Rail Vehicle Battery Segmentation for DC Link Voltage
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Solution Overview
Problem
In rail vehicle technology, the connection of secondary circuits to DC voltage intermediate circuits often requires costly DC/DC converters to step down voltage, and existing solutions do not efficiently manage voltage differences between battery units, leading to inefficiencies and higher costs.
Innovation Solution
Connecting two battery units in series with a middle connection grounded or indirectly connected to ground, allowing the secondary circuit to utilize the halved battery voltage directly, potentially eliminating the need for DC/DC converters and using a balancing device to manage voltage deviations between the units.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a DC/DC converter is used to step down voltage from the DC voltage intermediate circuit to the secondary circuit, then the voltage level requirement is met, but the system cost and device complexity increase
Solution Approach 1:
The battery system is segmented into two separate battery units (first battery unit and second battery unit) connected in series, each capable of independently supplying voltage to the secondary circuit. This segmentation eliminates the need for a DC/DC converter by providing direct voltage supply from individual battery units at the required voltage level.
2Reliability
If battery units with high insulation capacity (1400-2000 V) are used to match the DC voltage intermediate circuit, then the voltage requirement is met, but the cost increases compared to using lower insulation capacity battery units
Solution Approach 1:
The high voltage battery system is segmented into two separate battery units, each with lower insulation capacity (700-1000 V). When connected in series, they collectively provide the required 1400-2000 V insulation capacity for the DC voltage intermediate circuit, while each individual unit can be manufactured at lower cost.
Solution Approach 2:
Each battery unit is designed with local quality appropriate for its specific voltage rating (700-1000 V insulation capacity), rather than requiring all battery units to have the highest insulation capacity. This localized optimization reduces manufacturing costs while maintaining overall system requirements through the series connection configuration.
3Reliability
If two battery units are connected in series to provide full voltage to the secondary circuit, then the voltage requirement is met, but the voltage distribution between battery units may deviate, requiring additional balancing control
Solution Approach 1:
A balancing device is introduced as an intermediary component that monitors and regulates the voltage distribution between the two battery units. This balancing device equalizes the state of charge and voltage levels between battery units, preventing excessive voltage deviation and ensuring reliable operation of the secondary circuit.
Data Source
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AI summary
The invention relates to a vehicle, in particular a rail vehicle (10), with a DC link (14) and at least one secondary circuit (17) connected to the DC link (14), which has a lower voltage level than the DC link (14). According to the invention, two battery units (31, 32) connected in series are connected to the DC link (14), the center terminal (M) located electrically between the battery units (31, 32) is connected directly or indirectly to ground potential (MP) via an impedance (Z), and the secondary circuit (17) is connected to the center terminal (M) and is supplied with the battery voltage (U1, U2) of one of the two battery units (31, 32).