| 摘要 |
1362849 Inverting; control of AC motors GENERAL ELECTRIC CO 15 Oct 1971 [19 Oct 1970] 48060/71 Headings H2F and H2J A variable frequency 3-phase inverter, e.g. for controlling the speed of an A.C. motor 64 comprises three pairs of series-connected switching devices such as thyristors 18, 20; 30, 32; 40, 42 for sequentially connecting each phase to a D.C. source 22, 24, the average voltage being adjusted by time-ratio control of one device at a time only during the 60 degrees at the mid-time of each half cycle. As described, the frequency is determined by a voltage-controlled oscillator 154, controlled by the output of an amplifier 164 in response to a command signal at 150 from a potentiometer or tachogenerator (not shown). The motor speed is also modified in response to motor current from a transformer 80, feeding an input 90 and by a regeneration limit signal at 170. The oscillator frequency is reduced by a binary divider 156 and outputs at selected submultiples driving a ring counter 158 which distributes pulses to the three phases to supply the main thyristors 18, 20; 30, 32; 40, 42 and commutating thyristors 18A, 20A; 30A, 32A; 40A, 42A. Time-ratio control.-The output voltage is monitored at 80 and compared at 216 with a voltage proportional to oscillator frequency derived at 208. A square wave at a selected sub-multiple frequency is selected at 201 and converted at 202 into a triangular waveform, pulses being derived at 204 at the coincidence of the triangular waveform with the voltage control signal from amplifier 216. These pulses are used to determine the on/off periods in the 60 degrees control interval at the mid-time of each half cycle. Commutation.-Turn off of the main thyristors 18, 20; 30, 32; 40, 42 is achieved by commutating circuits such as 58, 62 connected by commutating thyristors 18A, 20A. The commutating current is monitored by transformers 94 and fed to a delay switch which signals completion of commutation to the logic system 162. |
