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A power system is a collection of individual components that compete for system resources. This paper presents a game theoretic approach to the control decision process of individual sources and loads in small-scale and dc power systems. Framing the power system as a game between players facilitates the definition of individual objectives, which adds modularity and adaptability. The proposed methodology enhances the reliability and robustness of the system by avoiding the need for a central or supervisory control. It is also a way to integrate and combine supply and demand side management into a single approach. Examples are presented that use a simple nine bus dc power system to demonstrate the proposed method for various scenarios and player formulations. Index Terms--DC power systems, demand side management, distributed control, distributed energy, game theory, microgrids.

Supervisory control and data-acquisition (SCADA) systems are control systems for many national infrastructures. In the past, SCADA systems were designed without security functionality because of the closed operating environment. However, the security of SCADA systems has become an issue with connection to open networks becoming more common. Any damage to the SCADA system can have a widespread negative effect to society. In this paper, we review constraints and security requirements for SCADA systems and then investigate whether the existing key-management protocols for the SCADA systems satisfy these requirements. Afterward, we propose an advanced key-management architecture fitted for secure SCADA communications. The contributions of our work are two-fold. First, our scheme supports both message broadcasting and secure communication. Second, by evenly spreading much of the total amount of computation across high power nodes (MTU or SUB-MTU), our protocol avoids any potential performance bottleneck of the system while keeping the burden on low power nodes (RTU) at minimal. Index Terms--Key management, power system security, supervisory control and data-acquisition (SCADA) systems.

This paper deals with the important issue of proper treatment of information security for electric power utilities. It is based on the efforts of CIGRE Working Group (WG) D2.22 on 'Treatment of Information Security for Electric Power Utilities (EPUs)' carried out between 2006 and 2008/2009. The WG produces a Technical Brochure (TB), where the purpose is to emphasize three main issues: Security Frameworks, Risk Assessment, and Security Technology. Here, guidance is given on different Security Frameworks based on an Information Security Domain Model. Also, baseline controls are treated. For Risk Assessment, a survey has been carried out. Only few commonalities, but several differences, have been found. Here, a methodology must be developed together with practical recommendations. For Security Technologies, guidance is given for deployment of different solutions, based on a logical diagram using different controls. Last, proposal on further work is given. Index Terms--Communication systems, control systems, cyber security, information security, ISO/IEC standard, IT security, power system communications, power system control, power systems, risk assessment, SCADA, security framework, security technology, substation automation.

This paper proposes an optimization-based method of planning reactive power control for electric transmission systems to endow them with the capability of being reconfigured to a secure configuration under a list of contingencies. The overall objective function is to minimize the installation cost of new controls such as mechanically switched capacitors, while satisfying the requirements of voltage stability margin and voltage magnitude under a contingency list. The backward/forward search algorithm with linear complexity is used to select candidate locations for switched capacitors. Optimal locations and amounts of new switch controls are obtained by solving a sequence of mixed integer programming problems. The modified New England 39-bus system and a North American power system with 6358 buses are adopted to illustrate the effectiveness of the proposed method. Index Terms--Mixed integer programming, reactive power planning, reconfiguration, voltage stability.

To study the competitive behavior among individual generating companies (GENCOs), an incomplete information game model is proposed in this paper in which each GENCO is modeled as an agent. Each agent makes strategic generation capacity expansion decisions based on its incomplete information on other GENCOs. The formation of this game model falls into a bi-level optimization problem. The upper level of this problem is the GENCOs' own decision on optimal planning strategies and energy/reserve bidding strategies. The lower-level problem is the ISO's market clearing problem that minimizes the cost to supply the load, which yields price signals for GENCOs to calculate their own payoffs. A co-evolutionary algorithm combined with pattern search is proposed to optimize the search for the Nash equilibrium of the competition game with incomplete information. The Nash equilibrium is obtained if all GENCOs reach their maximum expected payoff assuming the planning strategies of other GENCOs' remain unchanged. The physical withholding of capacity is considered in the energy market and the Herfindahl-Hirschman Index is utilized to measure the market concentration. The competitive behaviors are analyzed in three policy scenarios based on different market rules for reserve procurement and compensation. Index Terms--agent modeling, generation expansion, market design, market power, noncooperative game, physical withholding, power system planning.

