BLDC Inverter Commutation Control for Lower Torque Ripple
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Solution Overview
Problem
Existing BLDC motor control techniques suffer from power loss, torque ripple, and increased system cost due to diode conduction during commutation, and are not robust against disturbances and nonlinear behavior.
Innovation Solution
A trapezoidal current reference signal is generated with specific ramp-up and ramp-down phases, and the duty cycle of inverter leg switching is adjusted to force current flow through power switches instead of body diodes, using a controller with feedback and feedforward control loops to follow this reference signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If current flows through body diode during commutation, then commutation is achieved, but power loss and torque ripple increase
Solution Approach 1:
The patent implements dynamic current control during commutation by adjusting the duty cycle of inverter switches. Instead of allowing current to flow through body diodes with fixed characteristics, the system dynamically modulates the switching duty cycle to force current through active power switches, thereby reducing power loss and torque ripple while maintaining commutation effectiveness.
Solution Approach 2:
The patent changes the operating parameters of the inverter switches during commutation by adjusting the duty cycle. This parameter modification enables the system to transition from diode conduction mode to active switch conduction mode, achieving lower power loss and reduced torque ripple through controlled parameter variation.
2Measurement precision
If sensing and logic circuits are added to detect demagnetization, then demagnetization detection is improved, but system cost increases
Solution Approach 1:
The patent employs self-service principles by utilizing existing control circuits to detect demagnetization events. The controller monitors current waveforms and switching behaviors through existing sensing and logic circuits, eliminating the need for additional dedicated demagnetization detection hardware. This approach maintains detection capability while avoiding increased system cost.
3Ease of operation
If predetermined switching pattern is used, then control is simplified, but robustness against disturbances and nonlinear behavior decreases
Solution Approach 1:
The patent implements feedback control by continuously monitoring system state and adjusting switching patterns in real-time. Instead of relying on fixed predetermined patterns, the controller adapts switching duty cycles based on actual current waveforms, temperature variations, and load conditions, thereby maintaining robustness against disturbances and nonlinear behaviors while preserving control simplicity.
Data Source
AI summary
A method of controlling a BLDC (brushless DC) motor having a plurality of phases each energized by a different leg of an inverter includes: generating a trapezoidal current reference signal for each phase of the BLDC motor that has a current ramp-up phase with a step profile along which the trapezoidal current reference signal has zero slope for a portion of the current ramp-up phase and non-zero slope elsewhere, and a current ramp-down phase with a step profile along which the trapezoidal current reference signal has zero slope for a portion of the current ramp-down phase and non-zero slope elsewhere; and adjusting a duty cycle of a switching control signal for each leg of the inverter, such that a current through each inverter leg is forced to follow the trapezoidal current reference signal for the corresponding phase. A corresponding controller is also described.