KR102530588B1 - Energy storage system and ferro-resonance preventing algorithm for energy storage system - Google Patents

Abstract

An energy storage system configured to prevent a battery from being overcharged, and a ferroresonance anti-resonance algorithm for the energy storage system are disclosed. The energy storage system includes an energy storage system (Energy Storage System, hereinafter referred to as ESS) linkage transformer that converts high-voltage AC power of the grid power unit into low-voltage AC power; A power control system (Power Control System, hereinafter referred to as PCS) that converts low-voltage AC power supplied from the ESS-linked transformer into DC power; a battery unit for storing the DC power converted by the PCS; and a ferroresonance suppression unit disposed between the ESS linkage transformer and the PCS, and having a capacitive reactance (or capacitance) calculated based on ferroresonance characteristics to suppress ferroresonance.

Description

Energy storage system and ferroresonance prevention algorithm for energy storage system

The present invention relates to an energy storage system and a ferroresonance prevention algorithm for an energy storage system, and more particularly, to an energy storage system configured to prevent a battery from being overcharged, and to a ferroresonance prevention algorithm for an energy storage system.

In a lithium-ion battery-based energy storage system (ESS) installed and operated with a large capacity, there is a possibility that ferroresonance occurs due to unintended saturation of the linkage transformer for ESS, affecting the battery part. Ferroresonance is a non-linear vibration phenomenon that occurs through interaction with the capacitance of the system when the inductor with the iron core is saturated by abnormal voltages such as overvoltage and switching surge.

In transmission/distribution systems, transformers operate in the linear region of the magnetization curve, but when circuit breakers are opened, magnetic flux increases due to overvoltage, switching surges, and capacitance components, and the inductance of the iron core can reach the saturation region of the magnetization curve. Here, the capacitance exists between the bus and ground, between the bus and the bus, and between both poles when the circuit breaker is opened, and there is a possibility of momentarily high voltage ferroresonance through interaction with nonlinear inductance.

The ferroresonance phenomenon has been widely studied since it was first named by Boucherot in 1920, but it has a complex generation mechanism, and due to the switching operation performed for commissioning of a 400 kV substation in Ireland in July 2003, There is an example of an iron resonance accident.

In addition, in a lithium-ion battery-based ESS installed and operated with a large capacity, ferroresonance occurs due to unintended saturation of the linkage transformer for the ESS, resulting in a voltage several times higher than the normal voltage on the secondary side of the transformer. Serious effects due to overcharging of the battery has the potential to affect

Republic of Korea Patent Publication No. 10-2020-0107630 Republic of Korea Patent Publication No. 10-2019-0002080 Republic of Korea Patent No. 10-2009919

Accordingly, the technical problem of the present invention is focused on this point, and the object of the present invention is to generate a voltage higher than the normal voltage on the secondary side of the linkage transformer for ESS due to ferroresonance due to unintended saturation of the linkage transformer for ESS. It is to provide an energy storage system configured to prevent overcharging.

Another object of the present invention is to provide a ferroresonance prevention algorithm for an energy storage system.

In order to realize the object of the present invention described above, an energy storage system according to an embodiment includes an energy storage system (Energy Storage System, hereinafter referred to as ESS) linkage transformer for converting high-voltage AC power of a system power unit into low-voltage AC power; A power control system (Power Control System, hereinafter referred to as PCS) that converts low-voltage AC power supplied from the ESS-linked transformer into DC power; a battery unit for storing the DC power converted by the PCS; and a ferroresonance suppression unit disposed between the ESS linkage transformer and the PCS, and having a capacitive reactance (or capacitance) calculated based on ferroresonance characteristics to suppress ferroresonance.

In one embodiment, the capacitance of the ferroresonance suppression unit may be smaller than the inductive reactance (or inductance) of the saturation region.

In one embodiment, the capacitance of the ferroresonance suppression unit may be greater than the inductive reactance (or inductance) of the linear region.

In order to realize the object of the present invention described above, a capacitance calculation method in a ferroresonance prevention algorithm for an energy storage system according to an embodiment includes (a) linear and saturated inductance parameters of a linkage transformer for an ESS, capacitance parameters between poles of a circuit breaker, and Assuming a filter capacity parameter of a power control system (hereinafter referred to as PCS) that converts low-voltage AC power provided from the ESS linkage transformer into DC power and stores it in a connected battery unit; (b) calculating a ferroresonance generation area according to the characteristics of an interlocking transformer for an ESS based on the above parameters, and determining whether a ferroresonance generation area is included when a circuit breaker operates; (c) If the ESS linkage transformer has a possibility of ferroresonance, in order to prevent this, the appropriate capacitive reactance of the PCS filter is recalculated, and the process of determining whether it is included in the ferroresonance generation area by returning to step (b) repeat; and (d) terminating the algorithm when the linkage transformer for the ESS is out of the possibility of ferroresonance.

