Electric Motor Braking Current Limiting via Winding Reactance
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Solution Overview
Problem
In electric motors, especially in aerospace applications, it is undesirable for electrical currents to be generated when the power supply is switched off, as these currents can undesirably flow into other parts of the electrical network, requiring large and heavy resistors to dissipate the power, which adds size and weight to the system.
Innovation Solution
An electric motor with a stator, rotor, and controller that disconnects windings from the power supply during braking and shorts at least one winding to generate a braking current, limiting the current amplitude to the rated current level through high reactance, preventing damage and allowing controlled braking without the need for large resistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a resistor is provided to dissipate electrical power generated during braking, then the harmful effect of generated currents is mitigated, but the size and weight of the system increase
Solution Approach 1:
The invention extracts the braking current dissipation function from an external resistor and relocates it to the motor's own windings by short-circuiting them. This eliminates the need for a separate resistor component, thereby reducing system size and weight while still achieving the desired current dissipation during braking
Solution Approach 2:
The invention merges the braking function with the motor's existing windings structure. By short-circuiting the windings during braking, the windings themselves serve as both the motor operation component and the braking current dissipation path, eliminating the need for separate braking components
2Use of energy by moving object
If the motor operates as a generator during braking, then power can be recovered, but electrical currents are transmitted to other parts of the electrical network which is undesirable
Solution Approach 1:
The invention converts the potentially harmful generated current into a beneficial braking force. By short-circuiting the windings, the generated current flows through the windings themselves, creating a magnetic field that opposes rotor motion and provides controlled braking, while preventing current transmission to the electrical network
3Force
If the braking current amplitude is high, then effective braking is achieved, but the motor circuit may be damaged
Solution Approach 1:
The invention changes the electrical parameters of the motor circuit by adjusting the reactance value. By selecting an appropriate reactance value, the braking current amplitude is limited to a safe level that provides effective braking force while preventing damage to the motor circuit components
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
This solution effectively limits the braking current to the rated current, preventing damage to the motor circuit and reducing the need for large resistors, thereby minimizing size and weight while maintaining controlled braking performance.
Implementation Method 1
the magnet is able to generate a braking current in the shorted phase or winding
Implementation Method 2
the motor is configured to operate at a rated current in the drive mode and to have a reactance such that the amplitude of the braking current is the same or lower than the amplitude of the rated current
Data Source
AI summary
An electric motor comprising: a stator; a rotor having a magnet mounted thereto; an electric circuit comprising a plurality of phases or windings for driving rotation of a rotor, in a drive mode; and a controller configured to control the electric circuit, in a motor braking mode, to short at least one of said phases or windings such that the magnet is able to generate a braking current in the shorted phase or winding wherein the motor is configured to operate at a rated current in the drive mode and to have a reactance such that the amplitude of the braking current is the same or lower than the amplitude of the rated current.