CN110417275B - Three-level converter synchronous modulation method under even number times carrier ratio of 3 - Google Patents

Three-level converter synchronous modulation method under even number times carrier ratio of 3 Download PDF

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CN110417275B
CN110417275B CN201910658661.6A CN201910658661A CN110417275B CN 110417275 B CN110417275 B CN 110417275B CN 201910658661 A CN201910658661 A CN 201910658661A CN 110417275 B CN110417275 B CN 110417275B
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triangular
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CN110417275A (en
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赵鲁
高瞻
葛琼璇
李耀华
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Institute of Electrical Engineering of CAS
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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
    • H02M1/00—Details of apparatus for conversion
    • H02M1/12—Arrangements for reducing harmonics from ac input or output
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M5/00—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases
    • H02M5/40—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc
    • H02M5/42—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters
    • H02M5/44—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac
    • H02M5/453—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M5/458—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M5/4585—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only having a rectifier with controlled elements
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P27/00—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage
    • H02P27/04—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage
    • H02P27/06—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage using dc to ac converters or inverters
    • H02P27/08—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage using dc to ac converters or inverters with pulse width modulation

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Abstract

Three-level converter with even number times carrier ratio of 3The current device synchronizes the modulation method. Defining a zero sequence component U0＝(1‑(Umin+Umax) /2) by superposition of a three-phase sine wave with a zero-sequence component U0Obtaining a three-phase modulation wave; simultaneously generating two groups of in-phase laminated triangular carriers with the phase difference of 180 degrees, and selecting one of the two groups of triangular carriers which cannot cause phase voltage two-level jump as an actual comparison triangular carrier at a first sampling point after the phase modulation angle is 0 degree, 60 degrees, 120 degrees, 180 degrees, 240 degrees and 300 degrees; and C is defined as a carrier ratio, and synchronous C/2+1 modulation of the three-level converter is realized based on actual comparison of a triangular carrier and a three-phase modulation wave on the premise of ensuring that the carrier ratio C is an even integer multiple of 3. The modulation method can realize synchronous modulation under the even number times of carrier ratio of 3, and has the advantages of simple calculation and easy realization.

Description

Three-level converter synchronous modulation method under even number times carrier ratio of 3
Technical Field
The invention relates to a PWM (pulse-width modulation) method, in particular to a synchronous modulation method based on carrier waves.
Background
A common three-level converter includes a three-level anpc (active Neutral Point clamped) converter, and a main circuit topology thereof is shown in fig. 1. Compared with a two-level converter, the three-level converter has the advantages of high output power, low device voltage stress and the like; compared with a cascaded H-bridge multi-level topology, the cascaded H-bridge multi-level topology has the advantages of simple circuit structure, convenience in back-to-back operation and the like. Based on the advantages, the three-level converter is widely applied to the medium-high voltage variable frequency speed control system.
The medium-high voltage variable frequency speed control system has the characteristic of large carrier ratio variation range in the whole speed control range. In order to fully utilize the switching frequency of a power device, asynchronous modulation is generally adopted when the carrier ratio is relatively high, and the influence caused by asymmetry of positive and negative half cycles of voltage pulse can be ignored; and when the carrier ratio is lower, a plurality of synchronous modulations are adopted according to the change of the carrier ratio, so that the symmetry of the output voltage is improved, and the current harmonic distortion is reduced. SVPWM (space Vector Pulse width modulation) has the advantage of flexible switch sequence design, and is a modulation method widely used in a three-level converter.
The voltage space vector distribution of SVPWM in a three-level converter is shown in fig. 2. The dc side voltage of the three-level converter is defined as 2E, and the corresponding amplitudes and classes of the voltage space vectors are summarized in table 1.
TABLE 1 amplitude and class corresponding to each voltage space vector of SVPWM
Figure GDA0002499607360000011
Aiming at synchronous SVPWM under low carrier ratio, the document 'synchronous SVPWM algorithm of three-level NPC inverter under low carrier ratio' (Puxing [ J ]. Motor and control academy, 2018,22(9):24-32.) indicates that the output voltage satisfies the synchronization and can eliminate fractional harmonics, three-phase symmetry and triple-frequency harmonics, half-wave symmetry and even-number harmonics, so synchronous modulation should ensure that the waveform of the output phase voltage satisfies the synchronization, three-phase symmetry and half-wave symmetry, and the harmonic performance of synchronous SVPWM of different vector sequences is contrastively analyzed.
The synchronous SVPWM can reduce the harmonic content of the output voltage by reasonably designing the vector sequence, and the vector sequence design is flexible. However, in the implementation process of the synchronous SVPWM, the action time of each voltage space vector needs to be calculated at a fixed sampling point, the calculation amount is large, the implementation is complex, and the method is not beneficial to engineering application.
The synchronous SPWM directly realizes synchronous modulation by comparing a modulation wave with an in-phase laminated triangular carrier wave, and compared with synchronous SVPWM, the synchronous SPWM has the advantages of simple calculation and convenient realization. However, the existing synchronous SPWM can only ensure that the phase voltage waveform satisfies synchronization, three-phase symmetry and half-wave symmetry at odd-numbered carrier ratios of 3, and cannot realize synchronous modulation that the phase voltage waveform satisfies synchronization, three-phase symmetry and half-wave symmetry at even-numbered carrier ratios of 3. The above disadvantages make the existing synchronous SPWM have fewer synchronous modulation segments, and the difference between carrier frequencies corresponding to adjacent synchronous modulation segments is large, which limits the use of the synchronous SPWM.
