Abstract:
A control device for rectifier stations in a high-voltage DC transmission system has a rectifier drive unit and an inverter drive unit for driving power rectifier stations that are working either as a rectifier or as an inverter. The trigger angles for the rectifier or for the inverter can be adjusted and regulated by way of the rectifier drive unit and the inverter drive unit respectively. A delay element is placed between the rectifier drive unit and the inverter drive unit with which the start time for regulating the trigger angle for the inverter relative to the start time for regulating the trigger angle for the rectifier can be delayed by a predetermined delay time. Because of less mutual interaction of the trigger angle control processes, a relatively faster transition from an initial operating state into a new stationary state results.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a control device for converter stations in a high-voltage direct-current transmission device. 
     For high-voltage direct-current transmission, it is necessary for converter stations which operate as a rectifier or as an inverter depending on the current flow direction to be driven in a defined manner when the operating state of the high-voltage direct-current transmission device changes. With the modern conventional design of converter stations using thyristors, this is normally done by setting trigger angle regulators, which drive the converter stations, to previously calculated values which are defined to correspond to the new operating state. After simultaneous enabling of the trigger pulses at the converter stations, the trigger angle regulators are enabled at the same time, with the trigger angles then being set to the rated values, on the basis of the previously calculated values, via a control loop. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention is based on the object of specifying a control device for converter stations in a high-voltage direct-current transmission device, by means of which a new steady-state operating state can be reached in a relatively short time starting from an initial operating state. 
     In the case of a control device for converter stations in a high-voltage direct-current transmission device, this object is achieved according to the invention by a rectifier drive unit for driving a converter station which operates as a rectifier and by an inverter drive unit for driving a further converter station which operates as an inverter, which each have a trigger angle regulator for setting and regulating trigger angles for the rectifier and the inverter, respectively, with a delay element being located between the rectifier drive unit and the inverter drive unit, by means of which a predetermined delay time can be enabled after the enabling of the trigger angle regulator of the rectifier drive unit for regulating the trigger angle of the rectifier and the trigger angle regulator of the inverter drive unit for regulating the trigger angle of the inverter. 
     Since, according to the invention, the trigger angle regulator for the inverter is enabled with a time delay after the trigger angle regulator for the rectifier, the trigger angle for the rectifier can first of all be regulated from a value previously calculated on the basis of the new operating state to a transitional value which is already relatively close to a subsequent, quasi-steady-state value, with this control process taking place without being influenced by processes at the inverter drive unit. Only when, after the delay time, the inverter drive unit for driving the inverter is connected for the trigger angle of the inverter on the basis of the initial previously calculated value does the corresponding control process at the inverter influence the rectifier drive unit, although this avoids relatively long-lasting equalization processes resulting from the control process having already been substantially completed there. Overall, this results in a relatively short time period for the transition of the high-voltage direct-current transmission device from the initial operating state to the further operating state. 
     Further expedient refinements of the invention are the subject matter of the dependent claims. 
     The invention will be explained in more detail in the following text using one exemplary embodiment and with reference to the figures of the drawing, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIG. 1  shows a block diagram of a high-voltage direct-current transmission device having a control device for converter stations, and 
         FIG. 2  shows an illustration of the signals for driving the various components of the rectifier drive unit and of the inverter drive unit. 
     
    
    
     DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a high-voltage direct-current transmission device  1  schematically, in the form of a block diagram. In this exemplary embodiment, the high-voltage direct-current transmission device  1  has a first direct-current line  2  and a second direct-current line  3 , which are each represented by relatively thick lines, with a load  4  being shown symbolically in the second direct-current line  3 , in order to represent the various losses which undoubtedly occur. 
     The direct-current lines  2 ,  3  are respectively connected to a thyristor-based rectifier  5 , as a first converter station, and to a thyristor-based inverter  6 , as a second converter station. The rectifier  5  couples the high-voltage direct-current transmission device  1  on the feed side via a first AC voltage line arrangement  7 , which is shown as a thick line, to a first AC voltage system  8 , while the inverter  6  couples the high-voltage direct-current transmission device  1  on the output side via a second AC voltage line arrangement  9 , which is shown by a thick line, to a second AC voltage system  10 , such that the AC voltage systems  8 ,  10  are connected to one another for transmission of power, in this case from the first AC voltage system  8  to the second AC voltage system  10 . 
     Furthermore, as can be seen from  FIG. 1 , the high-voltage direct-current transmission device  1  has a central unit  11  and, as converter drive units, a rectifier drive unit  12 , which is connected to the rectifier  5 , and an inverter drive unit  13 , which is connected to the inverter  6 , with the lines for transmission of control signals being illustrated considerably thinner than the direct-current lines  2 ,  3  and the AC voltage line arrangements  7 ,  9  in  FIG. 1 , for clarity reasons. 
     The rectifier  5  can be driven, as will be explained in more detail further below, by the rectifier drive unit  12  via an enable module  14 , a trigger angle transmitter  15  and a trigger angle regulator  16 . 
     In a corresponding manner, the inverter drive unit  13  for driving the inverter  6  is likewise equipped with an enable module  17 , a trigger angle transmitter  18  and a trigger angle regulator  19 . 
     The trigger pulses for the rectifier  5  and the inverter  6  can be activated by the enable modules  14 ,  17 . The trigger angle transmitters  15 ,  18  feed previously calculated trigger angles to the rectifier  5  and to the inverter  6  as a function of the initial operating state and of the new operating state to be assumed. 
