Control device and control method for a DC power transmission system

Abstract

To suppress a frequency change rate of an accident occurrence system compatibly with preventing an accident wave propagation to a sound-side system in pseudo inertia control by a DC power transmission system.SOLUTION: In a control device for a DC power transmission system, two or more DC systems cooperate via an AC / DC converter. The control device comprises: a normal-time control unit by which, when a frequency change of the AC system is within a predetermined value, a valid power command value is generated and outputted to the AC / DC converter so as to cancel the frequency change; and an emergency-time control unit by which, when the frequency change of the AC system is equal to or more than the predetermined value, the valid power command value is generated and outputted to the AC / DC converter in a direction of eliminating the frequency change. In the control device for the DC power transmission system, the emergency-time control unit includes system inertia correction means which corrects the valid power command value in response to variations in system inertia of the AC system.SELECTED DRAWING: Figure 1

Description

Technical Field

[0006]

[0001] The present invention relates to a control device and a control method for a DC power transmission system that suppresses frequency fluctuations occurring due to a system accident.

Background Art

[0002] Many renewable energy power sources such as solar power generation devices and wind power generation are connected to the power grid via an inverter. An inverter is a static electrical device using power semiconductor devices that converts DC power into AC power.

[0003] On the other hand, conventional power sources such as thermal power generation and nuclear power generation are connected to the power grid using a synchronous generator. When connected using a synchronous generator, it has the effect of suppressing fluctuations in the system frequency due to the inertial force of the rotating body, but when connected via an inverter, this effect does not exist.

[0004] With the increasing introduction and expansion of renewable energy power sources, when the connection ratio of conventional power sources decreases and accidents such as power source disconnection or system separation occur, the system frequency may fluctuate significantly. In particular, due to the decrease in inertial force, the rate of change of frequency per unit time (RoCoF: Rate of Change of Frequency) tends to increase.

[0005] Therefore, a technique for achieving system stabilization by giving the inverter a pseudo-inertial force to supply or absorb instantaneous active power is known as pseudo-inertial control. Usually, for the implementation of pseudo-inertial control, a power storage device for supplying or absorbing energy is required to be installed together with the inverter. Hereinafter, the instantaneous adjustment force within 2 seconds that can be provided by pseudo-inertial control is defined as the fast frequency response (FFR).

[0006] On the other hand, with the promotion of renewable energy sources, it is expected that the use of DC transmission for long-distance power transmission from suitable renewable energy sites to demand centers will increase in the future. In particular, DC transmission systems using self-commutated converters enable high-speed control of active and reactive power. Furthermore, when pseudo-inertia control is implemented using a DC transmission system during a grid fault, the healthy side of the DC-connected grid can be used as an energy source. Due to these characteristics, the supply of instantaneous adjustment power through pseudo-inertia control utilizing DC transmission systems is expected in the future.

[0007] Conventional emergency frequency control functions in DC power transmission systems include emergency AFC (Auto Frequency Control) and EPPS (Emergency Power Presetting Switch). These functions control the power flow in the interconnection line to maintain the balance between supply and demand when a power source or load is lost in one of two DC interconnected systems via a power converter, causing the frequency to deviate from a specified range.

[0008] For example, Patent Document 1 describes a DC interconnection frequency control device that, when an accident occurs in one of the DC interconnected systems and emergency automatic frequency control is implemented to suppress frequency fluctuations, corrects the emergency power adjustment sensitivity in advance according to load fluctuations, thereby realizing an emergency power supply that matches the system capacity. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 6-54450 [Overview of the project] [Problems that the invention aims to solve]

[0010] Conventional emergency frequency control functions in DC power transmission systems aim to suppress the frequency deviation Δf of the fault-affected system, thus limiting the RoCoF (Road of Cost of Frequency) reduction effect. Therefore, implementing pseudo-inertia control as an emergency frequency control method for DC power transmission systems is being considered.

