A bridge arm multiplexing MMC wide voltage range modulation method

Abstract

The invention discloses a bridge arm multiplexing MMC wide voltage range modulation method, belonging to the technical field of power system; the technical characteristics are: the bridge arm multiplexing MMC topological structure is composed of a multiplexing submodule bridge arm, a conventional submodule bridge arm, a three-phase switch bridge and a bridge arm inductor; the conventional submodule bridge arms are respectively connected to the middle points of the three-phase switch bridges, the multiplexing submodule bridge arms are connected in parallel with the corresponding three-phase switch bridges, the bridge arm multiplexing MMC wide voltage range modulation method, the multiplexing submodule bridge arm voltage is modulated by three times the power frequency cycle, the on-off of the upper tube and the lower tube of the three-phase switch bridge is reasonably controlled, the energy balance in the power frequency cycle is achieved when the multiplexing submodule bridge arm is multiplexed by any phase of the conventional submodule bridge arm, and the voltage modulation range of the bridge arm multiplexing MMC is widened, and the flexible operation capability of the topology under different voltage operating conditions is effectively improved.

Description

Technical Field

[0001] The invention belongs to the technical field of power systems, and in particular relates to a bridge arm multiplexing MMC wide voltage range modulation method. Background Art

[0002] With the continuous development of science and technology, the current modular multilevel converter (MMC) has shown its great potential in medium-voltage DC transmission and distribution power exchange with its advantages of high modularity, low harmonics, and high reliability. However, in actual DC transmission projects, MMC has exposed the problems of large footprint, low power density and high cost. The huge number of MMC sub-modules is one of the reasons for the above situation. Among them, Chinese patent CN113595424A (a bridge arm multiplexing MMC topology structure) discloses an upper and lower bridge arm multiplexing type MMC topology structure, which is based on the traditional MM A three-phase switch bridge is connected in series at the upper and lower ends of C, and the operation of the three-phase switch bridge is controlled to realize time-sharing multiplexing of the reused bridge arm by the conventional bridge arm, thereby reducing the number of MMC sub-modules. In addition, the proposed modulation method further reduces the capacitance requirements of the reused bridge arm and the conventional bridge arm sub-module, thereby reducing the overall cost and volume; however, the proposed modulation method of the bridge arm multiplexing MMC makes it work in a narrow voltage modulation range, which limits its flexible operation capability at different AC / DC voltage transmission ratios. At the same time, the bridge arm multiplexing MMC does not have the ability to flexibly supply energy to AC ports of different voltage levels in a multi-terminal flexible DC system. Summary of the invention

[0003] In view of the deficiencies of the prior art, the purpose of the present invention is to provide a bridge arm multiplexing MMC wide voltage range modulation method, which solves the technical problem that the voltage modulation range of the modulation method in the prior art is relatively narrow.

[0004] The object of the present invention can be achieved by the following technical solutions: A bridge arm multiplexing MMC wide voltage range modulation method, comprising: a bridge arm multiplexing MMC topology structure comprising: a multiplexing submodule bridge arm, a conventional submodule bridge arm, a three-phase switch bridge and a bridge arm inductor, the multiplexing submodule bridge arm is connected in parallel with the three-phase switch bridge, the conventional submodule bridge arm corresponds to the middle point of the three-phase switch bridge respectively, the multiplexing submodule bridge arm comprises an upper multiplexing submodule bridge arm and a lower multiplexing submodule bridge arm, the conventional submodule bridge arm of any phase comprises an upper conventional submodule bridge arm and a lower conventional submodule bridge arm, and the method comprises the following steps:

[0005] The voltage of the bridge arm of the multiplexing submodule is modulated by three times the power frequency cycle, and the bridge arm of the multiplexing submodule is multiplexed by the bridge arm of any phase conventional submodule, and together shapes the required voltage;

[0006] The upper tube and the lower tube of any phase in the three-phase switch bridge are alternately turned on and off; when the lower tube of the upper three-phase switch bridge of any phase is turned on, the upper multiplexing submodule bridge arm is reused by the upper conventional submodule bridge arm, and the upper multiplexing submodule bridge arm is energy balanced within the power frequency cycle; when the upper tube of the lower three-phase switch bridge arm of any phase is turned on, the lower multiplexing submodule bridge arm is reused by the lower conventional submodule bridge arm, and the lower multiplexing submodule bridge arm is energy balanced within the power frequency cycle;

[0007] When the upper multiplexing submodule bridge arm is reused by the upper conventional submodule bridge arm of any phase, the upper conventional submodule bridge arm modulation voltage is the difference between the positive DC voltage and the upper multiplexing submodule bridge arm modulation voltage, and the upper conventional submodule bridge arm is energy balanced during the power frequency cycle; when the lower multiplexing submodule bridge arm is reused by the lower conventional submodule bridge arm of any phase, the lower conventional submodule bridge arm modulation voltage is the difference between the lower multiplexing submodule bridge arm voltage and the negative DC voltage, and the lower conventional submodule bridge arm is energy balanced during the power frequency cycle.

[0008] Preferably, the upper tubes and the lower tubes of the upper three-phase switch bridge of any phase and the lower three-phase switch bridge of any phase are complementarily conductive.

[0009] Preferably, the working states of the three-phase switch bridge on any phase and the three-phase switch bridge on any phase are as follows:

[0010]

[0011] Among them, γ is the energy balance control angle of the multiplexing submodule bridge arm, is the initial phase of phase j, S ju1 and S ju2 are the switch states of the upper and lower switches of the three-phase switch bridge on phase j, S jl1 and S jl2 They are the switching states of the upper and lower tubes of the three-phase switch bridge under phase j respectively.

[0012] Preferably, when S ju1 / S ju2 =1, the upper and lower tubes of the three-phase switch bridge on phase j are turned on; when S ju1 / S ju2 = 0, the upper and lower tubes of the three-phase switch bridge on phase j are turned off; when S jl1 / S jl2 =1, the upper and lower tubes of the three-phase switch bridge under phase j are turned on; when S jl1 / S jl2 =0, the upper tube / lower tube of the three-phase switch bridge under phase j is turned off.

[0013] Preferably, the reference voltage signal of the bridge arm of the multiplexing submodule is a piecewise function, as follows:

[0014]

[0015] Among them, vmu is the modulation voltage of the bridge arm of the upper multiplexing submodule, v ml is the modulation voltage of the bridge arm of the lower multiplexing submodule, v dc is the DC port voltage, α1 and α2 are proportional coefficients, and ω is the power angular frequency.

[0016] Preferably, the bridge arm modulation voltages of the conventional submodule on any phase and the conventional submodule on any phase are as follows:

[0017]

[0018] m=2v j / v dc

[0019] Among them, v cju 、v cjl are the modulation voltages of the upper and lower conventional submodule bridge arms of phase j respectively; m is the modulation ratio; v j is the j-phase AC port voltage.

[0020] Preferably, the multiplexing submodule bridge arm realizes energy balance within the power frequency cycle, and the energy balance principle of the upper multiplexing submodule bridge arm and the lower multiplexing submodule bridge arm is the same, and the energy accumulation is expressed as:

[0021]

[0022] By calculating the above formula, we can get the energy balance control angle γ of the bridge arm of the multiplexing submodule, the modulation index m, and the power factor under fixed α1 and α2: The relational expression of .

