Motor torque control method and apparatus

• US 5,334,923 A
• Filed: 03/27/1992
• Issued: 08/02/1994
• Est. Priority Date: 10/01/1990
• Status: Expired due to Fees

• Current Assignee: Wisconsin Alumni Research Foundation (University of Wisconsin System)
• Original Assignee: Wisconsin Alumni Research Foundation (University of Wisconsin System)
• Inventors: Moreira, Julio C., Hung, Kam T., Lipo, Thomas A., Lorenz, Robert D.
• Primary Examiner(s): Shoop, Jr., William M.
• Assistant Examiner(s): Cabeca, John W.
• Application Number:
  US07/858,172
• Time in Patent Office: 858 Days
• Field of Search: 318/807, 318/800, 318/803, 318/805, 318/811, 318/808, 318/798, 318/806, 187/29 R
• US Class Current: 318/805
• CPC Class Codes: H02P 21/141 Flux estimation
• CPC Class Codes: H02P 21/18 Estimation of position or speed
• CPC Class Codes: H02P 6/187 using the star point voltage

Abstract

A method and apparatus for controlling torque by correcting slip gain error in an operating induction motor is provided. This is accomplished by measuring the amplitude and position of a flux in the motor such as rotor flux. Rotor flux position and amplitude can be estimated from the air gap flux. The slip gain can then be corrected in a single step or a few steps to provide a deadbeat control.

Claims

1. A method of controlling the torque of an operating multiple phase induction motor having rotor means, stator means and an air gap therebetween comprising the steps of:

a) determining the third harmonic component of stator voltage and calculating the third harmonic component of air gap flux from said third harmonic component of stator voltage;

b) measuring the amplitude of a representative stator current;

c) measuring the phase angle between the fundamental component of said stator current and said third harmonic component of air gap flux;

d) determining the fundamental air gap flux and its magnitude from said third harmonic component of air gap flux;

e) calculating the rotor flux position and amplitude parameters from said fundamental air gap flux;

f) calculating a slip gain error from said rotor flux parameters;

g) calculating a correct slip gain based on said slip gain error; and

h) controlling the input slip frequency to said motor based on said correct slip gain using motor power voltage and input power frequency.

2. A method for controlling the rotor field orientation in an operating multiphase induction machine having stator means, rotor means and an air gap therebetween, said method comprising the steps of:

a) determining the third harmonic component of air gap flux from the third harmonic component of stator phase voltage;

b) determining the maximum value of the fundamental component of said air gap flux from said third harmonic air gap flux component;

c) measuring the phase angle between the maximum value of the stator current and the maximum value of said fundamental air gap flux component;

d) passing said phase angle and also the maximum value of said third harmonic air gap flux component through a quadrature oscillator means which produces direct and quadrature components of said fundamental air gap flux component;

e) computing the rotor flux from said direct and said quadrature components;

f) comparing said computed rotor flux to a reference motor flux, thereby generating a phase angle value which represents the difference between the fully oriented rotor field orientation and the actual rotor field orientation;

g) inputing said phase angle signal into a regulator means along with reference signals for said direct and said quadrature values of current being input into said machine, thereby generating current values for each phase of said machine; and

h) charging said current values into a current regulator from which power is fed to said machine, thereby regulating input power to control said rotor field orientation.

3. An apparatus for controlling rotor field orientation in an operating multiphase induction machine having stator means, rotor means and an air gap therebetween, said apparatus comprising in combination:

a) means for determining the third harmonic component of air gap flux from the third harmonic component of stator phase voltage;

b) means for determining the maximum value of the fundamental component of said air gap flux from said third harmonic air gap flux component;

c) means for measuring the phase angle between the maximum value of the stator current and said maximum value of said fundamental air gap flux component;

d) means for passing said phase angle and the maximum value of said third harmonic air gap flux component through a quadrature oscillator means which produces direct and quadrature components of said fundamental air gap flux component;

e) means for computing the rotor flux from values for said direct and said quadrature components of said fundamental air gap flux component and for identifying rotor field orientation;

f) means for comparing said rotor flux to a desired rotor field orientation and for generating an output signal representation of such comparison; and

g) means for regulating input current and frequency thereof to said machine, thereby to control rotor field orientation.

