WO2022059945A1 - Method, system and computer program for designing high voltage direct current transmission system based on modular multi-level converter - Google Patents

Abstract

The present invention relates to a method, a system, and a computer program for designing a high voltage direct current transmission system based on a modular multi-level converter and, more specifically, to a method, a system, and a computer program for designing a high voltage direct current transmission system based on a modular multi-level converter, the method, the system, and the computer program reflecting dynamic analysis in a state in which a modular multi-level converter operates in connection with a power system and comprehensively considering the characteristics of various parameters in terms of the overall system, and thus enable a design to progress effectively.

Description

Modular multilevel converter-based high voltage direct current transmission system design method, system and computer program

The present invention relates to a method, system, and computer program for designing a modular multilevel converter-based high voltage direct current transmission system, and more particularly, to reflect dynamic analysis in a state in which the modular multilevel converter operates in conjunction with a power system and The present invention relates to a method, system, and computer program for designing a modular multi-level converter-based high-voltage DC power transmission system that can effectively design by comprehensively considering the characteristics of various parameters at the system level.

Recently, research and development of high voltage direct current transmission (HVDC) systems have been widely conducted to improve power control and stability of large-scale power systems.

High-voltage direct-current transmission (HVDC) refers to a transmission method in which a power transmission station converts AC power produced at a power plant into DC power, transmits it, and then reconverts it to AC power at a power receiving station to supply power. Long-distance transmission, asynchronous grid connection, submarine It has the advantage of being able to use a cable.

On the other hand, there are various types of voltage converters used in high voltage direct current transmission (HVDC) systems, but recently, modular multi-level converters (MMCs) are receiving great attention.

Modular Multi-Level Converter (MMC) is a device that converts DC power into AC power using a plurality of sub-modules, and charges, discharges, and bypasses each sub-module. to operate under control.

However, in the prior art, when designing a high-voltage DC power transmission system based on a modular multi-level converter, a design procedure degree limited to only the internal parameters of a modular multi-level converter (MMC) has been proposed, and characteristics and operation of individual parameters It only satisfies the design conditions for the system, and a dynamic analysis in the state of operation in connection with the power system and a comprehensive design at the overall system level in consideration of this have not been made.

Accordingly, there is a continuous need for a design method that can effectively design a modular multi-level converter that reflects the dynamic analysis in the state in which it operates in connection with the power system and comprehensively considers the characteristics of various parameters at the overall system level. However, an appropriate alternative to this has not yet been proposed.

The present invention is to solve the problems of the prior art as described above, and in designing a modular multi-level converter-based high voltage direct current transmission system (MMC-HVDC), the modular multi-level converter operates in connection with the power system Provides a modular multi-level converter-based high-voltage direct-current transmission system (MMC-HVDC) design method, system and computer program that reflects the dynamic analysis in aim to do

Other detailed objects of the present invention will be clearly grasped and understood by experts or researchers in the technical field through the detailed contents described below.

A modular multilevel converter (MMC)-based high voltage direct current transmission (HVDC) system design method according to an aspect of the present invention for solving the above problems, a modular multilevel converter based high voltage direct current transmission (MMC-HVDC) system A design method comprising: a DC voltage calculation step of calculating, by a design system, a DC voltage (V _dc ) in a DC cable of the MMC-HVDC system; Sub-module power device voltage calculating step of calculating the power device voltage (V _IGBT ) of the sub-module (SM) in the modular multi-level converter (MMC) in consideration of the DC voltage (V _dc ); Transformer output voltage calculating step of calculating the MMC side output voltage (V _c ) in the transformer of the MMC-HVDC system; MAMI calculation step of calculating a maximum allowable modulation index (MAMI) value for the modular multi-level converter (MMC); and a dark current and power device current capacity calculation step of calculating the dark current (I _arm ) and the power device current capacity (I _IGBT ) for the modular multi-level converter (MMC); And, when the power device current capacity (I _IGBT ) calculated in the iteration period does not meet the first predetermined reference value, the iteration period (iteration) is performed again, and the power element current capacity (I _IGBT ) is When the first reference value is satisfied, a system loss verification step of calculating and verifying a system loss for the modular multi-level converter (MMC) is performed.

At this time, in the iteration period, the sub-module (SM) capacitor capacity estimation step of calculating the capacitor capacity (C _sm ) of the sub-module (SM) is further included; in the system loss verification step, the system When the loss does not meet the second predetermined reference value, the sub-module SM capacitor capacity calculation step of the iteration may be performed again.

In addition, prior to the iteration, active power (P _s ), reactive power (Q _s ), AC voltage (V _s ) and DC power ( P _dc ) of the design information acquisition step of acquiring one or more information; may further include.

In addition, the iteration period is an initial value of obtaining one or more information among the initial values of the capacitance capacitance (C _sm ), the female inductance (L _arm ), and the transformer leakage inductance (L _Tr ) of the sub-module (SM) Acquisition step; may further include.

