circle of radius and the parting line (straight line where A 'B' is located) of the small sectors 4, 5.
As shown in fig. 6-8, coarseThe solid line is the motion track of the reference voltage vector set in the overmodulation I region, the dotted arc is the original motion track of the reference voltage vector, and the virtual vector distribution coefficient is combined: when the reference voltage vector magnitude is large (ζ>2/3), the motion trail of the reference voltage vector in the first sector can be divided into linear areas AB, CD and nonlinear areas BC, the BC segment is located on the boundary of the linear modulation hexagon compared with the original motion trail, namely the original modulation algorithm can be utilized to synthesize the reference voltage vector, when the voltage vector is located on the COB, the BC segment can be compensated, and the basic vector V 'is used for' S1 、V′ M And V L1 (V PPN ) Synthesis (rotation angle θ)<30 °) or by the basis vector V' S2 ，V′ M And V L2 (V PNN ) Synthesis (rotation angle θ)>60 °) and the action time is respectively determined by
And (5) determining. V (V) L1 (V PPN ) The phase A and the phase B work in a P high level state, and the phase C works in an N low level state; v (V) L2 (V PNN ) Is a large vector in the other direction.Representation and large vector V L1 Another large vector V of different direction L2 Is used for the action time of the (a); />Representation and virtual small vector V' S1 Another virtual small vector V 'with different direction' S2 Is used for the action time of the (a). T (T) S The switching period, i.e. the on-time of the three-phase controllable power switching tube, is indicated.
The magnitude of the resulting resultant voltage vector decreases. AB. The CD section is arranged in the linear modulation hexagon and has larger voltage amplitude adjustment allowance, and an overmodulation compensation coefficient eta is introduced, wherein the formula is as follows:
m represents the modulation ratio of the reference voltage vector.Wherein |V ref And I is the amplitude of the reference voltage of the converter.
AB. The CD segment voltage vector on time can be expressed as the compensation coefficient respectively:
representation and virtual small vector V S ′ 1 Another virtual small vector V with different direction S ′ 2 The time of action before the compensation is carried out,representation and large vector V L1 Another large vector V of different direction L2 The time of action before compensation.
The reference voltage amplitude loss of the BC segment is compensated by utilizing the voltage amplitude margin, so that the amplitude of a voltage vector output by a modulation algorithm is ensured to be stable to the greatest extent in a period, and the harmonic wave is reduced; when the amplitude of the reference voltage vector is smaller (ζ < 2/3), the motion track of the reference voltage vector in the first sector can be divided into a nonlinear area BC, a linear area B 'B, C' C, a linear compensation area OA ', an OD', BC, B 'B, C' C sections and ζ >2/3, the modulation strategies are the same, when the reference voltage vector falls in the 3 and 4 areas, the voltage amplitude adjustment allowance is smaller, the amplitude phase mixing compensation is adopted, the original long vector is used for representing the reference voltage vector, and the action time is respectively:
(2) As shown in fig. 8, the thick solid line is the motion track of the reference voltage vector set in the overmodulation II region, the dotted arc is the original motion track of the reference voltage vector, and the motion track of the reference voltage vector in the first sector can be divided into linear compensation regions OA, OD and nonlinear region BC, and the BC segment has the same modulation strategy as the nonlinear region of the overmodulation I region; when the reference voltage vector falls on the fan-shaped AOB and COD (still being a linear modulation area), the reference voltage amplitude adjustment margin is too small to compensate the voltage loss of the BC segment, and an amplitude phase simultaneous compensation strategy is adopted, namely OA and OD are adopted to replace the original reference voltage vector motion track to correct the voltage vector in the period.
In the embodiment, the virtual vector distribution coefficient is adopted to adjust the duty ratio of the middle and small vectors in virtual middle and small vector synthesis according to the amplitude of the reference voltage vector, so that the influence of the middle and small vectors on the neutral point potential is offset to the maximum extent; the optimized dual-mode overmodulation algorithm is adopted, the overmodulation problem is considered in the partition, the utilization rate of direct-current voltage is improved, and the distortion of output voltage is reduced; an overmodulation compensation coefficient is adopted to compensate the amplitude of the output voltage, so that the distortion is reduced; and the strategy of simultaneous compensation of the amplitude phase angles of the reference voltages in the overmodulation I region and the overmodulation II region is adopted to realize maximum compensation of the voltage drop of the reference voltages caused by overmodulation time distribution.
