JPH0474949B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a phase continuous comparison type synchronization signal detection circuit for a power conversion device used for DC power transmission or the like.

[Technical background of the invention]

FIG. 1 is a block diagram showing the configuration of a DC power transmission system. 1-1 is the power transmission side three-phase AC bus, 1
-2 is a three-phase AC bus on the receiving side, and this bus 1-
Smooth reactor 3-1, 3-2 between 1, 1-2
A DC line 2 is provided which connects the . Further, converter pressure vessels 4-1, 4-2 and power converters 5-1, 5-2 are provided between the AC buses 1-1, 1-2 and the DC line 2, respectively. Each power conversion device 5-1, 5-2 is composed of thyristor elements connected in series and parallel, one forward conversion device 5-1 converts AC to DC, and the other inverse conversion device 5-2 converts DC to AC. Each converts power. And this conversion device 5
-1, 5-2, the instrument transformers 6-1, 6-2, the synchronous signal detection circuit 7-
1 and 7-2 and phase control circuits 8-1 and 8-2, respectively. In each synchronous signal detection circuit 7-1, 7-2, an instrument converter 6-1, 6-
2, the synchronizing signal is detected and applied to each phase control circuit 8-1, 8-2. Then, in the phase control circuits 8-1 and 8-2, using the synchronization signal as a reference signal, a firing pulse is generated by a control signal from another control circuit (not shown), and each conversion device 5-1, 5 −2 to the thyristor, etc. Thereby, for example, the forward converter 5-1 performs constant current control when converting three-phase alternating current given from the power transmission side AC bus 1-1 into direct current, and supplies the direct current to the direct current line 2. On the other hand, the inverter 5-2 on the power receiving side performs constant voltage control when converting the DC sent via the DC line 2 into three-phase AC, and applies it to the AC bus 1-2 on the power receiving side.

Conventionally, various circuit systems have been adopted as the synchronization signal detection circuits 7-1 and 7-2 in such a DC power transmission system, but in recent years, with the advancement of digital technology, a phase continuous comparison type synchronization signal detection circuit has been adopted. It has come to be.

FIG. 2 is a block diagram showing the configuration of conventional phase continuous comparison type synchronization signal detection circuits 7-1 and 7-2. In the figure, 10 is a 3-phase to 2-phase conversion circuit that converts the 3-layer AC synchronizing signal into two orthogonal phases, and the output signal of this 3-phase to 2-phase conversion circuit 10 is given to a phase difference detection calculation circuit 11. . The phase difference detection calculation circuit 11 inputs the output signal of the three-phase to two-phase conversion circuit 10 and the output signals of the sine wave generation circuit 12 and cosine wave generation circuit 13 that generate feedback signals, and calculates the phase difference. , loop filter 14
It is applied to the voltage controlled oscillator 15 via. The voltage controlled oscillator 15 is controlled by the output signal of the loop filter 14 and outputs a pulse signal of a predetermined frequency.
It is given to the counter 16. Then, the counter 16 counts the pulse signals and outputs a synchronizing signal, which is applied to the phase control circuits 8-1, 8-2, the sine wave generating circuit 12, and the cosine wave generating circuit 13.

Next, the operation of the synchronizing signal detection circuits 7-1 and 7-2 configured as described above will be explained. now,
The instantaneous value of the output voltage of the 3-phase to 2-phase conversion circuit 10 is
V _1d , V _1g , their amplitude (maximum value) is T ₁ , phase is θ ₁
The output of the sine wave generating circuit 12, which is the feedback signal obtained via the counter 16, is V _fg ,
If the output of the cosine wave generating circuit 13 is V _fd and the detected phase is θ, then the following equation holds true.

V _1d = V ₁・cosθ ₁ …(1) V _1g = V ₁・sinθ ₁ …(2) V _fd = cosθ …(3) V _fg = sinθ …(4) Therefore, the phase difference △ θ=θ ₁ -θ is obtained by calculating the following equation using the phase difference detection calculation circuit 11.