In addition, the iteration interval (iteration), the arm inductance (L _arm ) calculating step of calculating the arm inductance (L arm ) of the sub-module (SM) further comprises; The _{arm inductance (L arm )} calculating step includes , determining whether a circulating current suppression mode is set; When the circulating current suppression mode is set to ON, calculating a compensation signal U _2f for circulating current in the modular multilevel converter (MMC) and calculating the arm inductance L _arm ; may be included.

Here, in the arm inductance (L _arm ) calculating step, when the circulating current suppression mode is set to OFF, the second harmonic circulating current (I _2f ) in the modular multi-level converter (MMC) is calculated and , calculating the arm inductance (L _arm ); may be further included.

In addition, after the step of calculating the arm inductance L _arm , when the reactive power loss Q _Loss does not meet the third predetermined reference value, the step of calculating the arm inductance L _arm may be performed again.

In addition, the system loss verification step, a switching frequency evaluation step of evaluating the switching frequency of the modular multi-level converter (MMC); further comprising, a system loss for the modular multi-level converter (MMC) ) can be calculated and verified.

Here, in the switching frequency evaluation step, the capacitor voltage ripple of the sub-module SM in the modular multi-level converter MMC may also be evaluated.

In addition, in the DC voltage calculation step, the DC current (I _dc ) in the DC cable can also be calculated.

In addition, in the sub-module power device voltage calculation step, the voltage V _SM of the sub-module SM in the modular multi-level converter MMC may also be calculated.

In addition, the computer program according to another aspect of the present invention executes each step of the modular converter (MMC)-based high voltage direct current transmission (HVDC) system design method according to any one of claims 1 to 11 in the computer It is characterized in that it is stored in a computer-readable medium for

Accordingly, in the method, system, and computer program for designing a modular multi-level converter-based high-voltage DC power transmission system according to an embodiment of the present invention, in designing a modular multi-level converter-based high-voltage DC power transmission system (MMC-HVDC), It is possible to effectively design a modular multi-level converter by reflecting the dynamic analysis in the state in which it operates in connection with the power system and comprehensively considering the characteristics of various parameters at the overall system level.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are included as a part of the detailed description to help the understanding of the present invention, provide embodiments of the present invention, and together with the detailed description, explain the technical spirit of the present invention.

1 is an exemplary diagram of a high voltage direct current transmission system based on a modular multilevel converter according to an embodiment of the present invention.

2 is an exemplary diagram of a modular multilevel converter according to an embodiment of the present invention.

3 is a flowchart of a method for designing a modular multi-level converter-based high voltage direct current transmission system according to an embodiment of the present invention.

4 is a flowchart of a method for designing a detailed modular multi-level converter-based high voltage direct current transmission system according to an embodiment of the present invention.

5 is a view for explaining the calculation of the DC voltage (V _dc ) in the DC cable according to an embodiment of the present invention.

The present invention can apply various transformations and can have various embodiments. Hereinafter, specific embodiments will be described in detail based on the accompanying drawings.

The following examples are provided to provide a comprehensive understanding of the methods, systems and/or systems described herein. However, this is merely an example, and the present invention is not limited thereto.

In describing the embodiments of the present invention, if it is determined that the detailed description of the known technology related to the present invention may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted. And, the terms to be described later are terms defined in consideration of functions in the present invention, which may vary according to intentions or customs of users and operators. Therefore, the definition should be made based on the content throughout this specification. The terminology used in the detailed description is for the purpose of describing embodiments of the present invention only, and should not be limiting in any way. Unless explicitly used otherwise, expressions in the singular include the meaning of the plural. In this description, expressions such as “comprising” or “comprising” are intended to indicate certain features, numbers, steps, acts, elements, some or a combination thereof, one or more other than those described. It should not be construed to exclude the presence or possibility of other features, numbers, steps, acts, elements, or any part or combination thereof.

In addition, terms such as first, second, etc. may be used to describe various components, but the components are not limited by the terms, and the terms are for the purpose of distinguishing one component from other components. is used only as

Hereinafter, exemplary embodiments of a modular multi-level converter-based high voltage direct current transmission system design method, system, and computer program according to the present invention will be described in detail with reference to the accompanying drawings.

First, FIG. 1 illustrates a Modular Multilevel Converter (MMC)-based High Voltage Direct Current (HVDC) system 100 according to an embodiment of the present invention. As can be seen in FIG. 1 , in the modular multi-level converter-based high voltage direct current transmission (MMC-HVDC) system 100 according to an embodiment of the present invention, the transformer 130 is connected to the power system 120 . The alternating current (AC) supplied through the first modular multi-level converter 110a is converted to direct current (DC) and transmitted through the DC cable 140, and the second modular multi-level converter 110b is again AC It is converted into (AC) and supplied to the power system 120 again.

