Joachim Froeschl

Experimental investigation on voltage stability in vehicle power nets for power distribution management

The power demand and the complexity of vehicle power nets has increased continuously during the last years. Especially the high demands of chassis control systems can cause voltage drops that endanger the power nets stability. A power net test bench that enables experimental research on voltage stability in vehicular power nets is presented in this paper. Thereby the relevance of voltage stability issues in todays and future vehicles was analyzed. Furthermore, proposals on counteractions using a power distribution management system are pointed out and the possibility of verifying dynamic power net simulation tools is provided.

Voltage Stability Analysis of Automotive Power Nets based on Modeling and Experimental Results

In recent years, there has been a trend toward increasing electrification in automotive engineering. On the one hand, the quantity of electronic control units (ECUs) as well as installed functions has increased. With the goal of reduced fuel consumption, engine-start-stop systems were being introduced, and more and more components which were previously mechanically driven are now electrically operated. In today’s luxury class vehicles there are up to 80 ECUs (Polenov et al., 2007; Hillenbrand & Muller-Glaser, 2009) servicing an wider range of customer needs in the areas of comfort, driving dynamics, and safety. On the other hand, the demands for electrical power as well as the power dynamics have permanently been increasing, as well. Loads like electrical power steering, chassis control systems, and engine cooling fans with more than 1 kW peak power are installed in the 12 V power net. Fig. 1 presents the increase of both installed alternator power and the total nominal current of the fuses in the latest decades. As the electric power demand increases, automotive power nets must operate close to their limits and it has become increasingly difficult to guarantee voltage stability within the 12 V system (Surewaard & Thele, 2005; Gerke & Petsch, 2006; Polenov et al., 2007). In the example of a luxury class vehicle, the continuous power of heating in winter, air conditioning in summer, ECUs, sensors, and consumer electronics can be more than 600 W. If this load is augmented by electric chassis control systems, voltage drops will be inevitable. Voltages below a certain level across the terminals of electrical components can lead to non specified behaviour. This can be manifested in a flicker of lights or changes in noise of the blower fans (Surewaard & Thele, 2005), a malfunction of the navigation system or even an ECU reset. Therefore, such complex problems are not only be noticeable to passengers, but are also a safety relevant issue. To guarantee the proper functioning of all electrical components, a stable voltage supply must be realized during the development and design of the electrical power net. For this reason, a thorough understanding of the electrical phenomena in distributed power nets is necessary. Voltage Stability Analysis of Automotive Power Nets Based on Modeling and Experimental Results 30

Topology and Design Optimization of a 14 V Automotive Power Net Using a Modified Discrete PSO in a Physical Simulation

In the last years, hydraulic powered chassis control systems have been replaced by electrical systems due to efficiency reasons. Additionally, more and more comfort electronics have been integrated. These circumstances have lead to a high power demand in todays automotive power nets. For this reason, voltage stability has become an important design criterion of the power net. This paper describes a simulation based method to optimize the power net topology and the dimensioning of components with regard to voltage stability requirements. A Modified Discrete Particle Swarm Optimization is used in combination with a physical power net simulation. In order to optimize the topology itself, a tool flow for an automated change of the simulation model is presented. To achieve best possible performance, the influence of the configuration parameters on the algorithm performance is evaluated and appropriate parameters are chosen for the given problem. Finally, exemplary optimization results are shown by pointing out optimal topologies for different constraints of the minimum terminal voltage.

From Simulation to Testbench Using the FMI-Standard

The power demand in 14V automotive power nets has increased continuously in the last years. New approaches for energy and power management systems are essential in order to ensure a safe and efficient operation of the power supply. This paper describes a method, how to export the physical models of a power net system simulation to a test bench using the FMI standard. For this purpose, an existing test bench is adapted in its architecture and converted to a real-time system that is scalable by the new PXImc-technology. Finally the method is validated by two simple models.

