JPS62114435A - Power converter for system interconnection - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a power converter for power grid connection that transfers power to and from a power grid.

[Conventional technology]

Fig. 4 is a block connection diagram of a conventional power converter for grid connection. ), 6 is a branch line switch, and 7 is a load, which together are referred to as a power system 8 (hereinafter referred to as the system). 9 is a power output means for generating or accumulating power; 10 is a power conversion device; and 11 is a linkage switch. Usually, the power output means 9
The power from is exchanged with the grid 8 via the power conversion device 10. By the way, in the power system 8, for maintenance 9 inspection, expansion and modification, the switch 4°6 is opened.
In other words, the grid is often disconnected to cause a power outage (no voltage) on the load side. On the other hand, distributed power sources and the like linked by the power conversion device 10 are usually provided at a lower part (load end) of the system due to their scale. In this case, even if the grid switches 4 and 6 are opened, the output voltage of 1ilo is applied during power conversion, creating a dangerous situation called reverse pressure. , the connection switch 11 must be opened immediately to release the connection. In this case, if a method is adopted in which the interlocking switch 11 is operated using the auxiliary contact of the power system switch 4.6, the length of the electric wire will be reduced because many switches are installed at very distant locations. increased and impractical.

In contrast, the present applicant has proposed that the power converter 1
A method has already been proposed in which the detection is performed at 0 and the linked switch 11 is opened. This is the convention shown in FIG. In the figure,
12 is a semiconductor power converter (power converter); 13 is a reactor, for example, a transformer with a built-in reactance; 14 is a phase difference detector (circuit) that detects the phase difference between the voltage signals 5l-8s at both terminals of the handle 13; , 15 is a phase difference reference signal generator, 16 is an automatic phase control circuit having an amplifier, 1
7 is a power converter control circuit, 18 is a frequency abnormality detection circuit, and 19 is a frequency specified value generator.

Next, the operation will be explained.

First, consider a state in which the power conversion device IO is linked to the power grid 8 and is transmitting and receiving power. The capacity of the grid is sufficiently large compared to the capacity of the power converter, and the frequency of the power grid is maintained approximately constant by the control of the generator 1 of the grid, so the transfer of power does not cause fluctuations in the grid frequency. I won't give it. In this case, the phase of the voltage signal S2 on the grid side is used as a reference, the phase difference of the output signal S1 of the power converter 12 with respect to this is detected by the phase difference detector 14, and the phase difference is detected so that this value becomes equal to the phase difference reference signal. The phase control circuit 16 is activated, and the power converter control circuit 17 determines the operating frequency of the power converter 12 according to this output.

That is, if the phase of the output signal St advances υ compared to the command value, this is detected and fed back, and when the operating frequency is transiently lowered, the phase of the output signal S1 is delayed because the system frequency is constant, and this is fed back. , becomes equal to the command value.

As a result, the frequency of the power converter follows the system frequency, and the power converter operates with a predetermined phase difference given by the phase difference command. -1 In this case, the power converter 10
Needless to say, power is exchanged between the power system 8 and the power system 8 in accordance with the phase difference.

Next, when the switch 6 on the grid side is opened, the generator 1 on the grid
The power supply to the load 7 is stopped, and the power to the load 7 is supplied only from the power conversion device 10, and a phase difference corresponding to the amount of power is generated between each signal S*-Ss. At this time, if the amount of power supplied from the power converter 10 increases to P4P+ΔP before and after the switch 6 is opened, the output θ of the phase difference detector 14 increases from θ→θ+Δθ, and the phase control is performed based on the deviation. Due to the function of the circuit 16, the operating frequency f of the power converter 12 also decreases from f to f-Δf. At this time, since there is no generator that keeps the grid frequency at the load end constant, it follows this and maintains the phase difference of θ + Δθ if the load is constant, so the information on the frequency change is not fed back, and this As a result, the operating frequency decreases in an increasingly divergent manner. The frequency abnormality detection circuit 18 detects that this frequency exceeds a predetermined reference range output by the frequency regulation value generator 19, and opens the linkage switch 11 to release the linkage with the grid.

