CN109861550A - Bi-directional frequency converter and its control method - Google Patents
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Abstract
The present invention relates to frequency transform techniques fields, and in particular to a kind of bi-directional frequency converter and its control method, it is therefore an objective to a kind of input is provided, output can be with the converter of same frequency.Bi-directional frequency converter of the invention includes: three-phase tietransformer, cascade converter A ', B ', C ' and D '.Wherein, three-phase tietransformer uses triangle/star-like connection form, and the star contact of vice-side winding is connected to the terminal n of single phase ac side；Vice-side winding terminal a, b, c of three-phase tietransformer pass through the terminal x that cascade converter A ', B ', C ' are connected to single phase ac side respectively；Parallel cascade current transformer D ' between the terminal x and terminal n of single phase ac side；Using three terminals of three-phase tietransformer primary side winding as input, terminal x and terminal n as output, three-phase input-single-phase output is realized；Or in turn by input and output, single-phase input-three-phase output is realized.The present invention reduces intermediate link, system loss is reduced, and can realize input and output same frequency.
Description
Technical Field
The invention relates to the technical field of frequency conversion, in particular to a bidirectional frequency converter and a control method thereof.
Background
The power frequency conversion device for three-phase ac input and single-phase ac output has many uses in special cases, for example, in the case of converting three-phase commercial ac power into single-phase high-frequency induction heating power, in the case of converting three-phase 50Hz public ac power grid into 16.7Hz single-phase ac power for electric locomotives.
The conventional patent document CN108923664A (published japanese: 2018.11.30) discloses a three-phase input single-phase output frequency converter and a control strategy, where the frequency converter realizes ac-ac conversion, reduces intermediate links and system loss compared with the scheme of ac-dc-ac conversion, but cannot realize the same frequency at the input end and the output end.
Disclosure of Invention
In order to solve the above problems in the prior art, the present invention provides a bidirectional frequency converter and a control method thereof, which implement input and output with the same frequency.
In one aspect of the present invention, a bidirectional frequency converter is provided, which includes: the three-phase transformer, the cascade converter A ', the cascade converter B', the cascade converter C 'and the cascade converter D';
the three-phase connection transformer adopts a triangular/star connection mode, and a star contact point of a secondary winding is connected to a terminal n on a single-phase current-crossing side;
secondary winding terminals a, B and C of the three-phase connection transformer are connected to a terminal x on the single-phase current-intersecting side through the cascade current transformer A ', the cascade current transformer B ' and the cascade current transformer C ' respectively;
the cascade converter D' is connected in parallel between the terminal x and the terminal n on the single cross current side;
three terminals of a primary winding of the three-phase connecting transformer are used as input terminals, and a terminal x and a terminal n on the single-phase current-intersecting side are used as output terminals, so that three-phase input-single-phase output is realized; or,
and the terminal x and the terminal n on the single-phase current-intersecting side are used as input terminals, and the three terminals of the primary winding of the three-phase connecting transformer are used as output terminals, so that single-phase input-three-phase output is realized.
Preferably, the cascaded converter a ', the cascaded converter B ' and the cascaded converter C ' are all formed by cascading M identical power modules;
the cascade converter D' is formed by cascading N identical power modules;
wherein M and N are both positive integers.
Preferably, the cascaded converter a ', the cascaded converter B', the cascaded converter C 'and the cascaded converter D' are controlled by a double closed loop in which a power module capacitor voltage outer loop and respective currents are used as inner loops.
