Modular multilevel converter parameter configuration method and control method for regenerating ripple

Abstract

The application relates to the technical field of voltage source converters, in particular to a method for configuring and controlling a ripple regeneration parameter of a modular multilevel converter. The method for configuring the ripple regeneration parameter comprises the following steps: determining basic parameters and modulation parameters of the modular multilevel converter; the modulation parameters comprise a reference modulation ratio and unit capacity energy storage; adjusting the modulation parameters based on the basic parameters of the modular multilevel converter to obtain modulation parameters meeting preset conditions; determining the ripple regeneration parameters of the modular multilevel converter according to the basic parameters and the modulation parameters meeting the preset conditions; the ripple regeneration parameters comprise an AC grid phase voltage effective value and a sub-module capacitance value. The application adopting the above scheme can greatly reduce the capacitance requirement of the modular multilevel converter and greatly reduce the cost and volume of the modular multilevel converter.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of voltage source converters, and in particular to a method for configuring and controlling the parameters of a ripple regeneration of a modular multilevel converter. BACKGROUND

[0002] A modular multilevel converter (MMC) has the advantages of easy realization of a large number of levels, good harmonic performance, and modular design, and has become the main topology structure of a high-voltage flexible direct-current transmission converter. However, there are power fluctuations mainly at the fundamental frequency and the double fundamental frequency on the MMC bridge arm, which causes a corresponding frequency ripple on the capacitor voltage of the sub-module and becomes an important factor affecting the analysis of the operating characteristics and the design of the parameters of the MMC. In order to limit the peak value of the capacitor voltage within a safe range, a relatively large sub-module capacitor value is usually designed, resulting in a large MMC cost and volume.

[0003] In addition, increasing the upper limit of the sub-module capacitor voltage ripple rate allows the sub-module to select a smaller capacitor value, and a high-ripple MMC can be obtained. However, from the perspective of device safety, the increase in the sub-module capacitor voltage ripple should not increase the peak value of the sub-module capacitor voltage. Therefore, when increasing the upper limit of the sub-module capacitor voltage ripple rate, the direct current component of the sub-module capacitor voltage should be correspondingly reduced to keep the maximum peak value of the sub-module capacitor voltage unchanged. However, if the direct current component of each sub-module is reduced and the number of sub-modules does not change, the AC output voltage capability of the MMC will be affected. Therefore, the related art increases the number of cascaded sub-modules of the bridge arm while reducing the direct current component of the sub-module to maintain the AC output voltage capability of the MMC, but this increases the number of additional sub-modules and switching devices.

[0004] Therefore, the prior art cannot accurately calculate the impact of the reduction of the direct current component of the capacitor voltage and the increase of the upper limit of the capacitor voltage ripple rate on the linear modulation region and the AC output voltage capability of the MMC, and cannot accurately design the sub-module capacitor value, so that accurate parameter configuration and operation control of the high-ripple MMC cannot be achieved. SUMMARY

[0005] The present application aims to at least partially solve one of the technical problems in the related art.

[0006] To this end, a first object of the present application is to provide a method for configuring the parameters of a ripple regeneration of a modular multilevel converter, to solve the technical problem that the prior art cannot accurately configure the parameters of a high-ripple modular multilevel converter.

[0007] The second object of the present application is to provide a control method of a modular multilevel converter to solve the technical problem that the prior art cannot realize the operation control of a high-ripple modular multilevel converter.

[0008] The third object of the present application is to provide a computer device.

[0009] To achieve the above object, the first aspect of the present application provides a ripple regeneration parameter configuration method of a modular multilevel converter, the input end of the modular multilevel converter being connected to an AC power grid, the modular multilevel converter comprising at least two bridge arms, each bridge arm comprising at least two cascaded sub-modules, the method comprising:

[0010] determining basic parameters and modulation parameters of the modular multilevel converter; the modulation parameters comprising a reference modulation ratio, a unit capacity energy storage;

[0011] adjusting the modulation parameters based on the basic parameters of the modular multilevel converter to obtain modulation parameters satisfying a preset condition;

[0012] determining ripple regeneration parameters of the modular multilevel converter according to the basic parameters and the modulation parameters satisfying the preset condition; the ripple regeneration parameters comprising an effective value of an AC grid phase voltage and a sub-module capacitance value.

[0013] Optionally, in an embodiment of the present application, the determination of the basic parameters of the modular multilevel converter comprises:

[0014] determining a DC voltage rated value, a rated capacity, a sub-module capacitance voltage rated value, and a maximum upper limit value of a sub-module capacitance voltage of the modular multilevel converter,

[0015] determining the number of sub-modules included in each bridge arm according to the DC voltage rated value and the sub-module capacitance voltage rated value;

[0016] determining a sub-module capacitance voltage peak upper limit coefficient according to the maximum upper limit value of the sub-module capacitance voltage and the sub-module capacitance voltage rated value;

[0017] determining a sub-module capacitance voltage ripple rate upper limit value according to the sub-module capacitance voltage peak upper limit coefficient;

[0018] determining a sub-module capacitance voltage DC component reference value according to the sub-module capacitance voltage peak upper limit coefficient and the sub-module capacitance voltage ripple rate upper limit value.

[0019] Optionally, in an embodiment of the present application, the adjustment of the modulation parameters based on the basic parameters of the modular multilevel converter to obtain modulation parameters satisfying a preset condition comprises:

[0020] determining an operating range of the modular multilevel converter, the operating range comprising an active power range and a reactive power range;

[0021] initializing a reference modulation ratio, determining an increment step of the reference modulation ratio, performing point-by-point scanning calculation on operating points of boundaries of the operating range, if no overmodulation phenomenon occurs in all operating points, increasing the value of the reference modulation ratio according to the increment step of the reference modulation ratio until overmodulation phenomenon occurs in any operating point, and recording the reference modulation ratio at this time;

[0022] in the process of gradually increasing the value of the reference modulation ratio according to the increment step of the reference modulation ratio, for each increased reference modulation ratio, determining the minimum value of the unit capacity energy corresponding to the each increased reference modulation ratio through iterative calculation.

[0023] Optionally, in an embodiment of the present application, the point-by-point scanning calculation on the operating points of the boundaries of the operating range comprises:

[0024] determining a double-frequency reference voltage modulation ratio and a double-frequency reference voltage phase angle based on a steady-state mathematical model of the modular multilevel converter, with the goal of suppressing double-frequency circulating current of the modular multilevel converter to zero;

[0025] determining a fundamental-frequency reference voltage modulation ratio and a fundamental-frequency reference voltage phase angle based on a ripple effect model of the modular multilevel converter;

[0026] determining the bridge arm reference voltage instantaneous per-unit value corresponding to each operating point according to the double-frequency reference voltage modulation ratio, the double-frequency reference voltage phase angle, the fundamental-frequency reference voltage modulation ratio and the fundamental-frequency reference voltage phase angle;

[0027] if the minimum value of the bridge arm reference voltage instantaneous per-unit value is less than 0 or the maximum value is greater than 1, it indicates that overmodulation phenomenon occurs.