[0011] However, in situations where both systems connected by a DC transmission system have low inertia, if an accident such as a power outage or system separation occurs in one system and the DC transmission system implements pseudo-inertia control, the RoCoF of the healthy system may rise, potentially leading to accident propagation.

[0012] As described in Patent Document 1 above, by correcting the emergency power adjustment sensitivity considering the grid capacity, maximum emergency power flow control is achieved within a range that does not cause large frequency fluctuations in the healthy grid. Therefore, the emergency power adjustment sensitivity is set higher during the daytime when the power load capacity is large compared to the nighttime when the power load capacity is small.

[0013] However, during the daytime when the power load capacity is large, and renewable energy sources such as solar power generation generate a lot of electricity, and grid inertia is low, if the emergency power adjustment sensitivity is high, the fault may spread to the healthy side of the grid. Thus, Patent Document 1 does not mention the effect of grid inertia.

[0014] The present invention has been made in view of the above, and aims to achieve both suppression of the frequency change rate of the fault-causing system and prevention of the fault spreading to the healthy system in pseudo-inertia control using a DC power transmission system. [Means for solving the problem]

[0015] Based on the above, the present invention is defined as "a control device for a DC power transmission system in which two or more AC systems are connected via an AC / DC converter, wherein the control device comprises a normal operation control unit that generates an active power command value to cancel out the frequency change when the frequency change of the AC system is within a predetermined value and outputs it to the AC / DC converter, and an emergency operation control unit that generates an active power command value in a direction to eliminate the frequency change when the frequency change of the AC system is greater than or equal to a predetermined value and outputs it to the AC / DC converter, and the emergency operation control unit comprises a system inertia correction means that corrects the active power command value in accordance with fluctuations in the system inertia of the AC system."

[0016] Furthermore, the present invention is defined as "a control method for a DC power transmission system in which two or more AC systems are interconnected via an AC / DC converter, characterized in that when the frequency change of the AC system is within a predetermined value, an active power command value is generated to cancel out the frequency change and the AC / DC converter is controlled; when the frequency change of each of the AC systems is greater than or equal to a predetermined value, an active power command value is generated in a direction to eliminate the frequency change and the AC / DC converter is controlled; and the active power command value is corrected in accordance with the fluctuations in the system inertia of each of the AC systems." [Effects of the Invention]

[0017] According to the present invention, by correcting the effective power command value in emergencies using pseudo-inertia control according to the grid inertia, it is possible to supply the maximum amount of pseudo-inertia within a range that does not cause large frequency fluctuations in the healthy grid. Furthermore, by realizing pseudo-inertia control using a DC power transmission system, the cost of countermeasures using other inverter power supplies and grid stabilization equipment can be reduced. [Brief explanation of the drawing]

[0018] [Figure 1] A diagram showing an example of the overall configuration of a DC power transmission system according to Embodiment 1 of the present invention. [Figure 2] A diagram showing the state of switch 50 when emergency control is performed. [Figure 3] A diagram showing an example configuration of the frequency calculation unit. [Figure 4] Figure showing a configuration example of the frequency calculation unit. [Figure 5] Figure showing an example of the processing flow of the control input calculation unit. [Figure 6] Figure showing an example of the variation pattern of system inertia. [Figure 7] Figure showing a configuration example of the emergency control unit in Example 2. [Figure 8] Figure showing an example of the variation pattern of the upper and lower limit limiter in Example 2.

Mode for Carrying Out the Invention

[0019] Hereinafter, a DC power transmission control device and a control method according to an embodiment of the present invention will be described with reference to the drawings.

