Power system and method for controlling power system

Abstract

This power system comprises a central control device that executes secondary control to control a plurality of power converters, and the plurality of power converters, each including: a power conversion unit that converts and outputs power that has been input; a control unit that executes output control, which is primary control, by controlling the power conversion unit on the basis of a reference function that includes a drooping characteristic defined in accordance with an input value, and the voltage or power of a bus to which the power conversion unit is connected; and an updating unit that updates an output control method. The central control device performs secondary control on the power converters by update commands to update the control method. The updating units update the control method in accordance with the update command output from the central control device. During a period in which the plurality of power converters update the control method, the control method is updated in such a manner that there is always at least one power converter performing voltage control among the plurality of power converters.

Description

[Technical field]

[0001] The present invention relates to a power system and a method for controlling a power system. [Background technology]

[0002] As an alternative to large-scale power networks that rely on fossil and nuclear energy, power networks that use locally produced and consumed electricity are attracting attention. A wide variety of devices will be connected to power networks that use locally produced and consumed electricity, including photovoltaic (PV) power generation devices that generate electricity using renewable energy, stationary power storage devices, and electric vehicles (EVs). As each of the above devices uses direct current (DC) power sources, studies are underway to build a direct current (DC) power network (DC grid).

[0003] As a method for controlling a DC grid, there is a method in which a power converter connected to each of the above devices performs constant current control or constant voltage control on each of the above devices based on an instruction from a central control unit, thereby centrally controlling the amount of power on the DC bus of the DC grid. Although the above centralized control method can easily control the entire DC grid, it has a problem that it is difficult to smoothly respond to sudden fluctuations in power supply and demand. In addition, the above centralized control method has a problem that, particularly when constant voltage control is performed at multiple locations over a wide range, the voltage control becomes unstable, which may cause voltage oscillations on the DC bus. In addition, constant voltage control at multiple locations has a problem that it is not possible to share the load of power interchange among the devices, that is, the devices cannot cooperate to supply power to the DC bus at a constant voltage according to the power supply capacity of each device.

[0004] Therefore, a DC grid is controlled by assigning a reference function based on the power (P) and voltage (V) of each power converter in an autonomous and decentralized manner (Patent Documents 1 to 3). When a reference function is used that gives a droop characteristic to the target voltage value according to the amount of power required for the DC bus, that is, gives a droop characteristic, this control is sometimes called droop control. By controlling each power converter in an autonomous and decentralized manner, the voltage of the DC bus can be stabilized while sharing the load of power interchange of each device according to the amount of power required for the DC bus. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6371603 [Patent Document 2] International Publication No. 2019 / 103059 [Patent Document 3] JP 2018-29408 A Summary of the Invention [Problem to be solved by the invention]

[0006] Among the multiple power converters connected to the DC bus, there are a mixture of power converters that observe the output voltage to determine a target power and perform feedback control (power control) so that the difference between the target power and the output power becomes zero, and power converters that observe the output power to determine a target voltage and perform feedback control (voltage control) so that the difference between the target voltage and the output voltage becomes zero. When changing the feedback control method in response to an instruction from the central control unit, for example, if a delay occurs in communication from the central control unit to the power converters, the power converter that changes from voltage control to power control may complete the change of control method first, and the change of control method in the power converter that changes from power control to voltage control may be delayed. In this case, there is a state in which there is no power converter that performs feedback control so that the difference between the target voltage and the output voltage becomes zero, and there is a risk of an unintended voltage rise or fall occurring on the DC bus.

[0007] The present invention has been made in view of the above, and has an object to suppress the occurrence of unintended voltage increases and decreases when updating a control method in a power converter. [Means for solving the problem]

[0008] One aspect of the present invention is a power system comprising: a plurality of power converters having a power conversion unit that converts input power and outputs it; a reference function having a drooping characteristic defined according to an input value; a control unit that controls the power conversion unit to perform primary control of the output based on the voltage or power of a bus to which the power conversion unit is connected; and an update unit that updates a control method of the output; a central control unit that performs secondary control to control the power converters; a bus connected to the power conversion unit; and power elements connected to the power converters that can supply, consume or charge power, wherein the central control unit secondarily controls the power converters with an update command that updates the control method, and the update unit updates the control method in accordance with the update command output from the central control unit, and during a period in which the control method is updated in the plurality of power converters, the control method is updated so that there is always at least one power converter among the plurality of power converters that performs voltage control.

[0009] In a power system according to one aspect of the present invention, the primary control, which is the control of the output, may be performed based on the voltage or current of the bus without via commands from a central control device.

[0010] In a power system according to one aspect of the present invention, a power converter among the plurality of power converters that is performing voltage control may update the control method after a predetermined time has elapsed since obtaining the update command.

[0011] In a power system according to one embodiment of the present invention, the central control device may output the update command to a power converter among the plurality of power converters that is performing power control, and then output the update command to a power converter among the plurality of power converters that is performing voltage control.

