FAST RESPONSE ACTIVE REACTIVE POWER (KVAR) COMPENSATOR

Abstract

Legacy automatic variable capacitor KVAR compensation systems typically use either electromechanical devices such as relays or contactors of various forms and types to switch the selected capacitors in and out of the electrical system under some form of electronic control. These systems are slow and discontinuous in their ability to closely regulate the exact value of compensatory capacitance needed to compensate the variable and rapidly changing reactive power KVAR in the electrical power transmission and distribution networks. The present invention provides a fast response active KVAR compensator based on a variable transimpedance topology.

Claims

1. A reactive power (KVAR) compensator for compensating leading or lagging KVAR in alternating current (AC) distribution systems, the KVAR compensator comprising: a first and a second independently controllable AC bidirectional switches; a first power inductor; a first current transformer for generating a first power inductor current direction data signal indicating the first power inductor current direction; an output capacitor with a fixed capacitance or an output inductor with a fixed inductance; and a control circuitry for receiving an AC input voltage, an AC output voltage, and the first power inductor current direction data signal, measuring a KVAR value, and setting a variable gain to generate an apparent impedance across the AC input for compensating the KVAR.

2. A reactive power (KVAR) compensator for compensating leading or lagging KVAR in alternating current (AC) distribution systems, the KVAR compensator comprising: a first unipolar paths, comprising: a first half-bridge, comprising a first and a second rectifiers connected in series with a first and a second independently controllable unipolar switches respectively, a first power inductor, and a first current transformer for generating a first power inductor current direction data signal indicating the first power inductor current direction; a second unipolar paths, comprising: a second half-bridge, comprising a third and a forth rectifiers connected in series with a third and a forth independently controllable unipolar switches respectively, a second power inductor, and a second current transformer for generating a second power inductor current direction data signal indicating the second power inductor current direction; an output capacitor with a fixed capacitance or an output inductor with a fixed inductance; and a control circuitry for receiving an AC input voltage signal, an AC output voltage signal, the first power inductor current direction data signal, and the second power inductor current direction data signal, measuring a KVAR value, and setting a variable gain to generate an apparent impedance across the AC input for compensating the KVAR.

3. A reactive power (KVAR) compensator for compensating leading or lagging KVAR in alternating current (AC) distribution systems, the KVAR compensator comprising: a first unipolar paths, comprising: a first half-bridge, comprising a first and a second unipolar switching devices, a first power inductor, and a first current transformer for generating a first power inductor current direction data signal indicating the first power inductor current direction; a second unipolar paths, comprising: a second half-bridge, comprising a third and a forth unipolar switching devices, a second power inductor, and a second current transformer for generating a second power inductor current direction data signal indicating the second power inductor current direction; an output capacitor with a fixed capacitance or an output inductor with a fixed inductance; and a control circuitry for receiving an AC input voltage signal, an AC output voltage signal, the first power inductor current direction data signal, and the second power inductor current direction data signal, measuring a KVAR value, and setting a variable gain to generate an apparent impedance across the AC input for compensating the KVAR.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Embodiments of the invention are described in more detail hereinafter with reference to the drawings, in which

[0012] FIG. 1 depicts a logical diagram illustrating a general variable transimpedance topology;

[0013] FIG. 2 depicts a circuit diagram of an embodiment of the fast response active KVAR compensator in accordance to the present invention; and

[0014] FIG. 3 depicts a circuit diagram of another embodiment of the fast response active KVAR compensator in accordance to the present invention.

DETAILED DESCRIPTION

[0015] In the following description, methods and systems for compensating reactive power (KVAR) in electrical power generation and distribution networks and the like are set forth as preferred examples. It will be apparent to those skilled in the art that modifications, including additions and/or substitutions may be made without departing from the scope and spirit of the invention. Specific details may be omitted so as not to obscure the invention; however, the disclosure is written to enable one skilled in the art to practice the teachings herein without undue experimentation.

[0016] FIG. 1 depicts a logical diagram illustrating a general variable transimpedance topology and it is used herein to show the general operating principle of a transimpedance system in which the value of an output impedance (Z.sub.o) across the output 103 of the alternating current (AC) amplifier 101 is transferred and reflected onto the input 102 of the AC amplifier. The value of this transferred input impedance (Z.sub.in) is related the output impedance (Z.sub.o) by the gain of the controlled gain AC amplifier (A.sub.v). Thus, if the gain of the AC amplifier (Ag) is controllable and variable, not only a controlled transimpedance can be generated across the input 102 from the fixed output impedance (Z.sub.o) across the output 103, the apparent impedance (Z.sub.in) across the input 102 can be smoothly and accurately controlled with a very fast response. The quickness of change of the apparent impedance (Z.sub.in) across the input 102 is due to the fact that it only depends upon the response speed of the control electronics.

[0017] Still referring to FIG. 1. The relationship between the apparent input impedance (Z.sub.in) and the output impedance (Z.sub.o) is governed by the following equation.

[00001]$\begin{array}{cc}{Z}_{\mathrm{in}}=\frac{1}{{\mathrm{Av}}^2}\times Z_o& \left(2\right)\end{array}$

In specifying a particular value of the output impedance (Z.sub.o), either a capacitor across the output 103 with a fixed capacitance value (C.sub.o) or an inductor across the output 103 with a fixed inductance value (L.sub.o) can be used. Then, the relationship between the reflected apparent input capacitance (C.sub.in) and the output capacitance (C.sub.o) is governed by the following equation.

