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Controlled resistive loads can contribute to damping of
electro-mechanical oscillations. This paper presents an on-off damping
controller for a single machine system. It was used at a field test in
Southern Sweden to damp oscillations of a 0.9 MW hydro power generator.
The controller used estimated machine frequency as input and controlled
a 20 kW...
Context in source publication
Context 1
... electric water heater is a typical example of a controlled load. It consumes real power and its hot water acts as an energy reservoir that makes short power interruptions uncritical. During the experiments, the heating elements of four 5 kW heating fans (see Fig. 4) were used to simulate water heaters. The switching function of the thermostats was replaced by commercially available three-phase thyristor switches with isolated low voltage control input. A hydro power plant from 1906 owned by Sydkraft was selected for the experiments. The choice was mainly motivated by small machine rating and low ...
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Citations
... The potential of additional damping, system inertia or load voltage sensitivity to mitigate system oscillations has also been investigated in [20,22]. The third aspect is the study of LFO suppression measures, which is the application basis for achieving stable operation of the power system [21,[25][26][27][28]. Although mechanism studies have pointed out a variety of factors that affect LFO, considering the possibility of realization, the suppression measures commonly used for LFO mainly include controller parameter optimization, reduction of the proportion of hydropower in the grid, direct current power support and the addition of power system stabilizers (PSSs) [29][30][31][32][33][34]. ...
In hydropower dominated power systems, low-frequency oscillations (LFO), that challenge the safe and stable operation of the system, occur from time to time. Although the study of system damping is an important way to reveal the mechanism of LFO, relevant analysis is mainly based on simplified models that consider a single scale, leading to an incomplete understanding of the phenomenon. Against this background, a cluster of hydropower units in a real power station is taken in this paper as the research object. Firstly, a refined non-linear model of the hydro-turbine regulation system with the layout of three units sharing one common tailrace tunnel is established and validated based on mechanism analysis and measured data. Then, an accurate quantitative evaluation method of damping for complex systems is proposed to overcome the application limitations of traditional methods. Finally, the variation laws of the damping of a hydropower unit with the hydraulic-electrical network structures and the operating conditions, studied from the scales of hydraulic coupling and electrical coupling, respectively, reveal the influence mechanism of the hydraulic-mechanical-electrical coupling on unit damping. The results show that the increase in the complexity of the hydraulic or electrical network structure will reduce the damping of the hydropower unit, which changes from 1.3860 to -1.3223 for hydraulic factor and from 1.1869 to -0.8817 for electrical factor. The operating conditions of the adjacent units have different degrees of influence on the damping of the unit itself due to their hydraulic or electrical connections. Some measures to suppress LFO are also given.
... A robust design technique of such a controller is explained in section IID. In this paper, thyristor switched control is proposed for controlling the load current [23]. It consists of a thyristor bridge whose firing angle is controlled by the proposed controller. ...
... A washout filter of time constant 5s ensures that the controller only operates at transient state. Similarly, a zero in (23) ensures that the controller has zero dc gain. The responses of the shaped plant and the original plant were compared. ...
Conventional distribution systems are transforming into smarter networks by accommodating renewable energy resources, communication infrastructure and control devices. While the grids are transforming to be smart grids, issues relating to grid stability and control are emerging due to proximity and interactions among generator units and associated controllers. The existence of low damped oscillations could be harmful to power transfer capacity and generator stability. This work presents small signal stability and control issue of emerging distribution systems. A robust control methodology for motor load current is proposed for stability enhancement. System loads are ranked based on their relative influence on small signal instability. The proposed methodology controls current of the selected motor load during system disturbances to improve overall small signal stability of the distribution system. The proposed methodology has been successfully implemented on a 16- bus distribution network.
... heating adjustments to houses, to have a big affect higher up the grid. Such ideas have been suggested for system level control previously [35] and now have potential in the harnessing of new power electronic developments [10]. ...
The topic of smart grids has received a lot of attention but from a scientific point of view it is a highly imprecise concept. This paper attempts to describe what could ultimately work as a control process to fulfill the aims usually stated for such grids without throwing away some important principles established by the pioneers in power system control. In modern terms, we need distributed (or multi-agent) learning control which is suggested to work with a certain consensus mechanism which appears to leave room for achieving cyber-physical security, robustness and performance goals.
... This can be a very effective strategy, since it only deals with the most critical oscillation , and the maximum power rating of FACTS can be used. The effectiveness of this discontinuous control method has long been recognized [13], and can also be applied for active load modulation [14], [15]. The problem of optimal switching time has been studied for simple systems, using nonlinear optimization methods [16], [17]. ...
In this paper, we develop a new damping control scheme for FACTS devices, using bang-bang modulation of FACTS signals. The scheme is used to attenuate quickly the system's most dominant mode which is identified using online Prony analysis. An analysis framework to evaluate the robustness of the control schemes to changes in operating conditions and to time-delay is also proposed. Simulation results on various test systems show that following large disturbances, the proposed control scheme is very effective to mitigate the power system critical modes of oscillation. Furthermore, the problem of control interactions is completely avoided with the proposed control scheme.
... Damping of electro-mechanical oscillations through the control of active power loads was first studied in detail in [112]. References [113,114,115,116] are based on [112]. With respect to the application of direct load control for stability enhancement, [112] examines modal analysis for the selection of load buses for control implementation, selection of appropriate feedback signals for the load controller that capture the poor damping characteristics, type of load controller for load modulation, controller design and practical considerations in implementing direct load control for oscillatory stability enhancement. ...
