JPH0218017B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a method for controlling a power conversion device such as a DC power transmission device or a frequency conversion device that operates while coordinating a forward converter and an inverse converter. The present invention relates to a control method for a power conversion device that reduces disturbances that occur in a DC power transmission device, a frequency conversion device, etc. in the event of a fault in a converter or the like.

[Technical background of the invention]

FIG. 1 is a DC two-terminal power transmission system diagram as an example of a power conversion device, where 10 and 11 are AC systems;
20 and 21 are transformers, 30 and 31 are converters, 40
and 41 are DC reactors, and 50 and 51 are DC lines, respectively.

In FIG. 1, consider the case where converter 30 performs forward conversion and converter 31 performs inverse conversion.
0 will be called a forward converter, and the converter 31 will be called an inverse converter.

Conventionally, the forward converter 30 is operated by constant current control to determine the current Id of the DC line 50, and the inverse converter 31 is operated by constant voltage control or constant margin angle control to determine the DC voltage Vd of the DC line 50. It has been decided.
FIG. 2 is a control characteristic diagram when the above control is performed, where -1 and -2 indicate the control characteristics of the forward converter 30, and -1 and -2 indicate the control characteristics of the inverse converter 31. ing. FIG. 3 illustrates a control device that produces the control characteristics shown in FIG. 2. In FIG. 3, 60 is a switch, 70 and 71 are adders, 80 is a constant current control circuit, 81 is a constant voltage control circuit, 82 is a constant margin angle control circuit, and 90 is a minimum value selection circuit. The forward converter 30 and the inverse converter 31 are each controlled by a control device shown in FIG.

However, in the control device of the forward converter 30, the switch 6
0 is open, and in the control device of the inverter 31 the switch 61 is closed. As a result, in the control device of the inverter 31, the DC current setting value Idp is reduced by the current margin ΔIdp by the adder 70, and the constant current control circuit 80 produces the characteristic -2 in FIG. The −2 characteristic produced by the constant current control circuit 80 of the converter 30 is characterized by a difference in current margin ΔIdp. The -1 control characteristic of the forward converter 30 is a characteristic when the operation is performed at the minimum value of the control angle determined by the characteristics of the forward converter. The constant voltage control circuit 81 performs control based on the difference between the DC voltage setting value Vdp from the adder 71 and the DC voltage Vd, but the forward converter 30 changes the direction of the DC voltage Vd in FIG. 1 to a negative value. For this purpose, the control angle from the constant voltage control circuit 81 is the maximum value determined by the constant voltage control circuit 81. On the other hand, in the inverter 31, since the direction of the DC voltage Vd shown in Fig. 1 is regarded as a positive value, the control angle is determined by the constant voltage control from the constant voltage control circuit 81, and the -1 characteristic shown in Fig. 2 is obtained. It will be done. The constant margin angle control circuit 82 controls the inverter 30 during normal operation.
This is a circuit that generates a control angle to ensure a certain margin angle γ to prevent commutation failure. The control angle determined by is calculated. X is commutation reactance. Constant current circuit 80 explained above
The minimum value selection circuit 90 selects the smallest control angle among the control angles outputted from the constant voltage circuit 81 and the constant margin angle circuit 82, and operates the forward converter 30 and the inverse converter 31 as the control angle α. do. As a result, the forward converter 30 obtains the control characteristics -1 and -2 in Fig. 2, and the inverse converter 31 obtains the control characteristics -1 and -2. It will be operated at point A on Figure 2. Note that the control characteristic 1 of the inverse converter 31 in FIG. The control angle may be smaller, so that it may be determined by the control angle from the constant margin angle control circuit.

