CN107579536B - Droop control converter station control method and device - Google Patents

Droop control converter station control method and device Download PDF

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CN107579536B
CN107579536B CN201710892693.3A CN201710892693A CN107579536B CN 107579536 B CN107579536 B CN 107579536B CN 201710892693 A CN201710892693 A CN 201710892693A CN 107579536 B CN107579536 B CN 107579536B
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value
direct current
droop
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CN107579536A (en
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郭敬梅
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Electric Power Research Institute of Guangdong Power Grid Co Ltd
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Abstract

The invention discloses a control method of a droop control converter station, which comprises the steps of firstly judging whether the droop control converter station is fully loaded, subtracting a preset increment from a droop coefficient if the droop control converter station is fully loaded, and continuously subtracting the preset increment from the droop coefficient until the droop control converter station is not fully loaded if the droop control converter station is fully loaded after adjustment; calculating the direct current voltage of the droop control converter station, judging whether the maximum value of the direct current voltage is greater than the preset maximum limit value of the direct current voltage or whether the minimum value of the direct current voltage is smaller than the preset minimum limit value of the direct current voltage, if so, calculating the corresponding common voltage reference value when the maximum value of the direct current voltage is equal to the maximum limit value of the direct current voltage or the minimum value of the direct current voltage is equal to the minimum limit value of the direct current voltage according to the linear relation between the common voltage reference value and the direct current voltage, wherein all the direct current voltages cannot be greater than the maximum limit value of the direct current voltage or smaller than the minimum limit value of the direct current voltage at the moment, and the technical problem that the full load of the droop control converter station and the direct current.

Description

Droop control converter station control method and device
Technical Field
The invention relates to the field of control, in particular to a droop control converter station control method and device.
Background
Compared with a two-end direct-current system, a multi-terminal direct-current power transmission system (MTDC) can realize multi-power supply power transmission and multi-drop flashlight, and a reliable technical scheme is provided for the problems of large-scale distributed energy grid connection, large-capacity long-distance power transmission, urban interconnection and the like.
The stable control of the direct current voltage and the reasonable distribution of the useful power are two major core problems of the stable operation of the multi-terminal direct current transmission system. The direct current stability control mode can be divided into single-point control and multi-point control, and specifically comprises master-slave control, voltage margin control, droop control, combination control and the like. Since the droop control does not depend on high-speed communication between converter stations, voltage can be controlled by a plurality of converter stations, and the system reliability is high, and the droop control is attracted by much attention in recent years.
There are four existing droop control methods: in the scheme 1, a droop coefficient is in a proportional relation with the rated capacity of a converter station and is taken as a constant; the scheme 2 is that a power reference value is set to change a droop control intercept and stabilize the allowable operation range of the direct-current voltage; scheme 3, a translational droop curve is combined with a change of the slope of the droop curve, and the static deviation of direct current and active power is eliminated; scheme 4, the droop coefficient of the leading converter station is adaptively determined by the power margin of each converter station.
However, for the scheme 1, the fixed droop coefficient is adopted, so that the direct-current voltage rigidity is poor, full load of the droop control converter station can be caused, and the capability of responding to the change of the direct-current network tide is lost; schemes 2 and 3 solve the problem that the direct-current voltage of the system is out of limit, but the unnecessary full load of the droop control converter station still cannot be avoided; the fourth scheme solves the problem that the droop control converter station is unnecessarily fully loaded, but does not solve the problem that the direct-current voltage is out of limit. Therefore, the technical problems that the existing droop control method cannot simultaneously solve the full load of the droop control converter station and the direct-current voltage is out of limit are caused.
Disclosure of Invention
The invention provides a droop control converter station control method and device, and solves the technical problem that the existing droop control method cannot simultaneously solve the technical problems of full load and direct-current voltage out-of-limit of a droop control converter station.
The invention provides a droop control converter station control method, which comprises the following steps:
s1: obtaining a first input variable before the command is issued by the dispatching system, a second input variable after the command is issued by the dispatching system and a droop coefficient k of the droop control converter station, substituting the first input variable, the second input variable and the droop coefficient k into a state equation of the multi-terminal flexible direct current transmission system to calculate the direct current power P of the droop control converter station after the command is issued by the dispatching system*Infinity, and whether or not there is DC power P*The absolute value of the infinity is larger than or equal to the preset direct current power limit value, if yes, the corresponding droop is carried outThe droop coefficient k of the converter station is controlled to subtract the preset increment a, the step S1 is executed again, and if not, the step S2 is executed;
s2: substituting the first input variable, the second input variable and the droop coefficient k into a state equation of the multi-terminal flexible direct current transmission system to calculate and record the maximum value U of direct current voltage of all droop control converter stations in the multi-terminal flexible direct current transmission systemmax0And minimum value U of DC voltagemin0；
S3: when the maximum value U of the DC voltagemax0Greater than a preset maximum limit value V of DC voltagemaxCalculating a new maximum value U of the DC voltage of the multi-terminal flexible DC power transmission system according to the linear relation between the common reference voltage and the DC voltage of the multi-terminal flexible DC power transmission systemmax1Equal to the preset maximum limit value V of the direct current voltagemaxTime corresponding second common voltage reference value UrefnewOr, when the DC voltage is minimum value Umin0Less than a preset minimum limit value V of DC voltageminCalculating a new minimum value U of the DC voltage of the multi-terminal flexible DC power transmission system according to the linear relation between the common reference voltage and the DC voltage of the multi-terminal flexible DC power transmission systemmin1Equal to a preset minimum limit value V of the DC voltageminTime corresponding second common voltage reference value UrefnewAnd the second common voltage reference value U is setrefnewReplacing a first common voltage reference value U in a second input variableref0And obtaining a third input variable, and replacing the second input variable with the third input variable to control the multi-terminal flexible direct-current transmission system.
Preferably, step S1 specifically includes:
s101: performing stability analysis on a state equation of the multi-terminal flexible direct current transmission system, calculating a value range of a droop coefficient k of the droop control converter station, and obtaining a maximum limit value of the droop coefficient of each droop control converter station;
s102: adjusting the droop coefficients k of the droop control converter stations through a preset scheme, so that the sum of the droop coefficients k of the droop control converter stations is equal to the minimum maximum value of the maximum values of the droop coefficients of the droop control converter stations;
s103: obtaining a first input variable before the command is issued by the dispatching system, a second input variable after the command is issued by the dispatching system and a droop coefficient k of the droop control converter station, substituting the first input variable, the second input variable and the droop coefficient k into a state equation of the multi-terminal flexible direct current transmission system to calculate the direct current power P of the droop control converter station after the command is issued by the dispatching system*Infinity, and whether or not there is DC power P*And if the absolute value of the (∞) value is greater than or equal to the preset direct current power limit value, subtracting a preset increment a from the droop coefficient k of the corresponding droop control converter station, returning to execute the step S102, and if the absolute value of the (∞) value is not greater than the preset direct current power limit value, executing the step S2.
