Hybrid Vehicles have two or more different energy storage systems which supply propulsion power to the vehicles. Hybrid Electric Vehicles essentially have a battery storage system, an electric motor, and power electronic components. The other propulsion power sources in HEVs could be:
Internal Combustion Engine (ICE)
Fuel Cell (FC)
Flywheel
Supercapacitors
Topologies of HEVs are differentiated on the basis of how the propulsion power gets transferred from its source to the wheels. Firstly, we will look at these topologies in general. Later, we will discuss the topologies with particular cases of power sources.
Series Hybrid Topology :
In series hybrid topology, the wheels are directly driven by an electric machine. The electric machine is fed with electric power from a battery storage system. The power from other source is translated to electrical energy using a power converter and this power is used to charge the battery. As we can observe, the power transfer takes place through only single path.
Parallel Hybrid Topology :
In parallel hybrid topology, the power transfer can take place in three modes. A special arrangement of gearbox and clutch facilitates all three modes.
In the first mode, the driving power is supplied by only the battery while another power transfer path is disengaged from the driven shaft using a clutch. In the second mode, the power is provided by another source while the battery and electric machine are unused. In the last mode, the overall power fed to the wheel is the addition of powers provided by both the sources. This power addition takes place at the gearbox. So to say, the powers are fed ‘parallelly’.
Hybrid Power Split or Series - Parallel Topology
The hybrid power split topology is a combination of series and parallel topologies. It can work as either series or parallel topology. A ‘power splitter’ decides the path of power transfer and so, the working topology. This topology provides advantages of both the topologies and allows flexible operation.
Following are some typical examples of power source combinations for Hybrid Electric Vehicles:
ICE - Battery
ICE - Battery - Flywheel
ICE - Battery - Supercapacitor
Battery - Fuel Cells
Battery - Supercapacitors
Battery - Fuel Cells - Supercapacitors
Two different types of batteries (High Energy and High Power)
ICE - Battery HEVs
Next, we will discuss the most common topologies for ICE - Battery HEVs. These topologies can be observed in most of the hybrid passenger vehicles available currently in the market. They are classified according to the size of the Internal Combustion Engine and the battery.
Micro-Hybrid:
Micro hybrid vehicles are almost similar to conventional IC Engine vehicles. But they have slightly higher battery storage capacity than conventional vehicles to support additional functions such as comfort start-stop and little regenerative braking.
Mild or Medium Hybrid:
Mild-Hybrid Vehicle has a smaller IC engine compared to conventional vehicles. They are fitted with a larger battery or an additional 48V battery system. The electric machine in Mild Hybrid configuration provides limited driving support, and also allows moderate regenerative braking.
Full or Plug-in Hybrid:
Currently, the Plug-in Hybrid Vehicle is the hot topic in the automotive sector. Most of the related research is directed to make these vehicles more energy-efficient and cost-competitive to conventional vehicles. With a large battery pack and external battery charging possibility, all-electric operation of these vehicles is viable. Simultaneously, a small IC engine on-board helps to prevent the range-anxiety. These vehicles have a big electric machine to provide full driving support. This topology is the most efficient one, with the highest regeneration capacity.
The ICE - Battery HEVs can be further differentiated according to their Series, Parallel, or Power Split topology.
Author : Payas Vartak
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