CN109347349B - Three-level carrier modulation method - Google Patents
Three-level carrier modulation method Download PDFInfo
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- CN109347349B CN109347349B CN201811346498.1A CN201811346498A CN109347349B CN 109347349 B CN109347349 B CN 109347349B CN 201811346498 A CN201811346498 A CN 201811346498A CN 109347349 B CN109347349 B CN 109347349B
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/483—Converters with outputs that each can have more than two voltages levels
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
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Abstract
The invention discloses a three-level carrier modulation method, which comprises two modes: when the amplitude of the modulation wave in a certain switching period is lower than a specific value, a mode 1 modulation mode is adopted, the phase modulation wave is decomposed into a positive modulation wave and a negative modulation wave, the positive modulation wave and the negative modulation wave are compared with a triangular carrier wave, the switching sequences of all power switching tubes of the three-level NPC converter are finally obtained, and the requirement of the minimum pulse width of each power switching tube is guaranteed to be met. When the amplitude of the modulation wave in a certain switching period is larger than a specific value, a mode 2 modulation mode is adopted, the modulation wave is compared with two in-phase laminated carriers, the switching sequences of all power switching tubes of the three-level NPC converter are finally obtained, and the requirement of the minimum pulse width of the power switching tubes is met. The invention solves the problem of the minimum pulse width possibly occurring in three-level carrier modulation, and simultaneously can ensure that the average values of the output phase voltage and the line voltage are not distorted.
Description
Technical Field
The invention belongs to the technical field of frequency converter control, and particularly designs a three-level carrier modulation method for solving the problem of minimum pulse width.
Background
With the rapid development of power electronic technology, the application of a three-level Neutral-point-clamped (NPC) frequency converter in high-capacity and medium-high voltage fields such as alternating current driving, locomotive traction, wind power generation and the like is more and more extensive, and the three-level NPC frequency converter is continuously developed to the low-voltage field.
Power electronic power devices have limitations on minimum on-time and minimum off-time, which require that the pulse width of the pulse width modulated output cannot be infinitely narrow. When the pulse width is less than the minimum switching time required by the power device, the device cannot operate normally. Therefore, excessively narrow pulses must be processed to meet the minimum pulse width requirement. The Pulse width Modulation method commonly used in the current three-level NPC frequency converter mainly includes Space Vector Pulse Width Modulation (SVPWM) SVPWM and carrier Pulse width Modulation. SVPWM modulation generally uses the Nearest three-vector method (N3V), the minimum pulse width problem inevitably occurs in a specific region, and generally uses a method of filtering or expanding pulses smaller than the minimum pulse width to the minimum pulse width, but changes the pulse width of one phase, which inevitably causes distortion of the output line voltage. Some documents propose a carrier Pulse Width Modulation (SPWM) method based on sinusoidal Pulse Width Modulation, in which when a narrow Pulse occurs in a Modulation Pulse of one phase, the narrow Pulse is eliminated or expanded while the other two-phase pulses are compensated accordingly to ensure that the output line voltage remains unchanged. However, this method requires the simultaneous change of three-phase pulses, and in some cases, the compensated pulses of other two phases may have new narrow pulses, which affects the compensation effect.
Disclosure of Invention
The invention aims to solve the defects of the prior art and provides a three-level carrier modulation method for solving the problem of minimum pulse width.
A three-level carrier modulation method comprises two modulation modes:
in a switching period, when the modulation degree is less than VmWhen, or with a degree of modulation greater than VmBut modulating wave V in current carrier periodrxThe amplitude is [ -Vm, Vm]In the middle, the mode 1 modulation mode is adopted to modulate the wave VrxDecomposed into two modulated waves V of positive and negativerx1And Vrx2Same triangular carrier VcAnd finally obtaining the switching sequences of all the power switching tubes.
