JPS6243416B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a DC power transmission system.

One of the major advantages of direct current power transmission between two or more stations is that it provides better controllability compared to alternating current power transmission. However, this requires a correct control program that makes optimum use of the controllability, which is often difficult to achieve. Furthermore, such programs usually presuppose the use of telecommunication links for data transmission between stations regarding measurement parameters and evaluation commands. The control program therefore becomes sensitive to any disturbances in these telecommunication links. The DC power transmission system includes at least one rectifier station and at least one inverter station at each end of a DC transmission line, and a desired power transmission amount between the two stations and operating parameters of an AC network connected to the inverter station;
Both stations are controlled based on values (operating values) of (eg frequency, etc.). In this case, a control program is usually set so that the inverter station operates under voltage control, and the other stations individually operate under voltage control. In case of communication link failure,
In the prior art, for example, control was performed by fixing the control parameters of each station to the values immediately before the failure. However, this type of control has the problem that even if the operating parameters of the AC network connected to the inverter station fluctuate, each station operates under the conditions immediately before the failure, so it cannot respond to the fluctuation. To solve this problem, the present invention provides a DC power transmission system in which both stations are controlled according to the operating values of the AC network connected to the inverter station even in the event of a communication link failure. The purpose is to

The principle of the present invention is to operate the rectifier station under voltage control by reducing the maximum voltage of the rectifier station in case of a communication link failure and controlling the rectifier station with a current command with a current margin between both stations. On the other hand, the above object is achieved by operating the inverter station under current control.

In practice, control devices are usually based on basic parameters such as voltage and current, and for the sake of clarity, the present invention will be described in the detailed description of the invention and in the claims as being based on basic parameters such as voltage and current. I will explain. Depending on the specific power transmission requirements, said fundamental parameters depend on or are derived from other parameters, namely the transmitted power, the frequency of the alternating current network connected to the station and similar operating parameters. However, it is usually possible to directly control power transmission using such other parameters, and such cases are also included in the scope of the claims.

Regulators are used which control the current or its corresponding magnitude by controlling the angle of the valves of the stationary converter for each station. A device for such purpose can be designed, for example, according to US Pat. No. 3,551,778. This device has a current regulator 3 which controls angle control devices 4 to 6 with pulse transducers 7 to set the valves of the converter according to the set current command of the station and the actual DC current. The angle control device includes a limit value control device (transducer) 8 to set the upper and lower limits of the control angle within the range of 0 to 180° to ensure correct commutation of the rectifier and inverter operation.
81 and 9,91 are provided.

A DC power transmission with two stations according to these principles can be designed according to the attached FIG. 1, in which the two A, B stations are given the same reference numerals as in the said US patent.
When it is necessary to distinguish between A and B stations, suffixes a and b are added to these numbers, respectively. In Figure 1, A station is a rectifier, B station is
It is assumed that the station operates as an inverter. This is evident from the fact that the A station has a limit transducer 81 for a certain minimum control angle, and the B station has a limit transducer 91 for a minimum commutation margin. These limit value transducers are
Both are connected to the control angle transducers 4 to 7 via an AND circuit 8 and an OR circuit 9. Converter transformer 17 is assumed to have a step switch indicated by an arrow.

Power transmission is controlled by a main controller 33, in which current commands for both stations are set in accordance with, for example, a certain desired average power. The main controller 33 can be configured, for example, in the rectifier station A, and the current commands to the B station are transmitted via a pair of parabolic antennas and a telecommunications link 34, shown by the arrow. In adder 35b in inverter station B, the current command is reduced by a current margin ΔI from transducer 36b connected to adder 35b via switching member 37b. The current command can also be set manually.

In addition to using the direct current transmission, e.g. to transmit the desired average power according to a programmed master command, it also operates in response to variations in the operating parameters, e.g. the frequency, of the alternating current network 2b, e.g. It is also used to stabilize this. Usually the rectifier station is set to operate under current control and the inverter station to operate under voltage control. AC circuit network 2
The variations in the operating parameters of b are controlled by adjusting the power transmitted from the rectifier station to the inverter station, which is done by adjusting the command given to the rectifier station operating as a current control. The operating parameters of the alternating current network 2b, e.g. Device 3
3 and is used as a current control command for station A. That is, the current command for station A is the sum of the main command corresponding to the desired average power transmission power and an additional command (for example, a signal from frequency transducer 21) for stabilizing AC network 2b. This sum signal is also sent via communication link 34 to the B station.

