CN111817578A - Single-three phase power supply conversion system based on power electronic transformer - Google Patents
Single-three phase power supply conversion system based on power electronic transformer 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
- H02M5/00—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases
- H02M5/40—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc
- H02M5/42—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters
- H02M5/44—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac
- H02M5/453—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a triode or transistor type requiring continuous application of a control signal
- H02M5/458—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
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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
- H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
- H02M1/088—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters for the simultaneous control of series or parallel connected semiconductor devices
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/12—Arrangements for reducing harmonics from ac input or output
- H02M1/126—Arrangements for reducing harmonics from ac input or output using passive filters
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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
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
- H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
- H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
- H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
- H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/33569—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements
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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
- H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
- H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
- H02M7/06—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes without control electrode or semiconductor devices without control electrode
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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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Abstract
The invention relates to a single-three phase power supply conversion system based on a power electronic transformer and a control method. The single-three phase power conversion system includes: the system comprises a single-phase rectification input stage, a high-frequency transformation isolation stage, a three-phase inversion output stage and a low-pass filter; an uncontrolled rectification strategy is adopted for the secondary side diode rectifying circuits of the transformer in the single-phase rectifying input stage and the high-frequency voltage transformation isolation stage; outputting high-frequency square waves by adopting an EPWM control strategy for a primary side single-phase inversion H-bridge circuit of a transformer in the high-frequency voltage transformation isolation stage; and the SVPWM control strategy is adopted for the three-phase inversion output stage, so that the variable-frequency variable-voltage control of the three-phase inversion output voltage is realized. The transformation system and the control method can avoid the problems of distortion and harmonic pollution of the three-phase alternating voltage waveform after inversion; the direct current bus can obtain voltages of different grades through the transformation of the high-frequency transformer, the transformation and frequency conversion output after three-phase inversion is realized, and the direct current bus is used for power utilization occasions where single-phase power is converted into three-phase power.
Description
Technical Field
The invention relates to the field of power systems, in particular to a single-three phase power supply conversion system based on a power electronic transformer and a control method.
Background
In an electric railway system, an industrial power system, and a domestic power system, a technology for converting a single-phase power supply into a three-phase power supply has not been well solved for a long time.
The circuit in the prior art mostly adopts a typical AC-DC-AC topological structure, and although the circuit topological structure is simple, the circuit control is simple, and the dynamic response is good, the isolation of a rectification stage and an inversion stage in a single-three-phase inversion power supply is lacked, and the distortion, harmonic pollution and the like of the waveform of the inverted three-phase alternating voltage can be caused. Meanwhile, the circuit topology of the prior technical scheme does not realize the function of voltage transformation, and the three-phase high-voltage power utilization occasion after single-three-phase power transformation cannot be met.
Disclosure of Invention
The invention aims to provide a single-three phase power supply conversion system and a control method based on a power electronic transformer, which aim to solve the problems that the prior art scheme circuit lacks the isolation of a rectifier stage and an inverter stage in a single-three phase inverter power supply, and the distortion and harmonic pollution of the waveform of three-phase alternating voltage after inversion can be caused.
In order to achieve the purpose, the invention provides the following scheme:
a power electronic transformer based single-three phase power conversion system comprising: the system comprises a single-phase rectification input stage, a high-frequency transformation isolation stage, a three-phase inversion output stage and a low-pass filter;
from left to right, the single-phase rectification input stage, the high-frequency transformation isolation stage, the three-phase inversion output stage and the low-pass filter are connected in sequence; the single-phase rectification input stage is used for rectification; the high-frequency voltage transformation isolation stage is used for reducing voltage ripples and oscillation of the direct-current bus, so that the direct-current bus obtains voltages of different levels, and voltage transformation and frequency conversion output after three-phase inversion is realized; the three-phase inversion output stage is used for outputting the voltage transformation and frequency conversion after three-phase inversion; the low-pass filter is used for filtering out clutter in the three-phase alternating current;
an uncontrolled rectification strategy is adopted for the single-phase rectification input stage and the secondary side diode rectification circuit of the transformer in the high-frequency voltage transformation isolation stage; outputting a high-frequency square wave by adopting an Equal Pulse Width Modulation (EPWM) control strategy for a primary side single-phase inverter H-bridge circuit of a transformer in a high-frequency voltage transformation isolation stage; and a voltage Space Vector Pulse Width Modulation (SVPWM) control strategy is adopted for the three-phase inversion output stage, so that the variable-frequency variable-voltage control of the three-phase inversion output voltage is realized.
Optionally, the single-phase rectification input stage specifically includes: AC side filter inductor LpFirst diode uncontrolled rectification H bridge and direct current voltage stabilization filter capacitor Cp(ii) a The diode uncontrolled rectifying H bridge comprises a first diode, a second diode, a third diode and a fourth diode;
AC side filter inductor LpIs connected in series withBetween the first diode and the second diode in the diode uncontrolled rectifying H bridge, the diode uncontrolled rectifying H bridge and the DC voltage stabilizing filter capacitor CpParallel connection; after the sine alternating current is introduced into the power grid side, if the voltage of the power grid side is positive and negative, the current sequentially passes through the first diode, the inductance-resistance load and the fourth diode from the positive electrode and flows back to the negative electrode; and if the voltage on the grid side is positive and negative, the current sequentially passes through the third diode, the resistance-inductance load and the second diode from the positive electrode and flows back to the negative electrode.
