CN112217409A - Variable carrier pulse width modulation system and method of three-phase four-bridge arm voltage type inverter - Google Patents
Variable carrier pulse width modulation system and method of three-phase four-bridge arm voltage type inverter Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
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- H02M1/00—Details of apparatus for conversion
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- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
- H02M7/5387—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 in a bridge configuration
- H02M7/53871—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 in a bridge configuration with automatic control of output voltage or current
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- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
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Abstract
The invention provides a variable carrier pulse width modulation method of a three-phase four-bridge arm voltage type inverter, which comprises the following steps of: acquiring a three-phase output sinusoidal current expected value of the inverter, and sampling a three-phase output current instantaneous value of the inverter in real time; subtracting the actual instantaneous current value from the three-phase current expected value of the inverter in each control sampling period to obtain a three-phase current deviation value; calculating the three-phase current control quantity; selecting a three-phase carrier signal required by pulse width modulation according to the three-phase current control quantity; and comparing each phase modulation signal with the corresponding each phase carrier signal to obtain a three-phase switch driving signal with variable pulse width, and using the three-phase switch driving signal to control the on-off operation of a three-phase bridge arm of the inverter circuit. The input end of the N-phase bridge arm controller is connected with the driving signals of the three-phase bridge arm, and the driving signals of the N-phase bridge arm are generated according to the driving signals of the three-phase bridge arm. The invention effectively reduces the electromagnetic interference to the earth leakage current and the like caused by the common mode disturbance voltage of the neutral point.
Description
Technical Field
The invention belongs to the technical field of inverter pulse width modulation, and particularly relates to a variable carrier pulse width modulation system and method of a three-phase four-leg voltage type inverter.
Background
The energy problem is always an important factor for restricting the development of the human society, and every major progress of the society cannot leave the improvement and the replacement of energy. Energy conservation and environmental protection are important options for human sustainable development and prevention of catastrophic climate change. The use of electric power energy in the world today accounts for approximately 40% of total energy.
On the electricity utilization side, the motor (especially a three-phase motor) is a high-energy-consumption power device with large application amount and wide application range. For example, according to statistics, the electricity consumption of the motor in China approximately accounts for 60% -70% of the total amount of industrial electricity consumption. At present, about 90% of electric machines in all countries of the world use asynchronous motors, wherein the small-sized asynchronous motors account for more than 70%. In the total load of the power system, the power consumption of the asynchronous motor accounts for a large proportion. In China, the electricity consumption of the asynchronous motor accounts for more than 60% of the total load. However, a large number of industrial devices such as fans and pumps, traditional industrial sewing machines and machining devices, etc. are operated by adopting a constant-speed transmission scheme of an asynchronous motor, so that the efficiency of the alternating-current motor is generally low. In addition, in industrial sewing machines and machining equipment, a clutch and a friction plate are often adopted to adjust the speed, so that a large amount of standby loss and braking energy consumption are caused. If the variable frequency speed regulation device based on the power electronic inverter is adopted to drive motor equipment, industrial users can save more than 18 percent of electric energy on the existing basis. Therefore, the energy conservation is realized by actively encouraging industrial enterprises to promote advanced means such as frequency conversion and speed regulation in multiple countries and China in the world, and meanwhile, the working performance of the electric transmission equipment can be obviously improved. In addition, mobile devices such as electric vehicles are also charged and discharged by connecting to a power grid through an inverter interface.
On the power generation side, clean renewable energy sources (including wind energy, solar energy, hydrogen energy and the like) are adopted for power generation, and the method is an important means for ensuring energy safety, reducing carbon emission and avoiding global warming in all countries in the world. In the last decade, the energy structure of China is continuously improved and optimized, and the proportion of the development and utilization of clean energy (including wind energy, solar energy, hydrogen energy and the like) is rapidly increased. The power electronic inverter is an indispensable power interface for clean energy power generation regardless of grid-connected power generation or off-grid power generation, and is a key device for fully and high-quality development and utilization of clean energy.
