Methods, systems, and vehicles with electromechanical variable transmission

A system for operating a first motor/generator and a second motor/generator in a vehicle drive, the first motor/generator electrically coupled to the second motor/generator by a DC bus and the vehicle drive configured to propel a vehicle, the system comprising a processing circuit configured to:

• operate the vehicle drive in a first operating mode and thereby:
• operate the first motor/generator as a generator when a speed of the first motor/generator is above a threshold speed, wherein the first motor/generator provides electrical power to the DC bus to maintain a first voltage on the DC bus when operated as a generator, and wherein the first motor/generator provides all of an electrical power required by the second motor/generator and an electrical power required to offset electrical power losses;
• and
• operate the second motor/generator as a motor when the speed of the first motor/generator is above the threshold speed, wherein the second motor/generator consumes electrical power from the DC bus when operated as a motor, and wherein a sum of the electrical power provided by the first motor/generator, the electrical power losses, and the electrical power consumed by the second motor/generator is zero;
• wherein the first motor/generator provides electrical power to the DC bus and the second motor/generator consumes electrical power from the DC bus without doing either of (a) providing electrical power to an energy storage device or (b) consuming electrical power from an energy storage device;
• and
• operate the vehicle drive in a second operating mode and thereby:
• operate the second motor/generator as a generator when the speed of the first motor/generator is below the threshold speed, wherein the second motor/generator provides electrical power to the DC bus to maintain a second voltage on the DC bus when operated as a generator, and wherein the second motor/generator provides all of the electrical power required by the first motor/generator and the electrical power required to offset electrical power losses;
• and
• operate the first motor/generator as a motor when the speed of the first motor/generator is below the threshold speed, wherein the first motor/generator consumes electrical power from the DC bus when operated as a motor, and wherein the sum of the electrical power provided by the second motor/generator, the electrical power losses, and the electrical power consumed by the first motor/generator is zero;
• wherein the second motor/generator provides electrical power to the DC bus and the first motor/generator consumes electrical power from the DC bus without doing either of (a) providing electrical power to an energy storage device or (b) consuming electrical power from an energy storage device.