Three-Phase Motor Braking Control to Limit Battery Energy Return
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Solution Overview
Problem
Existing motor braking schemes for three-phase motors in electric tools result in significant energy return to the battery or power supply, leading to reduced battery life and potential damage to the electric tool.
Innovation Solution
A control device for a three-phase motor featuring a switching unit with two sets of switching elements and a control unit that generates specific control signals to implement various brake modes, including a dual down tube brake mode, maximum braking current mode, and single down tube brake mode, to effectively consume motor energy without returning it to the power supply.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a power switching device and capacitor are used to consume motor energy during braking, then motor energy can be consumed, but energy returns to the battery or power supply causing reduced battery life and potential damage
Solution Approach 1:
The switching unit is divided into two independent sets (first switching unit and second switching unit), each with multiple switching elements. This segmentation allows selective control of different switching elements to achieve different brake modes, enabling the system to consume motor energy while preventing energy return to the power supply.
Solution Approach 2:
The control unit dynamically adjusts the switching states of switching elements based on real-time motor operating conditions. By generating control signals that adaptively control which switching elements are on or off during braking, the system optimizes energy consumption while preventing harmful energy return to the battery or power supply.
2Volume of moving object
If a small-sized capacitor is used in miniaturized AC-EC corded electric tools, then the tool size is reduced, but the capacitor has small capacity resulting in limited motor energy consumption and high energy return to power supply
Solution Approach 1:
The switching unit is divided into two independent sets (first switching unit and second switching unit), each with multiple switching elements. This segmentation allows selective control of different switching elements to achieve different brake modes, enabling the system to consume motor energy while preventing energy return to the power supply.
Solution Approach 2:
The control unit dynamically adjusts the switching states of switching elements based on real-time motor operating conditions. By generating control signals that adaptively control which switching elements are on or off during braking, the system optimizes energy consumption while preventing harmful energy return to the battery or power supply.
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 proposed solution achieves high braking efficiency with minimal energy return to the power supply, thereby extending battery life and preventing damage to the electric tool.
Implementation Method 1
each switching element of the first switching unit is connected in series with a corresponding switching element of the second switching unit, and both are separately electrically connected to one phase of the driving circuit of the three-phase motor
Implementation Method 2
a control unit configured to be electrically connected to the switching unit, and to generate a first control signal for controlling switching states of the respective switching elements
Implementation Method 3
three-phase motors are widely used in electric tools, and they convert electrical energy into mechanical energy, so as to provide the electric tools with driving force
Data Source
AI summary
An electric tool, a control device and a method for a three-phase motor thereof is disclosed. The control device includes a switching unit that has a first switching unit and a second switching unit. The first switching unit and the second switching unit each includes a plurality of switching elements corresponding to respective phases of a driving circuit of the three-phase motor. The respective switching element of the first switching unit are connected in series with corresponding switching elements of the second switching unit, respectively. The control unit further includes a control unit configured to be electrically connected to the switching unit and to generate a first control signal for controlling switching states of the respective switching elements so as to realize a first brake mode of the three-phase motor. Under the control of the first control signal, the respective switching elements of the first switching unit are turned off, and in each sub-period interval of one electrical period, the switching element in the second switching unit corresponding to a phase with a maximum back electromotive force of the three-phase motor is turned off, and the other switching elements in the second switching unit are turned on.