CN109802586B - Three-level converter synchronous 3-times SVPWM carrier implementation method - Google Patents
Three-level converter synchronous 3-times SVPWM carrier implementation method Download PDFInfo
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Abstract
Three-level converter synchronous 3-times SVPWM carrier wave realityThe method is now presented. According to the method, even number of sampling points are distributed at a fixed angle in each 60-degree sector; for non-head-tail sampling points in each 60-degree sector, zero-sequence component U is superposed through three-phase sine waves0Obtaining a monotone wave-modulating expression (1-Vmax-Vmin) as 0.5; selecting corresponding double modulation wave expressions according to the modulation ratio region for the head and tail sampling points in each 60-degree sector; generating falling edge double carriers at first sampling points in sectors with space angles of 330-30 degrees, 90-150 degrees and 210-270 degrees, and generating rising edge double carriers at first sampling points in other sectors to obtain a double carrier expression; and comparing the double carrier waves with the single modulation waves or the double modulation waves to obtain the switching action of each sampling point, thereby realizing the synchronous 3-time SVPWM control of the three-level converter based on the carrier waves. Compared with the traditional synchronous 3-time SVPWM control, the method has the advantages of small calculated amount and convenience for engineering application.
Description
Technical Field
The invention relates to a PWM control method, in particular to a method for realizing 3-time SVPWM carrier synchronization of a three-level converter.
Background
Common three-level converters include npc (neutral Point clamped) three-level converter and anpc (activenpc) three-level converter. Taking an ANPC three-level converter as an example, the main circuit topology is as shown in fig. 1, and the ac side can output three different level states by controlling on/off of each switching device. The ANPC three-level converter is proposed by German scholars T.Bruckner in 2001 for the first time on an IEEE-PESC conference, and is widely applied to the speed regulation occasions of medium-high voltage high-power motors by virtue of the characteristics of high loss balance distribution and fault-tolerant capability.
A space Vector Pulse Width modulation (svpwm) strategy is a modulation method widely used in a three-level converter. SVPWM sees the three-phase system of converter and motor as an organic whole, thereby establishes the intrinsic relation of converter on-off state and voltage space vector. Based on a volt-second equivalent principle, SVPWM controls the switching state of the three-level converter by solving the action time of each switching state, so that the stator flux linkage of the motor approaches to an ideal circular track.
The distribution of the space vectors of the SVPWM voltages in the three-level converter is shown in fig. 2, and the meaning of the space vectors of the voltages is shown in table 1, taking sector 1 of 330 degrees to 30 degrees as an example. The total dc-side voltage of the three-level converter is defined to be 2E, in table 1, the P state corresponds to the ac-side phase voltage of the three-level converter to be 2E, the O state corresponds to the ac-side phase voltage of the three-level converter to be E, and the N state corresponds to the ac-side phase voltage of the three-level converter to be 0.
Table 1330-degree to 30-degree sector SVPWM voltage space vector types
| Big vector | Middle vector | P type small vector | N type small vector | Zero vector |
| PNN | PON、PNO | POO | ONN | OOO、NNN、PPP |
For SVPWM, according to whether the carrier ratio is fixed in each fundamental wave period, the SVPWM can be divided into two categories of asynchronous SVPWM and synchronous SVPWM. The three-level converter has the characteristic of wide frequency output range when being applied to the traction speed regulation occasion of a medium-high voltage high-power motor, and when the fundamental frequency is lower and the carrier ratio is higher, the asynchronous SVPWM can fully utilize the switching frequency to obtain better harmonic performance; as the fundamental frequency increases, the carrier ratio decreases, and the adverse effect of the non-characteristic sub-harmonics generated by the asynchronous SVPWM on the harmonic performance is exacerbated. For a three-level converter under a low carrier ratio, synchronous SVPWM (space vector pulse width modulation) is used for optimizing harmonic performance.
To obtain better harmonic performance at low carrier ratios, synchronous SVPWM should make the output phase voltage waveform satisfy synchronous, Three-phase symmetry (TPS), half-wave symmetry (HWS) and quarter-cycle symmetry (QWS), the document Modified SVPWM algorithm Three L ev VSI With Synchronized and symmetric Waveforms (Beig a R, [ J ] IEEE Transactions on Industrial Electronics,2007,54 (1): 486 494.) states that to achieve any synchronous 3-fold SVPWM, an even number of sampling points need to be distributed in each 60-degree sector, and the output phase voltage waveform satisfies the switching state change rule of synchronous, TPS, HWS, QWS, as follows:
the three-level voltage space vector is divided into 6 sectors of 60 degrees as shown in fig. 2, and each sector of 60 degrees is divided into 6 parts according to the modulation ratio. Even number M sampling points are distributed in each sector, and the sampling points correspond to synchronous 3M/2 times SVPWM. The M sampling points are all arranged in the sector, wherein the sampling points outside the head and the tail act according to a traditional SVPWM seven-segment method, the action modes of the head and the tail sampling points are special, and taking a sector 1 and a sector 2 in fig. 2 as an example, the switching states of the head and the tail sampling points of the two sectors in each modulation ratio area are summarized in a table 2.
TABLE 2 sector 1 and sector 2 start and end sampling points switching states
The number of sampling points in each 60-degree sector is even and the sampling points act according to the switching states, so that the three-level converter synchronous 3-time SVPWM control in any linear modulation ratio region can be realized, and the phase voltage output waveform of the three-level converter meets the requirements of synchronization, TPS, HWS and QWS. However, the method needs to calculate the action time of each voltage space vector at each sampling point when realizing synchronous 3-time SVPWM control, and the calculation steps are complex and the calculation amount is large, so that the method is not beneficial to practical engineering application.
Disclosure of Invention
In order to overcome the defects of the traditional synchronous 3-time multiple SVPWM control method, the invention provides a method for realizing the synchronous 3-time multiple SVPWM carrier wave of a three-level converter. According to the invention, the switching action of the non-head-tail sampling point in each 60-degree sector is obtained by utilizing the comparative equivalence of the double carrier and the single modulating wave, and the switching action of the head-tail sampling point in each 60-degree sector is obtained by utilizing the comparative equivalence of the double carrier and the double modulating wave, so that the SVPWM control is realized for 3 times based on the carrier, and the waveform of the output phase voltage meets the requirements of synchronization, three-phase symmetry (TPS), half-wave symmetry (HWS) and quarter-cycle symmetry (QWS). The invention reduces the calculation amount of synchronous 3 times SVPWM and is easier to realize engineering application.
In order to realize synchronization, the method for realizing 3 times of SVPWM carrier synchronization of the three-level converter distributes even number of sampling points at fixed angles in each 60-degree spatial angle sector; for non-head-tail sampling points in each 60-degree sector, the invention superposes a zero-sequence component U on a three-phase sine wave0Obtaining a monotone wave-modulating expression (1-Vmax-Vmin) as 0.5; for the head and tail sampling points in each 60-degree sector, selecting a corresponding dual-modulation-wave expression according to the modulation ratio region; the method comprises the steps that a falling edge double carrier is generated at the first sampling point in sectors with the spatial angles of 330-30 degrees, 90-150 degrees and 210-270 degrees, and a rising edge double carrier is generated at the first sampling point in the other sectors to obtain a double carrier expression; the invention obtains the switch action corresponding to each sampling point by comparing the double carrier waves with the single modulation waves or the double modulation waves, thereby realizing the same level of the three-level converter based on the carrier wave comparisonAnd 3, performing SVPWM control for times.
