CN112187075A - Three-phase four-bridge arm inverter interference pulse width modulation system and method - Google Patents
Three-phase four-bridge arm inverter interference pulse width modulation system and method 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
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
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- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
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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
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
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Abstract
The invention provides a three-phase four-bridge arm inverter interference pulse width modulation system and a method, which comprises the following steps: acquiring a three-phase output sinusoidal current expected value, and sampling a three-phase output current instantaneous value 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; calculating an offset according to the three-phase current control quantity, and injecting the control quantity of each phase to obtain a three-phase modulation signal; selecting a three-phase carrier signal required by pulse width modulation; comparing each phase modulation signal with each corresponding phase carrier signal to generate a three-phase square wave signal with variable pulse width, wherein the three-phase square wave signal is used for controlling the on-off operation of a three-phase bridge arm of the inverter circuit; and comparing the offset serving as an N bridge arm modulation signal with the N bridge arm carrier signal to obtain a pulse width signal for controlling the on-off of the N bridge arm switch. The invention reduces the electromagnetic interference brought by the neutral point to the earth leakage current.
Description
Technical Field
The invention belongs to the technical field of inverter pulse width modulation, and particularly relates to a three-phase four-leg inverter interference pulse width modulation system and method.
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 three-phase four-wire, three-phase three-wire and even single-phase power interfaces according to actual needs, can flexibly deal with the problem of unbalanced three-phase load by controlling the auxiliary leg N, improves the electromagnetic compatibility, reliability and the like of an inverter system, and is widely applied to occasions such as electric vehicle charging and discharging, new energy grid-connected power generation, motor driving and the like. The existing three-phase four-leg voltage type inverter mostly adopts a pulse width modulation technology to realize accurate control of output voltage or current, and when the inverter adopting a single carrier conventional pulse width modulation method (such as sine pulse width modulation, space voltage vector modulation and the like) is used for driving a star-connected three-phase load (particularly a three-phase balanced asynchronous motor) or a transformer, the amplitude of common-mode disturbance voltage of a star-connected neutral point can be up to half of the direct-current bus voltage of the inverter, and the problems of serious electromagnetic interference, insulation performance reduction and the like of the neutral point to earth leakage current and the like can be caused.
Disclosure of Invention
The invention aims to solve the defects in the prior art, and provides a three-phase four-leg inverter interference pulse width modulation system and method, which can greatly reduce electromagnetic interference brought by a neutral point to a ground leakage current.
The technical scheme adopted by the invention is as follows: a three-phase four-leg inverter interference pulse width modulation method 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;
D. calculating an offset according to the three-phase current control quantity, and injecting the offset generated by calculation into each phase control quantity to obtain a three-phase modulation signal;
E. selecting a three-phase carrier signal required by pulse width modulation according to the three-phase current control quantity;
F. comparing the input phase modulation signals with corresponding phase carrier signals to generate three-phase square wave signals with variable pulse widths, and using the three-phase square wave signals to control the on-off operation of a three-phase bridge arm of the inverter circuit;
G. selecting a carrier signal subjected to pulse width modulation by an N bridge arm;
H. and comparing the offset serving as an N bridge arm modulation signal with the N bridge arm carrier signal to obtain a pulse width signal for controlling the on-off of the N bridge arm switch.
In the above technical solution, the three-phase carrier signal in the step E 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 E 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, the judgment logic of the carrier selection table 1 is as follows:
when v isa>vb≥vcWhen the carrier wave selection is carried out, the carrier wave selection 1 is selected for the A-phase carrier wave, the carrier wave selection 2 is selected for the B-phase carrier wave, and the C-phase carrier wave selectionUsing a carrier 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>vbIn the process, the carrier 1 is selected for the phase A carrier, the carrier 1 is selected for the phase B carrier, and the carrier 2 is selected for the phase C carrier.
In the above technical solution, in the step D, the three are adoptedPhase current control quantity va,vb,vcCalculating the offset v according to a given formulap：
Wherein, max (v)a,vb,vc) And max (v)a,vb,vc) Respectively controlled by three-phase currenta,vb,vcMaximum and minimum values of; wherein, V dc2 is the amplitude of the carrier signal;
the three-phase current control quantity va,vb,vcRespectively adding the offset vpWill yield:
wherein v isao,vbo,vcoA, B, C three-phase modulation signals respectively.
