Sensorless Brushless DC Motor Control via Inductive Rise Time Derivative
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Solution Overview
Problem
Conventional sensorless startup methods for brushless DC motors are inefficient and consume excessive power due to the reliance on inductive rise times and complementary commutation states, which affect driving torque and power consumption.
Innovation Solution
A method that determines the current commutation state of a brushless DC motor by calculating the derivative of inductive rise times and advancing the motor to the next commutation state based on the magnitude of this derivative, using a drive circuit, sense circuit, and control circuitry to measure and calculate inductive rise times during specific intervals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If conventional sensorless startup methods use complementary commutation states and compare inductive rise times, then the motor can be started without external sensors, but the driving torque efficiency deteriorates and power consumption increases
Solution Approach 1:
The patent changes the parameter used for commutation state determination from comparing inductive rise times to detecting the derivative of inductive rise time. By monitoring when the derivative transitions from positive to negative (indicating a peak), the system achieves sensorless startup with improved energy efficiency and torque performance
Solution Approach 2:
The patent replaces the conventional method of using complementary commutation states and rise time comparison with a derivative-based detection method. This substitution eliminates the need for coast intervals and sensing intervals, reducing the off-time and improving overall system efficiency
2Measurement precision
If conventional systems use coast intervals and sensing intervals to measure inductive rise times, then commutation switching points can be detected, but the motor startup efficiency deteriorates and torque performance decreases
Solution Approach 1:
The patent enables continuous measurement of the derivative of inductive rise time during motor operation, eliminating the need for intermittent coast and sensing intervals. This continuous measurement approach maintains motor operation without interruptions, improving startup efficiency while preserving accurate commutation detection
Solution Approach 2:
The patent calculates and stores derivative values of inductive rise time in advance during normal operation, so that commutation switching points can be identified without requiring the motor to enter special coast or sensing modes. This preliminary calculation approach maintains productivity while enabling precise commutation control
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 improves the efficiency of motor startup by optimizing commutation states and reducing power consumption, allowing for more precise control and efficient operation of the brushless DC motor.
Implementation Method 1
the inductance, measured from phase-to-phase, is a function of the rotor's position... the rise time of the current can be used to determine inductance
Data Source
AI summary
A conventional method used for a startup mode for a brushless direct current (DC) motor employed complementary inductive rise times. Specifically, inductive rise times rise times for a driving state and its complementary state were compared to one another such that when the inductive rise times cross a switching point had been reached. This methodology, however, significantly affects the efficiency of the driving torque and power consumption. Here, however, a derivative of the inductive rise time is employed, which can determine the switching event without the need for a use of a complementary state, improving motor performance.