[0012] One aspect of the present invention is a control method for a power system provided with a plurality of power converters connected to a bus and having a power conversion unit that converts and outputs input power, power elements connected to the power converters and capable of supplying, consuming or charging power, and a central control device that controls the power converters, the control method including the steps of: a step of the power conversion unit converting and outputting the input power; a step of controlling the power conversion unit to perform primary control of the output based on a reference function having a drooping characteristic defined according to an input value and the voltage or power of the bus to which the power conversion unit is connected; a step of the central control device performing secondary control of the power converter with an update command that updates the control method; and a step of the power converter updating a control method for the output in response to the update command, the control method being updated during a period in which the control method is updated in the plurality of power converters, such that there is always at least one power converter among the plurality of power converters that performs voltage control. Effect of the Invention

[0013] According to the power system of the present invention, a central control device that performs secondary control to control the power converters secondarily controls the power converters with an update command to update the control method, and the update unit updates the control method in response to the update command output from the central control device. During a period in which the control method is updated for the multiple power converters, the control method is updated so that there is always at least one power converter that performs voltage control among the multiple power converters. Therefore, when the control method is updated, the voltage of the bus to which the power converters are connected is controlled by at least one power converter that performs voltage control, and the occurrence of unintended voltage increases and decreases in the bus is suppressed.

[0014] According to the power system control method of the present invention, in a power system provided with a plurality of power converters connected to a bus and having a power conversion unit that converts and outputs input power, power elements connected to the power converters and capable of supplying, consuming or charging power, and a central control device that controls the power converters, the following steps are executed: a step of the power conversion unit converting and outputting the input power, a step of controlling the power conversion unit to execute control of the output, which is primary control, based on a reference function having a drooping characteristic defined according to an input value and the voltage or power of the bus to which the power conversion unit is connected, a step of the central control device secondarily controlling the power converter with an update command that updates the control method, and a step of the power converter updating a control method of the output in response to the update command. During a period in which the control method is updated by the plurality of power converters, the control method is updated so that there is always at least one power converter that performs voltage control among the plurality of power converters. Therefore, when the control method is updated, the voltage of the bus to which the power converters are connected is controlled by at least one power converter that performs voltage control, and the occurrence of unintended voltage increases and decreases in the bus is suppressed. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a diagram showing the configuration of a power system according to the first embodiment. [Diagram 2] FIG. 2 is a diagram illustrating a configuration of the power converter illustrated in FIG. [Diagram 3] FIG. 3 is a diagram illustrating a configuration of the control unit illustrated in FIG. [Figure 4A] FIG. 4A is a diagram illustrating an example of power conversion characteristics. [Figure 4B] FIG. 4B is a diagram showing an example of power conversion characteristics. [Figure 4C] FIG. 4C is a diagram illustrating an example of power conversion characteristics. [Figure 4D] FIG. 4D is a diagram illustrating an example of power conversion characteristics. [Diagram 5] FIG. 5 is a flowchart showing the flow of processing performed by the control unit of the power converter. [Figure 6] FIG. 6 is a sequence diagram showing an example of a control method for a power system. [Figure 7] FIG. 7 is a flowchart showing the flow of processing performed by the control unit of the power converter. [Figure 8A] FIG. 8A is a diagram showing the timing at which reference function information and a feedback control method are updated in a power converter. [Figure 8B] FIG. 8B is a diagram showing the timing at which reference function information and a feedback control method are updated in a power converter. [Figure 9] FIG. 9 is a diagram showing the configuration of a control unit of the power converter according to the second embodiment. [Figure 10] FIG. 10 is a flowchart showing a flow of processing performed by a control unit of the power converter according to the second embodiment. [Figure 11] FIG. 11 is a sequence diagram showing an example of a control method for the power system according to the second embodiment. [Figure 12] FIG. 12 is a diagram showing timings at which reference function information and a feedback control method are updated in the power converter according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiment described below. Furthermore, in the description of the drawings, the same parts are appropriately designated by the same reference numerals.

[0017] (First embodiment) <Power system configuration> Fig. 1 is a diagram showing the configuration of a power system according to a first embodiment. The power system 100 includes a plurality of power converters 11, 12, 13, 14, a plurality of power elements 21, 22, 23, 24, and a bus 30. The power system 100 further includes an EMS (Energy Management System) 40. The EMS 40 is an example of a central control device.

[0018] Power converters 11, 12, and 13 are DC / DC converters, and power converter 14 is an AC / DC converter. Power converters 11, 12, 13, and 14 have a function of performing wired or wireless information communication. The configurations and functions of power converters 11, 12, 13, and 14 will be described in detail later.

[0019] Bus 30 is a DC bus in power system 100, and is connected to power converters 11, 12, 13, and 14. In power system 100, a power network including a DC grid is configured.

[0020] As an example, the power element 21 is a stationary power storage device capable of supplying, consuming, and charging power, and is connected to the power converter 11. The stationary power storage device is an example of a permanently installed in-facility power storage device. The power converter 11 has a function of converting the voltage of the DC power supplied by the power element 21 and outputting it to the bus 30, and also converting the voltage of the DC power supplied from the bus 30 and outputting it to the power element 21 for charging.

