KR101550420B1 - Power flow calculation method and system of distribution according to decentralized power supply - Google Patents

Abstract

The present invention relates to a method and system for calculating an algae flow in a distribution system according to a distributed power supply connection, and more particularly, to a method and system for calculating an algae flow in a distribution system based on a distributed power supply modeling method. Calculating a phase current output by the phase current calculation unit in a steady state of the distributed power supply; And a tidal current calculation unit calculating an electric power tidal current of the distributed power source based on the phase current; .
With this configuration, the algae calculation method and system of the distribution system according to the present invention can accurately determine the distribution of the voltage and the current power at the point where the distributed power supply of the distribution system is connected, There is an effect that the power distribution system can be stabilized.
Further, the method and system for calculating the flow rate of the power distribution system according to the present invention can prevent the phase of the distributed power source from varying even under unbalanced operating conditions of the power distribution system.

Description

TECHNICAL FIELD The present invention relates to a method and a system for calculating a flow of a distribution system according to a distributed power supply connection,

The present invention relates to a method and a system for calculating an algae flow in a distribution system in connection with a distributed power supply, and more particularly, to a method and a system for algae calculation in a distribution system according to a distributed power supply linkage capable of stabilizing a power distribution system connected to a distributed power supply.

In recent years, interest in electric vehicles using electric energy as driving energy instead of conventional fossil fuel is increasing for the purpose of depleting fossil fuels and reducing environmental pollution due to global warming. As the interest in electric vehicles increases, battery-related technologies that charge electric power are attracting attention as well.

In order to drive the electric vehicle, the electric power of the battery is charged. However, there is a disadvantage that the charging cost is expensive in the electric charging process. In addition, as the use of the electric vehicle increases, The electric power charge of the car can be driven at once, and it is difficult to charge the battery.

In order to solve these difficulties, technologies that combine smart technology with electric charge and discharge of electric vehicles are being studied. Smart Grid represents the next generation power grid that combines IT technology in the grid to optimize energy use. These smart grid technologies enable intelligent power distribution systems such as intelligent power grid and intelligent power grid to enable real-time monitoring and control of power facilities, enabling more stable supply of high-quality electricity, It is advantageous in that the facility can be made more efficient and operation cost can be reduced.

Particularly, the most important role in such a smart grid is small cogeneration power generation and renewable energy source as distributed power sources. However, production of electricity using renewable energy has a problem that it takes too much investment cost compared with the production amount. In addition, it has been difficult to develop new generation renewable energy as a distributed generation power generation system because it is difficult to produce electricity at an appropriate peak load time.

Therefore, when the small-sized cogeneration system is used, it is possible to generate electricity at the peak load time, stop the operation at a low-load time, and generate and supply electric power at a desired time.

As a result, a technique for connecting a distributed power source to a power distribution system of a small cogeneration power plant is emerging. However, because distributed power sources (especially inverter-interfaced DGs) are very different from those of conventional generators, it is important to consider the operating characteristics of the distributed power source.

In particular, among the operating characteristics of the distributed power source, the power algae calculation can easily grasp the characteristics of the distributed power source by calculating the power algae which determines the distribution of voltage and current power at each point of the power distribution system.

However, since the operation conditions of the power distribution system are basically unbalanced, it is difficult to stabilize the power distribution system connected with the distributed power supply because the phases of the distributed power supply are different according to the phase voltage in the unbalanced operation condition.

In order to solve the problems of the prior art as described above, it is an object of the present invention to prevent the phase of the distributed power source from varying even under unbalanced operating conditions, Method and system.

According to another aspect of the present invention, there is provided a method for calculating a flow rate of a power distribution system according to an embodiment of the present invention, comprising: determining a type of a distributed power generation based on an output filter; Calculating a phase current output by the phase current calculation unit in a steady state of the distributed power supply; And a tidal current calculation unit calculating an electric power tidal current of the distributed power source based on the phase current; .

