Study On Selected Harmonic Elimination Technique For Medium Frequency Power Inverter Of A Gyroscope

Medium frequency500Hz power inverter is an essential part of aship’s gyroscope power supply unit, which requires stable output voltageand frequency, and high quality of sinusoidal output waveform. To ensurehigh quality of output AC voltage, a power inverter with constant voltageand frequency must be used. The presence of harmonics easily causesharmful torque, which will lead to serious instability of the load and theinverter itself. Thus, in order to better suppress harmonics and get highquality of sinusoidal output voltage, selective harmonic eliminationtechnology is deeply studied in this thesis.Firstly, the principle of PWM waveform generation has beenintroduced, as well as several commonly used PWM inverter technologies:SPWM technology, random PWM technology and selective harmonicelimination PWM technology. The comparison and analysis of thesetechnical characteristics show that the use of selective harmonicelimination PWM technology can reach high voltage utilization, andoptimize the waveform of output voltage with lower switching frequency,which has certain advantages and practicality.Secondly, the mathematical model of selective harmonic eliminationPWM inverter’s output voltage waveform has been built. When usingNewton iterative method for solving a selective harmonic eliminationPWM mathematical model, the initial value of the iteration requires high.So the homotopy algorithm with a wide range and fast convergence hasbeen used to solve this problem. By comparing the switching angles ofnonlinear equations using Newton iteration method and homotopyalgorithm, the superiority of the homotopy algorithm was improved. However, considering the homotopy algorithm is not accurate, a newalgorithm combing Newton iteration method and homotopy algorithm wasproposed.Besides, the single-phase PWM inverter for bipolar selectiveharmonic elimination has been simulated, analysis of its output voltagewaveform and its frequency spectrogram has proved that the use ofhomotopy Newton algorithm, which has a wide range of convergence andfast convergence speed, can quickly and accurately to solve the harmonicelimination inverter model. Taking into account the reduced powerswitching losses and reduce the difficulty of hardware implementation,through the study of the distribution of switching angles, an optimizationof directly narrow pulse judge and omit has been proposed and verified bysimulation. Meanwhile, the harmonic of three-phase inverter using SPWMand selective harmonic elimination PWM has been simulated andcompared.Finally, since SHEPWM inverter has no low-harmonic, the two-stagelow-pass LC filter was used to make the inverter be of a good sine waveoutput, and a design and parameter calculation method of the filter wereproposed.