BLDC Direct Drive Circuit With Back-EMF-Matched Current Shaping
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Solution Overview
Problem
Conventional DC motor drive systems face inefficiencies at high motor speeds due to limitations in back EMF handling, leading to high power losses and reactive currents, especially in star topology configurations, and require additional switches in separated coil configurations to achieve higher back EMF, increasing complexity.
Innovation Solution
A method and circuitry for a BLDC motor with separate coils, utilizing unipolar controlled current sources, a controller for phase and magnitude control, and a polarity switch to convert unipolar current to bipolar, ensuring current matches the back EMF shape and magnitude, allowing bidirectional operation and efficient power transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If Field Weakening Control is implemented to achieve high motor speeds, then motor speed increases, but power losses increase and efficiency decreases
Solution Approach 1:
The invention changes the control parameters by using back EMF-based current control instead of traditional Field Weakening Control. By adjusting the current magnitude and phase based on back EMF sensing, the system achieves high motor speeds without the high reactive currents and power losses associated with Field Weakening Control.
2Power
If separated coils are used to accommodate higher back EMF, then back EMF capacity increases, but device complexity increases due to double number of switches
Solution Approach 1:
The invention merges the functions of multiple switches into a single polarity switch that handles bidirectional current flow. Instead of using double number of switches as in traditional separated coil configurations, this single switch controls current direction while the back EMF sensing and control circuitry manages the remaining functionality, thereby reducing device complexity while maintaining high back EMF capacity.
Solution Approach 2:
The polarity switch serves multiple functions: it controls current direction, enables bidirectional operation, and works in conjunction with the back EMF sensing system to achieve precise current control. This multi-functional approach eliminates the need for additional switches while maintaining the ability to handle high back EMF.
3Ease of operation
If current is not precisely matched to back EMF shape, then control simplicity is maintained, but efficiency decreases due to reactive currents
Solution Approach 1:
The invention implements feedback control by sensing the back EMF and using this information to precisely control the current magnitude and phase. The controller continuously monitors back EMF and adjusts the current waveform to match it, eliminating reactive currents and maximizing efficiency while maintaining ease of operation through automated 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 enables efficient motor operation at high speeds with reduced power losses by precisely matching current to back EMF, improving torque control and reducing the need for additional switches, thus enhancing efficiency and simplifying the drive system.
Implementation Method 1
When a coil is activated, the generated magnetic field attracts/detracts some of the poles of the rotor magnets in order to start and maintain rotation
Implementation Method 2
a voltage source representing the electromotive force (EMF) generated when the inductor passes (via rotation) a permanent magnet
Data Source
AI summary
Circuitry for directly providing drive power to a BLDC motor having separated coils, comprising unipolar controlled current sources for supplying current to each of the separated coils; a controller, for controlling the level and phase of the unipolar controlled current sources; a polarity switch for converting the unipolar current to a bipolar (AC) current, supplied to the separated coils. The controller is adapted to shape the current being fed to the BLDC motor by the current source via the polarity switch, to be in phase with the back EMF sensed on the separated coils, and of a magnitude that corresponds to a required torque.