We propose a component model for the scheduling of combined-cycle gas turbine (CCGT) units by mixed-integer programming (MIP) in which combustion turbines (CTs) and steam turbines (STs) are modeled as individual units. The hourly schedule of CCGT based on the component model is compared with that of the mode model. The modeling of modes, which includes a combination of CTs and STs, would require certain approximations for representing fuel input-power output curves, ramping rate limits, minimum operating time limits, etc. The approximations can result in sub-optimal schedules. Furthermore, the commitment and dispatch of CCGTs based on the mode model will require a real-time dispatch to individual CT and ST components of CCGT. In comparison, the mode modeling approximations will no longer be required in the component model as individual CTs and STs are modeled and dispatched. The enhancement tools such as duct burners, foggers, and peak firing for increasing the CCGT output can be easily modeled in the component model. Case studies show that the proposed component model is effective for representing CCGTs, and verify that the proposed component model can potentially save CCGT operating costs. Numerical simulations in this paper also demonstrate the application of the component model of CCGT to schedule a cogeneration unit. Index Terms--Combined-cycle gas turbine, component model, mixed-integer programming, mode model, short-term unit commitment, state transition diagram.

In the framework of liberalized electricity markets, distributed generation and controllable demand have the opportunity to participate in the real-time operation of transmission and distribution networks. This may be done by using the virtual power plant (VPP) concept, which consists of aggregating the capacity of many distributed energy resources (DER) in order to make them more accessible and manageable across energy markets. This paper provides an optimization algorithm to manage a VPP composed of a large number of customers with thermostatically controlled appliances. The algorithm, based on a direct load control (DLC), determines the optimal control schedules that an aggregator should apply to the controllable devices of the VPP in order to optimize load reduction over a specified control period. The results define the load reduction bid that the aggregator can present in the electricity market, thus helping to minimize network congestion and deviations between generation and demand. The proposed model, which is valid for both transmission and distribution networks, is tested on a real power system to demonstrate its applicability. Index Terms--Air-conditioning, load management, optimal control.

Flexible ac Transmission Systems (FACTS) play an important role in improving the transfer capability and stability of a power system. In the application of voltage-sourced converter (VSC)-based FACTS controllers, it is important to study how a VSC impacts the flows in a power system. In this paper, we investigate this flow control problem using two sensitivity approaches, one using an injected voltage source formulation and the other an equivalent impedance formulation. The applications of sensitivity analysis for line active power redispatch and for new series VSC siting in a 1673-bus system are presented. Index Terms--Equivalent impedance, FACTS controllers, sensitivity analysis, voltage source model, voltage-sourced converter.

Complexities of computer program codes for Newton--Raphson load flow (NRLF) analysis are usually enhanced during power flow modeling of an interline power flow controller (IPFC). This is due to the fact that the contributions of the series converters of the IPFC are needed to be accounted for while computing bus power injections and Jacobian matrix elements. Also, the IPFC real power injection term along with its associated Jacobian matrix call for new codes to be written. In this paper an advanced IPFC model is proposed to address this issue, wherein an existing power system installed with IPFC(s) is transformed into an augmented equivalent network without any IPFC. To obtain the solution of the original network containing IPFC(s), the augmented network can easily be solved by reusing the existing NRLF codes, as this network is now devoid of any IPFC. Consequently, the complexities of the computer program codes are reduced substantially. Various practical device limit constraints of the IPFC can also be taken into account by the proposed model. Index Terms--Flexible ac transmission systems (FACTS), interline power flow controller (IPFC), Newton power flow.

Harmonics are one of the major quality concerns. The increasing use of power semiconductor devices (i.e., nonlinear loads) is keeping harmonic distortion in electrical installations on the rise. Harmonics generally cause the distortions of voltage and current waveforms, which result in many harmful effects on both utilities and customers. A parallel active harmonic conditioner can be used to compensate current harmonics demanded by nonlinear devices so that the supply current remains quasi-sinusoidal. In principle, this conditioner consists of a voltage-source inverter connected in parallel between the utility system and the customer. The control of such an inverter is an essential step in harmonic compensation. Most of the existing control methods are formulated as a classical tracking problem that requires reference generation. In a previous work, a parallel active harmonic conditioner was formulated as a perturbation rejection problem rather than a reference tracking one, and a linear state feedback [H.sub.[infinity]] controller was synthesized in order to drive the inverter. The objective of this paper is to reduce the number of measured outputs, and therefore to design a linear output feedback [H.sub.[infinity]] controller by noniterative means. The robustness of such a controller with respect to the system impedance uncertainties is investigated. Moreover, the validity of the synthesized output feedback control law is revealed through both simulation and experimental results. Index Terms--Harmonics, output feedback control, perturbation rejection problem, power quality, shunt active filter.

