Elongated triangle modular multi-level AC-AC converter

Abstract

The invention discloses an extended triangle modular multilevel AC-AC converter which is characterized in that an a phase, a b phase and a c phase of an input side three-phase AC power grid are respectively connected with one end of a first input bridge arm, one end of a second input bridge arm and one end of a third input bridge arm; the u phase, the v phase and the w phase of the output side three-phase alternating current power grid are respectively connected with one end of the first output bridge arm, one end of the second output bridge arm and one end of the third output bridge arm; the other end of the first input bridge arm and the other end of the first output bridge arm are connected to form a first node, the other end of the second input bridge arm and the other end of the second output bridge arm are connected to form a second node, and the other end of the third input bridge arm and the other end of the third output bridge arm are connected to form a third node. And two ends of the three circulation bridge arms are respectively connected with two adjacent nodes. Compared with an existing M3C topology scheme, the use amount of the submodules can be reduced by about one third, and the coupling degree between the input side system and the output side system is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of AC-AC converters, in particular to a Yanbian triangle modular multi-level AC-AC converter. Background Art

[0002] In the process of accelerating the construction of new power systems, high-voltage and large-capacity AC-AC converters are being used more and more widely, including offshore wind power transmission, Shagohuang new energy base transmission, asynchronous power grid interconnection, railway traction power supply, high-power variable frequency speed regulation and other scenarios.

[0003] Modular Multilevel Matrix Converter (M3C) is the most widely used high-voltage and large-capacity AC-AC converter topology in actual engineering. M3C contains nine bridge arms, and the three-phase systems on both sides are matrix-interconnected. M3C has the advantages of modular multilevel converter (MMC) in flexible DC transmission system, with high voltage level, large power capacity, low harmonic content and flexible regulation. However, each bridge arm of the M3C topology contains both input side voltage components and output side voltage components, resulting in a large number of sub-modules and high costs.

[0004] In order to reduce the number of sub-modules, some studies have proposed the hexagonal topology Hexverter, Y-type topology, bipolar topology, etc. of modular multi-level converters. The common idea is to construct different voltage components in the bridge arm voltage, and then construct the electrical circuits on the input and output sides for superposition and offset. While achieving stable AC-AC conversion, the total number of bridge arms is reduced or the number of sub-modules in the bridge arms is reduced, effectively improving the economy of the AC-AC converter topology. However, the disadvantage of these solutions is that each phase on the input side is directly connected to the three phases on the output side, and the degree of coupling is deep. Summary of the invention

[0005] In order to overcome the problem of deep coupling between the input side and the output side of the existing M3C topology sub-module, the present invention provides a Yanbian triangle modular multi-level AC-AC converter. The AC-AC converter is equivalent to reducing three bridge arms. Compared with the M3C topology solution, the amount of sub-modules can be reduced by about one third, and the coupling degree between the input side system and the output side system can be reduced.

[0006] To achieve the above-mentioned invention object, the present invention adopts the following technical solution: a Yanbian triangle modular multi-level AC-AC converter, which includes a first input bridge arm, a second input bridge arm, a third input bridge arm, a first output bridge arm, a second output bridge arm, a third output bridge arm, a first circulating bridge arm, a second circulating bridge arm and a third circulating bridge arm; Phase a, phase b, and phase c of the three-phase AC power grid on the input side are respectively connected to one end of the first input bridge arm, one end of the second input bridge arm, and one end of the third input bridge arm; phase u, phase v, and phase w of the three-phase AC power grid on the output side are respectively connected to one end of the first output bridge arm, one end of the second output bridge arm, and one end of the third output bridge arm; The other end of the first input bridge arm and the other end of the first output bridge arm are connected to form a first node, the other end of the second input bridge arm and the other end of the second output bridge arm are connected to form a second node, the other end of the third input bridge arm and the other end of the third output bridge arm are connected to form a third node, the two ends of the first circulating bridge arm are respectively connected to the first node and the second node, the two ends of the second circulating bridge arm are respectively connected to the second node and the third node, and the two ends of the third circulating bridge arm are respectively connected to the third node and the first node.