In a switching period, when the modulation degree is larger than VmAnd modulating the wave V in the current carrier periodrxThe amplitude is [ -1, -Vm]Or [ Vm,1]In the middle, a mode 2 modulation mode is adopted, and a modulated wave and two in-phase laminated carriers V are usedc1And Vc2And comparing to obtain the switching sequences of all the power switching tubes.
When the amplitude of the modulated wave is equal to VmThe mode 1 or the mode 2 can be adopted, and the specific value is determined to be a reasonable range according to the minimum pulse width required by the power switch tube and the switching period of the carrier modulation.
The above-mentioned modulated wave VrxThe amplitude value is in the range of [ -1, 1 ] per unit value](ii) a Triangular carrier VcThe amplitude value is in the range of [ -1, 1 ] per unit value](ii) a x is three phases a, b and c of the converter; vmIs a reasonable value determined according to the minimum pulse width required by the power switch tube used and the switching period of the carrier modulation.
The invention has the beneficial effects that:
(1) the three-level carrier modulation method adopts different modulation modes according to the amplitude of the modulation wave in the switching period, and solves the problem of the possible minimum pulse width.
(2) The three-level carrier modulation method has the advantages that each phase is modulated independently, the minimum pulse width problem is solved, and meanwhile, the average values of the output phase voltage and the line voltage are ensured not to be distorted.
(3) The three-level carrier modulation method is simple and clear, easy to realize and high in reliability according to the carrier pulse width modulation principle, and is suitable for the three-level NPC frequency converter adopting a high-voltage high-capacity power device.
Drawings
Fig. 1 is a typical three-level NPC converter topology.
Fig. 2 is a schematic diagram of mode 1 modulation scheme of the three-level carrier modulation method of the present invention.
FIG. 3a is a diagram of a three-level carrier modulation method according to the present inventionMedium modulation wave VxAnd when the modulation mode is larger than 0, the principle schematic diagram of the mode 2 modulation mode is shown.
FIG. 3b shows a modulation wave V in the three-level carrier modulation method of the present inventionxAnd when the modulation mode is smaller than 0, the principle of the mode 2 modulation mode is shown schematically.
Fig. 4a is a waveform diagram of phase voltage and line voltage obtained by simulation of the present invention when the modulation degree is 0.1 in the three-level carrier modulation method of the present invention.
Fig. 4b is a waveform diagram of phase voltage and line voltage obtained by simulation of the present invention when the modulation degree is 0.4 in the three-level carrier modulation method of the present invention.
Fig. 4c is a waveform diagram of phase voltage and line voltage obtained by simulation of the present invention when the modulation degree is 0.8 in the three-level carrier modulation method of the present invention.
Detailed Description
Embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.
The invention is illustrated with a typical three-level NPC converter topology as shown in fig. 1; in the figure, C1 and C2 are dc capacitors, and Sa1 to Sa4, Sb1 to Sb4, and Sc1 to Sc4 are three-phase power switches of the inverter A, B, C and their anti-parallel diodes, respectively.
The invention relates to a three-level carrier modulation method, which comprises two modulation modes:
mode 1: in a switching period, when the modulation degree is less than VmWhen, or with a degree of modulation greater than VmBut modulating wave V in current carrier periodrxAmplitude less than Vm, i.e. modulated wave VrxAt [ -Vm, Vm]In between, the mode 1 modulation scheme is adopted.
Mode 2: in a switching period, when the modulation degree is larger than VmAnd modulating the wave V in the current carrier periodrxAmplitude greater than VmI.e. modulating waves VrxAt [ -1, -Vm]Or [ Vm,1]In between, the mode 2 modulation scheme is adopted.
When the amplitude of the modulated wave is equal to VmAnd in the process, the switching sequence of the power switching tube obtained by adopting the mode 1 or the mode 2 can meet the requirement of minimum pulse width.
