Power conversion device, motor drive unit, and refrigeration cycle apparatus
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Solution Overview
Problem
Conventional power conversion devices cause high current to flow to the smoothing capacitor, leading to faster aging degradation and increased costs due to the need for higher capacitance or more resistant capacitors, which in turn increase the size and cost of the apparatus.
Innovation Solution
A power conversion device that includes a rectification unit, a capacitor, an inverter connected to both ends of the capacitor, and a control unit that reduces the current flowing to the capacitor by controlling the inverter to output AC power with a pulsation dependent on the pulsation of power flowing from the rectification unit to the capacitor, without a discharge circuit or overvoltage protection circuit for the capacitor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the capacitance of the smoothing capacitor is increased to reduce ripple variation, then the capacitor degradation is reduced, but the apparatus size and cost increase
Solution Approach 1:
The inverter is controlled to operate in a periodic action mode where it periodically draws current from the capacitor during specific intervals. This periodic current draw compensates for the ripple voltage variations, allowing the use of a smaller capacitor while maintaining reliability and reducing degradation.
2Reliability
If a smoothing capacitor with high resistance to degradation is used, then the capacitor aging is reduced, but the component cost increases
Solution Approach 1:
By implementing periodic action control of the inverter, the system reduces the stress on the capacitor through controlled current draw patterns. This allows the use of standard, lower-cost capacitors while achieving the same degradation resistance that would otherwise require expensive specialized capacitors.
3Reliability
If the capacitance of the smoothing capacitor is increased to prevent ripple variation, then the capacitor degradation is reduced, but the apparatus cost increases
Solution Approach 1:
The periodic action control strategy enables the system to achieve reliable capacitor operation with smaller, less expensive capacitors. The inverter's controlled periodic current draw compensates for ripple effects, eliminating the need for high-capacitance expensive components while maintaining degradation resistance.
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 reduces the degradation of the smoothing capacitor, prevents an increase in apparatus size, and achieves these goals while maintaining efficient power conversion and reducing operational costs.
Implementation Method 1
a rectification unit that rectifies first alternating current power supplied from a commercial power supply
Implementation Method 2
a capacitor connected to an output end of the rectification unit
Implementation Method 3
an inverter that converts power output from the rectification unit and from the capacitor into second alternating current power
Data Source
AI summary
A power conversion device includes a rectification unit that rectifies first alternating current (AC) power supplied from a commercial power supply, a capacitor connected to an output end of the rectification unit, an inverter that converts power output from the rectification unit and from the capacitor into second AC power, and outputs the second AC power to a load including a motor, which inverter is connected to both ends of the capacitor, and a control unit that controls operation of the inverter to output the second AC power from the inverter to the load to reduce current flowing to the capacitor, which second AC power includes a pulsation that depends on a pulsation of power flowing from the rectification unit to the capacitor. No discharge circuit and no overvoltage protection circuit are provided for the capacitor.