4. A method for correcting slip gain error in an operating multi-phase induction motor whose stator winding is connected to a power-providing inverter, said method comprising the steps of:

a) determining the third harmonic component of stator voltage by summing the stator voltage components and integrating said third harmonic component of stator voltage to calculate the third harmonic component of stator flux;

b) estimating the amplitude of the fundamental component of the air gap flux from (i) the characteristic relationship existing in said motor between the amplitude of said third harmonic component of said stator flux and said amplitude fundamental of said air gap flux, and (ii) the relative position with respect to the stator current as measured by the phase displacement between a first point which is along the waveform of said third harmonic component of said stator flux and which corresponds with the maximum value of said fundamental component of said air gap flux and a second point which is along the waveform of said stator current which corresponds with the maximum value of said stator current;

c) calculating each of the q-axis and the d-axis components of the rotor flux using q-axis and d-axis components of each of (i) the amplitude of said amplitude fundamental component of said air gap flux and (ii) said stator current;

d) comparing said q-axis and said d-axis components of said rotor flux with respective model reference values of said q-axis and said d-axis components of said rotor flux and calculating from the resulting difference values a slip gain error, said model reference values being selected from the rotor position;

e) calculating the reference slip gain from the reference values for each of (i) the q-axis value of said stator current and (ii) said d-axis value of said rotor flux;

f) comparing said slip gain error with the reference slip gain to produce the actual slip gain;

g) charging said actual slip gain, the rotor position, and each of said q-axis and said d-axis values of said stator current to an indirect field oriented controller and producing phased current outputs which are corrected for said slip gain error;

h) charging said corrected phase current outputs to a current regulated pulse width modulated inverter and generating currents and voltages which are corrected for said slip gain error; and

i) powering said motor with said corrected currents and voltages.

5. The method of claim 4 wherein, in step (c), said calculating is carried out using the following relationships:

##EQU13## where;

λ

indicates flux,

L_r indicates rotor self inductance,

L_m indicates magnetizing inductance,

L_lr indicates rotor leakage inductance,

i indicates current,

superscript e indicates synchronous reference frame,

subscript s indicates stator,

subscript q indicates q-axis,

subscript d indicates d-axis, and

subscript r indicates rotor.

6. The method of claim 4 wherein, in step (d), said slip gain error is so calculated using the following relationship:

space="preserve" listing-type="equation">Δ

K.sub.s =Δ

m×

λ

.sub.dr.sup.e*-1

where

Δ

indicates a variation in a quantity,

K_s indicates slip gain,

m indicates machine parameters,

λ

indicates flux,

subscript d indicates d-axis,

subscript r indicates rotor,

superscript e indicates synchronous reference frame, and

* indicates the reference value of an indicated variable.

7. An apparatus for on-line, feed forward correcting of the slip gain error in a continuously operating multi-phase induction motor whose stator winding is connected to a power-providing inverter, said apparatus comprising in combination:

a) means for determining the third harmonic component of stator voltage;

b) means for estimating the amplitude of the fundamental component of air gap flux including a reference table interrelating for said motor the amplitude of the third harmonic component of the stator flux with said amplitude of the fundamental component of air gap flux and further including means for measuring the phase displacement between the point along the waveform of said third harmonic component of stator flux which corresponds with the maximum value of said fundamental component of air gap flux and the point along the stator current waveform which corresponds with the value thereof;

c) means for calculating each of the q-axis and the d-axis components of each of the stator current and the fundamental air gap flux amplitude, and also for calculating from such components each of the q-axis and the d-axis components of the rotor flux;

d) means for determining model reference values of said q-axis and said d-axis components from the rotor position and for comparing said q-axis and said d-axis components of said rotor flux with said respective model reference values;

e) means for calculating the reference slip gain from said reference values for each of said q-axis value of the stator current and said d-axis value of the rotor flux;

f) means for comparing the slip gain error with the reference slip gain to produce the actual slip gain;

g) indirect field oriented controller means responsive to said actual slip gain, the rotor position, and each of said q-axis and said d-axis values of said stator current and productive of phased current outputs which are corrected for said slip gain error; and

h) current regulated pulse width modulated inverter means responsive to said corrected phased current outputs and productive of current and voltage outputs which are corrected for said slip gain error.

8. A method for controlling torque by correcting slip gain error in an operating three phase, wye connected induction motor having rotor means, stator means, and an air gap therebetween, said motor being powered through a current-regulated inverter means, said method comprising the steps of:

a) determining the fundamental component of the air gap magnetic flux by;

(1) summing the stator phase voltages to produce resultantly the third harmonic component of stator voltage;

(2) integrating said third harmonic component of stator voltage to produce the third harmonic component of said air gap magnetic flux; and

(3) identifying the fundamental component of said air gap magnetic flux from said third harmonic component of said air gap magnetic flux;

b) estimating information for the rotor flux position and amplitude;

c) resolving said fundamental component of said air gap magnetic flux into its d-axis and q-axis components;

d) comparing said d-axis and q-axis components to a field oriented reference model and calculating slip gain error;

e) comparing said so calculated slip gain error to the calculated slip gain to produce an output signal;

f) regulating an indirect field oriented controller with said output signal and with said rotor flux position information to produce a resultant signal;

g) regulating phase voltages in said inverter by said resultant signal; and

h) operating said motor from the voltage and the current outputs of said inverter.