Disclosure of Invention
In order to overcome the defects that the calculation of synchronous SVPWM is complex and the existing synchronous SPWM is not suitable for the carrier ratio of 3 even multiples, the invention provides a carrier-based synchronous modulation method of a three-level converter under the carrier ratio of 3 even multiples. The invention simultaneously generates two groups of in-phase laminated triangular carriers with the phase difference of 180 degrees, and selects one group of triangular carriers to compare with the modulation wave at the first sampling point after the phase angles of the modulation wave are 0 degree, 60 degree, 120 degree, 180 degree, 240 degree and 300 degree, so that the output phase voltage waveform can meet the requirements of synchronization, three-phase symmetry and half-wave symmetry under the even number multiple carrier ratio of 3. The invention widens the synchronous modulation section range applicable to the traditional synchronous SPWM, and has simple calculation and very convenient engineering realization.
Defining a zero sequence component U0＝(1-(Umin+Umax) 2), the invention 3 synchronously modulates the three-level converter under the even number times of carrier ratio by superposing a zero-sequence component U on a three-phase sine wave0Obtaining a three-phase modulation wave; simultaneously generating two groups of in-phase laminated triangular carriers with the phase difference of 180 degrees; selecting one of the two groups of triangular carriers which can not cause phase voltage two-level jump as an actual comparison triangular carrier at a first sampling point after the modulation wave phase angle is 0 degree, 60 degrees, 120 degrees, 180 degrees, 240 degrees and 300 degrees; and C is defined as a carrier ratio, and synchronous C/2+1 modulation of the three-level converter is realized based on actual comparison of a triangular carrier and a three-phase modulation wave on the premise of ensuring that the carrier ratio C is an even integer multiple of 3.
The invention relates to a three-level converter synchronous modulation method under the carrier ratio of even number times of 3, which comprises the following steps:
1. determining three-phase sine wave expressions
The present invention defines a three-phase sine wave as follows:
Figure GDA0002499607360000021
in the formula (1), m represents the amplitude of a sine wave, f1Representing the frequency of the sine wave, t representing the time elapsed after the modulation was initiated, Ua、Ub、UcIs a three-phase sine wave.
2. Calculating the zero sequence component
The invention defines the zero sequence component as follows:
U0＝(1-(Umin+Umax))/2 (2)
in the formula (2), U0Is a zero sequence component, UmaxRepresenting a three-phase sine wave Ua、UbAnd UcThe maximum value of the negative value plus 1 is the constant positive value, UminRepresents Ua、UbAnd UcThe value is the minimum value of the negative value plus 1 when the positive value is unchanged.
Umax、UminThe specific judgment mode of (3) is as follows:
Figure GDA0002499607360000031
to Umax、UminIn the determination mode, Ua' represents an A-phase sine wave UaThe positive value is unchanged, the negative value is added with 1, Ub' represents a B-phase sine wave UbThe positive value is unchanged, the negative value is added with 1, Uc' represents a C-phase sine wave UcThe positive value is unchanged, and the negative value is added with 1.
3. Determining three-phase modulated wave expressions
The invention obtains three-phase modulation waves by three-phase sine wave superposition zero-sequence components, namely:
Figure GDA0002499607360000032
in the formula (4), Uma、UmbAnd UmcFor three-phase modulated waves, Ua、UbAnd UcIs a three-phase sine wave, U0Is a zero sequence component.
4. Generating two groups of in-phase laminated triangular carriers with phase difference of 180 degrees
The invention simultaneously generates two groups of triangular carriers with phase difference of 180 degrees, and each group of triangular carriers is formed by laminating an upper triangular carrier and a lower triangular carrier which have the same amplitude and frequency in the same phase.
Wherein the first set of in-phase stacked triangular carriers is defined as follows:
Figure GDA0002499607360000033
in the formula (5), Vcarr1Upper triangular carrier, V, representing a first set of in-phase stacked triangular carrierscarr2Lower triangular carrier representing a first set of in-phase stacked triangular carriers, fcRepresenting the carrier frequency, tcCorresponding to a time factor, tcThe calculation method is as follows (6):
tc＝t-N/fc(6)
in equation (6), t represents the time elapsed after the modulation is started, and N represents an integer multiple of t to the period of the triangular carrier.
The second set of in-phase stacked triangular carriers is defined as follows:
Figure GDA0002499607360000041
Figure GDA0002499607360000042
in the formula (7), Vcarr3Upper triangular carrier, V, representing a second set of in-phase stacked triangular carrierscarr4Lower triangular carrier representing a second set of in-phase stacked triangular carriers, fcRepresenting the carrier frequency, tcCorresponding to a time factor.
5. Judging the respective corresponding directions of the two groups of triangular carriers
The invention judges the corresponding directions of two groups of in-phase laminated triangular carriers at the positions of 0 degree, 60 degrees, 120 degrees, 180 degrees, 240 degrees and 300 degrees of the phase angle of the modulation wave.
Definition Vcarr_up1Upper triangular carrier, V, representing in-phase stacked triangular carrier in the rising directioncarr_up2Lower triangular carrier, V, representing in-phase stacked triangular carrier in the rising directioncarr_dn1Upper triangular carrier, V, representing in-phase stacked triangular carrier in the down directioncarr_dn2The specific judgment method for the directions of the two groups of in-phase laminated triangular carriers is as follows:
Figure GDA0002499607360000043
in the formula (8), tcCorresponding to the time factor, fcRepresenting the carrier frequency.
6. Determining actual comparison triangular carriers
The invention selects one of two groups of triangular carriers which can not cause two-level jump of phase voltage as an actual comparison triangular carrier at the first sampling point after the modulation wave phase angle is 0 degree, 60 degrees, 120 degrees, 180 degrees, 240 degrees and 300 degrees. The actual selection rule for comparing the triangular carriers is as follows:
1) selecting the same-phase laminated triangular carrier wave in the descending direction as an actual comparison triangular carrier wave at the first sampling point after 0 degree, 120 degrees and 240 degrees of the corresponding modulation wave phase angle;
2) and selecting the in-phase laminated triangular carrier wave in the ascending direction as an actual comparison triangular carrier wave at the first sampling point after 60 degrees, 180 degrees and 300 degrees of the corresponding modulation wave phase angle.
