A high level definition of the hybrid system type. The pros and cons and a look at the battery.
The mechanical output could be to the wheels of a vehicle, the propeller of a boat or aircraft. The requirements for each system will influence the sizing of the system and the balance between battery storage capacity and onboard fuel storage. Thus changing the pros and cons of each system to some extent.
However, at the highest level the hope is that this intoduction will promote the thinking and optimisation.
Series Hybrid
The series hybrid is used in diesel-electric trains as it allows some optimisation of the diesel engine as it doesn’t need to operate over the full torque and speed map and removes the requirement for a multi-speed gearbox.
| Pros | Cons |
| no battery | energy losses through conversion |
| simple system | no regen / recuperation |
| fuel to electricity conversion can be remote | electrical power demand mapped to conversion |
| no multi-speed gearbox and clutch |
Series Hybrid with Storage
Adding energy storage to this system opens up a number of opportunities. Mechanical energy can be recuperated and stored in the battery. Also, electricity produced by conversion from fuel can also be stored in the battery, allowing the conversion to be optimised.
| Pros | Cons |
| recuperation of mechanical energy | more complexity |
| optimisation of the fuel to electricity conversion | higher cost |
| slower reacting fuel to electricity conversion | |
| ev only operation possible |
This post has been built based on the support and sponsorship from: Thermo Fisher Scientific, Eatron Technologies, About:Energy and Quarto Technical Services.
Parallel Hybrid
Here we see that the connection between the two systems is at the mechanical outputs. This means that the fuel to mechanical system has to operate over a wider speed and torque range, but being mechanically connected means the fuel to mechanical output is more efficient overall.
| Pros | Cons |
| recuperation of mechanical energy | complex system calibration |
| optimisation of the fuel to mechanical system | |
| single refuelling system |
The original Toyota Prius is perhaps the most famous use of this approach.
Plug-in Parallel Hybrid Electric Drive
The main addition here is you can charge the battery pack from the grid. To make this worthwhile the battery pack is made larger, extending the electric only range.
| Pros | Cons |
| recuperation of mechanical energy | complex system calibration |
| optimisation of the fuel to mechanical system | two refuelling options |
| longer electric only operation |
Range Extended Electric Drive
Removing the mechanical link and creating an electrical output from the fuel conversion allows the systems to be optimised more independently. Breaking the mechanical link does though increase the losses and hence there is a trade.
| Pros | Cons |
| recuperation of mechanical energy | two systems to be packaged |
| optimisation of the fuel to electrical conversion | two refuelling options |
| electrical connection more flexible than mechanical |
Battery Electric Driveline
The pure battery electric drive is perhaps the simplest. The downside is the energy density of the onboard storage system.
| Pros | Cons |
| recuperation of mechanical energy | low energy storage density |
| simple system to design and calibrate | |
There will be variations on each of these systems, including how the fuel is converted to mechanical or electrical energy: internal combustion and a generator or a fuel cell.