Study On Harmonic Detection And Suppression Methods For Power System

With the development of power electronic technology, more and more nonlinear power electronic devices are used in power system. The non-linearity of these devices would produce much harmonic pollution which will be a great threat to the safe and efficient operation of power systems and devices. So it is necessary to study the harmonic detection and suppression technique to deal with harmonic pollution. Up to now, there have already been many harmonic detection and suppression methods. But most of them are based on the assumption with Gaussian noise or without noise. Thus, the performance of these existing methods would decline significantly due to the effect of impulse noise of the actual power systems, which has large amplitudes suddenly and appears randomly.To remedy this problem, in this thesis, the harmonic detection and suppression methods under impulse noise environment are studied. The main works of this thesis are shown as follows.(1) The existing harmonic detection and suppression methods are first summaried. The basic theory of alpha stable distribution is also introduced and it is adopted for the impulse noise modeling in power systems.(2) A novel harmonic suppression method based on fractional lower order statistics (FLOS) is proposed, which adopts the signal processing tool of alpha stable distribution theory to deal with impulse noise. In this method, the ESPRIT algorithm and recursive least squares (RLS) algorithm are improved by FLOS and used to estimate the fundamental frequency of power signal and the amplitude of each harmonic component, respectively. Then, a harmonic compensation signal is generated by the active power filter based on the estimated parameters, and is used to cancel the impulse noise in power systems. The proposed method has some competitive advantages, such as it can suppress harmonics well even if the impulse noise activating and has a fast tracking ability for changing harmonics. Also, due to the use of self-sensing actuator principle, it can also ensure not to amplify harmonics in case of malfunction. The simulation results show that the proposed method has a better harmonic suppression performance than the existing ones under impulse noise environment. The real experiments also verify the feasibility of the proposed method.(3) Considering that the application of Kalman filter has some limiltations in harmonic detection field, such as Gaussian constraint, a novel harmonic detection method based on particle filter is proposed. In this method, the system model of harmonic detection is first constructed. And then, the system state vector is updated by particle filter. Finally, the harmonic amplitudes and phases are calculated from the updated state vector. Simulation results show that the detection performance of the particle filter-based method is better than the Kalman filter-based ones under impulse noise environment.