JPS5947938A - Cooperating system between inverter and power system - 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] [Technical Field of the Invention] The present invention relates to a system in which a separately excited inverter is connected to a power grid, and in particular to a system that can reduce the amount of grid voltage fluctuation at a point of connection. Regarding interconnection systems between inverters and power grids.

[Technical background of the invention]

In recent years, for the purpose of energy saving, research and development has been actively conducted in various fields on so-called inverter-power system interconnection systems, which convert DC power into AC power using an inverter and supply it to the power system. At this time, several kW to several k
A relatively small-scale W system needs to be as inexpensive as possible since it is installed in large quantities, so a separately excited type is used as the internal regulator, and a thyristor is used as a component. A method using .

FIG. 1 shows an example of the main circuit configuration of this type of interconnection system. In the figure, reference numeral 1 denotes a DC power source using a fuel cell, a solar cell, etc., to which the DC side of a separately excited inverter 4 is connected via a DC breaker 2 and a DC reactor 3. The separately excited inverter 4 is controlled by a control device 5 at a control angle β, and the AC side is connected to the line impedance and the leakage reactance of a grid transformer (not shown) via a grid interconnection transformer 6 and a grid breaker 7. A power grid 9 having a grid impedance 8 including .

Furthermore, a filter device 1 with a predetermined capacity that also serves as a phase advance capacitor is connected to the secondary side of the interconnection transformer 6 on the AC side of the separately excited inverter 4 via an AC breaker IO, as shown in the figure. . In addition, in Fig. 1, separately excited inverter 4
The system consists of six inexpensive and well-proven thyristors connected in a three-phase bridge.

In such a grid-connected system, DC power from a DC power supply 1 is applied to a DC input side of a separately excited inverter 4 via a DC breaker 2 and a DC reactor 3. The AC output power is then supplied to the power system 9 via the interconnection transformer 6 and the interconnection breaker 7. The power is controlled to a predetermined value by the control device 5 at a control angle β. As is well known, the input/output voltage relationship of the separately excited inverter 4 is 1 Ed-IaRa =-y'T Va(casβ+2 I
a x )π.

Here, Ed is DC power supply voltage, Ed is DC current, Rd
is the DC circuit resistance, v8 is the inverter-side AC voltage of the interconnection transformer 6, Ia is the inverter output current, and X is the commutation reactance, most of which is the leakage reactance of the interconnection transformer 6. Still, in the above, the control angle β is the DC voltage drop Id
-Rd, determined in consideration of the variation range of AC voltage Va,
During rated operation, the electrical angle is often around 45°. Since the power factor is approximately expressed by strong β, the reactive power Q required by the inverter 4 is approximately the same as the active power βVB11eQSβ=P.

On the other hand, in this case, the harmonic current generated by the separately excited inverter 4 has an order of 6n±1st (n=1°2, . . . ) and is proportional to the inverter output current, which is approximately the reciprocal of the harmonic current.

The filter device 11, which also serves as a phase advance capacitor, reduces this harmonic current to a predetermined value, compensates for the reactive power required by the inverter 4, and lowers the rated operating power factor to 45°.
〇, improve from 7 to 1. This filter device 11 may take a known form such as a fifth-order or seventh-order resonance filter or a high-pass filter.

Now, when power is supplied to the power grid 9, a voltage fluctuation ΔV occurs due to the grid impedance 8, which is ΔV=RP−X
It is represented by Q. Here, R is the system impedance 8
Most of the reactance is the leakage reactance of the system transformer (not shown), which generally has the relationship of X)H, and -XQ is the inverter 4.
indicates a voltage drop due to delayed reactive power being taken from the grid.

FIG. 2 shows the relationship between the seven interconnection point voltages and the inverter output. Generally, the upper limit of the capacity of an inverter connected to a power grid is about 20%, and if the grid impedance is 20 inches, this translates to 4% on the inverter side.

[Problems with background technology]

In this case, when there is no filter device 11 that also serves as a phase advance capacitor, the delayed reactive power taken by the inverter 4 from the grid is about the same as the active power supplied to the grid as described above, and In this case, as shown by straight line A in FIG. 2, the interconnection point voltage vA decreases by 0.96, or 4 inches, when the output is at the rated output.

On the other hand, if the filter device 11 is used to reduce the harmonics to below a predetermined value (for example, each harmonic of 1%, total voltage distortion factor of 2ch) and compensate for the delayed reactive power of the inverter 4, then the straight line B in FIG.
As shown in , when the inverter output is 1, the interconnection point voltage V
However, when the input output is 0, it becomes 1.
This will result in an increase of 04 cm.

It is desirable that the system voltage fluctuation caused by the inverter be as small as possible, but in this respect, the fluctuations are large in all of the above examples.

[Purpose of the invention]

The present invention was made to solve the above problems, and its purpose is to provide an interconnection system between an inverter and a power grid that can reduce grid voltage fluctuations caused by a separately excited inverter. be.