Preferably, the terminal T of the first power module in the cascaded converter a1A terminal a connected to the secondary winding of the three-phase connection transformer; terminal T of kth power module in the cascaded converter A2Terminal T connected to the (k + 1) th power module1K is 1, 2, …, M-1; terminal T of Mth power module in the cascaded converter A2A terminal x connected to the single cross flow side;
terminal T of the first power module in the cascaded converter B1A terminal b connected to the secondary winding of the three-phase connection transformer; terminal T of kth power module in the cascaded converter B2Terminal T connected to the (k + 1) th power module1K is 1, 2, …, M-1; terminal T of Mth power module in the cascaded converter B2A terminal x connected to the single cross flow side;
a first one of the cascaded converters CTerminal T of power module1A terminal c connected to the secondary winding of the three-phase connection transformer; terminal T of kth power module in the cascaded converter C2Terminal T connected to the (k + 1) th power module1K is 1, 2, …, M-1; terminal T of Mth power module in the cascade converter C2A terminal x connected to the single cross flow side;
terminal T of the first power module in the cascaded converter D1A terminal x connected to the single cross flow side; terminal T of kth power module in the cascaded converter D2Terminal T connected to the (k + 1) th power module1K is 1, 2, …, N-1; terminal T of Nth power module in the cascade current transformer D2A terminal n connected to the single cross flow side.
Preferably, the current i of the secondary winding terminals a, b, c of the three-phase link transformera、ib、icThree-phase current i of primary side of transformer connected with three-phaseA、iB、iCSatisfies the following relationship:
iA＝iAB-iCA＝Ktr*(ia-ic)
iB＝iBC-iAB＝Ktr*(ib-ia)
iC＝iCA-iBC＝Ktr*(ic-ib)
wherein, KtrThe ratio of the secondary side voltage to the primary side voltage of the three-phase connection transformer is as follows:
iAB＝Ktr*ia
iBC＝Ktr*ib
iCA＝Ktr*ic
iAB、iBC、iCAcurrents respectively flowing through three-phase windings of the primary sides of the three-phase connection transformers;
current i in the cascaded converter DdAnd the load current ixSecondary winding current ia、ibAnd icSatisfies the following relationship:
id＝ia+ib+ic-ix。
in another aspect of the present invention, a method for controlling a bidirectional frequency converter is provided, where the method includes:
controlling the output voltage of each power module, so that the voltages of the cascaded converter A ', the cascaded converter B ' and the cascaded converter C ' are all composed of alternating current components with two frequencies, and the following relations are satisfied:
uax＝uax1+uax2
ubx＝ubx1+ubx2
ucx＝ucx1+ucx2
wherein u isax、ubxAnd ucxThe voltages of the cascaded converter A ', the cascaded converter B ' and the cascaded converter C ' are respectively; u. ofax1、ubx1And ucx1All the frequencies of the three-phase connection transformer are the same as the voltage frequency of the primary side three-phase alternating current side of the three-phase connection transformer, uax2、ubx2And ucx2All of the frequencies of (a) are the same as the frequency of the alternating voltage between the single-phase alternating-current-side terminal x and the terminal n.
Preferably, the control method further includes:
controlling the voltage u of the cascaded converter DdContaining only AC components of single-phase side frequency and being approximately equal to the AC between the single-phase AC-side terminal x and the terminal nVoltage uxn。
Preferably, the control method further includes:
and under the condition that the input side and the output side have different frequencies, respectively controlling the sum of active power formed by the voltage of two different frequencies and the current of two different frequencies of the cascade converter A ', the cascade converter B' and the cascade converter C 'to be zero, and controlling the active power formed by the voltage and the current of the cascade converter D' to be zero.
Preferably, the control method further includes:
and under the condition that the input side and the output side have the same frequency, respectively controlling the sum of active power formed by the voltage and the current of the cascade converter A ', the cascade converter B', the cascade converter C 'and the cascade converter D' to be zero.
Compared with the closest prior art, the invention has the following beneficial effects:
the invention is the same as the patent document CN108923664A, realizes AC-AC conversion, reduces intermediate links and reduces system loss compared with the scheme of AC-DC-AC conversion; in addition, the invention realizes the same frequency of the input end and the output end by adding the cascade current transformer D' on the single-phase current-intersecting side, which cannot be realized by the frequency converter of the patent CN 108923664A.
Drawings
FIG. 1 is a schematic diagram of the principal components of an embodiment of the bi-directional frequency converter of the present invention;
FIG. 2 is a schematic diagram of a circuit for implementing a power module in an embodiment of a bi-directional frequency converter of the present invention;
fig. 3 is a schematic diagram of the main steps of an embodiment of the control method of the bidirectional frequency converter of the present invention.
