Power converter, power system, and method for controlling power converter

Abstract

A power converter that comprises a control unit that controls the power conversion characteristics of a power conversion unit in accordance with an input value and a reference function to which a plurality of droop functions are connected. For each droop function, the power converter acquires a control area that defines a voltage and power or current range for which voltage control or power or current control is to be performed. The control area is set such that, when an operating point has deviated from the droop function, the variation or the number of variations in the voltage or the power or current is minimized during the time until the voltage or the power or current, without converging outside a range defined by the connection point of the droop function, converges on a given droop function after varying. A control method for the power conversion characteristics is set on the basis of the control area and the operating point. When the operating point has transitioned through the control area, the control area is altered in accordance with the droop function that corresponds to the post-transition control area.

Description

[Technical field]

[0001] The present invention relates to a power converter, a power system, and a method for controlling a power converter. [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] When the power of a device connected to a power converter fluctuates, other power converters connected to the same DC bus and performing droop control adjust their output with a delay. For this reason, for example, when the constant power load increases suddenly, the voltage of the DC bus drops suddenly, and when the constant power load decreases suddenly, the voltage of the DC bus rises suddenly, and the DC bus may have a voltage or power that is significantly different from the drooping characteristic of the reference function. In a power converter performing droop control, feedback control (power control) that observes the output voltage to determine the target power and make the difference between the target power and the output power zero, and feedback control (voltage control) that observes the output power to determine the target voltage and make the difference between the target voltage and the output voltage zero are switched according to the power range and voltage range of the DC bus. However, when the voltage of the DC bus suddenly changes in this way, if the switching of the feedback control is not appropriate, problems such as a long settling time and a steady-state deviation may occur when trying to return to the voltage and power according to the reference function.

[0007] The present invention has been made in view of the above, and has an object to suppress the occurrence of steady-state deviation with respect to a reference function determined during voltage control, power control, or current control, and to shorten the settling time. [Means for solving the problem]

[0008] One aspect of the present invention is a power converter comprising: a power conversion unit that converts input power and outputs it; and a control unit that controls the power conversion characteristics of the power conversion unit in accordance with an input value by voltage control, power control, or current control corresponding to a reference function having a droop characteristic defined in accordance with an input value, based on the reference function, the reference function being configured by connecting a plurality of droop functions having different droop characteristics at connection points, and a control area is obtained for each of the plurality of droop functions, the control area defining a range of voltage, power, or current for which corresponding voltage control, power control, or current control is performed, the control area being set such that, when an operating point determined from the input value fluctuates to deviate from the droop function, the droop function does not converge to a position outside the range defined by the connection points, and the amount of fluctuation or the number of fluctuations in voltage, power, or current after the fluctuation is minimized until the operating point converges to a certain droop function, the control method of the power conversion characteristics is set to voltage control, power control, or current control based on the control area and the operating point, and, when the operating point transitions between the control areas, the control area is changed in accordance with the droop function corresponding to the control area after the transition.

[0009] One aspect of the present invention includes a power conversion unit that converts and outputs input power, and a control unit that controls the power conversion characteristics of the power conversion unit in accordance with the input value by voltage control, power control, or current control corresponding to a reference function having a droop characteristic defined in accordance with an input value, the reference function being configured by connecting a plurality of droop functions having different droop characteristics from each other, and a control area is obtained for each of the plurality of droop functions, the control area defining the range of voltage, power, or current for which corresponding voltage control, power control, or current control is performed, and when an operating point determined from the input value is on the droop function that performs voltage control, the vicinity of the droop function is set as the control area for droop functions other than the droop function on which the operating point is located, and the control area for the droop function on which the operating point is located is set as the control area excluding the control areas of the other droop functions, a power converter which sets a control method for the power conversion characteristics to voltage control, power control, or current control based on the control area and the operating point; and, if the operating point is on a droop function that performs power control or current control, and the droop function has a constant power or constant current droop characteristic, the control area is set so that control corresponding to the droop function connected is performed when the voltage of the operating point exceeds a connection point of the droop function; and, if the operating point is on a droop function that performs power control or current control, and the droop function does not have a constant power or constant current droop characteristic, the control area is set so that control corresponding to the droop function connected is performed when the power of the operating point exceeds a connection point of the droop function; and, if the operating point transitions between control areas, the control area is changed in accordance with the droop function corresponding to the control area after the transition.

[0010] The power converter may include a measurement unit that acquires a measurement value of an electrical characteristic value of the input or output power, and the control unit may control the power conversion characteristics based on a control target value of the electrical characteristic value based on the measurement value and a target value of the electrical characteristic value based on the reference function.

[0011] The control unit may select types of electrical characteristic values ​​of the measurement value, the control object value, and the target value in accordance with a droop characteristic of the droop function.

[0012] The control unit may select, as the measurement value, a power value or a current value when an absolute value of a droop coefficient of the droop function is smaller than a predetermined value, and select a voltage value when the absolute value of the droop coefficient is equal to or greater than a predetermined value.

[0013] The reference function may be switched or updated based on an external command.

[0014] The power converter may include a storage unit that stores the reference function in a switchable or updatable manner.

[0015] One aspect of the present invention is a power system comprising: the power converter; a bus connected to the power converter; and a power element connected to the power converter, capable of supplying, consuming or charging power.

[0016] The power system may include a plurality of the power converters and a central control device that outputs an instruction to switch or update a reference function of at least one of the plurality of power converters, and the central control device may output the instruction based on a power condition of the power system.

[0017] The central control device may output the command based on information obtained from the plurality of power converters.

[0018] One aspect of the present invention is a control method for a power converter, comprising a control step of controlling power conversion characteristics of the power converter with voltage control, power control, or current control corresponding to a reference function having droop characteristics defined in accordance with an input value, based on the reference function having droop characteristics different from each other and connected at connection points, the reference function being configured by connecting a plurality of droop functions having different droop characteristics at connection points, the control step comprising the steps of acquiring a control area for each of the plurality of droop functions, the control area defining a voltage and power range for performing corresponding voltage control, power control, or current control, when an operating point determined from the input value transitions between the control areas, changing the control area in accordance with the droop function corresponding to the control area after the transition, and setting a control method for the power conversion characteristics to voltage control, power control, or current control based on the control area and the operating point, the control area being set such that, when the operating point determined from the input value fluctuates so as to deviate from the droop function, the droop function does not converge to a position outside the range defined by the connection points, and the amount of fluctuation or the number of fluctuations of the voltage, power, or current until the operating point converges to a certain droop function after the fluctuation is minimized.