Optionally, the high-frequency voltage transformation isolation stage specifically includes: a DC-DC high frequency isolation converter;
the primary side of the DC-DC high-frequency isolation converter comprises an IGBT single-phase inversion H bridge; the secondary side of the DC-DC high-frequency isolation converter comprises a second diode uncontrolled rectifying H bridge;
for a primary side single-phase H-bridge inverter circuit topology of a high-frequency voltage transformation isolation stage transformer, an EPWM high-frequency modulation algorithm is adopted; compiling and downloading an EPWM program into a DSPF28335 through a C compiler and a Code Composer Studio (CCS) software in a computer, controlling four pins of an EPWM-1A, EPWM-1B, EPWM-2A, EPWM-2B of the DSP, and outputting a high-frequency square wave signal with a duty ratio of 50%, a frequency of 10kHz and a voltage of 15V as a driving signal of an Insulated Gate Bipolar Transistor (IGBT) switching tube through level amplification of an optical coupling level conversion module; through EPWM algorithm modulation, input waveforms of a switch tube S1 and a switch tube S4 in the IGBT single-phase inversion H bridge are the same, input waveforms of a switch tube S3 and a switch tube S2 are the same, and input waveforms of an upper switch tube and a lower switch tube of the same bridge arm are complementary; and operating the EPWM program, inverting the direct-current voltage into high-frequency square waves to be output, and further coupling the high-frequency square waves to the secondary side through a high-frequency transformer.
Optionally, the three-phase inverter output stage specifically includes: DC voltage-stabilizing filter capacitor CsAnd an IGBT three-phase inversion H bridge; the direct current voltage-stabilizing filter capacitor CsThe IGBT three-phase inversion H bridge is connected in parallel;
and controlling the three-phase inversion output stage based on an SVPWM algorithm under a 120-degree coordinate system.
Optionally, the low-pass filter is an LCL low-pass filter; the LCL low pass filter specifically includes: six inductors and three capacitors;
the six inductors are connected in series in pairs, a connecting wire between the two serially connected inductors is connected with one end of a capacitor, and one ends of the two serially connected inductors are connected with connecting wires of two switching tubes in one bridge arm of the IGBT three-phase inverter H bridge; the other ends of the three capacitors are connected.
Optionally, the method further includes: a load;
and the load is connected with the other ends of the two inductors connected in series in the low-pass filter.
A control method for a power electronic transformer based single-three phase power conversion system, the control method comprising:
single-phase electric USThe conversion from alternating current to direct current is completed through a single-phase rectification input stage and is processed through a direct current voltage-stabilizing filter capacitor CpPost-output voltage-stabilizing direct current Udc1The polarity is positive, negative and positive, and is supplied to a middle high-frequency voltage transformation isolation stage;
Udc1obtaining a high-frequency square wave voltage U after passing through a primary side single-phase inversion H bridge of a transformer in the high-frequency transformation isolation stage1And obtaining secondary side high-frequency square wave U after coupling and voltage transformation of a high-frequency transformer2And then the direct current bus voltage U is rectified and output by a secondary side diode uncontrolled rectification H bridgedc2；
Compiling and downloading the SVPWM algorithm program into DSPF28335 through CCS software in a computer, controlling the SVPWM algorithm program in the DSP, and using Udc2Three-phase symmetrical alternating current with adjustable output frequency and amplitude is output through three-phase inversion of an H bridge, and then is processed by an LCL low-pass filter to drive a load to operate.
According to the specific embodiment provided by the invention, the invention discloses the following technical effects: the invention provides a single-three phase power supply conversion system based on a power electronic transformer and a control method, wherein the single-three phase power supply conversion system topology can reduce the voltage ripple and oscillation of a direct current bus by isolating through a high-frequency transformer, improve the voltage utilization rate of the direct current bus and avoid the problems of distortion and harmonic pollution of the waveform of three-phase alternating current voltage after inversion; meanwhile, the direct current bus can obtain voltages of different levels through the transformation of the high-frequency transformer, so that transformation and frequency conversion output after three-phase inversion is realized, and the direct current bus can be used in power utilization occasions where single-phase power is converted into three-phase power.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.
FIG. 1 is a circuit diagram of a single-three phase power conversion system based on a power electronic transformer according to the present invention;
FIG. 2 is a schematic diagram of a single-phase rectification input stage circuit topology according to the present invention;
FIG. 3 is a schematic diagram of a topology of a high frequency transformer isolation stage circuit according to the present invention;
fig. 4 is a circuit topology structure diagram of a three-phase inverter output stage provided by the present invention;
FIG. 5 is a sector space distribution diagram under a 120 ° coordinate system provided by the present invention;
FIG. 6 is a timing diagram of the PWM output of each phase provided by the present invention;
FIG. 7 is a graph of simulation results provided by the present invention; FIG. 7(a) shows an input stage input voltage U provided by the present inventionsA waveform simulation diagram; FIG. 7(b) shows the input voltage U of the isolation stage provided by the present inventiondc1A waveform simulation diagram; FIG. 7(c) is a diagram of a primary-side inverted square wave U of the isolated-stage transformer according to the present invention1A simulation graph; FIG. d shows a secondary side coupled square wave U of the isolation stage transformer provided by the present invention2A simulation graph; FIG. 7(e) shows the output voltage U of the isolation stage provided by the present inventiondc2A waveform simulation diagram; fig. 7(f) is a waveform diagram of an output stage three-phase inverter phase voltage provided by the present invention;
FIG. 8 is a block diagram of an experimental platform for a single-three phase power conversion system according to the present invention;
FIG. 9 is a schematic diagram of experimental results provided by the present invention; FIG. 9(a) is a diagram of the input stage voltage waveform provided by the present invention; FIG. 9(b) shows the input voltage U of the DC-DC isolation stage provided by the present inventiondc1Output voltage Udc2A waveform diagram; FIG. 9(c) shows the primary side inverted voltage U of the DC-DC isolated-stage transformer provided by the present invention1And secondary side coupling voltage U2An interface diagram; fig. 9(d) is a three-phase sinusoidal phase voltage interface diagram of a three-phase inverter output stage according to the present invention; fig. 9(e) is an interface diagram of the three-phase sinusoidal phase voltage effective value provided by the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention aims to provide a single-three phase power supply conversion system and a control method based on a power electronic transformer, which can avoid the problems of distortion and harmonic pollution of the waveform of three-phase alternating voltage after inversion; meanwhile, the direct current bus can obtain voltages of different levels through the transformation of the high-frequency transformer, the transformation and frequency conversion output after three-phase inversion is realized, and the method is used for power utilization occasions where single-phase power is converted into three-phase power.
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.
Fig. 1 is a circuit diagram of a single-three phase power conversion system based on a power electronic transformer, as shown in fig. 1, which sequentially comprises a single-phase rectification input stage, a high-frequency transformation isolation stage, a three-phase inversion output stage and an LCL low-pass filter from left to right.
The single-phase rectification input stage is composed of an AC side filter inductor LpUncontrolled rectification of diodeH-bridge and DC voltage-stabilizing filter capacitor CpForming; the input stage is analyzed, a circuit after the input stage stabilizes the direct current capacitor is equivalent to a resistance-inductance load, as shown in fig. 2, because the diode has the characteristic of unidirectional conduction, in order to make the topological structure and the control strategy simpler and more practical and reduce the switching loss brought by the switch tube, the input stage adopts the control strategy of uncontrolled rectification. After sine alternating current is introduced to the power grid side, if the voltage of the power grid side is positive and negative, current sequentially flows through the 1 tube and the inductance-resistance load from the positive electrode (upper), and the 4 tube flows back to the negative electrode (lower); when the voltage on the grid side is positive and negative, the current passes through the 3 tubes from the positive electrode (lower) in sequence, the resistance-inductance load is carried out, and the 2 tubes flow back to the negative electrode (upper). Obviously, the sine alternating current is rectified after passing through an H-bridge converter consisting of uncontrolled diodes and filtering and stabilizing the direct current by a direct current capacitor, and the rectified direct current voltage Udc1The polarity of (1) is positive at the top and negative at the bottom.
The high-frequency transformation isolation stage is composed of a DC-DC high-frequency isolation converter, wherein the primary side of the high-frequency transformer is composed of an IGBT single-phase inversion H bridge, and the secondary side of the high-frequency transformer is composed of a diode uncontrolled rectification H bridge; the high-frequency transformer has the advantages of high power density, small volume, high efficiency and the like, and is very suitable for occasions of high-frequency transformation isolation. The isolation stage transfers the electric energy from the input stage to the output stage through a proper control strategy, and the conversion of voltage grades on two sides is realized through a high-frequency transformer. The isolation stage is composed of a high-frequency transformer, a primary side IGBT single-phase inversion H bridge and a secondary side diode uncontrolled rectification H bridge. The topological structure is shown in figure 3:
and for a primary side single-phase H-bridge inverter circuit topology of the high-frequency voltage transformation isolation stage transformer, an EPWM high-frequency modulation algorithm is adopted. The EPWM program is compiled and downloaded into DSPF28335 through CCS software in a computer, four pins of EPWM-1A, EPWM-1B, EPWM-2A, EPWM-2B of the DSP are controlled, and four paths of high-frequency square wave signals with duty ratio of 50%, frequency of 10kHz and voltage of 15V are output as driving signals of an IGBT switching tube through level amplification of an optical coupling level conversion module. In the experiment, the input waveforms of the S1 and S4 switching tubes are the same, the input waveforms of the S3 and S2 switching tubes are the same, and the input waveforms of the upper switching tube and the lower switching tube of the same bridge arm are complementary through EPWM algorithm modulation. Running EPWM program to convert the DC voltage Udc1Is converted intoOutputting the high-frequency square wave, and further coupling the high-frequency square wave to a secondary side through a high-frequency transformer; and for the topology of the single-phase H-bridge rectification circuit at the secondary side of the isolation-level transformer, the uncontrolled rectification control strategy which is the same as that of the input stage is adopted.
