K. Koyanagi

Modeling of doubly-fed adjustable-speed machine for analytical studies on long-term dynamics of power system

This paper gives some considerations concerning modeling of doubly-fed machines for analytical studies, especially on long term dynamics of a power system in the time range of beyond 10 seconds in which the doubly-fed machines are operating and being controlled. The mathematical models are briefly presented first for short-term analysis (transient stability and dynamic stability analyses, up to 10 seconds) and then for long term analysis (frequency control analysis). The possible two control schemes of doubly-fed machine for long term analysis are presented and discussed. The dynamic simulations were performed to show the behavior of doubly-fed machines in a power system during pumping operation.

Modeling and dynamic simulations of doubly-fed rotary frequency converter in power systems

The doubly-fed (or adjustable speed) pumped storage generating systems which have been newly developed with progress of power electronic technology as its setting can contribute not only to power system frequency control at night, but also to improvement of power system stability. In this paper, a new rotary frequency converter is proposed that consists of a couple of rotary machines and at least one of them is the doubly-fed machine. Compared with a conventional rotary frequency converter that consists of a couple of synchronous machines, the new doubly-fed rotary frequency converter can control power transfer actively. The mathematical models of the proposed new converter and basic considerations for their fundamental control strategy based on the models are described, and the results of dynamic simulations for investigating the characteristics of control and operation of the converter in a power system are presented.

Evaluation technique of turbine shaft fatigue in private-generation systems using consumption rate of shaft life cycle

Under the action of disturbances in power systems, the turbine-generator shaft is subjected to mechanical stress caused by severe torsional torques. Shaft torque is proportional to the shaft twist, which is caused by the angle difference between both ends. However, observing the angle difference in an actual generation system is difficult technically. On the other hand, measuring the rotational speed of the shaft ends is relatively easy. Then if the shaft torque could be estimated effectively, it would be used in order to control the rotational speed for shaft torque reduction.

Observer-based excitation control of turbine-generator shaft oscillation

During disturbances in a power system, turbine-generator shafts are subjected to mechanical stress caused by severe torsional torques. Shaft torque is proportional to the shaft twist, which is caused by angle difference between both ends. However, observing the angle difference in an actual generation system is difficult technically. On the other hand, measuring rotational speed of the shaft ends is relatively easy. Then, if the shaft torque could be estimated effectively, it would be used in order to control the rotational speed for shaft torque reduction. This paper proposes a shaft torque excitation control for rotating machine by making use of an observer for the shaft torque. Firstly, the relationship between the observation signals and the accuracy of the estimation are discussed, and secondly a shaft torque reduction control system developed by using the excitation control based on the estimate by an identity observer. An in-house 7-mass system comprised of joints, shear-pins, and an exciter is used for the test model and Parks equation for the synchronous machine is employed. The controller is established by feeding back the error between the target output and the observer output. Linear quadratic regulator theory (LQR) is employed to design the observer gain, which provides acceptable estimation.

Stabilizing control for long-term low damping oscillation in multi-regional power system

To analyze and solve the problem of long-term low damping oscillation phenomena, a method is presented to find the best allocation and to design a power system stabilizer (PSS) for damping inter-area power oscillations. The method is based on the single-machine-infinite-bus models derived from the multi-machine power system by coherency-based reduction technique. Dynamic simulations using a 10-machine power system model are presented in order to show the effectiveness of the PSS designed according to the proposed method.