• Proceedings of the KIPE Conference
• /
• 2014.07a
• /
• pp.146-147
• /
• 2014

This paper presents an operation of the modular multilevel converter-high voltage direct current (MMC-HVDC) system as a Statcom to support the grid voltage. The advantage of the MMC-HVDC system is that it can control the active and reactive powers independently. The proposed control scheme will be designed by combining this performance and the control method of the Statcom. The grid voltage is regulated by the control of the reactive power, meanwhile the active power is controlled according to its applications. The simulation results based on the PSCAD/EMTDC simulation program will evaluate the effectiveness of the control scheme.

• Journal of the Korean Society of Industry Convergence
• /
• v.24 no.4_1
• /
• pp.377-385
• /
• 2021

High voltage direct current(HVDC) systems has been an alternative method of a power transmission to replace high voltage alternate current(HVAC), which is a traditional AC transmission method. Due to technical limitations, Line commutate converter HVDC(LCC-HVDC) was mainly used. However, result from many structural problems of LCC-HVDC, the voltage source converter HVDC(VSC-HVDC) are studied and applied recently. In this paper, after analyzing the reactive power and output voltage ripple, which are the main problems of LCC-HVDC, the characteristics of each HVDC are summarized. Based on this result, a new LCC-HVDC structure is proposed by combining LCC-HVDC with the MMC structure, which is a representative VSC-HVDC topology. The proposed structure generates lower reactive power than the conventional method, and greatly reduces the 12th harmonic, a major component of output voltage ripple. In addition, it can be easily applied to the already installed LCC-HVDC. When the proposed method is applied, the control of the reactive power compensator becomes unnecessary, and there is an advantage that the cut-off frequency of the output DC filter can be designed smaller. The validity of the proposed LCC-HVDC is verified through simulation and experiments.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.61 no.9
• /
• pp.1221-1225
• /
• 2012

This paper describes CSC(Current Sourced Converters)-based HVDC operational strategy for voltage stability enhancement in the power system. In case of CSC-based HVDC system, rectifier and inverter consume reactive power up to about 60% of converter rating. Therefore, CSC-based HVDC is basically not useful system for voltage stability even if AC filters and shunt capacitors are attached. But, If the particular power system condition is fulfilled, CSC-based HVDC also can be the rapid reactive power source for voltage stability enhancement using a cooperative control with converter and AC filters/Shunt Capacitors. In this paper, the cooperative control algorithm is presented and simulated to ${\pm}80kV$ 60MW HVDC system in Jeju island.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.65 no.9
• /
• pp.1479-1485
• /
• 2016

This paper presents DC voltage recovery time improvement method in DC link of High Voltage Direct Current (HVDC) with offshore wind farm. The wind farm should be satisfied Low Voltage Ride Through(LVRT) control strategy when grid faults occur. The LVRT control strategy indicates actions which have to be executed according to the voltage dip ratio and the fault duration. However, The LVRT control strategy makes between wind farm and power system through DC Link voltage when grid fault occurs. The de-loading scheme is one of the method to control the DC voltage. But de-loading scheme need to long DC voltage recovery time. Thus, this paper proposes an improved de-loading scheme and we analysis DC voltage and active power reference through a simulation.

• Proceedings of the KIPE Conference
• /
• 2000.07a
• /
• pp.645-650
• /
• 2000

this paper deals with HVDC Light(High Voltage Direct Current) system using space vector PWM(SVPWM) method. Because the system of this paper has d-q control scheme for HVDC Light system. HVDC Light system represented in this paper is capable of controlling active and reactive power independently. For this system. V-I curve and control methods are proposed. Also this paper describes the design of a digital system for applications in power converters such as those that would be used in the next generation of HVDC system. Finally HVDC system is implemented using DSP TMS320C31

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.64 no.8
• /
• pp.1193-1201
• /
• 2015

This paper presents a study of circulating current of modular multi-level converter (MMC) based a high voltage direct current (HVDC) system under unbalanced grid conditions. Due to the connection of a dependent DC source in each phase, the MMC system inherently generates the power ripple of double-line-frequency components in the AC-side and as a result, the additional sinusoidal current named circulating current flows through the each arm. Reliability improvement of HVDC system under an unbalanced grid condition is one of the important criteria. Generally, the modeling of the circulating current is based on the power relation between DC-side and AC-side. However, the method is not perfectly matched in the MMC system due to the difference of the structural characteristic. In this paper, improved modeling method of circulating current is proposed, which is based on the inner arm power. The proposed method is verified by several simulations to have good agreement of the circulating current components.

• Journal of Power Electronics
• /
• v.17 no.1
• /
• pp.127-135
• /
• 2017

Recently the researches on modular multi-level converter (MMC) are being highlighted because high quality and efficient power transmission have become key issues in high voltage direct current (HVDC) systems. This paper proposes an improved pre-charging method for the sub-module (SM) capacitor of MMC-based HVDC systems, which operates in the nearest level control (NLC) modulation and does not need additional circuits or pulse width modulation (PWM) techniques. The feasibility of the proposed method was verified through computer simulations for a scaled 3-phase 10kVA MMC with 12 SMs per each arm. Hardware experiments with a scaled prototype have also been performed in the lab to confirm the simulation results.

• JOURNAL OF ELECTRICAL WORLD
• /
• s.435
• /
• pp.54-59
• /
• 2013

• Journal of Electrical Engineering and Technology
• /
• v.9 no.5
• /
• pp.1746-1752
• /
• 2014

This paper presents an application of proportional-resonant (PR) current controllers in modular multilevel converter-high voltage direct current (MMC-HVDC) system under unbalanced voltage conditions. The ac currents are transformed and controlled in the stationary reference frame (${\alpha}{\beta}$-frame). Thus, the complex analysis of the positive and negative sequence components in the synchronous rotating reference frame (dq-frame) is not necessary. With this control method, the ac currents are kept balanced and the dc-link voltage is constant under the unbalanced voltage fault conditions. The simulation results based on a detailed PSCAD/EMTDC model confirm the effectiveness of the proposed control method.

• The Transactions of the Korean Institute of Electrical Engineers B
• /
• v.54 no.9
• /
• pp.437-443
• /
• 2005

This paper deals with an experimental study for Klippon reiay in Cheju-Heanam HVDC system Klippon relay was troubled many times for years, and Klippon relay's fault caused the HVDC system trip. So for several years, these reasons of Klippon relay fault were investigated. The malfunction of Klippon relay in Cheju-Haenam HVDC system has been caused by the incoming of random surge(current source and voltage source). This paper has stu야ed the theoretic리 analysis and experimental study of Klippon relay, and the solutions against the problems were suggested according to their causes. Among the problems, grounding problem was removed by one-point earth connection and by modification of grounding circuit. The effects of inrush current was removed by inserting the blocking diodes by series in Klippon relay circuits. Finally, The over-voltage induced on Klippon relay, by a relay excitation coil, was removed by inserting a free-wheeling diode in Parallel with the excitation coil.