Three-phase inversion output stage filter capacitor C stabilized by direct currentsAnd an IGBT three-phase inversion H bridge; the SVPWM technology has the advantages of high direct-current voltage utilization rate, low alternating-current harmonic content and the like, and becomes the mainstream of the current three-phase inversion technology. For a three-phase inversion output stage, the topological structure is shown in fig. 4, and the invention adopts a novel SVPWM algorithm based on a 120-degree coordinate system for control. The coordinate of a voltage space vector under a 120-degree coordinate system is obtained by subtracting three-phase reference voltages through the algorithm. The action time of the sector where the voltage space vector is located and the basic voltage vector can be accurately obtained by performing simple four-rule operation and logic judgment on the coordinate, and the complex coordinate transformation and operation process is really eliminated, so that the SVPWM algorithm structure is effectively simplified, the operation time of an algorithm program is shortened, and the operation efficiency of the algorithm is improved.
The novel 120 ° SVPWM algorithm inverse modulation rationale is given below:
(1) sector determination
As shown in FIG. 5, which is a spatial distribution diagram of sectors in a 120 coordinate system, the plane is divided into three 120 regions by the A axis, the B axis and the C axis. When the direction of the axis A is taken as the positive direction of a transverse axis under a 120-degree coordinate system, and the direction of the axis B is taken as the positive direction of an oblique axis, defining the area AOB as a No. 1 large sector; similarly, the BOC of the defined area is a No. 2 large sector; the area COA is defined as large sector number 3. For the convenience of subsequent processing, the A axis is classified as the large sector No. 1, the B axis is classified as the large sector No. 2, and the C axis is classified as the large sector No. 3.
The three-phase reference voltage respectively obtains coordinates of a voltage space vector under a No. 1, No. 2 and No. 3 120-degree coordinate system through No. 1, No. 2 and No. 3 coordinate transformation, and the coordinates are shown in formulas (1), (2) and (3):
coordinate transformation No. 1:
coordinate transformation No. 2:
coordinate transformation No. 3:
in the formula of UA、UB、UCRespectively three-phase reference voltage value, x1And x2Respectively, a horizontal axis coordinate and an oblique axis coordinate of the voltage space vector under a 120-degree coordinate system. The coordinate x of the voltage space vector under three different 120-degree coordinate systems can be obtained through three coordinate transformations1And x2. If the x is obtained by coordinate transformation of i (i is 1, 2, 3)1>0 and x2>0, the available voltage space vector is in the i-th large sector. From x1And x2The magnitude relationship of (a) can be obtained as the number of small sectors where the voltage space vector is located, when x1>x2When j is 1, the space vector is in the small sector of (i); otherwise j is 2, the space vector is in # 2 small sector. The specific sector in which the available voltage space vector is located is thus as shown in equation (4):
N＝2*(i-1)+j (4)
where I is the number of large sectors where the voltage space vector is located, j is the number of small sectors where the voltage space vector is located, and N ═ I (I, II, III, IV, V, VI)
(2) Fundamental voltage space vector action time solution
Assuming that the voltage space vector is in the large sector of i (i is 1, 2, 3), the coordinate of the voltage space vector in the coordinate system of i is (x)1，x2) For convenience of subsequent calculation, for x1And x2And (3) carrying out normalization treatment: m is 3x1/2Udc，n＝3x2And/2 Udc, Udc is the direct current bus voltage.
At this time, the effect of the voltage space vector in the carrier period Ts may be synthesized by two basic voltage space vectors on the coordinate axis. According to the principle of 'volt-second equivalence': t is1＝mTs，T2N Ts, wherein T1Is a 120 degree coordinateTime of action, T, of the space vector of the basic voltage on the lower horizontal axis2The action time on the oblique axis.
The projection of the basic voltage space vector on the coordinate axis of 120 degrees on the non-coordinate axis is the basic voltage space vector on the coordinate axis, and the action effect in unit time is equal to the effect of the two basic vectors on the coordinate axis acting together in the same time. Defining vectors on non-coordinate axes as strong vectors, e.g. U in FIG. 53、U5、U6The vector on the coordinate axis is a weak vector, such as U in FIG. 41、U2、U4. The effect of the voltage space vector on the carrier period can be synthesized from the two base vectors in the sector in which it is located. Table 1 shows a strong vector and weak vector action time table of six sectors provided by the present invention, where Tq is the action time of the strong vector and Tr is the action time of the weak vector, as shown in table 1.
