System and method for connecting a converter to a utility grid

Patent metadata

Field	Value
Publication number	US-9496717-B2
Application number	US-200913125067-A
Country	US
Kind code	B2
Filing date	Oct 28, 2009
Priority date	Oct 28, 2008
Publication date	Nov 15, 2016
Grant date	Nov 15, 2016

Abstract

The present invention relates to a system and a method for connecting and/or interfacing a converter, such as a switched mode converter, to an electrical power grid. The invention furthermore relates to control of the converter. The present invention facilitates that the point of common coupling (PCC) between a utility grid and a converter is provided at the converter output. This facilitates that a converter, and thereby an electrical power source, may be connected to an electrical power grid without use of an inductor, such as a reactor.

First claim

The invention claimed is:

1. A system for connecting a converter to an electrical power grid operating with a predefined real power P and a predefined reactive power reference Q, said system comprising:
a) means for providing a grid reference signal, said means for providing a grid reference signal being operative to: provide a sampling connection between the grid and a Phase Locked Loop entity and to measure the amplitude and the phase of the grid voltage,
b) means for setting an internal converter voltage to be the grid reference signal using the Phase Locked Loop entity,
c) means for connecting the converter to the grid,
d) means for measuring a current from the converter to the grid,
e) means for calculating the real power p(t) and/or the reactive power q(t) exchanged between the converter and the grid based on the internal converter voltage and the current measured by means d),
f) means for determining if said real power p(t) is different from the predefined power P and/or if said reactive power q(t) is different from the predefined reactive power reference Q,
g) means for adjusting the converter by changing the phase and/or the amplitude of the internal converter voltage, if it has been determined by means f) that said real power p(t) is different from the predefined power P and/or if said reactive power q(t) is different from the predefined reactive power reference Q, said means for adjusting the converter operating on a repeated basis until the real power p(t) equals P and/or the reactive power q(t) equals Q whereby the converter is interfaced with the electrical power grid without use of an inductor.

2. The system of claim 1 , wherein the system is operative to regulate a three-phase AC system and wherein the system is operative to transform the three AC quantities of the internal converter voltage and the measured current to DC quantities by means of a suitable mathematical transformation.

3. The system of claim 2 , wherein the three AC quantities of the internal converter voltage e a,b,c at sampling time t is transformed to two DC quantities e α,β according to the following formula:

[

e
α

⁡

(
t
)

e
β

⁡

(
t
)

]

=

2
3

⁡

[

1

-

1
2

-

1
2

0

3

2

-

3

2

]

·

[

e
a

⁡

(
t
)

e
b

⁡

(
t
)

e
c

⁡

(
t
)

]

.

4. The system of claim 2 , wherein the three AC quantities of the measured current i a,b,c at sampling time t is transformed to two DC quantities i α,β according to the following formula:

[

i
α

⁡

(
t
)

i
β

⁡

(
t
)

]

=

2
3

⁡

[

Assignees

• Rasmussen Tonny Wederberg
• Univ Denmark Tech Dtu

Inventors

• Rasmussen Tonny Wederberg

Classifications

• H02J3/40 Primary

  Synchronisation of generators for connection to a network or to another generator · CPC title

• H02J3/48

  Controlling the sharing of active power · CPC title

• H02J3/50

  Controlling the sharing of reactive power · CPC title