JPH07227044A - Controller for ac-dc converter - Google Patents

Abstract

PURPOSE:To minimize the influence of an AC-DC converter on an AC system by continuously operating the converter by continuously giving a signal to a converter phase control circuit from a synchronism detecting circuit even when the synchronism detecting circuit cannot operate normally for some reason. CONSTITUTION:A storage circuit M temporarily stores the output of a voltage- controlled oscillator (synchronism detecting circuit) VCO and, whenever the new output of the oscillator VCO is inputted, the circuit M updates its content and outputs the value to a converter phase control circuit TPC. A switch operation judging circuit SWJ prevents an abnormal-frequency signal from being inputted to the control circuit TPC by opening switches SW1 and SW2 and, at the same time, continuously outputs the preceding frequency stored in the storage circuit M, namely, a normal frequency to the circuit TPC when the circuit SWJ judges that the oscillator VCO cannot operate normally for some reason. Therefore, a converter can be continuously operated and the influence of the converter on an AC system can be minimized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an AC / DC converter used in DC power transmission equipment having a plurality of terminals, frequency conversion equipment, asynchronous interconnection equipment for interconnection of two different AC systems, and the like.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram of a conventional two-terminal DC power transmission facility during bipolar operation. In FIG. 4, A and B are terminals and Ea and Eb are AC systems. CONV1, CON
V2, CONV3, CONV4 are AC / DC converters,
The transformers TR1, TR2, TR3 and TR4 are connected to the AC systems Ea and Eb.

AC / DC converters CONV1 and CONV3
And CONV2 and CONV4 are DC reactors DCL1 and DCL2 and DCL3 and DCL4, respectively.
Is connected to the DC power transmission lines L1 and L2. N is the neutral line. Here, the case where there is no DC transmission line is called asynchronous interconnection equipment, and the case where the frequencies of the interconnected AC grids are different from each other is called frequency conversion equipment.

FIG. 3 is a schematic block diagram of a controller for operating the AC / DC converter. In the figure, the control device for each terminal uses the value obtained by converting the operating power command value into the current command value Idp to obtain the required control angle by the control angle calculation circuit CAC. From this control angle and the frequency and phase of the actual AC system obtained from the synchronization detection circuit SDC, the phase control circuit PCC determines at what point in time the firing pulse should be issued.

According to an instruction from the phase control circuit PCC, the pulse generation circuit PLC actually causes the converter CONV
The firing pulse applied to the is shaped. That is, the converter CONV cannot operate unless the frequency and phase of the AC system are correctly detected by the synchronization detection circuit SDC. This synchronization detection circuit SDC has a so-called PLL (Ph
ase Locked Loop) method is used.

FIG. 2 is a schematic block diagram of this PLL circuit. The PLL circuit is a negative frequency feedback circuit, and operates so that the frequency of the voltage controlled oscillator VCO in the closed circuit always matches the input signal frequency.

The AC system voltage is input to the phase comparator PC as the frequency f, the frequency and the phase output from the voltage controlled oscillator VCO are compared, and the voltage corresponding to the difference is passed to the low pass filter LPF. Of this difference, only the system frequency component is extracted by the low pass filter LPF,
The amplifier AMP increases the loop gain to make it easier to use. With this PLL circuit, the low-pass filter LP
The AC system voltage and phase are detected with a time delay of about F, and used to control the converter.

[0008]

Although the AC system voltage is detected as the frequency of the AC system, the AC system voltage is lowered in voltage due to line failure or the like, or the phase is temporarily shifted. In such a state, the synchronization detection circuit cannot operate normally, and the operation of the converter has to be stopped.

The present invention has been made in view of the above circumstances, and an object thereof is to synchronize even if the synchronization detection circuit cannot operate normally due to a drop in the AC system voltage or a temporary phase shift. It is an object of the present invention to provide a control device for an AC / DC converter in which a signal is continuously supplied from the detection circuit to the phase control circuit to keep the converter operating as much as possible to minimize the influence on the AC system.

