GE SX TRANSISTOR CONTROL IC3645SR4U404N2 Manuel D’Utilisation

SX TRANSISTOR CONTROL

 

 

 

Page 5

 

 

January 2000 

following description provides a brief introduction to 

examples of some of these features. 

 
Section 1. 2 Solid-State Reversing 
 

The direction of armature rotation on a shunt motor is 

determined by the direction in which current flows through 

the field windings. Because of the of the shunt motor field 

only typically requires about 10% of the armature current at 

full torque,  it is normally cost effective to replace the 

double-pole, double-throw reversing contactor with a low 

power transistor H-Bridge circuit (Figure 4).  

 

 

By energizing the transistors in pairs, current can be made 

to flow in either direction in the field.  The armature control 

circuit typically operates at 12KHZ to 15KHZ,  a frequency 

range normally above human hearing. This high frequency 

coupled with the elimination of directional contactors, 

provides very quiet vehicle operation.  The field control 

circuits typically operate at 2 KHZ. 

 

The line contactor is normally the only contactor required 

for the shunt motor traction circuit. This contactor is used 

for both pre-charge of the line capacitors and for 

emergency shut down of the motor circuit, in case of 

problems that would cause a full motor torque condition. 

The line can be energized and de-energized by the various 

logic combinations of the vehicle, i.e. activate on key, seat 

or start switch closure, and de-energize on time out of idle 

vehicle. Again, these options add to the quiet operation of 

the vehicle. 

  
Section 1. 3 Flexible System Application  

 

Because the shunt motor controller has the ability to 

control both the armature and field circuits independently, 

the system can normally be adjusted for maximum system 

efficiencies at certain operating parameters. Generally 

speaking, with the ability of independent field and 

armature, the motor performance curve can be maximized 

through proper control application.  

 
Section 1. 4 More Features with Fewer Components  
 
Field weakening with a series wound motor is 

accomplished by placing a resistor in parallel with the field 

winding of the motor. Bypassing some of the current 

flowing in the field into the resistor causes the field current 

to be less, or weakened. With the field weakened, the motor 

speed will increase, giving the effect of “overdrive”.  To 

change the “overdrive speed”, it is necessary to change 

the resistor value.  In a separately excited motor, 

independent control of the field current provides for 

infinite adjustments of “overdrive” levels, between 

motor base speed and maximum weak field. The 

desirability of this feature is enhanced by the 

elimination of the contactor and resistor required for 

field weakening with a series motor. 

 

 With a separately excited motor, overhauling speed 

limit, or downhill speed, will also be more constant. By 

its nature, the shunt motor will try to maintain a 

constant speed downhill. This characteristic can be 

enhanced by increasing the field strength with the 

control. Overhauling load control works in just the 

opposite way of field weakening, armature rotation 

slows with the increase of current in the field.  

 

Regenerative braking (braking energy returned to the 

battery) may be accomplished completely with solid-state 

technology. The main advantage of regenerative braking is 

increased motor life. Motor current is reduced by 50% or 

more during braking while maintaining the same braking 

torque as electrical braking with a diode clamp around the 

armature. The lower current translates into longer brush 

life and reduced motor heating. Solid state regenerative 

braking also eliminates a power diode, current sensor and 

contactor from the circuit. 

 

For GE, the future is now as we make available a new 

generation of electric traction motor systems for electric 

vehicles having separately excited DC shunt motors and 

controls. Features that were once thought to be only 

available on future AC or brushless DC technology vehicles 

systems are now achievable and affordable. 

 
 
 
 
 
 
 
 
 
 
 

NEG

Figure 4