[0007] Furthermore, the first input bridge arm, the second input bridge arm, the third input bridge arm, the first output bridge arm, the second output bridge arm and the third output bridge arm are all composed of bridge arm inductance and N / 2 full-bridge sub-modules are connected in series, and the first circulating bridge arm, the second circulating bridge arm and the third circulating bridge arm are all composed of bridge arm inductors and N The full-bridge sub-modules are connected in series.

[0008] Furthermore, the first input bridge arm, the second input bridge arm and the third input bridge arm adopt capacitor voltage average control and constant reactive power control, and the voltages of these three bridge arms are equal to the phase voltage of the opposite phase of the three-phase AC power grid on the output side in steady state.

[0009] Furthermore, the first output bridge arm, the second output bridge arm and the third output bridge arm are controlled by a constant AC voltage amplitude and a constant AC voltage frequency, and the voltages of these three bridge arms are equal to the phase voltage of the opposite phase of the three-phase AC power grid on the input side in a steady state.

[0010] Furthermore, the arm voltages of the first circulating bridge arm, the second circulating bridge arm and the third circulating bridge arm are decomposed into a d-axis input component, a q-axis input component, a d-axis output component and a q-axis output component. The d-axis input component and the q-axis input component adopt energy balance control and constant reactive power control between bridge arms, and the d-axis output component and the q-axis output component adopt constant reactive power control. When the three bridge arm voltages are in steady state, they are equal to the three-phase AC grid line voltage on the input side superimposed on the three-phase AC grid line voltage on the output side.

[0011] The present invention has the following beneficial effects: The Yanbian triangle modular multi-level AC-AC converter of the present invention comprises nine bridge arms in total, but six of the bridge arms only comprise voltage components on the input side or the output side, which is equivalent to reducing three bridge arms. Compared with the existing M3C topology solution, the amount of sub-modules is reduced by about one third; each phase on the input side of the AC-AC converter is directly connected to only one phase on the output side, which effectively reduces the degree of coupling. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a topological structure diagram of the Yanbian triangle modular multi-level AC-AC converter of the present invention; Figure 2 It is a control principle diagram of the Yanbian triangle modular multi-level AC-AC converter of the present invention; Figure 3 It is an equivalent circuit diagram of the Yanbian triangle modular multi-level AC-AC converter of the present invention; Figure 4 It is a voltage waveform diagram of the Yanbian triangle modular multi-level AC-AC converter of the present invention. DETAILED DESCRIPTION

[0013] The present invention is described in detail below in conjunction with the accompanying drawings and specific implementation methods. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0014] like Figure 1 As shown, the present invention provides a Yanbian triangle modular multi-level AC-AC converter, including a first input bridge arm x1, a second input bridge arm x2, a third input bridge arm x3, a first output bridge arm y1, a second output bridge arm y2, a third output bridge arm y3, a first circulating bridge arm z1, a second circulating bridge arm z2 and a third circulating bridge arm z3.

[0015] Phase a, phase b and phase c of the three-phase AC power grid on the input side are respectively connected to one end of the first input bridge arm x1, one end of the second input bridge arm x2 and one end of the third input bridge arm x3; phase u, phase v and phase w of the three-phase AC power grid on the output side are respectively connected to one end of the first output bridge arm y1, one end of the second output bridge arm y2 and one end of the third output bridge arm y3; the other end of the first input bridge arm x1 and the other end of the first output bridge arm y1 are connected to form a first node, the other end of the second input bridge arm x2 and the other end of the second output bridge arm y2 are connected to form a second node, the other end of the third input bridge arm x3 and the other end of the third output bridge arm y3 are connected to form a third node, the two ends of the first circulating bridge arm z1 are respectively connected to the first node and the second node, the two ends of the second circulating bridge arm z2 are respectively connected to the second node and the third node, and the two ends of the third circulating bridge arm z3 are respectively connected to the third node and the first node.

[0016] The first input bridge arm, the second input bridge arm, the third input bridge arm, the first output bridge arm, the second output bridge arm and the third output bridge arm are all composed of bridge arm inductance and N / 2 full-bridge sub-modules are connected in series, and the first circulating bridge arm, the second circulating bridge arm and the third circulating bridge arm are all composed of bridge arm inductors and N The full-bridge sub-modules are connected in series.

