Elevator Motor Back-EMF Braking With Energy Storage Discharge
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Solution Overview
Problem
Conventional elevator systems face challenges in effectively braking the elevator car when the machine brake is malfunctioning or insufficient to handle large loads, necessitating alternative braking methods to comply with safety codes.
Innovation Solution
An elevator machine assembly with a motor, energy storage device, and converter switches that utilize a short-circuiting module to control and limit the back electromotive force (EMF) of the motor, preventing excessive rotation by selectively discharging energy through resistors and IGBTs/MOSFETs, ensuring the voltage remains within a preselected range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the machine brake is used to stop the elevator car, then the braking function is provided, but the brake may malfunction or be insufficient for large loads
Solution Approach 1:
The patent introduces an intermediary braking system using the motor itself as a braking device. The motor controller converts the motor into a generator mode, where the back EMF generated during rotation creates a counter-torque that opposes the rotation direction, providing an additional braking force independent of the mechanical brake system.
Solution Approach 2:
The patent changes the operational parameters of the motor by controlling the voltage and current supplied to it. During braking, the motor controller adjusts the electrical parameters to enable the motor to generate sufficient back EMF and counter-torque to supplement or replace the mechanical brake, thereby improving overall braking reliability.
2Use of energy by moving object
If the motor rotates freely generating back emf, then energy is stored in the energy storage device, but the motor speed may become excessive
Solution Approach 1:
The patent implements a feedback control mechanism where the motor controller continuously monitors the motor's rotation speed and the voltage across the energy storage device. Based on this feedback, the controller dynamically adjusts the switching of power electronic components to regulate the charging current to the energy storage device and prevent excessive motor speed.
Solution Approach 2:
The patent uses periodic switching of power electronic components (such as IGBTs or MOSFETs) to control the flow of current to the energy storage device. This periodic action allows the system to regulate energy charging in controlled intervals, preventing runaway speed increases while maximizing energy recovery.
3Speed
If the back emf is not controlled, then the motor can rotate at high speed, but the voltage may exceed safe operating limits
Solution Approach 1:
The patent introduces an intermediary energy storage device (such as a capacitor) between the motor and the power source. This energy storage device acts as a buffer that absorbs excess voltage during regenerative braking, preventing voltage spikes from damaging other system components while allowing the motor to operate at higher speeds.
Solution Approach 2:
The patent dynamically changes the electrical parameters of the system by controlling the switching frequency and duty cycle of power electronic components. This allows the system to maintain voltage within safe operating limits while enabling the motor to achieve higher rotation speeds during braking operations.
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 provides reliable machine braking, maintaining the elevator car's speed below a threshold even when the machine brake is inadequate, ensuring safe and controlled movement by managing the back EMF and voltage effectively.
Implementation Method 1
the motor generating a back emf as the motor rotates in response to a torque applied to the motor
Implementation Method 2
an energy storage device that is situated to be charged in response to the motor generating a back emf
Implementation Method 3
A short-circuiting module that is selectively coupled with the energy storage device through the converter switches selectively discharges the energy storage device
Data Source
AI summary
An elevator machine assembly includes a motor and an elevator drive configured to control power supply to the motor. The elevator drive includes at least a plurality of converter switches and an energy storage device that is situated to be charged in response to the motor generating a back emf as the motor rotates in response to a torque applied to the motor when the elevator drive is not providing power to the motor. A short-circuiting module that is selectively coupled with the energy storage device through the converter switches selectively discharges the energy storage device to limit the back emf of the motor and a corresponding speed at which the motor rotates.