[0028] Optionally, in an embodiment of the present application, the determining, for each increased reference modulation ratio, the minimum value of the unit capacity energy corresponding to the each increased reference modulation ratio through iterative calculation comprises:

[0029] initializing the unit capacity energy, determining an increment step of the unit capacity energy;

[0030] performing point-by-point scanning calculation on operating points of boundaries of the operating range, determining the maximum value of the submodule capacitor voltage peak value corresponding to each operating point based on a submodule capacitor voltage instantaneous per-unit value time function;

[0031] if the peak maximum value of the submodule capacitor voltage is greater than the maximum upper limit value of the submodule capacitor voltage, then the unit capacity energy storage is increased according to an incremental step of the unit capacity energy storage, and the running point of the boundary of the operating range is recalculated by point-by-point scanning until the peak maximum value of the submodule capacitor voltage is equal to the maximum upper limit value of the submodule capacitor voltage;

[0032] The unit capacity energy storage corresponding to the determination that the peak maximum value of the submodule capacitor voltage is equal to the maximum upper limit value of the submodule capacitor voltage is the minimum value of the unit capacity energy storage.

[0033] Optionally, in an embodiment of the present application, the point-by-point scanning calculation of the running point of the boundary of the operating range comprises:

[0034] determining and initializing a power factor angle;

[0035] determining an incremental step of the power factor angle;

[0036] incrementing the power factor angle step by step according to the incremental step of the power factor angle until the power factor angle is not less than 2π, so as to complete the point-by-point scanning of the running point of the boundary of the operating range.

[0037] Optionally, in an embodiment of the present application, before the determination of the double-frequency reference voltage modulation ratio and the double-frequency reference voltage phase angle based on the steady-state mathematical model of the modular multilevel converter, so as to suppress the double-frequency circulating current of the modular multilevel converter to zero, the method further comprises:

[0038] determining an active component unit value of alternating current and a reactive component unit value of alternating current according to the power factor angle;

[0039] determining an effective value unit value of alternating current and a phase angle of alternating current according to the active component unit value of alternating current and the reactive component unit value of alternating current.

[0040] Optionally, in an embodiment of the present application, the determination of the ripple regeneration parameter of the modular multilevel converter according to the basic parameter and the modulation parameter satisfying the preset condition comprises:

[0041] determining the effective value of the alternating current grid phase voltage according to the following formula:

[0042]

[0043] wherein, U SN is the effective value of the alternating current grid phase voltage, M 0_set is the reference modulation ratio satisfying the preset condition, U dcN is the rated value of the direct current voltage;

[0044] determining the submodule capacitor value according to the following formula:

[0045]

[0046] wherein, C sm is the sub-module capacitance value, E nom_set is the unit capacity energy storage that meets the preset condition, S N is the rated capacity, N is the number of sub-modules included in each bridge arm, U cap_dc_pu is the sub-module capacitor voltage DC component unit value, U capN is the sub-module capacitor voltage rated value.

[0047] To achieve the above object, the second aspect of the present application proposes a control method applying the parameter configuration method of the modular multilevel converter proposed in the first aspect of the present application, comprising:

[0048] configuring parameters of the modular multilevel converter;

[0049] determining the time function of the number of sub-modules of each bridge arm of the modular multilevel converter;

[0050] based on the time function of the number of sub-modules, generating the control signal of each bridge arm of the modular multilevel converter according to the pulse width modulation controller, so as to realize the control of the modular multilevel converter.

[0051] To achieve the above object, the third aspect of the present application proposes a computer device, comprising a memory, a processor and a computer program stored in the memory and executable on the processor, when the processor executes the computer program, realizing the parameter configuration method of the modular multilevel converter proposed in the first aspect of the present application, or the control method of the modular multilevel converter proposed in the second aspect of the present application.

[0052] In summary, the technical scheme provided by the embodiments of the present application at least brings the following beneficial effects:

[0053] 1) The sub-module capacitor voltage ripple generates the fundamental frequency AC voltage component through pulse width modulation at the AC port of the modular multilevel converter, which offsets the influence of the reduction of the sub-module voltage DC component, thereby reducing the influence on the AC output voltage capacity of the modular multilevel converter;

[0054] 2) In the case of increasing the upper limit of the capacitor voltage ripple rate, the peak value of the bridge arm reference voltage is reduced by the double-frequency circulating current suppression link; based on the influence of the capacitor voltage ripple effect on the sub-module capacitor voltage peak value, the minimum value of the unit capacity energy storage that meets the sub-module capacitor voltage non-exceeding limit condition is accurately calculated; by increasing the upper limit of the capacitor voltage ripple rate, the capacitor capacity of the modular multilevel converter is greatly reduced, and the cost and volume of the device are greatly reduced;

[0055] 3) In the case of increasing the upper limit of the capacitor voltage ripple rate and reducing the capacitor voltage DC component, based on the ripple regeneration voltage and the double-frequency circulating current suppression effect, the maximum value of the linear modulation constraint condition of the AC side rated voltage under full operating condition is accurately calculated;

[0056] 4) Under the premise of constant sub-module capacitor voltage peak value limit and bridge arm sub-module number, for different sub-module capacitor voltage DC component setting values and capacitor voltage ripple rate upper limit values, a parameter configuration method of AC power grid phase voltage effective value and sub-module capacitor value is provided, and an operation control method of high ripple modular multilevel converter based on ripple regeneration is provided.

[0057] The additional aspects and advantages of the present application will be partially given in the following description, partially become obvious from the following description, or be known by the practice of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0058] The above and / or additional aspects and advantages of the present application will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings, in which:

[0059] Figure 1 A flowchart of a ripple regeneration parameter configuration method of a modular multilevel converter provided by an embodiment of the present application;

[0060] Figure 2 A structural schematic diagram of a bridge arm provided by an embodiment of the present application;

[0061] Figure 3 A voltage fluctuation waveform schematic diagram provided by an embodiment of the present application;

[0062] Figure 4 A running range schematic diagram provided by an embodiment of the present application;

[0063] Figure 5 A structural schematic diagram of a six-arm modular multilevel converter provided by an embodiment of the present application;

[0064] Figure 6 A parameter configuration calculation result schematic diagram provided by an embodiment of the present application.

[0065] Figure 7A flowchart of a control method of a modular multilevel converter device provided by an embodiment of the present application. DETAILED DESCRIPTION

[0066] Embodiments of the present application are described in detail below with reference to examples illustrated in the accompanying drawings, in which the same or similar components are denoted by the same or similar reference numerals throughout. The embodiments described below by reference to the accompanying drawings are exemplary and are for the purpose of explanation only, and are not to be understood as limiting the present application. On the contrary, the embodiments of the present application include all modifications, equivalents and alternatives falling within the spirit and scope of the appended claims.