Preferably, step S3 specifically includes:
s301: when the maximum value U of the DC voltagemax0Greater than a preset maximum limit value V of DC voltagemaxIf so, executing step S302, otherwise, executing step S303;
s302: by presetting the minimum limit value V of the DC voltageminReplacing the first common voltage reference U in the second input variableref0Obtaining a fourth input variable, calculating and recording the maximum value U of the direct current voltage of all the corresponding converter stations according to the first input variable and the fourth input variablemax2And pass through point (U)ref0，Umax0) And point (V)min，Umax2) Determining the linear relation between the common reference voltage and the DC voltage of the multi-terminal flexible DC power transmission system, and establishing a first preset formula to calculate the maximum value U of the new DC voltage of the multi-terminal flexible DC power transmission systemmax1Equal to the preset maximum limit value V of the direct current voltagemaxTime corresponding second common voltage reference value UrefnewReference value U of the second common voltagerefnewReplacing a first common voltage reference value U in a second input variableref0Obtaining a third input variable, and replacing the second input variable with the third input variable to control the multi-terminal flexible direct-current transmission system;
s303: when the minimum value U of the DC voltagemin0If the voltage is less than the preset DC voltage minimum limit value, executing the step S304, otherwise, the second common voltage reference value UrefnewIs equal to the first common voltage reference valueUref0Reference value U of the second common voltagerefnewReplacing a first common voltage reference value U in a second input variableref0Obtaining a third input variable, and replacing the second input variable with the third input variable to control the multi-terminal flexible direct-current transmission system;
s304: by presetting the maximum limit value V of the DC voltagemaxReplacing the first common voltage reference value U in the second input variableref0Obtaining a fifth input variable, calculating and recording the minimum value U of the direct current voltage of all the corresponding converter stations according to the first input variable and the fifth input variablemin2And pass through point (U)ref0，Umin0) And point (V)max，Umin2) Determining the linear relation between the common reference voltage and the DC voltage of the multi-terminal flexible DC power transmission system, establishing a second preset formula to calculate the minimum value U of the new DC voltage of the multi-terminal flexible DC power transmission systemmin1Equal to the preset maximum limit value V of the direct current voltageminTime corresponding second common voltage reference value UrefnewReference value U of the second common voltagerefnewReplacing a first common voltage reference value U in a second input variableref0And obtaining a third input variable, and replacing the second input variable with the third input variable to control the multi-terminal flexible direct-current transmission system.
Preferably, step S0 is further included before step S1;
s0: and constructing a state space model of the multi-terminal flexible direct current transmission system only considering active power balance, and obtaining a state equation of the multi-terminal flexible direct current transmission system.
Preferably, the first preset formula and the second preset formula are specifically:
the first preset formula:
Figure BDA0001421549480000041
the second preset formula:
the invention provides a droop control converter station control device, which comprises:
a coefficient adjusting module, configured to obtain a first input variable before the command is issued by the scheduling system, a second input variable after the command is issued by the scheduling system, and a droop coefficient k of the droop control converter station, and substitute the first input variable, the second input variable, and the droop coefficient k into an equation of state of the multi-terminal flexible direct current transmission system to calculate a direct current power P of the droop control converter station after the command is issued by the scheduling system*Infinity, and whether or not there is DC power P*The absolute value of the (∞) is larger than or equal to the preset direct current power limit value, if yes, the preset increment a is subtracted from the droop coefficient k of the corresponding droop control converter station, the coefficient adjusting module is triggered again, and if not, the voltage calculating module is triggered;
a voltage calculation module for substituting the first input variable, the second input variable and the droop coefficient k into a state equation of the multi-terminal flexible direct current transmission system to calculate and record the maximum value U of the direct current voltage of all the droop control converter stations in the multi-terminal flexible direct current transmission systemmax0And minimum value U of DC voltagemin0；
A comparison and replacement module for comparing the maximum value U of the DC voltagemax0Greater than a preset maximum limit value V of DC voltagemaxCalculating a new maximum value U of the DC voltage of the multi-terminal flexible DC power transmission system according to the linear relation between the common reference voltage and the DC voltage of the multi-terminal flexible DC power transmission systemmax1Equal to the preset maximum limit value V of the direct current voltagemaxTime corresponding second common voltage reference value UrefnewOr, when the DC voltage is minimum value Umin0Less than a preset minimum limit value V of DC voltageminCalculating a new minimum value U of the DC voltage of the multi-terminal flexible DC power transmission system according to the linear relation between the common reference voltage and the DC voltage of the multi-terminal flexible DC power transmission systemmin1Equal to a preset minimum limit value V of the DC voltageminTime corresponding second common voltage reference value UrefnewAnd the second common voltage reference value U is setrefnewReplacing a first common voltage reference value U in a second input variableref0A third input variable is obtained which is,and replacing the second input variable with the third input variable to control the multi-terminal flexible direct-current power transmission system.
Preferably, the coefficient adjusting module specifically includes:
the high-limit calculation submodule is used for performing stability analysis on a state equation of the multi-terminal flexible direct current transmission system, calculating the value range of a droop coefficient k of the droop control converter station, and obtaining the maximum limit value of the droop coefficient of each droop control converter station;
the constraint limiting submodule is used for adjusting the droop coefficients k of the droop control converter stations through a preset scheme, so that the sum of the droop coefficients k of the droop control converter stations is equal to the minimum maximum value of the maximum values of the droop coefficients of the droop control converter stations;
and the full-load adjusting submodule is used for acquiring a first input variable before the dispatching system sends a command, a second input variable after the dispatching system sends a command and a droop coefficient k of the droop control converter station, substituting the first input variable, the second input variable and the droop coefficient k into a state equation of the multi-terminal flexible direct current transmission system to calculate the direct current power P (∞) of the droop control converter station after the dispatching system sends the command, judging whether the absolute value of the direct current power P (∞) is greater than or equal to a preset direct current power limit value, if so, subtracting a preset increment a from the droop coefficient k of the corresponding droop control converter station, and triggering the constraint limiting submodule, and if not, triggering the voltage calculating module.
Preferably, the comparison and replacement module specifically includes:
a high limit comparison submodule used for comparing the maximum value U of the DC voltagemax0Greater than a preset maximum limit value V of DC voltagemaxIf so, triggering a high limit replacement submodule, otherwise triggering a low limit comparison submodule;
high limit replacement submodule for using a preset minimum limit value V of the DC voltageminReplacing the first common voltage reference U in the second input variableref0Obtaining a fourth input variable, calculating and recording the maximum value U of the direct current voltage of all the corresponding converter stations according to the first input variable and the fourth input variablemax2And pass through point (U)ref0，Umax0) And point (V)min，Umax2) Determining the linear relation between the common reference voltage and the DC voltage of the multi-terminal flexible DC power transmission system, and establishing a first preset formula to calculate the maximum value U of the new DC voltage of the multi-terminal flexible DC power transmission systemmax1Equal to the preset maximum limit value V of the direct current voltagemaxTime corresponding second common voltage reference value UrefnewReference value U of the second common voltagerefnewReplacing a first common voltage reference value U in a second input variableref0Obtaining a third input variable, and replacing the second input variable with the third input variable to control the multi-terminal flexible direct-current transmission system;
a low limit comparison submodule for comparing the DC voltage with a minimum value Umin0Triggering the low limit replacement submodule when the voltage is smaller than the preset minimum limit value of the direct current voltage, otherwise, triggering the second common voltage reference value UrefnewEqual to the first common voltage reference value Uref0Reference value U of the second common voltagerefnewReplacing a first common voltage reference value U in a second input variableref0Obtaining a third input variable, and replacing the second input variable with the third input variable to control the multi-terminal flexible direct-current transmission system;
a low limit replacement submodule for replacing the maximum limit value V of the preset DC voltagemaxReplacing the first common voltage reference value U in the second input variableref0Obtaining a fifth input variable, calculating and recording the minimum value U of the direct current voltage of all the corresponding converter stations according to the first input variable and the fifth input variablemin2And pass through point (U)ref0，Umin0) And point (V)max，Umin2) Determining the linear relation between the common reference voltage and the DC voltage of the multi-terminal flexible DC power transmission system, establishing a second preset formula to calculate the minimum value U of the new DC voltage of the multi-terminal flexible DC power transmission systemmin1Equal to the preset maximum limit value V of the direct current voltageminTime corresponding second common voltage reference value UrefnewReference value U of the second common voltagerefnewReplacing a first common voltage reference value U in a second input variableref0Obtaining a third input variable and replacing the third input variableAnd the second input variable controls the multi-terminal flexible direct-current power transmission system.
