JPH0254013B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a stopping method for a bipolar DC power transmission system,
In particular, the present invention relates to a method for stopping a bipolar DC power transmission system that shuts down only the positive side or the negative side of a bipolar DC power transmission system in which the positive and negative sides have a common DC current return path.

[Background of the invention]

Figure 1 shows the schematic configuration of a typical bipolar DC power transmission system. This diagram shows how power from AC system A is converted to AC system B.
The figure shows the case of transporting the power from the AC system A to the forward converter REC ₁ and the DC reactor during bipolar operation of the DC transmission system.
DCL ₁ , DCL ₃ , DC transmission line HL ₁ , and inverter
The alternating current is distributed into a positive DC transmission system P consisting of INV ₁ and a negative DC transmission system N consisting of forward converter REC ₂ , DC reactors DCL ₂ , DCL ₄ , DC transmission line HL ₂ , and inverter INV _2. Sent to system B.

In the bipolar DC transmission system shown in Figure 1, a total shutdown in which DC transmission systems P and N are stopped simultaneously can be performed using the conventional shutdown method, but an individual shutdown in which only DC transmission systems P or N is stopped cannot be performed using the conventional method. It turned out to be impossible.

An overview of the conventional stopping method will be described below, taking the case of total stopping as an example, and then problems of the conventional stopping method in individual stopping will be described.

Figure 2a shows the operation of the bipolar DC power transmission system in Figure 1 when the entire system is stopped.At time _t0 in Figure 2a, the stop command signal _S1 changes from High to
When it changes to Low, the soft stop control function (control function that smoothly lowers the DC voltage and DC current) of the converter control device (not shown) is activated, and as shown in the figure, the current voltage v ₁ , v ₂ , DC current i ₁ and i ₂ decrease smoothly. . Next, at time t ₁ when the DC voltages v ₁ , v ₂ and the DC currents i ₁ , i ₂ have decreased to a certain level, the bypass pair signals SBPP ₁ , SBPP ₂ change from Low to low.
The voltage changes to High, each converter enters a bypass pair state, and the DC voltages v ₁ and v ₂ become O(pu). Then, at time t ₂ , the bypass pair signals SBPP ₁ and SBPP ₂
Simultaneously with the change from High to Low, the gate block signals S _GB1 and S _GB2 change from High to Low, each converter enters the gate block state, and the DC current i ₁ ,
i ₂ becomes O(pu). Note that 1 and 2 attached to each signal in this figure mean control signals to the positive and negative side converters, respectively.

FIG. 2b shows the operation when the above-described stopping method is applied to the individual stopping of stopping only the negative side DC power transmission system N shown in FIG. 1.

In this case, the DC voltage v ₂ on the negative side and the DC current i ₂ on the negative side begin to decrease at time t ₀ , and the forward converter REC ₂ and the inverse converter INV ₂ enter the bypass pair state at time t ₁ . Thereafter, at time t ₂ , the forward converter REC ₂ and the inverse converter INV ₂ enter the gate block state, but the first
Depending on the size ratio of the impedance Z _L of the neutral line HL and the impedance Z _H of the negative DC transmission line HL ₂ in the figure, the positive DC current i ₁ changes to the negative DC transmission system N
, the thyristor valve pair that was conducting before time t ₂ continues to be conducting after time t ₂ ,
Cannot be stopped individually.

Therefore, with the conventional shutdown method, it is not possible to individually shut down only the positive pole side or the negative pole side of a bipolar DC power transmission system.

[Purpose of the invention]

An object of the present invention is to provide a method for stopping a bipolar DC power transmission system that is capable of stopping only the positive side or the negative side of the bipolar DC power transmission system.

[Summary of the invention]

In a bipolar DC transmission system, when the DC current of one of the poles to be stopped decreases, the present invention causes the converter of the pole that is not to be stopped to operate as a bypass pair, and during that operation period, the converter of the pole to be stopped is operated as a bypass pair. By stopping the generation of firing pulses in the forward converter or reverse converter on the side, the current margin for stopping can be reduced, and the inability to stop due to the inflow of DC current on the other pole side can be prevented, This makes it possible to stop only the positive electrode side or the negative electrode side.