The above-mentioned modulated wave VrxIs a per unit value, amplitudeIn the range of [ -1, 1](ii) a Triangular carrier VcThe amplitude value is in the range of [ -1, 1 ] per unit value](ii) a And x is three phases a, b and c of the converter. VmAnd determining a reasonable range value according to the minimum pulse width required by the power switch tube and the switching period of carrier modulation. Taking sinusoidal modulation as an example, assume that the minimum pulse width of a power switch in a frequency converter is TminCarrier period of TsThen the amplitude of the modulated wave in the modulation degree or the current carrier period is less than Tmin/TsIn time, the mode 2 is adopted to calculate that the turn-on time of the power switch device is less than the minimum pulse width time, so VmMust not be less than Tmin/Ts. The amplitude of the modulation wave in the current carrier wave period is more than 0.5-2Tmin/TsThe turn-off time of the power device calculated by adopting the mode 1 is less than the minimum pulse width time, so VmNot more than 0.5-2Tmin/Ts. In summary, the specific value VmHas a value range of [ Tmin/Ts，0.5-2Tmin/Ts]. For example, for a high voltage high power device IGCT, the minimum pulse width is set to 100uS in a typical application, the carrier frequency is 500Hz, and the period is 2mS, then the range of the specific value Vm is [0.05, 0.4 ]]The specific value can be set to 0.2.
The following describes modulation schemes of mode 1 and mode 2:
A. the mode 1 modulation mode specifically includes:
firstly, modulating wave VrxDecomposed into two modulated waves V of positive and negativerx1And Vrx2The decomposition method is as follows:
subsequently, two modulated waves Vrx1And Vrx2With the same triangular carrier VcAnd comparing to obtain the phase output level signal. The comparison method is as follows:
when V isc＜Vrx2The x-phase output of the three-level converter is positive;
when V isc＞Vrx1Three, 2The x-phase output negative level of the level converter;
when V isrx2＜Vc＜Vrx1And the x-phase of the three-level converter outputs zero level.
And finally, obtaining the switching sequences of all the power switching tubes according to the phase output voltage waveforms.
As shown in fig. 2, the x-phase modulated wave V is generated in one switching cyclexAmplitude of 0.1 and less than 0.2, and phase output level signal U is obtained according to the comparison principle of the modulation wave and the carrier wavexo. At the same time, Vrx2And carrier wave VcComparing to obtain a switching sequence PWM1, V of the No. 1 power switching tuberx1And carrier wave VcComparing to obtain a switching sequence PWM2 of the No. 2 power switching tube; and the switching sequences PWM1 and PWM2 of the No. 1 power switch tube and the No. 2 power switch tube are subjected to logic processing to obtain the switching sequences of the four power switch tubes on the phase.
B. The mode 2 modulation mode specifically includes:
firstly, modulating wave VrxCarrier wave V laminated in phase with twoc1And Vc2And comparing to obtain the phase output level signal, wherein the comparison mode is as follows:
when V isrx＞Vc1The x-phase output of the three-level converter is positive;
when V isrx＜Vc2The x-phase output negative level of the three-level converter;
when V isc2＜Vrx＜Vc1And the x-phase of the three-level converter outputs zero level.
The two in-phase laminated carriers adopt per unit value Vc1Has an amplitude in the range of [0, 1 ]]，Vc2Has an amplitude in the range of [ -1, 0 [)]And, and:
Vc2＝Vc1-1 (2)
and then, obtaining the switching sequence of all the power switching tubes according to the phase output voltage waveform.
Fig. 3a and 3b are schematic diagrams of the mode 2 modulation scheme adopted when the modulation wave amplitude is 0.6 and-0.6, respectively. Obtaining phase output according to the principle of comparing the modulated wave with the carrier waveLevel signals, simultaneously VrxAnd carrier wave Vc1Comparing to obtain the pulse driving signal PWM1, V of No. 1 power switch tuberxAnd carrier wave Vc2And comparing to obtain a pulse driving signal PWM2 of the No. 2 power switch tube, and logically processing the control signals PWM1 and PWM2 to obtain driving signals of four power switch tubes on the phase.
