Control method for self-commutated converter for controlling power exchange
View Patent ↗A self-commutated converter is connected to further self-commutated converters by its AC voltage connection via an inductive component using a coupling point, which is common to all the converters, in an AC voltage network. An active power P and a frequency f N are determined from a network voltage at the coupling point and a converter current flowing via the inductive component. An active power difference value ΔP is supplied to an orthogonal controller and to a parallel controller. The output value from the parallel controller is used to minimize the reactive power exchanged between converter and coupling point. The frequency difference value Δf is supplied to a frequency controller and the output value from the frequency controller is logically combined with the output value from the orthogonal controller and the output value from the parallel controller, the frequency difference value Δf being simultaneously minimized.
1. A method for controlling a first self-commutated converter, which is connected to a plurality of second self-commutated converters through an AC terminal thereof and via an inductive component at a coupling point of an alternating current network that is common to all converters, the method comprising:
determining an active power P and a frequency f N from a network voltage ascertained at the coupling point and a converter current flowing through the inductive component;
forming a difference between the active power P and a specified set point active power P soll to obtain an active power difference value ΔP; and
forming a difference between the frequency f N and a specified set point frequency F soll to obtain a frequency difference value Δf;
supplying the active power difference value ΔP to an orthogonal controller and to a parallel controller; and
determining an active power exchanged between the first self-commutated converter and the coupling point from an output value of the orthogonal controller, and minimizing a reactive power exchanged between the converter and the coupling point with an output value of the parallel controller;
supplying the frequency difference value Δf to a frequency controller, and combining an output value of the frequency controller with the output value of the orthogonal controller and the output value of the parallel controller, and at the same time minimizing the frequency difference value Δf.
2. The method according to claim 1 , which further comprises adding a pre-control value to the output value of the orthogonal controller and/or to the output value of the parallel controller and/or to the output value of the frequency controller to thereby obtain an orthogonal pre-control regulator addition value, a parallel pre-control regulator addition value and/or a frequency pre-control regulator addition value, respectively.
3. The method according to claim 2 , which further comprises additively combining the orthogonal pre-control regulator addition value multiplied by j with the parallel pre-control regulator addition value to form an additive combination, and ascertaining an amplitude |z| and a pre-phase of a converter voltage =|z|·e f·arg{z} from the additive combination, corresponding to a converter voltage that provides for a transmission of the active power P that corresponds as closely as possible to the specified set point active power P soll , and with which the reactive power is minimized.
4. The method according to claim 3 , which comprises additively combining the frequency pre-control regulator addition value with the pre-phase, to thereby obtain a phase of a converter voltage to be set.
5. The method according to claim 4 , wherein the frequency pre-control regulator addition value additively includes an output of a phase synchronization controller which takes into account a supply of the alternating current network through an auxiliary supply line.
6. The method according to claim 5 , which comprises forming a difference between a set point auxiliary active power P Aux,soll and an auxiliary active power P Aux transmitted via the auxiliary supply line, to thereby obtain an auxiliary active power difference value ΔP Aux , and supplying the auxiliary active power difference value ΔP Aux to the phase synchronization controller as an input.
7. The method according to claim 4 , wherein the frequency pre-control regulator addition value additively comprises a compensation angle φ KOMP that compensates for dead-time effects in a control loop of the first self-commutated converter.
8. The method according to claim 2 , which comprises subtracting a pre-control value obtained from a formula
u
→
RE
,
VOR
,
⊥
=
-
j
·
2
3
·
P
Soll
·
X
K
u
->
VP
,
1
+
from a negative output of the orthogonal controller.
9. The method according to claim 2 , which comprises adding a magnitude of the network voltage | |, or, if a current reference vector for faces in an opposite direction, positive output of the parallel controller, to a negative output of the parallel controller.
10. The method according to claim 2 , which comprises adding a frequency value of the network voltage , as a pre-control value to the output value of the frequency controller.
11. The method according to claim 1 , which comprises subtracting a supplementary set point value C Q *Q, which results from a product of a specified reactive power parameter C Q and a reactive power Q or a magnitude |Q | thereof ascertained from the network voltage and the converter current from the frequency difference value Δf.
12. The method according to claim 1 , which comprises taking into account only a positive sequence part of a fundamental oscillation by the network voltage .
13. The method according to claim 1 , which comprises acquiring the network voltage and the converter current by way of measuring sensors, sampling output signals thereof to obtain sampled values, and digitizing the sampled values, and forming an average over sequential N digitized sampled values.
14. The method according to claim 1 , wherein the alternating current network is connected through a direct current connection to a power supply network U Netz comprising an energy source, wherein the direct current connection comprises a diode rectifier that is connected via the direct current connection to a further converter which is connected to the power supply network U Netz .
15. A self-commutated converter for transmitting a power, the converter comprising:
an alternating current terminal for connecting a high-voltage AC electrical network;
a direct current terminal for connecting a direct current network; and
a control unit connected to power semiconductor switches to be switched on or off, said control unit being configured to adjust a transmission of the power by carrying out the method according to claim 1 .
16. A wind farm, comprising a multiplicity of wind turbines, each of said wind turbines including the self-commutated converter according to claim 15 configured for connection to the alternating current network.
17. The wind farm according to claim 16 , wherein said self-commutated converters are connected via the alternating current network and via a direct current connection to a power supply network comprising an energy source, wherein the direct current connection includes a diode rectifier connected via a direct current network to a further converter that is connected to the power supply network U Netz .