CN110635485B - Load flow model calculation method for multi-terminal direct current system self-adaptive droop control - Google Patents

Load flow model calculation method for multi-terminal direct current system self-adaptive droop control Download PDF

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CN110635485B
CN110635485B CN201910956096.1A CN201910956096A CN110635485B CN 110635485 B CN110635485 B CN 110635485B CN 201910956096 A CN201910956096 A CN 201910956096A CN 110635485 B CN110635485 B CN 110635485B
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droop control
adaptive droop
direct current
adaptive
current
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CN110635485A (en
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廖长风
谭益
李勇
曹一家
韩蓉蓉
汪慧颖
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Hunan University
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/04—Circuit arrangements for ac mains or ac distribution networks for connecting networks of the same frequency but supplied from different sources
    • H02J3/06—Controlling transfer of power between connected networks; Controlling sharing of load between connected networks

Abstract

The method for calculating the power flow of the multi-terminal direct current system with the self-adaptive droop control comprises the following steps of: (1) firstly, assuming an initial value of the node voltage as a voltage reference value, and calculating to obtain a node current through a load flow equation; (2) calculating a self-adaptive droop control parameter according to the node current; (3) performing first-order Taylor expansion on the adaptive droop control equation according to the magnitude relation between the node current and the reference current to obtain a corresponding adaptive droop control linear equation; (4) calculating to obtain updated node current by combining a multi-terminal direct current system power flow formula; (5) judging whether the updated node current and the node current before updating have the same size relationship with the reference current, and if the same size relationship does not exist, repeating the steps (2) - (5) according to the modified node current; if the same magnitude relationship exists, the loop is ended.