(여기서,

: 각속도[rad/s],

: 선형영역에서 인덕턴스[H],

: 포화영역에서 인덕턴스[H],

: 커패시턴스[F])에 의해 산정될 수 있다. In one embodiment, the capacitive reactance is

(here,

: angular velocity [rad/s],

: Inductance [H] in the linear region,

: Inductance [H] in the saturation region,

: It can be calculated by capacitance [F]).

According to the energy storage system and the ferroresonance prevention algorithm for the energy storage system, ferroresonance can be prevented from occurring due to unintentional saturation of the linkage transformer for the ESS. Accordingly, since a voltage higher than the normal voltage is not generated on the secondary side of the interlocking transformer for the ESS, it is possible to prevent the battery from being overcharged.

1 is a circuit diagram for explaining a nonlinear LC series ferroresonance circuit.
2 is a graph for explaining a schematic analysis of a steady state circuit.
3 is a graph for explaining a schematic analysis of a ferroresonant circuit.
4 is a graph for explaining a schematic analysis of a ferroresonant circuit according to an applied voltage.
5 is a circuit diagram for explaining a nonlinear LC series/parallel ferroresonance equivalent circuit of an ESS.
6 is a configuration diagram for explaining distribution system modeling.
7 is a configuration diagram for explaining the configuration of a vacuum circuit breaker.
8 is a configuration diagram for explaining series capacitance modeling by circuit breaker operation.
9 is a graph for explaining nonlinear saturation characteristics of an iron core.
10 is a configuration diagram for explaining nonlinear LC series ferroresonance modeling.
11 is a configuration diagram for explaining ferroresonance modeling of an LC series/parallel circuit.
12 is a configuration diagram for explaining an energy storage system according to an embodiment of the present invention.
13 is a graph for explaining a schematic analysis method of ferroresonance according to an increase in capacitance.
14 is a graph for explaining calculation of a ferroresonance avoidance area using a schematic analysis method.
15 is a waveform diagram for explaining ferroresonance characteristics by LC resonance.
16 is a waveform diagram for explaining transformer inductance characteristics due to LC ferroresonance.
17 is a waveform diagram for explaining voltage characteristics due to ferroresonance when a circuit breaker operates.
18 is a waveform diagram for explaining transformer inductance characteristics due to ferroresonance when a circuit breaker operates.
19 is a waveform diagram for explaining voltage characteristics by a ferroresonance prevention algorithm.
20 is a waveform diagram for explaining transformer inductance characteristics by a ferroresonance prevention algorithm.

Hereinafter, with reference to the accompanying drawings, the present invention will be described in more detail. Since the present invention may have various changes and various forms, specific embodiments are illustrated in the drawings and described in detail in the text. However, it should be understood that this is not intended to limit the present invention to the specific disclosed form, and includes all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

Like reference numerals have been used for like elements throughout the description of each figure. In the accompanying drawings, the dimensions of the structures are shown enlarged than actual for clarity of the present invention.

Terms such as first and second may be used to describe various components, but the components should not be limited by the terms. These terms are only used for the purpose of distinguishing one component from another. For example, a first element may be termed a second element, and similarly, a second element may be termed a first element, without departing from the scope of the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

In this application, terms such as "comprise" or "have" are intended to designate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, but one or more other features It should be understood that it does not preclude the possibility of the presence or addition of numbers, steps, operations, components, parts, or combinations thereof.

In addition, unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the related art, and unless explicitly defined in the present application, they should not be interpreted in an ideal or excessively formal meaning. don't

In general, ferroresonance is a nonlinear vibration phenomenon that occurs through interaction with capacitance of a system when an inductor having an iron core is saturated by an abnormal voltage such as an instantaneous voltage increase caused by a first-line ground fault in an upper system. In addition, ferroresonance occurs when a circuit breaker operates in a system because the inductance component of the transformer and the capacitance component of both ends of the circuit breaker are configured in series.

In this specification, a circuit as shown in FIG. 1 is assumed to analyze the mechanism of nonlinear L-C ferroresonance.

1 is a circuit diagram for explaining a nonlinear L-C series ferroresonance circuit.

Referring to FIG. 1, the nonlinear L-C series ferroresonance circuit assumes a series circuit composed of an AC voltage source, an inductance of a transformer, and a capacitance component of both ends of a circuit breaker.

2 and 3 show the current and voltage in the L-C steady state circuit and the ferroresonant circuit of FIG. 1 using a graphical solution.

2 is a graph for explaining a schematic analysis of a steady state circuit.

First, in the steady-state circuit of FIG. 2, the voltage EL across the inductor and the voltage EC across the capacitor have the form of a straight line with a slope of wL and 1/wC, respectively. That is, there is only one intersection between EL and Es-Ec, and the steady-state current, EL, and EC are obtained at this intersection.