[0019] One aspect of the present invention is a control method for a power converter, comprising a control step of controlling a power conversion characteristic of the power converter with voltage control, power control, or current control corresponding to a reference function having a droop characteristic defined according to an input value, based on the reference function having a droop characteristic defined according to the input value, the reference function being configured by connecting a plurality of droop functions having different droop characteristics from each other, and the control method includes the steps of: acquiring a control area that specifies a voltage, power, or current range for performing corresponding voltage control, power control, or current control for each of the plurality of droop functions; changing the control area according to the droop function corresponding to the control area after the transition, when an operating point determined from the input value transitions between the control areas; and setting a control method for the power conversion characteristic to voltage control, power control, or current control based on the control area and the operating point, When the operating point is on a droop function that performs power control or current control, for droop functions other than the droop function on which the operating point is located, the vicinity of the droop function is set as the control area, and for the droop function on which the operating point is located, the area excluding the control areas of the other droop functions is set as the control area. When the operating point is on a droop function that performs power control or current control and the droop function has a constant power or constant current droop characteristic, the control area is set so that control corresponding to the droop function connected is performed when the voltage of the operating point exceeds a connection point of the droop function. When the operating point is on a droop function that performs power control or current control and the droop function does not have a constant power or constant current droop characteristic, the control area is set so that control corresponding to the droop function connected is performed when the power of the operating point exceeds the connection point of the droop function. Effect of the Invention

[0020] The power converter and power system of the present invention include a power conversion unit that converts input power and outputs it, and a control unit that controls the power conversion characteristics of the power conversion unit in accordance with the input value by voltage control, power control, or current control corresponding to a reference function having a droop characteristic defined in accordance with an input value, based on the reference function, the droop function having different droop characteristics, connected at a connection point, and a control area that specifies the range of voltage, power, or current for which corresponding voltage control, power control, or current control is performed is obtained for each of the multiple droop functions, and the control area is set so that, when an operating point determined from the input value fluctuates to deviate from the droop function, the droop function does not converge to a position outside the range specified by the connection point, and the amount of fluctuation or the number of fluctuations of the voltage, power, or current until the operating point converges to a certain droop function after the fluctuation is minimized, and a control method for the power conversion characteristics is set to voltage control, power control, or current control based on the control area and the operating point, and when the operating point transitions between the control areas, the control area is changed in accordance with the droop function corresponding to the control area after the transition. Since the control area is set so that the operating point does not converge outside the range of the connection point of the droop function and the amount or number of fluctuations in voltage, power or current until it converges to the droop function is small, no steady-state deviation occurs, and since the control area is changed in response to the operating point transitioning across the control area, the settling time can be reduced.

[0021] The power converter and power system of the present invention include a power conversion unit that converts input power and outputs it, and a control unit that controls the power conversion characteristics of the power conversion unit according to the input value with voltage control, power control, or current control corresponding to a reference function having a droop characteristic defined according to an input value, the reference function being configured by connecting a plurality of droop functions having different droop characteristics from each other, and a control area that specifies the range of voltage, power, or current for performing corresponding voltage control, power control, or current control is obtained for each of the plurality of droop functions, and when an operating point determined from the input value is on the droop function performing voltage control, a vicinity of the droop function other than the droop function on which the operating point is located is set as the control area, and for the droop function on which the operating point is located, an area excluding the control areas of the other droop functions is set as the control area. The control area is set to an area, the operating point is on a droop function that performs power control or current control, and when the droop function has a droop characteristic of constant power or constant current, the control area is set so that control corresponding to the droop function connected is performed when the voltage of the operating point exceeds a connection point of the droop function, and when the operating point is on a droop function that performs power control or current control, and when the droop function does not have a droop characteristic of constant power or constant current, the control area is set so that control corresponding to the droop function connected is performed when the power of the operating point exceeds a connection point of the droop function, and a control method of the power conversion characteristic is set to voltage control, power control, or current control based on the control area and the operating point, and when the operating point transitions between the control areas, the control area is changed according to the droop function corresponding to the control area after the transition. Since the control area is set so that the operating point does not converge outside the range of the connection points of the droop function and the amount or number of fluctuations of the voltage, power, or current until the operating point converges to the droop function is small, no steady-state deviation occurs, and since the control area is changed in response to the transition of the operating point between the control areas, the settling time can be reduced.

[0022] The control method for a power converter of the present invention includes a control step of controlling power conversion characteristics of the power converter with voltage control, power control, or current control corresponding to a reference function having droop characteristics defined in accordance with an input value, the reference function being configured by connecting a plurality of droop functions having different droop characteristics at connection points, and the control method includes the steps of acquiring a control area for each of the plurality of droop functions, the control area defining a voltage and power range for performing corresponding voltage control, power control, or current control, when an operating point determined from the input value transitions between the control areas, changing the control area in accordance with the droop function corresponding to the control area after the transition, and setting a control method for the power conversion characteristics to voltage control, power control, or current control based on the control area and the operating point, the control area being set such that, when the operating point determined from the input value fluctuates so as to deviate from the droop function, the droop function does not converge to a position outside the range defined by the connection points, and the amount or number of fluctuations in voltage, power, or current until the operating point converges to a certain droop function after the transition is minimized. Since the control area is set so that the operating point does not converge outside the range of the connection point of the droop function and the amount or number of fluctuations in voltage, power or current until it converges to the droop function is small, no steady-state deviation occurs, and since the control area is changed in response to the operating point transitioning across the control area, the settling time can be reduced.

