超電導マグネット電流のディジタル制御

抄録

DDC (direct digital control) of superconducting magnet current by using the microcomputer has been studied. An inductor-converter (I-C) unit composed of a 6-pulse thyristor converter of Graetz bridge type and a superconducting magnet (SM) has been developed. A microcomputer based controller and its input/output interfaces are connected to the I-C unit and its current is feedback controlled.
The closed loop system is formed via the following steps: detection of the SC current by using DCCT (direct current current transformer), A/D conversion of the SM current and input to the microcomputer, comparison with the reference input for generating the error signal, computation for compensation by PID, Dahlin or more sophisticated optimal control such as FTSC (finite time settling control), via FTSO (finite time settling observer) and generation of trigger pulses. These operations are performed by the program instructions of the microcomputer.
The specifications of the developed system are: Inductor 3kJ, 93.5A at 5T, 0.585H, Converter 6 pulse Graetz bridge, 100V, 400A; Microcomputer TLCS 12A, 12 bits, RAM 2kW, PROM 0.5kW, 1.2MHz.
By using this system, experimental studies have been performed. The control algorithms for digital control have been tested by experimental works as well as by computer simulations. The control methods PID and Dahlin have been implemented by the microcomputer and the accurate agreements between the results of the experiments and those of simulations have been found. These algorithms are simple and can be implemented by the fixed point operations. The computation time is less than 1/360sec. The optimal parameters can be obtained by the frequency domain method and by the simulations. The moderate oscillations have been found by PID compensation although the quite stable responses have been achieved by Dahlin algorithm.
For the feedback control by FTSC via FTSO the floating operations are required, although the algorithm is quite simple. The simulated result reveals the closely fitted response to the reference waveform. If the control algorithm is implemented by using DEC LSI-11, the computation time is estimated 1/60sec or so.