[0017] The basic operating principle of the above-mentioned Yanbian triangle modular multi-level AC-AC converter topology structure is explained as follows.

[0018] The positive direction of the voltage and current in each bridge arm is as follows Figure 1 As shown, according to Kirchhoff's law, the loop voltage equation and node current equation of the Yanbian triangle modular multi-level AC-AC converter are: (1) (2) (3) In the formula, , , Respectively represent the three-phase voltages of the input side ports; , , Respectively represent the three-phase voltages of the output side ports; , , Respectively represent the input bridge arm inductance, output bridge arm inductance, and circulating bridge arm inductance; , , Respectively represent the voltages of the first, second and third input bridge arms; , , Respectively represent the voltages of the first, second and third output bridge arms; , , Respectively represent the voltages of the first, second and third circulating bridge arms; , , Respectively represent the three-phase currents of the input side ports; , , Respectively represent the three-phase currents of the output side ports; , , Represent the currents of the first, second and third circulating bridge arms respectively.

[0019] Since the voltage and current of the three-phase AC power grid on the input side are three-phase symmetrical, and assuming that the voltage of the input bridge arms x1~x3 is three-phase symmetrical, equation (2) can be rewritten as: (4) Assuming that the currents of the circulating bridge arms z1~z3 are three-phase symmetrical, equation (3) can be rewritten as: (5) Using the equal power Clark transformation, the voltage equation and current equation are transformed from the abc coordinate system to Coordinate system, Clark transformation matrix is ​​as follows: (6) Multiplying the equal power Clark transformation matrix by equation (1), equation (4), and equation (5) on the left yields: (7) (8) (9) in, , The three-phase AC power grid on the input side is Shaft voltage, Shaft voltage, , They are the three-phase AC power grid on the input side. Shaft current, Shaft current, , They are the three-phase AC power grid on the output side Shaft voltage, Shaft voltage, , They are the three-phase AC power grid on the output side Shaft current, Shaft current, , The input bridge arm Shaft voltage, Shaft voltage, , The output bridge arms are Shaft voltage, Shaft voltage, , The circulation bridge arms Shaft voltage, Shaft voltage, , The circulation bridge arms Shaft current, Shaft current.

[0020] The voltage of the input bridge arm x1~x3 and the output bridge arm y1~y3 contains only one component, so equation (7) can be decomposed into the input component equation and the output component equation: (10) (11) The voltage and current of the circulating bridge arm z1~z3 contain two components, so let: (12) In the formula, , Respectively The input side component and output side component of , Respectively The input side component and output side component of , Respectively The input side component and output side component of , Respectively The input side component and the output side component.

[0021] After substituting equation (11) and equation (12) into equation (8), equation (8) can be decomposed into input component equation and output component equation: (13) (14) Substituting equation (12) into equation (9), equation (9) can be decomposed into input component equation and output component equation: (15) (16) Then, Park transformation is used for the above input side and output side voltage and current equations, respectively, from The coordinate system is transformed to the dq coordinate system. The Park transformation matrix is ​​as follows: (17) in, yes The angular frequency of the coordinate system, t is the time. For the input side AC power grid system, let = , can be obtained , represents the rotation frequency of the three-phase system on the input side; for the AC power grid system on the output side, let = , can be obtained , Represents the rotation frequency of the three-phase system on the output side. The Park transformation matrix , Multiplying equations (10) to (11) and (13) to (16) on the left yields: (18) (19) (20) (twenty one) (twenty two) (twenty three) In the formula, , Respectively represent the d-axis voltage and q-axis voltage of the output bridge arm; , They represent the d-axis current and q-axis current of the input bridge arm respectively; , They represent the d-axis voltage and q-axis voltage of the input bridge arm respectively; , They represent the d-axis current and q-axis current of the output bridge arm respectively; , They represent the input side component of the d-axis voltage of the circulating bridge arm and the input side component of the q-axis voltage of the circulating bridge arm respectively; , They represent the input side component of the d-axis current of the circulating bridge arm and the input side component of the q-axis current of the circulating bridge arm respectively; , They represent the output side component of the d-axis voltage of the circulating bridge arm and the output side component of the q-axis voltage of the circulating bridge arm respectively; , They represent the output side component of the d-axis current of the circulating bridge arm and the output side component of the q-axis current of the circulating bridge arm respectively; , They represent the d-axis feedforward decoupling and q-axis feedforward decoupling of the output bridge arm voltage equation respectively. , They represent the d-axis feedforward decoupling and q-axis feedforward decoupling of the input bridge arm voltage equation respectively. , They represent the feedforward decoupling of the d-axis input component and the q-axis input component of the circulating bridge arm voltage equation respectively. , They represent the feedforward decoupling of the d-axis output component and the q-axis output component of the circulating bridge arm voltage equation respectively. The feedforward decoupling expression of each bridge arm is: (twenty four) (25) (26) (27) In the formula, , They represent the d-axis voltage and q-axis voltage of the three-phase AC power grid at the input side respectively; , They respectively represent the d-axis voltage and q-axis voltage of the three-phase AC power grid on the output side.