[0021] One example of the power element 22 is a solar power generation device capable of generating and supplying electric power, and is connected to the power converter 12. The solar power generation device is an example of a power generation device that generates electric power using renewable energy. The power converter 12 has a function of converting the voltage of the DC power supplied by the power element 22 and outputting it to the bus 30.

[0022] Power element 23 is, for example, an on-board power storage device capable of supplying, consuming, and charging power, and is connected to power converter 13. The on-board power storage device is mounted on an electric vehicle EV and is an example of a mobile non-stationary power storage device. Power converter 13 has a function of converting the voltage of DC power supplied by power element 23 and outputting it to bus 30, and also converting the voltage of DC power supplied from bus 30 and outputting it to power element 23 for charging. Power converter 13 is provided, for example, in a charging station or residential charging equipment, but may also be mounted on electric vehicle EV.

[0023] As an example, the power element 24 is a commercial power system, and is connected to the power converter 14. The power converter 14 converts the AC power supplied by the power element 24 into DC power and outputs it to the bus 30, and also converts the DC power supplied from the bus 30 into AC power and outputs it to the power element 24. The output of power from the bus 30 to the power element 24 is also called reverse power flow.

[0024] The EMS 40 has a function of comprehensively managing the state of the power system 100. The EMS 40 includes a control unit 41, a storage unit 42, and a communication unit 43.

[0025] The control unit 41 performs various arithmetic processing to realize the functions of the EMS 40, and is configured to include processors such as a CPU (Central Processing Unit), an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), a DSP (Digital Signal Processor), a GPU (Graphics Processing Unit), etc. The functions of the control unit 41 are realized as functional units by the control unit 41 reading out and executing various programs from the storage unit 42.

[0026] The storage unit 42 includes, for example, a ROM (Read Only Memory) in which various programs and data used by the control unit 41 to perform arithmetic processing are stored. The storage unit 42 also includes, for example, a RAM (Random Access Memory) used for storing a working space when the control unit 41 performs arithmetic processing and results of the arithmetic processing of the control unit 41. The storage unit 42 may include an auxiliary storage device such as an HDD (Hard Disk Drive) or an SSD (Solid State Drive).

[0027] The communication unit 43 includes a communication module that performs information communication by wire or wirelessly. The communication unit 43 performs information communication with the power converters 11, 12, 13, and 14 and the external server 200 via a network NW that is configured from an Internet network, a mobile phone network, or the like.

[0028] The external server 200 is a server provided outside the power system 100. The external server 200 is, for example, an information processing device configured to function as an EMS in another power system, or an information processing device that includes a database and functions as a data server for the EMS 40. The external server 200 stores various types of information that may affect the operation of the power system 100.

[0029] <Power converter configuration> Next, a specific configuration of the power converter 11 will be described. Fig. 2 is a diagram showing the configuration of the power converter 11. The power converter 11 has a power conversion unit 11a, a sensor 11b, a control unit 11c, and a communication unit 11d.

[0030] The power conversion unit 11a performs DC / DC conversion to convert the voltage of DC power input from the discharging power element 21 and output it to the bus 30. The power conversion unit 11a can also convert the voltage of DC power input from the bus 30 and output it to the power element 21 for charging. The power conversion unit 11a is configured with an electric circuit including, for example, a coil, a capacitor, a diode, a switching element, and the like. The switching element is, for example, a field effect capacitor or an insulated gate bipolar transistor. The power conversion unit 11a can control the power conversion characteristics by, for example, PWM (Pulse Width Modulation) control.

[0031] The sensor 11b measures an electrical characteristic value of the power on the bus 30 side of the power conversion unit 11a. Thus, the sensor 11b measures an electrical characteristic value of the power input to the power converter 11 or output from the power converter 11. The sensor 11b can measure a current value, a voltage value, a power value, etc. The sensor 11b is an example of a measurement unit that acquires a measurement value. The sensor 11b outputs the measurement value of the electrical characteristic value to the control unit 11c.

[0032] The control unit 11c includes a processor and a storage unit that perform various arithmetic processing for controlling the operation of the power conversion unit 11a in order to realize the power conversion function of the power converter 11. The processor and the storage unit may be the same as those exemplified as the configurations of the control unit 41 and the storage unit 42, respectively. The functions of the control unit 11c are realized as a functional unit by the processor reading and executing various programs from the storage unit. For example, the control unit 11c controls the power conversion characteristics of the power conversion unit 11a based on a reference function. Specifically, the control unit 11c outputs a PWM signal including information on an operation amount (for example, a duty ratio) for PWM control to the power conversion unit 11a, and performs PWM control on the power conversion unit 11a. The control unit 11c may directly output the operation amount to the power conversion unit 11a, or may output the operation amount to the power conversion unit 11a via another functional unit (for example, a loop control unit) not shown in the figure.