The method for realizing the three-level converter synchronous 3-time SVPWM carrier wave comprises the following specific steps:
1. calculating the position of each sampling point in each 60-degree sector
The invention is distributed with even number of sampling points at fixed angle in each 60-degree space angle sector, the number of sampling points in each 60-degree sector is defined as M, and the corresponding fixed angle of each sampling point is β respectively1,β2.....βMThe calculation method of each sampling point position in each 60-degree sector is as follows:
1) defining theta as a space angle corresponding to a middle shaft of each 60-degree sector, and for the sectors from 330 degrees to 30 degrees, the theta is equal to 0 degree; for a 30 degree to 90 degree sector, θ is 60 °; for a 90 degree to 150 degree sector, θ is 120 °; for a sector of 150 degrees to 210 degrees, θ is 180 °; for a sector 210 degrees to 270 degrees, θ is 240 °; for a 270 degree to 0 degree sector, θ is 300 °;
2) each sample point is spaced pi/(3M), and the M/2 th sample point position is first determined βM/2＝θ-π/(6M)；
3) Definitions βm(M1, 2.. M) is the spatial angle corresponding to any sampling point in each 60-degree sector according to βm＝βM/2And pi/(3M) × (M/2-M), and sequentially determining the corresponding spatial angular positions of the rest sampling points.
2. Solving single wave-making expression corresponding to non-head-tail sampling points
For non-head-tail sampling points in each 60-degree space angle sector, the invention obtains a monotone wave modulation expression by superposing the zero-sequence components of the three-phase sine waves. Wherein, the three-phase sine wave is defined as follows:
in the formula (1), Ua,Ub,UcThe sine waves are respectively an A-phase sine wave, a B-phase sine wave and a C-phase sine wave, kv is the amplitude value after the three-phase sine waves are per unit, omega is the angular velocity, and t corresponds to time.
The zero sequence component is defined as follows:
U0＝0.5*(1-Vmax-Vmin)
in the formula (2), U0The three-phase sine wave is zero-sequence component, Vmax and Vmin are respectively the maximum value and the minimum value of three-phase sine wave when the three-phase sine wave is greater than or equal to zero and after 1 is added when the three-phase sine wave is less than zero.
Three-phase sine wave Ua,b,cU after zero sequence component superposition0Obtain a single modulated wave Ura,rb,rcI.e. Ura,rb,rc＝Ua,b,c+U0。
3. Dividing modulation ratio region
For the head and tail sampling points in each 60-degree sector, the invention selects corresponding dual-modulation-wave expressions according to the modulation ratio region. The invention divides the modulation ratio area at the head and tail sampling points in each 60-degree sector as follows:
1) corresponding the head and tail sampling points in each 60-degree sector to a space angle β value (namely β)1,βM) Rotated to the 0 to pi/3 region, corresponding to a spatial angle of β '(i.e., β'1,β′M)；
2) The time calculation factor for defining the modulation ratio region is as follows:
in the formula (3), kv is the amplitude value after the three-phase sine wave is per unit, and ta, tb, and tc are time factors for calculating the modulation ratio region at the head-to-tail sampling point.
3) When ta is more than or equal to 0, tb is less than 0, tc is more than or equal to 0, and the modulation ratio area is defined as a low modulation ratio area; when ta is larger than or equal to 0, tb is larger than or equal to 0, tc is larger than or equal to 0, and the modulation ratio area is defined as a medium modulation ratio area; in the rest cases, the region with the modulation ratio is defined as a region with a high modulation ratio.
4. Solving double modulation wave expressions corresponding to head and tail sampling points in low modulation ratio area
The three-phase double modulation wave is defined as Vxp and Vxn (x is a, b and c), the method for calculating the double modulation wave expression corresponding to the head and tail sampling points in the low modulation ratio region is as follows:
when the sampling points are located in the sector from 330 degrees to 30 degrees, the expressions of the double modulation waves corresponding to the head and tail sampling points in the low modulation ratio region are as follows:
the low-modulation-ratio region dual-modulation-wave expressions of the head and tail sampling points in the sectors of 90 degrees to 150 degrees and 210 degrees to 270 degrees can be obtained by rotating the expression (4) by 120 degrees and 240 degrees respectively, namely:
when the sampling points are located in a sector from 30 degrees to 90 degrees, the corresponding double modulation wave expressions of the head sampling point and the tail sampling point in a low modulation ratio area are as follows:
the dual-modulation wave expressions of the low-modulation-ratio region of the head and tail sampling points in the sectors of 150 degrees to 210 degrees and 270 degrees to 330 degrees can be obtained by respectively rotating the expression (6) by 120 degrees and 240 degrees;
β in formulae (4) to (6)1、βMCorresponding to the spatial angle positions of the head and tail sampling points in each 60-degree sector, Vxp and Vxn (x is a, b, c) correspond to the three-phase double-modulation wave, Z0And Z1Double modulation wave expressions, Z, corresponding to two phases of low modulation ratio region action in sectors of 330 degrees to 30 degrees, 90 degrees to 150 degrees and 210 degrees to 270 degrees2And Z3And the double modulation wave expressions corresponding to two phases of action of the low modulation ratio region in the sector of 30 degrees to 90 degrees, 150 degrees to 210 degrees and 270 degrees to 330 degrees. Z0、Z1And Z2、Z3The definition is as follows:
in the formula (7), Umax, Umin and Umid are maximum values, minimum values and intermediate values in the equal-area single modulation wave corresponding to the double modulation wave, and the calculation method is as follows:
in formula (8), βmCorresponding to a space angle, U, of any sampling point in each 60-degree sectora,Ub,UcThe three-phase sine waves are respectively an A-phase sine wave, a B-phase sine wave and a C-phase sine wave, Vmax and Vmin are respectively a maximum value and a minimum value which are respectively constant when the three-phase sine waves are more than or equal to zero and are less than a zero value plus 1, and Ura2,Urb2,Urc2The two-phase double-modulation waves are equal-area single-modulation waves corresponding to the A-phase, B-phase and C-phase double-modulation waves respectively.
5. Solving double modulation wave expressions corresponding to head and tail sampling points in middle modulation ratio area
The method for calculating the double modulation wave expression corresponding to the head and tail sampling points in the middle modulation ratio region comprises the following steps:
when the sampling points are located in a sector from 330 degrees to 30 degrees, the expression of the double modulation waves corresponding to the head and tail sampling points in the middle modulation ratio area is as follows:
the double modulation wave expressions of the head and tail sampling points in the sectors of 90-150 degrees and 210-270 degrees in the medium modulation ratio region can be obtained by respectively rotating the expressions (9) by 120 degrees and 240 degrees;
when the sampling points are located in a sector from 30 degrees to 90 degrees, the corresponding double modulation wave expressions of the head sampling point and the tail sampling point in the middle modulation ratio region are as follows:
the dual-modulation wave expressions of head and tail sampling points in the sectors of 150 degrees to 210 degrees and 270 degrees to 330 degrees in the medium modulation ratio region can be obtained by respectively rotating the expressions (10) by 120 degrees and 240 degrees;
formula (9)) In the formula (10), Z4And Z5Corresponding to the double-phase double-modulation-wave expression of middle modulation ratio region action two times in sectors of 330 degrees to 30 degrees, 90 degrees to 150 degrees and 210 degrees to 270 degrees, Z6And Z7And the double modulation wave expressions corresponding to two phases of the middle modulation ratio region action in the sectors of 30 degrees to 90 degrees, 150 degrees to 210 degrees and 270 degrees to 330 degrees. Z4、Z5And Z6、Z7The definition is as follows:
in the formula (11), Umax and Umin are the maximum value and the minimum value in the equal-area monotone modulation wave corresponding to the double modulation wave.
