Dual-Voltage Vehicle Electrical System Energy Management
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Solution Overview
Problem
Existing mild hybrid and micro-hybrid vehicle systems face challenges in optimizing fuel efficiency and managing energy distribution between sub-networks with different voltage levels, particularly during peak loads and energy fluctuations.
Innovation Solution
A vehicle electrical system with a first sub-network at 24 V and a second sub-network at 48 V, connected by a DC/DC converter, includes a second electric machine in the 24 V sub-network that can operate as a generator or motor to support the 24 V system, controlled by a control unit to manage energy distribution and compensate for voltage drops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the vehicle uses a dual-subnetwork electrical system with 48V and 24V voltage levels, then the power supply capability and energy recovery capacity are improved, but the system complexity and energy management difficulty increase
Solution Approach 1:
The electrical system is segmented into two independent sub-networks with different voltage levels (48V and 24V). Each sub-network has its own energy storage device and can operate independently or in coordination. This segmentation allows the system to provide high power when needed while maintaining compatibility with existing 24V consumers, resolving the contradiction between power supply capability and system complexity.
Solution Approach 2:
The control device is designed with multi-functionality to manage both sub-networks, perform voltage conversion, control the second electric machine in multiple modes (motor/generator), and coordinate energy distribution. This universal control approach simplifies the overall system architecture despite the dual-voltage complexity, addressing the contradiction between power capability and management difficulty.
2Reliability
If the voltage converter supplies the 24V sub-network from the 48V sub-network during peak loads, then the power demand is met, but the energy loss and reduced fuel efficiency occur
Solution Approach 1:
The second electric machine operates dynamically in different modes (motor mode during engine start, generator mode during recuperation) based on real-time vehicle conditions. This dynamic operation allows the system to meet peak power demands locally without relying solely on voltage conversion from the 48V sub-network, thereby reducing energy losses while maintaining reliability.
Solution Approach 2:
The control device continuously monitors the state of charge of energy storage devices, vehicle load conditions, and sub-network voltages to dynamically adjust energy distribution strategies. This feedback mechanism ensures that power is supplied from the most efficient source at any given moment, minimizing energy losses while meeting power demand requirements.
3Use of energy by moving object
If the second electric machine operates in generator mode to supply the 24V sub-network, then the fuel efficiency is improved, but the system complexity and control difficulty increase
Solution Approach 1:
The control functions for the second electric machine (motor/generator control), voltage converter management, and energy distribution are merged into a single integrated control device. This consolidation simplifies the control architecture despite the multiple functions required, making the system easier to manage while enabling the second electric machine to operate in generator mode for improved fuel efficiency.
4Use of energy by moving object
If the system uses a start-stop function with engine restart via electric motor, then the fuel consumption is reduced, but the reliability requirements for the electrical system increase
Solution Approach 1:
The system incorporates energy storage devices in both the 48V and 24V sub-networks that are charged in advance during normal operation and recuperation phases. This beforehand cushioning ensures that sufficient energy is available to reliably restart the engine via the electric motor when the start-stop function is activated, meeting the increased reliability requirements while maintaining fuel efficiency benefits.
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
Enhances fuel efficiency by optimizing energy use and reducing reliance on the 48 V sub-network during peak loads and energy fluctuations, leading to increased energy recovery and storage capacity.
Implementation Method 1
a voltage converter that couples the first and second sub-networks and is configured to supply the first sub-network, at least temporarily, with electrical energy from the second sub-network
Implementation Method 2
the generator in the second subnetwork can also be used for recuperation, whereby kinetic energy released during vehicle deceleration is converted (recuperated) into electrical energy
Implementation Method 3
an electric motor (starter generator) is used to start the combustion engine
Data Source
Figure 1
AI summary
The invention relates to an electrical system for a motor vehicle, in particular an electrical system of a mild hybrid or micro hybrid vehicle with a start-stop function. The invention further relates to a motor vehicle with such an electrical system. The electrical system (1) comprises a first sub-network (2) in which a first nominal voltage (U1) is applied, comprising a first energy storage device (5) and a first load resistance (6) formed by several consumers; and a second sub-network (3) in which a second nominal voltage (U2) is applied, comprising a first electric machine (10) that can be operated as a generator and as a motor and is configured to drive an internal combustion engine of the motor vehicle at least temporarily and to generate electrical energy in recuperation mode; and a second energy storage device (9) that is configured to supply the first electric machine (10) with electrical energy at least temporarily.The vehicle electrical system also includes a voltage converter (4) that couples the first and second subnetworks (2, 3) and is configured to supply the first subnetwork (2) with electrical energy from the second subnetwork (3), at least temporarily. To increase the vehicle's fuel efficiency, a second electric machine (8) capable of generating electricity is provided in the first subnetwork (2). This second electric machine can be controlled by a control unit (12) to supply the first subnetwork (2) with electrical energy, at least temporarily.