JPH0410302B2 - - Google Patents

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.
is the power transmission line, 3 is the main distribution line, 4 is the main switch, 5
6 is a branch line (feeder), 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 a system). 9 is a power output means for generating or accumulating power; 10 is a power conversion device; and 11 is a linkage switch. Normally, power from the power output means 9 is exchanged with the grid 8 via the power converter 10. By the way, in the power system 8, switches 4,
6 is opened, that is, the grid is disconnected, and the load side is often cut off (no voltage). On the other hand, distributed power sources and the like linked by the power conversion device 10 are usually provided at the 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 the power converter 10 is applied, resulting in a dangerous situation called reverse pressure. ,
Immediately, the linkage switch 11 must be opened to release the linkage. In this case, the auxiliary contacts of the power system switches 4 and 6 are used to connect the link switch 11
If you use the method of operating the switch, many switches are installed at very distant locations, which increases the length of the wire and is not practical.

In response, the present applicant has already proposed a method in which the power converter 10 detects a state in which the grid switches 4 and 6 are opened and voltage is no longer applied from the grid, and the linked switch 11 is opened. ing. This is as 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, and 14 is a phase difference that detects the phase difference between the voltage signals S ₁ and S ₂ at both terminals of the reactor 13. Detector (circuit), 15 is a phase difference reference signal generator, 16 is an automatic phase control circuit having an amplifier, 17 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 10 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 power exchange described above will cause fluctuations in the grid frequency. not give.
In this case, the phase of the voltage signal S ₂ on the grid side is used as a reference, and the phase difference of the output signal S ₁ of the power converter 12 with respect to this is detected by the phase difference detector 14, and this value becomes equal to the phase difference reference signal. Similarly, the phase control circuit 16
operates, and the power converter control circuit 17 determines the operating frequency of the power converter 12 according to this output. In other words, if the phase of the output signal S ₁ is ahead of the command value, this will be detected and fed back, and if the operating frequency is reduced excessively, the phase of the output signal S ₁ will be delayed because the frequency of the grid is constant. It is fed back and 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. Note that in this case, the power converter 10
It goes without saying that 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, power is no longer supplied from the generator 1 of the grid, and power to the load 7 is supplied only from the power converter 10, and a phase difference corresponding to the amount of power is generated. occurs between each signal S ₁ and S ₂ . At this time, if the amount of power supplied from the power converter 10 increases from P→P+ΔP before and after the switch 6 is opened, the output θ of the phase difference detector 14 will change from θ→θ+
The operating frequency of the power converter 12 also decreases as →-Δ due to the action of the phase control circuit 16 based on the deviation. At this time, since there is no generator that keeps the grid side frequency at the load end constant, it follows this, and if the load is constant, the phase difference of θ + Δθ is maintained, so information about the frequency change is not fed back. , which results in an increasingly divergent reduction in operating frequency. 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 left and right power is balanced around the switch 6,
If , of course, the power supplied from the power converter 10 does not change, and as described above, no divergence occurs due to the 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. It was hot.

Furthermore, a method has been proposed in which the phase difference reference signal is constantly changed to disrupt the balance with the load and cause a disturbance. The problem is that the control performance deteriorates because the signals appear as they are.

This invention was made in order to solve the above-mentioned problems, and it is possible to reliably connect the power system and the power converter within a predetermined time even if the switch in the power system is opened in any state. The purpose of this invention is to obtain a power conversion device for grid connection that can be released.

[Means for solving problems]

The power converter for grid connection according to the present invention includes:
A signal with a predetermined amplitude and a frequency sufficiently lower than the operating frequency of the power converter generated by a periodic disturbance generator is added to the frequency command signal to detect frequency abnormalities based on the added signal when the power grid is disconnected. However, the structure is such that the connection with the above-mentioned power system is thereby cut off.

[Effect]

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. In FIG. 1, 20 is a periodic disturbance generation circuit that generates a synchronous disturbance output signal _S5 to be added to the output of the phase control circuit 16, and serves as part of the operating frequency command input that determines the operating frequency of the power converter 12. Become.
Note that other blocks that are the same as those shown in FIG. 5 are designated by the same reference numerals, and redundant explanation thereof will be omitted. Further, S ₃ is the output signal of the phase difference detector 14, S ₄ is the output signal of the phase control circuit 14, S ₅ is the output signal of the periodic disturbance generation circuit 20, and S ₆ is the operating frequency to the power converter control circuit 17. The command signal _S7 is an opening operation signal for the interconnection switching path 11, and time charts of these signal waveforms are as shown in FIGS. 2a and 2b.