6. Solving double modulation wave expressions corresponding to head and tail sampling points in high modulation ratio area
The method for calculating the dual modulation wave expression corresponding to the head and tail sampling points in the high modulation ratio region comprises the following steps:
when the sampling points are located in the sector from 330 degrees to 30 degrees, the expressions of the double modulation waves corresponding to the head and tail sampling points in the high modulation ratio area are as follows:
the dual modulation wave expressions of the head and tail sampling points in the sectors of 90-150 degrees and 210-270 degrees in the high modulation ratio region can be obtained by respectively rotating the expression (12) by 120 degrees and 240 degrees;
when the sampling points are located in a sector from 30 degrees to 90 degrees, the expressions of the double modulation waves corresponding to the head and tail sampling points in the high modulation ratio region are as follows:
the dual-modulation wave expressions in the high-modulation-ratio region of head and tail sampling points in the sectors of 150 degrees to 210 degrees and 270 degrees to 330 degrees can be obtained by respectively rotating the expressions of the expression (13) by 120 degrees and 240 degrees;
in formulae (12) to (13), Z8And Z9Double modulation wave expressions, Z, corresponding to high modulation ratio region action two-time phase in sectors of 330-30 degrees, 90-150 degrees and 210-270 degrees10And Z11And the double modulation wave expressions correspond to two phases of action of a high modulation ratio region in a sector of 30 degrees to 90 degrees, 150 degrees to 210 degrees and 270 degrees to 330 degrees. Z8、Z9And Z10、Z11Defined as follows:
in the equation (14), Umax, Umin, and Umid are the maximum value, minimum value, and intermediate value in the equal-area single modulation wave corresponding to the double modulation wave.
7. Solving dual carrier expressions
The dual-carrier expression is obtained by generating a falling edge dual-carrier at the first sampling point in the sectors with the spatial angles of 330 degrees to 30 degrees, 90 degrees to 150 degrees and 210 degrees to 270 degrees and generating a rising edge dual-carrier at the first sampling point in the other sectors. Defining the carrier frequency as fc, and generating the rising edge double carrier and the falling edge double carrier as follows:
1) definition of tβFor command voltages passing through the odd sample point locations β in each 60 degree sector1,β3.....βM-1Time of day, let tcarr be t-tβThen tcarr is a value that varies from 0 to 1/fc over time;
2) generating falling edge dual-carrier Vcarr1 and Vcarr2 at the first sampling point in sectors with the spatial angles of 330 degrees to 30 degrees, 90 degrees to 150 degrees and 210 degrees to 270 degrees, wherein the expressions are as follows:
3) generating rising edge dual-carrier Vcarr1 and Vcarr2 at the first sampling point in the sectors with the spatial angles of 30 degrees to 90 degrees, 150 degrees to 210 degrees and 270 degrees to 360 degrees, wherein the expressions are as follows:
8. making comparison rule between double carrier waves and single modulated wave
The invention obtains the switching action corresponding to the non-head-tail sampling point in each 60-degree sector by comparing the double carrier waves with the single modulation wave. Defining the total voltage of the DC side of the three-level converter to be 2E, the double carriers to be Vcarr1 and Vcarr2, and the single modulation wave to be UrxThe specific rule for comparing the dual carrier with the single modulation wave is as follows:
when U is turnedrx>Vcarr1, controlling the on-off of each switch element of the corresponding phase to enable the voltage output of the phase at the alternating current side to be 2E; when U is turnedrx<Vcarr2, controlling the on-off of each switch element of the corresponding phase to enable the voltage output of the phase at the alternating current side to be 0; otherwise, the on-off of each switch device of the corresponding phase is controlled to enable the voltage output of the alternating-current side phase to be E.
9. Making a dual-carrier and dual-modulation wave comparison rule
The invention obtains the switching action corresponding to the head and tail sampling points in each 60-degree sector by comparing the double carrier waves with the double modulation waves. Defining dual carrier waves as Vcarr1 and Vcarr2, and dual modulation waves as Vxp and Vxn, wherein the specific rule for comparing the dual carrier waves with the dual modulation waves is as follows:
1) when Vxp is Vxn, when Vxp > Vcarr1, the on-off of each switching element of the corresponding phase is controlled, so that the voltage output of the alternating-current side phase is 2E; when Vxp < Vcarr2, the on-off of each switch device of the corresponding phase is controlled to enable the voltage output of the phase at the alternating current side to be 0; under other conditions, controlling the on-off of each switch device of the corresponding phase to enable the voltage output of the alternating-current side phase to be E;
2) when Vxp! When Vxn > is 0, Vxp > Vcarr1 and Vxn < Vcarr1, controlling the on-off of each switching element of the corresponding phase to enable the phase voltage output of the alternating current side to be 2E, and otherwise, enabling the phase voltage output of the alternating current side to be E; when Vxn is less than 0, when Vxp > Vcarr2 and Vxn < Vcarr2, the on-off of each switching element of the corresponding phase is controlled so that the voltage output of the alternating-current side phase is 0, and the voltage output of the alternating-current side phase is E under the other conditions;
3) when Vxp! When Vxn > is 0, Vxp > Vcarr1 and Vxn < Vcarr1, controlling the on-off of each switching element of the corresponding phase to enable the voltage output of the alternating-current side phase to be E, and enabling the voltage output of the alternating-current side phase to be 2E under the other conditions; when Vxn <0, Vxp > Vcarr2 and Vxn < Vcarr2, the on-off of each switching element of the corresponding phase is controlled, so that the voltage output of the alternating-current side phase is E, and the voltage output of the alternating-current side phase is 0 in the rest cases.
Drawings
FIG. 1 is a topology diagram of a main circuit of a three-level ANPC converter;
FIG. 2 is a three-level SVPWM space voltage vector diagram and sector and region division;
fig. 3 shows a switching sequence corresponding to the sampling points from beginning to end of sector 1;
the three-level SVPWM of fig. 4a, 4b and 4c corresponds to the low modulation ratio, the middle modulation ratio and the high modulation ratio regions, wherein: FIG. 4a corresponds to a low modulation ratio region, FIG. 4b corresponds to a medium modulation ratio region, and FIG. 4c corresponds to a high modulation ratio region;
FIG. 5 is a schematic diagram of dual carrier to dual modulator comparison in a low modulation ratio region for the first sample in sector 1 and sector 2;
fig. 6a, 6b show the action sequence of the first sampling point in the sector 1 and sector 2 in the high modulation ratio region and the corresponding equal-area single-wave-modulation action sequence, in which: FIG. 6a corresponds to sector 1 and FIG. 6b corresponds to sector 2;
FIG. 7a is a schematic diagram of PNN-PNO-POO by comparing an equal-area single-modulation wave with a carrier wave, and FIG. 7b is a schematic diagram of PPN-PON-OON by comparing an equal-area single-modulation wave with a carrier wave;
FIG. 8 is a schematic diagram of dual carrier to dual modulation wave comparison in the middle modulation ratio region for the first sampling points of sector 1 and sector 2;
FIG. 9 is a schematic diagram of dual carrier to dual modulator comparison in high modulation ratio region for the first sample point in sector 1 and sector 2;
FIG. 10 is a flow chart of an embodiment of the present invention;
FIG. 11 is a three-phase voltage corresponding to 9 times of synchronization in the control method of the present invention in the high modulation ratio region at a constant frequency in the embodiment;
FIG. 12 is a FFT analysis result of the phase line A voltage corresponding to 9 times of synchronization in the control method of the present invention in the high modulation ratio region at the constant frequency in the embodiment;
FIG. 13 is a three-phase voltage corresponding to 6 times of synchronization in the control method of the present invention in the high modulation ratio region at a constant frequency in the embodiment;
FIG. 14 is a FFT analysis result of the phase line A voltage corresponding to 6 times of synchronization in the control method of the present invention in the high modulation ratio region at the constant frequency in the embodiment;
FIG. 15 is a three-phase voltage corresponding to 3 times of synchronization in the control method of the present invention in the high modulation ratio region at a constant frequency in the embodiment;
fig. 16a and 16b are FFT analysis results and fundamental line voltage amplitudes of phase a line voltages corresponding to 3 times of synchronization in the control method of the present invention in the high modulation ratio region under the constant frequency in the embodiment, in which: FIG. 16a corresponds to the FFT analysis of the A-phase line voltage, and FIG. 16b corresponds to the fundamental line voltage amplitude;
fig. 17a and 17b are fundamental amplitudes of a phase voltage, a line voltage and a line voltage corresponding to 3 times of synchronization in the control method of the present invention in the middle modulation ratio region at a constant frequency in the embodiment, in which: FIG. 17a corresponds to phase A voltage, line voltage, and FIG. 17b corresponds to line voltage fundamental amplitude;
fig. 18a and 18b are fundamental amplitudes of a phase voltage, a line voltage and a line voltage corresponding to 3 times of synchronization in the control method of the present invention in a low modulation ratio region at a constant frequency in the embodiment, in which: FIG. 18a corresponds to phase A voltage, line voltage, and FIG. 18b corresponds to line voltage fundamental amplitude;
Detailed Description
The invention is further described with reference to the following figures and detailed description.
