Circuit apparatus for transformerless conversion of an electric direct voltage into an alternating voltage

Abstract

In a circuit apparatus for transformerless conversion of an electric direct voltage of a two-pole direct voltage source (1) connected to ground having a first voltage pole (+) and a second voltage pole (−) into an alternating voltage, hazardous capacitive leakage currents are avoided by connecting the direct voltage source (1) to ground and the DC-AC converter (400) is operated at a controlled intermediate circuit voltage, a DC-DC converter stage (300) being connected between the direct voltage source (1) and the DC-AC converter (400), said DC-DC converter stage providing at its output a + / − voltage that is symmetrical with respect to the grounding point, two series-connected capacitors (41, 42) having the same polarity and being connected to ground at their connecting point (V) and controlled are charged by two buck-boost choppers (100, 200) connected one behind the other.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application claims Priority from European Application Nos. EP 07005140.4 filed on 13 Mar. 2007 and EP 078001035.8 filed on 21 Jan. 2008FIELD OF THE INVENTION[0002]The invention relates in particular to a circuit apparatus for transformerless conversion of an electric direct voltage, e.g., from a solar generator, into an alternating voltage for feeding into a grid, dangerous capacitive leakage currents being prevented from occurring by connecting the direct voltage source to ground. Direct voltage sources such as solar generators, fuel cells, batteries and the like often have a strongly varying voltage and high inner impedance. In order to feed electric energy from such sources into a grid, a matching device is needed. For converting direct voltage supplied for example by a solar generator into alternating voltage, solar inverters are known. It is known to feed electric energy into a grid, which may be a utility grid or an island netw...

AI Technical Summary

Benefits of technology

This patent describes a DC-AC converter that uses semiconductor switches that are timed according to control, which results in higher efficiency. The switches are designed for a specific operating point, reducing power loss and leakage currents. The converter is particularly useful in solar plants, where it compensates for changes in grid voltage and ensures efficient power conversion. It is transformerless, which makes it more efficient and cost-effective. The invention also provides a high-efficiency inverter that can feed directly into the grid, regardless of the voltage level. The inverter is designed to handle varying direct voltage from a solar generator and avoids hazardous leaks of capacitive leakage currents. The invention also includes a DC-DC converter that allows for independent control of two capacitors, providing high touch protection and high efficiency. Additionally, the invention compensates for grid voltage fluctuations to ensure stable power conversion.

Problems solved by technology

The disadvantage of this circuit is that the reference ground potential of a solar generator that is not connected to ground changes dynamically with the timing pulses of the inverter.

These leakage currents constitute a hazard for humans touching the solar generator on the one side; on the other side, damages may occur to the solar generator itself.

As a result, the solar generator is uncoupled from the alternating voltage side.

A disadvantage however is that the solar generator has no defined relation to a ground potential.

For, as a matter of principle, it is not possible to connect the generator to ground.

Although in this solution hazardous leakage currents are prevented from occurring by connecting the solar generator to ground, the buck-boost chopper does not allow for a fixed point of operation for the DC-AC converter but only for the charging of the second half-bridge capacitor.

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