Power converter, power converter control method, power system, power system control method and program

Abstract

This electric power converter is provided with an electric power converting unit for converting and outputting input electric power, and a control unit for controlling an electric power conversion characteristic of the electric power converting unit on the basis of a reference function, wherein: the reference function is configured by connecting a plurality of droop functions having mutually different drooping characteristics, defined in accordance with an input value; and the control unit controls the electric power conversion characteristic using mutually different control schemes corresponding to the drooping characteristics of the droop functions.

Description

[Technical Field]

[0001] The present invention relates to a power converter, a control method for a power converter, a power system, a control method for a power system, and a program. [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 energy storage devices, and electric vehicles (EVs). As each of the above devices uses direct current (DC) power, studies are underway to build a direct current (DC) power network (DC grid).

[0003] One method for controlling a DC grid involves centralized control of the amount of power on the DC bus of the DC grid, with power converters connected to each device controlling the device at constant current or constant voltage based on instructions from a central control unit. While this centralized control method can easily control the entire DC grid, it has the problem of making it difficult to smoothly respond to sudden fluctuations in power supply and demand. Furthermore, when constant voltage control is performed at multiple locations over a wide area, the centralized control method can lead to unstable voltage control, potentially causing voltage fluctuations on the DC bus. Furthermore, constant voltage control at multiple locations does not allow for load sharing of power among devices, i.e., devices cannot cooperate to supply power to the DC bus at a constant voltage according to their respective power supply capacities.

[0004] Therefore, DC grids are controlled by assigning each power converter a reference function based on the power (P) and voltage (V) at its own end and controlling it in an autonomous, decentralized manner (Patent Documents 1 to 3). When a reference function is used that imparts a droop characteristic to the target voltage value according to the amount of power required for the DC bus, this control is sometimes called droop control. By performing droop control on each power converter in an autonomous, decentralized manner, the voltage of the DC bus can be stabilized while sharing the load of power interchange among 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] Japanese Patent Application Publication No. 2018-29408 Summary of the Invention [Problem to be solved by the invention]

[0006] However, if the reference function is configured as a single droop function with a single droop characteristic, the droop coefficient is constrained to some extent for the sake of voltage control stability, making it difficult to realize flexible control characteristics that can be adapted to various applications, such as meeting various load sharing characteristic requirements.

[0007] The present invention has been made in consideration of the above, and aims to provide a power converter, a control method for a power converter, a power system, a control method for a power system, and a program that realize flexible control characteristics that can be used for various applications. [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 based on a reference function, wherein the reference function is configured by connecting multiple droop functions that are defined according to an input value and have different droop characteristics, and the control unit controls the power conversion characteristics using different control methods according to the droop characteristics of the droop functions.

[0009] The power converter may include a measurement unit that acquires a measurement value of an electrical characteristic of the power input or output, and the control unit may control the power conversion characteristics based on a control target value of the electrical characteristic based on the measurement value and a target value of the electrical characteristic based on the reference function.

[0010] 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 the drooping characteristics of the droop function.

[0011] The control unit may be configured to select a power value or a current value as the measured value and a voltage value as the control object value and the target value when the absolute value of the droop coefficient of the droop function is smaller than a predetermined value, and to perform feedback control of the voltage value, and to select a voltage value as the measured value and a power value or a current value as the control object value and the target value when the absolute value of the droop coefficient is equal to or greater than a predetermined value, and to perform feedback control of the power value or the current value.

[0012] The reference function may be switched or updated based on an external command.

[0013] The power converter may include a storage unit that stores the reference function in a switchable or updatable manner.

[0014] 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 that can supply, consume, or charge power.

[0015] The power system may include a plurality of the power converters and 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, and the central control device may output the command based on a power status of the power system.

[0016] The central control device may output the command based on information obtained from the plurality of power converters.

[0017] 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 based on a reference function, wherein the reference function is configured by connecting a plurality of droop functions, each having different droop characteristics, defined according to an input value, and wherein the control step controls the power conversion characteristics using different control methods according to the droop characteristics of the droop functions.

[0018] One aspect of the present invention is a control method for a power system including a plurality of power converters, a bus connected to the plurality of power converters, and power elements connected to each of the plurality of power converters and capable of supplying, consuming, or charging power, the control method comprising the steps of: controlling power conversion characteristics of the power converters based on a reference function; acquiring information about the power status of the power system; and switching or updating the reference function of at least one of the plurality of power converters based on the information about the power status, wherein the reference function is configured by connecting a plurality of droop functions defined according to input values ​​and each having different droop characteristics, and in the control step, the power conversion characteristics are controlled using different control methods according to the droop characteristics of the droop functions.