In order to realize synchronization, the method for realizing 3 times of SVPWM carrier synchronization of the three-level converter distributes even number of sampling points at fixed angles in each 60-degree space angle sector; for non-head-tail sampling points in each 60-degree sector, the invention superposes a zero-sequence component U on a three-phase sine wave0Obtaining a monotone wave-modulating expression (1-Vmax-Vmin) as 0.5; for the head and tail sampling points in each 60-degree sector, selecting a corresponding dual-modulation-wave expression according to the modulation ratio region; the invention is realized by the first sampling point in the sectors of 330 degrees to 30 degrees, 90 degrees to 150 degrees, 210 degrees to 270 degrees of space angleGenerating a falling edge double carrier, and generating a rising edge double carrier at the first sampling point in the other sectors to obtain a double carrier expression; the invention obtains the switching action corresponding to each sampling point by comparing the double carrier with the single modulation wave or the double modulation wave, thereby realizing the synchronous 3 times SVPWM control of the three-level converter based on the carrier comparison.
The method comprises the following steps:
1. calculating the position of each sampling point in each 60-degree sector
According to the method for realizing the synchronous 3-times SVPWM carrier of the three-level converter, even number of sampling points are distributed in each 60-degree sector, and in order to perform sampling, the positions of the sampling points in each 60-degree sector need to be calculated firstly. For convenience of subsequent understanding, the division of each 60-degree sector of the three-level SVPWM is uniformly shown in fig. 2, i.e., a sector with a spatial angle of 330 degrees to 30 degrees is defined as sector 1, a sector with a spatial angle of 30 degrees to 90 degrees is defined as sector 2, a sector with a spatial angle of 90 degrees to 150 degrees is defined as sector 3, a sector with a spatial angle of 150 degrees to 210 degrees is defined as sector 4, a sector with a spatial angle of 210 degrees to 270 degrees is defined as sector 5, and a sector with a spatial angle of 270 degrees to 360 degrees is defined as sector 6.
2. Solving single wave-making expression corresponding to non-head-tail sampling points
Sampling points in each 60-degree sector can be divided into head and tail sampling points and non-head and tail sampling points, and the corresponding switching sequence characteristics of the two sampling points are different. For non-head and tail sampling points in each 60-degree sector, the switching action sequence is consistent with that of the traditional seven-segment SVPWM, the switching action sequence is based on a three-vector method, the action time of two redundant small vectors is the same, the switching state of each phase in each sampling period acts once, and the method can be equivalently realized by using a single wave modulation and double-carrier comparison mode. In order to realize the action sequence of the non-head-tail sampling points based on the carrier wave, firstly, a monotone wave-making expression corresponding to the non-head-tail sampling points is solved.
3. Dividing modulation ratio region
The switching characteristics of the head and tail samples in different 60 degree sectors are analyzed from table 2. For each 60 degree sector area 1,2, it is known from table 2 that the first sampling point of sector 1 corresponds to the action sequence OOO-ONO-OOO-POO, the last sampling point corresponds to the action sequence POO-OOO-OON-OOO, and the head and tail sampling point actions are as shown in fig. 3. In fig. 3, the action sequences corresponding to the head and tail sampling points all use only P-type redundancy small vectors, and in one sampling period, one phase switch does not act, one phase switch acts once, and one phase switch acts twice. The corresponding action sequence of the first sampling point of the sector 2 is OOO-POO-OOO-OON, the corresponding action sequence of the second sampling point is OON-OOO-OPO-OOO, the action sequences corresponding to the head sampling point and the tail sampling point are observed, only N-type redundant small vectors are used, in a sampling period, one phase of switch does not act, one phase of switch acts once, and the other phase of switch acts twice. And then, the fact that only P-type redundant small vectors are used at the head and tail sampling points of the sectors 1, 3 and 5, only N-type redundant small vectors are used at the head and tail sampling points of the sectors 2, 4 and 6 can be deduced, and in one sampling period, one-phase switch does not act, one-phase switch acts once, and one-phase switch acts twice.
The same idea can be analyzed in the areas 3, 4 and 5, 6 of each 60-degree sector, only P-type redundant small vectors are used at the head and tail sampling points of the sectors 1, 3, 5, only N-type redundant small vectors are used at the head and tail sampling points of the sectors 2, 4, 6, and in one sampling period, one-phase switch does not act, one-phase switch acts once, and one-phase switch acts twice.
Because the head and tail sampling points have two phases of no action and action, the corresponding switch action can not be obtained by using the traditional single modulation wave and double carrier wave comparison mode, and the equivalence is realized by using the double modulation wave and double carrier wave comparison. And aiming at the head and tail sampling points of each 60-degree sector, the corresponding double modulation wave expressions are different according to different modulation ratio areas. In order to select the correct dual-modulation-wave expression, the modulation ratio region where the head and tail sampling points are located needs to be determined. The modulation ratio region where the head and tail sampling points are located can be divided into a low modulation ratio region corresponding to fig. 4a, a medium modulation ratio region corresponding to fig. 4b and a high modulation ratio region corresponding to fig. 4c according to the corresponding modulation ratio. The method for dividing each modulation ratio region specifically comprises the following steps:
1) corresponding the head and tail sampling points in each 60-degree sector to a space angle β value (namely β)1,βM) Rotated to the 0 to pi/3 region, corresponding to a spatial angle of β '(i.e., β'1,β′M) β' calculation method such asThe following:
definition Y-int { β/(pi/3) }, int denotes an integer, β' ═ β -Y (pi/3);
2) the time calculation factor for defining the modulation ratio region is as follows:
in the formula (17), kv is the amplitude value after the three-phase sine wave is per unit, and ta, tb, and tc are time factors for calculating the modulation ratio region at the head-to-tail sampling point. the derivation process of ta, tb, tc is as follows:
assuming that the command voltage falls within region 1.4 of FIG. 2, according to the recent three-vector principle, there are:
in the formula (18), | VrefAnd | is the amplitude of the command voltage, and 2E corresponds to the total voltage on the direct current side. Equation (17) can be obtained by solving equation (18).
3) When ta is more than or equal to 0, tb is less than 0, tc is more than or equal to 0, and the modulation ratio area is defined as a low modulation ratio area; when ta is larger than or equal to 0, tb is larger than or equal to 0, tc is larger than or equal to 0, and the modulation ratio area is defined as a medium modulation ratio area; in the rest cases, the region with the modulation ratio is defined as a region with a high modulation ratio.
