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Three-Phase Rectifier

This example shows how to use the diode block to simulate a three-phase rectifier.

G. Sybille (Hydro-Quebec)

Description

A 10 ohm load is fed in DC through a three-phase rectifier from an inductive source (5 mH; 120 V rms). The rectified current is filtered by a 200mH inductance.

Diodes are connected in parallel with RC snubbers (1000 ohms-0.1 uF) The measurement output of Diode2 and Diode3 is used to observe the diode voltage and current.

Simulation

1. Simulation with continuous integration method

Check the simulation parameters in the Simulation -> Configuration Parameters menu. The Variable-step auto (Automatic solver selection) solver is selected. Note that the Simulation type parameter of the Powergui block is not accessible, and it is set to Continuous. Start the simulation and observe waveforms on the four-trace Scope block. Note that Simulink selected the Ode23tb solver to simulate the model.

After a transient period, the load current Id stabilizes at 12.7 A. Note that most of the third harmonic which can be seen in the rectified voltage Vd (mean value 127 V) is filtered out by the smoothing reactor.

Also observe the commutation period due to the source inductances. The 3.3 degrees overlap is clearly seen on trace 3 of the scope showing currents in diodes 2 and 3.

Zoom on the Diode3 voltage (trace 4) during the conduction period. The voltage magnitude is the sum of the specified forward voltage (0.8 V) and the voltage developed across the diode resistance (0.01 ohm).

2. Simulation with discretized system

Open the Configuration parameters of the model and select the Fixed-step auto (Automatic solver selection) solver. Restart the simulation. Note that the Simulation type parameter of the Powergui is automatically changed to Discrete, with a sample time of 50e-6 usec. Note that Simulink selected the FixedStepDiscrete solver to simulate the model.

Compare waveforms with those obtained with the continuous integration algorithm.

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