Single-phase Current Source Inverter
Single – phase current source Inverter:
Fig: Voltage and current waveforms Fig: Single phase current source inverter (CSI) of ASCI type
- The circuit of a Single-phase Current Source Inverter (CSI) is shown. 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.
- 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.
- MODE 1 operation
- MODE 2 operation