Motor Starter Reverse-Phase Braking for Fast Light-Load Stops
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Solution Overview
Problem
Motor starters face challenges in efficiently stopping lightly-loaded motors, which can act like flywheels due to inertia, leading to prolonged spin-down times and potential mechanical damage from high starting torque and inrush currents.
Innovation Solution
Implementing a motor starter system that applies a reverse phase sequence to the motor after a predetermined dwell time, with a lower frequency than the driving sequence, and terminates braking when the motor current reaches a predetermined limit, indicating zero speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If a motor is de-energized to stop it, then energy consumption is reduced, but stopping time becomes excessively long due to rotor inertia
Solution Approach 1:
The patent applies periodic reverse-phase sequences at reduced frequency to create controlled negative torque pulses that accelerate motor deceleration. By periodically reversing phase connections during the braking period, the system generates sufficient braking force to overcome rotor inertia without requiring continuous high-energy DC injection, thus reducing stopping time while managing energy consumption.
Solution Approach 2:
The system changes operational parameters by transitioning from normal forward-phase operation to reverse-phase braking sequence, and further adjusting the frequency of phase switching during braking. This parameter transformation enables the motor to generate its own braking torque through electromagnetic induction, eliminating the need for external braking energy input.
2Force
If DC current is applied to the stator for braking, then braking force is improved, but risk of mechanical damage from high torque increases
Solution Approach 1:
Instead of applying full DC braking current that would generate excessive torque, the patent uses partial action by implementing reverse-phase sequences at reduced frequency. This generates sufficient braking force to stop the motor while keeping torque levels within safe mechanical limits, preventing damage to windings and coupled components.
Solution Approach 2:
The periodic application of reverse-phase sequences creates pulsed braking torque rather than continuous high torque. This periodic action allows the motor to decelerate effectively while avoiding sustained high-stress conditions that could cause mechanical damage.
3Speed
If reverse phase sequence is applied at high frequency, then braking speed is improved, but motor current exceeds safe limits
Solution Approach 1:
The patent transforms the frequency parameter from high-frequency operation during normal running to low-frequency operation during braking. This parameter change ensures that braking torque is generated at safe current levels while still achieving effective deceleration, as the reverse-phase sequences are applied at frequencies one-tenth or less of the fundamental line frequency.
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 method effectively brakes lightly-loaded motors by demagnetizing remnant flux and reducing spin-down time, preventing mechanical damage and voltage dips, while ensuring safe shutdown.
Implementation Method 1
braking the motor by connecting pairs of phases of the AC power source to pairs of phases of the motor in a second sequence that is reversed with respect to the first sequence
Implementation Method 2
the polarity of the supply line voltage and the voltage induced by back electromotive force (emf) in the motor
Implementation Method 3
DC current flowing through the stator produces a stationary magnetic field, with motion of the rotor in this field inducing a voltage in the rotor winding and causing energy to be dissipated in the rotor circuit resistance
Data Source
AI summary
Pairs of phases of an AC power source are connected to pairs of phases of a motor in a first sequence that repeats at a first frequency. The motor is braked by connecting pairs of phases of the AC power source to pairs of phases of the motor in a second sequence that is reversed with respect to the first sequence and that repeats at a second frequency less than the first frequency. In further aspects, pairs of phases of an AC power source are connected to pairs of phases of a motor in a first sequence. The motor is subsequently disconnected from the AC power source for a predetermined dwell interval having a duration greater than a time constant of the motor. The motor is braked using a second sequence that is reversed with respect to the first sequence.