Abstract
Automatic Generation Control (AGC) and Automatic Voltage Control (AVC) are key approaches to frequency and voltage regulation in power systems. However, based on the assumption of decoupling of active and reactive power control, the existing AGC and AVC systems work independently without any coordination. In this paper, a concept and method of hybrid control is introduced to set up an Integrated Coordinated Optimization Control (ICOC) system for AGC and AVC. Concerning the diversity of control devices and the characteristics of discrete control interaction with a continuously operating power system, the ICOC system is designed in a hierarchical structure and driven by security, quality and economic events, consequently reducing optimization complexity and realizing multi-target quasi-optimization. In addition, an innovative model of Loss Minimization Control (LMC) taking into consideration active and reactive power regulation is proposed to achieve a substantial reduction in network losses and a cross iterative method for AGC and AVC instructions is also presented to decrease negative interference between control systems. The ICOC system has already been put into practice in some provincial regional power grids in China. Open-looping operation tests have proved the validity of the presented control strategies.
Highlights
Automatic Generation Control (AGC) and Automatic Voltage Control (AVC) systems are crucial parts in a modern Energy Management System (EMS)
Economic Dispatch Control (EDC) is formulated to satisfy the hourly load demand based on load prediction ahead of day; LoadFrequency Control (LFC) is responsible for frequency volatility with cycles ranging from 10 seconds to several minutes, while Primary Frequency Regulation (PFR) deals with the real time balance of generation and load [1]
As the changes in network losses and control inaccuracy in pilot bus voltage reflect the interactive impact between AGC and AVC systems, the two elements are adopted as monitoring indices, which builds an effective communication bridge between the AGC and AVC systems
Summary
Automatic Generation Control (AGC) and Automatic Voltage Control (AVC) systems are crucial parts in a modern Energy Management System (EMS). From the perspective of economical operation, the active and reactive optimization should not be separated; Active power/frequency control and reactive power/voltage control are not completely decoupled even under normal conditions, for example, frequent fluctuation of active power affects the voltage quality; interactions between AGC and AVC control commands result in weakened control effects and reciprocal regulation. Wind generation operation requires a large amount of reactive power support and flexible frequency regulation ability, putting higher demands on AGC and AVC systems, especially for the cascading trip-off accident tangling with active and reactive power control at the same time [5]. Concerning economically coordinated dispatch, in [8], an active/reactive coordinated optimization model is set up to allocate network losses to each generator under the principle of minimizing total generation cost, but in dealing with conflicting inequality constraints, the converting bus and branch type methods proposed in this paper may cause frequent transformation and affect convergence of the algorithm.
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