[0023] Preferably, the conventional submodule bridge arm achieves energy balance within the power frequency cycle, and the energy accumulation is expressed as:

[0024]

[0025] Beneficial effects of the present invention:

[0026] The present invention realizes the wide voltage range modulation of the bridge arm multiplexing MMC by reasonably designing the multiplexing bridge arm modulation voltage and the multiplexing bridge arm energy balance control angle, thereby enhancing its flexible operation capability under different AC / DC voltage transmission ratios; the designed bridge arm energy balance control angle increases the number of multiplexed bridge arm sub-modules, thereby further reducing the overall cost and volume. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0028] Figure 1 It is a bridge arm multiplexing MMC topology diagram of the present invention;

[0029] Figure 2 This is a diagram of a bridge arm multiplexing MMC wide voltage range modulation method of the present invention;

[0030] Figure 3 : is a diagram of driving signals of upper and lower three-phase switch bridges according to an embodiment of the present invention;

[0031] Figure 4 is a diagram showing the relationship between the energy balance control angle γ of the bridge arm of the multiplexing submodule and the modulation ratio m in an embodiment of the present invention;

[0032] Figure 5 This is a diagram of the simulation results of the bridge arm voltage and current under the modulation method when the modulation ratio is 0.9 in an embodiment of the present invention. DETAILED DESCRIPTION

[0033] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] like Figure 1 As shown, the bridge arm multiplexing MMC topology structure includes a multiplexing submodule bridge arm, a conventional submodule bridge arm, a three-phase switch bridge and a bridge arm inductor; the conventional submodule bridge arm is respectively connected to the middle point of the three-phase switch bridge, and the multiplexing submodule bridge arm is connected in parallel with the corresponding three-phase switch bridge.

[0035] In the embodiment of the present invention, preferably, the multiplexed submodule bridge arm and the conventional submodule bridge arm can select a half-bridge submodule, a full-bridge submodule, other structural submodules or a hybrid submodule; the three-phase full-bridge switch can select a series-connected fully-controlled power device or an anti-parallel half-controlled device;

[0036] In this embodiment, both the conventional bridge arm and the multiplexed bridge arm adopt a half-bridge submodule (HBSM). A wide voltage range modulation method of the present invention is described in detail below. Figure 2As shown. The voltage of the bridge arm of the multiplexing submodule is modulated by three times the power frequency cycle. The bridge arm of the multiplexing submodule is reused by the bridge arm of the conventional submodule of the phase in any one-third cycle, and the required voltage is shaped together. The upper tube and the lower tube of any phase in the three-phase switch bridge are switched on and off alternately; when the lower tube of the three-phase switch bridge on any phase is turned on, the bridge arm of the upper multiplexing submodule is reused by the bridge arm of the conventional submodule on the phase, and the bridge arm of the upper multiplexing submodule is energy balanced in the power frequency cycle; when the upper tube of the three-phase switch bridge arm on any phase is turned on, the bridge arm of the lower multiplexing submodule is reused by the bridge arm of the conventional submodule on the phase, and the bridge arm of the lower multiplexing submodule is energy balanced in the power frequency cycle. When the bridge arm of the upper multiplexing submodule is reused by the bridge arm of the conventional submodule on any phase, the modulation voltage of the bridge arm of the upper conventional submodule is the difference between the positive DC voltage and the modulation voltage of the bridge arm of the upper multiplexing submodule, and the bridge arm of the conventional submodule on the phase is energy balanced in the power frequency cycle. When the lower multiplexing submodule bridge arm is reused by the lower normal submodule bridge arm of any phase, the lower normal submodule bridge arm modulation voltage is the difference between the lower multiplexing submodule bridge arm voltage and the negative DC voltage, and the lower normal submodule bridge arm of this phase is energy balanced in the power frequency cycle.

[0037] The upper and lower three-phase switch bridge switch drive signals are as follows Figure 3 As shown, the upper and lower tubes of any phase upper and lower three-phase switch bridge are complementary and turned on, and the working principle is consistent, so the working state of any phase upper and lower three-phase switch bridge is as follows:

[0038]

