BLDC Motor Braking Circuit for Fast Stop Without Mechanical Brakes
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Solution Overview
Problem
Brushless DC (BLDC) electric motors in power tools are difficult to brake safely and quickly without substantial damage, often requiring additional mechanical brakes.
Innovation Solution
A motor braking device and method using a switching circuit with high and low side switch groups, controlled by a unit to brake the motor upon trigger release or sensor detection, employing strategies like switching element states and Power Width Modulation (PWM) to manage braking force and speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a BLDC motor is braked by conventional methods, then the motor can be stopped, but the braking time is long and the motor may suffer substantial damage
Solution Approach 1:
The patent applies dynamic switching control where the switching elements transition between on-state and off-state based on real-time motor speed conditions. During high-speed braking, switches are turned off to enable regenerative braking; during low-speed braking, switches are turned on to provide mechanical braking force, creating a dynamic adaptation to changing operating conditions that achieves both safety and speed.
Solution Approach 2:
The patent changes the electrical parameters of the motor circuit during braking by switching elements between conductive and non-conductive states. This parameter change enables the motor to operate in different braking modes (regenerative vs. mechanical) depending on the required braking force and speed, resolving the contradiction between braking time and motor safety.
2Reliability
If extra braking components (mechanical brakes) are added to the motor system, then braking reliability improves, but device complexity increases
Solution Approach 1:
The patent makes the existing motor and switching circuit perform multiple functions: normal motor operation and braking. By controlling the switching elements to connect motor phases in different configurations, the same hardware achieves both propulsion and braking, eliminating the need for separate mechanical brake components while maintaining braking reliability.
Solution Approach 2:
The motor system performs its own braking function using its existing components (stator windings, rotor, switching elements). The motor acts as both the actuator and the brake, with the control unit orchestrating the switching elements to create braking torque without requiring external braking mechanisms, thereby reducing device complexity.
3Speed
If switching elements are switched rapidly during braking, then braking speed increases, but risk of motor damage increases
Solution Approach 1:
The patent implements dynamic switching strategies where the switching frequency and pattern are adapted based on real-time motor speed. At high speeds, switching is optimized for regenerative braking; at low speeds, switching transitions to mechanical braking mode. This dynamic adaptation enables rapid braking while preventing damage by avoiding excessive current at critical speed transitions.
Solution Approach 2:
The control unit monitors motor speed and adjusts switching element states based on feedback from speed sensing. This closed-loop control ensures that switching actions are appropriate for the current operating condition, enabling fast braking response while preventing motor damage through real-time adaptation of switching parameters.
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
Enables safe and rapid motor braking without additional components, preventing damage and allowing adaptable braking methods for various applications.
Implementation Method 1
The BLDC motor is used as a generator when the tool is braking
Implementation Method 2
The BLDC motor is used as a generator when the tool is braking
Data Source
AI summary
Provided is a motor braking device for a N-phase brushless motor. The motor braking device includes a switching circuit adapted to connect the N-phase brushless motor to a power supply, the switching circuit comprising a high side switch group and a low side switch group, each of the high side switch group and the low side switch group comprising N switching elements, and a control unit configured to control the switching circuit to brake the motor based on occurrence of a first event, the first event chosen from a group consisting of release of a trigger by a user, and occurrence of a predetermined condition as detected by a sensor. The control unit is configured to, upon occurrence of the first event, switch all the switching elements of one of the high side switch group or the low side switch group to an on-state, and simultaneously switch all the switching elements of the other one of the high side switch group and the lower side switch group to an off-state.