Electricity: power supply or regulation systems – For reactive power control – Using converter
Reexamination Certificate
2001-04-19
2002-06-25
Berhane, Adolf Deneke (Department: 2838)
Electricity: power supply or regulation systems
For reactive power control
Using converter
Reexamination Certificate
active
06411066
ABSTRACT:
TECHNICAL FIELD
The invention relates to a method for controlling active power flow in a high voltage direct current transmission system having a first and a second converter station coupled to each other via a direct current link, each converter station with a voltage source converter, wherein the first converter station controls the voltage of the direct current link, at the first converter station, in dependence on a first voltage reference value, and the second converter station controls the active power flow through the second converter station, and to a high voltage direct current transmission system for carrying out the method.
BACKGROUND ART
For a general description of control systems for voltage source converters reference is made to Anders Lindberg: PWM and Control of Two and Three Level High Power Voltage Source Converters. Royal Institute of Technology, Department of Electric Power Engineering. Stockholm 1995, in particular pages 1, 77-104, and appendix A.
FIG. 1
shows in the form of a schematic single line and block diagram a high voltage direct current transmission system as known in the prior art. A first and a second converter station STN
1
and STN
2
respectively, are coupled to each other via a direct current (dc) link having two pole conductors W
1
and W
2
respectively. The pole conductors are typically cables but may also at least to a part be in the form of overhead lines. Each converter station has a capacitor equipment, in this embodiment schematically shown as capacitors C
1
and C
2
respectively, coupled between the pole conductors, and comprises a voltage source converter, CON
1
and CON
2
respectively. Each converter comprises two three-phase groups of semiconductor valves in six-pulse bridge connections The semiconductor valves comprises, in a way known per se, branche of gate turn on/turn off semiconductor elements, for example power transistors of so-called IGBT-type, and diodes in anti-parallel connection with these elements.
Each converter is via phase inductors, PI
1
and PI
2
respectively, coupled to a respective three-phase alternating current (ac) electric power network, N
1
and N
2
. Although not shown in the figure, it is well known in the art that the converters may be coupled to the three-phase networks via transformers, in which case the phase inductors in some cases may be omitted. Filter equipment F
1
and F
2
respectively is coupled in shunt connection at connection points between the phase inductors and the three-phase networks.
The ac-voltage of the alternating current network N
1
at the connection point of the filter F
1
is designated UL
1
and is sensed with a sensing device M
1
. The ac-current at the converter CON
1
is designated Iv
1
and is sensed with a measuring device M
2
. Similarly, the ac-voltage at the connection point of the filter F
2
is designated UL
2
and is sensed with a sensing device M
3
, and the ac-current at the converter CON
2
is designated Iv
2
and is sensed with a measuring device M
4
.
The dc-voltage across the capacitor equipment C
1
is designated Udc
1
and is sensed with an only symbolically shown sensing device M
5
, and the dc-voltage across the capacitor equipment C
2
is designated Udc
2
and is sensed with an only symbolically shown sensing device M
6
.
The first converter station comprises control equipment CTRL
1
and the second converter station control equipment CTRL
2
of similar kind.
The control equipments operate in a conventional way with three phase units (voltages and currents) converted to and expressed in a two-phase &agr;&bgr;-reference frame as well as in a rotating two-phase dq-reference frame. The phases of the three-phase alternating current electric power networks are referred to as the abc-reference frame. Vector units are in the following illustrated with a dash on top ({overscore (x)}). In the following text and in the figures the reference frame is, where appropriate, indicated in an upper index (for example x
dq
).
Control equipment CTRL
1
comprises a dc-voltage controller UdcREG, an ac-voltage controller UacREG, selector means SW
1
and SW
2
respectively, and an internal converter current control IREG.
The dc-voltage controller is supplied with the sensed dc-voltage Udc
1
and a first voltage reference value Udc
1
R thereof, and forms in dependence of the deviation of the actual value Udc
1
and the first voltage reference value Udc
1
R an output signal P
1
C.
The ac-voltage controller is supplied with the sensed ac-voltage UL
1
and a voltage reference value UL
1
R thereof, and forms in dependence of the deviation of the actual value UL
1
and the reference value UL
1
R an output signal Q
1
C.
Each of the dc-voltage controller and ac-voltage controller comprises a (not shown) difference forming member, forming the deviation between respective reference values and actual values, which deviation is supplied to and processed in a (not shown) controller member having for example a proportional/integrating characteristic. The voltage controllers thus provide feedback control of the respective voltages.
The output signal P
1
C and a reference value P
1
R for the active power flow through the converter CON
1
are supplied to two different inputs on the selector means SW
1
, and the output signal Q
1
C and a reference value Q
1
R for the reactive power flow through the converter CON
1
are supplied to two different inputs on the selector means SW
2
. The reference values P
1
R and Q
1
R may be set manually, in particular the reference value P
1
R may also be the output of another controller such as a frequency controller.
In dependence on a first mode signal MD
11
either of the output signal P
1
C and the reference value P
1
R is transferred and supplied to the internal converter current control IREG in the form of a signal designated p
ref1
, having the significance of an active power order.
In dependence on a second mode signal MD
21
either of the output signal Q
1
C and the reference value Q
1
R is transferred and supplied to the internal converter current control IREG in the form of a signal designated q
ref1
, having the significance of a reactive power order.
Thus, each converter station can operate in four different modes, one of dc-voltage control and active power control and one of ac-voltage control and reactive power control. Usually, one of the converter stations, for example the first one, operates under dc-voltage control, whereas the second converter station (as well as other, not shown, converter stations, which may be coupled to the first converter station via other direct current links) operates under active power control and under ac-voltage or reactive power control.
The operation modes are set either manually by an operator, or, under certain conditions, automatically by a not shown sequential control system.
The internal converter current control IREG is of a kind known per se and comprises a current-order calculating unit and a converter control unit (not shown).
The current-order calculating unit comprises a current-order calculating member and a current limiting member. The above mentioned active and reactive power order signals, p
ref1
and q
ref1
respectively, are supplied to the current-order calculating unit. In the current-order calculating member current reference values, expressed in the dq-reference frame as i
ref
d
and i
ref
q
respective, are calculated in dependence on the power orders. The calculation is performed according to the per se known relations
p
ref
=u
d
i
ref
d
+u
q
i
ref
q
q
ref
=u
d
i
ref
q
−u
q
i
ref
d
wherein the voltages u
d
and u
q
represent voltages sensed in the alternating current network and transformed to the dq-reference frame in a manner known per se. The current reference values i
ref
d
and i
ref
q
are supplied to the current limiting member and therein limited, as the case may be, in accordance with specified operating conditions for the transmission system. The current limiting member outputs the so limited values as a current vector {overscore (i)}
ref
xdq
to th
ABB AB
Berhane Adolf Deneke
LandOfFree
Method to control the flow of active power in a high voltage... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method to control the flow of active power in a high voltage..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method to control the flow of active power in a high voltage... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2940138