[0033] The communication unit 11d includes a communication module that communicates information by wire or wirelessly, and a communication control unit that controls the operation of the communication module. The communication unit 11d communicates information with the EMS 40 via the network NW. The communication unit 11d receives, for example, information and commands from the EMS 40 and outputs them to the control unit 11c. The communication unit 11d also transmits, for example, information on the power status input from the control unit 11c to the EMS 40. Note that, when the information on the power status is a measurement value of the sensor 11b, the communication unit 11d may transmit, for example, the measurement value input from the sensor 11b to the EMS 40.

[0034] 3 is a diagram showing a configuration of the control unit 11c mainly related to the power conversion function. The control unit 11c includes an operation amount setting unit 11ca, a determination unit 11cb, and an update unit 11cc, which are functional units realized in a software manner by executing a program, and a storage unit 11cd.

[0035] The update unit 11cc stores the reference function information and the control method information included in the update command input from the communication unit 11d in the storage unit 11cd, and updates the reference function information and the control method information stored in the storage unit 11cd. Here, the reference function information is various information for identifying the droop function constituting the reference function, which will be described in detail later.

[0036] The determination unit 11cb determines the method of feedback control performed by the operation amount setting unit 11ca based on the control method information stored in the storage unit 11cd, and outputs the determination result as the determination information. The feedback control method includes feedback control (hereinafter referred to as droopP control) in which a target power Pref (an example of a target value) is determined based on the voltage measurement value Vo by the sensor 11b and reference function information, and the operation amount is set so that the difference between Pref and the power measurement value Po (an example of a control target value) by the sensor 11b is within a tolerable range, and feedback control (hereinafter referred to as droopV control) in which a target voltage Vref (an example of a target value) is determined based on the power measurement value Po by the sensor 11b and reference function information, and the operation amount is set so that the difference between Vref and the voltage measurement value Vo (an example of a control target value) by the sensor 11b is within a tolerable range. The droopP control, which is an example of power control, and the droopV control, which is an example of voltage control, are examples of control methods for controlling the output of the power conversion unit 11a. The aforementioned control method information is information representing droopP control or droopV control, and the judgment unit 11cb judges the method of feedback control based on the control method information stored in the memory unit 11cd, and outputs the judgment result of performing droopP control or the judgment result of performing droopV control as judgment information.

[0037] The manipulated variable setting unit 11ca sets the feedback control method according to the judgment information input from the judgment unit 11cb, sets the manipulated variable based on the measured value input from the sensor 11b and the reference function information acquired from the storage unit 11cd, and outputs the manipulated variable to the power conversion unit 11a. The feedback control performed by the manipulated variable setting unit 11ca can be performed using a known method such as PID control that is executed by reading out parameters such as proportional gain, integral time, and differential time stored in the storage unit 11cd.

[0038] The storage unit 11cd or the manipulated variable setting unit 11ca outputs information on the power situation, reference function information, and other information to the communication unit 11d.

[0039] The other power converters 12, 13, and 14 may have the same configuration as the power converter 11. However, the power conversion unit 11a of the power converter 14 is a so-called inverter that converts AC power input from the power element 24 into DC power and outputs it to the bus 30, or converts DC power input from the bus 30 into AC power and outputs it to the power element 24.

[0040] <Characteristics of reference functions> Next, a reference function on which the control unit 11c controls the power conversion characteristics of the power conversion unit 11a will be described. Figures 4A to 4D are diagrams showing an example of the power conversion characteristics.

[0041] 4A is a diagram showing the VP characteristic, which is the relationship between power (P) and voltage (V) on the bus 30 side of the power conversion unit 11a of the power converter 11, and shows the power conversion characteristic of the power conversion unit 11a of the power converter 11. Note that P is a positive value when the power conversion unit 11a supplies power to the bus 30, i.e., when the power element 21 is in a discharging state, and is a negative value when the power is supplied from the bus 30, i.e., when the power element 21 is in a charging state.

[0042] The line DL1 shown in FIG. 4A is a straight or curved line that is bent halfway. The reference function represented by this line DL1 is configured by connecting a plurality of droop functions that are defined according to the range of the input value and have different droop characteristics. Specifically, the line DL1 is configured by connecting lines that represent five droop functions that have different droop characteristics, and is specified by the reference function information. The reference function information includes, for example, coordinate information of the boundary of the droop function in a coordinate system with the horizontal axis being P and the vertical axis being V, intercept information of the droop function, information on the slope (i.e., droop coefficient), and information on the shape (straight line, curve, etc.). In the power converter 11, the control unit 11c controls the power conversion characteristics of the power conversion unit 11a so that they become the characteristics of the reference function represented by the line DL1. That is, the control unit 11c of the power converter 11 controls the power conversion unit 11a so that the operating point defined by the value of V and the value of P is located on the line DL1.

[0043] FIG. 4B is a diagram showing the VP characteristics, which are the relationship between power (P) and voltage (V) on the bus 30 side of the power conversion unit 11a of the power converter 12, and shows the power conversion characteristics of the power conversion unit 11a of the power converter 12.

