05-03-2013, 04:05 PM
Modeling and Analysis of Slip Power Recovery Controlled Induction Motor Drive
Modeling and Analysis.pdf (Size: 416.49 KB / Downloads: 61)
Abstract
A control system based on PI_PI controller is used to improve the dynamic performance of slip power recovery motors, in which one PI controller is used as auto speed regulator (ASR) and second is used as auto current regulator (ACR). This controller tracks the need of speed and limit the stator current. The parameter values of PI controller are adjusted relaying on mathematical model value such as electromagnetic time constant and magnification factor. The simulation results of this control strategy for motor drive show that this system has high anti-disturbance capacity, fast response, low overshoot, so the system dynamic performance is improved.
INTRODUCTION
The technology of slip power recovery controlled by chopper for slip ring induction motor has been widely applied in high-voltage large-capacity motor because of higher power factor, higher efficiency and lower control voltage than those without chopper. In this, both inner current loop and outer speed loop are designed with conventional proportional-integral-derivative (PID) controller to control the motor drive automatically.
PROPOSED CONTROL SCHEME
This new type of double closed loop control system shown in Fig. 1 is proposed for the speed control of the nonlinear, time varying and complex motor system, in which one PI controller is used as auto speed regulator and second is used as auto current regulator.
Principle of speed regulation
From the slip power recovery circuit shown in Fig. 1, the three-phase full-wave diode bridge rectifier connects to the rotor windings via slip rings, converters a portion of slip power into DC which in turn converted into line frequency AC by a three-phase-thyristor inverter and fed back to the AC mains. The inductor L1, L2 between rectifier and inverter are placed to reduce the DC current ripple. The diode between L1 and L2 is used to keep current when IGBT is off and isolate when IGBT is on. The capacitor C is used to store the energy in the loop by keeping voltage Uc at low ripples.
By using IGBT as chopper, the inverter is always fixed at the smallest inverter angle of about π/6rad and the equivalent additional reverse electromotive force is obtained by changing the duty cycle of IGBT chopper. As a result, the electromagnetic torque and motor speed is changed. So the purpose of changing the motor speed can be achieved by adjusting the duty ratio of IGBT chopper.
Design of ACR_PI in inner current loop
In double closed loop design procedure, the first
step is to design the controller for inner current loop and
to tune the parameters. The current response is fast
because the time constant of inner loop is small.
According to a typical design method explain in [5], PI
controller for auto current regulator (ACR) used for
meeting the demand of servo performance is designed as
follows.
CONCLUSION
In this paper, simulation of a double closed loop
slip power recovery in induction motor, with chopper is
obtained by using PI controller as both speed regulator
and current regulator. The PI controller for double
closed-loop is designed and the simulations are
performed. The simulation results show that the PI_PI
double-loop speed control system reduced the peak
overshoot and obtained the rapid and smooth response
against the modeling uncertainty and disturbance. So, it
is an effective method to improve the robust and
adaptability performance for induction motor.