POSITIVE AND NEGATIVE BIPOLAR MODULAR MULTILEVEL ALTERNATING CURRENT-ALTERNATING CURRENT FREQUENCY CONVERTER

Abstract

The present disclosure provides a positive and negative bipolar modular multilevel alternating current (AC)-AC frequency converter, including a modular multilevel frequency converter and a three-phase three-winding bipolar transformer. The modular multilevel frequency converter has an ABC three-phase structure, each phase includes the same upper bridge arm and lower bridge arm, and the upper and lower bridge arms include n full-bridge sub-modules (FBSMs) and a bridge arm inductor connected in series. The positive and negative bipolar modular multilevel AC-AC frequency converter can be further expanded and enable bidirectional energy flow. In the present disclosure, by introducing a positive and negative bipolar three-winding transformer, an AC-AC frequency converter topology with simple structure, high efficiency, flexibility and reliability is realized, which has high practical value.

Claims

1. A positive and negative bipolar modular multilevel alternating current (AC)-AC frequency converter, comprising a modular multilevel frequency converter and a three-phase three-winding bipolar transformer, wherein the modular multilevel frequency converter has an ABC three-phase structure, a power frequency side is connected to a power frequency power grid, and a low frequency side is connected to a low frequency power grid through the three-phase three-winding bipolar transformer; the three-phase three-winding bipolar transformer comprises two Y-connected secondary transformers T1 and T2, T1 is a positive transformer, and T2 is a negative transformer; and three-phase ports of the Y-connected secondary transformer T1 are connected to upper ends of three-phase upper bridge arms of the modular multilevel frequency converter, and three-phase ports of the Y-connected secondary transformer T2 are connected to lower ends of three-phase lower bridge arms of the modular multilevel frequency converter; and in the three-phase three-winding bipolar transformer, a neutral point o of T1 and a neutral point o of T2 are connected with each other, a voltage relationship between T1 and T2 transformer ports is that a phase difference between X and x ports is 180, a phase difference between Y and y ports is 180, and a phase difference between Z and z ports is 180.

2. The positive and negative bipolar modular multilevel AC-AC frequency converter according to claim 1, wherein each phase of the modular multilevel frequency converter comprises the same upper bridge arm and the same lower bridge arm, and the upper and lower bridge arms respectively comprise n full-bridge sub-modules (FBSMs) and a bridge arm inductor connected in series.

3. The positive and negative bipolar modular multilevel AC-AC frequency converter according to claim 2, wherein the FBSM comprises first to fourth insulated gate bipolar transistors (IGBTs) and a first electrolytic capacitor, an emitter of the first IGBT is connected to a collector of the second IGBT, and a connection point is used as a positive terminal of the FBSM; an emitter of the third IGBT is connected to a collector of the fourth IGBT, and a connection point is used as a negative end of the FBSM; a collector of the first IGBT, a collector of the third IGBT and a positive electrode of the first electrolytic capacitor are connected; an emitter of the second IGBT, an emitter of the fourth IGBT and a negative electrode of the first electrolytic capacitor are connected; and the first to fourth IGBTs are all connected to anti-parallel diodes.

4. The positive and negative bipolar modular multilevel AC-AC frequency converter according to claim 1, wherein a number of modular multilevel frequency converters is M, all of which are on the power frequency side, M is a positive integer greater than or equal to 1, the upper ends of the upper bridge arms of the M modular multilevel frequency converters are connected to the three-phase ports of the three-phase three-winding bipolar transformer T1, and the lower ends of the lower bridge arms of the M modular multilevel frequency converters are connected to the three-phase ports of the three-phase three-winding bipolar transformer T2.

5. The positive and negative bipolar modular multilevel AC-AC frequency converter according to claim 1, wherein the positive and negative bipolar modular multilevel AC-AC frequency converter has power flowing from the power frequency side to the low frequency side or from the low frequency side to the power frequency side.

