The Research And Realization On Digital Asymmetric Sine Inverter With Adjustable Frequency And Amplitude

The power supply used for microarc oxidation plays a decisive role in theprocess of Microarc oxidation and the performance of ceramic layer. But there arelittle literatures on the asymmetric sine inverter, and there is no power supply thatcan be used in industrial areas. Based on this background, an asymmetric sineinverter with adjustable frequency and amplitude is studied in this paper. The inverteris controlled by digital theory, and it’s power is up to2.6kW which meets the generalrequirements of Microarc oxidation process.Considering the zero crossing oscillation of this inverter, the detainedtheoretical analysis and the impact of power parameters and dead time on theoscillation are given. Through the MATLAB simulation, the conclusion is verified.To control by DSP, the paper deduced math formula of generating SPWMsignals based on two-dot asymmetry regular sampling method, based on that themethod of adjusting frequency and amplitude is realized. For the phenomenon ofphase mutation in the process of changing frequency, a detailed analysis is given, andthe method of solution using software is proposed. The simulation results verify thatthis method can effectively restrain the voltage and current surge.By means of Fourier analysis, the harmonic component and characteristic of theasymmetric sine wave are obtained. It contains not only fundamental wave, but alsoDC component and even harmonic components, and the higher degree of asymmetrythe more DC component and even harmonic components. Based on this, the LC filteris designed. In the paper, digital control is adopted to realize the overall functions.TMS320F28335DSP is selected as the control chip and the corresponding circuits aredesigned. From it, four SPWM drive signals are acquired and a digital closed-loop isrealized. Details of parameter design are given in the paper. Through theMATLAB simulation, the conclusion is made that appropriate parameters caneffectively suppress the zero crossing oscillation.On the basis of theoretical analysis and simulation results, an experimentalplatform was built and the closed-loop control scheme is programed for open-loopand closed-loop. The experimental results indicate that the inverter suppresses thezero crossing oscillation and phase mutation very well, and verify the validity of the theoretical analysis.