| 摘要 |
1,148,297. Automatic control systems. ENGLISH ELECTRIC CO. Ltd. June 6, 1967 [Aug.25, 1966], No.38157/66. Heading G3R. [Also in Division H2] A closed loop control system for controlling the D.C. level of an electrical output has a high gain at zero frequency and at, at least, one predetermined frequency above zero, and a relatively low gain at other frequencies. As shown in Fig. 1, the system is applied to an A.C. to D.C. converter to eliminate ripple components in the D.C. output. A multi-phase arrangement 5 of grid controlled rectifiers, e.g. of the mercury arc type, is supplied from an A.C. source 6 and produces a D.C. output on high voltage transmission lines 8; a phase control unit 10 controls the firing angle of the arrangement 5, and thus the level of the D.C. output, in response to a control signal Vc which has a first component dependent upon the difference between actual and desired values of the D.C. output and a second component dependent on the presence of ripple in the D.C. output at at least one predetermined frequency. The first component of the signal Vc, on line 20, is derived from a comparator 24 which receives one input from a D.C. transformer 27 and another input from a reference source 30, and the second component, on line 22, is derived from a frequency selective circuit 36 which receives an input from a voltage divider 38 connected across the D.C. output lines 8. The two components are combined in an adder 41 to produce the control signal Vc. The circuit 36 may include a number of band pass filters corresponding to a plurality of particular frequencies which it is desired to suppress Fig.2 (not shown). In operation, the unit 10 responds to the signal Vc by adjusting the phase of firing pulses on lines 12 relative to the phase of the incoming A.C. as represented on a line 14 so as to alter the output from arrangement 5 in such a direction as tends to reduce Vc to zero; thus not only is the error between the desired and actual D.C. level reduced to zero, but the harmonics selected by the circuit 36 are also eliminated.
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