Author: admin
-
Battery Electrical Vehicle
We begin our discussion of vehicles by first exploring the use of a battery to store energy for an all-electric vehicle. In a battery electric vehicle (BEV), the battery provides all of the power and energy needs. As mentioned earlier in the chapter, here are three key aspects to sizing the battery: energy capacity, power,…
-
Regenerative Braking
Before turning to specific vehicle architectures, we pause to consider regenerative braking, which plays an important role in increasing hybrid vehicle efficiency. A key benefit of the vehicle strategies considered in this chapter is that kinetic and potential energy can be recovered during braking. Clearly, energy is required to accelerate a vehicle to a higher…
-
Driving Schedules and Power Demand in Vehicles
In evaluating powertrain systems, the vehicle speed is often prescribed as a function of time. This relationship is generalized with a driving schedule. Figure 12.3 provides such a relationship for an urban dynamometer driving schedule, one of many standardized schedules that are available. This plot shows speed versus time for the vehicle driven in an…
-
Why Electric and Hybrid-Electric Systems?
A key feature of systems that include energy storage is that excess energy can be accumulated for later use. Our focus will be on vehicles, but applications for hybrid power systems are common. For example, a renewable energy system based on wind power alone will struggle to match electrical power production and demand. What do…
-
Pseudo-Capacitance
Other than self-discharge, our discussion of EDLCs has not involved faradaic reactions; that is, we have assumed that no charge is transferred across the double layer, and that there is no change in oxidation state due to reaction. The resulting current–voltage behavior is purely capacitive and would approximate the ideal box shown earlier in Figure 11.9. The…
-
Cell Design, Practical Operation, and Electrochemical Capacitor Performance
Construction of a typical cell sandwich for an EDLC is shown in Figure 11.18. The differences in how energy is physically stored aside, these EDLCs have many similarities to batteries, two porous electrodes coated onto current collectors and separated by an electrolyte. The cell designs are similar too. Typical configurations for EDLCs include cylindrical, prismatic, button,…
-
Power and Energy Capabilities
Both the energy and power density are important characteristics of capacitors, and are considered in this section. The change in energy associated with a change in capacitor voltage is (11.36)The total energy stored in the capacitor can be obtained by integration (11.37)where we have assumed that C is constant. Recall that capacitance has units of…
-
Impedance Analysis of EDLCs
In this section, we apply impedance spectroscopy to electrochemical double-layer capacitors in order to gain insight into their transient behavior. Additionally, we use the impedance results as a basis for a simplified EDLC model that will facilitate our analysis of these devices. Analysis for Highly Conductive Solid PhaseIn order to use impedance to examine the…
-
Porous Edlc Electrodes
As we noted in Chapter 5, a porous electrode is an effective means of increasing the surface area of an electrode. As with any porous electrode, the local resistance is a function of position in the electrode. An equivalent circuit diagram for an EDLC using a porous electrode is shown in Figure 11.10. The resistances along the…
-
Current–Voltage Relationship for Capacitors
We are interested in how a capacitor behaves under a variety of circumstances. In particular, we seek out the current–voltage behavior of a capacitor under different conditions. This section explores these aspects. We begin with the expression for current from a capacitor (see Chapter 6): (6.6) This equation describes an ideal capacitor, where the capacitance, C, is…