Example

[0020] FIG. 1 is a diagram showing an overall configuration example of a DC power transmission system according to Embodiment 1 of the present invention, and describes the configuration of a power system and its control device 10. In this embodiment, when there are a plurality of devices and members having the same configuration, the same numbers are assigned to them. Also, for example, it is distinguished that the symbol A is a facility on the power system GA side and the symbol B is a facility on the power system GB side. <00th>

[0021]

[0022] The power converters 41A and 41B in each AC system are self-commutated power converters that convert AC power to DC power, or DC power to AC power, and transmit power. Power converter 41A is controlled by control terminal 42A, and power converter 41B is controlled by control terminal 42B. Power converter 41A is connected to power system GA by transformer 3A, and power converter 41B is connected to power system GB by transformer 3B.

[0023] The DC line 6 connects the DC side of power converter 41A and the DC side of power converter 41B. The power converters may be connected at close range, or they may be connected via DC reactors, overhead transmission lines, or transmission cables.

[0024] With this configuration, power is transmitted from power grid GA to power grid GB, or from power grid GB to power grid GA, via the DC power transmission system 40.

[0025] The DC power transmission system 40 described above is controlled by the control system 10. The control system 10 shown in Example 1 receives the frequencies of the respective AC systems detected by voltage detectors 5A and 5B installed at the terminals of the DC-connected power systems GA and GB.

[0026] The control system 10, which receives the frequency input, includes a normal operation control unit 20 that functions to stably control the frequency when the power system is operating normally, an emergency operation control unit 30 that stably controls the frequency when the power system is operating abnormally due to an accident or the like, and a switch 50 that switches between these control units 20 and 30. Control signals from these control units 20 and 30 are output to the control terminals 42A and 42B of the DC power transmission system 40 via the switch 50, and control the power converters 41A and 41B.

[0027] The present invention is particularly characterized by the control of the emergency control unit 20. When the deviation of the frequency or frequency change rate in each AC system (hereinafter collectively referred to simply as the frequency change) exceeds a predetermined value, the emergency control unit 20 outputs an emergency active power command value obtained by multiplying the deviation by a pseudo-inertia coefficient to the control terminals 42A and 42B of the DC power transmission system 40. Note that the switch 50 shown in Figure 1 is in the "0" position, indicating that normal operation by the normal control unit 30 has been selected.

[0028] To explain the detailed operation of these control units 20 and 30, first, the normal operation control unit 20 includes a calculation unit 31, a subtraction unit 33, and a limiter 32. In normal operation, the normal operation control unit 20 calculates the deviation Δf1 obtained by subtracting the reference frequency f1nom (for example, the commercial frequency of 60 Hz) from the frequency f1 of the power system GA, and the deviation Δf2 obtained by subtracting the reference frequency f2nom from the frequency f2 of the power system GB. The subtraction unit 33 calculates the value obtained by subtracting the deviation Δf2 from the deviation Δf1 and inputs it to the calculation unit 31.

[0029] The frequency f1 of power system GA is detected based on the output information of voltage detector 5A, which detects the voltage at the connection point with AC bus 4A. Similarly, the frequency f2 of power system GB is detected based on the output information of voltage detector 5B, which detects the voltage at the connection point with AC bus 4B.

[0030] The calculation unit 31 generates a normal operating active power command value ΔP such that the value obtained by subtracting the deviation Δf2 from the deviation Δf1 (Δf1-Δf2) is small. The calculation unit 31 is composed of a combination of a PI controller and an integrator. The limiter 32 restricts the normal operating active power command value ΔP output by the calculation unit 31 so that it does not exceed a limit value determined by a preset normal frequency adjustment capacitance.

[0031] Figure 2 shows the state of switch 50 when emergency control is performed. In Figure 2, switch 50 is in the "1" position, indicating that emergency operation by the emergency control unit 20 has been selected.

[0032] In Figure 1, the emergency control unit 20 includes, for example, a frequency calculation unit 21A, a frequency calculation unit 21B, a control input calculation unit 22, a proportional control unit 23A, a proportional control unit 23B, a system inertia correction unit 24A, a system inertia correction unit 24B, and an adder 25. The outputs of the system inertia correction unit 24A and the system inertia correction unit 24B are added in the adder 25 to obtain the final output of the emergency control unit 20. However, since only one of these outputs is output, in reality, either the output of the system inertia correction unit 24A or 24B will be provided to the control terminals 42A and 42B.