3 is a graph for explaining a schematic analysis of a ferroresonant circuit.

In the ferroresonant circuit of FIG. 3, EC is a straight line with a slope of 1/wC and is proportional to current, but EL has a curve that does not change proportionally at currents above a certain value due to saturation.

That is, since EL has a high slope value of wLlinear in a low current region and a very low slope value of wLsat in a current region above a certain value, the number of intersections between EL and Es-EC is from 1 to 3 depending on the system constant. can happen Here, depending on the size of EL and EC, it can be represented as an inductive region and a capacitive region. Cross point 1 is the non-ferroresonant state of the inductive region, cross point 2 is the transient state of the inductive region, and The intersection point represents the ferroresonant state of the capacitive region.

Therefore, due to ferroresonance characteristics due to saturation of the transformer, the voltage across the inductor of the transformer at the same applied voltage (Es) can have three solutions, and there is a possibility of an instantaneous voltage rise from one crossing point to another crossing point. .

The ferroresonance mechanism of the L-C series circuit is explained.

An instantaneous (within 30 cycles) voltage rise may occur due to a single-line ground fault in the upper system, sudden dissipation of a large-capacity load, or input of a large-capacity capacitor bank. In order to analyze the ferroresonance phenomenon due to the instantaneous voltage rise, the ferroresonance characteristics are shown according to the magnitude of the voltage rise using a schematic analysis method, as shown in FIG.

4 is a graph for explaining a schematic analysis of a ferroresonant circuit according to an applied voltage.

Referring to FIG. 4, with the applied voltage (E's) at which EL and Es-EC come into contact as a reference point, when a higher voltage (E"s) is applied, an intersection occurs at 3", resulting in ferroresonance. However, when a voltage lower than the reference point is applied, as shown in FIG. 3, it has three crossing points, and ferroresonance may occur depending on system conditions such as residual magnetic flux of the iron core and capacitor capacity.

Therefore, it can be seen that a transient ferroresonance phenomenon occurs due to the instantaneous voltage rise, and the ferroresonance is irregularly vibrated until energy is consumed below a value required to maintain the ferroresonance phenomenon.

Meanwhile, the ferroresonance mechanism of the L-C series/parallel circuit is explained.

In the case of the nonlinear L-C series/parallel ferroresonance circuit, since the resonance phenomenon between the inductance and parallel capacitance components of the transformer is also considered, the possibility of occurrence of ferroresonance increases compared to the L-C series ferroresonance circuit.

This L-C series/parallel ferroresonance circuit can also appear in an ESS composed of a system power supply unit, a linkage transformer for ESS, a PCS, and a battery section, where the C filter for output stabilization of the PCS becomes a parallel capacitance component and the linkage transformer for ESS is the L component becomes Therefore, the L-C series/parallel circuit of the ESS can be represented by the system power supply unit (Ein), the circuit breaker (CCB), the ESS linkage transformer (Lsat), and the capacitance component (CPCS) of the PCS as shown in FIG.

On the other hand, in the case of an L-C series/parallel circuit, the schematic analysis method as described above has limitations due to many factors to be considered.

5 is a circuit diagram for explaining a nonlinear L-C series/parallel ferroresonance equivalent circuit of an ESS.

When the circuit breaker operates in FIG. 5, the relational expression between the input voltage (Ein) and the output voltage (Eout) can be expressed as in Equation 1, which is calculated according to the equivalent impedance (Z) and the C component (XCB) of the circuit breaker. do.

[Formula 1]

[Formula 2]

은 입력전압[V],

은 출력전압[V],

은 권수비,

는 변압기와 PCS 필터의 병렬 등가 임피던스[Ω],

는 차단기의 리액턴스[Ω],

은 변압기의 리액턴스[Ω],

는 PCS 필터의 리액턴스[Ω]이다. here,

is the input voltage [V],

is the output voltage [V],

Eun Soo-bi Kwon,

is the parallel equivalent impedance of the transformer and the PCS filter [Ω],

is the reactance of the breaker [Ω],

is the reactance of the transformer [Ω],

is the reactance [Ω] of the PCS filter.

As shown in Equation 2, the equivalent impedance can be represented by the L component of the transformer ( _XL ) and the C component of the PCS (X _PCS ), and _XL can be reduced by saturation.

Therefore, when the circuit breaker operates, the transformer is saturated, and if ferroresonance occurs between the C components composed of series/parallel, the voltage ratio in Equation 1 becomes higher than 1, and the secondary side of the transformer has a voltage several times higher than the normal voltage. Since this may occur, there is a possibility of having a serious effect due to overcharging of the battery.

If a distribution system composed of a main voltage generator and a high-voltage distribution line of a distribution substation is modeled using power system analysis software (PSCAD/EMTDC), it can be represented as shown in FIG. 6 .

6 is a configuration diagram for explaining distribution system modeling.

