Harmonic filter equipment

Abstract

To provide harmonic filter equipment capable of suppressing an occurrence of resonance by a high voltage side and a low voltage side of an interconnection point.SOLUTION: There is provided harmonic filter equipment 100 which is used in an electrical power system 10 supplying power from an AC power supply 50 to a power cable 60 through an interconnection point bus 40, and which suppresses a harmonic component included in AC voltage of the interconnection point bus 40. The harmonic filter equipment includes a resistance element 11 connected in series between the interconnection point bus 40 and the power cable 60, and a fundamental wave resonance circuit 20 which is connected in parallel to the resistance element 11, and in which a rector element 21 and a capacitor element 22 are connected in series to resonate at a fundamental wave.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to harmonic filter equipment.

Background Art

[0002] Conventionally, harmonic filter equipment has been used to suppress harmonic components generated in the AC voltage at the connection point of a power source. For this harmonic filter equipment, a harmonic resonance avoidance system has been proposed to avoid resonance with harmonic components such as the third, fifth, and seventh harmonics.

[0003] For example, in the harmonic resonance avoidance system of Patent Document 1, as shown in FIG. 4, a series reactor having an inductance of a predetermined value is connected in series between a main transformer and a power cable. This equipment calculates the resonance frequency based on the combined value of the inductances of the power supply system, the main transformer, the series reactor, and the power cable and the combined value of the capacitance of the power cable. Then, this equipment avoids the resonance frequency and odd harmonic components from overlapping by setting the value of the inductance of the series reactor.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In this case, the above harmonic filter equipment has capacitive power cables located on the lower voltage side of the interconnection point. On the other hand, the above equipment has inductive main transformers and series reactors located on the higher voltage side of the interconnection point. Therefore, the above equipment only considers the case where the higher voltage side of the interconnection point is inductive. However, if capacitive elements such as long-distance cables are located on the higher voltage side of the interconnection point, the characteristics of the system may exhibit capacitiveness in a given harmonic component. As a result, resonance may occur between the high-voltage and low-voltage sides of the interconnection point, potentially increasing voltage distortion at the interconnection point.

[0006] Therefore, the present invention has been made in view of the above problems, and its main objective is to provide a harmonic filter system that suppresses the occurrence of resonance on the high-pressure and low-pressure sides of the interconnection point. [Means for solving the problem]

[0007] In other words, the harmonic filter equipment according to the present invention is used in a power supply system that supplies power from a power grid to a power cable via a connection point, and is a harmonic filter equipment that suppresses the amplification of harmonic components contained in the AC voltage at the connection point, and is characterized by comprising a resistive element connected in series between the connection point and the power cable, and a fundamental wave resonant circuit connected in parallel to the resistive element, and having a reactor element and a capacitor element arranged in series, configured to resonate at the fundamental wave.

[0008] In this configuration, a resistive element is connected in series between the interconnection point and the power cable. Therefore, for harmonic components of a predetermined order, such as the 5th or 7th harmonic, the low-voltage side of the interconnection point will exhibit resistance due to the resistive element. Consequently, even if the high-voltage side of the interconnection point exhibits either inductive or capacitive properties, the low-voltage side of the interconnection point will exhibit resistance, thus suppressing the occurrence of resonance on both the high-voltage and low-voltage sides of the interconnection point. Furthermore, when harmonic components pass through the resistive element, the harmonic components can be reduced by the resistive element, thereby suppressing the expansion of voltage distortion caused by the installation of power cables. Here, inductive means that the reactance of a reactor, such as a series reactor, is greater than the reactance of a capacitor, such as a power cable. Capacitive means that the reactance of a capacitor is greater than the reactance of a reactor. Resistive means that the impedance of a resistive element is greater than the impedance of both the reactor and the capacitor. Furthermore, regarding the fundamental wave, since the reactor and capacitor elements resonate with the fundamental wave, the fundamental wave passes through the fundamental wave resonant circuit rather than the resistive elements. As a result, the fundamental wave loss caused by the fundamental wave passing through the resistive elements can be reduced.

[0009] It is desirable that the impedance of the resistive element is smaller than the impedance of the reactor element in a frequency range greater than the impedance of the power cable.

[0010] In this configuration, since the impedance of the resistive element is smaller than the impedance of the reactor element, if harmonic components are generated, they can pass through the resistive element. Furthermore, in the frequency range where the impedance of the resistive element is larger than the impedance of the power cable, the harmonic components can be reduced by the resistive element as they pass through it, and the lower voltage side of the interconnection point can be made resistive.

[0011] The harmonic filter equipment preferably further comprises a bypass circuit having a switch element connected in parallel with the resistive element and the fundamental wave resonant circuit, and which switches the electrical connection with the interconnection point.