4. Solving double modulation wave expressions corresponding to head and tail sampling points in low modulation ratio area
The single modulation wave and the double carrier wave are compared to generate a switching action at most once in each sampling period, and the head and tail sampling points have a switching phase with twice actions, and at the moment, the double modulation wave and the double carrier wave are compared to be equivalent.
For the low modulation ratio region, the double modulation waves are Vxp and Vxn, the values of Vxp and Vxn are the same, and Vxp > is Vxn. When Vxp is Vxn, the equivalence is single modulation wave and double carrier wave comparison, and the comparison rule is consistent with the common SVPWM; when Vxp! When Vxn is equal to 0, Vxp and Vxn are compared with the upper triangular carrier Vcarr1, Vxp > Vcarr1 and Vxn < Vcarr1, and P level is output, and O level is output in other cases; when Vxp! When Vxn is equal to Vxn and Vxn <0, Vxp and Vxn are compared with the lower triangular carrier Vcarr2, with Vxp > Vcarr2 and Vxn < Vcarr2, outputting N level, and the rest outputting O level.
The dual carrier to dual modulator ratio for the low modulation ratio region for sector 1 and sector 2 first sample is shown in fig. 5.
The mathematical expressions of modulated wave Vxp and Vxn are derived according to the above comparison principle. Since the types of the corresponding discarded redundant small vectors of sectors 1, 3, and 5 and sectors 2, 4, and 6 are different, they will be discussed separately.
The action sequence corresponding to the first sampling point of the sector 1 is OOO-ONO-OOO-POO, and the sampling period is TsOOO action time of 2T0ONO duration of action of T1POO action time of T2Then, there are:
in formula (19), Ura2,Urb2,Urc2For the single modulated wave under the equal area corresponding to the double modulated wave of the three-phase head and tail sampling points, U is addedra2,Urb2,Urc2Each can be divided into two parts, an up-modulated wave and a down-modulated wave: vap/Van、Vbp/VbnAnd Vcp/VcnAccording to the principle of comparing the dual modulated wave with the dual carrier wave, fig. 5 shows:
in the formula (20), Umax, Umin and Umid are the maximum value, the minimum value and the intermediate value of the monotone modulation wave under the condition that the head-tail sampling point double modulation waves correspond to equal areas, and the values are as follows:
in formula (21), Ura2,Urb2,Urc2The dual-modulation waves of the three-phase head and tail sampling points correspond to the single modulation waves under the equal area respectively.
The dual modulation wave expressions corresponding to the first sampling point of the sector 1 are obtained through the expressions (19) to (21), and the dual modulation wave expressions corresponding to the last sampling point of the sector 1 are the same as the first sampling point according to the same principle.
The action sequence corresponding to the first sampling point of the sector 2 is OOO-POO-OOO-OON, and the sampling period is TsOOO action time of 2T0POO action time of T1OON action time T2Then, there are:
according to the principle of comparing the dual-modulated wave with the dual-carrier wave, fig. 5 shows that:
then the dual modulation wave expression corresponding to the first sampling point of the sector 2 is obtained, and the dual modulation wave expression corresponding to the last sampling point of the sector 2 is the same as the first sampling point according to the same principle.
Following the above reasoning, the same situation for sectors 3, 5 as sector 1 and for sectors 4, 6 as sector 2, we can conclude that when Vxp! When the modulation ratio is Vxn, the low modulation ratio region in the full angle range corresponds to the expression of the double modulation wave, and the expression is as follows:
in the formula (24), Z0And Z1Double-modulation-wave expression, Z, corresponding to two phases of operation in low-modulation-ratio regions in sectors 1, 3, 52And Z3And Umax, Umin and Umid are the maximum value, the minimum value and the intermediate value of the monotone modulation wave under the equal area corresponding to the monotone modulation wave of the start and tail sampling point dimodulation wave.
In order to obtain a uniform double-modulation-wave expression of head and tail sampling points, the requirement is solved under the condition that the head and tail sampling points double-modulation waves correspond to equal areasSingle modulation wave expression Ura2,Urb2,Urc2. On the premise that the area of the modulated wave is not changed, the head and tail sampling points are enabled to act at most once corresponding to the three-phase switch sequence in a sampling period by moving the position of the voltage space vector, and then the monotone wave-modulating expression of the head and tail sampling points under the condition that the double modulated waves correspond to the equal area can be obtained. The calculation principle is as follows:
fig. 6a shows the action sequence of the first sampling point of sector 1 corresponding to the monotone wave-modulating action sequence after the action sequence of the high modulation ratio region and the position of the space vector of the moving voltage. For the single wave-modulating action sequence, the sampling period is set as TsPNN acting on time T in one sampling period1PNO duration of action T2POO action time (1-k) T3ONN time of action kT3Then, there are:
in formula (25), Ura2,Urb2,Urc2The single modulated wave, U, under the equal area is corresponding to the double modulated wave of the three-phase head and tail sampling pointsa、UbAnd UcIs a three-phase sine wave, U1The zero-sequence component corresponding to the monotone wave modulation with equal area of the head and tail sampling points in the sector 1.
A schematic diagram of PNN-PNO-POO obtained by comparing an equal-area monotone modulation wave with a carrier wave is shown in FIG. 7a, and formula (26) can be obtained from FIG. 7 a:
by substituting formula (26) for formula (25), it is possible to obtain:
in equation (27), when k is the N-type redundant small vector operating time and k is 0 in the operation sequence of fig. 6a, there are:
in expression (28), Vmax is the maximum value of the three-phase sine wave when the value is equal to or greater than zero and is smaller than the zero value plus 1. Under the same principle, the single modulation wave expression is U under the condition that the head and tail sampling points of the sector 3 and the sector 5 correspond to each other in equal arearx2＝Ux+1-Vmax。
Fig. 6b is the corresponding equal area single-wave-modulation action sequence of the first sampling point of the sector 2 after the action sequence of the high modulation ratio region and the position of the space vector of the moving voltage. The schematic diagram of PPN-PON-OON obtained by comparing the equal-area single modulation wave with the carrier wave is shown in FIG. 7 b. The same considerations apply to FIG. 6b and FIG. 7b, given equation (29):
in formula (29), U2The vector is a zero sequence component corresponding to the monotone wave modulation with equal area of the head and tail sampling points in the sector 2, and Vmin is the minimum value of a three-phase sine wave after the value is not changed when the value is more than or equal to zero and is less than the value of zero and the value is added by 1. Under the same principle, the single modulation wave expression is U under the condition that the head and tail sampling points of the sector 4 and the sector 6 correspond to each other in equal arearx2＝Ux-Vmin。
In the full angle range, the expression of the single modulation wave under the condition that the head and tail sampling points correspond to the double modulation waves with equal areas is as follows:
5. solving double modulation wave expressions corresponding to head and tail sampling points in middle modulation ratio area
And obtaining a switch sequence corresponding to head and tail sampling points by comparing a double-carrier wave with a double-modulation wave, wherein for a middle modulation ratio region, the double-modulation wave is Vxp and Vxn, the values of Vxp and Vxn are the same, and Vxp > is Vxn. When Vxp is Vxn, the equivalence is single modulation wave and double carrier wave comparison, and the comparison rule is consistent with the common SVPWM; when Vxp! When Vxn is equal to 0, Vxp and Vxn are compared with the upper triangular carrier Vcarr1, Vxp > Vcarr1 and Vxn < Vcarr1, output O level, and otherwise output P level; when Vxp! When Vxn is equal to Vxn and Vxn <0, Vxp and Vxn are compared with the lower triangular carrier Vcarr2, with Vxp > Vcarr2 and Vxn < Vcarr2, outputting O level, and the rest outputting N level.