[0067] According to some embodiments, the modular multilevel converter is a new type of converter suitable for high voltage applications that has attracted much attention in recent years. It uses a sub-module cascade manner, and by controlling the state of each sub-module, the output AC voltage of the converter can be approximated to a sine wave, thereby reducing the harmonic content of the output voltage. Its emergence solves the problem of series voltage sharing of two-level voltage source converters, and has broad application prospects.

[0068] In some embodiments, when designing parameters of a modular multilevel converter (MMC), the rated voltage level of the switching device used in the sub-module is used to determine the DC component of the sub-module capacitor voltage rating, and then the upper limit of the sub-module capacitor voltage ripple is determined according to the operating safety of the switching device. Therefore, according to the operating conditions of the converter during operation and the upper limit of the sub-module capacitor voltage ripple, the sub-module capacitor value is designed according to the calculation and analysis results of the MMC steady-state characteristics, so that the maximum fluctuation rate of the capacitor voltage during operation does not exceed the upper limit of the sub-module capacitor voltage ripple. However, in the related art, the upper limit of the sub-module capacitor voltage ripple is set to 10%, which leads to a large required capacitor capacity, causing problems of large MMC cost and volume. If the required capacitor value of the sub-module in the MMC can be reduced, the cost and volume of the MMC can be reduced.

[0069] The present application will be described in detail below with reference to specific embodiments.

[0070] Figure 1 A flowchart of a parameter configuration method of a modular multilevel converter provided by an embodiment of the present application.

[0071] As Figure 1 shown, the parameter configuration method of the modular multilevel converter provided by an embodiment of the present application includes the following steps:

[0072] Step 110, determining basic parameters and modulation parameters of the modular multilevel converter; the modulation parameters include a reference modulation ratio and a unit capacity energy storage;

[0073] Step 120, adjusting the modulation parameters based on the basic parameters of the modular multilevel converter to obtain modulation parameters meeting preset conditions;

[0074] Step 130, determining a ripple regeneration parameter of the modular multilevel converter according to the basic parameters and the modulation parameters meeting the preset conditions; the ripple regeneration parameter includes an AC grid phase voltage effective value and a sub-module capacitance value.

[0075] According to some embodiments, the modular multilevel converter to which the embodiments of the present application are applied is not a fixed modular multilevel converter, wherein an input end of the modular multilevel converter is connected to an AC grid, the modular multilevel converter includes at least two bridge arms, each bridge arm includes at least two cascaded sub-modules, as shown in Figure 2 The structure of the modular multilevel converter includes but is not limited to a half-H bridge type MMC, a full-H bridge type MMC and a double clamping type MMC.

[0076] It should be noted that the AC port output voltage of the MMC can be inverted from the sub-module capacitor voltage to the AC port voltage through pulse width modulation. Thus, in the case that the DC component of each sub-module capacitor voltage is reduced and the number of sub-modules is unchanged, the output capability of the AC port of the MMC can be reduced. Secondly, the sub-module capacitor voltage ripple will regenerate a fundamental frequency AC voltage component, i.e., a ripple regeneration voltage, at the AC port during the modulation process. The ripple regeneration voltage can improve the output capability of the AC port voltage under capacitive working conditions. Increasing the sub-module capacitor voltage ripple can enhance the ripple regeneration effect. Therefore, the output capability of the AC port voltage of the MMC is closely related to the rated voltage parameter of the AC grid, and greatly affects the operating characteristics, cost and volume of the MMC.

[0077] In some embodiments, in the case that the DC voltage rating and the rated capacity of the MMC are constant, the higher the design value of the rated voltage parameter of the AC grid, the smaller the bridge arm current rating of the MMC, the smaller the current stress of the switching device of the sub-module, and the smaller the loss and the capacity of the MMC. However, due to the limitation of the output capability of the AC port voltage of the MMC, the higher the rated voltage of the AC grid, the more likely the MMC enters an over-modulation state. Therefore, when designing the rated voltage of the AC grid, the maximum value of the rated voltage of the AC grid when all possible operating conditions meet the linear modulation constraint condition, i.e., all possible operating conditions do not enter the over-modulation state, is adopted.

[0078] Therefore, the rated voltage of the AC grid is a key parameter affecting the linear modulation region of the MMC. When the operating condition changes, the required output voltage of the MMC can also change. The reference modulation ratio, which is the modulation ratio corresponding to zero power output of the MMC, will change up and down with the value of the required output voltage of the MMC in other operating conditions. The reference modulation ratio is defined according to the following formula:

[0079]

[0080] wherein M0 is the reference modulation ratio, U SN is the effective value of the phase voltage of the AC grid, and U dcN is the rated value of the DC voltage. When the rated value of the DC voltage of the MMC is constant, the reference modulation ratio represents the normalized rated voltage of the AC grid.

[0081] In some embodiments, the power fluctuation in the MMC bridge arm can cause a double-frequency circulating current flowing between the MMC bridge arms. It is necessary to suppress the double-frequency circulating current to make the internal circulating current of the bridge arm of the MMC zero. The basic principle of double-frequency circulating current suppression is to inject a double-frequency component into the reference voltage, thereby interfering with the size of the double-frequency circulating current. If the goal is to completely suppress the circulating current, the goal of the double-frequency reference voltage is to suppress the double-frequency circulating current to zero. However, the injected double-frequency reference voltage will also affect the reference voltage waveform of the bridge arm, and further affect the linear modulation region of the MMC.

[0082] It is easy to understand that the higher the design value of the reference modulation ratio, the smaller the bridge arm current rating of the MMC, and the more conducive to reducing the bridge arm current stress of the MMC, and reducing the loss and sub-module capacitance value of the MMC. However, the higher the design value of the reference modulation ratio, the higher the rated voltage of the AC grid, and the higher the requirement for the output voltage of the AC port of the MMC, that is, it is easier to enter the over-modulation state.

[0083] Therefore, considering the influence of the ripple regenerative voltage and the influence of the double-frequency circulating current suppression, the maximum value of the reference modulation ratio is adopted when the constraint condition of ensuring that the linear modulation is met in all possible operating conditions.

[0084] According to some embodiments, one goal of the high-ripple MMC is to reduce the total capacitance of the MMC. Therefore, in order to unify the capacitance of the MMC of different voltage levels and capacities, the unit capacity energy storage is used as the normalization index of the total capacitance of the MMC. The unit capacity energy storage is determined according to the following formula:

[0085]

[0086] wherein E nom is the unit capacity energy storage, and E nomThe unit is MJ / MVA or kJ / MVA, N is the number of sub-modules included in each bridge arm, C sm C is the sub-module capacitor value, U cap_dc_pu U is the sub-module capacitor voltage DC component unit value, U capN U is the sub-module capacitor voltage rated value, S N S is the rated capacity of the MMC.

