JPH0353847B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] [The present invention relates to a method of controlling a converter in DC power transmission, and particularly to a control method suitable for digitally controlling a converter using an arithmetic processing circuit. .

[Prior art]

Phase control of converters in DC power transmission is based on constant current control, which keeps the DC current constant, and constant voltage control, which keeps the DC voltage constant.
During normal operation, the forward converter side is under constant current control, and the inverse converter side is under constant voltage control. In addition, in the event of a transient situation such as a power flow reversal operation or a ground fault on a power transmission line, each converter will switch from constant current control mode to constant voltage control mode, or from constant voltage control mode to constant current control mode. Switch. Switching between control modes in the phase control of the converter needs to be fast in order to prevent failures of DC power transmission equipment and disturbances in the AC system due to occurrences of DC overvoltages, DC overcurrents, DC current interruptions, etc. Conventionally, measures have been taken to suppress the saturation level of constant current control systems and constant voltage control systems to the necessary minimum, and to install limiters (saturation level limiters) to reduce the time delay in switching between control modes. There is. When controlling the phase of a converter using an analog control method, the response speed of the constant current control system and constant voltage control system can be made sufficiently fast, so high-speed switching between control modes is possible simply by installing a saturation level limiter. be. However, in the case of digital control using an arithmetic processing circuit, the response speed of the constant current control system and constant voltage control system cannot be made as fast as in the case of analog control due to the time delay caused by the arithmetic processing time of the arithmetic processing circuit. Can not. Therefore, high-speed switching of control modes cannot be achieved simply by providing a saturation level limiter. For example, when talking about the response of an inverter when a DC power transmission line has a ground fault, when a saturation level limiter is installed, in analog control it switches from constant voltage control mode to constant current control mode in about 5 ms. It takes approximately 15ms to switch the control mode in digital control after a ground fault occurs. Therefore, in the case of digital control, the decrease in the DC current on the inverter side during a ground fault is large, and current interruption is likely to occur.

The arithmetic processing contents of conventional digital processing can be expressed as a block diagram as shown in FIG. Here, a constant current control system 21 includes a constant current control function 26 and a constant current control signal limiter 27, a constant voltage control system 22 includes a constant voltage control function 28 and a constant voltage control limiter 29, and a margin angle control function 30. Among the outputs P _c (constant current control signal), P _v (constant voltage control signal), and P _r (margin angle control signal) of each control system of the margin angle control system 23, the signal with the smallest value is selected as the minimum value selection system 2.
4 to select the phase control signal P, and then use the phase control signal limiter 25 to select the phase control signal (P) _L <≦
The output is limited to the range of P≦(P) _H . However, the values of (P) _L and (P) _H differ depending on the operation mode.

According to this configuration, the constant current control system 21 and the constant voltage control system 22 each have a previously calculated value,
Since the configuration is such that calculations are performed using the values of P _c and P _v , the control operation mode cannot be smoothly switched in the event of a ground fault or the like.

FIG. 8 shows operating waveforms when the conventional circuit is used when a ground fault occurs in a DC power transmission line.

Figure 8 1 shows the response of the control signal on the forward converter side, and since the phase control signal P remains P = P _c even after _t7 when the ground fault occurred, constant current control operation You can see that it is in the mode.

FIG. 8 2 shows the response of the control signal on the inverter side, and the phase control signal P is at the time t ₇ when the ground fault occurs.
Since P=P _v is switched to P=P _c in , it can be seen that the operation mode is switched from the constant voltage control operation mode to the constant current control operation mode.

3 and 4 in Figure 8 show the operating waveforms of the DC current on the forward converter side and the DC current on the inverse converter side, respectively. Since the switching to the control operation mode is not smooth, the current drop is large and current interruptions are likely to occur.

Next, FIG. 9 shows operating waveforms when the power flow is reversed in the conventional example.

1 in FIG. 9 shows the response of the control signal when switching from forward converter operation to inverse converter operation. At the time _ts when the DC current setting value changes from 1.0 _pu to 0.9 _pu , the constant current control signal P _c first becomes a value that makes the DC current 0.9 _pu , and then changes to a value that makes the control delay angle 180 degrees. stand up. The constant voltage control signal P _v has a DC voltage of -
When it becomes 1.0 _pu or less, it changes as shown in the figure,
Finally, it settles on a value that makes the DC voltage −1.0 _pu .
Therefore, the phase control signal becomes as shown in the figure.

