Laundry Drum Rotation Detection Using Induced Stator Currents
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current sensorless safety systems for washing machines are unreliable in determining the rotation of the laundry drum during power failures, as they fail to accurately estimate rotor speed without stator current or voltage references, compromising safety.
Innovation Solution
A sensorless safety system that injects direct currents into the stator phases of the three-phase asynchronous motor during a predetermined magnetizing time interval, then measures the time pattern of induced currents to determine if the rotor is rotating or stationary, using the presence or absence of zero crossings to differentiate between rotating and stationary states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If sensorless control is used to estimate rotor speed based on stator currents and voltages, then system cost is reduced by eliminating speed sensors, but reliability is compromised during power failure when stator current or voltage references are lost
Solution Approach 1:
The control device performs preliminary magnetization of the rotor by supplying direct currents to the stator phases before attempting to determine rotor rotation status. This preliminary action ensures the rotor has the necessary magnetic field to induce detectable currents during the determination phase, enabling reliable detection even after power failure when normal reference signals are unavailable.
Solution Approach 2:
The invention uses induced stator currents as an intermediary signal to indirectly determine rotor rotation status. Instead of relying on direct speed sensors or normal operating reference signals, the system measures the currents induced in the stator by the rotating rotor, which serve as a mediator to infer rotation state without requiring direct measurement of rotor speed.
2Reliability
If direct current injection is used to magnetize the rotor, then rotation detection reliability is improved during power failure, but additional control complexity is introduced
Solution Approach 1:
The existing inverter components and control device are made multi-functional by enabling them to perform both normal motor control operations and safety determination functions. The same power circuit and control device used for driving the motor are also utilized to supply magnetizing currents and measure induced currents, eliminating the need for separate dedicated safety system hardware.
Solution Approach 2:
The motor itself serves the dual purpose of both driving the laundry drum and enabling safety detection. The rotor's rotation, which naturally occurs during washing operations, automatically generates the induced currents needed for detection. The system uses the motor's own operational characteristics to provide safety information without requiring external monitoring equipment.
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 reliable determination of the laundry drum's rotation status after a power failure without additional electronic components, providing a cost-effective and safe solution by using existing inverter components and generating a braking effect on the rotor to prevent accidental door opening.
Implementation Method 1
the control device is designed to supply, during a predetermined magnetizing time interval, three direct currents to three power phases of the stator to magnetize the rotor; and cut off supply of the three direct currents to the three power phases of the stator at the end of the predetermined magnetizing time interval; and determine the time pattern of at least one of the three currents induced by the rotor in the stator
Data Source
AI summary
An electric household appliance (1) having a casing (2); a laundry drum (3) mounted inside the casing (2) to rotate about an axis of rotation; a three-phase asynchronous motor (6) for rotating the laundry drum (3); and a sensorless safety system (7) for determining rotation of the rotor (32), to determine rotation or no rotation of the laundry drum (3). The sensorless safety system (7) is designed to supply three direct currents (las, lbs, Ics) to the three stator power phases (31) during a predetermined time interval (ΔT), so as to magnetize the rotor (32); to cut off supply of the direct currents (las, lbs, Ics); to determine the time pattern of at least one of the three induced currents (Iar, Ibr, Icr) induced in the stator (30) in response to magnetizing the rotor (32); and to determine rotation or no rotation of the rotor (32) on the basis of the time pattern of at least one of the three induced currents (Iar, Ibr, Icr).