Multivoltage level output variable-frequency power source and control method thereof

Abstract

The invention discloses a multivoltage level output variable-frequency power source and a control method thereof. A high-voltage charging circuit is connected with a phase-shifting transformer, which is connected with a frequency converter; and the frequency converter is connected with a contactor. Each phase of the frequency converter of the multivoltage level output variable-frequency power source adopts one basis current conversion chain, wherein the basis current conversion chain comprises a power unit and an electric reactor. A three-phase voltage enters into a phase-shifting input transformer through the high-voltage charging circuit, and supplies power for the power unit of the frequency converter after subjecting to voltage reduction of the phase-shifting input transformer. The power unit outputs a single-phase alternating voltage after subjecting to rectifying, filtering and inverting-inversion; and through changing a switch state of a contactor combination, a series connection way and parallel connection way of each basis current conversion chain are changed, so that outputs of rated capacities of different voltage levels are achieved. By adopting the multivoltage level output variable-frequency power source, the rated capacity outputs of multivoltage levels are achieved, each current conversion chain is connected with a sharing reactor, the parallel connection current-sharing effect is good, the circular current phenomenon generated when the current conversion chains are connected in parallel is avoided, the device and production cost is reduced.

Description

technical field [0001] The invention relates to a variable frequency power supply and a control method thereof, in particular to a variable frequency power supply capable of outputting rated capacities of multiple voltage levels and a control method thereof. Background technique [0002] With the development of frequency conversion speed regulation technology, high-voltage frequency conversion speed regulation technology as a large-capacity transmission has been widely used. Among the various topological structures of high-voltage inverters, the topology of cascaded high-voltage inverters uses several low-voltage variable-frequency power units in series to achieve direct high-voltage output. The high-voltage inverters using this topology have little harmonic pollution to the power grid. With the advantages of high input power factor and good output waveform, it is one of the most widely used forms of variable frequency power supply at present. [0003] In many occasions, hi...

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Problems solved by technology

Although the devices involved in the above documents realize the output of rated capacities of various voltage levels through a series-parallel connection of multiple variable frequency power units, due to the inherent differences in the parameters of the inverter power modules, based on this circuit topology , it is difficult to achieve the same output voltage between different branches through control, and its parallel current sharing effect is completely determined by the consistency characteristics of the system itself, which is likely to cause circulation between different parallel branches, reduce the system output capacity, and increase the system. failure rate

At the same time, as the rated voltage level of the circuit topology decreases, the number of series variable frequency power units in each converter chain decreases continuously, resulting in a continuous decrease in the output level of the frequency converter, which makes the sine degree of the output waveform of the frequency converter worse. Can not meet the requirements of national standards

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