6. The positive and negative bipolar modular multilevel AC-AC frequency converter according to claim 2, wherein the positive and negative bipolar modular multilevel AC-AC frequency converter has power flowing from the power frequency side to the low frequency side or from the low frequency side to the power frequency side.

7. The positive and negative bipolar modular multilevel AC-AC frequency converter according to claim 3, wherein the positive and negative bipolar modular multilevel AC-AC frequency converter has power flowing from the power frequency side to the low frequency side or from the low frequency side to the power frequency side.

8. The positive and negative bipolar modular multilevel AC-AC frequency converter according to claim 4, wherein the positive and negative bipolar modular multilevel AC-AC frequency converter has power flowing from the power frequency side to the low frequency side or from the low frequency side to the power frequency side.

9. The positive and negative bipolar modular multilevel AC-AC frequency converter according to claim 1, wherein the positive and negative bipolar modular multilevel AC-AC frequency converter has an upper bridge arm modulation wave y.sub.ju and a lower bridge arm modulation wave y.sub.jl of j phase calculated by using the following formulas: $\{\begin{array}{c}{y}_{ju}=y_{j\_l}-y_{j\_g}\\ y_{jl}=y_{j\_l}+y_{j\_g}\end{array}$ where y.sub.j_l is a low frequency modulated wave component, y.sub.j_g is a power frequency modulated wave component, and j=a, b, c.

10. The positive and negative bipolar modular multilevel AC-AC frequency converter according to claim 2, wherein the positive and negative bipolar modular multilevel AC-AC frequency converter has an upper bridge arm modulation wave y.sub.ju and a lower bridge arm modulation wave y.sub.jl of j phase calculated by using the following formulas: $\{\begin{array}{c}{y}_{ju}=y_{j\_l}-y_{j\_g}\\ y_{jl}=y_{j\_l}+y_{j\_g}\end{array}$ where y.sub.j_l is a low frequency modulated wave component, y.sub.j_g is a power frequency modulated wave component, and j=a, b, c.

11. The positive and negative bipolar modular multilevel AC-AC frequency converter according to claim 3, wherein the positive and negative bipolar modular multilevel AC-AC frequency converter has an upper bridge arm modulation wave y.sub.ju and a lower bridge arm modulation wave y.sub.jl of j phase calculated by using the following formulas: $\{\begin{array}{c}{y}_{ju}=y_{j\_l}-y_{j\_g}\\ y_{jl}=y_{j\_l}+y_{j\_g}\end{array}$ where y.sub.j_l is a low frequency modulated wave component, y.sub.j_g is a power frequency modulated wave component, and j=a, b, c.

12. The positive and negative bipolar modular multilevel AC-AC frequency converter according to claim 4, wherein the positive and negative bipolar modular multilevel AC-AC frequency converter has an upper bridge arm modulation wave y.sub.ju and a lower bridge arm modulation wave y.sub.jl of j phase calculated by using the following formulas: $\{\begin{array}{c}{y}_{ju}=y_{j\_l}-y_{j\_g}\\ y_{jl}=y_{j\_l}+y_{j\_g}\end{array}$ where y.sub.j_l is a low frequency modulated wave component, y.sub.j_g is a power frequency modulated wave component, and j=a, b, c.

13. The positive and negative bipolar modular multilevel AC-AC frequency converter according to claim 9, wherein expressions of the low frequency modulation wave y.sub.j_l and the power frequency modulation wave y.sub.j_g of j phase are as follows: $\{\begin{array}{c}{y}_{j\_l}=m_l.Math.\sin \left({}_{l}t+{}_{jl}\right)-1\\ y_{j\_g}=m_g.Math.\sin \left({}_{g}t+{}_{jg}\right)\end{array}$ where m.sub.g is a power frequency modulation degree, m.sub.l is a low frequency modulation degree, .sub.g is a power frequency angular frequency, .sub.l is a low frequency angular frequency, .sub.jg is a j-phase power frequency phase shift angle, and .sub.jl is a j-phase low frequency phase shift angle.