[Embodiments of the invention]

FIG. 3 shows an embodiment of the present invention, in which the present invention is applied to an individual shutdown in which only the negative side DC transmission system N is stopped in a bipolar DC transmission system consisting of a positive side DC transmission system P and a negative side DC transmission system N. This shows the case where

Figure 4a shows the operation of the control system when the forward converter REC ₂ prevents the inflow of DC current when individually stopping the DC power transmission system N, and the DC voltage v _2r on the forward converter REC ₂ side. and DC current i _2r , DC voltage v _2i on the inverter INV ₂ side, and DC current i _2i responses.

In Fig. 3, the central command station CC is connected to the group command station LC _2r on the forward converter side in order to specify the flow direction in advance.
power flow command S ₂ to the group command station LC _2i on the inverter side.
A power flow command S ₂ ′ is given to the constant current control ACR of both.
(not shown) is performing an operation of switching the application of a current margin setting value. In Figure 3, the tidal flow command
By applying S ₂ and S ₂ ', the current direction is set such that power is transmitted from AC system A to AC system B, as in the case of FIG. In this case, as shown in Figure 3, the power flow command S ₂ is the bypass pair circuit on the forward converter side.
It is also given to BPP _r to lock the same circuit BPP _r . Further, the power flow command S ₂ ' is given to the bypass pair circuit BPP _i on the inverter side, but this command S ₂ ' does not contribute to the locking of the circuit BPP _i .

Now, in Figure 3 and Figure 4 a, the central command station
When CC commands a stop command S ₁ on the DC system N side at time t ₀ , the forward converter REC ₂ and the inverse converter INV ₂ control the DC voltage v _2r of the same system by the soft stop control described above.
and gradually decrease v _2i and direct current i _2i and i _2i .
After that, the bypass pair signal SBPP _i from the bypass pair circuit BPP _i is applied to the inverter INV ₂ side at time t ₁ and the inverter INV ₂ enters the bypass state.
The DC voltage v _2i becomes 0. However, since the forward converter REC ₂ at time t ₁ continues commutation operation,
Direct currents i _2r and i _2i continue to be energized. Then the point
At t ₂ , the signal SGB _r of the gate block circuit GB _r
is applied to the pulse generating phase shifter APPS _r of the forward converter REC ₂ , stopping the firing pulse of the pulse generating phase shifter APPS _r and blocking the gate of the forward converter REC ₂ . The DC voltage v _2r and DC current i _2r of the forward converter REC ₂ at this time t ₂ have sufficiently decreased,
The forward converter REC ₂ can stop the DC current i ₂ on the DC system N side and prevent the DC current from flowing on the DC system P side. The inverter INV ₂ then
At time i ₃ the signal of gate block circuit GB _i
The SGB _i stops the generation of firing pulses in the pulse generation phase shifter APPS _i , gates the inverter INV ₂ , and completes the stopping operation.

That is, in one embodiment of FIG. 4a in FIG. 3, the forward converter REC ₂ is made to stop the process of bypass pair operation, and the gate is immediately blocked when the DC current has sufficiently decreased, and the DC system N side is This is intended to prevent the inflow of DC current from the DC system P side.

Next, an embodiment will be described in which, when stopping the DC system N side, the above-mentioned stopping means is performed by the inverter INV ₂ . The configuration of the control circuit, etc. in the stopping operation in this case is the same as that shown in Fig. 4a, so we will use Fig. 3.
This will be explained with reference to FIG. 4b.

As already described in the embodiment shown in Figure 4a, the central command station CC sends the tidal flow command _S2 to the group command station in advance.
A power flow command S 2 ' is given to LC _2r and a power flow command S 2 _' is given to the group command station LC _2i , and the power flow direction is from AC system A to AC system B as in the above case. However, in this embodiment, the power flow command _S2 given by the central command station CC to the bypass pair circuit BPP _r on the side of the forward converter REC ₂ is a command that does not lock the circuit BPP _r , and is also a command for reverse conversion. Power flow command given to bypass pair circuit BPP _i on device INV ₂ side
S ₂ ' is a command to lock the circuit BPP _i . Therefore, in the embodiment in this case the inverter INV ₂
side is contributed to the termination of the DC current on the DC transmission line HL ₂ .

