KR-20260062723-A - MEDIUM VOLTAGE DIRECT CURRENT SYSTEM

KR20260062723AKR 20260062723 AKR20260062723 AKR 20260062723AKR-20260062723-A

Abstract

A high-voltage direct current distribution system (MVDC) is initiated. The high-voltage direct current distribution system according to an embodiment of the present invention is characterized by comprising a three-winding transformer, a first modular multi-level converter configured to be connected to the secondary winding of the three-winding transformer, and a second modular multi-level converter configured to be connected to the tertiary winding of the three-winding transformer.

Inventors

김석웅
김욱원
김주용
채우규

Assignees

한국전력공사

Dates

Publication Date: 20260507
Application Date: 20241029

Claims (11)

As a medium voltage direct current (MVDC) distribution system, 3-winding transformer; A first modular multilevel converter configured to be connected to the secondary winding of the above-mentioned three-winding transformer; and A high-voltage DC distribution system comprising a second modular multilevel converter configured to be connected to the third winding of the above-mentioned three-winding transformer.
In Article 1, The primary winding of the above three-winding transformer is Y-connected, and The secondary winding of the above three-winding transformer is Y-connected, and A high-voltage DC distribution system in which the tertiary winding of the above-mentioned 3-winding transformer is delta-connected.
In Article 1, A high-voltage DC power distribution system further comprising a neutral line connected to a lower arm provided in each leg included in the first modular multi-level converter and connected to an upper arm provided in each leg included in the second modular multi-level converter.
In Paragraph 3, A first control module configured to control the first modular multilevel converter; and A high-voltage DC power distribution system further comprising a second control module configured to control the second modular multi-level converter.
In Paragraph 4, The above-described first control module is a high-voltage DC distribution system that feedback-controls the first modular multi-level converter so that the current value of the neutral line becomes zero.
In Paragraph 5, A high-voltage DC distribution system, wherein the first control module calculates a voltage command value based on the current value of the neutral line, the output voltage value and output current value of the first modular multilevel converter, and the output voltage value and output current value of the second modular multilevel converter, and controls the first modular multilevel converter according to the difference between the voltage command value and the output voltage value of the first modular multilevel converter.
In Paragraph 6, The above-mentioned first control module is a high-voltage DC power distribution system that calculates the voltage command value through the following mathematical formula 1: [Mathematical Formula 1] (Here, V p ' is the voltage command value, V Pref is the nominal voltage, I G is the neutral line current value, P p is the output power value of the first modular multilevel converter, P N is the output power value of the second modular multilevel converter, I P is the output current value of the first modular multilevel converter, and I N is the output current value of the second modular multilevel converter.)
In Paragraph 4, The above-mentioned first control module is a high-voltage direct current distribution system comprising a voltage limiter configured to prevent DC voltage violation.
In Paragraph 4, The above-described second control module is a high-voltage DC distribution system that feedback-controls the second modular multi-level converter so that the current value of the neutral line becomes zero.
In Article 9, A high-voltage DC distribution system, wherein the second control module calculates a voltage command value based on the current value of the neutral line, the output voltage value and output current value of the second modular multilevel converter, and the output voltage value and output current value of the first modular multilevel converter, and controls the second modular multilevel converter according to the difference between the voltage command value and the output voltage value of the second modular multilevel converter.
In Paragraph 4, The above second control module is a high-voltage DC distribution system comprising a voltage limiter configured to prevent DC voltage violation.

Description

Medium Voltage Direct Current Distribution System The present invention relates to a bipolar high-voltage direct current distribution system. Existing HVDC or MVDC systems are composed of a single stage, and since the output of the multi-level converter operates as a monopole, there is a problem in that a neutral point does not exist. Accordingly, symmetrical monopole HVDC or MVDC systems are being studied, which combine a zigzag transformer configured to form a neutral point with a multi-level converter. Meanwhile, in the case of conventional symmetrical monopole HVDC or MVDC systems, there is a problem that if a fault occurs at either the P pole or the N pole of the system, the voltage of the other pole rises and the system may stop at the same time. The background technology of the present invention is disclosed in Korean Published Patent Application No. 10-2020-0007164 (January 22, 2020). FIG. 1 is an exemplary diagram showing a high-voltage direct current distribution system according to an embodiment of the present invention. Figure 2 is an example diagram for explaining the first control module. Figure 3 is an example diagram illustrating the relationship between the current value of the neutrality and the amount of change in the output voltage value of the first modular multilevel converter. Figure 4 is an example diagram illustrating a feedback controller. Figure 5 is another example diagram for explaining the first control module. Figure 6 is an example diagram to explain the neutral line current. FIG. 7 is an illustrative diagram for explaining the performance of a high-voltage direct current distribution system according to an embodiment of the present invention. Hereinafter, a high-voltage direct current distribution system according to an embodiment of the present invention will be described in detail with reference to the attached drawings. In this process, the thickness of lines or the size of components depicted in the drawings may be exaggerated for the sake of clarity and convenience of explanation. Furthermore, the terms described below are defined considering their functions in the present invention, and these may vary depending on the intention or convention of the user or operator. Therefore, the definitions of these terms should be based on the content throughout this specification. FIG. 1 is an exemplary diagram showing a high-voltage direct current distribution system according to an embodiment of the present invention. Referring to FIG. 1, a high-voltage DC power distribution system according to an embodiment of the present invention may include a three-winding transformer (100), a first modular multi-level converter (200), a second modular multi-level converter (300), a first control module (400), and a second control module (500). A high-voltage DC power distribution system according to an embodiment of the present invention may include various additional components in addition to the components shown in FIG. 1, or may not include some of the components shown in FIG. 1. A three-winding transformer (100) can step down and output extra-high voltage (e.g., 22.9 kV/60 Hz) output from a substation. The three-winding transformer (100) may include primary to tertiary windings. The primary winding of the three-winding transformer (100) can be Y-connected. The secondary winding of the three-winding transformer (100) can be Y-connected. The tertiary winding of the three-winding transformer (100) can be Delta (Δ)-connected. That is, the three-winding transformer (100) can be a Y-Y-Δ connected transformer. Extra-high voltage output from a substation may be applied to the primary winding of the three-winding transformer (100). A first modular multi-level converter (200) may be connected to the secondary winding of the three-winding transformer (100). A second modular multi-level converter (300) may be connected to the tertiary winding of the three-winding transformer (100). The primary winding of the three-winding transformer (100) constitutes the primary side of the three-winding transformer (100), and the secondary and tertiary windings of the three-winding transformer (100) may constitute the secondary side of the three-winding transformer (100). The secondary side of the three-winding transformer (100) may include a Y-connected secondary winding and a delta-connected tertiary winding. The first modular multi-level converter (MMC, 200) can convert AC power into DC power and output it. The first modular multi-level converter (200) can be responsible for supplying the P-pole voltage of a DC power distribution system. The first modular multi-level converter (200) may include a plurality of sub-modules. The sub-modules may include power semiconductor devices and capacitors. The first modular multilevel converter (200) may include a plurality of legs arranged by phase. Each leg may be equipped with an upper arm (210) and a lower arm (220). Each of the upper arm (210) and the lower arm (220) ma