Six-Step Flux Controller for Electric Machine Torque Control
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Solution Overview
Problem
Controlling AC motor/generators in six-step mode is challenging due to loss of controllability, specifically the inability to adjust voltage magnitude, which limits torque capability and makes it difficult to employ asynchronous frame current regulators.
Innovation Solution
A voltage source inverter controller with a current command generator, six-step flux controller, and current regulator that includes a proportional-integral feedback controller, anti-windup elements, dq voltage limit, and voltage magnitude limiter, which generates a flux modifier to regulate flux in the flux-weakening speed/load region, allowing for closed-loop current control and pulsewidth-modulated stator current generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the inverter operates in six-step mode to maximize output voltage magnitude and increase torque capability, then torque capability is improved, but voltage magnitude becomes uncontrollable and controllability is reduced
Solution Approach 1:
The patent implements dynamic switching between six-step mode and PWM mode based on operating conditions. The controller dynamically adjusts the control strategy: using six-step mode when maximum torque capability is needed, and switching to PWM mode when voltage magnitude control is required. This dynamic adaptation resolves the contradiction by allowing the system to have both high torque capability and controllability depending on the operational requirements.
2Stress or pressure
If six-step mode is used to achieve maximum voltage magnitude, then voltage magnitude is improved, but the ability to regulate voltage magnitude is lost
Solution Approach 1:
The controller is designed with multi-functionality to handle both six-step mode and PWM mode operations. It universally supports both control strategies, allowing the system to achieve maximum voltage magnitude when needed while retaining the ability to regulate voltage magnitude through PWM mode. The controller can adapt its function based on the required operation, resolving the contradiction between achieving maximum voltage and maintaining voltage control.
3Device complexity
If asynchronous frame current regulator is employed with six-step mode, then current control is simplified, but controllability is reduced due to loss of degree of freedom
Solution Approach 1:
The patent introduces a synchronous frame current regulator as an intermediary control layer between the current commands and the six-step inverter. This regulator transforms the control problem by working in the synchronous reference frame, which simplifies the current control while maintaining the ability to control both magnitude and angle of the voltage through flux weakening control. The intermediary regulator resolves the contradiction by providing a control framework that works effectively with six-step mode without sacrificing controllability.
Data Source
AI summary
A voltage source inverter controller for controlling an inverter electrically connected to an electric machine includes a current command generator, a six-step flux controller and a current regulator. The six-step flux controller generates a flux modifier to regulate flux in a flux-weakening speed/load operating region of the electric machine when operating the electric machine in a six-step mode. The current command generator converts a desired torque to three-phase desired currents that are input to a dq0-dq transformer and combined with the flux modifier to determine a modified-flux direct-quadrature (dq) current request. The current regulator includes a proportional-integral feedback controller, anti-windup elements, a dq voltage limit element and a voltage magnitude limiter. The proportional-integral feedback controller and the anti-windup elements perform closed-loop current control on the modified-flux dq current request to determine commanded dq voltages.