Driving apparatus and driving system for electric motor

Abstract

An apparatus for controlling the drive of an electric motor, having a current detector for detecting the current through an externally connected electric motor; a controller for generating a control signal to control the electric motor on the basis of the current detected by the current detector and the speed command for specifying the rotational speed of the electric motor; wherein the apparatus includes a load estimator for estimating the mechanical load condition associated with the electric motor on the basis of the current detected by the current detector and the speed command, and the controller controls the electric motor current on the basis of the detected current, the speed command and the estimated load condition.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows the overall constitution of an AC motor driving system as an embodiment of this invention;

FIG. 2 is a diagram for explaining the effective and the virtual angular positions of the rotor of the electric motor used with the system shown in FIG. 1;

FIG. 3 schematically shows the constitution of the load estimator used in the control device of the system shown in FIG. 1;

FIG. 4 schematically shows the constitution of the speed compensator used in the control device of the system shown in FIG. 1;

FIG. 5 schematically shows the constitution of the current command generator used in the control device of the system shown in FIG. 1;

FIG. 6 shows several graphs used for explaining an operation of the control device of the system shown in FIG. 1;

FIG. 7 shows a graph used for explaining the operation of the current command generator incorporated in the control device of the system shown in FIG. 1;

FIG. 8 shows several graphs used for explaining another operation of the control device of the system shown in FIG. 1;

FIG. 9 shows several graphs used for explaining yet another operation of the control device of the system shown in FIG. 1;

FIG. 10 shows several graphs used for explaining still another operation of the control device of the system shown in FIG. 1;

FIG. 11 schematically shows the overall constitution of an AC motor driving system as another embodiment of this invention;

FIG. 12 schematically shows the constitution of the current command generator used in the control device of the system shown in FIG. 11;

FIG. 13 shows several graphs used for explaining an operation of the control device of the system shown in FIG. 11;

FIG. 14 shows several graphs used for explaining another operation of the control device of the system shown in FIG. 11;

FIG. 15 is a circuit diagram used to explain how a current detection method according to this invention works; and

FIG. 16 is a circuit diagram used to explain how another current detection method according to this invention works.

Claims

1. An apparatus for controlling the drive of an electric motor comprising: a current detecting means for detecting the current to flow through an externally connected electric motor; anda controlling means for generating a control signal to control the electric motor on the basis of both the current detected by the current detecting means and the speed command value for specifying the rotational speed of the electric motor,wherein the apparatus further includes a load estimating means for estimating the mechanical load condition associated with the electric motor on the basis of both the current value detected by the current detecting means and the speed command value, and the controlling means controls the motor current on the basis of the detected current value, the speed command value and the estimated load condition.

2. An apparatus for controlling the drive of an electric motor, as claimed in claim 1, wherein the electric motor is a poly-phase AC motor having a stator and a rotor to rotate with respect to the stator;the current detecting means detects the current values decomposed into two components one of which is along the virtual magnetic flux axis advanced by an axial displacement Δθ in the direction of the rotation of the rotor with respect to the magnetic flux axis of the rotor and the other of which is along the virtual torque axis advanced by 90 degrees in the direction of the rotation with respect to the virtual magnetic flux axis; andthe motor current component along the virtual torque axis is controlled.

3. An apparatus for controlling the drive of an electric motor, as claimed in claim 2, wherein the controlling means includes an axial displacement estimator for estimating the axial displacement between the magnetic flux axis of the rotor and the virtual magnetic flux axis used for control; andthe motor current is controlled by the compensatory speed command value obtained by compensating the speed command value on the basis of the estimated axial displacement and the estimated load condition and the speed command value.

4. An apparatus for controlling the drive of an electric motor, as claimed in claim 1, wherein the controlling means includes a speed compensating means for compensating the speed command value depending on the load condition; andthe motor current is controlled on the basis of the speed command value and the compensated speed command value.

5. An apparatus for controlling the drive of an electric motor, as claimed in claim 4, wherein the speed command value is compensated by using the estimated load condition when the speed command value is smaller than a predetermined threshold; andthe speed command value is compensated by using the estimated axial displacement when the speed command value is not smaller than the predetermined threshold.

6. An electric motor driving system comprising an electric motor;a power converter for generating the motor current to flow through the electric motor;a current detecting means for detecting the motor current; anda controlling means for generating the control signal to control the electric motor on the basis of the current values detected by the current detecting means, and the speed command value to command the rotational speed of the electric motor;wherein the system further includes a load estimating means for estimating the mechanical load condition imposed on the electric motor on the basis of the electric motor current and the speed command value; andthe controlling means controls the power converter on the basis of the detected current values, the speed command value and the estimated load condition.