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DC T&D System

Hyosung Heavy Industries was the first company in Korea to successfully develop a high-voltage direct current (HVDC) system using the MMC method, which is the most advanced technology for voltage converters.

By installing a 25 MVA MMC-type HVDC system on Jeju Island, we have verified the performance and dependability of converters and control systems comprising the MMC-type HVDC system.

We are in the process of developing a 200 MW MMC-type HVDC, and by completing the installation of a 30 MW medium-voltage direct current (MVDC), we will be Korea's first company to apply the voltage-type MMC converter to HVDC and MVDC technology.
In addition, we were the first in Korea to secure DC transmission and distribution system technology for all voltage ranges from low voltage to extra-high-voltage by winning an order for 40 kW low-voltage direct current (LVDC).

Features and Benefits

We offer specialized solutions based on superior technology.

  • Modular Structure

    • It is easy to expand the system's capacity and voltage, allowing it to be tailored to the diverse needs of customers.
    • The modular multi-level converter's technical characteristics permit the use of industry-standard components, resulting in high reliability and low maintenance costs.
  • Advantages of Modular Structure

    • Even if a certain number of sub-modules fail, it is possible to increase the availability rate by bypassing the failed sub-modules.
    • It is possible to use a standard AC transformer, which is advantageous for ensuring reliability and permits highly efficient operation.
  • HVCD Transmission

    • It is possible to configure a DC grid with multiple terminals, enabling the integration and connection of several systems, and independent control of reactive power allows stable connection to a weak AC grid.
    • Low loss enables highly efficient transmission of power.
  • Various Solutions Considering User Convenience

    • Possible to install a converter in a small area, allowing for connection to both the metropolitan area and offshore wind power systems.
    • Through the black start function, power failure recovery is possible in the event of a blackout.
  • Proven Full-range DC Transmission and Distribution Technology

    • Proven technology capable of handling a full range of voltages from low voltage to extra-high voltage by DC transmission and distribution method with multiple cases of MMC-type HVDC, MVDC and LVDC installations.
  • 20+ Years of Continuous Product Innovation

    • The Hyosung Power & Industrial Systems R&D Center ensures world-class competitiveness through the development of innovative heavy electrical equipment products (e.g. flexible power transmission system, high-voltage DC transmission).

Product Specifications

Learn about DC T&D system specifications.

25MVA, 22.9kV,
HVDC Converter Station

Size 50mx50m
Capacity 20MW
Topology Half-Bridge
Num./Arm 12
(2 for Redundancy)

213MVA, 154kV,
HVDC Converter Station

Size 147m x 55m
Capacity 200MW
Topology Half-Bridge
Num./Arm 108(8 for Redundancy)


Discover custom solutions that meet your needs.

  • 01

    Eco Solutions

    • By utilizing the steel tower of the existing AC overhead line, it is possible to transmit more than twice as much power, thereby avoiding environmental damage associated with the construction of additional lines.
    • Long-distance undergrounding is possible when it is difficult to install new transmission lines to prevent forest damage and preserve natural scenery.
    • Active power and reactive power can be regulated to facilitate a stable connection to the grid when renewable energy sources are linked.
  • 02

    Linkage between heterogeneous systems

    • The back-to-back (BTB) HVDC transmission system is utilized to connect national or regional grids with varying AC grid frequencies and phases
    • The point-to-point (PTP) HVDC transmission system is used to connect the systems of islands regions.
    • Connecting renewable energy to multiple DCs makes it possible to control the flow of energy.
  • 03

    Long-distance power
    (offshore, onshore, and underground)

    • DC transmission is the only option for long-distance transmissions of approximately ≥80km for submarine cables and ≥120km for underground cables.
    • In the case of overhead power transmission, DC is more cost-effective than AC when transmitting large amounts of power over distances ≥800km.
  • 04

    Multi-terminal configuration

    • It is easy to link grids across continents or countries, allowing expansion to supergrids.
    • It is possible to connect multiple DC outputs to direct current to construct multiple terminals that regulate energy flow.
    • DC network configuration makes it possible to adjust the supply and demand balance because it is simple to connect to various power sources and it is possible to regulate power flow.


Our track records speak for ourselves.

  • Republic of Korea

    Naju 30MW-class MMC-based VSC MVDC Project

    • Green Energy Institute
    • Naju, Jeollanam-do
  • Republic of Korea

    Development/Demonstration of rectifier and inverter for LVDC demonstration in Hongcheon-gun and Donghae

    • Korea Electric Power Corporation
    • Hongcheon-gun and Donghae, Gangwon-do
  • Republic of Korea

    Jeju Offshore Wind Power Connection Project for 20MW-class Voltage-type HVDC Connection

    • Korea Institute of Energy Technology Evaluation and Planning
    • Haengwon-ri, Jeju-do


We adhere to global standards and maintain an environment of the highest quality.

View all certifications
  • IEC


  • ISO9001


  • ISO14001


  • ISO45001