This paper establishes the linearized Phillips-Heffron model of a power system equipped with UPFC and demonstrates the application of the model in analyzing the damping effect of the UPFC and designing UPFC based stabilizer to improve power system oscillation stability. A comprehensive approach to the design of UPFC based stabilizer (power flow control, DC-voltage regulator and damping controller) is presented. In this case, the multi-machine power system with UPFC is studied and an example of power system is presented. It is shown that the DC voltage contributes negative damping to power system oscillations, which is confirmed by both eigenvalue computation and nonlinear simulation. To counterattack the negative damping effect due to the DC voltage regulator, UPFC based stabilizer is designed and its effectiveness is demonstrated by both eigenvalue computation and nonlinear simulation. Then the effects of UPFC and PSS on power systems are compared. Simulation results show that the performance of UPFC based stabilizer on damping of power system is better than PSS. Key words: Phillips-heffron model, UPFC, stabilizer, PSS, INTRODUCTION The Unified Power Flow Controller (UPFC) is a FACTS device which can control power system parameters such as terminal voltage, line impedance and phase angle (1-2). The primary function [...]

A conventional power system stabilizer (PSS) can improve the steady-state stability margin and increase the system positive damping, but it has some drawbacks, such as the time-consuming tuning and nonoptimal damping in the entire operating process. A proportional--integral (PI) adaptive control law in simple adaptive control (SAC) can overcome these drawbacks. However, it can only be applied to the plants with almost strict positive realness (ASPR), and the computation of adaptive control law is really complex. A new improved SAC (ISAC) based on quadratic performance index was proposed. A new PSS can be designed using the ISAC. The simulation and experimental results show that this stabilizer possesses good dynamic characteristics and regulation precision. They also show that the new PSS can improve the dynamic stability of the power system and suppress the low-frequency oscillation effectively. Index Terms--Almost strict positive realness (ASPR), improved simple adaptive control (ISAC), model reference adaptive control (MRAC), parallel feedforward compensator, power system stabilizer (PSS), simple adaptive control (SAC).

This paper presents allocation of energy losses to consumers connected to radial distribution networks in a deregulated environment. A detailed comparison of the proposed 'Exact Method' with three alternative algorithms, namely, pro rata, quadratic allocation and proportional allocation are presented. Pro rata procedure is based on the load demand of each consumer, quadratic and proportional allocations are based on identifying the real and reactive parts of current in each branch and the losses are allocated to each consumer, and the proposed 'Exact Method' is based on the actual contribution of real power loss by each consumer. A case study based on a 30-node distribution system is provided. Index Terms--Deregulation, energy loss allocation, radial distribution systems.

This paper describes a novel stabilizing control strategy for dc power systems with constant power loads. The destabilizing element associated with a constant power load is eliminated by reformulating the system dynamic equations in terms of the rate of change of energy, or instantaneous power. A power shaping control strategy is employed to regulate the output voltage, while essentially maintaining large-signal system stability with increased region of attraction. The proposed control strategy is simple and easy to design and implement. Its utility and effectiveness are demonstrated by simulations and experiments. Index Terms--DC power systems, power system control, power system stability.

In order to be able to successfully apply interline power flow controllers (IPFCs) for power-system transient-stability improvement and for the damping of oscillations, proper control strategies should be applied to these devices. The basis for the implementation of such a strategy that is proposed in this paper is to know the energy function of a power system that includes IPFCs. Already-known energy functions that proved to be suitable for an electric-power system do not include such a device. Therefore, in this paper an energy function that considers the IPFC's action in the form of a supplement to the already-known structure-preserving energy functions was constructed. Furthermore, the strategy for implementing the newly developed IPFC energy functions in order to ensure a globally optimum control strategy in the Lyapunov sense is presented. The results of the numerical examples show that the magnitudes of the IPFC's series-injected voltages remain set to their maximum values and that only the angles of these voltages change, similar to the 'bang-bang' control strategies proposed for some other FACTS devices. Index Terms--FACTS devices, interline power flow controller (IPFC), Lyapunov energy function, power system control, power system dynamic stability.