Preferably, the system further comprises an equation building module;
and the equation building module is used for building a state space model of the multi-terminal flexible direct current transmission system only considering active power balance and obtaining a state equation of the multi-terminal flexible direct current transmission system.
Preferably, the first preset formula and the second preset formula are specifically:
the first preset formula:
Figure BDA0001421549480000061
the second preset formula:
Figure BDA0001421549480000062
according to the technical scheme, the invention has the following advantages:
the invention discloses a droop control converter station control method, which comprises the following steps: s1: obtaining a first input variable before the command is issued by the dispatching system, a second input variable after the command is issued by the dispatching system and a droop coefficient k of the droop control converter station, substituting the first input variable, the second input variable and the droop coefficient k into a state equation of the multi-terminal flexible direct current transmission system to calculate the direct current power P of the droop control converter station after the command is issued by the dispatching system*Infinity, and whether or not there is DC power P*The absolute value of the (∞) is greater than or equal to the preset direct current power limit value, if yes, the preset increment a is subtracted from the droop coefficient k of the corresponding droop control converter station, the step S1 is executed again, and if not, the step S2 is executed; s2: substituting the first input variable, the second input variable and the droop coefficient k into a state equation of the multi-terminal flexible direct current transmission system to calculate and record the maximum value U of direct current voltage of all droop control converter stations in the multi-terminal flexible direct current transmission systemmax0And minimum value U of DC voltagemin0(ii) a S3: when the maximum value U of the DC voltagemax0Greater than a preset maximum limit value V of DC voltagemaxCalculating a new maximum value U of the DC voltage of the multi-terminal flexible DC power transmission system according to the linear relation between the common reference voltage and the DC voltage of the multi-terminal flexible DC power transmission systemmax1Equal to the preset maximum limit value V of the direct current voltagemaxTime corresponding second common voltage reference value UrefnewOr, when the DC voltage is minimum value Umin0Less than a preset minimum limit value V of DC voltageminCalculating a new minimum value U of the DC voltage of the multi-terminal flexible DC power transmission system according to the linear relation between the common reference voltage and the DC voltage of the multi-terminal flexible DC power transmission systemmin1Equal to a preset minimum limit value V of the DC voltageminTime corresponding second common voltage reference value UrefnewAnd the second common voltage reference value U is setrefnewReplacing a first common voltage reference value U in a second input variableref0And obtaining a third input variable, and replacing the second input variable with the third input variable to control the multi-terminal flexible direct-current transmission system.
The control method firstly solves the problem that the power of the droop control converter station is full load and then solves the problem of voltage out-of-limit, firstly judges whether the droop control converter station is full load or not, subtracts a preset increment a from a droop coefficient of the droop control converter station with full load if the droop control converter station is full load, judges whether the droop control converter station is full load or not after adjustment, and continuously subtracts the preset increment a from the droop coefficient until the absolute value of the power of the droop control converter station is lower than a preset direct current power limit value if the droop control converter station is full load; then calculating the direct current voltage of each droop control converter station, judging whether the maximum value of the direct current voltage is larger than the preset maximum value of the direct current voltage or whether the minimum value of the direct current voltage is smaller than the preset minimum value of the direct current voltage, if the voltage out-of-limit condition occurs, correspondingly adjusting the common voltage reference value according to the linear relation between the common voltage reference value and the direct current voltage, calculating the corresponding common voltage reference value when the maximum value of the direct current voltage is equal to the maximum limit value of the direct current voltage or the minimum value of the direct current voltage is equal to the minimum limit value of the direct current voltage, when the maximum value of the direct current voltage is equal to the maximum limit value of the direct current voltage or the minimum value of the direct current voltage is equal to the minimum limit value of the direct current voltage, all the direct current voltages are not greater than the direct current voltage maximum limit value or less than the direct current voltage minimum limit value, and the technical problem that the existing droop control method cannot simultaneously solve full load of the droop control converter station and direct current voltage out-of-limit is solved.
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In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without inventive exercise.
Fig. 1 is a schematic flow chart of an embodiment of a droop control converter station control method according to an embodiment of the present invention;
fig. 2 is a schematic flow chart of another embodiment of a droop control converter station control method according to an embodiment of the present invention;
fig. 3 is a schematic structural diagram of an embodiment of a droop control converter station control apparatus according to an embodiment of the present invention;
fig. 4 is a schematic structural diagram of another embodiment of a droop control converter station control apparatus according to an embodiment of the present invention;
fig. 5 is a schematic connection relationship diagram of a four-terminal flexible dc transmission system according to an embodiment of the present invention.
Detailed Description
The embodiment of the invention provides a droop control converter station control method and device, and solves the technical problem that the existing droop control method cannot simultaneously solve the technical problems of full load and direct-current voltage out-of-limit of a droop control converter station.
In order to make the objects, features and advantages of the present invention more obvious and understandable, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the embodiments described below are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Referring to fig. 1, an embodiment of a droop control converter station control method according to the present invention includes:
step 101: obtaining a first input variable before the command is issued by the dispatching system, a second input variable after the command is issued by the dispatching system and a droop coefficient k of the droop control converter station, substituting the first input variable, the second input variable and the droop coefficient k into a state equation of the multi-terminal flexible direct current transmission system to calculate the direct current power P of the droop control converter station after the command is issued by the dispatching system*Infinity, and whether or not there is DC power P*The absolute value of the (∞) is greater than or equal to the preset direct current power limit value, if yes, the preset increment a is subtracted from the droop coefficient k of the corresponding droop control converter station, the step 101 is executed again, and if not, the step 102 is executed;
the method comprises the steps that a dispatching system controls a converter station by sending an input variable, the method is actually a process of regulating the input variable sent by the dispatching system and controlling a droop coefficient of the converter station by droop, a second input variable is an assumed input variable, the dispatching is only sent when the second input variable meets the requirement of a multi-terminal flexible direct-current transmission system, and the dispatching and sending are carried out through subsequent steps when the second input variable does not meet the requirement of the multi-terminal flexible direct-current transmission system;
in the embodiment, the droop coefficient k refers to the respective droop coefficient of all droop control converter stations;
DC power P*(∞) refers to the respective dc power of all droop control converter stations;
the common voltage reference value is adjusted to affect the direct-current voltage level but not the power distribution, and the droop coefficient is adjusted to affect the power distribution but also the direct-current voltage, so that the problem of full power load is solved firstly and then the problem of voltage out-of-limit is solved;
and the droop coefficient is reduced, so that the full-load range of power is reduced, and the overload droop control converter station enters a normal operation state.
Step 102: change the first input intoSubstituting the quantity, the second input variable and the droop coefficient k into a state equation of the multi-terminal flexible direct current transmission system to calculate and record the maximum value U of the direct current voltage of all droop control converter stations in the multi-terminal flexible direct current transmission systemmax0And minimum value U of DC voltagemin0；
It should be noted that there is a difference in the dc voltage of each droop control converter station, and the maximum value and the minimum value of the dc voltage are calculated and recorded.