7. Determining a carrier ratio
The carrier ratio C is defined as a carrier ratio, and on the premise of ensuring that the carrier ratio C is an even integer multiple of 3, the invention realizes synchronous C/2+1 modulation of the three-level converter based on actual comparison of a triangular carrier and a three-phase modulation wave, so that the carrier ratio C can satisfy the following formula:
C＝fc/f1＝3I(I＝1,2,3....) (9)
in the formula (9), C represents a carrier ratio, fcRepresenting the carrier frequency, f1Represents the modulated wave frequency, and I represents a positive integer.
8. Obtaining PWM signal by comparing actual comparison triangular carrier wave with three-phase modulation wave
The invention obtains the switching signals of each power device based on the actual comparison of the triangular carrier wave and the three-phase modulation wave, thereby realizing the synchronous C/2+1 modulation of the three-level converter. Defining that four power devices from top to bottom of each phase of the three-level converter are respectively P1, P2, P3 and P4, and the voltage of the direct current side is 2E, the specific comparison rule of actually comparing the triangular carrier wave with the three-phase modulation wave is as follows:
1) when the three-phase modulation wave is simultaneously larger than the upper triangular carrier and the lower triangular carrier of the actual comparison triangular carrier, controlling power devices P1 and P2 of the corresponding phase of the three-level converter to be conducted, and outputting a phase voltage E;
2) when the three-phase modulation wave is smaller than the upper triangular carrier and the lower triangular carrier of the actual comparison triangular carrier at the same time, controlling power devices P3 and P4 of the corresponding phase of the three-level converter to be conducted, and outputting a phase voltage of-E;
3) when the three-phase modulation wave is positioned between the upper triangular carrier and the lower triangular carrier of the actual comparison triangular carrier, the power devices P2 and P3 of the corresponding phases of the three-level converter are controlled to be conducted, and the output phase voltage is 0.
Drawings
FIG. 1 is a three-level ANPC converter topology;
fig. 2 shows a SVPWM space vector distribution diagram corresponding to the three-level converter;
fig. 3a and 3b are graphs of vector sequence variation within one sampling period, wherein: FIG. 3a corresponds to the vector sequence for the first P-type small vector, and FIG. 3b corresponds to the vector sequence for the first N-type small vector;
fig. 4a and 4b are vector sequence diagrams corresponding to the conventional three-level SPWM, wherein: fig. 4a adopts a vector sequence of N-type small vector transmission corresponding to each region, and fig. 4b adopts a vector sequence of P-type small vector transmission corresponding to each region;
FIGS. 5a and 5b are vector sequence diagrams corresponding to the modulation method of the present invention;
in fig. 6a and 6b, 60-degree regions each select a triangular carrier in different directions as an actual comparison carrier, where: fig. 6a does not cause phase voltage two-level hopping corresponding to actual comparison carrier, and fig. 6b causes phase voltage two-level hopping corresponding to actual comparison carrier;
FIG. 7 shows a carrier ratio of 12, and the modulation method of the present invention has a switching state variation in one fundamental period;
FIG. 8 is a flowchart of an embodiment of a three-level converter synchronous modulation method according to the present invention 3 with an even carrier ratio;
fig. 9a and 9b show an a-phase modulation wave, an actual comparison triangular carrier wave and a-phase voltage corresponding to 16 times of synchronization under the action of the modulation method of the present invention under the conditions of the fundamental frequency of 22Hz and the carrier ratio of 30 in the embodiment, wherein: fig. 9a correctly selects actual comparison triangular carriers corresponding to each 60-degree region, and fig. 9b incorrectly selects actual comparison triangular carriers corresponding to each 60-degree region;
FIG. 10 shows three-phase voltages corresponding to 16 times of synchronization in the method of the present invention under the conditions of fundamental frequency of 22Hz and carrier ratio of 30 in the embodiment;
FIG. 11 shows three-phase voltages corresponding to 13 times of synchronization in the method of the present invention under the conditions of fundamental frequency of 26Hz and carrier ratio of 24 in the embodiment;
FIG. 12 shows three-phase voltages corresponding to 10 times of synchronization in the method of the present invention under the conditions of fundamental frequency of 32Hz and carrier ratio of 18 in the embodiment;
FIG. 13 shows three-phase voltages corresponding to 7 times of synchronization in the method of the present invention under the conditions of fundamental frequency of 50Hz and carrier ratio of 12 in the embodiment;
FIG. 14 shows three-phase voltages corresponding to 4 times of synchronization in the method of the present invention under the conditions of the fundamental frequency of 70Hz and the carrier ratio of 6 in the embodiment;
FIG. 15 is a schematic diagram of switching frequencies of carrier ratio sections at variable frequencies in the embodiment;
FIG. 16 is a graph of phase A voltage and three phase current synchronized 16 to 13 times with variable frequency in accordance with the method of the present invention in an embodiment;
FIG. 17 is a graph of phase A voltage and three phase current synchronized for 13 to 10 switches in accordance with the method of the present invention in an embodiment of variable frequency;
FIG. 18 is a graph of phase A voltage and three phase current synchronized 10 to 7 times for switching in accordance with the method of the present invention in an embodiment of variable frequency;
fig. 19 shows the a-phase voltage and three-phase current synchronized 7 to 4 times with variable frequency in accordance with the method of the present invention in the example.
Detailed Description
The invention is further described with reference to the following figures and detailed description.