결선방식이며, 3차 권선은 제3 고조파를 제거하기 위하여

결선방식을 채용하고 있다. 또한 주변압기 2차측은 배전계통의 지락전류를 제한하기 위하여, 0.6[Ω]의 NGR을 설치하는 것으로 가정한다. 그리고, 고압 배전선로는 3상 4선식의 π형 등가회로이며, 선종은 ACSR 160㎟ 로 상정한다.Referring to FIG. 6, the main voltage generator (45/60 [MVA]) for 154/22.9 [kV] has three windings Yg-Yg-

It is a wiring method, and the tertiary winding is used to remove the third harmonic.

A wiring method is used. In addition, it is assumed that an NGR of 0.6 [Ω] is installed on the secondary side of the main transformer to limit the ground fault current of the distribution system. And, the high-voltage distribution line is a π-type equivalent circuit of a three-phase, four-wire type, and the type of line is assumed to be ACSR 160 mm2.

Hereinafter, modeling of the series capacitance component by circuit breaker operation will be described.

The configuration of the vacuum circuit breaker used in the high-voltage distribution line is as shown in FIG. 7, and when the circuit breaker operates to open, a capacitance component appears between the two poles.

7 is a configuration diagram for explaining the configuration of a vacuum circuit breaker.

In FIG. 7 , the capacitance of the circuit breaker during the opening operation is proportional to the width of the electrode plates and inversely proportional to the inter-electrode distance, as shown in Equation 3.

[Formula 3]

는 진공차단기의 양극간 커패시터[F],

은 진공의 유전율(

[F/m]),

는 극판의 넓이[

],

는 개방 동작 시 극간 거리[m]이다. here,

is the capacitor between the poles of the vacuum circuit breaker [F],

The permittivity of the silver vacuum (

[F/m]),

is the area of the plate [

],

is the inter-pole distance [m] during the opening operation.

Therefore, modeling the circuit breaker using power system analysis software (PSCAD/EMTDC) can be represented as shown in FIG. 8 .

8 is a configuration diagram for explaining series capacitance modeling by circuit breaker operation.

], 극판의 넓이 0.25[

]을 상정하고, 상기한 수식 3에 따라 C 성분을 구하면 약 2[nF]이 구해진다. 또한 3상 차단기는 각상별로 제어가 가능하며 개방 시 양극간 커패시턴스를 고려하여 구성한다.In FIG. 8, the distance between the poles during the opening operation is 12 [

], the width of the electrode plate 0.25 [

] is assumed, and the C component is obtained according to Equation 3 above, about 2 [nF] is obtained. In addition, the three-phase circuit breaker can be controlled for each phase, and is configured by considering the capacitance between the two poles when opening.

The saturation characteristics of an inductor with an iron core in an L-C series circuit are shown in FIG. 9.

9 is a graph for explaining nonlinear saturation characteristics of an iron core.

까지, 경계영역은

~

까지, 포화영역은

이후가 된다. 여기서,

에 해당되는 무릎점은 자속밀도가 10% 증가 시, 자화전류의 50% 증가를 가져오는 지점을 의미한다. 또한 정격 전압에서 인덕턴스

과 무릎점에서 인덕턴스

에 대한 접선 방정식은 그림에서와 같이 정의될 수 있다.Referring to FIG. 9, the characteristic of inductance, which decreases as the magnetizing current increases, can be divided into a linear region, a boundary region, and a saturation region. In the linear region, the current ranges from 0 to 0.

Until, the boundary area is

~

, the saturation region is

it comes after here,

The knee point corresponding to means the point at which the magnetizing current increases by 50% when the magnetic flux density increases by 10%. Also at rated voltage the inductance

and the inductance at the knee point

The tangent equation for can be defined as in the figure.

,

,

)에 따라, 수식 4 내지 수식 6에 의하여 산정된다. 여기서, 수식 4는 철심의 포화특성에 따라 산정되는 자화전류의 크기이며, 수식 5는 정격 전압에서 철심에 쇄교되는 자속의 크기를 나타낸다.9, the magnetization current is the saturation characteristic of the iron core (

,

,

), it is calculated by Equations 4 to 6. Here, Equation 4 is the magnitude of the magnetizing current calculated according to the saturation characteristics of the iron core, and Equation 5 represents the magnitude of the magnetic flux linked to the iron core at the rated voltage.

[Formula 4]

[Formula 5]

[Formula 6]

은 자화전류[A],

은 정격 전압에서 쇄교되는 자속[Wb·turn],

는 쇄교자속의 무릎점[Wb·turn],

는 포화 시 변압기 등가 리액턴스[H],

은 정격 전압의 RMS값[V],

은 정격 전압에서 자화전류[A]이다. here,

is the magnetizing current [A],

is the magnetic flux linked at the rated voltage [Wb turn],

is the knee point of the flux linkage [Wb turn],

is the transformer equivalent reactance at saturation [H],

is the RMS value of the rated voltage [V],

is the magnetizing current [A] at the rated voltage.