With such control, rectifier station A
and inverter station B operate with the current-voltage characteristics shown in FIG. In Figure 2, the horizontal axis is current,
The vertical axis indicates voltage, the solid line indicates normal operating characteristics, and the power transmission operating point is the intersection D of the two. Also, the vertical lines of both characteristics are the set current commands I _L and I _V of both stations.
, and I _V is the current margin Δ from I _L as described above.
is reduced by I. Also, the nearly horizontal straight lines indicate the maximum DC voltages E _L and _EV of each station.
The normal operation is the same for both the present invention and the prior art.
As is clear from the figure, the normal operating current I _L is determined by the operating characteristics of the rectifier station, and the operating voltage _EV is determined by the operating characteristics of the inverter station B. That is, under normal conditions, the rectifier station operates under current control, and the inverter station operates under voltage control.

Said maximum DC voltage can be determined by adjusting limit value switches 81, 91 in the rectifier station or inverter station according to U.S. Pat. No. 3,551,778 or by converter transformer 17 of said U.
It can be changed using the step switch. Reference is also made in this regard to US Pat. No. 3,339,083.

In case of communication link failure, the maximum voltage of the rectifier station is lower than the maximum voltage of the inverter station in the present invention, and the current margin ΔI
is added to the current command of the rectifier station instead of subtracting it from the current command of the inverter station, so that the rectifier station is operated by voltage control and the inverter station is operated by current control. When the maximum voltage of rectifier station A decreases to the value corresponding to the dashed line in Figure 2, the power transmission operating point moves to point D', so that rectifier station A operates under voltage control and inverter station B under current control. The functions of both stations are reversed. However, at the operating point D', the power transmission power is the current command I _L
It will decrease from to the value corresponding to _IV . In order to prevent this, a current margin ΔI is added to the current command of the rectifier station so that the operating point becomes D''.This point will be explained in more detail below.

The telecommunications links 22, 34 typically have known failure indicators 20 in both stations, so that failures in signal transmission at both stations are immediately detected and necessary action is taken in accordance with the present invention. .

In the case of a failure of the communication link, in order to continue the frequency control of the AC network 2b connected to the B station, which is carried out by an additional command from the frequency transducer 21, the additional command is sent to the rectifier station A side. Therefore, control must be performed at the B station. However, B
Since the station operates under voltage control, frequency control cannot be performed as is. For this reason, the present invention performs frequency control by forcibly operating the B station as current control. As described above, the B station can forcibly control the current by reducing the maximum voltage E _L of the A station to the broken line in FIG. This can be done by adjusting the tap changer of the transformer 17 or, even more quickly, by increasing the minimum control angle set in the limit value transducer 81. It is preferable to start this control in the latter manner and reset the tap changer after a certain delay time.

As is well known, the DC output voltage of the rectifier is controlled by the control angle α of the rectifier. The DC voltage is maximum when the control angle α is 0°, and minimum when the control angle α is 90°. Minimum control angle α of normal rectifier station
is selected by limit transducer 81 to be approximately 5°. A limit transducer is a type of delay circuit that generates a pulse when a time interval corresponding to the minimum control angle α has elapsed from the moment when the AC voltage rises from zero to positive during each cycle of the AC power applied to the rectifier. do. On the other hand, the control angle α of the rectifier in the rectifier station is controlled by the current regulator 3 based on the sum of the above-mentioned main command and additional command, and is controlled by control pulses generated by the angle control device 4-7. In the rectifier station, the angle controller pulse usually occurs after the limit transducer pulse, so under normal conditions:
It is controlled at a control angle larger than the minimum control angle α determined by the limit transducer 81 and determined by the sum of the main command and the additional command, and operates at point D in FIG. 2 so that the rectifier station operates under current control. It's getting old.

