DC/DC Converter Capacitor Voltage Matching Before Battery Connection

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Solution Overview

Problem

Existing bidirectional DC/DC voltage transformers struggle to match the voltage of the primary-side smoothing capacitor to the primary battery before connection, leading to potential high inrush currents during reconnection.

Innovation Solution

A method that utilizes the series resonance of the clamping capacitor with the leakage inductance of the transformer to quickly charge the primary-side smoothing capacitor to the primary battery voltage, limiting current through semiconductor switches and achieving optimal switching conditions without additional components.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If the primary battery is disconnected and reconnected to the high-voltage bus, then the DC/DC converter can be isolated for maintenance or operation changes, but high inrush currents occur in the switch due to voltage mismatch between the smoothing capacitor and the primary battery

Engineering Contradiction:

ImproveAbility to disconnect and reconnect primary batteryVSAvoidHigh inrush currents in switch

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

The patent applies preliminary action by charging the smoothing capacitor to the primary battery voltage before the battery is connected to the high-voltage bus. This pre-charging process ensures that when the battery is subsequently connected, there is no voltage difference between the capacitor and battery, thereby preventing high inrush currents in the switch. The method performs the voltage matching operation in advance, eliminating the harmful effect at the moment of connection.

Inventive Principle:

Principle #10Preliminary action

2Object-affected harmful factors

If additional components are added to match the capacitor voltage before battery connection, then inrush currents can be limited, but the device complexity and cost increase

Engineering Contradiction:

ImproveInrush current limitationVSAvoidNumber of additional components

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The patent applies self-service by utilizing the existing clamping capacitor and transformer leakage inductance within the DC/DC converter to charge the smoothing capacitor before battery connection. Instead of adding external components, the method uses the converter's own internal components to perform the voltage matching function. The control unit orchestrates this self-service process, making the system self-sufficient and avoiding increased device complexity.

Inventive Principle:

Principle #25Self-service

3Productivity

If the smoothing capacitor is charged quickly to the primary battery voltage, then the system can be reconnected faster, but switching losses and EMF emissions increase

Engineering Contradiction:

ImproveSpeed of capacitor chargingVSAvoidSwitching losses and EMF emissions

Core Design Contradiction:

ProductivityVSLoss of energy

Solution Approach 1:

The patent applies periodic action by using cyclic charge transfer from the clamping capacitor to charge the smoothing capacitor in controlled steps. Instead of a continuous high-current charge that would cause excessive switching losses and EMF emissions, the method uses periodic charge transfers timed with the resonant frequency of the clamping capacitor and transformer leakage inductance. This periodic approach achieves fast charging while maintaining low switching losses and minimal EMF emissions.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The patent applies the resonance principle by utilizing the series resonance between the clamping capacitor and the transformer leakage inductance. By operating at the resonant frequency, the system achieves natural oscillation that facilitates efficient energy transfer without requiring high switching frequencies or excessive voltages. This resonant approach enables fast charging while minimizing switching losses and electromagnetic interference, as the system exploits its natural vibrational characteristics rather than forcing non-resonant operation.

Inventive Principle:

Principle #18Mechanical vibration

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 method rapidly charges the smoothing capacitor to the primary battery voltage in under 0.2 seconds, reducing switching losses, EMF emissions, and eliminating the need for extra components, while being resilient to component tolerance variations.

Implementation Method 1

the invention utilizes the series resonance of the clamping capacitor with the leakage inductance of the transformer in order to limit the current through the semiconductor switch and to achieve optimal switching conditions

Methodology Applied

Scientific EffectSeries resonance: Resonance

Data Source

PatentUS11496042B2Method and device for matching the voltage of the smoothing capacitor of a DC/DC converter before a high-voltage battery is connected

Publication Date: 2022.11.08 BRUSA HYPOWER AG

AI summary

The invention relates to a method and to a device for operating a bidirectional voltage transformer connectable to a primary battery and having a primary-side smoothing capacitor, an inductive transformer, and a secondary-side clamping capacitor, wherein, before the primary battery is connected, a voltage at the primary-side smoothing capacitor is matched to a voltage of the primary battery by a cyclical transfer of charge from the secondary-side clamping capacitor. The voltage of the primary-side smoothing capacitor is matchable in this way to the voltage of the primary battery before the primary battery is connected, and current spikes thus avoided during connection of the primary battery.