In this paper, a robust sensor and actuator fault detection and isolation (FDI) method based on unknown input observers (UIO) is adopted and applied to the load frequency control loops of interconnected power systems. Changes in load demand are regarded as the unknown disturbances in the system and the designed UIOs and thus the proposed method are robust to these disturbances. Using selected different sets of measured variables in the UIO design, simulations are performed for the dynamical model of a power control system composed of two areas. As we distinguish the cases for successful and unsuccessful sensor and controller FDI, it is shown that the proposed scheme is able to detect and isolate sensor and controller faults for proper selections of measured variables. By using residuals generated by the UIOs, the designed 'fault detection and isolation logic' system shows the operator which sensor or controller is faulty. Hence the faulty sensor or controller can be replaced by a healthy one for a more reliable operation. Index Terms--Fault diagnosis, load frequency control, power system operation.

Using an energy-based method, this paper investigates the [L.sub.2] disturbance attenuation excitation control of multimachine power system connected with constant power loads. First, a general result is presented for the [L.sub.2] disturbance attenuation control of nonlinear differential algebraic systems with dissipative Hamiltonian realization. Then, pre-feedback is employed to transform the power system into a dissipative Hamiltonian form. Based on this, a decentralized [L.sub.2] excitation control scheme is proposed to improve the transient stability of the system. Simulation results demonstrate the effectiveness of the controller. Index Terms--Dissipative Hamiltonian realization, [L.sub.2] disturbance attenuation, multimachine multiload power systems, nonlinear differential algebraic systems.

New approach based on structured singular value ([mu]-synthesis) was proposed for the robust decentralized unified power flow controller (UPFC) design. To achieve decentralization, using the Schauder fixed point theorem the synthesis and analysis of multi-input multi-output (MIMO) control system translated into a set of equivalent multi-input single-output (MISO) control system. Power systems similar to other industrial plants contain different kinds of uncertainties which should be considered in controller design procedure. For this reason, the idea of [mu]-synthesis technique being used for designing of UPFC controllers. The proposed [mu]-based controller had a decentralized scheme and advantage of a decentralized controller design reduction in the controller complexity and suitability for practical implementation. The effectiveness of the proposed control strategy evaluated under operating conditions on damping of low frequency oscillations in comparison with the classical controller to demonstrate its robust performance through nonlinear time simulation and some performance indices. Key words: Unified power flow controller, decentralized control, [mu]-synthesis, Flexible Ac Transmission Systems (FACTS), robust control, structured singular value, INTRODUCTION In recent years, the fast progress in the field of power electronics has opened new opportunities for the power industry via utilization of the controllable FACTS devices such as [...]

A new approach to improve the reconfiguration operations of distribution systems is presented in two papers. In this first part n economic dispatch (ED) through radialization method for medium voltage (MV) distribution networks with several alternative supply points and several energy prices is presented. The optimization criterion is based on energy purchase cost minimization to supply both the load and the loss. The ED through radialization (EDR) method assesses the economic impact of different energy prices for alternative supply points on the operative radial topology for a specific load level. Capacity limits of supply points and MV lines are considered, as well as the quality technical product using ac power flow calculations. The results obtained for a distribution network widely used in the literature show the effectiveness of the proposed methodology. The second part presents a methodology to determine the optimal reconfiguration plan for short and medium terms. This approach integrates purchase and switching costs associated to the reconfiguration plan. Index Terms--Ac power flow, economic dispatch, energy price, loss, minimization costs, network reconfiguration, radialization.

This paper presents a very efficient, two-stage method for the distribution system reconfiguration for loss minimization. The efficiency of the method stems from the use of real power loss sensitivity with respect to the impedances of the candidate branches. The proposed method uses these sensitivities in the first stage. A branch exchange procedure is used in the second stage to refine the solution. Results for five test systems have been obtained with the proposed method in order to demonstrate the effectiveness of the algorithm. Index Terms--Distribution system, loss minimization, network reconfiguration, sensitivity.

In this paper, the concepts related to loss partitioning among the phase currents in three-phase distribution systems are revisited in the light of new findings identified by the authors. In particular, the presence of a paradox in the classical loss partitioning approach, based on the use of the phase-by-phase difference between the input and output complex power, is highlighted. The conditions for performing effective loss partitioning without the occurrence of the paradox are thus established. The corresponding results are then used to extend the branch current decomposition loss allocation method for enabling its application to three-phase unbalanced distribution systems with distributed generation. Several numerical examples on a three-phase line with grounded neutral and on the modified IEEE 13-node test system are provided to assist the illustration and discussion of the novel conceptual framework. Index Terms--Distributed generation, distribution systems, loss allocation, loss partitioning, losses, paradox, unbalanced systems.