The space vector pulse width modulation method based on the virtual space vector in the embodiment has the following advantages:
1) Introducing a virtual vector distribution coefficient, and replacing a traditional SVPWM (space vector pulse width modulation) switch state vector by a dynamic virtual space vector, so as to realize the inhibition of midpoint potential fluctuation in an overmodulation region under the condition of not increasing hardware; 2) Combining the virtual vector distribution coefficient with an optimized overmodulation algorithm to further compensate the voltage drop of the reference voltage under the high modulation ratio; 3) Still adopt the principle of the latest three vectors (NTV) to synthesize the reference voltage vector in the overmodulation region, guarantee the three-level characteristic of the converter, reduce the output voltage harmonic effectively; 4) Through the algorithm of the technical scheme, the distortion of the output voltage of the converter is effectively reduced; 5) Through the algorithm of the technical scheme, the utilization rate of the direct-current voltage is effectively improved.
A further embodiment of the present invention provides a space vector pulse width modulation apparatus based on a virtual space vector, as shown in fig. 9, including:
a space vector diagram obtaining unit 011, configured to obtain a space vector diagram corresponding to a voltage of the three-phase inverter circuit in one switching period; the space vector diagram comprises: six sectors.
A virtual small vector calculation unit 012 for calculating a virtual small vector from the vector sum of the positive small vector and the negative small vector in the space vector diagram.
The virtual middle vector calculation unit 013 is configured to calculate a virtual middle vector according to the virtual space vector allocation coefficient, the positive small vectors in two different directions in the space vector diagram, and the middle vector in the space vector diagram.
A first time calculating unit 014, configured to calculate, for any sector, an acting time of the base vector based on the overmodulation compensation coefficient if the reference voltage vector is in the overmodulation I region and the amplitude of the reference voltage vector is greater than the set value; the base vector includes: virtual small vectors, virtual medium vectors, and large vectors in the space vector diagram.
A second time calculating unit 015, configured to calculate, for any sector, an active time of the base vector based on the mode of amplitude-phase hybrid compensation if the reference voltage vector is in the overmodulation I region and the amplitude of the reference voltage vector is less than or equal to the set value.
The third time calculating unit 016 is configured to calculate, for any sector, the acting time of the base vector based on the mode of simultaneous compensation of amplitude phase if the reference voltage vector is in the overmodulation II region.
The pulse width modulation unit 017 is configured to perform space vector pulse width modulation according to the active time of the basic vector in one switching period.
The modulation device can be applied to occasions such as an inverter, an uninterruptible power supply (Uninterruptible Power Supply, UPS) and a static var compensator (Static Var Compensator, SVC).
According to the space vector pulse width modulation equipment provided by the embodiment of the invention, the original small vector in the space vector diagram is replaced by the calculated virtual small vector, so that the midpoint potential fluctuation caused by the original small vector is reduced; according to the virtual space vector distribution coefficient, the positive small vectors in two different directions and the original medium vector, the virtual medium vector replaces the original medium vector, the medium vector is reserved to participate in the synthesis of the reference voltage vector, the characteristics of the three-level converter are ensured, and the harmonic wave and distortion of the output voltage are reduced.
Yet another embodiment of the present invention provides a space vector pulse width modulation apparatus based on a virtual space vector, as shown in fig. 10, the apparatus comprising:
a processor 021, a communication interface (Communications Interface) 022, a Memory 023, and a control bus 024.
Processor 021, communication interface 022, memory 023 completes communication with each other through control bus 024.
A communication interface 022 for communicating with the network element.
A processor 021 for executing a program 025, specifically for executing the relevant steps in the method embodiment shown in fig. 1.
The sampling unit 026, and the inversion unit 027, the sampling unit 026 is used for obtaining the data information of the electric current of outside electric wire netting and the data information of voltage, and the inversion unit 027 is used for carrying out the output result of target vector among the space vector pulse width modulation, forms control loop and obtains the output voltage value.
In particular, program 025 may comprise program code comprising computer-operating instructions.
