CN112187076B - Optimized pulse width modulation system and method for three-phase four-bridge arm inverter - Google Patents
Optimized pulse width modulation system and method for three-phase four-bridge arm 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
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/381—Dispersed generators
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/44—Circuits or arrangements for compensating for electromagnetic interference in converters or inverters
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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
- 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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- 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
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/20—The dispersed energy generation being of renewable origin
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Abstract
The invention provides an optimized pulse width modulation system and method for a three-phase four-bridge arm inverter, comprising 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 three-phase current expected value of the inverter from the detected actual instantaneous current value in each control sampling period to obtain a three-phase current deviation value; calculating a three-phase current control quantity; calculating the offset, and injecting the offset generated by calculation into each phase of control quantity to obtain a three-phase modulation signal; selecting a three-phase carrier signal required by pulse width modulation; comparing the input modulation signals of each phase with corresponding carrier signals of each phase to obtain three-phase square wave signals with variable pulse width, wherein the three-phase square wave signals are used for controlling the on-off operation of three-phase bridge arms of an inverter circuit; and comparing the offset with the N bridge arm carrier signal as an N bridge arm modulation signal to obtain a pulse width signal for controlling the on-off of the N bridge arm switch. The invention reduces electromagnetic interference caused by neutral points to the earth leakage current.
Description
Technical Field
The invention belongs to the technical field of inverter pulse width modulation, and particularly relates to an optimized pulse width modulation system and method for a three-phase four-bridge arm inverter.
Background
The energy problem is always an important factor limiting the development of a human society, and every important progress of the society is not separated from the improvement and replacement of energy. Energy conservation and environmental protection would be an important option for human sustainable development and avoidance of catastrophic climate change. The use of electric energy in the world today is about 40% of the total energy.
On the electricity utilization side, the motor (especially a three-phase motor) is high-energy-consumption power equipment with large application amount and wide application range. For example, it is counted that about 90% of the electric machines in the world currently use asynchronous motors, with small asynchronous motors accounting for more than about 70%. In the total load of the power system, the power consumption of the asynchronous motor occupies a large proportion. However, a large number of industrial devices such as fans, pumps, and conventional industrial sewing machines, machining devices, etc., are often operated by adopting a constant-speed transmission scheme of an asynchronous motor, resulting in generally low efficiency of the ac motor. In industrial sewing machines and machining equipment, clutches and friction plates 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 regulating device based on the power electronic inverter is used for driving motor equipment, industrial users can save more than 18% of electric energy at least on the basis of the prior art. Therefore, various countries in the world are actively encouraged to promote advanced means such as variable frequency speed regulation and the like for realizing energy conservation, and meanwhile, the working performance of the electric transmission equipment can be obviously improved. In addition, mobile devices typified by electric vehicles are also charged and discharged by being connected 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, so that the method is an important means for ensuring energy source safety, reducing carbon emission and avoiding global warming. In recent decades, energy structures are continuously improved and optimized, and the development and utilization specific gravity of clean energy (including wind energy, solar energy, hydrogen energy and the like) is rapidly improved. The power electronic inverter is an indispensable power interface for clean energy power generation, and is a key device for fully and high-quality development and utilization of clean energy.
In the middle and high power application occasions, the three-phase voltage type inverter is a core component for motor speed regulation, power supply by using clean energy, and the like, and the modulation and control scheme 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-bridge arm voltage type inverter can flexibly provide three-phase four-wire, three-phase three-wire or even single-phase power interfaces according to actual needs, can flexibly cope with the problem of unbalanced three-phase load by controlling the auxiliary bridge arm N, improves electromagnetic compatibility performance, reliability and the like of an inverter system, and is widely applied to occasions such as charging and discharging of electric automobiles, grid-connected power generation of new energy sources, motor driving and the like. The current three-phase four-bridge arm 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 (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 the problems of serious electromagnetic interference of the neutral point to earth leakage current and the like, insulation performance reduction and the like are caused.