14. The positive and negative bipolar modular multilevel AC-AC frequency converter according to claim 10, wherein expressions of the low frequency modulation wave y.sub.j_l and the power frequency modulation wave y.sub.j_g of j phase are as follows: $\{\begin{array}{c}{y}_{j\_l}=m_l.Math.\sin \left({}_{l}t+{}_{jl}\right)-1\\ y_{j\_g}=m_g.Math.\sin \left({}_{g}t+{}_{jg}\right)\end{array}$ where m.sub.g is a power frequency modulation degree, m.sub.l is a low frequency modulation degree, .sub.g is a power frequency angular frequency, .sub.l is a low frequency angular frequency, .sub.jg is a j-phase power frequency phase shift angle, and .sub.jl is a j-phase low frequency phase shift angle.

15. The positive and negative bipolar modular multilevel AC-AC frequency converter according to claim 11, wherein expressions of the low frequency modulation wave y.sub.j_l and the power frequency modulation wave y.sub.j_g of j phase are as follows: $\{\begin{array}{c}{y}_{j\_l}=m_l.Math.\sin \left({}_{l}t+{}_{jl}\right)-1\\ y_{j\_g}=m_g.Math.\sin \left({}_{g}t+{}_{jg}\right)\end{array}$ where m.sub.g is a power frequency modulation degree, m.sub.l is a low frequency modulation degree, .sub.g is a power frequency angular frequency, .sub.l is a low frequency angular frequency, .sub.jg is a j-phase power frequency phase shift angle, and .sub.jl is a j-phase low frequency phase shift angle.

16. The positive and negative bipolar modular multilevel AC-AC frequency converter according to claim 12, wherein expressions of the low frequency modulation wave y.sub.j_l and the power frequency modulation wave y.sub.j_g of j phase are as follows: $\{\begin{array}{c}{y}_{j\_l}=m_l.Math.\sin \left({}_{l}t+{}_{jl}\right)-1\\ y_{j\_g}=m_g.Math.\sin \left({}_{g}t+{}_{jg}\right)\end{array}$ where m.sub.g is a power frequency modulation degree, m.sub.l is a low frequency modulation degree, .sub.g is a power frequency angular frequency, .sub.l is a low frequency angular frequency, .sub.jg is a j-phase power frequency phase shift angle, and .sub.jl is a j-phase low frequency phase shift angle.

17. The positive and negative bipolar modular multilevel AC-AC frequency converter according to claim 13, wherein expressions of an upper bridge arm voltage u.sub.ju and a lower bridge arm voltage u.sub.jl of j phase are as follows: $\{\begin{array}{c}{u}_{ju}=\frac{n{u}_c}{2}\left(1+y_{j\_l}-y_{j\_g}\right)\\ u_{jl}=\frac{n{u}_c}{2}\left(1+y_{j\_l}+y_{j\_g}\right)\end{array}$ where n is a number of sub-modules, and u.sub.c is an average capacitor voltage of sub-modules.

18. The positive and negative bipolar modular multilevel AC-AC frequency converter according to claim 14, wherein expressions of an upper bridge arm voltage u.sub.ju and a lower bridge arm voltage u.sub.jl of j phase are as follows: $\{\begin{array}{c}{u}_{ju}=\frac{n{u}_c}{2}\left(1+y_{j\_l}-y_{j\_g}\right)\\ u_{jl}=\frac{n{u}_c}{2}\left(1+y_{j\_l}+y_{j\_g}\right)\end{array}$ where n is a number of sub-modules, and u.sub.c is an average capacitor voltage of sub-modules.

19. The positive and negative bipolar modular multilevel AC-AC frequency converter according to claim 15, wherein expressions of an upper bridge arm voltage u.sub.ju and a lower bridge arm voltage u.sub.jl of j phase are as follows: $\{\begin{array}{c}{u}_{ju}=\frac{n{u}_c}{2}\left(1+y_{j\_l}-y_{j\_g}\right)\\ u_{jl}=\frac{n{u}_c}{2}\left(1+y_{j\_l}+y_{j\_g}\right)\end{array}$ where n is a number of sub-modules, and u.sub.c is an average capacitor voltage of sub-modules.