More preferably, the distributed power modeling unit that determines the type of the distributed power source based on the topology of the output filter may include a step of determining the type of the distributed power source.

In particular, it may include an output filter including at least one of an L filter, an LC filter, and an LCL filter.

More preferably, when the output filter is an L filter, the phase current calculation unit calculating the grid current may include calculating a phase current.

More preferably, when the output filter is an LC filter or an LCL filter, the phase current calculation unit may calculate the phase current to calculate the voltage source current or the grid current.

Determining a type of a bus connected to the distributed power supply; Calculating a reactive power of the load bus among the determined buses; Determining a current mismatch or a voltage mismatch of a bus line connected to the distributed power source; And calculating a Jacobian matrix between the vector for the voltage mismatch and the vector for the reactive power, and calculating a power algae of the distributed power source.

According to an aspect of the present invention, there is provided a system for calculating an algae flow in a power distribution system according to an embodiment of the present invention includes a distributed power modeling unit for determining a type of a distributed generation based on an output filter; A phase current calculator calculating a phase current output from the steady state of the distributed power source; And a tidal current calculator for calculating a tidal current of the distributed power source based on the phase current.

In particular, it may include an output filter including at least one of an L filter, an LC filter, and an LCL filter.

In particular, the bus line connected to the distributed power source may be a load bus line or a PV bus line.

The method and system for calculating the algae flow of the power distribution system according to the present invention can accurately determine the distribution of the voltage and the current power at the point where the distributed power sources of the power distribution system are connected to each other to stabilize the power distribution system There is an effect that can be.

Further, the method and system for calculating the flow rate of the power distribution system according to the present invention can prevent the phase of the distributed power source from varying even under unbalanced operating conditions of the power distribution system.

1 is a block diagram of a distribution system algae calculation system according to an embodiment of the present invention.
2 is a power control block diagram of a distributed power supply according to vector control.
3 is a table showing the types of distributed power sources.
Fig. 4 is a diagram showing a radial system in which three distributed power sources are connected and a Jacobian matrix structure therefor. Fig.
5 is a graph showing voltage vectors and current vectors.
6 is a diagram illustrating a bus determination process.
7 shows an IEEE 13-bus system.
8 is a table summarizing variable values of the distributed power source.
9 is a graph showing the values of active power and reactive power measured on each phase measured by PSCAD.
10 is a graph showing the maximum value of voltage magnitude and phase angle difference.
11 is a graph comparing the PSCAD model with the tidal current calculation using the dispersion voltage.
12 is a graph comparing the PSCAD model with the tidal current calculation using the dispersion voltage.
13 is a graph showing values obtained by measuring the reference voltage, the steady voltage, and the voltage of each phase in the PSCAD model.
14 is a table showing major parameters of the distributed power source.
15 is a graph showing the number of iterations of three cases according to the number of distributed power sources.
16 is a graph showing the number of repetitive operations in three cases according to the number of distributed power sources.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Hereinafter, the present invention will be described in detail with reference to preferred embodiments and accompanying drawings, which will be easily understood by those skilled in the art. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

Hereinafter, a tidal current calculation system of a power distribution system according to the present invention will be described in detail with reference to FIG.

1 is a block diagram of a distribution system algae calculation system according to an embodiment of the present invention.

1, the distribution system algae calculation system 100 according to the present invention includes a distributed power modeling unit 120, a phase current calculation unit 140, and a tidal current calculation unit 160 .

The distributed power modeling unit 120 determines the type of the distributed power generation based on the output filter. The output filter may include at least one of an L filter, an LC filter, and an LCL filter. Further, a bus line connected to the distributed power source may be a load bus line or a PV bus line.

The phase current calculation unit 140 calculates a phase current output from the steady state of the distributed power source.

The algae calculation unit 160 calculates the power algae of the distributed power supply based on the phase current.