Disclosure of Invention
The invention aims to solve the defects in the background art, and provides an optimized pulse width modulation system and an optimized pulse width modulation method for a three-phase four-bridge arm inverter, which greatly reduce electromagnetic interference caused by neutral points on earth leakage current.
The technical scheme adopted by the invention is as follows: the optimized pulse width modulation method for the three-phase four-bridge arm inverter is characterized by comprising the following steps of:
A. acquiring a three-phase output sinusoidal current expected value of an inverter, and sampling a three-phase output current instantaneous value of the inverter in real time;
B. subtracting the three-phase current expected value of the inverter from the detected actual instantaneous current value in each control sampling period to obtain a three-phase current deviation value;
C. calculating a three-phase current control quantity according to the three-phase current deviation value;
D. calculating the 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 each input phase modulation signal with corresponding each phase carrier signal to generate a three-phase square wave signal with a variable pulse width, and using the three-phase square wave signal for controlling the on-off operation of a three-phase bridge arm of an inverter circuit;
G. selecting carrier signals modulated by N bridge arm pulse width;
H. and comparing the offset with the N bridge arm carrier signal as an N bridge arm modulation 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 paths of carrier signal sources consist of a carrier 1 and a carrier 2 which are bipolar triangles or crenellations with the same frequency and 180 degrees phase difference.
In the above technical solution, the step E specifically includes the following steps: and sorting the three-phase current control quantity according to the numerical value of each phase of control quantity, determining the grouping type of the control quantity, and then carrying out change selection from a carrier selection table 1 or a carrier selection table 2 by looking up a table aiming at the grouping type of the control quantity to obtain the three-phase carrier.
In the above technical solution, the judgment logic of the carrier selection table 1 is as follows:
when v a >v b ≥v c When the method is used, the carrier 1 is selected as the A phase carrier, the carrier 2 is selected as the B phase carrier, and the carrier 1 is selected as the C phase carrier;
when v c ≥v b >v a When the method is used, the carrier 2 is selected as the carrier of the A phase, the carrier 1 is selected as the carrier of the B phase, and the carrier 2 is selected as the carrier of the C phase;
when v b ≥v a >v c When the method is used, the carrier 1 is selected as the carrier of the A phase, the carrier 2 is selected as the carrier of the B phase, and the carrier 2 is selected as the carrier of the C phase;
when v c >v a ≥v b When the method is used, the carrier 2 is selected as the carrier of the A phase, the carrier 1 is selected as the carrier of the B phase, and the carrier 1 is selected as the carrier of the C phase;
when v b >v c ≥v a When the method is used, the carrier 1 is selected as the carrier of the A phase, the carrier 1 is selected as the carrier of the B phase, and the carrier 2 is selected as the carrier of the C phase;
when v a ≥v c >v b When the method is used, the carrier 2 is selected as the carrier of the phase A, the carrier 2 is selected as the carrier of the phase B, and the carrier 1 is selected as the carrier of the phase C;
the judgment logic of the carrier selection table 2 is as follows:
when v a >v b ≥v c When the method is used, the carrier 2 is selected as the carrier of the A phase, the carrier 1 is selected as the carrier of the B phase, and the carrier 2 is selected as the carrier of the C phase;
when v c ≥v b >v a When the method is used, the carrier 1 is selected as the A phase carrier, the carrier 2 is selected as the B phase carrier, and the carrier 1 is selected as the C phase carrier;
when v b ≥v a >v c When the method is used, the carrier 2 is selected as the carrier of the A phase, the carrier 1 is selected as the carrier of the B phase, and the carrier 1 is selected as the carrier of the C phase;
when v c >v a ≥v b When the method is used, the carrier 1 is selected as the carrier of the A phase, the carrier 2 is selected as the carrier of the B phase, and the carrier 2 is selected as the carrier of the C phase;
when v b >v c ≥v a When the method is used, the carrier 2 is selected as the carrier of the phase A, the carrier 2 is selected as the carrier of the phase B, and the carrier 1 is selected as the carrier of the phase C;
when v a ≥v c >v b When the method is used, the carrier 1 is selected as the A phase carrier, the carrier 1 is selected as the B phase carrier, and the carrier 2 is selected as the C phase carrier.
