Harmonic Elimination Algorithm And Its Application In Multi-level Invert

With the rapid development of power electronics technology, the PWM inverter is widely used in AC drive system, high voltage and high frequency applications. However, as the efficiency of the inverter waveform quality have become increasingly demanding, the hazards of the harmonics generated by the inverter to the grid and electrical equipment have been paid gradually attention. Selective harmonic elimination PWM (SHEPWM) technology enables the elimination of harmonics, the control of the fundamental component in the output waveform. Thesis focused on the study of SHEPWM techniques.The mathematical model of SHEPWM technology is a set of nonlinear equations. Solving equations is to focus on the content of thesis. Thesis has derived the iterative formula of Newton iteration method and homotopy algorithm to solve nonlinear equations for SHEPWM nonlinear equations, and found that the different initial value of iteration formula has great impact on convergence rate of using Newton iterative method to solve the nonlinear equations, while the homotopy convergence rate has little effect, but the homotopy algorithm of computing time is longer, the overall convergence speed is slow, and iteration precision is very low.For the different initial value of iteration formula has great impact on convergence rate of using Newton iterative method to solve the nonlinear equations, thesis has further studied the method of obtaining initial for numerical solution of nonlinear equations. Used empirical formula method, the SPWM method and the Cg-superposition SPWM method to respectively to obtain the initial sequence in the same condition, and is applied in the Newton iterative method to solving nonlinear equations. The results showed that the initial value calculated using Cg-superposition SPWM method can better the iterative convergence.Based on MATLAB to build diode clamped SPWM and SHEPWM three-level inverter simulation platform, the focus of the initial sequence of heavy legal calculated using Newton’s iterative method for solving nonlinear equations, numerical solutions obtained by the use of harmonic elimination algorithm in SHEPWM as switching angle control pulse sequence generation SHEPWM sequence. Simulation results show that: SHEPWM method under the control of the output waveform harmonic content is lower than levels under control SPWM output harmonic method, that is, under the same primary circuit, input voltage, switching frequency, load conditions, SHEPWM in harmonic suppression better than SPWM.Calculated the initial sequence using Cg-superposition SPWM method in the SHEPWM harmonic elimination algorithm, and used Newton iterative method for solve nonlinear equations. The obtained numerical solution is as switch angle sequence to produce SHEPWM pulse sequence. The simulation results show that:The harmonic content of the output waveform under the control of the SHEPWM method is lower than that under the control of the SPWM method, that is, under the same main circuit, input voltage, switch frequency, load conditions, SHEPWM in harmonic suppression better than SPWM.