Defining a zero sequence component U0＝(1-(Umin+Umax) 2), the invention 3 synchronously modulates the three-level converter under the even number times of carrier ratio by superposing a zero-sequence component U on a three-phase sine wave0Obtaining a three-phase modulation wave;simultaneously generating two groups of in-phase laminated triangular carriers with the phase difference of 180 degrees; selecting one of the two groups of triangular carriers which can not cause phase voltage two-level jump as an actual comparison triangular carrier at a first sampling point after the modulation wave phase angle is 0 degree, 60 degrees, 120 degrees, 180 degrees, 240 degrees and 300 degrees; and C is defined as a carrier ratio, and synchronous C/2+1 modulation of the three-level converter is realized based on actual comparison of a triangular carrier and a three-phase modulation wave on the premise of ensuring that the carrier ratio C is an even integer multiple of 3.
The invention relates to a three-level converter synchronous modulation method under 3 even times carrier ratio based on carrier waves, which comprises the following steps:
1. determining three-phase sine wave expressions
The invention realizes the synchronous C/2+1 modulation of the three-level converter based on the actual comparison of the triangular carrier wave and the three-phase modulation wave. To realize modulation, the expression of the three-phase modulated wave is first determined. The three-phase modulation wave is obtained by superposing three-phase sine waves with zero-sequence components, and in order to obtain the three-phase modulation wave, an expression of the three-phase sine waves is determined firstly.
2. Calculating the zero sequence component
The modulation method of the invention obtains the three-phase modulation wave by superimposing the zero-sequence component on the three-phase sine wave, and further calculates the zero-sequence component on the basis of determining the three-phase sine wave expression. Defining a zero sequence component U0＝(1-(Umin+Umax) 2, wherein, Umax、UminRespectively representing a three-phase sine wave Ua、UbAnd UcThe maximum value and the minimum value of the negative value plus 1 are the same as the positive value. The derivation process for the zero sequence component is as follows:
assuming that the reference voltage is located in the area a.5 in fig. 2, the three-phase level state change in one sampling period is shown in fig. 3a and fig. 3b, where fig. 3a corresponds to the vector sequence of the first P-type small vectors and fig. 3b corresponds to the vector sequence of the first N-type small vectors. When the first small vector is a P-type small vector in one sampling period, the vector sequence is POO-PON-PNN-ONN. Defining the sampling period as Ts, and the action time of POO, PON, PNN and ONN in one sampling period as kT1，T2，T3And (1-k) T1Then, the area equivalence principle can be used:
Figure GDA0002499607360000071
in the formula (10), k is a redundant small vector action time factor, Uma、UmbAnd UmcIs a three-phase modulated wave.
If the sampling value of the three-phase modulation wave remains unchanged in one sampling period, it can be further known from fig. 3a that:
Figure GDA0002499607360000072
formula (12) can be obtained by substituting formula (10) and formula (11) for formula (4) and making k 0.5:
Figure GDA0002499607360000073
in formula (12), Ua、UbAnd UcIs a three-phase sine wave. By substituting formula (12) for formula (4), U can be obtained0Is as in formula (13):
Figure GDA0002499607360000074
defining the phase angle of 0 degree to 60 degree sector as region f, 60 degree to 120 degree sector as region a, 120 degree to 180 degree sector as region b, 180 degree to 240 degree sector as region c, 240 degree to 300 degree sector as region d, and 300 degree to 360 degree sector as region e in fig. 2, applying the same principle to obtain the zero sequence component expressions corresponding to the regions 5 and 6 in each 60 degree sector of fig. 2, which are summarized in formula (14):
Figure GDA0002499607360000075
the same principle can be used to obtain the zero sequence component expressions corresponding to the areas 1 and 2 in the remaining 60-degree sector of fig. 2, which are summarized in equation (15).
Figure GDA0002499607360000076
The same principle can be used to obtain the zero sequence component expressions corresponding to the areas 3 and 4 in the remaining 60-degree sector of fig. 2, which are summarized in equation (16).
Figure GDA0002499607360000081
Definition of Umax、UminRespectively representing a three-phase sine wave Ua、UbAnd UcIf the positive value is unchanged and the negative value is added with 1 to obtain the maximum value and the minimum value, the equations (14), (15) and (16) can be reduced to be the following equations:
U0＝(1-(Umin+Umax))/2 (17)
the expression (17) is a uniform zero sequence component expression in each region.
3. Determining three-phase modulated wave expressions
The modulation method of the invention obtains three-phase modulation waves by superimposing zero-sequence components on three-phase sine waves, and obtains the expression of the three-phase modulation waves on the basis of determining the three-phase sine wave expression and the zero-sequence component expression of each region, as shown in formula (18).
Figure GDA0002499607360000082
In formula (18), Uma、UmbAnd UmcFor three-phase modulated waves, Ua、UbAnd UcIs a three-phase sine wave, U0For zero sequence components, m represents the amplitude of the sine wave, f1Representing the frequency of the sine wave, t representing the time elapsed after the modulation was initiated, UmaxRepresenting a three-phase sine wave Ua、UbAnd UcThe maximum value of the negative value plus 1 is the constant positive value, UminRepresents Ua、UbAnd UcThe value is the minimum value of the negative value plus 1 when the positive value is unchanged.
4. Generating two groups of in-phase laminated triangular carriers with phase difference of 180 degrees
The modulation method of the invention realizes the synchronous C/2+1 modulation of the three-level converter based on the actual comparison of the triangular carrier wave and the three-phase modulation wave. On the basis of obtaining the expression of the three-phase modulated wave, the expression of the actual comparison triangular carrier wave needs to be determined.
The conventional three-level synchronous SPWM only uses a three-phase modulation wave to compare with a set of in-phase stacked triangular carriers, that is, the directions of the triangular carriers corresponding to the first sampling point of each 60-degree region in fig. 2 are the same. As can be seen from fig. 3a and 3b, the vector sequence of the P-type small vector initial transmission can be obtained by comparing the three-phase modulated wave with the triangular carrier in the ascending direction, and the vector sequence of the N-type small vector initial transmission can be obtained by comparing the three-phase modulated wave with the triangular carrier in the descending direction, so that under the action of the conventional three-level SPWM, the vector sequences in each 60-degree region all use the same type of small vector initial transmission, for example, all use the N-type small vector initial transmission or all use the P-type small vector initial transmission, and the corresponding vector sequences are respectively shown in fig. 4a and 4 b. Under the action of the vector sequences shown in fig. 4a and 4b, the phase voltage waveforms can only satisfy synchronization, three-phase symmetry and half-wave symmetry at odd carrier ratios of 3.