Accordingly, in the present invention, in the modular multi-level converter-based high voltage direct current transmission (MMC-HVDC) system 100, AC power is converted into DC power, transmitted, and then converted back into AC power to supply power over a long distance. It has advantages such as power transmission, asynchronous grid connection, and the use of submarine cables.

In addition, FIG. 2 shows an exemplary diagram of a modular multi-level converter (MMC) 110 according to an embodiment of the present invention.

As can be seen in FIG. 2 , in the present invention, the modular multi-level converter (MMC) 110 may be configured to include a plurality of sub-modules (SM) 111 . At this time, the modular multi-level converter (MMC) 110 converts DC power into AC power or converts DC power to AC while controlling the plurality of sub-modules (SM) 111 to charge, discharge, and bypass states, respectively. converted to power.

However, in the prior art, when designing the modular multilevel converter-based high voltage direct current transmission (MMC-HVDC) system 100 , it is simply limited to the internal parameters of the modular multilevel converter (MMC) 110 and individually design standards , it was difficult to perform a dynamic analysis in a state of operation in connection with the power system 120 and a comprehensive design in consideration of this at the overall system level.

In contrast, FIG. 3 illustrates a flowchart of a method for designing a modular multilevel converter-based high voltage direct current transmission (MMC-HVDC) system 100 according to an embodiment of the present invention.

As can be seen in FIG. 3 , in the method for designing a modular multilevel converter-based high voltage direct current transmission (MMC-HVDC) system 100 according to an embodiment of the present invention, the design system is the MMC-HVDC system 100 . DC voltage calculation step (S110) of calculating the DC voltage (V _dc ) in the DC cable 140 of the sub-module in the modular multi-level converter (MMC) 110 in consideration of the DC voltage (V _dc ) Sub-module power device voltage calculation step (S120) for calculating the power device voltage (V _IGBT ) of the (SM) 111, the MMC side output voltage (V _c ) in the transformer 130 of the MMC-HVDC system 100 ) of the transformer output voltage calculation step (S130), the MAMI calculation step (S140) of calculating the maximum allowable modulation index (MAMI) value for the modular multi-level converter (MMC) 110, and the modular multi-level The dark current (I _arm ) and the power device current capacity (I _IGBT ) for the converter (MMC) 110 , the dark current and power device current capacity calculation step (S150) for calculating; And, if the power device current capacity (I _IGBT ) calculated in the iteration period does not meet the first predetermined reference value (S160), the iteration period (iteration) is performed again, and the power element current capacity (I) When the _IGBT ) meets the first reference value (S160), a system loss verification step (S170) of calculating and verifying a system loss for the modular multi-level converter (MMC) 110 is performed. characterized in that

In addition, in the modular multi-level converter-based high voltage direct current transmission (MMC-HVDC) system 100 design method according to an embodiment of the present invention, in the DC voltage calculation step S110 , the DC cable 140 Along with the DC voltage (V _dc ), the DC current (I _dc ) can also be calculated.

In addition, in the sub-module power device voltage calculation step S120 , the voltage V _SM of the sub-module SM in the modular multi-level converter (MMC) 110 may also be calculated.

Furthermore, in the method for designing a modular multi-level converter-based high voltage direct current transmission (MMC-HVDC) system 100 according to an embodiment of the present invention, in the iteration period, the capacitor capacity of the sub-module SM ( A sub-module (SM) capacitor capacity calculation step of calculating C _sm ) may be further included, and in this case, in the system loss verification step S170 , if the system loss does not meet the second predetermined reference value, the repetition period (iteration) may be performed again from the step of calculating the capacitor capacity of the sub-module (SM).

In addition, in the modular multi-level converter-based high voltage direct current transmission (MMC-HVDC) system 100 design method according to an embodiment of the present invention, prior to the iteration, the power system of the MMC-HVDC system ( grid) may further include a design information acquisition step of acquiring one or more of active power (P _s ), reactive power (Q _s ), AC voltage (V _s ), and DC power (P _dc ) at the connection point. .

In addition, in the method for designing a modular multi-level converter-based high voltage direct current transmission (MMC-HVDC) system 100 according to an embodiment of the present invention, the iteration period is, the capacitance capacity of the sub-module SM ( C _sm ), the arm inductance (L _arm ), the transformer leakage inductance (L _Tr ) may further include an initial value acquisition step of acquiring information about one or more of the initial values.

In addition, in the method for designing the modular multi-level converter-based high voltage direct current transmission (MMC-HVDC) system 100 according to an embodiment of the present invention, the iteration period is, the female inductance of the sub-module SM ( The method may further include calculating an arm inductance (L _arm ) for calculating L _arm ). At this time, in the step of calculating the arm inductance (L _arm ), the step of determining whether a circulating current suppression mode is set, and when the circulating current suppression mode is set to ON, in the modular multi-level converter (MMC) Calculating the compensation signal U _2f for the circulating current and calculating the arm inductance L _arm may be included.

