Comparative study of efficiency improvement with adjustable DC-link voltage powertrain using DC-DC converter and Quasi-Z-Source inverter

Adjusting the DC-link voltage in the electric pow-ertrain has proven to be beneficial for enhancing powertrain efficiency. This paper presents a comparative study between two adjustable DC-link voltage powertrain solutions: (1) Voltage Source Inverter (VSI) integrated with a DC-DC converter (VSI+DC-DC) and (2) Quasi-Z-Source Inverter (QZSI). Based on the different operation principles of the two solutions, DC-link voltage adjustment strategies have been proposed to maximize powertrain efficiency over drive cycle operation. With the help of simulation in the PLECS environment, the powertrain losses of the two solutions are examined over the WLTC drive cycle. The results suggest both solutions can achieve significant powertrain loss reduction compared to the conventional powertrain with fixed DC-link voltage. In addition, the QZSI solution sees a 20% higher loss in power electronics than the VSI+DC-DC solution, as the DC-link voltage in the QZSI solution has to be boosted to higher values. Nevertheless, from an overall powertrain perspective, the QZSI solution has only 3% higher powertrain losses compared to the VSI+DC-DC solution, making QZSI remain an attractive alternative for adjustable DC-link powertrain given its advantages such as fewer active switches and improved system reliability.