Electric Motor Control Using Voltage Flank Trigger for Back-EMF Measurement
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Solution Overview
Problem
Existing methods for determining the angular difference between the phase position of the excitation current and counter-EMF in electric motors require long measurement phases, leading to inefficient operation, torque irregularities, and acoustic disturbances, with inaccuracies due to interpolation and computational effort.
Innovation Solution
Detecting the voltage flank at zero crossing of the winding current as a trigger for measuring counter-EMF, allowing for precise timing of zero crossing detection and enabling short measurement phases, thus maintaining continuous torque application and improving efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the measurement phase is extended to allow winding current overshoot to decay and to enable interpolation of zero crossing, then the angular difference can be determined with sufficient accuracy, but the measurement phase duration increases, causing torque interruptions and reducing motor efficiency
Solution Approach 1:
The patent applies preliminary action by detecting the zero crossing of the winding current using the voltage flank before the measurement phase begins. This allows the measurement phase to start immediately at the precise zero crossing moment, eliminating the need to wait for overshoot decay and enabling accurate angular difference determination without extending the measurement phase duration, thus maintaining motor efficiency.
Solution Approach 2:
The patent replaces the mechanical/wait-based method (waiting for overshoot to decay) with an electrical/detection-based method (detecting voltage flank at zero crossing). This substitution allows immediate identification of the zero crossing point without temporal delay, resolving the contradiction between measurement accuracy and measurement phase duration.
2Measurement precision
If two measured values for counter-EMF are recorded with sufficient time spacing to enable interpolation, then the angular difference can be determined, but the measurement phase duration increases, causing torque irregularities and acoustic disturbances
Solution Approach 1:
The patent performs the zero crossing detection using voltage flank detection before the measurement phase begins. This preliminary action provides the exact starting point for measurement, allowing the measurement phase to be executed quickly and continuously without extended duration, thereby preventing torque irregularities and acoustic disturbances while still enabling accurate angular difference determination.
3Measurement precision
If the measurement phase is extended to allow for computational interpolation, then the angular difference can be determined, but the torque application is interrupted for longer periods, reducing power output
Solution Approach 1:
The patent applies preliminary action by detecting the zero crossing of the winding current using voltage flank detection before the measurement phase commences. This provides the precise starting point in advance, allowing the measurement phase to be executed immediately and briefly without extended interruptions, thereby maintaining high power output while determining the angular difference accurately.
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 and efficient determination of the angular difference, allowing the electric motor to operate smoothly with high efficiency and reduced computational effort, minimizing interruptions in torque delivery.
Implementation Method 1
applying the phase voltages to the output terminals of the output stage in such a way that a traveling magnetic field is induced in the field winding, which causes a relative movement between the primary part and the secondary part
Implementation Method 2
Measurement of the electrical counter-EMF, which is induced in the phase winding connected to this output connection by the relative movement between the primary and secondary parts
Data Source
Figure 1
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AI summary
The invention relates to a method for operating an electric motor with a primary section and a secondary section, wherein the primary section has a multi-phase exciter winding comprising winding strands, each of the phase connections of said exciter winding being connected to an output connection of an end stage, wherein the end stage has controllable semiconductor switches for applying phase voltages to the output connections, said method comprising the following steps: a) introducing an operating phase by applying the phase voltages to the output connections of the end stage such that a moving magnetic field is induced in the exciter winding, said moving field effecting a relative motion between the primary section and the secondary section, b) turning off the phase voltage at at least one of the output connections in order to introduce a measurement phase, c) measuring the electrical back emf induced in the winding strand connected to said at least one of the output connections by virtue of the relative motion between the primary section and the secondary section in order to determine the angular difference between the phase position of the exciter current and that of the back emf, d) optionally, repeating steps a) through c). After turning off the phase voltage, the winding current in the winding strand for which the phase voltage was turned off is conducted and maintained by way of at least one free-wheeling element having a non-linear characteristic curve. A flank (13) in the winding voltage, the flank occurring upon zero-crossing of the winding current flowing in said winding strand, is detected and is used as a triggering signal for the measurement of the back emf of the respective winding strand.