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METHOD FOR INVERTER CROWBAR AND USE THEREOF

IP.com Disclosure Number: IPCOM000243477D
Publication Date: 2015-Sep-24
Document File: 3 page(s) / 115K

Publishing Venue

The IP.com Prior Art Database

Abstract

The invention relates to electrical machines or generators operated with inverters connected to an electrical grid, and to improvements in handling of major disturbances thereof. The method works by short circuiting the inflowing current by use of the inverter IGBTs. Instead of normal switching operation, all IGBTs connected between the AC terminals and one polarity of the DC-link are short-circuited. High overload currents are detected by the standard current transducers at the inverter. The short-circuiting is applied thereafter. Advantages of the invention include keeping the DC-link voltage at rated condition, reducing standard operating area requirements of the semiconductors. The method further obviates AC-crowbars between machine/generator or DC-link choppers that would otherwise be required to handle fault ride through events.

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METHOD FOR INVERTER CROWBAR AND USE THEREOF

BACKGROUND

The invention relates to electrical machines or generators operated with inverters connected to an electrical grid, and to improvements thereof. Doubly fed induction generators (DFIG) have a stator directly coupled with the electrical grid as shown in FIG. 1. The rotor is fed by an inverter system to reduce the inverter in comparison to a fully fed system. During major disturbances known otherwise as fault ride through (FRT) events, the electrical grid causes over currents in the stator. Due to the magnetic coupling high currents are induced in the rotor windings, which can be much higher than the trip level of the inverter system. If pulse blocking of the IGBTs is applied, the DC-link voltage rises due to the rectification of incoming overcurrents. Crowbar circuits are used (J. Niiranen, 2004) to reduce the level of overcurrents coming from the rotor or to dissipate the overcurrents. Another possible solution to the problem of high induced currents is to keep the DC-link voltage within defined limits through the use of DC link choppers. The invention discloses a method of using short-circuiting to protect inverter-generator circuits during major line disturbances.

FIG. 1: Typical doubly fed induction generator wind turbine connected to source

BRIEF DESCRIPTION OF DRAWINGS

The invention discloses system, apparatus and method for protecting inverter-generator circuits during major line disturbances, wherein:

FIG. 1 shows typical doubly fed induction generator wind turbine connected to source.

FIG. 2 illustrates basic principle of inverter crowbar using a 2-level inverter.

DETAILED DESCRIPTION

The invention as illustrated in FIG. 2 is a method applied to a multilevel inverter (2- or 3-level inverter) which is connected to an electrical drive system. The method works by short circuiting


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the inflowing current by use of the inverter IGBTs. Instead of normal switching operation, all IGBTs connected between AC terminals and one polarity of the DC-link are turned on as illustrated in FIG. 2 (either S2, S4, S6 or S1, S3 and S5 are turned on). The invention uses increased gate-emitter voltage Vge (outside of semiconductor specification) to improve or enable the surge current capability of IGBTs (increase of de-saturation level).

FIG. 2: Basic principle of inverter crowbar using a 2-level inverter

The inventio...