DC/DC Converter Precharge Sequence for Relay Inrush Protection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In power supply systems with multiple voltage subsystems, the inrush current during precharging can cause the main relay to weld and overload the internal circuitry of the DC/DC converter, particularly when switching from a lower voltage to a higher voltage.
Innovation Solution
A DC/DC converter is configured to perform a stepwise precharging sequence, initially providing a lower voltage from the 12V battery to charge the capacitance, then increasing it to match the 48V battery's voltage, thereby eliminating the voltage difference and reducing the inrush current before closing the main relay.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the main relay is switched closed immediately when the capacitance is not charged, then the power supply system can be activated quickly, but a high inrush current flows into the main relay which may result in welding the main relay
Solution Approach 1:
The DC/DC converter performs preliminary action by precharging the capacitance C to the battery voltage before the main relay is switched closed. This is achieved by controlling the converter to charge the capacitance through the insulated gate bipolar transistors (IGBTs) in advance, eliminating the voltage difference between the capacitance and battery, thereby preventing inrush current when the relay closes.
2Reliability
If the capacitance is precharged by the 12V battery to prevent main relay welding, then the main relay is protected from welding, but an inrush current flows through the DC/DC converter internal circuitry which may result in load applied to the converter
Solution Approach 1:
The patent replaces the conventional mechanical precharge switch with insulated gate bipolar transistors (IGBTs) as switching elements within the DC/DC converter. This substitution allows for controlled precharging where the IGBTs can be gradually turned on to limit inrush current, and provides electronic control over the precharge process rather than relying on mechanical switching.
Solution Approach 2:
The DC/DC converter changes the voltage parameter gradually during precharging. The converter initially outputs a lower voltage than the battery voltage, then progressively increases the output voltage to match the battery voltage. This gradual voltage change ensures that the current through the IGBTs remains controlled and prevents excessive inrush current while still charging the capacitance effectively.
3Device complexity
If a mechanical relay is used as the main relay in the 48V subsystem, then the system structure is simple, but the relay may be welded due to inrush current and requires manual intervention
Solution Approach 1:
The patent substitutes the mechanical relay with insulated gate bipolar transistors (IGBTs) as switching elements in the DC/DC converter. This replacement eliminates the mechanical moving parts that are prone to welding, provides solid-state reliability, and enables electronic control of the switching operation. The IGBTs can be controlled to open and close without the risks associated with mechanical contact welding.
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 protects the internal circuitry of the DC/DC converter from inrush currents and prevents the main relay from welding by precharging the capacitance with a lower voltage, ensuring a smooth transition and reduced load on the converter's components.
Implementation Method 1
the DC/DC converter 360 is configured to be operated bidirectionally so that mutual power exchange is possible between the 12V and 48V subsystems
Implementation Method 2
In the 48V subsystem, a capacitance C exists in parallel to the 48V load 340. This is a capacitance which is generated e.g. by a capacitive component which is inherent to the 48V load 340, and/or by a stray capacitance(s) existing in the 48V subsystem
Data Source
AI summary
A power supply system including: a first voltage subsystem including a first battery connected to a load via a relay; a second voltage subsystem including a second battery, the second battery having a lower voltage than the first battery; and a DC/DC converter disposed between the first voltage subsystem and the second voltage subsystem, wherein before switching the relay to be closed, the DC/DC converter is configured to: provide a lower voltage than a voltage of the second battery to the first voltage subsystem; subsequently provide the voltage of the second battery to the first voltage subsystem; and subsequently increase the voltage of the second battery to be equal to a voltage of the first battery and provide the voltage of the second battery to the first voltage subsystem.