Discrete-Time Current Control for Salient AC Motor Time-Constant Symmetry
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Solution Overview
Problem
Classical motor control techniques struggle with command tracking errors and poor disturbance rejection in asymmetric/salient AC motors, particularly at low fundamental-to-sampling ratios, making them difficult to analyze and control in real-time.
Innovation Solution
A direct discrete-time current controller modifies the asymmetric time constant of salient AC motors by independently manipulating d-axis and q-axis inductance and resistance, virtually translating it into a symmetric time constant using virtual inductive and resistive terms, enabling selective disturbance rejection at various frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If classical motor control techniques are applied to asymmetric/salient AC motors, then the motors can be controlled, but command tracking errors occur and disturbance rejection is poor
Solution Approach 1:
The patent transforms the asymmetric motor parameters (different d-axis and q-axis inductances) into symmetric equivalent parameters through mathematical transformation. By changing the parameter representation from physical asymmetric values to virtual symmetric values, the control system can apply simpler control algorithms while maintaining accuracy for salient machines.
Solution Approach 2:
The patent introduces virtual d-axis and q-axis inductances as intermediary parameters that do not physically exist but mathematically represent the asymmetric motor characteristics. These virtual parameters serve as a bridge between the physical asymmetric motor and the symmetric control algorithm, enabling accurate control without directly handling the complexity of asymmetric parameters.
2Speed
If asymmetric/salient AC motors are used for higher-speed applications, then speed range is expanded, but control complexity increases due to saliency
Solution Approach 1:
The patent changes the parameter representation from asymmetric physical inductances to symmetric virtual inductances, allowing the use of simpler symmetric control algorithms for high-speed asymmetric motors. This parameter transformation reduces control logic complexity while enabling high-speed operation.
Solution Approach 2:
The patent creates a virtual copy of the asymmetric motor model with symmetric parameters. Instead of directly controlling the complex asymmetric motor, the system controls a simplified symmetric virtual model that replicates the essential dynamics, reducing control complexity for high-speed applications.
3Productivity
If virtual translation is applied to asymmetric machines, then control bandwidth is improved, but computational requirements increase
Solution Approach 1:
The patent transforms asymmetric parameters into symmetric virtual parameters, enabling the use of faster symmetric control algorithms with higher bandwidth. The parameter transformation is computationally efficient, achieving improved control bandwidth without excessive computational burden.
Data Source
AI summary
An electric drive system of a motor vehicle or another battery electric system includes a power inverter module (PIM) connected to a DC power supply, an alternating current (AC) motor connected to the PIM and to a load, and a controller. The motor is a salient machine. Control logic of the controller includes a plant model of the electric drive system. The plant model includes an asymmetric time constant of the motor. The controller selectively modifies the asymmetric time constant via selective and independent operating point-specific manipulation of direct axis (d-axis) and quadrature axis (q-axis) inductance and resistance. The asymmetric time constant is virtually translated in the control logic into a symmetric modified time constant by manipulating or adding virtual inductive and virtual resistive terms independently and per operating point. The controller controls the motor at the operating point using the symmetric modified time constant.