Elevator Braking via Inverter Duty Cycle Control
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Solution Overview
Problem
Existing battery-powered elevator systems rely on costly and complex braking resistors and relays to provide braking, which increases system complexity and cost.
Innovation Solution
A battery-powered elevator system that uses a controller and speed sensor to apply braking signals to switches in the inverter, adjusting the duty cycle of these signals based on the machine's speed to achieve braking without external resistors or relays, utilizing the motor's self-resistance for braking force.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a braking resistor and braking relay are used to provide braking, then braking function is achieved, but system cost and complexity increase
Solution Approach 1:
The patent extracts and eliminates the braking resistor and braking relay from the system by utilizing the inherent resistance of the motor windings for braking. The controller achieves braking by controlling the inverter switches to connect the motor to the DC bus, using the motor's own resistance to generate braking torque without requiring external braking components.
Solution Approach 2:
The motor serves itself by using its own winding resistance for braking instead of requiring separate braking components. The motor's electrical characteristics are exploited to provide the braking function, making the system self-sufficient and eliminating the need for additional dedicated braking hardware.
2Reliability
If a braking resistor and braking relay are used to provide braking, then braking function is achieved, but system cost increases
Solution Approach 1:
The patent removes the braking resistor and braking relay components from the system architecture, thereby eliminating their associated costs. The braking function is achieved through software control of existing inverter switches, reducing bill of materials costs and simplifying manufacturing.
Solution Approach 2:
The inverter switches serve dual functions: motor control during normal operation and braking during deceleration. This multi-functionality eliminates the need for separate braking components, reducing system cost while maintaining braking capability.
3Speed
If duty cycle is adjusted based on speed signal, then smooth speed reduction is achieved, but control complexity increases
Solution Approach 1:
The patent implements dynamic control by continuously adjusting the duty cycle of the inverter switches based on real-time speed feedback from the speed sensor. The controller modifies the braking torque dynamically as the motor speed changes, ensuring smooth and controlled deceleration while adapting to varying load conditions.
Solution Approach 2:
The system uses speed feedback from the speed sensor to regulate the braking process. The controller compares the actual speed with the target speed and adjusts the duty cycle accordingly, creating a closed-loop control system that achieves smooth speed reduction through continuous feedback and adjustment.
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 reduces motor peak currents, protects components, allows braking for any load without external components, minimizes brake wear, and ensures smooth speed reduction, thereby reducing costs and complexity.
Implementation Method 1
an inverter having a plurality of switches to convert DC power from the battery to AC power for the machine in a motoring mode
Implementation Method 2
a speed sensor coupled to the machine, the speed sensor to generate a speed signal indicative of machine speed
Implementation Method 3
a controller to apply braking signals to a group of the switches in a braking mode, the braking signals having a duty cycle in response to the speed signal
Data Source
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AI summary
An elevator system includes a battery; a machine having a motor to impart motion to an elevator car; an inverter having a plurality of switches to convert DC power from the battery to AC power for the machine in a motoring mode; a speed sensor coupled to the machine, the speed sensor to generate a speed signal indicative of machine speed; and a controller to apply braking signals to a group of the switches in a braking mode, the braking signals having a duty cycle in response to the speed signal.