With most active rectifiers the output voltage is controlled to be a constant value even with changes in the input voltage magnitude and load. In this applet the dynamics and parameters of the control loop are explored.

The switch signal is generated by using the hysteresis controller as presented in a previous applet. The magnitude of the current reference signal is given by ‘G,ref’. This signal is generated by the output voltage controller. In the output voltage controller the output voltage is measured and is compared with the required reference value. The voltage error is passed to the controller, which in this case is a proportional plus integral (PI) controller. Both the proportional and integral gains are adjustable in this applet and the PI controller’s transfer function is graphical shown as the black line in the controller box. If the gains are made too large then a sinusoidal current is no longer produced.

The capacitor value has an influence on the output voltage control system. The response of the capacitor (1/sC) is shown as the grey line inside the controller box. The transfer function of the controller plus the capacitor is graphically shown as the blue line in the controller box.

• Adjust the proportional and integral gains values and observe the input current waveform and the current harmonic magnitudes.
• Change the capacitor value and observe the change in the input current waveform.
• Adjust the hysteresis, input voltage magnitude, inductor and load resistor values and observe the change in the current waveform. In particular, what happens to the current waveform when the input voltage is minimum and the inductor value is maximum?