Switched Reluctance Motor Alignment Without Position Sensor
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Solution Overview
Problem
Switched reluctance motors (SRM) require a rotor position sensor for alignment, which increases complexity and cost, and can fail due to dirt, leading to long and uncomfortable alignment phases, potentially causing user dissatisfaction and false defect perceptions.
Innovation Solution
A method and device that control phase voltage based on phase current progression to quickly align the rotor without a position sensor, reducing the alignment phase duration to less than a second by regulating voltage after local extreme values, thereby minimizing vibrations and ensuring rapid motor startup.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a rotor position sensor is used to determine initial rotor position, then alignment precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent removes the rotor position sensor from the system entirely. Instead of using a sensor to detect rotor position, the invention uses the phase current profile itself as the sensing mechanism. The current profile naturally indicates rotor position during alignment, eliminating the need for separate sensing hardware and reducing system complexity while maintaining alignment precision.
Solution Approach 2:
The phase current serves dual purposes: it both drives the motor during alignment and simultaneously provides information about rotor position. By monitoring the current profile characteristics (amplitude, shape, rate of change), the system self-determines rotor position without external sensors, making the system self-sufficient and reducing complexity.
2Measurement precision
If a rotor position sensor is used for alignment, then alignment precision is improved, but reliability decreases due to sensor failure risk
Solution Approach 1:
By removing the vulnerable rotor position sensor from the system, the patent eliminates the primary failure point. Optical sensors are particularly susceptible to contamination and mechanical failure. The invention replaces this fragile component with a robust electrical measurement approach using phase current, which has no moving parts and is not susceptible to environmental contamination.
Solution Approach 2:
The patent replaces the expensive, fragile optical sensor with a simple, robust electrical current measurement approach. Phase current monitoring uses existing motor windings and basic electrical measurements rather than delicate optical components, creating a system that is inherently more reliable and resistant to harsh operating conditions.
3Reliability
If a worst-case timeframe is assumed for rotor alignment without position sensor, then reliability is improved by ensuring alignment, but alignment time increases significantly
Solution Approach 1:
The patent implements real-time feedback by continuously monitoring the phase current profile during alignment. By analyzing current characteristics (amplitude, rate of change, waveform shape), the system dynamically determines when alignment is complete. This feedback mechanism allows the motor to start immediately upon achieving alignment rather than waiting for a predetermined time, significantly reducing alignment duration while ensuring proper positioning.
Solution Approach 2:
The alignment process transitions from a static, time-based approach to a dynamic, condition-based approach. Instead of using a fixed worst-case timeframe, the system adaptively monitors phase current characteristics and adjusts the alignment duration based on actual motor behavior. This allows fast alignment for low-inertia motors while still ensuring proper alignment for all cases, optimizing both speed and reliability.
4Speed
If phase voltage is applied to align rotor quickly, then alignment speed is improved, but rotor oscillation increases
Solution Approach 1:
The patent applies phase voltage in a controlled, periodic manner during alignment. By monitoring the phase current profile and detecting when the rotor reaches alignment (indicated by specific current characteristics), the system applies voltage pulses or maintains voltage only for the necessary duration. This periodic or pulsed voltage application achieves rapid alignment while preventing excessive oscillation that would occur with continuous high-voltage application.
Solution Approach 2:
The patent uses just enough phase voltage to achieve alignment quickly, rather than applying maximum voltage continuously. By monitoring the phase current profile, the system determines the precise moment when alignment is achieved and stops or reduces voltage application. This partial action approach provides sufficient driving force for rapid alignment while avoiding the excessive energy input that causes prolonged oscillation and instability.
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 method significantly shortens the alignment phase, making the motor startup process acceptable to users, reducing vibrations, and eliminating the need for a rotor position sensor, thus enhancing reliability and user experience.
Implementation Method 1
The amplitude of the phase current changes because the phase inductance depends on the rotor's position
Implementation Method 2
When a defined, e.g., constant, DC voltage is applied, the rotor will therefore rotate into an alignment position
Data Source
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AI summary
The invention relates to a method for controlling a switched reluctance motor, comprising applying a defined phase voltage to at least one phase of the stationary reluctance motor, determining the phase current profile within that phase, and controlling the phase voltage depending on the phase current profile. The invention further relates to a control circuit for a reluctance motor for carrying out the method and to a household appliance including this method.