Research On Selective Harmonic Detection Algorithm And Mitigation Technology Of Active Power Filter

Power electronics, which is widely used in industrial application, on one hand,plays an important role in energy conversion field and industrial control field, on theother hand, leads to the serious power quality problems, such as harmonic pollution andvoltage fluctuation. As a generally accepted device to suppress harmonic current, APF(Active Power Filter) is being paid close attention to power quality improvement bydomestic and international scholars.In this dissertation, the cause and the negative effect of harmonic current, theharmonic current standards, and the ways to suppress harmonic current are presented,and then the development of APF technology is also summarized. The advantages anddisadvantages of APF based on different topologies are derived from a comparison ofdifferent operating principles. This dissertation also builds mathematical models forAPF at abc three-phase frame and αβ two-phase frame and dq synchronous rotatingframe. Based on these mathematical models, the design principles of the main parts ofAPF are proposed.Harmonic detection algorithm is a key part of APF. The instantaneous reactivepower theory is introduced in this dissertation to explain the instantaneous energytransmission in detail. Based on this important theory, the internal instantaneous energytransmission in APF applied fundamental current extraction algorithm and harmoniccurrent extraction algorithm is studied. This result presents that fundamental currentextraction algorithm makes a serious effect to DC link voltage, but harmonic currentextraction algorithm doesn’t. In order to solve these common problems in harmonicdetection algorithm, the design principles of the DPLL (Digital Phase Locked Loop) andthe DLPF (Digital Low Pass Filter) are also proposed.In order to improve the compensation ability of APF, the selective harmoniccurrent control strategy is proposed based on traditional double closed-loop controlstrategy. The principle of selective harmonic current control strategy is introduced at abcthree-phase frame and αβ two-phase frame and dq synchronous rotating frame in thisdissertation. The design principles of the selective harmonic current regulator indifferent coordinates are also discussed. The internal relations of these selective harmonic current strategies are analyzed to derive the general advantages anddisadvantages among those strategies. The influence between DC link voltage and thecompensation ability of APF is also researched to direct an effective DC link voltagecontrol strategy.Finally, the design scheme of APF prototype is presented to discuss the schematicand the function of the discrete modules of this prototype. A number of studies ondiscrete modules, SVPWM modulation strategy, reactive current compensation controlstrategy, selective harmonic current control strategy are presented through the prototypein this dissertation. These theories and control strategies in this dissertation are verifiedby experimental wave forms and data reports.