Vehicle Electrical System Voltage Dip Prevention
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Solution Overview
Problem
Modern motor vehicles equipped with start-stop functions face challenges in ensuring reliable engine restarts while minimizing CO2 emissions and managing voltage fluctuations in the electrical system, particularly due to high starter currents causing voltage dips in the battery.
Innovation Solution
A motor vehicle electrical system with a switching element having two states, controlled by a unit to manage current flow between energy stores and a generator, ensuring stable voltage and preventing voltage dips by increasing the DC/DC converter output voltage, and using a battery management module to assess restart capability and battery health.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the starter draws high current (up to 800 A) to restart the engine, then the engine can be restarted reliably, but the terminal voltage drops to 6 V which causes voltage dips in the electrical system
Solution Approach 1:
The electrical system is segmented into two separate areas: a first area containing the starter and first energy store (starter battery), and a second area containing the generator and second energy store (traction battery). The switching element isolates these areas, preventing voltage dips in the second area when the starter operates in the first area.
Solution Approach 2:
A switching element is introduced as an intermediary between the first and second areas. This switching element can be controlled to connect or disconnect the two areas, acting as a mediator that prevents the propagation of voltage dips from the starter circuit to the generator circuit.
2Object-affected harmful factors
If the switching element isolates the first and second areas, then voltage dips are prevented in the second area, but the system complexity increases
Solution Approach 1:
The switching element serves multiple functions: it isolates the two areas to prevent voltage dips, enables controlled current flow between areas, and works with the DC/DC converter to manage energy transfer. This multi-functionality reduces the need for additional separate components.
Solution Approach 2:
The switching element is integrated with the DC/DC converter system, combining the isolation function with the existing power conversion architecture. This merging approach adds the voltage dip prevention capability without requiring a completely separate control system.
3Stability of the object's composition
If the DC/DC converter output voltage is increased, then voltage stability is maintained in the second area, but the risk of current flow issues increases
Solution Approach 1:
The control unit monitors the voltage levels and switching element state, using feedback control to adjust the DC/DC converter output. This ensures the output voltage is increased only when necessary to maintain stability, and the switching element is properly controlled to prevent current flow issues.
Solution Approach 2:
The switching element is controlled to ensure proper isolation before the DC/DC converter increases its output voltage. This preliminary action prevents current flow issues by establishing the correct circuit configuration before voltage changes occur.
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
Ensures reliable engine restarts by stabilizing the vehicle electrical system, preventing voltage dips, and detecting battery defects, thereby maintaining efficient start-stop operations and prolonging battery life.
Implementation Method 1
a switching element is arranged between the first and second area in the vehicle electrical system, which has at least two switching states, wherein in a first switching state a current flow is only possible in the direction from the first area to the second area or the current flow is interrupted in both directions
Implementation Method 2
The second energy store is connected to the generator via a DC/DC converter. A (possibly second) control unit increases the voltage at the DC/DC converter output
Implementation Method 3
a measuring unit recording and evaluating the voltage level across the switching element
Data Source
Figure 1
AI summary
The invention relates to a motor vehicle electrical system (1), wherein by means of a control unit (9) a start-stop command (S-S-B) for the internal combustion engine can be sensed or detected, wherein when a start-stop command (S-S-B) is sensed or detected a switching element (4) is switched into the first switching state and the voltage at the DC/DC output, which is connected to the switching element (4), is increased by a control unit by means of a control command (S2), wherein a measuring unit senses and evaluates the voltage condition over the switching element (4), wherein depending upon the evaluation the start-stop command is or is not carried out by a control unit (9) by means of a control command (S3). The invention further relates to a method for operating a motor vehicle electrical system (1).