Motor Controller Back-EMF Detection via PWM Duty Cycle Control
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Solution Overview
Problem
Conventional sensorless driving methods for three-phase motors face challenges in accurately detecting back electromotive force due to unstable floating phase pin voltage, often resulting in insufficient stabilization time, which complicates phase switching and reduces detection success rates.
Innovation Solution
A motor controller with a switch circuit, driving circuit, and pulse width modulation circuit that generates specific voltage vectors to create a Y-shaped configuration of coils, allowing for controlled phase switching and stabilizing the floating phase pin voltage by limiting the second duty cycle of the pulse width modulation signal to ensure adequate ON time intervals for accurate back electromotive force detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the ON time interval of the pulse width modulation signal is reduced to enable faster phase switching, then the switching speed is improved, but the floating phase pin voltage does not have enough time to stabilize, making it difficult to detect the back electromotive force
Solution Approach 1:
The patent applies preliminary action by ensuring the floating phase pin voltage stabilizes before the pulse width modulation signal is turned on. The detection is performed during the OFF time interval when the voltage has already stabilized, rather than during the ON time interval. This preliminary stabilization action resolves the contradiction by allowing fast switching while maintaining detection accuracy.
2Measurement precision
If the ON time interval of the pulse width modulation signal is increased to allow voltage stabilization, then the back electromotive force detection accuracy is improved, but the phase switching speed is reduced
Solution Approach 1:
The patent performs the voltage stabilization and detection action before the actual power switching occurs. By detecting the back electromotive force during the OFF time interval when voltage is stable, and only then switching phases, the system achieves both accurate detection and fast switching without requiring a long ON time interval.
3Adaptability or versatility
If the pulse width modulation signal duty cycle is increased to improve motor speed control, then the motor speed adjustment range is improved, but the floating phase pin voltage stability is reduced due to switching noise
Solution Approach 1:
The patent extracts the detection function from the ON time interval (where switching noise occurs) and places it in the OFF time interval (where voltage is stable). By separating the detection action from the noisy switching period, the system maintains voltage stability while still achieving wide speed control range through duty cycle adjustment.
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
The solution enables easy and reliable detection of back electromotive force, increasing the success rate of phase switching and allowing for efficient speed adjustment of the three-phase motor by ensuring sufficient stabilization of the floating phase pin voltage.
Implementation Method 1
The pulse width modulation circuit receives a first pulse width modulation signal for generating a second pulse width modulation signal to the driving circuit, where the first pulse width modulation signal has a first duty cycle and the second pulse width modulation signal has a second duty cycle.
Implementation Method 2
The driving circuit generates a first control signal, a second control signal, a third control signal, a fourth control signal, a fifth control signal, and a sixth control signal for respectively controlling the ON/OFF states of the first transistor, the second transistor, the third transistor, the fourth transistor, the fifth transistor, and the sixth transistor.
Data Source
AI summary
A motor controller comprises a switch circuit, a driving circuit, and a pulse width modulation circuit. The switch circuit is coupled to a three-phase motor for driving the three-phase motor. The driving circuit generates a plurality of control signals to control the switch circuit. The pulse width modulation circuit receives a first pulse width modulation signal for generating a second pulse width modulation signal to the driving circuit, where the first pulse width modulation signal has a first duty cycle, and the second pulse width modulation signal has a second duty cycle. When the motor controller starts a floating phase to detect a back electromotive force of the floating phase, the motor controller enables the second duty cycle to be greater than or equal to a minimum value.