Subject : Power Electronics
Unit : AC to DC Converters
Input current and its fundamental component of a fully controlled bridge rectifier
Input current and its fundamental components:
- By observing the voltage waveforms we can conclude that the current waveform is also periodic over an interval π, so finding out an expressions for i_{0} over an interval of length π will be sufficient.
- Therefore, in the interval α ≤ ωt ≤ π α,
- Now at steady statei_{0}|_{ωt = α} = i_{0}|_{ωt = π α} since i_{0} is periodic over the interval α ≤ ωt ≤ π α. Using this boundary condition we get:
- The input current displacement factor defined as the cosine of the angle between input voltage (v_{i}) and the fundamental component of input current (i_{i1}) waveforms is cosα (lagging).
We can get,
- The i/p current distortion factor is
- The i/p power factor is
- The rectifier appears as a lagging power factor load to the input ac system. Larger the ‘α’ poorer is the power factor.
- The input current i_{i }also contain significant amount of harmonic current (3^{rd}, 5^{th}, etc) and therefore appears as a harmonic source to the utility.