Furthermore, in the arm inductance (L _arm ) calculating step, when the circulating current suppression mode is set to OFF, the second harmonic circulating current (I _2f ) in the modular multi-level converter (MMC) is calculated and , calculating the arm inductance L _arm may be further included.

Furthermore, in the modular multilevel converter-based high voltage direct current transmission (MMC-HVDC) system 100 design method according to an embodiment of the present invention, after the arm inductance (L _arm ) calculating step, reactive power loss ( When Q _Loss ) does not satisfy the third predetermined reference value, the step of calculating the arm inductance L _arm may be performed again.

In addition, in the method for designing a modular multilevel converter-based high voltage direct current transmission (MMC-HVDC) system 100 according to an embodiment of the present invention, the system loss verification step includes switching of the modular multilevel converter (MMC) By evaluating the frequency, the method may further include a switching frequency evaluation step of calculating and verifying a system loss for the modular multi-level converter (MMC).

In this case, in the switching frequency evaluation step, it is also possible to evaluate the capacitor voltage ripple of the sub-module SM in the modular multi-level converter MMC.

Accordingly, in the modular multilevel converter-based high voltage direct current transmission (MMC-HVDC) system 100 design method according to an embodiment of the present invention, the modular multilevel converter (MMC) 110 is the power system 120 . It is possible to effectively design by reflecting the dynamic analysis in the operating state in conjunction with and comprehensively considering the characteristics of various parameters at the overall system level.

In addition, FIG. 4 exemplifies a flowchart of a method for designing a detailed modular multilevel converter-based high voltage direct current transmission (MMC-HVDC) system 100 according to an embodiment of the present invention.

Hereinafter, a method for designing a modular multi-level converter-based high voltage direct current transmission (MMC-HVDC) system 100 according to an embodiment of the present invention will be described in more detail with reference to FIG. 4 .

First, in step S1010, active power (P _s ), reactive power (Q _s ), AC voltage (V _s ) and DC power (P _dc ) at the power grid connection point of the MMC-HVDC system 100 ) to obtain one or more of the information. At this time, the active power (P _s ), reactive power (Q _s ), and AC voltage (V _s ) at the power grid connection point are parameters defined before the determination process of the main parameters, and the power grid (grid) It may be predetermined during the planning process.

Next, in step S1020, the DC voltage (V _dc ) and DC current (I _dc ) in the DC cable 140 of the MMC-HVDC system 100 can be calculated.

In general, the DC voltage (V _dc ) may be determined by loss-cost optimization, and the DC current (I _dc ) may be determined in consideration of the cable cost over a long distance. First, if the DC voltage (V _dc ) is optimized according to the transmission distance in the high voltage direct current transmission (HVDC), the parameters of the other modular converter (MMC) 110 may be calculated according to the design process of FIG. 4 .

In addition, in the present invention, the DC voltage (V _dc ) can be calculated in a state in which the cost estimate is selected as the maximum value as shown in FIG. 5 , and also in step 9 of FIG. It can be re-established in consideration of the rated current (I _IGBT ). Also, as shown in FIG. 5 , a DC voltage (V _dc ) and a DC current (I _dc ) for satisfying the DC power required are inversely proportional to each other. Accordingly, in a state in which the DC voltage V _dc is fixed, the design process is repeated as shown in FIG. 4 to verify the required design conditions and to calculate the DC current I _DC .

Next, in step S1030, the power device voltage (V _IGBT ) of the sub-module (SM) 111 in the modular multi-level converter (MMC) 110 is calculated in consideration of the DC voltage (V _dc ). .

At this time, the voltage (V _SM ) of the sub-module (SM) 111 in the modular multi-level converter (MMC) 110 may also be calculated.

For a more specific example, the voltage of the individual sub-modules (SM) 111 in the modular multi-level converter (MMC) 110 is the rated voltage of the power device (switching device) and the modular multi-level converter (MMC) The number of sub-modules (SM) 111 is determined according to the DC voltage (V _dc ) of 110, which is related to the rated voltage of the power device (switching device), so each sub-module (SM) 111 The magnitude of the voltage (V _SM ) can be applied as an optimization target in economic evaluation.

Accordingly, in the present invention, in Equation 1 below, a recommended voltage utilization value (λ _v ) of 60% of the rating of the power device is recommended according to product specifications of the power device, such as can be used However, this is only one example, and the present invention is not necessarily limited thereto.

[Equation 1]

where V _dc is the DC voltage of the modular multilevel converter (MMC) 110 , N ₀ is the number of sub-modules (SM) 111 , V _sm is the nominal voltage of the sub-modules (SM) 111 . ), λ _v is a voltage utilization factor, and V _IGBT is a voltage rating of the power device (IGBT).

Next, in step S1040, one or more of the initial values of the capacitance capacitance (C _sm ), the female inductance (L _arm ), and the transformer leakage inductance (L _Tr ) of the sub-module (SM) 111 are acquired and updated. can

More specifically, in step S1040, the initial values of parameters necessary to obtain the secondary voltage of the transformer in step S1050 below are set.