[0022] Therefore, for the input bridge arm voltage, the output bridge arm voltage, and the two components of the circulating bridge arm voltage, the feedforward decoupling combined with the PI controller method can be used to control the current of each bridge arm to form an inner loop current control, such as Figure 2 As shown. For the outer loop voltage control, the input bridge arms x1~x3 use capacitor voltage average control and constant reactive power control, and the reference value of the input bridge arm current in the dq coordinate system can be obtained. , , and then the reference value of the output bridge arm voltage is obtained through the inner loop current control , The output bridge arms y1~y3 are controlled by constant AC voltage amplitude and constant AC voltage frequency, and the reference value of the output bridge arm voltage in the dq coordinate system can be obtained. , ; The circulating bridge arms z1~z3 adopt energy balance control and constant reactive power control between bridge arms, and the reference value of the corresponding component of the bridge arm current in the dq coordinate system can be obtained. , and , , and then the reference value of the corresponding component of the circulating bridge arm voltage is obtained through the inner loop current control , and , .

[0023] According to equations (18) to (21), the eight bridge arm currents in the dq coordinate system are , , , , , , , The first-order dynamic equation, combined with the error feedback controller, can obtain the eight bridge arm voltage reference values ​​in the dq coordinate system , , , , , , , , and then through the inverse Park transformation, the voltage reference values ​​of the nine bridge arms can be obtained , , , , , , , , , considering that the reference value of the bridge arm voltage is equal to the actual value in steady state, the voltage and current dynamic equation decomposed in the abc coordinate system can be obtained, and the following can be derived: Figure 3 The equivalent circuit diagram of the Yanbian triangle modular multi-level AC-AC converter is shown.

[0024] (28) (29) (30) (31) In the formula, , , Respectively represent the input side components of the first, second and third circulating bridge arm currents; , , Respectively represent the input side components of the first, second and third circulating bridge arm voltages; , , Respectively represent the output side components of the first, second and third circulating bridge arm currents; , , Respectively represent the output side components of the first, second and third circulating bridge arm voltages.

[0025] Application Examples The above-mentioned Yanbian triangle modular multi-level AC-AC converter is used for the following applications: the phase voltage amplitude of the input side AC system is U m1 =1000V, the voltage frequency is f 1=50Hz, the initial phase angle of phase a voltage is θ 1=0°; the phase voltage amplitude of the output side AC system is U m2 =800V, voltage frequency is f 2=20Hz, the initial phase angle of phase a voltage is θ 2=90°. Then, the three-phase voltage expressions of the input side AC system and the output side AC system are:

[0026]

[0027] according to Figure 3The equivalent circuit diagram of the Yanbian triangle modular multilevel AC-AC converter is shown in the figure. The rated voltage of the input port of the Yanbian triangle modular multilevel AC-AC converter is 1225V, and the rated voltage of the output port of the Yanbian triangle modular multilevel AC-AC converter is 980V. When the voltage drop on the bridge arm inductance is ignored, the steady-state operating voltage expression of the first input bridge arm x1, the second input bridge arm x2, and the third input bridge arm x3 is:

[0028] When the voltage drop on the bridge arm inductance is ignored, the steady-state operating voltage expressions of the first output bridge arm y1, the second output bridge arm y2, and the third output bridge arm y3 are:

[0029] When the voltage drop on the bridge arm inductance is ignored, the steady-state operating voltage expressions of the first circulating bridge arm z1, the second circulating bridge arm z2, and the third circulating bridge arm z3 are:

[0030] like Figure 4 As shown, it is the voltage waveform of the Yanbian triangle modular multi-level AC-AC converter under the parameters of this application example, from top to bottom, they are the three-phase voltage waveform of the input port, the three-phase voltage waveform of the output port, the voltage waveform of the input bridge arm x1~x3, the voltage waveform of the output bridge arm y1~y3, and the voltage waveform of the circulating bridge arm z1~z3.

