Emergency Brake Control for AC Drive Systems
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Solution Overview
Problem
Existing drive systems face challenges in smooth emergency stopping, particularly in situations where active control of braking is not allowed, leading to jarring stops, especially in passenger conveyance systems like elevators during power failures.
Innovation Solution
A system comprising a converter connected to an AC power source and a DC bus, an inverter connected to a motor, and a controller that commands a brake drop through a passive delay circuit, reducing voltage on the DC bus by dropping AC power phases or using a dynamic braking resistor, and applying a voltage down ramping function to smoothly halt the motor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If active control of braking is not allowed during emergency conditions, then the braking system can be simpler and more reliable, but the stopping becomes more jarring and less comfortable for passengers
Solution Approach 1:
The system performs preliminary actions by commanding the inverter to an off state and applying voltage down ramping to the motor before the brake physically drops. This preparatory deceleration reduces the speed difference between the motor and load, so when the brake engages, the jarring effect is minimized. The passive delay circuit ensures these preliminary actions occur in the correct sequence before mechanical braking.
Solution Approach 2:
The patent introduces intermediary elements between the emergency stop condition and the brake engagement. The passive delay circuit acts as a temporal intermediary, while the inverter off-state command and voltage down ramping serve as functional intermediaries that gradually reduce motor speed before the brake engages, thereby mediating the transition and reducing shock to passengers.
2Loss of time
If the brake is dropped immediately during emergency stop, then the stopping time is reduced, but the stopping becomes more abrupt and jarring
Solution Approach 1:
The system executes preliminary deceleration actions through the inverter off-state command and voltage down ramping before the brake physically engages. This reduces the motor speed in advance, so the subsequent brake engagement requires less deceleration force, achieving faster overall stopping while minimizing the jarring effect during the critical brake engagement moment.
Solution Approach 2:
The patent applies beforehand cushioning by using the passive delay circuit to sequence operations such that the motor is already decelerating through electrical means before the mechanical brake engages. This cushioning effect prepares the system for smoother brake engagement, reducing the shock that would otherwise occur from immediate mechanical braking.
3Speed
If voltage is not reduced before brake engagement, then the braking response is faster, but the motor continues to drive the load at high speed causing a harsh stop
Solution Approach 1:
The controller performs preliminary voltage reduction through the inverter off-state command and voltage down ramping function before the brake physically engages. This electrical pre-deceleration reduces the motor's driving speed, so when the brake engages, the difference between motor speed and load speed is minimized, resulting in faster response without harsh stopping.
Solution Approach 2:
The patent replaces purely mechanical braking with a combined electrical-mechanical approach. The inverter and voltage control system provide electrical braking action that substitutes for some of the mechanical brake function, allowing the mechanical brake to engage more gently while achieving the same overall deceleration effect, thereby reducing harshness.
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
Enhances emergency stopping by reducing the jarring effect, ensuring a smoother stop of the load driven by the motor, thereby improving passenger safety and comfort.
Implementation Method 1
using a dynamic braking resistor prior to the brake physically dropping
Implementation Method 2
a passive delay circuit responsive to detection of an emergency stop condition
Data Source
AI summary
A system includes a converter operatively connected to an alternating current (AC) power source and a direct current (DC) bus, an inverter operatively connected to a motor and the DC bus, and a controller. The converter includes a first plurality of switching devices in selective communication with each phase of the AC power source and the DC bus. The inverter includes a second plurality of switching devices in selective communication with each phase of a plurality of phases of the motor and the DC bus. The controller is operable to command dropping of a brake through a passive delay circuit responsive to detection of an emergency stop condition for a load driven by the motor and reduce a voltage on the DC bus by dropping at least one phase of the AC power source and/or using a dynamic braking resistor prior to the brake physically dropping.