That is, in FIGS. 3 and 4b, the central command station CC issues a stop command S ₁ of the DC power transmission system N at time t ₀ .
When commanded, the forward converter REC ₂ and the inverse converter INV ₂ gradually reduce the DC voltages v _2r and v _2i and the DC currents i _2r and i _2i of the same system by soft stop control.
Thereafter, the bypass pair signal SBPP _r from the bypass pair circuit BPP _r is applied to the forward converter REC ₂ at time t ₁ , and the forward converter REC ₂ enters the bypass pair state.
Therefore, the direct current v _2r on the forward converter REC ₂ side at time t ₁ becomes zero. When the DC voltage electromotive force disappears in the forward converter REC ₂ due to this bypass pair current, the inverter INV ₂ , which continues commutation operation, moves from the point in time t ₁ to the forward converter operating range under constant current control. , and the DC currents i _2r and i _2i of the DC transmission system N are passed through. Then, at time t ₂ , the pulse generating phase shifter APPS _i of the inverter INV ₂ is connected to the gate block circuit.
Given the signal SGB _i of GB _i , pulse generation phase shifter APPS _i
ignition pulse is stopped and the gate of inverter INV ₂ is blocked. Since the DC voltage v _2i and DC current i _2i of the inverter INV ₂ at this time t ₂ have sufficiently decreased, the inverter INV ₂ stops the DC current i ₂ of the DC transmission system N, and It is possible to prevent direct current from flowing into the system P side. The forward converter REC ₂ then stops the firing pulses of the pulse generating phase shifter APPS _r at time t ₃ by means of the signal SGB _r of the gate block circuit GB _r , and the forward converter REC ₂
The stop operation is completed by performing gate blocking.

That is, in one embodiment of FIG. 4b, the inverse transformer
INV ₂ is made to stop the process of bypass pair operation, and when the DC current has sufficiently decreased, the gate is immediately blocked, and the DC transmission system is connected to the DC transmission system N side as in the case of the embodiment shown in Fig. 4a. This is intended to prevent direct current from flowing into the P side.

When stopping either the positive or negative side of a bipolar DC transmission system, the stopping method of the present invention is such that the AC/DC converter connected to the DC transmission system to be stopped is connected to the central control station CC. This is an essential stopping method when stopping either one of the DC systems.

FIG. 5 shows the relative relationship in the stopping operation of both AC/DC converters connected to both ends of the transmission line of the DC power transmission system to be stopped in the stopping method of the present invention.

The a side of the figure shows the stopping operation of the AC/DC converter where gate blocking is performed to stop the DC current in the DC system that should be stopped, and the b side shows the bypass pair state to suppress the generation of overvoltage. This is the stopping operation of the AC/DC converter. As shown in the figure, the AC/DC converters on the a side and the b side, which are in steady operation RO, are subjected to soft stop control SC at time t ₀ by a stop command, and then the AC/DC converters on the b side are point in time
Enter the bypass pair BPP state at t ₁ . Thereafter, in order to stop the DC current in the DC transmission system, the AC/DC converter on the a side is gate blocked GB at time _t2 during the period of this bypass pair BPP. Then the point
At _t3 , the AC/DC converter on the b side is gate-blocked, and the stopping operation according to the stopping method of the present invention is completed.

In this case, the gate blocking of the AC/DC converter on the a side, that is, the AC/DC converter that stops the DC current of the DC power transmission system, is performed during the bypass pair period of the AC/DC converter on the b side in order to suppress the occurrence of overvoltage. In this stopping system, even if the AC/DC converter on the a side is operated as a forward converter or an inverse converter, and the AC/DC converter on the b side is operated as a forward converter or an inverse converter, the a side and b side in FIG. There is no change in the operational relationship.

In this way, by using bypass pair operation in combination, the voltage ripples of the paired converters are not added, the current margin to prevent current interruption can be reduced, and voltage fluctuations during gate blocking can be reduced. As mentioned above, this has the effect of suppressing the occurrence of overvoltage.

FIG. 6 shows an embodiment of a bipolar DC power transmission device to which another stopping method of the present invention is applied.