[0023] The control method for a power converter of the present invention includes a control step of controlling a power conversion characteristic of the power converter with voltage control, power control, or current control corresponding to a reference function having a droop characteristic defined according to an input value, the reference function being configured by connecting a plurality of droop functions having different droop characteristics from each other, and includes a step of acquiring a control area that specifies a voltage, power, or current range for performing corresponding voltage control, power control, or current control for each of the plurality of droop functions, a step of changing the control area in accordance with the droop function corresponding to the control area after the transition when an operating point determined from the input value has transitioned from one control area to another, and a step of setting a control method for the power conversion characteristic to voltage control, power control, or current control based on the control area and the operating point, and performing voltage control. When the operating point is on a droop function, the vicinity of the droop function is set as the control area for droop functions other than the droop function on which the operating point is located, and the area excluding the control areas of the other droop functions is set as the control area for the droop function on which the operating point is located, when the operating point is on a droop function that performs power control or current control and the droop function has a droop characteristic of constant power or constant current, the control area is set so that control corresponding to the droop function connected is performed when the voltage of the operating point exceeds the connection point of the droop function, when the operating point is on a droop function that performs power control or current control and the droop function does not have a droop characteristic of constant power or constant current, the control area is set so that control corresponding to the droop function connected is performed when the power of the operating point exceeds the connection point of the droop function. The control area is set so that the operating point does not converge outside the range of the connection point of the droop function and the amount or number of fluctuations of the voltage, power, or current until the operating point converges to the droop function is small, so that no steady-state deviation occurs, and the control area is changed in response to the transition of the operating point to the control area, so that the settling time can be reduced. [Brief description of the drawings]

[0024] [Figure 1] FIG. 1 is a diagram showing a configuration of a power system according to an 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 a control area indicated by the control area information. [Figure 4C] FIG. 4C is a diagram showing an example of a control area indicated by the control area information. [Figure 4D] FIG. 4D is a diagram showing an example of a control area indicated by the control area information. [Figure 5A] FIG. 5A is a diagram illustrating an example of power conversion characteristics. [Figure 5B] FIG. 5B is a diagram showing an example of a control area indicated by the control area information. [Figure 5C] FIG. 5C is a diagram showing an example of a control area indicated by the control area information. [Figure 5D] FIG. 5D is a diagram showing an example of a control area indicated by the control area information. [Figure 6] FIG. 6 is a flowchart showing the flow of processing performed by the control unit of the power converter. [Figure 7A] FIG. 7A is a diagram showing a comparative example of a control area. [Figure 7B] FIG. 7B is a diagram showing a comparative example of a control area. [Figure 7C] FIG. 7C is a diagram showing a comparative example of a control area. [Figure 7D] FIG. 7D is a diagram showing a comparative example of a control area. [Figure 8] FIG. 8 is a sequence diagram showing an example of a control method for a power system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] 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.

[0026] (Embodiment) <Power system configuration> Fig. 1 is a diagram showing the configuration of a power system according to an embodiment. The power system 100 includes a plurality of power converters 11, 12, 13, and 14, a plurality of power elements 21, 22, 23, and 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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).

[0036] 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.

[0037] 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.

[0038] <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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] The update unit 11cc stores the reference function information and the control area 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 area information stored in the storage unit 11cd. Here, the reference function information is various information for identifying the droop function constituting the reference function, and the control area information is various information for specifying the method of feedback control performed by the manipulated variable setting unit 11ca, which will be described in detail later.

[0045] The determination unit 11cb acquires control area information from the storage unit 11cd, determines the method of feedback control performed by the operation amount setting unit 11ca based on the control area information, and outputs the determination result as 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 an allowable 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 an allowable 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] <Characteristics of reference functions> Next, a reference function and control area information on which the control unit 11c controls the power conversion characteristics of the power conversion unit 11a will be described. Fig. 4A is a diagram showing an example of the power conversion characteristics, and Figs. 4B to 4D are diagrams showing an example of the control area.

[0050] 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.

[0051] 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 with different droop characteristics defined according to the range of the input value. Specifically, the line DL1 is configured by connecting lines DL11, DL12, DL13, and DL14 that represent four droop functions with different droop characteristics, and is specified by the reference function information.

[0052] 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 as to become the characteristics of the reference function shown 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 P defined by the value of V and the value of P on the bus 30 side of the power conversion unit 11a is located on the line DL1. Note that, on the line DL1, the slope of the line DL11 is greater than the slope of the line DL13, and is perpendicular to the P axis.

[0053] 4B to 4D are diagrams showing an example of a control area represented by the control area information corresponding to the line DL1 stored in the storage unit 11cd. The control area specifies a feedback control method to be performed according to the position of the operating point P, and specifies the voltage and power ranges for performing the corresponding droopP control or droopV control for each droop function. Specifically, the control area sets the types of electrical characteristic values ​​of the measurement value, the control target value, and the target value according to the droop characteristic of the corresponding droop function, and when the absolute value of the droop coefficient of the droop function is equal to or greater than a predetermined value, the voltage value is selected as the measurement value, the control target value, and the power value is selected as the target value, and the droopP control is set. When the absolute value of the droop coefficient is smaller than the predetermined value, the power value is selected as the measurement value, the control target value, and the voltage value is selected as the target value, and the droopV control is set. In addition, each control area is set so that the operating point P does not converge outside the range of the connection point of the corresponding droop function. The judgment unit 11cb judges the method of feedback control to be performed by the operation amount setting unit 11ca based on the position of the operating point P on the control area, and outputs the judgment result as judgment information.

[0054] 4B, a control area AR111 shown by hatching with diagonal lines downward to the left including the line DL11 indicates an area where control is performed to position the operating point P on the line DL11 by droopP control, a control area AR113 shown by hatching with diagonal lines downward to the right including the line DL13 indicates an area where control is performed to position the operating point P on the line DL13 by droopP control, and a control area AR114 shown by hatching with dashed lines horizontally including the line DL14 indicates an area where control is performed to position the operating point P on the line DL14 by droopV control. Also, a control area AR112 shown by hatching with dashed lines vertically including the line DL12 and excluding the control areas AR111, AR113, and AR114 indicates an area where control is performed to position the operating point P on the line DL12 by droopV control.