In medium and high power application occasions, a three-phase voltage type inverter is a core component for carrying out motor speed regulation, utilizing clean energy to supply power and the like, and the modulation and control scheme of the three-phase voltage type inverter has decisive influence on the running performance, reliability and safety of a motor speed regulation system and a clean energy power generation system. As a three-phase voltage type inverter, the three-phase four-leg voltage type inverter can flexibly provide a three-phase four-wire system, three-phase three-wire power and even a single-phase interface for a system, can improve the power supply quality and reliability of the inverter under the conditions of three-phase imbalance and the like by utilizing an auxiliary leg, and is widely applied to charging and discharging of electric automobiles, new energy grid-connected power generation and motor driving. The current three-phase four-leg voltage-type inverter usually adopts a pulse width modulation technology to realize accurate control of output voltage or current, and a pulse width modulator of the three-phase four-leg voltage-type inverter generally adopts a fixed carrier signal. However, when an inverter adopting a single carrier pulse width modulation scheme (such as sinusoidal pulse width modulation, space voltage vector modulation, discontinuous pulse width modulation, etc.) is used for driving a star-connected three-phase load (especially a three-phase balanced asynchronous motor) or a transformer, the amplitude of common mode disturbance voltage of a star-connected neutral point is as high as half of the dc bus voltage of the inverter, and serious problems of electromagnetic interference, such as a neutral point to earth leakage current, and reduction of insulation performance are caused.
Disclosure of Invention
The invention aims to solve the defects of the background technology, and provides a variable carrier pulse width modulation system and method of a three-phase four-leg voltage type inverter, which can effectively reduce the problems of electromagnetic interference on earth leakage current and the like caused by neutral point common mode disturbance voltage, insulation reduction and the like.
The technical scheme adopted by the invention is as follows: a variable carrier pulse width modulation method of a three-phase four-bridge arm voltage type inverter is characterized by comprising the following steps:
A. acquiring a three-phase output sinusoidal current expected value of the inverter, and sampling a three-phase output current instantaneous value of the inverter in real time;
B. subtracting the actual instantaneous current value from the three-phase current expected value of the inverter in each control sampling period to obtain a three-phase current deviation value;
C. calculating three-phase current control quantity according to the three-phase current deviation value to serve as a three-phase modulation signal;
D. selecting a three-phase carrier signal required by pulse width modulation according to the three-phase current control quantity;
E. and comparing each phase modulation signal with each corresponding phase carrier signal to generate a three-phase switch driving signal with variable pulse width, and using the three-phase switch driving signal to control the on-off operation of a three-phase bridge arm of the inverter circuit.
In the above technical solution, the three-phase carrier signal in the step D is formed by combining two paths of carrier signal sources; the two carrier signal sources consist of a bipolar triangular or sawtooth carrier 1 and a carrier 2 which have the same frequency and 180-degree phase difference.
In the above technical solution, the step D specifically includes the following steps: and then, the three-phase carrier waves are obtained by changing and selecting from the carrier wave selection table 1 or the carrier wave selection table 2 through table look-up according to the grouping type of the control quantity.
In the above technical solution, in the step a, the expected value of each phase output current of the inverter is:
wherein,
effective values for the desired values of the three-phase output current from inverter A, B, C,
phase angles that are respectively A, B, C three-phase output current expected values; ω is the angular frequency of the output current.
In the above technical solution, in the step a, instantaneous values of three-phase desired output currents of the inverter A, B, C are respectively:
wherein, Ia,Ib,IcEffective values of the three-phase output current transients of inverter A, B, C,
respectively, A, B, C phase angles of the three-phase output current transients.