The processor 021 may be a central processing unit CPU or a specific integrated circuit ASIC (Application Specific Integrated Circuit) or one or more integrated circuits configured to implement embodiments of the present invention.
A memory 023 for storing a program 025. Memory 023 may comprise high-speed RAM memory, and may also include non-volatile memory (non-volatile memory), such as at least one disk memory. Program 025 may specifically include:
acquiring a space vector diagram corresponding to the voltage of the three-phase inverter circuit in one switching period; the space vector diagram comprises: six sectors;
calculating a virtual small vector according to the vector sum of the positive small vector and the negative small vector in the space vector diagram;
calculating a virtual middle vector according to the virtual space vector distribution coefficient, the positive small vectors in two different directions in the space vector diagram and the middle vector in the space vector diagram;
for any sector, if the reference voltage vector is in the overmodulation I region and the amplitude of the reference voltage vector is larger than a set value, calculating the acting time of the basic vector based on the overmodulation compensation coefficient; the base vector includes: virtual small vectors, virtual medium vectors and large vectors in the space vector diagram;
for any sector, if the reference voltage vector is in the overmodulation I region and the amplitude of the reference voltage vector is smaller than or equal to a set value, calculating the acting time of the basic vector based on an amplitude-phase hybrid compensation mode;
for any sector, if the reference voltage vector is in the overmodulation II area, calculating the acting time of the basic vector based on the mode of amplitude phase simultaneous compensation;
and in one switching period, performing space vector pulse width modulation according to the action time of the basic vector.
The specific implementation of each module in the program 025 may refer to the corresponding module in the embodiment shown in fig. 9, which is not described herein.
According to the space vector pulse width modulation equipment provided by the embodiment of the invention, the original small vector in the space vector diagram is replaced by the calculated virtual small vector, so that the midpoint potential fluctuation caused by the original small vector is reduced; according to the virtual space vector distribution coefficient, the positive small vectors in two different directions and the original medium vector, the virtual medium vector replaces the original medium vector, the medium vector is reserved to participate in the synthesis of the reference voltage vector, the characteristics of the three-level converter are ensured, and the harmonic wave and distortion of the output voltage are reduced.
In the several embodiments provided in this application, it should be understood that the disclosed apparatus and method may be implemented in other ways. For example, the above-described apparatus embodiments are merely illustrative, and for example, the division of the units is merely a logical function division, and there may be additional divisions when actually implemented, for example, multiple units or components may be combined or integrated into another system, or some features may be omitted or not performed. Alternatively, the connections shown or discussed may be made through some interface, electrical, mechanical, or other form.
In addition, in the apparatus and the system in the embodiments of the present invention, each functional unit may be integrated in one processing unit, or each unit may be physically included separately, or two or more units may be integrated in one unit. And each unit can be realized in a form of hardware or a form of hardware and a form of software functional unit.
All or part of the steps for implementing the above method embodiments may be implemented by hardware associated with program instructions, where the foregoing program may be stored in a computer readable storage medium, and when executed, the program performs steps including the above method embodiments; and the aforementioned storage medium includes: a U-disk, a removable hard disk, a Read Only Memory (ROM), a random access Memory (Random Access Memory, RAM), a magnetic disk, or an optical disk, or other various media capable of storing program codes.