[0055] 4C, a control area AR121 shown by hatching with diagonal lines slanting downward to the left and including the line DL11 indicates an area where control is performed to position the operating point P on the line DL11 by droopP control. A control area AR122 shown by hatching with vertical dashed lines, which includes the line DL12 and is an area excluding the control area AR121 on the negative side of the P axis from the connection point p12 of the line DL12 and the line DL13, indicates an area where control is performed to position the operating point P on the line DL12 by droopV control. A control area AR123 shown by hatching with diagonal lines slanting downward to the right and including the line DL13, is an area in the P axis direction between the connection point p12 of the line DL12 and the line DL13 and the connection point p13 of the line DL13 and the line DL14, indicates an area where control is performed to position the operating point P on the line DL13 by droopP control. A control area AR124, which includes line DL14 and is hatched with horizontal dashed lines on the positive side of the P axis from the connection point p13 between lines DL13 and DL14, indicates the area where droopV control is performed to position the operating point P on line DL14.

[0056] 4D, a control area AR131 shown by hatching with diagonal lines slanting downward to the left and including a line DL11 indicates an area where control is performed to position an operating point P on the line DL11 by droopP control, a control area AR132 shown by hatching with vertical dashed lines slanting to the left and including a line DL12 indicates an area where control is performed to position an operating point P on the line DL12 by droopV control, and a control area AR133 shown by hatching with diagonal lines slanting downward to the right and including a line DL13 indicates an area where control is performed to position an operating point P on the line DL13 by droopP control. Also, a control area AR134 shown by hatching with horizontal dashed lines, which includes a line DL14 and is an area excluding the control areas AR131, AR132, and AR133, indicates an area where control is performed to position an operating point P on the line DL14 by droopV control.

[0057] FIG. 5A is a diagram showing an example of power conversion characteristics, and FIGS. 5B to 5D are diagrams showing other examples of control areas. FIG. 5A shows the power conversion characteristics of the power conversion unit 11a. The line DL2 shown in FIG. 5A is a straight or curved line bent halfway. The reference function represented by this line DL2 is configured by connecting lines representing four 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 in the same manner as the line DL1. Specifically, the line DL2 is configured by connecting lines DL21, DL22, DL23, and DL24 representing four droop functions with different droop characteristics, and is specified by the reference function information.

[0058] When the reference function information represents the reference function shown in Fig. 5A, 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 14 controls the power conversion unit 11a so that the operating point P defined by the value of V and the value of P is located on the line DL2. Note that the lines DL21 and DL23 are perpendicular to the P axis.

[0059] 5B to 5D are diagrams showing an example of a control area represented by control area information corresponding to the line DL2 stored in the storage unit 11cd. In FIG. 5B, a control area AR211 shown by hatching with diagonal lines slanting downward to the left including the line DL21 indicates an area where control is performed to position the operating point P on the line DL21 by the droopP control, and a control area AR212 shown by hatching with vertical dashed lines including the line DL22 indicates an area where control is performed to position the operating point P on the line DL22 by the droopV control. In addition, a control area AR213 shown by hatching with diagonal lines slanting downward to the right including the line DL23 indicates an area where control is performed to position the operating point P on the line DL23 by the droopP control, and a control area AR214 shown by hatching with horizontal dashed lines including the line DL24 indicates an area where control is performed to position the operating point P on the line DL24 by the droopV control.

[0060] 5C, control area AR221 shown by hatching with diagonal lines downward to the left and including line DL21 indicates an area where control is performed to position operating point P on line DL21 by droopP control, control area AR223 shown by hatching with diagonal lines downward to the right and including line DL23 indicates an area where control is performed to position operating point P on line DL23 by droopP control, and control area AR224 shown by hatching with horizontal dashed lines and including line DL24 indicates an area where control is performed to position operating point P on line DL24 by droopV control. Also, control area AR222 shown by hatching with vertical dashed lines, which is an area including line DL22 and excluding control area AR221, control area AR223, and control area 224, indicates an area where control is performed to position operating point P on line DL22 by droopV control.

[0061] 5D, a control area AR231 shown by hatching with diagonal lines slanting downward to the left and including the line DL21 indicates an area where control is performed to position the operating point P on the line DL21 by droopP control, a control area AR232 shown by hatching with vertical dashed lines slanting to the left and including the line DL22 indicates an area where control is performed to position the operating point P on the line DL22 by droopV control, and a control area AR233 shown by hatching with diagonal lines slanting downward to the right and including the line DL23 indicates an area where control is performed to position the operating point P on the line DL23 by droopP control. Also, a control area AR234 shown by hatching with horizontal dashed lines, which includes the line DL24 and is an area excluding the control areas AR231, AR232, and 233, indicates an area where control is performed to position the operating point P on the line DL24 by droopV control.

[0062] <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.

[0063] <Self-control> First, a control method for the power converters 11, 12, 13, and 14 in self-end control will be described using the power converter 11 as an example. A control method similar to that described below may be appropriately executed for the other power converters 12 and 13. If 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 according to the amount of power generated from the power element 22 is input, so that the output power to the bus 30 is maximized at that amount of power generation.

[0064] 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 information and the control area information.

[0065] An example of the contents of the control steps will be described more specifically with reference to Figures 4B to 4D, 5B to 5D, 6, and 7A to 7D. Figure 6 is a flowchart showing the flow of the process performed by the control unit 11c.

[0066] First, in the control unit 11c, the manipulated variable setting unit 11ca acquires a measurement value from the sensor 11b (step S101). Next, in the control unit 11c, the manipulated variable setting unit 11ca acquires reference function information from the storage unit 11cd (step S102).

[0067] Next, in the control unit 11c, the determination unit 11cb determines the feedback control method to be executed by the operation amount setting unit 11ca based on the position of the operating point P on the control area, based on the measured value and the control area information already acquired from the storage unit 10cd (step S103). The process in which the determination unit 11cb reads the control area information from the storage unit 11cd is an example of a step in which the determination unit 11cb acquires the control area information. Next, the control unit 11c determines whether the feedback control method determined by the determination unit 11cb is the same as the current feedback control method being executed by the operation amount setting unit 11ca (step S104).

[0068] When the feedback control method determined by the determination unit 11cb is the same as the current feedback control method being executed by the manipulated variable setting unit 11ca (YES in step S104), the control unit 11c proceeds to step S106.

