Elevator Drive Back-EMF Braking for Brake Failure Control
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Solution Overview
Problem
Existing elevator systems face challenges in effectively braking the elevator car when the machine brake is malfunctioning or the load exceeds the brake's capacity, necessitating alternative methods to prevent unwanted movement.
Innovation Solution
An elevator drive system that includes a short-circuiting module with resistors and a switch, controlled by a controller, to manage back electromotive force (back emf) generated by the motor, thereby limiting its speed and maintaining the voltage within a preselected range, using converter switches like IGBTs or MOSFETs to discharge energy storage devices such as capacitors.
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 under normal conditions, but the braking capability is insufficient when the brake malfunctions or the load exceeds brake capacity
Solution Approach 1:
The system changes the electrical parameters (voltage, current) by controlling the converter switches to dissipate regenerative energy through the braking resistor, thereby providing additional braking force when the mechanical brake is insufficient
Solution Approach 2:
The energy storage device and braking resistor act as intermediary components to manage and dissipate the regenerative energy that would otherwise cause unwanted motor rotation, providing a controlled braking mechanism
2Stability of the object's composition
If the converter switches are controlled to dissipate regenerative energy, then unwanted motor rotation is prevented, but the system complexity increases due to additional control mechanisms
Solution Approach 1:
The converter switches perform multiple functions: they control motor operation during normal operation and also function as switching elements for dissipating regenerative energy during braking, eliminating the need for separate braking switches
Solution Approach 2:
The control circuit merges the motor control functions with the regenerative energy dissipation control into a single integrated control system that manages both functions using the same converter switches
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
Effectively brakes the elevator car by controlling back emf, ensuring safe stationary positioning even when the machine brake fails, by maintaining motor speed and voltage within predetermined limits.
Implementation Method 1
an energy storage device that is situated to be charged in response to the motor generating a back emf as the motor rotates
Implementation Method 2
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
Data Source
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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.