JPS6362985B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control device for controlling a two-terminal DC power transmission system that interconnects two AC systems using a self-excited AC/DC converter.

In general, DC transmission systems have faster power flow control than AC transmission systems, and the amount of power adjustment can be freely selected, but due to the characteristics of the converter,
% reactive power is required. For this reason, a phase advance capacitor for adjusting reactive power is required in the past.
This capacitor was opened and closed depending on the operating status of the converter. This is because a separately excited converter is used as the AC/DC converter.

A conventional DC power transmission system using this type of separately excited converter is shown in FIG. In Figure 1, 1 and 2 are the first and second AC systems, respectively, 3 and 4 are the first and second transformers, and 5 and 6 are the first and second separately excited AC/DC converters (hereinafter referred to as , first and second converters), 7 and 8 are DC reactors, and 9 and 10 are DC transmission lines. These separately excited AC/DC converters 5 and 6 are composed of a six-phase bridge of controllable valves or a combination thereof, and are connected to the DC terminal of the converter by controlling the phase angles α and β of the ignition signal to the controllable valve. DC voltage can be variably controlled. 11 is an AC current transformer (hereinafter referred to as CT); 12 is an AC transformer (hereinafter referred to as PT); 13 is a power detection circuit; 14 is a voltage reference generation circuit; 15 is a subtracter;
6 is a power regulator, 17 is a direct current transformer (hereinafter referred to as DCCT)
), 18 is a subtracter, 19 is a current regulator, 2
0 are phase control output circuits, which control the firing signal of the first converter 5. On the other hand, 21 is a margin angle reference generation circuit, 22 is PT, 23 is DCCT, 2
4 is a constant margin angle adjuster, and 25 is a phase control output circuit, which controls the firing signal of the second converter 6.

Describing the operation based on such a configuration, the target value controlled by the DC power transmission system is the transmitted power, and in order to improve the power transmission efficiency, it is necessary to maintain the power transmission voltage high. These controls are shared by the first and second AC/DC converters 5 and 6, and in particular, the first converter 5 is configured to determine the transmitted power, and the second converter 6 is configured to determine the transmitted voltage. . CT11 and PT1
The power detection circuit 13 calculates the transmitted power from the voltage and current detected in step 2. This power value is compared with the power reference value from the voltage reference generation circuit 14 by a subtracter 15, and the reference value of the current command is outputted from the power adjustment circuit 16 as a deviation signal. Therefore, the power detected by the power detection circuit 13 is equal to the power detected by the power reference generation circuit 1.
If the current command is larger than the reference value of 4, the reference value of the current command decreases, and conversely, if it is smaller, it increases, and the actual transmitted power is controlled so as to always match the power reference value. on the other hand,
The DC current detected by the DCCT 17 is compared with the output reference value of the above-mentioned current command in the subtracter 18, the current adjustment circuit 19 outputs a manipulated variable based on this deviation signal, and the output circuit 20 is connected to the first converter. Outputs a phase designation signal to 5. This phase command is
Phase delay angle α between the voltage phase of and the firing angle of converter 5
This is the ignition signal that gives . As a result, the current in the DC wire is controlled to be equal to the current reference value.

On the other hand, the constant margin angle adjustment circuit 24 receives the margin angle reference value γ from the margin angle reference generation circuit 21, the AC voltage V detected by the PT 22, and the DC current I _DC detected by the DCCT 23, and then A phase command determined by the formula is calculated, and as a result, the output circuit 25 outputs a phase command signal to the second converter 6.

The phase command of the output circuit 25 is a firing signal that provides a phase advance angle β between the voltage phase of the AC system 2 and the firing angle of the converter 5.

As a result, the valve margin angle of the second converter 6 is γ
is maintained. By setting the command value of γ to the minimum value required for commutation of the valve, the DC voltage is always kept at the maximum value.

Conventional control devices for DC power transmission systems have been configured as described above, but it is necessary to accurately control the margin angle on the second converter side, and power control on the first converter side is also directly controlled by AC power. It was complicated because it was not possible to control only the power on the side.

