Power system security enhancement by OPF with phase shifter

This paper presents an integrated optimal power flow (OPF) with phase shifter approach to enhance power system security. The general OPF calculations are hourly based and the control variables of OPF are continuous. However, the calculations of phase shifter are daily based, and the variables related to phase shifter are discrete. Therefore, the general OPF cannot be directly used to solve this problem. The paper develops the rule-based OPF with phase shifter scheme to bridge the problems. In order to effectively alleviate the line overloads, the ranking of phase shifter locations is conducted based on contingency analysis and sensitivity analysis. The best phase shifter sites are identified and selected into a rule-based system accordingly. The handshaking procedure between the adjustment of the selected phase shifters and OPF calculation is proposed using a rule-based method. The hourly-based OPF problem is solved by the extended quadratic interior point method. The IEEE 30-bus system is used to test the proposed scheme     

Power system stability enhancement by static var system using self-commutated inverters

This paper deals with static var compensators using self-commutated inverters (which is so-called SVG) compared with conventional SVC and Rotary Condenser. Improvement of power system stability is explained by using simple system model and checked by dynamic digital simulation. In the latter part of this paper, system outline, basic specifications and control diagram of the SVG rated 154 kV, ±80 MVA, which has been installed at INUYAMA Switching Station, are briefly presented. Field tests at INUYAMA verify that power swing is effectively damped and transmission capacity is increased.     

Power system transient stability enhancement by optimal control of static VAR compensators

A study of power system transient stability enhancement through the effective use of static VAR compensators is presented. The optimal control strategy resulting from the direct Lyapunov method and Pontryagin's maximum principle requires a control signal based on the state variables not available at the compensator bus. It is proved that this optimal signal can be replaced by the time derivative of an electric quantity derived from local measurements. A control algorithm based on this quantity gives smooth and very effective regulation. Tests done for two-machine and multi-machine systems have confirmed the validity and robustness of the proposed control algorithm.     

Power system stabilization by superconducting magnetic energystorage with solid-state phase shifter

In this paper, a new configuration of power system controller with a combination of superconducting magnetic energy storage and phase shifter, is proposed to improve the stability of a long distance bulk power transmission system. A power system stabilizing control scheme is also proposed. A related simulation shows that the proposed controller is effective for enhancement of power system stability independent of the location of the controller in a long distance bulk power transmission system     

Enhancement of interconnected power system stability using a control strategy involving static phase shifters

The static phase shifting transformer is one of the potential options of the recently proposed FACTS (flexible AC transmission systems). Promising results have been obtained for enhancing the small-disturbance and the transient stability of interconnected power systems.

In this paper, the important concept of involving in the same control strategy both generating units and static phase shifters has been considered. A systematic procedure for designing co-ordinated and decentralized controllers of these components is provided to assure a satisfactory dynamic performance of an interconnected power system under both small and large perturbations. The approach uses optimal control theory as a basis for the co-ordination of static phase shifter and governor controllers. A suboptimal decentralized control scheme is derived from the designed optimal controller by using a ‘minimum norm’ nearness criterion. The resulting feedback control signals for each generating unit and for each phase shifter is expressed in terms of measurable and local variables only.

Test results show the effectiveness of the proposed control strategy and the usefulness of control actions on static phase shifters.     

移相器自动测试系统

移相器是相控阵雷达中用于实现波束移相功能的基本电路.本文描述移相器自动测试系统的原理和组成,着重介绍了测试夹具、控制电路、驱动和测试软件设计等关键技术.经过实际应用证明,该测试系统通用性好,自动化程度高,很容易实现移相器的自动测试需求,为移相器的研制和验收提供了极好的测试手段.     