Hereinafter, the method of calculating the algae of the distribution system according to the distributed power supply connection will be described in detail.

First, the distributed power modeling unit determines the type of the distributed power supply based on the output filter. In particular, based on the topology of the output filter including at least one of the L filter, the LC filter, and the LCL filter, It can be judged.

The phase current calculation unit calculates the phase current output from the steady state of the distributed power source. In particular, when the output filter is an L filter, the phase current calculation unit can calculate the grid current. Or the voltage source current or the grid current when the output filter is an LC filter or an LCL filter.

Then, the algae calculation unit calculates the power algae of the distributed power supply based on the phase current. The details of the calculation of the tidal current of the distributed power source are as follows. First, the type of the bus connected to the distributed power source is determined, and the reactive power of the load bus among the determined buses is calculated. Next, a current mismatch or a voltage mismatch of a bus line connected to the distributed power source is determined, and a Jacobian matrix between the vector for the voltage mismatch and the vector for the reactive power is calculated.

Hereinafter, a detailed description will be made of a system and method for calculating a tidal current of a power distribution system according to the present invention.

Since the vector controlled distributed power source controls the three-phase output rather than the single-phase output, the a-b-c phase output should be modeled to represent the distributed power source in the TCIM algae calculation. Thus, distributed power supplies are classified into three types according to the topology of the output filter and current control point. The steady state phase current output equation can be expressed according to each kind.

The vector control method is widely used to control the output of the distributed power source in which the VSC is used, since the active power and the reactive power can be independently controlled.

2 is a power control block diagram of a distributed power supply according to vector control.

As shown in FIG. 2 (a), three-phase active power and reactive power reference values are used to calculate the reference values of the d and q-axis currents, and as a further option, the dc link voltage is used for active power control, The three-phase ac voltage is used for reactive power control.

Through Figure 2 (b), three different distributed power modes determined by the topology of the output filter can be identified.

)를 제어한다. 반면에 LC나 LCL 필터[20,22,23]가 있는 분산전원에서는 VSC 출력전류(

)나

가 제어 변수로 사용된다.As shown in FIG. 2 (b), in the distributed power supply having the L filter, the current controller controls the grid current

). On the other hand, in a distributed power supply with an LC or LCL filter [20,22,23], the VSC output current

)I

Is used as a control variable.

In steady state, the a-b-c phase current at the current control point is in a balanced state since the d-axis and q-axis currents are maintained at the values specified by the controller. Thus, the steady-state output of the distributed power supply can be modeled as a three-phase balanced current source (BTCS).

3 is a table showing the types of distributed power sources.

As shown in FIG. 3, three types of steady state distributed power (DG) models can be identified according to the topology of the output filter and the current to be controlled. The current output model of the Type 3 distributed power source (DG) is obtained first because the steady-state current output formula of the Type 1, 2 distributed power source (DG) can be obtained by modifying the formula of the Type 3 distributed power source (DG) model.

The phase current output of the BTCS is expressed by the following equations (1) to (3).

|과 θ는 각각 a상의 전류 페이저의 크기와 위상각을 나타낸다. 도 3에 도시된 등가회로(equivalent circuit)로부터, 모선 k에 연결된 type 3 분산전원(DG)의 s상 출력 전류는 하기의 수학식 4와 같이 표현될 수 있다.|

| And? Represent the magnitude and phase angle of the current phasor on a phase, respectively. From the equivalent circuit shown in FIG. 3, the s-phase output current of the type 3 distributed power supply (DG) connected to the bus k can be expressed by the following equation (4).

는 모선 k에서 s상의 전압이고,

와

는 출력필터의 등가저항과 리액턴스이며, 하기의 수학식 5 내지 6과 같이 나타낼 수 있다. here

Is the voltage of s on the bus k,

Wow

Is the equivalent resistance and reactance of the output filter, and can be expressed by the following equations (5) to (6).

