Sensorless Induction Motor Control via Feed-Forward Angular Position
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Solution Overview
Problem
Conventional speed-sensorless vector control methods for induction motors face challenges in estimating motor speed at low stator angular frequencies, leading to limitations in load capability and stability, especially when operating near zero angular frequency.
Innovation Solution
A sensorless control apparatus and method that includes a rotating-speed locked loop and a feed-forward magnetizing-axis angular position emulator, which produces an emulated torque current and emulated rotor angular speed to generate a feed-forward stator angular frequency command, ensuring the stator angular frequency remains above a minimum threshold, thereby avoiding zero angular frequency conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional speed-adaptive flux observers are used for speed feedback, then speed-sensorless vector control can be implemented, but the system becomes unstable and loses load capability at low stator angular frequencies near zero
Solution Approach 1:
The patent applies preliminary action by calculating a feed-forward stator angular frequency command in advance using the relationship between electromagnetic torque, rotor speed, and stator frequency. This pre-calculated frequency command is then used to adjust the operating point before the system reaches low-frequency conditions, preventing the instability that would otherwise occur near zero frequency. The feed-forward mechanism proactively compensates for the inherent limitations of flux observers at low frequencies.
2Speed
If the stator angular frequency is allowed to approach zero, then the motor can operate at very low speeds, but the flux observer cannot accurately estimate motor speed leading to control failure
Solution Approach 1:
The patent introduces an intermediary mechanism - the feed-forward stator angular frequency command calculation - that mediates between the desired low-speed operation and the flux observer's inability to accurately estimate speed at low frequencies. By calculating the required stator frequency based on torque and speed relationships, the system ensures the flux observer operates within its accurate measurement range while still achieving very low speed operation through proper frequency adjustment.
3Reliability
If flux-weakening method is used to avoid zero angular frequency, then the stator angular frequency is maintained above minimum, but the load capability is reduced
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the stator angular frequency based on the calculated feed-forward command that considers the actual load conditions. Instead of using a fixed flux-weakening approach that reduces load capability, the system modifies the operating parameters (stator frequency) in real-time based on torque and speed requirements, maintaining both reliability by avoiding zero frequency and preserving load capability through adaptive parameter adjustment.
Data Source
AI summary
A control apparatus for an induction motor is provided and includes a rotating-speed locked loop and a feed-forward magnetizing-axis angular position emulator. The rotating-speed locked loop emulates a speed control loop of the induction motor for producing an emulated torque current and an emulated rotor angular speed. The feed-forward magnetizing-axis angular position emulator receives the emulated torque current and the emulated rotor angular speed for producing a feed-forward estimated magnetizing-axis angular position, wherein according to the feed-forward estimated magnetizing-axis angular position, a first voltage controlling the induction motor is transformed from a synchronous reference coordinate system of the induction motor to a static reference coordinate system of the induction motor, and a two-phase current detected from the induction motor is transformed from the static reference coordinate system to the synchronous reference coordinate system. The state the stator angular frequency is at zero can be skipped through the apparatus.