     Typical changes of operating states are, for example, the transitions from a switched-off state to a minimum-power state, the sudden change from an initial nominal power to a new nominal power, or a change in the power direction, with the opposite power flow direction, and therefore a change in the functionalities of the converter stations. 
     Furthermore, the high-voltage direct-current transmission device  1  is equipped with a delay element  20  which, in this exemplary embodiment, can expediently be driven via the central unit  11 , and is connected to the rectifier drive unit  12  and to the inverter drive unit  13 . The delay element  20  makes it possible to enable the trigger angle regulator  19  of the inverter drive unit  13  for regulating the trigger angle for the inverter  6  when a predetermined delay time has elapsed after enabling of the trigger angle regulator  16  of the rectifier drive unit  12  for regulating the trigger angle for the rectifier  5 . 
     In the steady operating state, there is a connection via the central unit  11  between the rectifier  5  and the inverter  6  in order, for example, to calculate the resistance, which is dependent on temperature fluctuations, in the direct-current lines  2 ,  3 , which resistance is required for the advance calculation of the new steady-state trigger angles of the trigger angle regulators  16 ,  19 . 
     As an example of a change to an operating state,  FIG. 2  illustrates the transition from a switched-off state to an operating state with a predetermined rating, for example the minimum power, illustrated in the form of a graph of specific signal profiles for major components in the high-voltage direct-current transmission device  1  as explained in  FIG. 1 . The time t is plotted on a time axis  21  as the abscissa, with characteristic times t 1 , t 2 , t 3 , t 4 . Signal values S are plotted in arbitrary units along a signal axis  22  as the ordinate, which is at right angles to the time axis  21 . 
     The lowermost signal profile in  FIG. 2  shows the trigger pulse enable signal  23  from the enable module  14  of the rectifier drive unit  12 . Until the time t 1 , the trigger pulse enable signal  23  is blocked, so that the rectifier drive unit  12  does not emit any trigger pulses to the rectifier  5 . At the time t 1 , the trigger pulse enable signal  23  changes from the low level to a high level, where it then remains, and at which the rectifier drive unit  12  passes trigger pulses to the rectifier  5 . 
     The signal profile located immediately above the trigger pulse enable signal  23  in  FIG. 2  shows the trigger angle signal  24  from the trigger angle transmitter  15  of the rectifier drive unit  12 . Until the time t 1 , the trigger angle signal  24  is at a value which corresponds to a trigger angle of 90 degrees, while, from the time t 1  until a later time, it is changed to the previously calculated value for the trigger angle of the rectifier  5 . 
     The signal profile located immediately above the trigger angle signal  24  in  FIG. 2  shows the trigger angle regulator enable signal  25 , by means of which the trigger angle regulator  16  of the rectifier drive unit  12  to regulate the trigger angle signal  24 , at a time t 2  after characteristic parameters of the direct-current circuit come within regulator limits, as is shown in the illustration in  FIG. 2  by the change in the trigger angle regulator enable signal  25  from a mid-level to a high level. In consequence, after the level change of the trigger angle regulator enable signal  25 , the rectifier  5  is in a steady operating state, except for minor fluctuations in the trigger angle signal  24  resulting from the control process. 
     The signal profile which is located a certain distance above the trigger angle regulator enable signal  25  in  FIG. 2  shows the trigger pulse enable signal  26  from the enable module  17  of the inverter drive unit  13 . The trigger pulse enable signal  26  for the inverter  6  changes from a mid-level to a high level at the time t 1 , corresponding to the trigger pulse enable signal  23  for the rectifier  5 . 
     The signal profile shown immediately above the trigger pulse enable signal  26  for the inverter  6  in  FIG. 2  shows the trigger angle signal  27  from the trigger angle transmitter  18  for the inverter drive unit  13 . At the time t 1 , the trigger angle signal  27  changes from an initial level to a previously calculated value at an appropriate level for initial driving of the inverter  6 , which was calculated previously taking account of the operating characteristics of the high-voltage direct-current transmission device  1  in the new operating state. 
     The signal profile located immediately above the trigger angle signal  27  for the inverter  6  in  FIG. 2  shows the trigger angle regulator enable signal  28  for enabling the trigger angle regulator  19  of the inverter drive unit  13 , which changes at a time t 3  from a low level to a high level in order to enable the trigger angle regulator  19  for the inverter drive unit  13 , such that, after the time t 3 , the trigger angle regulator  19  for the inverter drive unit  13  regulates the trigger angle for the inverter  6 . This delay time Δt=t 3 −t 2  is governed by the delay element  20 . 
     At a specific time t 4 , which occurs later than the time t 3 , the high-voltage direct-current transmission device  1  is then in the new and also steady operating state. 
     Typically, the time period from the time t 1  to the time t 4  is about 250 milliseconds, while the change in the operating state, based on conventional technology, lasts for about 1 second. 
     It is self-evident that the approach according to the invention, specifically switching the trigger angle regulator enable signal  28  for the converter station which operates as an inverter  6  to enable a delay with respect to the trigger angle regulator enable signal  25  for the converter station which operates as a rectifier  5 , with this delay being sufficient for the trigger angle signal  24  for the rectifier  5  to lead to a trigger angle which fluctuates only to a relatively minor extent within a predetermined lower regulator limit and a predetermined upper regulator limit, can be used appropriately in a corresponding manner for other changes in operation, for example for a change in the power flow direction.