Decentralized robust adaptive-output feedback controller for power system load frequency control

In this paper, a new model reference-decentralized robust adaptive-output feedback controller is proposed for the load frequency control (LFC) of large-scale power systems with unknown parameters. This control strategy requires only local input–output data and can follow random changes in the operating conditions. The controller is designed such that the trajectory errors and the control gains of each area remain uniformly bounded. In the proposed method, firstly an adaptive observer is designed to estimate the state variables and system parameters using local data only. Then a locally linear combination of the estimated states and the model reference states are used to design a robust adaptive-output feedback controller for each area. Simulation results for a three-area power system show that the proposed controller achieves good performance even in the presence of plant parameter changes and system non-linearities. Received: 18 October 2001/Accepted: 24 October 2001     

Decentralized load frequency based on H∞ control

This paper presents a decentralized load frequency control (LFC) based on H_∞ optimal control theory with an observer. A few LFC schemes have been proposed based on the optimal control theory, but they have not considered the change of system parameters in operation and the characteristics of load disturbances in a target system. In this paper, H_∞ robust control is introduced to address such problems. Owing to its practical merit, the proposed control scheme is a decentralized LFC. Employing observer theory, the proposed method requires only frequency and tie‐line power deviation in each area. Numerical simulations are shown to demonstrate the effectiveness of the proposed method. H_∞ control was proven to show greater effectiveness of damping disturbance over the conventional optimal control by the design of control systems aimed at restricting the H_∞ norm of its transfer function. In particular, when a decentralized LFC is applied, by reducing the system size, H_∞ norm is easier to dampen; thus H_∞ control is more effective in the decentralized control. Future research topics include the design of H_∞ control system with a weight on frequency response. © 2001 Scripta Technica, Electr Eng Jpn, 136(3): 28–38, 2001     

Decentralized load frequency controller for a multi-area interconnected power system

This paper proposes a control scheme for the load frequency control (LFC) problem of multi-area power systems. These systems are treated as interconnected dynamical systems. In the design of the proposed controller, each local area network is overlapped with states representing the interconnections with the other local area networks in the global system. Then, a decentralized control scheme is developed as function of the local area state variables and those resulting from the overlapped states which represent an approximation of the interconnection variables. The proposed controller guarantees the asymptotic stability of the overall closed loop system.The simulation results indicate that the proposed control scheme works well. In addition, they show that the controlled system is robust to changes in the parameters of the power system and to bounded input disturbances acting on the system. Moreover, the simulation results show that the controlled system behaves well even when there is a maximum limit on the rate of change in power generation.     

Decentralized robust adaptive load frequency control using interactions estimation

In this paper, a new model reference decentralized adaptive output feedback controller is proposed for load-frequency control (LFC) of large-scale power systems with unknown parameters. The main problem with a decentralized robust LFC is that the interactions are treated as disturbances. This results in a conservative control action to maintain stability in the worst-case scenario. Furthermore, to improve the performance of the decentralized LFC, the proposed method estimates the interactions from other subsystems to modify the adaptive controller so that the interactions are effectively neutralized. The other important features of the proposed controller are: (1) no prior information about the system parameters is required, (2) random changes in the operating conditions are traced, (3) only the local input–output data are needed, (4) the robustness of the overall system against the system parameter uncertainties is guaranteed. To show the effectiveness of the proposed controller, a three-area power system is studied. The simulation results are promising and highlight the remarkable performance of the controller even in the presence of both plant parameter changes and high interactions.     

Effect of load characteristics on frequency control in power systems

The load-frequency control (LFC) problem is investigated on assumptions considered realistic for most power systems. Voltage and frequency dependence of system loads, and load inertia effects, are taken into account. Results include system dynamic response to changes in load, and effects of LFC parameter settings. Using a performance index based on squared tie-line flow error plus squared area frequency error, the effect of load representation on optimum integrator gain is examined.     

