JPH0452052B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a DC power transmission system.

As is well known, in a DC power transmission system, AC power is converted to DC by a thyristor forward converter and supplied to a DC transmission line, and on the receiving side, the thyristor reverse converter converts it to AC and supplies it to a load.

FIG. 4 shows the overall configuration of a DC power transmission system to which the present invention is applied, in which the power generated by the generator 1 is transferred to the transformer 2, the breaker 3, the bus 4, the breaker 3, It is applied to an AC/DC converter (forward converter) 6 via a converter transformer 5, and its DC output is supplied to a DC power transmission line 7. The electric power transmitted by this DC transmission line 7 is converted into AC by an AC/DC converter (inverse converter) 6, and the electric power is supplied to the load via a converter transformer 5, a breaker 3, and a bus 4. Ru.

FIG. 5 shows the basic configuration of the control system of the AC/DC converter 6 shown in FIG.

In the figure, the DC current and DC voltage of the DC transmission line 7 are detected by a DC current transformer 8 and a DC voltage transformer 9, respectively, and these detected values are sent to one of the comparison inputs by a current setting device 10, Each set value of the voltage setter 11 is supplied to each other comparison input of the given deviation detector 12. Each deviation detector 1
2 is supplied to a constant current control amplifier 13 and a constant voltage control amplifier 14, and their amplified outputs are supplied to a low value selector 15. This low value selector 15
The selected output is supplied to a variable limiter 16, which is converted into a pulse signal by an automatic pulse phase shifter 17, amplified by a pulse amplifier 18, and supplied to an AC/DC converter 6.

Here, the setting value given by the current setting device 10 is:
In a forward converter, the current is set to, for example, 10 (%) of the rated current at the initial stage of startup, whereas in the reverse converter side, the so-called current margin (for example, 7 (%)) is subtracted (3 (%) of the rated current). ) equivalent). For this reason, as is commonly known, the output of the current control system on the forward converter side and the output of the voltage control system on the inverse converter side are selected as the output of the low value selector 15, respectively. controlled.

The startup of such a DC power transmission system is such that the control angles of both converters are set at 90°, which is close to the critical operating range.
After that, at startup, the control angle of each converter is set in the respective control range (for forward converters, the control angle
This is done by shifting the angle in the 0° direction (or 180° in the inverse converter).

That is, in the past, the upper and lower limits of the limiters 16 on the forward converter side and the inverse converter side were initially fixed at 90°,
After that, the upper and lower limit existence regions of the control angle by each converter limiter are gradually opened as shown in a and b in Fig. 1, and in this case, as shown in Fig. 2, Current control is performed at , and the DC voltage is increased according to the opening degree of the limiter on the inverter side. In addition, in Figures 1 and 2, 102
104 represents the control characteristic on the inverse converter side, 104 represents the control characteristic on the forward converter side, and DEB represents the start time.

Therefore, the power transmitted by the above DC power transmission system changes as shown in Figure 3, and reaches the minimum operating power P _nio determined by the minimum current carrying current and rated DC voltage at a predetermined time constant after startup. . Here, the minimum conduction current is set to the lowest value at which the DC current does not become intermittent, depending on the value of the DC reactor, etc., and therefore, the minimum value of the DC transmission power is determined by this.

By the way, when a generator starts up, the rise time until it reaches its minimum operating power P _nio gradually increases like a ramp function, taking about 10 minutes. It is preferable that the rising time is also timed to match this.

To achieve this, it is conceivable to set the rate of change of the limiter characteristics shown in _FIG .
When such control is performed, the loss in the damping circuit of each thyristor increases, and in this case, a problem arises in that the cost of the system increases in order to cool the thyristors. In other words, the loss of the damping circuit described above is affected by the thyristor control angle, and more specifically, a forward converter is operated in an area with a control angle of 40 degrees or more, and an inverse converter is operated in an area with a control angle of 140 degrees or less. If this is done, transient current during commutation will flow into the thyristor's snapper circuit, increasing resistance loss. Currently, if the capacity of the thyristor is not increased, the permissible operating time in this region is about one minute, and it cannot withstand long-term operation of several tens of minutes.

The present invention has been made in view of the above-mentioned conventional problems, and its purpose is to provide a DC power transmission system that can start up a DC power transmission system together with a generator in a ramp function manner without increasing costs. be.

