JPS5920023A - Controlling system of making voltage constant at ac/dc connection point - Google Patents

Abstract

PURPOSE:To suppress suitably the voltage variance at an AC/DC connection point when the operation state of a DC system is changed suddenly, by increasing or reducing the reactive power at the AC/DC connection point in accordance with a DC current of a DC power transmission system or a phase control angle of an AC/DC converter. CONSTITUTION:The controlling system for making the voltage constant at the AC/DC connection point is provided with a reactive power correcting circuit 13 where a DC current Id and an angle alpha of delay obtained through a DC current detecting circuit 12 are inputted to correct a reactive power control signal (q) with a closed loop. In this case, a reactive power correcting system is a closed loop, and it is unnecessary to give a time delay element to the circuit 13; and therefore, when the operation state of the DC system is changed suddenly and the current Id or the angle alpha of delay is changed, the circuit 13 is operated without a time delay to change the reactive power correcting signal q2, and the reactive power control signal (q) obtaines as the sum of a reactive power control signal q1 and the reactive power correcting signal q2 is changed. Thus, the voltage variance at the AC/DC connection point is suppressed effectively.

Description

[Detailed description of the invention] The present invention is based on AC/DC interconnection point voltage of AC/DC interconnection system - Ashikaga (2)
In particular, the present invention relates to an AC/DC interconnection point constant pressure control method suitable for suppressing AC/DC interconnection point voltage fluctuations when the operating condition of a DC system suddenly changes.

The AC bottom pressure at an AC/DC interconnection point in an AC/DC interconnection system fluctuates according to changes in DC transmitted power. In particular, when the ratio of the short-circuit capacity of the interconnected AC system to the transmitted power of the DC system (short-circuit capacity ratio) becomes smaller, the AC voltage fluctuation at the AC/DC interconnection point due to fluctuations in the DC transmitted power becomes more severe, and the AC/DC interconnection 1d pressure instability phenomenon at a point is likely to occur. In order to suppress such AC flexural change, it has traditionally been the practice to control the reactive power at AC/DC interconnection points. An AC/DC interconnection point voltage constant control method is adopted in which the AC pressure at the AC/DC interconnection point is kept constant by adjusting the AC/DC interconnection point.

First, an outline of a conventional AC/DC interconnection point voltage constant control system will be explained with reference to FIG.

The main circuit in FIG. 1 includes an AC system consisting of a three-phase AC power supply 1 and an AC transmission line 2, a DC system consisting of a converter 4, a DC reactor 5, and a DC transmission line 6, and a connection between the AC system and the DC system. It consists of a converter transformer 3.

The converter 4 is operated by a converter controller 7 that provides a control delay angle α (degrees) and a phase control circuit 8 that generates a firing pulse having a control delay angle α (degrees).

The AC/DC interconnection point core pressure-Ashikaga control system in FIG.
The reactive power control circuit 10 is composed of a closed loop consisting of the AC/DC interconnection point voltage setting value ■o (V) and the AC/DC interconnection point voltage v (v) obtained as the output of the AC heavy pressure detection circuit 9.
), that is, the control deviation ε, is input, and the reactive power control signal q is used to keep the AC/DC interconnection point voltage V (■) constant.
Output. Further, the reactive power compensator 11 compensates for reactive power having a magnitude proportional to the magnitude of q, for example, depending on the magnitude of q.

In such an AC/DC interconnection point voltage setting control method, closed loop 1. In order to stabilize the control system, the response characteristics of the reactive power control circuit 10 need to have a certain time constant. Therefore, when the operating state of the DC system suddenly changes, the operation of the reactive power compensator 11 is delayed due to the time delay element of the closed loop control system, and an overvoltage or the like occurs at the AC/DC interconnection point.

In particular, when an accident occurs in the DC system, the DC system comes to an emergency stop, the DC breaker connected in series with the DC transmission line 6 opens, or the control delay angle α (
If the temperature suddenly changes, a huge overvoltage will occur at the AC/DC interconnection point, and it is possible that the power transmission terminals and equipment will break down.

An object of the present invention is to provide an AC/DC interconnection point heavy pressure-Ashikaga control system suitable for suppressing AC/DC interconnection point voltage fluctuations when the operating state of a DC system changes suddenly.

At the beginning of this book, we focused on the fact that the DC gravity of a DC system depends on the magnitude of the DC current and the magnitude of the ・Iil control angle of the converter, and compared it to the conventional AC/DC interconnection point voltage-Ashikaga control system. , a function is added to correct the reactive power supplied to the AC/DC interconnection point according to the magnitude of the DC-current and the magnitude of the book advance angle.

