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Electric Superbike Twente

Electric Superbike Twente has been an explorer of electric motorcycle racing since 2017. Our pursuit for speed was partially obstructed by the COVID-19 restrictions over the past two years. This resulted in two unfinished motorcycles with huge potentials. It is up to us, the fifth team, to extract this potential on the race track. With the knowledge gained in the previous years, during tests and on the race track, we have now set our sights on our race in Finland which starts on the 1st of July.

Within Electric Superbike Twente there are four sub-teams. We have a Chassis team, the Powertrain team, the communications team and the management team. Each sub-team is responsible for a different task. The Chassis team works on the structural part of the bike, like the frame, electromotor and the battery casing. The Communications team is busy working on the marketing strategies, organising events and recruiting partners. The Management team keeps a clear overview of the entire team and facilitates everyone in order to reach the team’s goals.

The fourth sub-team is the Powertrain team. Our Powertrain engineers are responsible for all the electric components of the bike. This includes designing and making all the hardware like the Electronic Control Unit (ECU), CAN modules, the battery pack including the Battery Management System (BMS), choosing the correct traction inverter but also the software development. As a powertrain engineer, you have to work very closely together with the chassis engineers to make sure every component is provided with our energy from the batteries and given the right directions. You also get the opportunity to work closely together with the engineers of our partners by for example improving the PCB’s of our ECU at Prodrive, choosing the correct battery cells with our battery cell partner Melasta, stress testing the bike at the dynamometer from Ten Kate Racing Products or implementing the CCS protocol together Intech and Heliox.

The latest of the two bikes is called the Delta-XE. This bike is the furthest in development and hence I will give a detailed explanation on the electrical workings of the Delta-XE.

Photographed by Marel Blumink

Photographed by Marel Blumink

Low voltage system

You may want to know more about the power electronics in our bike immediately, but an equally important system in our bike is the low voltage system. The low voltage system monitors all the data from the sensors, such as all the coolant data and the throttle input given by the driver. The low voltage system also provides the instructions for the power electronics. The low voltage is still the brains of our bike.

The low voltage system runs on 12V. However, we don’t use a conventional lead acid battery but lithium ion batteries in combination with a buck converter. The reason being that with the li-ion batteries we have a higher energy density and can put the low voltage battery in every orientation desired.

The data in our bike is gathered using a Controller Area Network (CAN). In the previous bike all the analog sensors were read out by the ECU using long cables running to the ECU. This posed two problems, a lot of cables were necessary which made it hard to keep the bike organised and difficult to do repairs. Secondly, because these long wires running through our bike were prone to interference, these could influence the readings of the analog sensors. To solve both these problems, a CAN system was implemented in the Delta-XE. Small microcontrollers were placed around the bike which read out the analog sensors with relatively short wires. After processing the data on the microcontroller, i.e. filtering or converting the data. Each microcontroller then puts the data on the central CAN bus. The data is available for all the other devices connected to the CAN bus and can take actions accordingly. The CAN bus is a robust decentralised system widely used in the automotive industry which has already proven its useability for a long time, hence the reason why we have chosen for the CAN system. Technologies such as the CAN network is one of the many technologies where you get experience on while developing the bike.

High voltage system

Now the low voltage system is functioning properly and has all the data to drive safely we can begin at the fun stuff, powering the motor with our battery pack of 800 VOLTS!! The battery pack uses lithium polymer pouch cells with high discharge ratings in order to let our bike accelerate as fast as possible without damaging the cells. The battery pack consist of 12 modules with each its own BMS chip. Each module has 16 cells in series and 3 in parallel, totalling in a capacity of 13.5 kWh for the whole battery pack. So, our battery pack has 576 lithium polymer pouch cells. The voltage and temperature of each tri-cell is monitored by our own designed BMS system. The BMS system disconnects the battery pack when a cell’s voltage becomes too high while charging or too low while discharging or when the temperature of a cell becomes too high. The BMS also takes care that all the cell voltages are the same so that we will get the most capacity out of the battery pack.

With the battery pack delivering the 800VDC, we need a way of controlling the 3 phase motor. This conversion is done with a traction inverter from Cascadia Motion. This is the only component in the powertrain which is bought off the shelf due to its complexity. In the future, however, it might be possible for us to make a custom inverter. The traction inverter can handle the 800V the battery pack is delivering and can deliver 170kW peak (30 seconds) to the motor at 15,000 rpm. The motor uses a IGBT power stage and is controlled by the CAN network.

The electromotor is a so called internal permanent magnet synchronous motor (IPMSM) which is made in collaboration with AE GROUP. We are using field-oriented control, also called “vector control” to send current commands to the three phases of the AC motor. The three phases are converted to a vector where one component defines the magnetic flux of the motor, the other the torque. To get the most efficiency and torque out of an IPM style motor, you have to characterize the flux and inductance of the motor. When this is done, the motor can be operated with feedforward control using a lookup table, generated by the characterization tests. When operating at feedforward, a specific current is requested. A PI (proportional-integral) controller inside the traction inverter uses its feedback to follow the current command.

The motor controller requires positional feedback from the motor. Inside the motor a resolver is housed, a type of rotary electrical transformer. It exists out of 3 wire windings. The primary winding, fixed to the stator, is excited with a sine wave. The two two-phase windings, fixed at right (90°) angles to each other on the stator, produce a sine and cosine feedback current. This way it is possible to know the rotation of the stator inside of the electromotor.

Photographed by Jari Schottink

Photographed by Jari Schottink

Being part of a student team

Being a part of Electric Superbike Twente, you a get to know how it is to work on a large-scale project were all the facets of engineering come together including those of Electrical Engineering. Together with your enthusiastic colleagues, you will contribute in making the racing of tomorrow more sustainable, such that future generations can still experience the amazing world or racing. By doing so you will also meet businesses were you maybe end up working later, as well as see what the latest developments are in the electric vehicle industry. This can be done by going to expo’s like the Battery show Europe in Stuttgart were all the big players in the world show off there latest innovation in Electric vehicles technologies by talking to the CEO’s and CTO’s of the companies. Next to going to expo’s, there is also the opportunity to get guided tours at our partners to see their latest innovations.

Cover image photograped by Jari Schottink.