[0069] In the control unit 11c, when the feedback control method determined by the determination unit 11cb is different from the current feedback control method being executed by the operation amount setting unit 11ca (NO in step S104), the control area information used by the determination unit 11cb to determine the feedback control method is obtained from the storage unit 11cd and changed (step S105). Step S105 is an example of a step of changing the control area.

[0070] Specifically, when the feedback control method determined in step S103 is droopV control, the determination unit 11cb changes the control area information to a vicinity of the droop function for a droop function other than the droop function that causes the operating point P to converge with the droopV control, and changes the control area information to a control area information for a droop function that causes the operating point P to converge with the droopV control, with the other area being the control area. The vicinity of the droop function is, for example, an area of ​​a predetermined width in a direction perpendicular to the straight line if the droop function is a straight line, and an area of ​​a predetermined width in a direction perpendicular to the tangent to the curve if the droop function is a curve. This predetermined width is set to a width according to the desired control.

[0071] For example, when the feedback control method determined in step S103 is droopV control for converging the operating point P to the line DL12, the determination unit 11cb changes the control area information to that shown in Fig. 4B, and when the feedback control method determined in step S103 is droopV control for converging the operating point P to the line DL14, the determination unit 11cb changes the control area information to that shown in Fig. 4D. Also, when the feedback control method determined in step S103 is droopV control for converging the operating point P to the line DL22, the determination unit 11cb changes the control area information to that shown in Fig. 5C, and when the feedback control method determined in step S103 is droopV control for converging the operating point P to the line DL24, the determination unit 11cb changes the control area information to that shown in Fig. 5D.

[0072] Furthermore, when the feedback control method determined in step S103 is droopP control and the slope of the droop function that causes the operating point P to converge in this droopP control is not perpendicular to the P axis, the determination unit 11cb changes the droop function of the droopP control, whose slope is not perpendicular to the P axis, to control area information indicating a control area divided at the connection points of the droop function in the P axis direction. For example, when the feedback control method determined in step S103 is droopP control that causes the operating point P to converge to line DL13, the determination unit 11cb changes to the control area information shown in FIG. 4C.

[0073] Furthermore, when the feedback control method determined in step S103 is droopP control and the slope of the droop function that converges the operating point P in this droopP control is perpendicular to the P axis, the determination unit 11cb changes the droop function of the droopP control perpendicular to the P axis to a control area that has a range from the upper end to the lower end of the droop function in the V axis direction and a range in the vicinity of the droop function in the P axis direction, and changes the droop function of the droopV control to control area information indicating a control area divided at the connection points of the droop function in the P axis direction. For example, when the feedback control method determined in step S103 is droopP control that converges the operating point P to the line DL21 or the line DL23, the determination unit 11cb changes to the control area information shown in FIG. 5B.

[0074] Next, in the control unit 11c, the manipulated variable setting unit 11ca acquires the judgment information output from the judgment unit 11cb, sets the manipulated variable for executing the feedback control in the control method based on the acquired judgment information based on the measured value and the reference function information, and outputs it to the power conversion unit 11a (step S106). This causes the control of the power conversion unit 11a to be executed. Step S106 is an example of a step of setting the control method of the power conversion characteristics to voltage control or power control.

[0075] Next, an example of the operation of power converter 11 when the output of a device connected to bus 30 fluctuates will be described in comparison with a configuration in which the control area is not appropriately set and the control area information is not changed.

[0076] First, Fig. 7A is a diagram showing an example in which the control area is divided by voltage for the reference function shown by line DL1. In Fig. 7A, a control area AR31 including line DL11 indicates an area where control is performed to position the operating point P on line DL11 by droopP control, and a control area AR32 including line DL12 indicates an area where control is performed to position the operating point P on line DL12 by droopV control. Also, in Fig. 7A, a control area AR33 including line DL13 indicates an area where control is performed to position the operating point P on line DL13 by droopP control, and a control area AR34 including line DL14 indicates an area where control is performed to position the operating point P on line DL14 by droopV control.

[0077] When the control unit 11c performs feedback control based on the reference function and control area shown in FIG. 7A, if the operating point P is on the line DL12, the control unit 11c executes droopV control. In this state, for example, if the load of the power element connected to the bus 30 drops, the current supplied to the bus 30 rises, and if the transient response characteristic is slow, the voltage of the bus 30 rises transiently, so that the operating point P transitions to the control area AR31 as shown by the arrow (1). When the operating point P transitions from the control area AR32 to the control area AR31, the control unit 11c executes droopP control so that the operating point P is located on the line DL11, so that the output current of the power element 21 connected to the power converter 11 drops suddenly, and the operating point P moves as shown by the arrow (2). When the output current of the power element 21 drops, the voltage of the bus 30 drops transiently, so that the operating point P transitions to the control area AR33 as shown by the arrow (3). When the operating point P transitions from the control area AR31 to the control area AR33, the control unit 11c executes the droopP control so that the operating point P is located on the line DL13, so that the output current of the power element 21 connected to the power converter 11 rises suddenly, and the operating point P moves as shown by the arrow (4). When the output current of the power element 21 rises suddenly, the voltage of the bus 30 rises transiently, and the operating point P transitions again to the control area AR31 as shown by the arrow (5). In this way, when the control areas are divided by voltage, the operating point P does not converge to the line DL1, and the voltage and current of the bus 30 repeatedly fluctuate between rising and falling, that is, the operating point P repeatedly fluctuates beyond the droop function, which may occur.

[0078] In contrast, in this embodiment, when the operating point P is on the line DL12, the control area is as shown in Fig. 4B. In this case, when the load of the power element connected to the bus 30 decreases, the current supplied to the bus 30 increases and the voltage of the bus 30 increases transiently, but the position of the operating point P is located in the control area AR112. Here, the control unit 11c executes the droopV control so that the operating point P is located on the line DL12, so that the operating point P converges on the line DL12 and the voltage and current of the bus 30 do not repeatedly rise and fall as in the comparative example described above, that is, the operating point P does not repeatedly fluctuate beyond the droop function.