In the above technical solution, in the step E, the three-phase modulation signal and the corresponding three-phase carrier signal are subtracted to obtain a three-phase difference signal; the three-phase difference signal is compared with zero, so that a three-phase square wave signal with variable pulse width is generated to control the on-off of a three-phase bridge arm of the inverter circuit; when any phase difference signal is greater than or equal to zero, the generated switch driving signal S & ltx + & gt is 1, and the upper bridge arm of the corresponding phase bridge arm is switched on and the lower bridge arm is switched off; on the contrary, when any phase difference value signal is less than zero, the generated switch driving signal S + is 0, the upper bridge arm of the corresponding phase bridge arm is disconnected, and the lower bridge arm is switched on; and SA + refers to a switch driving signal of the bridge arm of the phase A, SB + refers to a switch driving signal of the bridge arm of the phase B, and SC + refers to a switch driving signal of the bridge arm of the phase C.
In the technical scheme, when the inverter runs in three-phase four-wire mode, the N-phase bridge arm switch controller checks an N-phase bridge arm switch control table in real time according to the state of the three-phase switch driving signal to generate a switch driving signal of an N-phase bridge arm; when the inverter operates in three-phase and three-wire mode, all switches of the N bridge arms are set to be turned off, and the inverter is directly connected to a three-phase and three-wire load or a transformer to normally operate.
In the above technical solution, the judgment logic of the carrier selection table 1 is as follows:
when v isa>vb≥vcWhen the carrier wave is a carrier wave 1, the carrier wave of the phase A is a carrier wave 2, and the carrier wave of the phase C is a carrier wave 1;
when v isc≥vb>vaWhen the carrier wave is a carrier wave 2, the carrier wave 1 is a carrier wave of the phase A, and the carrier wave 2 is a carrier wave of the phase C;
when v isb≥va>vcWhen the carrier wave is a carrier wave 1, the carrier wave 2 is a carrier wave 2, and the carrier wave 2 is a carrier wave 2;
when v isc>va≥vbWhen the carrier wave is a carrier wave 2, the carrier wave 1 is selected as the carrier wave of the phase A, and the carrier wave 1 is selected as the carrier wave of the phase C;
when v isb>vc≥vaWhen the carrier wave is a carrier wave 1, the carrier wave 1 is selected as the A-phase carrier wave, and the carrier wave 2 is selected as the C-phase carrier wave;
when v isa≥vc>vbWhen the carrier wave is a carrier wave 2, the carrier wave 2 is a carrier wave 2, and the carrier wave 1 is a carrier wave 1;
the judgment logic of the carrier selection table 2 is as follows:
when v isa>vb≥vcWhen the carrier wave is a carrier wave 2, the carrier wave 1 is a carrier wave of the phase A, and the carrier wave 2 is a carrier wave of the phase C;
when v isc≥vb>vaWhen the carrier wave is a carrier wave 1, the carrier wave of the phase A is a carrier wave 2, and the carrier wave of the phase C is a carrier wave 1;
when v isb≥va>vcWhen the carrier wave is a carrier wave 2, the carrier wave 1 is selected as the carrier wave of the phase A, and the carrier wave 1 is selected as the carrier wave of the phase C;
when v isc>va≥vbWhen the carrier wave is a carrier wave 1, the carrier wave 2 is a carrier wave 2, and the carrier wave 2 is a carrier wave 2;
when v isb>vc≥vaWhen the carrier wave is a carrier wave 2, the carrier wave 2 is a carrier wave 2, and the carrier wave 1 is a carrier wave 1;
when v isa≥vc>vbWhen the carrier wave is a carrier wave 1, the carrier wave 1 is selected as the A-phase carrier wave, and the carrier wave 2 is selected as the C-phase carrier wave;
wherein v isaMeans phase A current control quantity, vbMeans phase A current control quantity, vcRefers to the C-phase current control amount.