Detailed Description
Preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are only for explaining the technical principle of the present invention, and are not intended to limit the scope of the present invention.
It should be noted that the terms "first" and "second" in the description of the present invention are used for convenience of description only and do not indicate or imply relative importance of the devices, elements or parameters, and therefore should not be construed as limiting the present invention.
Fig. 1 is a schematic diagram of the main components of an embodiment of the bidirectional frequency converter of the present invention. As shown in fig. 1, the bidirectional frequency converter in the present embodiment includes: three-phase connection transformer, cascade current transformer A ', cascade current transformer B', cascade current transformer C 'and cascade current transformer D'.
The primary winding of the three-phase connection transformer adopts a triangular connection form, the secondary winding adopts a star connection form, and a star connection point of the secondary winding is connected to a terminal n on a single-phase current-crossing side; the secondary winding terminals a, B and C of the three-phase connection transformer are respectively connected to a terminal x on the single-phase current-crossing side through a cascade current transformer A ', a cascade current transformer B ' and a cascade current transformer C '; the single-phase current-intersecting side is connected with the terminal x and the terminal n in parallel to form a cascade current transformer D'. Namely, two ends of the cascaded current transformer A 'are respectively connected to the terminal a and the terminal x, and two ends of the cascaded current transformer B' are respectively connected to the terminal B and the terminal x; the two ends of the cascade current transformer C' are respectively connected to the terminal C and the terminal x; both ends of the cascaded current transformer D' are connected to the terminal x and the terminal n, respectively.
In fig. 1, three terminals of the primary winding of the three-phase coupling transformer are taken as input terminals, and a terminal x and a terminal n on the single-phase current-intersecting side are taken as output terminals, so that three-phase input-single-phase output is realized. If the terminal x and the terminal n on the single-phase current-intersecting side are used as input terminals and the three terminals A, B, C of the primary windings of the three-phase connection transformer are used as output terminals, single-phase input-three-phase output can be realized.
In the embodiment, the cascade converter A ', the cascade converter B ' and the cascade converter C ' are all formed by cascading M identical power modules; the cascade converter D' is formed by cascading N identical power modules; wherein M and N are both positive integers. The cascade converter A ', the cascade converter B', the cascade converter C 'and the cascade converter D' are controlled by a double closed loop with a power module capacitor voltage outer loop and respective current as inner loops.
Specifically, each of the cascaded converters in this embodiment is configured as follows:
terminal T of the first power module PM-1 in the cascaded converter A1A terminal a connected to the secondary winding of the three-phase connection transformer; terminal T of kth power module in cascade converter A2Terminal T connected to the (k + 1) th power module1K is 1, 2, …, M-1; terminal T of Mth power module PM-M in cascade converter A2To the terminal x on the single cross flow side.
Terminal T of the first power module PM-1 in the cascaded converter B1A terminal b connected to the secondary winding of the three-phase connection transformer; terminal T of kth power module in cascade converter B2Terminal T connected to the (k + 1) th power module1K is 1, 2, …, M-1; terminal T of Mth power module PM-M in cascade converter B2To the terminal x on the single cross flow side.
Terminal T of the first power module PM-1 in the cascaded converter C1A terminal c connected to the secondary winding of the three-phase connection transformer; terminal T of kth power module in cascade converter C2Terminal T connected to the (k + 1) th power module1K is 1, 2, …, M-1; terminal T of Mth power module PM-M in cascade converter C2To the terminal x on the single cross flow side.
Cascade converterTerminal T of the first power module PM-1 in D1A terminal x connected to the single cross flow side; terminal T of kth power module in cascade converter D2Terminal T connected to the (k + 1) th power module1K is 1, 2, …, N-1; terminal T of Nth power module PM-N in cascade converter D2To the terminal n on the single cross flow side.