[0044] The line DL2 shown in FIG. 4B is a straight or curved line that is bent halfway. The reference function represented by this line DL2 is configured by connecting lines representing five droop functions with different droop characteristics defined according to the range of the input value, and the line DL2 is specified by the reference function information like the line DL1. In the power converter 12, the control unit 11c controls the power conversion characteristics of the power conversion unit 11a so that they become the characteristics of the reference function shown by the line DL2. That is, the control unit 11c of the power converter 12 controls the power conversion unit 11a so that the operating point defined by the value of V and the value of P is located on the line DL2.

[0045] FIG. 4C is a diagram showing the VP characteristics, which are the relationship between power (P) and voltage (V) on the bus 30 side of the power conversion unit 11a of the power converter 13, and shows the power conversion characteristics of the power conversion unit 11a of the power converter 13.

[0046] The line DL3 shown in FIG. 4C is a straight or curved line that is bent halfway. The reference function represented by this line DL3 is configured by connecting lines representing nine droop functions with different droop characteristics defined according to the range of the input value, and the line DL3 is specified by the reference function information like the line DL1. In the power converter 13, the control unit 11c controls the power conversion characteristics of the power conversion unit 11a so that they become the characteristics of the reference function shown by the line DL3. That is, the control unit 11c of the power converter 13 controls the power conversion unit 11a so that the operating point defined by the value of V and the value of P is located on the line DL3.

[0047] FIG. 4D is a diagram showing the VP characteristics, which are the relationship between power (P) and voltage (V) on the bus 30 side of the power conversion unit 11a of the power converter 14, and shows the power conversion characteristics of the power conversion unit 11a of the power converter 14.

[0048] The line DL4 shown in FIG. 4D is a straight or curved line that is bent halfway. The reference function represented by this line DL4 is configured by connecting lines representing three droop functions with different droop characteristics defined according to the range of the input value, and the line DL4 is specified by the reference function information like the line DL1. In the power converter 14, the control unit 11c controls the power conversion characteristics of the power conversion unit 11a so that they become the characteristics of the reference function shown by the line DL4. That is, the control unit 11c of the power converter 14 controls the power conversion unit 11a so that the operating point defined by the value of V and the value of P is located on the line DL4.

[0049] <Control method> Next, a control method for the power converters 11, 12, 13, and 14 and a control method for the power system 100 will be described. In the power system 100, so-called local-end control, in which the power converters 11, 12, 13, and 14 individually perform control in an autonomous and distributed manner, and centralized control, in which the EMS 40 cooperatively controls the power converters 11, 12, 13, and 14 according to the power status of the power system 100, can be performed. Note that, for example, the local-end control is repeatedly performed at a relatively short period, and the centralized control is performed at intervals longer than the period of the local-end control. The local-end control is also called primary control, and the centralized control is also called secondary control. These control methods are performed, for example, by a program in each power converter or the EMS 40, which causes a processor to execute the control.

[0050] <Self-control> First, a control method for the power converters 11, 12, 13, and 14 in the self-end control will be described using the power converter 11 as an example. The other power converters 12, 13, and 14 may also appropriately execute a control method similar to that described below. When the power element 22 is an element that does not control the amount of power generated from the viewpoint of efficiency, such as a solar power generation device, the power converter 12 may execute MPPT (Maximum Power Point Tracking) control, which operates when power corresponding to the amount of power generated is input from the power element 22 so that the output power to the bus 30 is maximized at that amount of power generation. For example, FIG. 4B shows an example of a reference function when executing MPPT control.

[0051] In the control method for the power converter 11, the control unit 11c executes a control step of controlling the power conversion characteristics of the power converter 11, that is, the power conversion characteristics of the power conversion unit 11a, based on the reference function.

[0052] An example of the contents of this control step will be described more specifically with reference to Figures 3 and 5. Figure 5 is a flow chart showing the flow of processing performed by the control unit 11c.

[0053] First, in the control unit 11c, the operation amount setting unit 11ca acquires a measurement value from the sensor 11b (step S101). Next, in the control unit 11c, the operation amount setting unit 11ca acquires reference function information from the storage unit 11cd (step S102). Next, in the control unit 11c, the judgment unit 11cb judges a feedback control method based on the control method information stored in the storage unit 11cd (step S103). Next, in the control unit 11c, the operation amount setting unit 11ca acquires judgment information output from the judgment unit 11cb, sets an operation amount for executing feedback control in a control method based on the acquired judgment information based on the measurement value and the reference function information, and outputs it to the power conversion unit 11a (step S104). This causes the control of the power conversion unit 11a to be executed.

[0054] <Centralized control> Next, the centralized control will be described. In the example shown below, an EMS 40 provided outside the power converters 11, 12, 13, and 14 executes the centralized control by updating the reference function and the feedback control method used for control by the power converters 11, 12, 13, and 14 by a command. Updating the reference function and the feedback control method by a command means that the command includes reference function information on the reference function and control method information on the feedback control method, and a part or the whole of the reference function and the feedback control method are updated by the command. The memory unit 11cd of each of the power converters 11, 12, 13, and 14 stores the reference function information and the control method information in an updatable manner.

