Flying capacitor hybrid three-level DC-AC (Direct Current-Alternating Current) inverter and control method thereof

Abstract

The invention relates to a flying capacitor hybrid three-level DC-AC (Direct Current-Alternating Current) inverter and a control method thereof. The inverter comprises a bridge circuit, wherein the left half bridge of the bridge circuit is provided with a first switching element, a second switching element, a third switching element and a fourth switching element which are connected in series, the right half bridge of the bridge circuit is provided with a fifth switching element and a sixth switching element which are connected in series, a flying grading capacitor CBLK is connected between the series point of the first switching element S1 and the second switching element S2 and the series point of the third switching element S3 and the fourth switching element S4, and the output ends of the bridge circuit are connected with an output transformer T1. Because the control method for the flying capacitor hybrid three-level DC-AC inverter adopts 180-degree phase-staggered carrier control and can output frequency-multiplied SPWM (Sinusoidal Pulse Width Modulation) signals, under the condition that the output harmonic quality is met, the switching frequency can be decreased, and thereby the circuit loss can be reduced.

Description

technical field [0001] The invention relates to a three-level DC-AC inverter, in particular to a floating capacitor hybrid three-level DC-AC inverter and a control method thereof, which are mainly used in switching power supplies, photovoltaic grid-connected devices, and the like. Background technique [0002] In recent years, three-level conversion has become a hot spot in the application of DC-AC inverters, mainly because compared with two-level conversion, the voltage stress of the switching device on each bridge arm is half of the input voltage of the DC side , so that the withstand voltage of the switching device can be reduced by half, thereby reducing the loss of the switching device. At the same time, at the same carrier frequency, the harmonic component of the line voltage of the three-level inverter device is much smaller than that of the two-level inverter. Therefore, under the requirement of the same output waveform quality, the switching frequency of the three-l...

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Problems solved by technology

In the design of a three-level inverter, switching frequency and switching loss are a pair of contradictions. Increasing the switching frequency can obtain a higher carrier frequency, thereby obtaining better output waveform quality (the higher the carrier frequency, the easier filter, so as to obtain a better power frequency sine wave waveform), however, increasing the switching frequency will bring greater switching loss and reduce the transmission efficiency of the inverter, especially when the inverter is used in a photovoltaic grid-connected device , it is particularly important to reduce the loss of the inverter and improve its transmission efficiency. Therefore, how to minimize the loss of the inverter under the condition that the output waveform harmonic quality meets the standard is the goal that people have been pursuing.

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