Asymmetric Sensorless Motor Control for Counter-EMF Measurement
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Solution Overview
Problem
Conventional sensorless electric motors are limited by the need to measure counter-EMF at zero current, restricting commutation angles and reducing motor output and efficiency, as the measurement process limits the maximum adjustable advanced ignition angle.
Innovation Solution
The method involves controlling motor phases asymmetrically by reducing specific commutation angles relative to others, allowing for larger measurement and output commutation angles, and using advanced ignition to enhance motor output and efficiency without transferring limitations to all phases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the commutation angle is increased to improve motor output and efficiency, then the motor output and efficiency increase, but the measurement of counter-EMF becomes impossible because the phase cannot be kept at zero current for the required measurement duration
Solution Approach 1:
The commutation cycle is segmented into distinct phases: a first commutation angle for power delivery, a measurement angle for counter-EMF detection, and a second commutation angle for continued power delivery. This segmentation allows the measurement to occur during a dedicated time window when the phase is at zero current, while the overall commutation angle remains large for high motor output.
Solution Approach 2:
The measurement angle is positioned at the beginning of the commutation cycle, before the main power-delivering commutation angles. This preliminary measurement action ensures that the counter-EMF is captured at zero current before the phase is energized, allowing accurate rotor position detection without interfering with the subsequent high-power commutation periods.
2Measurement precision
If the commutation angle is limited to allow counter-EMF measurement at zero current, then measurement is possible, but the net commutation time decreases reducing motor output
Solution Approach 1:
Different quality requirements are applied to different parts of the commutation cycle: the measurement angle requires zero current for accurate counter-EMF detection, while the commutation angles are optimized for maximum power delivery with current flowing. This local differentiation of operational characteristics allows each phase to be optimized for its specific function.
Solution Approach 2:
The control system dynamically switches between different operational modes: during the measurement angle, the phase is controlled to maintain zero current for measurement; during the commutation angles, the phase is energized for power delivery. This dynamic switching allows the system to achieve both measurement accuracy and high motor output.
3Power
If advanced ignition is used to increase motor output, then the motor output increases, but the maximum adjustable advanced ignition angle is limited by the intermediate circuit voltage
Solution Approach 1:
The measurement of counter-EMF is performed in advance, during the measurement angle before the main commutation. This preliminary measurement provides the rotor position information needed to trigger the advanced ignition at the optimal moment, allowing the advanced ignition angle to be set based on actual measured positions rather than being constrained by voltage limitations.
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 increases the net commutation time and motor output, reduces loading on buffer capacitors, and improves EMV properties, achieving higher efficiency and output without the need for expensive components.
Implementation Method 1
a three-phase network is generated across a converter circuit, passed to the coils of the stator of the electric motor and a rotating stator magnetic field thus generated
Implementation Method 2
The rotor of the electric motor often has one or more permanent magnet(s) by which a static rotor magnetic field is generated
Implementation Method 3
A torque, which sets the rotor in motion, results from the interaction of the stator magnetic field with the rotor magnetic field
Implementation Method 4
the counter-electromotive force (counter-EMF) of the electric motor, i.e. the voltage induced in the stator coils by the rotating rotor magnetic field
Data Source
AI summary
A particularly high level of performance in a sensorless, electronically commutated multiphase electric motor can be achieved, wherein for one full cycle at least, one motor phase is controlled in an asymmetrical manner relative to a further motor phase by controlling a commutation angle of one motor phase by reduction relative to a corresponding commutation angle of the other motor phase. Alternatively or in addition, according to the aforementioned method, at least one motor phase is asymmetrically controlled by reduction by self-reference for a full cycle, a commutation angle being controlled by reduction relative to a preceding or subsequent commutation angle or the size of the intermediate angles between two commutation angles being varied, the reduced commutation angle always being preceded or followed by a measurement angle within which the relevant motor phase is switched at zero current for detecting the rotor position by measuring the counter-electromotive force.