[0039] Among them, γ is the energy balance control angle of the multiplexing submodule bridge arm, is the initial phase of phase j, S ju1 and S ju2 are the switch states of the upper and lower switches of the three-phase switch bridge on phase j, S jl1 and S jl2 are the switching states of the upper and lower tubes of the three-phase switch bridge under phase j respectively. ju1 / S ju2 =1, the upper and lower tubes of the three-phase switch bridge on phase j are turned on; when S ju1 / S ju2 = 0, the upper and lower tubes of the three-phase switch bridge on phase j are turned off; when S jl1 / S jl2 =1, the upper and lower tubes of the three-phase switch bridge under phase j are turned on; when S jl1 / S jl2 =0, the upper tube / lower tube of the three-phase switch bridge under phase j is turned off;

[0040] Because the multiplexed submodule bridge arm has consistency when being multiplexed by the conventional submodule bridge arm, the conventional submodule bridge arm under phase A and the lower multiplexed submodule bridge arm are taken as examples for analysis.

[0041] The modulation voltage of the bridge arm of the lower multiplexing submodule is three times the power frequency cycle modulation, and α1 and α2 are defined as:

[0042]

[0043] Where m is the modulation ratio, expressed as

[0044] m=2v j / v dc (3)

[0045] v mumax 、v mlmax are the maximum modulation voltages of the bridge arms of the upper and lower multiplexing submodules, respectively, which can be expressed as:

[0046]

[0047] The reference voltage signal of the bridge arm of the multiplexing submodule is a piecewise function, which is expressed as follows:

[0048]

[0049] Among them, v mu is the modulation voltage of the bridge arm of the upper multiplexing submodule, v ml is the modulation voltage of the bridge arm of the lower multiplexing submodule, v dc is the DC port voltage, ω is the power frequency angular frequency, v j is the j-phase AC port voltage.

[0050] The modulation voltage of the bridge arm of the upper and lower conventional submodules of any phase is as follows:

[0051]

[0052] Among them, v cju 、v cjl They are the bridge arm modulation voltages of the upper and lower conventional submodules of phase j respectively.

[0053] The multiplexing submodule bridge arm is the power frequency cycle energy balance. Taking the multiplexing submodule bridge arm as an example, its energy accumulation is expressed as:

[0054]

[0055] By calculating (7), we can obtain the energy balance control angle γ of the bridge arm of the multiplexing submodule, the modulation index m, and the power factor The relational expression is (8)

[0056]

[0057] Similarly, the conventional submodule bridge arm can also achieve energy balance in the power frequency cycle. Taking the conventional submodule bridge arm as an example, its energy accumulation is (9). In the range of 0≤γ≤2π, the calculation result is 0, indicating that the conventional submodule bridge arm can also achieve energy balance under the proposed modulation method.

[0058]

[0059] according to Figure 2 In the definition of γ, when When the power factor is unity, the implicit function of expression (7) is plotted in the range of 0≤γ≤2π / 3, 0≤m≤1. It can be obtained that when the energy of the multiplexed submodule bridge arm is balanced, the relationship between γ and the modulation index m is as follows: Figure 3 As shown. Figure 3 It can be seen that when m = 0, γ = 2π / 3, the maximum modulation voltage of the bridge arm of the multiplexing submodule is 1 / 2v dc , of course, this is an ideal situation. When m = 0.9, γ = 0.959, at this time, the maximum modulatable voltage of the bridge arm of the multiplexing submodule is 0.31v dc , the maximum modulation voltage of the conventional submodule bridge arm is 0.69v dc Compared with the total of 6n half-bridge submodules in the traditional MMC, the proposed modulation method can save 20.68% of submodules. According to the modulation method described in "A bridge arm multiplexing MMC topology structure" disclosed in Chinese patent CN113595424A, when m=0.9, the multiplexed bridge arm can reuse up to 0.308vdc, which can save 20.56% of submodules compared with the traditional MMC. Therefore, the wide voltage range modulation method proposed in the present invention helps to further reduce the number of submodules of the bridge arm multiplexing MMC, reducing costs and volume.