A comparison of dual carrier and dual modulated wave at the medium modulation ratio region for sector 1 and sector 2 first sample points is shown in fig. 8.
From the above comparison principle, mathematical expressions of modulated wave Vxp and Vxn are derived with the aid of fig. 8. Since the types of the corresponding discarded redundant small vectors of sectors 1, 3, and 5 and sectors 2, 4, and 6 are different, they will be discussed separately. Can be derived when Vxp! When Vxn, the dual modulation wave expression corresponding to the middle modulation ratio region in the full angle range is as follows:
in the formula (31), Umax, Umin and Umid are the maximum value, the minimum value and the intermediate value of the monotone modulation wave under the condition that the head and tail sampling point double modulation waves correspond to the equal area.
6. Solving the expression of the corresponding double modulation waves of the head and tail sampling points in the high modulation ratio area
And obtaining a switch sequence corresponding to head and tail sampling points by comparing a double-carrier wave with a double-modulation wave, and setting the double-modulation wave to be Vxp and Vxn for a high-modulation-ratio area, wherein the Vxp and the Vxn have the same value direction and Vxp > is equal to Vxn. When Vxp is Vxn, the equivalence is single modulation wave and double carrier wave comparison, and the comparison rule is consistent with the common SVPWM; when Vxp! When Vxn is equal to 0, Vxp and Vxn are compared with the upper triangular carrier Vcarr1, Vxp > Vcarr1 and Vxn < Vcarr1, and P level is output, and O level is output in other cases; when Vxp! When Vxn is equal to Vxn and Vxn <0, Vxp and Vxn are compared with the lower triangular carrier Vcarr2, with Vxp > Vcarr2 and Vxn < Vcarr2, outputting N level, and the rest outputting O level.
A comparison of dual carrier and dual modulated wave at the first sampling points of sector 1 and sector 2 in the high modulation ratio region is shown in fig. 9.
From the above comparison principle, mathematical expressions of modulated wave Vxp and Vxn are derived with the aid of fig. 9. Since the types of the corresponding discarded redundant small vectors of sectors 1, 3, and 5 and sectors 2, 4, and 6 are different, they will be discussed separately. Can be derived when Vxp! When Vxn, the dual modulation wave expression corresponding to the middle modulation ratio region in the full angle range is as follows:
in the formula (32), Umax, Umin and Umid are the maximum value, the minimum value and the intermediate value of the monotone modulation wave under the condition that the head sampling point and the tail sampling point double modulation waves correspond to the equal area.
7. Solving dual carrier expressions
The invention utilizes the comparison of double carriers and single modulating waves to equivalently obtain the switching action of the non-head-tail sampling point in each 60-degree sector, and utilizes the comparison of the double carriers and the double modulating waves to equivalently obtain the switching action of the head-tail sampling point in each 60-degree sector, thereby realizing the synchronous 3-time SVPWM control based on the carriers. In the above steps, the single modulation wave or dual modulation wave expressions corresponding to the sampling points are obtained through solving, and the dual carrier expressions corresponding to the sampling points need to be further solved for comparison.
The dual-carrier expression is obtained by generating a falling edge dual-carrier at the first sampling point in the sectors with the spatial angles of 330 degrees to 30 degrees, 90 degrees to 150 degrees and 210 degrees to 270 degrees and generating a rising edge dual-carrier at the first sampling point in the other sectors.
8. Making comparison rule between double carrier waves and single modulated wave
On the basis of obtaining a double-carrier expression and a single-wave-making expression by solving, a double-carrier and single-wave-making comparison rule is formulated for obtaining a switch action sequence corresponding to a non-head-tail sampling point in each 60-degree sector for final equivalence.
9. Making a dual-carrier and dual-modulation wave comparison rule
On the basis of obtaining a double-carrier expression and a double-modulation-wave expression through solving, a double-carrier and double-modulation-wave comparison rule is formulated for obtaining a switch action sequence corresponding to head and tail sampling points in each 60-degree sector through final equivalence.
An implementation flow of the method for realizing the SVPWM carrier wave of the three-level converter for synchronizing 3 times is shown in fig. 10.
According to the invention, the switching action of the non-head-tail sampling point in each 60-degree sector is equivalently obtained by comparing the double carrier waves with the single modulating waves, and the switching action of the head-tail sampling point in each 60-degree sector is equivalently obtained by comparing the double carrier waves with the double modulating waves, so that synchronous 3-time SVPWM control is realized based on the carrier waves, and the waveform of the output phase voltage meets the requirements of synchronization, TPS, HWS and QWS. The invention reduces the calculation amount of synchronous 3 times SVPWM and is easier to realize engineering application.
The following examples are provided to illustrate the effects of the present invention.
According to the embodiment of the invention, a three-level ANPC inverter model is established by means of PSIM software, and the effectiveness of the three-level converter synchronous 3-times SVPWM carrier implementation method provided by the invention is verified by utilizing simulation. In the embodiment, the simulation step length is set to be 1e-6s, the total voltage on the direct current side is 5000V, the 5-ohm resistor on the side of the inversion output side is connected with a 10mH inductor in series, and the fixed fundamental frequency f1 is 50 Hz.
The number of sampling points in each 60-degree sector is set to be 6, 4 and 2 respectively, corresponding to 9/6/3 times of synchronous SVPWM control, and the carrier frequencies are respectively 18 × f1, 12 × f1 and 6 × f 1. The effectiveness of the method for realizing the SVPWM carrier wave of the three-level converter for synchronizing 3 times is verified by observing whether the waveform of the output phase voltage meets the requirements of synchronization, TPS, QWS and HWS under constant frequency.
For a high modulation ratio region, setting the modulation ratio under SVPWM to be 0.92, and corresponding to the amplitude of the fundamental wave of the line voltage 4600V; for the middle modulation ratio region, setting the modulation ratio under SVPWM to be 0.6, and corresponding to the amplitude of line voltage fundamental wave to be 3000V; for the low modulation ratio region, the modulation ratio under SVPWM is set to be 0.2, and the amplitude of the fundamental wave of the line voltage corresponds to 1000V.
Fig. 11 is a three-phase voltage corresponding to 9 times of synchronization in the control method of the present invention in the high modulation ratio region under the constant frequency in the embodiment, and fig. 12 is a result of FFT analysis of a phase voltage corresponding to 9 times of synchronization in the control method of the present invention in the high modulation ratio region under the constant frequency in the embodiment. As can be seen from fig. 11 and 12, when the number of sampling points in each 60-degree sector is 6, the single modulation wave or the double modulation wave is compared with the double carrier, so that the synchronous 9-order SVPWM control can be realized based on the carrier, the output line voltage does not contain even harmonics, multiple harmonics of 3, and fractional harmonics, and the three-phase voltage waveform satisfies synchronization, TPS, QWS, and HWS.
Fig. 13 is a three-phase voltage corresponding to 6 times of synchronization in the control method of the present invention in the high modulation ratio region under the constant frequency in the embodiment, and fig. 14 is an FFT analysis result of an a-phase voltage corresponding to 6 times of synchronization in the control method of the present invention in the high modulation ratio region under the constant frequency in the embodiment. As can be seen from fig. 13 and 14, when the number of sampling points in each 60-degree sector is 4, the single modulation wave or the double modulation wave is compared with the double carrier, and synchronous 6-time SVPWM control can be realized based on the carrier, the output line voltage does not contain even harmonics, multiple harmonics of 3, and fractional harmonics, and the three-phase voltage waveform satisfies synchronization, TPS, QWS, and HWS.