[Problems in the Background Art] Conventionally, when operating a DC power transmission system as shown in FIG. 1 with the control device shown in FIG.
If one or two of the three phases of the AC voltage drop due to the accident mentioned above, resulting in voltage imbalance, the control angle determined by the constant margin angle control circuit of the control device of the converter 31 Since the commutation margin angle becomes insufficient, the inverse converter 31 causes commutation failure. Then, the inverse converter 31 becomes a DC short circuit, but even in this state, the forward converter 30 maintains the DC current Id of the DC power transmission system in Fig. 1 due to the constant current control circuit 80.
Operate to maintain the DC current setting value Idp.
For this reason, the inverter 31 is unable to return to normal operation from the commutation failure due to the voltage unbalance, and the commutation margin angle is insufficient, and the commutation failure continues. There were problems such as situations where the operation of the plant had to be stopped.

[Purpose of the invention]

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a control method for a power conversion device that speeds up recovery from a commutation failure of a converter performing reverse conversion operation.

In order to achieve the above-mentioned object, the present invention performs constant current control of a control device of a power converter, and when the DC voltage becomes less than a predetermined value, the DC current is set to the value of the difference between the predetermined value and the DC voltage. The process is performed using a temporary DC current setting value obtained by subtracting a value corrected by a constant corresponding to the value from the DC current setting value.

[Embodiments of the invention]

Hereinafter, a control device for a power conversion device according to the present invention will be explained with reference to FIGS. 4, 5, and 6. Fourth
In the figures, FIGS. 5 and 6, the same symbols are attached to the same functions as those in FIGS. 1, 2, and 3.

FIG. 4 Vdp ₁ is a predetermined value of DC voltage lower than the DC voltage setting value Vdp, |Vd| is the DC voltage Vd
is the absolute value of 72 and 73 are adders. 1
00 is a level detector which outputs zero when the input is a negative value, but outputs the same value as the input when the input is a positive value. 101 is a variable gain amplifier, which outputs the input multiplied by K (Idp).
K(Idp) is a variable gain that changes depending on the DC current setting value Idp. Idp ₁ is a temporary DC current setting value.

The control device for the power conversion device of the present invention is configured to use the temporary DC current setting value Idp 1, which is the output from the Idp correction circuit in FIG. 4, instead of the DC current setting value Idp in FIG. ₃ . It is something.

Next, we will discuss the effect. In the Idp correction circuit shown in FIG.
Outputs (Vdp ₁ - |Vd|), which is obtained by subtracting the absolute value of DC voltage |Vd| from Vdp ₁ . Level detector 1
00 outputs zero if (Vdp ₁ − | Vd |) is a negative value, but if it is a positive value, (Vdp ₁ − | Vd |)
Output. The output from the level detector 100 is multiplied by K (Idp) by the variable gain amplifier 101.
(Idp) * (Vdp ₁ − |Vd|), and the adder 72
added to. Adder 72 sets DC current setting value Idp
and the output from the amplifier 101, and a temporary DC current setting value Idp ₁ is output.

FIG. 5 shows control characteristics when the DC power transmission system shown in FIG. 1 is operated with the control device for the power converter according to the present invention. -1, -2, and -3 in FIG. 5 indicate the control characteristics of the forward converter 30, and -1
and -2 and -3 are control characteristics of the inverse converter 31. In the Idp correction circuit shown in FIG. 4, when the absolute value of the DC voltage |Vd| is larger than the predetermined value of the DC voltage Vdp ₁ , the output from the level detector 100 is zero, so the temporary DC current setting value Idp ₁ is set to DC Current setting value
It has become an IDP. Therefore, -1 and -2 in Figure 5 and -1 and -2 in Figure 3 are respectively -1 and -2 and -1 and -2 in Figure 3.
It has the same characteristics as 1 and -2 and -1 and -2. However, when _the absolute value |Vd| of the DC voltage becomes smaller than the predetermined value Vdp ₁ of the DC voltage, the temporary DC current setting value Idp ₁ from the Idp correction circuit in FIG. Vdp−|Vd|) Therefore, the constant current control circuit 80 in FIG. 3 works to lower the DC current Id in accordance with the DC voltage Vd.
As a result, the forward converter 30 has a control characteristic of -3 in FIG.
It will have the control characteristics shown in -3 in the figure.

