BLDC Motor Rotor Position Detection Using Phase Current Deviation
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Solution Overview
Problem
BLDC motors in reciprocating compressors, such as those in household refrigeration appliances, face challenges in accurately determining rotor position before starting, especially under uneven loads, where existing methods like back EMF methods are ambiguous and not applicable at standstill conditions.
Innovation Solution
A method involving a controlled test run with a three-phase voltage vector to measure phase current values, calculate a current curve, and assign rotor position to a magnetic pole pair based on deviations, allowing for unambiguous detection of rotor position even before motor operation, using a compressor controller with a microprocessor to execute this process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If back EMF method is used for rotor position detection, then position detection is possible during motor operation, but the method is ambiguous and not applicable at standstill conditions
Solution Approach 1:
The patent applies preliminary action by performing rotor position detection before the motor starts operating. A test run is executed at a low rotational speed (1 Hz) to detect the rotor position while the motor is still essentially stationary, allowing the system to determine the correct starting position before full operation begins.
Solution Approach 2:
The patent changes the operational parameters by running the motor at a specific low speed (1 Hz) during the test run, which is different from both complete standstill and normal operating speed. This parameter change enables the detection of rotor position under controlled conditions that bridge the gap between stationary and full operation states.
2Reliability
If rotor is pre-positioned before starting, then motor can start against applied load, but the rotor position detection remains ambiguous with multiple permanent-magnetic pole pairs
Solution Approach 1:
The patent uses feedback by measuring phase current values during the test run and comparing them against a calculated current curve. The system detects deviations between measured and expected current values to identify the characteristic external load moment, thereby resolving the position ambiguity through feedback from the actual motor response.
Solution Approach 2:
The patent replaces direct mechanical position sensing with an electrical measurement approach. Instead of using mechanical sensors or direct observation of rotor position, the system uses electrical measurements (phase current values) and mathematical analysis of the current curve to indirectly determine the rotor position, substituting mechanical detection with electrical field-based measurement.
3Measurement precision
If controlled test run is performed at low rotational speed, then rotor position can be detected before starting, but additional time is required for the test run
Solution Approach 1:
The patent applies partial action by performing only a minimal test run at low speed (1 Hz) rather than a complete operational cycle. The test run executes just enough rotations to detect the rotor position and identify the characteristic load moment, then stops to allow normal starting procedures to begin, performing only the necessary portion of the detection sequence.
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
Enables precise detection of rotor position before starting, optimizing start-up conditions, reducing noise, and ensuring reliable motor operation by accurately pre-positioning the rotor, thus improving start-up efficiency and avoiding false starts.
Implementation Method 1
Magnetic pole pairs are generated electrically in the stator windings by suitably controlled energization of the windings. This is often done with a circulating voltage vector with one or more, in particular three, phases. The circulating magnetic pole pairs take the permanent magnetic pole pairs and thus the rotor with them.
Implementation Method 2
it is precisely in this area that most sensorless position determination methods can be found, which evaluate the voltages induced in the windings using the so-called back EMF method
Data Source
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AI summary
The invention relates to a method for detecting the rotor position of a BLDC motor, for example in a domestic refrigeration appliance, having at least two permanently magnetic pole pairs and controlled magnetic pole pairs electrically produced in windings, containing the steps: a. controlled test run (71) for detecting the rotor position; b. association (72) of the rotor position of a characteristic outer load torque with an associated controlled magnetic pole pair. Said steps are performed in order to achieve an association of a mechanical rotor position with an electrical rotor position, which association is already available before a start of operation of the motor for control purposes. For example, the rotor position of the characteristic outer load torque in time interval 34 can be associated with the associated controlled magnetic pole pair on the basis of a characteristic deviation of the phase current values.