Buck-Boost DC-DC Converter Virtual Ground for High-Voltage ESMs
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Solution Overview
Problem
Traditional DC-to-DC converters are limited in high-voltage applications due to insulation voltage rating constraints, especially when ground faults occur, leading to potential damage to energy storage modules (ESMs) and increased costs with 3-level converters.
Innovation Solution
The implementation of 2-level buck-boost DC-to-DC converters with a virtual ground configuration, which allows for bidirectional current flow and reduces voltage stress on ESMs by maintaining them near a chassis ground potential without a direct ground connection, enabling the use of low-voltage ESMs in high-voltage applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If traditional DC-to-DC converters are used in high-voltage applications, then voltage conversion is achieved, but insulation voltage rating constraints limit the application and increase costs
Solution Approach 1:
The patent introduces a virtual ground as an intermediary reference point between the positive and negative DC link rails. This virtual ground serves as a mediator that allows low-voltage ESMs to operate in high-voltage environments without requiring high insulation voltage ratings, as the ESMs only need to withstand voltage relative to the virtual ground rather than the full DC link voltage
Solution Approach 2:
The patent changes the reference voltage parameter by establishing a virtual ground at a potential between the positive and negative DC link rails. This parameter change transforms the voltage stress conditions, allowing ESMs to operate at lower voltage levels relative to the virtual ground even when connected to high-voltage DC link rails
2Reliability
If 3-level converters are used to handle ground faults, then protection is improved, but costs increase
Solution Approach 1:
The virtual ground acts as a protective intermediary during ground faults. When a ground fault occurs on either the positive or negative DC link rail, the virtual ground reference remains stable and allows the control system to maintain proper operation of the DC-to-DC converter and protect the ESMs without requiring expensive 3-level converter topology
Solution Approach 2:
The patent creates a virtual copy of a ground reference point through the virtual ground, which replicates the protective functions of a physical ground connection without the associated costs and complexity. This virtual ground copy provides the necessary reference for fault detection and protection while allowing the use of simpler, lower-cost 2-level converter topology
3Device complexity
If low-voltage ESMs are used in high-voltage applications, then costs are reduced, but voltage stress on ESMs increases
Solution Approach 1:
The virtual ground serves as a protective intermediary that shields low-voltage ESMs from high-voltage stress. By referencing the ESM voltage to the virtual ground rather than to physical ground or the full DC link voltage, the ESMs only experience voltage stress within their rated capabilities even when operating in high-voltage applications
Solution Approach 2:
The patent changes the voltage reference parameter for the ESMs by introducing the virtual ground. This parameter change transforms the voltage stress from the full DC link voltage level down to a manageable level relative to the virtual ground, enabling low-voltage ESMs to operate safely in high-voltage environments
Data Source
AI summary
A conversion circuit is disclosed and includes a DC link, a first DC-to-DC converter, an inverter and a second inverter. The DC link includes DC link rails. The first DC-to-DC converter includes a first phase leg and a second phase leg. The first reactor is connected between a first center terminal of the first phase leg and at least one energy storage module. The second reactor is connected between a second center terminal of the second phase leg and the at least one energy storage module. The first reactor, the at least one energy storage module and the second reactor are connected in series between the first center terminal and the second center terminal such that the first DC-to-DC converter has a virtual ground.