The three-phase complex power output of the distributed power supply is equal to the power sum of each phase as shown in Equation (7) below.

The superscript * denotes the complex conjugate. The three-phase complex power output is obtained by substituting the equations (1) to (3) into the equation (4) and substituting the equations (1) to (3) into the equation (7) 8).

는 positive sequence 전압을 나타내며, 하기의 수학식 9와 같이 정의된다. here

Represents a positive sequence voltage, and is defined by Equation (9).

Then, the above equation (8) is rearranged to calculate the current output at the phase a of the BTCS by the following equation (10).

Finally, the phase current output can be expressed as a function of the three-phase active power, the reactive power, the phase voltage, and the impedance of the output filter, and substituting the above equation (10) into equations (1) Substituting Equations (1) to (3) into Equation (4), Equation (11) to Equation (13) can be given.

가

와 같고

가

와 같다는 것만 제외하고는 상기 수학식 (11) 내지 (13)과 그 형태가 같다.In Type 1 distributed voltage divider (DG), only the first term of equations (11) to (13) is used because there is no parallel or series impedance. That is, the Type 1 distributed power source (DG) flows the three-phase balanced current even when the voltage is unbalanced. The current output equation of Type 2 distributed power (DG)

end

And

end

(11) to (13), except that they are the same as the above equations (11) to (13).

In addition, the bus line to which the distributed power source is connected in the algae calculation process can be modeled as a load bus (PQ bus line) or PV bus line according to the reactive power control mode of the distributed power source. However, unlike the existing bus model, given values are three - phase values. The three-phase active power and the reactive power of the PQ bus, the three-phase active power of the PV bus and the positive-sequence voltage are used to calculate the algae calculation of the distribution system according to the distributed power supply linkage.

We first describe the algebraic computation of Type 2 and 3 Distributed Power (DG) models (which have the same phase current output equations), followed by a modified algebraic computation method for the Type 1 distributed power (DG) model .

The current discrepancy equation on the s-axis of the k bus represented by the rectangular coordinate system in consideration of the phase current output of the distributed power supply is defined by the following equations (14) to (15).

The last term of the above equations (14) to (15) is newly introduced to express the current injection of the distributed power source and is calculated from the following equations (16) to (24)

Also, to represent the PV bus, a three-phase voltage mismatch equation must be defined. Since the distributed power supply generally controls the magnitude of the positive-sequence voltage, the voltage mismatch equation at bus k is defined as: < RTI ID = 0.0 >

는 positive-sequence 전압 크기의 레퍼런스 값을 나타낸다; 그리고 |

|는 조류계산으로 얻은 positive-sequence 전압의 크기이다:here

Represents the reference value of the positive-sequence voltage magnitude; And |

| Is the magnitude of the positive-sequence voltage obtained by the algae calculation:

For algae calculation, it is important to find the voltage that makes the mismatch values defined in equations (14) to (15) and (25) above zero.

)와 전압 벡터(

)는 하기의 수학식 27 내지 28과 같이 정의된다. In order to solve this algae calculation by the Newton-Raphson method, a current discrepancy vector (Δ

) And the voltage vector (

) Is defined by the following equations (27) to (28).

In particular, because bus 1 is considered to be the reference bus, the current mismatch and voltage on bus 1 are not included in equations 27 through 28 above. At this time, the order of the real part and the imaginary part changes in the current discrepancy vector and the voltage vector.

)와 삼상 무효전력 벡터(

)는 하기의 수학식 29 내지 30과 같이 정의된다.Thus, the three-phase reactive power vector is introduced to represent the PV bus, and the three-phase voltage mismatch vector

) And the three-phase reactive power vector (

) Are defined as shown in the following equations (29) to (30).

과

는 불일치 벡터 Δ

와 Δ

를 이용해서 하기의 수학식 31과 같이 업데이트된다:Through the h-th iteration of the Newton-Raphson method, the state variable vector

and

Lt; RTI ID = 0.0 > Δ

And?

