Thesis work - Six-step operation of a motor drive

About this opportunity - Background

For Volvo cars, the future is electric meaning that all future drivelines contain at least one electrical machine. Since the cars are using batteries, the amount of energy in the car is limited and it is therefore important to also include energy efficiency in the optimization of the machine’s operation points.  Installed components add to the vehicle payload, thus affect the CO2 budget.

Scope of the thesis work

For electric drives in Battery Electric Vehicles (BEVs) with electric drive units, a large speed range with constant maximum power is necessary since fixed ratio transmissions are used. At higher speed, the maximum output power is limited by the limited AC voltage output of the inverter. One way to increase the maximum AC-voltage is to use quasisquare-wave operation, also called “six-step”. This can increase the AC-voltage with more than 10% compared to “normal” symmetrical sinusoidal (“space-vector”) PWM. The drawback is more torque and DC-current ripple.

The objective of the thesis is to compare six-step operation of a motor drive with standard space-vector PWM at high-speed operation with respect to output power and losses. Another goal is to implement in simulations a control method that provides a rapid torque control response (within half a fundamental-frequency period) without introducing torque oscillations caused by DC-flux disturbances.

Main tasks
•    Literature study
•    Calculation of losses and max power/torque for the electric drive for space-vector PWM and six-step operation, respectively. Harmonic iron losses may be neglected. 
o    For a synchronous PM machine electric drive unit
o    For an induction machine electric drive unit
•    Implement (in a simulation model) and simulate a suitable sixstep electric drive control. Compare closed-loop torque control response and mode-changes between PWM and six-step. 
•    Compare 
o    symmetrical sinusoidal (“space-vector”) PWM
o    six-step PWM

The scope of the work will depend on the number of students.

What you'll bring

You have studied power electronics, electric machines, electric motor drives and electrical power engineering. 
The student(s) is also expected to be present on site at Volvo Cars in Gothenburg during most of the thesis work, and any living arrangements needs be to be organized by the student(s).

Duration

•    The work will start in January 2026 
•    The duration for this thesis work is 20 weeks.
•    30 ECTS (Master academic credits) in agreement with your Thesis Advisor in University
•    This thesis is to be conducted by 1 Student or 2 Students working in pair.