In the above technical solution, in the step D, the three-phase current control amount v is adopted a ,v b ,v c Calculating the offset v according to a given formula p ：
v p ＝(max(v a ,v b ,v c )+min(v a ,v b ,v c ))/2
Wherein max (v a ,v b ,v c ) And max (v) a ,v b ,v c ) Respectively three-phase current control quantity v a ,v b ,v c Maximum and minimum values of (a); wherein V is dc 2 is the amplitude of the carrier signal;
the three-phase current control quantity v a ,v b ,v c Respectively adding the offset v p The following steps are obtained:
wherein v is ao ,v bo ,v co A, B, C three-phase modulated signals, respectively.
In the above technical solution, in the step F, the three-phase modulating signal and the corresponding three-phase carrier signal are subtracted to obtain a three-phase difference signal; comparing the three-phase difference signal with zero; when any phase difference signal is greater than or equal to zero, the generated switch driving signal S+ is 1, an upper bridge arm of a corresponding phase bridge arm is opened, and a lower bridge arm is disconnected; conversely, when any phase difference signal is smaller 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 opened; wherein, SA+ refers to the switch driving signal of the A phase bridge arm, SB+ refers to the switch driving signal of the B phase bridge arm, and SC+ refers to the switch driving signal of the C phase bridge arm.
In the above technical solution, when the inverter operates in a three-phase four-leg mode, the offset is used as a modulation signal of an N-leg, a carrier signal of the N-leg is selected from one of carrier 1 and carrier 2, and the modulation signal of the N-leg and the carrier signal of the N-leg are subtracted to obtain a difference signal of the N-leg; comparing the three-phase difference signal with zero; when the difference signal of the N bridge arm is more than or equal to zero, opening an upper bridge arm of the corresponding N bridge arm and disconnecting a lower bridge arm of the breaker; otherwise, when the difference signal of the N bridge arm is smaller than zero, the upper bridge arm of the N bridge arm is disconnected and the lower bridge arm of the N bridge arm is opened.
In the above technical scheme, when the inverter operates in a three-phase three-leg mode, all switches of the N leg are set to be turned off.
The invention provides an optimized pulse width modulation system of a three-phase four-bridge arm inverter, which comprises a current controller, a bias amount calculating module and a pulse width controller, wherein the bias amount calculating module is used for calculating the bias amount of the current 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 to a current controller; the current controller calculates a three-phase current control quantity according to the current deviation; the current controller outputs three-phase current control quantity to the offset calculating module; the offset calculation module calculates and generates an offset according to the three-phase current control quantity; the three-phase current control quantity and the offset are added and calculated to generate a three-phase modulation signal, and the three-phase modulation signal is output to the input end of the pulse width controller; and a comparator in the pulse width controller compares the input modulation signals of each phase with corresponding carrier signals of each phase to generate driving signals of the three-phase bridge arms.
In the technical scheme, the device further comprises an N-bridge arm comparator, the offset amount calculation module outputs an offset amount 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 amount 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 on-off of an N-bridge arm switch.
The beneficial effects of the invention are as follows: the invention provides an optimized pulse width modulation scheme for the three-phase four-bridge arm inverter, and the optimized pulse width modulation method is equivalent to the conventional space voltage vector modulation in terms of modulating signals, and has the advantages of wide linear modulation range, high utilization rate of direct current bus voltage, good waveform quality of output current and the like. When the inverter operates in a three-phase four-bridge arm mode, compared with the conventional single-carrier three-dimensional space voltage vector 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 load/transformer connected by the three-phase star from half of the voltage of the direct current bus to one fourth, so that the problems of electromagnetic interference and the like caused by the neutral point on the floor drain current are greatly reduced; in addition, the inverter can be directly converted into a three-phase three-bridge arm mode to operate by directly switching off the N bridge arm and keeping the control method of the other three phases unchanged from the three-phase four-bridge arm mode, and compared with the conventional single-carrier two-dimensional space voltage vector 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 be one sixth of the voltage of a direct current bus, and the electromagnetic interference of the neutral point to the floor drain current is greatly reduced.
