JPS5921236A - Interlocking system of inverter to 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 interconnected with a power grid, and is capable of reducing the amount of grid voltage fluctuation at a VC interconnection point by %. This paper relates to an interconnection system between an inverter and a power grid.

[Technical weight of the invention]

In recent years, DC power has become increasingly popular for the purpose of energy conservation.
Research and development is actively being carried out in various fields on so-called "in-day-out" and power grid interconnection systems, which convert alternating current power in the evening and supply it to the power grid. At this time, relatively small-scale systems of several kW to several tens of kW are installed in large numbers - it is necessary to make them as inexpensive as possible, and for this reason, as internal systems, separately excited type A method is being considered that employs a dual-lister and uses a two-ristor as a component.

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 3 is connected via a DC reactor 2. In addition, the AC side button of this separately excited inverter 30 is connected to the interconnection transformer 4.
A power system 6 having a system impedance 5 including line impedance and leakage reactance of a system transformer (not shown) is interconnected via the power system 6 . Furthermore, on the secondary side of the interconnection transformer 4 on the AC side of the separately excited type in/outer 3,
A filter device 7 which also serves as a phase advancing capacitor is connected as shown. In addition, in Figure 1, the DC side and the current □ side -'
: and interrupter, and others,! lJ type inverter 39 control system.

The location is omitted from illustration. In addition, six Zyristors, which are inexpensive and have a good track record, are configured on a three-phase bridge connection.

In such a grid interconnection system 1, DC power from a DC power supply 1 is applied to a separately excited inverter 3 through a DC reactor 2. The AC output power is then supplied to the power grid 6 via the interconnection transformer 4. The electric power is controlled to a predetermined value by a control angle □β by a control device shown in the figure. As is well known, the input/output voltage relationship of the separately excited type in-p'7p's is expressed by □.

Here, Ed is the DC power supply 14. Voltage 11d is a DC current, Rd is a DC circuit resistance, va is an AC voltage on the inverter side of the interconnection transformer 4, Ia is the inverter output current, and X is a commutation reactance, most of which is the DC circuit resistance of the interconnection transformer 4. It is leakage reactance. In addition, the control angle 1β above is determined in consideration of the variation range of the DC voltage drop Id-Rd and the AC voltage V-, and is often about 45 degrees in electrical angle during rated operation.

Then, the power factor is expressed as t4 tx□□□β), so
, the reactive power Q required by the inverter 3 is the active power 5V.
It is approximately the same as ala(2)β=P.

On the other hand, in this case, the harmonic current generated by the separately excited impark 3 has an order of 61 ± 1st ("n"" 1 * 2 t
...) and is approximately proportional to the reciprocal of the shimper output current. The filter device 7, which also serves as a phase advance capacitor, reduces the harmonic current □ of □ to a predetermined value, and also compensates for the reactive power required by the inverter 3 □.
Set the driving power factor to 45° = 0. '7 will improve to about 1. This filter device 7 is of 5th order.

A well-known form such as a 7th order resonant filter or a high-pass filter can be used.

Now, when power is supplied to the power grid 6, a voltage fluctuation ΔV occurs due to the grid impedance 5, which is ΔV-RP-X
It is represented by Q. Here, R system impedance 5
The resistance component, X, is also the reactance component, and most of the reactance is the leakage reactance of the system transformer (not shown), and generally there is a relationship of X>H.1. XQ indicates the voltage drop due to ξ and K when the inverter 3 receives delayed reactive power from the grid.

Figure 2 shows the relationship between the interconnection point voltage vA and the inverter output. For general use, the upper limit of the inverter capacity interconnected to the power grid is about 2°, and the grid impedance is set to 20%. This corresponds to 4% when converted to the inverter side.

C. Problems of Background Art] In the case of Jin, when there is no filter device 7 that also serves as a phase advance capacitor, the delayed reactive power taken by the inverter 3 from the grid is about the same as the active power supplied to the grid, as described above. Since each is proportional to the inverter output, in this case, as shown by MA in FIG. 2, the interconnection point voltage Vm decreases by 0.96 or 4% at the rated output.

