Hitachi, Ltd.

Yasuhiro Tennichi

Toshihiko Higashi

Naganobu Honda

Hiroshi Matsumoto

Yoshio Sato

Katsukuni Hisano

Shigeyoshi Kawano

Hiromasa Yamaoka

Tadayoshi Saito

Fumio Kato

Yoshiyuki Nakano

Yasuhiko Otawara

Sadao Yanada

Katsuto Kashiwahara

Jube Matsumura

Takumi Kawai

Mitsuaki Kobayashi

Tadahiko Iijima

Koichiro Fukushima

Yurio Eki

A process control method and a process control apparatus using a fuzzy control with reducing rules and membership functions. The process control apparatus for determining a manipulating variable of a controlled object, includes an input/output unit for inputting a present value of a controlled variable and for outputting the determined manipulating variable, a predicting unit having a simulator of a controlled object, for calculating a control variable after a predetermined time has passed, assuming now that a present value of the manipulating variable is continued, and a fuzzy controlling unit for inferring a manipulating variable at a present time by inputting a deviation value between a preset set-point value and a predicted value. The simulator simulates the controlled object as dead time and a first order delay. Since only the predicted value of the controlled variable is employed as the input of the fuzzy control, fuzzy inference can be simplified and noise resistance can be improved.

Process control method and system with employment of fuzzy inference

A process control system has a timer circuit which fixes operational periods by issuing an instruction for starting each of a plurality of time periods in such a manner that the computation of control blocks will occur during periods of fixed duration. A periodic operation selection circuit selects control blocks to be computed within each time period in response to an instruction from the timer circuit. Control blocks selected by the periodic operation selection circuit and an instruction for completion of the computation of control blocks for each time period are stacked in an operation instruction circuit, which issues an instruction for consecutively executing the operation of the control blocks and an instruction for effecting an idle operation after completion of the operation of control blocks for each time period. When an instruction for starting an ensuing time period is issued from the timer circuit at a time when computation of a control block has not been completed within a predetermined time period, an operation completion determining circuit issues an instruction for starting the computation of the ensuing time period beginning with computation of the remaining control blocks in the predetermined time period and an instruction for stacking control blocks in the ensuing time period in the operation instruction circuit by means of the periodic operation selection circuit.

Process control system and method thereof

A steam turbine governor system including two governor electronic sections for producing a turbine valve opening command to control the opening of steam valves thereby controlling a flow of steam into the turbine in dependence upon a difference between an actual turbine speed and a target turbine speed and a target turbine load. One governor electronic sections is actually used for controlling the opening of the steam valves, while the other governor electronic section is a stand-by. A first value relating to the turbine speed acceleration rate based on the turbine valve opening command produced by each of the governor electronic sections is obtained so that the first values are obtained parallelly and independently of each other in the two governor electronic sections. Turbine valve opening commands produced by the respective governor electronic sections are compared with each other and produce a start signal when the difference between them exceeds a predetermined level. A second value relating to the turbine speed acceleration rate based on the actual turbine speed is obtained, and a majority logic is applied to the first values obtained by the two governor electronic sections and the second value. An abnormality of any of the governor electronic sections is obtained based on the result of application of the majority logic.

Steam turbine governor system and method of controlling the same

In a steam turbine used with a power plant operated under variable pressure of the steam which is fed to the turbine through control valves, the control apparatus is arranged to control the control valves according to a signal obtained by adding an opening set signal with a compensation signal which is determined in dependence on a difference between a turbine stage steam pressure signal and a signal derived by multiplying the opening set signal with a ratio of the actual value of the control valve inlet steam pressure to a rated value thereof.

Control apparatus for steam turbine

The present stress in the turbine rotor is estimated at each control period, from the steam temperature and pressure at the turbine inlet. In addition, the future turbine inlet steam temperature or pressure is preestimated once every n.sub.T control cycles, for a given speed or load changing rate, making use of data concerning the changing rate of the turbine steam inlet temperature or pressure in relation with the change of the speed or load, which has been obtained by a learning of the past turbine operating condition. This future steam temperature or pressure at the turbine inlet is used as a factor for preestimating the future stress expected to be caused in the turbine rotor. The preestimation of the rotor stress is performed for a plurality of assumed speed or load changing rates. The turbine is controlled at the maximum speed increase-rate or load changing rate which would not cause the future stress preestimated over a given preestimation time to exceed a limit stress. An observation of the present stress is made at each control period to check whether the limit stress is not exceeded by the present stress.

Rotor-stress preestimating turbine control system

An electro-hydraulic governer employing a duplex digital controller system for the optimum speed control of a steam turbine running with increasing speed in the starting stage or under load. Each of the digital controllers is operable with both a control mode and a stand-by mode, and when one of the digital controllers is placed in the control mode for controlling the rotating speed of the turbine, the other is placed in the stand-by mode to prepare for possible failure of the controller operating with the control mode. A failure detecting unit detects failure of the digital controller operating with the control mode. An output switching unit disconnects the faulty digital controller from the control system and switches over the operating mode of the stand-by digital controller from the stand-by mode to the control mode for the continuous control of the rotating speed of the turbine. A display is provided on an operator's console to display the outputs of these two digital controllers, and the faulty digital controller is detected by non-coincidence of the displayed information. The faulty digital controller having been disconnected from the control system by the output switching unit is repaired as quickly as possible, and after necessary repair, it stands by to prepare for possible failure of the other controller operating with the control mode.

Electro-hydraulic governor employing duplex digital controller system

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Hitachi, Japan

Yasuhiro Tennichi