In order to realize synchronous modulation at even number times of carrier ratio of 3, different types of small vectors should be adopted for each 60-degree region to be transmitted first, and the corresponding vector sequences are shown in fig. 5a and 5 b.
In order to obtain the vector sequences shown in fig. 5a and 5b based on the carrier wave, the modulation method of the present invention needs to use the in-phase laminated triangular carrier waves in different directions in adjacent 60-degree regions as the actual comparison triangular carrier waves. Therefore, two groups of in-phase laminated triangular carriers with the phase difference of 180 degrees are simultaneously generated at the initial moment, and then judgment and selection are carried out in corresponding areas.
5. Determining actual comparison triangular carriers
On the basis of generating two groups of in-phase laminated triangular carriers with phases different by 180 degrees, one group of the two groups of in-phase laminated triangular carriers is selected as an actual comparison triangular carrier. The selection principle is that the used triangular carrier does not cause the two-level jump of the phase voltage, namely the situation that the phase voltage is changed from E to-E does not occur.
Adjacent 60 degree regions use triangular carriers in different directions, which corresponds to two cases. Assuming that the modulation wave frequency is 50Hz, the triangular carrier frequency is 600Hz, and the carrier ratio is 12, the two cases are shown in fig. 6a and 6b, respectively. As shown in fig. 6a, the in-phase stacked triangular carrier wave in the descending direction is selected as the actual comparative triangular carrier wave at 0 degree, 120 degree and 240 degree of the modulation phase angle, and the in-phase stacked triangular carrier wave in the ascending direction is selected as the actual comparative triangular carrier wave at 60 degree, 180 degree and 300 degree of the modulation phase angle, which does not cause the two-level jump of the phase voltage; as shown in fig. 6b, the in-phase stacked triangular carrier wave in the rising direction is selected as the actual comparative triangular carrier wave at 0 degrees, 120 degrees, and 240 degrees of the modulation phase angle, and the in-phase stacked triangular carrier wave in the falling direction is selected as the actual comparative triangular carrier wave at 60 degrees, 180 degrees, and 300 degrees of the modulation phase angle, which causes a two-level jump in the phase voltage.
Definition Vcarr_up1Upper triangular carrier, V, representing in-phase stacked triangular carrier in the rising directioncarr_up2Lower triangular carrier, V, representing in-phase stacked triangular carrier in the rising directioncarr_dn1Upper triangular carrier, V, representing in-phase stacked triangular carrier in the down directioncarr_dn2A lower triangular carrier representing an in-phase stacked triangular carrier in a down direction. Comparing fig. 6a and fig. 6b, a specific selection rule for actually comparing the triangular carriers can be obtained:
1) selecting the same-phase laminated triangular carrier wave in the descending direction as the actual comparison triangular carrier wave, namely V, at the first sampling point after 0 degree, 120 degrees and 240 degrees of the corresponding modulation wave phase anglecarr_dn1And Vcarr_dn2Comparing the triangular carriers for reality;
2) selecting the same-phase laminated triangular carrier wave in the ascending direction as the actual comparison triangular carrier wave, namely V, at the first sampling point after 60 degrees, 180 degrees and 300 degrees of the corresponding modulation wave phase anglecarr_up1And Vcarr_up2The triangular carriers are actually compared.
In order to correctly select the triangular carrier wave in the corresponding direction at the first sampling point after the modulation wave phase angle of 0 degree, 60 degrees, 120 degrees, 180 degrees, 240 degrees and 300 degrees and avoid the phase voltage two-level jump, V needs to be determined at the positions of 0 degree, 60 degrees, 120 degrees, 180 degrees, 240 degrees and 300 degrees of the modulation wave phase anglecarr_up1And Vcarr_up2、Vcarr_dn1And Vcarr_dn2The respective corresponding values. Vcarr_up1And Vcarr_up2、Vcarr_dn1And Vcarr_dn2The determination method of (2) is as follows:
Figure GDA0002499607360000101
in the formula (19), Vcarr1And Vcarr2Representing a first set of in-phase stacked triangular carriers, Vcarr3And Vcarr4Representing a second set of in-phase stacked triangular carriers, fcRepresenting the carrier frequency, tcCorresponding to the time factor, N represents an integer multiple of t to the period of the triangular carrier wave, Vcarr_up1Upper triangular carrier, V, representing in-phase stacked triangular carrier in the rising directioncarr_up2Lower triangular carrier, V, representing in-phase stacked triangular carrier in the rising directioncarr_dn1Upper triangular carrier, V, representing in-phase stacked triangular carrier in the down directioncarr_dn2A lower triangular carrier representing an in-phase stacked triangular carrier in a down direction.
Through the above steps, the actual comparative triangular carrier used by the modulation method of the present invention can be determined.
6. Determining carrier wave ratio and synchronous section corresponding to each carrier wave ratio section
The carrier ratio is defined as C, and the modulation method can enable the three-phase voltage waveform to meet the requirements of synchronization, three-phase symmetry and half-wave symmetry when the C is even times of 3, so that the carrier frequency is divided by the even integer times of the modulation wave frequency of 3, namely the value of the C is 30, 24, 18, 12 and 6. And further analyzing synchronous modulation sections corresponding to different carrier ratio sections on the basis of the clear carrier ratio C.