When the DC power transmission system shown in FIG. ₁ is operated with the control characteristics shown in FIG. Since only direct current flows, inverter 3
1 makes it easier to recover from commutation failure.

Next, another embodiment of the present invention will be described.

FIG. 6 is a diagram showing another embodiment of the present invention.
Components with the same functions as in Figure 4 are marked with the same symbols.
701 is a maximum value selection circuit. Idp ₂ is a predetermined value of the DC current, and is a value smaller than the DC current setting value Idp. The maximum value selection circuit 701 selects the maximum of the temporary DC current setting value Idp ₁ and the predetermined DC current value Idp ₂ , and the temporary DC current setting value Idp ₁
becomes smaller than the predetermined value of DC current Idp ₂ ,
The configuration is such that a predetermined value of direct current is selected. When the DC power transmission system shown in FIG. 1 is operated by setting the output I'dp ₁ from the maximum value selection circuit 701 to the DC current setting value Idp shown in FIG. 3, the control characteristics shown in FIG. 7 are obtained. The control characteristics of the forward converter 30 are -
1, -2, -3 and -4, and inverse converter 3
The control characteristics of 1 are -1, -2, -3 and -4
becomes. By using the embodiment shown in FIG. 6 and setting the predetermined value _Idp2 of the DC current to a value that does not cause current interruption in the forward converter 30, even if the inverse converter 31 causes a commutation failure, the forward converter 30 can flow a predetermined value of DC current Idp ₂ that does not cause current interruption,
Disturbances occurring in the DC power transmission system shown in Figure 1 can be reduced.

Up to now, the explanation has been given assuming that the DC current setting value Idp is a certain constant value, but FIG. 9 shows changes in the control characteristics of the forward converter when the DC current setting value Idp changes. FIG. 9 explains the case where the DC current setting value Idp is changed in the embodiment of FIG. 6, and the same characteristics as in FIG. 7 are given the same reference numerals. When the DC current setting value Idp is lowered to Idp ₃ , the characteristics are -1
and -2-1, -3-1 and -4. ―
The characteristic 2-1 is caused by performing constant current control when the DC current setting value Idp is Idp ₃ , and is the same constant current control characteristic as the characteristic -2. The characteristic of -3-1 is that when the DC voltage Vd becomes less than the predetermined voltage Vdp ₁ , the temporary DC current setting value Idp ₁ = Idp ₃ -K
(Idp ₃ ) (Vdp+|Vd|) This is a characteristic caused by constant current control. The difference in slope between characteristic-3 and characteristic-3-1 occurs because the gain constant of variable gain amplifier 101 changes as the DC current setting value Idp changes. The gain constant of the variable gain amplifier 101 changes according to the DC current setting value Idp so that the constant current control characteristic based on the temporary DC current setting value Idp ₁ passes through a certain predetermined DC voltage value Vdp ₂ on characteristic-4. I'm letting you do it. By changing the gain constant of the variable gain amplifier 101 as described above, it is possible to hasten the recovery of the inverter from commutation failure and to reduce disturbances.

Although the control device for the power conversion device has been described above as being configured with an electric circuit, the present invention can also be applied to a case in which the control device of the power conversion device is configured with a computer. FIG. 8 is a flowchart for implementing constant current control on a computer including the Idp correction circuit of FIG. 4 and the constant current control circuit 80 of FIG. 2 according to the present invention. In Figure 8, if the absolute value |Vd| of the DC voltage is smaller than the predetermined value Vdp ₁ of the DC voltage, the temporary DC current setting value Idp ₁ is set to Idp - K (Idp).
*(Vdp + |Vd|), but if the absolute value of the DC voltage |Vd| is not smaller than the predetermined value of the DC voltage Vdp ₁ , the temporary DC current setting value Idp ₁ is assumed to be equal to the DC current setting value Idp, Temporary DC current setting value Idp ₁
This figure shows how constant current control is performed with and DC current Id to calculate the control angle. As described above, it is also possible to configure the control device for the power conversion device according to the present invention with a computer.

