Previously, we discussed the advantages of the series hybrid vehicle architecture over parallel hybrid designs that results in superior fuel savings and reduced emissions. Now we will examine the electrical systems of the series hybrid.
The key to the series hybrid system is the conversion of the power generated by the electric motor coupled to the engine. The output from the motor (acting as a generator) is converted from a three phase alternating current (AC) at a variable frequency proportional to its running speed – to smooth direct current (DC) to charge the batteries and/or capacitor.
The main traction drive motor, or motors, are typically induction or Permanent Magnet AC (PMAC) type. A bi-directional motor controller or inverter sources its power from the batteries and provides a variable frequency output to control the speed and torque of the main traction motor based on the driver’s command.
Electrical System Components
The electrical system of most hybrid vehicles consists of the following subsystems: traction drive, Auxiliary Power Unit (APU), energy storage system, onboard diagnostics and vehicle control, and auxiliary equipment.
Traction Drive Subsystem
This consists of the components that actually drive the wheels: electric motor or motors, bi-directional inverter(s), gear reduction system, driveline, and related components.
Auxiliary Power Unit (APU)
The charging system consists of a gasoline or diesel powered Internal Combustion Engine (ICE), an electric generator, and related components.
Energy Storage System
This can consist of batteries, capacitors, fuel cells, or any storage or generating technology, along with the applicable monitoring, charging, equalization, and thermal control devices.
Onboard Diagnostics and Vehicle Control
These include battery management controls to ensure that charging is accomplished, dashboard displays, diagnostic tools, and related components. The accelerator and brake pedals interface with the power conversion components.
In a typical series hybrid vehicle, this includes electrical power steering and braking systems, ventilation and air conditioning systems, and related components.
Continued improvements in battery design to enable higher power density, lower cost and better charge cycles, will be crucial to the continued progress of hybrid vehicle technology. For technical details, please reference this white paper: Basic Elements of the Series Hybrid Vehicle.
Hybrid vehicle technology
The discussion on series hybrid vehicle technology spans three blog posts: