Hybrid MMC bridge arm grouping control method and system based on module reference wave reconstruction

Abstract

The invention discloses a hybrid MMC bridge arm grouping control method and system based on module reference wave reconstruction, and belongs to the field of multi-level converters, and the control method specifically comprises the steps: firstly, obtaining reference waves of a half-bridge module and a full-bridge module through bridge arm reference waves according to a reference wave reconstruction algorithm; respectively modulating reference waves of the half-bridge module and the full-bridge module, and adopting a capacitor voltage balance control method to obtain driving signals of the half-bridge module and the full-bridge module; according to the method, the bridge arm modules are divided into two groups according to the half-bridge module and the full-bridge module and are respectively controlled, and different from a traditional voltage-sharing control method in which all the bridge arm modules are sorted together, the problem of high coupling of charging and discharging behaviors of the half-bridge module and the full-bridge module is avoided, the flexibility of bridge arm energy control is improved, and the energy consumption is reduced. And the complexity of a capacitor voltage balance algorithm is reduced.

Description

Technical Field

[0001] The invention relates to the field of multi-level converters, and in particular to a hybrid MMC bridge arm grouping control method based on module reference wave reconstruction. Background Art

[0002] MMC (modular multilevel converter) is easy to expand the number of output levels, has high efficiency, and has low AC output harmonics, so it is very suitable for medium, high voltage and high power power electronic conversion occasions. The hybrid MMC bridge arm is configured with a number of half-bridge modules and full-bridge modules in series in proportion. Compared with the traditional half-bridge MMC, the hybrid MMC has the ability to block DC short-circuit fault current and can operate in overmodulation. It has higher flexibility in design and control and is suitable for a variety of complex working conditions. It has broad application prospects in the fields of flexible DC transmission, AC / DC distribution network, and new energy storage.

[0003] The existing control scheme of the hybrid MMC is similar to that of the traditional half-bridge MMC. First, the bridge arm reference wave is modulated to obtain the number of output levels of the bridge arm; then, according to the number of output levels and their positive and negative signs, the direction of the bridge arm current, the capacitor voltage of all modules in the bridge arm, etc., the drive signal of all modules in the bridge arm is obtained according to the capacitor voltage balance control based on sorting. However, since all modules participate in the sorting and voltage balancing in this process, the charging and discharging behaviors of the half-bridge module and the full-bridge module are highly coupled, and the dynamic energy regulation between the half-bridge and full-bridge modules is difficult. The difference in energy distribution between the half-bridge and full-bridge modules further affects the selection, thermal stress, reliability, etc. of active and passive devices. In addition, the complexity of the sorting algorithm increases rapidly with the increase in the number of modules. For example, the average time complexity of the bubble sort method for N capacitor voltages is O(N 2 ). Therefore, it is necessary to invent new control methods to address the above problems, improve the flexibility of energy regulation of hybrid MMC half-bridge and full-bridge modules, optimize the energy between half-bridge modules and full-bridge modules, and reduce the complexity of the sorting algorithm. Summary of the invention

[0004] The technical problem to be solved by the present invention is: in view of the shortcomings of the prior art, the present invention proposes a hybrid MMC bridge arm grouping control method based on module reference wave reconstruction, in which the bridge arm reference wave is divided into a half-bridge module reference wave and a full-bridge module reference wave according to two types of modules in the bridge arm, and the reference waves of the half-bridge and full-bridge modules can be changed by a dynamic adjustment factor.

[0005] In order to solve the above technical problems, the present invention is implemented through the following technical solutions:

[0006] The present invention proposes a hybrid MMC bridge arm grouping control method based on module reference wave reconstruction, comprising the following steps:

[0007] The bridge arm reference wave y xj Get the reference wave y of the half-bridge module and the full-bridge module in the bridge arm xj_H and xj_F :

[0008]

[0009] Among them, k H and k F They are the number of half-bridge modules N in the bridge arm. H and the number of full-bridge modules N F The total number of modules in the bridge arm (N H +N F ), i.e., k H =N H / (N H +N F ), k F =N F / (N H +N F ), satisfying k H +k F =1;h xj is a dynamic adjustment factor obtained according to the adjustment algorithm; subscript x = u, l, respectively, represents the upper and lower bridge arms; subscript j = a, b, c, respectively, represents the three phases A, B, and C;

