Transformer with flux linkage control and method for suppressing magnetizing inrush current of transformer

Patent metadata

Field	Value
Publication number	US-11735903-B2
Application number	US-201817055497-A
Country	US
Kind code	B2
Filing date	Jun 22, 2018
Priority date	May 15, 2018
Publication date	Aug 22, 2023
Grant date	Aug 22, 2023

Abstract

A method for suppressing magnetizing inrush current of the transformer with flux linkage control includes connecting a small-capacity direct current/alternating current (DC/AC) converter with the secondary winding or auxiliary winding of transformer, detecting the primary side phase voltage before closing load, inducing the core flux linkage reference according to the relationship between the winding voltage and core flux linkage. The core flux linkage closed-loop PI control system is constructed to control the converter voltage in the synchronous coordinate, then the core flux linkage can track its reference with no static error, thus the sinusoidal flux linkage with 90-degree difference from the grid voltage can be pre-established in the core before no-load closing. By these methods, no matter when the main transformer closes, the core flux linkage is always in the steady state, and the magnetizing inrush current can be eliminated completely.

First claim

What is claimed is:

1. A transformer with flux linkage control, the transformer comprising a main transformer, a direct current/alternating current (DC/AC) converter and an auxiliary power source, wherein the main transformer has a single-phase dual-winding structure or a single-phase three-winding structure, and the DC/AC converter is a single-phase full-bridge converter; or the main transformer has a three-phase dual-winding structure or a three-phase three-winding structure, and the DC/AC converter is a three-phase half-bridge converter, a neutral line for splitting two dc-link capacitors of the three-phase half-bridge DC/AC converter is drawn out; wherein the auxiliary power source is connected with the dc-link capacitors of the DC/AC converter in parallel, and output ends of the DC/AC converter are connected with a secondary winding or an auxiliary winding of the main transformer.

2. The transformer with flux linkage control according to claim 1 , further comprising a core flux linkage control module to establish a synchronous steady-state flux linkage for a main transformer core before the main transformer is connected to a power grid by controlling the DC/AC converter.

3. The transformer with flux linkage control according to claim 2 , wherein before the main transformer is closed with no-load, a terminal voltage of the DC/AC converter is controlled by the core flux linkage control module, and the core flux linkage of the main transformer tracks given steady-state references thereof in real time, so as to eliminate DC magnetic bias.

4. The transformer with flux linkage control according to claim 1 , wherein when a dual-winding structure is adopted, the main transformer comprises a primary winding and the secondary winding, the output ends of the DC/AC converter are connected with the secondary winding of the main transformer; when a three-winding structure is adopted, the main transformer comprises the primary winding, the secondary winding and an auxiliary winding, the output ends of the DC/AC converter are connected with the auxiliary winding of the main transformer; the primary winding of the main transformer is connected with a power grid through a grid-side circuit breaker, and the secondary winding supplies power for a load.

5. The transformer with flux linkage control according to claim 1 , wherein the single-phase full-bridge converter comprises an inductor, a dc-link capacitor, and two bridge arms connected with each other in parallel, the secondary winding or the auxiliary winding of the main transformer is connected with a midpoint of one bridge arm through the inductor; the three-phase half-bridge converter comprises an a-phase inductor, a b-phase inductor and a c-phase inductor, three bridge arms respectively connected with the a-phase inductor, the b-phase inductor and the c-phase inductor in parallel, and a dc-link capacitor unit, wherein the dc-link capacitor unit comprises two dc-link capacitors connected with each other in series; an a-phase secondary winding or an a-phase auxiliary winding, a b-phase secondary winding or a b-phase auxiliary winding, and a c-phase secondary winding or a c-phase auxiliary winding of the main transformer are connected with a midpoint of an a-phase bridge arm, a b-phase bridge arm and a c-phase bridge arm through an a-phase inductor, a b-phase inductor and a c-phase inductor, respectively; the auxiliary power source comprises a current-limiting resistor, a DC-side circuit breaker and a battery connected with each other in series.