In the above technical solution, the logic for judging the N-phase bridge arm switch control table is as follows: wherein, SN + refers to a switch driving signal of the N-phase bridge arm;
when SA + (0), SB + (0) and SC + (0), SN + (1), the upper bridge arm of the N-phase bridge arm is switched on and the lower bridge arm is switched off;
when SA + (0), SB + (0) and SC + (1), SN + (1) and the upper bridge arm and the lower bridge arm of the N-phase bridge arm are switched on and off;
when SA + (0), SB + (1) and SC + (0), SN + (1), the upper bridge arm of the N-phase bridge arm is switched on and the lower bridge arm is switched off;
when SA + (0), SB + (1) and SC + (1), SN + (1) and the upper bridge arm of the N-phase bridge arm are disconnected and the lower bridge arm is switched on;
when SA + ═ 1, SB + ═ 0 and SC + ═ 1, SN + ═ 0, the upper bridge arm of the N-phase bridge arm is switched on and the lower bridge arm is switched off;
when SA + ═ 1, SB + ═ 0 and SC + ═ 0, SN + ═ 1, the upper bridge arm of the N-phase bridge arm is disconnected and the lower bridge arm is switched on;
when SA + (1), SB + (1) and SC + (0), SN + (0), the upper bridge arm of the N-phase bridge arm is disconnected and the lower bridge arm is switched on;
when SA + ═ 1, SB + ═ 1, and SC + ═ 1, SN + ═ 0, the upper arm of the N-phase arm is turned off and the lower arm is turned on.
The invention provides a variable carrier pulse width modulation system of a three-phase four-bridge arm voltage type inverter, which is characterized by comprising a current controller, a pulse width modulator and an N-phase bridge arm controller; the expected value of each phase output current of the three-phase voltage type inverter and the instantaneous value of the output current are input into a current controller; the current controller calculates three-phase current control quantity as a three-phase modulation signal according to the current deviation and outputs the three-phase modulation signal to the pulse width modulator; the input end of the pulse width controller is connected with a three-phase carrier signal; a comparator in the pulse width controller compares the input phase modulation signals with corresponding phase carrier signals to generate driving signals of a three-phase bridge arm; the input end of the N-phase bridge arm controller is connected with the driving signals of the three-phase bridge arm, and the driving signals of the N-phase bridge arm are generated according to the driving signals of the three-phase bridge arm.
The invention has the beneficial effects that: compared with the conventional single-carrier sine pulse width modulation scheme, when a system operates in three-phase four-wire mode, the modulation scheme provided by the invention can remarkably reduce the common-mode disturbance voltage of a load neutral point connected with an N bridge arm under the condition of linear modulation or overmodulation while obtaining the same operation performance (such as a linear modulation range, a direct-current voltage utilization rate, output current waveform quality and the like), and realize that the neutral point voltage is equal to or close to zero in a three-phase basic balance and linear modulation range, thereby effectively reducing the problems of electromagnetic interference and the like brought by a neutral point to a drain current; under the condition that the N bridge arm switches are completely switched off, the inverter can be directly powered and operated in a three-phase three-wire mode, and when the load or the transformer is in three-phase star connection, common-mode voltage disturbance of star connection neutral points can be greatly reduced, and electromagnetic interference of a system is reduced.
Drawings
FIG. 1 is a schematic diagram of the system connection of the present invention;
FIG. 2 is a schematic diagram of a three-phase four leg voltage-type inverter;
FIG. 3 is a schematic illustration of a carrier signal 1;
FIG. 4 is a schematic illustration of a carrier signal 2;
fig. 5 is a schematic diagram of carrier selection table 1;
fig. 6 is a schematic diagram of carrier selection table 2;
FIG. 7 is a waveform diagram of an embodiment.
Detailed Description
The invention will be further described in detail with reference to the following drawings and specific examples, which are not intended to limit the invention, but are for clear understanding.
The invention provides a variable carrier pulse width modulation method of a three-phase four-bridge arm voltage type inverter, which is characterized by comprising the following steps of:
A. acquiring a three-phase output sinusoidal current expected value of the inverter, and sampling a three-phase output current instantaneous value of the inverter in real time;
B. subtracting the actual instantaneous current value from the three-phase current expected value of the inverter in each control sampling period to obtain a three-phase current deviation value;
C. calculating three-phase current control quantity according to the three-phase current deviation value to serve as a three-phase modulation signal;
D. selecting a three-phase carrier signal required by pulse width modulation according to the three-phase current control quantity;
E. and comparing each phase modulation signal with each corresponding phase carrier signal to generate a three-phase switch driving signal with variable pulse width, and using the three-phase switch driving signal to control the on-off operation of a three-phase bridge arm of the inverter circuit.