TABLE 1
(3) Fundamental voltage space vector action timing
The timing of the action of the basic vector is illustrated by the output timing of the seven-segment PWM as used herein. As shown in fig. 6, each phase PWM state transition time point divides one carrier period into seven periods.
The operation time of each phase PWM can be obtained according to the formula (5):
in the formula T1For operating the PWM reversal time of phase in advance in a PWM cycle, T2Is the turn-over time, T, of the secondary operating phase PWM3The inversion time of the post-phase PWM. Table 2 shows the operation sequence of each phase of the voltage space vector provided by the present invention in each sectorTable, as shown in table 2:
TABLE 2
| N | T1 | T2 | T3 |
| 1 | A | B | C |
| 2 | B | A | C |
| 3 | B | C | A |
| 4 | C | B | A |
| 5 | C | A | B |
| 6 | A | C | B |
The invention uses the novel 120-degree SVPWM algorithm to realize SVPWM inversion debugging, and a corresponding SVPWM algorithm program is compiled according to the principle.
The LCL low-pass filter is composed of six inductors and three capacitors.
The input stage realizes a rectification function (AC/DC conversion function), wherein a DC energy storage capacitor CpHas the function of stabilizing voltage. The inversion full-control H bridge of the subsequent isolation stage realizes the functions of electric energy conversion and energy transfer, and the electric energy conversion and the energy transfer work cooperatively, so that the control difficulty is reduced.
The full-control H-bridge circuit on the primary side of the isolation-level transformer is composed of four high-voltage high-power switching devices to realize the function of converting electric energy, and the middle high-frequency transformer is a power electronic transformer and provides a hardware basis for realizing energy flow, electrical isolation and voltage grade conversion.
The three-phase full-control bridge structure of the inverter stage consists of 6 high-voltage or low-voltage high-power components, is a three-phase inverter circuit and outputs three-phase alternating current, an LCL low-pass filter can filter out clutter in the three-phase alternating current, and finally, the inverter stage outputs the three-phase alternating current with adjustable frequency and voltage to drive a load to operate.
The invention is mainly characterized in that a hardware basis for realizing electric energy transmission transformation, voltage grade transformation and electrical isolation of a rectifier stage and an inverter stage is provided, and finally, the isolated transformation of a single-three phase power supply is realized.
The transformation isolation type single-three phase power supply conversion system based on the power electronic transformer only uses almost half of full control type switching devices, greatly reduces the conduction loss of matching circuits and systems of driving, protection and the like of the switching devices on the premise of realizing high-performance single-three phase power supply conversion, and promotes the system to obtain higher efficiency. Meanwhile, the use of a high-frequency transformer in the DC-DC converter enables the whole system topology to realize voltage transformation isolation, and meanwhile, the system topology has a simplified hardware structure, a smaller volume and higher power density.
Energy flow and power variation analysis in the entire system can be divided into the following three steps:
1) single-phase electric USThe conversion from alternating current to direct current is completed through a single-phase rectification input stage and is processed through a direct current voltage-stabilizing filter capacitor CpPost-output voltage-stabilizing direct current Udc1The polarity is positive at the top and negative at the bottom and is supplied to the middle isolation stage;
2)Udc1obtaining a high-frequency square wave voltage U after passing through a primary side single-phase inversion H bridge of an isolation-stage transformer1And coupling and transforming (boosting or reducing) the voltage by a high-frequency transformer to obtain a secondary side high-frequency square wave U2And then the direct current bus voltage U is rectified and output by a secondary side diode uncontrolled rectification H bridgedc2。
3) The SVPWM algorithm program is compiled by CCS software in a computer and downloaded into DSPF 28335. Controlled by SVPWM algorithm program in DSP, Udc2Three-phase symmetrical alternating current with adjustable output frequency and amplitude is output through three-phase inversion of an H bridge, and then is processed by an LCL low-pass filter to drive a load to operate.
The whole system can complete the transfer (flow) conversion of electric energy, the electric isolation between the rectifier stage and the inverter stage and the conversion of voltage grade. Meanwhile, the use of a high-frequency transformer in the power electronic transformer enables the whole system topology to realize voltage transformation isolation, and meanwhile, the power electronic transformer has a simplified hardware structure, a smaller volume and higher power density.
The single-three phase power supply conversion system based on the power electronic transformer provides a hardware basis for realizing single-three phase power supply conversion, and simultaneously adopts an SVPWM (space vector pulse width modulation) inversion modulation algorithm to realize three-phase inversion (variable frequency and variable voltage) control. The operation process is as follows: a specific switching mode is formed by controlling six power switching tubes of a three-phase inversion H bridge to generate three-phase PWM waves, and the output waveform is close to an ideal sine wave as much as possible.