Drawings
FIG. 1 is a schematic diagram of a 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 diagram of a carrier signal 1;
fig. 4 is a schematic diagram of a carrier signal 2;
fig. 5 is a schematic diagram of a carrier selection table 1;
fig. 6 is a schematic diagram of a carrier selection table 2;
fig. 7 is a schematic waveform diagram of an embodiment.
Detailed Description
The invention will now be described in further detail with reference to the drawings and specific examples, which are given for clarity of understanding and are not to be construed as limiting the invention.
As shown in fig. 1, the invention provides a system and a method for optimizing pulse width modulation of a three-phase four-bridge arm inverter, which are 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 to a current controller; the current controller calculates a three-phase current control quantity according to the current deviation; the current controller outputs three-phase current control quantity to the offset calculating module; the offset calculation module calculates and generates an offset according to the three-phase current control quantity; adding and calculating 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 a 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 each phase with corresponding carrier signals of each phase to generate driving signals of the three-phase bridge arms. The offset calculation module outputs 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 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 aims to provide an optimized pulse width modulation method for a three-phase four-bridge arm voltage type inverter, on one hand, according to the state of A, B, C three-phase control quantity, a carrier selection algorithm is adopted to select a A, B, C three-phase carrier signal which is changed and combined by two paths of carrier signal sources with the same-frequency phase angle difference of 180 degrees; on the other hand, A, B, C three-phase control quantity is adopted to generate offset in real time according to a given formula, and the offset is injected into the three-phase control quantity to obtain A, B, C three-phase modulation signals. The optimized pulse width modulation method is equivalent to the conventional space voltage vector modulation in terms of modulation signals, and has the advantages of wide linear modulation range, high utilization rate of direct current bus voltage, good output current waveform quality and the like. When the three-phase four-bridge arm mode is used, compared with the conventional single-carrier three-dimensional space voltage vector 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 load/transformer connected in a three-phase star mode from half of the voltage of a direct current bus to one fourth, so that the problems of electromagnetic interference and the like caused by the neutral point on the floor drain current are greatly reduced; in addition, the inverter can be directly converted into a three-phase three-bridge arm mode to operate by directly switching off the N bridge arm and keeping the control method of the other three phases unchanged from the three-phase four-bridge arm mode, and compared with the conventional single-carrier two-dimensional space voltage vector 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 from half of the voltage of the direct current bus to one sixth, and the risks of electromagnetic interference and the like caused by the neutral point on the floor drain current are also greatly reduced.
The technical scheme adopted by the invention is as follows: a three-phase four-bridge arm inverter optimizing pulse width modulation method comprises the following steps:
A. acquiring a three-phase output sinusoidal current expected value of an inverter, and sampling a three-phase output current instantaneous value of the inverter in real time;
B. subtracting the three-phase current expected value of the inverter from the detected actual instantaneous current value in each control sampling period to obtain a three-phase current deviation value;
C. calculating a three-phase current control quantity according to the three-phase current deviation value;
D. calculating the 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 each input phase modulation signal with corresponding each phase carrier signal to generate a three-phase square wave signal with a variable pulse width, and using the three-phase square wave signal for controlling the on-off operation of a three-phase bridge arm of an inverter circuit;
G. selecting carrier signals modulated by N bridge arm pulse width;
H. and comparing the offset with the N bridge arm carrier signal as an N bridge arm modulation 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 inverter according to the present invention includes a power conversion circuit, a filter circuit, a controller, and a three-phase star 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, and 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 gives out three-phase output sine current expected values of the inverter according to power requirements, the controller samples three-phase output current instantaneous values of the inverter in real time, the A, B, C three-phase expected current values and the detected actual instantaneous current values are subtracted in each sampling period to obtain three-phase current deviation values, and then the current controller calculates three-phase current control amounts according to the current deviation values.