[Problem that the invention seeks to solve]

Since the conventional power converter for grid connection is configured as described above, if the switch 6 is opened in a state where the left and right power is balanced around the switch 6, naturally,
The power supplied from the power converter 10 also does not change, and as described above, no divergence occurs due to phase deviation. In this case, even if some disturbance occurs in the phase control loop and the frequency shifts, there is no function to fix the frequency on the grid side, and the shift will appear as is. As a result, if disturbances continue to occur, the frequency will shift significantly, and this can be detected and the linkage can be canceled. However, in this case, the operation is affected by the uncertain element of disturbance, and there is no guarantee that the link can be reliably released within a predetermined time, making the safety measure of preventing back pressure mentioned above unreliable. was there.

Furthermore, by constantly changing the phase difference reference signal,
A method of creating a disturbance by disrupting the balance with the load has also been proposed, but in this case, the problem is that this disturbance results in fluctuations in the amount of power exchanged during normal coordination and appears as is, resulting in poor control performance. There was a point.

This invention was made to solve the above-mentioned problems, and it ensures that the power system and the power converter are connected within a predetermined time even if a switch in the power system is opened in any state. It is an object of the present invention to obtain a power conversion device for grid connection that can cancel connection.

[Means for solving problems]

The power converter for power grid connection according to the present invention adds a signal generated by the periodic disturbance generator with a predetermined amplitude and a frequency sufficiently lower than the operating frequency of the power converter to a frequency command signal, and disconnects the power grid. The system is configured to occasionally detect a frequency abnormality based on the added signal, and thereby cut off the connection with the power grid.

[For production]

The periodic disturbance generating device according to the present invention outputs a periodic function disturbance signal whose amplitude exceeds the operating frequency range of a normal power system and can sufficiently respond to a phase control operation. When a switch in the system is opened or closed, the connection between the system and the power converter is reliably released, and reverse pressure is prevented.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
In the figure, 20 is a periodic disturbance generation circuit which generates a synchronous disturbance output signal S6 to be added to the output of the phase control circuit 1G.
It becomes part of the operating frequency command input that determines the operating frequency of the power converter 12. Note that blocks that are the same as those shown in FIG. 5 other than are given the same reference numerals, and redundant explanation thereof will be omitted. Further, Ss is the output signal of the phase difference detector 14, S4 is the output signal of the phase control circuit 14, Ss is the output signal of the periodic disturbance generation circuit 20, Sa is the operating frequency command signal to the power converter control circuit 17, and sr are opening operation signals for the interconnection switching path 11, and time charts of these signal waveforms are as shown in FIGS. 2(a) and 2(b).

Next, the operation will be explained. First, consider a case where the power conversion device 10 is linked to the grid 8. Similar to the conventional example shown in FIG. 5, the output voltage signal S1 of the power converter 12
A phase difference signal s3 with respect to the phase of the system side voltage signal S2 across the phase adjustment handle 13 is detected by the phase difference detection circuit 14. The deviation between this phase difference signal S3 and the reference phase difference signal of the reference signal generator 15 is input to the phase control circuit 16 having a sufficiently large gain, and the sum S6 of the output S4 and a periodic disturbance such as a sine wave is added. If the sum output is inputted as the operating frequency reference of the power converter control circuit 17, the output voltage signal Sl of the power converter operates at this frequency. The phase of the voltage signal Sl is the integral of this frequency υ, while the frequency of the voltage signal S2 is fixed by the linkage, so a closed loop of phase control is formed. At this time, if the phase control circuit 16 sufficiently responds to the change in the periodic disturbance and has a high gain in the frequency band where the disturbance changes, its input value is zero, that is, Sl and 82
The phase difference S3 is υ (strictly speaking,
This produces a deviation of 1/the gain of the periodic disturbance s5, but it is very small).

The power supply to the grid is constant and stable. At this time, a signal S4 that cancels the periodic disturbance generator is generated at the output of the phase control circuit, and in the end, despite the periodic disturbance being applied, the frequency command signal S· becomes the same constant value as the system frequency.

Next, a state in which power is not transferred through the system opening/closing 856 in FIG. 1 will be described. Figure 2(a)
, even if the switch 56 is opened at time tl, the state of power supply from the power converter 10 to the load 7 in the system does not change, and therefore, no change occurs in the phase difference signal Ss (that is, the phase difference command (The amount of power corresponding to the load 7 is equal to the amount of power consumed by the load 7). In this case, the phase control circuit 16
The input of is completely zero υ, and its output S4 is kept at a constant value or becomes zero. On the other hand, the periodic disturbance output signal Sfi
is added as is, and the frequency command S6 to the power odor changer control circuit 17 changes greatly due to the periodic disturbance.

