Method for generating three-phase pulse width modulation (PWM) by adopting quasi-sinusoidal flat modulating wave

Abstract

The invention relates to a method for generating three-phase pulse width modulation (PWM) by adopting a quasi-sinusoidal flat modulating wave, and the method is characterized in that after an optimum modulating wave is formulated, a triangular carrier is modulated by adopting an asymmetric rule sampling method so as to further enhance a maximal output fundamental voltage amplitude, namely, the direct-current voltage utilization rate. The maximal output fundamental voltage amplitude of the three-phase PWM wave which is formed by utilizing the novel modulation wave to modulate the triangular carrier is improved by 19 percent compared with that of a method adopting the sinusoidal pulse width modulation (SPWM) technology and increased by 3.2 percent compared with that of a method adopting the space vector pulse width modulation (SVPWM) technology, and the PWM algorithm is simpler than the SVPWM technology.

Description

technical field [0001] The invention relates to technical fields such as power electronics and DSP, in particular to a method for generating three-phase PWM by using quasi-sine flat-top modulation waves. Background technique [0002] The three-phase PWM technologies commonly used at present are: [0003] 1. SPWM (Sinusoidal PWM sinusoidal pulse width modulation) technology. Among various SPWM technologies, asymmetric regular sampled SPWM (asymmetric regular sampled SPWM) technology has less harmonic content and THD (total harmonic voltage distortion) Low advantage, and widely used. The technical method of asymmetric regular sampling SPWM refers to the sinusoidal modulation wave U in each carrier cycle rm sin ωt is sampled twice, and the sampling points are located at the apex and bottom of the triangular carrier wave respectively, such as figure 1 shown. [0004] figure 1 t in 1 , t 2 =t 1 +T C / 2 is the two sampling moments of the top and bottom points in a carrie...

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Problems solved by technology

[0021] 1. SPWM (Sinusoidal Pulse Width Modulation) technology, the advantage of this technology is that it is simple to calculate the PWM wave in real time, and the harmonic distortion THD of the generated PWM wave is small, but the disadvantage is that the DC voltage utilization rate is low, and its maximum output line voltage is basically The amplitude value is only the DC voltage U d 0.866; 2. SVPWM (Space Voltage Vector Pulse Width Modulation) technology, the advantage of this technology is that it has a higher DC voltage utilization rate, and its maximum output line voltage fundamental wave amplitude reaches the DC voltage value U d , that is, the DC voltage utilization rate is 1, which is 15% higher than that of SPWM technology, and the harmonic distortion THD of the generated PWM wave is better than that of SPWM in some intervals of M (modulation degree), but the disadvantages are also obvious. In real-time calculation During the PWM wave process, the output voltage vector U needs to be determined ref The sector number where it is located makes the calculation method of PWM more complicated than that of SPWM; 3. The third harmonic injection method PWM technology, that is, the third harmonic of an appropriate size is superimposed in the phase voltage sine wave modulation signal

When synthesizing the line voltage, the third harmonic of each phase voltage cancels each other, the line voltage does not contain the third harmonic, but the modulation signal can contain the fundamental wave component with a larger amplitude, and the maximum output line voltage fundamental wave amplitude is correspondingly increased , its DC voltage utilization rate is 15% higher than that of SPWM technology, but the calculation method of PWM is also more complicated than that of SPWM

In addition, there is also SHEPWM (Selective Harmonic Elimination Pulse Width Modulation) technology, which has the advantage of eliminating PWM low-order harmonics that have a large impact on the load, enabling power devices to maximize the elimination of low-order harmonics at lower switching frequencies. The influence of harmonics on motor current and torque, so this technology is of great significance to the application of high-power low-frequency switching device GTO in low switching loss, but its PWM calculation involves solving transcendental equations, which is time-consuming and difficult to use a microprocessor or DSP devices for real-time calculations, so the application of this technology is limited

[0022] In summary, among the various existing three-phase PWM technologies, SPWM technology has the advantages of low THD value and simple calculation method of PWM, but the DC voltage utilization rate is low, only 0.866; SVPWM and third harmonic injection method PWM The DC voltage utilization rate of the technology has been increased to 1, but it still cannot meet the application requirements of further improving the DC voltage utilization rate, and the PWM calculation method is relatively complicated

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