In the above technical solution, in the step F, 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; 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 operates in a three-phase four-bridge arm mode, the offset is used as a modulation signal of an N-bridge arm, a carrier signal of the N-bridge arm is selected from one of a carrier 1 and a carrier 2, and the modulation signal of the N-bridge arm and the carrier signal of the N-bridge arm are subtracted to obtain a difference signal of the N-bridge arm; the three-phase difference signal is compared with zero; when the difference signal of the N bridge arms is more than or equal to zero, the upper bridge arm of the corresponding N bridge arm is switched on, and the lower bridge arm of the disconnector is switched off; and conversely, when the difference signal of the N bridge arms is less than zero, disconnecting the upper bridge arm of the N bridge arms and switching on the lower bridge arm of the N bridge arms.
In the above technical scheme, when the inverter operates in a three-phase three-leg mode, all switches of the N legs are set to be turned off.
The invention provides a three-phase four-bridge arm inverter interference pulse width modulation system which is characterized by comprising a current controller, a bias amount calculation module and a pulse width 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 the three-phase current control quantity according to the current deviation; the current controller outputs three-phase current control quantity to the offset quantity calculation module; the offset calculation module feeds back the calculated and generated offset to the current controller; the current controller generates a three-phase modulation signal based on the three-phase current control quantity and the offset quantity and outputs the three-phase modulation signal to the pulse width controller; the input end of the pulse width controller is connected with a three-phase carrier signal; and a comparator in the pulse width controller compares the input modulation signals of all phases with corresponding carrier signals of all phases to generate and obtain driving signals of the three-phase bridge arm.
In the technical scheme, the bridge arm switching control circuit further comprises an N-bridge arm comparator, the offset calculation module outputs the offset to the N-bridge arm comparator, the input end of the N-bridge arm comparator is also connected with a carrier signal of the N-bridge arm, and the N-bridge arm comparator compares the offset serving as an N-bridge arm modulation signal with the carrier signal of the N-bridge arm to obtain a pulse width signal for controlling the on-off of the N-bridge arm switch.
The invention has the beneficial effects that: the invention provides a pulse width modulation scheme for a three-phase four-bridge arm inverter, and the pulse width modulation method can be equivalent to variable-carrier three-phase discontinuous pulse width modulation. Like the conventional single carrier discontinuous modulation, the pulse width modulation method has the advantages of small switching loss, high utilization rate of direct current bus voltage, good output current waveform quality and the like. When the inverter operates in a three-phase four-bridge arm mode, compared with the conventional single carrier pulse width modulation, the optimized pulse width modulation method adopts a variable carrier signal, and can reduce the amplitude of the common mode disturbance voltage of the neutral point of the three-phase star-connected load/transformer from half to one fourth of the voltage of a direct current bus, thereby greatly reducing the problems of electromagnetic interference and the like caused by the neutral point to the earth leakage current; in addition, the inverter can be directly converted from a three-phase four-bridge arm mode into a three-phase three-bridge arm mode to operate by directly switching off the N bridge arms and keeping the control method of the rest three phases unchanged, and compared with the conventional single carrier pulse width modulation, the optimized pulse width modulation method can reduce the amplitude of the common-mode disturbance voltage of the neutral point of the load/transformer to one sixth of the voltage of a direct-current bus, and also greatly reduce the electromagnetic interference brought to the earth leakage current by the neutral point.
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.
As shown in fig. 1, the invention provides a three-phase four-leg inverter interference pulse width modulation system, which is characterized by comprising a current controller, a bias amount calculation module and a pulse width 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 the three-phase current control quantity according to the current deviation; the current controller outputs three-phase current control quantity to the offset quantity calculation module; the offset calculation module calculates and generates an offset according to the three-phase current control quantity; adding the three-phase current control quantity and the offset quantity to generate a three-phase modulation signal and outputting the three-phase modulation signal to the pulse width controller; the input end of the pulse width controller is connected with a three-phase carrier signal; and a comparator in the pulse width controller compares the input modulation signals of all phases with corresponding carrier signals of all phases to generate and obtain driving signals of the three-phase bridge arm. The N bridge arm comparator compares the offset serving as an N bridge arm modulation signal with the N bridge arm carrier signal to obtain a pulse width signal for controlling the on-off of the N bridge arm switch
The invention aims to provide a low-switching-loss and low-common-mode voltage disturbance pulse width modulation method for a three-phase four-leg voltage type inverter, on one hand, according to the state of A, B, C three-phase control quantity, a changed A, B, C three-phase carrier signal is selected by adopting a provided carrier selection algorithm, and the three-phase carrier signal is formed by changing and combining two paths of carrier signal sources with the same-frequency phase angle difference of 180 degrees; and on the other hand, A, B, C three-phase control quantities are adopted to generate offset quantities in real time according to a given formula, the offset quantities are injected into the three-phase control quantities to obtain A, B, C three-phase modulation signals, and the three-phase modulation signals always have one phase modulation signal in a full modulation state (namely, the modulation signal value is equal to the peak value of the carrier signal) in each carrier period in a linear modulation range, so that discontinuous pulse width modulation is obtained (namely, the switching action is not generated in all three-phase arms and only one phase arm in A, B, C three-phase arms of the inverter in each carrier period). Discontinuous pulse width modulation has the advantage of low switching loss due to the fact that one third of the switching action of the inverter is reduced, and has the advantages of high utilization rate of direct current bus voltage, good output current waveform quality and the like.