[0012] With this configuration, if an abnormality occurs in the LC series resonant circuit or the fundamental wave resonant circuit, the switching element of the bypass circuit can be turned on, allowing the AC current to flow through the bypass circuit to the power cable, thus enabling the continuation of power transmission through the power cable. [Effects of the Invention]

[0013] According to the present invention configured in this manner, it is possible to provide a harmonic filter system that suppresses the occurrence of resonance on the high-pressure and low-pressure sides of the interconnection point. [Brief explanation of the drawing]

[0014] [Figure 1] This is a schematic diagram showing the harmonic filter equipment in this embodiment. [Figure 2] This graph shows the impedance characteristics of the harmonic filter equipment in the same embodiment. [Figure 3] This graph shows the phase characteristics of the harmonic filter equipment in the same embodiment. [Figure 4] This is a schematic diagram showing a conventional harmonic filter system. [Modes for carrying out the invention]

[0015] Embodiments of the harmonic filter equipment according to the present invention will be described below with reference to the drawings. Note that, for the sake of clarity, some details in the following drawings may be omitted or exaggerated for illustrative purposes. The same components are denoted by the same reference numerals, and their descriptions will be omitted as appropriate.

[0016] <1.Device configuration> The harmonic filter equipment 100 in this embodiment is used in a power supply system 10 that supplies power from an AC power source 50, which is a power supply system, to a power cable 60. It suppresses the amplification of harmonic components, such as the 5th harmonic and the 7th harmonic, contained in the AC voltage of the interconnection bus 40 connected to the AC power source 50. As shown in Figure 1, the harmonic filter equipment 100 is installed between the interconnection bus 40 and the power cable 60. In this power supply system 10, a back impedance 70, consisting of a resistor and a reactor, is provided between the interconnection bus 40 and the AC power source 50.

[0017] The harmonic filter facility 100 includes a resistance element 11 connected to the low-voltage side of the connection point bus 40, a fundamental wave resonance circuit 20 connected in parallel with the resistance element 11, and a bypass circuit 30 connected in parallel with the resistance element 11 and the fundamental wave resonance circuit 20. Hereinafter, each part will be described in detail.

[0018] The resistance element 11 is connected in series between the connection point bus 40 and the power cable 60, and the low-voltage side with respect to the connection point bus 40 is resistive. Specifically, as shown in FIG. 1, the resistance element 11 is provided on the low-voltage side of the connection point bus 40 and the high-voltage side of the power cable 60, and is connected in series to the connection point bus 40 and the power cable 60.

[0019] Also, in order for the low-voltage side with respect to the connection point bus 40 to exhibit resistance, the impedance R of the resistance element 11 is configured to be sufficiently larger than the impedance of the element on the low-voltage side of the resistance element 11 in a predetermined harmonic component. In the present embodiment, in a predetermined harmonic component, the impedance R of the resistance element 11 is configured to be sufficiently larger than the impedance Z1 of the power cable 60 provided on the low-voltage side of the resistance element 11.

[0020] The fundamental wave resonance circuit 20 prevents the fundamental wave from flowing through the resistance element 11 by resonating at the fundamental wave. Specifically, as shown in FIG. 1, the fundamental wave resonance circuit 20 is connected in parallel with the resistance element 11, and the reactor element 21 and the capacitor element 22 are connected in series in this order.

[0021] The fundamental wave resonance circuit 20 is configured to resonate at the fundamental wave. Specifically, when resonating at the fundamental wave, the reactance X L of the reactor element 21 and the reactance X C of the capacitor element 22 are equal, so the reactance X L of the reactor element 21 and the reactance X C of the capacitor element 22 are represented by equation (1). In equation (1), let the voltage be V and the angular frequency in the fundamental wave be ω0.

[0022]

number

[0023] According to equation (1), the inductance L of the reactor element 21 and the capacitance C of the capacitor element 22 are expressed by the following equations (2) and (3).

[0024]

number

[0025]

number

[0026] Furthermore, the fundamental wave resonant circuit 20 is configured so that harmonic components pass through the resistive element 11. Specifically, in the frequency range where the impedance R of the resistive element 11 is greater than the impedance Z1 of the power cable 60, the impedance R of the resistive element 11 is greater than the impedance Z of the reactor element 21. L It is configured to be significantly smaller than that. From the above, in a given harmonic component, the impedance R of the resistive element 11, the impedance Z1 of the power cable 60, and the impedance Z of the reactor element 21 L The relationship is expressed by equation (4) below.

[0027]

number

[0028] The bypass circuit 30 sends current from the interconnection bus 40 to the power cable 60 when an abnormality occurs in the resistive element 11 or the fundamental wave resonant circuit 20. Specifically, as shown in Figure 1, the bypass circuit 30 is connected in parallel with the resistive element 11 and the fundamental wave resonant circuit 20.