[0087] In some embodiments, the unit capacity energy storage is a key indicator affecting the ripple amplitude of the sub-module capacitor voltage. Therefore, when designing the unit capacity energy storage, the sub-module capacitor voltage peak value needs to be limited within the maximum upper limit value of the sub-module capacitor voltage. However, the larger the unit capacity energy storage is, the larger the capacitor usage of the MMC is, and the higher the volume and cost of the MMC are. Therefore, when designing the unit capacity energy storage, the minimum value of the unit capacity energy storage that meets the constraint condition that the sub-module capacitor voltage peak value does not exceed the limit under all possible operating conditions, that is, all possible operating conditions meet the sub-module capacitor voltage peak value within the maximum upper limit value of the sub-module capacitor voltage.

[0088] In some embodiments, the sub-module capacitor voltage peak value can be jointly determined by the ripple amplitude of the sub-module capacitor voltage and the DC component of the sub-module capacitor voltage. Due to the ripple effect existing in the MMC, the sub-module capacitor voltage ripple also affects the DC component of the sub-module capacitor voltage. The DC component of the sub-module capacitor voltage does not always run at the set value of the DC component, but deviates with the change of the operating condition, for example, the DC component of the sub-module capacitor voltage is higher than the set value under inductive operating condition, and is lower than the set value under capacitive operating condition.

[0089] In the embodiments of the present application, the basic parameters of the modular multilevel converter are determined, including:

[0090] The DC voltage rated value, the rated capacity, the sub-module capacitor voltage rated value, and the maximum upper limit value of the sub-module capacitor voltage of the modular multilevel converter are determined,

[0091] The number of sub-modules included in each bridge arm is determined according to the DC voltage rated value and the sub-module capacitor voltage rated value;

[0092] The sub-module capacitor voltage peak value upper limit coefficient is determined according to the maximum upper limit value of the sub-module capacitor voltage and the sub-module capacitor voltage rated value;

[0093] The sub-module capacitor voltage ripple rate upper limit value is determined according to the sub-module capacitor voltage peak value upper limit coefficient;

[0094] The sub-module capacitor voltage DC component unit value is determined according to the sub-module capacitor voltage peak value upper limit coefficient and the sub-module capacitor voltage ripple rate upper limit value.

[0095] Specifically, the number of sub-modules included in each bridge arm is determined according to the following formula:

[0096]

[0097] Where N is the number of sub-modules included in each bridge arm, and U dcN U is the rated DC voltage. capN This refers to the rated voltage of the submodule capacitor.

[0098] Specifically, the upper limit coefficient of the peak voltage of the submodule capacitor is determined according to the following formula:

[0099]

[0100] Where, γ lim U is the upper limit coefficient for the peak voltage of the submodule capacitor. cap_lim U represents the maximum upper limit of the capacitor voltage of the submodule. capN This refers to the rated voltage of the submodule capacitor.

[0101] The maximum upper limit of the capacitor voltage in the submodule is determined based on the voltage withstand capability of the components within the submodule.

[0102] According to some embodiments, the submodule capacitor voltage ripple rate is the ratio of the submodule capacitor voltage ripple amplitude to the submodule capacitor's rated voltage. For example, when the DC component of the submodule capacitor voltage operates at its rated value of 1.0 pu, if the peak value upper limit coefficient γ of the submodule capacitor voltage is determined... lim The upper limit of the submodule capacitor voltage ripple rate is thus limited to γ. lim -1. For example, when the peak voltage limit coefficient γ of the submodule capacitor... lim The upper limit of the submodule capacitor voltage ripple rate ε when it is 1.1 pu. lim It is 0.1%, or 10%.

[0103] It should be noted that the purpose of high-ripple MMC is to increase the upper limit of the submodule capacitor voltage ripple rate without increasing the peak value of the submodule capacitor voltage, thereby achieving the goal of reducing the required submodule capacitor value. If the peak value of the submodule capacitor voltage remains unchanged, increasing the upper limit of the submodule capacitor voltage ripple rate must correspondingly reduce the DC component value of the submodule capacitor voltage.

[0104] Specifically, the relationship between the rated value of the submodule capacitor voltage, the per-unit value of the DC component of the submodule capacitor voltage, the upper limit coefficient of the peak value of the submodule capacitor voltage, and the upper limit value of the ripple rate of the submodule capacitor voltage is as follows: Figure 3 As shown. The per-unit value of the DC component of the submodule capacitor voltage is determined using the rated value of the submodule capacitor voltage as the base value, according to the following formula:

[0105] U cap_dc_pu =γlim -ε lim

[0106] wherein U cap_dc_pu is a sub-module capacitor voltage DC component unit value, γ lim is a sub-module capacitor voltage peak upper limit coefficient, ε lim is a sub-module capacitor voltage ripple upper limit value;

[0107] In some embodiments, the larger the sub-module capacitor voltage ripple upper limit value ε lim is, the lower the sub-module capacitor voltage DC component is, so as to ensure that the sub-module capacitor voltage peak value does not increase. For example, when the sub-module capacitor voltage peak upper limit coefficient γ lim is 1.1pu, if the sub-module capacitor voltage ripple upper limit value ε lim is increased to 0.15, i.e. 15%, the sub-module capacitor voltage DC component unit value U cap_dc_pu should be reduced to 0.95.

[0108] In the embodiments of the present application, based on the basic parameters of the modular multilevel converter, the modulation parameters are adjusted to obtain modulation parameters that meet the preset conditions, including:

[0109] determining the operating range of the modular multilevel converter, the operating range including an active power range and a reactive power range;

[0110] initializing a reference modulation ratio, determining an incremental step of the reference modulation ratio; performing point-by-point scanning calculation on the operating points of the boundaries of the operating range, if all the operating points have not experienced modulation phenomenon, increasing the value of the reference modulation ratio according to the incremental step of the reference modulation ratio until any operating point experiences modulation phenomenon, and recording the reference modulation ratio at this time;

[0111] In the process of gradually increasing the value of the reference modulation ratio according to the incremental step of the reference modulation ratio, for each increased reference modulation ratio, the minimum value of the unit capacity energy storage corresponding to each increased reference modulation ratio is determined through iterative calculation.

[0112] In some embodiments, the reference modulation ratio is initialized, the scanning starting value of the reference modulation ratio is defined as m0_start, and the incremental step of the reference modulation ratio is determined as Δm0. Starting from M0=m0 -start , the value of M0 is gradually increased by the step Δm0, scanning calculation is performed until the constraint condition of linear modulation is not met, and the maximum value of the reference modulation ratio that can be designed is obtained.

[0113] Specifically, the scanning starting value of the reference modulation ratio is a value satisfying the constraint condition of linear modulation, for example, can be 0.7. In order to ensure the fineness and accuracy of the scanning calculation, the incremental step of the reference modulation ratio can be set to 0.001, for example.

