External Power System Research Articles

A dynamic equivalent using modal coherency and frequency response

A general method has been developed to determine a dynamic equivalent of a large external power system. The combination of modal coherency and frequency response is a new approach. The frequency response formula, used to determine the coherency, is obtained by linearizing the total system and diagonalizing the linearized system. The method is tested for classical generator models as well as for fifth-order generator models plus second-order exciter models. The Dutch power system, which is coupled with the West-European UCPTE power system, has been used to illustrate the method. A comparison of the time responses of the original model and the reduced model provides a reliable picture. >

A Novel Decentralized Control of Large Scale Power System Based on the Disturbance Observer

A novel decentralized control method of a Large scale power system is proposed. The whole system has been divided into some generator sub-systems. The interferences on the sub-system are treated as unknown disturbances. Any sub-system can be decoupled from the other ones by means of the fast feedforward compensation based on the estimated disturbances obtained by the disturbance observer. This compensation allows us to design the small-scale decentralized controller. This design method has the advantage that the controller is invariant even when the external power system's structure changes. Finally, the effectiveness of the proposed method is confirmed by numerical simulations.

Boundary constrained external network power system state estimation

A method of External Network Power System State Estimation which uses equality constrained boundary node voltage magnitudes and phase angle differences to enforce multiple observable island internal network solutions is presented. It is described in the context of on-line energy control center security calculations and is currently being implemented in seven energy control centers.

Low-order valid models for dynamic studies of multi-machine power systems

A dynamic equivalent of an external electric power system is estimated from locally measured information. A sensitivity method is used to select the most suitable model for the equivalent external system among several hypotheses. Local system responses, due to an intentional disturbance, are used for the parameter identification of external equivalent model. The estimated dynamic equivalent is verified by comparing the dynamic interacting effects of the original external system with those of the equivalent external system. It is further verified by short-circuit tests.

Myo-electric controls--a challenge to occupational therapists?

Developments in the field of electronics have made it possible to use physiological signals in the control of external power systems. The relationship between man and machine is complex and difficult. Review of myo-electric controls and functional electrical stimulation in prosthetics, orthotics and other fields indicates the extent of current clinical application. Advantages and disadvantages of 2-state, 3-state, proportional and other control systems are considered, and problems related to lack of sensory feedback, delay in movement response, etc. explored. The role of the occupational therapist as an interface between man and machine, using unique skills in patient assesment, selection of controls, training and evaluation of systems is discussed. The need for occupational therapists to become involved in research and development and to acquire specialized knowledge in applied sciences and biomechanics is emphasised.

A synchronous control system for a totally implanted circulatory assist device

This paper has been prepared with the point of view that rehabilitative circulatory assist devices or heart replacements must not require permanent attachment of the patient to an external power and control system through percutaneous tubes. The Artificial Heart Program recently conducted a series of experiments designed to evaluate the problems of integrating the components of a circulatory assist device into a totally implantable system (including pump, controls and a source of power). This paper describes the work on 2 such systems, with reference to physiologic variables and the problem of control. A control method is described for a left ventricle to aorta pump. It produced synchronous operation, required no sensors in the blood stream, did not use the electrocardiogram and required no percutaneous leads. Evidence is presented which suggests that a single, fixed, best setting can be made which results in achieving the secondary goals: maximal reduction in peak left ventricular pressure and normal aortic pressure as a function of time (though shifted in phase with respect to pressure in the pulmonary artery). Evidence is presented which suggests that achievement of the secondary goals achieves the primary goal: support of the entire body in the presence of a failing heart. Finally, it is shown that information gained from developing an optimal control system for an assist device can, in turn, be valuable in improving and fixing the design of the device, subject to constraints of reliability, efficiency, materials, size, weight, cost and effectiveness. The systems described (including the control approach) were developed by a team effort of personnel in the Artificial Heart Program and many investigators working under contract; they should not be identified with the authors.

Transient theory of synchronous generators connected to power systems

Practical methods of predetermining the transient performance of synchronous generators have in the past been based more on general considerations than on a strictly logical theory. On the other hand, general equations for the synchronous machine were derived by R. H. Park and are well known, but the equations have not been widely used in practice because a direct solution is laborious. The paper shows how, by making a number of approximations, simple solutions of the equations can be obtained for short-circuit and other fault conditions, both for the generator by itself and when it is operating with an external power system, assuming the circuits to remain balanced.The formulae obtained for the transient reactances and time-constants agree, in the main, with those deduced from general considerations. The present treatment, however, demonstrates clearly what are the underlying approximations, and shows what simplifications can be made when some of the components of the transient currents can be neglected.