Rotor Position Detection Using Single Current Sensor
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Solution Overview
Problem
Existing methods for determining the position of a rotor in brushless permanent-magnet electric motors, such as those used in camshaft adjusters and devices for changing compression ratios in internal combustion engines, are inefficient and require multiple current sensors, leading to high calibration and material costs, and are unsuitable for long-term PWM operation or changes between BEMF and PWM modes.
Innovation Solution
A method using a sequence of voltage pulses to set currents in phase windings, with a common current sensor measuring peak values, reduces measurement errors by using only peak current values to determine rotor position, allowing for reduced expenditure and improved detection accuracy, especially at low speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple current sensors are used to measure currents in individual phase windings, then measurement accuracy is improved, but device complexity and material costs increase
Solution Approach 1:
The patent combines multiple current measurement functions into a single current sensor that measures the sum of currents in all phase windings. By using the relationship that the sum of currents in a three-phase system equals zero (Ia + Ib + Ic = 0), the system can determine individual phase currents from the single sensor measurement, thereby reducing device complexity while maintaining measurement capability
Solution Approach 2:
The patent introduces an intermediary mathematical relationship (the current sum relationship) that allows derivation of individual phase currents from a single measured value. This intermediary approach enables the system to obtain information about all phase currents without requiring separate sensors for each phase
2Measurement precision
If multiple current sensors are calibrated to reduce measurement errors, then measurement consistency is improved, but calibration costs and time increase
Solution Approach 1:
The patent extracts and eliminates the calibration requirement by using a single current sensor instead of multiple sensors. Since calibration errors typically arise from differences between multiple sensors, using one sensor removes the need for inter-sensor calibration while still providing sufficient measurement consistency for the application
3Measurement precision
If peak current values are used instead of continuous current measurements, then detection accuracy at low speeds is improved, but measurement complexity is reduced
Solution Approach 1:
The patent applies preliminary action by pre-defining specific voltage pulse sequences with known timing and magnitude relationships. These predetermined pulse patterns ensure that peak current values occur at specific rotor positions, allowing the system to determine rotor position by simply detecting peak values rather than processing continuous current signals
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 rapid and safe operation of devices like camshaft adjusters with improved detection accuracy, reducing the need for multiple current sensors and allowing operation under high disturbance variables, achieving a resolution of up to 30° electrical angle with a single common current sensor.
Implementation Method 1
several phase windings are provided on the stator, which are controlled such that they generate a rotating magnetic field, which carries with it the permanent magnet rotor
Implementation Method 2
the phase windings are excited by a sequence of voltage pulses comprising a plurality of successive voltage pulses, such that a current is set successively in each of the phase windings
Implementation Method 3
a common current sensor measuring a peak value for the current being set during the duration of each voltage pulse, and the voltage pulse in the voltage pulse sequence being determined during which the peak current value having the greatest magnitude was measured
Data Source
AI summary
A circuit, comprising a plurality of phase windings in an electric motor, an inverter configured to excite the phase windings by a sequence of voltage pulses including a plurality of successive voltage pulses that a current can be set in each of the phase windings, wherein the voltage pulses are selected in such a manner that a positive and a negative current are produced in all the phase windings during the voltage pulses, a current sensor for measuring a peak value for the current being set during a duration of each voltage pulse in each phase winding, and an evaluation circuit connected to the current sensor, wherein the evaluation circuit is configured to determine the voltage pulse in the voltage pulse sequence during a duration of which peak current value having a greatest magnitude was measured.