Higher pulse number converters
Higher pulse number converters:
Fig: Higher pulse number converters (a) series connection (b) parallel connection (c) Transformer connection
- For Parallel connection the inductance in between the converters has been included to limit circulating harmonic current. In both these figures CONV – I and CONV – II have identical construction and are also fired at the same firing angle α. Their input supplies also have same magnitude but displaced in phase by an angle φ.
- For series connection,
- Now if cos 3Kφ = 0 for some K then the corresponding harmonic disappear from the fourier series expression of v0.
- In particular if φ = 30° then cos 3Kφ = 0 for K = 1, 2, 3, 5…….
This phase difference can be obtained by the arrangement in the transformer connection.
- The frequency of the harmonics present in the output voltage has the form
12ω, 24ω, 36ω………..
Similarly it can be shown that the input side line current iABC have harmonic frequency of the form
11ω, 13ω, 23ω, 25ω, 35ω, 37ω, ………….
Which is the characteristic of a 12 pulse converter.