Figure 2 (d) is a schematic diagram of the present invention and shows the DC current Ia (A) obtained through the DC current detection circuit 12 and the control wholesale delay angle at the AC/DC interconnection point double pressure-Ashikaga inverted system in Figure 52 Episode 1. α
A reactive power correction circuit 13 is added which corrects the reactive power control circuit q in an open loop using (degrees) as an input. In this case, the reactive force correction system is an open loop, and there is no need to provide the reactive force correction circuit 13 with a time delay element, so the operating state of the DC system changes suddenly, and the DC current I6 (A
), or when the control delay angle α (degrees) changes, the reactive power correction circuit 13 operates without time delay, changes the reactive power correction signal q2, and converts it to the sum of the reactive power control signal q1 and the reactive force correction signal q2. The reactive power control signal q, which is obtained by -1, is changed.

The third [4] is an explanatory diagram of Akira Motoike's principle, and according to this diagram, the reactive power compensator 11 is
ar), and the AC quasi-pressure V (V) at the AC/DC interconnection point. If the effective power and reactive power of the DC system are Pa (W) and Qa (Var), respectively, they flow from the AC system to the DC system. The current ↑1 (A) is as follows. In addition, the current i flowing through the reactive power compensator 11,
(A) becomes . From equations (1) and (2), the current in the AC system'
I■ becomes the required size.

Therefore, if the resistance and reactance of the AC power transmission line 2 are r (Ω) and X (Ω), respectively, then the AC/DC interconnection point Z voltage V (V) and the voltage E (V ) is the difference between
It can be approximately expressed by the following equation.

In order to keep (2) constant, it is sufficient to set EV=0, so from equation (4), Q-Q11+-·P a (5) is obtained. However, the DC current of a DC system is I, (A),! Knee IL
, Q, a (var), and Pa (w) are proportional to 1, sin α, and ■dCO5α, respectively, and using the proportionality coefficient k, equation (5) can be rewritten as follows.

Q, ==, Ia (sin a +, 4. cos
a) (6) However, t-1.

From the above, DC current of DC system 1. (A) and the value of the control delay angle α (degrees), if the reactive power Q (Var) found by equation (6) is compensated by the reactive power compensator fll, the voltage at the AC/DC interconnection point will be almost constant. be able to.

In other words, if the reactive power correction circuit 13, which uses the DC current ■d (A) and the control delay angle α (degrees) as control inputs, changes the reactive power Q (Var) according to equation (6), the operation of the DC system can be improved. Even if the state changes rapidly, voltage fluctuations at the AC/DC interconnection point can be suppressed.

FIG. 4 is a block diagram showing the characteristics of the reactive cardiac force correction circuit 13. However, the reactive power 1vi11 elevation signal q in the reactive power compensator 11 and the reactive cardiac force Q (Va
r) was defined as the following equation.

Q=f(q) (7) Here, f is a function representing reactive power Q (Var).

In the block diagram of FIG.
Create α, and use blocks 22 and 23 to create z
, create cosα, and in block 24, block 2
DC current 1, (
A), multiplied by block 25, and then the function f
92 is created through the inverse function f-1. That is, the value of q2 is given by the following equation.

qz"f-'("Ia ・(sin α+z-cosα)
l (B)I~ Therefore, the present invention can be realized by customizing the reactive power correction circuit 13 as shown in equation (8).

An embodiment in which the reactive power correction circuit 13 is implemented using a digital arithmetic processing device will now be described with reference to FIGS. 5, 6, 7, and 8.

FIG. 5 is a circuit configuration diagram of a digital arithmetic processing device, which includes a pulse generation circuit 31, an arithmetic processing circuit 32, and a storage circuit 3.
3. Consists of an input circuit 34 and an output circuit 35,
The arithmetic processing circuit 32 is activated by the pulse generated periodically by the nox pulse generating circuit 31, and according to the arithmetic processing procedure previously stored in the memory circuit 33, the input circuit 34 is activated.
through the direct current Ia (A) and the control delay angle α
(degrees) as digital quantities λ and μ, respectively,
A digital quantity ρ corresponding to the reactive power correction signal q2 is created and outputted via the output circuit 35 as the reactive power correction signal q2. The output circuit 35 holds the value of ρ until a new digital value ρ is given. The most common method for creating the digital acid ρ is to calculate the digital acid ρ in advance, create a table and store it in the memory circuit 33, and then index the table according to the sizes of the digital quantities λ and μ. , the method for determining the digital stitch ρ is γ.

Next, we will explain how to create a table.

DC flow 1. [), control creation angle α (degrees) input circuit 34
Ia+α is converted into a digital quantity by
When α<Δα・(,14-1), λ=1. μ=J. However, ΔIa and Δα are each minute components of If1+α, and i and j are integers. Also, L"Δ■6・
The value of q2 for i, α=Δα·J is found from equation (8), and a digital quantity ρ representing the magnitude of q2 is obtained.

At this time, the value of ρ corresponding to λ=i, μ=J is 01.1
As shown in FIG. 6, it is possible to create a table of digital quantities ρ using the values of sea urchin, λ, and μ as parameters.

Here, m and n are the maximum values of it, i, and j, respectively.

