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Master of Science Thesis in Electric Power Engineering - page 14 / 114

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THREE PHASE CONTROLLED RECTIFIERS

    • 2.2

      Universal bridge topology

      • 2.2.1

        Steady state operation

Figure 2.2 : Rectifier schematics [9]

Figure 2.2 shows basic diagram of the three phase boost converter. uL is the line voltage and uS is the bridge converter voltage controllable from de the dc side. We can draw a general phasor diagram and diagrams for both rectification and regeneration operation at unity power factor (UPF).

a) General phasor diagram

b) Rectification (at UPF) Figure 2.3 : Phasor diagrams [9]

c) Regeneration (at UPF)

The line current iL is controlled by the voltage drop across the inductance L interconnecting the two voltage sources (line and converter). When we control the phase angle and the amplitude of converter voltage uS , we control indirectly the phase and amplitude of the line current. In this way, the average value and sign of the dc current is subject to control that is proportional to the active power conducted through the converter. The reactive power can be controlled independently with a shift of the fundamental harmonic current IL with respect to voltage UL [9] .

Remark : Inductors connected between the line and the rectifier input bring a current source character of the input circuit and provide the boost feature of the converter [9] .

2.2.2 Mathematical model

DESCRIPTION OF INPUT VOLTAGE AND CURRENT The three phase line voltage and current are

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