BLDC Motor Commutation Circuit for Negative Transient Current Control
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Solution Overview
Problem
Existing brushless direct current (BLDC) motors in power tools experience negative transient currents during commutation, which can disrupt the current supply and cause interruptions, particularly in low-capacitance battery packs.
Innovation Solution
Implementing a dissipative control method in the power switching circuit of the BLDC motor, where energy is dissipated from energized phases before the next sequential energization, using a combination of high-side and low-side switches with varying duty cycles to manage these transient currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional commutation control is used in BLDC motors, then the motor can operate with simple control circuitry, but negative transient currents occur during commutation causing disruptions in current supply
Solution Approach 1:
The patent applies preliminary action by dissipating energy from the de-energized phase before the commutation event occurs. The controller actively manages the decay of current in the phase being de-energized, preventing the buildup of negative transient currents that would otherwise disrupt the current supply during commutation. This proactive energy dissipation ensures smooth transitions between phases.
2Reliability
If energy is dissipated from energized phases before next sequential energization, then negative transient currents are reduced, but additional switching operations increase circuit complexity
Solution Approach 1:
The patent implements multi-functionality by having the existing high-side and low-side switches perform dual roles: they both energize the motor phases during normal operation and dissipate energy from de-energized phases during commutation. The same power switching circuitry used for motor control is repurposed for energy dissipation, eliminating the need for additional dedicated dissipation switches or circuitry.
3Device complexity
If high-side switches and low-side switches are used for both energizing and dissipating energy, then the same hardware can be utilized for multiple functions, but the control signal requirements increase
Solution Approach 1:
The patent applies periodic action through the use of PWM (pulse-width modulation) signals to control the switching of high-side and low-side switches. The controller generates periodic control signals with specific duty cycles that rhythmically energize and de-energize phases in sequence. This periodic switching pattern manages the complex control requirements by establishing a predictable, repeating commutation cycle.
Data Source
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AI summary
A power tool including a brushless direct current ("BLDC") motor having a plurality of phases, a power switching circuit electrically coupled to the motor and having a plurality of high-side switches and a plurality of low-side switches, and an electronic controller electrically coupled to the power switching circuit. The electronic controller sequentially energizes, using the power switching circuit, the plurality of phases to drive the BLDC motor and dissipates, using the power switching circuit, energy from an energized phase of the plurality of phases prior to next sequential energization of the plurality of phases.