[0010] Reference wave y of half-bridge module xj_H The number of output levels n of the half-bridge module in the bridge arm is obtained by modulation xj_H , ranging from 0 to N H Then, according to the direction of the bridge arm current, the size of the capacitor voltage and the sorting voltage control method, the driving signals of all the half-bridge modules in the bridge arm are obtained;

[0011] At the same time, the reference wave y of the full-bridge module xj_F The number of output levels n of the full-bridge module in the bridge arm is obtained by modulation xj_F , the range is -N F ~N F Then, according to the sign of the reference wave, the direction of the bridge arm current, the size of the capacitor voltage and the sorting and voltage-sharing control method, the driving signals of all the full-bridge modules in the bridge arm are obtained.

[0012] Furthermore, in the control method proposed by the present invention, the dynamic adjustment factor h xj The adjustment algorithm consists of the following two sub-steps:

[0013] S1, through the voltage balance control algorithm of the half-bridge module and the full-bridge module, the average voltage of the full-bridge module is subtracted from the average voltage of the half-bridge module to obtain the voltage error. The voltage error is determined by the proportional-integral controller and the direction of the bridge arm current to obtain h xj ,as follows

[0014]

[0015] Wherein, sign(x) is a sign function. If x>0, sign(x)=1; if x=0, sign(x)=0; if x<0, sign(x)=-1.

[0016] S2, h xj Correct according to the following formula:

[0017]

[0018] Furthermore, in the control method proposed by the present invention, the half-bridge module sorting and voltage equalization control method is: if the bridge arm current is greater than or equal to zero, then the half-bridge module with the lowest capacitor voltage whose number is equal to the number of modulation levels is put into use; otherwise, the half-bridge module with the highest capacitor voltage whose number is equal to the number of modulation levels is put into use.

[0019] Furthermore, in the control method proposed by the present invention, the full-bridge module sorting and voltage-equalizing control method is: if the product of the full-bridge module reference wave and the bridge arm current is greater than or equal to zero, the full-bridge module with the lowest capacitor voltage whose number is equal to the number of modulation levels is put into use; otherwise, the full-bridge module with the highest capacitor voltage whose number is equal to the number of modulation levels is put into use. The number of modulation levels greater than zero indicates positive input, and the number of modulation levels less than zero indicates negative input.

[0020] Furthermore, the present invention also proposes a hybrid MMC bridge arm grouping control system based on module reference wave reconstruction, wherein the hybrid MMC bridge arm comprises N H half-bridge modules and N F A full-bridge module, the control system comprises:

[0021] The bridge arm reference wave acquisition module is used to obtain the reference waves of the half-bridge module and the full-bridge module in the bridge arm according to the bridge arm reference wave. The specific calculation formula is:

[0022]

[0023] where y xj is the bridge arm reference wave, y xj_H and xj_ are the reference waves of the half-bridge module and the full-bridge module, k H and k F They are the number of half-bridge modules N in the bridge arm. H and the number of full-bridge modules NF The proportion of the total number of modules in the bridge arm, h xj is a dynamic adjustment factor obtained according to the adjustment algorithm; subscript x = u, l, respectively, represents the upper and lower bridge arms; subscript j = a, b, c, respectively, represents the three phases A, B, and C;

[0024] A half-bridge module drive signal acquisition module is used to obtain the number of output levels of the half-bridge modules in the bridge arm according to the modulation of the half-bridge module reference wave, and then obtain the drive signals of all the half-bridge modules in the bridge arm according to the direction of the bridge arm current, the size of the capacitor voltage and the sorting and voltage-sharing control method;

[0025] The full-bridge module drive signal acquisition module is used to obtain the output level number of the full-bridge module in the bridge arm according to the modulation of the full-bridge module reference wave, and then obtain the drive signal of all the full-bridge modules in the bridge arm according to the sign of the reference wave, the direction of the bridge arm current, the size of the capacitor voltage and the sorting and equalizing control method.

