Power flow calculation and AC/DC hybrid power flow calculation method for flexible DC transmission system

Patent metadata

Field	Value
Publication number	US-12578367-B2
Application number	US-202318128595-A
Country	US
Kind code	B2
Filing date	Mar 30, 2023
Priority date	Aug 15, 2022
Publication date	Mar 17, 2026
Grant date	Mar 17, 2026

Abstract

A power flow calculation and AC/DC hybrid power flow calculation method for a flexible DC transmission system, the method including: according to the flexible DC transmission system under different control strategies, constructing a unified power flow model with a unified structure; determining a current main converter station, a current control strategy and an initial value and a limit value thereof, and forming the power balance equations under the current control strategy according to the unified power flow model; updating the current DC node voltage according to the voltage variation obtained by solving the power balance equations, and, if the updated DC node voltage exceeds the limit value, switching the control strategy; and if the updated DC node voltage does not exceed the limit value and the iteration constraints are not satisfied, alternating the main converter station according to the priority until iteration is completed.

First claim

What is claimed is:

1 . A power flow calculation method for a flexible direct current (DC) transmission system, comprising:
according to the flexible DC transmission system under different control strategies, constructing a unified power flow model with a unified structure; determining a current main converter station, a current control strategy and an initial value and a limit value thereof, and forming a power balance equation under the current control strategy according to the unified power flow model; the power balance equation in the unified power flow model is:

Δ
⁢

P
i

=

(

P
dci

+

α
·

U
dci

(

I
dcrefi

-

U
dci

-

U
dcrefi

k
di

)

-

β
⁢

U
dci

-

U
dcrefi

k
dpi

+

P
Gi

-

P
Li

)

-

U
dci

⁢

∑

j
=
1

n

U
dcj

⁢

G
ij

(

i
=
1

,
2
,
…

,
n

)

;

wherein, ΔP i is the imbalance power of a DC node i, P dci is the injection power from a converter station to the DC node i, U dci is the DC voltage of the DC node i, P Gi is the active power emitted by a power supply at the DC node i, P Li is the active power absorbed by a load at the DC node i, G ij is the admittance between the node i and a node j, I dcrefi is the direct current reference value of the DC node i, k di is a droop coefficient under the current-voltage droop control mode, U dcrefi is the DC voltage reference value of the DC node i, k dpi is a droop coefficient under the active power-voltage droop control mode, U dcj is the DC voltage of the DC node j, and n is the number of nodes; α and β are adjustable variables;
updating the current DC node voltage according to the voltage variation obtained by solving the power balance equations, then judging whether the updated DC node voltage exceeds the limit value, so as to judge whether the flexible DC transmission system exceeds the limit, wherein:
if the updated DC node voltage exceeds the limit value modifying DC voltages of all the converter stations; then if the active power of the DC node exceeds the limit value during a voltage deviation control of the DC node, putting a back-up converter station into operation at this moment; and then if the active power of the converter station exceeds the limit value during a droop control, re-modifying the active power of the converter station exceeding the limit value and the active power of the converter station not exceeding the limit value;
and if the updated DC node voltage does not exceed the limit value and the iteration constraints are not satisfied, alternating the main converter station according to the priority until iteration is completed.

2 . The power flow calculation method for the flexible DC transmission system according to claim 1 , wherein the current control strategy comprises a master-slave control strategy, a voltage deviation control strategy, an active power-voltage droop control strategy, and a current-voltage droop control strategy.

3 . The power flow calculation method for the flexible DC transmission system according to claim 1 , wherein in the unified power flow model, by changing the values of the adjustable variables a and B, the unified power flow model represents different control strategies.

4 . An AC/DC alternating current/direct current (AC/DC) hybrid power flow calculation method, comprising:
acquiring a current main converter station, a current control strategy and an initial value and a limit value thereof of a flexible DC transmission system; according to the flexible DC transmission system under different control strategies, constructing a unified power flow model with a unified structure; determining a current main converter station, a current control strategy and an initial value and a limit value thereof, and forming a power balance equation under the current control strategy according to the unified power flow model; the power balance equation in the unified power flow model is:

Δ
⁢

P
i

=

(

P
dci

+

Assignees

• Univ Shandong

Inventors

• Li Changgang
• Ma Zhenhe
• Liu Yutian
• Ye Hua

Classifications

• H02J2103/35

  Grid-level management of power transmission or distribution systems, e.g. load flow analysis or active network management · CPC title

• G01R19/2513 Primary

  Arrangements for monitoring electric power systems, e.g. power lines or loads; Logging · CPC title

• G01R21/133

  by using digital technique · CPC title

• Y02E60/60

  Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD] · CPC title

• H02J2103/30

  Simulating, planning, modelling, reliability check or computer assisted design [CAD] of electric power networks · CPC title