BLDC Motor Commutation Control for Negative Current Dissipation

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Solution Overview

Problem

The occurrence of adverse currents during commutation sequences in brushless DC (BLDC) motor control schemes for power tools can lead to MOSFET failure, reduced motor performance, increased maintenance costs, and safety hazards, which traditional hardware solutions like larger capacitors and higher-rated MOSFETs fail to address effectively without increasing costs and module size.

Innovation Solution

A multi-phase trapezoidal commutation scheme is implemented with a current dissipation path through high-side or low-side power switches, extending the conduction band of low-side switches during motor commutation, delaying the next sector's commutation, or maintaining the ON-cycle of high-side switches to prevent negative current flow into the bus line.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If traditional hardware solutions like larger capacitors and higher-rated MOSFETs are used to mitigate adverse currents, then MOSFET reliability is improved, but device complexity and cost increase

Engineering Contradiction:

ImproveMOSFET reliabilityVSAvoidcontrol module size

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent changes the control parameters of the power switch circuit by extending the conduction band of low-side switches and maintaining high-side switch ON-cycles during commutation transitions. This parameter adjustment creates alternative current dissipation paths that prevent negative currents without requiring hardware upgrades, thereby improving MOSFET reliability while avoiding increased device complexity

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent applies preliminary action by extending the conduction band of low-side power switches before the actual commutation occurs. This preparatory extension ensures that when commutation happens, negative currents are prevented from flowing into the bus line, thereby protecting MOSFETs in advance without requiring larger components

Inventive Principle:

Principle #10Preliminary action

2Reliability

If traditional hardware solutions like larger capacitors and higher-rated MOSFETs are used to mitigate adverse currents, then MOSFET reliability is improved, but manufacturing cost increases

Engineering Contradiction:

ImproveMOSFET reliabilityVSAvoidmanufacturing cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent uses parameter changes in the control signals (extending conduction bands, adjusting ON-cycles) to prevent adverse currents during commutation. This software-based solution avoids the need for more expensive hardware components, thereby improving MOSFET reliability while keeping manufacturing costs low

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces the mechanical/hardware approach (larger capacitors, higher-rated MOSFETs) with an electronic control approach (modified PWM signals, extended conduction bands). This substitution achieves the same protective function at lower cost by using control logic instead of upgraded physical components

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Power

If six-step trapezoidal commutation scheme is used to drive BLDC motor, then motor performance is achieved, but adverse currents occur during commutation

Engineering Contradiction:

Improvemotor performanceVSAvoidadverse currents

Core Design Contradiction:

PowerVSObject-generated harmful factors

Solution Approach 1:

The patent applies preliminary action by extending the conduction band of low-side switches before commutation occurs. This ensures that when the six-step commutation transitions between sectors, negative currents are prevented from flowing into the bus line, thereby maintaining motor performance while eliminating adverse currents

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent converts the potentially harmful negative current flow into a beneficial controlled current path by extending the conduction band of low-side switches. This redirects the current through safe dissipation paths during commutation, transforming what would be a harmful effect into a controlled and useful current flow that protects the system

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Data Source

PatentUS20260025090A1Motor drive control scheme for reducing negative currents

Publication Date: 2026.01.22 BLACK & DECKER CORP

AI summary

A tool is provided including a motor powered by a battery, a power switch circuit, and a controller that controls the power switch circuit using a multi-phase trapezoidal commutation scheme including at least six commutation sectors for each rotation of the motor. The power switch circuit includes high-side power switches and low-side power switches configured as an inverter circuit. Within at least one phase of the motor that includes a first sector and a second sector driven by pulse-width modulation (PWM) control, a dissipation current path is provided through at least two of the high-side or two of the low-side power switches, for a current dissipation period that starts immediately after a motor commutation from the first sector to the second sector, for dissipation of the motor current associated with the first sector to avoid negative flow of motor current into the bus line.