BLDC Motor Commutation With Dissipative Phase Energy Control
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Solution Overview
Problem
Existing brushless direct current (BLDC) motors in power tools experience negative transient currents during commutation events, which can disrupt the current supply and cause interruptions, particularly in low-capacitance battery packs.
Innovation Solution
Implementing dissipative control through an electronic controller that selectively switches the power switching circuit to dissipate energy from energized motor phases before the next sequential energization, using a combination of PWM and pulse signals with varying duty cycles to manage current flow and prevent negative transient currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional commutation control is used in BLDC motors, then the motor can be driven sequentially by energizing phases, but negative transient currents occur during commutation events causing interruptions 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 outgoing phase through controlled switching sequences, preventing the buildup of negative transient currents that would otherwise disrupt the current supply during commutation.
Solution Approach 2:
The patent introduces an intermediary energy dissipation mechanism between the power source and the motor phases. By using the low-side switches and high-side switches in specific configurations during commutation, the system creates a controlled path for energy dissipation that mediates the transition between phases and prevents harmful transient currents.
2Reliability
If energy is dissipated from energized phases before next sequential energization, then negative transient currents are prevented, but additional switching operations increase device complexity
Solution Approach 1:
The patent applies universality by making the existing high-side and low-side switches perform multiple functions. During normal operation, these switches control phase energization, but during commutation events, they are reconfigured to dissipate energy from de-energized phases. This multi-functionality allows the same switching components to handle both motor driving and transient current management without adding extra hardware.
Solution Approach 2:
The patent changes the operational parameters of the switching circuit during commutation events. By modifying the duty cycles and timing of PWM signals to the high-side and low-side switches, the system dynamically alters the electrical characteristics to enable energy dissipation. This parameter-based control allows complex behavior to be achieved through software/firmware control rather than hardware complexity.
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 dissipative control reduces interruptions in commutation control and limits large in-rush currents, ensuring stable current supply to the BLDC motor and minimizing disruptions in battery packs, especially in low-capacitance systems.
Implementation Method 1
dissipate, 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
Data Source
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.