On the other hand, according to the ferroresonance mechanism of the L-C series circuit, series ferroresonance modeling consisting of an AC voltage source, line resistance, series capacitor, and a transformer having nonlinear characteristics of Equations 4 to 6 is shown in FIG. 10.

10 is a configuration diagram for explaining nonlinear L-C series ferroresonance modeling.

In FIG. 10, the nonlinear saturation characteristics of the iron core are simulated by using a compensation current source in the secondary coil of the transformer. Line resistance plays a role of suppressing the magnitude of current during L-C series resonance.

According to the ferroresonance mechanism of the L-C series/parallel circuit, ferroresonance modeling composed of an AC voltage source, a three-phase circuit breaker, an ESS linkage transformer, a PCS, and a battery unit can be represented as shown in FIG. 11.

11 is a configuration diagram for explaining ferroresonance modeling of an L-C series/parallel circuit.

Referring to FIG. 11, the filter for stabilizing the output of the PCS acts as a parallel C component, and the ferroresonant operating characteristic is configured using the resonance condition of the inductance of the saturated transformer and the capacitance component on the PCS filter side.

Modeling the entire distribution system composed of the main transformer, high-voltage distribution line, linkage transformer for ESS, PCS, and battery unit based on the above information can be represented as shown in FIG. 12 .

12 is a configuration diagram for explaining an energy storage system according to an embodiment of the present invention.

Referring to FIG. 12 , an energy storage system according to an embodiment of the present invention includes a main pressure unit 100, a linked transformer unit 200, and a charging unit 300 connected in series.

The main voltage unit 100 includes a main voltage generator 110 and a high voltage distribution line (primary feeder) 120 receiving power from the main voltage generator 110 . Since a plurality of main transformers are installed in one substation and a plurality of high voltage distribution lines can be drawn from one main transformer, dozens of high voltage distribution lines can be drawn out from the substation.

The connected transformer 200 includes a 3-phase circuit breaker (CB) 210 connected to the rear end of the main voltage unit 100 and a grid-connected TR 220 for ESS. Here, the three-phase circuit breaker 210 operates to protect against earth leakage that normally occurs due to a change in capacitance to ground or insulation resistance to ground in a three-phase line such as R, S, and T. In addition, the linkage transformer 220 for ESS converts the high-voltage AC power of the system power unit into low-voltage AC power.

The charging unit 300 includes a power control system (hereinafter referred to as PCS) 310 connected to the rear end of the coupled transformer 200, a battery unit 320, and a ferroresonance suppressor 330. .

Specifically, the PCS 310 converts the low-voltage AC power supplied from the ESS linkage transformer 220 into DC power and charges the battery unit 320, or withdraws the charged DC power to use an external electric device (not shown). ) to supply

The battery unit 320 stores the DC power converted by the PCS 310.

The ferroresonance suppression unit 330 is disposed between the linkage transformer 220 for ESS and the PCS 310, and suppresses ferroresonance by having capacitive reactance (or capacitance) calculated based on ferroresonance characteristics. In FIG. 12 , the ferroresonance suppression unit may be a C filter in which capacitors are connected in parallel.

In this embodiment, the capacitance of the ferroresonance suppression unit 330 may be set to be smaller than the inductive reactance (or inductance) of the saturation region. Also, the capacitance of the ferroresonance suppression unit 330 may be set to be greater than the inductive reactance (or inductance) of the linear region.

Based on the ferroresonance mechanism described above, a schematic analysis method according to the capacitance of the L-C series ferroresonance circuit can be represented as shown in FIG.

13 is a graph for explaining a schematic analysis method of ferroresonance according to an increase in capacitance.

In FIG. 13, since the slope of the capacitive reactance (or capacitance) (1/wC) decreases as the capacitance increases, the straight line Es-EC rotates around the y-axis intercept Es. Therefore, since the number of crossing points is changed according to the capacitance, it can be seen that ferroresonance characteristics are determined by the capacitance.

In FIG. 13, the range of capacitive reactance (or capacitance) in which ferroresonance may occur is shown in Equation 7, and it can be seen that ferroresonance can be prevented by calculating the capacitance by avoiding the range.

[Formula 7]

는 각속도[rad/s],

는 선형영역에서 인덕턴스[H],

는 포화영역에서 인덕턴스[H],

는 커패시턴스[F]이다. here,

is the angular velocity [rad/s],

is the inductance [H] in the linear region,

is the inductance [H] in the saturation region,

is the capacitance [F].

If this is represented using a schematic analysis method, it is shown in FIG. 14.

14 is a graph for explaining calculation of a ferroresonance avoidance area using a schematic analysis method.