[0033] The frequency calculation unit 21A calculates the frequency change (deviation or rate of change) of the system frequency f1 of power system GA based on, for example, the voltage frequency f1 of AC bus 4A. Similarly, the frequency calculation unit 21B calculates the frequency change (deviation or rate of change) of the system frequency f2 of power system GB based on, for example, the voltage frequency f2 of AC bus 4B.

[0034] Here, an example of the configuration of the frequency calculation unit 21A and frequency calculation unit 21B is shown in Figures 3 and 4. In Figure 3, the input frequency f(f1, F2) is differentiated by the differentiation means 211, and an output is generated when the derivative value exceeds a certain value in the dead zone 212. The output u is set to "0" when it is below the certain value, and to "1" when it is above the certain value.

[0035] In Figure 4, the deviation between the input frequency f(f1, F2) and the preset reference frequency fnom is calculated, and an output is generated when the deviation exceeds a certain value in the dead zone 213. The output u is set to "0" when it is below the certain value, and to "1" when it is above the certain value.

[0036] Next, the control input calculation unit 22 will be described. In the following explanation, the inputs of the control input calculation unit will be defined as u1 and u2, and the outputs as y1, y2, and y3, as shown in Figure 2. However, the symbols 1 and 2 attached to input u and output y indicate that they are the inputs and outputs of the power system GA and GB sides, respectively. Also, y3 is a discrimination output for normal operation and emergency operation, taking the value "0" in the former case and "1" in the emergency case, and it determines the position of switch 50 in Figure 1.

[0037] The control input calculation unit 22 calculates and outputs three outputs y1, y2, and y3 based on two inputs u1 and u2. Here, input u1 corresponds to the output of the frequency calculation unit 21A, and input u2 corresponds to the output of the frequency calculation unit 21A. Output y1 is input to the proportional control unit 23A, output y2 is input to the proportional control unit 23B, and output y3 is input to the switch 50.

[0038] Figure 5 shows an example of the processing flow of the control input calculation unit 22. First, in step S100, the control input calculation unit 22 determines whether at least one of u1 and u2 is not 0. In this case, as mentioned above, u1 and u2 are set to "0" when the frequency change (deviation or rate of change) is less than or equal to a certain value, and to "1" when it is greater than or equal to a certain value. Therefore, the state in which at least one is not 0 (YES in step S100) means that a frequency fluctuation is occurring in either or both of the power systems GA and GB. Conversely, the state in which at least one is not 0 (NO in step S100) means that no frequency fluctuation is occurring in either the power systems GA or GB.

[0039] In the determination in step S100, if both u1 and u2 are 0 (NO), it can be determined that it is in a normal operating state, so y1=y2=y3=0 is output. In response to this, in step S102, because y3=0, the switch 50 shown in Figure 1 is in the "0" position, and the normal operation control unit 30 performs normal operation.

[0040] In the determination in step S100, if at least one of u1 and u2 is not 0 (YES), the process proceeds to step S101 to determine if both u1 and u2 are not 0. If both are not 0 (YES in step S101), it means that frequency fluctuations are occurring in both power system GA and GB. If neither is 0 (NO in step S101), it means that frequency fluctuations are occurring in either power system GA or GB.

[0041] In the determination in step S101, if both u1 and u2 are not 0 (u1≠0, u2≠0), it is considered that there is an anomaly in both power systems GA and GB. In this case, in step S103, the magnitude of the system inertia of power systems GA and GB is determined, and either step S1035 or step S106 is selected. Here, the inertia of each system used for determining the magnitude of system inertia may be the average value of system inertia over a certain period that has been registered in advance, or it may be the system inertia acquired in real time.