[0060] In addition, the capacitance requirements of the reused submodule bridge arm and the conventional submodule bridge arm are analyzed and calculated. Taking the transmission project parameters of a converter station at the fifth end of Zhoushan as a reference, sm is 1.6kV, DC bus voltage v dc The bridge arm is 400kV, with 250 submodules in a single bridge arm, ε=5%, m=0.9, and a capacity of 400MVA. The bridge arm reuse MMC uses 78 HBSMs for the reused bridge arm, and 172 HBSMs for the conventional submodule bridge arm. Taking the reused submodule bridge arm as an example, its energy fluctuation in the range of π / 6-γ≤ωt≤5π / 6 is

[0061]

[0062] The energy fluctuation of the bridge arm of the multiplexing submodule can also be expressed as

[0063] ΔE ml =2n m C msm v sm2 ε (11)

[0064] Calculate ΔE ml is 0.0414MW. Combining (10) and (11), we get C msm =2.1mF.

[0065] Similarly, the energy fluctuation of the conventional submodule bridge arm is

[0066]

[0067] ΔE al =2n al C csm v sm 2 ε (13)

[0068] Calculate ΔE ml is 0.4635MW. Combining (12) and (13), we get C csm =10.5mF.

[0069] The submodule capacitance of a converter station in Zhoushan is 12mF, the capacitance requirement of the multiplexed bridge arm submodule can be reduced by 82.5%, and the capacitance requirement of the conventional bridge arm submodule can be reduced by 12.5%. Therefore, in summary, the proposed modulation method of the bridge arm multiplexing MMC not only reduces the number of submodules and the cost, but also greatly reduces the volume and weight of the device.

[0070] In addition, the proposed topology of the bridge arm multiplexing MMC was simulated and verified at ±10kV, S=1MVA, with 3 multiplexing bridge arm submodules and 9 conventional bridge arm submodules. The submodule voltage was 1.67kV and the modulation ratio was 0.9. The simulation results are shown in Figure 5 As shown, au 、i al They are the upper and lower conventional submodule bridge arm currents of phase A, i u 、i l are the bridge arm currents of the upper and lower multiplexing submodules, v cau 、v cal They are the upper and lower conventional submodule bridge arm voltages of phase A, v mu 、v ml are the bridge arm voltages of the upper and lower multiplexing submodules, v causm 、v calsm They are the upper and lower conventional bridge arm submodule voltages of phase A, v musm 、v mlsm They are the voltages of the upper and lower multiplexed bridge arm submodules respectively.

[0071] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0072] The above shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited by the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. A bridge arm multiplexing MMC wide voltage range modulation method, characterized in that: include: The bridge arm multiplexing MMC topological structure includes: a multiplexing submodule bridge arm, a conventional submodule bridge arm, a three-phase switch bridge and a bridge arm inductor, wherein the multiplexing submodule bridge arm is connected in parallel with the three-phase switch bridge, the conventional submodule bridge arms respectively correspond to the middle points of the three-phase switch bridge, the multiplexing submodule bridge arm includes an upper multiplexing submodule bridge arm and a lower multiplexing submodule bridge arm, and the conventional submodule bridge arm of any phase includes an upper conventional submodule bridge arm and a lower conventional submodule bridge arm, and the method includes the following steps: The voltage of the bridge arm of the multiplexing submodule is modulated by three times the power frequency cycle, and the bridge arm of the multiplexing submodule is multiplexed by the bridge arm of any phase conventional submodule, and together shapes the required voltage; The upper tube and the lower tube of any phase in the three-phase switch bridge are alternately turned on and off; when the lower tube of the upper three-phase switch bridge of any phase is turned on, the upper multiplexing submodule bridge arm is reused by the upper conventional submodule bridge arm, and the upper multiplexing submodule bridge arm is energy balanced within the power frequency cycle; when the upper tube of the lower three-phase switch bridge arm of any phase is turned on, the lower multiplexing submodule bridge arm is reused by the lower conventional submodule bridge arm, and the lower multiplexing submodule bridge arm is energy balanced within the power frequency cycle; When the upper multiplexing submodule bridge arm is reused by the upper conventional submodule bridge arm of any phase, the modulation voltage of the upper conventional submodule bridge arm is the difference between the positive DC voltage and the modulation voltage of the upper multiplexing submodule bridge arm, and the upper conventional submodule bridge arm is energy balanced during the power frequency cycle. When the lower multiplexing submodule bridge arm is reused by the lower conventional submodule bridge arm of any phase, the modulation voltage of the lower conventional submodule bridge arm is the difference between the lower multiplexing submodule bridge arm voltage and the negative DC voltage, and the lower conventional submodule bridge arm is energy balanced during the power frequency cycle.