)를 포화영역의 유도성 리액턴스(또는 인덕턴스)(

)보다 작거나(① 영역), 선형영역의 유도성 리액턴스(또는 인덕턴스)(

)보다 큰 경우(② 영역)로 산정하면, 정상상태의 교차점(③ 영역)에서 운용되므로 철공진을 방지할 수 있다. Referring to FIG. 14, capacitive reactance (or capacitance) (

) is the inductive reactance (or inductance) of the saturation region (

) is less than (① area), or the inductive reactance (or inductance) of the linear area (

), ferroresonance can be prevented because it is operated at the intersection point (region ③) in a steady state.

That is, since the slope of EC in the ① region is smaller than the slope of EL in the saturation region, one intersection occurs in the 1st quadrant, and in the ② region, one intersection occurs in the 3rd quadrant, and it has a relatively low current value, so it is stable. state will be maintained.

On the other hand, although the L-C series ferroresonance circuit was briefly equalized and analyzed in the above, in an actual system, various factors such as a circuit breaker configured in series/parallel with a transformer, anode capacitors, and a PCS filter should be considered.

Therefore, in an actual system, there is a limit to calculating the ferroresonance avoidance area using the schematic analysis method, and the ferroresonance avoidance area must be calculated by simulating various conditions through simulation.

Methods for preventing ferroresonance can be divided into two broad categories. A method for preventing ferroresonance by adding an L-C filter or a saturable reactor such as Butterworth and the like, and a method for preventing ferroresonance as shown in FIG. It is classified as a method of configuring with appropriate parameters so that it cannot be formed.

However, in the method of adding a filter or saturable reactor, even if ferroresonance is suppressed, the added element may interact with other elements of the system, and may cause problems such as continuous loss.

Therefore, the present invention calculates the appropriate capacity of the PCS filter based on the ferroresonance characteristics according to the capacitance, and proposes a ferroresonance prevention algorithm of the ESS linkage transformer as follows.

[Step 1] Assume parameters such as inductance at linearity and saturation of the linkage transformer for ESS, capacitance between poles of circuit breaker, and filter capacity of PCS.

[Step 2] Calculate the ferroresonance generation area according to the characteristics of the linkage transformer for ESS based on the parameters of [Step 1] and Equation 7 and FIG. 14, and determine whether the ferroresonance area is included when the circuit breaker operates do. If it is included in the ferroresonance generation area, it proceeds to [Step 3], and if it is out of the ferroresonance generation area, it moves to [Step 4].

[Step 3] If there is a possibility of ferroresonance occurring in the ESS linkage transformer, recalculate the appropriate capacitance of the PCS filter to prevent this, and repeat the process of determining whether it is included in the ferroresonance area by returning to [Step 2] do.

[Step 4] If the linkage transformer for ESS is out of the possibility of ferroresonance, the algorithm ends.

Then, simulation results and analysis will be described below.

First, the simulation conditions are as follows.

In order to analyze the ferroresonance characteristics generated in the L-C series circuit, simulation conditions are assumed as shown in Table 1.

Table 1 shows the ferroresonance simulation conditions of the L-C series circuit.

[Table 1]

Here, the power supply unit is a single-phase voltage source of 380 [V], 60 [Hz], and the nonlinear inductor is assumed to have an inductance of 4510 [mH] in the linear region and at least 10 [mH] in the nonlinear region according to the saturation characteristics described above. In addition, the line resistance is 0.01 [Ω], and the series capacitance is considered to be 5 [uF] to simulate ferroresonance in the L-C series circuit.

Meanwhile, in order to analyze the ferroresonance characteristics of the L-C series/parallel circuit of the ESS, simulation conditions are assumed as shown in Table 2.

Table 2 shows the ferroresonance simulation conditions of the L-C series/parallel circuit.

[Table 2]

의 선로긍장은 10[km]를 고려한다, 또한 3상 차단기는 차단 극간 거리 12[mm], 극판 넓이 0.25[

]을 상정하고, 상술된 산정식을 통해 2[nF]의 커패시턴스를 적용한다. 그리고, 3각 철심구조의 Yg-△ 결선방식의 ESS용 연계변압기는 22.9[kV]의 고압을 380[V]로 변환하며, PCS의 용량은 1[MVA]이고, 필터용 커패시턴스는 380[uF]으로 상정한다.Here, the main transformer for 45/60 [MVA] has a voltage ratio of 154/22.9 [kV], ACSR 160

The line length of 10 [km] is considered, and the distance between poles for 3-phase circuit breakers is 12 [mm], and the width of electrode plates is 0.25 [

] is assumed, and a capacitance of 2 [nF] is applied through the above-described calculation formula. In addition, the linkage transformer for ESS with Yg-Δ wiring method of triangular core structure converts high voltage of 22.9[kV] to 380[V], the capacity of PCS is 1[MVA], and the capacitance for filter is 380[uF] ] is assumed.

The analysis of the ferroresonance characteristics of the L-C series circuit is explained.

