Static compensator and method for controlling thereof

• US 8,508,197 B2
• Filed: 09/28/2010
• Issued: 08/13/2013
• Est. Priority Date: 09/30/2009
• Status: Expired due to Fees

• Current Assignee: Korea Electric Power Corporation (Government of South Korea)
• Original Assignee: Korea Electric Power Corporation (Government of South Korea)
• Inventors: Yoon, Jong-Su, Kim, Yong-Hak
• Primary Examiner(s): Zhang, Jue
• Assistant Examiner(s): LEE III, HENRY E
• Application Number:
  US12/892,495
• Publication Number:
  US 20110074367A1
• Time in Patent Office: 1,050 Days
• Field of Search: 323/205, 323210-211, 323/255, 323/301, 323355-356
• US Class Current: 323/255
• 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 40/20 Active power filtering [APF]

Abstract

The present invention relates to a static compensator and a method for controlling thereof, more particularly, to a static compensator including a transformer connected with a bus of a power system; an inverter operating according to a control signal and connected to the transformer in series; a tap changer changing turn ratio of the transformer; and a controller generating the control signal to operate the inverter and generating a tap up or a tap down signal to provide to the tap changer and a method for controlling thereof.

Claims

1. A static compensator comprising:

a transformer connected with a bus of a power system;

an inverter operating according to a control signal and connected to the transformer in series;

a tap changer changing turn ratio of the transformer;

a voltage controller controlling an output quantity of a reactive current according to a predetermined voltage control reference value;

a reactive current controller controlling a phase angle of an output voltage of the inverter using a difference in values between a reactive current inputted by the voltage controller and a reactive current measured by the inverter; and

a tap changer controller extracting an integrated value of a bus voltage if the bus voltage inputted from the bus and the reactive current controller is greater or smaller than a predetermined reference value, comparing the extracted integrated value with a predetermined excessive integration threshold value, and outputting any of a tap up signal or a tap down signal controlling the tap changer,

wherein the voltage controller comprises;

a first D/Q changing unit receiving the bus voltage and converting the bus voltage into and outputting an active voltage of the bus voltage and a reactive voltage of the bus voltage;

an intensity calculating unit outputting a bus voltage by using an active power and a reactive power from the D/Q changing unit; and

a first PI controller controlling an output quantity of the reactive current by compensating a difference between the predetermined voltage control reference value and the bus voltage outputted from the intensity calculating unit, and

wherein the tap changer controller comprises;

a first comparing unit generating an ON or OFF signal by comparing the bus voltage with the predetermined reference value;

an integrator extracting an integrated value of the bus voltage;

a timer placed between the integrator and the first comparing unit and transmitting a time delay signal to the integrator if the ON signal is received from the comparing unit; and

a second comparing unit outputting the tap up or tap down signal by comparing the integrated value with the excessive integration threshold value.

2. The static compensator of claim 1, wherein the voltage controller further comprises an upper/lower limit limiter outputting a reactive current output quantity inputted from the PI controller within a predetermined range.

3. The static compensator of claim 1, wherein the reactive current controller comprises:

a second D/Q changing unit converting an inverter current value of 3 phase inputted from the inverter to a current of 2 phase and calculating and outputting a reactive current value; and

a second PI controller outputting a voltage phase angle by using a difference between a reactive current inputted from the voltage controller and a reactive current inputted from the second D/Q changing unit.

4. The static compensator of claim 1, wherein the predetermined reference is an upper limit or a lower limit of an operating voltage of the power system.

5. The static compensator of claim 1, wherein the voltage controller calculates reactive power using a difference between the bus voltage and the predetermined voltage and provides the calculated first reactive current to the reactive current controller,

and the reactive current controller calculates a voltage phase angle using a difference between the first reactive current and a predetermined reactive current and provides a phase angle of an output voltage of the inverter using the calculated voltage phase angle and a bus voltage phase angle.