The present invention provides a control device for a DC power transmission system that does not require control of the margin angle by using a self-excited AC/DC converter, which has not been previously proposed, as an AC/DC converter for the DC power transmission system. It is an object.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 shows a basic configuration diagram of a DC power transmission system using a self-excited AC/DC converter. In the figure, the same reference numerals as in FIG. 1 indicate the same or corresponding parts, and therefore the explanation will be omitted. 35 and 36 are first and second self-excited AC/DC converters, respectively, and 37 and 38 are smoothing capacitors. The self-excited AC/DC converters 35 and 36 are composed of elements having self-extinguishing capability, such as a thyristor inverter with a forced extinguishing circuit or a gate turn-off (GTO) thyristor as shown in FIG. It is a phase bridge connection inverter or a combination thereof.

FIG. 3 is a specific configuration diagram of a self-excited AC/DC converter. In the figure, P, N are DC terminals, U, V, W
is an AC terminal, 3 is a transformer, 37 is a line capacitor, 201, 202, 203, 204, 205,
206 are both main thyristors, 211, 21
2, 213, 214, 215, 216 are freewheel diodes, 221, 222, 223,
224, 225, 226 are auxiliary thyristors, 23
1,232,233 is a commutation reactor, 241,
242 and 243 are capacitors. The process by which square-wave AC voltages proportional to the DC voltage between DC terminals P and N are generated at U, V, and W is well known, so a description thereof will be omitted. The phase of the output AC voltage is controlled by controlling the phases of the firing pulses of the main thyristors 201 to 206 and the auxiliary thyristors 221 to 226.

FIG. 4a is an explanatory diagram showing the principle of power conversion by a self-excited AC/DC converter. Now, the voltage vector generated by the self-excited converter is V〓 _I , the voltage vector of the AC system is V〓 _S , and the resistance component of the impedance (leakage impedance of the transformer) between the AC system and the self-excited AC/DC converter is R. , let X be the reactance.
When the converter voltage V〓 _I is controlled to be delayed in phase by δ with respect to the system voltage V〓 _S , the vector relationship of each voltage and current is as shown in Fig. 4b. Normal vectors V〓 _S and V〓 _I have almost the same absolute value,
The resistance component R is sufficiently smaller than the reactance component X. Therefore, the power P flowing into the converter from the AC system
is approximately given by the following equation.

P≒ |V _S | |V _I |/X・δ In this equation, when δ>0, power flows from the AC system to the converter, and when δ<0, power flows from the converter to the system. flows. Further, the magnitude of the supplied power is proportional to δ. That is, by controlling δ, the amount and direction of power flow can be controlled.

Next, vectors V〓 _S and V〓 _I have the same phase (δ=0)
Fig. 4c shows a vector relationship diagram when the vector is controlled and the magnitude is changed to the vector V〓 _I. At this time, the current I〓 has a phase perpendicular to the voltages V〓 _S and V〓 _I , and becomes a reactive component. As shown in Figure 4c, when the voltage vector relationship is |V〓 _I |>|V〓 _S |, the reactive power becomes phase advanced and flows from the AC system to the converter, and conversely, |V〓 _I |<|
At V〓 _S |, the phase becomes slow and flows into the AC system from the converter. At this time, the reactive power Q is expressed as Q=|V _S |/X (|V〓 _I |−|V〓 _S |). That is, this shows that by controlling the voltage vector |V〓 _I | (this is nothing but controlling the DC voltage), it is possible to control the flow of reactive power including its direction. This invention utilizes this principle to create a second
This system controls a DC power transmission system using the self-excited AC/DC converter shown in FIGS.

FIG. 5 shows a first embodiment of the invention. In FIG. 5, the same reference numerals as those in FIGS. 1 and 2 indicate the same or corresponding parts, so the explanation will be omitted. 4
0 is a change rate suppression circuit, 41 is a subtracter, 42 is a power adjustment circuit, 43 is a direct current transformer (hereinafter referred to as DCPT), 44 is a voltage reference generation circuit, 45 is a subtracter,
46 is a power adjustment circuit.