Loop power system control by high-speed phase shifter

Recently, power systems have become larger and more complex. Particularly, the looping of power systems is becoming highly desirable to improve the stability. The main features of such looped power systems are: (i) comparatively fewer losses; and (ii) improved angle stability as well as voltage stability. However, these systems have demerits, such as, in case of route off fault in a loop power system, power disturbances increase more and more, etc. If these demerits are overcome, the loop power systems are going to be more beneficial. In an attempt to obtain a solution to such problems, this paper describes several results of applying a high-speed phase shifter in the control system of a loop power system.     

Power system stabilizing control by a superconducting magnetic energy storage with a high-speed phase shifter

Electric power demand has increased rapidly and this is expected to continue. Undamped power swings with low frequency tend to occur in large power systems with complex configuration. Therefore, several stabilizing control schemes, e.g., a power system stabilizer (PSS), have already been investigated. On the other hand, superconducting magnetic energy storage (SMES) is expected to be an effective apparatus in power systems since any SMES located in power systems is capable of leveling load demand, compensating for load changes, maintaining bus voltages and stabilizing power swings. The effectiveness of each function, however, depends upon the location of the SMES in the power system because output power from the SMES is distributed according to the impedance ratio of the transmission line at the SMES location. Therefore, it is difficult for SMES to serve two different purposes simultaneously. This paper proposes a combination of SMES with a high-speed phase shifter (HSPS). The HSPS, which consists of a phase shift transformer and a set of power converters, is capable of controlling the power flow of the transmission line by adjusting the phase angle of a phase shift transformer. Therefore, it is expected that the combination of SMES and HSPS can realize a highly effective controller independent of its location. Numerical examples demonstrate that the proposed apparatus located far from a generator in a long distance bulk power transmission system is capable of stabilizing the power swing as effectively as the SMES located at a generator terminal. In addition, the effectiveness of both load change compensation and power system stabilization is confirmed numerically.     

Dynamic and static voltage stability enhancement of power systems

The static voltage stability and the dynamic voltage stability are integrated. To consider a shunt compensator and/or a more general load which is dependent on voltage, a modified criterion for the static voltage stability is developed and the system is controlled to satisfy this static stability criterion. For an accurate analysis of the dynamic voltage stability, the system model includes excitation systems, tap-changers, capacitors and power system stabilizers in addition to network equations. A parameter optimization technique with a modal performance measure is developed to determine optimal control parameters for dynamic voltage stability enhancement     

Power system transient stability enhancement by STATCOM with nonlinear H∞ stabilizer

A robust control design is presented for a single machine infinite bus system (SMIB) with a STATCOM. The controller for the nonlinear system is designed using the recently developed nonlinear H_∞ theory. The approach combines state feedback exact linearization with linear H_∞ principle, which avoids the difficulty of solving Hamilton–Jacoby–Issacs inequality. Simulation results with a number of disturbances like torque pulses and three-phase faults on the generator show that the proposed robust controller can ensure transient stability of the power system over a wide range of operating points     

Power system transient stability margin estimation using neural networks

This paper proposes a methodology for estimating a normalized power system transient stability margin (ΔV_n) using multi-layered perceptron (MLP) neural network with a fast training approach. The nonlinear mapping relation between the ΔV_n and operating conditions of the power system is established using the MLP neural network. The potential energy boundary surface (PEBS) method along with a time-domain simulation technique is used to obtain the training set of the neural network. Results on the New England 10-machine 39-bus system demonstrate that the proposed method provides a fast and accurate tool to evaluate online power system transient stability with acceptable accuracy. In addition, based on the examination of generators rotor angles after faults, a method is presented to select the power system operating conditions that most effect the ΔV_n for each fault.     

Power system stability improvement using dynamic output feedback compensators

A novel approach is presented for the design of physically realizable dynamic output feedback compensators for linear time-invariant single-input single-output systems. The simplicity and effectiveness of the proposed method is demonstrated by an example of feedback compensator design for a power system.     