As shown in fig. 1, the present invention provides a variable carrier pulse width modulation system of a three-phase four-leg voltage-type inverter, which is characterized by comprising a current controller, a pulse width modulator, and an N-phase bridge arm controller; the expected value of each phase output current of the three-phase voltage type inverter and the instantaneous value of the output current are input into a current controller; the current controller calculates three-phase current control quantity as a three-phase modulation signal according to the current deviation and outputs the three-phase modulation signal to the pulse width modulator; the input end of the pulse width controller is connected with a three-phase carrier signal; a comparator in the pulse width controller compares the input phase modulation signals with corresponding phase carrier signals to generate driving signals of a three-phase bridge arm; the input end of the N-phase bridge arm controller is connected with the driving signals of the three-phase bridge arm, and the driving signals of the N-phase bridge arm are generated according to the driving signals of the three-phase bridge arm.
The invention aims to provide a variable carrier sine pulse width modulation method capable of eliminating power supply common-mode voltage interference for a three-phase four-bridge arm voltage type inverter, wherein A, B, C three-phase carriers are formed by changing and combining two paths of carrier signal sources with same-frequency phase cross difference of 180 degrees according to a provided selection algorithm, and the on-off state of an N bridge arm is determined by the on-off state of A, B, C three phases. Compared with single-carrier sine pulse width modulation, the three-phase four-leg inverter adopts the proposed variable carrier sine pulse width modulation, so that not only are the main operation technical indexes (such as direct-current voltage utilization rate, output current waveform quality, switching loss and the like) basically the same, but also the neutral point common mode disturbance voltage amplitude of a star-connected three-phase load/transformer can be obviously reduced, and the neutral point common mode disturbance voltage is zero under the condition of three-phase balance, so that the problems of electromagnetic interference on earth leakage current and the like, insulation reduction and the like caused by the neutral point common mode disturbance voltage are effectively reduced.
As shown in fig. 2, the three-phase four-leg voltage-type inverter of the present invention includes a power conversion circuit, a filter circuit, a controller, and a three-phase star-type load/transformer.
The output end of the inverter is connected with a three-phase star-shaped load, and the star-shaped connection neutral point of the load is n.
The power conversion circuit comprises an A bridge arm, a B bridge arm, a C bridge arm and an N bridge arm which are connected in parallel, wherein each bridge arm is formed by connecting an upper bridge arm switch and a lower bridge arm switch in series. And the output of the power conversion circuit is connected with a three-phase star-shaped load through the filter circuit.
The controller calculates and provides an expected value of three-phase output sinusoidal current of the inverter according to the power demand, and the controller samples the instantaneous value of the three-phase output current of the inverter in real time. As shown in fig. 1, the current controller subtracts A, B, C three-phase desired current values from detected actual instantaneous current values at each sampling period to obtain three-phase current deviation values, and then calculates three-phase current control quantities thereof according to the current deviation values.
The expected value of each phase output current of the three-phase voltage type inverter is as follows:
wherein,
desired values for three-phase output currents of inverter A, B, CThe effective value is the value of the maximum,
phase angles that are respectively A, B, C three-phase output current expected values; ω is the angular frequency of the output current.
Instantaneous values of the three-phase desired output current of the inverter A, B, C are:
wherein, Ia,Ib,IcEffective values for the instantaneous values of the three-phase output currents of inverter A, B, C,
respectively, A, B, C phase angles of the three-phase output current transients.
The controller will A, B, C three-phase desired output current in each control cycle
Respectively with the detected actual current ia,ib,icSubtracting to form a deviation, and calculating a current control quantity v by the current controller according to the deviationa,vb,vc。
The three-phase current control quantity va,vb,vcAs a three-phase modulated signal, directly to the pulse width modulator.