[0026] At the same time, the present invention proposes an electronic device, which includes a memory, a processor, and program instructions stored in the memory and executable by the processor to implement each step of the control method proposed by the present invention.

[0027] Finally, a computer-readable storage medium storing computer instructions is provided, wherein the computer instructions are used to enable the computer to execute the steps of the control method described in the present invention.

[0028] Compared with the prior art, the present invention adopts the above technical solution and has the following beneficial effects:

[0029] The method proposed in the present invention can separate the capacitor voltage balance control of the half-bridge module and the full-bridge module, and the control of the bridge arm module is divided into two groups. The reference wave of the half-bridge module is modulated and the capacitor voltage balance control is performed to obtain the driving signal of the half-bridge module; the reference wave of the full-bridge module is modulated and the capacitor voltage balance control is performed to obtain the driving signal of the full-bridge module. Using this method, the capacitor voltage balance control of the half-bridge module and the full-bridge module is separated, avoiding the problem of highly coupled charging and discharging behaviors caused by all modules participating in the sorting and voltage balancing.

[0030] Accordingly, by adjusting the reference wave of the half-bridge module and the full-bridge module, the energy of the two modules can be flexibly adjusted. In addition, the division of the bridge arm modules into two groups also reduces the overall sorting complexity and the amount of calculation of the algorithm. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a topological structure diagram of the three-phase hybrid MMC and its submodules of the present invention.

[0032] Figure 2 It is an overall schematic diagram of the control method of the present invention.

[0033] Figure 3 The h of the present invention xj Control block diagram of the voltage balance control algorithm for the half-bridge module and full-bridge module in the regulation algorithm.

[0034] Figure 4 This is a simulation waveform diagram of the bridge arm reference wave and the half-bridge and full-bridge module reference wave of the control method proposed in the present invention.

[0035] Figure 5 This is a simulation waveform diagram of the capacitor voltage of the half-bridge and full-bridge modules of the control method proposed in the present invention. DETAILED DESCRIPTION

[0036] 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.

[0037] like Figure 1 The three-phase hybrid MMC topology is shown. Each phase consists of an upper and lower bridge arm, each bridge arm includes N H half-bridge modules and N F A full bridge module.

[0038] Embodiment 1:

[0039] like Figure 2 FIG. 1 is a schematic diagram of the overall control method proposed by the present invention. The method comprises the following steps:

[0040] 1) The bridge arm reference wave y xj Get the reference wave y of the half-bridge module and the full-bridge module in the bridge arm xj_H and xj_F :

[0041]

[0042] Among them, k H and k F They are the number of half-bridge modules N in the bridge arm. H and the number of full-bridge modules N F The total number of modules in the bridge arm (N H +N F ), that is, k H =N H / (N H +N F ), k F =N F / (NH +N F ), satisfying k H +k F =1;h xj is a dynamic adjustment factor obtained according to the adjustment algorithm; the subscript x=u, l represents the upper and lower bridge arms respectively; the subscript j=a, b, c represents the three phases A, B, and C respectively.

[0043] 2) Half-bridge module reference wave y xj_H The number of output levels of the half-bridge module in the bridge arm is obtained by modulation. xj_H , ranging from 0 to N H Then, according to the direction of the bridge arm current, the size of the capacitor voltage and the sorting voltage control method, the driving signals of all the half-bridge modules in the bridge arm are obtained;

[0044] 3) At the same time, the full-bridge module reference wave y xj_F The number of full-bridge module output levels in the bridge arm is obtained by modulation. xj_F , the range is -N F ~N F Then, according to the sign of the reference wave, the direction of the bridge arm current, the size of the capacitor voltage and the sorting and voltage-sharing control method, the driving signals of all the full-bridge modules in the bridge arm are obtained.

[0045] In step 1) of the proposed method, the bridge arm reference wave is generated by other controllers according to the specific operating requirements of the MMC, including a DC component, a fundamental frequency component, a double frequency component, etc., which is used to realize functions such as control of AC current, voltage or power and circulating current control, including but not limited to control methods such as vector controller or resonant controller of AC current, vector controller or resonant controller of circulating current.