Step 103: when the maximum value U of the DC voltagemax0Greater than a preset maximum limit value V of DC voltagemaxCalculating a new maximum value U of the DC voltage of the multi-terminal flexible DC power transmission system according to the linear relation between the common reference voltage and the DC voltage of the multi-terminal flexible DC power transmission systemmax1Equal to the preset maximum limit value V of the direct current voltagemaxTime corresponding second common voltage reference value UrefnewOr, when the DC voltage is minimum value Umin0Less than a preset minimum limit value V of DC voltageminCalculating a new minimum value U of the DC voltage of the multi-terminal flexible DC power transmission system according to the linear relation between the common reference voltage and the DC voltage of the multi-terminal flexible DC power transmission systemmin1Equal to a preset minimum limit value V of the DC voltageminTime corresponding second common voltage reference value UrefnewAnd the second common voltage reference value U is setrefnewReplacing a first common voltage reference value U in a second input variableref0And obtaining a third input variable, and replacing the second input variable with the third input variable to control the multi-terminal flexible direct-current transmission system.
In addition, the maximum limit value V of the DC voltage is presetmaxOr preset DC voltage minimum limit VminCorresponding second common voltage reference value UrefnewReplacing a first common voltage reference value U in a second input variableref0Obtaining a third input variable, and calculating a new maximum value U of the direct current voltage of each converter station through the first input variable and the third input variablemax1Equal to the preset maximum limit value V of the direct current voltagemaxOr a new DC voltage minimum value Umin1Equal to a preset minimum limit value V of the DC voltageminI.e. the new dc voltage of each converter station is not greater than the preset dc voltage maximum limit VmaxOr less than a preset minimum limit value V of the DC voltageminThe condition that the direct current voltage is out of limit is avoided;
therefore, the method solves the technical problem that the existing droop control method cannot simultaneously solve the technical problems of full load and direct-current voltage out-of-limit of the droop control converter station.
The above is an embodiment of a method for controlling a droop control converter station according to an embodiment of the present invention, and the following is another embodiment of a method for controlling a droop control converter station according to an embodiment of the present invention.
Referring to fig. 2 and fig. 5, another embodiment of a droop control converter station control method according to an embodiment of the present invention includes:
step 201: constructing a state space model of the multi-terminal flexible direct current transmission system only considering active power balance, and obtaining a state equation of the multi-terminal flexible direct current transmission system;
it should be noted that, taking the four-terminal flexible direct-current power transmission system in fig. 5 as an example, a state space model of the multi-terminal flexible direct-current power transmission system is constructed only considering active power balance, and a process of obtaining a state equation of the multi-terminal flexible direct-current power transmission system is as follows:
the VSC1 and the VSC2 adopt droop control, and the VSC3 and the VSC4 adopt constant-power control. The direct current transmission line adopts a pi-type equivalent circuit, and the naming and direction of the line current are marked;
the voltage and power distribution problem of the multi-terminal direct current is only related to the active power balance of the system and is not related to reactive power, and the direct current response of the whole system is required to be known when the overvoltage level of the system is accurately calculated, so that only a state space model considering only the active power balance is constructed;
the converter station adopting the droop control mode has the following relations:
Uref-Ui+(Prefi-Pi)/Ki＝0 (1)
wherein U isrefIs a common voltage reference value; u shapeiFor the converter station i to be practicalA direct current voltage; prefiThe power fixed value of the ith converter station is given by the scheduling system; piActual active power of the ith converter station; kiIs the droop coefficient of the ith converter station; i.e. idrefiRefers to the current reference value of the ith converter station;
when the DC power grid has unbalanced power, the stable point of the converter station is defined by (P)i,Ui) Become (P)i′,Ui') for stabilizing the full grid dc voltage, the dc voltage reference is set by UrefBecome UrefThe method comprises the following steps:
U′ref-U′i+(Prefi-Pi′)/Ki＝0 (2)
the simultaneous equations (1) and (2) have:
U′ref-Uref+ΔUi+ΔPi/Ki＝0 (3)
Δ P is the unbalanced power, which can be expressed as:
Figure BDA0001421549480000111
for a direct current power grid, voltage fluctuation caused by unbalanced power has the characteristic of being consistent with the whole grid, namely delta U is approximately equal to delta UiThus, there are:
it can be seen that the protection is ensuredChanging the common voltage reference value U without changingrefThe DC voltage level can be linearly varied, and thus, the common voltage reference U can be adjustedrefThe overvoltage or low voltage problem of the system under the unbalanced power is improved;
simultaneous equations (3) and (4) can be obtained:
Figure BDA0001421549480000114
therefore, the droop coefficient k determines the magnitude of the unbalanced power distributed to each droop control converter station, and for the overload problem of the converter station, the droop coefficient is mainly changed to adjust;
the following derivation process is based on the following assumptions, with the symbol "to" number being a per unit value variable: 1. the connected AC power grid is a strong system, so the influence of PLL can be ignored; 2. the current inner loop of the droop control has the characteristic of a first-order inertia element, i.e.
Figure BDA0001421549480000115
Wherein idi *Is the d-axis current of the converter station i, idrefiIs the corresponding d-axis current reference value, TiIs the time constant of the d-axis of the current inner loop;
meanwhile, the following per unit value power balance relation holds (applicable to any converter station, the voltage term hasAnd
Figure BDA0001421549480000117
)：
Figure BDA0001421549480000118
wherein,
Figure BDA0001421549480000119
is a voltage of the d-axis,
Figure BDA00014215494800001110
and
Figure BDA00014215494800001111
direct current voltage and direct current for the converter station i;
the dynamic model of each link is introduced as follows:
for the droop control converter station i, a per unit value control equation is provided:
Figure BDA0001421549480000121
wherein a isiAnd biAre the proportional and integral constants of the droop controller. Introduction of an intermediate variable yiSo that the user can easily and conveniently select the required position,
Figure BDA0001421549480000122
the simultaneous equations (7) to (10) are:
Figure BDA0001421549480000123
for a constant active power controller, there are:
Figure BDA0001421549480000124
introducing variable ziSo that:
Figure BDA0001421549480000125
the simultaneous equations (7), (12) and (13) have:
Figure BDA0001421549480000126
at the node of the converter, the equivalent capacitance of the converter and the capacitance of the direct current line can be equivalent to CiNamely:
Figure BDA0001421549480000127
wherein C isioIs the sub-module capacitance value, N, of converter iiIs the number of sub-module levels, CLijThe equivalent capacitance of the pi-type equivalent circuit of the line ij;
the mathematical model at the converter station dc outlet node may be represented by:
wherein, IbaseIs a DC reference value, UbaseIs a reference value of the direct-current voltage,
Figure BDA0001421549480000129
is the actual current per unit value between lines i, j;
in addition, there is a linear line equation:
Figure BDA00014215494800001210
equations (12) to (17) describe the dynamic process of the whole multi-terminal flexible direct current transmission system, and the state space model can be organized into the form of the following state equation:
Figure BDA00014215494800001211
wherein the coefficient matrix M, N is determined by the system inner and outer ring control parameters, the converter parameters and the direct current circuit parameters, and is a fixed parameter;
the left side of the equation is the derivative of x, which is the state variable of the system, including the DC side voltage, current, i.e.
Figure BDA0001421549480000131
h is an input variable including a common reference voltage and a station power reference command, i.e., h ═ Uref,Uref,Pref1,Pref2,Pref3,Pref4]TThe instruction value may be obtained by the scheduling system. The change of the state of the multi-terminal flexible direct current transmission system is determined by an input variable, when the input variable changes, the state variable x of the system is caused to change, namely a dynamic response process occurs on a direct current side, and an initial value of x can be obtained by the following formula:
x0＝-inv(M)*N*h0(19)
in summary, as long as the initial value h of the input variable before the command is sent by the dispatching system is known0And final value h of input variable after issuance of order1And the voltage, the current and the power of the direct current side of each converter station can be obtained.