6. The transformer with flux linkage control according to claim 1 , wherein when a single-phase dual-winding structure is adopted, the single-phase full-bridge converter is connected with the secondary winding of the main transformer in parallel; when a single-phase three-winding structure is adopted, the single-phase full-bridge converter is connected with the auxiliary winding of the main transformer in parallel; when a three-phase dual-winding structure is adopted, the secondary windings of the main transformer supply power for the load by a three-phase four-wire method; an a-phase output end, a b-phase output end and a c-phase output end of the three-phase half-bridge converter all of which are drawn out from a midpoint of the dc-link capacitor unit are respectively connected with a beginning of the a-phase secondary winding, a beginning of the b-phase secondary winding and a beginning of the c-phase secondary winding, the midpoint of the dc-link capacitor unit is connected with a neutral point of the a-phase secondary winding, the b-phase secondary winding and the c-phase secondary winding; when a three-phase three-winding structure is adopted, the auxiliary windings of the main transformer adopt a star-shaped neutral point connection method, the a-phase output end, the b-phase output end and the c-phase output end of the three-phase half-bridge converter all of which are drawn out from the midpoint of the dc-link capacitor unit are respectively connected with a beginning of the a-phase auxiliary winding, a beginning of the b-phase auxiliary winding and a beginning of the c-phase auxiliary winding, the midpoint of the dc-link capacitor unit is connected with a neutral point of the a-phase auxiliary winding, the b-phase auxiliary winding and the c-phase auxiliary winding.

7. A method for suppressing no-load closing magnetizing inrush current of a main transformer with flux linkage control, the method comprising: connecting a direct current/alternating current (DC/AC) converter with a secondary winding or an auxiliary winding of the main transformer in parallel, and pre-establishing a synchronous steady-state flux linkage for a main transformer core by controlling the DC/AC converter before the main transformer is connected to a power grid, so as to completely eliminate the magnetizing inrush current when the power grid is closed.

8. The method for suppressing the no-load closing magnetizing inrush current of the main transformer with the flux linkage control according to claim 7 , wherein the method specifically comprises:
(1) before the main transformer is closed with no-load through a grid-side circuit breaker, charging a dc-link capacitor of the DC/AC converter through an auxiliary power source with small power, and when a voltage of the dc-link capacitor of the DC/AC converter reaches a stable value, disabling the auxiliary power source; and
(2) controlling the core flux linkage by controlling a terminal voltage of the DC/AC converter, tracking given steady-state references in real time by the core flux linkage of the main transformer for eliminating DC magnetic bias to fundamentally eliminate the magnetizing inrush current, and stopping the DC/AC converter after the grid-side circuit breaker is closed for finishing tracking.

9. The method for suppressing the no-load closing magnetizing inrush current of the main transformer with the flux linkage control according to claim 8 , wherein in the step of (2), controlling the core flux linkage specifically comprises: according to a relationship between an amplitude of the core flux linkage and an effective value of the grid voltage, calculating the amplitude of the core flux linkage, and taking the calculated amplitude as a reference value of q-axis flux linkage in a dq synchronous rotating coordinate system; detecting an instantaneous value of the core flux linkage, constructing a quadrature flux linkage signal of the instantaneous value in a two-phase static coordinate system through 90-degree delay, performing coordinate transformation on the quadrature flux linkage signal in the two-phase static coordinate system, taking a q-axis flux linkage signal in the dq synchronous rotating coordinate system obtained by the coordinate trans

Assignees

• Univ Xi An Jiaotong

Inventors

• Liu Yibin
• Liang Deliang
• Liang Yang
• Zhang Mingkang

Classifications

• H02H7/04 Primary

  for transformers · CPC title

• H01F27/28

  Coils; Windings; Conductive connections · CPC title

• H02H9/02

  responsive to excess current {(current limitation for voltage regulators G05F1/573; disconnection after limiting H02H3/025)} · CPC title

• H02M7/5387 Primary

  in a bridge configuration · CPC title

• H02M7/5395

  by pulse-width modulation · CPC title