2 in FIG. 9 shows the response of the control signal when changing from inverse converter operation to forward converter operation. Looking at this, the time point when the phase control signal P becomes P=P _c is considerably after the time point t _s .

3 in Figure 9 shows the response of the DC current Id,
Due to the operation delay of the constant current control system on the inverter side,
Current oscillations as shown by symbol C occur.

4 in Figure 9 shows the response of the DC voltage Vd,
Due to the delay in the operation of the constant voltage control system at 1 in FIG. 9, voltage oscillations as shown by symbol D occur.

As described above, in the conventional control system, the current drop in the inverter during a ground fault is large, and current interruption is likely to occur. Furthermore, when the power flow is reversed, the switching between operating modes is not smooth, and current and voltage vibrations occur in the DC transmission line.

[Purpose of the invention]

An object of the present invention is to speed up switching between control modes such as constant current control mode and constant voltage control mode in digital control of a DC power transmission converter, thereby reducing DC overvoltage, DC overcurrent, and DC overcurrent during transients. The purpose is to prevent the occurrence of current interruptions, etc.

[Summary of the invention]

The present invention provides constant current control signals for constant current control of a converter, constant voltage control signals for constant voltage control of a converter, etc. By using this as an initial value in the process of creating a current control signal and a constant voltage control signal, high-speed switching between control modes is achieved.

[Embodiments of the invention]

An overview of the digital control system in a two-terminal DC power transmission system will be described according to FIGS. 1, 2, and 3, and 2.
A control algorithm and its effects when the present invention is applied to control of a terminal DC power transmission system will be explained.

Figure 1 shows three-phase AC systems 1 and 2, a converter 3,
4 shows a system configuration when a two-terminal DC power transmission system consisting of DC reactors 5, 6, and a DC power transmission line 7 is operated by digital control. The digital control system 8 consists of a central control device 9 and terminal control devices 10 and 11, and each terminal control device 10 and 11 converts the conversion devices 3 and 4, respectively, in response to a command signal from the central control device 9. performs phase control.

FIG. 2 shows the circuit configuration of the terminal control devices 10 and 11. The arithmetic processing circuit 13 is activated by the pulse O generated by the pulse generation circuit 12, and receives the DC current I ₄ , the DC voltage V _d , the minimum commutation voltage E _nio , and the input from the central controller via the input circuit 15 . DC current setting value I _d0 , DC voltage setting value
V _d0 , start/stop command signal S ₁ , power flow control command signal S ₂
is taken in as a digital quantity, digital arithmetic processing is performed according to an arithmetic processing procedure stored in advance in the storage circuit 14, a phase control signal P is created, and the phase control signal P is outputted to the phase control circuit 17 via the output circuit 16. The phase control circuit 17 receives the phase control signal P as a control input, generates a firing pulse Q having a control delay angle α proportional to the magnitude of the phase control signal P, and drives the converter.

The time chart in FIG. 3 represents the operation of the terminal control device shown in FIG. The pulse waveform generated by the pulse generation circuit 12 periodically becomes H (High) or L (Low) as shown in 1 in FIG. 3, and the arithmetic processing circuit 13 changes the pulse waveform O from L to H.
, and if the time from when the arithmetic processing circuit 13 is started until the phase control signal P changes, that is, the arithmetic processing time, is T ₁ second, the phase control signal P is Depending on the calculation result of the circuit 13, it changes stepwise as shown by the solid line 2 in FIG. Further, the sampling period at this time is the pulse period T ₂ of the pulse waveform O. The phase control circuit 17 in FIG. 2 internally creates a ramp waveform corresponding to each phase of the converter as shown by the broken line 2 in FIG. 3, compares the magnitude of the phase control signal P and the ramp waveform, and When the waveform of the control signal P crosses the ramp waveform, a pulse Q as shown at 3 in FIG. 3 is generated, and the pulse Q is distributed to each phase of the converter to create an ignition pulse. However, the third
The maximum value P _nax of the ramp waveform in 2 in the figure corresponds to a control delay angle of 180 degrees, and the phase control signal P =
When P _nax , the control delay angle of the ignition pulse is 180 degrees. Furthermore, the minimum value P _nio of the lamp waveform at 2 in Fig. 3 corresponds to a control delay angle of 0 degrees, and when the phase control signal P = P _nio , the control delay angle of the ignition pulse is 0 degrees. . In this way, the control delay angle of the ignition pulse is proportional to the magnitude of the phase control signal P. Taking the ramp waveform _l1 of 2 in FIG. 3 as an example, _l1 is the time point t. If the waveform of the phase control signal P rises linearly from ₂ to time t ₆ as shown by the solid line 2 in Fig. 3, then the ignition pulse corresponding to l ₁ becomes q ₁ , and then The time corresponding to the control delay angle is _t3 .