The three-phase current control quantity va,vb,vcAnd the input quantity is used for selecting three-phase carrier signals: first, the controller controls the three-phase control amount va,vb,vcAnd then according to the grouping type, selecting the corresponding three-phase carrier from a carrier selection table 1 (or a carrier selection table 2) by looking up a table, wherein the three-phase carrier is formed by combining two paths of bipolar triangular (or sawtooth type) signal source carriers 1 and 2 which have the same frequency and have the phase difference of 180 degrees.
In the embodiment shown in fig. 3, during the time period t 1-t 2, if table 1 is selected according to carriers, the a-phase and C-phase carriers are selected as carrier 1, and the B-phase carrier is selected as carrier 2; if table 2 is selected according to carriers, carrier 2 is selected for the a-phase and C-phase carriers, and carrier 1 is selected for the B-phase carrier.
The pulse width modulator subtracts the input A, B, C three-phase modulation signal and the corresponding A, B, C three-phase carrier signal to obtain a three-phase difference signal. And the three-phase difference value signal is compared with zero through a comparator, so that a three-phase square wave signal with variable pulse width is generated to control the on-off of a three-phase bridge arm of the inverter circuit.
In an embodiment, when any phase difference signal is greater than or equal to zero, the generated driving signal S ═ 1 (where ═ a, B, or C) will turn on the upper bridge arm and turn off the lower bridge arm of the corresponding phase bridge arm; on the contrary, when any phase difference value signal is less than zero, the generated driving signal of the phase bridge arm can disconnect the upper bridge arm and switch on the lower bridge arm of the corresponding phase bridge arm.
When the inverter operates in three-phase and four-wire mode, the N-arm switch controller searches for and generates the switch driving signals of the N-arm in real time according to the state of A, B, C three-phase switch driving signals and a provided switch list, for example, when the driving signals of A, B, C three-phase arm switches are SA + ═ 0, SB + ═ 0 and SC + ═ 1, respectively, the switching signals of the N-arm will be SN + ═ 1.
When the inverter operates in three phases and three lines, all switches of the N bridge arm are set to be turned off, namely SN < + >, SN < - > 0.
The invention can greatly reduce the neutral point common mode voltage disturbance of the star-connected three-phase load/transformer without changing the main performance indexes (such as linear modulation range, direct current bus voltage utilization rate, output voltage/current waveform quality, switching loss and the like) of the three-phase voltage type inverter system: when the inverter supplies power by a three-phase four-wire system, the variable carrier sine modulation can eliminate the neutral point common mode disturbance voltage of a three-phase balanced star-shaped load/transformer to be zero in a linear modulation range, and can also reduce the amplitude of the neutral point common mode disturbance voltage to be one fourth of the voltage value of a direct current bus under saturation modulation; when the inverter is supplied by a three-phase three-wire system, the amplitude of the neutral point common mode disturbance voltage of the three-phase balanced star-shaped load/transformer can be reduced to one sixth of the voltage value of the direct-current bus. Therefore, the variable-carrier sine pulse width modulation provided by the invention can improve the electromagnetic compatibility characteristic and the insulation characteristic of a star-shaped three-phase load (especially a three-phase balanced motor) or a transformer, and has important significance.
Those not described in detail in this specification are within the skill of the art.
Claims (10)
1. A variable carrier pulse width modulation method of a three-phase four-bridge arm voltage type inverter is characterized by comprising the following steps:
A. acquiring a three-phase output sinusoidal current expected value of the inverter, and sampling a three-phase output current instantaneous value of the inverter in real time;
B. subtracting the actual instantaneous current value from the three-phase current expected value of the inverter in each control sampling period to obtain a three-phase current deviation value;
C. calculating three-phase current control quantity according to the three-phase current deviation value to serve as a three-phase modulation signal;
D. selecting a three-phase carrier signal required by pulse width modulation according to the three-phase current control quantity;
E. and comparing each phase modulation signal with each corresponding phase carrier signal to generate a three-phase switch driving signal with variable pulse width, and using the three-phase switch driving signal to control the on-off operation of a three-phase bridge arm of the inverter circuit.