Lt; RTI ID = 0.0 > (31) < / RTI &

는 야코비안 행렬을 나타낸다. 이러한 야코비안 행렬은 상태변수 벡터와 불일치 벡터 사이의 민감도 행렬을 말한다. At this time,

Represents a Jacobian matrix. These Jacobian matrices refer to the sensitivity matrix between the state variable vector and the mismatch vector.

The Jacobian matrix is divided into parts as shown in Equation (32) below:

Since there is no bi-function equation between the three-phase voltage mismatch and the three-phase reactive power, the corresponding sub-matrix is calculated by the chain law as shown in Equation 33 below.

However, if the submatrix obtained from equation (33) is used, the Jacobian matrix does not have a full rank and, as a result, does not have an inverse matrix. In order to prevent this problem from occurring in advance, the submatrix is replaced with a zero matrix as described in equation (32) above.

Fig. 4 is a diagram showing a radial system in which three distributed power sources are connected and a Jacobian matrix structure therefor. Fig.

과

은 24

1 열벡터이다. 두 개의 분산전원(DG 1과 DG 3)이 전압 제어 모드로 동작하기 때문에,

와 Δ

는 2

1 열벡터이다. 따라서 야코비안 행렬은 26

26행렬이 된다. As shown in Fig. 4, since there are four bus bars (excluding the reference bus line), and each bus line has six terms including a current discrepancy and a voltage expressed in Cartesian coordinates,

and

Is 24

It is a one column vector. Since the two distributed power supplies (DG 1 and DG 3) operate in the voltage control mode,

And?

2

It is a one column vector. Therefore, the Jacobian procession is 26

26 matrix.

6행렬, 6

1 열벡터, 1

6 행벡터이다. 분산전원의 삼상 무효전력은 오직 분산전원이 연결된 모선의 전류 불일치에 의해서만 영향을 받으므로,

과

는 0이 아닌 값을 가지고,

의 다른 벡터들은 0벡터가 된다. 이와 유사하게,

과

는

에서 유일한 0이 아닌 벡터들이다.In the Jacobian matrix, A, B, and C partial matrices are 6

6 matrix, 6

1 column vector, 1

It is the 6th row. Since the three-phase reactive power of the distributed power source is affected only by the current mismatch of the bus line to which the distributed power source is connected,

and

Has a non-zero value,

The other vectors are 0 vectors. Similarly,

and

The

Are the only non-zero vectors in.

The elements of the matrix A can be calculated by partially differentiating the above equations (14) to (15) in terms of a rectangular voltage. To compute the elements of the non-diagonal blocks, these elements are not related to the current output of the distributed power supply (DG), so that the original TCIM equation (12) can be used without modification. On the other hand, the elements of the diagonal block should be corrected as shown in Equation 34 below.

A _{kk , 0} is the same matrix as in equation (13), A _{kk , DG} is the partial derivative of the current result value of the distributed power source (DG).

A _{kk and DG} can be obtained by partial differentiation of the equations (16) to (21) to obtain the following equations (36) to (44).

The non-zero elements of the partial matrix B of the K-th bus can be obtained by a partial differentiation of the equations (14) to (15) in terms of three-phase reactive power.

Similarly, the partial matrix C can be expressed by the following equation (46).

In general, the reactive power limit of a vector-controlled distributed power supply (DG) can be represented by the q-axis current limit, not the result of three-phase reactive power.

5 is a graph showing the current vector of the BTCS and the voltage vector of the bus connected to the DG.

As described above, the three-phase voltage is generally not in an equilibrium state while the current is in an equilibrium state. Accordingly, the phase angle difference? Between the voltage and the current continuously changes. In the algae calculation process, the average value of [theta] _av can be expressed by the following equation (47). The phase angle of the voltage uses the phase angle of the positive-sequence voltage and the average of the negative and zero-sequence is zero.