[0019] One aspect of the present invention is a program that causes a processor to execute a control method for a power converter, the program including a control step of controlling power conversion characteristics of the power converter based on a reference function, the reference function being configured by connecting a plurality of droop functions, each having different droop characteristics, defined according to an input value, and the control step controlling the power conversion characteristics using different control methods according to the droop characteristics of the droop functions.

[0020] One aspect of the present invention is a program that causes a processor to execute a control method for a power system that includes a plurality of power converters, a bus connected to the plurality of power converters, and power elements that are connected to each of the plurality of power converters and are capable of supplying, consuming, or charging power, the program comprising: a control step of controlling power conversion characteristics of the power converters based on a reference function; a step of acquiring information about the power status of the power system; and a step of switching or updating the reference function of at least one of the plurality of power converters based on the information about the power status, wherein the reference function is configured by connecting a plurality of droop functions that are defined according to input values ​​and have different droop characteristics, and in the control step, the power conversion characteristics are controlled using different control methods according to the droop characteristics of the droop functions.

[0021] One aspect of the present invention is a control method for a power system including a plurality of power converters, a bus connected to the plurality of power converters, power elements connected to each of the plurality of power converters and capable of supplying, consuming, or charging power, and a central control device capable of communicating with an external server that holds information on the plurality of power converters and power demand, the method comprising the steps of: controlling power conversion characteristics of the power converters based on a reference function; acquiring information on the power status of the power system; acquiring the demand information from the external server; and switching or updating the reference function of at least one of the plurality of power converters based on the information on the power status and the demand information, wherein the reference function is configured by connecting a plurality of droop functions defined according to input values ​​and each having different droop characteristics, and in the control step, the power conversion characteristics are controlled using different control methods according to the droop characteristics of the droop functions. [Effects of the Invention]

[0022] According to the present invention, it is possible to realize a power converter, a control method for a power converter, a power system, and a control method for a power system that realize flexible control characteristics that can be used for various applications. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 is a diagram showing the configuration of a power system according to the first embodiment. [Figure 2] FIG. 2 is a diagram illustrating a configuration of the power converter illustrated in FIG. [Figure 3] FIG. 3 is a diagram illustrating a configuration of the control unit illustrated in FIG. [Figure 4A] FIG. 4A is a diagram showing a first example of power conversion characteristics. [Figure 4B] FIG. 4B is a diagram showing a first example of a logic value table indicating control. [Figure 4C] FIG. 4C is a diagram showing a first example of a logic value table indicating control. [Figure 5A] FIG. 5A is a diagram showing an example of power conversion characteristics in comparative example 1A. [Figure 5B] FIG. 5B is a diagram showing an example of power conversion characteristics in comparative example 1B. [Figure 6] FIG. 6 is a diagram showing a second example of the power conversion characteristics. [Figure 7] FIG. 7 is a diagram showing an example of power conversion characteristics in comparative example 2A. [Figure 8] FIG. 8 is a diagram showing an example of power conversion characteristics in comparative example 2B. [Figure 9] FIG. 9 is a diagram showing an example of power conversion characteristics in comparative example 2C. [Figure 10] FIG. 10 is a flowchart showing the operation of the manipulated variable setting unit. [Figure 11] FIG. 11 is a sequence diagram showing an example of a control method for a power system. DETAILED DESCRIPTION OF THE INVENTION

[0024] 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.

[0025] (Embodiment 1) <Power system configuration> Fig. 1 is a diagram showing the configuration of a power system according to embodiment 1. 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.

[0026] 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 the 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.

[0027] Bus 30 is a DC bus in power system 100, and is connected to power converters 11, 12, 13, and 14. Power system 100 configures a power network including a DC grid.

[0028] As an example, power element 21 is a stationary power storage device that can supply, consume, and charge power, and is connected to power converter 11. A stationary power storage device is an example of a permanently installed in-facility power storage device. Power converter 11 has the function of converting the voltage of DC power supplied by power element 21 and outputting it to bus 30, and also converting the voltage of DC power supplied from bus 30 and outputting it to power element 21, causing charging.

[0029] 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.

[0030] 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 the 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 the electric vehicle EV.

[0031] 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.

[0032] 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.

[0033] 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), and a GPU (Graphics Processing Unit). The functions of the control unit 41 are realized as functional units by the control unit 41 reading and executing various programs from the storage unit 42.

[0034] The storage unit 42 includes, for example, a ROM (Read Only Memory) that stores various programs and data used by the control unit 41 to perform arithmetic processing. The storage unit 42 also includes, for example, a RAM (Random Access Memory) that is used as a workspace when the control unit 41 performs arithmetic processing and for storing the results of the arithmetic processing of the control unit 41. The storage unit 42 may also include an auxiliary storage device such as an HDD (Hard Disk Drive) or an SSD (Solid State Drive).