[0031] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention, and should be included in the protection scope of the present invention.

Claims

1. A Yanbian triangle modular multi-level AC-AC converter, characterized in that: It includes a first input bridge arm, a second input bridge arm, a third input bridge arm, a first output bridge arm, a second output bridge arm, a third output bridge arm, a first circulating bridge arm, a second circulating bridge arm and a third circulating bridge arm; Phase a, phase b, and phase c of the three-phase AC power grid on the input side are respectively connected to one end of the first input bridge arm, one end of the second input bridge arm, and one end of the third input bridge arm; phase u, phase v, and phase w of the three-phase AC power grid on the output side are respectively connected to one end of the first output bridge arm, one end of the second output bridge arm, and one end of the third output bridge arm; The other end of the first input bridge arm and the other end of the first output bridge arm are connected to form a first node, the other end of the second input bridge arm and the other end of the second output bridge arm are connected to form a second node, the other end of the third input bridge arm and the other end of the third output bridge arm are connected to form a third node, the two ends of the first circulating bridge arm are respectively connected to the first node and the second node, the two ends of the second circulating bridge arm are respectively connected to the second node and the third node, and the two ends of the third circulating bridge arm are respectively connected to the third node and the first node.

2. The Yanbian triangle modular multi-level AC-AC converter according to claim 1, characterized in that: The first input bridge arm, the second input bridge arm and the third input bridge arm are all composed of bridge arm inductance and N / 2 full-bridge sub-modules are connected in series.

3. The Yanbian triangle modular multi-level AC-AC converter according to claim 2, characterized in that: The first output bridge arm, the second output bridge arm and the third output bridge arm are all composed of bridge arm inductance and N / 2 full-bridge sub-modules are connected in series.

4. The Yanbian triangle modular multi-level AC-AC converter according to claim 3, characterized in that: The first circulating bridge arm, the second circulating bridge arm and the third circulating bridge arm are all composed of bridge arm inductance and N The full-bridge sub-modules are connected in series.

5. The Yanbian triangle modular multi-level AC-AC converter according to claim 1, characterized in that: The first input bridge arm, the second input bridge arm and the third input bridge arm adopt capacitor voltage average control and constant reactive power control.

6. The Yanbian triangle modular multi-level AC-AC converter according to claim 5, characterized in that: The voltages of the three input bridge arms are equal to the phase voltages of the three-phase AC power grid at the output side in the opposite phase when in steady state.

7. The Yanbian triangle modular multi-level AC-AC converter according to claim 1, characterized in that: The first output bridge arm, the second output bridge arm and the third output bridge arm are controlled by a constant AC voltage amplitude and a constant AC voltage frequency.

8. The Yanbian triangle modular multi-level AC-AC converter according to claim 7, characterized in that: The voltages of the three output bridge arms are equal to the phase voltages of the three-phase AC power grid on the input side in the opposite phase when in steady state.

9. The Yanbian triangle modular multi-level AC-AC converter according to claim 1, characterized in that: The bridge arm voltages of the first circulating bridge arm, the second circulating bridge arm and the third circulating bridge arm are decomposed into a d-axis input component, a q-axis input component, a d-axis output component and a q-axis output component. The d-axis input component and the q-axis input component adopt energy balance control and constant reactive power control between bridge arms, and the d-axis output component and the q-axis output component adopt constant reactive power control.

10. The Yanbian triangle modular multi-level AC-AC converter according to claim 9, characterized in that: The voltages of the three circulating bridge arms are equal to the sum of the three-phase AC grid line voltage on the input side and the three-phase AC grid line voltage on the output side in a steady state.

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