Bipolar modulation control device of high frequency pulse alternating current link inverter

Abstract

The invention discloses a bipolar modulation control device of a high frequency pulse alternating current link inverter. The bipolar modulation control device comprises a triangle carrier generator I, a comparator I, an inverter I, a subtractor, a grid current closed loop regulator, a triangle carrier generator II, a comparator II, a differential circuit, a delay circuit III, an RS trigger II, an XOR gate circuit, an inverter II, an AND gate circuit I, a delay circuit I, an AND gate circuit II, a delay circuit II, an RS trigger I and a dead zone generation circuit. In the invention, high-quality grid-connected current is obtained by timely adjusting duty ratio b virtue of closed loop feedback power grid current, a phenomenon that the traditional bipolarly modulated high frequency pulse alternating current link inverter distorts when the grid-connected current is at zero moment can be avoided, and the high-quality grid-connected current is obtained. The bipolar modulation control device disclosed by the invention has the advantages of two stages of power conversion, high conversion efficiency, small volume and light weight, overcomes influence of a photovoltaic cell to common mode current produced by parasitic capacitance over the ground and is applicable to a photovoltaic generating grid-connected system.

Description

technical field [0001] The invention relates to a bipolar modulation control device for a high-frequency pulse AC link inverter, and belongs to the technical field of power electronic control. Background technique [0002] Due to the shortage of fossil energy and higher and higher prices, new energy power generation technology has been widely valued by people. The circuit structure of the entire new energy power generation system will have a crucial impact on the weight, volume, cost and efficiency of the system. For power generation systems with DC input such as photovoltaic cells and fuel cells, the usual grid-connected power generation device structures are: ① single-stage non-isolated grid-connected inverter (DC / AC); ② direct-to-direct conversion Converter (DC / DC) + Inverter (DC / AC) + Power Frequency Transformer; ③ High Frequency Isolated Direct-Direct Converter (DC / DC) + Inverter (DC / AC); ④ High Frequency Pulse AC link inverter. The first structure is the simplest an...

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Problems solved by technology

The first structure is the simplest and the cost is the lowest, but the single-stage inverter needs to undertake tasks such as maximum power point tracking and grid-connected current waveform control; and filter design put forward higher requirements; in addition, since the system does not have an isolation transformer, the system has a common-mode current and a DC component of the grid-connected current. Although a corresponding control strategy is proposed for these two problems, due to the Uncertainty of parameters, causing such problems cannot be completely eliminated

The second structure uses a power frequency transformer. Although the electrical isolation between the grid-connected system and the grid is realized, its volume, weight and cost are greatly increased.

[0005] from image 3 It can be seen that although the high-frequency pulse AC link inverter with bipolar modulation obtains high-frequency pulse AC with fixed frequency and fixed width on the primary side of the transformer, the existing bipolar modulation method needs to introduce a filter inductor current pole The detection of polarity, while the filter inductor current changes greatly within a switching cycle, and the polarity will change repeatedly during the process of changing from positive to negative or from negative to positive, and the detection of inductor current is susceptible to electromagnetic interference. Judgment of polarity adds to the difficulty

Therefore, the output voltage waveform of the high-frequency pulse AC link inverter with bipolar modulation is easily distorted during the polarity change of the inductor current, and a large low-order harmonic component is introduced into the grid-connected current.

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