Decentralized voltage control in multiarea power system

This paper discusses the feasibility of a decentralized voltage control scheme for large-scale power systems. The algorithm is intended to apply to a reactive normal operating state from an emergency state caused by illcondition and also to keep the operating state away from approaching unstable boundaries in preventive control. The procedure for releasing voltage deviation (over/under voltage) is formulated as a multistage decision process over a certain time interval. The optimization problem is transformed into a two-point boundary value problem using the discrete maximum principle and is solved easily by using the discrete Riccati equation. For a large-scale power system, control values must be computed from a large number of state variables, and this inevitably prolongs the slow dynamics with controllers. The centralized control system in a large-scale system cannot be justified from the economical and technical viewpoints. To resolve the foregoing problems, a decentralized voltage control system incorporating slow voltage dynamics is presented.     

Optimal decentralized load frequency control

A new approach for optimal decentralized load frequency control of a multi-area interconnected power system is presented, which includes the optimal design of a decentralized load frequency controller, an observer for unmeasurable local states and load disturbances, and a quadratic estimator for tie-line power flow information transmitted at intervals. The optimal design of the decentralized controller is based on a modified application of the singular perturbation theory, and the decentralized Luenberger observer uses techniques of state augmentation for exponential disturbance functions and the representation of tie-line power flows as indirectly controlled inputs. The approach presented herein is tested numerically through a two-area load frequency system model, and the results demonstrate remarkable advantages over the conventional ones.     

应用于电厂鼓风机变频运行的MMC控制技术研究

鼓风机是发电厂锅炉的重要辅助设备,采用高压变频器对鼓风机进行变频调速能够极大提高效率,减小损耗。对一种基于MMC的高压变频器结构进行研究,提出了相应的控制策略,并对提出的控制策略进行了仿真和实验研究,仿真和实验结果验证了所提出控制策略的正确性和实用性。     

火电厂全厂负荷优化分配及其控制方式的研究

在全厂负荷经济分配的基础上,引入变负荷成本的概念,提出了解决AGC频繁变负荷情况下全厂负荷优化分配及控制的策略,并提出了一些具体的实施方案。全厂负荷优化控制系统能根据电网负荷指令调节全厂负荷,及时满足电网要求,保证机组运行在允许的负荷范围内和安全的工况下,合理地调配各台机组的负荷调节任务,降低机组的负荷调节频度,提高机组的稳定性,延长主、辅机组设备的寿命,经济分配各台机组的负荷,降低全厂的供电煤耗。     

Decentralized exciter stabilizing control for multimachine power systems

In this paper, a systematic approach to design controllers based on H‐infinity theory for a multimachine power system is presented. Generally, a centralized control scheme is difficult for a large‐scale interconnected power system because of the necessity of obtaining information on the whole system, computation times, and so on. In order to handle these problems, two decentralized control schemes are proposed. One is based on the decomposition of information. The feedback gains for the whole system are obtained, and after decomposing the gains into subblocks for each area, the diagonal block is used to design the controller for each generator. The other is based on area decompositions. The procedure is carried out by decomposing the original system into blocks for each area and the local feedback gain is obtained by using information for each decomposed system. Furthermore, to improve the robustness of the system, an effective weighting matrix design, which involves the allocation of eigenvalues, is also proposed. Several simulation tests show the effectiveness of the proposed methods. © 2002 Scripta Technica, Electr Eng Jpn, 139(1): 35–43, 2002; DOI 10.1002/eej.1144     

Decentralized adaptive backstepping control of electric power systems

In this paper, a decentralized adaptive backstepping excitation controller, tuned using a Particle Swarm Optimization technique (PSO), is designed for stability enhancement of multi-machine power systems. To achieve decentralization, each machine is modeled as an independent uncertain dynamic subsystem, where the uncertainty is a disturbance that represents the effects of the rest of the system on that particular machine. This disturbance is expressed as a polynomial function of electric power deviation, and its parameters are adapted using PSO. The proposed technique is illustrated with a two-area benchmark power system. This system exhibits inter-area oscillations which are effectively damped with the proposed decentralized controllers under severe contingencies, for which traditional power system stabilizers fail.     