Description

Load flow model calculation method for multi-terminal direct current system self-adaptive droop control
Technical Field
The invention relates to a power system load flow calculation method, in particular to a multi-terminal direct current system load flow calculation method with self-adaptive droop control.
Background
So far, many scholars consider that basic control strategies of a multi-terminal direct-current system can be divided into three types, namely master-slave control, voltage margin control, direct-current voltage droop control and the like, wherein the direct-current voltage droop control can reasonably set the proportion of droop control coefficients of each converter station in the multi-terminal direct-current system, so that each converter station simultaneously participates in power regulation to improve the active power distribution of the system.
In recent years, scholars of Liuying culture and the like of the university of North China electric power propose a self-adaptive droop control method by improving V-I droop control.
However, the adaptive droop control equation has strong nonlinear characteristics, and brings great obstruction to load flow calculation and optimization planning of a multi-terminal direct-current power system.
Disclosure of Invention
The technical problem to be solved by the invention is to overcome the defects in the prior art and provide a power flow calculation method for a multi-terminal direct current system with adaptive droop control.
The technical scheme adopted by the invention for solving the technical problem is that the load flow calculation method for the multi-terminal direct current system with the self-adaptive droop control comprises the following steps:
step 1: initial bus voltage of DC bus assuming connection of VSC converter station
Figure BDA0002225995640000011
The injection power of the initial node on the DC bus can be calculated through a first direct current flow formula, and then the injection current of the initial node on the DC bus is obtained
Figure BDA0002225995640000012
Figure BDA0002225995640000021
Wherein, the reference source of the formula I is Roger Wiget,
Figure BDA0002225995640000029
Andersson,“DC Optimal Power Flow Including HVDC Grids”，2013 IEEE Electrical Power&Energy Conference.
step 2: determining alpha according to a formula II, wherein alpha is a parameter in the adaptive droop control equation
Figure BDA0002225995640000022
And step 3: according to
Figure BDA0002225995640000023
The size of the droop control system is represented by a self-adaptive droop control formula
Figure BDA0002225995640000024
A first order taylor expansion is performed.
Figure BDA0002225995640000025
Wherein, the reference sources of the formula two and the formula three are as follows: yingpei Liu, La Zhang and Haiping Liung, "DC Voltage Adaptive Droop Control Stratagy for a Hybrid Multi-Terminal HVDC System", Energies, 2019;
when in use
Figure BDA0002225995640000026
And when the adaptive droop control linear equation is obtained by performing first-order Taylor expansion on the formula III, the adaptive droop control linear equation is as follows:
Figure BDA0002225995640000027
when in use
Figure BDA0002225995640000028
And when the adaptive droop control linear equation is obtained by performing first-order Taylor expansion on the formula III, the adaptive droop control linear equation is as follows:
Figure BDA0002225995640000031
and 4, step 4: combining the adaptive droop control linear equation obtained in the step 3 with a direct current system power flow formula I, and calculating to obtain idc；
And 5: judgment of idcAnd
Figure BDA0002225995640000032
whether simultaneously greater or less than
Figure BDA0002225995640000033
If yes, then idcFor the final solution, if not, let
Figure BDA0002225995640000034
And returning to the step 2.
The method can effectively process the nonlinear characteristics of the power flow model of the multi-terminal direct current system with the self-adaptive droop control.
Drawings
FIG. 1 is a block flow diagram of the method of the present invention;
FIG. 2 is a topology diagram of a multi-terminal DC system used in an embodiment;
FIG. 3 is a comparison graph of DC1 point current values calculated by the method of the present invention versus a method that does not employ droop control equation approximation;
FIG. 4 is a comparison graph of DC2 point current values calculated by the method of the present invention versus a method that does not employ droop control equation approximation;
FIG. 5 is a graph comparing the voltage value at DC1 calculated by the method of the present invention with a method that does not use the droop control equation approximation;
FIG. 6 is a comparison graph of voltage values at DC2 calculated by the method of the present invention compared to a method that does not employ the droop control equation approximation.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples.
The specific flow of this embodiment is shown in fig. 1, and the adopted topology structure of the multi-terminal dc system is shown in fig. 2. Ten scenarios were randomly generated from the normal distribution (the loads on the DC3 and DC4 nodes obeyed a normal distribution with expected values of 0.3p.u. and 0.6p.u., respectively, and a standard deviation of 10% of the expected values).
And carrying out load flow calculation by using the calculation method of the invention aiming at the ten scenes.
Bus voltage reference for DC1 and DC2
Figure BDA0002225995640000041
Are all set to 1.0p.u., current reference value
Figure BDA0002225995640000042
Set to 0.26p.u. and 0.7p.u., respectively, converter station capacity PmaxSet to 0.5p.u. and 1.0p.u., respectively, and the droop control coefficient K is set to 2.
The calculation method comprises the following steps:
step 1: assuming that there is a bus voltage on the DC bus of the VSC converter station connected thereto
Figure BDA0002225995640000043
Calculating to obtain the injection power of the upper node of the DC bus by combining with the first direct current flow formula, and further obtaining the injection current of the upper node of the DC bus
Figure BDA0002225995640000044
Figure BDA0002225995640000045
Wherein, the reference source of the formula I is Roger Wiget,
Figure BDA0002225995640000048
Andersson,“DC Optimal Power Flow Including HVDC Grids”，2013 IEEE Electrical Power&Energy Conference.
electric current
Figure BDA0002225995640000046
The values of (A) are shown in the following table:
scene 1 Scene 2 Scene 3 Scene 4 Scene 5 Scene 6 Scene 7 Scene 8 Scene 9 Scene 10
DC1 0.2281 0.2995 0.2247 0.2484 0.2527 0.2229 0.2335 0.2631 0.2973 0.2886
DC2 0.6071 0.8376 0.6511 0.6737 0.6256 0.6256 0.6461 0.7366 0.7946 0.7795
Step 2: judgment of
Figure BDA0002225995640000047
And the reference value of the droop control device, and accordingly determining alpha, which is a parameter in the adaptive droop control equation.
Figure BDA0002225995640000051
And step 3: according to
Figure BDA0002225995640000052
The size of the droop control system is represented by a self-adaptive droop control formula
Figure BDA0002225995640000053
A first order taylor expansion is performed.
Figure BDA0002225995640000054
Wherein, the reference sources of the formula two and the formula three are as follows: yingpei Liu, La Zhang and Haiping Liung, "DC Voltage Adaptive Droop Control Stratagy for a Hybrid Multi-Terminal HVDC System", Energies, 2019;
when in use
Figure BDA0002225995640000055
The adaptive droop control linear equation is:
Figure BDA0002225995640000056
when in use
Figure BDA0002225995640000057
And when the adaptive droop control linear equation is obtained by performing first-order Taylor expansion on the formula III, the adaptive droop control linear equation is as follows:
Figure BDA0002225995640000058
and 4, step 4: combining the adaptive droop control linear equation obtained in the step 3 with a direct current system power flow formula I, and calculating to obtain idcThe results are shown in the following table.
Figure BDA0002225995640000059
Figure BDA0002225995640000061
And 5: judgment of idcAnd
Figure BDA0002225995640000062
whether simultaneously greater or less than
Figure BDA0002225995640000063
With scenario 5 i on DC1 busdcAnd
Figure BDA0002225995640000064
does not satisfy the condition, order
Figure BDA0002225995640000065
And returning to the step 2 and entering a loop.
And (3) circulation 1: to obtain idcThe results are shown in the following table.
Scene 1 Scene 2 Scene 3 Scene 4 Scene 5 Scene 6 Scene 7 Scene 8 Scene 9 Scene 10
DC1 0.2237 0.3591 0.2456 0.2523 0.2581 0.2332 0.2422 0.2845 0.3345 0.3220
DC2 0.6114 0.7780 0.6301 0.6698 0.6944 0.6153 0.6373 0.7152 0.7574 0.7461
With scenario 5 i on DC1 busdcAnd
Figure BDA0002225995640000066
does not satisfy the condition, order
Figure BDA0002225995640000067
And returning to the step 2 and entering a loop.
And (3) circulation 2: to obtain idcThe results are shown in the following table.
Scene 1 Scene 2 Scene 3 Scene 4 Scene 5 Scene 6 Scene 7 Scene 8 Scene 9 Scene 10
DC1 0.2237 0.3591 0.2456 0.2523 0.2591 0.2332 0.2422 0.2845 0.3345 0.3220
DC2 0.6114 0.7780 0.6301 0.6698 0.6933 0.6153 0.6373 0.7152 0.7574 0.7461
All buses under all scenesAll satisfy the condition idcIs the final solution.
Fig. 3 to fig. 6 are schematic diagrams comparing the calculation result of the method with the calculation result of the load flow algorithm which does not adopt the linear approximation of the droop control equation, and the results show that the errors of the two calculation results are very close, which also shows that the calculation method of the invention is feasible and effective.
Various modifications and variations of the embodiments of the present invention may be made by those skilled in the art, and they are still within the scope of the present patent invention, provided they are within the scope of the claims and their equivalents.
What is not described in detail in the specification is prior art that is well known to those skilled in the art.

