Low cost electronic ultracapacitor interface technique to provide load leveling of a battery for pulsed load or motor traction drive applications

DETAILED DESCRIPTION One object of the invention is to provide a simplified load leveling system for a battery in an electric drive system.
Another object of the invention is to provide an interface for a passive auxiliary energy storage device which does not require a DC- to-DC converter and associated control.
Another object of the invention is to provide a simple interface for coupling an ultracapacitor to a DC link.
In general, in accordance with a preferred embodiment of the invention, an electric power control arrangement is provided for an electrically propelled vehicle having a battery coupled to a DC link with the DC link coupled to an electronic power regulator for supplying regulated electric power to a motor.
An energy storage device, such as an ultracapacitor, is coupled to the DC link by a diode poled to provide a low impedance path from the energy storage device to the DC link.
The diode allows the storage device to supplement battery current when battery voltage drops below the voltage of the device plus the diode drop.
Recharging of the storage device is through a second current limited path coupled in parallel with the diode.
The current limited path includes a current-sensitive resistance or switch and a fixed resistance.
At low recharge currents, current passes through the low resistance of the switch with minimal thermal loss.
At higher recharge currents, the switch exhibits an impedance higher than the fixed resistance so that current transfers to the fixed resistance path which limits the average magnitude of recharge current.
The current-limited path can also include another switched path of lower resistance to allow faster charging during regenerative braking.