In this paper, a grid-connected distributed generation system, which consists of engine-generator, dc link with multiple energy sources, and inverter, is proposed. All six of the stator leads of the generator, which is the surface-mount permanent-magnet machine, are brought out to the terminal of the generator. Three leads are connected to the inverter, and the others are connected to the utility grid. In this proposed system, the power from the engine-generator and the power from dc link can be controlled simultaneously by only one three-phase power converter. Furthermore, the inductance of the generator functions also as the reactor of ac--dc converter. A control algorithm for the system is developed and verified by experimental results. Index Terms--Distributed generation system, enginegenerator, open-winding machine.

This paper sets forth and demonstrates an approach to the design of power electronics based power systems using evolutionary computing techniques. Key features of the paper are the use of evolutionary computing in the context of classical control design, construction of appropriate multievent based performance metrics, and the use of multiobjective evolutionary computing in the selection of control parameters based on system performance versus control effort. The proposed approach is demonstrated in a power electronics based power distribution system similar to those being designed for next generation warships. Index Terms--Evolutionary algorithms (EAs), optimization methods, power electronics, power system controls.

The reactive power capability of wind generation (WG) producers can be used to provide volt/voltampere reactive (var) support in electrical distribution systems. In practice, the distribution network operator (DNO) is not able to dispatch reactive power of all generators, and such units are referred to as nondispatchable generators. Then, the reactive power of these nondispatchable generators is not a defined value, and it should accomplish the limits settled by national grid codes. This paper addresses the optimal reactive power provision of nondispatchable WG units under a loss allocation strategy based on incremental generation use of the system (GUoS) tariffs. The optimization problem is set from generators' viewpoint aiming to find the reactive power provision that minimizes the loss charges subject to operational constraints. Optimal solutions are compared with the DNOs mandatory dispatches using a reactive optimal power flow tool. Two test systems are analyzed: a 10-kV 28 bus and 60-kV 55-bus system throughout 672 and 168 h, respectively. The proposal permits to identify which units can be dispatched by the DNO due to its effect on the network. Index Terms--Loss allocation, losses, mathematical programming, reactive power, wind power generation.

At high-frequency applications, the gate drive loss of the power metal oxide semiconductor field-effect transistor (MOSFET) becomes quite significant. A new dual-channel low side resonant gate drive circuit is proposed in this paper. The proposed drive circuit can provide two symmetrical drive signals for driving two MOSFETs. It charges and discharges the MOSFET gate capacitor with a constant current source. Both gate drive loss and, more importantly, switching loss can be reduced significantly. The proposed resonant gate drive circuit can be used to drive the synchronous MOSFETs in a current doubler or full-wave rectifier configuration. It can also be used to drive the primary MOSFETs in push-pull converters. Analysis, computer simulation, and experimental results show that significant power loss reduction is achieved by the proposed circuit. Index Terms--Gate drive loss, MOSFET driver, resonant gate drive circuit, switching converters, switching loss.

In this paper, two different approaches are applied to the Hydro-Quebec network in order to select the most effective signals to damp inter-area oscillations. The damping is obtained by static var compensator (SVC) and synchronous condenser (SC) modulation. The robustness analysis, the simulations, and statistical results show, unambiguously, that in the case of wide-area signals, the geometric approach is more reliable and useful than the residues approach. In fact, this study shows that the best robustness and performances are always obtained with the stabilizer configuration using the signals recommended by the geometric approach. In addition, the results confirm that wide-area control is more effective than local control for damping inter-area oscillations. Index Terms--Compensator, control loop selection, geometric measures, inter-area oscillations, power system stabilizer, residues, wide-area control.

A novel power system frequency control strategy is designed in this paper, which is mainly used to improve the stability of the islanding power system. Detecting the change of circuit breaker status, it is feasible to identify the serious accidents, for instance, a generator outage or disconnection from main grids, and so on. The balanceable power before disturbance and the capacity of the removed power can be used to calculate the power deficiency. Then, appropriate load can be shed adaptively. In the subsequent regulating process, adapting to the various stages of frequency variation, the concepts of rough-adjusting step and fine-adjusting step are proposed to obtain a balance between shedding loads quickly and refining the load shed in every step. The concept of proportional-integral-differential (PID) is introduced to design a closed-loop control strategy to trace frequency variation, with which a balance between restraining the sharp drop of frequency effectively and releasing the reserved system capacity thoroughly can be obtained. Moreover, the frequency recovery curve can be optimized and the dead zone of control during the frequency rising stage can be avoided. Compared with the conventional under-frequency loading shedding (UFLS) schemes, the effectiveness of the control strategy presented has been verified by EMTDC simulation tests. Index Terms--Emergency pick-up step, fine-adjusting step, proportional-integral-differential (PID) closed-loop control, rough-adjusting step, under-frequency loading shedding (UFLS).