[0035] The communication unit 43 includes a communication module that performs wired or wireless information communication and communicates information with the power converters 11, 12, 13, and 14 and the external server 200 via a network NW that includes the Internet, a mobile phone network, etc.

[0036] 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.

[0037] <Power converter configuration> Next, a specific configuration of the power converter 11 will be described. FIG.

[0038] The power converter 11 includes 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, converting the voltage of DC power input from the discharging power element 21 and outputting the converted power to the bus 30. The power conversion unit 11a can also convert the voltage of DC power input from the bus 30 and output the converted power 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 the electrical characteristic values ​​of the power on the bus 30 side of the power conversion unit 11a. Therefore, the sensor 11b measures the electrical characteristic values ​​of the power input to or output from the power converter 11. The sensor 11b can measure current values, voltage values, power values, etc. The sensor 11b is an example of a measurement unit that acquires measurement values. The sensor 11b outputs the measurement values ​​of the electrical characteristic values ​​to the control unit 11c.

[0041] The control unit 11c includes a processor and a storage unit that perform various arithmetic operations to control the operation of the power conversion unit 11a, primarily to realize the power conversion function of the power converter 11. The processor and storage unit may use the configurations exemplified for the control unit 41 and 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 a manipulated variable (e.g., a duty ratio) for PWM control to the power conversion unit 11a, thereby performing PWM control of the power conversion unit 11a. The control unit 11c may output the manipulated variable to the power conversion unit 11a directly, or may output the manipulated variable to the power conversion unit 11a via another functional unit (e.g., a loop control unit) not shown.

[0042] The communication unit 11d includes a communication module that communicates information via a wired or wireless connection, 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. For example, the communication unit 11d receives commands from the EMS 40 and outputs the commands to the control unit 11c. For example, the communication unit 11d transmits information about the power status input from the control unit 11c to the EMS 40. Note that if the information about the power status is a measurement value of the sensor 11b, the communication unit 11d may transmit the measurement value input from the sensor 11b to the EMS 40.

[0043] 3 is a diagram showing the configuration of the control unit 11c, mainly related to the power conversion function. The control unit 11c includes an operation amount setting unit 11ca and a determination unit 11cb, which are functional units realized by software through the execution of a program, and a storage unit 11cc.

[0044] The manipulated variable setting unit 11ca sets a manipulated variable based on the measurement value input from the sensor 11b, the determination information input from the determination unit 11cb, and the droop function information stored in the memory unit 11cc, and outputs the set manipulated variable to the power conversion unit 11a. Here, the droop function information is various information for identifying the droop function constituting the reference function, and will be described in detail later. The determination unit 11cb generates determination information based on the measurement value input from the sensor 11b, the droop function information stored in the memory unit 11cc, and, in some cases, a command input from the communication unit 11d, and outputs the determination information to the manipulated variable setting unit 11ca. In addition, the memory unit 11cc or the manipulated variable setting unit 11ca outputs information related to the power status, the droop function information, and other information to the communication unit 11d.

[0045] The other power converters 12, 13, and 14 may have the same configuration as the power converter 11. However, the power conversion unit 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.

[0046] <Characteristics of reference functions> Next, a reference function that is the basis for the control unit 11c to control the power conversion characteristics of the power conversion unit 11a will be described. FIG. 4A is a diagram showing a first example of the power conversion characteristics, and FIGS. 4B and 4C are diagrams showing a first example of a logic value table showing control. FIG. 4A is a diagram showing the VP characteristics, which are the relationship between power (P) and voltage (V) on the bus 30 side of the power conversion unit 11a, and shows the power conversion characteristics of the power conversion unit 11a. Note that P is a positive value when the power element 21 is in a discharging state, in which the power conversion unit 11a supplies power to the bus 30, and is a negative value when the power element 21 is in a charging state, in which power is supplied from the bus 30.

[0047] The control unit 11c controls the power conversion characteristics of the power conversion unit 11a so that they correspond to the characteristics of a reference function indicated by line DL1. That is, the control unit 11c controls the power conversion unit 11a so that an operating point defined by the values ​​of V and P is located on line DL1. Line DL1 is a straight or curved line that is bent halfway. This reference function is configured by connecting multiple droop functions with different droop characteristics that are defined according to input value intervals. Specifically, line DL1 is configured by connecting lines DL11, DL12, DL13, and DL14 that represent multiple droop functions with different droop characteristics. When the input value is V, line DL11 is defined in the interval where V is equal to or greater than V1 and P is approximately zero, and is an approximately straight line with a large absolute value and a negative slope. Line DL14 is defined in the interval where V is equal to or less than V3 and P is approximately P2, and is an approximately straight line with a large absolute value and a negative slope. Line DL12 is defined by the section between V1 and V2 and between approximately 0 and P1, and is a substantially straight line with a negative slope whose absolute value is smaller than that of lines DL11 and DL14. Line DL13 is defined by the section between V2 and V3 and between P1 and approximately P2, and is a substantially straight line with a negative slope whose absolute value is smaller than that of lines DL11 and DL14 and larger than that of line DL12.