20. The positive and negative bipolar modular multilevel AC-AC frequency converter according to claim 16, wherein expressions of an upper bridge arm voltage u.sub.ju and a lower bridge arm voltage u.sub.jl of j phase are as follows: $\{\begin{array}{c}{u}_{ju}=\frac{n{u}_c}{2}\left(1+y_{j\_l}-y_{j\_g}\right)\\ u_{jl}=\frac{n{u}_c}{2}\left(1+y_{j\_l}+y_{j\_g}\right)\end{array}$ where n is a number of sub-modules, and u.sub.c is an average capacitor voltage of sub-modules.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to explain the examples of the present disclosure or the technical solutions in the related art more clearly, a brief description will be given below with reference to the drawings which are used in the description of the examples or the prior art. Obviously, other drawings can be obtained according to these drawings without creative work for those ordinary skilled in the art.

[0031] FIG. 1 is a schematic diagram of a topological structure of a positive and negative bipolar modular multilevel AC-AC frequency converter according to an example of the present disclosure.

[0032] FIG. 2 is an extended schematic diagram of the positive and negative bipolar modular multilevel AC-AC frequency converter according to an example of the present disclosure.

DETAILED DESCRIPTION

[0033] Technical solutions in the examples of the present disclosure will be described clearly and completely in the following with reference to the accompanying drawings in the examples of the present disclosure. Obviously, all the described examples are only some, rather than all examples of the present disclosure. Based on the examples in the present disclosure, all other examples obtained by those ordinary skilled in the art without creative efforts belong to the protection scope of the present disclosure.

[0034] As shown in FIG. 1, the present disclosure provides a positive and negative bipolar modular multilevel AC-AC frequency converter, the system includes two main parts: the first part is a modular multilevel frequency converter 1, the modular multilevel frequency converter is an ABC three-phase structure, each phase includes the same upper bridge arm and lower bridge arm, and the upper and lower bridge arms include n FBSMs 1-1 and a bridge arm inductor 1-2 connected in series. The second part is a three-phase three-winding bipolar transformer 2, a Y-connected secondary transformer T1 of the three-phase three-winding bipolar transformer is a positive transformer, three-phase ports of T1 are X, Y and Z, a Y-connected secondary transformer T2 is a negative transformer, and three-phase ports of T2 are x, y and z. In the proposed positive and negative bipolar modular multilevel AC-AC frequency converter, a power frequency side of the modular multilevel frequency converter is connected to a power frequency grid, and a low frequency side is connected to a low frequency grid through the three-phase three-winding bipolar transformer.

[0035] The FBSM includes first to fourth IGBTs and a first electrolytic capacitor, an emitter of the first IGBT is connected to a collector of the second IGBT, and a connection point is used as a positive terminal of the FBSM; an emitter of the third IGBT is connected to a collector of the fourth IGBT, and a connection point is used as a negative end of the FBSM; a collector of the first IGBT, a collector of the third IGBT and a positive electrode of the first electrolytic capacitor are connected; an emitter of the second IGBT, an emitter of the fourth IGBT and a negative electrode of the first electrolytic capacitor are connected; and the first to fourth IGBTs are all connected to anti-parallel diodes.

[0036] In the three-phase three-winding bipolar transformer, a neutral point o of the Y-connected secondary transformer T1 and a neutral point o of the Y-connected secondary transformer T2 are connected to each other. A voltage relationship between T1 and T2 transformer ports is that a phase difference between X and x ports is 180, a phase difference between Y and y ports is 180, and a phase difference between Z and z ports is 180.

