Power factor corrector for A.C. induction motors

• US 5,637,975 A
• Filed: 11/17/1994
• Issued: 06/10/1997
• Est. Priority Date: 10/16/1992
• Status: Expired due to Term

• Current Assignee: John E. Powers, John F. Davis
• Original Assignee: Alexander C. Pummer, Dwight D. Burchak, John E. Powers
• Inventors: Pummer, Alexander C., Powers, John E., Burchak, Dwight D.
• Primary Examiner(s): Martin, David S.
• Application Number:
  US08/343,887
• Time in Patent Office: 936 Days
• Field of Search: 318/438, 318/729, 318/767, 318/798-811
• US Class Current: 318/729
• CPC Class Codes: H02P 23/26 Power factor control [PFC]
• CPC Class Codes: Y02P 80/10 Efficient use of energy, e.g. using compressed air or pressurized fluid as energy carrier

Abstract

A Power Factor Corrector system for use with AC induction motors which detects information from the motor voltage and motor current and decreases the power input to the motor proportional to the detected phase displacement between the current and voltage resulting in reduced electrical power input to the motor as the mechanical load is decreased.

Claims

1. A Power Factor Corrector System for an AC induction motor using multiple chopping of the input current during one period of the AC line frequency, comprising:

current sampling means in circuit with each phase winding of a said motor for providing an AC output signal in phase with the current through each phase said winding;

voltage sampling means for sensing the voltage of an electrical input applied to said each phase winding and for providing an output signal in phase with said voltage across said each phase winding;

phase detection means responsive to the outputs of said current sampling means and said voltage sampling means for providing output pulses which vary in accordance with the difference in phase between said AC output signal and said output signal; and

a loop filter means responsive to the output of said phase detection means for providing a dc level proportional to an integrated value of said pulses provided by said phase detector; and

a ramp generator means generating a linear ramp with a repetition frequency this frequency being a chopping frequency;

a pulse width modulator means responsive to the output of said loop filter means and said ramp generator means for generating pulses with a duty cycle established as a function of said inputs; and

,

an input filter means and an output filter means with a fixed cut-off frequency which attenuate said chopping frequency and any related by products from affecting said each of said phase winding winding and said input line; and

a current switch responsive to the output of said pulse width modulator controlling the current of said each phase winding;

a control means electrically connected in series with each said phase winding of said motor, and responsive to the output of said phase detection means for varying the duty cycle of each cycle of each period of the chopping frequency to said winding inversely proportional to the difference in phase between said current and said voltage;

whereby an increase in difference between the magnitude of said voltage and the magnitude of load applied to said motor is compensated for by a reduction in power to said motor, improving its efficiency.

2. A control system as set forth in claim 1 wherein said current sampling means includes a current transformer wherein the primary winding of the current transformer is to be placed in series with said each phase winding of said motor and means of providing a signal with phase information of the primary current.

3. A control system as set forth in claim 2 wherein said control means includes:

chopping means placed in circuit with said each phase winding of said motor and responsive to said pulse width modulator for varying average value of said winding current by controlling said duty cycle of said chopping frequency.