Worawut Sae-Kok

Excitation control system design of rotary type frequency converter for performance improvement of power system dynamics

A rotary type frequency converter using two sets of adjustable speed generators/motors is expected to be applied at the interconnections between 50 Hz and 60 Hz power systems in Japan. The rotary type frequency converter can work not only as a power interchanger, but also as a power system stabilizer by effectively utilizing energy stored in rotors. In this paper, we investigate how the rotary type frequency converter affects power system dynamics. Since shaft torsional oscillation and slow response due to mechanical connections are inevitable and may lead to instability in power systems, we also present some countermeasures and control schemes to handle such inherent problems, and to improve the performance of power system dynamics. Control performance and effectiveness is examined for a test model system by digital transient simulation.

Nonlinear excitation control for rotary type frequency converter using two sets of adjustable speed generators/motors

At present, there are 50 Hz and 60 Hz power systems in Japan, which are connected by power electronics-based frequency converter stations. A frequency converter can also be realized by using an adjustable speed motor (ASGM) whose structure is similar to induction machine, however; it is excited by AC voltage. The controller in this paper is designed for an excitation system of each set of ASGM in the frequency converter by using local information of ASGM, in order to regulate the voltage and control the active power. The control performance is examined for a model power system by digital dynamic simulation. It is made clear that this kind of controller is effective even though the controller uses just local information of ASGM. However, its performance depends on the capacity of the ASGM, the load flow conditions and the oscillatory mode of the target.

Energy function based controllers of superconducting generators with high response excitation

High response excitation type superconducting generator has various advantages such as high efficiency, small size, light weight, including the low synchronous reactance yielding in improvement of power system stability. In addition, it also has a particular characteristic due to its structure, called SMES effect; it can enables rapid changes and the excitation power will be large and have a rapid change enough to affect the conditions of power system in self-excited operation of the generator. In this paper, energy function, which is commonly used for transient stability evaluation, is considered in designing the excitation control system for high response excitation type superconducting generator in order to improve the power system dynamics; SMES effect is taken into account in the control design so as to be used effectively for stability improvement. The control performance is examined in IEEJ East 10-machine model system

Robust control for rotary type frequency converter using two sets of adjustable speed generators/motors

Japan has two different frequency power systems, 50 Hz system and 60 Hz system. A frequency converter is required for interconnection between them. A power electronics based frequency converter, which is called static type frequency converter, is exploited at the interconnection points. The frequency converter can also be realized by using two sets of adjustable speed generator/motor (ASGM), whose structure is identical to that of an induction machine; rotor windings are excited by an AC voltage, and so called rotary type frequency converter. When applying this type of frequency converter to the interconnection points between two systems, where nonlinearity and disturbance inherently exist, in addition to functioning for interchange power between two systems, it should enhance power system stability by use of an effective and appropriate controller. Robust control for this kind of frequency converter has been studied in this paper and an effective controller is designed against disturbance and uncertainty in the power systems and examined in model power systems by digital simulation.