Research of Harmonic Detection Methods in APF
|School||Beijing University of Chemical Technology|
|Course||Detection Technology and Automation|
|Keywords||harmonic detection instantaneous reactive power MATLAB simulation APF low-pass filters|
With the rapid development of modern industry and widespread application of power electronic devices,which leads to more and more serious pollution to power network for their non-linear feature and diversity Harmonic pollution has a serious negative impact on the power quality and the normal operation of various electrical equipments.Real-time and accurate detection of harmonic quantity on power network is very necessary for preventing the harmonic harm and protecting safe operation of power network. The active power filter(APF) can overcome the limitations of the passive filter.It also can precisely track and compensate the harmonics.Furthermore, it’s performance doesn’t depend on the system characteristics,so more and more concern is put on the APF in the last few years.This paper researched on harmonic current detection methods in APF.The main contents are as follows:Firstly,the basic principles of harmonics,present situation and development trend of the active power filter were studied.Harmonic detection methods and the control methods in APF were introduced.Secondly,the categories of APF were introduced,the instantaneous reactive power theory was analyzed among which the principle of Shunt APF were analysed.Then instantaneous reactive power theory based p-q harmonic current calculation mode and i_p-i_q harmonic current calculation mode were studied.And they focused on the impact of low-pass filter on accuracy and speed of the harmonic current detection.A reasonable range of cut-off frequency was made theoretically.And at the same time,the wavelet analysis theory in harmonic detection was studied as a representative of new harmonic detection methods.Thirdly,a harmonic detection model was established with a three-phase thyristor based rectifier circuit of resistive and inductive load as its harmonic source in MATLAB/Simulink according to i_p-i_q harmonic current calculation mode in different firing angles.The simulation were carried focused on the impact of low-pass filters on accuracy and speed of harmonic detection and the results verified the cut-off frequency.The order and cut-off frequency of low-pass filters were chosen based on the simulation in different firing angles. At the same time,harmonic detection methods based on Wavelet analysis theory were simulated and results with different wavelet decompositions analyzed.The application scope,advantages and disadvantages of the two methods were discussed.Fourthly,the simulation of the control system of harmonic compensation in active power filter were carried.The result of the simulation further validate the validity of i_p-i_q harmonic current calculation method.Finally,hardware circuit for harmonic detection system was designed with TMS320F2812DSP as the core on the basis of theory analysis and simulation research.Hardware circuit for harmonic detection system was designed,including signal acquisition circuit,generation circuit for square waveform signal and signal conditioning circuit.The software for harmonic detection system was also designed.