In the event of a failure of the communication link, the delay time of the pulse generation of the limit transducer 81 increases and the pulses of the limit transducer 81 occur later than the pulses of the angle controllers 4 to 7, so that the activation of the rectifier is is controlled by the pulse generated by the limit transducer 81, and its maximum voltage decreases as the delay time increases. This increase in delay time is preset such that the maximum voltage at rectifier station A is lower than the maximum voltage at inverter station B, to a level indicated by the dashed line in FIG. This allows the rectifier station to operate under voltage control and the inverter station to operate under current control. However, as mentioned above,
If this is done alone, the operating point will shift from D to D' in Figure 2, and the power transmission power will decrease from the value corresponding to I _L to the value corresponding to I _V , so the current margin Δ
Adding I to the rectifier station current command,
The operating point should be D''. This is done, for example, in the circuit of FIG. 3a.

3a, if the communication links 22, 34 are intact, the pulse of the angle controller 4-7a occurs later than the pulse of the limit transducer 81, so the gate 82 is not activated, and therefore the switch 37 is not activated.
a and 38a also do not operate. However, communication link 2
2 or 34, an indicator 20a in the rectifier station is actuated to increase the delay time of the limit transducer 81 pulse generation. Therefore, the pulse of the angle controller 4-7a will occur earlier than the pulse of the limit transducer, and the pulse of the angle controller will cause the gate 82 to be generated earlier than the pulse of the limit transducer.
operates to generate a pulse and switch 37a, 38
Close a. By closing switch 37a, the current margin is transferred from the inverter station to the rectifier station. In the case of a communication link failure, the indicator 20b also turns on the switch 37 at the inverter station, as shown in FIG. 3b.
b is opened and switch 23 is closed, the signal from the frequency transducer 21 is supplied to the current regulator 3b of the inverter station to control the current of the station.

At the same time, a suitable current command must be set at the rectifier station, which can be done in various ways.

One possible method is to fix or lock the current command set in the main controller 33 to its current state. In order to ensure power transmission stability, the current margin set in the transducer 36 is also converted to the rectifier station at the same time, preventing the risk that the current command of the inverter station temporarily exceeds the current command of the rectifier station and power transmission is stopped. ensure that

In the inverter station, when the communication link fails, the main command from the main controller 33 stops, so the value of the main command sent via the communication link 34 before the failure is locked by an appropriate means.
This is the main command in the event of a failure. This main command and the signal sent from the frequency transducer 21 when the switch 23 is closed as described above are used as additional commands, and the sum of the two is used as the current command. Based on this and the actual DC current 30 of the inverter station, the current regulator 3. Inverter 11- by angle control device 4-7
16. As mentioned above, the inverter operates under current control at this time.

If a large vibration occurs in the additional command, the current command of the inverter station may temporarily become larger than the current command of the rectifier station, and the current margin may become negative. This may cause the voltage regulators in both stations to interfere and cause the transmission voltage to drop to zero. However, this can be avoided by limiting the upper limit of the current command of the inverter station to a value that always ensures a positive current margin with respect to the current command set at the rectifier station before the telecommunications link fails. Can be done.

On the other hand, momentary interruptions in power transmission due to negative current margins are often tolerable as best transmission utilization is thus achieved. Therefore, it is justified to set the upper limit of the current command of the inverter station to a high value that corresponds to the slight negative current margin between both converters. This is especially true if the system has low responsiveness and the oscillations of the additional commands do not persist long enough to affect current and voltage control.

Instead of fixing the current command of the rectifier station to the value immediately before the failure of the telecommunications system, the current command of this station is the DC value measured at the station at that moment, i.e. the transmission current read at the inverter station at that moment. value can be used. This can be done by connecting a measuring transducer 30a in the A station via a switching member 38 to a summer 35a in this station. This switching member operates simultaneously with the switching member 37 shown in FIG. 3a. Therefore, regardless of the fluctuations in the transmission current caused by the inverter station, the current margin is always equal to
The value ΔI set for a becomes the value ΔI. At the same time, control device 3
The command from 3 is canceled. Furthermore, the effects of transient disturbances such as power transmission line disturbances and communication disturbances can be removed by performing appropriate filtering using the measurement transducer 30a and the adder 35a.