However, since the grid switch 6 is opened and the function of fixing the frequency on the grid side is lost, the load frequency follows the frequency change of the power converter 12, and the phase difference S
3 does not change (load consumption room power is constant). As a result, the phase control loop does not operate, and the periodic disturbance appears as it is in the operating frequency of the power converter. Therefore, if the amplitude of the periodic disturbance is selected to be larger than the normal frequency fluctuation width (usually ±0.5 to IHz) of the system in which frequency abnormality can be detected, the frequency abnormality detection circuit 18 detects the frequency at time t2. exceeds the specified value output by the frequency specified value generator 19, and the switch operation signal S? can be generated to open the linkage switch 11 and release the linkage. In this case, from the time t1 when the switch 6 is opened to the detection time h')
Then, if the periodic disturbance is at most half a cycle, it can be reliably detected.

FIG. 2(b) shows the operating waveform when the switch 6 is opened while power is being exchanged via the grid switch 6.
When opened, a deviation from the phase difference command occurs, and the phase control circuit 16
The output of will diverge. As a result, the frequency reference signal S6
It can be detected in the same way that it oscillates and diverges due to periodic disturbances.

FIG. 3 is a block connection diagram showing another embodiment according to the present invention, in which the phase difference reference signal generator 15 in FIG. A power control circuit 23 is used to adjust the phase difference command so that the power supplied from the power converter 10 to the multiple system 8 becomes equal to a predetermined value. Further, a general frequency abnormality detection relay 18a is used to detect frequency abnormalities. Furthermore, for periodic disturbance generation,
A triangular wave generating circuit 20a is used. Further, the output signal υ of the power converter 12 input to the phase difference detection circuit 14 is
The signal from the control circuit 17 that drives this is used instead. Part or all of these elements can be used in place of the embodiment shown in FIG. 1.

〔Effect of the invention〕

As described above, according to the present invention, a periodic disturbance whose amplitude is larger than the frequency fluctuation range of the power grid and whose period is large enough to sufficiently respond to the phase control loop is used as a frequency command element for the power converter. The system is configured to ensure that no matter what state the grid is in, the control characteristics during linkage will not be impaired, and when the grid is disconnected, it will quickly and reliably reach an abnormal operating frequency within a predetermined time, and this will be detected. By doing so, the linking switch can be opened immediately and the risk of back pressure can be effectively avoided.

[Brief explanation of drawings]

FIG. 1 is a block connection diagram of a power converter for grid connection according to an embodiment of the present invention, FIG. 2 is a time chart showing signal waveforms of each block in each state with and without grid disconnection, and FIG. A block connection diagram of another embodiment, FIG. 4 is a block connection diagram showing the general configuration of a power conversion system,
FIG. 5 is a block connection diagram of a conventional power conversion device. 8 is a power system, 9 is a power output means, 10 is a power converter, 11 is a grid connection switch, 12 is a power converter, 13 is a reactor, 14 is a phase difference detection circuit, and 15 is a phase difference reference signal generator. , 16 is a phase control circuit, 17 is a power converter control circuit, 18 is a frequency abnormality detection circuit, 19 is a frequency specified value generator, and 20 is a periodic disturbance generation circuit. In addition, in the figures, the same reference numerals indicate the same or equivalent parts. Patent applicant Mitsubishi Electric Co., Ltd. Agent Patent attorney 1) Hiroshi Sawa (2 others) L ----w Figure 2 (a) 1t2

Claims (1)

[Claims] The above-mentioned power conversion is performed using the deviation between the output voltage phase of the power converter connected to the power grid via the reactor with respect to the voltage phase on the power grid side and a preset phase difference reference command value as a frequency command. In a power converter for grid connection that determines the operating frequency of a power system, a periodic disturbance generator is provided that adds a signal with a predetermined amplitude and a frequency sufficiently lower than the operating frequency to the frequency command, and A power conversion system for power grid connection, characterized in that when the voltage supplied from the power grid disappears due to a power grid, an abnormality in the frequency based on the added signal is detected and the connection with the power grid is interrupted. Device.