Experimental Investigations on an Autonomous Load Shutdown Mechanism in Respect to Voltage Stability in Automotive Power Nets

The power demand in 14V automotive power nets has steadily increased in recent years. On the one hand, more and more comfort electronics have been integrated. On the other hand, previously hydraulically driven chassis control systems have been replaced by electrically powered systems in order to increase efficiency. This trend has led to a drastic increase of the loads combined peak power. For this reason, voltage stability has become an important design criterion of automotive power nets. This paper experimentally investigates the influence of an autonomous load shutdown mechanism on voltage stability. The mechanism temporarily shuts down non-safety-critical heating systems with high continuous power consumption, e.g. seat heaters. This mechanism is implemented on a generic ECU hardware. In order to achieve the most realistic behavior of the system, the hardware is integrated into a 14V power net test bench, consisting of a car chassis and the wiring harness. Concluding measurements reveal that this mechanism is able to increase the terminal voltage at the most critical positions of the power net by about 1V.

Modeling of an electromechanical actuator in respect to voltage stability in automotive power nets

Due to efficiency reasons, more and more previously mechanically driven systems have been electrified in recent years. While this development reduces fuel consumption in conventional drive trains, it is essential in electric vehicles due to the omission of the combustion engine. The transient peak power of these systems has a negative influence on voltage stability in automotive power buses. For this reason, voltage stability has become an important criterion in the design process of a power net. Beside the electrical power steering, the electro hydraulic breaking systems is one of the critical systems regarding peak power consumption. In this paper, a dynamic model of an electromechanical actuator for an automotive breaking system is presented. The model is validated by comparison of simulation and measurement from a real car. Furthermore, a sensitivity analysis examines the influence of parameters on the occurring peak current during the startup process. It is shown, that temperature and correlating armature resistance have an significant influence on the peak starting current.

Design optimization of a 14 V automotive power net using a parallelized DIRECT algorithm in a physical simulation

The high power demand of electrical components in cars and the associated complexity of the 14 V power net have steadily increased in recent years. An important design criterion of the power net is the voltage stability during peak loads. This paper describes a simulation-based optimization method to fulfill the voltage stability requirements in a minimum-weight configuration of the power net. The method is applied to different power net topologies which are configured using a mixture of discrete and continuous parameters. Finally, the performance of the optimization algorithm as well as the optimization results are presented and evaluated.

Autonomous load shutdown mechanism as a voltage stabilization method in automotive power nets

The power demand in 14 V automotive power buses has steadily increased in recent years. Due to the high peak power of electrified chassis control systems, significant voltage drops can occur within the power net. These voltage drops can lead to malfunctions of ECUs (Electronic Control Units). This paper describes the influence of an autonomous load shutdown mechanism on voltage stability in automotive power buses. The mechanism is applied to heating systems, which feature a combined peak power demand of over 1 kW in modern luxury class vehicles. A temporary shutdown of these heating systems for a few seconds is unnoticeable for the costumer due to large time constants of these systems. The influence of the mechanism on the voltage stability is investigated within a physical power net simulation. It is shown, that the mechanism allows the negligence of power-hungry heating systems in the design process of the power bus regarding peak power scenarios.

Applications of the Viable System Model in automotive and battery storage systems

The renewable electric power generation in low voltage distribution grids is continuously increasing, which can lead to overload of power transformers. Battery storages can help reducing the load of the transformer and increase the percentage of self sufficiency of distribution grids. In this paper applications of the Viable System Model proposed by Stafford Beer in different fields of research are presented. Finally an approach for a scalable battery storage system based on this cybernetic method is introduced. The system shows a high efficiency even in partial load operation, fault tolerance and availability in error cases, maintainability and a high flexibility regarding the used storage technology.

Using the Viable System Model to control a system of distributed DC/DC converters

The complexity of control of the energy flow in automotive power nets has significantly increased in the last decades. Due to the introduction of a second voltage level with new degrees of freedom for an energy and power management, the complexity will further increase. The cybernetic approach of the Viable System Model (VSM) by Stafford Beer has successfully been used as a structural concept for the implementation of an energy management system for a single automotive power net and has significantly reduced the complexity of the control. This paper applies the VSM to the control problem of a group of DC/DC converters, distributed over the whole vehicle, coupling two automotive power nets. Initially it is shown how this new viable system of the converter group fits into the existing approach and how the viable systems of the two power nets form a new VSM. Subsequently, the application of the VSM in the converter group and how it forms a hierarchical control system is described. Additionally, a maximization efficiency point tracking (MEPT) algorithm is implemented in order to have each converter in its best operating point. Finally, the whole system is validated using a physical simulation.