Step 202: performing stability analysis on a state equation of the multi-terminal flexible direct current transmission system, calculating a value range of a droop coefficient k of the droop control converter station, and obtaining a maximum limit value of the droop coefficient of each droop control converter station;
it should be noted that the obtaining of the state equation may obtain a value range of a droop coefficient of the droop control converter station when the multi-terminal flexible direct current transmission system operates stably according to a linear system stability criterion, and respectively obtain a maximum value of the droop coefficient of each droop control converter station according to the value range of the droop coefficient.
Step 203: adjusting the droop coefficients k of the droop control converter stations through a preset scheme, so that the sum of the droop coefficients k of the droop control converter stations is equal to the minimum maximum value of the maximum values of the droop coefficients of the droop control converter stations;
it should be noted that, in order to find a suitable droop coefficient without affecting the subsequent voltage regulation process, a constraint condition of the droop coefficient needs to be added, taking the four-terminal flexible dc power transmission system of fig. 5 as an example:
Figure BDA0001421549480000132
wherein,
Figure BDA0001421549480000133
the sum of the droop coefficients, min K, for the droop control converter station VSC1 and the droop control converter station VSC21max，K2maxThe sum mu is the minimum maximum value of the maximum values of the droop coefficients of the droop control station VSC1 and the droop control station VSC 2;
the preset adjusting schemes may be various, for example, A, B, C three droop control converter stations exist, when the droop coefficient k of the converter station a subtracts the preset increment a, the converter station B increases by 0.3a, the converter station C increases by 0.7a, or the converter station B increases by 0.4a, the converter station C increases by 0.6a, and other preset schemes, so that the sum of the droop coefficients k of the droop control converter stations is always equal to the minimum maximum limit value of the droop coefficients of the droop control converter stations, and it is ensured that when the droop coefficient of one of the droop control converter stations is equal to 0, the droop coefficients of other droop control converter stations exceed the stable range thereof.
Step 204: obtaining a first input variable before the command is issued by the dispatching system, a second input variable after the command is issued by the dispatching system and a droop coefficient k of the droop control converter station, substituting the first input variable, the second input variable and the droop coefficient k into a state equation of the multi-terminal flexible direct current transmission system to calculate the direct current power P of the droop control converter station after the command is issued by the dispatching system*Infinity, and whether or not there is DC power P*The absolute value of the (∞) is greater than or equal to the preset direct current power limit value, if yes, the preset increment a is subtracted from the droop coefficient k of the corresponding droop control converter station, the operation returns to the step 203, and if not, the step 204 is executed;
it should be noted that since the droop coefficient of the fully loaded droop control converter station is subtracted by the preset increment a, the droop coefficients of the remaining droop control converter stations need to be adjusted according to the preset scheme of step 203.
Step 205: substituting the first input variable, the second input variable and the droop coefficient k into a state equation of the multi-terminal flexible direct current transmission system to calculate and record the maximum value U of direct current voltage of all droop control converter stations in the multi-terminal flexible direct current transmission systemmax0And minimum value U of DC voltagemin0；
Step 206: when the maximum value U of the DC voltagemax0Greater than a preset maximum limit value V of DC voltagemaxIf yes, go to step 207, otherwise go to step 208;
step 207: by presetting the minimum limit value V of the DC voltageminReplacing the first common voltage reference U in the second input variableref0Obtaining a fourth input variable from the value of the first input variable andcalculating and recording the maximum value U of the direct current voltage of all the corresponding converter stations by the fourth input variablemax2And pass through point (U)ref0，Umax0) And point (V)min，Umax2) Determining the linear relation between the common reference voltage and the DC voltage of the multi-terminal flexible DC power transmission system, and establishing a first preset formula to calculate the maximum value U of the new DC voltage of the multi-terminal flexible DC power transmission systemmax1Equal to the preset maximum limit value V of the direct current voltagemaxTime corresponding second common voltage reference value UrefnewReference value U of the second common voltagerefnewReplacing a first common voltage reference value U in a second input variableref0Obtaining a third input variable, and replacing the second input variable with the third input variable to control the multi-terminal flexible direct-current transmission system;
it should be noted that the common voltage reference value U is changedrefThe system voltage level can be varied linearly (i.e., the system maximum and minimum values can be varied linearly), which provides the convenience of quantitatively controlling the dc voltage of the VSC-MTDC.
Step 208: when the minimum value U of the DC voltagemin0If the voltage is smaller than the preset minimum limit value of the direct current voltage, executing a step 209, otherwise executing a step 210;
step 209: by presetting the maximum limit value V of the DC voltagemaxReplacing the first common voltage reference value U in the second input variableref0Obtaining a fifth input variable, calculating and recording the minimum value U of the direct current voltage of all the corresponding converter stations according to the first input variable and the fifth input variablemin2And pass through point (U)ref0，Umin0) And point (V)max，Umin2) Determining the linear relation between the common reference voltage and the DC voltage of the multi-terminal flexible DC power transmission system, establishing a second preset formula to calculate the minimum value U of the new DC voltage of the multi-terminal flexible DC power transmission systemmin1Equal to the preset maximum limit value V of the direct current voltageminTime corresponding second common voltage reference value UrefnewReference value U of the second common voltagerefnewReplacing a first common voltage reference value U in a second input variableref0Obtaining a third input variable, and inputting the third input variableThe variable replaces a second input variable to control the multi-terminal flexible direct-current power transmission system;
step 210: second common voltage reference value UrefnewEqual to the first common voltage reference value Uref0Reference value U of the second common voltagerefnewReplacing a first common voltage reference value U in a second input variableref0And obtaining a third input variable, and replacing the second input variable with the third input variable to control the multi-terminal flexible direct-current transmission system.
It should be noted that, in steps 205 to 209, it is determined whether the dc voltage of each converter station is out of limit, and the common voltage reference value is correspondingly adjusted according to whether the dc voltage exceeds the preset maximum limit value of the dc voltage or exceeds the preset minimum limit value of the dc voltage, so as to change the common voltage reference value UrefThe system voltage level can be changed linearly (i.e., the system maximum and minimum values can be changed linearly);
the first preset formula and the second preset formula are specifically as follows:
the first preset formula:
Figure BDA0001421549480000151
the second preset formula:
Figure BDA0001421549480000152
the traditional droop control has the following defects that firstly, when the system power is greatly unbalanced, the voltage on the direct current side is greatly changed, and overvoltage or low voltage is easily caused; secondly, the actual power margin is not considered, the droop control station is easy to overload and is switched to be operated at a constant power, and the capability of responding to the change of the system power flow is lost; thirdly, the selected droop coefficient does not consider the influence of the stability of the multi-terminal flexible direct current transmission system;
the control method judges whether the full load condition occurs by judging whether the absolute value of the direct current power of the regulated converter station is greater than or equal to the preset direct current power limit value, and correspondingly regulates the droop coefficient of the converter station when the full load occurs to avoid the generation of the full load condition;
meanwhile, whether the direct-current voltage exceeds the limit is judged according to the comparison of the direct-current voltage and the maximum limit value and the minimum limit value of the preset direct-current voltage, and the common voltage reference value is correspondingly adjusted according to the judgment result and the linear relation between the common reference voltage and the direct-current voltage of the multi-terminal flexible direct-current power transmission system to avoid the direct-current voltage exceeding the limit;
controlling the multi-terminal flexible direct-current transmission system through the droop coefficient k and the third input variable after each droop control converter station is adjusted, and avoiding full load or direct-current voltage out-of-limit of the droop control converter stations;
the technical problem that the existing droop control method cannot simultaneously solve the problems of full load of the droop control converter station and out-of-limit of direct current voltage is solved.
