Bridge Rectifier Switch Control for Capacitor Discharge in OBCs
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Solution Overview
Problem
Existing on-board chargers for automotive applications face challenges in meeting increased efficiency requirements and higher power density, particularly in safely discharging components during loss of communication or critical faults, and in efficiently managing capacitor discharge processes.
Innovation Solution
A system comprising an AC-DC converter with a bulk capacitor and a DC-DC converter, including a bridge rectifier and filter capacitor, controlled by controllers to manage the discharge of capacitors in both grid-to-battery and battery-to-grid operations, ensuring safe discharge below HV safety values and optimizing energy transfer without additional hardware.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If capacitor discharge control is implemented to meet HV safety requirements, then safety is improved, but system complexity increases
Solution Approach 1:
The bridge rectifier switch is made multi-functional by using it for both normal rectification operation and capacitor discharge operation. The same switch component performs dual purposes: rectifying AC to DC during charging and discharging capacitors during fault conditions, eliminating the need for separate discharge switches or circuits.
Solution Approach 2:
The system uses its own existing components (bridge rectifier switch, bulk capacitor, filter capacitors) to perform the discharge function without requiring external or additional dedicated discharge components. The controller activates the bridge rectifier switch to redirect energy from filter capacitors through the bulk capacitor to the battery, making the system self-sufficient for discharge operations.
2Loss of energy
If traditional capacitor discharge methods are used, then discharge function is provided, but efficiency and power density requirements are not met
Solution Approach 1:
The discharge process continuously transfers energy from filter capacitors through the bulk capacitor to the battery until voltage thresholds are met, maintaining continuous useful energy utilization rather than simple dissipation. This continuous energy transfer maximizes discharge efficiency and recovers energy that would otherwise be wasted.
Solution Approach 2:
The system dynamically changes operational parameters (switching the bridge rectifier switch on/off based on voltage thresholds) to optimize discharge behavior. By monitoring and responding to voltage levels of filter capacitors and bulk capacitor, the system adjusts discharge timing and duration to meet efficiency and power density requirements.
3Use of energy by moving object
If filter capacitor discharge to bulk capacitor is controlled, then energy transfer efficiency is improved, but control complexity increases
Solution Approach 1:
The controller implements feedback control by continuously monitoring the voltage of filter capacitors and the bulk capacitor, and adjusting the bridge rectifier switch operation accordingly. When filter capacitor voltage exceeds a threshold, the controller activates discharge; when bulk capacitor voltage reaches a target level, discharge stops. This closed-loop feedback optimizes energy transfer efficiency.
Solution Approach 2:
The system performs preliminary assessment of capacitor voltage levels before initiating discharge operations. The controller checks whether filter capacitor voltage exceeds the discharge threshold before activating the bridge rectifier switch, and determines when discharge should terminate based on bulk capacitor voltage, preventing unnecessary discharge operations.
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
The system effectively discharges capacitors efficiently, ensuring safety and meeting efficiency and power density requirements by controlling the bridge rectifier switch to transfer energy from filter capacitors to bulk capacitors, thereby maintaining voltage limits and extending component life.
Implementation Method 1
the filter capacitor is configured to filter a high frequency ripple from electric power supplied to the battery
Implementation Method 2
one or more controllers configured to control an operation of the bridge rectifier switch to control a discharge of the filter capacitor to the bulk capacitor
Data Source
AI summary
A system includes: an alternating current (AC) to direct current (DC) converter (AC-DC converter) including a bulk capacitor, the AC-DC converter connectable to a line voltage; a DC to DC converter (DC-DC converter) connected to the AC-DC converter, the DC-DC converter including: one or more transformers having a secondary side connectable to a battery, a bridge rectifier connected to the secondary side of the one or more transformers, the bridge rectifier including a bridge rectifier switch, and a filter capacitor; and one or more controllers configured to control an operation of the bridge rectifier switch to control a discharge of the filter capacitor to the bulk capacitor.