Claims (1)

1. The method for calculating the power flow of the multi-terminal direct current system with the self-adaptive droop control is characterized by comprising the following steps of:
step 1: DC bus voltage assuming connection of VSC converter station
Figure FDA0002225995630000011
The injection power of the upper node of the DC bus can be calculated through a first direct current flow formula, and then the injection current of the upper node of the DC bus is obtained
Figure FDA0002225995630000012
Figure FDA0002225995630000013
Step 2: determining alpha according to the formula II, wherein the alpha is a parameter in the adaptive droop control equation
Figure FDA0002225995630000014
And step 3: according to
Figure FDA0002225995630000015
The size of the droop control system is represented by a self-adaptive droop control formula
Figure FDA0002225995630000016
Performing first-order Taylor expansion;
Figure FDA0002225995630000017
when in use
Figure FDA0002225995630000018
And when the adaptive droop control linear equation is obtained by performing first-order Taylor expansion on the formula III, the adaptive droop control linear equation is as follows:
Figure FDA0002225995630000019
when in use
Figure FDA00022259956300000110
And when the adaptive droop control linear equation is obtained by performing first-order Taylor expansion on the formula III, the adaptive droop control linear equation is as follows:
Figure FDA0002225995630000021
and 4, step 4: combining the adaptive droop control linear equation obtained in the step 3 with a direct current system power flow formula I, and calculating to obtain idc；
And 5: judgment of idcAnd
Figure FDA0002225995630000022
whether simultaneously greater or less than
Figure FDA0002225995630000023
If yes, then idcFor the final solution, if not, let
Figure FDA0002225995630000024
And returning to the step 2.
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