2014
Authors
de Castro, R; Tanelli, M; Araujo, RE; Savaresi, SM;
Publication
VEHICLE SYSTEM DYNAMICS
Abstract
The new vehicle platforms for electric vehicles (ENTs) that are becoming available are characterised by actuator redundancy, which makes it possible to jointly optimise different aspects of the vehicle motion. To do this, high-level control objectives are first specified and solved with appropriate control r strategies. Then, the resulting virtual control action must be translated into actual actuator commands by a control allocation layer that takes care of computing the forces to be applied at the wheels. This step, in general, is quite demanding as for as computational complexity is considered. In this work, a safety-oriented approach to this problem is proposed. Specifically, a four-wheel steer EV with four in-wheel motors is considered, and the high-level motion controller is designed within a sliding mode framework with conditional integrators. For distributing the forces among the tyres, two control allocation approaches are investigated. The first, based on the extension of the cascading generalised inverse method, is computationally efficient but shows some limitations in dealing with unfeasible force values. To solve the problem, a second allocation algorithm is proposed, which relies on the linearisation of the tyre road friction constraints. Extensive tests, carried out in the CarSim simulation environment, demonstrate the effectiveness of the proposed approach.
2014
Authors
Ramos, JC; Araujo, RE;
Publication
2014 IEEE 23RD INTERNATIONAL SYMPOSIUM ON INDUSTRIAL ELECTRONICS (ISIE)
Abstract
It is demonstrated that in grid-tied-inverter control, resonant integrators can be moved from the current loop to the input voltage filter allowing for better accuracy of voltage rms and frequency measurements whithout compromising controlability. Design of the input filter is discussed to ensure good performance and phase compensation and a robust feed-forward is built upon this filter that, together with the elimination of output distortion, results in a fair open-loop control response. By closing the loop with a PI controller and by turning off supposedly non-conducting IGBTs, a current transient results that competes with state-of-the-art control strategies and is only limited by output filter inductance while allowing for a fast and accurate estimator of grid parameters such as voltage rms and frequency, essential for fast droop control.
2014
Authors
de Castro, R; Tanelli, M; Araujo, RE; Savaresi, SM;
Publication
VEHICLE SYSTEM DYNAMICS
Abstract
The coordinated control of vehicle actuators is gaining more and more importance as new platforms are becoming available, with chassis endowed with many different actuators that may help controlling the vehicle motion. Furthermore, wheel individual motors allow using a single system to apply both positive and negative torques at the wheels, which can be actuated independently one from the other. In electric vehicles (EVs), moreover, such a freedom in the actuation mechanisms opens the way to the combined optimisation of performance and energy consumption issues. In this paper, the problem of minimum-time manoeuvring in EVs is addressed, and the proposed strategy is compared against a benchmark, a-causal optimal solution showing that only a negligible loss of performance is experienced.
2014
Authors
Araujo, RE; de Castro, R; Pinto, C; Melo, P; Freitas, D;
Publication
IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY
Abstract
This paper is concerned with the study of combined sizing and energy management algorithms for electric vehicles (EVs) endowed with batteries and supercapacitors (SCs). The main goal is to find the number of cells of each source that minimizes the installation and running costs of the EV, taking into account the performance requirements specified for the vehicle and the technical constraints of the energy sources. To tackle this problem, two methodologies will be investigated. The first considers a filter-based approach to perform the power split among the sources; it will be shown that, under some practical assumptions, the resultant sizing problem can be posed as a linear programming problem and solved using efficient numerical techniques. The second methodology employs an optimal noncausal energy management, which, when integrated with the sizing problem, yields a nonlinear optimization problem. These two methodologies will be then applied to size the storage unit of a small EV. The results indicate that the filter-based approach, although simple and numerically efficient, generally requires an oversized storage unit. Furthermore, it was also concluded that, if the range requirements of the EV are not very high (below 50 km, in our case study), the use of SCs enables energy savings of up to 7.8%.
2014
Authors
Azevedo, LS; Parker, D; Papadopoulos, Y; Walker, M; Sorokos, I; Araujo, RE;
Publication
MODEL-BASED SAFETY AND ASSESSMENT, IMBSA 2014
Abstract
Contemporary safety standards prescribe processes in which system safety requirements, captured early and expressed in the form of Safety Integrity Levels (SILs), are iteratively allocated to architectural elements. Different SILs reflect different requirements stringencies and consequently different development costs. Therefore, the allocation of safety requirements is not a simple problem of applying an allocation "algebra" as treated by most standards; it is a complex optimisation problem, one of finding a strategy that minimises cost whilst meeting safety requirements. One difficulty is the lack of a commonly agreed heuristic for how costs increase between SILs. In this paper, we define this important problem; then we take the example of an automotive system and using an automated approach show that different cost heuristics lead to different optimal SIL allocations. Without automation it would have been impossible to explore the vast space of allocations and to discuss the subtleties involved in this problem.
2014
Authors
Barreras, JV; Pinto, C; de Castro, R; Schaltz, E; Andreasen, SJ; Araujo, RE;
Publication
2014 IEEE VEHICLE POWER AND PROPULSION CONFERENCE (VPPC)
Abstract
While a great number of battery balancing circuit topologies have been proposed, the unique control objective typically pursued is equalization of single cell charge. However, a balancing circuit could offer potentially more control features, especially with topologies able to provide bidirectional power flow control. This has not been explored yet in literature or at least not with enough thoroughness. Thus, in addition to charge balancing, up to three more objectives could be pursued simultaneously. Firstly, virtual resistance control, in order to provide dynamic compensation for variations in terminal cell voltage. Secondly, thermal management, to achieve a more uniform temperature distribution within a battery pack. Third, on-board diagnosis or fault detection tools, e.g. to perform characterization tests or to identify and even isolate problematic cells. In this paper, this issue is discussed and evaluated for a battery pack made up of 48 large format Li-Ion cells in series in a e-mobility application. Simulation results demonstrate the technical feasibility of this newly defined concept.
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