2. The method for modulating the variable carrier pulse width of the three-phase four-leg voltage-type inverter according to claim 1, wherein the method comprises the following steps: the three-phase carrier signal in the step D is formed by combining two paths of carrier signal sources; the two carrier signal sources consist of a bipolar triangular or sawtooth carrier 1 and a carrier 2 which have the same frequency and 180-degree phase difference.
3. The method for modulating the variable carrier pulse width of the three-phase four-leg voltage-type inverter according to claim 2, wherein the method comprises the following steps: the step D specifically comprises the following steps: and then, the three-phase carrier waves are obtained by changing and selecting from the carrier wave selection table 1 or the carrier wave selection table 2 through table look-up according to the grouping type of the control quantity.
4. The method for modulating the variable carrier pulse width of the three-phase four-leg voltage-type inverter according to claim 1, wherein the method comprises the following steps: in the step a, the expected value of each phase output current of the inverter is:
wherein,
effective values for the desired values of the three-phase output current from inverter A, B, C,
phase angles that are respectively A, B, C three-phase output current expected values; ω is the angular frequency of the output current.
5. The method for modulating the variable carrier pulse width of the three-phase four-leg voltage-type inverter according to claim 1, wherein the method comprises the following steps: in step a, instantaneous values of three-phase desired output currents of the inverter A, B, C are:
wherein, Ia,Ib,IcEffective values of the three-phase output current transients of inverter A, B, C,
phase angles of A, B, C three-phase output current transients, respectively; ω is the angular frequency of the output current.
6. The method for modulating the variable carrier pulse width of the three-phase four-leg voltage-type inverter according to claim 1, wherein the method comprises the following steps: in the step E, subtracting the three-phase modulation signal from the corresponding three-phase carrier signal to obtain a three-phase difference signal; the three-phase difference signal is compared with zero, so that a three-phase square wave signal with variable pulse width is generated to control the on-off of a three-phase bridge arm of the inverter circuit; when any phase difference signal is greater than or equal to zero, the generated switch driving signal S & ltx + & gt is 1, and the upper bridge arm of the corresponding phase bridge arm is switched on and the lower bridge arm is switched off; on the contrary, when any phase difference value signal is less than zero, the generated switch driving signal S + is 0, the upper bridge arm of the corresponding phase bridge arm is disconnected, and the lower bridge arm is switched on; and SA + refers to a switch driving signal of the bridge arm of the phase A, SB + refers to a switch driving signal of the bridge arm of the phase B, and SC + refers to a switch driving signal of the bridge arm of the phase C.
7. The method for modulating the variable carrier pulse width of the three-phase four-leg voltage-source inverter according to claim 6, wherein the method comprises the following steps: when the inverter operates in three-phase four-wire mode, the N-bridge arm switch controller checks an N-phase bridge arm switch control table in real time according to the state of the three-phase switch driving signal to generate a switch driving signal of an N-bridge arm; when the inverter operates in three-phase and three-wire mode, all switches of the N bridge arms are set to be turned off, and the inverter is directly connected to a three-phase and three-wire load or a transformer to normally operate.
