Dc power regulator incorporating high power ac to dc converter with controllable dc voltage and method of use

• US 6,433,520 B1
• Filed: 05/29/2001
• Issued: 08/13/2002
• Est. Priority Date: 05/29/2001
• Status: Active Grant

• Current Assignee: Siemens Power Generation, Inc.
• Original Assignee: Siemens Power Transmission & Distribution Incorporated (Siemens AG)
• Inventors: Schauder, Colin David
• Primary Examiner(s): NGUYEN, MATTHEW VAN
• Application Number:
  US09/867,165
• Time in Patent Office: 441 Days
• Field of Search: 323/205, 323/207, 323/208, 323/209, 363/39, 363/40, 363/44, 363/50, 363/52, 363/53, 363/55
• US Class Current: 323/207
• CPC Class Codes: H02J 3/1842 wherein at least one reactive element is actively controlled by a bridge converter, e.g. active filters
• CPC Class Codes: Y02E 40/10 Flexible AC transmission systems [FACTS]
• CPC Class Codes: Y02E 40/20 Active power filtering [APF]

Abstract

A high power dc power regulator utilizes a voltage sourced inverter connected on the ac side in series with a large inductance to an ac power system through a coupling transformer. The dc side of the inverter is connected to the dc load. The inductance is sized such that the voltage at the ac terminals of the inverter can be varied from zero to a maximum specified value for use, for example, in melting ice on transmission lines. As there is only infrequent need for ice melting operation, the large inductance can be shunted and the dc load disconnected so that the inverter may be operated for the majority of the time as a conventional STATCOM to provide reactive compensation for the ac power system.

Claims

1. A dc power regulator for connecting an ac power supply to a dc load and controlling the voltage applied to the dc load, the regulator comprising:

an inverter having ac terminals and dc terminals;

an input circuit including an inductance connected between the ac terminals and the ac power supply, the inductance being scaled to maintain current drawn through the ac terminals below a rated maximum level for the inverter when voltage at the ac terminals is zero;

an output circuit connecting the dc terminals of the inverter to the dc load; and

a controller controlling the inverter to generate a selected dc voltage at the dc terminals.

2. The regulator of claim 1 wherein the controller controls the inverter to generate the selected voltage at the dc terminals which varies from substantially zero to a selected maximum value.

3. The regulator of claim 2 wherein the controller comprises means controlling a phase angle between voltage on the ac power supply and voltage at the ac terminals of the inverter.

4. The regulator of claim 2 wherein the controller comprises means controlling a ratio of voltage magnitude at the dc terminals of the inverter to voltage magnitude at the ac terminals.

5. The regulator of claim 1 wherein the input circuit includes a first switch device shunting the inductance when closed, and the output circuit includes a second switch device disconnecting the dc load from the dc terminals of the inverter when opened, and the controller operates the inverter to provide reactive compensation to the ac power supply with the first switch device closed and the second switch device open.

6. The regulator of claim 5 wherein the dc load comprises an electric power transmission line which is connected to the dc terminals of the inverter with the second switch device closed.

7. The regulator of claim 6 wherein the inverter comprises a pair of inverters having dc terminals connected in parallel through the second switch device to the electric power transmission line with the second switch device closed.

8. Apparatus for melting ice on an electric power transmission line using power from an ac transmission system, the apparatus comprising:

an inverter having ac terminals and dc terminals;

an input circuit comprising a coupling transformer connected in shunt with the ac transmission system and an inductance connected in series with the ac terminals of the inverter and the coupling transformer, the inductance being scaled to maintain current drawn through the ac terminals of the inverter below a rated maximum level for the inverter when voltage at the ac terminals is zero;

an output circuit connecting the dc terminals of the inverter to the electric power transmission line; and

a controller controlling the inverter to produce a dc voltage at the dc terminals selectively variable between about zero and a maximum dc value.

9. The apparatus of claim 8 wherein the input circuit includes a first switch device shunting the inductance when closed, the output circuit includes a second switch device disconnecting the dc terminals of the inverter from the electric power transmission line when open, and the controller operates the inverter to provide reactive compensation to the ac transmission system when the first switch device is closed and the second switch device is open.

10. A method of providing dc power to a load from an ac transmission system, the method comprising the steps of:

connecting a load to the dc terminals of an inverter;

connecting ac terminals of the inverter to the ac transmission system through an inductance having a value sufficient to maintain current drawn through the ac terminals below a rated maximum level for the inverter when the voltage at the ac terminals is zero; and

operating the inverter to produce a dc voltage at the dc terminals which varies from about zero up to a maximum dc value.

11. The method of claim 10 wherein the step of operating the inverter comprises phase adjustment of the ac voltage at the ac terminals of the inverter relative to voltage on the ac transmission system.

12. The method of claim 10 wherein the step of operating the inverter comprises generating dc voltage at the dc terminals as a function of the magnitude of the ac voltage, and adjusting the function to adjust the magnitude of the dc voltage.

13. The method of claim 10 comprising disconnecting the dc load from the dc terminals of the inverter, shunting the inductance, and operating the inverter to provide reactive compensation to the ac transmission system.

14. A method of melting ice on an electric power transmission line using power from an ac transmission system, comprising the steps of:

connecting ac terminals of an inverter to the ac transmission system;

connecting dc terminals of the inverter to the electric power transmission line;

operating the inverter to generate a controlled dc voltage at the dc terminals that increases to a selected maximum value and then decreases toward zero; and

limiting current provided to the ac terminals of the inverter from the ac transmission system to a rated maximum level.

15. The method of claim 14 wherein limiting current provided to the ac terminals of the inverter comprises connecting in series with the ac terminals, an inductance scaled to limit the ac current provided to the ac terminals of the inverter to the rated maximum level.

16. The method of claim 15 comprising disconnecting the dc terminals from the electric power transmission line, shunting the inductance, and operating the inverter to provide reactive compensation to the ac transmission system.