FIG. 4 is a block diagram showing a control algorithm when the present invention is applied to arithmetic processing by the arithmetic processing circuit 13. In this figure, 21 Constant current control system 21 performs constant current control calculations using the previous value of phase control signal P (value determined by calculation processing one sample period before) as an initial value to obtain constant current control signal P _c .
The voltage control system 22 obtains the previous value of the phase control signal P or the previous value of the constant voltage control signal _Pv as an initial value by switching the switch 31, and obtains the constant voltage control signal _Pv by constant voltage control calculation. Constant voltage control system, 23 is a margin angle control signal P〓 which limits the size of the control delay angle α in order to prevent commutation failure of the converter.
This is the margin angle control system 23 that obtains the following. Each output P _c , P _v ,
Minimum value selection system 24 for the signal with the smallest value among P〓
to select the phase control signal P, and then select the phase control signal P with the phase control signal limiter 25 so that (P) _L ≦
The output is limited to the range of P≦(P) _H . However, the values of (P) _L and (P) _H differ depending on the operation mode. In other words, (P) _H is (P) _H0 (corresponding to a control delay angle of 90 degrees) when the converter is stopped, and (P) _H1 when the converter is in rated operation.
(corresponds to a control delay angle of 160 degrees), and during the soft start period and soft stop period, (P) _H0 , (P) _H1
change linearly between (P) _L differs between when the converter is operated as a forward converter and when it is operated as an inverse converter. When the converter is operated as a forward converter, (P) _L0 (control delay angle of 80 degrees) (equivalent), becomes (P) _L1 (equivalent to a control delay angle of 10 degrees) during rated operation of the converter, and changes linearly between (P) _L0 and (P) _L1 during the soft start period and soft stop period. . Furthermore, in the case of inverse converter operation, (P) _L is always (P) _L0 . However, when the tide reverses,
The value of (P) _L changes stepwise when the phase control signal P reaches P=(P) _L0 . In addition, the switch 31 is used when the converter is operated as a reverse converter.
And only when the phase control signal P is (P≧P _L0) , the previous value of the phase control signal P is used as the initial value in the constant voltage control calculation, and in other cases, that is, when P is
When the angle becomes smaller than 90° and reaches the lower limiter P _L0 (80°), the converter will shift to forward converter operation, so at this time, the previous value of the constant voltage control signal P _v is used for constant voltage control calculation. Operate so that the initial value is set to . The purpose of providing such a switch 31 is to prevent deterioration of control performance due to mutual interference between the constant current control system and the constant voltage control system when the initial value in the constant voltage control calculation is always the previous value of the phase control signal P. This is to do so.

For example, if a ground fault occurs in the power transmission line while the converter is operating the converter using the previous value of the phase control signal P as the initial value in constant current control calculation and constant voltage control calculation, the constant current control system will perform constant current control. It operates to suppress DC overcurrent by increasing the signal P _c , but since the response of the constant voltage control system is generally slower than the response of the constant current control system, the constant voltage control signal P _v is
It becomes smaller than the constant current control signal P _c and enters constant voltage control mode. As a result, a huge amount of DC overcurrent occurs.

The constant current control system 21 uses a constant current control function 26 to create a constant current control signal P _c for constant current control of the converter, and uses a constant current control signal limiter 27 to control the magnitude of the constant current control signal P _c . Output with a limit (control delay angle limited to a range of 0 to 180 degrees). In addition, when creating the constant current control signal P _c using the constant current control function 26, the value (P) o of the phase control signal for each sampling period is used as the initial value, and the DC current setting value and the value (P) _o of the phase control signal for each sampling period of the DC current are Using the values (I _d0 ) _o and (I _d ) _o as control inputs, the constant current control signal (P _e ) after one sampling period according to the following formula:
Create _o+1 and output as P _c .

(P _c ) _o+1 = K _c (P) _o + F _c [(I _d0 ) _o , (I _d ) _o ] …(1) where K _c is the control constant, F _e is (I _d0 ) _o , (I _d ) is a function with _o as a parameter, and n is an integer representing a sampling time point.

The constant voltage control system 22 uses a constant voltage control function 28 to create a constant voltage control signal P _v for constant voltage control of the converter, and uses a constant voltage control signal limiter 29 to control the magnitude of the constant voltage control signal P _v . Output with a limit (control delay angle limited to a range of 0 to 180 degrees).