Based on the above-described structure of the bidirectional frequency converter, the current i of the secondary winding terminals a, b, c of the three-phase connection transformera、ib、icCurrent i to primary winding terminal A, B, C of three-phase connected transformerA、iB、iCSatisfies the relationships shown in the formulas (1) to (3):
iA＝iAB-iCA＝Ktr*(ia-ic) (1)
iB＝iBC-iAB＝Ktr*(ib-ia) (2)
iC＝iCA-iBC＝Ktr*(ic-ib) (3)
wherein, KtrThe ratio of secondary side voltage to primary side voltage of three-phase connected transformer, and the current i flowing in the primary side windingAB、iBC、iCACurrent i to secondary winding terminala、ib、icSatisfies the relationships shown by the formulas (4) to (6):
iAB＝Ktr*ia(4)
iBC＝Ktr*ib(5)
iCA＝Ktr*ic(6)
current i in cascaded converter DdAnd the load current ixSecondary winding current ia、ibAnd icSatisfies the relationship shown in formula (7):
id＝ia+ib+ic-ix(7)
fig. 2 is a schematic diagram of a circuit for implementing a power module in an embodiment of a bidirectional frequency converter of the present invention. The PM of the power module is composed of a direct current capacitor CdcSwitch S1-S4And a diode D1-D4Forming; switch S1And switch S2Has a common connection point of T1Switch S3And switch S4Has a common connection point of T2Switch S1And switch S3Are all connected to a DC capacitor CdcPositive pole of (2), switch S2And switch S4Is connected to a DC capacitor CdcThe negative electrode of (1); switch SRCollector and diode DRCathodes are connected together, switch SREmitter and diode DRThe anodes are connected together, where R is 1, 2, 3, 4.
Each power module has a corresponding control circuit, which can be implemented by conventional techniques, and is not shown in fig. 1 and 2.
The present invention also provides a control method for the bidirectional frequency converter based on the above converter, and the following description is made specifically.
Fig. 3 is a schematic diagram of the main steps of an embodiment of the control method of the bidirectional frequency converter of the present invention. As shown in fig. 3, the control method of the present embodiment includes:
step S1, controlling the output voltage of each power module so that the voltages of the cascade current transformer a ', the cascade current transformer B ' and the cascade current transformer C ' are composed of ac components of two frequencies and satisfy the relationships shown in equations (8) to (10):
uax＝uax1+uax2(8)
ubx＝ubx1+ubx2(9)
ucx＝ucx1+ucx2(10)
wherein u isax、ubxAnd ucxThe voltages of the cascade converter A ', the cascade converter B ' and the cascade converter C ' are respectively; u. ofax1、ubx1And ucx1The frequency of the primary side three-phase AC side voltage of the three-phase connection transformer is the same as that of the primary side three-phase AC side voltage of the three-phase connection transformer, uax2、ubx2And ucx2Is the same as the frequency of the alternating voltage between the single-phase alternating-current-side terminals x and n. u. ofax1、uax2Are each uaxA first alternating current component and a second alternating current component ubx1、ubx2Are each ubxA first alternating current component and a second alternating current component ucx1、ucx2Are each ucxThe first alternating current component and the second alternating current component.
Step S2, controlling the voltage u of the cascade current transformer DdContaining only AC components of single-phase side frequency and being approximately equal to AC voltage u between single-phase AC-side terminal x and terminal nxn。
Step S3, in the case that the input side and the output side have different frequencies, respectively controlling the sum of active power formed by the two voltages with different frequencies and the two currents with different frequencies of the cascaded converter a ', the cascaded converter B' and the cascaded converter C 'to be zero, and controlling the voltage u of the cascaded converter D' to be zerodAnd current idThe active power formed is also zero; under the condition that the input side and the output side have the same frequency, the sum of active power formed by the voltage and the current of the cascade converter A ', the cascade converter B', the cascade converter C 'and the cascade converter D' is controlled to be zero.