[0046] In step 1) of the proposed method, the dynamic adjustment factor h xj The adjustment algorithm consists of the following two sub-steps:

[0047] S1, h is obtained through the voltage balance control algorithm of the half-bridge module and the full-bridge module xj , the control block diagram is as follows Figure 3 Specifically, the average voltage of the full-bridge module is subtracted from the average voltage of the half-bridge module to obtain the voltage error, which is then determined by the proportional-integral controller and the direction of the bridge arm current to obtain h xj . It can be expressed as

[0048]

[0049] Wherein, sign(x) is a sign function. If x>0, sign(x)=1; if x=0, sign(x)=0; if x<0, sign(x)=-1.

[0050] S2, h xj Correct according to the following formula:

[0051]

[0052] In steps 2) and 3) of the proposed method, modulation includes but is not limited to nearest level approximation modulation NLM, carrier phase shift modulation CPS-PWM, carrier cascade modulation PD-PWM and other methods.

[0053] In step 2) of the proposed method, the sorting and voltage-equalizing control method of the half-bridge modules is as follows: if the bridge arm current is greater than or equal to zero, the half-bridge module with the lowest capacitor voltage whose number is equal to the number of modulation levels is put into use; otherwise, the half-bridge module with the highest capacitor voltage whose number is equal to the number of modulation levels is put into use.

[0054] In step 3) of the proposed method, the sorting and voltage-equalizing control method of the full-bridge module is: if the product of the full-bridge module reference wave and the bridge arm current is greater than or equal to zero, the full-bridge module with the lowest capacitor voltage whose number is equal to the number of modulation levels is put into operation; otherwise, the full-bridge module with the highest capacitor voltage whose number is equal to the number of modulation levels is put into operation. The number of modulation levels greater than zero indicates positive input, and the number of modulation levels less than zero indicates negative input.

[0055] Taking the bubble sort method as an example, the average time complexity of the sorting algorithm in the voltage balancing control of the half-bridge module and the full-bridge module in the control method proposed by the present invention is Smaller than the average time complexity of the traditional sorting and balancing algorithm O((N H +N F ) 2 ).

[0056] Embodiment 2:

[0057] This embodiment proposes a hybrid MMC bridge arm grouping control system based on module reference wave reconstruction, wherein the hybrid MMC bridge arm includes N H half-bridge modules and N F A full-bridge module, the control system comprises:

[0058] The bridge arm reference wave acquisition module is used to obtain the reference waves of the half-bridge module and the full-bridge module in the bridge arm according to the bridge arm reference wave. The specific calculation formula is:

[0059]

[0060] where y xj is the bridge arm reference wave, y xj_H and xj_ are the reference waves of the half-bridge module and the full-bridge module, k H and k FThey are respectively the number N of half - bridge modules in the arm H and the number N of full - bridge modules F which account for the proportion h of the total number of modules in the arm. xj α is the dynamic adjustment factor, obtained according to the adjustment algorithm; the subscript x = u, l respectively represents the upper and lower arms; the subscript j = a, b, c respectively represents the three phases A, B, and C.

[0061] The half - bridge module drive signal acquisition module is used to obtain the output level number of the half - bridge modules in the arm according to the modulation of the half - bridge module reference wave, and then obtain the drive signals of all the half - bridge modules in the arm according to the direction of the arm current, the magnitude of the capacitor voltage and in combination with the sorting equal - voltage control method.

[0062] The full - bridge module drive signal acquisition module is used to obtain the output level number of the full - bridge modules in the arm according to the modulation of the full - bridge module reference wave, and then obtain the drive signals of all the full - bridge modules in the arm according to the sign of the reference wave, the direction of the arm current, the magnitude of the capacitor voltage and in combination with the sorting equal - voltage control method.

[0063] In order to verify a hybrid MMC arm grouping control method based on module reference wave reconstruction proposed by the present invention, it is further described below in combination with simulation examples. The simulation parameters of the three - phase hybrid MMC grid - connected circuit are shown in Table 1.