The AC/DC converters of the bipolar DC power transmission system shown in FIG. 6 are assumed to be operated as forward converters on the AC system A side and inverse converters on the AC system B side as described above.
In the stopping method shown in the figure, when stopping an AC/DC converter of a DC system to be stopped, both the forward converter side and the inverse converter side are gate blocked to stop the DC current of the same DC system. The case of FIG. 6 also takes as an example the case where the N side of the DC power transmission system is stopped. In the case of Fig. 6, input of the power flow command S ₂ (and S ₂ ') from the central control station CC is stopped to the bypass pair circuit BPP _r (and BPP _i ) as described in Fig. 3, and a stop command is issued. A method is adopted in which the command S ₃ is output following S ₁ to lock the bypass pair circuit BPP _r (and BPP _i ).

FIG. 7 shows a stopping operation on the N side of the DC system in the bipolar DC transmission system of FIG.

When the central command station CC issues a stop command S ₁ at time t ₀ to stop the DC power transmission system N, the forward converter REC ₂ and the inverse converter INV ₂ control the DC voltage of the same system by soft stop control. Gradually lower v _2r and v _2i and direct current i _2r and i _2i . Based on the stop command _{S1 ,} the central command station CC outputs _a command _S3 as shown in _{FIG .} lock. Thereafter, at time t ₁ , the forward converter REC ₂ side stops the ignition pulse of the pulse generator phase shifter APPS r by the signal SGB _r of the gate block circuit GB _r , and the inverse converter INV ₂ side stops the ignition pulse of the pulse generator phase shifter APPS _r by the signal SGB r of the gate block circuit GB r. The ignition pulse of the pulse generation phase shifter APPS _i is stopped by the signal SGB _r of GB _r , and the gates of the forward converter REC ₂ and the inverse converter INV ₂ are both blocked, and the DC on the N side of the DC system is The purpose is to stop the current and prevent the inflow of DC current from the DC system P side.

When stopping the DC system that should be stopped in this manner, the DC current of the DC system that should be stopped can also be stopped by blocking both the gates of the forward converter and the reverse converter.

Fig. 8 shows another embodiment of the present invention, which differs from the embodiment shown in Fig. 6 in that it detects changes in direct current, and each AC/DC converter is equipped with a current detection device. be done. As shown in the figure, the forward converter REC ₁ has a current detection device D _1r , the forward converter REC ₂ has the same device D _2r , the inverse converter INV ₁ has the same device D _1i , and the inverse converter INV ₂ has a current detection device D 1r. The same device D _2i is provided and used in the stopping method of the present invention. In these current detection devices, the DC current i _1r , i _2r , i _1i or i _2i of the relevant AC/DC converter and the relevant DC current i _o1 or i _o2 of the neutral line NL are detected by a DC current transformer. The input signals SD _1r , SD _2r , SD _1i obtained by this current change are
Or connect the SD _2i to the group control station of the relevant AC/DC converter.
Input to LC _1r , LC _2r , LC _1i or LC _2i .

This embodiment will be explained in detail by taking as an example the case where the N side of the DC system is stopped, similar to the embodiment shown in FIG. Forward converter as shown in Figure 8
The current detection device D _2r used to stop REC ₂ is connected to the DC current of the neutral wire NL by the DC current transformer CT ₅ .
i _o1 and the DC current i _1r on the DC system P side are input through the DC current transformer CT ₁ , and the inverse converter
The current detection device D _2i used to stop INV ₂ includes:
The DC current transformer CT ₆ converts the DC current i _o2 in the neutral line NL and the DC current transformer CT ₃ converts the DC current P into the DC system P.
DC current i _1i is input on the side. Current detection device on forward converter REC ₂ side when stopping DC system N side
Since the operations of D _2r and the current detection device D _2i on the side of the inverter INV ₂ are basically the same, the detection operation of the current detection device D _2r will be explained below, and the stopping method will be described according to this embodiment.

The current detection device D _2r is connected to the neutral wire NL as described above.
The DC current i _o1 of the DC system P side and the DC current i _1r of the DC system P side are input, and when these two currents are compared and a comparison level is reached, the signal SD _2r is output and the group command station
Input to LC _2r . This group command station LC _2r has already received the gate block signal SGB ₂ that follows the stop command S ₁ from the central command station CC ₂ , and when the AND condition of these two signals is satisfied, the forward converter
REC ₂ is gateblocked.

FIG. 9 shows a block diagram of the current detection device. 1
is the DC current input terminal on the DC system P or N side, 2
3 and 4 are amplifiers, 5 is a comparator, 6 is a timer, 7 is a flip-flop, 8 is a detection level setting input terminal, and 9 is an output terminal.