[0079] Next, Fig. 7B is a diagram showing an example in which the control area is divided by power for the reference function shown by line DL1. In Fig. 7B, a control area AR41 including line DL11 indicates an area where control is performed to position the operating point P on line DL11 by droopP control, and a control area AR42 including line DL12 indicates an area where control is performed to position the operating point P on line DL12 by droopV control. Also, in Fig. 7B, a control area AR43 including line DL13 indicates an area where control is performed to position the operating point P on line DL13 by droopP control, and a control area AR44 including line DL14 indicates an area where control is performed to position the operating point P on line DL14 by droopV control.

[0080] When the control unit 11c performs feedback control based on the reference function and control area shown in Fig. 7B, if the operating point P is on the line DL11, the control unit 11c performs droopP control. In this state, for example, if the load increases in the power element connected to the bus 30, the current supplied to the bus 30 decreases, and if the transient response characteristic is slow, the voltage of the bus 30 decreases transiently, so that the operating point P decreases as shown by the arrow (1). Here, since the control unit 11c performs droopP control according to the control area AR41, the operating point P remains located on the extension of the line DL11, causing a steady-state deviation.

[0081] In contrast, in this embodiment, when the operating point P is on the line DL11, the control area is as shown in Fig. 4C. In this case, when the load of the power element connected to the bus 30 increases, the current supplied to the bus 30 decreases and the voltage of the bus 30 decreases transiently, so that the operating point P decreases, but the position of the operating point P is located in the control area AR122. Here, the control unit 11c executes the droopV control so that the operating point P is located on the line DL12. In addition, since the feedback control method to be executed is the droopV control different from the droopP control executed up to that point, the control unit 11c changes the control area used for determining the control method to be executed to the control area shown in Fig. 4B in the above-mentioned step S105.

[0082] Next, when the control unit 11c performs droopV control so that the operating point P converges on the line DL12 according to the changed control area shown in FIG. 4B, the operating point P transitions to the control area AR113. Here, the control unit 11c performs droopP control so that the operating point P is located on the line DL13. In addition, since the feedback control method to be executed is droopP control different from the droopV control executed up until then, the control unit 11c changes the control area used to determine the control method to be executed to the control area shown in FIG. 4C in the above-mentioned step S105. Next, when the control unit 11c performs droopP control so that the operating point P converges on the line DL13 according to the changed control area shown in FIG. 4C, the operating point P converges on the line DL13, so that the operating point P does not remain located on the extension line of the line DL11, and no steady-state deviation occurs.

[0083] Next, the case where the control unit 11c performs feedback control based on the reference function and control area shown in FIG. 7B and the operating point P is on the line DL12 will be described. In this case, the control unit 11c performs droopV control. In this state, for example, if the load increases in the power element connected to the bus 30, the current supplied to the bus 30 decreases, and if the transient response characteristic is slow, the voltage of the bus 30 decreases transiently, so that the operating point P decreases as shown by the arrow (2). Here, the control unit 11c performs droopV control so as to converge to the line DL12 according to the control area AR42, so that the output current of the power element 21 connected to the power converter 11 increases, and the operating point P moves as shown by the arrow (3).

[0084] When the output current of the power element 21 rises, the operating point P transitions to the control area AR43. When the operating point P transitions from the control area AR42 to the control area AR43, the control unit 11c executes the droopP control so that the operating point P is located on the line DL13, and therefore the output current of the power element 21 rises sharply. When the output current of the power element 21 rises sharply, the voltage of the bus 30 rises transiently, and therefore the operating point P is located above the line DL13 as shown by the arrow (4). Here, the control unit 11c executes the droopP control so that the operating point P is located on the line DL13, and therefore the output current of the power element 21 falls, and the operating point P moves as shown by the arrow (5). When the output current of the power element 21 falls sharply, the voltage of the bus 30 falls transiently, and therefore the operating point P is located below the line DL13 as shown by the arrow (6). Here, the control unit 11c executes droopP control so that the operating point P is located on the line DL13, and the output current of the power element 21 rises sharply again. In this way, if the control area is divided by power for the droop function of the line DL13 that is not perpendicular to the P axis, the fluctuations in the voltage and current become large, and the voltage and current fluctuate repeatedly, that is, the operating point P fluctuates repeatedly beyond the droop function, and a problem occurs in that it takes time for the operating point P to converge to the line DL13.

[0085] In contrast, in this embodiment, when the operating point P is on the line DL12, the control area is as shown in FIG. 4B. In this state, when the load of the power element connected to the bus 30 increases, the current supplied to the bus 30 decreases and the voltage of the bus 30 decreases transiently, so that the operating point P decreases. Here, the control unit 11c executes the droopV control according to the control area AR112, so that the operating point P moves to the positive side of the P axis and transitions to the control area AR113. When the operating point P transitions to the control area AR113, the control unit 11c executes the droopP control so that the operating point P is located on the line DL13. Here, since the control area AR113 is in the vicinity of the line DL13, the output current of the power element 21 does not suddenly rise. In addition, since the feedback control method to be executed is the droopP control, which is different from the droopV control executed up to that point, the control unit 11c changes the control area used for determining the feedback control method to be executed to the control area shown in FIG. 4C. Next, when the control unit 11c performs droopP control in accordance with the changed control area shown in Figure 4C, the operating point P converges onto the line DL13, so that the voltage and current do not fluctuate repeatedly, i.e., the operating point P does not fluctuate repeatedly beyond the droop function. As a result, the number of times the operating point fluctuates is reduced compared to the comparative example, the settling time is shortened, and it does not take much time for the operating point P to converge to the line DL13.

[0086] Next, Fig. 7C is a diagram showing an example of a control area in the case where the area including the droop function performing droopV control is widened for the reference function shown by line DL1. In Fig. 7C, a control area AR51 including line DL11 indicates an area where control is performed to position the operating point P on line DL11 by droopP control, and a control area AR52 including line DL12 indicates an area where control is performed to position the operating point P on line DL12 by droopV control. Also, in Fig. 7C, a control area AR53 including line DL13 indicates an area where control is performed to position the operating point P on line DL13 by droopP control, and a control area AR54 including line DL14 indicates an area where control is performed to position the operating point P on line DL14 by droopV control.

