Induction motor speed control

Claim 2

Motor speed control circuit for reducing the speed of an AC induction motor comprising: a. a solid state switching element connected between an AC power source and the AC induction motor being controlled; b. means for selectively energizing said switching element to either a high conductivity or substantially non-conducting state to provide a resulting voltage waveform to said AC induction motor having a frequency lower than the AC power source; c. said energizing means including means for driving said switching element to a high conduction state for periods of substantially one-half cycle of the AC power source, thereby providing an electrical path between said AC power source and said AC induction motor during said periods; and d. said energizing means additionally including means for driving said switching element to a high conduction state only during said half cycle conduction periods beginning approximately every nth zero voltage crossing of the AC power source, where n is an odd integer larger than one, so that alternate positive and negative waveforms are provided to said AC induction motor from said AC power source at a resulting frequency of 1/nth of that of the AC power source.

Claim 3

Motor speed control circuit as in claim 1 including a voltage smoothing circuit connected therein.

Claim 4

Motor speed control circuit as in claim 2 wherein said solid state switching device comprises a triac.

Claim 5

Motor speed control circuit as in claim 3 wherein n is three.

Claim 6

Motor speed control circuit as in claim 3 wherein n is five.

Claim 7

Motor speed control circuit as in claim 2 wherein said solid state switching device comprises a pair of SCR''s connected in parallel, and opposite to each other.

Claim 8

Motor speed control circuit for reducing the speed of an AC induction motor comprising: a. first solid state switching means connected between an AC power source and the AC motor being controlled, b. second solid state switching means connected between the AC power source and the AC motor being controlled; c. means for alternatively energizing said first and second solid state switching means between high and low conduction states; d. said energizing means including means for driving alternate ones of said first and second switching means to the high conduction state for periods of substantially one-half cycle of the AC power source, thereby providing alternate paths between said AC power source and said AC induction motor during said periods; e. said energizing means additionally including means for alternately driving said first and second switching means to a high conduction state only during those half cycle conduction periods beginning every mth zero voltage crossing of the AC power source, where m is an even integer; and f. wherein said second switching means includes means for inverting the voltage applied to said motor so that alternate positive and negative waveforms are provided to said AC induction motor from said AC power source at a resulting frequency of 1/mth of that of the AC power source.

Claim 9

Motor speed control circuit for reducing the speed of an AC induction motor comprising: a. first solid state switching means connected between an AC power source and the AC motor being controlled, b. second solid state switching means connected between the AC power source and the AC motor being controlled; c. means for alternatively energizing said first and second solid state switching means between high and low conduction states; d. said energizing means including means for driving alternate ones of said first and second switching means to the high conduction state for periods of substantially one-half cycle of the AC power source, thereby providing alternate paths between said AC power source and said AC induction motor during said periods; e. said energizing means additionally including means for alternately driving said first and second switching means to a high conduction state only during those half cycle conduction periods beginning every mth zero voltage crossing of the AC power source, where m is an even integer; and f. wherein said second switching means includes means for inverting the voltage applied to said motor so that alternate positive and negative waveforms are provided to said AC induction motor from said AC power source at a resulting frequency of 1/mth of that of the AC power source.

Claim 10

Motor speed control circuit as in claim 1 wherein said first switching means comprises a first pair of silicon controlled switching elements forming one half of a bridge circuit, and said second switching means comprises a second pair of silicon controlled switching elements forming the second half of said bridge circuit.

Claim 11

Motor speed control circuit as in claim 8 wherein said first and second pairs of silicon controlled switching elements comprise triacs.

Claim 12

Motor speed control circuit as in claim 9 including a voltage smoothing circuit connected therein.

Claim 13

Motor speed control circuit as in claim 8 wherein m is the integer two.

Claim 14

Motor speed control circuit as in claim 8 wherein m is the integer 4.

Claim 17

The method of claim 44 including the additional step of smoothing the resulting voltage waveform.

Claim 18

Power frequency converter for reducing the frequency of an AC power source comprising: a. first and second solid state switching means connected with the AC power source; b. means for alternatively energizing said first and second solid state switching means between high and low conduction states; c. said energizing means including means for driving alternate ones of said first and second switching means to the high conduction state for periods of substantially one-half cycle of the AC power source, thereby providing alternate paths between said AC power source and said AC induction motor during said periods; d. said energizing means additionally including means for alternately driving said first and second switching means to a high conduction state only during those half cycle conduction periods beginning every mth zero voltage crossing of the AC power source, where m is an even integer; and e. wherein said second switching means includes means for inverting the voltage applied to said motor so that alternate positive and negative waveforms are provided to said AC induction motor from said AC power source at a resulting frequency of 1/mth of that of the AC power source.

Claim 19

Power frequency converter for reducing the frequency of an AC power source comprising: a. first and second solid state switching means connected with the AC power source; b. means for alternatively energizing said first and second solid state switching means between high and low conduction states; c. said energizing means including means for driving alternate ones of said first and second switching means to the high conduction state for periods of substantially one-half cycle of the AC power source, thereby providing alternate paths between said AC power source and said AC induction motor during said periods; d. said energizing means additionally including means for alternately driving said first and second switching means to a high conduction state only during those half cycle conduction periods beginning every mth zero voltage crossing of the AC power source, where m is an even integer; and e. wherein said second switching means includes means for inverting the voltage applied to said motor so that alternate positive and negative waveforms are provided to said AC induction motor from said AC power source at a resulting frequency of 1/mth of that of the AC power source.

Claim 20

Power frequency converter as in claim 15 wherein said first switching means comprises a first pair of silicon controlled switching elements forming one half of a bridge circuit, and said second switching means comprises a second pair of silicon controlled switching elements forming the second half of said bridge circuit.

Claim 21

Power frequency converter as in claim 15 wherein said first and second pairs of silicon controlled switching devices comprise triacs.

Claim 22

Power frequency converter as in claim 15 wherein m is the integer two.

Claim 23

Power frequency converter as in claim 15 including a voltage smoothing circuit connected therein.