[0010]

In order to achieve the above object, the first aspect of the present invention provides a voltage-controlled oscillator that follows an input signal in order to detect the frequency and phase of the input signal from the AC system. In the controller of the AC / DC converter including a synchronization detection circuit that compares the output and the input signal with a comparator and adjusts this voltage-controlled oscillator to eliminate the difference, the output from the synchronization detection circuit is temporarily A storage circuit that stores and updates each time there is a new output, a determination circuit that determines a state in which the synchronization detection circuit cannot operate normally, and prevents update of the storage circuit, and a control angle calculated according to an operation command value. Accordingly, a control circuit for controlling an ignition pulse to the AC / DC converter based on the output signal of the storage circuit is provided.

According to a second aspect of the present invention, in the controller of the AC / DC converter according to the first aspect, a first switch circuit for turning on / off the input to the storage circuit is provided, and the determination circuit is in a state where the synchronization detection circuit cannot operate normally. Is determined and the first switch circuit is turned off to prevent updating of the memory circuit.

According to a third aspect of the present invention, in the control device for the AC / DC converter according to the first aspect, a second switch circuit for turning on / off the output of the voltage controlled oscillator to the comparator is provided, and the determination circuit is a synchronization detection circuit. It is characterized in that a state in which it cannot operate normally is judged, update of the memory circuit is blocked, and the second switch circuit is turned off.

According to a fourth aspect of the present invention, in the control device for an AC / DC converter according to the third aspect, when the AC system returns to a normal state and the synchronization detection circuit returns to a state where it can operate normally, the second
The switch circuit is turned on, and the update inhibition of the memory circuit is released thereafter.

According to a fifth aspect of the present invention, in the control device for an AC / DC converter according to the first aspect, the judgment circuit is such that when the voltage of the AC system falls below a predetermined value, or the frequency of the AC system deviates from a predetermined upper and lower limit value. At this time, it is determined that the synchronization detection circuit cannot operate normally.

According to a sixth aspect of the present invention, in the control device for the AC / DC converter according to the first aspect, the judgment circuit cannot normally operate the synchronization detection circuit based on the AC system voltage condition and the operating condition of the AC / DC converter. The feature is that it is judged as a state.

[0016]

According to the present invention, the frequency of the voltage controlled oscillator is stored in advance even when the synchronous detection circuit cannot operate normally due to a drop in the AC system voltage. The output can be continued and the converter can be continuously operated.

[0017]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a block diagram of an embodiment of the present invention. As shown in FIG. 1, a so-called PLL, which is a phase synchronization circuit that follows the phase of an input signal for detecting the frequency and phase of an AC system, is shown.
In a synchronization detection circuit using the (Phase Locked Loop) system, a switch S for turning on / off this control loop in a control loop returning from the voltage controlled oscillator VCO to the phase comparator PC.
A switch S which is provided with W2 and turns on / off the output of the voltage controlled oscillator VCO, that is, the output from the synchronization detection circuit.
W1 is provided. These two switches SW1, SW2
Are turned on and off in cooperation with a command from the switch operation determination circuit SWJ.

A storage circuit (memory) M is provided for temporarily storing the output of the voltage controlled oscillator VCO, that is, the output from the synchronization detection circuit. This memory circuit M rewrites the contents each time there is a new input from the voltage controlled oscillator VCO, and outputs the value to the converter phase control TPC.

Normally, the switches SW1 and SW2 are closed, the synchronization detection circuit by the PLL system operates normally due to the closed loop through the switch SW2, and the memory circuit M is rewritten to a new value one after another and converted. It is output to the instrument phase control TPC.

Now, if the switch operation determination circuit SWJ determines that the PLL system cannot operate normally for some reason, the switches SW1 and SW2 are opened by a command from the switch operation determination circuit SWJ, and an abnormal frequency signal is generated. While being prevented from being input to the converter phase control circuit TPC, the previous frequency value stored in the storage circuit M is continuously output to the converter phase control circuit TPC.

When it returns to normal, the switch operation judgment circuit S
If WJ judges, first close switch SW2 and then PLL
The operation of the system sync detection circuit is restored to normal. After that, the switch SW1 is closed to rewrite the frequency value of the memory circuit M to the normal circuit configuration.

