Hybrid carrier phase shift modulation method for hybrid cascaded H-bridge multi-level inverter

Abstract

The invention relates to a hybrid carrier phase shift modulation method for a hybrid cascaded H-bridge multi-level inverter, which comprises the steps of (1) modulating all high-voltage units by usinga step wave modulation method so as to enable all high-voltage units to operate at the fundamental frequency and enable th inverter to output more levels; and (2) carrying out pulse width modulationon all low-voltage units based on the carrier phase shift modulation method so as to enable the inverter to obtain frequency doubling properties and improve the output voltage waveform quality. The hybrid carrier phase shift modulation method not only can enable the high and low-voltage units to output voltage with the same polarity and effectively eliminate the problem of current backward flow, but also can enable the low-voltage units to operate at a high-frequency PWM state and improve the waveform quality of the output voltage of the inverter; and the hybrid carrier phase shift modulationmethod can further be described by a unified mathematical model so as to reduce the design difficulty of the modulation method when the number of the cascaded units increases.

Description

technical field [0001] The invention relates to the technical field of cascaded multilevel inverters, in particular to a hybrid carrier phase-shift modulation method applied to a hybrid cascaded H-bridge multilevel inverter. Background technique [0002] Cascaded multilevel inverters are widely used in power industries such as high-voltage and high-power transmission systems and photovoltaic power generation systems due to their advantages such as small switching voltage stress, large number of output levels, and high waveform quality. Multi-level inverters can be divided into three types: diode clamp type, flying capacitor type and cascaded H bridge type. Among them, diode clamp type and flying capacitor type generally require capacitor voltage balance control, while cascaded H bridge Type does not need capacitor voltage balance control, so the cascaded H-bridge inverter has been more extensively researched and applied. The cascaded H-bridge multi-level inverter can be div...

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Problems solved by technology

[0004] However, when the above-mentioned mixed carrier stacking methods based on carrier stacking modulation are applied to the occasion of hybrid cascaded H bridges with more than three units, the modulation methods designed to eliminate the problem of current backfeeding and improve the quality of the output voltage all have three shortcomings: First, multiple high-voltage units must work at high frequencies; second, this type of inverter loses the frequency doubling characteristics of the cascaded H-bridge topology; third, with the increase in the number of cascaded units, the design of the modulation method is difficult will increase sharply, thus limiting the increase in the number of hybrid cascaded H-bridge inverter units

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