This thesis addresses an optimal current operation strategy and harmonic
interaction analysis of delta-connected cascaded H-bridge (CHB)
multilevel converter based shunt active power filter (APF). An optimal
current operation strategy for a delta-connected CHB based shunt APF
under non-ideal grid conditions is presented that minimizes the shunt
APF apparent power and satisfies requirements on average power balance,
power factor constraint, source current distortion and imbalance
characteristics in compliance with grid codes. The optimization problem
is formulated using a convex quadratic objective function and non-convex
quadratic constraints and solved by sequential convex programming (SCP).
The presented harmonic interaction analysis is based on the derivation
of a time-invariant model in dq-frame from a time-varying model in
abc-frame. In the derived time-invariant model, the symmetrical
components of each frequency order in the shunt APF variables can be
decoupled while preserving the interaction with other variables. The
harmonic interaction analysis technique is able to predict how harmonics
propagate through the system and quantify the shunt APF variables. The
proposed current strategy and harmonic interaction analysis are
evaluated by simulations in comparison with related approaches from
literature, to demonstrate the effectiveness.
