Brushless Motor Speed Control Using Inductive Shunt Voltage Detection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Brushless motors face challenges in precise speed control due to parasitic inductance in measuring resistors, leading to distorted voltage measurements and poor synchronization at high rotational speeds, especially when using low-resistance resistors.
Innovation Solution
A method to determine the voltage generated by the inductive part of a measuring resistor in an electronic circuit, involving energizing the circuit with a signal generator, measuring voltages across the resistor, and using a differential amplifier to calculate the inductive voltage as the difference between total and resistive voltages, allowing for precise real-time determination without a differential filter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If low-resistance measuring resistors are used to limit power dissipation, then power loss is reduced, but measurement precision deteriorates due to significant parasitic inductance effects
Solution Approach 1:
The voltage measurement is segmented into two separate measurements: first measuring the total voltage across the measuring resistor, then measuring the voltage across the inductive component alone. This segmentation allows the control unit to subtract the inductive voltage from the total voltage to obtain the accurate resistive voltage, thereby eliminating the distortion caused by parasitic inductance while maintaining low resistance values
Solution Approach 2:
The patent introduces an intermediary measurement approach by using the control unit to separately measure and calculate the inductive voltage component. This intermediary calculation serves as a mediator to isolate and remove the parasitic inductance effect from the total voltage measurement, enabling accurate current measurement even with low-resistance measuring resistors
2Measurement precision
If differential filters are added to eliminate parasitic inductance effects, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent extracts the inductive voltage component as a separate measurable quantity and removes its distorting effect from the total voltage measurement through calculation. Instead of adding complex filtering hardware, the solution takes out the parasitic inductance effect mathematically by measuring it separately and subtracting it from the total voltage, thereby simplifying the overall device architecture
Solution Approach 2:
The patent replaces the mechanical/electrical differential filter system with a computational approach. Instead of using physical filtering components to eliminate parasitic inductance effects, the solution uses the control unit to calculate and subtract the inductive voltage component digitally, substituting a complex electrical filtering system with a simpler computational method
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 provides precise and robust motor control by accurately determining the inductive voltage, improving measurement precision and reducing parasitic inductance effects, leading to enhanced performance and synchronization of the motor.
Implementation Method 1
measuring the current in the phases of the motor through a measuring resistor between the power stages and the stator windings
Implementation Method 2
The measuring resistors have a parasitic inductance of a few nanohenries, which implies that the voltage measured across the terminals of the measuring resistor does not exactly reflect the image of the current
Implementation Method 3
a differential amplifier for the voltage across the terminals of the measuring resistor
Data Source
AI summary
Method for determining the voltage UL generated by the inductive part of a measuring resistor present in an electronic circuit including a signal generator, at least one stator winding connected to the signal generator and to the measuring resistor and a differential amplifier for the voltage across the terminals of the measuring resistor, the method including: a step of energizing the electronic circuit for a predetermined period of time t; a step of measuring the voltage UT across the terminals of the measuring resistor at the end of the energizing step; a step of determining the voltage UR generated by the resistive part of the measuring resistor at the end of the energizing step; and a step of determining the voltage UL generated by the inductive part of the measuring resistor as a function of the voltage UT and the voltage UR.