Synthesis of load-independent ac drive systems

• US 4,967,134 A
• Filed: 02/27/1989
• Issued: 10/30/1990
• Est. Priority Date: 02/27/1989
• Status: Expired due to Fees

• Current Assignee: Ljubomir D. Varga, Losic, Novica A.
• Original Assignee: Ljubomir D. Varga, Losic, Novica A.
• Inventors: Varga, Ljubomir D., Losic, Novica A.
• Primary Examiner(s): Miska, Vit W.
• Assistant Examiner(s): MARTIN, DAVID S
• Application Number:
  US07/316,664
• Time in Patent Office: 610 Days
• Field of Search: 318/599, 318/714-715, 318/721-724, 318/737, 318/798-812, 318/650, 318/652-655, 318/560, 388/800-801, 388/809-815
• US Class Current: 318/802
• CPC Class Codes: H02P 23/16 Controlling the angular speed of one shaft H02P23/18 takes precedence
• CPC Class Codes: H02P 25/03 with brushless excitation

Abstract

A method of synthesizing load invariant ac synchronous and asynchronous motor drive systems comprising positive stator current feedback of exactly specified nature and value of its transfer functions. The system transfer function independent of load is realized while stability and dynamics of the system are controlled by additional voltage loop.

Claims

1. A method for synthesizing load independent alternating current drive system comprising:

accepting a source of electrical energy of a constant voltage at an input,

coupling mechanically an alternating current synchronous motor shaft to a load to be drive at an output,

controlling a power flow from said input to said output, modulating a power converter for the control of said power flow in a pulse width modulation control manner, supplying a total control signal for modulating said power converter,

supplying position feedback pulses,

feeding back side position feedback pulses in a negative feedback loop with respect to a position command pulses and comparing frequency and phase of the two pulse trains in a phase frequency detector;

thereby producing a position error voltage signal proportional to a difference in frequency and phase between the two pulse trains, supplying a velocity feedback signal,

feeding back said velocity feedback signal in a negative feedback loop with respect to a velocity command voltage and the position error signal and summing the three voltages, passing a signal obtained as the algebraic sum of the velocity feedback signal and the velocity command signal and the position error signal through a cascas connection of a filtering and stabilizing network and a control circuit;

thereby producing a control signal proportional to the algebraic sum of the velocity command signal and the velocity feedback signal and the position error signal,

sensing a current through an alternating current synchronous motor stator,

feeding back the sensed current signal through a current feedback circuit in a positive feedback loop with respect to said control signal and summing the two signals,

supplying said total control signal, obtained as the sum of said control signal and the current signal fed through said current feedback circuit, for modulating said power converter for the control of the flow of power from the input electrical source to the output mechanical load, whereby the alternating current synchronous motor shaft position and velocity is made independent of said load.

2. The method of claim 1 wherein said current feedback circuit in said positive feedback loop is synthesized using an equation providing transfer function in laplace domain of said current feedback circuit

3. The method of claim 2 wherein said equation providing transfer function of said current feedback circuit is physically implemented, thereby implementing said current feedback circuit, as a differentiator circuit with a direct current path wherein said differentiator circuit with said direct current path is arranged to provide a differentiating time constant equal to

4. A method for synthesizing load independent alternating current drive system comprising:

accepting a source of electrical energy of a constant voltage at an input,

coupling mechanically an alternating current asynchronous motor shaft to a load to be driven at an output,

controlling a power flow from said input to said output, modulating a power converter for the control of said power flow in a pulse width modulation control manner, supplying a total control signal for modulating said power converter,

supplying position feedback pulses,

feeding back said position feedback pulses in a negative feedback loop with respect to a position command pulses and comparing frequency and phase of the two pulse trains in a phase frequency detector;

thereby producing a position error voltage signal proportional to a difference in frequency and phase between the two pulse trains,

supplying a velocity feedback signal,

feeding back said velocity feedback signal in a negative feedback loop with respect to a velocity command voltage and the position error signal and summing the three voltages, passing a signal obtained a the algebraic sum of the velocity feedback signal and the velocity command signal and the position error signal through a cascade connection of a filtering and stabilizing network and a control circuit;

thereby producing a control signal proportional to the algebraic sum of the velocity command signal and the velocity feedback signal and the position error signal,

sensing a current through an alternating current asynchronous motor stator,

feeding back the sensed current signal through a current feedback circuit in a positive feedback loop with respect to said control signal and summing the two signals,

supplying said total control signal, obtained as the sum of said control signal and the current signal fed through said current feedback circuit, for modulating said power converter for the control of the flow of power from the input electrical source to the output mechanical load, wehreby the alternating current asynchronous motor shaft postion and velocity is made independent of said load.

5. The method of claim 4 wherein said current feedback circuit in said positive feedback loop is synthesized using an equation providing transfer function in laplace domain of said current feedback circuit

6. The method of claim 5 wherein said equation providing transfer function of said current feedback circuit is physically implemented, thereby implementing said current feedback circuit, as a parallel connection of a two signal processing circuits, the first of th two circuits processing a stator effects and physically implemented as a differentiator circuit with a direct current path wherein said differentiator circuit with said direct current path is arranged to provide a differentiating time constant equal to