State estimation uses measurements to obtain important power system operating information ('states'). This paper uses a tabular representation to quantify the effects of measurement failure (i.e., sensor failure or measurement communications failure). The concept of a measurement outage table is introduced to evaluate the state estimator performance under measurement failure conditions. The concept of a condition indicator is used and this includes a study of certain elements of the singular spectrum of the state estimator process matrix. Examples are shown to illustrate the concept. The analysis also shows that using condition indicators for measurement placement may improve the response of the state estimator under measurement failure conditions. Index Terms--Condition number, eigenvalues, phasor measurement unit (PMU), power system measurements, singular values, state estimation, synchrophasor.

In distribution systems, network reconfiguration and capacitor control, generally, are used to reduce real power losses and to improve voltage profiles. Since both capacitor control and network reconfiguration belong to the complicated combinatorial optimization problems, it is hard to combine them efficiently for better optimization results. In this paper, a joint optimization algorithm of combining network reconfiguration and capacitor control is proposed for loss reduction in distribution systems. To achieve high performance and high efficiency of the proposed algorithm, an improved adaptive genetic algorithm (IAGA) is developed to optimize capacitor switching, and a simplified branch exchange algorithm is developed to find the optimal network structure for each genetic instance at each iteration of capacitor optimization algorithm. The solution algorithm has been implemented into a software package and tested on a 119-bus distribution system with very promising results. Index Terms--Capacitor control, genetic algorithm, joint optimization, loss minimum, network reconfiguration.

This paper deals with distribution network (DN) reconfiguration for loss minimization. To solve this combinatorial problem, a genetic algorithm (GA) is considered. In order to enhance its ability to explore the solution space, efficient genetic operators are developed. After a survey of the existing DN topology description methods, a theoretical approach based on the graph and matroid theories (graphic matroid in particular) is considered. These concepts are used in order to propose new intelligent and effective GA operators for efficient mutation and crossover well dedicated to the DN reconfiguration problem. All resulting individuals after GA operators are claimed to be feasible (radial) configurations. Moreover, the presented approach is valid for planar or nonplanar DN graph topologies and avoids tedious mesh checks for the topology constraint validation. The proposed method is finally compared to some previous topology coding techniques used by other authors. The results show smaller or at least equal power losses with considerably less computation effort. Index Terms--Distribution network (DN), genetic algorithm (GA), graph theory, matroid, minimal loss reconfiguration, planar graph, spanning tree.

A method of calculating the communication delay (latency) for measurements and control signals in a power system is shown. The basis of the calculation is a dedicated communication channel for control signals. The time delay calculation is examined using a dynamic equivalent of the Western Electricity Coordinating Council transmission system. The impact on control system response is discussed. The application given is a wide area control system for interarea mode damping. Results demonstrate that control signal latency can degrade the performance of controls in a wide area control system. Index Terms--Damping, latency, network delay, power system control, power system stabilizer, queuing, wide area control systems, wide area measurement systems.

A load model is one of the most important elements in power system simulation and control. Recently, the constant impedance, constant current, and constant power load in combination with the induction motor load have been widely used as the composite load model, whose parameters are all identified from the field measurements in measurement-based load modeling practices so far. However, there is virtually no research conducted on whether all these parameters could really be identified. This paper investigates the possibility on reducing the number of composite load model parameters to be identified from field measurements. This paper first shows that direct application of the IEEE load motor parameters in the composite load model may be inadequate on describing the load dynamics over different operating status. Then the perturbation method is used to derive the trajectory sensitivities of the equivalent motor parameters, based on which the reduction on the identified parameters of the composite load model is presented. Two cases of measurement-based load modeling in North China and Northeast China are studied to illustrate the validity of the reduction method. It is shown that the reduction does not lose the model's capability on describing the load dynamics. The reduction on the number of identified parameters not only provides a possible way to solve the multi-valued load model problem based on the current practices on measurement-based load modeling, but it also facilitates building of the load model with more components included in it. Meanwhile, reducing the identified parameters reduces the identification time; thus, the proposed strategy significantly enhances the efficiency of the load modeling work. Index Terms--Composite load model, field measurements, power system stability, trajectory sensitivity.