Therefore, the single-three phase power conversion system based on the power electronic transformer adopts an uncontrolled rectification strategy for the secondary side diode rectification circuits of the input stage transformer and the isolation stage transformer; outputting a high-frequency square wave to a primary side single-phase inverter H-bridge circuit of an isolation-stage transformer by adopting an EPWM control strategy; and the SVPWM control strategy is adopted for the three-phase inversion output stage, so that the variable-frequency variable-voltage control of the three-phase inversion output voltage can be realized, and the overall performance of the system is improved. The so-called SVPWM control is to generate a three-phase PWM wave by controlling six power switching tubes of a three-phase inverter H-bridge to form a specific switching pattern and to make an output waveform close to an ideal sine wave as much as possible.
In practical application, the invention can also adopt an SPWM inversion modulation algorithm to realize three-phase inversion (variable frequency and variable voltage) control. The operation process is as follows: the three-phase bridge inversion SPWM algorithm is used for modulating waves into three-phase symmetrical voltages with phase angles of 120 degrees, and carrier waves are isosceles triangle waves. A bipolar PWM control mode is adopted, the on-off of a switching tube of a certain bridge arm is controlled by comparing the size of a sine modulation wave Ur with the size of a carrier Uc, and the process is the same as single-phase inversion.
When Ur is larger than Uc, controlling the upper bridge arm of a certain phase to be switched on, and switching off the lower bridge arm; and when Ur is less than Uc, controlling the upper bridge arm of a certain phase to be switched off, and controlling the lower bridge arm to be switched on. Three sine waves with the mutual difference of 120 degrees are compared with the same triangular wave, so that the on-off time and the on-off time of the three bridge arm switching tubes can be obtained.
The amplitude and the frequency of the three-phase sine modulation wave Ur are changed, so that the amplitude and the frequency of the three-phase inversion output voltage can be changed.
The invention adopts Matlab/Simulink software to establish a simulation model of a single-three phase power supply conversion system, which mainly comprises a single-phase rectification input stage, a high-frequency isolation stage and a three-phase inversion output stage.
The parameters in the simulation model are as follows: the effective value of the input stage voltage Us is 20V, the inductance Lp is 0.004H, and the capacitance Cp on both sides of the isolation stage is 0.08F. In the output stage, in view of the fact that a power supply conversion system is an open loop system and in order to enable SVPWM algorithm to be more convenient to calculate, the method carries out macro definition on some common parameters in the algorithm, and supposes that three-phase inversion input direct current bus voltage U is adopteddc2100V, three-phase AC reference voltage phase voltage UA，UB，UCPeak value Upk50V, frequency f 50Hz, carrier frequency fcIs 10kHz. When the actually input direct current bus voltage is other values, the actually output three-phase inverter phase voltage peak value is in direct proportion (U)dc2/Upk2) increase or decrease accordingly. The simulation time was set to 3 s.
After simulation operation, data of oscilloscopes at all levels are exported and redrawn by OriginPro 9.1 software, so that the following simulation result can be obtained, and fig. 7 is a simulation result curve chart provided by the invention and is shown in fig. 7.
The positive line AC voltage Us with 20V effective value is input to the input stage, and as shown in FIG. 7(a), the DC regulated voltage U is obtained after uncontrolled rectificationdc1The peak value is about 23.2V, and as shown in FIG. 7(b), 2.8-3.0 s of amplification observation shows that the voltage value oscillates between 23.10-23.20V and the peak is large. U shapedc1The input is input to the primary side of a DC-DC isolation stage transformer controlled by the EPWM to obtain an inverted square wave U1As shown in FIG. 7, the amplified observation is performed for 1.4-1.5 s, and it is seen that the upper and lower voltages are symmetrical, the absolute peak values are 23V, and the frequency is 50 HZ. Square wave U1Obtaining a secondary side coupling square wave U after passing through a single-transformer high-frequency transformer2As shown in FIG. 7(d), the voltage waveform and the numerical value and U are observed under the same magnification of 1.4-1.5 s1And (5) the consistency is achieved. Will U2The input voltage is input to the uncontrolled rectifying circuit at the secondary side of the transformer to obtain an isolation stage output voltage Udc2As shown in fig. 7 (e). And 2.8-3.0 s of amplification observation is carried out, and the voltage value only oscillates between 23.02-23.07V and the peak is very small. Thus, comparing the analysis simulation chart with the simulation charts, U is found from (b), (c), (d) and (e)dc1U obtained after DC-DC isolation level electrical isolationdc2The ripple component and the oscillation peak of the waveform are both greatly reduced (by nearly 50%), and the waveform linearity is better. Will Udc2Inputting the input signal to a three-phase inverter circuit controlled by an SVPWM algorithm, taking 2.9-3.0 s for amplification and analysis to obtain a simulation graph shown in (f), wherein the three-phase inverter sine alternating current U isA，UB，UCThe amplitude of the phase voltage is about 11.5V-0.5Udc2The frequency f is 50Hz, the phases are mutually different by 120 degrees, the phases are symmetrical, and the sine degree is very good.