[0042] In the determination in step S103, if the inertia of power system GA is less than the inertia of power system GB, in step S105, y1 is output as 0, y2 as u1-u2, and y3 as 1. If the inertia of power system GA is greater than the inertia of power system GB, in step S106, y1 is output as u1-u2, y2 as 0, and y3 as 1.

[0043] In the determination in step S101, if only one of u1 or u2 is 0, it means that a frequency fluctuation is occurring in either the power system GA or GB. Therefore, in step S104, it is determined whether u1 is 0 in order to determine which anomaly it is. In the determination in step S104, if u1 is 0 (u1=0, u2≠0), it is determined that the anomaly is on the GB side of the power system, and in step S107, y1 is output as 0, y2 as u1-u2, and y3 as 1. In the determination in step S104, if u1 is not 0 (u1≠0, u2=0), it is determined that the anomaly is on the GA side of the power system, and in step S108, y1 is output as u1-u2, y2 as 0, and y3 as 1.

[0044] Based on the above determination, y3 switches between normal operation and emergency operation, and the proportional control unit 23 and the system inertia correction unit 24 on the side that is given a non-zero value (u1-u2) for y1 and y2 will perform processing on the input.

[0045] Here, as an example, we will describe the operation of the control input calculation unit 22 when a power supply failure occurs in power system GB and power system GA is in a normal state. When a power supply failure occurs in power system GB, the frequency of power system GB decreases significantly, and the output u2 of the frequency calculation unit 21B becomes negative, so u2≠0. On the other hand, since power system GA is in a normal state, the output of the frequency calculation unit 21A becomes u1=0. When u1=0 and u2≠0 due to the power supply failure in power system GB, in step S107, the control input calculation unit 22 outputs y1=0 and y2=u1-u2=-u2.

[0046] In this case, the proportional control unit 23 and system inertia correction unit 24 on the side where u=0 are given do not respond, while the proportional control unit 23 and system inertia correction unit 24 on the side where u≠0 are given respond. In the case of a power outage in power system GB, y2=-u2 is processed on the proportional control unit 23B side, multiplied by a pseudo-inertia coefficient, and then corrected by the system inertia correction unit 24B to calculate the emergency active power command value ΔP. Also, y3=1 is transmitted to the switch 50 as a switching signal.

[0047] Regarding the operation of the control input calculation unit 22 in the case of a power supply failure in power system GA and power system GB being in a normal state, the above explanation can be understood by simply swapping GA and GB, y1 and y2, and u1 and u2, so a detailed explanation is omitted.

[0048] Through the processing described above, the control input calculation unit 22 determines the fault-causing system based on the values ​​of inputs u1 and u2, and outputs the deviation of the input values ​​u1-u2 to y1 or y2, thereby switching between the control system composed of the proportional control unit 23A and the system inertia correction unit 23B and the control system composed of the proportional control unit 23B and the system inertia correction unit 24B.

[0049] Next, the operation of the control input calculation unit 22 in the event of a power supply failure in both power system GA and power system GB will be described. If a power supply failure occurs in power system GA, the frequency of power system GA will decrease significantly, and the output of the frequency calculation unit 21A will become negative, so u1 ≠ 0. Similarly, if a power supply failure occurs in power system GB, the frequency of power system GB will decrease significantly, and the output u2 of the frequency calculation unit 21B will become negative, so u2 ≠ 0.

[0050] In step S101, if u1≠0 and u2≠0, then in step S105, the relative magnitudes of the system inertia of power system GA and power system GB are determined, and the outputs y1 and y2 of the control input calculation unit 22 are calculated.

[0051] In step S105, if the system inertia of power system GA is smaller than the system inertia of power system GB, the control input calculation unit 22 outputs y1=0 and y2=u1-u2, and the proportional control unit 23B and the system inertia correction unit 24B calculate the emergency active power command value ΔP.

[0052] On the other hand, if the system inertia of power system GB is smaller than the system inertia of power system GA, the control input calculation unit 22 outputs y1=u1-u2, y2=0, and the proportional control unit 23A and the system inertia correction unit 24A calculate the emergency active power command value ΔP.