The above is another embodiment of the method for controlling a droop control converter station according to the embodiment of the present invention, and the following is an embodiment of a device for controlling a droop control converter station according to the embodiment of the present invention.
Referring to fig. 3, an embodiment of a droop control converter station control apparatus according to the present invention includes:
a coefficient adjusting module 301, configured to obtain a first input variable before the dispatching system issues a command, a second input variable after the dispatching system issues a command, and a droop coefficient k of the droop control converter station, and substitute the first input variable, the second input variable, and the droop coefficient k into an equation of state of the multi-terminal flexible direct current transmission system to calculate a direct current power P of the droop control converter station after the dispatching system issues a command*Infinity, and whether or not there is DC power P*The absolute value of the (∞) is greater than or equal to the preset direct current power limit value, if yes, the preset increment a is subtracted from the droop coefficient k of the corresponding droop control converter station, the coefficient adjusting module 301 is triggered again, and if not, the voltage calculating module 302 is triggered;
a voltage calculating module 302, configured to substitute the first input variable, the second input variable, and the droop coefficient k into a state equation of the multi-terminal flexible direct current transmission system to calculate and record all the state equations in the multi-terminal flexible direct current transmission systemMaximum value U of direct-current voltage of droop control converter stationmax0And minimum value U of DC voltagemin0；
A comparison and replacement module 303 for comparing the maximum value U of the DC voltagemax0Greater than a preset maximum limit value V of DC voltagemaxCalculating a new maximum value U of the DC voltage of the multi-terminal flexible DC power transmission system according to the linear relation between the common reference voltage and the DC voltage of the multi-terminal flexible DC power transmission systemmax1Equal to the preset maximum limit value V of the direct current voltagemaxTime corresponding second common voltage reference value UrefnewOr, when the DC voltage is minimum value Umin0Less than a preset minimum limit value V of DC voltageminCalculating a new minimum value U of the DC voltage of the multi-terminal flexible DC power transmission system according to the linear relation between the common reference voltage and the DC voltage of the multi-terminal flexible DC power transmission systemmin1Equal to a preset minimum limit value V of the DC voltageminTime corresponding second common voltage reference value UrefnewAnd the second common voltage reference value U is setrefnewReplacing a first common voltage reference value U in a second input variableref0And obtaining a third input variable, and replacing the second input variable with the third input variable to control the multi-terminal flexible direct-current transmission system.
The above is an embodiment of a droop control converter station control apparatus according to an embodiment of the present invention, and the following is another embodiment of a droop control converter station control apparatus according to an embodiment of the present invention.
Referring to fig. 4, another embodiment of a droop control converter station control apparatus according to an embodiment of the present invention includes:
a coefficient adjusting module 401, configured to obtain a first input variable before the dispatching system issues a command, a second input variable after the dispatching system issues a command, and a droop coefficient k of the droop control converter station, and substitute the first input variable, the second input variable, and the droop coefficient k into an equation of state of the multi-terminal flexible direct current transmission system to calculate a direct current power P of the droop control converter station after the dispatching system issues a command*Infinity, and whether or not there is DC power P*Absolute value of (∞) is greater than or equal to preset DC power limitIf yes, subtracting a preset increment a from a droop coefficient k of the corresponding droop control converter station, and triggering the coefficient adjusting module 401 again, otherwise, triggering the voltage calculating module 402;
a voltage calculating module 402, configured to substitute the first input variable, the second input variable, and the droop coefficient k into a state equation of the multi-terminal flexible direct current transmission system to calculate and record a maximum value U of direct current voltages of all droop control converter stations in the multi-terminal flexible direct current transmission systemmax0And minimum value U of DC voltagemin0；
A comparison and replacement module 403 for comparing the maximum value U of the DC voltagemax0Greater than a preset maximum limit value V of DC voltagemaxCalculating a new maximum value U of the DC voltage of the multi-terminal flexible DC power transmission system according to the linear relation between the common reference voltage and the DC voltage of the multi-terminal flexible DC power transmission systemmax1Equal to the preset maximum limit value V of the direct current voltagemaxTime corresponding second common voltage reference value UrefnewOr, when the DC voltage is minimum value Umin0Less than a preset minimum limit value V of DC voltageminCalculating a new minimum value U of the DC voltage of the multi-terminal flexible DC power transmission system according to the linear relation between the common reference voltage and the DC voltage of the multi-terminal flexible DC power transmission systemmin1Equal to a preset minimum limit value V of the DC voltageminTime corresponding second common voltage reference value UrefnewAnd the second common voltage reference value U is setrefnewReplacing a first common voltage reference value U in a second input variableref0And obtaining a third input variable, and replacing the second input variable with the third input variable to control the multi-terminal flexible direct-current transmission system.
Further, the coefficient adjusting module 401 specifically includes:
the high-limit calculation submodule 4011 is configured to perform stability analysis on a state equation of the multi-terminal flexible direct current transmission system, calculate a value range of a droop coefficient k of each droop control converter station, and obtain a maximum limit value of the droop coefficient of each droop control converter station;
the constraint limiting sub-module 4012 is configured to adjust the droop coefficients k of the droop control converter stations according to a preset scheme, so that the sum of the droop coefficients k of the droop control converter stations is equal to the minimum maximum value among the maximum values of the droop coefficients of the droop control converter stations;
and the full-load adjustment submodule 4013 is configured to obtain a first input variable before the dispatching system issues a command, a second input variable after the dispatching system issues a command, and a droop coefficient k of the droop control converter station, substitute the first input variable, the second input variable, and the droop coefficient k into a state equation of the multi-terminal flexible direct current transmission system to calculate a direct current power P (∞) of the droop control converter station after the dispatching system issues a command, determine whether an absolute value of the direct current power P (∞) is greater than or equal to a preset direct current power limit value, if yes, subtract a preset increment a from the droop coefficient k of the corresponding droop control converter station, and trigger the constraint limitation submodule 4012, and if not, trigger the voltage calculation module 402.
Further, the comparing and replacing module 403 specifically includes:
a high limit comparison submodule 4031 for comparing the maximum value U of the DC voltagemax0Greater than a preset maximum limit value V of DC voltagemaxIf so, triggering a high limit replacing sub-module 4032, otherwise, triggering a low limit comparing sub-module 4033;
a high limit replacement submodule 4032 for replacing the minimum limit value V of the preset DC voltage by a predetermined valueminReplacing the first common voltage reference U in the second input variableref0Obtaining a fourth input variable, calculating and recording the maximum value U of the direct current voltage of all the corresponding converter stations according to the first input variable and the fourth input variablemax2And pass through point (U)ref0，Umax0) And point (V)min，Umax2) Determining the linear relation between the common reference voltage and the DC voltage of the multi-terminal flexible DC power transmission system, and establishing a first preset formula to calculate the maximum value U of the new DC voltage of the multi-terminal flexible DC power transmission systemmax1Equal to the preset maximum limit value V of the direct current voltagemaxTime corresponding second common voltage reference value UrefnewReference value U of the second common voltagerefnewReplacing a first common voltage reference value U in a second input variableref0Obtaining a third input variable and transforming the third input into a variableReplacing a second input variable with the quantity to control the multi-terminal flexible direct-current power transmission system;
a low limit comparison submodule 4033 for comparing the minimum value U of the DC voltagemin0When the voltage is smaller than the preset minimum limit value of the direct current voltage, the low limit replacement sub-module 4034 is triggered, otherwise, the second common voltage reference value U is usedrefnewEqual to the first common voltage reference value Uref0Reference value U of the second common voltagerefnewReplacing a first common voltage reference value U in a second input variableref0Obtaining a third input variable, and replacing the second input variable with the third input variable to control the multi-terminal flexible direct-current transmission system;
a low limit substitution submodule 4034 for substituting the maximum limit value V of the preset DC voltagemaxReplacing the first common voltage reference value U in the second input variableref0Obtaining a fifth input variable, calculating and recording the minimum value U of the direct current voltage of all the corresponding converter stations according to the first input variable and the fifth input variablemin2And pass through point (U)ref0，Umin0) And point (V)max，Umin2) Determining the linear relation between the common reference voltage and the DC voltage of the multi-terminal flexible DC power transmission system, establishing a second preset formula to calculate the minimum value U of the new DC voltage of the multi-terminal flexible DC power transmission systemmin1Equal to the preset maximum limit value V of the direct current voltageminTime corresponding second common voltage reference value UrefnewReference value U of the second common voltagerefnewReplacing a first common voltage reference value U in a second input variableref0And obtaining a third input variable, and replacing the second input variable with the third input variable to control the multi-terminal flexible direct-current transmission system.
