Isolation contactor transition polarity control

A method of operating an electrical power system on a hybrid-electric vehicle, the

• electrical power distribution system including at least a first dual mode electrical motor/generator, high voltage traction batteries, bi-directional direct current power transmission lines connectable between the dual mode electrical motor/generator and the high voltage traction batteries, first and second isolation contactors including magnetic blow out and connected into the power transmission lines to exhibit opposed polarity and an electrical system controller, the method comprising the steps of:
• responsive to a request to deenergize the electrical power distribution system determining the polarity of current on the bi-directional direct current power transmission lines;
• selecting one of the first and second isolation contactors to open;
• establishing a steady state for the bi-directional direct current power transmission lines during which polarity remains unchanged;
• opening the selected isolation contactor;
• and
• thereafter opening the non-selected isolation contactor.

A hybrid vehicle comprises:

• a rechargeable energy storage system;
• electrical motor/generators for charging the rechargeable energy storage system;
• means for providing bi-directional direct current electrical power transmission between the electrical motor/generators and the rechargeable energy storage system;
• a control system responsive to requests for changes in state of the electrical power distribution system for determining polarity of power flow on the bi-direction electrical power bus;
• first and second isolation contactors providing magnetic blow out arc interruption in the means for providing, the first and second isolation contactors being connected into the means for providing so as to exhibit opposed polarities;
• and
• the control system being further responsive to a request for a change of state of the electrical power distribution system from on to off and to determination of the polarity of power flow for selecting one of the first and second isolation contactors to open first.