[0053] Thus, if a grid fault occurs in both power grid GA and power grid GB, the emergency active power command value ΔP is corrected to suppress the impact of frequency fluctuations on grids with low grid inertia.

[0054] Next, the proportional control units 23A and 23B will be described. The proportional control unit 23A outputs a value obtained by multiplying y1 by a pre-set pseudo-inertia coefficient. Similarly, the proportional control unit 23B outputs a value obtained by multiplying y2 by a pre-set pseudo-inertia coefficient.

[0055] The grid inertia correction unit 24A corrects the pseudo-inertia coefficient of the proportional control unit 23A moment by moment using a correction gain set from a pre-stored grid inertia pattern of power system GB. Similarly, the grid inertia correction unit 24B corrects the pseudo-inertia coefficient of the proportional control unit 23B moment by moment using a correction gain set from a pre-stored grid inertia pattern of power system GA.

[0056] Here, let's clarify the relationship between the two sets of proportional control units 23 and the system inertia correction unit 24, distinguished by symbols A and B shown in Figure 1. First, the proportional control unit 23 that receives input from the control input calculation unit 22 outputs a value obtained by multiplying it by a pre-set pseudo-inertia coefficient for the power system represented by that symbol, for example. The subsequent system inertia correction unit 24 then corrects the pseudo-inertia coefficient of the proportional control unit 23 moment by moment using the correction gain in the power system to which this power system is relative.

[0057] In other words, the approach adopted is to respond to an accident by providing power support from the healthy system to the faulty system (or from one system to the other when both systems are abnormal), but the amount of support will be limited to what is available at any given moment, taking into account the latest system inertia of the supporting system.

[0058] Figure 6 shows an example of a system inertia fluctuation pattern that is pre-stored in the system inertia correction unit 24A and system inertia correction unit 24B. The horizontal axis represents time, and the vertical axis represents the correction gain (=system inertia), with the typical system inertia over 24 hours expressed as a ratio to the maximum inertia value over 24 hours. According to this characteristic, system inertia fluctuates even within a 24-hour day. For example, at 11:00, the system inertia is at its maximum, so it takes a peak value of 1, and at 0:00, the system inertia is low, so it is 0.58. In this invention, for example, the system inertia correction units 24A and 24B grasp this moment-to-moment inertia fluctuation, and regardless of when a system fault occurs, the amount of power support is determined by the correction gain (system inertia) that matches the latest system state.

[0059] In this way, by taking a correction gain of less than 1 during periods of low system inertia, the pseudo-inertia coefficient of the proportional control unit 23A is reduced. As a result, when a fault occurs in power system GA, the system inertia correction unit 24A adjusts the pseudo-inertia coefficient, preventing the fault from spreading to the healthy power system GB while supplying the maximum possible pseudo-inertia to system GA.

[0060] The system inertia fluctuation patterns pre-stored in the system inertia correction units 24A and 24B are not limited to 24 hours; patterns may be switched between weekdays and holidays, or seasonal fluctuation patterns throughout the year may be taken into account. Alternatively, the system inertia values ​​acquired in real time may be used to repeatedly calculate and update the values ​​at predetermined time intervals.

[0061] Next, we will explain switch 50. In normal operation, switch 50 is always maintained in the state shown in Figure 1, and switches from the normal operation control unit 30 to the emergency operation control unit 20 based on the output y3 of the control input calculation unit 22. When the output y3 of the control input calculation unit 22 is 0, it is connected to the normal operation control unit 30, and when the output y3 is 1, it switches to the emergency operation control unit 20.