Experimental verification of single-three phase power supply conversion system
In order to verify the correctness, feasibility and effectiveness of the single-three phase power conversion system provided by the invention, a system experiment platform is built by utilizing a DSPTMS20F28335, an IGBT module, a single-transformer high-frequency transformer, an optocoupler level conversion module and the like according to the topological structure of the single-three phase power conversion system, and experiment verification is carried out. The experimental platform site is shown in fig. 8:
experimental parameters and procedures:
parameters of elements in the circuit: the frequency of the high-frequency transformer is 10kHz, and the transformation ratio is 1. AC side inductor LpAnd 2mH, the two-side voltage stabilizing direct-current capacitors Cp and Cs are 400V/820 uF. The sine alternating current commercial power with the effective value of 220V is regulated into sine alternating current U with the effective value of 20V and the frequency of 50HZ by a contact voltage regulatorsAnd (4) supplying the voltage to an input stage, and respectively testing output waveforms of all stages by using a FLUKE oscilloscope and a HIOKI power quality analyzer.
Experimental results and analysis:
the experimental results are shown in FIG. 9, where the DC-DC isolation stage input voltage U in FIG. 9(b)dc1Output voltage Udc2A waveform; in fig. 9(c), primary side inverted voltage U of DC-DC isolated stage transformer1(B blue) secondary side coupling voltage U2(ii) a FIG. 9(d) three-phase inverter output stage three-phase sinusoidal phase voltage UA，UB，UC。
The input stage inputs a sinusoidal alternating current U with an effective value of 20V and a frequency of 50HZ through the voltage regulation of a contact voltage regulatorsAs shown in fig. 9 (a). U shapesObtaining a direct current voltage U after input-stage uncontrolled rectificationdc125V, as shown in fig. 9(b), it was observed to have a large oscillation spike. U shapedc1Obtaining a high-frequency square wave voltage U after primary side inversion of an isolation stage transformer1The value was 23V and the frequency was 10kHz, as shown in FIG. 9 (c). U shape1Coupling and isolating the single-transformer high-frequency transformer to obtain secondary side high-frequency square wave voltage U2The value was 23V and the frequency was 10kHz, as shown in FIG. 9 (c). U shape2Obtaining stable direct current voltage U through uncontrolled rectification of secondary side of isolation stage transformerdc2As shown in fig. 9(b), 23V was observed to have a voltage ripple and oscillation spike smaller than Udc1Is greatly reduced. Then the bus DC voltage U is applieddc2Input to three-phase inverter circuitFinally, three-phase symmetrical sine alternating current U is outputA，UB，UCThe phase voltages are shown in waveforms in FIG. 9(d), the effective values of the three-phase voltages are shown in FIG. 9(e), and the peak value U of each phase voltagepkAbout the dc bus voltage U1.414 Urms 11.31V dc21/2, frequency f is 50Hz, the phases are 120 degrees different from each other, the phases are symmetrical, the sine degree is very good, and the result accords with simulation and expectation.
Therefore, the present invention can achieve the following effects:
Udc1u obtained after DC-DC high-frequency isolation level electrical isolationdc2The ripple component and the oscillation peak of the waveform are greatly reduced, and the waveform straightness is better.
The single-phase power can be directly connected into the single-three-phase power conversion system provided by the invention to output ideal symmetrical three-phase sinusoidal alternating current to supply to a three-phase load. The three-phase inversion sine alternating current waveform controlled by the SVPWM inversion modulation algorithm has symmetrical phase, good sine degree and small harmonic wave.
The single-three phase power supply conversion system topological structure based on the power electronic transformer only uses almost half of fully controlled switching devices, greatly reduces the conduction loss of matching circuits and systems of driving, protection and the like of the switching devices on the premise of realizing high-performance single-three phase power supply conversion, and promotes the system to obtain higher efficiency. The use of the high-frequency transformer enables the whole system topology to realize electrical transformation isolation, and meanwhile, the high-frequency transformer has the advantages of simple hardware structure, smaller volume, lower manufacturing cost and system reliability improvement.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other.
The principles and embodiments of the present invention have been described herein using specific examples, which are provided only to help understand the method and the core concept of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.
Claims (7)
1. A single-three phase power conversion system based on a power electronic transformer, comprising: the system comprises a single-phase rectification input stage, a high-frequency transformation isolation stage, a three-phase inversion output stage and a low-pass filter;
from left to right, the single-phase rectification input stage, the high-frequency transformation isolation stage, the three-phase inversion output stage and the low-pass filter are connected in sequence; the single-phase rectification input stage is used for rectification; the high-frequency voltage transformation isolation stage is used for reducing voltage ripples and oscillation of the direct-current bus, so that the direct-current bus obtains voltages of different levels, and voltage transformation and frequency conversion output after three-phase inversion is realized; the three-phase inversion output stage is used for outputting the voltage transformation and frequency conversion after three-phase inversion; the low-pass filter is used for filtering out clutter in the three-phase alternating current;
an uncontrolled rectification strategy is adopted for the single-phase rectification input stage and the secondary side diode rectification circuit of the transformer in the high-frequency voltage transformation isolation stage; outputting high-frequency square waves by adopting an EPWM control strategy for a primary side single-phase inversion H-bridge circuit of a transformer in the high-frequency voltage transformation isolation stage; and the three-phase inversion output stage adopts an SVPWM control strategy to realize the variable-frequency variable-voltage control of the three-phase inversion output voltage.