Specifically, when the output side current i is different in the input side and output side frequenciesxWhen the cascaded converters a ', B ' and C ' are equally divided, the relationships shown by the equations (11) to (14) are satisfied:
P(uax1,ia-ix/3)+P(uax2,ix/3)＝0 (11)
P(ubx1,ib-ix/3)+P(ubx2,ix/3)＝0 (12)
P(ucx1,ic-ix/3)+P(ucx2,ix/3)＝0 (13)
P(ud,id)＝0 (14)
in fact, when the input-side and output-side frequencies are different, it is sufficient to ensure that the sum of the active power formed by the voltage of the first ac component and the current of the first ac component and the active power formed by the voltage of the second ac component and the current of the second ac component is 0, and therefore, the more general relationship is as shown in equations (15) to (18):
P(uax1,ia-kaix)+P(uax2,kaix)＝0 (15)
P(ubx1,ib-kbix)+P(ubx2,kbix)＝0 (16)
P(ucx1,ic-kcix)+P(ucx2,kcix)＝0 (17)
P(ud,id)＝0 (18)
wherein ixIs a load current of single phase side, ka，kb，kcAre coefficients.
Specifically, in the case where the input side and output side frequencies are the same, the satisfied relationships are as shown in equations (19) to (22):
P(uax,ia)＝0 (19)
P(ubx,ib)＝0 (20)
P(ucx,ic)＝0 (21)
P(ud,id)＝0 (22)
wherein u isaxIs the voltage between terminals a, x, ubxIs the voltage between terminals b, x, ucxIs the voltage between terminals c, x, udIs the voltage between terminals d, n.
Wherein the function P (x)1，x2) Representing variables with respect to x1And x2Active power in between, i in the formulaxIs the load current on the single phase side. The voltage stability of the power module can be ensured by the control method of the step.
Although the foregoing embodiments describe the steps in the above sequential order, those skilled in the art will understand that, in order to achieve the effect of the present embodiments, the steps may not be executed in such an order, and may be executed simultaneously (in parallel) or in an inverse order, and these simple variations are within the scope of the present invention.
Those of skill in the art will appreciate that the method steps of the examples described in connection with the embodiments disclosed herein may be embodied in electronic hardware, computer software, or combinations of both, and that the components and steps of the examples have been described above generally in terms of their functionality in order to clearly illustrate the interchangeability of electronic hardware and software. Whether such functionality is implemented as electronic hardware or software depends upon the particular application and design constraints imposed on the solution. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.
So far, the technical solutions of the present invention have been described in connection with the preferred embodiments shown in the drawings, but it is easily understood by those skilled in the art that the scope of the present invention is obviously not limited to these specific embodiments. Equivalent changes or substitutions of related technical features can be made by those skilled in the art without departing from the principle of the invention, and the technical scheme after the changes or substitutions can fall into the protection scope of the invention.
Claims (9)
1. A bidirectional frequency converter, characterized in that the bidirectional frequency converter comprises: the three-phase transformer, the cascade converter A ', the cascade converter B', the cascade converter C 'and the cascade converter D';
the three-phase connection transformer adopts a triangular/star connection mode, and a star contact point of a secondary winding is connected to a terminal n on a single-phase current-crossing side;
secondary winding terminals a, B and C of the three-phase connection transformer are connected to a terminal x on the single-phase current-intersecting side through the cascade current transformer A ', the cascade current transformer B ' and the cascade current transformer C ' respectively;
the cascade converter D' is connected in parallel between the terminal x and the terminal n on the single cross current side;
three terminals of a primary winding of the three-phase connecting transformer are used as input terminals, and a terminal x and a terminal n on the single-phase current-intersecting side are used as output terminals, so that three-phase input-single-phase output is realized; or,
and the terminal x and the terminal n on the single-phase current-intersecting side are used as input terminals, and the three terminals of the primary winding of the three-phase connecting transformer are used as output terminals, so that single-phase input-three-phase output is realized.
2. The bidirectional frequency converter of claim 1,
the cascade converter A ', the cascade converter B ' and the cascade converter C ' are all formed by cascading M identical power modules;
the cascade converter D' is formed by cascading N identical power modules;
wherein M and N are both positive integers.
3. The bi-directional frequency converter according to claim 2, characterized in that said cascaded current transformer a ', said cascaded current transformer B', said cascaded current transformer C 'and said cascaded current transformer D' are controlled by a double closed loop with an outer loop of power module capacitor voltage and respective current as inner loop.