In this case, the initial capacitance capacitance C ₀ of the sub-module (SM) 111 may be calculated using Equation 2 below.

[Equation 2]

Here, C ₀ is the initial value of the capacitance capacity of the sub-module (SM) 111 and is a value that can be updated during the design process, and EP ₀ is the capacitance that allows the normal operation of the modular multi-level converter (MMC) 110. energy per power ratio (eg 20-50 [kJ/MVA] or 10-100 [ _kJ / _MVA ]), where S _n is the apparent power ( apparent power). However, this is only one example, and the present invention is not necessarily limited thereto.

In addition, the initial value of the arm inductance L _arm may be calculated using Equation 3 below on the assumption that the second harmonic circulating current I2f is a specific value.

[Equation 3]

Here, L ₀ is the initial value of the arm inductance (L _arm ), which can be updated during the design process, I _2f is the second harmonic circulating current and ω ₀ is the nominal angular frequency.

In addition, to specify the value of the second harmonic circulating current, X _Lpu is an empirically an estimate due to the reactive power consumption of the dark reactance, a constant chosen by the designer as a requirement early in the design phase, for example approximately 0.1 [ pu] can be used. However, this is only one example, and the present invention is not necessarily limited thereto. Accordingly, the per unit value of the female inductance may be defined as in Equation 4 below.

[Equation 4]

Here, Z _base is an impedance base value, V _LL is a line to line AC voltage, and m is a modulation index.

Accordingly, for example, assuming that the value per unit of X _Lpu is 0.1 [pu] and the modulation index is 1, the second harmonic circulating current I _2f may be calculated through Equation 5 below. However, this is only one example, and the present invention is not necessarily limited thereto.

[Equation 5]

In the present invention, the initial value of the secondary high-frequency circulating current (I2f) can be selected as a simple value, but then has a profound effect on PQ capability, stability, and fault current rising limitation It is recalculated to a more appropriate value taking into account.

In addition, the leakage inductance Ltr of the transformer 130 may use a value provided by a transformer manufacturer, but the present invention is not limited thereto, and other suitable values may be used.

Next, in step S1050, the MMC-side output voltage (secondary voltage, V _c ) in the transformer 130 of the MMC-HVDC system 100 is calculated.

More specifically, the secondary-side voltage (secondary) of the transformer 130 is within a limited range that meets the modulation index operable in the modular multi-level converter (MMC) 110 while providing the necessary active and reactive power (modulation index) should be decided in At this time, in order to calculate the secondary-side voltage, using a PQ capability curve formula, the maximum value in the available range of the modular multi-level converter (MMC) 110 voltage may be selected.

In this case, the capacity curve formula may be defined as in Equation 6 below.

[Equation 6]

However, in the present invention, it can be assumed that L _f = 0 (since the transformer is installed close to the modular multilevel converter (MMC)), and therefore the line impedance between them is negligible, and V _c is also V _t and will have the same value.

Furthermore, since the primary-side voltage of the transformer 130 is in a limited range allowed by the connected power system 120 , the secondary-side voltage also has a limited voltage range.

Accordingly, as long as the modular multilevel converter (MMC) 110 performs pure reactive power compensation (STATCOM mode) (at this time, the rating of the modular multilevel converter (MMC) 110 ) It has a maximum voltage while supplying Q _max in the power), the secondary voltage may have a range in which the AC voltage is regulated, for example, from 0.95 to 1.05 [pu], which is a voltage according to the grid code It may be selected in consideration of the stability range. However, this is only an example, and the present invention is not necessarily limited thereto.

In addition, in Equation 6, under the conditions of P _s = 0, Q _max and V _spu = 1.05 [pu], the secondary voltage may be calculated as in Equation 7 below.

[Equation 7]

Here, V _cpu is the AC voltage of the transformer 130 side, X _eqpu is the equivalent total reactance, Q _maxpu is the maximum reactive power requirement, V _spu is the value per unit of AC voltage on the power grid side (grid side AC voltage at per unit value).

Also, considering the secondary voltage with the modulation index, the secondary voltage is associated with the DC voltage providing the AC terminal voltage of the modular multilevel converter (MMC) 110, and the activated sub-module (SM) 111 ) and the product of the individual sub-module (SM) 111 voltage can be calculated. Accordingly, the DC voltage of the modular multi-level converter (MMC) 110 may be calculated as in Equation 8 below.

[Equation 8]

Here, k _max is a voltage ripple factor, and _{ΔV ripple} is k _max ·V _sm . From Equation 8, the minimum DC voltage can be calculated as in Equation 9 below (because k _max = -k _min ).

[Equation 9]

Under the condition of Equation 9, the value calculated in Equation 7 becomes 1 [pu], so the maximum transformer-side AC voltage for the Line-to-Line RMS value can be calculated as Equation 10 below. there is.