[0055] For example, in information communication between EMS 40 and power converters 11, 12, 13, 14, a command signal for updating the reference function includes reference function information and control method information. As described above, the reference function information is coordinate information of the boundary of the droop function, intercept information of the droop function, information on the slope (i.e., droop coefficient), and information on the shape (straight line, curve, etc.). The control method information is information representing droopP control or droopV control. The reference function information used for updating is stored in memory unit 42 of EMS 40, and is read out and used by control unit 41 as appropriate.

[0056] Next, an example of a control method for the power system 100 as centralized control will be described with reference to a sequence diagram of FIG.

[0057] First, the EMS 40 calls its own timer and starts timing (step S201). Next, the EMS 40 requests its own-end measurement information from each of the power converters 11, 12, 13, and 14 (step S202). The own-end measurement information is an example of information related to the power status of the power system 100, and includes measurements taken by the sensors of each of the power converters 11, 12, 13, and 14 and the measurement times.

[0058] Next, the power converters 11, 12, 13, and transmit their own-end measurement information to the EMS 40 (step S203). The EMS 40 stores the respective own-end measurement information in the storage unit .

[0059] Next, the EMS 40 requests various pieces of information that may affect the operation of the power system 100 from the external server 200 as an example of information related to the power status of the power system 100 (step S204). In this example, the EMS 40 requests power generation and demand forecast information from the external server 200. The power generation and demand forecast information includes forecast information on the amount of power generated in the power system 100 and forecast information on the demand for power, and may include, for example, information on the season of the area in which the power system 100 is installed, the current weather, and future weather forecasts. In addition, when the external server 200 functions as an EMS for another power system, and when the operational state of the other power system may affect the operation of the power system 100, the power generation and demand forecast information may include forecast information on the amount of power generated in the other power system and forecast information on the demand for power.

[0060] Next, the external server 200 transmits the power generation amount / demand forecast information to the EMS 40 (step S205). The EMS 40 stores the power generation amount / demand forecast information in the storage unit .

[0061] Next, the control unit 41 of the EMS 40 reads out each piece of transmitted information, i.e., information related to the power status of the power system 100, from the memory unit 42, and performs an operational optimization calculation for the power system 100 based on this information (step S206).

[0062] The operation optimization calculation is executed so as to be applicable to various conditions. For example, it is assumed that the power system 100 is controlled so that the bus 30 is at an operating point of a predetermined voltage. In this state, it is assumed that the EMS 40 determines, based on the power generation amount and demand forecast information, that the future weather in the area where the power element 22, which is a photovoltaic power generation device, is installed is expected to be sunny and the amount of power generation is expected to increase, and based on the self-terminal measurement information acquired from the power converter 12 connected to the power element 22, the power element 22 has a margin in terms of power supply. In this case, the EMS 40 determines to update the reference function of the power converter 11 connected to the power element 21 so that the power element 21, which is a stationary power storage device, is charged at the operating point. In addition, at the same time as the update, the EMS 40 determines to update the reference function of the power converter 14 connected to the power element 24 so that power is not supplied from the power element 24, which is a commercial power system.

[0063] In addition, the operational optimization calculation can also be performed with conditions set from the perspective of not exceeding the contract power of the power element 24, which is the commercial power system, such as peak cutting and utilization of nighttime power, and from the perspective of optimizing electricity rates.

[0064] Furthermore, the memory unit 42 of the EMS 40 may store a trained model, and the EMS 40 may execute the operation optimization calculation using the trained model. The trained model may be, for example, a trained model generated by deep learning using a neural network, using information on the power status of the power system 100 and the corresponding results of switching or updating the reference functions for the power converters 11, 12, 13, and 14 as training data.

[0065] Next, based on the result of the operation optimization calculation, EMS 40 sets reference function information and control method information suitable for the power converter to be updated among power converters 11, 12, 13, and 14, and outputs an update command for the reference function (droop function) and feedback control method including the set reference function information and control method information (step S207). Next, EMS 40 resets the timer (step S208).

[0066] Next, the power converter to be updated among power converters 11, 12, 13, and 14 receives a command to update the reference function and the feedback control method, and updates the reference function and the feedback control method (step S209).

[0067] 7 is a flowchart showing a flow of a process of updating a reference function and a feedback control method performed by the power converter. In the control unit 11c of the power converter that has received an update command, the update unit 11cc refers to the control method information stored in the storage unit 11cd and determines whether the feedback control method before the update is the droopV control (step S301).

[0068] If the control method represented by the control method information before the update is droopP control (NO in step S301), the control unit 11c proceeds to step S303. If the control method represented by the control method information before the update is droopV control (YES in step S301), the control unit 11c judges whether a predetermined time has elapsed since the update command was acquired (step S302). If the predetermined time has not elapsed since the update command was acquired (NO in step S302), the control unit 11c repeats the process of step S302 until the predetermined time has elapsed. If the predetermined time has elapsed since the update command was acquired (YES in step S302), the control unit 11c updates the reference function information and control method information stored in the storage unit 11cd with the reference function information and control method information included in the received update command (step S303).

