Synthesis of zero-impedance converter

• US 5,013,998 A
• Filed: 12/18/1989
• Issued: 05/07/1991
• Est. Priority Date: 12/18/1989
• Status: Expired due to Fees

• Current Assignee: Ljubomir D. Varga, Losic, Novica A.
• Original Assignee: Ljubomir D. Varga, Losic, Novica A.
• Inventors: Losic, Novica A., Varga, Ljubomir D.
• Primary Examiner(s): Stephan, Steven L.
• Assistant Examiner(s): VOELTZ, EMANUEL T
• Application Number:
  US07/452,000
• Time in Patent Office: 505 Days
• Field of Search: 363/16, 363/21, 363/97, 323/285, 323/286, 323/287, 318/808, 318/809, 318/810, 318/811, 388/811, 388/815, 388/819, 388/821, 388/822, 388/823, 388/824
• US Class Current: 323/285
• CPC Class Codes: H02M 3/10 using discharge tubes with control electrode or semiconductor devices with control electrode H02M3/07 takes precedence

Abstract

A method of synthesizing a system which forces finite value of an impedance to zero comprising positive current feedback of exactly specified nature and value of its transfer function. The stability and dynamics of the system are controlled by additional voltage loop. The zero-impedance converter is used to synthesize load-independent systems including switch-mode power converters and pulse width modulated electric motor drive systems incorporating any kind of motor.

Claims

1. A method for synthesizing zero-impedance converter comprising:

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

coupling through an output filter to a load to be energized 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 manner,

supplying a resulting control voltage for modulating said power converter,

sampling a voltage across said load,

sensing a current through an output filter inductor,

feeding back the sampled voltage signal in a negative feedback loop with respect to a reference voltage and summing the two voltages,

passing a signal obtained as the algebraic sum of the sampled voltage and said reference voltage through a stabilizing network;

thereby producing a voltage loop processed error signal proportional to a difference between the two voltages,

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

supplying said resulting control voltage, obtained as the sum of said voltage loop processed error 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 source to the output load, whereby impedance of said output filter inductor is being forced to zero making said voltage across said load independent of said load and of variations of a parallel output filter capacitor and making a transfer function of the zero-impedance converter independent of a parameters of said output filter and said load.

2. The method of claim 1 wherein said source of electrical energy is being of said constant voltage or being of said feedforward compensated voltage adjusting a slope of a rising edge of a sawtooth waveform inherent in said pulse width modulation manner, whereby said slope is made in a direct proportion to the input voltage.

3. The method of claim 2 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

4. The method of claim 3 wherein said equation providing transfer function of said current feedback circuit is physically implemented, thereby implementing said current feedback circuit, in accordance with an expression giving said impedance of said output filter inductor in laplace domain

5. A method for synthesizing zero-impedance converter comprising:

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

coupling mechanically a shaft of an electric motor, including a direct current, an alternating current synchronous and asynchronous, and a step motor, 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 manner,

supplying a total control signal for modulating said power converter, supplying a 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 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 reference voltage and said position error signal and summing the three voltages,

passing a signal obtained as the algebraic sum of said velocity feedback signal and said velocity reference voltage and said position error signal through a stabilizing and control block;

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

sensing a current through said electric motor, including said direct current, or said alternating current synchronous or asynchronous, or said step motor,

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 impedance of said electric motor, including impedance of said direct current motor, or impedance of said alternating current synchronous or asynchronous motor, or impedance of said step motor, is being forced to zero making an angular shaft speed and position independent of said load and making a transfer function from said control signal, applied to the zero impedance converter, to said angular shaft speed and position a constant independent of a time constants of said electric motor and of a mechanisms of producing torque of said electric motor and of a mechanical parameters of said electric motor and said load.

6. The method of claim 5 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

7. The method of claim 6 wherein said equation providing transfer function of said current feedback circuit is physically implemented, thereby implementing said current feedback circuit, in case of the direct current motors, or the alternating current synchronous motors, or the step motors, in accordance with an expression giving said impedance of said electric motor in laplace domain Z_ekv (s) as a series connection of a resistance and an inductive reactance of said electric motor, and, in case of the alternating current asynchronous motors, in accordance with another expression giving said impedance of said electric motor in laplace domain Z_ekv (s) as a series connection of a stator impedance with parallel connection of a magnetizing reactance and a rotor impedance referred to stator of said electric motor.