... The modulation of load is performed at the transmission level of the system. It has also been shown in [116] that on-off modulation is more effective than sinusoidal modulation proportional to frequency for large oscillations. However for small oscillations, sinusoidal modulation is found to be more effective. ...
The transition to a competitive market structure raises significant concerns regarding reliability of the power grid. A need to build tools for security assessment that produce operating limit boundaries for both static and dynamic contingencies is recognized. Besides, an increase in overall uncertainty in operating conditions makes corrective actions at times ineffective leaving the system vulnerable to instability. The tools that are in place for stability enhancement are mostly corrective and suffer from lack of robustness to operating condition changes. They often pose serious coordination challenges. With deregulation, there have also been ownership and responsibility issues associated with stability controls. However, the changing utility business model and the developments in enabling technologies such as two-way communication, metering, and control open up several new possibilities for power system security enhancement. This research proposes preventive modulation of selected loads through direct control for power system security enhancement. Two main contributions of this research are the following: development of an analysis framework and two conceptually different analysis approaches for load modulation to enhance oscillatory stability, and the development and study of algorithms for real-time modulation of thermostatic loads. The underlying analysis framework is based on the Structured Singular Value (SSV or mu) theory. Based on the above framework, two fundamentally different approaches towards analysis of the amount of load modulation for desired stability performance have been developed. Both the approaches have been tested on two different test systems: CIGRE Nordic test system and an equivalent of the Western Electric Coordinating Council test system. This research also develops algorithms for real-time modulation of thermostatic loads that use the results of the analysis. In line with some recent load management programs executed by utilities, two different algorithms based on dynamic programming are proposed for air-conditioner loads, while a decision-tree based algorithm is proposed for water-heater loads. An optimization framework has been developed employing the above algorithms. Monte Carlo simulations have been performed using this framework with the objective of studying the impact of different parameters and constraints on the effectiveness as well as the effect of control. The conclusions drawn from this research strongly advocate direct load control for stability enhancement from the perspectives of robustness and coordination, as well as economic viability and the developments towards availability of the institutional framework for load participation in providing system reliability services.
... Instead of controlling generators, real and reactive power output of HVDC links and FACTS devices can also be modulated to increase damping [2]. A recent alternative is to control non-critical customer loads, typically heating or cooling loads [4][5][6][7][8]10]. The basic idea is to modulate real power loads and thereby affect the real power variations during electro-mechanical oscillations. ...
... The basic idea is to modulate real power loads and thereby affect the real power variations during electro-mechanical oscillations. A field test where a heating load was on-off controlled to damp a local mode in a distribution system is reported in [5]. To increase damping of transmission system modes, a load control damping system could make use of the functions for direct load control being part of many programs for Demand Side Management for peak shaving. ...
Modulation of customer loads for increased power system damping is
suggested as an alternative to control of HVDC links and FACTS devices.
The loads are modeled as real power controlled by local bus frequency,
which is equivalent to viscous damping in a mechanical system. The
qualitative aspects of the interaction between two load modulation
controllers are studied using linearized models of two test systems with
three and twenty-three machines respectively. Root locus plots show that
transfer function zeros limit damping. Tuning a controller for maximum
relative damping is equivalent to impedance matching. This is used to
explain the zero dynamics and why a second controller may not be able to
contribute to added damping. Time simulations of a nonlinear system
model verifies the final design of the controllers for the large test
system
Definition and Scope Who are the Players in Distribution Generation? Prominent Features of DRs Types of DGs Push Factors, Stay-Put Costs, and Investment Prospects for Electricity Investment Options Planning Sites for a DG Operation of DGs in an Electric Power System Islanding of an EPS Section from the Main Body Allowable Penetration Levels by DRs Synchronous Generator as a DG with Excitation Controls How Can a DG Earn Profits? Scope for Gas-Based DGs Diesel Generators Evaluation of Service Rendered by Stand-by DGs Reliability Cost for a DG Set Maintenance and Protection of Diesel Generators UK Policy on Generation of Low-Carbon Electricity References
The Present Scenario Types and Sizes of Hydroelectricity Projects Advantages of Hydroelectricity Slow progress of Hydroelectricity Projects Factors Propelling the Phased Progress of the Hydroelectric Industry Hydro Projects Fall Short of Attracting Private Investment Dam Building Progress Over a Century Desirable Configuration for Hydro Projects to Attract Private Investment Operation of a Hydroelectric Plant Unit Allocation within a Large HE Plant Speed Control of a Water Turbine Startup Process for a WTG Speed Controls are Rigid Speed Increase Due to Sudden Load Cutoff Frequency and Harmonic Behavior After a Sudden Load Rejection Effect of Penstock Pressure Pulsations AC Excitation of Rotor Field Unit Commitment from Hydroelectric Generators, Including Pumped Storage Systems ICMMS of Hydroelectric Generating Units Controls and Communications in hydro Systems General Maintenance Limitations of Scheduled and Breakdown Maintenance Reactive Maintenance—Key Elements Key Components of an ICMMS—Case of a Hydroelectric System Intelligent Electrohydraulic Servomechanism Online Monitoring and Forecasting Subsynchronous Resonance (SSR) and Twisting of Rotor Shafts References