[0048] For example, P2 is 300kW, and V1, V2, and V3 are 400V, 390V, and 370V, respectively.

[0049] Lines DL1, DL11, DL12, DL13, and DL14 are identified by droop function information. The droop function information includes, for example, coordinate information of the boundary of the droop function in a coordinate system with the horizontal axis as P and the vertical axis as V, information on the intercept of the droop function, information on the slope (i.e., droop coefficient), and information on the shape (straight line, curve, etc.). When the droop function is a curve, it is, for example, a quadratic curve or an exponential curve, but is not particularly limited.

[0050] Fig. 4B shows an example of a logic value table T1 used by the control unit 11c when performing control based on voltage. Fig. 4C shows an example of a logic value table T1 used by the control unit 11c when performing control based on power. Such logic value tables T1 and T2 are stored in the storage unit 11cc, for example, and are read out and used during control.

[0051] In the logic value tables T1 and T2, "dP1," "dP2," and "dP3" refer to a control method in which the control unit 11c determines a target power Pref (an example of a target value) based on the voltage measurement value Vo from the sensor 11b and droop function information, and executes a feedback control to set a manipulated variable so that the difference between Pref and the power measurement value Po from the sensor 11b (an example of a control target value) is within an allowable range; hereinafter, these may be referred to as dP1 control, dP2 control, and dP3 control, or simply dP control when no distinction is made between them. On the other hand, "dV" refers to a control method in which the control unit 11c determines a target voltage Vref (an example of a target value) based on the power measurement value Po from the sensor 11b and droop function information, and executes a feedback control to set the manipulated variable so that the difference between Vref and the voltage measurement value Vo from the sensor 11b (an example of a control target value) is within an allowable range; hereinafter, these may be referred to as dV control. These feedback controls can be performed using known techniques, such as PID control, which is executed by reading parameters such as proportional gain, integral time, and derivative time stored in the memory unit 11cc. Note that the feedback control parameters may be appropriately set and, for example, switched, to achieve more stable control depending on differences in droop function information (for example, differences in droop coefficients). For example, different feedback control parameters may be set for each of the dP1 control, dP2 control, dP3 control, and dV control. The dP control and dV control are examples of mutually different control methods.

[0052] As shown in the logical value tables T1 and T2, whether the control unit 11c executes dP control or dV control is selected according to the drooping characteristics of the droop function. Specifically, according to the logical value table T1, when V is equal to or greater than V1, dP1 control is used; when V is less than V1 and equal to or greater than V2, dV control is used; when V is less than V2 and equal to or greater than V3, dP2 control is used; and when P is less than V3, dP3 control is used. According to the logical value table T2, when P is approximately zero, dP1 control is used; when P is greater than zero and equal to or less than P1, dV control is used; when P is greater than P1 and less than P2, dP2 control is used; and when P2 or greater, dP3 control is used.

[0053] The determination unit 11cb determines whether the control unit 11c should execute dP control or dV control based on the measurement value input from the sensor 11b and the droop function information stored in the memory unit 11cc. The determination unit 11cb outputs the determination result as determination information to the manipulated variable setting unit 11ca, which then sets the manipulated variable. The control unit 11c selects the types of electrical characteristic values ​​for the measurement value, the control target value, and the target value according to the droop characteristic of the droop function. Specifically, when the absolute value of the droop coefficient is equal to or greater than a predetermined value, the voltage value is selected as the measurement value, and the power value is selected as the control target value and the target value, and dP control is executed. On the other hand, when the absolute value of the droop coefficient is smaller than the predetermined value, the power value is selected as the measurement value, and the voltage value is selected as the control target value and the target value, and dV control is executed. In the cases of Figures 4A, 4B, and 4C, for lines DL11, DL13, and DL14, the absolute value of the droop coefficient is equal to or greater than a predetermined value, and dP control, dP1 control, dP2 control, and dP3 control, respectively, are executed. For line DL12, the absolute value of the droop coefficient is smaller than a predetermined value, and dV control is executed. Note that with dP control or dI control (described later), the absolute value of the droop coefficient is relatively large and the virtual resistance is large, so that the load sharing is less susceptible to the influence of line resistance and relatively accurate. On the other hand, with dV control, the absolute value of the droop coefficient is relatively small and the virtual resistance is small, so that the voltage range can be narrowed, even though it is easily influenced by line resistance. The determination by the determination unit 11cb may be performed using either or both of the logic value tables T1 and T2.