△θ=sin ^-1 V _fd・V _1g −V _fg・V _1d /V ₁ ...(5) However, the maximum value (that is, absolute value) V ₁ is as shown in the following equation.

V ₁ = _1d ² + _1g ² ...(6) The phase difference △θ thus obtained by the phase difference detection calculation circuit 11 is error amplified by the loop filter 14, and the voltage controlled oscillator 15 is controlled by its output signal. The phase difference Δθ is feedback-controlled via the counter 16 so that the phase difference Δθ becomes zero.

[Problems with background technology]

However, in the phase continuous comparison type synchronizing signal detection circuits 7-1 and 7-2, if the voltage of the AC bus 1-1 shown in FIG. A three-phase AC synchronizing signal R, which is an input signal of the three-phase to two-phase conversion circuit 10 in the middle,
Since S and T were significantly reduced, the synchronization signal detection circuits 7-1 and 7-2 caused a loss of synchronization, resulting in a problem that protection operations could not be performed.

As a means to eliminate this problem, a method such as reducing the gain of the loop filter 14 can be considered. In other words, this method is a method that makes it difficult for synchronization to occur, but when this method is adopted, a problem arises in that once synchronization occurs, it takes a long time to regain synchronization. . This is an advantage of the continuous phase comparison type synchronizing signal detecting circuit compared to the conventional synchronizing signal detecting circuit, that is, by constantly comparing the phases, the proportionality constant of the loop filter 14 is increased, and the gain of the feedback system is increased. This is not preferable because the advantage of being able to detect the synchronization signal at high speed is lost.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned shortcomings of the conventional technology, and provides a power conversion system that does not cause synchronization even when the three-phase AC voltage significantly decreases, and that can detect synchronization signals at high speed. It is an object of the present invention to provide a phase continuous comparison type synchronization signal detection circuit for a device.

[Summary of the invention]

To achieve this objective, in the present invention, when the three-phase AC signal drops below a predetermined value, a feedback sine wave generator and a feedback cosine wave generator are used instead of the output signal of the three-phase to two-phase conversion circuit. The output signal of the generation circuit is supplied to the phase difference detection calculation circuit.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 3 is a block diagram showing the configuration of the phase continuous comparison type synchronization signal detection circuit according to this embodiment.
The same elements as in FIG. 2 are given the same reference numerals. The difference between this synchronizing signal detection circuit and the circuit shown in FIG.
2 was established.

The level detection circuit 20 detects when the voltages of the three-phase AC synchronizing signals R, S, and T have fallen below a predetermined value, and the output signal of the level detection circuit 20 is normally at level "0". However, when the voltage of the three-phase AC synchronizing signals R, S, T drops below a predetermined value, the level becomes "1", and the output signal is given to each changeover switch 21, 22. Changeover switch 21, 2
Reference numeral 2 is composed of a switching transistor or the like, which is switched based on the output signal of the level detection circuit 20, and is provided between the three-phase to two-phase conversion circuit 10 and the phase difference detection calculation circuit 11. When the output signal of the level detection circuit 20 is at level "0", each changeover switch 21, 22 is set to 3-phase.
The output signal of the two-phase conversion circuit 10 is applied to the phase difference detection calculation circuit 11. On the other hand, when the output signal of the level detection circuit 20 is at level "1", it is switched to the feedback sine wave generation circuit 12 and the feedback cosine wave generation circuit. The output signal of the circuit 13 is given to the phase difference detection calculation circuit 11.

Next, the operation of the phase continuous comparison type synchronization signal detection circuit configured as described above will be explained.

Now, if the three-phase AC synchronizing signals R, S, T, which are the input signals of the three-phase to two-phase conversion circuit 10, do not decrease to a normal value or a predetermined value, the output signal of the level detection circuit 20 will be "0". ” level, each changeover switch 21, 22 is connected to the 3-phase to 2-phase conversion circuit 1.
The phase difference detection calculation circuit 11 selects the output signal of 0.
give to Therefore, in this state, the operation is similar to that of the conventional phase continuous comparison synchronization signal detection circuit, that is, the phase difference Δθ is determined by the phase difference detection calculation circuit 11, and the phase difference Δθ is transmitted to the loop filter 14 and the voltage controlled oscillator. 15, counter 6, sine wave generation circuit 12
The three-phase AC synchronizing signals R,
Detection is performed following S and T.