Further, although the description has been given so far regarding the DC two-terminal power transmission system shown in FIG. 1, greater effects can be expected by applying the present invention to multi-terminal DC power transmission.

Although better effects can be obtained by applying the present invention as a control device for a forward converter, as can be seen from the above description, it can also be used as a control device for an inverse converter.

〔Effect of the invention〕

According to the above explanation, the present invention has the following effects.

(1) In a control device for a power conversion device such as a DC power transmission, when the DC voltage falls below a predetermined value of the DC voltage, the value of the difference between the predetermined value of the DC voltage and the DC voltage is adjusted according to the DC current setting value. By performing constant current control using a temporary DC current setting value that is obtained by subtracting the DC current setting value by a value corrected by a constant, even if a commutation failure occurs, it has the effect of speeding up recovery from a current failure. be.

(2) In a control device for a power conversion device such as a DC power transmission, when the DC voltage falls below a predetermined value of DC voltage, the difference between the predetermined value of the DC voltage and the DC voltage is adjusted according to the DC current setting value. Constant current control is performed using a temporary DC current setting value that is obtained by subtracting the DC current setting value by a value corrected by a constant. If the value falls below the specified value,
By performing constant current control at a predetermined value of the DC current, there is an effect that disturbance of the power conversion device can be reduced even if the inverse converter causes a commutation failure.

[Brief explanation of drawings]

Figure 1 is a DC two-terminal power transmission system diagram, Figure 2 is a conventional control characteristic diagram of Figure 1, Figure 3 is a configuration diagram of a conventional power converter control device, and Figure 4 is a correction according to the present invention. The circuit diagram, FIG. 5 is a control characteristic diagram of the power conversion device according to the present invention, FIG. 6 is a diagram showing another embodiment of the correction circuit of the present invention, and FIG. 7 is a case where the correction circuit of FIG. 6 is used. FIG. 8 is a flowchart for implementing the present invention using a computer, and FIG. 9 is a diagram showing control characteristics when changing the DC current setting value of the forward converter. . 10, 11... AC system, 20, 21... Transformer,
30, 31... Converter, 40, 41... DC reactor, 50, 51... DC line, 60... Switch, 7
0, 71, 72, 73... Adder, 80... Constant current control circuit, 81... Constant voltage control circuit, 82... Constant margin angle control circuit, 90... Minimum value selection circuit, 100... Level detector, 101... Variable gain Amplifier.

Claims (1)

[Claims] 1. In a power conversion device such as a DC power transmission device or a frequency conversion device that operates while coordinating a forward converter and an inverse converter, constant current control is changed to DC current setting when the DC voltage exceeds a predetermined value. When the DC voltage falls below the predetermined value, the value of the difference between the predetermined value and the DC voltage is corrected with a constant corresponding to the DC current setting value, and the DC current setting is performed. A method for controlling a power conversion device, characterized in that constant current control is performed using a temporary DC current setting value subtracted from a current value. 2. In power conversion equipment such as DC power transmission equipment and frequency conversion equipment that operate while coordinating forward converters and inverse converters, constant current control is performed using a DC current set value when the DC voltage exceeds a predetermined value, If the DC voltage falls below the predetermined value, the difference between the predetermined value and the DC voltage is calculated by subtracting the value corrected by a constant corresponding to the DC current setting value from the DC current setting value. Constant current control is performed using the DC current setting value, and if the temporary DC current setting value becomes less than the predetermined value of DC current, constant current control is performed using the specified DC current value as the temporary DC current setting value. A method for controlling a power conversion device, comprising: performing the following steps.