Parallel inverter

PARALLEL INVERTER

Parallel Inverters are those Inverters in which commutating components are connected parallel with the load. Circuit Detail: Parallel inverter circuit is shown in the figure A, which is consists of two SCRs T1 and T2, an inductor L, an output transformer and a commutating capacitor C. The function of L is to make the source current constant. During the working of this inverter, capacitor C comes in parallel with the load via the transformer. So it is called a parallel inverter. The turns ratio of half primary winding and secondary winding is kept unity.

Mode 1

I. When the SCR T1 is triggered, it will turned on and the current flows through the path as shown in figure 'B' of the above circuit Vdc (+)-L-c-a-SCR T1 - Vdc(-).

II. This will generate flux and resulting EMF in the Transformer Primary Winding ac and bc.

III. Due to this induced EMF., the capacitor will charge up to + 2Vdc voltage.

IV. As there is equal turns ratio between half primary and secondary winding, the same 2Vdc EMF will be induced in the secondary of transformer secondary and this EMF will result flow of current through load.

Mode 2

I. When the SCR T2 is triggered, it will be turned ON and the SCR T1 will be turned OFF due to capacitor reverse voltage 2Vdc applied across it.

II. As the SCR T2 is turned ON, the load current flows through path 'C' of the above circuit Vdc(+)- L-c-b- SCR T2 - Vdc(-) and capacitor will be discharged through SCR T2.

III. This will generate flux and resulting EMF. in the transformer primary winding bc and ac.

IV. The capacitor will again charged with opposite polarity upto (-2Vdc)

V. During this interval of time, the current will flow in reverse direction as that of when SCR T1 was turned ON.

VI. Similarly, again the SCR T1 will be turned ON when it triggered and SCR T2 will be in OFF condition during this interval and this process repeated again and again.

VII. Due to alternately switching of SCR T1 and SCR T2, the output voltage become rectangular.

Advantages of Parallel Inverter:

I. It is Simple forced commutation circuit.

II. It can give Sinusoidal waveform at output by using suitable filter circuit.

Disadvantages of Parallel Inverter:

I. The parallel inverter is useful only when load is fixed.

II. The parallel inverter does not useful for higher power for fixed value of inductor L and capacitor C.

III. The design of inverter for fixed voltage is possible.