The technical scheme adopted by the invention is as follows: a three-phase four-leg inverter interference pulse width modulation method 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;
D. calculating an offset according to the three-phase current control quantity, and injecting the offset generated by calculation into each phase control quantity to obtain a three-phase modulation signal;
E. selecting a three-phase carrier signal required by pulse width modulation according to the three-phase current control quantity;
F. comparing the input phase modulation signals with corresponding phase carrier signals to generate three-phase square wave signals with variable pulse widths, and using the three-phase square wave signals to control the on-off operation of a three-phase bridge arm of the inverter circuit;
G. selecting a carrier signal subjected to pulse width modulation by an N bridge arm;
H. and comparing the offset serving as an N bridge arm modulation signal with the N bridge arm carrier signal to obtain a pulse width signal for controlling the on-off of the N bridge arm switch.
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 to give an expected value of three-phase output sinusoidal current of the inverter according to power requirements, the controller samples instantaneous values of the three-phase output current of the inverter in real time, the expected current value of A, B, C three phases is subtracted from the detected actual instantaneous current value in each sampling period to obtain a three-phase current deviation value, and then the current controller calculates three-phase current control quantity of the current controller according to the current deviation.
The expected value of each phase output current of the three-phase voltage type inverter is as follows:
wherein the content of the first and second substances,
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.
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,vcCalculating the offset v according to a given formulap：
Wherein, max (v)a,vb,vc) And max (v)a,vb,vc) Respectively controlled by three-phase currenta,vb,vcMaximum and minimum values of; wherein, V dc2 is the amplitude of the carrier signal;
the three-phase current control quantity va,vb,vcRespectively adding the offset vpWill yield:
wherein v isao,vbo,vcoA, B, C three-phase modulation signals respectively.
The three-phase current control quantity va,vb,vcAnd is also used as an input quantity for selecting A, B, C 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 changing and 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 an embodiment, at t1—t2Within a time interval vc≥vb＞vaIf the table 1 is selected according to the carriers, the carrier 1 is selected for the phase A and the phase C, and the carrier 2 is selected for the phase B; 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 three-phase carrier signal to obtain a three-phase difference signal. And the three-phase difference 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 an A, B, C three-phase bridge arm of the inverter circuit. In one embodiment, the difference signal is greater than or equal toWhen the time is zero, the generated driving signal of the phase bridge arm turns on the upper bridge arm of the corresponding phase bridge arm and turns off the lower 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. Obviously, by va,vb,vcInjection offset vpAll and only one phase of the resulting three-phase modulated signal is equal to + Vdc/2 or-Vdc/2, the phase modulated signal has a peak value of + -VdcThe/2 carrier signal comparison will obtain a pulse width driving signal with a duty ratio of ± 100%, that is, the phase bridge arm switch driven by the pulse width signal will not have a switching action in the carrier period, so that the pulse width modulation is equivalent to a discontinuous pulse width modulation.
When the inverter operates in a three-phase four-bridge arm mode, the switch control signals of the N bridge arms are also generated in a pulse width modulation mode: said offset vpWill be a modulated signal whose carrier signal is available from either carrier 1 or carrier 2. When the inverter operates in a three-phase three-leg mode, all switches of the N-leg are set to be off, i.e., SN + ═ SN- ═ 0.
The invention provides a pulse width modulation scheme for a three-phase four-bridge arm inverter, and the pulse width modulation method can be equivalent to variable-carrier three-phase discontinuous pulse width modulation. The pulse width modulation method has the advantages of small switching loss, high utilization rate of direct current bus voltage, good output current waveform quality and the like, as in the conventional single carrier discontinuous modulation. When the inverter operates in a three-phase four-bridge arm mode, compared with the conventional single carrier pulse width modulation, the optimized pulse width modulation method adopts a variable carrier signal, and can reduce the amplitude of the common mode disturbance voltage of the neutral point of the three-phase star-connected load/transformer from half to one fourth of the voltage of a direct current bus, thereby greatly reducing the problems of electromagnetic interference and the like caused by the neutral point to the earth leakage current; in addition, the inverter can be directly converted from a three-phase four-bridge arm mode into a three-phase three-bridge arm mode to operate by directly switching off the N bridge arms and keeping the control method of the rest three phases unchanged, and compared with the conventional single carrier pulse width modulation, the optimized pulse width modulation method can reduce the amplitude of the common-mode disturbance voltage of the neutral point of the load/transformer to one sixth of the voltage of a direct-current bus, and also greatly reduce the electromagnetic interference brought to the earth leakage current by the neutral point.