Voltage characteristics analysis during ferroresonance is as follows.

Based on the simulation conditions of Table 1, when ferroresonance occurs in the L-C series circuit, voltage and current values are obtained as shown in FIG. 15.

15A and 15B are waveform diagrams for explaining ferroresonance characteristics by L-C resonance.

15a shows a schematic analysis method for current and voltage, and it can be seen that there is a possibility of ferroresonance because Es-EC and EL have three crossing points.

15B shows the values of the applied voltage, inductor voltage, and current. It can be seen that even though the applied voltage is a sine wave of 1 [pu], the inductor voltage is distorted by ferroresonance and instantaneously increases to about 3 [pu]. there is.

When ferroresonance occurs in the L-C series circuit, inductor voltage and inductance values are obtained as shown in FIG. 16 in order to analyze the inductance saturation characteristics of the nonlinear inductor.

16 is a waveform diagram for explaining transformer inductance characteristics due to L-C ferroresonance.

16, it can be seen that the inductance has a high value of about 4,000 [mH] before saturation and decreases to about 700 [mH] due to the saturation characteristic. That is, it can be seen that the inductance of the nonlinear inductor intermittently reached 1,407 [mH], which is the resonance point with the series capacitor of 5 [uF], and ferroresonance occurred.

The analysis of the ferroresonance characteristics of the L-C series/parallel circuit is as follows.

Based on the simulation conditions of Table 2, the voltage and current characteristics in the case where ferroresonance occurs due to the circuit breaker operation in the L-C series/parallel circuit are shown in FIG. 17.

17 is a waveform diagram for explaining voltage characteristics due to ferroresonance when a circuit breaker operates.

17, it can be seen that the voltage and current of the high-voltage circuit breaker and the secondary voltage of the transformer are all output as sine waves before the three-phase circuit breaker operates. On the other hand, as the three-phase circuit breaker opens simultaneously in 0.5 seconds, the through current of the circuit breaker becomes 0, but the voltage waveform on the secondary side of the transformer is distorted by ferroresonance and instantly increases to about 2.4 [pu], making it a linkage transformer for ESS. It can be seen that there is a possibility of having a serious effect due to overcharging of the secondary side battery.

When ferroresonance occurs due to the circuit breaker operation in the L-C series/parallel circuit, the secondary-side line-to-line voltage and inductance values of the linkage transformer for ESS are obtained as shown in FIG. 18.

18 is a waveform diagram for explaining transformer inductance characteristics due to ferroresonance when a circuit breaker operates.

18, it can be seen that the secondary side voltage of the linkage transformer for ESS before the circuit breaker operates is a sine wave, and the inductance has a periodic value of about 800 [mH] or less. On the other hand, it can be confirmed that the voltage is distorted by ferroresonance after the circuit breaker operates, and the inductance of the transformer has a relatively low value. That is, due to the operation of the circuit breaker, the inductance of the transformer reaches a level of 18.5 [mH], which is the resonance point with the PCS filter of 380 [uF], and it can be seen that ferroresonance has occurred.

In order to prevent ferroresonance caused by circuit breaker operation in L-C series/parallel circuits, if the capacitance of the PCS-side filter is increased to 450 [uF] according to the above-mentioned ferroresonance prevention algorithm, the front end of the high-voltage circuit breaker and linked transformer 2 for ESS The value of the secondary side voltage is obtained as shown in FIG. 19 .

19 is a waveform diagram for explaining voltage characteristics by a ferroresonance prevention algorithm.

In FIG. 19 , it was confirmed that although the three-phase circuit breakers were simultaneously opened at 0.5 seconds, the increased capacitance deviated from the ferroresonance generation area, so that ferroresonance did not occur and the voltage on the secondary side of the ESS linkage transformer was normally reduced. Therefore, it can be seen that when the capacitance of the PCS-side filter is calculated as an appropriate capacity, it is possible to prevent overcharging of the battery on the secondary side of the interlocking transformer for ESS, contributing to the stable operation of the ESS.

When the capacitance of the PCS side filter is increased to 450 [uF] according to the ferroresonance prevention algorithm proposed in the present invention, the secondary side voltage and inductance values of the ESS linkage transformer are obtained as shown in FIG. 20 .

20 is a waveform diagram for explaining transformer inductance characteristics by a ferroresonance prevention algorithm.

20, even if the three-phase circuit breaker operates, the inductance of the transformer does not reach the resonance point with the PCS filter due to the increased capacitance, so ferroresonance does not occur, and after the circuit breaker operates, it can be seen that it has a high inductance value in the linear region. . Therefore, when the capacitance of the PCS-side filter is calculated as an appropriate capacity, ferroresonance does not occur, confirming that the ESS is freed from the possibility of harm due to ferroresonance.

