Motor Control Apparatus Torque Limiting Converter Input Current
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Solution Overview
Problem
Existing motor control apparatuses for machine tools that convert AC to DC and back to AC face challenges in preventing excessive current from flowing into the AC side of the converter, leading to system shutdowns and inefficiencies, particularly when not all inverters operate at maximum power, resulting in oversized converters that increase costs and space requirements.
Innovation Solution
A motor control apparatus with a converter and inverter system that includes a detecting unit, determining unit, and notifying unit to monitor AC current or power input and adjust the torque or rotational speed of motors accordingly, ensuring operation within predetermined limits to prevent excessive current and optimize power usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the converter capacity is increased to handle maximum power from all inverters, then the system can supply sufficient output power without alarm conditions, but the installation space and cost increase
Solution Approach 1:
The patent implements dynamic control of inverter output power based on real-time monitoring of converter input current. When the current approaches the allowable limit, the system automatically reduces the torque command to inverters, thereby dynamically adjusting the power demand to match the converter's actual capacity. This eliminates the need for oversized converters while preventing alarm conditions.
Solution Approach 2:
The system continuously monitors the AC input current to the converter and uses this feedback to adjust the torque commands sent to inverters. The inverter control part receives current information from the converter control part and modifies output power accordingly, creating a closed-loop control system that optimizes converter utilization without requiring excess capacity.
2Reliability
If the converter capacity is increased to handle maximum power from all inverters, then the system can supply sufficient output power without alarm conditions, but the cost increases
Solution Approach 1:
The system dynamically adjusts inverter power output based on real-time converter load conditions. By monitoring AC input current and automatically reducing torque commands when limits are approached, the system enables the use of smaller, more cost-effective converters while maintaining operational reliability and preventing alarm conditions.
Solution Approach 2:
The patent changes the operating parameters of the inverter system by dynamically adjusting the torque command based on converter current status. This parameter adjustment allows the system to operate within the actual capacity of a smaller converter, reducing equipment cost while maintaining sufficient power supply capability.
3Object-affected harmful factors
If the AC output frequency is reduced to limit input AC current, then the compressor runs at low performance state, but the input AC current is limited
Solution Approach 1:
Instead of uniformly reducing the AC output frequency to all inverters, the patent applies selective torque command reduction only to specific inverters whose combined power demand would cause the converter current to exceed the allowable limit. This localized control maintains optimal frequency and performance for inverters that do not contribute to the overcurrent condition.
Solution Approach 2:
The system selectively changes the torque command parameter for specific inverters based on real-time current monitoring. Rather than globally reducing frequency, the patent adjusts individual inverter torque commands to achieve current limiting while preserving overall system performance and productivity.
4Reliability
If a safety device is installed to prevent excessive current, then the system is protected from damage, but the motor control apparatus stops with alarm condition
Solution Approach 1:
The patent implements preliminary action by proactively reducing the torque command to inverters before the converter current reaches the alarm threshold. The inverter control part continuously monitors current status and preemptively adjusts power output to prevent alarm conditions, thereby maintaining continuous operation while still providing protection.
Solution Approach 2:
The patent converts the potential harmful effect of excessive current into a beneficial control signal. By monitoring current status and using it to adjust torque commands, the system transforms what would be a protective shutdown scenario into an opportunity for smooth, continuous operation with optimized power distribution.
Data Source
AI summary
A motor control apparatus includes, a converter which converts input AC to DC for output, an inverter which converts the DC output of the converter to provide an AC output for driving a motor, and an inverter control part for controlling the same, and a numerical control part which outputs a motor operation command for commanding the operation of the motor, and wherein when AC current or power input to the converter lies outside a predetermined range, the inverter control part controls the AC output of the inverter so that the motor is operated in accordance with a limited torque command produced by limiting a torque command originally specified in the motor operation command.