Reliance electric GV3000 Instruction Manual page 86

Appendix B
Drive Regulation Overview
The GV3000is a digital drive that provides closed loop vector or open loop volts/hertz regulation of A-C
motors. The Volts/Hertz or Vector Regulation parameter (P.048) is used to select the type of regulation for the
application. See figures B.1 and B.2 for block diagrams of both regulators.
Volts/Hertz Regulation
Volts/hertz regulation provides general purpose open loop A-C drive control. It does not use a speed
feedback device. In this type of control, the regulator maintains a programmedratio of voltage to an output
frequency, which provides constant or variable motor torque across a wide speed range. An internal function
generator calculates the output motor voltage based on requested frequency and user-specified motor
characteristics. The control loop output switches the power device gates, generating a
pulse-width-modulated (PWM) waveform to the motor.
Vector Regulation
Vector regulation allows dynamic closed-loop performancein an A-C drive similar to that achieved with a D-C
drive. Torque is constant across the motor's base speed range in both forward and reverse directions. The
drive uses two digital control loops, speed and torque, to obtain vector performance.
The speed loop reference can beaninternal or an external source. Speed loop feedback is provided by a pulse
tachometer attached to the motor's shaft. A trim parameter is summed with the speed reference to provide a
torque reference, or to adjust a user-specified Torque Reference Source parameter,for the torque control loop.
An internally-generated flux referenceis also fed to the torque loop. The torque will vary to maintain the motor
at the requested speed. The torque control loop output switches the power device gates, generating a
pulse-width-modulated (PWM) waveform to the motor.
B-1