61 [Summary of the Invention] In order to achieve the above object, the present invention provides a system for converting DC power from a DC power source into AC power using a separately excited inverter and supplying it to the power system, in which the AC side of the separately excited inverter is A filter device with a predetermined capacity that also serves as a phase advancing capacitor is provided via an AC breaker, and the AC breaker is turned on when the output of the separately excited inverter is 30 to 70 inches or more than the rated value, and the inverter output is 30 to 70 inches or more than the rated value. The AC breaker is characterized in that the AC breaker shuts off at 70 inches or less.

[Embodiments of the invention]

An embodiment of the present invention shown in the drawings will be described below.

The configuration example of the interconnection system between an inverter and a power grid according to the present invention is completely the same as that shown in FIG.

Tsu-! In addition, in the grid interconnection system of the present invention, the AC breaker 10 for interconnecting the filter device 11 of a predetermined capacity, which also serves as a phase advance capacitor in FIG. It is designed to turn on at a temperature above 50% of the rating and shut off at 50% or less of the rating.

A predetermined capacitance is provided as a phase advance capacitance of the filter device 11,
In addition, when the output of the separately excited inverter 4 is 50% or more of the rated value or less, the filter device 11 is connected to and disconnected from the system by the AC breaker 1o, as shown in C in Fig. 3. As shown, when the inverter output is 0.5 to 1, the interconnection point voltage vA is about 1.02 to 1°oo, and when the inverter output is 0 to 0.5, the interconnection point voltage V is about 1.02˚oo. 00~0
．． It becomes 98. In other words, the inverter output is between 0 and 0.
5, the interconnection point voltage Vm decreases by 2cm, and when the inverter output is 1 to 0.5, the interconnection point voltage Vm increases by 2cm, and as a result, the interconnection point voltage by the separately excited inverter 4 The system voltage fluctuation at the system point is set to 1±0. o2, that is, can be reduced to about half.

On the other hand, in the above case, when the output of the separately excited inverter 4 is 50% or less of the rating, the above-mentioned harmonics are a concern because the filter device 11 is not introduced into the system. Since it is approximately proportional, there is no problem when the load is light because the harmonics are originally small and there is no need to use the filter device 11. Also, separately excited type in/J
- When operating at around 50% of the rated output, there is a risk that the AC breaker 1o will operate too frequently, so the hysteresis width δ of 10 to 20 inches is shown in Figure 3. We are trying to prevent this by ensuring that

As described above, in the system in which the DC power of the DC power source 1 is converted into AC power by the separately excited inverter 4 and is supplied to the power grid 9, the AC power is connected to the AC side of the separately excited inverter 4 via the AC breaker 1o. A filter device 11 with a predetermined capacity is provided, which also serves as a phase advancing capacitor for reducing harmonics generated by the inverter and compensating for delayed reactive power,
This filter device 11 is adapted to be connected to and disconnected from the system respectively when the output of the separately excited inverter 4 is 50% or more of the rated output or less than 50% of the rated output.

Therefore, it is possible to reduce the grid voltage fluctuation at the interconnection point caused by the separately excited inverter 4 by half compared to the conventional system.

In addition, in the above embodiment, inputting the filter device 11 into the system,
When disconnecting, the output of separately excited inverter 4 is 50% of the rated output.
Although the above was carried out based on the following criteria, similar effects can be obtained even if the range is 30 to 70%.

In addition, the present invention can be implemented with various modifications without changing the gist thereof.

〔Effect of the invention〕

As explained above, according to the present invention, a filter device provided on the AC side of a separately excited inverter via an AC breaker is installed when the in/output direction is 30 to 70 inches or more or less than the rated output. Since it was made to be inserted into the system and disconnected at the same time,
It is possible to provide an extremely reliable inverter and power grid interconnection system that can reduce grid voltage fluctuations caused by separately excited inverters.

10-

[Brief explanation of the drawing]

@Figure 1 is a diagram showing an example of the main circuit configuration of the inverter and the power system, Figure 2 is a diagram showing the relationship between interconnection point voltage and inverter output in the conventional system, and Figure 3 is the diagram showing the relationship between interconnection point voltage and inverter output in the system of the present invention. FIG. 3 is a diagram showing the relationship between point voltage and inverter output. DESCRIPTION OF SYMBOLS 1... DC power supply, 2... DC breaker, 3... DC reactor, 4... Separately excited inverter, 5... Control device, 6... Interconnection transformer, 7... grid breaker,
8... Grid impedance, 9... Power system, 10
...AC breaker, 11...filter device. Applicant's agent Patent attorney Takehiko Suzue 11- Stone - Jim Chikara -

Claims (1)

[Claims] In a system that converts DC power from a DC power supply into AC power using a separately excited inverter and supplies it to the power grid, a predetermined capacity capacitor that also serves as a phase advance capacitor is connected to the AC side of the separately excited inverter via an AC breaker. A filter device is provided, and means for turning on the AC breaker when the output of the separately excited inverter is 30 to 70% or more of the rated value, and turning off the AC breaker when the inverter output is 30 to 70% or less of the rated value. An interconnection system between an inverter and a power system, which is characterized by: