• The Transactions of the Korean Institute of Electrical Engineers A
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• v.49 no.2
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• pp.56-61
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• 2000

In the paper, the system loss sensitivity index that implies the incremental system loss with respect to the change of bus power is derived using optimization technique. The index λ reaches $\infty$ at critical loading point and can be applied to actual power systems for following purposes. 1) Evaluation of system voltage stability 2)Optimal investment of reactive power focused on minimizing system loss and maximizing system voltage stability 3)Optimal re-location of reactive power focused on minimizing system loss and maximizing system voltage stability 4)Optimal load shedding in case of severe system contingency focused on minimizing system loss and maximizing system voltage stability. Case studies for each application have proved their effectiveness.

• KIEE International Transactions on Power Engineering
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• v.4A no.2
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• pp.58-68
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• 2004

This paper presents an optimal routing algorithm (ORA) for maximizing voltage stability as well as for minimizing power loss in radial power systems. In the proposed ORA, a novel voltage stability index (VSI) for real-time assessment is newly introduced based on the conventional critical transmission path framework. In addition, the suggested algorithm can automatically detect the critical transmission paths resulting in voltage collapse when additional real or reactive loads are added. To implement an effective ORA, we have developed an improved branch exchange (IBE) method based on a loss calculation index and tie-branch power flow equations, which are suggested for real-time applications. The proposed algorithm has been tested with IEEE test systems as well as a large-scale power system in Korea to demonstrate its effectiveness and efficiency.

• Journal of the Korean Institute of Intelligent Systems
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• v.20 no.2
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• pp.220-225
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• 2010

This paper deals with the robust stability analysis of STATCOM (Static Synchronous Compensator) power system for power quality enhancement and power system stability. The STATCOM plays an important role in controlling the reactive power flow to the power network and hence the system voltage fluctuations and stability. The control areas of this plant are very large and the overall composition of the system is nonlinear. Also, STATCOM is influence of the uncertainties so that it is necessary to apply the new control technique. For solving these problems, we perform the fuzzy modeling and robust analysis for STATCOM system.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.10
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• pp.1454-1459
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• 2017

In spite of continuous increase of electric power demand and new generation plants, it is very difficult to install new transmission line. Therefore, it comes to be difficult to operate the power system stable, so it is required to find another way to get new transmission capacity. Because HVDC transmission system installation is the one of the best option for us, we have undertake the HVDC project in mainland. Buckdangjin-Goduck HVDC project(500kV, 3GW) is currently under construction and Eastern Power HVDC project(500kV, 8GW) is under the study for technical specification. Both of them have the Run-up SPS function for taking action of 765kV Transmission line fault. The Run-up SPS function increases the active power output of the HVDC rapidly when the transmission line between the power plant and network is tripped, thereby preventing the generator from overspeed and improving the power system stability. In this paper, we propose MEAC(Modified Equal Area Criteria) method based on traditional EAC method to quantitatively evaluate the effect of the HVDC run-up SPS function on the power system stability improvement.

• Journal of Electrical Engineering and Technology
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• v.9 no.1
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• pp.60-70
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• 2014

This paper discusses the impacts of large scale grid-connected wind farm equipped with permanent magnet synchronous generator (PMSG) on power system small signal stability (SSS) incorporating wind generation uncertainty and volatility. Firstly, a practical simplified PMSG model with rotor-flux-oriented control strategy applied is derived. In modeling PMSG generator side converter, the generator-voltage-oriented control strategy is utilized to implement the decoupled control of active and reactive power output. In modeling PMSG grid side converter, the grid-voltage-oriented control strategy is applied to realize the control of DC link voltage and the reactive power regulation. Based on the Weibull distribution of wind speed, the Monte Carlo simulation technique based is carried out on the IEEE 16-generator-68-bus test system as benchmark to study the impacts of wind generation uncertainty and volatility on small signal stability. Finally, some preliminary conclusions and comments are given.

