BLDC Inverter Block Commutation Reduces Diode Losses
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Brushless direct current (BLDC) motors experience significant power losses due to diode conduction losses during demagnetization, particularly at the end of a commutation step, which are not effectively reduced by existing techniques such as shorter dead times or using Schottky or MOS gated diodes, especially for high-voltage applications.
Innovation Solution
The solution involves a motor control system that senses the direction of current and rotor position to turn on the power transistor at the end of a commutation step, directing demagnetizing current through the lower impedance transistor channel instead of the body diode, and optionally turning on both high side and low side power transistors during demagnetization, thereby reducing diode losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the power transistor is turned on during demagnetization, then diode conduction losses are reduced by directing current through the lower impedance transistor channel, but device complexity increases due to the need for current direction sensing and precise timing control
Solution Approach 1:
The control circuit uses current direction sensing feedback to determine when to turn on the power transistor during demagnetization. The Hall sensor provides rotor position feedback that triggers the commutation sequence. This feedback mechanism enables precise timing control to redirect demagnetizing current through the transistor channel, reducing diode conduction losses while maintaining automated operation.
Solution Approach 2:
The power transistor serves dual functions: normal switching operation and demagnetization current path. By utilizing the existing transistor's lower impedance channel for demagnetization current, the system reduces losses without requiring separate dedicated components, allowing the transistor to serve itself in multiple roles.
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 significantly reduces overall power losses by minimizing diode conduction losses, improving efficiency, and is applicable to high-voltage BLDC motors where existing methods are ineffective.
Implementation Method 1
directing the demagnetizing current through the lower impedance transistor channel (e.g. the drain-source channel in case of MOSFETs) rather than through the body diode
Implementation Method 2
A Hall sensor senses a motor position
Implementation Method 3
BLDC motors may use an electronic controller to energize the stator coils with the correct timing for accurate speed and torque output. The magnetic field frequency of the stator synchronized to the rotation of the rotor
Data Source
Figure 1
Figure 2A~2C
Figure 3
AI summary
Techniques to sense the direction of current through the power transistor of an inverter drive circuit and the position of the rotor for a brushless direct current (BLDC) motor. During the time demagnetizing current flows, the power transistor is turned ON, directing the demagnetizing current through the lower impedance transistor channel rather than through the body diode. Directing current to the transistor channel may reduce the diode losses in the power transistors, thereby reducing the overall power losses. In other examples, the low side as well as the high side power transistor may be turned on during the time the demagnetizing current flows through the given power transistor.