[0087] When the control unit 11c performs feedback control based on the reference function and control area shown in Fig. 7C, if the operating point P is on the line DL12, the control unit 11c executes droopV control. In this state, for example, if the load of the power element connected to the bus 30 increases, the current supplied to the bus 30 decreases, and if the transient response characteristic is slow, the voltage of the bus 30 decreases transiently, so that the operating point P transitions to the control area AR54 as shown by the arrow (1). When the operating point P transitions to the control area AR54, the control unit 11c executes droopV control so that the operating point P is located on the line DL14, so that the operating point P converges to the extension of the line DL14 shown by the dashed line in Fig. 7C, and a steady-state deviation occurs.

[0088] In contrast, in this embodiment, when the operating point P is on the line DL12, the control area becomes as shown in Fig. 4B. In this case, when the load increases in the power element connected to the bus 30, the current supplied to the bus 30 decreases and the voltage of the bus 30 decreases transiently, but as described above, the operating point P converges on the line DL13, so no steady-state deviation occurs.

[0089] Next, Fig. 7D is a diagram showing an example of a control area in the case where an area including a droop function performing droopP control whose slope is not perpendicular to the P axis is widened for the reference function shown by the line DL1. In Fig. 7D, a control area AR61 including the line DL11 indicates an area where control is performed to position the operating point P on the line DL11 by the droopP control, a control area AR62 including the line DL12 indicates an area where control is performed to position the operating point P on the line DL12 by the droopV control, and a control area AR64 including the line DL14 indicates an area where control is performed to position the operating point P on the line DL14 by the droopV control. Also, in Fig. 7D, a control area AR63 including the line DL13 and excluding the control area AR61, the control area AR62, and the control area AR63 indicates an area where control is performed to position the operating point P on the line DL13 by the droopP control.

[0090] When the control unit 11c performs feedback control based on the control area shown in Fig. 7D, if the operating point P is on the line DL13, the control unit 11c executes droopP control. In this state, for example, if the load of the power element connected to the bus 30 drops, the current supplied to the bus 30 rises, and if the transient response characteristic is slow, the voltage of the bus 30 rises transiently, causing the operating point P to rise sharply as shown by the arrow (1). When the operating point P rises sharply, the control unit 11c executes droopP control so that the operating point P is located on the line DL13 as shown by the arrow (2), so that the operating point P converges to an extension of the line DL13 shown by the dashed line in Fig. 7D, causing a steady-state deviation.

[0091] In contrast, in this embodiment, when the operating point P is on the line DL13, the control area is as shown in FIG. 4C. In this case, when the load of the power element connected to the bus 30 drops, the current supplied to the bus 30 rises and the voltage of the bus 30 rises transiently, so that the operating point P rises. Here, the control unit 11c executes the droopP control so that the operating point P is located on the line DL13, so that the output current of the power element 21 connected to the power converter 11 drops, and the operating point P transitions to the control area AR122. Here, the control unit 11c executes the droopV control so that the operating point P is located on the line DL12. In addition, the control unit 11c changes the control area used to determine the control method to be executed to the control area shown in FIG. 4B, because the feedback control method to be executed is the droopV control, which is different from the droopP control executed up to that point. Next, when the control unit 11c executes the droopV control so that the operating point P converges on the line DL12 according to the changed control area shown in FIG. 4B, the operating point P converges on the line DL12, and no steady-state deviation occurs.

[0092] As described above, according to the self-end control of this embodiment, the control area is appropriately set, so that no steady-state deviation occurs even if the operating point P moves significantly. Furthermore, according to this embodiment, the control area is appropriately changed according to the position of the operating point P, so that the settling time can be reduced.

[0093] <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 control area information used for control by the power converters 11, 12, 13, and 14 by command. Updating the reference function and control area information by command means that the command includes reference function information related to the reference function and control area information, and a part or the whole of the reference function and the control area information 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 area information in an updatable manner.

[0094] For example, in the information communication between the EMS 40 and the power converters 11, 12, 13, and 14, the command signal for updating the reference function includes the above-mentioned reference function information and control area information. The reference function information and control area information used for the update are stored in the memory unit 42 of the EMS 40, and are read out and used by the control unit 41 as appropriate.

[0095] 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.

[0096] 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.

[0097] 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 .

[0098] 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.

[0099] 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 .

[0100] 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).

[0101] 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.

[0102] 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.

[0103] 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.

[0104] Next, EMS 40 sets reference function information and control area information suitable for the power converter to be updated among power converters 11, 12, 13, and 14 based on the result of the operation optimization calculation, and outputs an update command for the reference function (droop function) and the control area including the set reference function information and control area information (step S207). Next, EMS 40 resets the timer (step S208).

[0105] Next, the power converter to be updated among the power converters 11, 12, 13, and 14 receives a command to update the reference function and the control area, and updates the reference function and the control area (step S209). After updating the reference function and the control area, the power converter executes its own end control (step S210).

[0106] (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.

[0107] 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). In addition, for example, 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. This feedback control is also called droopI control and is executed in place of droopP control. When droopI control is performed, the horizontal axis of the control area is the current. In addition, in droopI control, a target voltage Vref is determined based on a measured current value Io by the sensor 11b and reference function information. The droopI control is an example of current control.

[0108] In the above-described embodiment, different reference function information and control area information may be stored in the memory unit 11cd, and the reference function information and control area information used by the operation amount setting unit 11ca may be switched among the stored reference function information and control area information by a command from the EMS40.

[0109] In each of the above-described embodiments, the feedback control performed by each power converter is not limited to droopV control or droopP control based on a reference function, but may be constant voltage control that keeps the voltage constant or constant power control that keeps the power constant. Constant voltage control, which is an example of voltage control, and constant power control, which is an example of power control, are examples of control methods for controlling the output of the power conversion unit 11a.