Since the current result of BTCS is in equilibrium state, the magnitude of the current vector (| i_BTCS |) is equal to the peak value of the three-phase current. Therefore, for the d-axis and the q-axis, i_BTCS is expressed by? _Av as shown in the following equations (48) to (49).

As shown in FIG. 5, when the current value of the q-axis converges to a specific value i_ _{(q, limit)} , the limit value (| i_ (BTCS, limit) |) of the current vector and the resulting phase angle The change? Is obtained by the following equations (50) to (51).

At this time, since the current is still in equilibrium, the change of the phase angle of the current phasor is also?. Therefore, the current phasor on a is expressed as: " (52) "

By comparing Equation (8) and Equation (52), the reactive power result value of the distributed power source (DG) in the limit current state of the q axis can be expressed by the following equation (53).

If the reactive power of the distributed power source (DG) in the voltage control mode is not limited, the bus connected to the distributed power source (DG) can be modeled as a PV bus.

However, if the q-axis current is limited, the bus should be modeled as a PQ bus. However, at this time, the resultant value of the reactive power is calculated not by the constant but by the equation (53).

Modeling with a PQ bus rather than a PV bus is determined via i_ (BTCS, q) computed via Equation 49 and? V ⁺ _k computed via Equation 25, as shown in FIG. In order to prevent instability where the modeling of the bus frequently changes, modeling of the bus requires that the change condition be repeated more than once in the code. Referring to FIG. 5, it can be seen that negative q-axis current has a negative value. Therefore, when i_ (q, limit) = i_ (q, min), the maximum reactive power can be obtained on the bus connected to the distributed power source DG. Therefore, when V ⁺ _k > 0, the bus is modeled as a PV bus. The opposite holds when i_ (q, limit) = i_ (q, max).

The above-described algae calculation process is briefly summarized as follows.

First, as shown in FIG. 6, it is determined to which bus the bus connected to the distributed power source DG is modeled. Subsequently, the reactive power of the PQ bus is calculated using Expression (53).

Then, using Equations (14) to (15) and (25), the degree of inconsistency between the current and the voltage is calculated.

It is determined whether or not the absolute value of the difference between all the values is acceptable, and then the convergence is determined and the Jacobian matrix is calculated.

Then, the value of the variable is changed using the equation (31), and again the process of determining to which bus the bus connected to the distributed power source (DG) is modeled is re-executed.

In the case of the Type 1 distributed power source (DG), the second term of the above Equations (16) to (21) is removed.

Then, the values of? _{K in} Equations (16) to (21) and (37) to (42) are set to zero.

Subsequently, the last two matrices of equation (36) are removed and equation (53) is modified.

In order to determine the accuracy of these algae calculation methods, a case study was conducted using MATLAB. All errors are less than 1.0 * 10 ^-6 pu, and the base value of the system is 100 kVA. The most complex Type 3 distributed power source (DG) among the three distributed power sources is used.

The accuracy of the algae calculation method according to the present invention can be determined by comparing the result of the algae calculation with the result of the model of the PSCAD.

7 shows an IEEE 13-bus system in which a bus connected to a distributed power source (DG) is connected to a bus 680 through a transformer. 8 is a table summarizing the variable values of the distributed power source.

As shown in Figs. 7 to 8, the distributed power source DG can supply the reactive power between -500 kVAr and 600 kVAr. In the PSCAD model, the distributed power supply (DG) is a three-wire two-level VSC using IGBT switches. In the switch control part, the SPWN (Sinusoidal Pulse Width Modulation) method was used, and the simulation was performed in 1 μs in one step.

In this simulation, the distributed power supply (DG) can control both active power and reactive power. We tested the results of five active powers (200kW, 400kW, 600kW, 800kW, 1000kW) with power factor of 1.

9 is a graph showing the values of active power and reactive power measured on each phase measured by PSCAD.