Further, an equation building module 400 is included;
and an equation constructing module 400, configured to construct a state space model of the multi-terminal flexible direct current power transmission system only considering active power balance, and obtain a state equation of the multi-terminal flexible direct current power transmission system.
Further, the first preset formula and the second preset formula are specifically:
the first preset formula:
Figure BDA0001421549480000191
the second preset formula:
Figure BDA0001421549480000192
it can be clearly understood by those skilled in the art that, for convenience and brevity of description, the specific working processes of the above-described apparatuses and modules may refer to the corresponding processes in the foregoing method embodiments, and are not described herein again.
In the several embodiments provided in the present application, it should be understood that the disclosed apparatus and method may be implemented in other ways. For example, the above-described apparatus embodiments are merely illustrative, and for example, a division of modules is merely a division of logical functions, and an actual implementation may have another division, for example, a plurality of modules or components may be combined or integrated into another system, or some features may be omitted, or not executed. In addition, the shown or discussed mutual coupling or direct coupling or communication connection may be an indirect coupling or communication connection through some interfaces, devices or modules, and may be in an electrical, mechanical or other form.
Modules described as separate parts may or may not be physically separate, and parts displayed as modules may or may not be physical modules, may be located in one place, or may be distributed on a plurality of network modules. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of the present embodiment.
In addition, functional modules in the embodiments of the present invention may be integrated into one processing module, or each of the modules may exist alone physically, or two or more modules are integrated into one module. The integrated module can be realized in a hardware mode, and can also be realized in a software functional module mode.
The integrated module, if implemented in the form of a software functional module and sold or used as a separate product, may be stored in a computer readable storage medium. Based on such understanding, the technical solution of the present invention may be embodied in the form of a software product, which is stored in a storage medium and includes instructions for causing a computer device (which may be a personal computer, a server, or a network device) to execute all or part of the steps of the method according to the embodiments of the present invention. And the aforementioned storage medium includes: a U-disk, a removable hard disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a magnetic disk or an optical disk, and other various media capable of storing program codes.
The above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.

Claims (8)

1. A droop control converter station control method, comprising:
s0: constructing a state space model of the multi-terminal flexible direct current transmission system only considering active power balance, and obtaining a state equation of the multi-terminal flexible direct current transmission system;
s1: obtaining a first input variable before the command is issued by the dispatching system, a second input variable after the command is issued by the dispatching system and a droop coefficient k of the droop control converter station, substituting the first input variable, the second input variable and the droop coefficient k into a state equation of the multi-terminal flexible direct current transmission system to calculate the direct current power P of the droop control converter station after the command is issued by the dispatching system*Infinity, and whether or not there is a direct currentPower P*The absolute value of the (∞) is greater than or equal to the preset direct current power limit value, if yes, the preset increment a is subtracted from the droop coefficient k of the corresponding droop control converter station, the step S1 is executed again, and if not, the step S2 is executed;
s2: substituting the first input variable, the second input variable and the droop coefficient k into a state equation of the multi-terminal flexible direct current transmission system to calculate and record the maximum value U of direct current voltage of all droop control converter stations in the multi-terminal flexible direct current transmission systemmax0And minimum value U of DC voltagemin0；
S3: when the maximum value U of the DC voltagemax0Greater than a preset maximum limit value V of DC voltagemaxCalculating a new maximum value U of the DC voltage of the multi-terminal flexible DC power transmission system according to the linear relation between the common reference voltage and the DC voltage of the multi-terminal flexible DC power transmission systemmax1Equal to the preset maximum limit value V of the direct current voltagemaxTime corresponding second common voltage reference value UrefnewOr, when the DC voltage is minimum value Umin0Less than a preset minimum limit value V of DC voltageminCalculating a new minimum value U of the DC voltage of the multi-terminal flexible DC power transmission system according to the linear relation between the common reference voltage and the DC voltage of the multi-terminal flexible DC power transmission systemmin1Equal to a preset minimum limit value V of the DC voltageminTime corresponding second common voltage reference value UrefnewAnd the second common voltage reference value U is setrefnewReplacing a first common voltage reference value U in a second input variableref0And obtaining a third input variable, and replacing the second input variable with the third input variable to control the multi-terminal flexible direct-current transmission system.
2. The method for controlling a droop control converter station according to claim 1, wherein the step S1 specifically comprises:
s101: performing stability analysis on a state equation of the multi-terminal flexible direct current transmission system, calculating a value range of a droop coefficient k of the droop control converter station, and obtaining a maximum limit value of the droop coefficient of each droop control converter station;
s102: adjusting the droop coefficients k of the droop control converter stations through a preset scheme, so that the sum of the droop coefficients k of the droop control converter stations is equal to the minimum maximum value of the maximum values of the droop coefficients of the droop control converter stations;
s103: obtaining a first input variable before the command is issued by the dispatching system, a second input variable after the command is issued by the dispatching system and a droop coefficient k of the droop control converter station, substituting the first input variable, the second input variable and the droop coefficient k into a state equation of the multi-terminal flexible direct current transmission system to calculate the direct current power P of the droop control converter station after the command is issued by the dispatching system*Infinity, and whether or not there is DC power P*And if the absolute value of the (∞) value is greater than or equal to the preset direct current power limit value, subtracting a preset increment a from the droop coefficient k of the corresponding droop control converter station, returning to execute the step S102, and if the absolute value of the (∞) value is not greater than the preset direct current power limit value, executing the step S2.
3. The method for controlling a droop control converter station according to claim 1, wherein the step S3 specifically comprises:
s301: when the maximum value U of the DC voltagemax0Greater than a preset maximum limit value V of DC voltagemaxIf so, executing step S302, otherwise, executing step S303;
s302: by presetting the minimum limit value V of the DC voltageminReplacing the first common voltage reference U in the second input variableref0Obtaining a fourth input variable, calculating and recording the maximum value U of the direct current voltage of all the corresponding converter stations according to the first input variable and the fourth input variablemax2And pass through point (U)ref0，Umax0) And point (V)min，Umax2) Determining the linear relation between the common reference voltage and the DC voltage of the multi-terminal flexible DC power transmission system, and establishing a first preset formula to calculate the maximum value U of the new DC voltage of the multi-terminal flexible DC power transmission systemmax1Equal to the preset maximum limit value V of the direct current voltagemaxTime corresponding second common voltage reference value UrefnewReference value U of the second common voltagerefnewReplacing a first common voltage reference value U in a second input variableref0Obtaining a third input variable, and replacing the second input variable with the third input variable to control the multi-terminal flexible direct-current transmission system;
s303: when the minimum value U of the DC voltagemin0If the voltage is less than the preset DC voltage minimum limit value, executing the step S304, otherwise, the second common voltage reference value UrefnewEqual to the first common voltage reference value Uref0Reference value U of the second common voltagerefnewReplacing a first common voltage reference value U in a second input variableref0Obtaining a third input variable, and replacing the second input variable with the third input variable to control the multi-terminal flexible direct-current transmission system;
s304: by presetting the maximum limit value V of the DC voltagemaxReplacing the first common voltage reference value U in the second input variableref0Obtaining a fifth input variable, calculating and recording the minimum value U of the direct current voltage of all the corresponding converter stations according to the first input variable and the fifth input variablemin2And pass through point (U)ref0，Umin0) And point (V)max，Umin2) Determining the linear relation between the common reference voltage and the DC voltage of the multi-terminal flexible DC power transmission system, establishing a second preset formula to calculate the minimum value U of the new DC voltage of the multi-terminal flexible DC power transmission systemmin1Equal to the preset maximum limit value V of the direct current voltageminTime corresponding second common voltage reference value UrefnewReference value U of the second common voltagerefnewReplacing a first common voltage reference value U in a second input variableref0And obtaining a third input variable, and replacing the second input variable with the third input variable to control the multi-terminal flexible direct-current transmission system.