[0054] Furthermore, the control unit 11c may be configured to include a control block capable of selectively executing both dP control and dV control. Furthermore, the control unit 11c may have, for example, a dP control block that executes dP control and a dV control block that executes dV control, separately. In this case, the control unit 11c may be configured such that the dP control block sets the manipulated variable for dP control, and the dV control block sets the manipulated variable for dV control independently, and the manipulated variable for the control to be executed is output to the power conversion unit 11a by a selector switch.

[0055] In the power converter 11 configured as described above, the reference function in the control unit 11c is configured by connecting multiple droop functions with different droop characteristics, and the control unit 11c controls the power conversion characteristics using different control methods according to the droop characteristics of the droop functions. Therefore, flexible control characteristics that can be used for a variety of applications can be realized based on the highly flexible reference function.

[0056] Furthermore, in the control unit 11c, when the absolute value of the droop coefficient of the droop function is smaller than a predetermined value, dV control is executed, and when the absolute value of the droop coefficient is equal to or greater than the predetermined value, dP control is executed. Therefore, an appropriate control method can be selected depending on the droop characteristics, and high responsiveness, high control performance, and high stability according to the droop characteristics can be simultaneously achieved.

[0057] As described above, power converter 11 can express various target values ​​(droop functions) with various droop characteristics in the reference function, thereby achieving high control performance capable of various load sharing. This eliminates the constraints imposed by a centralized control method that generates a droop function by optimizing the system using EMS 40 or the like, thereby improving the degree of freedom in expressing the reference function. It also becomes possible to express a reference function that allows for more accurate load sharing, taking into account the influence of line resistance, for example. Furthermore, by using a control method according to the droop coefficient, such as by executing dV control when the absolute value of the droop coefficient of the droop function is less than a predetermined value and executing dP control when the absolute value of the droop coefficient is equal to or greater than a predetermined value, the advantages of each control method can be more effectively utilized, and the stability and responsiveness of the control can be improved.

[0058] In power converters 12, 13, and 14, the respective control units control the power conversion characteristics of the respective power converters to match the characteristics of the respective set reference functions. Each reference function is configured by connecting multiple droop functions, each with different droop characteristics, defined according to the range of input values. However, each reference function is configured by a droop function specified by appropriate droop function information according to the characteristics of power converters 12, 13, and 14 and the characteristics of power elements 22, 23, and 24 connected to each.

[0059] Furthermore, the respective control units of power converters 12, 13, and 14 control the power conversion characteristics using different control methods according to the droop characteristics of the droop function. The control is set and executed in the same manner as the control in control unit 11c. As a result, flexible control characteristics that can be used for various applications can be realized, and an appropriate control method can be used depending on the droop characteristics, simultaneously achieving high responsiveness, high control performance, and high stability according to the droop characteristics. Furthermore, control is stabilized throughout the entire power system 100.

[0060] (Comparative form 1) The effects of the first embodiment will be described in more detail below in comparison with the first comparative embodiment. In the first embodiment and the first comparative embodiment, the operating voltage range of the bus 30 is assumed to be 300V to 400V, and the rated voltage of the bus 30 is assumed to be 380V. In this case, particularly for the power converters 11, 13, and 14, for example, among the power converters 11, 12, 13, and 14, a drooping characteristic is imparted to the reference function in order to share the power load within the operating voltage range of the bus 30. Generally, power converters are highly efficient when operated near their rated output (300 kW in this example). Therefore, within the operating voltage range, it is assumed that operation near the rated output is maintained while the drooping characteristic is imparted to the reference function. On the other hand, in a range near the upper limit of the operating voltage range (for example, 390V to 400V), it is assumed that the drooping characteristic is imparted to the reference function within a narrow voltage range so as not to affect the stability of the microgrid of the power system 100.

[0061] FIG. 5A is a diagram showing an example of power conversion characteristics in comparative example 1A, and FIG. 5B is a diagram showing an example of power conversion characteristics in comparative example 1B. FIG. 5A shows comparative example 1A, and the reference function shown by the solid line shows a case where the absolute value of the drooping coefficient is set smaller than a predetermined value and the control unit performs only dV control. FIG. 5B shows comparative example 1B, and the reference function shown by the solid line shows a case where the absolute value of the drooping coefficient is set larger than a predetermined value and the control unit performs only dP control. Note that V1 = 400 V, V2 = 390 V, V3 = 300 V, V4 = 370 V, and P2 = 300 kW. That is, the upper limit of the output of power converter 11 is 300 kW, which is also the rated output, and the output range is 0 kW to 300 kW.