As described above, in the present invention, in order to analyze ferroresonance characteristics, which is one of the electrical hazards of ESS, a mechanism for generating ferroresonance in L-C series circuits and LC series/parallel circuits is presented, and using PSCAD/EMTDC Modeling and simulation of the ferroresonant circuit was performed.

That is, ferroresonance mechanisms by L-C series circuits and L-C series/parallel circuits were defined, and conditions for ferroresonance generation were analyzed using schematic analysis methods and equivalent circuits. In particular, through a schematic analysis method for current and voltage, an intersection where ferroresonance can occur was obtained, and it was confirmed that ferroresonance could occur in the ESS.

In addition, the ferroresonance phenomenon modeling of the L-C series circuit and the L-C series/parallel circuit was performed, and the ferroresonance characteristics according to the capacitance were analyzed using a schematic analysis method. In addition, based on the ferroresonance characteristics according to the capacitance, a ferroresonance prevention algorithm for the ESS linkage transformer that calculates the appropriate capacity of the PCS filter was proposed.

In addition, as a result of analyzing the ferroresonance characteristics generated in the L-C series circuit, the inductance of the nonlinear inductor intermittently reaches 1,407[mH], which is the resonance point with the series capacitance, and ferroresonance occurs, the inductor voltage is distorted, and the voltage of the inductor is distorted momentarily by 3[pu] ] was confirmed to increase.

In addition, by the opening operation of the 3-phase circuit breaker in the L-C series/parallel circuit, the inductance of the linkage transformer for ESS is lowered to the level of 18.5[mH], which is the resonance point with the PCS filter of 380[uF], causing ferroresonance, and the voltage on the secondary side of the transformer It can be seen that this momentarily increases to about 2.4 [pu], confirming that there is a possibility of serious effects due to overcharging of the secondary battery of the linkage transformer for ESS.

In addition, if the capacitance of the PCS-side filter is increased to 450 [uF] based on the ferroresonance prevention algorithm, even if the three-phase circuit breaker operates, the inductance of the transformer does not reach the resonant point with the PCS filter, so ferroresonance does not occur. It was confirmed that the secondary side voltage of the linkage transformer was normally reduced. Therefore, it was confirmed that if the PCS-side filter is designed with an appropriate capacity, ferroresonance does not occur and the ESS can contribute to the stable operation of the ESS by escaping from the possibility of harm caused by ferroresonance.

Although the above has been described with reference to examples, those skilled in the art can variously modify and change the present invention without departing from the spirit and scope of the present invention described in the claims below. You will understand.

100: ambient pressure unit 110: ambient pressure unit
120: high voltage distribution line 200: connected transformer
210: 3-phase circuit breaker 220: Linked transformer for ESS
300: charging unit 310: PCS
320: battery unit 330: ferroresonance suppression unit

Claims (5)

A linkage transformer for an energy storage system (ESS) that converts high-voltage AC power of the grid power unit into low-voltage AC power;
A power control system (Power Control System, hereinafter referred to as PCS) that converts low-voltage AC power supplied from the ESS-linked transformer into DC power;
a battery unit for storing the DC power converted by the PCS; and
An energy storage system including a ferroresonance suppression unit disposed between the ESS linkage transformer and the PCS and suppressing ferroresonance with a capacitive reactance (or capacitance) calculated based on ferroresonance characteristics. The energy storage system of claim 1, wherein the capacitance of the ferroresonance suppression unit is smaller than the inductive reactance (or inductance) of the saturation region. The energy storage system of claim 1, wherein the capacitance of the ferroresonance suppression unit is greater than the inductive reactance (or inductance) of the linear region. (a) Inductance parameter at linearity and saturation of the linkage transformer for the Energy Storage System (ESS), capacitance parameter between poles of the circuit breaker, and low-voltage AC power supplied from the linkage transformer for the ESS Converted to DC power and connected to the battery unit assuming a filter capacity parameter of a power control system (hereinafter referred to as PCS) to be stored in;
(b) calculating a ferroresonance generation area according to the characteristics of an interlocking transformer for an ESS based on the above parameters, and determining whether a ferroresonance generation area is included when a circuit breaker operates;
(c) If the ESS linkage transformer has a possibility of ferroresonance, in order to prevent this, the appropriate capacitive reactance of the PCS filter is recalculated, and the process of determining whether it is included in the ferroresonance generation area by returning to step (b) repeat; and
(d) a capacitance calculation method in a ferroresonance prevention algorithm for an energy storage system comprising the step of terminating the algorithm if the linkage transformer for the ESS is out of the possibility of ferroresonance occurrence. 5. The method of claim 4, wherein the capacitive reactance is

(here,

: angular velocity [rad/s],

: Inductance [H] in the linear region,

: Inductance [H] in the saturation region,

: Capacitance [F]) Calculation method of capacitance in ferroresonance anti-resonance algorithm for energy storage system, characterized in that it is calculated by.

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