Induction motor driver

• US 8,779,711 B2
• Filed: 04/20/2011
• Issued: 07/15/2014
• Est. Priority Date: 04/20/2011
• Status: Active Grant

• Current Assignee: Canadian Solar Sses (UK) Ltd.
• Original Assignee: Princeton Power Systems Incorporated
• Inventors: Liu, Yang
• Primary Examiner(s): DUDA, RINA I
• Application Number:
  US13/090,426
• Publication Number:
  US 20120268056A1
• Time in Patent Office: 1,182 Days
• Field of Search: 318/727, 318/609, 318/610, 318/461, 318/798, 318/432, 318/434, 318/799
• US Class Current: 318/432
• CPC Class Codes: H02M 7/4826 operating from a resonant DC source, i.e. the DC input voltage varies periodically, e.g. resonant DC-link inverters
• CPC Class Codes: H02P 2201/13 DC-link of current link type, e.g. typically for thyristor bridges, having an inductor in series with rectifier
• CPC Class Codes: H02P 27/045 whereby the speed is regulated by measuring the motor speed and comparing it with a given physical value

Abstract

A switched resonant power converter applies AC to an induction motor. The power converter controls the magnitude and phase of the motor current, and tuning the stator flux accordingly in order to control the motor speed. A preprocessor operates on a speed command signal by getting the user speed command input to produce amplitude and phase-related signals for application to inputs of the power converter control.

Claims

1. A method for controlling the speed of an induction motor including a rotor, said method comprising the steps of:

selecting a desired rotor speed;

determining motor rotor speed;

comparing said motor rotor speed to said desired rotor speed, to thereby generate a speed error signal;

applying said speed error signal to a proportional-integral controller, to thereby generate a torque command signal;

normalizing said torque command signal to maximum specified torque to thereby generate normalized signals;

determining a magnetizing current of said motor;

generating a stator current amplitude command signal from said torque command signal;

determining ideal volts/Hz value for the motor;

subtracting an actual volts/Hz value from the ideal volts/Hz value for the motor, to thereby generate volts/Hz error;

multiplying said volts/Hz error by at least a constant and an integral to thereby generate a phase correction signal;

generating a current phase precursor signal from said torque command signal;

adding said current phase precursor signal to said phase correction signal to thereby generate a signal representing the phase of the stator current; and

controlling the switching of current to and from a central capacitor in response to said amplitude command signal and said signal representing the phase of said stator current.

2. A method according to claim 1, wherein said step of determining motor rotor speed further comprises the step of measuring rotor speed with a tachometer.

3. A method according to claim 1, wherein said step of generating a stator current amplitude command signal from said torque command is performed by iteratively calculating

4. A method according to claim 1, wherein said step of generating a current phase precursor signal from said torque command signal is performed by iteratively calculating

5. A method according to claim 1, wherein said step of generating a stator current amplitude command signal from said torque command is performed by iteratively calculating

6. A control apparatus for an induction motor, which induction motor includes a stator, said control apparatus comprising:

a source of three-phase alternating current;

a switching circuit including a source port coupled to said source of alternating current and a motor port coupled to said stator, said switching circuit including a central capacitor through which all charge flows between said source port and said motor port and also including controllable switches for routing said charge to create stator current;

a switching controller coupled to said controllable switches for establishing the timing of said controllable switches in response to digital command signals representing (a) the amplitude of the stator current and (b) the phase of the stator current;

a source of motor speed command signals;

a motor control arrangement coupled to said source of motor speed command signals and to said switching controller, said motor control arrangement comprising an error detector for generating a motor speed error signal, a torque command controller for generating a torque command signal from said speed error signal, a torque current normalizing arrangement for normalizing said torque command signal to the full-load motor torque to produce torque current signal, for processing said torque current signal for generating signals representing (a) the amplitude of the stator current and (b) the phase of the stator current, both adjusted by the magnetizing current of the motor;

said motor control arrangement further comprising a coupling path for coupling said amplitude of the stator current adjusted by the magnetizing current from said motor control arrangement to said switching controller for control of the timing of said switches, an error detector coupled to said motor port and to a source of nominal motor V/Hz signal, for generating V/Hz error signal, a summing circuit coupled to sum processed V/Hz error signal with said signals representing the phase of the stator current, to thereby generate phase- corrected signals representing the phase of the stator current, and a coupling path for coupling said phase-corrected signals representing the phase of the stator current to said switching controller.

7. A method for controlling the speed of an induction motor, said method comprising the steps of:

determining a torque command signal;

generating an amplitude command signal from said torque command signal;

generating a stator current amplitude command signal from said torque command signal;

determining a phase correction signal;

generating a current phase precursor signal from said torque command signal;

adding said current phase precursor signal to said phase correction signal to thereby generate a signal representing the phase of a stator current; and

controlling the switching of current to and from a capacitor in response to said amplitude command signal and said signal representing the phase of said stator current.