[0114] According to some embodiments, in the case of determining the basic parameters of the MMC, the minimum value of the required unit capacity energy storage is related to the reference modulation ratio, and for each obtained reference modulation ratio after increment, the minimum value of the unit capacity energy storage that can satisfy the constraint condition that the sub-module capacitor voltage peak value does not exceed the limit under all possible operating conditions can be obtained through iterative calculation.

[0115] In the embodiments of the present application, the operating points of the boundaries of the operating range are calculated point by point, including:

[0116] Based on the steady-state mathematical model of the modular multilevel converter, the reference voltage modulation ratio of the second harmonic and the reference voltage phase angle of the second harmonic are determined, aiming at suppressing the second harmonic circulating current of the modular multilevel converter to zero.

[0117] Based on the ripple effect model of the modular multilevel converter, the reference voltage modulation ratio of the fundamental frequency and the reference voltage phase angle of the fundamental frequency are determined.

[0118] According to the reference voltage modulation ratio of the second harmonic, the reference voltage phase angle of the second harmonic, the reference voltage modulation ratio of the fundamental frequency and the reference voltage phase angle of the fundamental frequency, the bridge arm reference voltage instantaneous per-unit value corresponding to each operating point is determined.

[0119] If the minimum value of the bridge arm reference voltage instantaneous per-unit value is less than 0 or the maximum value is greater than 1, it means that overmodulation occurs.

[0120] According to some embodiments, the equivalent connection reactance per-unit value between the modular multilevel converter and the AC power grid is determined according to the following formula:

[0121]

[0122] Wherein, X eq is the equivalent connection reactance per-unit value, X s is the internal reactance per-unit value of the AC power grid, and X arm is the MMC bridge arm reactance per-unit value.

[0123] In the case of determining the AC current active component per-unit value, the AC current reactive component per-unit value and the equivalent connection reactance per-unit value, the modulation ratio and the phase angle of the AC port voltage can be determined according to the following formula:

[0124]

[0125]

[0126] wherein M ac is the modulation ratio of the AC port voltage, δ ac is the phase angle of the AC port voltage, M0 is the reference modulation ratio, X eq is the equivalent connection reactance per unit, I q_pu is the reactive component of the AC current per unit, I p_pu is the active component of the AC current per unit.

[0127] In some embodiments, in order to accurately determine the influence of the second harmonic circulating current control link in the steady state analysis, the second harmonic reference voltage modulation ratio and the second harmonic reference voltage phase angle that make the second harmonic circulating current zero must be obtained for each operating point. Based on the steady state mathematical model of the MMC, the second harmonic reference voltage modulation ratio and the second harmonic reference voltage phase angle are determined according to the following formula, with the goal of suppressing the second harmonic circulating current of the MMC to zero:

[0128]

[0129] wherein φ ac is the phase angle of the AC current, M2 is the second harmonic reference voltage modulation ratio, β2 is the second harmonic reference voltage phase angle, c1 is the ripple effect coefficient, I ac_pu is the RMS value of the AC current.

[0130] wherein the ripple effect coefficient is determined according to the following formula:

[0131]

[0132]

[0133] wherein ω is the synchronous angular frequency of the AC power grid connected to the MMC, and T1 is the fundamental period of the AC power grid connected to the MMC.

[0134] According to some embodiments, due to the existence of the ripple regenerative voltage deviation, when the fundamental reference voltage modulation ratio of the pulse width modulation link is set to M ref and the fundamental reference voltage phase angle is set to δ ref , the MMC AC port voltage modulation ratio and the MMC AC port voltage phase angle will not be M ref and δ ref . In the steady state, in order to output the active current and the reactive current of the operating point, the steady state value of the MMC AC port voltage modulation ratio and the steady state value of the MMC AC port voltage phase angle should reach the values of M ac and δ ac .

[0135] In some embodiments, based on a ripple effect model of the modular multilevel converter, the steady-state value of the modulation ratio of the MMC AC port voltage and the steady-state value of the phase angle of the MMC AC port voltage are targeted to reach M ac and δ ac The fundamental reference voltage modulation ratio and the fundamental reference voltage phase angle are determined according to the following formula:

[0136]

[0137] In the embodiments of the present application, for each incremental reference modulation ratio, the minimum value of the unit capacity energy corresponding to each incremental reference modulation ratio is determined through iterative calculation, including:

[0138] The unit capacity energy is initialized, and an incremental step of the unit capacity energy is determined;

[0139] The running points at the boundaries of the operating range are calculated point by point, and based on the instantaneous per-unit time function of the sub-module capacitor voltage, the maximum value of the sub-module capacitor voltage corresponding to each running point is determined;

[0140] If the maximum value of the sub-module capacitor voltage is greater than the maximum upper limit value of the sub-module capacitor voltage, the unit capacity energy is increased according to the incremental step of the unit capacity energy, and the running points at the boundaries of the operating range are calculated point by point again until the maximum value of the sub-module capacitor voltage is equal to the maximum upper limit value of the sub-module capacitor voltage;

[0141] The unit capacity energy corresponding to the maximum value of the sub-module capacitor voltage equal to the maximum upper limit value of the sub-module capacitor voltage is determined as the minimum value of the unit capacity energy.

[0142] According to some embodiments, the unit capacity energy is initialized, and the scanning starting value of the unit capacity energy is defined as e nom_start , and the incremental step of the unit capacity energy is determined as Δe nom . In order to ensure the fineness and accuracy of the scanning calculation, the incremental step of the unit capacity energy can be set to 10 kJ / MVA, for example.

[0143] In the embodiments of the present application, the running points at the boundaries of the operating range are calculated point by point, including:

[0144] The power factor angle is determined and initialized;

[0145] The incremental step of the power factor angle is determined;

[0146] The power factor angle is gradually increased according to the incremental step of the power factor angle until the power factor angle is not less than 2π, so as to complete the point-by-point scanning of the running points at the boundaries of the operating range.

[0147] According to some embodiments, according to some embodiments, the MMC has four-quadrant output capability, and the operating range can be represented by a range circle diagram composed of active power and reactive power. Since the flexible HVDC transmission system is mainly used for transmitting active power, the AC power grid connected with the MMC does not need to reach the rated capacity with reactive power. Moreover, when a large reactive power is output, the voltage output capability of the MMC is required to be higher, thereby causing greater capacitor voltage fluctuation, so in practical applications, the reactive power output by the MMC is usually limited within a certain range, such as shown in FIG. 8, wherein the range of the reactive current corresponding to the reactive power is limited between -I Figure 4 and I q_pu_max . q_pu_max I q_pu_max is a per-unit value between 0 and 1.0.

