Power Conversion Device Phase-Shifted Carrier Wave Ripple Reduction
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Solution Overview
Problem
Inverters with a full-bridge configuration using complementary pulse width modulation experience significant leakage current of high-frequency components during grid interconnection, leading to increased capacitance requirements in smoothing capacitors, which in turn increase device size and generate heat due to high-frequency ripple currents.
Innovation Solution
A power conversion device incorporating a first conversion unit, a second conversion unit, and a control unit that synchronizes the frequencies of carrier waves for PWM control and bipolar modulation, shifting the phase of one carrier wave to ensure differing current timing into the capacitor from both units, thereby reducing high-frequency ripple current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a smoothing capacitor with large capacitance is used to stabilize DC voltage, then voltage stability is improved, but device size increases
Solution Approach 1:
The patent applies periodic action by synchronizing the PWM switching cycles of the converter and inverter, and using phase-shifted carrier waves to create periodic current patterns that naturally reduce ripple. The converter and inverter operate in synchronized periodic cycles, where the phase shift between carrier waves creates complementary current flow patterns that reduce the overall ripple current magnitude requiring capacitance for smoothing.
2Loss of energy
If complementary PWM operation is used in full-bridge inverter, then power conversion efficiency is improved, but high-frequency leakage current increases
Solution Approach 1:
The patent introduces an intermediary phase shift between the carrier waves of the converter and inverter. This phase shift acts as a mediator that decouples the direct high-frequency coupling between the complementary PWM operations, allowing the inverter to maintain efficient complementary PWM operation while the phase-shifted timing prevents simultaneous switching transitions that would generate high-frequency leakage current.
Data Source
AI summary
When an inverter and a converter are merely operated with their carrier waves synchronized with each other, current ripple of a smoothing capacitor connected therebetween might be increased. Accordingly, bipolar modulation PWM control is performed on the inverter, PWM control is performed on the converter, and the phase of the carrier wave for the inverter or the converter is shifted on the basis of AC output, whereby timings of currents flowing into the smoothing capacitor are made different from each other.