Jaime Rodríguez Arribas

Flexible low-cost system to test batteries and ultracapacitors for electric and hybrid vehicles in real working conditions

Batteries and ultracapacitors for hybrid and electric vehicles must satisfy very demanding working conditions that are not usual in other applications. In this sense, specific tests must be performed in order to draw accurate conclusions about their behaviour. To do so, new advanced test benches are needed. These platforms must allow the study of a wide variety of energy storage systems under conditions similar to the real ones. In this paper, a flexible, low-cost and highly customizable system is presented. This system allows batteries and ultracapacitors to be tested in many and varied ways, effectively emulating the working conditions that they face in an electric vehicle. The platform was specifically designed to study energy storage systems for electric and hybrid vehicles, meaning that it is suitable to test different systems in many different working conditions, including real driving cycles. This flexibility is achieved keeping the cost of the platform low, which makes the proposed test bench a feasible alternative for the industry. As an example of the functionality of the platform, a test consisting of a 17-minute ARTEMIS urban cycle with a NiMH battery pack is presented.

Energy storage systems for electric vehicles: Performance comparison based on a simple equivalent circuit and experimental tests

The decision to select the most suitable type of energy storage system for an electric vehicle is always difficult, since many conditionings must be taken into account. Sometimes, this study can be made by means of complex mathematical models which represent the behavior of a battery, ultracapacitor or some other devices. However, these models are usually too dependent on parameters that are not easily available, which usually results in nonrealistic results. Besides, the more accurate the model, the more specific it needs to be, which becomes an issue when comparing systems of different nature. This paper proposes a practical methodology to compare different energy storage technologies. This is done by means of a linear approach of an equivalent circuit based on laboratory tests. Via these tests, the internal resistance and the self-discharge rate are evaluated, making it possible to compare different energy storage systems regardless their technology. Rather simple testing equipment is sufficient to give a comparative idea of the differences between each system, concerning issues such as efficiency, heating and self-discharge, when operating under a certain scenario. The proposed methodology is applied to four energy storage systems of different nature for the sake of illustration.

Passenger Exposure to Magnetic Fields in Electric Vehicles

In electric vehicles, passengers sit very close to an electric system of significant power, usually for a considerable amount of time. The relatively high currents achieved in these systems and the short distances between the power devices and the passengers mean that the latter could be exposed to relevant magnetic fields. This implies that it becomes necessary to evaluate the electromagnetic environment in the interior of these vehicles before releasing them in the market. Moreover, the hazards of magnetic field exposure must be taken into account when designing electric vehicles and their components. For this purpose, estimation tools based on finite element simulations can prove to be very useful. With appropriate design guidelines, it might be possible to make electric vehicles safe from the electromagnetic radiation point of view.

Improved Predictive Direct Power Control of Doubly Fed Induction Generator During Unbalanced Grid Voltage Based on Four Vectors

This paper presents an improved strategy in the field of predictive direct power control (PDPC) of the doubly fed induction generator (DFIG). The proposed strategy applies four voltage vectors in every period in order to have constant switching frequency and low current total harmonic distortion. The appropriate voltage vectors in each period are recognized when estimated duration times of selected active vectors are positive. The suggested technique shows excellent performance during transient and steady-state conditions. The proposed PDPC can easily follow the power references under normal and abnormal voltage conditions even if the power references contain ac terms. Without any additional controller, the proposed technique could obtain smooth stator active and reactive powers or smooth electromagnetic torque, or could inject sinusoidal and balanced currents into the grid when the unbalanced voltage appears in DFIG stator windings. Simulation studies for this technique are carried out for 2-MW DFIG in MATLAB Simulink environment under balanced and unbalanced grid voltage. The results of this technique under unbalanced grid voltage are compared with two other previous PDPC strategies. Comparisons show that the performance of the proposed strategy under unbalanced grid voltage is superior to the two other strategies.

A novel educational proposal: Devising an electric power system

The study of electric power systems within the field of Electrical Engineering is usually approached by computer simulation because any actual test is quite complex to be implemented, especially with renewable energies. Having the aim to improve student learning about this topic, a new subject called “Devising an Electric Power System” was organized following a CDIO (Conceive-Design-Implement-Operate) approach. The subject is programmed for one academic year and based entirely on laboratory work. The students are divided into three teams. Every team would have to work on a power system that includes a solar PV generator and a pumping controlled drive, both connected to a three-phase grid. The third and last part of the subject is focused on “electric utility” business strategy. In the final day of the course a competition between the three teams takes place.

Minimum losses point tracking and minimum current point tracking in interior PMSMs

Advanced control strategies for efficiency optimization in interior PMSMs are usually model-based, potentially providing very accurate results and good performance at the cost of parameter dependency and the associated drawbacks. Search-based methods, on the contrary, perform more modestly but depend neither on models nor on parameters. This paper compares both approaches in terms of steady-state efficiency.

Passenger Exposure to Magnetic Fields due to the Batteries of an Electric Vehicle

In electric vehicles, passengers sit very close to an electric system of significant power. The high currents achieved in these vehicles mean that the passengers could be exposed to significant magnetic fields (MFs). One of the electric devices present in the power train are the batteries. In this paper, a methodology to evaluate the MF created by these batteries is presented. First, the MF generated by a single battery is analyzed using finite-elements simulations. Results are compared with laboratory measurements, which are taken from a real battery, to validate the model. After this, the MF created by a complete battery pack is estimated, and results are discussed.