On the other hand, if the filter device 2 is used to reduce the harmonics to below a predetermined value (for example, each harmonic of 1%, total voltage distortion factor of 2) and compensate for the delayed reactive power of the inverter 3, then the line B in FIG. Like this, when the inverter output is 1, the voltage is
However, when the inverter output is O, it increases by 1.04, tb4ch''2. ,
.

It is desirable that system voltage fluctuations 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-mentioned problems, and its purpose is to provide an interconnection system between an inverter and a power grid that is capable of reducing grid voltage fluctuations caused by a passive inverter. Then I'm very busy.

- [Summary of the Invention] In order to achieve the above object, the present invention provides a system in which DC power from a table current power supply is converted into power by a separately excited inverter and supplied to the power grid. A filter device that also serves as a phase advance capacitor is installed on the side, and the phase advance capacity of this filter device compensates for the 30 to 70 phase proportion of grid voltage fluctuation due to delayed reactive power generated by the separately excited inverter during rated operation. It is characterized by having a capacity that allows

[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 the inverter and the power grid according to the present invention is completely the same as that shown in FIG. 1 described above, so the illustration and explanation thereof will be omitted and only the different parts will be described here.

Finally, in the interconnection system of the present invention, the phase advance capacitance of the filter device 7 which also serves as the phase advance capacitor in FIG. In this case, it is easy to design the amount of harmonic reduction to a predetermined value.

By providing such a capacitance as the phase advance capacitance of the filter device 7, when the inverter output is 1, the pressure VA at the interconnection point 1 [1□ is about 0.98, as shown by C in FIG. Also, when the inverter output is 0, the interconnection point voltage ■^ is approximately 1.
It becomes 02. In other words, when the inverter output is 1, K
When the interconnection point Chigawa V decreases by 2 and the impark output is 0, the interconnection point voltage vA increases by 2L4.
j',! ), as a result, the system voltage fluctuation at the interconnection point due to the separately excited inverter 3 can be reduced to 1±0.02, that is, approximately half. In addition, this pigeon house also reduces the degree of power factor improvement by half, but on the other hand, the filter device 70 size is 2 times 1. It also becomes possible to reduce costs.

As mentioned above, in the system system which converts the DC power of the DC power source I into AC power using the separately excited inverter 3 and supplies it to the power grid 6, a filter that also serves as a phase advance capacitor is connected to the AC side of the separately excited inverter 3. The phase advance capacity of the device M7 is set to be equivalent to 50% of the delayed reactive power generated by the separately excited inverter 3 during rated operation.

Therefore, it is possible to compensate for about 50% of the amount of grid voltage drop due to the delayed reactive power generated by the separately excited inverter 30, and to reduce the grid voltage fluctuation at the interconnection point by half compared to the conventional system. Along with this, the filter device 70 dimensions 2 weight,
Costs can also be reduced.

In the above embodiment, the phase advance capacity of the filter device 7 is set to 5 of the delayed reactive power generated by the separately excited inverter 3 during rated operation.
Although it is assumed that the capacitance is equivalent to 0 inches, the same effect can be obtained even if the capacity is in the range of about 30 to 70 inches.

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, the phase advancing capacity of the filter device provided on the AC side of the separately excited inverter is set to 30 to 30% of the delayed reactive power generated by the separately excited inverter during rated operation.
Since the capacity is set to be equivalent to 70%, it is possible to provide a highly reliable interconnection system between an inverter and a power grid that can reduce grid voltage fluctuations caused by a separately excited inverter.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the main circuit configuration of an interconnection system between an inverter and a power grid, Fig. 2 is a diagram showing the relationship between interconnection point voltage and inverter output in a conventional system, and Fig. 3 is a diagram showing the relationship between an interconnection point voltage and an inverter output in a conventional system. It is a diagram showing the relationship between interconnection point voltage and inverter output in . 1... DC power supply, 3... Separately excited inverter, 4...
- Grid connection transformer, 5... Grid impedance, 6...
Power system, 7...filter device.

Claims (1)

[Claims] In a system that converts DC power from a DC power source into AC power using a separately excited inverter and supplies it to the power grid, a filter device that also serves as a phase advance capacitor is provided on the AC side of the separately excited inverter, and the phase advance capacity of this filter device is increased. 3 of the delayed reactive power generated by the separately excited inverter during rated operation.
An interconnection system between an inverter and a power system, characterized by having a capacity equivalent to 0 to 70%.