[0062] The emergency active power command value ΔP obtained through the above process is transmitted to control terminals 42A and 42B. The emergency control unit 20 detects the fault and identifies the faulty system, and corrects the emergency active power command value ΔP based on the inertia of the healthy system connected by the DC power transmission system 40, thereby enabling the supply of the maximum possible pseudo-inertia to the healthy system without causing large frequency fluctuations. [Examples]

[0063] The following describes Embodiment 2 of the present invention. In Embodiment 2, the emergency active power command value ΔP is corrected by performing a different process in the grid inertia correction unit 24A and the grid inertia correction unit 24B than in Embodiment 1.

[0064] In Example 2, compared to Example 1, the pseudo-inertia coefficient of the proportional control unit 23A or proportional control unit 23B is not corrected and is kept at a preset value, resulting in a higher RoCoF suppression effect against frequency fluctuations immediately after a grid fault. The configuration diagram of the DC power transmission system using the control system of Example 2 is shown in Figure 1, an example of the configuration of the frequency calculation unit is shown in Figures 3 and 4, and the processing flow of the control input calculation unit is shown in Figure 5, which is the same as in Example 1.

[0065] Figure 7 shows an example of the configuration of the emergency control unit 20 in Embodiment 2. In Embodiment 2, the system inertia correction units 24A and 24B limit the emergency active power command value ΔP output from the proportional control unit 23A or the proportional control unit 23B so as not to exceed preset upper and lower limits.

[0066] Here, the upper and lower limiters (upper limiters: LIM1, LIM2, lower limit limiters: -LIM1, -LIM2) of the grid inertia correction units 24A and 24B are set so that, in the event of an accident such as power outage or grid separation in one of the DC-connected grids, and when pseudo-inertia control is performed by the DC power transmission system, the RoCoF of the healthy grid does not exceed a predetermined value.

[0067] The following describes, as an example, how to set the upper and lower limiters of the grid inertia correction unit 24B when a power outage occurs in power grid GB and power grid GA is in a normal state.

[0068] If a power outage occurs in power system GB, the frequency of power system GB decreases significantly, and the output u2 of the frequency calculation unit 21B becomes negative, so u2≠0. On the other hand, power system GA is in a normal state, so the output of the frequency calculation unit 21A becomes u1=0. When u1=0 and u2≠0, from step S107 in Figure 5, the control input calculation unit 22 outputs y1=0 and y2=u1-u2=-u2. From this, y2=-u2 is input to the proportional control unit 23B, and the emergency active power command value ΔP is calculated by multiplying it by the pseudo-inertia coefficient. At this time, the direction of ΔP is the direction of power transmission from power system GA, which is a healthy system, to power system GB, which is a faulty system.

[0069] Here, the change in frequency that occurs in a healthy power system GA due to the emergency active power command value ΔP can be expressed as shown in equation (1). Note that ΔP is the emergency active power command value [MW], fnoma1 is the system frequency of power system GA [Hz], and Msys1 is the system inertia of power system GA [MW·s].

[0070]

number

[0071] According to equation (1), the larger the emergency active power command value ΔP and the smaller the system inertia of the power system GA, the larger the rate of frequency change occurring in the power system GA.

[0072] If the RoCoF of the power grid GA exceeds ±RoCoFlim [Hz / s] (for example, RoCoFlim = 2Hz / s) specified in the FRT requirements for renewable energy power sources to continue operation during a fault (hereinafter referred to as FRT requirements) due to the emergency active power command value ΔP, renewable energy power sources may fail in a chain reaction, potentially causing the fault to spread to the power grid GA.

[0073] Therefore, in order to prevent the fault from spreading to the power grid GA, equation (2) must be satisfied.

[0074]

number

[0075] From equations (1) and (2), in order to prevent fault propagation to the power grid GA due to the emergency active power command value ΔP, the emergency active power command value ΔP must satisfy the constraint of equation (3).

[0076]

number

[0077] Based on the above, the upper and lower limiters of the power system inertia correction unit 24B are calculated and stored from the fluctuation pattern of the power system inertia Msys1 of the power system GA as shown in (Equation 4).

