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Method and System For Automatically Selecting A Sensorless Brushless DC Motor's Direction Disclosure Number: IPCOM000033030D
Original Publication Date: 2004-Nov-22
Included in the Prior Art Database: 2004-Nov-22
Document File: 4 page(s) / 87K

Publishing Venue



The main idea for this invention is a method and system for allowing a sensorless BLDC motor to operate in the proper direction automatically with no code intervention.

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Method and System For Automatically Selecting A Sensorless Brushless DC Motor's Direction

Main Idea

Sensorless BLDC motors are difficult to reverse in software, as the process for starting such a motor is a complex state machine. Code grows large quickly when multiple versions of these state machines are employed as competitors do. The advantage of this invention is that it adds trivial cost to the hardware (under $2), and it completely invisible to software.

     Starting a BLDC motor is difficult since there are no position sensors to tell us which phase windings to energize. In the absence of said sensors, the following sequence is used:

     1.) Force motor to a known state, usually between a valid state by turning on a total of 3 devices (ie, rotor is resting between poles, 30 electrical degrees off of each "transistor pair active" location)

2.) Step to the next valid state (now only 2 transistors are on).
3.) Step to follow acceleration curve derived from system dynamics - OR - Accelerate by stealthing BEMF reads in between commutation subintervals to determine whether to accelerate faster or slower (BM patent)

     Either way, three discrete steps need to be coordinated. The problem with just changing the software is that it needs to be changed in all 3 places.

     There is no way to just change the phasing in software, as drive signals are generated with hardware PWMs in virtually all motor control DSP/Microcontrollers.

If we were to change the code, the following would need to happen
1.) Phase pair energize, Don't change this, it is the starting point, and we don't care whether we step left or right.

2.) Open loop step -- Must occur in the opposite direction this time
3.) Subsequent steps and stepping stat...