[0062] In the case of Comparative Example 1A, the drooping characteristic can be provided in a narrow voltage range between V1 and V2, i.e., between 390 V and 400 V, but conversely, the drooping characteristic cannot be provided in a wide voltage range because the drooping coefficient cannot be made large. Therefore, the drooping characteristic cannot be provided near the rated output at the operating voltage.

[0063] In the case of comparative configuration 1B, the drooping coefficient can be increased, so the drooping characteristic can be maintained over a wide voltage range, but conversely, the drooping characteristic cannot be reduced, so the drooping characteristic cannot be maintained over a narrow voltage range. As a result, the drooping characteristic cannot be maintained near the rated output.

[0064] In contrast to this, in the case of embodiment 1 shown in FIGS. 4A, 4B, and 4C, dV control in which the absolute value of the drooping coefficient is equal to or less than a predetermined value and dP control in which the absolute value is greater than the predetermined value are combined, so that it is possible to operate near the rated output while maintaining the drooping characteristic within the operating voltage range, while maintaining a different drooping characteristic within the narrow voltage range of 390V to 400V.

[0065] (Another example of power conversion characteristics) 6 is a diagram showing a second example of power conversion characteristics in the first embodiment. In this example, a configuration is assumed in which two storage batteries (storage battery 1 and storage battery 2) are connected in parallel via a relatively long line length as power elements 21 and 23. In addition, in this second example, it is intended to charge storage battery 1 while maintaining a drooping characteristic over a wider range of voltage range than storage battery 2.

[0066] In this second example, the control unit 11c of the power converter 11 controls the power conversion characteristics of the power conversion unit 11a to match the characteristics of the reference function indicated by line DL2. Line DL2 is configured by connecting lines DL21, DL22, DL23, and DL24, which represent multiple droop functions with different droop characteristics. When an input value is V, line DL21 is defined in the section where V is equal to or greater than V5 and P is approximately −P3, and is a substantially straight line with a large absolute value and a negative slope. Line DL24 is defined in the section where V is equal to or less than V10 and P is approximately P3, and is a substantially straight line with a large absolute value and a negative slope. Line DL22 is defined in the section where V is equal to or less than V5 and is equal to or greater than V8, and is a substantially straight line with a negative slope with a smaller absolute value than lines DL21 and DL24. The line DL23 is defined as the section between V8 and V10, and is a substantially straight line having a negative gradient with a smaller absolute value than the lines DL21, DL22, and DL24.

[0067] The control unit of the power converter 13 also controls the power conversion characteristics of the power conversion unit to match the characteristics of the reference function indicated by line DL3. Line DL3 is configured by connecting lines DL31, DL32, DL33, and DL34, which represent multiple droop functions with different droop characteristics. When an input value is V, line DL31 is defined in the section where V is equal to or greater than V5 and P is approximately −P3, and is a substantially straight line with a large absolute value and a negative slope. Line DL34 is defined in the section where V is equal to or less than V10 and P is approximately P3, and is a substantially straight line with a large absolute value and a negative slope. Line DL32 is defined in the section where V5 is equal to or less than V8 and is a substantially straight line with a negative slope whose absolute value is smaller than that of lines DL31 and DL34. Line DL33 is defined in the section where V8 is equal to or less than V10 and is a substantially straight line with a negative slope whose absolute value is smaller than that of lines DL31 and DL34 and larger than that of line DL32.

[0068] For example, P3 is 300kW, and V5, V6, V7, V8, V9, and V10 are 400V, 380V, 360V, 340V, 320V, and 300V respectively.

[0069] The lines DL2, DL3, DL21 to DL24, and DL31 to DL34 are specified by the droop function information.

[0070] The logic value table used by the control unit 11c and the control unit of the power converter 13 when performing control is stored in, for example, the memory unit of each control unit, and is read out and used when performing control. The logic value table specifies information for setting whether to perform dV control or dP control.

[0071] Whether each control unit executes dP control or dV control is selected based on the droop characteristic of the droop function. For example, the determination unit of each control unit determines the control method based on the measurement value input from the sensor and the droop function information stored in the memory unit. The determination unit outputs the determination result as determination information to the manipulated variable setting unit, which then sets the manipulated variable. Each control unit selects the types of electrical characteristic values ​​of the measurement value, control target value, and target value based on the droop characteristic of the droop function. In the example of FIG. 6, when lines DL21, DL22, and DL24 for storage battery 1 are used, the absolute value of the droop coefficient is equal to or greater than a predetermined value, and dP control is executed. When line DL23 is used, the absolute value of the droop coefficient is smaller than the predetermined value, and dV control is executed. When lines DL31, DL33, and DL34 are used for storage battery 2, the absolute value of the droop coefficient is equal to or greater than a predetermined value, and dP control is executed. When line DL32 is used, the absolute value of the droop coefficient is smaller than the predetermined value, and dV control is executed.