The switch operation determination SWJ monitors the AC system voltage and opens the switches SW1 and SW2 when the normal PLL type synchronization detection circuit does not operate, and when the AC system voltage is restored. First, the switch SW2 is closed to confirm that the normal operation is performed, and then the switch SW1 is closed. Further, the switch operation determination circuit SWJ monitors the AC system voltage, and switches according to the AND condition of the condition that the normal PLL type synchronization detection circuit does not operate and the condition that the AC / DC converter is operating the rectifier. SW1 and SW2
When the AC system voltage is restored, open the switch SW first.
The switch SW1 is closed and the switch SW1 is closed after the normal operation is confirmed. In addition,
The switch may be a semiconductor switch or a mechanical switch.

[0023]

As described above, according to the control device for the AC / DC converter of the present invention, the AC system voltage decreases,
Even if the phase is temporarily out of phase and the sync detection circuit cannot operate normally, the sync detection circuit continues to give a signal to the phase control circuit to keep the converter running as much as possible to minimize the effect on the AC system. can do.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a synchronization detection circuit according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of a conventional PLL system synchronization detection circuit.

FIG. 3 is a control block diagram of a general AC / DC converter.

FIG. 4 is a circuit diagram showing an example of an AC power transmission system.

[Explanation of symbols]

AMP ... Amplifier, CAC ... Control angle arithmetic circuit, CONV1
-CONV4 ... AC / DC converter, f ... Frequency signal, DCL
1-4: DC reactor, Ea, Eb ... AC system, LP
F ... Low-pass filter, M ... Storage circuit, PC ... Phase comparator, PCC ... Phase control circuit, PLC ... Pulse generation circuit,
SW1, SW2 ... Switch, SDC ... Sync detection circuit, S
WJ ... Switch operation determination circuit, TR1-TR4 ... Converter transformer, TPC ... Converter phase control, VCO ... Voltage controlled oscillator

Claims (6)

[Claims] 1. To detect the frequency and phase of an input signal from an AC system, the output of a voltage controlled oscillator that follows the input signal is compared with the input signal by a comparator, and this voltage control is performed so that the difference disappears. In a control device for an AC / DC converter including a synchronization detection circuit that adjusts an oscillator to obtain a synchronization signal, a storage circuit that temporarily stores the output from the synchronization detection circuit and updates each time a new output is output, and the synchronization detection circuit. A determination circuit that determines a state in which the storage circuit cannot be operated normally and blocks updating of the storage circuit, and a firing pulse to the AC / DC converter based on the output signal of the storage circuit according to the control angle calculated according to the operation command value. A control device for an AC / DC converter, comprising: a control circuit for controlling. 2. The control device for an AC / DC converter according to claim 1, further comprising a first switch circuit that turns on and off the input to the storage circuit, and the determination circuit determines a state in which the synchronization detection circuit cannot operate normally. A control device for an AC / DC converter, wherein the first switch circuit is turned off to prevent updating of the storage circuit. 3. The control device for an AC / DC converter according to claim 1, further comprising a second switch circuit that turns on and off the output of the voltage controlled oscillator to the comparator, and the judgment circuit is such that the synchronization detection circuit operates normally. A control device for an AC / DC converter, characterized in that it judges a state in which it cannot be operated, prevents updating of the memory circuit, and turns off the second switch circuit. 4. The control device for an AC / DC converter according to claim 3, wherein when the AC system returns to a normal state and the synchronization detection circuit returns to a state in which it can operate normally, the second switch circuit is turned ON, After that, the control device for the AC / DC converter is characterized in that the update inhibition of the storage circuit is released. 5. The control device for an AC / DC converter according to claim 1, wherein the determination circuit performs synchronous detection when the voltage of the AC system falls below a predetermined value or when the frequency of the AC system deviates from a predetermined upper and lower limit value. A control device for an AC / DC converter, which is characterized by determining that a circuit cannot operate normally. 6. The control device for an AC / DC converter according to claim 1, wherein the determination circuit determines that the synchronization detection circuit cannot operate normally based on the voltage condition of the AC system and the operating condition of the AC / DC converter. A control device for an AC / DC converter.