When it is desired to ensure a better current margin without increasing the initial value ΔI too much, the measured value can be sent from the transducer 30 to the adder 35 via an asymmetric filter 40, as shown in FIG. . As the transmitted current increases, the current command of the rectifier station increases at approximately the same rate as the current command, and as the current decreases, the current command decreases more slowly.

As an alternative to the above operating example in which the network 2b of the inverter station B has to be stabilized, it is also possible to stabilize the network 2a of the rectifier station A.

If the A station has been performing current control from the beginning, it must continue to do so even after the telecommunications link 34 fails. Therefore, the current command for the B station is maintained at the current value, and the current command for the A station is limited to be reduced to ensure a certain (preferably negative) current margin.

On the other hand, if the B station is performing current control from the beginning, its role must be changed as in the first example.

In the case of power transmission with more than two stations, the aforementioned principles according to the invention can be applied without additional equipment, even if the situation is somewhat complicated.

As shown in FIG. 5, a power transmission having three stations may consist of a rectifier station A and two inverter stations B and C. Each station is designed similarly to the station according to FIG. The current-voltage characteristics in this case can be shown as shown in FIG.

Inverter station C according to the example in FIG.
has the lowest maximum voltage and therefore determines the voltage, and the A, B stations determine the current in these stations individually. The current commands for the three stations follow the formula I _A = I _B + I _C + ΔI,
The current margin ΔI is extracted at the C station. For example, the main controller 33 is further supplied with a main command from the B station and an additional command from the C station, and these two commands together form the control command for the A station. In this regard, reference is made to US Pat. No. 3,526,780.

If the telecommunications link between the stations then fails, the C station must take charge of its own current control, which is done by reducing the maximum voltage of the A station, as shown in Figure 3a. The station is voltage controlled. This effect is promoted, for example, by simultaneously increasing the maximum voltage of the C station by means of a tap changer on the transformer 17 of the station. By this C
The station can control the current more quickly, resulting in characteristics as shown in FIG.

In a case like the example above, rectifier station A
A current command is preferably obtained from the measuring transducer 30, so that this command is always equal to the current DC current plus a current margin appropriately transferred from the C station to the A station.

The fact that the rectifier station is voltage-controlled in this case is very advantageous if, for example, a telecommunications link is disconnected and one of the inverter stations B, C is suddenly switched off. If the rectifier station is controlling the current with a constant current command, it means that the other inverter stations are overloaded. However, since the rectifier station is voltage controlled, the other inverter stations will only draw the current set to this station.

However, there is a short-term load increase in the remaining inverter stations, partly due to the inductance of the power line and partly due to the slope of the upper line of the rectifier characteristic.

This effect can be prevented by making the upper straight line horizontal as shown in FIG. This can be done by controlling the rectifier station A with a constant voltage, which is done by the device of FIG. 9 connected to the A station of FIG.

A measuring voltage divider 83 is connected to the power line 1, which is connected to a voltage regulator 85 with a device 84 for setting the desired value. Voltage regulator 85 controls limit angle transducer 81 via switching member 86 which is controlled by telecommunications link failure indicator 20a. In this case, the limit angle transducer 81 is not controlled directly from the indicator 20a, but is set such that the rectifier limit angle corresponds to the desired constant line voltage. Desired value setting device 8
4 is suitably set in relation to the line voltage just before the telecommunications link fails, but it can also be set in relation to appropriate system parameters.

From the above, it is clear that when applying the present invention to a facility, the principle of the present invention that is most suitable for the operation in question must be selected on a case-by-case basis. Another question is what special requirements are made for continuous operation in the event of various disturbances or failures.

It is clear that the invention is also relevant in cases where the current command has first and second components, and the second component relates to the parameters of an alternating current circuit connected to one station. As mentioned above, the first command component can be a programmed command that is generally more stable than the second command component, and may be temporarily zero. In the case of three or more stations, two (or more) command components are typically each associated with its own station.