2. A power electronic transformer based single-three phase power conversion system according to claim 1, wherein said single phase rectification input stage comprises: AC side filter inductor LpFirst diode uncontrolled rectification H bridge and direct current voltage stabilization filter capacitor Cp(ii) a The diode uncontrolled rectifying H bridge comprises a first diode, a second diode, a third diode and a fourth diode;
AC side filter inductor LpConnected in series between a first diode and a second diode in the diode uncontrolled rectifying H bridge, the diode uncontrolled rectifying H bridge and a DC voltage-stabilizing filter capacitor CpParallel connection; after sine alternating current is introduced to the power grid side, if the voltage on the power grid side is positive and negative, the power grid side is electrifiedThe current flows from the anode to the cathode through the first diode, the resistance-inductance load and the fourth diode in sequence; and if the voltage on the grid side is positive and negative, the current sequentially passes through the third diode, the resistance-inductance load and the second diode from the positive electrode and flows back to the negative electrode.
3. A power electronic transformer based single-three phase power conversion system as claimed in claim 1 wherein said high frequency transformer isolation stage comprises in particular: a DC-DC high frequency isolation converter;
the primary side of the DC-DC high-frequency isolation converter comprises an IGBT single-phase inversion H bridge; the secondary side of the DC-DC high-frequency isolation converter comprises a second diode uncontrolled rectifying H bridge;
for a primary side single-phase H-bridge inverter circuit topology of a high-frequency voltage transformation isolation stage transformer, an EPWM high-frequency modulation algorithm is adopted; the EPWM program is compiled and downloaded into DSPF28335 through CCS software in a computer, four pins of EPWM-1A, EPWM-1B, EPWM-2A, EPWM-2B of the DSP are controlled, and four paths of high-frequency square wave signals with duty ratio of 50%, frequency of 10kHz and voltage of 15V are output as driving signals of an IGBT switching tube through level amplification of an optocoupler level conversion module; through EPWM algorithm modulation, input waveforms of a switch tube S1 and a switch tube S4 in the IGBT single-phase inversion H bridge are the same, input waveforms of a switch tube S3 and a switch tube S2 are the same, and input waveforms of an upper switch tube and a lower switch tube of the same bridge arm are complementary; and operating the EPWM program, inverting the direct-current voltage into high-frequency square waves to be output, and further coupling the high-frequency square waves to the secondary side through a high-frequency transformer.
4. The single-three phase power conversion system based on power electronic transformer as claimed in claim 1, wherein said three phase inverting output stage comprises: DC voltage-stabilizing filter capacitor CsAnd an IGBT three-phase inversion H bridge; the direct current voltage-stabilizing filter capacitor CsThe IGBT three-phase inversion H bridge is connected in parallel;
and controlling the three-phase inversion output stage based on an SVPWM algorithm under a 120-degree coordinate system.
5. A power electronic transformer based single-three phase power conversion system according to claim 4 wherein said low pass filter is an LCL low pass filter; the LCL low pass filter specifically includes: six inductors and three capacitors;
the six inductors are connected in series in pairs, a connecting wire between the two serially connected inductors is connected with one end of a capacitor, and one ends of the two serially connected inductors are connected with connecting wires of two switching tubes in one bridge arm of the IGBT three-phase inverter H bridge; the other ends of the three capacitors are connected.
6. A power electronic transformer based single-three phase power conversion system according to claim 5 further comprising: a load;
and the load is connected with the other ends of the two inductors connected in series in the low-pass filter.
7. A control method for a single-three phase power conversion system based on a power electronic transformer, characterized in that the control method is applied to a single-three phase power conversion system based on a power electronic transformer as claimed in any one of claims 1-6, and the control method comprises:
single-phase electric USThe conversion from alternating current to direct current is completed through a single-phase rectification input stage and is processed through a direct current voltage-stabilizing filter capacitor CpPost-output voltage-stabilizing direct current Udc1The polarity is positive, negative and positive, and is supplied to a middle high-frequency voltage transformation isolation stage;
Udc1obtaining a high-frequency square wave voltage U after passing through a primary side single-phase inversion H bridge of a transformer in the high-frequency transformation isolation stage1And obtaining secondary side high-frequency square wave U after coupling and voltage transformation of a high-frequency transformer2And then the direct current bus voltage U is rectified and output by a secondary side diode uncontrolled rectification H bridgedc2；
Compiling and downloading the SVPWM algorithm program into DSPF28335 through CCS software in a computer, controlling the SVPWM algorithm program in the DSP, and using Udc2Three-phase inversion H-bridge inversion output frequency and amplitude adjustable three-phase inverterThe alternating current is called and processed by an LCL low-pass filter to drive a load to operate.
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