| With the worldwide applications of power electronic equipments which are used as thenonlinear and time-variant load of the power system, the harmonics produced by themmake power system suffer from severe pollution; the APF which is considered as effectiveequipments to restrain harmonics is widely being researched and applied.Based on the former research of APF, this article sum up the current researching statesand technical keys, and propose a new-type parallel active filtering method, i.e. usingcomposite APF. The composite APF is connected in parallel with harmonic source, controlthe output voltage of a inverter to follow the composite command voltage which is consistof fundamental voltage component of the connecting point and the grid harmonic currentcomponents, filter the high order harmonics and then inject it into the grid. When thecomposite command voltage satisfy a certain condition, APF exhibit low impedance whichis almost zero to harmonic current, therefore dredge the harmonics flow to the APFbranches. Simultaneously, it exhibits a variable reactor to fundamental current so as tocompensate reactive power.The control system of the composite APF is consist of grid harmonic currentcomponents and fundamental voltage component detecting links, DC bus voltagecontrolling link, composite command voltage compounding link, PWM controlling link anddriven circuit. The way to realize these links is analyzed and discussed in details and thecontrol algorithm and some main circuit parameters are emulated in PSIM. The rationalityof this composite control algorithm is proved by the emulation results.In order to put this composite control algorithm into practical application, a digitalcontrolled prototype based on DSP chip TMS320F2812is designed. The software of thecontrol algorithm is programmed and debugged in CCS3.3. The harmonics compensatingexperiment is also conducted. The feasibility of this hybrid APF is proved by the results. |
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