Method for automated measurement of the ohmic rotor resistance of an asynchronous machine

• US 6,774,664 B2
• Filed: 02/28/2002
• Issued: 08/10/2004
• Est. Priority Date: 09/17/1998
• Status: Expired due to Term

• Current Assignee: Danfoss Drives A/S (Danfoss A/S)
• Original Assignee: Danfoss Drives A/S (Danfoss A/S)
• Inventors: Godbersen, Jens
• Primary Examiner(s): Nguyen, Vinh P.
• Application Number:
  US10/085,304
• Publication Number:
  US 20020158658A1
• Time in Patent Office: 894 Days
• Field of Search: 324/772, 324/73.1, 324/158.1, 324/545, 318/490, 318/803, 318/806, 702/108, 702/113, 702/57, 702/58
• US Class Current: 324/545
• CPC Class Codes: G01R 27/02 Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant by measuring phase angle only G01R25/00
• CPC Class Codes: G01R 31/34 Testing dynamo-electric machines
• CPC Class Codes: G01R 31/346 Testing of armature or field windings

Abstract

Method of automated measurement of the ohmic rotor resistance (R_r) of an asynchronous machine (1) controlled via an inverter (8) while being acted upon by a non-rotating field, the method involving a. measuring the ohmic stator resistance (R_s), the leakage inductances (L_σs, L_σr) and the main inductance (L_m) of the asynchronous machine, b. leading a testing signal (U_sa) being formed by a predetermined direct signal with a superimposed alternating signal corresponding approximately to the nominal slip frequency (f_s) of the asynchronous machine (1), c. measuring the amplitude and the phase (φ) of the phase signal (I_sa) resulting from the testing signal, and d. calculating the ohmic rotor resistance (R_r) from the measured values according to a) and c).

Claims

1. Method for automated measurement of the ohmic rotor resistance (R_r) of an asynchronous machine controlled via an inverter while being acted upon by a non-rotating field, the method comprising

a. measuring the ohmic stator resistance (R_s), the leakage inductances (L_σ

s, L<sub>σ

r</sub>) and the main inductance (L_m) of the asynchronous machine,

b. applying a testing signal (U_sa) consisting of a predetermined direct signal with a superimposed alternating signal to a phase winding (a) of the asynchronous machine, the frequency of the alternating signal corresponding approximately to a nominal slip frequency (f_s) of the asynchronous machine,

c. measuring the amplitude and the phase (φ

) of the phase signal({overscore (I)}_sa) resulting from the testing signal, and

d. calculating the ohmic rotor resistance (R_r) from the measured values according to steps a) and c).

2. Method according to claim 1, in which an ohmic rotor resistance (R′

_r) transformed to the stator side is determined first, and the actual ohmic rotor resistance (R_r) is calculated by means of the measured values according to steps a) and c).

3. Method according to claim 1 in which the frequency (f_s) of the alternating signal is in the range from 1 to 8 Hz.

4. Method according to claim 1 in which the direct signal is a direct voltage which generates a direct current having an amplitude of less than half a nominal magnetising current (I_mn) of the asynchronous machine.

5. Method according to claim 4, in which the direct current is such that the dynamic main inductance (L_Dm) is approximately equal to the static main inductance (L_m) of the asynchronous machine, whereby the dynamic main inductance can be expressed by the equation $L_{D}$

 



m=

Lm

Im·

Im+Lm

In which L_Dm is the dynamic main inductance, L_m the static main inductance and I_m the magnetising current.

6. Method according to claim 1 in which the testing signal is a phase voltage (U_sa) having a reference (U_ref) set on the basis of a previously measured characteristic, stored in a memory, the characteristic describing the relation between the phase current (I_sa) and the reference.