[0072] In this second example as well, flexible control characteristics that can be adapted to a variety of uses can be realized, and further, high responsiveness, high control performance, and high stability can be realized simultaneously.

[0073] (Comparative form 2) The effects of this second example will be described in more detail below in comparison with comparative example 2. In this second example and comparative example 2, it is assumed that in a relatively high range of the operating voltage range (for example, 360 V to 400 V), it is desired to set a reference function that accurately shares the load between storage battery 1 and storage battery 2 in the charging direction. When the line length is long, accurate load sharing cannot be achieved unless the droop coefficient (= virtual resistance of the line) is large, so it is assumed that accurate load sharing is achieved between storage battery 1 and storage battery 2 using a large droop coefficient. On the other hand, in a relatively low range of the operating voltage range (for example, 300 V to 360 V), it is assumed that the reference function is biased as much as possible in the charging direction to fit within the operating range.

[0074] FIG. 7 is a diagram showing an example of power conversion characteristics in comparative example 2A. Comparative example 2A shows a case where the reference function shown by the solid line has the absolute value of the droop coefficient set smaller than a predetermined value, and the control unit performs only dV control. Note that V11 = 390 V and V12 = 350 V. The upper charge and discharge limits of power converters 11 and 12 are both 300 kW.

[0075] In the case of comparative example 2A, it is difficult to accurately share the load due to the constraint that the droop coefficient cannot be made large. For example, if the line length of storage battery 2 is longer than the line length of storage battery 1, the load sharing may result in a large droop of storage battery 2. Furthermore, since the droop coefficient cannot be made large, it may not be possible to effectively utilize the operating voltage range (300V to 400V).

[0076] 8 is a diagram showing an example of power conversion characteristics in Comparative Example 2B. Comparative Example 2B shows a case where the reference function shown by the solid line has the absolute value of the drooping coefficient set to a predetermined value or greater, and the control unit performs only dP control. Note that V13=200V.

[0077] In the case of comparative example 2B, the droop coefficient can be increased, allowing accurate load sharing. However, due to the constraint that the droop coefficient cannot be decreased, the voltage fluctuation range may become too large.

[0078] 9 is a diagram showing an example of power conversion characteristics in comparative example 2C. Comparative example 2C shows a case where the reference function shown by the solid line is such that the absolute value of the drooping coefficient for storage battery 1 is set to a predetermined value or more, causing the control unit to perform only dP control, and the absolute value of the drooping coefficient for storage battery 2 is set to a value smaller than the predetermined value, causing the control unit to perform only dV control. Note that V13=200V.

[0079] In the case of comparative form 2C, accurate load sharing is possible in the relatively higher range of the operating voltage range (360V to 400V), but the dP-controlled storage battery 1 may deviate from the operating voltage range, and storage battery 2 may not be able to effectively utilize the operating voltage range.

[0080] In contrast, in the second example shown in FIG. 6, accurate load sharing can be achieved by using a large droop coefficient in the range of 360V to 400V, and at the same time, in the relatively low range of the operating voltage range (for example, 300V to 360V), the operating voltage can be kept within the operating voltage range while applying a bias in the charging direction as much as possible.

[0081] <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 control each other in an autonomous and decentralized manner, and centralized control, in which the EMS 40 cooperatively controls the power converters 11, 12, 13, and 14 depending on the power status of the power system 100, can be performed. Note that, for example, the local-end control is repeatedly performed at relatively short intervals, and the centralized control is performed at intervals longer than the cycle 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 executed, for example, by a program executed by a processor in each power converter or the EMS 40.

[0082] <Self-end control> First, a control method for power converters 11, 12, 13, and 14 in self-end control will be described using power converter 11 as an example. A control method similar to that described below may also be executed as appropriate for the other power converters 12, 13, and 14. If power element 22 is an element that does not control the amount of power generated from the standpoint of efficiency, such as a solar power generation device, power converter 12 may execute MPPT (Maximum Power Point Tracking) control, which operates when power according to the amount of power generated by power element 22 is input so that the output power to bus 30 is maximized at that amount of power generated.

[0083] 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.

[0084] An example of the contents of this control step will be described in more detail with reference to Figures 3 and 10. Figure 10 is a flow chart showing the operation of the manipulated variable setting unit 11ca.

[0085] First, in step S101, the manipulated variable setting unit 11ca acquires a measurement value from the sensor 11b. Next, in step S102, the manipulated variable setting unit 11ca acquires droop function information from the memory unit 11cc. Next, in step S103, the manipulated variable setting unit 11ca acquires determination information from the determination unit 11cb. Next, in step S104, the manipulated variable setting unit 11ca sets a manipulated variable for executing feedback control using a control method based on the determination information, based on the measurement value and the droop function information, and outputs the set manipulated variable to the power conversion unit 11a. This causes the control of the power conversion unit 11a to be executed.

