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Current-Controlled Thyristor Rectifier

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This example shows the operation of a current-controlled thyristor rectifier.

Description

A DC motor represented by a simplified RL-E model is fed from an inductive three-phase source through a six-pulse thyristor bridge. A pulse generator synchronized on the source voltages provides the trigger pulses for the six thyristors.

The converter output current is controlled by a PI current regulator built with Simulink® blocks. A step signal is applied to the reference input to test the dynamic response of the current regulator.

In order to allow further signal processing, signals displayed on the Scope block are stored in a variable named ScopeData1 (in structure with time format).

Simulation

Start the simulation and observe current and voltage waveforms on the Scope block.

When simulation is completed, open the Powergui and select FFT Analysis to display the 0 - 2000 Hz frequency spectrum of signals saved in the ScopeData1 structure. The FFT will be performed on a 2-cycle window starting at t = 0.08 - 2/60 (last 2 cycles of recording). Input labeled Ia should be already selected. Click on Display and observe the frequency spectrum of the last two cycles of Ia. Harmonic currents (6n+/-1) are displayed in % of the fundamental component.

The value of the fundamental current (magnitude = 27.48 A peak) and the Total Harmonic Distortion (THD) are also displayed. Harmonics in the 0 - 2000 Hz range contribute to 29% in THD. If you specify a 0-4000 Hz frequency range, notice that contributions of harmonics above 2000 Hz are negligible in the current THD.

Now select the input labeled Vd and display its spectrum. The DC voltage contains harmonics (6n) and its DC component is 145.4 V.