The expected value of each phase output current of the three-phase voltage type inverter is:
wherein,effective values of three-phase output current expected values of inverter A, B, C respectively, +.>A, B, C three-phase outputs respectivelyThe phase angle of the current expectation value; ω is the angular frequency of the output current.
The instantaneous values of the three phases of desired output currents of the inverter A, B, C are respectively:
wherein I is a ,I b ,I c The effective values of the instantaneous values of the three-phase output currents of the inverter A, B, C respectively,each phase angle of A, B, C three-phase output current instantaneous values.
The controller outputs A, B, C three phases of desired output current in each control periodRespectively with the detected actual current i a ,i b ,i c Subtracting to form deviation, and the current controller calculates the current control value v according to the deviation a ,v b ,v c 。
The three-phase current control quantity v a ,v b ,v c Calculating the offset v according to a given formula p ：
v p ＝(max(v a ,v b ,v c )+min(v a ,v b ,v c ))/2
Wherein max (v a ,v b ,v c ) And max (v) a ,v b ,v c ) Respectively three-phase current control quantity v a ,v b ,v c Maximum and minimum values of (a); wherein V is dc 2 is the amplitude of the carrier signal;
the three-phase current control quantity v a ,v b ,v c Respectively adding the offset v p The following steps are obtained:
wherein v is ao ,v bo ,v co A, B, C three-phase modulated signals, respectively.
The three-phase current control quantity v a ,v b ,v c And is also used as input quantity for selecting A, B, C three-phase carrier signals: first, the controller controls the three-phase control quantity v a ,v b ,v c And sorting the three-phase carriers according to the magnitude of the control quantity of each phase to determine the grouping type, and then selecting the corresponding three-phase carrier from the carrier selection table 1 (or the carrier selection table 2) through a table lookup according to the grouping type, wherein the three-phase carrier is formed by changing and combining two paths of bipolar triangular (or saw-tooth) signal source carriers 1 and 2 which are the same in frequency and 180 degrees in phase difference. In an embodiment, at t 1 —t 2 Within a period of time v c ≥v b ＞v a If the table 1 is selected according to the carriers, the carriers of the A phase and the C phase are selected as the carrier 1, and the carriers of the B phase are selected as the carrier 2; if table 2 is selected according to the carriers, carrier 2 is selected for the a-phase and C-phase carriers, and carrier 1 is selected for the B-phase carriers.
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. The three-phase difference signal is compared with zero through a comparator, so that a three-phase square wave signal with a variable pulse width is generated to control the on-off of a A, B, C 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 of the phase leg opens the upper leg and opens the lower leg of the corresponding phase leg; otherwise, when any phase difference signal is smaller than zero, the generated driving signal of the phase bridge arm cuts off the upper bridge arm of the corresponding phase bridge arm and opens the lower bridge arm.
When the inverter operates in a three-phase four-leg mode, the switching control signals of the N leg are also generated in a pulse width modulation mode: the offset v p Will be the modulated signal, the carrier signal of which is available from either carrier 1 or carrier 2, or both. When the inverter operates in a three-phase three-leg mode, all switches of the N leg are set to off, i.e., sn+=sn- =0.