[0037] A connection mode of the three-phase three-winding bipolar transformer and the modular multilevel frequency converter is as follows: a port X of the Y-connected secondary transformer T1 is connected to an upper end of an A-phase upper bridge arm of the modular multilevel frequency converter, a port Y is connected to an upper end of a B-phase upper bridge arm of the modular multilevel frequency converter, and a port Z is connected to an upper end of a C-phase upper bridge arm of the modular multilevel frequency converter. A port x of the Y-connected secondary transformer T2 is connected to a lower end of an A-phase lower bridge arm of the modular multilevel frequency converter, a port y is connected to a lower end of a B-phase lower bridge arm of the modular multilevel frequency converter, and a port z is connected to a lower end of a C-phase lower bridge arm of the modular multilevel frequency converter.

[0038] As shown in FIG. 2, the positive and negative bipolar modular multilevel AC-AC frequency converter can be expanded on the power frequency side, and the expanded positive and negative bipolar modular multilevel AC-AC frequency converter can include M (M is greater than or equal to 2) modular multilevel frequency converters and the three-phase three-winding bipolar transformer. FIG. 2 shows the extended modular multilevel AC-AC frequency converter with M=2, the upper ends of the upper bridge arms of three phases A, B, and C and three phases A, B, and C are connected to the ports X, Y, and Z of the three-phase three-winding bipolar transformer T1, and the lower ends of the lower bridge arms of three phases A, B, and C and three phases A, B, and C are connected to the ports x, y, and z of the three-phase three-winding bipolar transformer T2.

[0039] In the positive and negative bipolar modular multilevel AC-AC frequency converter, power can flow from the power frequency side to the low frequency side, and can also flow from the low frequency side to the power frequency side.

[0040] When the positive and negative bipolar modular multilevel AC-AC frequency converter is controlled, expressions of an upper bridge arm modulation wave y.sub.ju and a lower bridge arm modulation wave y.sub.jl of j (j=a, b, c) phase are as follows:

[00004]$\{\begin{array}{c}{y}_{ju}=y_{j\_l}-y_{j\_g}\\ y_{jl}=y_{j\_l}+y_{j\_g}\end{array}$ [0041] where y.sub.j_l is a low frequency modulated wave component, y.sub.j_g is a power frequency modulated wave component, and the expressions are as follows:

[00005]$\{\begin{array}{c}{y}_{j\_l}=m_l.Math.\sin \left({}_{l}t+{}_{jl}\right)-1\\ y_{j_{-}g}=m_g.Math.\sin \left({}_{g}t+{}_{jg}\right)\end{array}$ [0042] where m.sub.g is a power frequency modulation degree, m.sub.l is a low frequency modulation degree, .sub.g is a power frequency angular frequency, .sub.l is a low frequency angular frequency, .sub.jg is a j-phase power frequency phase shift angle, and .sub.jl is a j-phase low frequency phase shift angle.

[0043] Expressions of an upper bridge arm voltage u.sub.au and a lower bridge arm voltage u.sub.al of j phase are as follows:

[00006]$\{\begin{array}{c}{u}_{ju}=\frac{n{u}_c}{2}\left(1+y_{j\_l}-y_{j\_g}\right)\\ u_{jl}=\frac{n{u}_c}{2}\left(1+y_{j\_l}+y_{j\_g}\right)\end{array}$ [0044] where n is a number of sub-modules, and u.sub.c is an average capacitor voltage of sub-modules.

[0045] In the description of this specification, descriptions referring to the terms an example, an instance, a specific instance, etc., mean that specific features, structures, materials, or characteristics described in connection with the example or instance are included in at least one example or instance of the present disclosure. In this specification, schematic representations of the above terms do not necessarily refer to the same example or instance. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more examples or instances.

[0046] The basic principle, main features and advantages of the present disclosure have been shown and described above. It is to be understood by those skilled in the art that the present disclosure is not limited by the above-mentioned examples, and what is described in the above-mentioned examples and descriptions only illustrates the principles of the present disclosure. There will be various changes and improvements in the present disclosure without departing from the spirit and scope of the present disclosure, which fall within the scope of the claimed protection of the present disclosure.