Electrical power system converter control

A method of controlling an electrical power system comprising an electrical machine, a DC electrical network, a controller, and a power electronics converter connected between the electrical machine and the DC electrical network, the method comprising:

• controlling switching of transistors of the power electronics converter to either invert a DC input from the DC electrical network to an AC output and supply the AC output to the electrical machine or rectify an AC power received from the electrical machine to DC power and provide the DC power to the DC electrical network;
• determining a condition to the effect that there is a fault in the DC electrical network;
• and
• responsive to the determination, controlling the switching of the transistors of the converter so that a fault current is shared between the transistors and the associated diodes of the converter, the controller being configured to control an on-time of the transistors, during which they conduct the fault current from the electrical machine, so as to be less than a full half-cycle with respect to the fault current;
• and
• wherein controlling the on-time of the transistors comprises determining a shifted phase angle by phase shifting a phase angle associated with a normal operation mode, and providing on gate pulses for the transistors according to the shifted phase angle;
• and
• wherein determining the shifted phase angle comprises phase shifting the phase angle associated with the normal operation mode by a predetermined angle aligned with a phase current vector.

A controller for an electrical power system configured to:

• during normal operation of the electrical power system, control switching of a plurality of transistors of a power electronics converter so as to either invert DC power received by the converter from a DC electrical network to AC power and provide the AC power to an electrical machine or rectify AC power received from the electrical machine to DC power and provide the DC power to the DC electrical network;
• responsive to a determination to the effect there is a fault in the DC electrical network, which is connected to a DC side of the converter, operate in a fault mode in which the controller controls the switching of the transistors of the converter so that a fault current, flowing from the electrical machine through the converter, is shared between the transistors and the associated diodes of the converter, the controller being configured to control an on-time of the transistors, during which they conduct the fault current from the electrical machine, so as to be less than a full half-cycle with respect to the fault current;
• wherein controlling the on-time of the transistors comprises determining a shifted phase angle by phase shifting a phase angle associated with a normal operation mode, and providing on gate pulses for the transistors according to the shifted phase angle;
• and
• wherein determining the shifted phase angle comprises phase shifting the phase angle associated with the normal operation mode by a predetermined angle aligned with a phase current vector.