FIG. 10 shows the detection operation of the current detection device of FIG. 9, and the current detection device D _2r in the forward converter REC ₂ of FIG. 8 is targeted. DC system P in Figure 8
When the DC current on the side and N side is operated with i _1i = i _2r , the DC current in the neutral wire NL is i _o1 =0. Now, in FIG. 10, the DC voltage v _2r (and v _2i ) on the DC system _{N side} and the DC current i _2r (and i _2i ) decreases, the above i _1r = i _2r
changes to i _1r > i _2r . Following this change, the DC current in the neutral line NL increases to i _o1 >0. At this time, a constant DC current i _1r on the DC system P side is input to the input terminal 1 in FIG. 9, and a DC current i _o1 in the neutral line NL is input to the input terminal 2. In this case, as shown in FIG. 10, the difference current Δi _o between the two before the time t ₀ when the stop command S ₁ is applied is the maximum, and the above-mentioned soft stop control is performed by applying the stop command S ₁ . When this is done, this difference current Δi _o gradually becomes smaller. Eventually, at time _t1 , when this difference current becomes smaller than the detection level _eb , the signal _Sepn is output, and at time _t2, the signal _SD2r is outputted to the output terminal 9 via the timer 6 and flip-flop 7. . The detection level e _b of the difference current Δi _o when outputting this signal SD _2r is set to the lowest possible current value.

The signal SD _2r obtained in this way is input to the group command station LC _2r shown in Fig. 8, and is sent to the forward converter as described above.
Used as a gate block in REC ₂ . In addition, such a detection operation is also performed in the same way in the current detection device D _2i on the side of the inverter INV ₂ , and the signal is sent to the group command station LC _2i.
It provides SD _2i and is used as the gate block of the inverter INV ₂ .

A major feature of this embodiment is that the gate of the AC/DC converter is blocked when the DC current of the DC system to be stopped reaches the minimum value, so the gate blocking operation when stopping the AC/DC converter can be easily performed. There is.

〔Effect of the invention〕

A bipolar DC power transmission system equipped with the stop method of the present invention can reliably stop the DC current of the DC system to be stopped based on a command from the central control station when either one of the DC systems in the system is stopped. It is also possible to prevent the occurrence of overvoltage, which has a great effect in ensuring stable shutdown operations in bipolar DC power transmission systems.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of a bipolar DC power transmission device, Figure 2 a
2 is an explanatory diagram of the conventional method for stopping all AC/DC converters at once, FIG. 2b is an explanatory diagram of the conventional method for stopping a single-polar DC system, and FIG. 3 is a bipolar DC power transmission device equipped with the stopping method of the present invention. , FIGS. 4a and 4b are explanatory diagrams of the operation of the stopping method of the present invention, FIG. 5 is an explanatory diagram of the operating system of the stopping method of the present invention, and FIG. 6 is a bipolar DC power transmission device equipped with the stopping method of the present invention, FIG. 7 is an explanatory diagram of its operation, FIG. 8 is an explanatory diagram of the bipolar DC power transmission device with a stop method in a modified example of the present invention, FIG. 9 is a current detection device, and FIG. 10 is an explanatory diagram of the operation of the current detection device. A and B...AC system, P and N...DC system, REC...forward converter, INV...inverse converter,
DCL...DC reactor, HL...DC transmission line,
NL...Neutral line, CT...DC current transformer, CC...
…Central command station, LC…Group command station, BPP…Bypass pair circuit, GB…Gate block circuit,
APPS...Pulse generation phase shifter, D...Current detection device.

Claims (1)

[Claims] 1. In a bipolar DC transmission system where the positive and negative DC currents have a common return path, or in a bipolar DC transmission system where only the negative side is shut down, each power converter on the positive and negative sides. Adding a function to the control circuit to make the converter perform bypass pair operation and a function to perform gate block operation, and after reducing the voltage and current on the positive and negative electrode sides, Among the two converters forming a pair, the converter that is not to be stopped is operated as a bypass pair, and the converter that is to be stopped during the bypass pair operation period is gate-blocked without being operated as a bypass pair. A method of shutting down a bipolar DC power transmission system.