Three-Phase Diode Bridge Rectifier: Function & Operation

In many high-powered applications, three-phase voltages need to be rectified to give rise to a single DC supply; such rectification can be accomplished using an extension of the bridge rectifier such as the three-phase diode bridge rectifier.

Let’s consider the balanced three-phase circuit shown in Figure 1.0 below; the three-phase wye-connected source is connected to a resistive load by means of a three-phase transformer, with a delta-connected primary and a wye-connected secondary. The circuit may also operate without the transformer.

Figure 1.0: Three-phase diode bridge rectifier

The three secondary currents i.e. i_a, i_b, and i_c, flow through pairs of diodes D₁ to D₆ in a way very similar to the single-phase rectifier. The diodes will conduct in pairs depending on the relative line voltages, according to the following sequence: D₁-D₂, D₂-D₃, D₃-D₄, D₄-D₅, D₅-D₆ and D₆-D₁.

The line-to-line voltage in a three-phase wye-connected source is √3 times the phase voltage. The instantaneous source voltages and the related diode conduction periods, in addition to the load voltage are shown in the Figure 1.1.

Figure 1.1: Waveforms and conduction times of three-phase bridge rectifier.

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John Mulindi

John Mulindi is an Industrial Instrumentation and Control Professional with a wide range of experience in electrical and electronics, process measurement, control systems and automation. In free time he spends time reading, taking adventure walks and watching football.