The foregoing is merely illustrative of the present invention, and the present invention is not limited thereto, and any person skilled in the art will readily recognize that variations or substitutions are within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (5)
1. A space vector pulse width modulation method based on virtual space vectors, comprising:
acquiring a space vector diagram corresponding to the voltage of the three-phase inverter circuit in one switching period; the space vector diagram comprises: six sectors;
calculating a virtual small vector according to the vector sum of the positive small vector and the negative small vector in the space vector diagram;
calculating a virtual middle vector according to the virtual space vector distribution coefficient, the positive small vectors in two different directions in the space vector diagram and the middle vector in the space vector diagram;
for any sector, if the reference voltage vector is in the overmodulation I region and the amplitude of the reference voltage vector is larger than a set value, calculating the acting time of the basic vector based on the overmodulation compensation coefficient; the base vector includes: virtual small vectors, virtual medium vectors and large vectors in the space vector diagram;
if the motion track of the reference voltage vector in a certain sector is a nonlinear region, calculating the action time of the basic vector according to the switching period, the action time of the intermediate vector and the rotation angle:
；
wherein,representing the time of action of the virtual vector; />Representing the time of action of the large vector; />Representing the time of action of the virtual small vector; />Representing a switching period; />Indicating the rotation angle;
if the motion track of the reference voltage vector in a certain sector is a linear region, calculating the acting time of the basic vector according to the overmodulation compensation coefficient:
；
wherein,representing the time of action of the virtual vector; />Representing the time of action of the large vector; />Representing the time of action of the virtual small vector;ηrepresenting an overmodulation compensation coefficient; />Representing the time of action of the vector in the virtual before compensation; />Representing the action time of the virtual small vector before compensation; />Representing the time of action of the large vector before compensation;
for any sector, if the reference voltage vector is in the overmodulation I region and the amplitude of the reference voltage vector is smaller than or equal to a set value, calculating the acting time of the basic vector based on an amplitude-phase hybrid compensation mode;
if the motion track of the reference voltage vector in a certain sector is a nonlinear region, calculating the acting time of the basic vector according to the switching period, the acting time of the middle vector and the rotation angle;
if the motion track of the reference voltage vector in a certain sector is a linear region, calculating the acting time of the basic vector according to the overmodulation compensation coefficient;
if the motion trail of the reference voltage vector in a certain sector is a linear compensation area, calculating the acting time of the basic vector by adopting an amplitude-phase hybrid compensation mode:
；
wherein,representing the time of action of the virtual vector; />Representing the time of action of the large vector; />Representing the time of action of the virtual small vector; />Representing a switching period;
for any sector, if the reference voltage vector is in the overmodulation II area, calculating the acting time of the basic vector based on the mode of amplitude phase simultaneous compensation;
and in one switching period, performing space vector pulse width modulation according to the action time of the basic vector.
2. The space vector pulse width modulation method based on the virtual space vector according to claim 1, wherein the calculation formula of the virtual small vector is:
；
wherein,representing a virtual small vector; />Representing a positive small vector; />Representing a negative small vector.
3. The space vector pulse width modulation method based on virtual space vector according to claim 1, wherein the calculation formula of the virtual middle vector is:
；
wherein,representing a virtual mid-vector; />Representing a positive small vector in one direction; />Representing a positive small vector in the other direction;V M representing a middle vector in the space vector diagram; />Representing the virtual space vector allocation coefficients.
4. The space vector pulse width modulation method based on the virtual space vector according to claim 1, wherein the set value is 2/3.
5. A space vector pulse width modulation apparatus based on a virtual space vector, to which the space vector pulse width modulation method according to any one of claims 1 to 4 is applied, comprising:
the space vector diagram acquisition unit is used for acquiring a space vector diagram corresponding to the voltage of the three-phase inverter circuit in one switching period; the space vector diagram comprises: six sectors;
a virtual small vector calculation unit for calculating a virtual small vector from the vector sum of the positive small vector and the negative small vector in the space vector diagram;
the virtual middle vector calculation unit is used for calculating a virtual middle vector according to the virtual space vector distribution coefficient, the positive small vectors in two different directions in the space vector diagram and the middle vector in the space vector diagram;
the first time calculation unit is used for calculating the acting time of the basic vector based on the overmodulation compensation coefficient if the reference voltage vector is in the overmodulation I area and the amplitude of the reference voltage vector is larger than a set value for any sector; the base vector includes: virtual small vectors, virtual medium vectors and large vectors in the space vector diagram;
the second time calculation unit is used for calculating the acting time of the basic vector based on the mode of amplitude-phase hybrid compensation if the reference voltage vector is in the overmodulation I area and the amplitude of the reference voltage vector is smaller than or equal to a set value for any sector;
the third time calculating unit is used for calculating the acting time of the basic vector based on the mode of amplitude phase simultaneous compensation if the reference voltage vector is in the overmodulation II area for any sector;
and the pulse width modulation unit is used for carrying out space vector pulse width modulation according to the action time of the basic vector in one switching period.
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| CN114142754A (en) * | 2021-11-30 | 2022-03-04 | 珠海格力电器股份有限公司 | Three-level inverter, modulation method and device thereof, and storage medium |
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