Taking the carrier ratio C as 12 as an example, the switching frequency under the action of the modulation method of the present invention is analyzed, which is shown in fig. 7. As can be seen from fig. 7, when the carrier ratio C is 12, the switching waveform satisfies half-wave symmetry and the number of switching taps in a half fundamental wave period is 7, and it is synchronous 7-segment modulation in which switching is performed 7 times for each power device.
By analyzing the corresponding synchronous modulation sections with carrier ratios C of 30, 24, 18 and 6, which are respectively synchronous 16, 13, 10 and 4 sections of modulation, the corresponding relationship between the carrier ratios and the synchronous sections can be summarized:
S＝C/2+1 (20)
in equation (20), S represents a synchronization segment, and C represents a carrier ratio. The value C is the carrier frequency divided by the modulated wave frequency, and the corresponding switching frequency under different carrier ratios can be further known:
fswitch＝fc/2+f1(21)
in the formula (21), fswitchFor the switching frequency of each power device, fcRepresenting the carrier frequency, f1Corresponding to the fundamental frequency.
7. The actual comparison of the triangular carrier wave and the three-phase modulation wave is utilized to obtain a PWM signal, and synchronous modulation is realized
On the basis of determining a three-phase modulation wave, an actual comparison triangular carrier wave, a carrier ratio and a corresponding synchronous section, the three-phase modulation wave and the actual comparison triangular carrier wave are compared to obtain PWM signals of each power device, so that synchronous 16, 13, 10, 7 and 4 times of modulation are realized under the carrier ratio of 30, 24, 18, 12 and 6, and synchronous modulation of a three-level converter under the carrier ratio of even number times of 3 is realized on the basis of the carrier.
The implementation flow of the three-level converter synchronous modulation method under the even number times carrier ratio of 3 is shown in fig. 8.
The invention overcomes the defects that the prior synchronous SPWM is not suitable for the carrier ratio of even number times of 3 due to the complex calculation of synchronous SVPWM, simultaneously generates two groups of in-phase laminated triangular carriers with the phase difference of 180 degrees, selects the triangular carrier in the descending direction as the actual comparison triangular carrier at the first sampling point after modulating the phase angle of 0 degree, 120 degrees and 240 degrees, selects the triangular carrier in the ascending direction as the actual comparison triangular carrier at the first sampling point after modulating the phase angle of 60 degrees, 180 degrees and 300 degrees, obtains PWM signals by comparing the actual triangular carrier with the modulating wave, and controls the waveform of the output phase voltage to meet the synchronization, three-phase symmetry and half-wave symmetry under the carrier ratio of even number times of 3. The invention widens the synchronous modulation section range applicable to the traditional synchronous SPWM, has simple calculation and convenient realization and is more beneficial to 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 inverter model is built by means of PSIM software, and the effectiveness of the three-level converter synchronous modulation method based on the carrier wave realizing even number times of carrier wave ratio of 3 is verified by utilizing simulation. The simulation conditions were as follows: the simulation step size is 1us, the direct current side voltage is 200V, the inversion output is 5 omega of resistance which is connected with 10mH of inductance in series, and the modulation ratio is fixed to be 0.8.
The effectiveness of synchronous modulation under even-numbered carrier ratios of different 3 is firstly verified under a fixed fundamental frequency.
Fixed fundamental frequency f122Hz, the carrier ratio is 30, i.e. the carrier frequency is fixed at 660Hz, corresponding to 16 modulations in sync. Fig. 9a and 9b are diagrams of a phase a modulated wave, an actual comparison triangular carrier wave and a phase a voltage corresponding to 16 times of synchronization by the method of the present invention in the embodiment, where: fig. 9a shows that the actual comparison triangular carrier is correctly selected for each 60-degree region, and fig. 9b shows that the actual comparison triangular carrier is incorrectly selected for each 60-degree region. As can be seen from fig. 9a and 9b, the switching states of the power devices are directly controlled according to the comparison result between the modulated wave and the actual comparison triangular carrier, and the principle is simple and convenient to implement. In order to avoid phase voltage two-level jump, the invention needs to select a triangular carrier wave in a descending direction as an actual comparison triangular carrier wave at the first sampling point after modulating the phase angle by 0 degree, 120 degrees and 240 degrees, and select a triangular carrier wave in an ascending direction as an actual comparison triangular carrier wave at the first sampling point after modulating the phase angle by 60 degrees, 180 degrees and 300 degrees. Fig. 10 shows three-phase voltages corresponding to 16 times of synchronization according to the method of the present invention in the embodiment. As can be seen from fig. 10, under the carrier ratio of 30, the three-phase modulation wave is compared with the actual comparative triangular carrier wave, so that the synchronous 16-time modulation can be simply and conveniently realized, and the three-phase voltage waveform of the three-phase modulation wave satisfies the requirements of synchronization, three-phase symmetry and half-wave symmetry.
Fixed fundamental frequency f1At 26Hz, the carrier ratio is 24, i.e. the carrier frequency is fixed at 624Hz, corresponding to 13 modulations in synchronization. Fig. 11 shows three-phase voltages corresponding to 13 times of synchronization according to the method of the present invention in the embodiment. As can be seen from fig. 11, at a carrier ratio of 24, three-phase modulated waves and real waves are usedThe three-phase comparison triangular carrier wave comparison can simply and conveniently realize synchronous 13-time modulation, and the three-phase voltage waveform of the three-phase comparison triangular carrier wave satisfies synchronization, three-phase symmetry and half-wave symmetry.
Fixed fundamental frequency f1At 32Hz, the carrier ratio is 18, i.e. the carrier frequency is fixed at 576Hz, corresponding to 10 modulations in synchronization. Fig. 12 shows three-phase voltages corresponding to 10 times of synchronization according to the method of the present invention in the embodiment. As can be seen from fig. 12, under the carrier ratio 18, the three-phase modulation wave is compared with the actual comparative triangular carrier wave, so that the synchronous 10-time modulation can be simply and conveniently realized, and the three-phase voltage waveform of the three-phase modulation wave satisfies the requirements of synchronization, three-phase symmetry and half-wave symmetry.
