Motor Control Device Torque Command Limiting for Power Failure
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Solution Overview
Problem
Existing motor control devices face challenges in urgently stopping motors during power failures while avoiding low voltage alarms, as excessive deceleration torque can lead to electric power consumption rather than regeneration, shortening the braking distance and potentially causing low voltage alarms.
Innovation Solution
A motor control device with a power failure detection unit, DC link voltage detection, torque limit value setting, and dynamic brake resistance switching, which compares torque limits with predicted deceleration torque values to switch between deceleration by control and hardware, optimizing torque commands to prevent low voltage alarms and minimize stopping distance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If deceleration torque is increased to shorten stopping distance, then stopping distance is reduced, but electric power is consumed instead of being regenerated, causing low voltage alarms
Solution Approach 1:
The patent applies dynamics by making the deceleration torque dynamic rather than fixed. The torque command is adjusted in real-time based on the DC link voltage level: when voltage is high, larger deceleration torque is applied to shorten stopping distance; when voltage is low, torque is reduced to prevent power consumption and low voltage alarms. This dynamic adjustment resolves the contradiction between stopping distance and power consumption.
Solution Approach 2:
The patent changes the parameter of deceleration torque based on the DC link voltage parameter. By monitoring voltage levels and adjusting torque commands accordingly, the system optimizes the balance between stopping distance and power regeneration. This parameter change strategy allows the system to adapt to different voltage conditions and avoid the harmful effect of power consumption.
2Loss of time
If deceleration torque is increased to achieve urgent stopping, then stopping time is reduced, but regenerative operation becomes powering operation, depleting DC link voltage
Solution Approach 1:
The patent implements feedback control by continuously monitoring the DC link voltage and using this information to adjust the deceleration torque command. The voltage detection unit provides feedback to the control unit, which then modifies the torque command to maintain regenerative operation. This feedback mechanism ensures that stopping is achieved quickly while preventing DC link voltage depletion that would occur with excessive torque.
3Length of moving object
If fixed high deceleration torque is applied during power failure, then stopping distance is minimized, but low voltage alarm occurs due to excessive power consumption
Solution Approach 1:
The patent makes the deceleration control dynamic by adjusting torque commands based on real-time DC link voltage conditions. Instead of applying fixed high torque that would cause low voltage alarms, the system dynamically modulates torque to maintain stable operation while achieving short braking distances. This dynamic approach resolves the contradiction between braking distance and operational reliability.
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
The solution effectively shortens the motor stopping distance and avoids low voltage alarms by dynamically adjusting torque limits and switching between deceleration methods, ensuring efficient energy use and reliable operation during power failures.
Implementation Method 1
when a motor is decelerating, due to a regenerative operation, motive energy decreases and electric power (electric energy) increases
Implementation Method 2
a method of applying a dynamic brake by connecting a resistance to the motor and allowing a current to flow therethrough, thereby allowing energy to be consumed
Data Source
AI summary
A motor control device includes: a power failure detection unit that detects a power failure; a voltage detection unit that detects a DC link voltage; a switch unit which connects a motor to an amplifier or a resistance; a voltage comparison unit which compares a DC link voltage with a threshold value; a limit value setting unit which sets a torque limit value in accordance with a result of comparison; a torque command limit unit which limits a torque command when a power failure is detected; a prediction value calculation unit which calculates, using an angular velocity, a torque prediction value of the motor when the motor is connected to the resistance; and a torque comparison unit which compares the torque limit value with the torque prediction value, in which in accordance with a result of comparison, the switch unit connects the motor to the amplifier or the resistance.