High gain dc-dc converter for electrified vehicles

An electric drive system, comprising;

• a power storage unit;
• a DC link;
• an inverter connected to the DC link and configured to connect to an electric machine;
• and
• a variable voltage converter adapted to transfer charge between the power storage unit and the DC link comprising:
• a first inductor coupled between a positive power storage node and a first switching node;
• a first switching device selectably coupling the first switching node to a negative power storage node;
• a first capacitor having a negative terminal coupled to the negative power storage node;
• a second inductor coupled between a positive terminal of the first capacitor and a second switching node;
• a second capacitor having a positive terminal coupled to the first switching node;
• and
• a second switching device selectably coupling the second switching node to a negative terminal of the second capacitor;
• wherein the first and second inductors are connected in series when the first and second switching devices are non-conducting so that the second inductor charges the DC link and the first inductor charges the first and second capacitors;
• and
• wherein the first and second inductors are energized in parallel by the power storage unit and the first and second capacitors when the first and second switching devices are conducting.

A method of boosting battery voltage onto a DC link of an electric drive comprising:

• regulating a PWM duty cycle according to a difference between a target voltage and a link voltage;
• switching first and second inductors in parallel during a duty cycle ON phase to energize the first inductor from the battery;
• and
• switching the inductors in series during a duty cycle OFF phase to de-energize the second inductor into the link.