Fixed fundamental frequency f1The carrier ratio is 12 at 50Hz, i.e. the carrier frequency is fixed at 600Hz, corresponding to 7 modulations in sync. Fig. 13 shows three-phase voltages corresponding to 7 times of synchronization according to the method of the present invention in the embodiment. As can be seen from fig. 13, in the carrier ratio of 12, the three-phase modulation wave is compared with the actual comparison triangular carrier wave, so that the synchronous 7-time modulation can be simply and conveniently realized, and the three-phase voltage waveform satisfies the requirements of synchronization, three-phase symmetry and half-wave symmetry.
Fixed fundamental frequency f1At 70Hz, the carrier ratio is 6, i.e. the carrier frequency is fixed at 420Hz, corresponding to 4 modulations being synchronized. Fig. 14 shows three-phase voltages corresponding to 4 times of synchronization according to the method of the present invention in the embodiment. As can be seen from fig. 14, under the carrier ratio of 6, the three-phase modulation wave is compared with the actual comparative triangular carrier wave, so that the synchronous 4-time modulation can be simply and conveniently realized, and the three-phase voltage waveform of the three-phase modulation wave satisfies the requirements of synchronization, three-phase symmetry and half-wave symmetry.
As shown in fig. 9a to fig. 14, the results of the embodiment verify the effectiveness of the three-level converter synchronous modulation method based on the carrier wave implementation with even number times carrier wave ratio of 3 under a constant frequency. Under the fixed frequency, the modulation method can realize synchronous modulation under the even number times of carrier ratio of 3, so that the three-phase voltage waveform meets the requirements of synchronization, three-phase symmetry and half-wave symmetry.
In order to verify the effectiveness of synchronous modulation under different carrier ratios of even number times of 3 under the condition of variable frequency, the carrier ratio is designed to be switched to be asynchronous-16-13-10-7-4, and the switching frequency of each carrier ratio section is designed as shown in figure 15 on the premise that the switching frequency does not exceed 420 Hz. The fixed modulation ratio was 0.8, the frequency increased by 6Hz per second, and the simulation results are shown in fig. 16 to 19.
Fig. 16 is a graph of a-phase voltage and three-phase current synchronized 16 to 13 times switching, fig. 17 is a graph of a-phase voltage and three-phase current synchronized 13 to 10 times switching, fig. 18 is a graph of a-phase voltage and three-phase current synchronized 10 to 7 times switching, and fig. 19 is a graph of a-phase voltage and three-phase current synchronized 7 to 4 times switching in accordance with the method of the present invention in an embodiment of variable frequency. The results of the embodiments of fig. 16 to 19 verify the effectiveness of the three-level converter synchronous modulation method based on the carrier wave implementation with even number times carrier wave ratio of 3 under the variable frequency. Under the condition of variable frequency, the modulation method can realize synchronous modulation under the condition of even number times of carrier ratio of 3, so that three-phase voltage waveforms meet the requirements of synchronization, three-phase symmetry and half-wave symmetry, and the current impact is small when each synchronous section is switched.
As shown in fig. 9a to fig. 19, the results of the embodiment verify the effectiveness of the three-level converter synchronous modulation method based on the even number times carrier ratio of 3 realized by the carrier wave. When the carrier ratio is an even integer multiple of 3, no matter the carrier ratio is variable frequency or fixed frequency, the modulation method can utilize the comparison of a three-phase modulation wave and an actual comparison triangular carrier to realize synchronous modulation, so that the three-phase voltage waveform meets the requirements of synchronization, three-phase symmetry and half-wave symmetry. The invention overcomes the defects that the calculation of the synchronous SVPWM is complex and the existing synchronous SPWM is not suitable for the carrier ratio of even number times of 3, has simple calculation and is more convenient for engineering application.

Claims (8)

1. A three-level converter synchronous modulation method under even number carrier ratio of 3 is characterized in that the modulation method defines zero sequence component U0＝(1-(Umin+Umax) /2) by superposition of the zero-sequence component U by a three-phase sine wave0Obtaining a three-phase modulation wave; simultaneously generating two groups of in-phase laminated triangular carriers with the phase difference of 180 degrees; selecting one of the two groups of triangular carriers which can not cause phase voltage two-level jump as an actual comparison triangular carrier at a first sampling point after the modulation wave phase angle is 0 degree, 60 degrees, 120 degrees, 180 degrees, 240 degrees and 300 degrees; c is defined as carrier ratio, and the carrier ratio is ensuredOn the premise that C is an even integer multiple of 3, synchronous C/2+1 modulation of the three-level converter is realized based on actual comparison of a triangular carrier wave and a three-phase modulation wave;
Umaxrepresenting a three-phase sine wave Ua、UbAnd UcThe maximum value of the negative value plus 1 is the constant positive value, UminRepresenting a three-phase sine wave Ua、UbAnd UcThe value is the minimum value of the constant positive time value and the negative time value plus 1;
the actual comparison triangular carrier wave has the specific selection rule that:
1) selecting the same-phase laminated triangular carrier wave in the descending direction as an actual comparison triangular carrier wave at the first sampling point after 0 degree, 120 degrees and 240 degrees of the corresponding modulation wave phase angle;
2) and selecting the in-phase laminated triangular carrier wave in the ascending direction as an actual comparison triangular carrier wave at the first sampling point after 60 degrees, 180 degrees and 300 degrees of the corresponding modulation wave phase angle.
2. The synchronous modulation method of three-level converter with even carrier ratio of 3 as claimed in claim 1, wherein the modulation method obtains three-phase modulation wave by three-phase sine wave superposition with zero-sequence component, that is:
Figure FDA0002499607350000011
in the above formula, Uma、UmbAnd UmcFor three-phase modulated waves, Ua、UbAnd UcIs a three-phase sine wave, U0Is a zero sequence component.
