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P a g e
The circuit of a Single-phase Current Source Inverter (CSI) is shown in Fig. 5.35.
The type of operation is
termed as Auto-Sequential Commutated Inverter (ASCI). A constant current source is assumed here,
which may be realized by using an inductance of suitable value, which must be high, in series with the
current limited dc voltage source.
The thyristor pairs, Th1 & Th3, and Th2 & Th4, are alternatively turned
ON
to obtain a nearly square wave current waveform. Two commutating capacitors − C1 in the
upper
half, and C2 in the lower half, are used. Four diodes, D1
–
D4 are connected in series with each thyristor to
prevent the commutating capacitors from discharging into the load. The output frequency of the inverter
is controlled in the usual way, i.e., by varying the half time period, (T/2), at which the thyristors in pair
are triggered by pulses being fed to the respective gates by the control circuit, to turn them ON, as can be
observed from the waveforms (Fig. 5.36). The inductance (L) is
taken as the load in this case, the
reason(s) for which need not be stated, being well known. The operation is explained by two modes.
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