Research On Fault-tolerant Operation With Three-Phase Three-Wire Shunt Active Power Filter

With the rapid development of science and technology,more and more power electronic converter and nonlinear loads have been connected to the electric power grid,which have incurred harmonic pollution of the grid.The APF(Active Power Filter),as a new electronic device,has been widely applied in the harmonic compensation of electric power grid because of its good performances.The traditional three-phase APF control system is designed under the condition of positive sequence,and if the grid is under other conditions,the APF system will fail to compensate the harmonic.This study is mainly using active power filter to detect the voltage phase sequence of the grid and the loss phase.This these is also devoting to studying a phase sequence adaptive control strategy and loss phase control strategy,to ensure the APF can compensate harmonic under different power grid failure types,and power distribution system can meet the power quality standards after the compensation.Studying the detection of voltage phase sequence,phase sequence adaptive control strategy and loss phase control strategy is really valuable.First part of this these introduces the generation and the hazard of harmonic as well as power quality standards of domestic and international.Briefly introduces of several methods of harnessing harmonics as well as their advantages and disadvantages was also described.In addition,the paper briefly introduces the classification of active power filter and its working principle.Next the mathematical model and its decoupling method of three-phase three-wire active power filter are introduced.Synchronous rotating coordinate transformation method and recursive discrete Fourier transform algorithm is studied to realize the load harmonic current extraction.A PI and repetitive composite controller is studied to achieve harmonic current static error tracking.Finally,the whole control system of active power filter to compensate the harmonic comes out.In order to enable APF to adapt to the phase sequence,it is necessary to accurately detect the phase sequence.The effects of positive and negative phase sequences on APF are analyzed.Then the d-axis component of the three-phase voltage is deduced by synchronous rotating coordinate transformation.The phase sequence detection method now shows up through synchronous rotation coordinate transformation and sliding window filter.After the simulated research,the phase sequence detection method is proven to be not only useful for detecting the voltage phase sequence but also for loss phase.Basing on the results of phase sequence detection,the phase sequence adaptive control strategy of three-phase APF realized by DSP is designed.The simulation and experiment are carried out.Regardless of the phase sequence of the grid voltage,APF controlled by phase sequence adaptive strategy is able to make the grid current and PCC voltage harmonic meeting the power quality standard after its compensation.The practical mathematical model and the load current characteristics of loss phase system turn out to also be key parts of the systematic design.At this time,the load-side current harmonics comprising zero sequence component.APF is actually a single-phase full-bridge inverter.Then the control system of APF for loss phase condition is designed basing on single phase space vector modulation.At last,experimental validation of this system is undergone in the Matlab/Simulink simulation model and a parallel three-phase three-wire system active power filter and the correctness of the correlation analysis and the control strategy is proved,verifying that the phase sequence adaptive control system can accurately detect the phase sequence of the three-phase power grid and the APF can actively adapt itself to current phase sequence and compensate the harmonic.It is also proved that the APF under the condition of one phase loss can also compensate harmonics to meet the power quality standards.This job will broaden the engineering applications of and facilitate the promotion of the three-phase three-wire active power filter.