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Explain single phase half wave converter drive for separately excited DC motor?

Mumbai University > Electronics Engineering > Sem7 > Power Electronics 2

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A separately excited dc motor, fed through single phase half wave converter, is shown in Figure (a) Motor field circuit is fed through a single phase semi converter in order to reduce the ripple content in the field circuit. Single phase half wave converter feeding a dc motor offers one quadrant drive, Figure (b)

  1. The waveforms for source voltage Vs , armature terminal voltage Vt , armature current ia , source current is and freewheeling diode current ifd are sketched in Fig (c) . Note that thyristor current iT=is . The armature current is assumed ripple free.

  2. For single phase half wave converter , average output voltage of converter, Vo = armature terminal voltage, Vt

    V0=Vt=Vm2π(1+cosα1)for   0<α1<π

    Where Vm = maximum value of source voltage

  3. For single phase semi converter in the field circuit, the average output voltage is given as Vf

    Vf=Vmπ(1+cosα2)for   0<α2<π

  4. It is seen from the waveforms of fig 12.7 (c) that

    rms value of armature current, Iar=Ia

    rms value of source or thyristor current

Iαt=I2απα2π=Iα(πα2π)1/2

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Fig. Single phase half-wave converter drive (a)circuit diagram (b) quadrant diagram and (c) waveforms

5) rms value of freewheeling diode current,

Ifdr=I2απ+α2π=Iα(π+α2π)1/2

6) Apparent input power = ( rms source voltage)*(rms source current) =VsIsr

7) Power delivered to motor = EaIa+I2ara=(Ea+Iara)Ia=VtIa

8) Input supply pf = pf=EaIa+I2araVa.Isr=Vt.IaVa.Isr

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