Method for determining the short-circuit inductance of an asynchronous machine

• US 5,477,162 A
• Filed: 08/24/1994
• Issued: 12/19/1995
• Est. Priority Date: 01/09/1992
• Status: Expired due to Fees

• Current Assignee: Abb Industry Oy (ABB Limited)
• Original Assignee: Abb Industry Oy (ABB Limited)
• Inventors: Heikkila, Samuli
• Primary Examiner(s): Wieder, Kenneth A.
• Assistant Examiner(s): WARDAS, MARK A
• Application Number:
  US08/256,274
• Time in Patent Office: 482 Days
• Field of Search: 324/772
• US Class Current: 324/765.01
• CPC Class Codes: G01R 31/343 in operation

Abstract

A method of determining a short-circuit inductance in an asynchronous machine even during operation of the machine includes the steps of causing a step change in the stator voltage (u_s); measuring both the stator voltage (u_s) and the stator current derivative (i'"'"'_s) both before and after the step change in the stator voltage; determining the difference between the measured stator voltages (u_s (t₁), u_s (t₂)) and the difference between the measured stator current derivatives (i'"'"'_s (t₁), i'"'"'_s (t₂)); and determining the quotient of the difference between the stator voltages and the difference between the stator current derivatives for obtaining a short-circuit inductance (σL_s).

Claims

1. Method of determining an instantaneous short circuit inductance in an asynchronous machine during operation thereof, comprising the steps of:

measuring a first stator voltage value and a first stator current derivative value;

generating a step change in the stator voltage immediately after the measurement of said first stator voltage value and the measurement of said first stator current value;

measuring a second stator voltage value and a second stator current derivative value immediately after said step change in the stator voltage;

determining the difference between the first and the second stator voltage values and the first and the second stator current derivative values, respectively, and

determining the instantaneous short circuit inductance by forming the quotient of the difference of said first and second stator voltage values and the difference of said first and second stator current derivative values.

2. A method as claimed in claim 1, wherein said step of measuring a first stator voltage value and a first stator current derivative value and said step of measuring a second stator voltage value and a second stator current derivative value occur respectively 100 us before and after said step change in the stator voltage and wherein the rotor time constant is 100 ms.

3. Apparatus for determining an instantaneous short circuit inductance in an asynchronous machine during operation thereof, comprising:

first means for measuring a first stator voltage value and a first stator current derivative value;

means for generating a step change in the stator voltage immediately after the measurement of said first stator voltage value and the measurement of said first stator current value;

second means for measuring a second stator voltage value and a second stator current derivative value immediately after said step change in the stator voltage;

means for determining the difference between the first and the second stator voltage values and the first and the second stator current derivative values, respectively, and

means for determining the instantaneous short circuit inductance by forming the quotient of the difference of said first and second stator voltage values and the difference of said first and second stator current derivative values.

4. Apparatus as claimed in claim 3, wherein said first means for measuring and said second means for measuring occur respectively 100 us before and after said step change in the stator voltage and wherein the rotor time constant is 100 ms.

5. A method for controlling torque in an asynchronous machine, comprising the steps of:

measuring a first stator voltage value and a first stator current derivative value;

generating a step change in the stator voltage immediately after the measurement of said first stator voltage value and the measurement of said first stator current value;

measuring a second stator voltage value and a second stator current derivative value immediately after said step change in the stator voltage;

determining the difference between the first and the second stator voltage values and the first and the second stator current derivative values, respectively;

determining the instantaneous short circuit inductance by forming the quotient of the difference of said first and second stator voltage values and the difference of said first and second stator current derivative values;

determining an estimate of the stator flux from said instantaneous short circuit inductance, measured stator voltage and stator current, stator resistance, stator inductance, rotor time constant and the rotation rate of said asynchronous motor in accordance with the equation;

##EQU13## multiplying said stator flux by the measured value of said stator current to obtain an estimate of the torque of said asynchronous machine;

subtracting a reference torque from said estimate of the torque to obtain a control parameter u; and

increasing the torque of said asynchronous machine where u<

0 and decreasing said torque where u>

0.

6. A method as claimed in claim 5, wherein said step of measuring a first stator voltage value and a first stator current derivative value and said step of measuring a second stator voltage value and a second stator current derivative value occur respectively 100 us before and after said step change in the stator voltage and wherein the rotor time constant is 100 ms.

8. A method as claimed in claim 6, wherein said first means for measuring and said second means for measuring operate respectively 100 us before and after said step change in the stator voltage and wherein the rotor time constant is 100 ms.

7. Apparatus for controlling torque in an asynchronous machine, comprising:

first means for measuring a first stator voltage value and a first stator current derivative value;

means for generating a step change in the stator voltage immediately after the measurement of said first stator voltage value and the measurement of said first stator current value;

second means for measuring a second stator voltage value and a second stator current derivative value immediately after said step change in the stator voltage;

means for determining the difference between the first and the second stator voltage values and the first and the second stator current derivative values, respectively;

means for determining the instantaneous short circuit inductance by forming the quotient of the difference of said first and second stator voltage values and the difference of said first and second stator current derivative values;

means for determining an estimate of the stator flux from said instantaneous short circuit inductance, measured stator voltage and stator current, stator resistance, stator inductance, rotor time constant and the rotation rate of said asynchronous motor in accordance with the equation;

##EQU14## means for multiplying said stator flux by the measured value of said stator current to obtain an estimate of the torque of said asynchronous machine;

means for subtracting a reference torque from said estimate of the torque to obtain a control parameter u; and

means for increasing the torque of said asynchronous machine where u<

0 and decreasing said torque where u>

0.