J. Machowski

Decentralized stability-enhancing control of synchronous generator

This paper describes new structures for stability-enhancing excitation controllers designed using a nonlinear multi-machine system model and Lyapunovs direct method. Two control structures are presented: a hierarchical structure In which the AVR is the master controller and the PSS the slave controller and a traditional structure in which the PSS constitutes a supplementary loop to the main AVR. Both controllers are shown to be robust, as the damping they introduce into the system is insensitive to changes in both the system topology/parameters and the pattern of network flows. Each individual controller contributes positively to the overall system damping with no undesirable interaction between controllers. These features should allow a decentralized approach to the design of the AVR+PSS. Such a design approach is compatible with the new competitive market structures and should result in savings on commissioning costs. Simulation results for a multi-machine power system are presented that confirm the above and show that the two control structures are very effective in damping both local and inter-area power swings.

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

Abstract 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 Pontryagins 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.

Damping of power swings by control of braking resistors

In this paper an analysis of the stability enhancement and improved damping of power swings in a multi-machine power system by means of thyristor-controlled braking resistor installed in the network has been presented. The control law has been derived using direct Lyapunov method and non-linear multi-machine system model. It is optimal in the sense that it causes the quickest dissipation of the power system energy released by a disturbance. Simple implementation of this control using only locally available signal has been also demonstrated. A computer simulation of a multi-machine power system model has verified the effectiveness of the proposed algorithm.

Optimal modulation controller for superconducting magnetic energy storage

Abstract A study of power system transient stability enhancement through effective use of the superconducting magnetic energy storage is presented. Simultaneous optimal modulation of the active and reactive power is formulated as a modulation which forces the fastest dissipation of energy released in the system by a given fault. For this definition the optimal modulation strategy has been derived from the direct Lyapunov method for a multi-machine nonlinear power system model. This theoretical optimal strategy can easily be technically realized as a nonlinear control using only locally measurable quantities. The validity and robustness of the proposed local control has been confirmed by simulation tests.

Power system stability screening for long-term planning of transmission network development

Stability analyses of a power system are performed at short-term and mid-term planning of transmission network development. Increased load demands and market economics are pushing transmission networks closer and closer to their operational limits. Therefore it is necessary to perform even a simplified power system stability assessment also at long-term planning. The article shows that very simple criteria of angle stability and voltage stability based on short-circuit power can be used as screening filters for fast contingency selection. The suggested criteria have been verified for a real large-scale system.

Comparison of different control structures for Lyapunov-based power system stabilizer

Recently it has been shown that it is possible to design a power system stabilizer (PSS) using a nonlinear multi-machine power system model in conjunction with Lyapunovs direct method. The resulting controller has been shown to be robust. It was also shown that each individual controller acted independently of all the others suggesting that no coordination of settings is necessary. These features should allow a decentralized approach to the design of the PSS. In this paper two control structures implementing the proposed control law have been compared: a hierarchical structure in which the automatic voltage regulator (AVR) is the master controller and the PSS is the slave controller, and a more traditional structure in which the PSS constitutes a supplementary loop to the main AVR. This paper shows that the AVR has to be designed in a different way for each of the structures. Theoretical analysis is supported by the results of simulations tests which highlighted the differences between the way in which the stabilizing signal was obtained for each controller. The tests performed on a multi-machine system model have shown a very good performance of both proposed structures when compared with a classical speed-based PSS.

Decentralised Lyapunov-based power system stabiliser

This paper describes a new structure for a stability-enhancing excitation controller designed using a nonlinear multimachine system model and Lyapunovs direct method. The controller is shown to be robust, as the damping it introduces into the system is insensitive to changes in both the system topology/parameters and the pattern of network flows. Each individual controller contributes positively to the overall system damping with no undesirable interaction between controllers. These features should allow a decentralised approach to the design of the AVR+PSS. Such a design approach is compatible with the new competitive market structures and should result in savings on commissioning costs. Simulation results for a multi-machine power system confirmed that the controllers are effective in damping local and inter-area power swings.

Contingency selection for power system stability analysis

Transmission expansion planning requires static and dynamic analyses. Planning criteria include the selection of contingencies consisting of faults and their clearing, performance standards, transmission system adjustments, and corrective action plan. Performance standards relating to power system dynamics mainly concern the voltage ride through and transient angle stability i.e. retaining synchronism after the occurrence of the contingencies mentioned. The selection of planning contingencies, for which performance standards must be complied with, is important in terms of capital expenditures in transmission network expansion and secure power system operation. This paper discusses planning contingencies accepted by various transmission network operators worldwide and describes a set of planning contingencies proposed by the authors.

Automatic Alleviation of Overloads in Transmission Network by Generation Curtailment

For economic reasons, expansions of transmission networks are based on a compromise between capital cost and security of power system operation. At the same time, the power system must withstand typical highly likely contingencies. Various emergency state control systems, also called special protections, prevent emergencies following less likely contingencies. This paper describes overloads emergency state control (OLEC) used for the alleviation of overload in transmission networks near a power plant. Such control uses the functions of automated power reduction of generating units and has been implemented for a large steam power plant. The OLEC presented here uses different methods of generation curtailment for steam generation units. A case study illustrates the efficiency of the proposed control method.

Automatyka odciążająca sieć przesyłową oparta na zaniżaniu wytwarzania

For financial reasons expansion of transmission networks is based on the compromise between investment costs and ability of power system to withstand disturbances. It is assumed, that power system must withstand typical credible and non-credible disturbances. To avoid blackouts following extreme disturbances the power systems are equipped with emergency control also referred to as special protection. In this paper an overload emergency control is described. It has been designed and implemented in order to alleviate overloads in transmission lines in the vicinity of large steam power plant. It utilizes capability of steam generating units to curtail automatically real power. (Overload emergency state control of transmission network based on generation curtailment) Słowa kluczowe: automatyka odciążająca, sieci przesyłowe, łagodzenie przeciążeń, zaniżanie wytwarzania.