The operation of the control device configured in this way will be described. From the power detection circuit 13 to which the detection signals of CT 11 and PT 12 are input, a power amount detection signal to be supplied from the AC system 1 to the first self-commutated converter 35 is given to the subtracter 41 . On the other hand, this subtracter 41 is supplied with the reference value of the electric energy from the voltage reference generation circuit 14 and is supplied via the change rate suppression circuit 40. Based on this deviation signal, the power adjustment circuit 42 outputs a manipulated variable of the value of the firing angle _δ1 , and via the phase control output circuit 20
is applied to the self-excited converter 35. Therefore, if the actual value of the electric energy is smaller than the reference value, the firing angle δ ₁ is adjusted to be larger, and conversely, if the actual value is larger than the reference value, the firing angle δ ₁ is adjusted to be smaller. The output operation amount of the power adjustment circuit 42 is converted by the output circuit 20 into a firing pulse with a firing angle δ ₁ suitable for driving the first converter 35, and the first The phase of the AC output voltage V 〓 _I of the converter 35 changes. As a result, a voltage V 〓 _I whose phase is delayed by a phase angle δ ₁ from the AC voltage phase of the AC system 1 is generated as the output voltage of the first converter 35 . Therefore, when this phase angle δ ₁ is increased, the amount of power flowing from the AC system 1 to the converter 35 increases, and when it is decreased, it decreases, so that the amount of supplied power is controlled by the adjustment circuit and the output circuit 20. It is possible to always control the value to be the same as the reference value.

On the other hand, on the second self-commutated converter 36 side, the voltage reference generation circuit 44 supplies the voltage reference value to the subtracter 45, and in this subtracter 45, the DC voltage across the smoothing capacitor 38 detected by the DCPT 43 is A deviation output between the actual measured value and the above-mentioned reference value is output. The voltage adjustment circuit 46 outputs a manipulated variable of the value of the firing angle δ ₂ based on this deviation signal, and the output is applied to the second self-excited converter 36 via the phase control output circuit 25 . Therefore, if the actual measured voltage value is larger than the reference value, the firing angle δ ₂ will be decreased, and if it is smaller, the firing angle δ ₂ will be decreased.
is adjusted to make it larger. Power adjustment circuit 4
6 is converted into an ignition pulse by the output circuit 25, and the second converter 36 is connected to the AC system 2.
A voltage whose phase is delayed by a phase angle δ ₂ with respect to the voltage phase of is generated. When this phase angle δ ₂ increases, the power flowing into the converter 36 from the AC system 2 increases, so the AC current flowing into the smoothing capacitor 36 increases, the voltage across both ends increases, and conversely, the phase angle δ ₂ increases. As becomes smaller, the power flowing into the converter 36 from the AC system 2 decreases, so the AC current flowing into the smoothing capacitor 38 decreases, and the voltage drops. Therefore,
The DC voltage across the smoothing capacitor 38 is always controlled to be equal to the voltage reference voltage.

In this way, in this embodiment, the transmitted power is controlled by controlling the firing angle δ ₁ of the first self-commutated converter 35, and by controlling the firing angle δ ₂ of the second self-commutated converter 36. The direct current voltage is controlled individually, and the same control as the conventional separately excited type is possible. Current direction is AC system 1
In the case of the direction of AC system 2 from , each phase angle is δ ₁ <
0 and δ ₂ >0, and conversely, in the case of the direction from AC system 2 to AC system 1, the relationship is only δ ₁ >0 and δ ₂ <0, and the process described above is exactly the same. Therefore, the power flow direction can also be reversed by simply changing the polarity of the power reference value of the voltage reference generation circuit 14. At this time, when the power transmission line is long and the inductance of the line is large, if the current polarity is rapidly changed, the voltage of the smoothing capacitor 37 becomes too high or too low. To prevent this, the change rate suppressing circuit 40 has a function of suppressing the change rate of the power reference value.