[0148] In some embodiments, in the process of point-by-point scanning calculation of the operating points on the boundary of the operating range, the power factor angle is increased from 0 by a step size until reaching 2π, and the amplitude of the output current per-unit value is limited on the boundary of the set operating range. At each value, the operating point calculation is performed to calculate whether the point meets the constraint condition of linear modulation and whether the constraint condition of the peak value of the capacitor voltage of the sub-module is not exceeded. In the embodiments of the present application, before determining the double-frequency reference voltage modulation ratio and the double-frequency reference voltage phase angle based on the steady-state mathematical model of the MMC, with the target of suppressing the double-frequency circulating current of the MMC to zero, the method further comprises the following steps:

[0149] determining the AC current active component per-unit value and the AC current reactive component per-unit value according to the power factor angle;

[0150] determining the AC current effective value per-unit value and the AC current phase angle according to the AC current active component per-unit value and the AC current reactive component per-unit value.

[0151] According to some embodiments, the AC current active component per-unit value and the AC current reactive component per-unit value are determined according to the following formula:

[0152] I p_pu = cosφ

[0153]

[0154] wherein I p_pu is the AC current active component per-unit value, I q_pu is the AC current reactive component per-unit value, and φ is the power factor angle.

[0155]

[0156] ​In some embodiments, the AC current effective value unit and the AC current phase angle are determined according to the following formula:

[0157]

[0158]

[0159] wherein, I ac_pu is the AC current effective value unit, and the AC current phase angle is φ ac .

[0160] In the embodiments of the present application, the ripple regeneration parameters of the modular multilevel converter are determined according to the basic parameters and the modulation parameters satisfying the preset condition, comprising:

[0161] The AC power grid phase voltage effective value is determined according to the following formula:

[0162]

[0163] wherein, U SN is the AC power grid phase voltage effective value, M 0_set is the reference modulation ratio satisfying the preset condition, U dcN is the DC voltage rated value;

[0164] The submodule capacitance value is determined according to the following formula:

[0165]

[0166] wherein, C sm is the submodule capacitance value, E nom_set is the unit capacity energy storage satisfying the preset condition, S N is the rated capacity, N is the number of submodules included in each bridge arm, U cap_dc_pu is the submodule capacitance voltage DC component unit, and U capN is the submodule capacitance voltage rated value.

[0167] Taking one scenario as an example, the structure of the six-arm modular multilevel converter is shown in Figure 5 , wherein the six-arm modular multilevel converter includes bridge arms ap, bp, cp, an, bn and cn. The ripple regeneration parameter configuration specifically includes the following steps:

[0168] Step 210, determining the basic parameters and modulation parameters of the modular multilevel converter; the modulation parameters include the reference modulation ratio and the unit capacity energy storage;

[0169] Step 220, determining the operating range of the modular multilevel converter, initializing the reference modulation ratio, and determining the incremental step of the reference modulation ratio; performing point-by-point scanning calculation on the operating points of the boundaries of the operating range;

[0170] Specifically, in the calculation of any operating point, the instantaneous unit time function of each bridge arm reference voltage is determined according to the following formula after the determination of the fundamental reference voltage modulation ratio and the fundamental reference voltage phase angle:

[0171]

[0172] wherein u ref_ap_pu (t), u ref_an_pu (t), u ref_bp_pu (t), u ref_bn_pu (t), u ref_cp_pu (t), u ref _ cn_pu (t) are the instantaneous unit time functions of the bridge arm reference voltages corresponding to the bridge arm ap, the bridge arm an, the bridge arm bp, the bridge arm bn, the bridge arm cp and the bridge arm cn respectively.

[0173] Since the six bridge arm reference voltages have symmetry, any bridge arm reference voltage instantaneous unit time function can be used to determine the constraint condition of linear modulation. For example, the bridge arm reference voltage instantaneous unit time function of the bridge arm ap, i.e. the upper bridge arm of phase A, is used for calculation, and the minimum value and the maximum value of the bridge arm reference voltage instantaneous unit in a fundamental period are determined according to the following formula:

[0174]

[0175]

[0176] wherein U ref_min is the minimum value of the bridge arm reference voltage instantaneous unit, U ref_max is the maximum value of the bridge arm reference voltage instantaneous unit, u ref_ap_pu (t) is the bridge arm reference voltage instantaneous unit time function corresponding to the bridge arm ap, and T1 is the fundamental period of the AC power grid connected to the modular multilevel converter.

[0177] If U ref_min < 0, it indicates that the reference voltage of the operating point exceeds the voltage range that can be output by the bridge arm, and over-modulation occurs.

[0178] If no over-modulation occurs in all operating points, the value of the reference modulation ratio is increased according to the incremental step of the reference modulation ratio until over-modulation occurs in any operating point, and the reference modulation ratio at this time is recorded.

[0179] In the process of gradually increasing the value of the reference modulation ratio according to the increment step size of the reference modulation ratio, for each incremented reference modulation ratio, the minimum value of energy storage per unit capacity corresponding to each incremented reference modulation ratio is determined by iterative calculation.

[0180] Specifically, considering the symmetry of the six bridge arms, the peak value of the submodule capacitor voltage is determined using the voltage waveform of the submodule capacitor in any bridge arm. For example, the submodule capacitor voltage corresponding to bridge arm ap is used for calculation. Based on the ripple effect, the instantaneous per-unit time function of the submodule capacitor voltage is determined according to the following formula:

[0181]

[0182] Among them, u cap (t) is the time function of the instantaneous per-unit value of the capacitor voltage of the submodule.

[0183] Based on the instantaneous per-unit time function of the submodule capacitor voltage, the maximum peak value of the submodule capacitor voltage within one fundamental frequency cycle is determined according to the following formula:

[0184]

[0185] Among them, U cap_peak_pu This represents the maximum peak value of the submodule capacitor voltage. If the maximum peak value of the submodule capacitor voltage is greater than the maximum upper limit of the submodule capacitor voltage, the unit capacity energy storage is increased step by step according to the incremental step size of the unit capacity energy storage, and the operating points at the boundary of the operating range are recalculated point by point until the maximum peak value of the submodule capacitor voltage equals the maximum upper limit of the submodule capacitor voltage, and the unit capacity energy storage at this time is recorded.

[0186] Step 230: Determine the effective value of the phase voltage of the AC grid and the capacitance value of the submodule based on the basic parameters and the reference modulation ratio and unit capacity energy storage obtained in step 220.

[0187] According to some embodiments, Figure 6 This is a schematic diagram illustrating the parameter configuration calculation results provided in an embodiment of this application. For example... Figure 7 As shown, the upper limit coefficient γ of the peak voltage of the submodule capacitor is... lim The per-unit value X of the connection reactance between the modular multilevel converter and the AC grid is 1.1 pu. eq The upper limit of the ripple rate for the capacitor voltage of the submodule is ε, which is 0.25. lim =0.1, ε lim =0.15, ε lim The calculation and parameter configuration for the three cases (=0.17) are performed using the method provided in the embodiments of this application.

