Inverter Capacitor Warm-Up for Low-Temperature Ripple Control
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Solution Overview
Problem
Conventional inverter devices using electrolytic capacitors in lower-temperature environments face increased equivalent series resistance, leading to excessive ripple voltage, which can exceed the capacitors' withstand voltages, preventing electric motor operation and requiring expensive large film capacitors to mitigate this issue.
Innovation Solution
An inverter device with a temperature measuring system that controls the drive of switching elements to restrict current supply to the electric motor during startup, warming the electrolytic capacitor to a target temperature to prevent voltage exceedance, allowing the use of smaller, lower-cost electrolytic capacitors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large film capacitor is used as the smoothing capacitor to reduce equivalent series resistance in lower-temperature environments, then the ripple voltage can be kept within allowable ranges, but the inverter device becomes large and production costs increase
Solution Approach 1:
The patent applies preliminary action by executing a warm-up operation before normal motor operation to raise the electrolytic capacitor temperature to a predetermined level. This preliminary heating action prevents the capacitor's equivalent series resistance from increasing during cold-temperature operation, thereby maintaining ripple voltage within allowable ranges without requiring an oversized film capacitor
Solution Approach 2:
The patent changes the temperature parameter of the electrolytic capacitor from a low initial state to a predetermined operating temperature through controlled warm-up operation. By changing the temperature parameter, the capacitor's electrical characteristics (equivalent series resistance) are improved, allowing it to function reliably without requiring a large film capacitor
2Reliability
If a large film capacitor is used as the smoothing capacitor to reduce equivalent series resistance in lower-temperature environments, then the ripple voltage can be kept within allowable ranges, but the inverter device size increases
Solution Approach 1:
The patent executes a warm-up operation before normal motor operation to raise the electrolytic capacitor temperature to a predetermined level. This preliminary heating action prevents the capacitor's equivalent series resistance from increasing during cold-temperature operation, thereby maintaining ripple voltage within allowable ranges without requiring an oversized film capacitor
Solution Approach 2:
The patent replaces the expensive, large film capacitor with a smaller, more economical electrolytic capacitor that can be warmed up temporarily before normal operation. The electrolytic capacitor serves its purpose effectively during cold-temperature conditions when properly conditioned, eliminating the need for oversized film capacitors
3Ease of manufacture
If the electrolytic capacitor is used in lower-temperature environments without warm-up, then the inverter device can be downsized and costs reduced, but the equivalent series resistance increases causing ripple voltage to exceed withstand voltages
Solution Approach 1:
The patent executes a warm-up operation before normal motor operation to raise the electrolytic capacitor temperature to a predetermined level. This preliminary heating action prevents the capacitor's equivalent series resistance from increasing during cold-temperature operation, thereby maintaining ripple voltage within allowable ranges
Solution Approach 2:
The patent employs feedback control by monitoring the electrolytic capacitor temperature and using this information to control the warm-up operation. The controlling device adjusts the warm-up duration and intensity based on temperature feedback, ensuring the capacitor reaches the optimal temperature range before normal operation begins
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 prevents defects in switching elements and electrolytic capacitors by maintaining ripple voltage within safe limits, enabling normal operation of electric motors in lower-temperature environments while downsizing the inverter device and reducing production costs.
Implementation Method 1
an electrolytic capacitor that smoothes a rectified voltage to a direct voltage
Implementation Method 2
equivalent series resistance of the electrolytic capacitor may increase
Implementation Method 3
an inverter circuit that generates an alternating voltage from the direct voltage, to drive an electric motor
Implementation Method 4
a temperature measuring device that measures a temperature of the electrolytic capacitor, to output the measured temperature to the controlling device
Implementation Method 5
the controlling device supplies the electric motor with a current which is restricted so that a ripple voltage generated when the rectified voltage is smoothened to the direct voltage falls within an allowable range, before starting a normal operation of the electric motor, so that the temperature of the electrolytic capacitor is raised to the target temperature
Data Source
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AI summary
The present invention includes: an electrolytic capacitor that smoothes a rectified voltage to a direct voltage; an inverter circuit that generates an alternating voltage from the direct voltage, to drive an electric motor; a controlling device that controls drive of switching elements included in the inverter circuit; and a temperature measuring device that measures a temperature of the electrolytic capacitor, to output the measured temperature to the controlling device, in which, when the temperature obtained by the temperature measuring device is lower than a predetermined target temperature, the controlling device supplies the electric motor with a current which is restricted so that a ripple voltage of the direct voltage falls within an allowable range, before starting a normal operation of the electric motor, so that the temperature of the electrolytic capacitor is raised to the target temperature. Thus, the electrolytic capacitor can be used even in a lower-temperature environment.