Single-Phase Motor PWM Control for Reliable Low-Duty Current Sensing
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Solution Overview
Problem
Single-phase electric motors, particularly sensorless ones, face challenges in reliable phase current measurement due to pronounced transient effects and long settling times when driven with PWM signals, especially during the starting phase with low duty cycles.
Innovation Solution
The method involves a single-phase electric motor with a static stator and a rotatable permanent-magnetic rotor, using switchable drive electronics and control electronics to generate a PWM drive energy signal with adjustable on-time intervals, ensuring reliable phase current measurement by defining a minimum on-time interval length based on the settling time, allowing for consistent and efficient motor operation across varying duty cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If PWM drive energy signal with low duty cycle is used during starting phase, then energy consumption is reduced, but phase current measurement reliability deteriorates due to long settling time
Solution Approach 1:
The system performs preliminary action by ensuring the stator coil is energized for a minimum settling time period before attempting phase current measurement. This preliminary energization allows the phase current to stabilize and transient effects to subside, ensuring reliable measurement even when the overall PWM duty cycle is low for energy efficiency.
2Use of energy by moving object
If PWM drive energy signal with low duty cycle is used during starting phase, then energy consumption is reduced, but motor starting performance deteriorates
Solution Approach 1:
The system applies preliminary action by energizing the stator coil for a minimum settling time period before measurement, ensuring reliable phase current data is obtained. This preliminary energization phase is separate from the measurement phase, allowing low duty cycle operation during measurement while maintaining adequate energization for motor starting performance.
3Loss of time
If phase current measurement is attempted during transient period, then measurement timing is simplified, but measurement precision deteriorates due to pronounced transient effects
Solution Approach 1:
The system extracts the measurement action from the transient period and performs it separately after the transient effects have subsided. By separating the energization phase (which includes the transient period) from the measurement phase (which occurs after settling time), the system ensures measurement precision while maintaining clear timing control through the minimum settling time parameter.
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 enables reliable phase current measurement and efficient starting of single-phase electric motors, even with low duty cycles, by optimizing the on-time intervals and ensuring the phase current stabilizes within the defined minimum interval, thus overcoming transient effects and ensuring consistent motor operation.
Implementation Method 1
a permanent-magnetic motor rotor which is driven by energizing a stator coil of a motor stator with an alternating drive energy
Data Source
Figure 1~2
Figure 3a~3c
AI summary
The invention is directed to a method for driving a single-phase electric motor (10), the electric motor (10) comprising: a static motor stator (12) with a stator coil (18), a rotatable motor rotor (14), a switchable drive electronics (22) electrically connected to the stator coil (18) for energizing the stator coil (18) with a pulse-width-modulated drive energy signal (E) with a defined effective duty cycle for driving the motor rotor (14), a control electronics (26) for switching the drive electronics (22) for generating the pulse-width-modulated drive energy signal (E), and a current sensor (28) for measuring a phase current flowing through the stator coil (18), and the method comprising: switching the drive electronics (22) to a first on-state during a first on-time interval (I1) of a pulse width modulation period (P) of the drive energy signal (E), switching the drive electronics (22) to a second on-state during a second on-time interval (I2) of the pulse width modulation period (P), switching the drive electronics (22) to an off-state between the two on-time intervals (I1, I2), and measuring the phase current with the current sensor (28), wherein the two on-time intervals (I1, I2) of one pulse width modulation period (P) are provided with different interval lengths (IL1, IL2) if the defined effective duty cycle is lower than a first duty cycle threshold value, to ensure that at least one on-time interval (I1) is provided with an interval length (IL1) being equal to or larger than a defined minimum on-time interval length (ILmin), and wherein the phase current is measured during that on-time interval (I1) with the defined minimum on-time interval length (ILmin).