Power system damping enhancement using unified power flow controller (UPFC)

The Unified Power Flow Controller (UPFC) can inject voltage with controllable magnitude and phase angle in series with a transmission line. It can also generate or absorb controllable reactive power. UPFC is expected to be able to damp power system oscillations more effectively than power electronics devices such as SVG and TCSC. In this paper, a control system design of a UPFC for power system damping enhancement based on the eigenvalue control method is proposed. It is made clear that the best design method for the power system damping enhancement is to determine steady‐state values of the UPFC control variables and the control parameters of the UPFC such as gains and time constants simultaneously, because the controllability of UPFC depends on the steady‐state values of UPFC and the power flow condition. The effectiveness of the proposed control system taking into account UPFC inverter ratings is verified by digital time simulation. Furthermore the effects of the input signals to the UPFC controller on small‐signal stability and transient stability enhancement are studied, and it is made clear that UPFC controllers using global information are more effective for power system damping enhancement than those using local information because global information has stronger observability for power system oscillations than local information. © 2000 Scripta Technica, Electr Eng Jpn, 133(3): 35–47, 2000     

Development of a large static VAr generator using self-commutatedinverters for improving power system stability

A static VAr generator (SVG) using self-commutated inverters of 80 MVA capacity was developed and successfully applied to an annual 154 KV power system to stabilize the power system. The SVG consists of 48 pulse multiple inverters whereby gate turn-off (GTO) thyristors are applied. After installing it at a power system site, a field test was conducted to confirm the system stabilizing effect. The test results displayed the expected performance, and the SVG was proven to be effective power system stabilizer. The outline of the 80 MVA SVG, technical features, and the test results are described     

Stabilizing interconnected power systems using static phase shifters

This paper presents a digital simulation study of proposed thyristor controlled static phase shifter applications in steady state stability enhancement of interconnected power systems. Incorporation of a detailed linearized model of a static phase shifter into the dynamics of the interconnected power system facilitates the investigation of different control strategies for static phase shifters to damp the electromechanical and torsional oscillations.     

满足静态电压稳定增强要求的发电机最佳调整方法

为增强电力系统的静态电压稳定性,同时最大限度地减小运行人员的操作工作量,提出了一种综合经济性和静态电压稳定性的发电机最佳调整模型。该模型以发电机参与调整台数最少和发电成本最小为目标,约束条件包括系统负荷裕度满足设定提升要求和电力系统安全运行要求。该问题的数学本质是一个多目标非线性混合整数规划问题。为实现上述问题的求解,首先以线性灵敏度方法快速估算所需调整出力的发电机,求解控制数量最少的整数规划问题。然后以发电成本最小为目标,利用线性规划法求解各台发电机的调整出力值。最后在IEEE39节点算例和IEEE118节点算例进行仿真验证,结果表明所提模型与求解方法能很好地解决系统的静态电压稳定性增强控制问题。     

Small signal stability enhancement of DFIG based wind power system using optimized controllers parameters

This paper presents the state space modelling of doubly fed induction generator (DFIG) for small signal stability assessment. The gains of PI controller in torque and voltage control loop of rotor-side converter (RSC) are optimized by particle swarm optimization (PSO) to improve the dynamic performance of DFIG. These optimized parameters results in improved damping of DFIG and minimizes the oscillations in rotor currents and electromagnetic torque. The nature of modes of oscillations for DFIG integrated to infinite bus are analysed under different operating conditions such as varying wind speed and grid strength. The transient analysis with optimized parameters shows the enhancement in LVRT capability during voltage sag and three phase fault as desired by grid codes.     

浙江电网各电厂发电机机组进相对系统稳定的影响研究

简要分析了浙江电网春节全网性高电压形成原因,机组进相作为调压手段所具有的优点及受制因素.从系统角度,研究了不同电厂发电机进相深度对浙江电网暂态稳定的影响程度,提出了可行的发电机深度进相控制策略,经浙江实际系统应用证明:该策略具有较好的适应性、可操作性,对抑制春节假日全网性高电压具有较好效果.