Adaptive Braking Control for Brushless DC Motors

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Existing brushless DC motor braking schemes face inefficiencies, such as large transistor area requirements and unstable speed control due to mechanical friction and 'ringing' issues, when attempting to quickly decelerate motors in applications like HDDs and DVD players.

Innovation Solution

An adaptive braking system using a controller with PWM generator, reverse current detector, and control logic that calculates a brake-to-off ratio based on target speed and rotational speed parameters to manage the inverter's braking intervals, eliminating the need for bulky discharge circuits and stabilizing deceleration.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If transistors Q7 and Q8 are made sufficiently large to carry reverse current through discharge circuit 108, then reverse current can be effectively discharged, but the transistors occupy a large portion of the area of IC 102-1

Engineering Contradiction:

Improvereverse current discharge capabilityVSAvoidIC area occupied by transistors

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

The patent extracts the discharge circuit (including transistors Q7 and Q8 and resistor R2) from the IC design entirely. Instead of integrating the discharge circuit within the IC, the invention routes reverse current through external pins (U, V, W) to the motor driver's supply pin VDD, eliminating the need for large transistors within the IC and freeing up valuable chip area.

Inventive Principle:

Principle #2Taking out (Extraction)

2Reliability

If inverter 106 is placed in high impedance mode to allow mechanical friction to slow the motor, then the motor can decelerate without reverse current flow, but the losses due to friction are so low that the motor does not reach the desired target speed within the desired deceleration period

Engineering Contradiction:

Improvedeceleration stabilityVSAvoiddeceleration speed

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The patent employs periodic action by implementing a braking mode that alternates between active braking periods and coasting periods. During active braking, transistors Q1, Q3, Q5 are inactivated while Q2, Q4, Q6 are activated to allow reverse current flow through resistor R1. This periodic braking approach provides controlled deceleration that is both stable and fast, overcoming the limitations of continuous high-impedance mode.

Inventive Principle:

Principle #19Periodic action

3Productivity

If transistors Q1, Q3, Q5 are inactivated and transistors Q2, Q4, Q6 are activated to allow reverse current to flow back through pin COMM, then the motor can be slowed to desired speed within desired deceleration period, but the speed is not stable and ringing occurs

Engineering Contradiction:

Improvedeceleration speedVSAvoidspeed stability

Core Design Contradiction:

ProductivityVSStability of the object's composition

Solution Approach 1:

The patent resolves the stability issue by implementing periodic braking rather than continuous braking. The controller alternates between braking intervals (where transistors Q2, Q4, Q6 are activated) and coasting intervals (where all transistors are inactivated, placing the inverter in high-impedance mode). This periodic approach allows the system to dissipate reverse current in controlled bursts while maintaining speed stability, eliminating the ringing problem associated with continuous braking.

Inventive Principle:

Principle #19Periodic action

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

The adaptive braking system effectively decelerates the motor to a desired speed within a target time without 'ringing' and without requiring large discharge circuits, ensuring efficient and stable speed control.

Implementation Method 1

a reverse current detector that is coupled to the PWM

Methodology Applied

Scientific EffectElectrical current detection: Conduction (electrical)

Implementation Method 2

a pulse width modulation (PWM) generator that is coupled to the inverter

Methodology Applied

Scientific EffectPulse width modulation:

Implementation Method 3

transistors Q1, Q3, and Q5 are inactivated or 'turned off,' while transistors Q2, Q4, and Q6 are activated or 'turned on'

Methodology Applied

Scientific EffectElectrical conduction and switching: Conduction (electrical)

Implementation Method 4

allows a reverse or negative current to flow back through the pin COMM so as to be dissipated by resistor R1

Methodology Applied

Scientific EffectJoule heating: Joule Heating

Data Source

PatentUS9013124B2Reverse current protection control for a motor

Publication Date: 2015.04.21 TEXAS INSTRUMENTS INC

AI summary

A method is provided. A command to correspond to a target speed of a motor is received. A rotational speed of the motor is measured, and a brake-to-off ratio for a braking interval is calculated based at least in part on the rotation speed, the target speed, a braking parameter. An off state for an inverter that is coupled to motor is induced during an off portion of the braking interval, and a brake signal is applied to the inverter during a braking portion of the braking interval.