چكيده به لاتين
Abstract:
With the increasing use of adjustable speed drives, arc furnace, controlled and uncontrolled rectifiers, and other nonlinear loads, the power distribution system is polluted with harmonics. Harmonic suppression is an important and challenging issue in electrical power systems and can be resolved by using hybrid active power filters with injection circuit (IHAPFs). In existing IHAPF systems, however, it is usually assumed that all parameters are determined accurately and unchanged over time, which is not true in real situations. It is well known that variations of system parameters may seriously degrade the performance of IHAPF systems.
The structure of this thesis is organised as follows; In the second chapter different topologies of hybrid active power filter and types of controllers had been introduced and compared together. In the third chapter an adaptive fuzzy dividing frequency-control method composed of a generalized PI control unit and fuzzy adjustor unit was proposed. In This control scheme, the generalized PI control unit is used to achieve dividing frequency control; the fuzzy adjustor unit is used to adjusted parameters of the PI control unit to produce better adaptive ability and dynamic response. Simulation results have shown that the new dividing frequency-control method is not only easy to be calculated and implemented, but also very effective in reducing harmonics when parameters are unchanged over time.
In the four chapter, a novel online control method with time-delay compensation is presented for IHAPF; it consists of two closed-control loops. The lower closed-control loop consists of a conventional proportional-integral (PI) controller and IHAPF designed with time-delay compensation, whereas the upper closed-control loop is composed of predictive neural network model, GPC criterion, PI controller and HAPF with Injection Circuit model. Simulation results have shown that the new control method is very effective in reducing harmonics when parameters are unchanged over time. Simulations Results have shown that the adjusting time of applying the neural method is shorter than the time of using fuzzy control method, but the fuzzy controller has a better steady state performance compared with neural controller.
To obtain both efficiency and robustness, this thesis proposes a novel method for the generalised controller design of a three-phase IHAPF system which can deal with deviations of system parameters. More specifically, the proposed control strategy, a combination of the conventional PI controller and the spatial repetitive controller (SRC), along with a generalised algorithm for determining optimal values of control coefficients are presented. Simulation results are provided to validate the correctness and effectiveness of the proposed method.
Keywords: hybrid active power filter, PI controller, fundamental resonance circuit, passive power filters.