Constant voltage control signal P _v by constant voltage control function 28
When the converter is operated as an inverse converter, and the previous value of the phase control signal P is greater than or equal to the value of P _L0 , the value (P) _o at the time of sampling of the phase control signal P is set to the initial value. and otherwise,
The value ( _Pv ) _o at the time of sampling of the constant voltage control signal _Pv is set as the initial value. At this time, the DC voltage setting value and DC voltage at the time of sampling are
Assuming (V _d0 ) _o and (V _d ) _o , respectively, the calculation formula for determining the constant voltage control signal (P _v ) _o+1 after one sampling period with (P) _o as the initial value is ( P _v ) _o+1 = K _v (P) _o + F _v [(V _d0 ) _o , (V _d ) _o ]...(2), and in other cases, it is expressed by the following formula.

(P _v ) _o+1 = K _v (P _v ) _o +F _v [(V _d0 ) _o , (V _d ) _o ] …(3) where K _v is the control constant and F _v is (V _d0 ) _o ,( _Vd ) _o
is a function whose parameter is n, where n is an integer representing a sampling time point.

The margin angle control system 23 works as a limiter to ensure the minimum necessary margin angle in order to prevent commutation failure in the converter and at the same time operate the converter at a high power factor. Therefore, the margin angle control function 30 is calculated from the DC current (I _d ) _o and the minimum commutation voltage (E _nio ) _o for each sampling period to ensure the minimum necessary margin angle according to the following formula. Find the value (P〓) _o+1 of the margin control signal after one sampling period and output it as P〓.

(P〓) _o+1 = F〓 [(I _d ) _o , (E _nio ) _o ...(4) However, F〓 is a function representing (P〓) _o+1 . When operating the DC power transmission system according to the control algorithm shown in FIG. 4, the DC current setting value I _d0 is changed depending on the operation mode. In other words, when the converter is operated as a forward converter, when stopped,
I _d0 = 0.1 _PU , I _d0 = 1.0 _PU during rated operation, and the value of I _d0 is changed linearly during the soft start period and soft stop period. Further, when the converter is operated as a reverse converter, the value of I _d0 is set to approximately 90% of the value of I _d0 during forward converter operation. Therefore, when performing power flow reversal, the forward converter side
Swap the value of I _d0 with the value of I _d0 on the inverse converter side. Further, the DC voltage set value V _d0 does not need to be changed depending on the operation mode and is always 1.0 _PU . however,
The value of the DC voltage V _d is set to be positive when the inverse converter is operating.

Operating waveforms when a two-terminal DC power transmission system is digitally controlled using the control system shown in FIG. 4 are shown below, and the effects of the present invention will be described.

FIG. 5 shows operating waveforms when a ground fault occurs in a DC transmission line, and 1 in FIG. 5 shows the response of the control system on the forward converter side.

In this case, the constant voltage control signal P _v on the forward converter side is
Since the previous value of the constant voltage control signal P _v is determined as the initial value, the value corresponds to a control delay angle of 180 degrees, and the limiter values (P) _L and (P) _H of the phase control signal limiter are controlled respectively. delay angle of 10 degrees, and
The value corresponds to 160 degrees. The margin angle control signal P〓 is
(P) has a value slightly smaller than _H and oscillates after the earth fault occurrence time t ₇ in response to the overcurrent during the earth fault. Further, when the forward converter is in operation, the constant current control signal P _c is selected by the minimum value selection system 24, so the phase control signal P matches P _c . That is, when the constant current control mode is entered and a ground fault occurs at time _t7 , the value of the phase control signal P increases as shown in the figure.

2 in Figure 5 shows the response of the control system on the inverter side, where the limiter value (P) _L is the control delay angle.
The value corresponds to 80 degrees. Since the constant current control signal P _c and the constant voltage control signal P _v are each determined using the phase control signal P as an initial value, P, P _c , P _v
The values almost match. Also, at the time of ground fault occurrence
Before _t7 , P= _Pv , that is, constant voltage control mode, and after the ground fault time _t7 , P= _Pc , that is, constant current control mode. Switching from constant voltage control mode to constant current control mode is performed by P, P _c , P _v
Since they almost match, the process is fast. As is clear from comparing this operating waveform with the operating waveform of the conventional example described above in FIG. 8, according to this method, the amount of decrease in the DC current on the inverter side when a ground fault occurs is small, This has the effect of preventing the occurrence of current interruption on the inverter side.