Fig. 15 is three-phase voltages corresponding to 3 times of synchronization in the control method of the present invention in the high modulation ratio region under the constant frequency in the embodiment, and fig. 16a and 16b are FFT analysis results and fundamental line voltage amplitudes of a-phase voltages corresponding to 3 times of synchronization in the control method of the present invention in the high modulation ratio region under the constant frequency in the embodiment. As can be seen from fig. 15, 16a, and 16b, when the number of sampling points in each 60-degree sector is 2, the single modulation wave or the double modulation wave is compared with the double carrier, so that synchronous 3-time SVPWM control can be realized based on the carrier, the output line voltage does not contain even harmonics, 3 multiple harmonics, and fractional harmonics, and the three-phase voltage waveform satisfies synchronization, TPS, QWS, and HWS.
Fig. 17a and 17b are fundamental amplitudes of a-phase voltage, line voltage and line voltage corresponding to 3 times of synchronization in the middle modulation ratio region of the control method of the present invention in the embodiment at a constant frequency, and fig. 18a and 18b are fundamental amplitudes of a-phase voltage, line voltage and line voltage corresponding to 3 times of synchronization in the low modulation ratio region of the control method of the present invention in the embodiment at a constant frequency. As can be seen from fig. 16a, 16b, 17a, 17b, 18a, and 18b, in the high modulation ratio region, the medium modulation ratio region, and the low modulation ratio region, the control method of the present invention controls the amplitude of the fundamental wave of the line voltage to be 4597V, 3098V, and 1038V, respectively, and the amplitude of the fundamental wave of the output line voltage can accurately track the modulation ratio. By calling different double modulation wave expressions in different modulation ratio areas, the control method can realize synchronous 3-time SVPWM control under any linear modulation ratio based on carrier comparison, and three-phase voltage waveforms meet the requirements of synchronization, TPS, QWS and HWS.
As shown in fig. 11 to 18a and 18b, the results of the embodiment verify the effectiveness of the method for implementing SVPWM carrier synchronization by 3 times in the three-level converter of the present invention. When the number of sampling points in each 60-degree sector is even, the SVPWM control method can realize the synchronous 3-times SVPWM control under any linear modulation ratio by calling corresponding double modulation wave expressions in different modulation ratio areas and then comparing single modulation waves or double modulation waves with double carriers. Under the action of the invention, the three-phase voltage waveform meets the requirements of synchronization, TPS, QWS and HWS, the fundamental amplitude of the voltage of the output line can accurately track the modulation ratio, and the line voltage harmonic distribution does not contain even harmonic, 3 times harmonic and fractional harmonic. The invention does not need to calculate the action time of each voltage space vector at each sampling point, reduces the calculation amount of synchronous 3 times of SVPWM, and is easier to realize engineering application.
Claims (5)
1. A three-level converter SVPWM carrier wave implementation method of 3 times of synchronization is characterized in that, in order to implement synchronization, even number of sampling points are distributed at a fixed angle in each 60-degree space angle sector; for non-head-tail sampling points in each 60-degree sector, zero-sequence component U is superposed through three-phase sine waves0Obtaining a monotone wave-modulating expression by 0.5 (1-Vmax-Vmin), wherein Vmax is the maximum value of the three-phase sine wave when the three-phase sine wave is greater than or equal to zero and is less than the value of the zero plus 1, and Vmin is the minimum value of the three-phase sine wave when the three-phase sine wave is greater than or equal to zero and is less than the value of the zero plus 1; selecting corresponding double modulation wave expressions according to the modulation ratio region for the head and tail sampling points in each 60-degree sector; generating falling edge double carriers at first sampling points in sectors with space angles of 330-30 degrees, 90-150 degrees and 210-270 degrees, and generating rising edge double carriers at first sampling points in other sectors to obtain a double carrier expression; the method obtains the switching action corresponding to each sampling point by comparing a double carrier with a single modulation wave or a double modulation wave, thereby realizing the synchronous 3-times SVPWM control of the three-level converter based on the carrier comparison;
the modulation ratio regions at the head and tail sampling points in each 60-degree sector are divided as follows:
1) rotating the corresponding spatial angle value of the head and tail sampling points in each 60-degree sector to a region from 0 to pi/3, wherein the corresponding spatial angle is β';
2) the time calculation factor for defining the modulation ratio region is as follows:
3) when ta is more than or equal to 0, tb is less than 0, tc is more than or equal to 0, and the modulation ratio area is defined as a low modulation ratio area; when ta is larger than or equal to 0, tb is larger than or equal to 0, tc is larger than or equal to 0, and the modulation ratio area is defined as a medium modulation ratio area; otherwise, defining the modulation ratio area as a high modulation ratio area;
the three-phase double-modulation wave is defined as Vxp and Vxn (x is a, b and c), and the double-modulation wave expression calculation method corresponding to the head and tail sampling points in the low modulation ratio region is as follows:
1)if(βm∈(330°～30°)),
the head and tail sampling points in the sectors from 90 degrees to 150 degrees and from 210 degrees to 270 degrees are obtained by respectively rotating the expressions of the double modulation waves in the low modulation ratio region by 120 degrees and 240 degrees, namely:
2)if(βm∈(30°～90°)),
the head and tail sampling points in the sectors of 150 degrees to 210 degrees and 270 degrees to 330 degrees are obtained by respectively rotating the expressions of the double modulation waves in the low modulation ratio region by 120 degrees and 240 degrees;
for definition of the expression of dual modulation wave, β1、βMRespectively corresponding to 60-degree sectorHead-to-tail sampling point positions Vxp and Vxn (x is a, b, c) correspond to three-phase double-modulation wave, Z0And Z1Double modulation wave expressions, Z, corresponding to two phases of low modulation ratio region action in sectors of 330 degrees to 30 degrees, 90 degrees to 150 degrees and 210 degrees to 270 degrees2And Z3Double modulation wave expressions corresponding to two phases of actions in a low modulation ratio area in a sector from 30 degrees to 90 degrees, from 150 degrees to 210 degrees and from 270 degrees to 330 degrees; z0、Z1And Z2、Z3The definition is as follows:
to Z0、Z1And Z2、Z3In definition, Umax、Umin、UmidFor the maximum value, the minimum value and the intermediate value in the equal-area single modulation wave corresponding to the double modulation wave, the calculation method is as follows:
to Umax、Umin、UmidIn definition, βmCorresponding to a space angle, U, of any sampling point in each 60-degree sectora,Ub,UcThe three-phase sine waves are respectively an A-phase sine wave, a B-phase sine wave and a C-phase sine wave, Vmax and Vmin are respectively a maximum value and a minimum value which are respectively constant when the three-phase sine waves are more than or equal to zero and are less than a zero value plus 1, and Ura2,Urb2,Urc2Equal-area single modulation waves corresponding to the A-phase, B-phase and C-phase double modulation waves respectively;
the method for calculating the double modulation wave expression corresponding to the head and tail sampling points in each 60-degree sector in the medium modulation ratio region is as follows:
1)if(βm∈(330°～30°)),
the double modulation wave expressions of the head and tail sampling points in the sectors from 90 degrees to 150 degrees and from 210 degrees to 270 degrees in the medium modulation ratio region are respectively obtained by rotating the expressions by 120 degrees and 240 degrees;
2)if(βm∈(30°～90°)),
the double modulation wave expressions of head and tail sampling points in sectors from 150 degrees to 210 degrees and from 270 degrees to 330 degrees in a medium modulation ratio region are obtained by rotating the expressions by 120 degrees and 240 degrees respectively;
for the definition of the expression of dual modulated waves, Z4And Z5Double modulation wave expressions, Z, corresponding to two phases of middle modulation ratio region action in sectors of 330 degrees to 30 degrees, 90 degrees to 150 degrees and 210 degrees to 270 degrees6And Z7Double modulation wave expressions corresponding to two phases of the middle modulation ratio region action in sectors of 30 degrees to 90 degrees, 150 degrees to 210 degrees and 270 degrees to 330 degrees; z4、Z5And Z6、Z7The definition is as follows:
to Z4、Z5And Z6、Z7In the definition, Umax and Umin are the maximum value and the minimum value in the equal-area single modulation wave corresponding to the double modulation wave;
for the head and tail sampling points in each 60-degree sector, the corresponding dual modulation wave expression calculation method in the high modulation ratio area is as follows:
1)if(βm∈(330°～30°)),
the dual modulation wave expressions of the head and tail sampling points in the sectors from 90 degrees to 150 degrees and from 210 degrees to 270 degrees in the high modulation ratio region are obtained by rotating the expressions by 120 degrees and 240 degrees respectively;
2)if(βm∈(30°～90°)),
the dual modulation wave expressions of head and tail sampling points in sectors from 150 degrees to 210 degrees and from 270 degrees to 330 degrees in the high modulation ratio region are obtained by rotating the expressions by 120 degrees and 240 degrees respectively;
for the definition of the expression of dual modulated waves, Z8And Z9Double modulation wave expressions, Z, corresponding to high modulation ratio region action two-time phase in sectors of 330-30 degrees, 90-150 degrees and 210-270 degrees10And Z11Double modulation wave expressions corresponding to two phases of high modulation ratio region action in sectors of 30 degrees to 90 degrees, 150 degrees to 210 degrees and 270 degrees to 330 degrees; z8、Z9And Z10、Z11Defined as follows:
to Z8、Z9And Z10、Z11In definition, Umax、Umin、UmidThe maximum value, the minimum value and the intermediate value in the equal-area single modulation wave corresponding to the double modulation wave.