This embodiment has been explained using a basic example of a control device for a DC power transmission system using a self-commutated converter, but as described in Fig. 4b, the magnitude of the converter output voltage V〓 _I is invalid. Since it is a power control element and the magnitude of this voltage is proportional to the DC voltage, the amount of reactive power supplied to the system 2 is changed using the second converter 36 that controls this DC voltage. It is possible to do so. Furthermore, when controlling transmitted power, it is often necessary to suppress the current value of the power transmission line to a certain maximum value.

FIG. 6 shows a second embodiment of a control device designed for such a case. In the figure, the fifth
The same reference numerals as in the illustrated embodiment indicate the same or corresponding parts. 50 is a CT, 51 is a PT, and 52 is a reactive power detector. 53 is a reactive power reference generation circuit, 54 is a subtracter, 55 is a reactive power adjustment circuit, and 56 is a limiter. Furthermore, 61 is a DCPT, 62 is a divider,
63 is a limiter, 64 is a subtracter, 65 is a current adjustment circuit, 66 is a limiter, 67 is a subtracter, and 68 is a power adjustment circuit. In such a configuration, the amount of reactive power exchanged between the AC system 2 and the second converter 36 is detected by the reactive power detector 52, and the actual measured value of this reactive power is combined with the reactive power reference generation value in the subtracter 54. A deviation signal between the reactive power and the reference value is outputted from the circuit 53, and the reactive power adjustment circuit 55 outputs a DC voltage reference value signal based on this deviation signal. In this case as well, if the actual measured value is larger than the reference value, the DC voltage reference value signal is adjusted to be lowered, and conversely, if it is smaller, the DC voltage reference value signal is adjusted to be increased. This DC voltage reference value is applied to a subtracter 45 after being limited by a limiter 56 . In the subtracter 45,
A deviation signal between the actual DC voltage value detected by the DCPT 43 and the above-mentioned DC voltage reference value is output, amplified by the voltage adjustment circuit 46, and sent from the output circuit 25 to the second converter 36 at the firing angle δ ₂ point. An arc pulse is given.
As a result, the DC voltage across the smoothing capacitor 38 is adjusted so that the reactive power between the AC system 2 and the second converter 36 is always the reference value of the reference generation circuit 53.

On the other hand, on the first converter 35 side, the power reference value from the power reference generation circuit 14 is divided by the detected DC voltage from the DCPT 61 in the divider 62, and the DC current required to achieve the reference power is calculated. ,
In order to keep this current within a predetermined range, limiter 6 is applied.
3, it is applied to a subtracter 64 as a current reference value. The subtracter 64 subtracts this reference value from DCCT1.
7 outputs a deviation signal from the actual measured value of the detected DC current, which is input to the current adjustment circuit 65 and further outputs a voltage reference value. Therefore, if the actual measured value of the DC current from the DCCT 17 is smaller than the reference value, the output voltage reference value is increased, and if it is larger than the reference value, the voltage reference value is lowered. This output voltage reference value is applied to a subtracter 67 via a limiter 66. This subtracter 67 outputs a deviation signal between the actual measured value of the detected voltage of the DCPT 61 and the previous voltage reference value, and controls the firing angle δ ₁ from the voltage adjustment circuit 68 via the output circuit 20 to control the DC voltage. A firing pulse is provided to the first transducer 35. This voltage control process is exactly the same as the limiter 56, DCPT 43, subtracter 45, and voltage adjustment circuit 46 performed in the second converter 36. Smoothing capacitor 37
Let V _A be the voltage across the smoothing capacitor 38, V _B be the voltage across the smoothing capacitor 38, and R _D be the resistance of the DC transmission line, then the DC current value will be I _D = 1/R _D (V _A − V _B ). , so the smoothing capacitor 37
By increasing or decreasing the voltage V _A across , the DC current _ID can be increased or decreased, and as a result, the current is controlled to a value equal to the current reference value given via the limiter 63 . By setting the level of the limiter 63 to a predetermined current limit value in advance, the maximum value of the DC current can be limited in the above process.

