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Application US20200006945
Published 2020-01-02
Anti-islanding Systems And Methods Using Harmonics Injected In A Rotation Opposite The Natural Rotation
An active anti-islanding architecture where a power converter injects a current component at a harmonic of the fundamental power frequency is injected with a phase sequence opposite to that which normally be present with that harmonic. (For example, a 5th harmonic frequency can be used with a positive phase sequence, or a 7th harmonic frequency with a negative phase sequence.) The injected current component can have a thousandth or less of the power transferred by the converter, since the distinctive phase sequence of the injected signal facilitates recognition of a corresponding term in the observed voltage.
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- 1. A method of anti-islanding, comprising the actions of:
a) converting power to provide, at output terminals, a multi-phase AC current at a predetermined base frequency, while also b) adding in a current component, on the output terminals, at the nth harmonic of the predetermined base frequency, with a distinctive phase sequence which is different from that normally present in the nth harmonic; c) testing whether a voltage corresponding to said nth harmonic and said distinctive phase sequence exceeds a threshold value on the output terminals, and, if so, detecting an islanding condition.
- 5. A system, comprising:
a) at least one local power source; b) at least one power converter, connected to draw power from the local power source and to drive power onto multiple phase lines of a power bus which is at least sometimes connected to a utility power grid; wherein the power converter also operates to add in a current component, on the output terminals, at the nth harmonic of the predetermined base frequency, with a distinctive phase sequence which is different from that normally present in the nth harmonic; and c) control circuitry which monitors the voltage on the multiple phase lines of the power bus, and controls the operation of the power converter accordingly; while also testing whether a voltage corresponding to said nth harmonic and said distinctive phase sequence exceeds a threshold value on the output terminals, and, if so, indicating an islanding condition.