2. The method for realizing the SVPWM carrier waves of the three-level converter with the 3-times synchronization according to claim 1, wherein the number of sampling points in each 60-degree sector is defined as M, and the corresponding fixed angles of the sampling points are β respectively1,β2…..βMThe specific position calculation method of each sampling point in each 60-degree sector is as follows:
1) defining theta as a space angle corresponding to a middle shaft of each 60-degree sector, and for the sectors from 330 degrees to 30 degrees, the theta is equal to 0 degree; for a 30 degree to 90 degree sector, θ is 60 °; for a 90 degree to 150 degree sector, θ is 120 °; for a sector of 150 degrees to 210 degrees, θ is 180 °; for a sector 210 degrees to 270 degrees, θ is 240 °; for a 270 degree to 0 degree sector, θ is 300 °;
2) each sample point is spaced pi/(3M), and the M/2 th sample point position is first determined βM/2＝θ-π/(6M)；
3) Definitions βm(M-1, 2 ….. M) is any in each 60 degree sectorSpatial angle corresponding to the ideal sampling point according to βm＝βM/2And pi/(3M) × (M/2-M), and sequentially determining the corresponding spatial angular positions of the rest sampling points.
3. The method for realizing 3 times of SVPWM carrier synchronization of a three-level converter according to claim 1, wherein said three-phase sine wave is defined as follows:
for three-phase sine wave definition, Ua,Ub,UcThe sine waves are respectively an A-phase sine wave, a B-phase sine wave and a C-phase sine wave, kv is the amplitude value after the three-phase sine waves are per unit, omega is the angular velocity, and t corresponds to time;
the zero sequence component is defined as follows:
U0＝0.5*(1-Vmax-Vmin)
in the definition of zero-order components, U0Is a zero sequence component, Ua,Ub,UcThe three-phase sine waves are respectively an A-phase sine wave, a B-phase sine wave and a C-phase sine wave, Vmax and Vmin are respectively a maximum value and a minimum value after the three-phase sine waves are larger than or equal to zero and 1 is added when the three-phase sine waves are smaller than the zero;
three-phase sine wave Ua,b,cU after zero sequence component superposition0Obtain a single modulated wave Ura,rb,rcI.e. Uta,rb,rc＝Ua,b,c+U0。
4. The method for realizing the SVPWM carrier wave of the three-level converter with the 3 times synchronization according to claim 1, wherein the carrier frequency is defined as fc, and the generating method of the rising edge dual carrier wave and the falling edge dual carrier wave is as follows:
1) definition of tβFor command voltages passing through the odd sample point locations β in each 60 degree sector1,β3…..βM-1Time of day, let tcarr be t-tβThen tcarr is a value that varies from 0 to 1/fc over time;
2) generating falling edge dual-carrier Vcarr1 and Vcarr2 at the first sampling point in sectors with the spatial angles of 330 degrees to 30 degrees, 90 degrees to 150 degrees and 210 degrees to 270 degrees, wherein the expressions are as follows:
3) generating rising edge dual-carrier Vcarr1 and Vcarr2 at the first sampling point in the sectors with the spatial angles of 30 degrees to 90 degrees, 150 degrees to 210 degrees and 270 degrees to 360 degrees, wherein the expressions are as follows:
5. the method for realizing the SVPWM carrier waves of the three-level converter with the synchronization times of 3 times according to claim 1, wherein the method obtains the switching actions corresponding to each sampling point by comparing the dual carrier waves with the monotone modulation waves or the dual modulation waves, and the rule of comparing the dual carrier waves with the monotone modulation waves or the dual modulation waves is as follows:
for dual carriers Vcarr1, Vcarr2 and single modulation wave UrxComparison, when U isrx>Vcarr1, controlling the on-off of each switch element of the corresponding phase to enable the voltage output of the phase at the alternating current side to be 2E; when U is turnedrx<Vcarr2, controlling the on-off of each switch element of the corresponding phase to enable the voltage output of the phase at the alternating current side to be 0; under other conditions, controlling the on-off of each switch device of the corresponding phase to enable the voltage output of the alternating-current side phase to be E;
for the dual carrier Vcarr1, Vcarr2 and dual modulated waves Vxp and Vxn comparisons, there are:
1) when Vxp is Vxn, when Vxp > Vcarr1, the on-off of each switching element of the corresponding phase is controlled, so that the voltage output of the alternating-current side phase is 2E; when Vxp < Vcarr2, the on-off of each switch device of the corresponding phase is controlled to enable the voltage output of the phase at the alternating current side to be 0; under other conditions, controlling the on-off of each switch device of the corresponding phase to enable the voltage output of the alternating-current side phase to be E;
2) when Vxp! When Vxn > is 0, Vxp > Vcarr1 and Vxn < Vcarr1, controlling the on-off of each switching element of the corresponding phase to enable the phase voltage output of the alternating current side to be 2E, and otherwise, enabling the phase voltage output of the alternating current side to be E; when Vxn is less than 0, when Vxp > Vcarr2 and Vxn < Vcarr2, the on-off of each switching element of the corresponding phase is controlled so that the voltage output of the alternating-current side phase is 0, and the voltage output of the alternating-current side phase is E under the other conditions;
3) when Vxp! When Vxn > is 0, Vxp > Vcarr1 and Vxn < Vcarr1, controlling the on-off of each switching element of the corresponding phase to enable the voltage output of the alternating-current side phase to be E, and enabling the voltage output of the alternating-current side phase to be 2E under the other conditions; when Vxn is less than 0, when Vxp > Vcarr2 and Vxn < Vcarr2, the on-off of each switching element of the corresponding phase is controlled so that the voltage output of the alternating-current side phase is E, and the voltage output of the alternating-current side phase is 0 under the other conditions;
in the above comparison rule, 2E corresponds to the total dc-side voltage of the three-level converter.
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