Braking circuit for alternating current induction motor

Claim 2

A braking circuit comprising: an electric motor having polyphase primary windings; a source of variable frequency voltage applied to said windings for operation of said motor at variable speeds in either a motoring mode or a braking mode; a plurality of resistors, with a different one of said resistors being connected in series with each of said primary windings; a plurality of solid state switch means, with a different one of said switch means being connected across each of said resistors for short-circuiting said resistors during said motoring mode; and means for controlling the conduction of said switch means to control the effective resistance of said resistors during said braking mode.

Claim 3

The combination claimed in claim 1 wherein said source comprises an inverter.

Claim 4

The combination claimed in claim 2 wherein each of said switch means comprises a thyristor.

Claim 5

The combination claimed in claim 3 including: a second thyristor connected across each of said resistors and poled in the opposite direction with respect to the thyristor comprising said first switch means.

Claim 6

A braking circuit comprising: an electric motor having polyphase primary windings; a source of variable frequency voltage applied to said windings for operation of said motor at variable speeds in either a motoring mode or a braking mode; rectifier means connected to said windings, and including a direct current load circuit connected to said rectifier means; and solid state switch means connected to short-circuit the rectifier means during said motoring mode.

Claim 7

A braking circuit comprising: an electric motor having polyphase primary windings; a source of variable frequency voltage applied to said windings for operation of said motor at variable speeds in either a motoring mode or a braking mode; rectifier means connected to said windings, and including a direct current load circuit connected to said rectifier means; and solid state switch means connected to short-circuit the rectifier means during said motoring mode.

Claim 8

The combination claimed in claim 5 wherein said source comprises an inverter.

Claim 9

The combination claimed in claim 6 wherein said switch means comprises a first plurality of thyristors.

Claim 10

The combination claimed in claim 7 including: a second plurality thyristor connected across said first plurality of thyristors and poled in the opposite direction.

Claim 11

The combination defined in claim 5 and including means for controlling the conduction of said switch means to control the effective resistance of said rectifier means during braking operation.

Claim 12

A braking system comprising: a direct current supply circuit; an inverter supplied by said direct current circuit and adapted to provide a polyphase, variable frequency alternating current output; an induction motor having polyphase primary windings connected to be energized by the output of said inverter for operation at variable speeds in either a motoring mode or a braking mode; and a plurality of resistors with a different one of said resistors being connected in series between each primary winding and a neutral point, such that the voltage applied to the motor windings is increased above the inverter output voltage during the braking mode, and including means for removing said resistors from the motor circuit during the motoring mode.

Claim 13

A braking system comprising: a direct current supply circuit; an inverter supplied by said direct current circuit and adapted to provide a polyphase, variable frequency alternating current output; an induction motor having polyphase primary windings connected to be energized by the output of said inverter for operation at variable speeds in either a motoring mode or a braking mode; and a plurality of resistors with a different one of said resistors being connected in series between each primary winding and a neutral point, such that the voltage applied to the motor windings is increased above the inverter output voltage during the braking mode, and including means for removing said resistors from the motor circuit during the motoring mode.

Claim 14

The combination defined in claim 10 and including solid-state switching means connected across said resistors, and means for making said switching means conductive during motoring operation and for controlling the conduction of said switching means to control the effective resistance of said resistors during said brAking mode.

Claim 15

A braking system comprising: a direct current supply circuit; an inverter supplied by said direct current circuit and adapted to provide a polyphase, variable frequency alternating current output; an induction motor having polyphase primary windings connected to be energized by the output of said inverter for operation at variable speeds in either a motoring mode or a braking mode; rectifier means connected in circuit relation with said windings such that the voltage applied to the motor windings is increased above the inverter output voltage during operation in the braking mode; means for connecting the output of said rectifier means to said direct current supply circuit; and solid state switch means connected across said rectifier means such that when said switch means is conductive said windings are connected together to a neutral point and said rectifier means is short-circuited, and including means for controlling said switch means such that said switch means is conductive during said motoring mode and the conduction of said switch means during the braking mode is controlled to vary the effective resistance of said rectifier means.

Claim 16

A braking system comprising: a direct current supply circuit; an inverter supplied by said direct current circuit and adapted to provide a polyphase, variable frequency alternating current output; an induction motor having polyphase primary windings connected to be energized by the output of said inverter for operation at variable speeds in either a motoring mode or a braking mode; rectifier means connected in circuit relation with said windings such that the voltage applied to the motor windings is increased above the inverter output voltage during operation in the braking mode; means for connecting the output of said rectifier means to said direct current supply circuit; and solid state switch means connected across said rectifier means such that when said switch means is conductive said windings are connected together to a neutral point and said rectifier means is short-circuited, and including means for controlling said switch means such that said switch means is conductive during said motoring mode and the conduction of said switch means during the braking mode is controlled to vary the effective resistance of said rectifier means.

Claim 17

The combination defined in claim 12 in which said rectifier means is connected to said primary winding by transformer means.