8. The method for modulating the variable carrier pulse width of the three-phase four-leg voltage-source inverter according to claim 3, wherein the judgment logic of the carrier selection table 1 is as follows:
when v isa>vb≥vcWhen the carrier wave is a carrier wave 1, the carrier wave of the phase A is a carrier wave 2, and the carrier wave of the phase C is a carrier wave 1;
when v isc≥vb>vaWhen the carrier wave of A phase is 2, BThe phase carrier wave is carrier wave 1, and the C phase carrier wave is carrier wave 2;
when v isb≥va>vcWhen the carrier wave is a carrier wave 1, the carrier wave 2 is a carrier wave 2, and the carrier wave 2 is a carrier wave 2;
when v isc>va≥vbWhen the carrier wave is a carrier wave 2, the carrier wave 1 is selected as the carrier wave of the phase A, and the carrier wave 1 is selected as the carrier wave of the phase C;
when v isb>vc≥vaWhen the carrier wave is a carrier wave 1, the carrier wave 1 is selected as the A-phase carrier wave, and the carrier wave 2 is selected as the C-phase carrier wave;
when v isa≥vc>vbWhen the carrier wave is a carrier wave 2, the carrier wave 2 is a carrier wave 2, and the carrier wave 1 is a carrier wave 1;
the judgment logic of the carrier selection table 2 is as follows:
when v isa>vb≥vcWhen the carrier wave is a carrier wave 2, the carrier wave 1 is a carrier wave of the phase A, and the carrier wave 2 is a carrier wave of the phase C;
when v isc≥vb>vaWhen the carrier wave is a carrier wave 1, the carrier wave of the phase A is a carrier wave 2, and the carrier wave of the phase C is a carrier wave 1;
when v isb≥va>vcWhen the carrier wave is a carrier wave 2, the carrier wave 1 is selected as the carrier wave of the phase A, and the carrier wave 1 is selected as the carrier wave of the phase C;
when v isc>va≥vbWhen the carrier wave is a carrier wave 1, the carrier wave 2 is a carrier wave 2, and the carrier wave 2 is a carrier wave 2;
when v isb>vc≥vaWhen the carrier wave is a carrier wave 2, the carrier wave 2 is a carrier wave 2, and the carrier wave 1 is a carrier wave 1;
when v isa≥vc>vbWhen the carrier wave is a carrier wave 1, the carrier wave 1 is selected as the A-phase carrier wave, and the carrier wave 2 is selected as the C-phase carrier wave;
wherein v isaMeans phase A current control quantity, vbMeans phase A current control quantity, vcRefers to the C-phase current control amount.
9. The method of claim 7, wherein the logic for determining the N-phase bridge arm switch control table is as follows: wherein, SN + refers to a switch driving signal of the N-phase bridge arm;
when SA + (0), SB + (0) and SC + (0), SN + (1), the upper bridge arm of the N-phase bridge arm is switched on and the lower bridge arm is switched off;
when SA + (0), SB + (0) and SC + (1), SN + (1) and the upper bridge arm and the lower bridge arm of the N-phase bridge arm are switched on and off;
when SA + (0), SB + (1) and SC + (0), SN + (1), the upper bridge arm of the N-phase bridge arm is switched on and the lower bridge arm is switched off;
when SA + (0), SB + (1) and SC + (1), SN + (0) and the upper bridge arm of the N-phase bridge arm are disconnected and the lower bridge arm is switched on;
when SA + ═ 1, SB + ═ 0 and SC + ═ 1, SN + ═ 0, the upper bridge arm of the N-phase bridge arm is switched on and the lower bridge arm is switched off;
when SA + ═ 1, SB + ═ 0 and SC + ═ 0, SN + ═ 1, the upper bridge arm of the N-phase bridge arm is disconnected and the lower bridge arm is switched on;
when SA + (1), SB + (1) and SC + (0), SN + (0), the upper bridge arm of the N-phase bridge arm is disconnected and the lower bridge arm is switched on;
when SA + ═ 1, SB + ═ 1, and SC + ═ 1, SN + ═ 0, the upper arm of the N-phase arm is turned off and the lower arm is turned on.
10. A variable carrier pulse width modulation system of a three-phase four-bridge arm voltage type inverter is characterized by comprising a current controller, a pulse width modulator and an N-phase bridge arm controller; the expected value of each phase output current of the three-phase voltage type inverter and the instantaneous value of the output current are input into a current controller; the current controller calculates three-phase current control quantity as a three-phase modulation signal according to the current deviation and outputs the three-phase modulation signal to the pulse width modulator; the input end of the pulse width controller is connected with a three-phase carrier signal; a comparator in the pulse width controller compares the input phase modulation signals with corresponding phase carrier signals to generate driving signals of a three-phase bridge arm; the input end of the N-phase bridge arm controller is connected with the driving signals of the three-phase bridge arm, and the driving signals of the N-phase bridge arm are generated according to the driving signals of the three-phase bridge arm.
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