Here, consider a case where the three-phase AC synchronizing signals R, S, and T are significantly reduced due to a lightning strike or the like. If this state is left as it is, the phase continuous comparison type synchronization signal detection circuit will lose synchronization as described above. However, since the loop filter 14 is provided as shown in FIG. 3, the phase continuous comparison type synchronization signal detection circuit immediately causes synchronization to occur when the three-phase AC synchronization signal drops significantly. There isn't. That is, even if the three-phase AC synchronizing signals R, S, and T become zero, the feedback sine wave generating circuit 12 and the feedback cosine wave generating circuit 13 continue to generate output signals for a certain period of time. Therefore, the level detection circuit 20 detects a significant drop in the three-phase AC synchronizing signal, switches the changeover switches 21 and 22 based on this detection signal, and controls the feedback sine wave generation circuit 12 and cosine wave generation circuit 1.
If the output signal No. 3 is applied to the phase difference detection calculation circuit 11, stable operation will continue and no synchronization will occur.

Note that in the above embodiment, the level detection circuit 2
Even if 0 is configured to output an analog signal and the changeover switches 21 and 22 are switched based on this output signal, the same effects and effects as in the above embodiment can be obtained.
be effective.

〔Effect of the invention〕

As described above, according to the present invention, a level detection circuit and a changeover switch are added to the conventional phase continuous comparison type synchronization signal detection circuit, and when the three-phase AC synchronization signal falls below a predetermined value, is detected by the level detection circuit, and based on this detection signal, the 3-phase - 2
Since the output signals of the phase AC circuit are switched and the output signals of the feedback sine wave generation circuit and the feedback cosine wave generation circuit are fed to the phase difference detection calculation circuit 11, synchronization does not occur even when the AC voltage drops, and high speed operation can be achieved. It is possible to provide a simple and accurate synchronization signal detection circuit that does not lose the advantage of the conventional phase continuous comparison type synchronization signal detection circuit that synchronization is achieved.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of a DC power transmission system, FIG. 2 is a block diagram of a conventional phase continuous comparison type synchronous signal detection circuit provided in FIG. 1, and FIG. 3 is a phase diagram according to an embodiment of the present invention. FIG. 2 is a block diagram of a continuous comparison type synchronization signal detection circuit. 1-1, 1-2... AC bus, 2... DC line, 5-1, 5-2... Power converter, 6-1,
6-2... Instrument transformer, 7-1, 7-2... Synchronous signal detection circuit, 8-1, 8-2... Phase control circuit, 10... 3-phase to 2-phase conversion circuit, 11... ...Phase difference detection calculation circuit, 12...Sine wave generation circuit, 13
... Cosine wave generation circuit, 14 ... Loop filter,
15... Voltage controlled oscillator, 16... Counter, 2
0... Level detection circuit, 21, 22... Changeover switch, 3-1, 3-2... Smooth sliding actuor, 4-
1, 4-2...Transformer for converter.

Claims (1)

[Claims] 1. A 3-phase to 2-phase conversion circuit that converts a 3-phase AC synchronous signal to two orthogonal phases, an output signal of the 3-phase to 2-phase conversion circuit, a feedback sine wave generation circuit, and a feedback cosine wave A phase difference detection calculation circuit that calculates the phase difference based on the output signal of the generation circuit, and a voltage controlled oscillator that outputs a synchronization signal by controlling oscillation by the phase difference signal input from the phase difference detection calculation circuit via a loop filter. A level detection circuit for detecting that the three-phase AC synchronization signal has fallen below a predetermined value; - a changeover switch that cuts off the output signal of the two-phase conversion circuit and supplies the output signal of the feedback sine wave generation circuit and the feedback cosine wave generation circuit to the phase difference detection calculation circuit; Synchronous signal detection circuit.