Showing papers in "Electrical Engineering in Japan in 1978"

Control and protection of HVDC systems with diode valve converter

Abstract: A HVDC transmission line carrying electric power from power plants in remote areas to urban areas transmits electric power always in the same direction. In such a case, the thyristor valves at the rectifier station can be replaced by diode valves. Although diode valves are less expensive than thyristor valves, the former may be inferior to the latter from viewpoints of valve control and protection. Various control and protection characteristics of the HVDC line using diode valve converters are discussed, such as abnormal voltage suppression in starting condition, coordinated control of the generator and HVDC line, reduction of ground fault current, quick restart, fault protection, etc. It is concluded that the HVDC system using the diode converter as rectifier is promising when the dc power is transmitted only in one direction.

Application and economical evaluation of the superposed AC and DC power transmission system

Abstract: The superposed ac and dc power transmission scheme has advantages of both ac and dc transmission schemes and makes it possible to overcome the defects of both schemes. Important technical problems concerning converter transformer and reclosing have already been discussed. It is expected that technical problems associated with the superposed ac and dc transmission scheme can be solved without much difficulty. The optimum properties of ac and dc transmitted powers and the economic advantages of the superposed ac and dc scheme over the ac or dc scheme are dicussed. Results of the economic studies confirm the effectiveness of the superimposed ac and dc scheme.

Suboptimal control for load-frequency control system using an area-decomposition method

Abstract: The feedback control theory has been applied successfully to the Load-Frequency Control (LFC) in the power system. At present, however, because of the large-scale power system, peculiar power flow phenomena due to flow variation in the tie line have been discovered. The optimum control theory has been developed to solve these problems with the assumption that the information for all systems is always available. Various techniques such as Kalman filters, observers, and the hierarchy control method have been studied. These techniques, however, require complicated algorithms and long computation time. The area-decomposition method is applied to the multiarea LFC system and the optimum control is performed in each subsystem. At the area decomposition, the tie-line variables generates the subordinate vector and the decomposed subsystems become unstable. For these subsystems, a peculiar matrix is transformed to a regular matrix by the power flow calculation. These unstable subsystems are stabilized and the suboptimal control is applied to the entire system. Further, the conventional tie-line power control method (TBC) is also adopted. The present method is applied to a 4-area cascaded system and the cost rate. The computation time for transient response, etc., is compared with those in the optimal and suboptimal control methods.more » Further, the present method is applied to the 4-area tie-line system containing a loop to confirm the effectiveness of the present method.« less

Control system of thyristor power converter for superconducting magnets

Abstract: A procedure is proposed for designing the control system of the superconducting magnet by the transfer function method The validity of the proposed procedure has been confirmed by simulation and experiments The energy transfer efficiency and the switching phenomenon of the superconducting switch were analyzed

Total stabilization of power swing by multistabilizing apparatus

Abstract: Many devices are used to improve the stability of power systems. The power system stabilizer (PSS), dynamic braking resistor (DBR), and switching capacitor (SWC) are some examples. These devices can be used to secure the stability of a wide area power system. The case where multistabilizing apparatus exists in a power system is considered, and the following problems are discussed: mutual interaction between these multistabilizing apparatuses; totalized control of the multistabilizing apparatus; optimal allocation of multistabilizing apparatus; and confirmation of the effectiveness of these apparatuses by simulation method.

Reduced order modeling for power system transient analysis

Abstract: With the development of power system interconnection and with the increase of transmitted power, some cases are arising where the capacity of a transmission network is limited by steady-state stability. Analysis of steady-state stability raises some difficulties, which are different in nature from those raised by transient stability analysis. To reduce the computational difficulty associated with steady-state stability analysis, a proposed method derives an equivalent network with a reduced number of generators. In some of these methods a part of the power system is simplified so as to keep invariant the short-circuit capacity at a specific point. Nevertheless, equivalency of the reduced model obtained by these methods has not been discussed in detail theoretically. A method to reduce the number of generators is proposed assuming that the electromotive force behind transient reactance of each generator is constant.

