Space vector modulation methods and structures for...

Details Space vector modulation methods and structures for... Space vector modulation methods and structures for...

2002-01-31

2003-11-25

Nappi, Robert E. (Department: 2837)

Electricity: motive power systems

Induction motor systems

Primary circuit control

C318S808000, C363S040000

Reexamination Certificate

active

06653812

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to electric motors and, more particularly, to control systems for electric motors.
2. Description of the Related Art
In many modern control systems, performance parameters (e.g., speed and torque) of electric motors (e.g., AC induction motors, brushless DC motors and synchronous motors) are controlled in accordance with space vector modulation which generates a reference voltage vector V
ref
whose angular speed determines a desired synchronous speed of a motor and whose amplitude determines a desired motor voltage.
The reference voltage vector V
ref
rotates with respect to a plurality of voltage vectors that each represent a respective one of switch states of an inverter that is coupled to the motor. The control system commands the inverter to generate patterns of the switch states as a function of the instantaneous magnitude and location of the reference voltage vector V
ref
. Feedback signals are often provided to the control system by a single current sensor that is coupled to one side of the inverter.
Although space vector modulation facilitates improved control performance (e.g., less harmonic distortion) and the single current sensor reduces system costs, it has been found that these systems sometimes contain errors which degrade system performance.
BRIEF SUMMARY OF THE INVENTION
The present invention is directed to space vector modulation methods and structures that reduce feedback errors which degrade motor control performance.
The invention recognizes that these errors generally occur when feedback signals become so narrow that they cannot be accurately processed. The invention further recognizes that narrow feedback signals correspond to certain relationships between a reference voltage vector V
ref
and voltage vectors that each represent a respective one of converter switch states.
In response to these recognitions, embodiments of the invention provide space vector modulation methods and structures which modify the reference voltage vector V
ref
to thereby avoid excessively narrow feedback signals. In particular, the rotation of a reference voltage vector V
ref
is modified as it rotates with respect to voltage vectors that each represent a respective one of converter switch states in an electric-motor control system. One embodiment modifies the reference voltage vector V
ref
as it approaches various voltage vectors and another modifies the reference voltage vector V
ref
when its magnitude is less than a predetermined magnitude.


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