JPS5825014B2 - Chiyokuryusoudennoseigiyohogohoushiki - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control system protection system in a system including a forward converter and an inverse converter, such as DC power transmission.

Conventionally, in DC transmission lines consisting of a forward converter, a DC transmission line, and an inverse converter, control and protection have been performed automatically by exchanging information between each other via communication lines such as microwaves. It's here.

This is because in the above system, it is necessary for the forward conversion device and the inverse conversion device to operate in coordination with each other, for example,
Constant current control is performed on the forward converter side, and constant margin angle control is performed on the inverse converter side.The inverse converter determines the DC voltage, and the forward converter side generates a voltage that is the DC voltage plus the transmission line loss voltage. Therefore, a control method is used in which a constant current flows.

Therefore, mutual cooperation is required when starting, operating, and stopping.

However, even if a failure occurs in the communication system, it is now sometimes necessary to operate the conversion device and send power.

At this time, for example, if there is an abnormality on the reverse converter side, the current can be transferred to the bypass switch and the reverse converter side can be stopped, but the forward converter side remains unchanged because the constant current is in effect. Flow an electric current.

At this time, since the control angle generates a voltage commensurate with the loss voltage of the power transmission line, its value becomes a large control angle, such as 60 el to 87 el.

At this time, the resistor connected in series with the capacitor connected inside the converter has fCE2
A loss of (α)+5IN2(α+U) is generated.

Here, f is the operating frequency, C is the capacitor capacity, E is the transformer secondary voltage, α is the control delay angle, and U is the overlap angle.

In this way, the larger α is, the greater the loss, and therefore, the cooling capacity of the valve cooler must be increased, or the amount of heat processed by the resistor must be increased, resulting in a significant increase in size and cost.

The present invention provides a method for safely and reliably stopping the converter even in such a case.

The main point of the present invention is that when the inverse converter is normally operating, the control angle is in the range of 10 to 30 el because the inverse voltage line voltage drop is generated on the forward converter side. Furthermore, if the inverter breaks down, turn on the bypass switch,
After disconnection, since there is no reverse voltage generated by the reverse converter, the forward converter only needs to generate the line voltage drop, so the control angle becomes 70 to 80 electrical degrees.

That is, in the case of three-phase bridge connection, the DC output voltage is applied.

Of course, to be precise, it should include the DC voltage drop of the converter transformer, the voltage drop of the converter, etc., but this will not affect the majority of people, so I will omit it.

Here, E2 is the transformer secondary voltage, IX is the transformer percent reactance, and α is the control delay angle.

Now, it is sufficient that Ed in the above equation is equal to the DC line voltage drop (dx-RL).

That is, here, IdN: rated DC current; dx: DC current set at that time (IdN=Idx).

Therefore, Idx-RL/1.35 E2:0.2, IX
When %=0.2 and Idx/IdN=1, α is 72
, 5 degrees electrical angle.

It is clear from equation (2) that the smaller the set DC current Idx and the smaller the line voltage drop, the closer α becomes to 90 degrees electrical angle.

Therefore, over a certain period of time, that is, this certain period of time is the time for α to pass through 70 to 90 el during startup, shutdown, power flow reversal, etc., which is about 0.3 seconds in normal DC power transmission, but Considering that the bridges are connected in several stages in cascade and the bridge is started and stopped for each stage, it is necessary to further increase the number of stages by the number of stages.

Therefore, as mentioned above, the control angle is between 70 and 90.
If it is detected that the time in el is longer than a certain period of time, an abnormality has occurred on the inverse converter side, and the forward converter side can determine that it has been disconnected from the DC circuit without going through a communication line. The converter can be stopped without needing to run for a long time.

A specific example of the present invention will be shown.

FIG. 1 is a block diagram showing general DC power transmission.

The converter 3 performs forward conversion when the control delay angle α is 0 to 90 el, and performs inverse conversion when the control delay angle α is 90 to 180 el.

The bypass switch 5 is used to disconnect the converter from the DC circuit. Although Figure 1 shows the case of a single bridge, in a system where multiple bridges are configured in cascade, the DC output terminal of each bridge is A bypass switch is installed in parallel with.

FIG. 2 is a diagram showing the principle of setting the control delay angle.

That is, A in FIG. 2 shows the voltage between the secondary lines of the transformer, and when the AC voltage crosses the zero point, a rectangular wave-like signal is generated.

This signal is integrated as shown in (c) to generate a triangular signal.

This triangular signal C is the intersection with the control signal Ec,
Generate a pulse as shown in step 2.

This pulse is amplified and shaped and is used as the firing signal for the arm in the transducer.

This control signal Ec always operates in proportion to the difference between the control signal set value EcO and the current feedback signal Ecx to make this difference zero.

Therefore, since this Ec has a one-to-one correspondence with the control delay angle, the voltage level of EC is detected, and if this level continues for a certain period of time or more, a signal is issued to stop the converter.

That is, as shown in Fig. 3, a comparator A operates when α0 is 70 or more, a port that integrates its output over time, a comparator C that outputs an output if the integral value is above a certain value, and an inverse converter operation. In the middle, since α is 90 or more, in that case, it consists of a NAND gate 2 that blocks the output of C.

α in Figure 3. is the control angle setting input for setting 7001 or more, t of C.

is an input to set the time when it continues for more than a certain period of time.

The details of the operation are simple and do not require further explanation, so they will be omitted.

According to the present invention, it is possible to safely stop the forward converter even when the communication line is disconnected, and it is also possible to stop the forward converter safely even when the communication line is disconnected. Since no vessels are required, the cost is low and the economic advantage is great.

In addition, since it is equivalent to directly detecting the control angle, it is also possible to prevent heating caused by increased loss in the damping resistance contained in the valve before it leads to a major accident. Therefore, the advantages of the present invention are significant.

Note that the present invention is characterized in that a control voltage equivalent to a control angle is directly detected and a protective operation is performed.

Therefore, it goes without saying that various specific implementation circuits can be considered within this range.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the main circuit of a DC power transmission system, FIG. 2 is a diagram showing the principle of a phase control circuit, and FIG. 3 is a diagram showing a detection circuit of the present invention. Explanation of symbols, 1... Conversion transformer, 2...
...DC reactor, 3...Converter, 4...
...DC line, 5...bypass switch,
6... Comparator, I... Integrator, 8...
····and.

Claims (1)

[Claims] 1. In a DC power transmission system consisting of a forward converter and a reverse converter equipped with a bypass switch that is turned on at the own end in the event of an abnormality at the own end, the control angle of the forward converter reaches a high value above a certain level, Moreover, the DC power transmission control and protection system is characterized in that it detects that the state remains for a certain period of time or more and stops the forward converter.