[0188] In some embodiments, when ε limWhen = 0.1, the per-unit value U of the DC component of the submodule capacitor voltage cap_dc_pu At 1.0 pu, the MMC is in normal ripple condition, the maximum reference modulation ratio can be designed to be 0.86, and the minimum design value for energy storage per unit capacity can be designed to be 33.1 kJ / MVA.

[0189] In some embodiments, when ε lim When = 0.15, the per-unit value U of the DC component of the submodule capacitor voltage cap_dc_pu At 0.95 pu, the MMC is ε. lim Even with a high ripple of 0.15, the maximum reference modulation ratio can still be designed to be 0.86, and the minimum design value for energy storage per unit capacity can be 20.9 kJ / MVA. Compared to a conventional normal ripple MMC, the MMC is ε... lim In the case of high ripple of 0.15, although the DC component of the submodule capacitor voltage is reduced to 0.95pu, the AC port output voltage capability of the MMC is not reduced due to the influence of the ripple regeneration voltage by using the method provided in the embodiments of this application. The maximum reference modulation ratio can still be designed to be 0.86, and the energy storage value per unit capacity can be reduced by 36.8%, which greatly reduces the amount of capacitor required, thereby significantly reducing the cost and size of the MMC.

[0190] In some embodiments, when ε lim When = 0.17, the per-unit value U of the DC component of the submodule capacitor voltage cap_dc_pu At 0.93 pu, the MMC is ε. lim With a high ripple of 0.17, the maximum designable reference modulation ratio is 0.82, and the minimum design value for energy storage per unit capacity is 19.7 kJ / MVA. Compared to a conventional normal ripple MMC, the MMC is ε... lim In the case of high ripple of 0.17, although the DC component of the submodule capacitor voltage is reduced to 0.93 pu, by using the method provided in the embodiments of this application, based on the influence of ripple regeneration voltage, the AC port output voltage capability of the MMC is reduced by only 0.02 pu, the maximum reference modulation ratio can be designed to be 0.82, and the energy storage value per unit capacity can be reduced by 40%, which greatly reduces the amount of capacitor required, thereby significantly reducing the cost and size of the MMC.

[0191] In summary, the method provided in the embodiments of the present application determines the basic parameters and modulation parameters of the modular multilevel converter; the modulation parameters include a reference modulation ratio and a unit capacity energy storage; the modulation parameters are adjusted based on the basic parameters of the modular multilevel converter to obtain modulation parameters that meet preset conditions; the ripple regeneration parameters of the modular multilevel converter are determined according to the basic parameters and the modulation parameters that meet the preset conditions; the ripple regeneration parameters include an AC power grid phase voltage effective value and a sub-module capacitance value. The present application can greatly reduce the capacity of the modular multilevel converter and greatly reduce the cost and volume of the modular multilevel converter.

[0192] To achieve the above-mentioned embodiments, the present application further provides a control method of a modular multilevel converter ripple regeneration parameter configuration method.

[0193] Figure 7 A flowchart of a control method of a modular multilevel converter device provided in the embodiments of the present application is shown in

[0194] As shown in Figure 7 , a control method of a modular multilevel converter device includes:

[0195] Step 710, configuring parameters of the modular multilevel converter;

[0196] Step 720, determining a sub-module input number time function of each bridge arm of the modular multilevel converter;

[0197] Step 730, based on the sub-module input number time function, generating a control signal of each bridge arm of the modular multilevel converter according to the pulse width modulation controller to achieve control of the modular multilevel converter.

[0198] Taking a scenario as an example, the structure of a six-arm modular multilevel converter is shown in Figure 5 , wherein the six-arm modular multilevel converter includes bridge arms ap, bp, cp, an, bn and cn. The control method specifically includes the following steps:

[0199] Step 810, configuring parameters of the six-arm modular multilevel converter;

[0200] Step 820, determining a sub-module input number time function of the six bridge arms according to the following formula:

[0201]

[0202] Step 830, setting n ap (t), n an (t), n bp (t), nbn (t), n cp (t), n cn (t) an input pulse width modulation controller, generating a control signal of the bridge arm of each modular multilevel converter to realize control of the modular multilevel converter.

[0203] To sum up, the control method provided by the embodiments of the present application, by configuring parameters of the modular multilevel converter; determining the time function of the number of submodules of the bridge arm of each modular multilevel converter; based on the time function of the number of submodules, according to the pulse width modulation controller, generating a control signal of the bridge arm of each modular multilevel converter to realize control of the modular multilevel converter. The present application can realize the operation control of the high ripple modular multilevel converter, at the same time, can greatly reduce the capacity of the capacitor of the modular multilevel converter, and greatly reduce the cost and volume of the modular multilevel converter.

[0204] To achieve the above object, the third aspect of the present application provides a computer device, comprising a memory, a processor and a computer program stored in the memory and executable on the processor, when the processor executes the computer program, realizing the ripple regeneration parameter configuration method of the modular multilevel converter as shown in the embodiments of the present application, or realizing the control method of the modular multilevel converter as shown in the embodiments of the present application. Figures 1-6 Figure 7

[0205] It should be noted that in the description of the present application, the terms "first", "second" and the like are only for the purpose of description, and cannot be understood as indicating or implying relative importance. In addition, in the description of the present application, unless otherwise specified, the meaning of "a plurality of" is two or more.

[0206] Any process or method descriptions in flow charts or described elsewhere herein can be understood as representing code modules, segments, or portions of code which include one or more executable instructions for performing specific logic functions or steps in the process, and that the various embodiments of the present application include the use of alternative orderings, including simultaneous performance or performance of functions according to the functions involved, as would be understood by those skilled in the art, and that the embodiments of the present application should not be limited to the precise sequences or orderings described herein.

[0207] ​​It should be understood that each of the elements of the present application can be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented in software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented in hardware, and in another embodiment, any of the following technologies known in the art or their combinations can be used: discrete logic circuitry having logic gates for implementing logic functions on data signals, application specific integrated circuits having appropriate combinational logic gates, programmable gate arrays (PGA), field programmable gate arrays (FPGA), etc.

[0208] Those skilled in the art of the present technology can understand that all or part of the steps carried out by the above-mentioned embodiment methods can be completed by programs instructing related hardware, and the programs can be stored in a computer readable storage medium, and when executed, include one or a combination of steps of the method embodiments.

[0209] In addition, each functional unit in each embodiment of the present application can be integrated into one processing module, or each unit can be physically present separately, or two or more units can be integrated into one module. The above-mentioned integrated module can be realized in the form of hardware or in the form of a software function module. The integrated module, if realized in the form of a software function module and sold or used as an independent product, can also be stored in a computer readable storage medium.

[0210] The above-mentioned storage medium can be a read-only memory, a magnetic disk or an optical disk, etc.

[0211] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" 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 application. In the present specification, the illustrative description of the above terms does not necessarily mean 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.