Those not described in detail in this specification are within the skill of the art.
Claims (10)
1. A three-phase four-leg inverter interference pulse width modulation method 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;
D. calculating an offset according to the three-phase current control quantity, and injecting the offset generated by calculation into each phase control quantity to obtain a three-phase modulation signal;
E. selecting a three-phase carrier signal required by pulse width modulation according to the three-phase current control quantity;
F. comparing the input phase modulation signals with corresponding phase carrier signals to generate three-phase square wave signals with variable pulse widths, and using the three-phase square wave signals to control the on-off operation of a three-phase bridge arm of the inverter circuit;
G. selecting a carrier signal subjected to pulse width modulation by an N bridge arm;
H. and comparing the offset serving as an N bridge arm modulation signal with the N bridge arm carrier signal to obtain a pulse width signal for controlling the on-off of the N bridge arm switch.
2. The three-phase four-leg inverter interference pulse width modulation method according to claim 1, characterized in that: the three-phase carrier signal in the step E 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 three-phase four-leg inverter disturbance pulse width modulation method according to claim 2, wherein the step E specifically includes the steps of: 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 three-phase four-leg inverter disturbance pulse width modulation method according to claim 3, characterized in that:
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>vbIn the process, the carrier 1 is selected for the phase A carrier, the carrier 1 is selected for the phase B carrier, and the carrier 2 is selected for the phase C carrier.
5. The three-phase four-leg inverter interference pulse width modulation method according to claim 1, wherein in the step D, the three-phase current control quantity v is adopteda,vb,vcCalculating the offset v according to a given formulap：
Wherein, max (v)a,vb,vc) And max (v)a,vb,vc) Respectively controlled by three-phase currenta,vb,vcMaximum and minimum values of; wherein, Vdc2 is the amplitude of the carrier signal;
the three-phase current control quantity va,vb,vcRespectively adding the offset vpWill yield:
wherein v isao,vbo,vcoA, B, C three-phase modulation signals respectively.
6. The three-phase four-leg inverter interference pulse width modulation method according to claim 1, characterized in that: in the step F, 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; 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 three-phase four-leg inverter interference pulse width modulation method according to claim 2, characterized in that: when the inverter operates in a three-phase four-bridge arm mode, the offset is used as a modulation signal of an N-bridge arm, a carrier signal of the N-bridge arm is selected from one of a carrier 1 and a carrier 2, and the modulation signal of the N-bridge arm and the carrier signal of the N-bridge arm are subtracted to obtain a difference signal of the N-bridge arm; the three-phase difference signal is compared with zero; when the difference signal of the N bridge arms is more than or equal to zero, the upper bridge arm of the corresponding N bridge arm is switched on, and the lower bridge arm of the disconnector is switched off; and conversely, when the difference signal of the N bridge arms is less than zero, disconnecting the upper bridge arm of the N bridge arms and switching on the lower bridge arm of the N bridge arms.
8. The three-phase four-leg inverter interference pulse width modulation method according to claim 2, characterized in that: when the inverter operates in a three-phase three-bridge arm mode, all switches of the N bridge arms are set to be turned off.
9. A three-phase four-bridge arm inverter interference pulse width modulation system is characterized by comprising a current controller, a bias amount calculation module and a pulse width 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 the three-phase current control quantity according to the current deviation; the current controller outputs three-phase current control quantity to the offset quantity calculation module; the offset calculation module calculates and generates an offset according to the three-phase current control quantity; adding the three-phase current control quantity and the offset quantity to generate a three-phase modulation signal and outputting the three-phase modulation signal to the pulse width controller; the input end of the pulse width controller is connected with a three-phase carrier signal; and a comparator in the pulse width controller compares the input modulation signals of all phases with corresponding carrier signals of all phases to generate and obtain driving signals of the three-phase bridge arm.
10. The three-phase four-leg inverter interference pulse width modulation system according to claim 9, further comprising an N-leg comparator, wherein the offset calculation module outputs an offset to the N-leg comparator, the input end of the N-leg comparator is further connected with a carrier signal of the N-leg, and the N-leg comparator compares the offset as the N-leg modulation signal with the carrier signal of the N-leg to obtain a pulse width signal for controlling on/off of the N-leg switch.
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