19-05-2016, 01:24 PM
20-05-2016, 04:03 PM
INTRODUCTION
The fully controlled converter can produce a reversible direct output voltage with output current in one direction, and in terms of a conventional voltage/ current diagram(Fig.1
is said to be capable of operation in two quadrants, the first and fourth. Such a range of operation is useful for certain purposes, examples being the control of a dc torque motor, i.e. a motor used to provide unidirectional torque with reversible rotation (Fig.2), and a DC transmission page link between two AC systems in which power can be transmitted in either direction according to the polarity of the voltage with current flows always in one direction. Equally a converter may be used under steady- stage conditions in the first quadrant only but transiently in the second quadrant in order to extract energy from the load quickly and thereby improve the response of the system to changing command signals.If four-quadrant operation of a DC motor is required, i.e. reversible rotation and reversible torque, a single converter needs the addition of either a change - over contractor to reverse the armature connections or a means of reversing the field current in order to change the relationship between the converter voltage and the direction of rotation of the motor. Both of these are practicable in suitable phase and three-phase dual-converter using bridge type converter circuits. The output terminals of each converter having the same potential are connected together through a reactor. The four possible quadrants of converter operation thus resulting can be translated into four (steady-state) combinations of motor-torque and rotation
The fully controlled converter can produce a reversible direct output voltage with output current in one direction, and in terms of a conventional voltage/ current diagram(Fig.1
is said to be capable of operation in two quadrants, the first and fourth. Such a range of operation is useful for certain purposes, examples being the control of a dc torque motor, i.e. a motor used to provide unidirectional torque with reversible rotation (Fig.2), and a DC transmission page link between two AC systems in which power can be transmitted in either direction according to the polarity of the voltage with current flows always in one direction. Equally a converter may be used under steady- stage conditions in the first quadrant only but transiently in the second quadrant in order to extract energy from the load quickly and thereby improve the response of the system to changing command signals.If four-quadrant operation of a DC motor is required, i.e. reversible rotation and reversible torque, a single converter needs the addition of either a change - over contractor to reverse the armature connections or a means of reversing the field current in order to change the relationship between the converter voltage and the direction of rotation of the motor. Both of these are practicable in suitable phase and three-phase dual-converter using bridge type converter circuits. The output terminals of each converter having the same potential are connected together through a reactor. The four possible quadrants of converter operation thus resulting can be translated into four (steady-state) combinations of motor-torque and rotation