Research On Online Calculation SHEPWM Converter Based On Step Modulation Newton Algorithm

Selective Harmonic Eliminated Pulse Width Modulation(SHEPWM)technology is a pulse width modulation method that eliminates specific low-order harmonics by controlling the switching angle of the inverter output voltage.It usually only controls the fundamental wave amplitude and does not consider the amplitude of each harmonic.To simplify the calculation,the output waveform can be symmetrically processed twice to obtain quarterwave symmetrical SHEPWM technology.The application of SHEPWM technology in the field of multi-frequency point frequency domain information control is not yet widespread.It can simultaneously control the amplitude and phase of multiple harmonics to preset values.In order to achieve precise control of the amplitude and phase of harmonics,it is necessary to abandon the symmetry of the output waveform and adopt half-wave symmetrical SHEPWM technology or full-cycle asymmetrical SHEPWM technology.These two technologies only perform symmetry once or do not perform symmetry on the output waveform.The reduction of the symmetry of the output waveform will cause the SHEPWM mathematical model to become more complex and the solution to become more difficult.At the same time,compared to the SHEPWM equation group that only controls the fundamental wave,the SHEPWM equation group that simultaneously controls the amplitude and phase of multiple harmonics is more difficult to solve.Due to the constraint of the symmetry of the output waveform and the time consumption of the mathematical model solving method,the SHEPWM technology cannot generate the pulse waveform with changing time-frequency domain information in real time,which limits the application range of the SHEPWM technology.In view of the above problems,this paper proposes a mathematical model of full-cycle asymmetrical SHEPWM,which can generate pulse waveforms with arbitrary timefrequency domain information.In addition,a step modulation Newton algorithm is proposed to solve the SHEPWM nonlinear equations.This method has the advantages of low initial value accuracy,fast solution speed and high solution accuracy,and can realize real-time online control of full-cycle asymmetrical SHEPWM technology.The main research contents are as follows :(1)In this paper,the mathematical models of quarter-wave symmetrical SHEPWM method and half-wave symmetrical SHEPWM method are given.Compared with quarterwave symmetrical SHEPWM method and half-wave symmetrical SHEPWM method,the full-cycle asymmetrical SHEPWM method has stronger frequency domain information control ability,which can adjust the amplitude,phase and quantity of each harmonic.(2)In this paper,a step modulation Newton algorithm is proposed.Compared with the traditional Newton iterative algorithm,this algorithm has a wider range of solutions for SHEPWM nonlinear equations.At the same time,according to the characteristics of SHEPWM nonlinear equations and the principle of step modulation Newton algorithm,a simple and convenient initial value selection formula is derived.The algorithm has a wider solution range and a simpler initial value selection method on the basis of maintaining rapidity.(3)In this paper,an online SHEPWM converter is designed based on the step modulation Newton algorithm.The converter adopts the cooperative implementation of the upper computer and the lower computer.The waveform is switched in one cycle,and the function of online calculation of SHEPWM converter is realized.This paper also verifies the converter by simulation and experiment,and analyzes the influence of different switching angles and different frequency points on the solution time and the maximum energy control ratio,which provides a reference for the needs of different scenarios.(4)In this paper,SHEPWM technology is tested and explored in two fields of frequency domain electromagnetic exploration and power filtering,which require multi-frequency point frequency domain information control.The results prove the effectiveness and feasibility of SHEPWM technology in the field of multi-frequency point control.