US 11,056,883 B1 · System and method for implementing a zero-sequence current filter for a three-phase power system

Abstract

In a three-phase, four-wire electrical distribution system, a zig-zag transformer and at least one Cascade Multilevel Modular Inverter (CMMI) is coupled between the distribution system and the neutral. A controller modulates the states of the H-bridges in the CMMI to build an AC waveform. The voltage is chosen by the controller in order to control an equivalent impedance that draws an appropriate neutral current through the zig-zag transformer. This neutral current is generally chosen to cancel the neutral current sensed in the line. In other embodiments, the chosen neutral current may be based on a remotely sensed imbalance, rather than on a local value, determined by the power utility as a critical load point in the system. The desired injection current is then translated by the controller into a desired zero-sequence reactive impedance, based on measurement of the local terminal voltage, allowing the controller to regulate the current without generating or consuming real power. In some embodiments, the zig-zag transformer is omitted.

A system for actively controlling zero-sequence current in a three-phase power distribution network having a phase A, a phase B, a phase C, and a neutral, the system comprising:

a transformer comprising:
a first primary winding comprising a first primary winding dot terminal and a first primary winding non-dot terminal;
a first secondary winding comprising a first secondary winding dot terminal and a first secondary winding non-dot terminal, wherein the first primary winding and the first secondary winding share a first common magnetic flux path;
a second primary winding comprising a second primary winding dot terminal and a second primary winding non-dot terminal;
a second secondary winding comprising a second secondary winding dot terminal and a second secondary winding non-dot terminal, wherein the second primary winding and the second secondary winding share a first common magnetic flux path;
a third primary winding comprising a third primary winding dot terminal and a third primary winding non-dot terminal;
and
a third secondary winding comprising a third secondary winding dot terminal and a third secondary winding non-dot terminal, wherein the third primary winding and the third secondary winding share a first common magnetic flux path;
wherein the third primary winding non-dot terminal is operatively coupled to the first secondary winding non-dot terminal;
wherein the first primary winding non-dot terminal is operatively coupled to the second secondary winding non-dot terminal;
wherein the second primary winding non-dot terminal is operatively coupled to the third secondary winding non-dot terminal;
wherein the first secondary winding dot terminal, the second secondary winding dot terminal, and the third secondary winding dot terminal are operatively coupled to the neutral;
a first Cascade Multilevel Modular Inverter (CMMI) comprising a first CMMI first terminal and a first CMMI second terminal, wherein the first CMMI first terminal is operatively coupled to phase A, and the first CMMI second terminal is operatively coupled to the first primary winding dot terminal;
a second CMMI comprising a second CMMI first terminal and a second CMMI second terminal, wherein the second CMMI first terminal is operatively coupled to phase B, and the second CMMI second terminal is operatively coupled to the second primary winding dot terminal;
a third CMMI comprising a third CMMI first terminal and a third CMMI second terminal, wherein the third CMMI first terminal is operatively coupled to phase C, and the third CMMI second terminal is operatively coupled to the third primary winding dot terminal;
and
a controller operatively coupled to the first CMMI, the second CMMI, and the third CMMI, the controller operable to:
a) modulate a first voltage produced by the first CMMI to control a first equivalent impedance between phase A and the neutral;
b) modulate a second voltage produced by the second CMMI to control a second equivalent impedance between phase B and the neutral;
and
c) modulate a third voltage produced by the third CMMI to control a third equivalent impedance between phase C and the neutral.

18 more elements

Facts

Application

17/148,136Filed 13 Jan 2021 · continuation

Priority

30 Apr 2020

Granted

6 Jul 2021

Term ends

Not estimatedThe source records don’t support an estimate.

Classification8 codes

H02J 3/1857
Having reactive elements actively controlled by bridge converters, e.g. active filters or static compensators [STATCOM]: the bridge converters…
H02J 3/26
Circuit arrangements for AC mains or AC distribution networks: arrangements for eliminating or reducing asymmetry in polyphase networks
H01F 30/12
Characterised by the structure: two-phase, three-phase or polyphase transformers
H02J 3/1878
Arrangements for adjusting, eliminating or compensating reactive power in networks: using tap changing or phase shifting transformers

System and method for implementing a zero-sequence current filter for a three-phase power system

Life of this patent

System and method for implementing a zero-sequence current filter for a three-phase power system

Life of this patent

Abstract

Claims12