[0069] Returning to Fig. 6, the power converters 11, 12, 13, and 14 then each execute their own-end control (step S210). Here, among the power converters 11, 12, 13, and 14, the power converter that has acquired the update command executes its own-end control using the updated reference function and feedback control method. These own-end controls are ones that reflect the power status of the power system 100, and the power converters 11, 12, 13, and 14 are cooperatively controlled.

[0070] Fig. 8A is a diagram showing the timing at which the reference function information and the feedback control method are updated in a power converter that has received an update command. For comparison with this embodiment, Fig. 8B shows the timing at which the reference function information and the feedback control method are updated when the power converter to be updated does not perform the process of Fig. 7.

[0071] As shown in FIG. 8B, if, for example, due to a communication delay, the update of power converter 11 from droopP control to droopV control lags behind the update of power converter 14 from droopV control to droopP control, during this delayed period, there will be no power converter performing droopV control, and there is a risk of an unintended voltage increase or decrease occurring on bus 30.

[0072] In contrast, in this embodiment, the power converter that receives the update command performs the processing of Figure 7, and the power converter 14 that updates from droopV control to droopP control updates its control method a predetermined time after receiving the update command. Therefore, as shown in Figure 8A, even if the update from droopP control to droopV control is delayed in the power converter 11, a power converter that performs droopV control will be present, and the occurrence of unintended voltage increases and decreases on the bus 30 can be suppressed.

[0073] Second embodiment Next, a second embodiment of the present invention will be described. The power system according to the second embodiment differs from the first embodiment in the method of centralized control and the method of updating the reference function and the feedback control method. Since the other configurations are the same as those of the first embodiment, the same reference numerals are used for the same configurations as those of the first embodiment and the description is omitted. In the following description, the differences from the first embodiment will be described.

[0074] 9 is a diagram showing a configuration mainly related to a power conversion function of a control unit 11c according to the second embodiment. The control unit 11c according to the second embodiment differs from the control unit 11c according to the first embodiment in that the update unit 11cc outputs information indicating that the update of the reference function and the feedback control method has been completed to the communication unit 11d.

[0075] 10 is a flowchart showing the flow of the update process of the reference function and the feedback control method performed by the power converter to be updated in the second embodiment. Note that the processes of steps S301 to S303 are the same as those in the first embodiment, and therefore the description will be omitted. After completing the process of step S303, the control unit 11c outputs update end information indicating that the update process of the reference function and the feedback control method has been completed to the communication unit 11d (step S304). This update end information is transmitted from the communication unit 11d to the EMS 40.

[0076] Next, the centralized control in the second embodiment will be described with reference to the sequence diagram of Fig. 11. Note that in the centralized control in the second embodiment, the processes of steps S201 to S206 shown in Fig. 6 are completed before step S401 shown in Fig. 11.

[0077] After executing the operation optimization calculation, EMS 40 outputs an update command to the power converters to be updated for the reference function and the feedback control method. Specifically, EMS 40 stores information indicating the feedback control methods executed by power converters 11-14 in storage unit 42, and identifies the feedback control methods executed by the power converters to be updated by referring to this information (step S401). Here, for example, it is identified that power converters 11 and 13 are executing droopP control, and power converter 14 is executing droopV control.

[0078] Next, the EMS 40 outputs an update command for the reference function (droop function) and the feedback control method to the power converter 11 that is executing the droopP control (step S402). Here, the EMS 40 does not output an update command to the other power converters to be updated until it receives update completion information transmitted from the power converter 11. The power converter 11 that receives the update command executes the process of FIG. 10 to update the reference function and the feedback control method (step S403). When the power converter 11 finishes updating the reference function and the feedback control method, it transmits update completion information to the EMS 40 (step S404) and executes its own end control (step S405).

[0079] The EMS 40, which has received the update completion information transmitted by the power converter 11, outputs an update command to the power converter 13, which is also executing the droopP control, to update the reference function (droop function) and the feedback control method (step S406). Here, the EMS 40 does not output an update command to the other power converters to be updated until it receives the update completion information transmitted from the power converter 11. The power converter 13, which has received the update command, executes the process of FIG. 10 to update the reference function and the feedback control method (step S407). When the power converter 13 finishes updating the reference function and the feedback control method, it transmits the update completion information to the EMS 40 (step S408) and executes its own end control (step S409).

[0080] When the EMS 40 receives the update end information transmitted by the power converter 13 and finishes outputting the update command to the power converter that was executing the droopP control, it then outputs an update command for the reference function (droop function) and the feedback control method to the power converter 13 that is executing the droopV control (step S410). The power converter 14 that received the update command executes the process of FIG. 10 and updates the reference function and the feedback control method (step S411). When the power converter 14 finishes updating the reference function and the feedback control method, it transmits the update end information to the EMS 40 (step S412) and executes its own end control (step S413). Next, the EMS 40 that receives the update end information transmitted by the power converter 14 resets the timer (step S414).