Decentralized two-level excitation control of multimachine power systems

A two-level decentralized scheme for the excitation control of multimachine power systems is presented. The control strategy is based on decomposing the control signal for each machine into two components generated by controllers at two different levels. At the first level, controllers are designed to optimize the performance of each generating unit, totally ignoring the couplings among the machines. The second control components are chosen to reduce the machine performance degradations due to the presence of interactions. With the developed two-level control scheme each machine is controlled entirely from its own state. The effectiveness of the proposed approach is illustrated by a numerical example involving a four-generator system.     

变频调速装置在某电厂高压电动机上的应用

广州某电厂现有2×125MW国产燃煤发电机组,为了实施企业"十一五"节能降耗规划,提高经济效益和社会竞争力,自2007年起,该厂对生产现场部分旋转机械(如:引风机、低加疏水泵、给粉机等)的电动机进行了变频调速改造。本文以锅炉4台引风机的高压电动机为例,对其改造前后的能耗状况进行阐述与分析对比。     

风机变频改造节能技术在火电厂的应用研究

在机组不同负荷下，通过风机工频和变频运行方式特性试验，定量地说明了风机变频改造的节能效果。河南3家电厂风机变频改造后运行实践表明风机变频调节方式运行，性能稳定可靠，能满足机组各种负荷需要；对风机变频器运行测试结果显示风机变频改造后运行中产生的谐波量较少，未对电厂一、二次系统产生明显影响，符合有关国际要求。     

Impact of energy storage system on load frequency control for diverse sources of interconnected power system in deregulated power environment

This paper focuses Load Frequency Control (LFC) mechanism for multi-generating two areas interconnected power systems with energy storage system in a deregulated power environment. The two areas, demarcated as Area-I and Area-II, consist of thermal, hydro and gas power units. This paper also incorporates the economic load dispatch mechanism into the LFC for economical division of load during load deviation. Small signal stability analysis through participating factor has also been done to determine the oscillation state of the system, i.e., frequency deviation in both areas. Therefore, proper controller is required to reduce the oscillation of the system. The optimum value of the integral gain of the integral controller has to be selected to achieve the goal. Hence, Opposition-based Harmonic Search (OHS) technique is used for the optimization purpose. During major disturbance in the areas, primary and secondary controllers are not sufficient to reduce the frequency and tie-line power oscillation due to slow response of the governor mechanism. Therefore, energy storage system, i.e., Redox Flow Battery (RFB), is used for improvement of the dynamic response of the system which has very small time constant and quick response. The proposed control mechanism has been analyzed in a deregulated power environment with the help of different simulation case studies to find out improved dynamic performance over integral control strategies.     

Decentralized control based on equilibrium point control for a three-machine electric power model system

Electric power systems have become larger and more complex year by year, and the number of decentralized power sources is rapidly increasing, Tberefore, to guarantee high reliability and security, decentralized control based on the decentralization of power systems needs to be developed. In this paper, a decentralized system is constructed by viewing the whole system from the perspective of the generator-bus with the largest power. Since the decentralized system is identified as a one-machine infinite-bus power model system with AVR and GOV, the equilibrium point control, proposed by the authors for a one-machine system, can be applied to it. Control inputs u_a · u_g for AVR · GOV are determined, and the equilibrium points of the decentralized system can be moved by changing the feedback gains. In particular, the unstable equilibrium point is set near the outside of the limiters for AVR · GOV, and stability in the limiters is guaranteed. Thus, it is shown that, by repeating the same steps for other generators, decentralized control for the three-machine model system can be attained. © 1998 Scripta Technica. Electr Eng Jpn, 122(3): 28–36, 1998     

LNG调峰电厂负荷优化分配的应用探讨

对于多机组的燃气-蒸汽联合循环调峰电厂,机组间负荷的合理分配直接关系到电厂运行的经济性.通过对惠州天然气电厂3×390 MW机组DCS运行数据进行分析,拟合构建了各机组燃耗特性函数,提出了在AGC指令下结合等微增率法进行机组负荷优化分配方法.计算结果表明,在机组非额定工况下采用该方法分配负荷的燃耗较单纯采用AGC指令分配有一定降低,可得出更经济的运行组合方式.