# Three Phase Half Wave Diode Rectifier

Published on 24/2/2012 & updated on 8/8/2018
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The three phase half wave diode rectifier is used for conversion of three-phase AC power to DC power. Half-wave diode rectifiers have been around for a very long time, both single phase and three phase rectifiers. However, diode based half-wave rectifiers are very rarely used,and the study of these converters are merely for theoretical interest.

Here the switches are diodes, and hence they are uncontrolled switches. That is to say, there is no way of controlling the on and off times of these switches. The three-phase half wave diode rectifier is generally constructed with a three-phase supply connected to a three-phase transformer where the secondary of the transformer is always instar connected as the neutral point is required to connect the load back to the transformer secondary providing the return path for the flow of power.

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Three Phase Half Wave Diode Rectifier

A typical configuration of a three-phase half wave diode rectifier supplying to a purely resistive load is shown below. Here, each phase of the transformer is considered as an individual alternating source. The simulation and measurement of voltages are as shown in the circuit below. Here we have connected an individual voltmeter across each source as well as across the load. The three-phase voltages are shown below. The voltage across the resistive load is shown below. The voltage is shown in black. So we can see from the above figure that the diode D1 conducts when the R phase has a value of thevoltage that is higher than the value of the voltage of the other two phases,and this condition begins when the R phase is at a 30o and repeats after every complete cycle. That is to say, the next time diode DI begins to conduct is at 390o. Diode D2 takes over conduction from D1 which stops conducting at angle 150o because at this instant the value of voltage in B phase becomes higher than the voltages in the other two phases. So each diode conducts for an angle of 150o - 30o = 120o. Here, the waveform of the resulting DC voltage signal is not purely DC as it is not flat,but rather it contains a ripple. And the frequency of the ripple is 3 × 50 = 150 Hz. The average of the output voltage across the resistive load is given by Where, The RMS value of the output voltage is given by Ripple voltage, Voltage ripple factor, The equation above shows that the voltage ripple is significant and this is disadvantageous as this leads to unnecessary power loss. DC output power, AC input power, Efficiency, Even though the efficiency of the three phase half-wave diode rectifier is high, it is still less than the efficiency provided by three phase full wave diode rectifier and its applications in industry are very small.

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