[0110] In the above-described embodiment, control area information is provided for each of the multiple control areas, and the multiple control area information is stored in the memory unit 11cd, but the judgment unit 11cb may generate the control area information according to the position of the operating point P and the reference function indicated by the reference function information. [Industrial Applicability]

[0111] The present invention can be used in a power converter, a power system, and a control method for a power converter. [Explanation of symbols]

[0112] 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, DL11~DL14, DL21~DL24: Line AR41~AR44, AR51~AR54, AR61~AR64: Control area AR111~AR114, AR121~AR124, AR131~AR134: Control area AR211~AR214, AR221~AR224, AR231~AR234: Control area 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 a power conversion characteristic of the power conversion unit according to an input value by voltage control, power control, or current control corresponding to a reference function having a drooping characteristic defined according to the input value; Equipped with The reference function is configured by connecting a plurality of droop functions having different droop characteristics at a connection point, obtaining a control area for each of the plurality of droop functions, the control area defining a range of voltage and power or current for performing the corresponding voltage control, power control, or current control; the control area is set so that, when the operating point determined from the input value varies so as to deviate from a droop function, the droop function does not converge to a position outside the range defined by the connection point, and the amount or number of fluctuations in voltage, power, or current from the variation until the operating point converges to a certain droop function is minimized; A control method of the power conversion characteristic is set to voltage control, power control, or current control based on the control area and the operating point; When the operating point transitions between the control areas, the control area is changed according to the droop function corresponding to the control area after the transition. Power converter.

2. a power conversion unit that converts input power and outputs the converted power; a control unit that controls a power conversion characteristic of the power conversion unit according to an input value by voltage control, power control, or current control corresponding to a reference function having a drooping characteristic defined according to the input value; Equipped with The reference function is configured by connecting a plurality of droop functions having different droop characteristics, obtaining a control area for each of the plurality of droop functions, the control area defining a range of voltage, power, or current for which the corresponding voltage control, power control, or current control is performed; When an operating point determined from the input value exists on a droop function that performs voltage control, for droop functions other than the droop function on which the operating point exists, the vicinity of the droop function is set as a control area, and for the droop function on which the operating point exists, an area excluding the control areas of the other droop functions is set as a control area; The operating point is on a droop function that performs power control or current control, and when the droop function has a constant power or constant current drooping characteristic, the control area is set so that when the voltage of the operating point exceeds a connection point of the droop function, control corresponding to the connected droop function is performed; The control area is set so that, when the operating point is on a droop function that performs power control or current control and the droop function does not have a constant power or constant current droop characteristic, when the power of the operating point exceeds a connection point of the droop function, control corresponding to the connected droop function is performed; A control method of the power conversion characteristic is set to voltage control, power control, or current control based on the control area and the operating point; When the operating point transitions between the control areas, the control area is changed according to the droop function corresponding to the control area after the transition. Power converter.

3. A measurement unit that acquires a measurement value of an electrical characteristic value of the power that is input or output, The control unit controls the power conversion characteristic based on a control object value of an electrical characteristic value based on the measured value and a target value of the electrical characteristic value based on the reference function. The power converter according to claim 1 or 2.

4. The control unit selects types of electrical characteristic values ​​of the measurement value, the control object value, and the target value according to a droop characteristic of the droop function.

4. The power converter of claim 3.

5. The control unit selects, as the measurement value, a power value or a current value when the absolute value of the droop coefficient of the droop function is smaller than a predetermined value, and selects a voltage value when the absolute value of the droop coefficient is equal to or greater than a predetermined value.

5. The power converter of claim 4.

6. The reference function is switched or updated based on an external command. The power converter according to any one of claims 1 to 5.

7. A storage unit that stores the reference function in a switchable or updatable manner is provided. The power converter according to claim 5 or 6.

8. A power converter according to any one of claims 1 to 7; a bus connected to the power converter; A power element capable of supplying, consuming or charging power, connected to the power converter; A power system comprising:

9. A plurality of the power converters; a central control device that outputs a command to switch or update a reference function of at least one of the plurality of power converters; Equipped with The central control device outputs the command based on the power status of the power system.

9. The power system of claim 8.

10. The central control device outputs the command based on information acquired from the plurality of power converters.

10. The power system of claim 9.

11. A method for controlling a power converter, comprising the steps of: A control step of controlling a power conversion characteristic of the power converter by voltage control, power control, or current control corresponding to a reference function having a drooping characteristic defined according to an input value, The reference function is configured by connecting a plurality of droop functions having different droop characteristics at a connection point, obtaining a control area for each of the plurality of droop functions, the control area defining a range of voltage and power for performing corresponding voltage control, power control, or current control; When the operating point determined from the input value transitions within the control area, changing the control area according to the droop function corresponding to the control area after the transition; setting a control method of the power conversion characteristic to voltage control, power control, or current control based on the control area and the operating point; having The control area is set so that, when the operating point determined from the input value varies so as to deviate from a droop function, the droop function does not converge to a position outside the range defined by the connection point, and the amount or number of variations in voltage, power, or current from the variation until the operation point converges to a certain droop function is minimized. A method for controlling a power converter.

12. A method for controlling a power converter, comprising the steps of: A control step of controlling a power conversion characteristic of the power converter by voltage control, power control, or current control corresponding to a reference function having a drooping characteristic defined according to an input value, The reference function is configured by connecting a plurality of droop functions having different droop characteristics, obtaining a control area for each of the plurality of droop functions, the control area defining a range of voltage, power, or current in which a corresponding voltage control, power control, or current control is performed; When the operating point determined from the input value transitions within the control area, changing the control area according to the droop function corresponding to the control area after the transition; setting a control method of the power conversion characteristic to voltage control, power control, or current control based on the control area and the operating point; having When the operating point is on a droop function that performs voltage control, for droop functions other than the droop function on which the operating point is located, the vicinity of the droop function is set as the control area, and for the droop function on which the operating point is located, the area excluding the control areas of the other droop functions is set as the control area; The control area is set so that, when the operating point is on a droop function that performs power control or current control and the droop function has a constant power or constant current drooping characteristic, when the voltage of the operating point exceeds a connection point of the droop function, control corresponding to the connected droop function is performed; When the operating point is on a droop function that performs power control or current control and the droop function does not have a constant power or constant current droop characteristic, the control area is set so that control corresponding to the connected droop function is performed when the power of the operating point exceeds a connection point of the droop function. A method for controlling a power converter.

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