BLDC Compressor Rheostatic Braking With Open-Phase Position Sensing
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Solution Overview
Problem
Existing braking techniques for BLDC motors in hermetic compressors, such as short-circuiting all phases or reducing revolutions, lead to high currents, loss of motor position information, and mechanical issues like excessive displacement and wear, which are not viable for refrigerating systems.
Innovation Solution
A rheostatic braking method that selectively short-circuits phases with the major and minor induced voltage, maintains a third phase for monitoring, and uses pulse width modulation to control braking current, ensuring minimal displacement and preserving motor position information by dividing electric positions into sections and adjusting switching configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If all phases are short-circuited for braking, then kinetic energy is dissipated quickly, but high currents are generated that exceed motor limits
Solution Approach 1:
The three-phase braking process is segmented into selective phase pairs. Instead of short-circuiting all phases simultaneously, only two phases are short-circuited at a time based on their induced voltage magnitudes. This segmentation divides the braking action into controlled segments that prevent excessive current while maintaining effective deceleration.
Solution Approach 2:
The braking method dynamically changes parameters by selecting different phase pairs based on real-time induced voltage measurements. The system adjusts which phases are short-circuited by monitoring voltage magnitudes and switching between phase combinations, thereby adapting the braking characteristics to prevent harmful current levels while maintaining productivity.
2Productivity
If phase short-circuiting is performed for braking, then kinetic energy is dissipated, but motor position information is lost
Solution Approach 1:
The method extracts and preserves the essential function of position detection by maintaining one open phase during braking. This open phase serves as a dedicated sensor channel that continuously provides position information independent of the braking action on the other two phases, thereby separating the braking function from the position sensing function.
Solution Approach 2:
The open phase serves multiple functions simultaneously: it acts as a position sensing channel and provides a reference for controlling the braking process. This multi-functionality allows the system to maintain position awareness while performing braking, eliminating the need for separate sensing mechanisms.
3Productivity
If braking is applied to stop the motor, then kinetic energy is dissipated, but mechanical stress and wear increase due to excessive displacement
Solution Approach 1:
The braking system dynamically adjusts its characteristics by selecting different phase pairs based on real-time voltage conditions. This dynamic adaptation allows the braking force to be modulated according to the motor's instantaneous state, preventing excessive displacement and mechanical stress while maintaining efficient stopping performance.
Solution Approach 2:
The system uses feedback from voltage monitoring on the open phase to control the braking process. By continuously measuring the induced voltage and using this information to determine which phases to short-circuit, the system achieves closed-loop control that prevents harmful mechanical effects while maintaining braking effectiveness.
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 effectively dissipates kinetic energy without high currents, maintains motor position information, and reduces mechanical stress, ensuring reliable compressor operation.
Implementation Method 1
maintaining a third open phase to monitor the electric position of the BLDC motor by means of monitoring the induced voltage at this third open phase
Implementation Method 2
A rheostatic braking method that selectively short-circuits phases with the major and minor induced voltage
Data Source
AI summary
This invention refers to a rheostatic braking method, applied on a BLDC motor (10) used in hermetic compressors, comprising:selecting a first phase and a second phase, connected to the BLDC motor (10), which will be short-circuited, at a certain electric position of the BLDC motor (10), wherein the first phase and the second phase selected are the phases having the major induced voltage and the minor induced voltage at a certain electric position of the BLDC motor (10);maintaining a third open phase to monitor the electric position of the BLDC motor (10) by means of monitoring the induced voltage at this third open phase; andseparating the rheostatic braking in six electric positions, each electric position being associated to two electric sections: a first section before zero crossing of the induced voltage of the third open phase; and a second section after the zero crossing.