4. The bidirectional frequency converter of claim 2,
terminal T of the first power module in the cascaded converter A1A terminal a connected to the secondary winding of the three-phase connection transformer; terminal T of kth power module in the cascaded converter A2Terminal T connected to the (k + 1) th power module1K is 1, 2, …, M-1; terminal T of Mth power module in the cascaded converter A2Connected to said single-phase ACA lateral terminal x;
terminal T of the first power module in the cascaded converter B1A terminal b connected to the secondary winding of the three-phase connection transformer; terminal T of kth power module in the cascaded converter B2Terminal T connected to the (k + 1) th power module1K is 1, 2, …, M-1; terminal T of Mth power module in the cascaded converter B2A terminal x connected to the single cross flow side;
terminal T of the first power module in the cascaded converter C1A terminal c connected to the secondary winding of the three-phase connection transformer; terminal T of kth power module in the cascaded converter C2Terminal T connected to the (k + 1) th power module1K is 1, 2, …, M-1; terminal T of Mth power module in the cascade converter C2A terminal x connected to the single cross flow side;
terminal T of the first power module in the cascaded converter D1A terminal x connected to the single cross flow side; terminal T of kth power module in the cascaded converter D2Terminal T connected to the (k + 1) th power module1K is 1, 2, …, N-1; terminal T of Nth power module in the cascade current transformer D2A terminal n connected to the single cross flow side.
5. The bidirectional frequency converter of claim 4,
current i of secondary winding terminals a, b, c of the three-phase connection transformera、ib、icThree-phase current i of primary side of transformer connected with three-phaseA、iB、iCSatisfies the following relationship:
iA＝iAB-iCA＝Ktr*(ia-ic)
iB＝iBC-iAB＝Ktr*(ib-ia)
iC＝iCA-iBC＝Ktr*(ic-ib)
wherein, KtrThe ratio of the secondary side voltage to the primary side voltage of the three-phase connection transformer is as follows:
iAB＝Ktr*ia
iBC＝Ktr*ib
iCA＝Ktr*ic
iAB、iBC、iCAcurrents respectively flowing through three-phase windings of the primary sides of the three-phase connection transformers;
current i in the cascaded converter DdAnd the load current ixSecondary winding current ia、ibAnd icSatisfies the following relationship:
id＝ia+ib+ic-ix。
6. a method of controlling a bidirectional frequency converter as claimed in any one of claims 2 to 5, characterized in that said method of controlling comprises:
controlling the output voltage of each power module, so that the voltages of the cascaded converter A ', the cascaded converter B ' and the cascaded converter C ' are all composed of alternating current components with two frequencies, and the following relations are satisfied:
uax＝uax1+uax2
ubx＝ubx1+ubx2
ucx＝ucx1+ucx2
wherein u isax、ubxAnd ucxThe voltages of the cascaded converter A ', the cascaded converter B ' and the cascaded converter C ' are respectively; u. ofax1、ubx1And ucx1All the frequencies of the three-phase connection transformer are the same as the voltage frequency of the primary side three-phase alternating current side of the three-phase connection transformer, uax2、ubx2And ucx2With alternating current between single-phase ac-side terminal x and terminal nThe compression frequency is the same.
7. The method of controlling a bidirectional frequency converter as recited in claim 6 further comprising:
controlling the voltage u of the cascaded converter DdContaining only AC components of single-phase side frequency and being approximately equal to AC voltage u between single-phase AC-side terminal x and terminal nxn。
8. The method of controlling a bidirectional frequency converter as recited in claim 7, further comprising:
and under the condition that the input side and the output side have different frequencies, respectively controlling the sum of active power formed by the voltage of two different frequencies and the current of two different frequencies of the cascade converter A ', the cascade converter B' and the cascade converter C 'to be zero, and controlling the active power formed by the voltage and the current of the cascade converter D' to be zero.
9. The method of controlling a bidirectional frequency converter as recited in claim 8, further comprising:
and under the condition that the input side and the output side have the same frequency, respectively controlling the sum of active power formed by the voltage and the current of the cascade converter A ', the cascade converter B', the cascade converter C 'and the cascade converter D' to be zero.
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