(A) study on application of voltage management system considering interaction minimization and effective reactive power reserve in the Korean power system

다국어 초록 (Multilingual Abstract)

This dissertation presents a voltage management system that uses multiple point control and an optimal shunt compensation algorithm to ensure peak power system performance. The control algorithm is applied to the Korean power system to prevent mutual coupling and reactive power reserve problems.
The voltage management system consists of two parts: (1) a continuous control system, and (2) a discrete control system. The former is used to maintain a pilot point voltage of a generator called the continuous voltage control (CVC), while the latter is used to secure the reactive power reserves of the control generator by means of a capacitor or a reactor called the discrete voltage control (DVC). When a voltage violation occurs at the pilot point in the power system, the control generator in the system regulates it to maintain the voltage at the point; then, discrete devices such as capacitors or reactors operate to get the pilot point back to the reactive power margin of the control generator. Thus, the voltage management system ensures that the power system can obtain control margins in an emergency condition by means of exchanges from the control generators into the capacitors or the reactors to maintain the voltage of the pilot point at a constant level.
In this dissertation, voltage management systems more advanced than that presently being utilized by the Jeju power system are proposed. The Jeju power system has only one control zone, so problems between adjacent zones do not occur. However, a complex power system that has many control zones is different. The existing voltage management system that is installed in a particular zone influences other zones. This makes it difficult to control the voltage at pilot points. To avoid reactive power flows between control zones, the voltage at neighboring pilot points must not be modified. This can be more difficult to achieve in a mesh network.
This dissertation deals with shunt compensation to eliminate voltage violations and enhance transfer capability, with a view towards implementation in the Korean power system. The main shunt compensation devices are capacitors and reactors. The effects of control devices are evaluated by a local subsystem's cost computations. This local subsystem is determined by the electrical distance in the entire system. The control objective at present is to keep the voltage profile within constraints with the minimum switching cost. We propose a robust control strategy to make control feasible and optimal for a set of important power-flow cases that may occur in the system. In order to efficiently operate the voltage management system, a criterion is necessary for coordinated control between the control generators and the discrete devices. This criterion is related to the reactive power reserves of the control generator. Thus, an accurate reactive power margin is defined for the voltage stability index and used as the coordination standard in this dissertation.
Generally, the current voltage management system controls only one pilot point of one zone. In contrast, our proposed control algorithm in conjunction with the CVC deals with multiple pilot points related to the entire system. As a result, we call it the multiple point algorithm for continuous voltage control (MCVC). It is applied only to the generator control section of the voltage management system. Similarly, the DVC algorithm, which takes into consideration increases in transfer capability, is called the optimal shunt compensation for discrete voltage control (ODVC) algorithm. By means of simulations, we illustrate example usages of the proposed algorithm using SCADA/EMS data from the Korean power system for 2008, and examine the results. The proposed system was simulated using the transient stability assessment tool (TSAT) and Compaq Visual Fortran 6 to show that the modified voltage management system is effective and suitable for utilization in the Korean power system.

목차 (Table of Contents)

• ABSTRACT I
• Contents V
• List of Figures VII
• List of Tables I
• Chapter 1. Introduction 1
• 1.1 Background and Motivation 1
• 1.2 Literature Review 4
• 1.3 Contribution of this Dissertation 11
• 1.4 Dissertation Contents 12
• Chapter 2. Overview of the Current VMS 14
• Chapter 3. Characteristic of the Korean Power System 20
• 3.1 Summary of the Korean Power System 20
• 3.2 Difficulties of the VMS Application in the Korean Power System 24
• Chapter 4. The Advanced VMS Control Framework 29
• 4.1 Multiple Point Control Algorithm for the CVC 29
• 4.1.1 Principle of the control algorithm 29
• 4.1.2 Operating mechanism of the control algorithm 31
• 4.2 Optimal Shunt Compensation Algorithm for the DVC 37
• 4.2.1 Calculation of the interface flow margin 37
• 4.2.2 Development of the control algorithm 39
• 4.3 Coordinated Control Index 43
• 4.3.1 Principle of the coordinated control between the CVC and the DVC 43
• 4.3.2 Definition of the control index 45
• 4.4 Coordinated Control Schemes 51
• Chapter 5. Simulation Results for the Korean Power System 54
• 5.1 Comparison of the Multiple Point Algorithm 54
• 5.2 Comparison of the Optimal Shunt Compensation Algorithm 56
• 5.3 Comparison of the Coordinated Control 60
• 5.3.1 Case 1) Load increase case with only the generators 61
• 5.3.2 Case 2) Load increase case with the generators and the capacitors 63
• Chapter 6. Conclusion 66
• APPENDIX 69
• A. User Defined Model for the multiple point control algorithm of the CVC in TSAT 69
• Bibliography 70
• 국문초록 77