Ideal Dual Converter

Ideal Dual Converter

Q. What is ideal dual converter?

Q. What is the essential condition for dual converter?

• An ideal dual converter consists of two ideal full converters.
• The ideal full converters are the ones which produce a pure ripple tree dc voltage at the outputs.

Block Diagram of Ideal Dual Converter :

• The block diagram for an ideal converters shown in Figure A. The converters are replaced by a variable dc voltage source in series with diodes that represent unidirectional current flow.
• The magnitudes of the output voltages and vary as the core of the firing angles of the converters.

Figure A

• The two converters shown in Figure A can be single phase or three phase full converters. We have just considered their equivalent circuits.
• As shown in Figure A the firing angle control common to both the converters. The fining angles of both the converters (α₁ and α₂ respectively) controlled by a common control voltage V_C.
• The firing angles are adjusted in such a way that the output voltages of both the converters are always exactly equal and of same polarity.

Figure B

• Thus both the converters produce the same terminal voltage, one converter operating as a rectifier and the other operating as an inverter.
• The output voltages of the two converter are given by the following equations,

V₀₁ = V_m cos α₁

and V₀₂ = V_m
cos α₂

In an ideal dual converter 

V₀ = V₀₁
= -v₀₂

V_m cos α₁
= – v_m cos α₂

cos α₁
+ cos α₂ = 0

α₁ + α₂
= 180^o

• Thus the control circuit is to be designed in such a way that the sum of the firing angles of the two converters is always 180^o, operating one of the converters as rectifier and the other as an inverter. Figure B shows terminal voltage as a function of firing angle for the two converters.
• In this ideal dual converter, the load terminal voltage is the same as the converter voltages and the current has equal freedom to flow through either converters.

	α1 < 90o, α2  > 90o	α1 > 90o, α2 < 90o
Converter I	Rectifier	Inverter
Converter II	Inverter	Rectifier

• α₁ + α₂ = 180^o  therefore, if α₁ < 90^o  then  α₂  must be greater than 90^o and vice versa. These results are tabulated in above table.