The invention provides an optimized pulse width modulation method of a three-phase four-bridge arm inverter for the inverter, and the optimized pulse width modulation method adopts a modulation signal equivalent to the conventional space voltage vector modulation and has the advantages of wide linear modulation range, high utilization rate of direct current bus voltage, good waveform quality of output current and the like. When the three-phase four-bridge arm mode is used, compared with the conventional single-carrier three-dimensional space voltage vector 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 load/transformer connected by the three-phase star from half of the voltage of the direct current bus to one fourth, so that the problems of electromagnetic interference and the like caused by the neutral point on the floor drain current are greatly reduced. The invention adopts the changed carrier wave to modulate according to the discovered rule, and obviously reduces the common-mode voltage disturbance of the neutral point of the star-connected three-phase load/transformer on the premise of not changing the main performance indexes (such as linear modulation range, DC bus voltage utilization rate, output voltage/current waveform quality, switching loss and the like) of the conventional pulse width modulation method. In addition, the inverter can be directly converted into a three-phase three-bridge arm mode to operate by directly switching off the N bridge arm and keeping the control method of the other three phases unchanged from the three-phase four-bridge arm mode, and compared with the conventional single-carrier two-dimensional space voltage vector 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 from half of the voltage of the direct current bus to one sixth, so that the risks of electromagnetic interference and the like caused by the neutral point on the floor drain current are greatly reduced.
What is not described in detail in this specification is prior art known to those skilled in the art.
Claims (6)
1. The optimized pulse width modulation method for the three-phase four-bridge arm inverter is characterized by comprising the following steps of:
A. acquiring a three-phase output sinusoidal current expected value of an inverter, and sampling a three-phase output current instantaneous value of the inverter in real time;
B. subtracting the three-phase current expected value of the inverter from the detected actual instantaneous current value in each control sampling period to obtain a three-phase current deviation value;
C. calculating a three-phase current control quantity according to the three-phase current deviation value;
D. calculating the 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 each input phase modulation signal with corresponding each phase carrier signal to generate a three-phase square wave signal with a variable pulse width, and using the three-phase square wave signal for controlling the on-off operation of a three-phase bridge arm of an inverter circuit;
G. selecting carrier signals modulated by N bridge arm pulse width;
H. comparing the offset with the N bridge arm carrier signal as an N bridge arm modulation signal to obtain a pulse width signal for controlling the on-off of an N bridge arm switch;
in the step D, the three-phase current control quantity v is adopted a ,v b ,v c Calculating the offset v according to a given formula p ：
v p ＝(max(v a ,v b ,v c )+min(v a ,v b ,v c ))/2
Wherein max (v a ,v b ,v c ) And max (v) a ,v b ,v c ) Respectively three-phase current control quantity v a ,v b ,v c Maximum and minimum values of (a); wherein V is dc 2 is the amplitude of the carrier signal;
the three-phase current control quantity v a ,v b ,v c Respectively adding the offset v p The following steps are obtained:
wherein v is ao ,v bo ,v co A, B, C three-phase modulation signals respectively;
the three-phase carrier signal in the step E is formed by combining two paths of carrier signal sources; the two paths of carrier signal sources consist of a carrier 1 and a carrier 2 which are bipolar triangles or saw teeth with the same frequency and 180 degrees phase difference;
the step E specifically comprises the following steps: sorting the three-phase current control quantity according to the numerical value of each phase control quantity, determining the grouping type of the control quantity, and then carrying out change selection from a carrier selection table 1 or a carrier selection table 2 by looking up a table for the grouping type of the control quantity to obtain three-phase carriers;
the judgment logic of the carrier selection table 1 is as follows:
when v a >v b ≥v c When the method is used, the carrier 1 is selected as the A phase carrier, the carrier 2 is selected as the B phase carrier, and the carrier 1 is selected as the C phase carrier;
when v c ≥v b >v a When the method is used, the carrier 2 is selected as the carrier of the A phase, the carrier 1 is selected as the carrier of the B phase, and the carrier 2 is selected as the carrier of the C phase;