[Brief explanation of the drawing]

FIG. 1 shows a two-station power transmission device according to the invention, FIG. 2 shows the current-voltage characteristics of the two stations, and FIGS. 3a, 3b and 4 show partial details of the station shown in FIG. 5 shows a multi-point power transmission device having three stations, FIGS. 6, 7 and 8 show its current-voltage characteristics, and FIG. 9 shows partial details of a rectifier station for multi-point power transmission. shows. Explanation of reference symbols, 2... AC circuit network, 3... Current regulator, 4 to 7... Angle control device, 8, 82... AND
circuit, 9...OR circuit, 17...converter transformer,
20... Fault indicator, 21... Frequency transducer, 22, 34... Telecommunications link, 23... Circuit breaker, 30... Measuring transducer, 3
3... Control system, 35... Adder, 36... Transducer, 37, 86, 87... Switching member, 40... Asymmetric filter, 81, 91... Limit value transducer, 83... Measuring voltage divider, 84... Desired value Setting device, 85...voltage regulator.

Claims (1)

[Claims] 1. A DC power transmission line 1 and at least one rectifier station A and an inverter station B connected to both ends thereof, each station controlling the control angle of a current regulator 3 and its own station to a predetermined value. A control device including a limit angle limiting device 81, 8; 91, 9 for limiting the limit angle,
A current command is set in the current regulator so as to provide a predetermined current margin (ΔI) between the rectifier side and the inverter side, and the current command is set in the main controller 33 according to the desired amount of power transmitted between both stations. The current command is determined based on the main command generated by the inverter station B and an additional command indicating the value of a parameter (referred to as an operating value) related to the operation of the AC circuit network 2b connected to the inverter station B, and at least one station receives the current command. is transmitted via the telecommunications links 22, 34, and the limiting angle limiting device and the current margin of each station are such that during normal operation, the inverter station operates as a voltage control and the other stations individually operate as a current control. In a DC power transmission system configured as such, a failure indicating device 20 is configured to operate and generate a signal in the event of a failure of the communication link, and for forcing the inverter station to operate under current control in the event of a failure of the communication link. , the failure indicating device 20
The maximum voltage of the rectifier station A is reduced in response to the operation of the rectifier station A so that the rectifier station operates under voltage control, and at the same time the current command given to the rectifier station is the sum of the current margin and a predetermined current value. (Article 3a)
The DC power transmission system is characterized in that it is provided with the following. 2. The DC power transmission system according to claim 1, wherein the predetermined current value is a DC current value measured at each point in time at the rectifier station. 3. The DC power transmission system according to claim 1, wherein the predetermined current value is fixed to a current value at the time of occurrence of a fault in the remote communication link. 4. Claim 1, characterized in that the predetermined current value is fixed to the current value at the time of failure of the telecommunications link, and the current margin is increased in relation to the margin before the failure of the telecommunications link. DC power transmission system. 5. In claim 1, the predetermined current value is fixed to the current value at the time of failure of the telecommunications link, while the current command of the station forced to undergo current control is within a certain minimum negative current margin. A direct current power transmission system characterized in that it is limited to a value corresponding to . 6. The DC power transmission system according to claim 1, wherein the voltage reduction at the other station is performed by first increasing its limit angle by a certain amount and then reducing its AC voltage. 7. A direct current according to claim 1, wherein the predetermined current value is a measured direct current value at each point in time at the station, and the measurement of the direct current 30 is performed by an asymmetric filter 40. power transmission system. 8 In claim 1, when a current control station is changed to voltage control and a voltage control station is changed to current control, the station current command changed to voltage control is fixed to the value at that time. A DC power transmission system characterized by: 9. In claim 1, when the other station A is a rectifier station, the predetermined current value is a DC current value measured at each point in time in the other station, and the voltage controls 83 to 86 are set to this value. A DC power transmission system characterized by being superimposed on a station. 10. A DC power transmission system according to claim 9, characterized in that the voltage of the other station is determined by some system parameters of an AC network connected to this station.