In order to verify the effectiveness of the invention, the simulation is verified by using power electronic simulation software PSIM. Fundamental frequency f in the modelo50Hz, switching frequency fc600Hz, 5000V DC voltage, 10mF C2 DC capacitance C1 of upper and lower groups, and V as the switching specific value of two modulation modesmThe minimum pulse width required for the power switching tube used is 100uS, 0.2. Using a sinusoidal pulse width carrier modulation mode, A-phase modulated wave VxSin (ω t), ω is the angular frequency of the modulated wave, t is the time, and the B, C-phase modulated wave leads and follows the a-phase modulated wave by 120 °, respectively. Fig. 4a, 4b and 4c show waveforms of driving signals of phase-a power tube 1 and phase-2, phase-a voltage and line-AB voltage of three-level NPC frequency converters at modulation degrees of 0.1, 0.4 and 0.8, respectively.
As can be seen from fig. 4a, 4b, and 4c, when the modulation degrees are 0.1, 0.4, and 0.8, respectively, the driving pulse widths of the power transistors are all greater than 100uS, which can meet the requirement of the minimum pulse width.
Claims (3)
1. A three-level carrier modulation method is characterized in that: two modulation modes are included:
in a switching period, when the modulation degree is less than VmWhen, or with a degree of modulation greater than VmBut modulating wave V in current carrier periodrxThe amplitude is [ -Vm, Vm]In the middle, the mode 1 modulation mode is adopted to modulate the wave VrxDecomposed into two modulated waves V of positive and negativerx1And Vrx2Are respectively identical with the same triangular carrier VcComparing to obtain the switching sequences of all the power switching tubes;
in a switching period, when the modulation degree is larger than VmAnd modulating the wave V in the current carrier periodrxThe amplitude is [ -1, -Vm]Or [ Vm,1]In between, mode 2 modulation is usedBy means of a modulated wave and two in-phase laminated carriers Vc1And Vc2Comparing to obtain the switching sequences of all power switching tubes;
when the amplitude of the modulated wave is equal to VmWhen, mode 1 or mode 2 may be employed;
the above-mentioned modulated wave VrxThe amplitude value is in the range of [ -1, 1 ] per unit value](ii) a Triangular carrier VcThe amplitude value is in the range of [ -1, 1 ] per unit value](ii) a x is three phases a, b and c of the converter; vmIs a reasonable value determined according to the minimum pulse width required by the power switch tube used and the switching period of the carrier modulation.
2. A three-level carrier modulation method according to claim 1, characterized in that: the mode 1 modulation mode specifically includes:
firstly, modulating wave VrxDecomposed into two modulated waves V of positive and negativerx1And Vrx2The decomposition method is as follows:
subsequently, two modulated waves Vrx1And Vrx2With the same triangular carrier VcComparing to obtain an output level signal of an x-phase output level signal of the three-level converter; the comparison method is as follows:
when V isc＜Vrx2The x-phase output of the three-level converter is positive;
when V isc＞Vrx1The x-phase output negative level of the three-level converter;
when V isrx2＜Vc＜Vrx1The x-phase of the three-level converter outputs zero level;
and finally, obtaining the switching sequences of all the power switching tubes according to the phase output voltage waveforms.
3. A three-level carrier modulation method according to claim 1, characterized in that: the mode 2 modulation mode specifically includes:
firstly, modulating wave VrxCarrier wave V laminated in phase with twoc1And Vc2And comparing to obtain an output level signal of an x-phase output level signal of the three-level converter, wherein the comparison mode is as follows:
when V isrx＞Vc1The x-phase output of the three-level converter is positive;
when V isrx＜Vc2The x-phase output negative level of the three-level converter;
when V isc2＜Vrx＜Vc1The x-phase of the three-level converter outputs zero level;
the two in-phase laminated carriers adopt per unit value Vc1Has an amplitude in the range of [0, 1 ]]，Vc2Has an amplitude in the range of [ -1, 0 [)]And, and:
Vc2＝Vc1-1 (2)
and then, obtaining the switching sequence of all the power switching tubes according to the phase output voltage waveform.
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