As described above, according to the present invention, since a self-excited AC/DC converter is applied to a two-terminal DC transmission system, it is possible to control the transmission voltage, current, power, or reactive power, and a separately excited AC/DC converter is used. This has the effect of making it possible to omit the need for phase adjustment equipment, which was not possible when using conventional methods.

[Brief explanation of drawings]

Figure 1 shows the configuration block diagram of a control device for a DC transmission system using a conventional separately excited converter, and Figure 2 shows the following:
FIG. 3 is a circuit diagram disclosing a configuration example of a self-excited AC/DC converter applied to the DC transmission system shown in FIG. 2. , Fig. 4a, b, and c are explanatory diagrams of the control principle of electric power and reactive power when using the self-excited AC/DC converter shown in Fig. 3, and Fig. 4a is an explanatory diagram of the circuit. FIGS. 4b and 4c each show vector diagrams, FIG. 5 is a block diagram of a control device for a DC power transmission system according to an embodiment of the present invention, and FIG. 1 shows a configuration block diagram of a control device for a DC power transmission system according to an embodiment of the present invention. 1, 2...AC system, 3, 4...Transformer, 3
5, 36... Self-excited AC/DC converter, 37, 38...
Smoothing capacitor, 9, 10...DC transmission line, 1
1,50...CT, 12,22,51...PT, 1
7, 23...DCCT, 43, 61...DCPT, 1
3... Power detector, 52... Reactive power detector, 2
0, 25... Phase control circuit, 14... Power reference generation circuit, 44... Voltage reference generation circuit, 53... Reactive power reference generation circuit, 15, 18, 41, 45,
54, 64, 67... Subtractor, 40... Change speed suppression circuit, 56, 63, 66... Limiter, 62
...Divider, 16,42...Power adjustment circuit, 1
9, 65... Current regulation circuit, 46, 68... Voltage regulation circuit, 55... Reactive power regulation circuit. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] 1. The first and second AC systems are mutually connected via first and second self-commutated AC/DC converters connected to a transformer on the AC side and a smoothing capacitor on the DC side, respectively. a power detection circuit that detects an actual measured value of active power at an interconnection point between a DC interconnected DC power transmission system, the first AC system and the first self-excited AC/DC converter; a first subtracter that outputs a first deviation signal from a reference value of active power generated by a power reference generation circuit; and a point of the first self-excited AC/DC converter based on the first deviation signal. a first output circuit that controls the arc angle; a voltage detection circuit that detects the measured value of the DC voltage across the smoothing capacitor of the second self-excited AC/DC converter; and a voltage reference generation circuit that detects the measured value of the DC voltage. a second subtractor that outputs a second deviation signal from a reference value generated by the second subtractor; and a second subtracter that controls the firing angle of the second self-excited AC/DC converter based on the second deviation signal. A power transmission system control device equipped with an output circuit. 2. The voltage reference generation circuit includes a reactive power detection circuit that detects an actual measured value of reactive power at an interconnection point of the second AC/DC converter and the second AC system, and a reactive power detection circuit that generates a reference value of reactive power. Control of a power transmission system according to claim 1, comprising a power reference generation circuit and a subtracter that outputs a deviation signal between the measured value of reactive power and the reference value, and which makes the reference value of the power transmission voltage variable. Device. 3. The power adjustment circuit is a current reference generation circuit that generates a reference value of DC current by dividing the actual value of the voltage of the smoothing capacitor of the first self-excited AC/DC converter by the reference value of the active power. , a DC voltage reference generation circuit that generates a DC voltage reference value based on a current deviation signal between the DC current reference value and an actual measurement value from the DC current detector of the power transmission line; and a DC voltage reference value. and the actual measured value of the voltage of the smoothing capacitor, the firing angle of the first self-excited AC/DC converter is controlled via the output circuit of the first control device based on the voltage deviation signal between The power transmission system control device according to item 1.