Motor Drive DC-Link Capacitor Protection Under Ripple Current
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Solution Overview
Problem
Existing power converters face a reduction in the life of smoothing capacitors due to increased ripple current when the potential difference across the first capacitor exceeds a reference value, especially when an inverter circuit and motor are connected, leading to pulsation of voltages and currents.
Innovation Solution
A power converter with a first and second smoothing capacitor connected in parallel, where the first capacitor has a lower breakdown voltage and the second has a higher breakdown voltage, and an interrupting device is used to control the rotation speed of the motor to maintain the ripple current within rated limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the potential difference across the first capacitor exceeds the reference value, then the capacitor protection is improved, but the ripple current increases exceeding rated limits
Solution Approach 1:
The patent dynamically adjusts motor rotation speed based on the potential difference across the first capacitor. When the potential difference exceeds the reference value, the controller reduces motor speed to a value that limits ripple current to rated levels, creating a dynamic response that balances protection needs with operational constraints
Solution Approach 2:
The patent changes the operating parameters of the motor (rotation speed) in response to capacitor voltage conditions. By adjusting motor speed, the system modifies the ripple current characteristics to ensure they remain within rated limits while maintaining capacitor protection
2Duration of action of stationary object
If the motor rotation speed is controlled to limit ripple current, then the capacitor life is improved, but the productivity decreases
Solution Approach 1:
The patent applies partial speed reduction only when necessary (when first capacitor voltage exceeds reference value). The motor operates at reduced speed only during periods when capacitor protection is needed, rather than maintaining reduced speed continuously, thus limiting the impact on overall productivity while still protecting capacitor life
Solution Approach 2:
The system dynamically adjusts motor speed based on real-time capacitor voltage conditions. When voltage is within acceptable ranges, motor operates at full speed for maximum productivity. When voltage exceeds thresholds, speed is dynamically reduced to protect capacitor life, creating an adaptive balance between durability and performance
Data Source
AI summary
A power converter includes: a first converter circuit; an inverter circuit; a first smoothing unit connected between the first converter circuit and the inverter circuit, the first smoothing unit including a first smoothing capacitor having a breakdown voltage equal to a second voltage threshold and a second smoothing capacitor having a breakdown voltage higher than a first voltage threshold, the first voltage threshold being higher than or equal to a second voltage threshold; an interrupting device connected in series to the first smoothing capacitor; a voltage detector that detects a voltage across the second smoothing capacitor; and a controller that, in a case where the detected voltage is higher than or equal to the second voltage threshold, opens the interrupting device and controls a rotation speed of a motor such that a ripple current through the second smoothing capacitor is less than or equal to a rated ripple current.