[0064] As Figure 4 shown are the arm reference wave and the simulation waveform diagrams of the half - bridge and full - bridge module reference waves of the arm grouping control method proposed by the present invention. According to the reference wave reconstruction method proposed by the present invention, from the reference wave y ua of the upper arm of phase A, the reference wave y ua_H of the half - bridge module and the reference wave y ua_F of the full - bridge module are obtained, and the sum of y ua_H and y ua_F is always equal to y ua .

[0065] Table 1 Hybrid MMC circuit simulation parameters

[0066] parameter Numeric Active power P(MW) 5 <![CDATA[DC voltage U dc (kV)]]> 8 <![CDATA[AC grid voltage u grid (kV)]]> 6 <![CDATA[Grid frequency f grid (Hz)]]> 50 <![CDATA[Module capacitor voltage rating U CN (kV)]]> 1 <![CDATA[Number N of half-bridge modules H > 6 <![CDATA[Number N of full-bridge modules F > 6 <![CDATA[Module capacitance value C sm (mF)]]> 5 <![CDATA[Bridge arm inductor L s (mH)]]> 5

[0067] As Figure 5 shown is the simulation waveform diagram of the capacitor voltage of the arm grouping control method proposed by the present invention. u Cua1 ~u Cua6 are the capacitor voltages of the half - bridge modules of the upper arm of phase A, and u Cua7 ~u Cua12 are the capacitor voltages of the full - bridge modules of the upper arm of phase A. Under the control method proposed by the present invention, the capacitor voltages of the half - bridge modules and the full - bridge modules always remain stable and balanced.

[0068] Figure 4 and Figure 5 The simulation results verify the feasibility and effectiveness of the hybrid MMC bridge arm grouping control method for base module reference wave reconstruction proposed in the present invention.

[0069] Embodiment 3:

[0070] This embodiment provides an electronic device, which includes a memory, a processor, and program instructions stored in the memory and executable by the processor to implement each step of the control method provided in the present invention.

[0071] Embodiment 4:

[0072] This embodiment provides a computer-readable storage medium storing computer instructions, where the computer instructions are used to enable the computer to execute each step of the control method provided in the present invention.

[0073] It should be noted that the processing flow of the embodiments 2 to 4 corresponds to the specific steps of the method provided in the embodiment of the present invention, and has the functional modules and beneficial effects corresponding to the execution method. For technical details not described in detail in this embodiment, please refer to the method provided in the embodiment of the present invention.

[0074] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to 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 hybrid MMC bridge arm grouping control method based on module reference wave reconstruction, wherein the hybrid MMC bridge arm includes N H half-bridge modules and N F A full-bridge module, characterized in that The following steps are involved: The bridge arm reference wave y xj Get the reference wave y of the half-bridge module and the full-bridge module in the bridge arm xj_H and xj_F : Among them, k H and k F They are the number of half-bridge modules N in the bridge arm. H and the number of full-bridge modules N F The proportion of the total number of modules in the bridge arm; h xj is a dynamic adjustment factor obtained according to the adjustment algorithm; subscript x = u, l, respectively, represents the upper and lower bridge arms; subscript j = a, b, c, respectively, represents the three phases A, B, and C; Half-bridge module reference wave y xj_H The number of output levels n of the half-bridge module in the bridge arm is obtained by modulation xj_H , ranging from 0 to N H Then, according to the direction of the bridge arm current, the size of the capacitor voltage and the sorting voltage control method, the driving signals of all the half-bridge modules in the bridge arm are obtained; At the same time, the reference wave y of the full-bridge module xj_F The number of output levels n of the full-bridge module in the bridge arm is obtained by modulation xj_F , the range is -N F ~N F Then, according to the sign of the reference wave, the direction of the bridge arm current, the size of the capacitor voltage and the sorting and voltage-sharing control method, the driving signals of all the full-bridge modules in the bridge arm are obtained.