[Equation 10]

Next, in step S1060 , the voltage change rate and capacitor capacity C _sm of the sub-module SM 111 may be calculated.

More specifically, the capacitor capacity (energy storage capacity) of the sub-module (SM) 111 may be calculated using the previously calculated parameter and an appropriate voltage ripple coefficient. In this case, the initial capacitor capacitance C ₀ of the sub-module (SM) 111 may be conservatively determined so as to be within a stable operating condition range.

Furthermore, the voltage ripple may be determined by the initial design value, but the voltage ripple is reduced by the Circulation Current Suppression Control (CCSC) algorithm that affects the internal operation of the modular multi-level converter (MMC) 110 . can be reduced Conversely, a voltage balancing algorithm for voltage ripple may exacerbate voltage ripple while causing forced ripple.

Therefore, the voltage ripple is related to the switching frequency affected by the system loss of the modular multilevel converter (MMC) 110, which is adopted by the developer of the modular multilevel converter (MMC) 110 . It is desirable to consider the specific switching principle.

Next, in step S1070, the arm inductance L _arm of the sub-module SM 111 is calculated.

At this time, the step S1070 is a step of determining whether the circulating current suppression mode is set (S1071), when the circulating current suppression mode is set to ON, the circulating current in the modular multi-level converter (MMC) It may include calculating the compensation signal U _2f for this (S1072a) and calculating the arm inductance L _arm (S1073a).

In addition, in the step S1070, when the circulating current suppression mode is set to OFF, the second harmonic circulating current I _2f in the modular multi-level converter (MMC) is calculated (S1072b), and the arm It may include calculating the inductance L _arm ( S1073b ).

Furthermore, after the step S1070, when the reactive power loss (Q _Loss ) does not meet a predetermined third reference value, the step S1080 of performing the calculating step of the arm inductance (L _arm ) again may be further included.

More specifically, when the circulating current suppression control CCSC is deactivated (OFF), the arm inductance L _arm may be determined by selecting the second harmonic circulating current value described in step S1040. However, since the circulating current suppression control (CCSC) can be activated in the MMC-HVDC system 100 in general, the arm inductance (L _arm ) must be calculated in consideration of whether the circulating current suppression control (CCSC) is activated or deactivated. do.

(Case a) When Circulating Current Suppression Control (CCSC) is Disabled

(a-1) Second harmonic circulating current calculation (I _2f ): I _2f can be calculated using Equation 5 and the above-described EP ₀ (energy power ratio).

(a-2) Calculation of arm inductance (L _arm ): The arm inductance can be calculated using Equation 3, and it is also desirable to check whether the calculated value of the arm inductance avoids the resonance point.

(Case b) When Circulating Current Suppression Control (CCSC) is Enabled

(b-1) Calculation of compensation voltage (U _2f ): Equation 3 provides a method of calculating female inductance in a state in which the circulating current suppression control (CCSC) is deactivated. However, it is also possible to calculate the second harmonic voltage across the arm inductor, assuming that the second harmonic current is included in the arm current, and calculate the arm inductance. Furthermore, when the circulating current suppression control (CCSC) is activated, the second harmonic circulating current item is removed to be derived as shown in Equation 11 below.

[Equation 11]

(b-2) Calculation of arm inductance (L _arm ): When cyclic current suppression control (CCSC) is enabled, the arm inductance is the fault current for the gate turn-off delay in the process of examining the resonance problem. It can be calculated in relation to the fault current rise rate, since the second harmonic circulating current is negligibly small.

Next, in step S1090 , a Maximum Allowable Modulation Index (MAMI) value for the modular multi-level converter (MMC) 110 is calculated.

Here, the initial value (m _max0 ) of the maximum allowable modulation index may be calculated based on Equation (10) with respect to the secondary voltage when the circulating current suppression control (CCSC) is deactivated. However, with respect to the compensation signal (m _U2f ) (Equation 11) obtained due to the voltage ripple naturally generated by the sub-module (SM) 111 capacitor, the maximum allowable modulation index MAMI is obtained by the following Equation 12 can be calculated.

[Equation 12]

Here, m _max0 is a maximum allowable modulation index (MAMI) when the circulating current suppression control (CCSC) is deactivated, and m _U2f is a compensation signal index.

Next, in step S1100 , the dark current I _arm and the power device current capacity I _IGBT for the modular multi-level converter (MMC) 110 are calculated.

More specifically, the current capacity (I _IGBT ) of the power device (switching device) of the modular multi-level converter (MMC) 110 is a voltage calculation in consideration of the heat generated in each sub-module (SM) 111 (Equation 1), including a current utilization factor, it can be expressed as Equation 13 below.

[Equation 13]

In addition, when the dark current I _arm is considered, the ratio k of the AC current and the DC current may be expressed as in Equation 14 below.

[Equation 14]

Here, assuming that DC power and AC power are the same as in a lossless system, it can be expressed as Equation 15 below.

