Abstract
Integrated battery chargers (IBCs) have been proposed as a low-weight, low-volume, and high-power solution to conventional conductive chargers. However, the design of such chargers is complicated, requiring special components or control techniques to solve inherent issues (such as galvanic isolation, torque generation, and system reconfiguration) associated with their design. Solutions vary based on charging power, drive topology, and motor technology. This chapter introduces designs for IBCs, including solutions as proposed in the literature. It also presents challenges in their industrial adoption. Finally, the chapter presents opportunities for fleet charging applications using IBCs.
TopIntroduction
Transportation electrification can be challenging, particularly when needing to charge a battery in a minimal timeframe. Large batteries require high-power chargers for fast charging. One barrier to overcome is ensuring a longer travel distance on a single charge. Fast chargers are conventionally bulky and heavy; therefore, they cannot be placed on the vehicle. Portable chargers that can be placed on the vehicle must be designed to have a lower weight and volume, resulting in lower power. A compromise in the literature provides high-power charging without added bulk and heavy components on the vehicle. The solution reuses existing components of the traction drive, reconfiguring components to implement an on-board integrated battery charger (IBC).
Background
Electric vehicle (EV) drivetrains usually consist of a battery, traction motor, and drive (see Figure 1). If a charger is needed, such as for plugin electric vehicles (PEVs), an additional power converter is required to connect to the direct current (DC) link created by the battery. The connected charger is classified as an on-board or off-board charger. On-board chargers must be on the vehicle and, therefore, are designed to have a small weight and size. This results in a low power charger. Most of the alternating current (AC) level 1 chargers are on-board chargers. Off-board chargers, on the other hand, are not placed on the vehicle. This gives them more flexibility in terms of size and weight; therefore, they can be designed for high-power charging. AC level 2 and DC chargers are often off-board and higher power as compared to AC level 1 chargers.
Figure 1. A typical EV drivetrain with battery charger
The main components of the charger include the power electronic converter and harmonic filter. An optional transformer can be added to provide galvanic isolation. However, if the personnel safety against electric shock is provided by another device, such as a residual current device (RCD), it can be omitted. On close observation, the traction drive has most, if not all, major components required by a charger.
Slicker (1985) and Thimmesch (1985) built on this to propose the IBC concept: reuse the existing components of the traction drive for charging. This is possible because of the mutual exclusivity of the two functions. When the EV traction drive is used for propulsion, its battery is not charged and when the EV battery is being charged, the vehicle is not required to move. In most cases, a topology change is required to switch between the propulsion mode and charging mode of the circuit. Therefore, most of the IBCs proposed require additional reconfiguration components (see Figure 2). The configuration of the battery charger in an IBC can be done in various ways and for different traction drive and motor topologies. The concept provides solutions from low-power level 1 chargers to high-power level 2 (and higher) chargers with an AC or DC supply interface.
Figure 2. Representation of an IBC that utilizes the motor windings as a filter
Ibc Types
A detailed representation of the electrical architecture of an EV (as shown in Figure 1) shows three main components that can be repurposed into multifunction components either individually or in combination. Each component can be included or excluded in the active circuit based on the mode of operation via a reconfiguration network. A generalized representation of the EV drivetrains with the reconfiguration network is shown in Figure 3.
The IBCs proposed in the literature consists of three categories, depending on the traction drive component in the integration: (1) IBCs using theDC-DC converters; (2) IBCs using thetraction drive converter; and (3) IBCs using thetraction motor. The following sections explain each category and offer examples.
Figure 3. Detailed view of the EV electrical architecture
Key Terms in this Chapter
Integrated Battery Charger (IBC): A system that reuses existing on-board components of an electric vehicle for charging purposes.
Torque Cancelation: The mitigation or complete cancelation of the unwanted torque produced on the traction motor shaft because of the current flowing through the motor windings during the charging operation.
Traction Drive: The components that constitute the on-board system in an electric vehicle responsible for controlling the electric vehicle traction. This includes the traction power converter and traction motor.
Vehicle-to-Grid (V2G): The ability of an electric vehicle charger to feed power to the grid. In this chapter, this term encompasses all vehicle-to-X technologies like Vehicle-to-Home, Vehicle-to-Load, etc.
Special Machines: Machines other than conventional three-phase machines (e.g., six-phase or five-phase machines).
Auxiliary Load: On-board components in an electric vehicle that consume power and are not part of the main traction drive (e.g., heating, ventilation, lights, etc.).