2. A bridge arm multiplexing MMC wide voltage range modulation method according to claim 1, characterized in that: The upper tubes and the lower tubes of the upper three-phase switch bridge of any phase and the lower three-phase switch bridge of any phase are complementarily turned on.

3. A bridge arm multiplexing MMC wide voltage range modulation method according to claim 2, characterized in that: The working states of the three-phase switch bridge on any phase and the three-phase switch bridge on any phase are as follows: Among them, γ is the energy balance control angle of the multiplexing submodule bridge arm, is the initial phase of phase j, S ju1 and S ju2 are the switch states of the upper and lower switches of the three-phase switch bridge on phase j, S jl1 and S jl2 They are the switching states of the upper and lower tubes of the three-phase switch bridge under phase j respectively.

4. A bridge arm multiplexing MMC wide voltage range modulation method according to claim 3, characterized in that: When S ju1 / S ju2 =1, the upper and lower tubes of the three-phase switch bridge on phase j are turned on; when S ju1 / S ju2 = 0, the upper and lower tubes of the three-phase switch bridge on phase j are turned off; when S jl1 / S jl2 =1, the upper and lower tubes of the three-phase switch bridge under phase j are turned on; when S jl1 / S jl2 =0, the upper tube / lower tube of the three-phase switch bridge under phase j is turned off.

5. A bridge arm multiplexing MMC wide voltage range modulation method according to claim 4, characterized in that: The reference voltage signal of the bridge arm of the multiplexing submodule is a piecewise function, as follows: Among them, v mu is the modulation voltage of the bridge arm of the upper multiplexing submodule, v ml is the modulation voltage of the bridge arm of the lower multiplexing submodule, v dc is the DC port voltage, α1 and α2 are proportional coefficients, and ω is the power angular frequency.

6. A bridge arm multiplexing MMC wide voltage range modulation method according to claim 5, characterized in that: The bridge arm modulation voltages of the conventional submodule on any phase and the conventional submodule under any phase are as follows: Among them, v cju 、v cjl are the modulation voltages of the upper and lower conventional submodule bridge arms of phase j respectively; m is the modulation ratio; v j is the j-phase AC port voltage.

7. A bridge arm multiplexing MMC wide voltage range modulation method according to claim 6, characterized in that: The multiplexing submodule bridge arm realizes energy balance within the power frequency cycle. The energy balance principle of the upper multiplexing submodule bridge arm and the lower multiplexing submodule bridge arm is the same. The energy accumulation is expressed as: By calculating the above formula, we can get the energy balance control angle γ of the bridge arm of the multiplexing submodule, the modulation index m, and the power factor under fixed α1 and α2: The relational expression of .

8. A bridge arm multiplexing MMC wide voltage range modulation method according to claim 7, characterized in that: The conventional submodule bridge arm achieves energy balance within the power frequency cycle, and the energy accumulation is expressed as:

9. A device, characterized in that: include: one or more processors; A memory for storing one or more programs; When the one or more programs are executed by the one or more processors, the one or more processors implement a bridge arm multiplexing MMC wide voltage range modulation method as described in any one of claims 1-8.

10. A storage medium containing computer executable instructions, characterized in that: The computer executable instructions are used to execute a bridge arm multiplexing MMC wide voltage range modulation method as described in any one of claims 1-8 when executed by a computer processor.

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