Spikeless motor starting circuit
First Claim
1. In a capacitor-start capacitor-run single phase AC induction motor having a main winding and an auxiliary winding both connected to an AC power source, a run capacitor for providing a phase shifted field for starting and running torque, a start capacitor for providing a phase shifted field for starting torque, a start switch for automatically connecting and disconnecting said start capacitor to and from said AC source in starting and running modes, respectively, said run capacitor and said start capacitor being connected in parallel in said starting mode such that during the first cycle of said AC source upon initiation of said starting mode there is an equalization of capacitor voltages and an exchange of current between said run and start capacitors resulting in current flow through a loop including said run and start capacitors and said start switch, which current flow may reach a high peak current spike if there is a large magnitude voltage differential between said run and start capacitors, an inhibit switch responsive to said magnitude of said voltage differential between said run and start capacitors and preventing said start switch from connecting said start capacitor to said AC source until said magnitude drops below a given maximum level, to reduce said first cycle current spike, and reduce damage to and extend the life of said start switch and said start capacitor.
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Abstract
A capacitor-start capacitor-run single phase AC induction motor control starting circuit is provided which minimizes first cycle current spiking magnitude, and also minimizes cycle to cycle current spiking magnitude, without a choke or inductor in the loop containing the run capacitor, start capacitor and start switch. The first cycle current spiking problem is solved by controlling when the start switch may be turned on at initiation of the starting mode in relation to the AC cycle, to permit turn-on of the start switch only within a known or predictable range of voltage differential between the run and start capacitors. The cycle to cycle current spiking problem is solved by proper phasing of gate current, and supplying gate current to the start switch in phase with the voltage across the run capacitor and out of phase with the current through the series connected start switch and start capacitor.
75 Citations
16 Claims
- 1. In a capacitor-start capacitor-run single phase AC induction motor having a main winding and an auxiliary winding both connected to an AC power source, a run capacitor for providing a phase shifted field for starting and running torque, a start capacitor for providing a phase shifted field for starting torque, a start switch for automatically connecting and disconnecting said start capacitor to and from said AC source in starting and running modes, respectively, said run capacitor and said start capacitor being connected in parallel in said starting mode such that during the first cycle of said AC source upon initiation of said starting mode there is an equalization of capacitor voltages and an exchange of current between said run and start capacitors resulting in current flow through a loop including said run and start capacitors and said start switch, which current flow may reach a high peak current spike if there is a large magnitude voltage differential between said run and start capacitors, an inhibit switch responsive to said magnitude of said voltage differential between said run and start capacitors and preventing said start switch from connecting said start capacitor to said AC source until said magnitude drops below a given maximum level, to reduce said first cycle current spike, and reduce damage to and extend the life of said start switch and said start capacitor.
- 6. In a capacitor-start capacitor-run single phase AC induction motor having a main winding and an auxiliary winding both connected to an AC power source, a run capacitor for providing a phase shifted field for starting and running torque, a start capacitor for providing a phase shifted field for starting torque, a start switch for automatically connecting and disconnecting said start capacitor to and from said AC source in starting and running modes, respectively, said run capacitor and said start capacitor being connected in parallel in said starting mode, said start switch comprising a semiconductor power switch connected in series with said start capacitor and being conductive during said starting mode and nonconductive during said running mode, said power switch having a gate circuit for controlling conduction thereof, the voltage across said run capacitor during said starting mode being in phase with the voltage across said start capacitor, the current through said series connected power switch and start capacitor being out of phase with said voltage across said run capacitor, said power switch in said starting mode requiring triggering into conduction by gate current from said gate circuit during each half cycle of said AC source following a zero-crossing of current through said series connected power switch and start capacitor, means supplying gate current to said gate circuit in phase with said voltage across said run capacitor and out of phase with said current through said series connected power switch and start capacitor.
- 11. In a capacitor-start capacitor-run single phase AC induction motor having a main winding and an auxiliary winding both connectable to an AC power source, a run capacitor for providing a phase shifted field for starting and running torque, a start capacitor for providing a phase shifted field for starting torque, a start switch for automatically connecting and disconnecting said start capacitor to and from said AC source in starting and running modes, respectively, said run capacitor and said start capacitor being connected in parallel in said starting mode such that during the first cycle of said AC source upon initiation of said starting mode there is an equalization of capacitor voltages and an exchange of current between said run and start capacitors resulting in current flow through a loop including said run and start capacitors and said start switch, which current flow may reach a high peak current spike if there is a large magnitude voltage differential between said run and start capacitors, an inhibit switch responsive to said magnitude of said voltage differential between said run and start capacitors and preventing said start switch from connecting said start capacitor to said AC source until said magnitude drops below a given maximum level, to reduce said first cycle current spike, and reduce damage to and extend the life of said start switch and said start capacitor, said start switch comprising a semiconductor power switch connected in series with said start capacitor and being conductive during said starting mode and nonconductive during said running mode, said power switch having a gate circuit for controlling conduction thereof, the voltage across said run capacitor during said starting mode being in phase with the voltage across said start capacitor, the current through said series connected power switch and start capacitor being out of phase with said voltage across said run capacitor, said power switch in said starting mode requiring triggering into conduction by gate current from said gate circuit during each half cycle of said AC source following a zero-crossing of current through said series connected power switch and start capacitor, means supplying gate current to said gate circuit in phase with said voltage across said run capacitor and out of phase with said current through said series connected power switch and start capacitor.
Specification