Intermediate-Bus Power Conversion for Reactive Current Separation
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Solution Overview
Problem
Traditional power conversion devices experience inefficiencies due to reactive currents flowing through boost converters, leading to increased size and losses, especially when connected to storage batteries with lower output impedance, which hampers compactification and efficiency improvements.
Innovation Solution
Implementing a minimum switching conversion method where the DC/DC converter handles only active currents and a separate DC/DC converter handles reactive currents, with a control unit managing switching operations to minimize losses and optimize power flow through an intermediate bus, using IGBTs or FETs as switching elements and capacitors to manage voltage and current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single DC/DC converter is used to handle both active and reactive currents, then the device structure is simple, but the peak current and effective current increase leading to larger device size and higher losses
Solution Approach 1:
The patent divides the DC/DC converter into two separate converters: a first DC/DC converter dedicated to active current and a second DC/DC converter dedicated to reactive current. This segmentation allows each converter to be optimized for its specific function, reducing the peak current requirements and enabling compact design while handling both current types effectively
2Productivity
If high-speed switching operations are performed continuously, then the power conversion is maintained, but switching loss and iron loss increase reducing conversion efficiency
Solution Approach 1:
The patent implements periodic switching control where the first DC/DC converter operates during periods when step-up operation is needed, and the second DC/DC converter operates during periods when step-down operation is needed. This periodic action with controlled stop periods reduces switching loss and iron loss while maintaining continuous power conversion capability
Solution Approach 2:
The control unit dynamically adjusts the switching operations of both DC/DC converters based on real-time conditions, optimizing the switching frequency and timing to minimize losses while maintaining required power conversion performance
3Device complexity
If reactive current flows through the first DC/DC converter, then the converter design is simplified, but the current amplitude doubles increasing losses and hampering compactification
Solution Approach 1:
The patent separates the handling of active and reactive currents into dedicated converters. The first DC/DC converter handles only active current while the second DC/DC converter handles reactive current, preventing current amplitude doubling and reducing losses in each converter while maintaining design feasibility
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 configuration reduces switching and iron losses, enhances conversion efficiency, and allows for a more compact design by minimizing the peak and effective current values through the DC/DC converter, thereby improving overall power conversion efficiency and reducing device size.
Implementation Method 1
the inverter circuit is caused to perform switching operation only during a period in which a step-down operation is needed
Implementation Method 2
switching loss and iron loss are reduced accordingly, leading to improvement in conversion efficiency
Data Source
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AI summary
This power conversion device performs DC/AC power conversion via an intermediate bus, and includes: a first DC/DC converter provided between a DC power supply and the intermediate bus; a second DC/DC converter provided between a DC-side capacitor and the intermediate bus; an intermediate capacitor connected to the intermediate bus; a DC/AC converter provided between the intermediate bus and an AC grid; and a control unit configured to control the first DC/DC converter, the second DC/DC converter, and the DC/AC converter, the control unit making such current command value setting that mainly the second DC/DC converter supplies a reactive current flowing through the intermediate bus.