Method and apparatus for controlling voltage of flying capacitor in multilevel inverter circuit

Abstract

The embodiment of the invention discloses a method and an apparatus for controlling the voltage of a flying capacitor in a multilevel inverter circuit. The method includes: obtaining the voltage value PV of an input terminal of a primary capacitor inversion unit; and controlling the actual voltage value of a first flying capacitor in at least one level switching unit to be the sum of a preset stable voltage value of the first flying capacitor and a bias voltage value if the voltage value PV of the input terminal is greater than a preset voltage value FV. According to the technical scheme, after the stable voltage of the first flying capacitor of the level switching unit is increased, the stress of switch tubes in a multilevel inverter is reduced, and type selection approaches of the switch tubes are increased.

Description

technical field [0001] Embodiments of the present invention relate to power electronics technology, and in particular to a method and device for controlling the voltage of a floating capacitor in a multilevel inverter circuit. Background technique [0002] The multi-level inverter circuit has the advantages of small output harmonics, fast dynamic response, wide transmission frequency bandwidth, good electromagnetic compatibility, light weight, small size and high efficiency, and is more and more valued by the photovoltaic industry, so that multi-level Inverters are widely used in medium-voltage and large-capacity applications. Such as figure 1 As shown, it is a schematic structural diagram of a multi-level inverter circuit in the prior art, the multi-level inverter circuit includes a primary capacitor inverter unit 11, and cascaded m level switching units 12, m is an integer greater than or equal to 1, wherein the input terminal of the primary capacitor inverter unit 11 is...

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Problems solved by technology

[0004] In the above inverter circuit, the voltage of the first floating capacitor needs to reach a certain value and remain stable during operation. For example, for the first level switching unit 12, the voltage value of the first floating capacitor C1 can be maintained at PV / 4 , where the voltage between the two terminals of PV is the DC power supply voltage value input to the primary capacitor inverter unit 11, at this time, as figure 1 As shown, if the switch tube in the primary capacitor inverter unit 11 is controlled so that the potentials between the two terminals of AP are equal, the voltage between the two terminals of BN is the voltage between the two terminals of the entire PV minus the first floating capacitor C1 The voltage at both ends, that is, 3PV / 4, if the voltage between the two terminals of PV is high, the switching tube set in the primary capacitor inverter unit 11 between the two terminals of NB needs to withstand a large voltage drop; similarly, if BN The voltage between the two terminals is equal, then the voltage between the two terminals of the AP is the voltage between the two terminals of the entire PV minus the voltage of the first floating capacitor C1, that is, 3PV / 4. If the voltage between the two terminals of the PV is higher, Then, the switch tube installed in the primary capacitor inverter unit 11 between the two terminals of the AP bears a large voltage drop, and the large voltage drop will increase the stress of the switch tube, which is not convenient for the selection of the switch tube.

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