This experiment is aimed to analyze the effect of capacitor filter or smoothing capacitor on rectified output voltage for both single phase and three phase uncontrolled rectifiers. The circuit is implemented in simulation as well as hardware and the performance is studied.
We saw in the previous experiment that the single phase halfwave rectifier produces an output wave every half cycle and that it was not practical to use this type of circuit to produce a steady DC supply. The fullwave bridge rectifier however, gives us a greater mean DC value with less superimposed ripple while the output waveform is twice that of the frequency of the input supply frequency. We can therefore increase its average DC output level even higher by connecting a suitable smoothing capacitor across the output of the bridge circuit as shown below.
The smoothing capacitor converts the fullwave rippled output of the rectifier into a smooth DC output voltage. Generally for DC power supply circuits the smoothing capacitor is an Aluminum Electrolytic type that has a capacitance value of 100µF or more with repeated DC voltage pulses from the rectifier charging up the capacitor to peak voltage.
However, there are two important parameters to consider when choosing a suitable smoothing capacitor and these are its Working Voltage, which must be higher than the noload output value of the rectifier and its Capacitance Value, which determines the amount of ripple that will appear superimposed on top of the DC voltage.
Too low a capacitance value and the capacitor has little effect on the output waveform. But if the smoothing capacitor is sufficiently large enough (parallel capacitors can be used) and the load current is not too large, the output voltage will be almost as smooth as pure DC. As a general rule of thumb, we are looking to have a ripple voltage of less than 100mV peak to peak.
The main advantages of a fullwave bridge rectifier is that it has a smaller AC ripple value for a given load and a smaller reservoir or smoothing capacitor than an equivalent halfwave rectifier. Therefore, the fundamental frequency of the ripple voltage is twice that of the AC supply frequency (100Hz) where for the halfwave rectifier it is exactly equal to the supply frequency (50Hz).
To simulate Single phase Diode Rectifier with Filter capacitor in MATLAB Simulink
Implement the 1phase uncontrolled full wave rectifier with a Capacitor filter of C = 5000µF in parallel with the R load of 100 Ω and observe the changes in the output voltage waveform. (Input voltage: 50V Peak = 35.35V (RMS) and 50Hz)
Form Factor = Vrms / Vdc
Ripple Factor = √(FF² − 1)
To simulate Three phase Diode Rectifier with Filter capacitor in MATLAB Simulink
Implement the 3phase uncontrolled full wave rectifier with a Capacitor filter of C = 5000µF in parallel with the R load of 100 Ω and observe the changes in the output voltage waveform. (Input voltage: Phasetophase RMS voltage (V) = 61.2V, 50Hz)
Form Factor = Vrms / Vdc
Ripple Factor = √(FF² − 1)
Obtain the results for the following.
Single phase
Three phase

Single Phase 
Three Phase 
V_{RMS}



I_{RMS}



V_{AVG}



I_{AVG}



Form factor



Ripple Factor




Single Phase 
Three Phase 
V_{RMS}



V_{AVG}



Form factor



Ripple Factor