4. The droop control converter station control method according to claim 3, wherein the first preset formula and the second preset formula are specifically:
the first preset formula:
Figure FDA0002282603190000031
the second preset formula:
Figure FDA0002282603190000032
5. a droop control converter station control apparatus, comprising:
the equation building module is used for building a state space model of the multi-terminal flexible direct current transmission system only considering active power balance and obtaining a state equation of the multi-terminal flexible direct current transmission system;
a coefficient adjusting module, configured to obtain a first input variable before the command is issued by the scheduling system, a second input variable after the command is issued by the scheduling system, and a droop coefficient k of the droop control converter station, and substitute the first input variable, the second input variable, and the droop coefficient k into an equation of state of the multi-terminal flexible direct current transmission system to calculate a direct current power P of the droop control converter station after the command is issued by the scheduling system*Infinity, and whether or not there is DC power P*The absolute value of the (∞) is larger than or equal to the preset direct current power limit value, if yes, the preset increment a is subtracted from the droop coefficient k of the corresponding droop control converter station, the coefficient adjusting module is triggered again, and if not, the voltage calculating module is triggered;
a voltage calculation module for substituting the first input variable, the second input variable and the droop coefficient k into a state equation of the multi-terminal flexible direct current transmission system to calculate and record the maximum value U of the direct current voltage of all the droop control converter stations in the multi-terminal flexible direct current transmission systemmax0And minimum value U of DC voltagemin0；
A comparison and replacement module for comparing the maximum value U of the DC voltagemax0Greater than a preset maximum limit value V of DC voltagemaxCalculating a new maximum value U of the DC voltage of the multi-terminal flexible DC power transmission system according to the linear relation between the common reference voltage and the DC voltage of the multi-terminal flexible DC power transmission systemmax1Equal to the preset maximum limit value V of the direct current voltagemaxTime corresponding second common voltage reference value UrefnewOr, when the DC voltage is minimum value Umin0Less than preSet minimum limit value V of DC voltageminCalculating a new minimum value U of the DC voltage of the multi-terminal flexible DC power transmission system according to the linear relation between the common reference voltage and the DC voltage of the multi-terminal flexible DC power transmission systemmin1Equal to a preset minimum limit value V of the DC voltageminTime corresponding second common voltage reference value UrefnewAnd the second common voltage reference value U is setrefnewReplacing a first common voltage reference value U in a second input variableref0And obtaining a third input variable, and replacing the second input variable with the third input variable to control the multi-terminal flexible direct-current transmission system.
6. The droop control converter station control device according to claim 5, wherein the coefficient adjusting module specifically comprises:
the high-limit calculation submodule is used for performing stability analysis on a state equation of the multi-terminal flexible direct current transmission system, calculating the value range of a droop coefficient k of the droop control converter station, and obtaining the maximum limit value of the droop coefficient of each droop control converter station;
the constraint limiting submodule is used for adjusting the droop coefficients k of the droop control converter stations through a preset scheme, so that the sum of the droop coefficients k of the droop control converter stations is equal to the minimum maximum value of the maximum values of the droop coefficients of the droop control converter stations;
and the full-load adjusting submodule is used for acquiring a first input variable before the dispatching system sends a command, a second input variable after the dispatching system sends a command and a droop coefficient k of the droop control converter station, substituting the first input variable, the second input variable and the droop coefficient k into a state equation of the multi-terminal flexible direct current transmission system to calculate the direct current power P (∞) of the droop control converter station after the dispatching system sends the command, judging whether the absolute value of the direct current power P (∞) is greater than or equal to a preset direct current power limit value, if so, subtracting a preset increment a from the droop coefficient k of the corresponding droop control converter station, and triggering the constraint limiting submodule, and if not, triggering the voltage calculating module.
7. The droop control converter station control device according to claim 5, wherein the comparing and replacing module specifically comprises:
a high limit comparison submodule used for comparing the maximum value U of the DC voltagemax0Greater than a preset maximum limit value V of DC voltagemaxIf so, triggering a high limit replacement submodule, otherwise triggering a low limit comparison submodule;
high limit replacement submodule for using a preset minimum limit value V of the DC voltageminReplacing the first common voltage reference U in the second input variableref0Obtaining a fourth input variable, calculating and recording the maximum value U of the direct current voltage of all the corresponding converter stations according to the first input variable and the fourth input variablemax2And pass through point (U)ref0，Umax0) And point (V)min，Umax2) Determining the linear relation between the common reference voltage and the DC voltage of the multi-terminal flexible DC power transmission system, and establishing a first preset formula to calculate the maximum value U of the new DC voltage of the multi-terminal flexible DC power transmission systemmax1Equal to the preset maximum limit value V of the direct current voltagemaxTime corresponding second common voltage reference value UrefnewReference value U of the second common voltagerefnewReplacing a first common voltage reference value U in a second input variableref0Obtaining a third input variable, and replacing the second input variable with the third input variable to control the multi-terminal flexible direct-current transmission system;
a low limit comparison submodule for comparing the DC voltage with a minimum value Umin0Triggering the low limit replacement submodule when the voltage is smaller than the preset minimum limit value of the direct current voltage, otherwise, triggering the second common voltage reference value UrefnewEqual to the first common voltage reference value Uref0Reference value U of the second common voltagerefnewReplacing a first common voltage reference value U in a second input variableref0Obtaining a third input variable, and replacing the second input variable with the third input variable to control the multi-terminal flexible direct-current transmission system;
a low limit replacement submodule for replacing the maximum limit value V of the preset DC voltagemaxReplacing the first common voltage reference value U in the second input variableref0To obtain the firstFive input variables, and calculating and recording the minimum value U of the DC voltage of all the corresponding converter stations according to the first input variable and the fifth input variablemin2And pass through point (U)ref0，Umin0) And point (V)max，Umin2) Determining the linear relation between the common reference voltage and the DC voltage of the multi-terminal flexible DC power transmission system, establishing a second preset formula to calculate the minimum value U of the new DC voltage of the multi-terminal flexible DC power transmission systemmin1Equal to the preset maximum limit value V of the direct current voltageminTime corresponding second common voltage reference value UrefnewReference value U of the second common voltagerefnewReplacing a first common voltage reference value U in a second input variableref0And obtaining a third input variable, and replacing the second input variable with the third input variable to control the multi-terminal flexible direct-current transmission system.
8. The droop control converter station control device according to claim 7, wherein the first preset formula and the second preset formula are specifically:
the first preset formula:
the second preset formula:
Figure FDA0002282603190000052
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