When storing the table of FIG. 6 in the storage circuit 33,
It is necessary to convert it into a one-dimensional table, and if the start address of the table is a, then the address A for λ=1, μ=j VC is A=a+(n+1)-i+j, and 011 is stored in the memory of address A as data. I will remember it myself.

That is, the address and data of the table in the unique circuit 33 are as shown in FIG. An arithmetic processing circuit 32 that uses this table to determine the value of the digital quantity ρ.
The arithmetic processing procedure is as shown in FIG. That is,
After the pulse generation circuit 31 generates a pulse, the arithmetic processing circuit 32 generates a digital signal λ in a process 41.

μ is taken in, and in step 42, an address A in the table is created from λ and μ. In step 43, the table is indexed to determine the value of ρ, and in step 44, ρ is output.

According to this embodiment, the nonlinear characteristics of the reactive power correction circuit can be easily realized.

Next, a modification of the present invention will be explained with reference to FIG.

If the characteristics of the reactive power correction circuit 13 are realized by the digital arithmetic processing device shown in FIG. 5, the control system may become unstable due to the discontinuous characteristics of the digital quantities. In this case, it is generally effective to provide a dead zone in the control system for stabilization.

FIG. 9 shows the arithmetic processing procedure when the reactive power correction signal q2 is changed only when the digital quantities λ and μ in FIG. , the value of μ is taken in, and in judgment 51.52,
λ, μ, and the value λ of λ and μ taken in the previous calculation process.

, μ. Compare 1λ−λ. 1 is greater than a prespecified value Δλ, or 1μ−μ. ] is the prespecified value Δ
If it is larger than μ, perform processes 42, 43, and 44,
The reactive power correction signal q is changed. Also, processing 53.5
4 is the imported λ and μ, each 2°.

This is a procedure to hold it as μ0.

According to this modification, it is possible to eliminate unstable phenomena in the control system due to discontinuous characteristics of digital quantities.

As another modification, the control delay angle α(
Consider the case where the control advance angle β (degrees) is used instead of the control advance angle β (degrees). The control advance angle β (degrees) is determined from the control delay angle α (degrees).
It is determined by the following formula.

β=180°−α (9) Substitute this equation (8
), we get q2=f” (k −]:, −(s inβ−z,
cosβ′11 (10>).

The characteristics of the reactive power correction circuit 13 in this case are as shown in the block diagram shown in FIG. 10, and when compared with the block diagram in FIG.
1 and block 23. The characteristics shown in FIG. 10 can also be easily realized using the digital arithmetic processing device 5, similar to the case where the characteristics shown in FIG. 4 are realized.

According to the present invention, the operating state of the DC system can suddenly change without impairing the characteristics of the conventional AC/DC connection point voltage-Ashikaga control method that keeps the AC/DC connection point voltage of the AC/DC connection system accurately constant in a closed loop. It is possible to effectively suppress the voltage fluctuation at the AC/DC interconnection point that has changed.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the conventional system, FIGS. 2, 3, and 4 are explanatory diagrams of the present invention, and FIGS. 5 and 6. Figures 7 and 8 are explanatory diagrams of the embodiment, Figure 9 and Figure 1.
FIG. 0 is an explanatory diagram of a modification. 1... 3-phase AC sub-source, 2... AC branch line, 3...
Transformer for conversion device, 4... Conversion device 4.5... DC reactor, 6... DC transmission line, 7... Control device for conversion device, 8... Phase control circuit, 9 ...AC voltage detection circuit, 10...Reactive power correction circuit, 11...Reactive power compensation device level, 12$ 3. 4. 5. Figure 72 (Address) (-r- Rin 1 1 1 1 $8th $9 Figure

Claims (1)

[Claims] 1. Controlling the AC/DC interconnection point voltage by increasing or decreasing reactive power at the AC/DC interconnection point in an AC/DC interconnection system that interconnects an AC transmission system and a DC transmission system. In the AC/DC interconnection point voltage-Ashikaga control method, a reactive power compensator is installed to control the AC/DC interconnection point voltage in a closed loop to keep the AC/DC interconnection point voltage constant. AC/DC interconnection point voltage-Ashikaga control characterized by providing an open loop control system that controls the reactive power compensator and increases/decreases reactive power at the AC/DC interconnection point according to the size of the control angle of the device. method. 2. In claim 1, depending on the DC current of the DC transmission system and the control angle of the AC/DC converter,
A constant voltage control system at an AC/DC interconnection point, comprising an open loop control system that controls the reactive power compensator and increases/decreases reactive power at an AC/DC interconnection point. 3.' The open loop control system according to claim 1 is characterized by providing a dead zone in which the open loop control system does not respond depending on the DC current of the DC transmission system or the magnitude of the control angle of the AC/DC converter. AC/DC interconnection point voltage constant control method. 4. The open loop control system in claim 2,
An AC/DC interconnection point voltage-Ashikaga control system characterized by providing a dead zone in which the open loop control system does not respond depending on the DC Wi current of the DC power transmission system and the control angle of the AC/DC converter.