Study On Harmonic Detecting And Control Method Of Digital Active Power Filter

As harmonic contamination is increasingly severe, the introduction of active power filter (APF) is an important development trend. The analog control method of APF is not flexible and the precision is not perfect. With the rapid development of low price and high performance DSP technology, digital control method is replacing the traditional anolog control method, so this dissertation mainly researches how the DSP can be used in APF.Firstly, some novel harmonic detecting methods based on instantaneous reactive power (IRP) theory are introduced in this dissertation. And emphases are placed on basic principles, advantages and disadvantages of different methods. Then, a novel harmonic detection method which suits DSP well is introduced. It roots from average power theory and energy balance theory. The control functions used in single phase circuit, three-phase three-wire circuit and three-phase four-wire circuit are developed with this method. It is simple, intuitionistic and universal. The detection delay and the distortion of voltage waveforms influence the compensating results slightly, and the reactive power of the circuit can be compensated as required.Secondly, a source program of DSP is written out in C and compile language based on the new method mentioned above. It takes full advantage of the TMS320LF240 DSP and its all-purpose interrupts. The APF is controlled in full digital way. And the program can build sine table automatically. With the program, the tasks such as A/D transformation, order current calculation, capturing the cross-zero points of voltage, exporting PWM waveforms, D/A transformation and so on all can be implemented. The program is tested on experimental board successfully and all the tasks are finished perfectly as well.Moreover, in order to satisfy the demand of DSP control, an A/D interface circuit is designed to upgrade and magnify the import signals. A signal source circuit is designed to test the A/D circuits. And a cross-zero compared circuit is built to capture the cross-zero points of voltage. All the circuits mentioned above are realized and tested successfully.