Motor Control Apparatus Power Failure Detection DC Link Voltage
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Solution Overview
Problem
Conventional motor control apparatuses incorrectly detect momentary power failures as permanent failures, leading to unnecessary protective actions that degrade machine efficiency by stopping operations even when the motor can continue running due to retained energy in the DC link.
Innovation Solution
A motor control apparatus with an AC voltage detector, voltage amplitude calculator, power failure detector, and DC voltage detector that only initiates a protecting operation when the DC voltage falls below a second threshold, ensuring that protective actions are only taken when the motor cannot continue normal operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a power failure detecting device is added to detect AC power supply failures, then the reliability of fault protection is improved, but the machine performs unnecessary protective operations during momentary power failures, degrading productivity
Solution Approach 1:
The system continuously monitors DC link voltage and uses this feedback to dynamically adjust the protecting operation decision. When DC voltage remains above the threshold during a power failure detection, the system feedback indicates no protecting operation is needed, allowing continuous operation. This feedback mechanism eliminates unnecessary protective operations while maintaining reliable fault protection.
Solution Approach 2:
The protecting operation determination is made dynamic by continuously checking the DC link voltage status. Instead of a static protecting operation trigger based solely on AC power failure detection, the system dynamically adjusts the protecting operation decision based on real-time DC voltage conditions, enabling the machine to adapt its operation mode according to actual power availability.
2Reliability
If protective operations are performed upon detecting power failure, then the reliability of avoiding faults is improved, but unnecessary operations during momentary power failures cause loss of time and reduced productivity
Solution Approach 1:
The system performs a preliminary check of DC link voltage status immediately upon detecting AC power failure. This preliminary action determines whether the power failure is momentary (DC voltage maintained) or permanent (DC voltage dropped). By taking this preliminary action, the system avoids unnecessary protective operations and associated time losses during momentary power failures while still providing timely protection when needed.
Solution Approach 2:
The continuous monitoring of DC link voltage provides real-time feedback that determines whether protective operations should be executed. This feedback mechanism ensures that protective operations are only performed when genuinely necessary (when DC voltage drops below threshold), thereby minimizing unnecessary operation interruptions and time losses while maintaining reliable fault avoidance.
3Device complexity
If the detecting method only monitors AC voltage amplitude, then the device complexity is reduced, but the measurement precision of power failure state is insufficient
Solution Approach 1:
The DC link voltage detection serves multiple functions: it indicates both the status of power failure and the ability of the motor to continue operation. By using this single detection parameter for multiple assessment purposes, the system achieves high measurement precision without significantly increasing device complexity. The same voltage detection mechanism provides comprehensive information about system state.
Solution Approach 2:
The DC link voltage acts as an intermediary parameter that bridges AC power supply status and motor operation capability. Instead of directly monitoring complex AC power failure conditions and motor state separately, the system uses DC link voltage as an intermediary indicator that reflects both aspects, achieving precise power failure state measurement with minimal additional complexity.
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 approach minimizes unnecessary protective operations during momentary power failures, maintaining machine efficiency by differentiating between momentary and permanent power failures based on DC link voltage levels.
Implementation Method 1
the voltage of the DC link, i.e., the DC output side of the rectifier, is kept as is even at the time of a power failure... the voltage of the DC link will not drop thanks to the effect of the accumulated electricity in the smoothing capacitor of the rectifier
Data Source
AI summary
A motor control apparatus includes: a rectifier converting AC power into DC power; a smoothing capacitor provided for a DC link; an inverter connected to the DC link and mutually converts power between DC power and AC power; an AC voltage detector detecting voltage of a power supply; a voltage amplitude calculator converting the AC voltage value into a power supply voltage amplitude value; a power failure detector detecting a state of power failure when the power supply voltage amplitude value has continued to be equal to or lower than a first threshold for a predetermined period; a DC voltage detector detecting the DC voltage of the smoothing capacitor; and, a protecting operation start determining unit notifying the inverter of the actuation of axis stoppage or axis retraction when a power failure is detected and when the DC voltage value is equal to or lower than a second threshold.