Chan-Ki Kim

A Series-Connected Topology of a Diode Rectifier and a Voltage-Source Converter for an HVDC Transmission System

In this letter, a novel converter topology of high-voltage direct current (HVDC) transmission for integrating the offshore wind farm (WF) with the grid is proposed, which consists of a series connection of the 12-pulse diode rectifiers and a voltage-source converter (VSC). For this topology, the PCC (point of common coupling) voltage of the offshore WF side is regulated at a constant magnitude and constant frequency by the WFVSC. Also, the current at the PCC becomes almost sinusoidal since the WFVSC functions as an active power filter for the 11th- and 13th-order harmonic current components. By virtue of the diode rectifier, the cost and power loss of HVDC converters is reduced compared with the case of the conventional fully rated VSC, whereas the performance is kept almost the same. The PSCAD/EMTDC simulation results for a 500-MW HVDC transmission system have been shown to verify the validity of the proposed scheme.

Dynamic coordination strategies between HVDC and STATCOM

This paper dealt with a STATCOM (Static Compensator), considered the combination of the robust performance against commutation failure and low capital cost of filter size in HVDC system. Especially, the main target of this paper is to improve the performance of dynamic voltage control at the inverters of very weak AC systems which has harmonic instability and commutation failure phenomena. PSCAD/EMTDC simulations are presented to demonstrate the robust performance and to validate the proposed system in case of considering a saturation phenomena of HVDC transformer.

Verification of Hybrid Real Time HVDC Simulator in Cheju-Haenam HVDC System

In this paper a Hybrid Real Time HYDC Simulator for both operator Training and Re-searching in the Cheju-Haenam HYDC System is proposed and its performance is studied by means of RTDS (Real Time Digital Simulator), EMTDC (Electro-Magnetic Transients system for DC), PSS/E (Power System Simulator for Engineering), and experienced scenarios. The objective of this paper is to represent the strategy in development for KEPCOs hybrid HYDC simulator for the Cheju-Haenam HYDC system. This simulator consists of two DC stations, DC cables, external digital/analog controllers, monitoring systems and control desk for education, and AC networks. Its suitability for operators education is tested during startup/shutdown and normal state operations. Dynamic performances of it are also verified.

Modeling strategies of Cheju-Haenam HVDC system and its dynamic performance study

This paper deals with the development of the simulation models of Cheju-Haenam HVDC system and its dynamic performance study and verifies the control characteristics of the HVDC system. It discusses the model development requirement and criteria. It provides guidelines for developing large-scale simulation models for detailed electromagnetic studies and presents the results of the modeling project.

Stability performance of new static excitation system with boost-buck converter

This paper deals with the design and evaluation of a new static-excitation system for generator excitation systems to improve the steady-state and transient stabilities. It increases or maintains the generator field current by boosting the field voltage in the case of an input AC line voltage drop during and immediately after a fault. The validity of the proposed excitation system is verified with computer simulation. The simulation results of the stability analysis on the generator with the proposed excitation system is better than that of a conventional static excitation system and a conventional AC excitation system. Also, this proposed excitation system can be simply implemented and controlled by modern power electronics technology.

Operating Region of Modular Multilevel Converter for HVDC With Controlled Second-Order Harmonic Circulating Current: Elaborating P-Q Capability

The operating region of the modular multilevel converter (MMC) is limited by the maximum-allowable voltage ripple of cells, which is associated with the arm energy variation. Injecting the controlled second-order harmonic component into the circulating current can reduce energy variation of the arm and, thus, extend the operating region of MMC. Care must be taken, however, that the second-order circulating current affects the arm current, and inappropriately injected harmonic current may cause an undesirable arm current polarity change. Therefore, this paper first investigates and proposes the maximum-allowable second-order circulating current for extending the operating region reliably and efficiently. The active and reactive power capability of MMC is further elaborated and illustrated in line with the maximum excess energy capability for two cases, running with: 1) the original operating region and 2) the extended operating region. Finally, the P- Q diagrams for contingent operating conditions with faulty or disabled submodules are presented. Understanding the unique shape and change of P- Q capability with credible submodule failure contingency should be crucial for planning MMC-HVDC lines, and determining the energy requirements and the level of redundancy in submodules properly in order to achieve the envisioned benefits of the new HVDC. The efficacy and accuracy of the research findings are validated for the MMC-HVDC system using PSCAD/EMTDC.

Transient performance of Cheju-Haenam HVDC system

This paper deals with the dynamic performance of Koreas Cheju-Haenam HVDC power system. The purpose of the study is to verify the control characteristics of the HVDC system and to analyze the dynamic performances by simulation study. Because the HVDC system consists of analogue and digital controller, the simulation is achieved with specification model incorporating nonlinear function. The dynamic performance simulations are performed by PSCAD/EMTDC.

Performance analysis for the modified excitation system of synchronous machine connected to HVDC system

This paper analyses the transient performance of the modified excitation system using 4-quadrant chopper for a synchronous machine connected to HVDC system. Conventionally, capacitors are used to supply reactive power requirement at a strong converter bus. And the installation of a synchronous machine is essential in an isolated weak network to re-start after a shutdown of HVDC and to increase the system strength. However, a conventional static excitation system has some problems which are harmonic instability and the system stress due to overvoltage. To reduce these problems, the new excitation system, which has 4-quadrant chopper, is proposed. As the proposed system provides the capability to allow reverse current and isolate between AC network and excitation power, problems of overvoltage and harmonic instability can be solved. The investigation is performed and confirmed by the time domain digital simulation using PSCAD/EMTDC program.

HVDC performance analysis according to ER-filter and single tuned filter

This paper deals with the novel HVDC filter topology. The proposed method is the combination the active filter with ER-filter (energy recovery-filter). The active filter of the proposed method is a kind of hybrid filter, consists of the passive filter and the voltage source. Also, the single tuned active filter to eliminate 11/sup th//13/sup th/ harmonics is proposed. This proposed active filter is very useful to reduce the cost of the active filter. ER-filter is to return the filter power to AC network, used to replace with the damped filter. Consequently, PSCAD/EMTDC is used to investigate the validation of the proposed topology.

Feasibility study of HVDC interconnection between south Korea and north Korea

The paper deals with the cost evaluation concerning the implementation of a 2000MW HVDC link over a 200km distance. Two different dc voltages have been considered, namely +/−300kVdc and 500kVdc. Two different scheme configurations have been considered, namely a single bipole system and a double bipole system.