Semiconductor Device for Sensorless Motor BEMF Detection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Sensor-less brushless DC motors face challenges in detecting back electromotive force (BEMF) at extremely low duty ratios due to short detection time periods, making precise speed control difficult, especially at low speeds.
Innovation Solution
A semiconductor device is configured to detect BEMF in the non-conduction phase during the regeneration period of a PWM signal, with a switch circuit and differential amplifier circuit to ensure accurate detection even at low duty ratios by adjusting the detection timing based on the duty ratio threshold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the duty ratio is made extremely low to achieve low-speed rotation, then the motor can rotate at low speed, but the duration of the back electromotive force generated in the stator winding becomes extremely short, making detection difficult
Solution Approach 1:
The patent applies preliminary action by extending the back electromotive force detection period into the regeneration period before the PWM cycle completely ends. By detecting BEMF during the regeneration period (when current flows through the freewheeling diode), the system accumulates sufficient detection time even when the main conduction period is extremely short, enabling reliable low-speed detection
2Speed
If the duty ratio is made extremely low, then low-speed control is achieved, but the on-time becomes shorter than the delay time of the control signal, making timing of reading the back electromotive force difficult
Solution Approach 1:
The system performs preliminary detection setup by configuring the detection circuit to operate during the regeneration period in advance. The control circuit is pre-programmed to switch detection timing based on duty ratio thresholds, eliminating real-time timing calculation complexity and enabling straightforward implementation even at extremely low duty ratios
Solution Approach 2:
The patent changes the detection timing parameter from the conventional conduction period to the regeneration period. By monitoring the duty ratio and switching detection windows accordingly, the system adapts to varying operating conditions without increasing overall control complexity, maintaining simplicity while extending detection capability to low-speed ranges
3Duration of action of moving object
If PWM frequency is reduced to extend on-time for back electromotive force detection, then detection becomes possible at low speed, but the PWM frequency limit is imposed on the system
Solution Approach 1:
The patent transitions from the time dimension (extending on-time by lowering PWM frequency) to a different operational dimension by utilizing the regeneration period. Instead of modifying PWM frequency, the system exploits the existing regeneration period within the same PWM cycle to provide extended detection time, thereby avoiding PWM frequency limitations while achieving sufficient BEMF detection duration
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
Enables reliable detection of BEMF at extremely low duty ratios, improving the control precision and performance of sensor-less brushless DC motors by extending the detection time in the regeneration period.
Implementation Method 1
a back electromotive force (BEMF) generated in a stator winding of a non-conduction phase because of rotation of a rotor of the motor is detected
Data Source
AI summary
To surely detect a back electromotive force generated in a non-conduction phase at an extremely low duty ratio, a motor driving system includes a three-phase motor, an inverter circuit, and a semiconductor device. A controller included in the semiconductor device compares a voltage at an output node corresponding to a non-conduction phase of the inverter circuit and a reference voltage with each other, thereby estimating a position of a rotor of the three-phase motor and generating a pulse width modulation signal based on the estimated position of the rotor. The controller detects the voltage at the output node of the non-conduction phase in a regeneration period of the pulse width modulation signal when a duty ratio of the pulse width modulation signal is less than a threshold value, the regeneration period being a period in which current is made to flow to the three-phase motor on a regeneration path.