[0029] Furthermore, the bypass circuit 30 has a switch element 31 that switches the electrical connection with the interconnection bus 40. The switch element 31 is turned on when an abnormality occurs in the resistive element 11 or the fundamental wave resonant circuit 20, electrically connecting the interconnection bus 40 and the power cable 60. The switch element 31 may be closed based on a signal from a control device (not shown) that detects an abnormality, or it may be a mechanical switch that is mechanically closed when an abnormality is detected by the user.

[0030] Next, a harmonic filter system 100 according to this embodiment was designed and simulated, and the results shown in Figures 2 and 3 were obtained. As shown in Figure 2, at the fundamental frequency of 50 Hz, the impedance of the harmonic filter system 100 is 0 Ω, indicating that the harmonic filter system 100 is resonating at the fundamental frequency. Furthermore, at the 5th and 7th harmonics, 250 Hz and 350 Hz, the combined impedance of the harmonic filter system 100 and the power cable 60 is 400 Ω or more.

[0031] Furthermore, as shown in Figure 3, at 250 Hz and 350 Hz, which are the 5th and 7th harmonics, the combined phase characteristics of the harmonic filter equipment 100 and the power cable 60 are 30 degrees or less. Therefore, at the 5th and 7th harmonics, the harmonic filter equipment 100 and the power cable 60 exhibit resistance, and thus the lower voltage side of the interconnection busbar 40 is also resistant.

[0032] <2. Effects of this embodiment> With such a harmonic filter system 100, since the resistive element 11 is connected in series between the interconnection bus 40 and the power cable 60, for example, in the case of harmonic components of a predetermined order, such as the 5th or 7th harmonic, the low-voltage side of the interconnection bus 40 will exhibit resistance due to the resistive element 11, thereby suppressing the occurrence of resonance on both the high-voltage and low-voltage sides of the interconnection bus 40. Furthermore, since the harmonic components pass through the resistive element 11, the harmonic components can be reduced by the resistive element 11, thereby suppressing the inflow of harmonic components into the power cable 60.

[0033] Furthermore, with respect to the fundamental wave, since the reactor element 21 and the capacitor element 22 resonate at the fundamental frequency, the fundamental wave passes through the fundamental wave resonant circuit 20 rather than the resistor element 11. As a result, the occurrence of fundamental wave loss due to the fundamental wave passing through the resistor element 11 can be prevented.

[0034] Furthermore, if an abnormality occurs in the resistive element 11 or the fundamental wave resonant circuit 20, the switch element 31 of the bypass circuit 30 can be switched on, allowing the AC current to flow through the bypass circuit 30 to the power cable 60, thereby enabling the continuation of power transmission through the power cable 60.

[0035] <3. Other Embodiments> However, the present invention is not limited to the embodiments described above.

[0036] In this embodiment, the background impedance 70 was composed of a resistor and a reactor, but the configuration of the background impedance 70 is not limited to this. For example, the background impedance 70 may be a capacitive element such as a long-distance cable. In this case, the high-voltage side of the interconnection busbar 40 is capacitive, but since a resistive element 11 is provided on the low-voltage side of the interconnection busbar 40, the low-voltage side of the interconnection busbar 40 will exhibit resistance. As a result, the occurrence of resonance on the high-voltage and low-voltage sides of the interconnection busbar 40 can be suppressed.

[0037] In this embodiment, the resistive element 11 exhibits resistance to, for example, the 5th and 7th harmonics, but the order of the harmonic components to which it exhibits resistance is not limited to these. By adjusting the impedance R of the resistive element 11, the resistive element 11 can exhibit resistance to harmonic components of any order.

[0038] Furthermore, it goes without saying that the present invention is not limited to the embodiments described above, and various modifications are possible without departing from its spirit. [Explanation of Symbols]

[0039] 100-harmonic filter equipment 10 ···Power System 11 ···Resistor element 20...Fundamental resonance circuit 21 ···Reactor element 22... Capacitor element 30 ···Bypass circuit 31... Switch element 40...Connection point bus 50...AC power supply 60 ···Power Cable

Claims

1. A harmonic filter device used in a power supply system that supplies power from a power grid to a power cable via an interconnection point, which suppresses the amplification of harmonic components contained in the AC voltage at the interconnection point, A resistive element connected in series between the interconnection point and the power cable, A harmonic filter device comprising a fundamental wave resonant circuit configured to resonate at the fundamental wave, with a reactor element and a capacitor element arranged in series and connected in parallel to the aforementioned resistive element.

2. The harmonic filter equipment according to claim 1, wherein the impedance of the resistive element is smaller than the impedance of the reactor element in a frequency range where the impedance of the power cable is greater than the impedance of the power cable.

3. The harmonic filter apparatus according to claim 1 or 2, further comprising a bypass circuit having a switch element connected in parallel with the resistive element and the fundamental wave resonant circuit for switching the electrical connection with the interconnection point.

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