Rotor Position Detection in PMSM Washing Machine Motors
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Solution Overview
Problem
In washing machines with permanent magnet synchronous motors, accurately determining the rotor position is crucial for starting the drum from a stopped position, especially when high torque is required, such as during the washing cycle, but existing methods lack precision, particularly during the stopping phase.
Innovation Solution
A method involving an A.C.-D.C. converter, a three-phase inverter, and an electronic motor controller that determines rotor position by measuring current polarities at the inverter load terminals, de-energizing the stator field coils, and using a look-up table or phase-locked loop to calculate the rotor position based on alpha-beta transformations and phase offsets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the rotor position is determined using conventional methods during the stopping phase, then the control system is simple, but the measurement precision of rotor position deteriorates
Solution Approach 1:
The system performs preliminary action by de-energizing the stator field coils before measuring current polarities to determine rotor position. This preparation step removes magnetic field interference that would otherwise corrupt the position measurement, enabling accurate detection during the stopping phase when the rotor is decelerating.
Solution Approach 2:
The patent uses current polarity measurements as an intermediary indicator to infer rotor position. Instead of directly measuring rotor position, the system measures the polarities of currents in the de-energized stator coils, which reflect the rotor's magnetic field position, and uses these measurements to calculate the actual rotor position through coordinate transformations.
2Measurement precision
If the stator field coils remain energized during position detection, then the control system operates continuously, but the current polarity measurements become inaccurate due to magnetic field interference
Solution Approach 1:
The system extracts the magnetic field from the measurement process by de-energizing the stator field coils temporarily. This removes the interfering magnetic field that would otherwise prevent accurate current polarity measurements, allowing the system to obtain clean position data during the stopping phase.
Solution Approach 2:
The control system implements periodic action by cycling the stator field coils between energized and de-energized states. During position detection intervals, the coils are de-energized to enable measurement, then re-energized for motor control, creating a periodic pattern that alternates between measurement and control modes.
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 method enables accurate determination of the rotor position, ensuring efficient starting and stopping of the drum, even at low speeds, thereby improving the washing machine's operational efficiency and reliability.
Implementation Method 1
a permanent magnet synchronous motor including a rotor and three stator field coils
Implementation Method 2
determine a first set of three current polarities at the three load terminals, while the rotor is rotating and the three stator field coils are de-energized and connected together
Data Source
AI summary
A device and method to determine the stopping rotor position of a washing machine motor includes an inverter, a permanent magnet synchronous motor, and an electronic motor controller. The controller determines the stopped rotor position of the motor by measuring induced currents in the stator field coils of the motor. While the motor is de-energized and slowly rotating, the controller directs the inverter to connect all of the stator field coils of the motor together. The stator field coils may be connected to a common D.C. rail, output from an A.C.-D.C. converter of the washing machine. In an embodiment, the controller determines the rotor position based on the polarities of current induced in the stator field coils. In another embodiment, the controller determines the rotor position based on the phase angle and angular frequency of the three phase currents, transformed into a stationary reference frame.