• 전기의세계
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• v.24 no.2
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• pp.71-77
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• 1975

This paper describes the results of a study for the stability of power system when the Kori Nuclear #1 P/P is operated with existing system. First, a transient disturbance, which effects the stability of entire power system, was analysed and to cope with the problem a load shedding method was studied to recover the fluctuation of the power system. Second, transient stability problem was studied when three phase fault occurs in 345 Extra High Voltage power System, and from this result, it was found to be highly effective that high speed protecting device should be provided and operated to recover the fault.

• Journal of Power Electronics
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• v.17 no.2
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• pp.542-550
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• 2017

Aiming at the deficiencies of power sharing control performances when a traditional droop control is adopted for microgrid inverters, this paper proposes a microgrid inverter power sharing control strategy based on a virtual synchronous generator. This control method simulates the electromechanical transient characteristics of a synchronous generator in a power system by an ontology algorithm and the control laws of a synchronous generator by control over the speed governor and excitation regulator. As a result, that the microgrid system is able to effectively retain the stability of the voltage and frequency, and the power sharing precision of the microgrid inverter is improved. Based on an analysis of stability of a microgrid system controlled by a virtual synchronous generator, design thoughts are provided for further improvement of the power sharing precision of inverters. The simulation results shows that when the virtual synchronous generator based control strategy was adopted, the power sharing performances of microgrid inverters are improved more obviously than those using the droop control strategy.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.66 no.4
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• pp.151-157
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• 2017

In this paper, it is the result of analysis of the stability by power system analysis about the influence on the power system when the southwest - offshore wind power demonstration complex is constructed to 60MW and it is linked with the onshore power system. Considering the position of the wind turbine actually installed and the length of the cooperating line, we modeled the wind generators, offshore substation and the turbine step-up transformer. Changes of voltage when internal and external faults occurred is analyzed and the reactive power demand according to the amount of electricity generation is derived. And also phase angle stability and frequency is observed through a transient analysis. This paper clarify that there is no problem in the system when only offshore wind power is linked with the grid and try to present the reactive power amount necessary for maintaining the voltage of the point of cooperation appropriately.

• Journal of Power Electronics
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• v.15 no.1
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• pp.202-215
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• 2015

This paper investigates the stability and performance of model predictive controlled active-front-end (AFE) rectifiers for energy storage systems, which has been increasingly applied in power distribution sectors and in renewable energy sources to ensure an uninterruptable power supply. The model predictive control (MPC) algorithm utilizes the discrete behavior of power converters to determine appropriate switching states by defining a cost function. The stability of the MPC algorithm is analyzed with the discrete z-domain response and the nonlinear simulation model. The results confirms that the control method of the active-front-end (AFE) rectifier is stable, and that is operates with an infinite gain margin and a very fast dynamic response. Moreover, the performance of the MPC controlled AFE rectifier is verified with a 3.0 kW experimental system. This shows that the MPC controlled AFE rectifier operates with a unity power factor, an acceptable THD (4.0 %) level for the input current and a very low DC voltage ripple. Finally, an efficiency comparison is performed between the MPC and the VOC-based PWM controllers for AFE rectifiers. This comparison demonstrates the effectiveness of the MPC controller.

• Journal of Power Electronics
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• v.19 no.5
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• pp.1270-1277
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• 2019

A problem with virtual synchronous generator (VSG) systems is that they are difficult to operate stably with photovoltaic (PV) power as the DC side. With this problem in mind, a PV-VSG control strategy considering the dynamic characteristics of the DC side is proposed after an in-depth analysis of the dynamic characteristics of photovoltaic power with a parallel energy-storage capacitor. The proposed PV-VSG automatically introduces DC side voltage control for the VSG when the PV enters into an unstable working interval, which avoids the phenomenon where an inverter fails to work due to a DC voltage sag. The stability of the original VSG and the proposed PV-VSG were compared by a root locus analysis. It is found that the stability of the PV-VSG is more sensitive to the inertia coefficient J than the VSG, and that a serious power oscillation may occur. According to this, a new rotor model is designed to make the inertial coefficient automatically change to adapt to the operating state. Experimental results show that the PV-VSG control strategy can achieve stable operation and maximum power output when the PV output power is insufficient.