Sensorless Single-Phase Motor Starting by Current-Threshold Commutation
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Solution Overview
Problem
Existing sensorless single-phase electric motors face challenges in achieving fast and reliable starting due to the need for slow rotor acceleration and limited drive energy when using indirect rotor position detection methods.
Innovation Solution
A method involving a permanent-magnetic motor rotor and a U-shaped ferromagnetic stator with a laminated stator coil, where the rotor moves into defined rest positions based on magnetic orientation, allowing for commutation based on current thresholds without direct position feedback, enabling continuous energizing and efficient starting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pulsed alternating current with predefined duty cycle is used to accelerate the motor rotor, then the CEMF can be analyzed in the OFF-phase for sensorless rotor position detection, but the necessary off-phases limit the effective drive energy so that the motor rotor acceleration is relatively slow
Solution Approach 1:
The patent applies periodic action by using pulsed alternating current with a predefined duty cycle to energize the stator coil. The current is periodically switched on and off, creating alternating phases where the stator coil is energized (ON-phase) and where it is not energized (OFF-phase). This periodic energizing allows the control electronics to analyze the CEMF during the OFF-phases for sensorless rotor position detection while still providing drive energy during the ON-phases to accelerate the motor rotor.
2Reliability
If the motor rotor is initially moved into a defined rotor rest position by energizing the stator coil with a defined positioning current, then reliable rotor position detection can be achieved, but the relatively slow initial positioning slows down the starting of the electric motor
Solution Approach 1:
The patent applies preliminary action by initially moving the motor rotor into a defined rotor rest position before starting the normal acceleration process. This is achieved by energizing the stator coil with a defined positioning current that creates a magnetic field aligning the permanent-magnetic motor rotor with the ferromagnetic stator, establishing a known starting orientation. This preliminary positioning ensures reliable rotor position detection from the outset, allowing the sensorless control method to function correctly from the beginning of operation.
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 rapid and reliable starting of the motor by continuously increasing drive energy and maintaining efficient commutation, independent of rotor position, resulting in improved motor acceleration and reduced starting time.
Implementation Method 1
Caused by the interaction of the permanent-magnetic motor rotor and the ferromagnetic stator, the motor rotor moves into one of two defined static rest positions if the motor stator is not energized
Implementation Method 2
If the stator coil is energized with a defined voltage, the motor rotor is accelerated toward one of two drive positions, dependent on the magnetic orientation of the electromagnetic stator field and, as a result, dependent on the polarity of the provided voltage
Implementation Method 3
the present rotor position has to be indirectly detected, for example, by analyzing transitions in the polarity of a counter-electromotive force (CEMF) caused by a rotating permanent-magnetic motor rotor
Data Source
Figure 1
Figure 2~2c
Figure 3~3b
AI summary
The invention is directed to a method for starting a sensorless single-phase electric motor (10), the electric motor comprising (10): - a permanent magnetic motor rotor (24), - an electromagnetic motor stator (12) with a stator coil (16), - a power electronics (26) for energizing the stator coil (16), - a current sensor (32) for measuring a current (I) flowing in the stator coil (16), and - a control electronics (28) for controlling the power electronics (26), the control motor electronics (28) being connected with the current sensor (32), the method comprising: - energizing the stator coil (16) with an alternating drive voltage (Vd), - monitoring a drive current (Id) being generated in the stator coil (16) by the drive voltage (Vd), and - commutating the drive voltage (Vd) each time when the drive current (Id) reaches a predefined positive current threshold value (Itp) or a predefined negative current threshold value (Itn). The method according to the invention provides a fast and reliable starting of the sensorless single-phase electric motor (10).