BLDC Motor Commutation State Detection Using Phase Voltage Time Delays
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Solution Overview
Problem
Determining the correct commutation state for brushless DC motors is challenging, especially when the motor is at rest, as there is no motion-induced back electromotive force (BEMF) to indicate the present commutation state, which can lead to improper starting direction and potential damage.
Innovation Solution
A system that includes a controller to control current applied to motor phases, a time delay system to measure the time difference between a driven phase and a floating phase crossing a predetermined threshold, and logic to determine the commutation state based on these measurements, allowing for accurate commutation state determination even at rest.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Hall effect sensing circuitry or rotary encoders are used to determine rotor position, then accurate commutation state determination is achieved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the position detection function from external sensors (Hall effect sensors, rotary encoders) and implements it using existing motor phase windings and controller resources. By utilizing the motor's own electrical characteristics (current flow, voltage thresholds) for position detection, the system eliminates the need for separate sensing components while maintaining commutation accuracy.
Solution Approach 2:
The patent makes the motor phases serve multiple functions: they both drive the motor and provide position detection information. The same phase windings used for motor operation are also used to generate detectable electrical signals for commutation state determination, eliminating the need for dedicated sensing components and reducing overall system complexity.
2Device complexity
If BEMF measurement is used to infer rotor position, then device complexity is reduced, but measurement precision deteriorates when the motor is at rest
Solution Approach 1:
The patent applies preliminary action by energizing a motor phase before attempting to determine commutation state. By proactively driving a phase and measuring the resulting electrical characteristics (current rise time, voltage thresholds), the system creates detectable signals even when the motor is stationary, enabling accurate position determination without relying on motion-induced BEMF.
Solution Approach 2:
The patent employs periodic action by repeatedly energizing phases in a sequence and measuring electrical characteristics at each step. This periodic driving and measurement approach allows the system to scan through possible commutation states and identify the correct one based on measured parameters, ensuring accurate position detection regardless of motor speed.
3Device complexity
If the motor starts without known rotor position, then device complexity is reduced, but harmful effects increase due to potential reverse rotation
Solution Approach 1:
The patent implements feedback by measuring electrical characteristics (current, voltage thresholds, time delays) during phase energization and using this information to determine the actual commutation state before starting motor rotation. This feedback loop ensures the controller has accurate position information, allowing it to initiate rotation in the correct direction and prevent harmful reverse rotation.
Solution Approach 2:
The patent performs preliminary commutation state determination by energizing phases and measuring electrical characteristics before initiating motor rotation. This preliminary action establishes the correct starting commutation state, ensuring the motor begins rotation in the intended direction and avoiding damage from reverse rotation.
Data Source
AI summary
A system for determining a commutation state for a brushless DC motor includes a controller configured to control current that is applied to drive each of a plurality of phases of the motor. A time delay system is configured to measure, for a given commutation state, a time delay from when a voltage associated with a driven phase of the plurality of phases crosses a predetermined threshold and a voltage associated with a floating phase of the plurality of motor phases crosses the predetermined threshold. Logic is configured to determine the commutation state for the motor based on the measured time delay.