Inverter Ripple Injection to Protect DC-Link Capacitors
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Solution Overview
Problem
Existing power conversion apparatuses face issues with accelerated aging of smoothing capacitors due to large current flow, leading to increased costs and device size when methods like increasing capacitor capacity or using high-deterioration-tolerance capacitors are employed.
Innovation Solution
A power conversion apparatus that includes a converter to rectify a three-phase alternating-current voltage, a capacitor to smooth the rectified voltage with a first ripple, an inverter to convert the smoothed voltage into a desired alternating-current voltage, and a detection unit to control the inverter such that a second ripple correlated with the first ripple is superimposed on the output voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the capacity of the smoothing capacitor is increased to prevent ripple change, then the capacitor can handle larger current, but the device size increases
Solution Approach 1:
The invention applies periodic action by superimposing a ripple component with the same frequency as the capacitor voltage ripple onto the inverter output voltage. This periodic ripple injection creates a counteracting effect that reduces the net ripple current through the smoothing capacitor, allowing the use of smaller capacitance values while maintaining reliable operation.
Solution Approach 2:
The invention converts the harmful ripple effect into a beneficial control mechanism. By intentionally injecting a ripple component that matches the capacitor's natural ripple frequency, the system creates a controlled interaction that reduces stress on the capacitor. The harmful ripple current is transformed into a useful control variable that actively mitigates capacitor deterioration.
2Reliability
If a smoothing capacitor with large deterioration tolerance is used to prevent ripple, then the capacitor can withstand larger current, but the cost increases
Solution Approach 1:
The invention changes the operational parameters of the capacitor by injecting a controlled ripple component that modifies the current waveform through the capacitor. This parameter change reduces the effective RMS current and thermal stress on the capacitor, allowing the use of lower-cost capacitors with standard deterioration tolerances while maintaining reliable operation.
3Stability of the object's composition
If the capacity of the smoothing capacitor is increased to smooth voltage, then the voltage ripple is reduced, but the device size increases
Solution Approach 1:
The invention uses periodic action by injecting a ripple component at the same frequency as the capacitor's natural ripple. This creates a controlled oscillation that counteracts the voltage ripple, achieving stable voltage output without requiring oversized capacitance values.
Solution Approach 2:
The injected ripple component acts as an intermediary that mediates between the capacitor's natural ripple and the desired stable output. By introducing this intermediate control signal, the system achieves voltage stability through active compensation rather than passive capacitance scaling.
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 solution effectively prevents the increase in device size while mitigating the deterioration of the smoothing capacitor, thereby maintaining efficient power conversion.
Implementation Method 1
a converter rectifying a first alternating-current voltage supplied from a three-phase alternating-current power supply
Implementation Method 2
a capacitor connected to an output end of the converter, the capacitor smoothing a first direct-current voltage obtained by rectification by the converter into a second direct-current voltage containing a first ripple
Implementation Method 3
an inverter connected across the capacitor, the inverter converting the second direct-current voltage into a second alternating-current voltage
Data Source
AI summary
A power conversion apparatus includes a converter that rectifies a first alternating-current voltage supplied from an alternating-current power supply that is a three-phase alternating-current power supply, a capacitor connected to an output end of the converter and smooths a first direct-current voltage obtained by rectification by the converter into a second direct-current voltage containing a first ripple, an inverter that is connected across the capacitor and converts the second direct-current voltage into a second alternating-current voltage dependent on a desired frequency, and a voltage detection unit that detects a physical quantity correlated with the second direct-current voltage, in which the second alternating-current voltage is controlled such that a second ripple correlated with the first ripple is superimposed on an output voltage from the inverter.