Harmonics in systems are conventionally suppressed using passive tuned filters, which have
practical limitations in terms of the overall cost, size and performance, and these are
particularly unsatisfactory when large number of harmonics are involved
Active power filtering is an alternative approach in which the filter injects suitable
compensation currents to cancel the harmonic currents, usually through the use of power
electronic converters. This type of filter does not exhibit the drawbacks normally associated
with its passive counterpart, and a large number of harmonics can be compensated by a single
unit without incurring additional cost or performance degradation.
This thesis investigates an active power filter configuration incorporating instantaneous
reactive power theory to calculate the compensation currents. Since the original equations for
determining the reference compensation currents are defined in two imaginary phases,
considerable computation time is necessary to transform them from the real three-phase values.
The novel approach described in the thesis minimises the required computation time by
calculating the equations directly in terms of the phase values i. e. three-phase currents and
voltages. Furthermore, by utilising a sufficiently fast digital signal processor ( DSP ) to
perform the calculation, real-time compensation can be achieved with greater accuracy.
The results obtained show that the proposed approach leads to further harmonic suppression
in both the current and voltage waveforms compared to the original approach, due to
considerable reduction in the computation time of the reference compensation currents.
A Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University.