when v b ≥v a >v c When the method is used, the carrier 1 is selected as the carrier of the A phase, the carrier 2 is selected as the carrier of the B phase, and the carrier 2 is selected as the carrier of the C phase;
when v c >v a ≥v b When the method is used, the carrier 2 is selected as the carrier of the A phase, the carrier 1 is selected as the carrier of the B phase, and the carrier 1 is selected as the carrier of the C phase;
when v b >v c ≥v a When the method is used, the carrier 1 is selected as the carrier of the A phase, the carrier 1 is selected as the carrier of the B phase, and the carrier 2 is selected as the carrier of the C phase;
when v a ≥v c >v b When the method is used, the carrier 2 is selected as the carrier of the phase A, the carrier 2 is selected as the carrier of the phase B, and the carrier 1 is selected as the carrier of the phase C;
the judgment logic of the carrier selection table 2 is as follows:
when v a >v b ≥v c When the method is used, the carrier 2 is selected as the carrier of the A phase, the carrier 1 is selected as the carrier of the B phase, and the carrier 2 is selected as the carrier of the C phase;
when v c ≥v b >v a When the method is used, the carrier 1 is selected as the A phase carrier, the carrier 2 is selected as the B phase carrier, and the carrier 1 is selected as the C phase carrier;
when v b ≥v a >v c When the method is used, the carrier 2 is selected as the carrier of the A phase, the carrier 1 is selected as the carrier of the B phase, and the carrier 1 is selected as the carrier of the C phase;
when v c >v a ≥v b When the method is used, the carrier 1 is selected as the carrier of the A phase, the carrier 2 is selected as the carrier of the B phase, and the carrier 2 is selected as the carrier of the C phase;
when v b >v c ≥v a When the method is used, the carrier 2 is selected as the carrier of the phase A, the carrier 2 is selected as the carrier of the phase B, and the carrier 1 is selected as the carrier of the phase C;
when v a ≥v c >v b When the method is used, the carrier 1 is selected as the A phase carrier, the carrier 1 is selected as the B phase carrier, and the carrier 2 is selected as the C phase carrier.
2. The optimized pulse width modulation method of the three-phase four-leg inverter according to claim 1, characterized in that: in the step F, the three-phase modulation signals and the corresponding three-phase carrier signals are subtracted to obtain three-phase difference signals; comparing the three-phase difference signal with zero; when any phase difference signal is greater than or equal to zero, the generated switch driving signal S+ is 1, an upper bridge arm of a corresponding phase bridge arm is opened, and a lower bridge arm is disconnected; conversely, when any phase difference signal is smaller 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 opened; wherein, SA+ refers to the switch driving signal of the A phase bridge arm, SB+ refers to the switch driving signal of the B phase bridge arm, and SC+ refers to the switch driving signal of the C phase bridge arm.
3. The optimized pulse width modulation method of the three-phase four-leg inverter 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; comparing the three-phase difference signal with zero; when the difference signal of the N bridge arm is more than or equal to zero, opening the upper bridge arm of the corresponding N bridge arm and disconnecting the lower bridge arm of the breaker; otherwise, when the difference signal of the N bridge arm is smaller than zero, the upper bridge arm of the N bridge arm is disconnected and the lower bridge arm of the N bridge arm is opened.
4. The optimized pulse width modulation method of the three-phase four-leg inverter according to claim 2, characterized in that: when the inverter operates in a three-phase three-leg mode, all switches of the N leg are set to be turned off.
5. The optimized pulse width modulation system of the three-phase four-bridge arm inverter is characterized in that the system is used for realizing the optimized pulse width modulation method of the three-phase four-bridge arm inverter according to claim 1; the device comprises a current controller, a bias amount calculating 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 to a current controller; the current controller calculates a three-phase current control quantity according to the current deviation; the current controller outputs three-phase current control quantity to the offset calculating module; the offset calculation module calculates and generates an offset according to the three-phase current control quantity; adding and calculating 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 a 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 each phase with corresponding carrier signals of each phase to generate driving signals of the three-phase bridge arms.
6. The optimized pulse width modulation system of the three-phase four-leg inverter according to claim 5, 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 the on-off of the N-leg switch.
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