[0212] Although the embodiments of the present application have been shown and described above, it should be understood that the above-mentioned embodiments are exemplary and cannot be understood as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above-mentioned embodiments within the scope of the present application.

Claims

1. A method for configuring ripple regeneration parameters of a modular multilevel converter, characterized in that, The input terminal of the modular multilevel converter is connected to the AC power grid. The modular multilevel converter includes at least two bridge arms, and each bridge arm includes at least two cascaded sub-modules. The method includes: Determine the basic parameters and modulation parameters of the modular multilevel converter; the modulation parameters include the reference modulation ratio and energy storage per unit capacity. Based on the basic parameters of the modular multilevel converter, the modulation parameters are adjusted to obtain modulation parameters that meet preset conditions; The ripple regeneration parameters of the modular multilevel converter are determined based on the basic parameters and the modulation parameters that meet the preset conditions; the ripple regeneration parameters include the effective value of the AC grid phase voltage and the value of the submodule capacitance. The step of determining the ripple regeneration parameters of the modular multilevel converter based on the basic parameters and the modulation parameters that meet the preset conditions includes: The effective value of the phase voltage of the AC power grid is determined according to the following formula: Among them, U SN M represents the effective value of the phase voltage of the AC power grid. 0_set To meet the preset conditions for the reference modulation ratio, U dcN This is the rated DC voltage. The capacitance value of the submodule is determined according to the following formula: Among them, C sm E represents the capacitance value of the submodule. nom_set To meet the preset conditions for energy storage per unit capacity, S N For rated capacity, N is the number of submodules included in each bridge arm, and U is the number of submodules included in each bridge arm. cap_dc_pu U represents the per-unit value of the DC component of the capacitor voltage in the submodule. capN This refers to the rated voltage of the submodule capacitor.

2. The method as described in claim 1, characterized in that, The determination of the basic parameters of the modular multilevel converter includes: Determine the DC voltage rating, rated capacity, submodule capacitor voltage rating, and maximum upper limit of the submodule capacitor voltage of the modular multilevel converter. The number of sub-modules included in each bridge arm is determined based on the DC voltage rating and the sub-module capacitor voltage rating. The peak voltage upper limit coefficient of the submodule capacitor voltage is determined based on the maximum upper limit value of the submodule capacitor voltage and the rated value of the submodule capacitor voltage. The upper limit value of the submodule capacitor voltage ripple rate is determined based on the upper limit coefficient of the peak voltage of the submodule capacitor; The per-unit value of the DC component of the submodule capacitor voltage is determined based on the upper limit coefficient of the peak voltage of the submodule capacitor and the upper limit value of the ripple rate of the submodule capacitor voltage.

3. The method as described in claim 2, characterized in that, The adjustment of the modulation parameters based on the basic parameters of the modular multilevel converter to obtain modulation parameters that meet preset conditions includes: Determine the operating range of the modular multilevel converter, which includes the active power range and the reactive power range; Initialize the reference modulation ratio and determine the increment step size of the reference modulation ratio; perform point-by-point scanning calculation on the operating points of the boundary of the operating range. If no modulation phenomenon has occurred at any operating point, increment the value of the reference modulation ratio according to the increment step size of the reference modulation ratio until any operating point has a modulation phenomenon, and record the reference modulation ratio at this time. In the process of gradually increasing the value of the reference modulation ratio according to the increment step size of the reference modulation ratio, for each incremented reference modulation ratio, the minimum value of energy storage per unit capacity corresponding to each incremented reference modulation ratio is determined by iterative calculation.

4. The method as described in claim 3, characterized in that, The step of performing point-by-point scanning calculations of the running points at the boundaries of the running range includes: Based on the steady-state mathematical model of the modular multilevel converter, with the goal of suppressing the second harmonic circulating current of the modular multilevel converter to zero, the modulation ratio and phase angle of the second harmonic reference voltage are determined. Based on the ripple effect model of a modular multilevel converter, the modulation ratio and phase angle of the fundamental frequency reference voltage are determined. The instantaneous per-unit value of the bridge arm reference voltage corresponding to each operating point is determined based on the second harmonic reference voltage modulation ratio, the second harmonic reference voltage phase angle, the fundamental frequency reference voltage modulation ratio, and the fundamental frequency reference voltage phase angle. If the minimum value of the instantaneous per-unit value of the bridge arm reference voltage is less than 0, or the maximum value is greater than 1, it indicates that overmodulation has occurred.

5. The method as described in claim 4, characterized in that, The step of determining the minimum energy storage per unit capacity corresponding to each incremented reference modulation ratio through iterative calculation includes: Initialize unit capacity energy storage and determine the increment step size of unit capacity energy storage; The operating points at the boundaries of the operating range are scanned and calculated point by point. Based on the instantaneous per-unit time function of the submodule capacitor voltage, the peak value of the submodule capacitor voltage corresponding to each operating point is determined. If the maximum peak value of the submodule capacitor voltage is greater than the maximum upper limit value of the submodule capacitor voltage, then the unit capacity energy storage is increased according to the incremental step size of the unit capacity energy storage, and the operating points of the boundary of the operating range are re-scanned and calculated point by point until the maximum peak value of the submodule capacitor voltage is equal to the maximum upper limit value of the submodule capacitor voltage. The minimum energy storage per unit capacity is determined when the maximum peak value of the submodule capacitor voltage is equal to the maximum upper limit value of the submodule capacitor voltage.

6. The method as described in any one of claims 4 or 5, characterized in that, The step of performing point-by-point scanning calculations of the running points at the boundaries of the running range includes: Determine and initialize the power factor angle; Determine the increment step size for the power factor angle; The power factor angle is gradually increased by an increment step size until the power factor angle is not less than 2π, so as to complete the point-by-point scanning of the operating points at the boundary of the operating range.

7. The method as described in claim 6, characterized in that, Before determining the second-harmonic reference voltage modulation ratio and second-harmonic reference voltage phase angle in the steady-state mathematical model based on the modular multilevel converter, with the goal of suppressing the second-harmonic circulating current of the modular multilevel converter to zero, the model further includes: Determine the per-unit values ​​of the active and reactive components of the AC current based on the power factor angle. The effective value per unit and the phase angle of the AC current are determined based on the per-unit values ​​of the active and reactive components of the AC current.

8. A control method for configuring ripple regeneration parameters of a modular multilevel converter according to any one of claims 1-7, characterized in that, include: Configure the parameters of the modular multilevel converter; Determine the number of submodules to be engaged in each arm of the modular multilevel converter using a time function; Based on the time function of the number of sub-modules, a control signal for each arm of the modular multilevel converter is generated according to the pulse width modulation controller to realize the control of the modular multilevel converter.

9. A computer device, characterized in that, The device includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the ripple regeneration parameter configuration method for a modular multilevel converter as described in any one of claims 1-7, or the control method for a modular multilevel converter as described in claim 8.

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