Bidirectional DC/DC Converter Surge Voltage Reduction
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Solution Overview
Problem
In bidirectional DC/DC converters for vehicles, sharp current flows through transformers due to switching element control, leading to excessive surge voltage at leakage inductance, potentially damaging switching elements.
Innovation Solution
The power conversion apparatus employs a control method where switching elements are turned on and off in a predetermined frequency pattern, with a control unit applying a predetermined voltage to the transformer over a specific time period before shifting states, allowing gradual current flow and reducing surge voltage by aligning current direction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If switching elements are turned on and off at high frequency for efficient power conversion, then power conversion efficiency is improved, but surge voltage increases due to sharp current changes through transformer leakage inductance
Solution Approach 1:
The control unit applies predetermined voltage to the transformer over a predetermined time period during the first control state before shifting to the second control state. This preliminary action allows current to gradually flow through the transformer, preventing sharp current changes and reducing surge voltage while maintaining efficient power conversion
2Speed
If switching elements are turned on and off rapidly for high-frequency operation, then power conversion speed is improved, but switching element damage risk increases due to excessive surge voltage
Solution Approach 1:
Before rapidly switching between states, the control unit executes a preliminary voltage application phase where predetermined voltage is applied to the transformer over a predetermined time period. This gradual current establishment prevents excessive surge voltage that could damage switching elements, enabling reliable high-frequency operation
Solution Approach 2:
The control method incorporates a cushioning phase where voltage is applied in advance during the first control state, creating a buffer that prevents sudden current spikes. This beforehand cushioning protects switching elements from surge voltage damage while maintaining the desired switching frequency
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 effectively reduces surge voltage occurrences, minimizing the risk of switching element damage and potentially eliminating the need for high-voltage transistors or surge suppression circuits, thereby lowering costs.
Implementation Method 1
one end of each of the series circuits being connected to an inductor... convert DC supplied to the series circuits through the inductor to AC
Implementation Method 2
a transformer that isolates the single-phase bridge inverters... each of junctions of the first switching element and the second switching element being connected to one side of a transformer
Data Source
AI summary
Provided are a control unit having a first control state in which a first switching element and a second switching element of one series circuit are turned on and a second control state to which the first control state shifts and in which a first switching element of another series circuit and the second switching element of the one series circuit are turned on, and executing control so as to apply predetermined voltage to the other side of a transformer during a predetermined time period during the first control state before shifting to the second control state.