Asea Brown Boveri Ab

Tomas Jonsson

Per-Erik Bjorklund

Lars-Erik Lennart Juhlin

Tommy Holmgren

Urban Strom

An installation for transmission of electric power by means of high-voltage direct current has two converters (SRI, SRII), each of which is connected to an alternating-voltage network (NI, NII) and which are connected to each other through a dc connection (L). One converter (SRI) is controlled as a rectifier and another converter (SRII) is controlled as an inverter. One converter (SRI) is current-controlling and another converter (SRII) is voltage-controlling. The installation has means (VARC.sub.rect) adapted, at such a change of the control angle (.alpha..sub.rect) of the current-controlling converter (SRI) that the angle reaches a limit of a predetermined interval (.alpha..sub.max nom rect -.alpha..sub.min nom rect) to control, by means of the voltage-controlling converter (SRII), the direct voltage (Ud) of the transmission in such a way that said change is limited.

High-voltage direct current transmission installation having a high

Control equipment (CE1) generates an ordered value (AOL) of a control angle (.alpha.) in dependence on a limiting signal (AMINL, AMAXL), capable of being influenced, for a converter included in a series-compensated converter station. A calculating value (AFIRL) of a control angle is calculated continuously according to a predetermined relationship (H'1, H'2) which at least approximately imitates a relationship according to which, at a firing voltage (Ufir) for the valves of the converter equal to a preselected value (Uvref), said control angle is a function (G'0) of a current (Id1) and a voltage (Un1) in the converter station and the limiting signal is formed in dependence on the calculating value. (FIG. 5 )

Method and device for control of a series-compensated converter station

A series-compensated converter station in an installation for transmission of high-voltage direct current is connected to an alternating-voltage network (N) with three phases (A, B, C, respectively). The converter station comprises at least two direct-voltage series-connected six-pulse converter bridges (SR1, SR2, respectively), a three-phase transformer coupling with two secondary windings (SW1, SW2, respectively), and a star-connected primary winding (PW) with a neutral point (NP) connected to ground as well as a series capacitor unit (CN) for each one of the three phases. Each one of the converter bridges is connected to a respective secondary winding and the primary winding is connected to the alternating-voltage network via the series-capacitor units. The transformer coupling exhibits a high impedance to zero-sequence currents through the primary winding of the transformer coupling.

Series-compensated converter station

Control equipment (CE2) generates an ordered value (AOL) of a control angle (.alpha.) in dependence on a limiting signal (AMAXL), capable of being influenced, for a converter included in a series-compensated converter station. A calculating value (AMARG) of a control angle is calculated continuously according to a predetermined relationship (M0, M1, M2, M3) which at least approximately resembles a relationship according to which, at a commutating margin (.gamma..sub.m) equal to a preselected value (.gamma..sub.p), said control angle is a function (F0) of a current (Id2) and a voltage (Un2) in the converter station and the limiting signal is formed in dependence on the calculating value.

A series-compensated converter station included in an installation for transmission of high-voltage direct current comprises a converter (SR1, SR2) with at least one 6-pulse bridge (BR). Via series capacitors (SCR, SCS, SCT) the 6-pulse bridge is connected to a three-phase alternating-voltage network (N1, N2) with a fundamental frequency (f.sub.01, f.sub.02). Control equipment (CE1, CE2) generates an ordered value (AOL) of a control angle (.alpha.) for valves (V1-V6) included in the 6-pulse bridge in dependence on a limiting signal (AMAXL) capable of being influenced. An amplitude signal (AMPL) is formed which corresponds to the amplitude (C.sub.1) for a component (C.sub.1 cos(2.pi.f.sub.0 t+.phi..sub.1)) of the fundamental frequency in the direct voltage (Udb) of the 6-pulse bridge and a compensating signal (ACOMP) is continuously calculated in dependence on a sensed voltage (Un1, Un2) at the converter station and on the amplitude signal. The limiting signal is formed in dependence on the compensating signal for the purpose of maintaining the commutating margin (.gamma..sub.m) for the valves equal to at least the preselected value (.gamma..sub.p) in case of unbalance between the voltages (UCR, UCS, UCT) of the series capacitors. (FIG. 6)

Method and device for compensation of unbalance in a series compensated

An installation for transmission of high-voltage direct current comprises a first and a second converter (SR1, SR2, respectively), each one controlled by a separate piece of control equipment (CE1, CE2, respectively). Each one of the pieces of control equipment comprises a current controller (CC). The current controller of the second converter is supplied with a second current reference value (IOL2) and a current margin (IOM). The control equipment of the second converter comprises a function-forming member (11), which in dependence on an applied measured value (UD) of the direct voltage forms the current margin such that, when the direct voltage exceeds a first preselected voltage level (Udf), it assumes a first value (IOMf) and, when the direct voltage is lower than the first voltage level, it assumes a second value (IOMs), the magnitude of the second value being greater than the magnitude of the first value.

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Grangesberg, Sweden

Tomas Jonsson