Sensorless Motor Stall Detection With SMO-HFI Position Switching
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Solution Overview
Problem
Existing sensorless control methods for brushless DC motors in power tools face challenges in smoothly transitioning between control schemes during stall conditions, particularly when the motor rotor comes to a sudden stop, leading to inefficiencies and torque ripple.
Innovation Solution
A controller is configured to use a sliding-mode observer (SMO) process to estimate back electromotive force (back-EMF) voltage and detect the angular position of the rotor, predicting stall conditions by monitoring rotational speed and phase current, and transitioning to a high-frequency injection (HFI) process to determine the angular position, ensuring smooth execution of sensorless field-oriented control (SFOC).
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If sensorless field-oriented control uses a single control scheme (SMO or HFI), then the control is simple to implement, but it cannot maintain high efficiency and accurate rotor position detection across all speed ranges including stall conditions
Solution Approach 1:
The system dynamically switches between SMO and HFI control schemes based on real-time rotor speed detection. When the rotor is rotating, SMO is used; when stall is detected ( rotor stops), HFI is activated. This dynamic adaptation allows the system to maintain optimal performance across varying operating conditions without requiring a permanently complex multi-scheme architecture.
Solution Approach 2:
The control system changes its operational parameters by switching between two distinct control modes (SMO for rotating state, HFI for stalled state) based on the rotor speed parameter. This parameter-based mode switching enables the system to handle different speed ranges effectively, improving adaptability without permanently increasing system complexity.
2Use of energy by moving object
If the motor operates at high speed using trapezoidal control, then efficiency is improved, but torque ripple occurs at low speeds due to commutation cycling between phases
Solution Approach 1:
The system changes control parameters based on speed: at high speeds, trapezoidal control with SMO is used for efficiency; at low speeds and stall conditions, HFI is employed to eliminate torque ripple by injecting high-frequency voltage pulses that provide continuous torque without commutation cycling. This parameter-based control adaptation resolves the trade-off between efficiency and torque smoothness.
3Measurement precision
If Hall sensors are used to detect rotor position, then accurate position detection is achieved, but the motor structure becomes more complex and costly
Solution Approach 1:
The patent replaces mechanical Hall sensors with an electronic sensorless control system that uses voltage injection and current measurement to estimate rotor position. By injecting known voltage patterns and measuring the resulting current responses, the system calculates rotor position electronically, eliminating the need for physical sensors and reducing structural complexity while maintaining detection accuracy.
Solution Approach 2:
The system introduces an intermediary estimation process that infers rotor position from electrical measurements (current and voltage) rather than direct sensing. The controller acts as an intermediary, using mathematical models and signal processing to derive position information from indirect measurements, thereby avoiding the need for direct mechanical sensors.
4Speed
If the rotor speed drops quickly during stall condition, then stall detection is rapid, but smooth transition between control schemes (SMO to HFI) becomes difficult
Solution Approach 1:
The system performs preliminary stall detection by monitoring rotor speed and predicting stall conditions before they fully develop. By detecting the onset of stall early (when speed begins to drop), the system can proactively switch from SMO to HFI control, ensuring a smooth transition before the rotor comes to a complete stop. This preliminary action prevents the instability that would occur with abrupt transitions at zero speed.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for efficient power input to the motor across various speed ranges, including during stall conditions, by accurately estimating rotor position and transitioning between control processes, thereby maintaining high efficiency and reducing torque ripple.
Implementation Method 1
operate a sliding-mode observer (SMO) process to estimate a back electromotive force (back-EMF) voltage of the motor based on a phase current of the motor and detect an angular position of the rotor based on the estimated back-EMF voltage
Implementation Method 2
operate a high-frequency injection (HFI) process in response to predicting the occurrence of the stall condition, wherein the HFI process includes injecting a plurality of voltage pulses to the motor and detecting corresponding high-frequency current components to determine the angular position of the rotor
Data Source
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AI summary
A controller for operating a brushless motor comprising a stator and a rotor is configured to: operate a sliding-mode observer (SMO) process detect an angular position of the rotor; predict an occurrence of a stall condition based on at least one of a rotational speed of the rotor or the phase current of the motor; operate a high-frequency injection (HFI) process in response to predicting the occurrence of the stall condition to determine the angular position of the rotor; determine whether the stall condition has occurred; and transition from the SMO process to the HFI process in response to the determination of the stall condition has occurred. In an embodiment, a power tool is provided including a motor and a controller as described above.