C.sub.in=Av.sup.2×C.sub.o  (3)

And the relationship between the reflected apparent input inductance (L.sub.in) and the output inductance (L.sub.o) is governed by the following equation.

[00002]$\begin{array}{cc}{L}_{\mathrm{in}}=\frac{L_o}{{\mathrm{Av}}^2}& \left(4\right)\end{array}$

It can be seen that by varying the gain of the AC amplifier (A.sub.v), the apparent value of reflected capacitance (C.sub.in) or reflected inductance (L.sub.in) at the input of the ac amplifier can be varied over a range not only continuously without discrete steps, but also with a very rapid response limited only by the response speed of the control electronics.

[0018] FIG. 2 depicts a circuit diagram of an embodiment of the fast response active KVAR compensator in accordance to the present invention. In this first preferred embodiment, the fast response active KVAR compensator utilizes the buck section with an output capacitor 203 of fixed capacitance (C.sub.o) across the output of the AC series buck-boost voltage regulator electronic circuitry described in the U.S. Pat. No. 9,148,058 and the same in the PCT International Patent Application No. PCT/CN2014/089721 to achieve the KVAR compensation function.

[0019] Still referring to FIG. 2. As the gain of the AC variable voltage topology is changed by the electronic control module 202 in response to the level of KVAR at the input 201, the value of the apparent input capacitance (C.sub.in) across the input 201 is accurately adjusted to compensate and cancel out the reactive power KVAR. This is done without discrete capacitor steps, thus the apparent input capacitance (C.sub.in) adjustment is achieved in smooth and continuous manner, and the response time depends only upon the response speed of the control electronics of the electronic control module 202.

[0020] Although it is described here with the preferred embodiment utilizing the buck section of the AC series buck-boost voltage regulator electronic circuitry described in the U.S. Pat. No. 9,148,058 and the same in the PCT International Patent Application No. PCT/CN2014/089721 to achieve the KVAR compensation function, it should be obvious to an ordinarily skilled person in the art to use the boost section of the aforesaid AC series buck-boost voltage regulator electronic circuitry instead of the buck section.

[0021] Also, although it is described here with the preferred embodiment utilizing a capacitor of fixed capacitance across the output of the buck section of the AC series buck-boost voltage regulator electronic circuitry described in the U.S. Pat. No. 9,148,058 and the same in the PCT International Patent Application No. PCT/CN2014/089721 to compensate for a lagging KVAR, it should be obvious to an ordinarily skilled person in the art to substitute the aforesaid capacitor with an inductor of fixed inductance to compensate for a leading KVAR.

[0022] FIG. 3 depicts a circuit diagram of another embodiment of the fast response active KVAR compensator in accordance to the present invention. In this second preferred embodiment, the fast response active KVAR compensator utilizes the buck section with an output capacitor 303 of fixed capacitance (C.sub.o) across the output of the AC series buck-boost voltage regulator electronic circuitry described in the U.S. patent application Ser. No. 14/565,444 and the same in the PCT International Patent Application No. PCT/CN2014/093475 to achieve the KVAR compensation function.

[0023] Still referring to FIG. 3. As the gain of the AC variable voltage topology is changed by the electronic control module 302 in response to the level of KVAR at the input 301, the value of the apparent input capacitance (C.sub.in) across the input 301 is accurately adjusted to compensate and cancel out the reactive power KVAR. This is done without discrete capacitor steps, thus the apparent input capacitance (C.sub.in) adjustment is achieved in smooth and continuous manner, and the response time depends only upon the response speed of the control electronics of the electronic control module 302.

[0024] Although it is described here with the preferred embodiment utilizing the buck section of the AC series buck-boost voltage regulator electronic circuitry described in the U.S. patent application Ser. No. 14/565,444 and the same in the PCT International Patent Application No. PCT/CN2014/093475 to achieve the KVAR compensation function, it should be obvious to an ordinarily skilled person in the art to use the boost section of the aforesaid AC series buck-boost voltage regulator electronic circuitry instead of the buck section.

[0025] Also, although it is described here with the preferred embodiment utilizing a capacitor of fixed capacitance across the output of the buck section of the AC series buck-boost voltage regulator electronic circuitry described in the U.S. patent application Ser. No. 14/565,444 and the same in the PCT International Patent Application No. PCT/CN2014/093475 to compensate for a lagging KVAR, it should be obvious to an ordinarily skilled person in the art to substitute the aforesaid capacitor with an inductor of fixed inductance to compensate for a leading KVAR.

[0026] Any ordinarily skilled person in the art can apply the inventive principles described herein to any poly-phase AC systems, such as three-phase electrical systems, without departing from the scope and spirit of the invention.

[0027] The embodiments disclosed herein may be implemented using general purpose or specialized computing devices, computer processors, microcontrollers, or electronic circuitries including but not limited to digital signal processors (DSP), application specific integrated circuits (ASIC), field programmable gate arrays (FPGA), and other programmable logic devices configured or programmed according to the teachings of the present disclosure. Computer instructions or software codes running in the general purpose or specialized computing devices, computer processors, or programmable logic devices can readily be prepared by practitioners skilled in the software or electronic art based on the teachings of the present disclosure.

[0028] The foregoing description of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations will be apparent to the practitioner skilled in the art.

[0029] The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, thereby enabling others skilled in the art to understand the invention for various embodiments and with various modifications that are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalence.