ELECTRIC DRIVES CONVERTERS IN ELECTRIC DRIVE SYSTEMS MODULE 2 Dr. Nik Rumzi Nik Idris Dept. of Energy Conversion, UTM 2013

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 SVM-based

AC-DC controlled rectifier + Vo   50Hz 1-phase 90o 180o Average voltage over 10ms 50Hz 3-phase + Vo   90o 180o Average voltage over 3.33 ms For steady state continuous current flow

 T AC-DC controlled rectifier Dual Converter – 4Q operation 3-phase supply + Vt  Non-simultaneous operation Simultaneous operation Q1 Q2 Q3 Q4  T

 T AC-DC controlled rectifier Single Converter – 4Q operation F1 F2 + Va - 3-phase supply F1 and F2  quadrants 1 and 4 R1 and R2  quadrants 2 and 3 Q1 Q2 Q3 Q4  T

? AC-DC controlled rectifier firing circuit controlled rectifier  + Va – vc vc(s) ? va(s) DC motor The relation between vc and va is determined by the firing circuit It is desirable to have a linear relation between vc and va

AC-DC controlled rectifier linear firing angle control Vm Input voltage  2 3 4 vt vc Sawtooth compared with control signal Results of comparison to trigger SCRs Output voltage

AC-DC controlled rectifier linear firing angle control Vm  2 3 4 vt vc vc    A non-linear relation between Va and vc

AC-DC controlled rectifier Cosine-wave crossing control Vm Input voltage  2 3 4 vc vs Cosine wave compared with vc Results of comparison trigger SCRs Output voltage

AC-DC controlled rectifier Cosine-wave crossing control Vscos() = vc Vscos(t) Vm  2 3 4 vc vs   A linear relation between vc and Va

AC-DC controlled rectifier e.g. cosine wave crossing control

AC-DC controlled rectifier Control model Va is the average voltage over one period of the waveform - sampled data system Delays depending on when the control signal changes – normally taken as half of sampling period

AC-DC controlled rectifier Control model Va is the average voltage over one period of the waveform - sampled data system Delays depending on when the control signal changes – normally taken as half of sampling period

AC-DC controlled rectifier Control model Single phase, 50Hz vc(s) Va(s) T=10ms Three phase, 50Hz T=3.33ms Simplified if control bandwidth is reduced to much lower than the sampling frequency

AC-DC controlled rectifier SIMULINK EXAMPLES MATLAB v7.1, SIMULINK v7.5 SympPowerSystems toolbox Open-loop control Closed-loop control

AC-DC controlled rectifier Open loop + Va – vc controlled rectifier firing circuit  DC motor modeled with R-L and Vdc

Load Controlled rectifier ‘Firing circuit’ Three-phase AC source scr_openloop_3phase.mdl

AC-DC controlled rectifier Closed loop + Va – iref current controller vc firing circuit  controlled rectifier To control the current – current-controlled converter Torque can be controlled Only operates in Q1 and Q4 (single converter topology)

Open-loop system from previous simulation Closed-loop elements scr_closedloop_3phase.mdl