Method and device for compensation of unbalance in a series compensated converter station

Claim 1

A method for controlling a series-compensated converter station included in an installation for transmission of high-voltage direct current, said converter station comprising a converter (SR1, SR2), controlled by control equipment (CE1, CE2), with at least one 6-pulse bridge (BR), said 6-pulse bridge via series capacitors (SCR, SCS, SCT) being connected to a three-phase alternating-voltage network (N1, N2) with a fundamental frequency (f 01 , f 02 ), said control equipment generating an ordered value (AOL) of a control angle (α) for valves (V1-V6) included in the 6-pulse bridge in dependence on a limiting signal (AMAXL) capable of being controlled, said method comprising the steps of: forming an amplitude signal (AMPL) which corresponds to the amplitude (C1) for a component (C1 cos (2πf 0 t+φ1)) of the fundamental frequency in the direct voltage (Udb) of the 6-pulse bridge, continuously calculating a compensating signal (ACOMP) in dependence on a sensed voltage (Un1, Un2) at the converter station and on the amplitude signal according to a relationship (H0, H1) which at least approximately imitates a relationship according to which a control-angle addition (Δα), at a commutating margin (τ m ) for the valves equal to a preselected value (τ p ), is a function (F0) of a current (Id1, Id2) in the converter station, said voltage in the converter station and the amplitude (C 1 ) for said component of the fundamental frequency in the direct voltage of the 6-pulse bridge, and forming the limiting signal in dependence on the compensating signal for the purpose of maintaining the commutating margin (τ m ) for the valves equal to at least the preselected value (τ p ) in case of unbalance between the voltages (UCR, UCS, UCT) of the series capacitors.

Claim 2

A method for controlling a series-compensated converter station included in an installation for transmission of high-voltage direct current, said converter station comprising a converter (SR1, SR2), controlled by control equipment (CE1, CE2), with at least one 6-pulse bridge (BR), said 6-pulse bridge via series capacitors (SCR, SCS, SCT) being connected to a three-phase alternating-voltage network (N1, N2) with a fundamental frequency (f 01 , f 02 ), said control equipment generating an ordered value (AOL) of a control angle (α) for valves (V1-V6) included in the 6-pulse bridge in dependence on a limiting signal (AMAXL) capable of being controlled, said method comprising the steps of: forming an amplitude signal (AMPL) which corresponds to the amplitude (C1) for a component (C1 cos (2πf 0 t+φ1)) of the fundamental frequency in the direct voltage (Udb) of the 6-pulse bridge, continuously calculating a compensating signal (ACOMP) in dependence on a sensed voltage (Un1, Un2) at the converter station and on the amplitude signal according to a relationship (H0, H1) which at least approximately imitates a relationship according to which a control-angle addition (Δα), at a commutating margin (τ m ) for the valves equal to a preselected value (τ p ), is a function (F0) of a current (Id1, Id2) in the converter station, said voltage in the converter station and the amplitude (C 1 ) for said component of the fundamental frequency in the direct voltage of the 6-pulse bridge, and forming the limiting signal in dependence on the compensating signal for the purpose of maintaining the commutating margin (τ m ) for the valves equal to at least the preselected value (τ p ) in case of unbalance between the voltages (UCR, UCS, UCT) of the series capacitors.

Claim 8

A device for control of a series-compensated converter station included in an installation for transmission of high-voltage direct current, said converter station comprising a converter (SR1, SR2), controlled by control equipment (CE1, CE2), with at least one 6-pulse bridge (BR), said 6-pulse bridge via series capacitors (SCR, SCS, SCT) being connected to a three-phase alternating-voltage network (N1, N2) with a fundamental frequency (f 01 , f 02 ), said control equipment generating an ordered value (AOL) of a control angle (α) for valves (V1-V6) included in the 6-pulse bridge in dependence on a limiting signal (AMAXL) capable of being controlled, and voltage measuring devices (UM1, UM2) for sensing the direct voltage (Udb11, Udb12, Udb21, Udb22) of at least one of the 6-pulse bridges, wherein the control equipment comprises an amplitude-value forming unit (AVU), which is supplied with a measured value (UDM) of the direct voltage of at least one of the 6-pulse bridges and forms an amplitude signal (AMPL) corresponding to the amplitude (C 1 ) for a component of the fundamental frequency in the direct voltage (Udb) of the 6-pulse bridge, a calculating unit (CALC2), which is supplied with said amplitude signal and a value (UDI01, UDI02) of the ideal no-load direct voltage (Udi01, Udi02) and forms a compensating signal (ACOMP) in dependence on a continuously calculated value of a control-angle addition (Δφ), calculated in dependence on a voltage (Un1, Un2) at the converter station and on the amplitude signal according to a relationship (H0, H1) which at least approximately imitates a relationship according to which the control-angle addition, at a commutating margin (τ m ) for the valves equal to a preselected value (τ p ), is a function (F0) of a current (Id1, Id2) in the converter station, said voltage at the converter station and the amplitude (C 1 ) for said component of fundamental frequency in the direct voltage of the 6-pulse bridge, and wherein the limiting signal is formed in dependence on the compensating signal for the purpose of maintaining the commutating margin (τ m ) for the valves equal to at least the preselected value (τ p ) in case of unbalance between the voltages (UCR, UCS, UCT) of the series capacitors.

Claim 9

A device for control of a series-compensated converter station included in an installation for transmission of high-voltage direct current, said converter station comprising a converter (SR1, SR2), controlled by control equipment (CE1, CE2), with at least one 6-pulse bridge (BR), said 6-pulse bridge via series capacitors (SCR, SCS, SCT) being connected to a three-phase alternating-voltage network (N1, N2) with a fundamental frequency (f 01 , f 02 ), said control equipment generating an ordered value (AOL) of a control angle (α) for valves (V1-V6) included in the 6-pulse bridge in dependence on a limiting signal (AMAXL) capable of being controlled, and voltage measuring devices (UM1, UM2) for sensing the direct voltage (Udb11, Udb12, Udb21, Udb22) of at least one of the 6-pulse bridges, wherein the control equipment comprises an amplitude-value forming unit (AVU), which is supplied with a measured value (UDM) of the direct voltage of at least one of the 6-pulse bridges and forms an amplitude signal (AMPL) corresponding to the amplitude (C 1 ) for a component of the fundamental frequency in the direct voltage (Udb) of the 6-pulse bridge, a calculating unit (CALC2), which is supplied with said amplitude signal and a value (UDI01, UDI02) of the ideal no-load direct voltage (Udi01, Udi02) and forms a compensating signal (ACOMP) in dependence on a continuously calculated value of a control-angle addition (Δφ), calculated in dependence on a voltage (Un1, Un2) at the converter station and on the amplitude signal according to a relationship (H0, H1) which at least approximately imitates a relationship according to which the control-angle addition, at a commutating margin (τ m ) for the valves equal to a preselected value (τ p ), is a function (F0) of a current (Id1, Id2) in the converter station, said voltage at the converter station and the amplitude (C 1 ) for said component of fundamental frequency in the direct voltage of the 6-pulse bridge, and wherein the limiting signal is formed in dependence on the compensating signal for the purpose of maintaining the commutating margin (τ m ) for the valves equal to at least the preselected value (τ p ) in case of unbalance between the voltages (UCR, UCS, UCT) of the series capacitors.