Improvement of dynamic stability of parallel AC‐DC power system by suboptimal control

Abstract: One of the advantages of dc power transmission over ac transmission is that the dynamic stability of the ac system can be improved greatly by connecting a dc transmission system in parallel to the ac system and controlling the dc power in the case of disturbance. The suboptimal feedback coefficient matrix for the parallel ac-dc system usign a linear model is derived. The suboptimal gain of the automatic voltage regulator (AVR) is derived and the effect of AVR gain on the control performance of the suboptimal regulator is analyzed. It is shown that the proposed suboptimal control, in which only two output variables (magnitude of generator terminal voltage and time derivative of terminal voltage phase angle) are used as feedback signals, is as effective as the optimal control in which all state variables are used as feedback signals.

A calculation method for power system transient stability using decomposition technique

Abstract: In analyzing the transient stability of a complicated power system, it is effective to represent the part near the fault point by an exact model and the remaining part far from the fault point by a simplified model. The former part is called the target system and the latter, the external system. The target system is represented by a nonlinear model and the external system by a linear model. Features of the method of transient stability analysis proposed are as follows: the nonlinear target system is analyzed by the Runge-Kutta-Gill method and the linear external system by the state transition method; and the load flow of the external system is obtained by repeating simple multiplications using the transition matrix. A method is described to decompose a differential equation, making clear its features. The following problems are discussed: introduction of machine-to-machine admittance matrix; calculation errors caused by (a) linear approximation of external system, (b) constant node voltage assumption of external system during calculation time step interval, and (c) series expansion of state transition matrix; comparison between the proposed method, and the conventonal exact Runge-Kutta-Gill method; and application of the proposed method to the 39-node loop system and 61-node longitudinal system.

Statistical Approach to the Optimal Control of a Thermal-Power Plant

Abstract: A method of optimal analog-digital plant control based on an autoregressive model is proposed. Advantages of the proposed ADC (analog-digital coordinated control) scheme over the APC (automatic plant controller) scheme are demonstrated by the simulation test of the once-through boiler. The proposed method is applicable to boilers in general and it would be useful in practice to change gain matrix and other control constants according to the variation of operating state or load level of the thermal plant. It was concluded that the proposed control system makes it possible to improve the load follow-up capability.

Magnetic damping characteristics of magnetically suspended ultrahigh-speed vehicles

Abstract: The induction repulsion-type superconducting levitation system is being studied for a 500 km/h ultrahigh-speed railway. The effects of various damping methods on the induction repulsion-type coil track system using a superconducting magnet are discussed. Two cases are considered in analyzing the characteristics of active damping, i.e., where one of four superconducting coils on one side loses its superconducting state and where the exciting current of one normal-conducting ground coal is interrupted. An analysis of magnetic damping and magnetic damping characteristics are presented.

Feeder sectioning of linear synchronous motors for high-speed railway

Abstract: In applying the linear synchronous motor to railways, it is rather difficult to feed the driving power to the moving coil. Therefore it is necessary to feed the driving power to the ground stator coils. Hence, the feeder sectioning of the linear synchronous motor becomes a very important problem. This paper analyzes the effects of train length, train velocity, sectioning speed and section length on the operating characteristics and power feeding characteristics of the linear synchronous motor.

Optimal control of electromagnetic levitation systems

Abstract: The magnetically levitated railway has great promise in solving the problems associated with maintenance requirement, noise level and speed limit. Among various magnetic levitation systems, the authors consider the attractive-force-type levitation system using a normal conducting magnet the most promising. Since this system is inherently unstable, some closed-loop control is indispensable in stabilizing it. This paper designs the optimal controller for an attractive-force-type levitation system based on optimal control theory. The proposed design method is applicable not only to the attractive-force-type levitation system but also to the repulsive-force-type levitation system using a superconducting magnet.