As shown in FIG. 9, in each case, the resultant value of the effective power is different for each phase, because the state of the bus and the load of the system do not form an equilibrium state. In addition, even if the reactive power is 0, it is because the reactive power is consumed in another phase if the reactive power is supplied in one phase. The difference between the effective power values becomes larger as the value of the active power output from the distributed power source DG becomes larger. For example, when the value of the active power is 1000kW, the difference between the active power and the reactive power is 22.16 kW and 18.81 kVAr, respectively.

The result of the calculation method of the distribution system according to the distributed power supply according to the present invention is almost the same as the simulation result through the PSCAD. The power difference between the two models is less than 0.13 kVA.

10 is a graph showing the maximum value of voltage magnitude and phase angle difference.

As shown in FIG. 10, the maximum values of the magnitude of the voltage and the difference in phase angle are 2.0 * 10 ^-5 pu (0.002%) and 0.023 degrees, respectively.

In all cases, the algae calculation converged into five iterations. This number of iterations is equal to the number of operations required for the original system. That is, the inclusion of the distributed power supply DG means that the number of repetitive operations is not affected.

11 is a graph comparing the PSCAD model with the tidal current calculation using the dispersion voltage.

As shown in Fig. 11, the maximum value of the difference between the voltage and the phase angle of one phase is 2.7 * 10 ^-3 pu (0.27%) and 0.112 degrees, respectively.

In the case of using the simple distributed power (DG) model shown in Fig. 12, a larger value is obtained in the case of a and c phases than in the case of PSCAD. Considering these points, it can be seen that the algae calculation method according to the present invention produces more accurate results in an unbalanced state.

In this simulation, the distributed power supply (DG) controls the normal voltage of bus 681 rather than the output value of reactive power. The three-phase active power of the distributed power supply (DG) is set to 400kW, and different voltage references (0.98pu, 1.01pu, 1.04pu) are applied to each phase.

13 is a graph showing values obtained by measuring the reference voltage, the steady voltage, and the voltage of each phase in the PSCAD model.

As shown in Fig. 13, since the operating states are not balanced, the magnitude of the voltage of each phase is noticeably different. In the second case (reference voltage = 1.01 pu), the distributed power supply (DG) can control the voltage of bus 681 within the reference voltage, while in the other two cases the voltage is controlled within the reference voltage due to the q- I could not. In the first case (reference voltage = 0.98 pu), the q-axis current reached the upper limit, and the three-phase reactive power was -497 kVAr and the steady voltage was 0.991 pu. On the other hand, in the third case (reference voltage = 1.04pu), the q-axis current reached the lower limit and the reactive power of three phases was 626kVAr and the steady voltage was 1.036pu.

The result of the algae calculation according to the present invention almost coincides with the simulation result of the PSCAD model. The maximum value of the difference of the three-phase reactive power according to the two methods is 0.25 kVAr, which corresponds to 0.05% of the reactive power limit. The difference in voltage magnitude is also very small.

As shown in FIG. 13 (b), the voltage magnitude difference between the two methods is at most 3.0 * 10 ^-5 pu. In the first case, 6 iterations were performed, and in the remaining cases, 5 iterations were performed.

Also, the IEEE 123-bus test system was used to investigate the effect of the number of distributed power sources (DG) on the convergence speed in the algae calculation method according to the present invention. The number of iterations was measured by repeatedly solving the algae calculations while adding the number of distributed power sources (DG) to the bus one by one. It is assumed that when the distributed power supply (DG) is connected to the bus, it is connected to a 150kVA 4.16 / 0.69kV transformer and a 60kW generator.

At this time, the main parameters of the distributed power source (DG) are summarized in FIG. To analyze the influence of the operating mode and the current limit on the convergence speed, the following three cases are simulated.

Case 1: All distributed power supplies (DG) operate in a mode to control reactive power. The reference value of the reactive power is 0 kVar. The bus connected to the distributed power supply (DG) was modeled as a PQ bus.