Figure 6 shows the operating waveforms at the time of tidal current reversal.
Figure 1 shows the response of the control system for a converter reversing from forward converter operation to inverse converter operation. This is the waveform when the power flow reversal starts at time _t8 and ends at time _t10 , and when the phase control signal P crosses the value of (P) _L0 , that is, at time _t9 , the limiter value (P) _L , and constant voltage control signal
P _v changes stepwise as shown in the figure. Before time t ₉ , only the constant current control signal P _c uses the previous value of the phase control signal P as the initial value, so only the values of P and P _c match, but after time t ₉ , the phase control signal is further adjusted. Since the signal P _v is also determined using the previous value of the phase control signal P as an initial value, the values of P, P _c , and P _v almost match. Therefore, switching from constant current control mode to constant voltage control mode at time _t10 is instantaneously performed. 2 in FIG. 6 shows the response of the control system for a converter that reverses from reverse converter operation to forward converter operation. Before the power flow reversal start time _t8 , the constant current control signal P _c ,
Since the constant voltage control signal P _v is determined using the previous value of the phase control signal P as an initial value, P, P _c , P _v
The values almost match. As can be seen by comparing Figure 6 with Figure 9, which shows the operating waveforms during power flow reversal of the conventional method, this method has a smooth switching of operation modes and is effective in suppressing the occurrence of current and voltage vibrations in the DC transmission line. There is.

〔Effect of the invention〕

Therefore, switching from constant voltage control mode to constant current control mode at time _t8 is performed at high speed. In this way, since the control modes in both converters are switched quickly, the DC overcurrent and DC overvoltage at the time of power flow reversal are small. Further, according to the present invention, switching of control modes at the time of starting and stopping becomes fast, so starting and stopping operations become smooth.

As described above, the present invention is effective in preventing the occurrence of DC overvoltage, DC overcurrent, DC current interruption, and the like.

Furthermore, the present invention can be applied to a complex control system (for example, a control system aimed at controlling a multi-terminal DC power transmission system) that includes a plurality of constant current control systems and a plurality of constant voltage control systems, and improves control performance. It is an effective means to improve your skills.

According to the present invention, switching between control modes such as constant current control mode, constant voltage control mode, margin angle control mode, and limiter control mode of the AC/DC converter can be made fast, so that the DC power transmission system can be activated. It is possible to suppress DC overvoltages and DC overcurrents that occur during power outages, stops, and power flow reversals. Also,
Since it is possible to suppress a drop in the direct current on the reverse converter side at the time of a ground fault, it is possible to prevent failure of the converter due to current interruption.

[Brief explanation of drawings]

Figure 1 shows the configuration of a digital control system for a DC power transmission system, Figure 2 shows the configuration of a terminal control device, Figure 3 shows a time chart for the operation of the terminal control device, and Figure 4 shows the control according to the present invention. System block diagrams, FIGS. 5 and 6 show operating waveforms of the control system according to the present invention, FIG. 7 is a control block diagram of the conventional example, and FIGS. 8 and 9 show the control system of the conventional system. It shows the operating waveforms of the system. 21... constant current control system, 22... constant voltage control system, 2
3... Margin angle control system, 24... Minimum value selection system, 25...
Phase control signal limiter, 26...constant current control function,
27... Constant current control signal limiter, 28... Constant voltage control function, 29... Constant voltage control signal limiter, 30...
Margin angle control function, 31...switch.

Claims (1)

[Scope of Claims] 1 Constant current calculation for keeping the DC current of DC power transmission constant and constant voltage calculation for keeping the DC voltage of DC power transmission constant are repeatedly executed, and the control delay angle of the conversion device is determined. In a method of controlling a converter in DC power transmission, in which the converter is controlled by selecting the calculation result that makes 1. A method of controlling a converter in DC power transmission, characterized in that the value of a phase control signal selected by the calculation is used as an initial value. 2 Repeatedly perform constant current calculation to make the DC current of DC power transmission constant and constant voltage calculation to make the DC voltage of DC power transmission constant, and calculate the side that makes the control delay angle of the converter smaller. In a method of controlling a converter in DC power transmission in which a calculation result is selected to control the converter, when the converter is operated in reverse conversion mode, the constant current calculation is based on the phase control signal selected in the previous calculation. 1. A control device for a converter in direct current power transmission, characterized in that constant voltage calculation is performed using a calculation result obtained in a previous constant voltage calculation as an initial value.