[0078]

number

[0079] Figure 8 shows an example of a variation pattern for the upper and lower limiters that are pre-stored in the system inertia correction unit. Note that the setting of the upper and lower limiters is not limited to 24 hours; patterns may be switched between weekdays and holidays, or seasonal variation patterns throughout the year may be taken into consideration. Alternatively, the system inertia values ​​acquired in real time may be used to repeatedly calculate and update the values ​​at predetermined time intervals.

[0080] The above describes how to set the upper and lower limiters of the system inertia correction unit 24B when a power outage occurs in power system GB and power system GA is in a normal state. However, the same method can be applied to setting the upper and lower limiters of the system inertia correction unit 24A when a power outage or system separation occurs in power system GA and power system GB is in a normal state. [Explanation of Symbols]

[0081] GA, GB: Power system 3A, 3B: Transformer 4A, 4B: Bus bar 5A, 5B: Voltage detectors 6: DC railway 10: Control System 20: Emergency Control Unit 21A, 21B: Frequency calculation unit 22: Control Input Calculation Unit 23A, 23B: Proportional control unit 24A, 24B: System inertia correction section 30: Normal operation control unit 31: Arithmetic section 32: Limiter 40: DC power transmission system 41A, 41B: Self-excited converter 42A, 42B: Control terminals 50: Switch

Claims

1. A control device for a DC power transmission system in which two or more AC systems are connected via an AC / DC converter, The control device includes a normal operation control unit that, when the frequency change of the AC system is within a predetermined value, generates an active power command value to cancel out the frequency change and outputs it to the AC / DC converter, The system includes an emergency control unit that, when the frequency change of the AC system exceeds a predetermined value, generates the active power command value in a direction that eliminates the frequency change and outputs it to the AC / DC converter. The control device for a DC power transmission system is characterized in that the emergency control unit includes a system inertia correction means for correcting the active power command value in accordance with fluctuations in the system inertia of the AC system.

2. A control device for a DC power transmission system according to claim 1, The control device for a DC power transmission system is characterized in that the emergency control unit generates the active power command value by multiplying the frequency change of the AC system by a pseudo-inertia coefficient.

3. A control device for a DC power transmission system according to claim 2, The control device for a DC power transmission system is characterized in that the system inertia correction means corrects the pseudo-inertia coefficient in advance in accordance with fluctuations in the system inertia of the AC system.

4. A control device for a DC power transmission system according to claim 1, A control device for a DC power transmission system, characterized in that the system inertia correction means has a limiter that limits the active power command value in advance according to fluctuations in the system inertia of the AC power system.

5. A control device for a DC power transmission system according to claim 4, A control device for a DC power transmission system, characterized in that the limiter of the system inertia correction means is set using the system inertia value of the AC system so that the frequency change rate of the AC system is within a predetermined value.

6. A control device for a DC power transmission system according to claim 1, The control device for a DC power transmission system is characterized in that the system inertia correction means corrects the active power command value in accordance with fluctuations in the system inertia of the healthy AC system that provides power support to the AC system on the faulty side.

7. A control device for a DC power transmission system according to claim 1, The control device for a DC power transmission system is characterized in that the emergency control unit comprises a first system inertia correction means for correcting the active power command value in accordance with fluctuations in the system inertia of a second AC system that provides power support to a first AC system, and a second system inertia correction means for correcting the active power command value in accordance with fluctuations in the system inertia of a first AC system that provides power support to a second AC system.

8. A control method for a DC power transmission system in which two or more AC systems are interconnected via an AC / DC converter, When the frequency change of the AC system is within a predetermined value, an active power command value is generated to cancel out the frequency change, and the AC / DC converter is controlled. When the frequency change of the AC system exceeds a predetermined value, the active power command value is generated in a direction that eliminates the frequency change, thereby controlling the AC / DC converter. A control method for a DC power transmission system, characterized by correcting the active power command value in accordance with fluctuations in the system inertia of the AC power system.

Images