Case 2: It operates in a mode to control the voltage of all distributed power sources (DG). The value of the reference voltage is 1.03pu. The current limit of the q-axis is not applicable. Therefore, the bus connected to the DG is always modeled as a PV bus.

Case 3: The value of the operation mode and the reference voltage is the same as the case of No. 2. However, the q-axis current limit is included. Therefore, it can be modeled as PV bus or PQ bus due to the error of current and voltage of q axis.

15 is a graph showing the number of iterations of three cases according to the number of distributed power sources.

As shown in FIG. 15, since there is no current limit in the case of No. 1 and No. 2, convergence occurs in a maximum of 6 iterations regardless of the number of distributed power sources DG. For example, adding 62 DGs means that only one iteration is added. In the case of No. 3, the average number of iterations is 7.8. The maximum number of iterations is 11 when 51 DGs are connected.

In this case, as shown in FIG. 16, it can be seen that the convergence speed does not decrease significantly when the number of distributed power sources DG is large even in the case of No. 3.

Also, the method and system for calculating the algae flow in the distribution system according to such distributed power supply connection can be stored in a computer-readable recording medium on which a program for executing by a computer is recorded. At this time, the computer-readable recording medium includes all kinds of recording apparatuses in which data that can be read by a computer system is stored. Examples of the computer readable recording medium include ROM, RAM, CD-ROM, DVD 占 ROM, DVD-RAM, magnetic tape, floppy disk, hard disk, optical data storage, and the like. In addition, the computer-readable recording medium may be distributed to network-connected computer devices so that computer-readable codes can be stored and executed in a distributed manner.

The method and system for calculating the algae flow of the power distribution system according to the present invention can accurately determine the distribution of the voltage and the current power at the point where the distributed power sources of the power distribution system are connected to each other to stabilize the power distribution system There is an effect that can be.

Further, the method and system for calculating the flow rate of the power distribution system according to the present invention can prevent the phase of the distributed power source from varying even under unbalanced operating conditions of the power distribution system.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, Do.

120: Distributed power modeling unit 140: Phase current calculation unit
160: Bird Calculation Section

Claims (10)

Determining a type of a distributed power generation based on a topology of the distributed power modeling unit output filter;
Calculating a phase current output by the phase current calculation unit in a steady state of the distributed power supply; And
Calculating a power algae of the distributed power source based on the phase current;
Wherein the method further comprises the steps of:
delete The method according to claim 1,
The output filter
L filter, an LC filter, and an LCL filter.
The method of claim 3,
The step of calculating the phase current calculating section phase current
And when the output filter is an L filter, the grid current is calculated.
The method of claim 3,
The step of calculating the phase current calculating section phase current
Wherein when the output filter is an LC filter or an LCL filter, a voltage source current or a grid current is calculated.
The method according to claim 1,
Wherein the step of calculating the power algae of the distributed power source
Determining a type of a bus connected to the distributed power supply;
Calculating a reactive power of the load bus among the determined buses;
Determining a current mismatch or a voltage mismatch of a bus line connected to the distributed power source; And
Calculating a Jacobian matrix between the vector for the voltage mismatch and the vector for the reactive power;
Wherein the distributed power supply is connected to the distribution system.
A computer-readable recording medium having recorded thereon a program for executing a method according to any one of claims 1 and 6 to a computer.
A distributed power supply modeling unit for determining a type of a distributed power supply based on a topology of the output filter;
A phase current calculator calculating a phase current output from the steady state of the distributed power source; And
A tidal current calculation unit for calculating a tidal current of the distributed power source based on the phase current;
Wherein the distribution system comprises:
9. The method of claim 8,
The output filter
L filter, an LC filter, and an LCL filter.
9. The method of claim 8,
And a bus line connected to the distributed power source is composed of a load bus line or a PV bus line.

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