GE IC3645SR4T405CT1 Installation And Operation Manual

GE IC3645SR4T405CT1 Installation And Operation Manual Manual pdf 5 page image

BASIC OPERATION AND FEATURESIT400 TRANSISTOR CONTROL Page 5January 2008Aside from the constant horsepower characteristicsdescribed above, there are many other features thatprovide increased performance and lower cost. Thefollowing description provides a brief introduction toexamples of some of these features.Section 1. 2 Solid-State ReversingThe direction of armature rotation on a shunt motor isdetermined by the direction in which current flowsthrough the field windings. Because of the of theshunt motor field only typically requires about 10% ofthe armature current at full torque, it is normally costeffective to replace the double-pole, double-throwreversing contactor with a low power transistor H-Bridge circuit (Figure 4).By energizing the transistors in pairs, current can bemade to flow in either direction in the field. Thearmature control circuit typically operates at 12KHZto 15KHZ, a frequency range normally above humanhearing. This high frequency coupled with theelimination of directional contactors, provides veryquiet vehicle operation. The field control circuitstypically operate at 2 KHZ.The line contactor is normally the only contactorrequired for the shunt motor traction circuit. Thiscontactor is used for both pre-charge of the linecapacitors and for emergency shut down of the motorcircuit, in case of problems that would cause a fullmotor torque condition. The line can be energizedand de-energized by the various logic combinationsof the vehicle, i.e. activate on key, seat or start switchclosure, and de-energize on time out of idle vehicle.Again, these options add to the quiet operation of thevehicle.Section 1. 3 Flexible System ApplicationBecause the shunt motor controller has the ability tocontrol both the armature and field circuitsindependently, the system can normally be adjustedfor maximum system efficiencies at certain operatingparameters. Generally speaking, with the ability ofindependent field and armature, the motorperformance curve can be maximized through propercontrol application.Section 1. 4 More Features with FewerComponentsField weakening with a series wound motor isaccomplished by placing a resistor in parallel with thefield winding of the motor. Bypassing some of thecurrent flowing in the field into the resistor causes thefield current to be less, or weakened. With thefield weakened, the motor speed will increase,giving the effect of “overdrive”. To change the“overdrive speed”, it is necessary to change theresistor value. In a separately excited motor,independent control of the field current providesfor infinite adjustments of “overdrive” levels,between motor base speed and maximum weakfield. The desirability of this feature is enhancedby the elimination of the contactor and resistorrequired for field weakening with a series motor.With a separately excited motor, overhaulingspeed limit, or downhill speed, will also be moreconstant. By its nature, the shunt motor will try tomaintain a constant speed downhill. Thischaracteristic can be enhanced by increasing thefield strength with the control. Overhauling loadcontrol works in just the opposite way of fieldweakening, armature rotation slows with the increaseof current in the field.Regenerative braking (braking energy returned to thebattery) may be accomplished completely with solid-state technology. The main advantage ofregenerative braking is increased motor life. Motorcurrent is reduced by 50% or more during brakingwhile maintaining the same braking torque aselectrical braking with a diode clamp around thearmature. The lower current translates into longerbrush life and reduced motor heating. Solid stateregenerative braking also eliminates a power diode,current sensor and contactor from the circuit.For GE, the future is now as we make available anew generation of electric traction motor systems forelectric vehicles having separately excited DC shuntmotors and controls. Features that were oncethought to be only available on future AC orbrushless DC technology vehicles systems are nowachievable and affordable.FUSELINECAPARM F2F1Q3Q4Q5Q6Q1POSNEGFigure 4A1 +A2 -Q2