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Engine Control System for Hybrid Electric Diesel Buses



Double-Decker Bus Retrofitted with B320 Hybrid System
Double-Decker Bus Retrofitted with B320 Hybrid System

The Challenge

Developing a hybrid powertrain that can be retrofitted into existing double-decker buses and can demonstrate a 40% fuel savings in real-world operating conditions. We needed to develop a completely new electronic controller to interface with more than 32 different inputs and outputs, and control more than 13 other devices, to make it the most energy-efficient hybrid bus on the road.


The Solution

Using CompactRIO and LabVIEW system-design software to create an onboard embedded controller for a hybrid vehicle. The system constantly calculates the optimal power split between engine and battery, whilst translating driver commands to provide a smooth-running vehicle, and ensuring all components are running within safe limits.

Left: Schematic of Series Hybrid Powertrain System using a Lithium-Ion Battery, Right: B320 Hybrid Retrofit System for Double-Decker Buses


While the cost of fuel increases, government subsidies for fuel decrease, and government pressure to clean up bus emissions mounts. Bus operators are facing huge regulations to clean up their fleets. Some of the largest fleet owners in the United Kingdom run more than 7,500 buses, each with a lifetime of more than 25 years. One of the only viable solutions to quickly make a meaningful difference to fleet fuel consumption is to retrofit existing vehicles with cleaner propulsion methods.

A typical hybrid bus powertrain consists of an electric drive motor; a power converter; a lithium-ion battery; a generator; and an engine. In the layout shown a series hybrid creates energy in series with the engine whilst being mechanically decoupled from the wheels. In this scenario, each of the main components in the energy conversion chain needs to be controlled so that their power output matches the requirement of the following component.


System Architecture

Due to the complexity in such a control system, we needed an architecture capable of very high-speed repetitive calculations with a high level of determinism to analyze and log the large sets of acquired data. In addition, the driver needs to be updated and information fed back to the other powertrain system components and the prototyping dashboard. CompactRIO is the ideal platform for our control system, because it delivers all of the benefits of a real-time processor and a user-programmable FPGA, perfectly integrated into one piece of hardware. The FPGA provides the best platform on which to implement highly deterministic and safety-critical functions, such as processing accelerator pedal inputs into commands to control acceleration and braking, as well as fault management. Functions that are not safety-critical and require less determinism, such as high-level power and thermal management, data logging, and providing data to the prototyping dashboard, run on the real-time processor.

While the cost of fuel increases, government subsidies for fuel decrease, and government pressure to clean up bus emissions mounts. Bus operators are facing huge regulations to clean up their fleets. Some of the largest fleet owners in the United Kingdom run more than 7,500 buses, each with a lifetime of more than 25 years. One of the only viable solutions to quickly make a meaningful difference to fleet fuel consumption is to retrofit existing vehicles with cleaner propulsion methods.

A typical hybrid bus powertrain consists of an electric drive motor; a power converter; a lithium-ion battery; a generator; and an engine. In the layout shown a series hybrid creates energy in series with the engine whilst being mechanically decoupled from the wheels. In this scenario, each of the main components in the energy conversion chain needs to be controlled so that their power output matches the requirement of the following component.


System Architecture

Due to the complexity in such a control system, we needed an architecture capable of very high-speed repetitive calculations with a high level of determinism to analyse and log the large sets of acquired data. In addition, the driver needs to be updated and information fed back to the other powertrain system components and the prototyping dashboard. CompactRIO is the ideal platform for our control system, because it delivers all of the benefits of a real-time processor and a user-programmable FPGA, perfectly integrated into one piece of hardware. The FPGA provides the best platform on which to implement highly deterministic and safety-critical functions, such as processing accelerator pedal inputs into commands to control acceleration and braking, as well as fault management. Functions that are not safety-critical and require less determinism, such as high-level power and thermal management, data logging, and providing data to the prototyping dashboard, run on the real-time processor.


Original Authors:

Toby Schulz, Vantage Power Ltd

Edited by Cyth Systems





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