[Equation 15]

In this case, the following Equation 16 can be derived using Equations 5 and 15 above.

[Equation 16]

Accordingly, the dark current I _arm may be expressed as in Equation 17 below.

[Equation 17]

In order to easily calculate the rated current, γ ₀ may be used as an arm current rating factor of the modular multi-level converter (MMC) 110 as shown in Equation 18 below, wherein the dark current The rating factor will have a minimum value of 1 for m = 1 and φ = 0.

[Equation 18]

However, since m and φ may vary depending on the operating point of Equation 6, when the MMC-HVDC system 100 according to the present invention operates with a single power factor (PQ curve linear ramp rate) condition), the modulation index obtainable in step S1050 becomes the minimum value. Accordingly, the operating angle under the above conditions may be calculated using Equation 19 below.

[Equation 19]

Therefore, using Equations 17 and 18, the dark current can be finally expressed as Equation 20 below.

[Equation 20]

In addition, the current capacity of the power device (switching device) can be determined through optimization in consideration of various products of various semiconductor manufacturers, verified in economic terms, and considering the current capacity and economy. In this case, the current capacity I _IGBT of the power device can be finally expressed as Equation 21 below using Equations 18 and 20.

[Equation 21]

Next, in step S1110 , it is determined whether the previously calculated power device current capacity I _IGBT satisfies a predetermined first reference value.

Accordingly, when the power device current capacity (I _IGBT ) does not meet the first predetermined reference value, the process returns to step S1020 and the design process is performed again, and the power device current capacity (I _IGBT ) is the first If the reference value is satisfied, the process proceeds to step S1120.

Accordingly, in step S1120, a system loss for the modular multi-level converter (MMC) 110 is calculated and verified.

More specifically, the system loss is affected by the capacitance of the sub-module (SM) 111 having a voltage ripple factor that limits the switching frequency that can be changed according to various modulation schemes. . In general, the voltage fluctuation of the sub-module (SM) 111 capacitor may be calculated as a natural voltage ripple and a forced voltage ripple.

The voltage ripple coefficient k _max when calculating the energy storage capacity in step S1060 may be regarded as the natural voltage ripple. However, due to the characteristics of the modular multi-level converter (MMC) 110 , voltage ripple by various modulation techniques may be additionally generated, which may correspond to a forced voltage ripple generated by an external factor.

Accordingly, in relation to the system loss, the voltage ripple may be determined according to a capacitor capacity and a modulation method. Furthermore, a switching frequency capable of satisfying the system loss is also calculated.

Subsequently, in step S1130, it is determined whether the system loss meets a predetermined second reference value.

Accordingly, when the system loss does not meet the second predetermined reference value, the process proceeds again from step S1060, and when the power device current capacity I _IGBT meets the first reference value, It proceeds to step S1140.

Finally, in step S1140 , the finally calculated design parameters may be verified and confirmed.

In the present invention, the calculated parameters are verified by PSCAD/EMTDC time domain simulation, but the present invention is not necessarily limited thereto.

Furthermore, as an embodiment of the present invention, the above salpin modular multi-level converter (MMC)-based high voltage direct current transmission (HVDC) system design method is implemented as a program stored in a computer readable recording medium for executing a series of steps in a computer it might be In this case, the computer program may be a computer program including a high-level language code that can be executed in a computer using an interpreter as well as a computer program including a machine language code generated by a compiler. In this case, the computer is not limited to a personal computer (PC) or a notebook computer, and includes a central processing unit (CPU) such as a server, smart phone, tablet PC, PDA, mobile phone, etc. to process any information that can execute a computer program. includes the device. In addition, the computer-readable recording medium includes all types of recording media in which programs and data can be stored so as to be read by a computer system. Examples thereof include ROM (Read Only Memory), RAM (Random Access Memory), CD (Compact Disk), DVD (Digital Video Disk)-ROM, magnetic tape, floppy disk, optical data storage device, etc. Included. In addition, such a recording medium may be distributed in a computer system connected through a network, and computer-readable codes may be stored and executed in a distributed manner.

Accordingly, in the modular multi-level converter (MMC)-based high-voltage direct-current transmission (HVDC) system 100 design method, system, and computer program according to an embodiment of the present invention, the modular multi-level converter-based high-voltage direct-current transmission system ( In designing 100), the modular multi-level converter 110 reflects the dynamic analysis in a state in which it operates in conjunction with the power system 120 and comprehensively considers the characteristics of various parameters at the overall system level to effectively design be able to proceed.

Although representative embodiments of the present invention have been described in detail above, those of ordinary skill in the art to which the present invention pertains will understand that various modifications are possible within the limits without departing from the scope of the present invention with respect to the above-described embodiments. . Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined by the claims described below as well as the claims and equivalents.

Claims (12)

1. A method for designing a modular multilevel converter-based high voltage direct current transmission (MMC-HVDC) system, the method comprising:

   DC voltage calculation step in which the design system calculates the DC voltage (V _dc ) in the DC cable of the MMC-HVDC system;

   Sub-module power device voltage calculating step of calculating the power device voltage (V _IGBT ) of the sub-module (SM) in the modular multi-level converter (MMC) in consideration of the DC voltage (V _dc );

   Transformer output voltage calculating step of calculating the MMC side output voltage (V _c ) in the transformer of the MMC-HVDC system;

   MAMI calculation step of calculating a maximum allowable modulation index (MAMI) value for the modular multi-level converter (MMC); and

   A dark current and power device current capacity calculation step of calculating the dark current (I _arm ) and the power device current capacity (I _IGBT ) for the modular multi-level converter (MMC); including an iteration including; ,

   If the power device current capacity (I _IGBT ) calculated in the iteration period does not meet the first predetermined reference value, the iteration period is performed again,

   When the power device current capacity (I _IGBT ) satisfies the first reference value,

   A modular multilevel converter (MMC)-based high voltage direct current transmission (HVDC) system, characterized in that performing; a system loss verification step of calculating and verifying a system loss for the modular multilevel converter (MMC) design method.
2. According to claim 1,

   In the iteration period,

   The sub-module (SM) capacitor capacity calculation step of estimating the capacitor capacity (C _sm ) of the sub-module (SM) is further included;

   In the system loss verification step,

   If the system loss does not meet a second predetermined threshold,

   A modular converter (MMC)-based high voltage direct current transmission (HVDC) system design method, characterized in that it proceeds again from the step of calculating the capacitor capacity of the sub module (SM) of the iteration.
3. According to claim 1,

   Prior to the iteration,

   Design to acquire information of at least one of active power (P _s ), reactive power (Q _s ), AC voltage (V _s ), and DC power (P _dc ) at the power grid connection point of the MMC-HVDC system Information acquisition step; Modular converter (MMC)-based high voltage direct current transmission (HVDC) system design method comprising further comprising.
4. According to claim 1,

   The iteration period is,

   An initial value acquisition step of acquiring information about one or more of the initial values of the capacitance capacity (C _sm ) of the sub-module (SM), the female inductance (L _arm ), and the transformer leakage inductance (L _Tr ); characterized by further comprising: A modular converter (MMC) based high voltage direct current transmission (HVDC) system design method.
5. According to claim 1,

   The iteration period is,

   The method further includes; an arm inductance (L _arm ) calculating step of calculating the arm inductance (L _arm ) of the sub-module (SM);

   In the step of calculating the arm inductance (L _arm ),

   determining whether a circulating current suppression mode is set;

   When the circulating current suppression mode is set to ON,

   Calculating the compensation signal (U _2f ) for the circulating current in the modular multi-level converter (MMC), and calculating the arm inductance (L _arm ); Modular converter (MMC) characterized in that it is included A method for designing a high-voltage direct current transmission (HVDC) system based on
6. 6. The method of claim 5,

   In the step of calculating the arm inductance (L _arm ),

   When the circulating current suppression mode is set to OFF,

   Calculating the second harmonic circulating current (I _2f ) in the modular multi-level converter (MMC), and calculating the arm inductance (L _arm ) Modular converter (MMC) characterized in that it further comprises; A method for designing a high-voltage direct current transmission (HVDC) system based on
7. 6. The method of claim 5,

   After the arm inductance (L _arm ) calculation step,

   Modular converter (MMC)-based high voltage direct current transmission (HVDC) system design, characterized in that when the reactive power loss (Q _Loss ) does not meet the third predetermined threshold value, the arm inductance (L _arm ) calculating step is performed again method.
8. The method of claim 1,

   The system loss verification step is,

   A switching frequency evaluation step of evaluating the switching frequency of the modular multi-level converter (MMC); further comprising,

   A modular converter (MMC)-based high voltage direct current transmission (HVDC) system design method, characterized in that calculating and verifying a system loss for the modular multi-level converter (MMC).
9. 9. The method of claim 8,

   In the switching frequency evaluation step,

   A modular converter (MMC)-based high voltage direct current transmission (HVDC) system design method, characterized in that the capacitor voltage ripple of the sub module (SM) is also evaluated in the modular multilevel converter (MMC).
10. According to claim 1,

    In the DC voltage calculation step,

    A modular converter (MMC)-based high voltage direct current transmission (HVDC) system design method, characterized in that the DC current (I _dc ) in the DC cable is also calculated.
11. According to claim 1,

    In the sub-module power device voltage calculation step,

    A modular converter (MMC)-based high-voltage direct-current transmission (HVDC) system design method, characterized in that the modular multi-level converter (MMC) also calculates the voltage (V _SM ) of the sub-module (SM).
12. A program stored in a computer readable medium for executing each step of the method for designing a modular converter (MMC) based high voltage direct current transmission (HVDC) system according to any one of claims 1 to 11 in a computer.

Images