[0081] 12 is a diagram showing the timing at which the reference function information and the feedback control method are updated in a power converter that has received an update command. In the second embodiment, after the power converter 11 that is executing the droopP control has finished updating to the droopV control, the EMS 40 outputs an update command to the droopP control to the power converter 14 that is executing the droopV control. This ensures that a power converter that is executing the droopV control is always present, and the occurrence of unintended voltage increases and decreases in the bus 30 can be suppressed.

[0082] In the second embodiment, when an update command to droopP control is output to a power converter executing droopV control, the power converter executing droopP control has completed the update to droopV control and a power converter executing droopV control exists, so the processing of steps S301 and S302 may not be executed.

[0083] (Modification) Although the embodiment of the present invention has been described above, the present invention is not limited to the above-mentioned embodiment and can be implemented in various other forms. For example, the above-mentioned embodiment may be modified as follows to implement the present invention. The above-mentioned embodiment and the following modifications may be combined with each other. The present invention also includes a configuration in which the components of the above-mentioned embodiments and modifications are appropriately combined. Further effects and modifications can be easily derived by a person skilled in the art. Therefore, the broader aspects of the present invention are not limited to the above-mentioned embodiment and modifications, and various modifications are possible.

[0084] In the above embodiment, a current value may be used instead of a power value as an electrical characteristic value such as a measured value, a target value, or a controlled value. In this case, for example, the reference function is defined as a VI characteristic that is a relationship between a current (I) and a voltage (V). Also, for example, feedback control in which the control unit 11c determines a target power Iref (an example of a target value) based on a measured voltage value Vo by the sensor 11b and reference function information, and sets a manipulated variable so that the difference between Iref and a measured current value Io (an example of a controlled value) by the sensor 11b is within an allowable range, is also called droopI control, and is executed in place of droopP control. Also, in droopV control, a target voltage Vref is determined based on a measured current value Io by the sensor 11b and reference function information.

[0085] In the above-described embodiment, different reference function information may be stored in the memory unit 11cd, and the reference function information used by the manipulated variable setting unit 11ca may be switched among the stored reference function information in response to a command from the EMS40.

[0086] In the first embodiment described above, as in the second embodiment, an update command may be output first to the power converter executing droopP control, and then an update command may be output to the power converter executing droopV control.

[0087] In each of the above-mentioned embodiments, the feedback control performed by each power converter is not limited to the droopV control or the droopP control based on the reference function, but may be a constant voltage control that keeps the voltage constant or a constant power control that keeps the power constant. The constant voltage control, which is an example of the voltage control, and the constant power control, which is an example of the power control, are examples of the control method for controlling the output of the power conversion unit 11a. [Industrial Applicability]

[0088] The present invention can be used in a power system and a control method for a power system. [Explanation of symbols]

[0089] 11, 12, 13, 14: Power converter 11a: Power conversion section 11b: Sensor 11c, 41: Control section 11ca: Operation amount setting section 11cb: Judgment part 11cc: Update section 11cd, 42: Storage section 11d, 43: Communications Department 21, 22, 23, 24: Power elements 30: Bus 40: EMS 100: Power Systems 200: External server DL1, DL2, DL3, DL4: Line EV: Electric vehicle NW: Network

Claims

1. a power conversion unit that converts input power and outputs the converted power; a control unit that controls the power conversion unit based on a reference function having a drooping characteristic defined according to an input value and a voltage or power of a bus to which the power conversion unit is connected, to execute control of the output, which is primary control; an update unit that updates the output control method; a plurality of power converters having a central control unit performing secondary control for controlling the power converter; A bus connected to the power conversion unit; A power element capable of supplying, consuming or charging power, connected to the power converter; Equipped with The central control device performs secondary control of the power converter with an update command for updating the control method; The update unit updates the control method in response to the update command output from the central control device, During a period in which the control method is updated for the plurality of power converters, the control method is updated so that there is always at least one of the plurality of power converters that performs voltage control. Power system.

2. The primary control, which is the control of the output, is based on the voltage or current of the bus without any command from a central controller. The power system of claim 1 .

3. Among the plurality of power converters, the power converter that executes voltage control updates the control method after a predetermined time has elapsed since acquiring the update command. The power system according to claim 1 or 2.

4. The central control device outputting the update command to a power converter that is performing power control among the plurality of power converters, and then outputting the update command to a power converter that is performing voltage control among the plurality of power converters The power system according to claim 1 or 2.

5. a plurality of power converters connected to the bus and having power conversion units that convert and output input power; A power element capable of supplying, consuming or charging power, connected to the power converter; A central control device that controls the power converter; A method for controlling a power system provided with a step of converting input power by the power conversion unit and outputting the converted power; A step of controlling the power conversion unit based on a reference function having a drooping characteristic defined according to an input value and a voltage or power of the bus to which the power conversion unit is connected, thereby executing a control of the output, which is a primary control; the central controller secondarily controls the power converter with an update command for updating the control method; updating a control method of the output by the power converter in response to the update command; having During a period in which the control method is updated for the plurality of power converters, the control method is updated so that there is always at least one of the plurality of power converters that performs voltage control. Power system control methods.

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