In order to achieve the above object, the present invention provides a DC power transmission system that converts AC power into DC using a thyristor forward converter, transmits the power to a DC transmission line, converts it to DC using a thyristor reverse converter, and supplies it to a load. In this method, a limiter is provided on the forward converter side to limit the control angle of the forward converter thyristor immediately after startup to a predetermined angle that is less than or equal to the allowable loss of the damping circuit of the forward converter, and DC power is transmitted on the forward converter side. By controlling the voltage of the system and the current of the DC transmission system on the inverter side, it is possible to prevent a stepwise increase in the transmitted power due to the DC converter, and to maintain a balance with the output increase rate of the generator. It is characterized by starting.

Preferred embodiments of the present invention will be described below based on the drawings.

FIG. 6 shows the limiter 1 when the present invention is adopted.
It takes several seconds on the forward converter side to shift the limiter lower limit value to a control angle corresponding to the damping loss limit (e.g. 40 degrees) or an appropriate control angle less than that, and then The control angle is maintained at this shifted control angle. In this case, the outputs of the current control system and voltage control system in FIG. There is. On the other hand, on the inverter side, the upper and lower limit values of the limiter 16 are controlled to shift as in the past, and the voltage control system gives a saturated output because its feedback value does not reach the target, whereas the rated The output of the current control system given the setting of 3 (%) provides a control output within the upper and lower limits of the limiter, and in the end, the current control is utilized in the inverter.

Note that if the current is about 3% of the rated value, there is no risk that the current will be interrupted, and there is no risk that the thyristor will be destroyed due to this.

In this way, as shown in FIG. 8, the inverse converter side performs constant current control, and the forward converter side performs DC voltage control using the control angle limited by the limiter. Furthermore, if a load tap changer is installed in the converter transformer 5 shown in FIG.
It is clear that by setting the tap value to the minimum value, the DC voltage can be lowered and the increase in transmitted power can be reduced. According to this embodiment,
On the forward converter side, the control angle is shifted to around 40 degrees, which is the damping loss limit point, so there is no need to worry about increasing the cost of the thyristor due to loss in the damping circuit. Further, as a result, the DC voltage can be kept low within a range that does not cause damping loss. FIG. 7 shows the output characteristics 100 according to the present invention, and it is possible to increase the DC power more slowly than in the past. In addition, in the control of the present invention, the DC voltage given by the forward converter is controlled by a limiter, and the DC current given by the reverse converter is controlled to 3%. Although we cannot explain the increase in , this is due to the increase in generator output. In other words, in conventional control, because the converter can be controlled at high speed (not suitable for slow control at startup), the generator output is adjusted to the minimum of the converter in accordance with the control of the converter output. The operating power was increased in steps up to P _nio , but this method was not suitable for the generator's mechanical system. In the present invention, since it is possible to operate for a long time with a small converted output, the generator output can be slightly increased accordingly. Characteristic 100 in FIG. 7 shows that the converter output increases with a slight increase in the generator output.

As described above, according to the present invention, it is possible to obtain transmitted power that is coordinated with the generated output at the time of starting the generator, and is extremely suitable for DC power transmission.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of the operation of the limiter of the AC/DC converter in the conventional system, Figure 2 is the control characteristic diagram of the AC/DC converter in the conventional system, Figure 3 is the minimum operating power characteristic diagram immediately after startup of the conventional system, and Figure 4 Figure 5 is an overall configuration diagram of a preferred embodiment of the present invention; Figure 5 is a configuration diagram of the control system of the AC/DC converter in Figure 6;
The figure is an explanatory diagram of the operation of the limiter in Figure 5, Figure 7 is a minimum operating power characteristic diagram immediately after startup of the preferred embodiment of the present invention, and Figure 8 is the control characteristic of the AC/DC converter in Figures 4 and 5. It is a diagram. 1... Generator, 6... AC/DC converter, 7... DC transmission line, 16... Variable limiter.

Claims (1)

[Scope of Claims] 1. In a DC power transmission system that converts AC power into DC using a thyristor forward converter, transmits it to a DC transmission line, converts it to DC using a thyristor inverse converter, and supplies it to a load, immediately after startup, A limiter is installed on the forward converter side to limit the control angle of the forward converter thyristor to a predetermined angle that is less than or equal to the allowable loss of the damping circuit of the forward converter, and the voltage of the DC power transmission system is controlled on the forward converter side. However, by controlling the current in the DC power transmission system on the inverter side, it is possible to prevent a stepwise increase in the transmitted power due to the DC converter and to perform a startup that is balanced with the output increase rate of the generator. Features of DC power transmission system. 2. The DC power transmission system according to claim 1, wherein the tap of the converter transformer of the forward converter is set at the lowest position in order to reduce the power transmission voltage immediately after startup. .