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.
A phase difference signal S 3 between the phase of the output voltage signal S ₁ of No. 2 and the phase of the grid side voltage signal S ₂ separated by the reactor _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 a phase control circuit 16 having a sufficiently large gain, and the sum S of the output _S4 and a periodic disturbance such as a sine wave is obtained. ₆ is obtained by the adder 30 and this sum output is input as the operating frequency reference of the power converter control circuit 17, the output voltage signal _S1 of the power converter operates at this frequency. The phase of the voltage signal S ₁ is the integral of this frequency, and the frequency of the voltage signal S ₂ is fixed by linkage, so a closed loop of phase control is formed. At this time, the phase control circuit 16 sufficiently responds to the change in the periodic disturbance,
If the gain in the frequency band where the disturbance changes is high, the input value is almost zero, that is, the phase difference S ₃ between S ₁ and S ₂ is equal to the phase difference command (strictly speaking, the periodic disturbance S ₅ However, the amount of power supplied to the grid remains constant and stable. At this time, a signal _S4 that cancels the periodic disturbance _S5 is generated at the output of the phase control circuit, and even though a periodic disturbance is given, the frequency command signal _S6 remains at the same constant value as the system frequency. Become.

Next, a state in which power is not transferred through the system switch 6 shown in FIG. 1 will be described. In FIG. 2a, even if the switch 6 is opened at time t ₁ , the state of power supply from the power converter 10 to the load 7 in the system does not change, so the phase difference signal
No change occurs in _S3 (that is, the amount of power corresponding to the phase difference command is equal to the amount of power consumed by the load 7). In this case, the input to the phase control circuit 16 is completely zero and its output S ₄ is held at a constant value or becomes zero. On the other hand, the yield signal S ₅ of the periodic disturbance is added as is, and the frequency command S ₆ to the power converter 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 frequency of the load follows the frequency change of the power converter 12, and the frequency of the load also changes, and the phase difference S ₃ changes. No (load power consumption 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 range (usually ±0.5 to 1 Hz) of the system in which frequency abnormality can be detected, the frequency abnormality detection circuit 18 detects that the frequency changes at time _t2 . It is possible to detect that the specified value output by the frequency specified value generator 19 has been exceeded, generate a switch operation signal _S7 , open the linkage switch 11, and release the linkage. In this case, from the time t ₁ when the switch 6 is opened until the detection time t ₂ , it is possible to reliably detect the periodic disturbance if it is about half a cycle at most.

Figure 2b shows the operating waveform when the switch 6 is opened while power is being transferred and received through the system switch 6. When the switch is opened, a deviation from the phase difference command occurs, and
The output of the phase control circuit 16 diverges. As a result, the frequency reference signal _S6 oscillates and diverges due to the periodic disturbance, which can be detected in the same way.

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, whereby the power converter 1
The phase difference command is adjusted so that the power supplied to the system 8 is equal to the predetermined value. Further, a general frequency abnormality detection relay 18a is used to detect frequency abnormalities. Furthermore, a triangular wave generation circuit 20a is used to generate periodic disturbances. Further, instead of the output signal of the power converter 12 inputted to the phase difference detection circuit 14, a signal from the control circuit 17 that drives the power converter 12 is used as a substitute. 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 the signal waveforms of each block in each state of grid disconnection, and FIG. FIG. 4 is a block connection diagram showing the general configuration of a power conversion system, and 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 conversion device, 11 is a grid connection switch, 12 is a power converter, 13 is a reactor, 14 is a phase difference detection circuit,
15 is a phase difference reference signal generator, 16 is a phase difference control circuit, 17 is a power converter control circuit, 18 is a frequency abnormality detection circuit, 19 is a frequency specified value generator, 2
0 is a periodic disturbance generation circuit. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] 1 The deviation between the output voltage phase of the power converter connected to the power grid via the reactor and the voltage phase on the power grid side and a preset phase difference reference command value is set as a frequency command, and the power In a power converter for grid connection that determines the operating frequency of a converter, a periodic disturbance generating device is provided that adds a signal with a predetermined amplitude and a frequency sufficiently lower than the operating frequency to the frequency command, and When the voltage supplied from this power system disappears due to disconnection, a frequency abnormality based on the added signal is detected, and the connection with the power system is interrupted. conversion device.