2. A hybrid MMC bridge arm grouping control method based on module reference wave reconstruction according to claim 1, characterized in that: Dynamic adjustment factor h xj The adjustment algorithm consists of the following two sub-steps: In the first step, the voltage balance control algorithm of the half-bridge module and the full-bridge module is used to subtract the average voltage of the full-bridge module from the average voltage of the half-bridge module to obtain the voltage error. The voltage error is determined by the proportional-integral controller and the direction of the bridge arm current to obtain h xj ,as follows Wherein, sign(x) is a sign function, if x>0, sign(x)=1; if x=0, sign(x)=0; if x<0, sign(x)=-1; Step 2, h xj Correct according to the following formula:

3. A hybrid MMC bridge arm grouping control method based on module reference wave reconstruction according to claim 1, characterized in that: The half-bridge module sorting and voltage balancing control method is: if the bridge arm current is greater than or equal to zero, the half-bridge module with the lowest capacitor voltage whose number is equal to the number of modulation levels is put into use; otherwise, the half-bridge module with the highest capacitor voltage whose number is equal to the number of modulation levels is put into use.

4. A hybrid MMC bridge arm grouping control method based on module reference wave reconstruction according to claim 1, characterized in that: The full-bridge module sorting and voltage-equalizing control method is as follows: if the product of the full-bridge module reference wave and the bridge arm current is greater than or equal to zero, then the full-bridge module with the lowest capacitor voltage whose number is equal to the number of modulation levels is put into use; Otherwise, a full-bridge module with the highest capacitor voltage whose number is equal to the number of modulation levels is put into use; A modulation level number greater than zero indicates a positive input, and a modulation level number less than zero indicates a negative input.

5. The hybrid MMC bridge arm grouping control method based on module reference wave reconstruction according to claim 1 is characterized in that: The reference wave modulation methods of the half-bridge module and the full-bridge module include the nearest level approximation modulation NLM, the carrier phase shift modulation CPS-PWM, and the carrier cascade modulation PD-PWM methods.

6. A hybrid MMC bridge arm grouping control method based on module reference wave reconstruction according to claim 1, characterized in that: The bridge arm reference wave includes a DC component, a fundamental frequency component, and a double frequency component, which are used to realize the control of AC current, voltage or power and the circulating current control function.

7. A hybrid MMC bridge arm grouping control method based on module reference wave reconstruction according to claim 1, characterized in that: The bridge arm reference wave is generated by other controllers according to the specific operation requirements of the MMC. The other controllers include a vector controller or a resonant controller for AC current, a vector controller or a resonant controller for circulating current.

8. A hybrid MMC bridge arm grouping control system based on module reference wave reconstruction, wherein the hybrid MMC bridge arm comprises N H half-bridge modules and N F A full-bridge module, characterized in that The control system comprises: The bridge arm reference wave acquisition module is used to obtain the reference waves of the half-bridge module and the full-bridge module in the bridge arm according to the bridge arm reference wave. The specific calculation formula is: where y xj is the bridge arm reference wave, y xj_H and xj_ are the reference waves of the half-bridge module and the full-bridge module, k H and k F They are the number of half-bridge modules N in the bridge arm. H and the number of full-bridge modules N F The proportion of the total number of modules in the bridge arm, h xj is a dynamic adjustment factor obtained according to the adjustment algorithm; subscript x = u, l, respectively, represents the upper and lower bridge arms; subscript j = a, b, c, respectively, represents the three phases A, B, and C; A half-bridge module drive signal acquisition module is used to obtain the number of output levels of the half-bridge modules in the bridge arm according to the modulation of the half-bridge module reference wave, and then obtain the drive signals of all the half-bridge modules in the bridge arm according to the direction of the bridge arm current, the size of the capacitor voltage and the sorting and voltage-sharing control method; The full-bridge module drive signal acquisition module is used to obtain the output level number of the full-bridge module in the bridge arm according to the modulation of the full-bridge module reference wave, and then obtain the drive signal of all the full-bridge modules in the bridge arm according to the sign of the reference wave, the direction of the bridge arm current, the size of the capacitor voltage and the sorting and equalizing control method.

9. An electronic device comprising a memory, a processor and program instructions stored in the memory and executable by the processor, characterized in that: The processor executes the program instructions to implement the steps of the control method according to any one of claims 1 to 7.

10. A computer-readable storage medium storing computer instructions, characterized in that: The computer instructions are used to enable the computer to execute the method according to any one of claims 1 to 7.

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