3. The three-level converter synchronous modulation method at even carrier ratio of 3 as claimed in claim 2, wherein said three-phase sine wave is defined as follows:
Figure FDA0002499607350000012
in the above formula, the first and second carbon atoms are,Ua、Uband UcIs a three-phase sine wave, m represents the amplitude of the sine wave, f1Representing the frequency of the sine wave and t representing the time elapsed after the modulation was initiated.
4. The three-level converter synchronous modulation method under the carrier ratio of even number times of 3 as claimed in claim 2, characterized in that said zero sequence component is defined as follows:
U0＝(1-(Umin+Umax))/2
in the above formula, U0Is a zero sequence component, UmaxRepresenting a three-phase sine wave Ua、UbAnd UcThe maximum value of the negative value plus 1 is the constant positive value, UminRepresenting a three-phase sine wave Ua、UbAnd UcThe value is the minimum value of the constant positive time value and the negative time value plus 1; u shapemax、UminThe judgment method is as follows:
Figure FDA0002499607350000021
to Umax、UminIn the determination mode, Ua' represents an A-phase sine wave UaThe positive value is unchanged, the negative value is added with 1, Ub' represents a B-phase sine wave UbThe positive value is unchanged, the negative value is added with 1, Uc' represents a C-phase sine wave UcThe positive value is unchanged, and the negative value is added with 1.
5. The three-level converter synchronous modulation method under even-number-times carrier ratio of claim 1, wherein said two sets of in-phase stacked triangular carriers with phase difference of 180 degrees are each composed of upper and lower triangular carriers with same amplitude and frequency stacked in-phase; wherein the content of the first and second substances,
the first set of in-phase stacked triangular carriers is defined as follows:
Figure FDA0002499607350000022
Figure FDA0002499607350000023
in the above formula, Vcarr1Upper triangular carrier, V, representing a first set of in-phase stacked triangular carrierscarr2Lower triangular carrier representing a first set of in-phase stacked triangular carriers, fcRepresenting the carrier frequency, tcCorresponding to a time factor; time factor tcThe calculation method of (2) is as follows:
tc＝t-N/fc
in the above formula, t represents the time elapsed after the modulation is started, and N represents the integral multiple of t to the period of the triangular carrier;
the second set of in-phase stacked triangular carriers is defined as follows:
Figure FDA0002499607350000024
Figure FDA0002499607350000025
in the above formula, Vcarr3Upper triangular carrier, V, representing a second set of in-phase stacked triangular carrierscarr4Lower triangular carrier representing a second set of in-phase stacked triangular carriers, fcRepresenting the carrier frequency, tcCorresponding to a time factor.
6. The three-level converter synchronous modulation method under carrier ratio of even number times of claim 1, characterized in that the modulation method judges the direction corresponding to each of two groups of in-phase stacked triangular carriers at 0 degree, 60 degree, 120 degree, 180 degree, 240 degree and 300 degree of modulation wave phase angle; definition Vcarr_up1Upper triangular carrier, V, representing in-phase stacked triangular carrier in the rising directioncarr_up2Lower triangular carrier, V, representing in-phase stacked triangular carrier in the rising directioncarr_dn1An upper triangular carrier representing an in-phase stacked triangular carrier in the down direction,Vcarr_dn2the specific judgment method for the directions of the two groups of in-phase laminated triangular carriers is as follows:
Figure FDA0002499607350000031
Figure FDA0002499607350000032
in the above formula, tcCorresponding to the time factor, fcRepresents a carrier frequency; vcarr1Upper triangular carrier, V, representing a first set of in-phase stacked triangular carrierscarr2Lower triangular carrier, V, representing a first set of in-phase stacked triangular carrierscarr3Upper triangular carrier, V, representing a second set of in-phase stacked triangular carrierscarr4A lower triangular carrier representing a second set of in-phase stacked triangular carriers.
7. The three-level converter synchronous modulation method under the condition of even-numbered times of carrier ratio of 3 as claimed in claim 1, characterized in that, on the premise of ensuring that the carrier ratio is an even-numbered times integer of 3, the modulation method realizes the synchronous C/2+1 times modulation of the three-level converter based on the comparison of actual comparison triangular carrier waves and three-phase modulation waves; defining C as a carrier ratio, then:
C＝fc/f1＝3I(I＝1,2,3....)
in the above formula, C represents a carrier ratio, fcRepresenting the carrier frequency, f1Represents the modulated wave frequency, and I represents a positive integer.
8. The three-level converter synchronous modulation method under the condition of even-numbered times of carrier ratio of 3 as claimed in claim 7, characterized in that, on the premise of ensuring that the carrier ratio is an even-numbered times integer of 3, the modulation method realizes the synchronous C/2+1 times modulation of the three-level converter based on the comparison of actual comparison triangular carrier waves and three-phase modulation waves; defining that four power devices from top to bottom of each phase of the three-level converter are respectively P1, P2, P3 and P4, and the voltage of the direct current side is 2E, the specific comparison rule for actually comparing the triangular carrier wave with the three-phase modulation wave is as follows:
1) when the three-phase modulation wave is simultaneously larger than the upper triangular carrier and the lower triangular carrier of the actual comparison triangular carrier, controlling power devices P1 and P2 of the corresponding phase of the three-level converter to be conducted, and outputting a phase voltage E;
2) when the three-phase modulation wave is smaller than the upper triangular carrier and the lower triangular carrier of the actual comparison triangular carrier at the same time, controlling power devices P3 and P4 of the corresponding phase of the three-level converter to be conducted, and outputting a phase voltage of-E;
3) when the three-phase modulation wave is positioned between the upper triangular carrier and the lower triangular carrier of the actual comparison triangular carrier, the power devices P2 and P3 of the corresponding phases of the three-level converter are controlled to be conducted, and the output phase voltage is 0.
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