Voltage control of an a.c. drive system during motor starting

Claim 2

Control means for use in an a-c drive system including a source of adjustable frequency, adjustable voltage electric power and at least one a-c motor coupled to the electric power source for receiving electric power therefrom, said control means comprising: first signal generating means for generating a speed signal over an acceleration period, the speed signal increasing in a predetermined gradual manner from a base level to a level corresponding to a desired motor speed, second signal generating means for generating a boost signal having an initial non-abrupt increase from a base level followed by a non-abrupt decrease back to the base level over a boost period, regulating means coupled to the electric power source, said regulating means including frequency control means for regulating the output frequency of the electric power source and voltage control means for regulating the output voltage of the electric power source, said frequency control means and said voltage control means being responsive to increasing input signals to increase output voltage and output frequency and being responsive to identical input signals to produce a desired substantially constant ratio of output voltage to output frequency, coupling means for simultaneously initially supplying both the speed signal and the boost signal to said regulating means, said coupling means further including means for supplying the speed signal to both said frequency control means and said voltage control means and for supplying the boost signal to said voltage control means, whereby the ratio of output voltage to output frequency is boosted during the initial portion of the acceleration period to provide adequate break-away torque and whereby the ratio of output voltage to output frequency thereafter is maintained at the desired constant ratio.

Claim 3

Control means as defined by claim 1 in which the boost period is substantially shorter than the acceleration period.

Claim 4

Control means as defined by claim 2 in which said coupling means includes interlocked switching means for simultaneously initially supplying both the speed signal and the boost signal to said regulating means.

Claim 5

Control means as defined by claim 2 in which said second signal generating means comprises a circuit having at least one reactive element for producing the boost signal.

Claim 6

Control means as defined by claim 4 in which said reactive element is a capacitor.

Claim 7

Control means as defined by claim 3 in which said interlocking switching means includes time delayed switching means for removing the boost signal from said regulating means after a predetermined period.

Claim 8

Control means as defined by claim 6 in which said second signal generating means comprises a circuit having at least one reactive element for producing the boost signal.

Claim 9

Control means as defined by claim 7 in which said reactive element is a capacitor.

Claim 10

An a-c drive system comprising: a source of adjustable frequency, adjustable voltage electric power, at least one a-c motor coupled to said electric power source for receiving electric power therefrom, control means comprising: first signal generating means for generating a speed signal over an acceleration period, the speed signal increasing in a predetermined gradual manner from a base level to a level corresponding to a desired motor speed, second signal generating means for generating a boost signal having an initial non-abrupt increase from a base level followed by a non-abrupt decrease back to the base level over a boost period substantially shorter than the acceleration period, regulating means coupled to said electric power source, said regulating means including frequency control means for regulating the output frequency of said electric power source and voltage control means for regulating the output voltage of said electric power source, said frequency control means and said voltage control means being responsive to increasing input signals to increase output voltage and output frequency and being responsive to identical input signals to produce a desired substantially constant ratio of output voltage to output frequency, coupling means for simultaneously initiaLly supplying both the speed signal and the boost signal to said regulating means, said coupling means further including means for supplying the speed signal to both said frequency control means and said voltage control means and for supplying the boost signal to said voltage control means, whereby the ratio of output voltage to output frequency of said electric power source is boosted during the initial portion of the acceleration period to provide said a-c motor with adequate break-away torque and whereby the ratio of output voltage to output frequency thereafter is maintained at the desired constant ratio.

Claim 11

An a-c drive system comprising: a source of adjustable frequency, adjustable voltage electric power, at least one a-c motor coupled to said electric power source for receiving electric power therefrom, control means comprising: first signal generating means for generating a speed signal over an acceleration period, the speed signal increasing in a predetermined gradual manner from a base level to a level corresponding to a desired motor speed, second signal generating means for generating a boost signal having an initial non-abrupt increase from a base level followed by a non-abrupt decrease back to the base level over a boost period substantially shorter than the acceleration period, regulating means coupled to said electric power source, said regulating means including frequency control means for regulating the output frequency of said electric power source and voltage control means for regulating the output voltage of said electric power source, said frequency control means and said voltage control means being responsive to increasing input signals to increase output voltage and output frequency and being responsive to identical input signals to produce a desired substantially constant ratio of output voltage to output frequency, coupling means for simultaneously initiaLly supplying both the speed signal and the boost signal to said regulating means, said coupling means further including means for supplying the speed signal to both said frequency control means and said voltage control means and for supplying the boost signal to said voltage control means, whereby the ratio of output voltage to output frequency of said electric power source is boosted during the initial portion of the acceleration period to provide said a-c motor with adequate break-away torque and whereby the ratio of output voltage to output frequency thereafter is maintained at the desired constant ratio.

Claim 12

An a-c drive system as defined by claim 9 in which said a-c motor is a synchronous motor.

Claim 13

An a-c drive system as defined by claim 9 wherein the boost signal increases and decreases exponentially.

Claim 14

An a-c drive system as defined by claim 9 in which said coupling means includes interlocked switching means for simultaneously initially supplying both the speed signal and the boost signal to said regulating means.

Claim 15

An a-c drive system as defined by claim 12 in which said second signal generating means comprises a circuit having at least one reactive element for producing the boost signal.

Claim 16

An a-c drive system as defined by claim 13 in which said reactive element is a capacitor.

Claim 17

An a-c drive system as defined by claim 12 in which said interlocked switching means includes time delayed switching means for removing the boost signal from said regulator means after a predetermined period.