ELECTRIC DRIVES CONVERTERS IN ELECTRIC DRIVE SYSTEMS MODULE 2 Dr. Nik Rumzi Nik Idris Dept. of Energy Conversion, UTM 2009

CONVERTERS - Module 2 AC-DC controlled rectifier approximate model SIMULINK examples open-loop closed-loop Switch Mode DC-DC converter 2-Q and 4-Q converters Small signal modeling unipolar bipolar SIMULINK example Current-controlled for SM converters Bridge converter hysteresis fixed frequency 3-phase VSI hysteresis PI controller

Current-Controlled Converters Current need to be controlled (in drives): To control the torque To limit the current – protect the switching devices Motor Example of current control in cascade control structure converter speed controller position controller  + ** 1/s + +  current controller T*T* **   k T KtKt

Current-Controlled Converters ON-OFF ControllersSeparated PWM block Hysteresis Non-linear controllers PI controllers Linear controllers

Current-Controlled Converters i ref + V dc − iaia iaia vava +Va+Va i err q q Hysteresis-based

Current-Controlled Converters Hysteresis-based - extending to 3-phase system Motor i* a i* b i* c Converter

Current-Controlled Converters Hysteresis-based - extending to 3-phase system High bandwidth, simple implementation, insensitive to parameter variations Variable switching frequency – depending on operating conditions Instantaneous error for isolated neutral load can reach double the band For isolated neutral load, i a + i b + i c = 0  control is not totally independent idid iqiq isis h h h h

Current-Controlled Converters Hysteresis-based – simulink block References Hysteresis comparators VSI Load

Current-Controlled Converters Hysteresis-based – simulation results Actual and reference currents Current error Actual current locus

Current-Controlled Converters Hysteresis-based – simulation results

Current-Controlled Converters PI-based v tri V dc q vcvc q Pulse width modulator vcvc V dc Pulse width modulator vcvc i ref PI +  q

Current-Controlled Converters PI-based – extending to 3-phase Motor i* a i* b i* c Converter PWM Sinusoidal PWM PI Interactions between phases  only require 2 controllers Tracking error

Interactions between phases  only require 2 controllers Tracking error Current-Controlled Converters Perform the control in synchronous frame - the current will appear as DC Perform the 3-phase to 2-phase transformation - only two controllers (instead of 3) are used PI-based

Current-Controlled Converters Motor i* a i* b i* c Converter PWM PI PI-based

Current-Controlled Converters Motor i* a i* b i* c Converter 3-2 SVM 2-3 PI PI-based

Current-Controlled Converters id*id* iq*iq* PI controller dq  abc abc  dq SVM or SPWM VSI IM va*va* vb*vb* vc*vc* idid iqiq + +   PI controller Synch speed estimator ss ss PI-based

Current-Controlled Converters Simulink and SimPowerSystems References 3  2 transformation VSI 3  2 transformation PI controllers Load PI-based – simulation with control in stationary frame

Current-Controlled Converters d and q current components viewed in rotating frame i a as viewed in stationary frame PI-based – simulation with control in stationary frame

Current-Controlled Converters Simulink and SimPowerSystems PI-based – simulation with control in synchronous frame

Current-Controlled Converters PI-based - simulation with control in synchronous frame d and q current components viewed in rotating frame i a as viewed in stationary frame