[0086] <Centralized control> Next, centralized control will be described. In the example shown below, an EMS 40 provided outside the power converters 11, 12, 13, and 14 executes centralized control by switching or updating the reference functions used for control by the power converters 11, 12, 13, and 14 according to a command. Here, switching the reference function according to a command means that the memory unit of each of the power converters 11, 12, 13, and 14 stores multiple reference functions, and switches the reference function used for control according to a command. Also, updating the reference function according to a command means that the command includes information related to the reference function, and part or all of the reference function is updated according to the command. The memory unit of each of the power converters 11, 12, 13, and 14 stores the reference function in a switchable or updatable manner.

[0087] For example, when information communication between EMS 40 and power converters 11, 12, 13, and 14 complies with the TCP / IP protocol, droop function information is included in the data portion of the IP packet of the command signal for updating the reference function. As described above, the droop function information is coordinate information of the boundary of the droop function, information on the intercept of the droop function, information on the slope (i.e., droop coefficient), or information on the shape (straight line, curve, etc.), and the data portion includes, as a data string, information to be updated among these pieces of information. The droop function information used for updating is stored in storage unit 42 of EMS 40, and is read out and used by control unit 41 as appropriate.

[0088] Next, an example of a control method for the power system 100 as centralized control will be described with reference to the sequence diagram of FIG.

[0089] First, in step S201, the EMS 40 calls its own timer and starts timing. Next, in step S202, the EMS 40 requests local-end measurement information from each of the power converters 11, 12, 13, and 14. The local-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, as well as the measurement times.

[0090] Next, in step S203, the power converters 11, 12, 13, and 14 each transmit their own-end measurement information to the EMS 40. The EMS 40 stores the respective own-end measurement information in the storage unit .

[0091] Next, in step S204, 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. 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 also include information such as the season, current weather, and future weather forecast for the area in which the power system 100 is installed. Furthermore, if the external server 200 functions as an EMS for another power system, and the operational status of the other power system may affect the operation of the power system 100, the power generation and demand forecast information may also include forecast information on the amount of power generated and demand for power in the other power system.

[0092] Subsequently, in step S205, the external server 200 transmits the power generation amount and demand forecast information to the EMS 40. The EMS 40 stores the power generation amount and demand forecast information in the storage unit .

[0093] Next, in step S206, the control unit 41 of the EMS 40 reads out the transmitted information, i.e., information relating 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.

[0094] The operational optimization calculation is performed to adapt to various conditions. For example, assume that the power system 100 is controlled so that the bus 30 is at a predetermined operating point. In this state, assume that the EMS 40 determines, based on power generation and demand forecast information, that the weather in the area where the power element 22, a solar power generation device, is installed is expected to be sunny and increase power generation in the future, and that, based on local measurement information acquired from the power converter 12 connected to the power element 22, the power element 22 has a surplus 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, a stationary energy storage device, so that the power element 21 is charged at the operating point. Simultaneously with this update, the EMS 40 also 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, a commercial power grid. The reference function may be switched instead of updated.

[0095] In addition, the operational optimization calculation can be performed with conditions set from the perspective of not exceeding the contracted 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.

[0096] 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.

[0097] Next, in step S207, EMS 40 outputs an update command for the reference function (droop function) to the power converter to be updated among power converters 11, 12, 13, and 14, and executes the update step. Next, in step S208, EMS 40 resets the timer. Next, in step S209, power converters 11, 12, 13, and 14 each execute local control. This local control is local control that reflects the power status of power system 100, and power converters 11, 12, 13, and 14 are cooperatively controlled.

[0098] According to the control method for power converters 11, 12, 13, and 14 and the control method for power system 100 described above, flexible control characteristics that can be used for a variety of applications are realized.

[0099] In the above-described embodiment, current values ​​may be used instead of power values ​​as electrical characteristic values ​​such as measured values, target values, and controlled values. In this case, the reference function is defined as a VI characteristic, which is the relationship between current (I) and voltage (V). Feedback control, in which the control unit 11c determines a target power Iref (an example of a target value) based on a voltage measurement value Vo from the sensor 11b and droop function information, and sets a manipulated variable so that the difference between Iref and a current measurement value Io from the sensor 11b (an example of a controlled value) falls within an allowable range, is also called dI control, and is performed instead of or in addition to dP control. In dV control, a target voltage Vref is determined based on a current measurement value Io from the sensor 11b and droop function information. dP control, dV control, and dI control are examples of mutually different control methods, and they may be used in appropriate combinations.

[0100] Furthermore, in the above embodiment, the reference function is configured by connecting four droop functions, but it may be configured by connecting two, three, or five or more droop functions.

[0101] Furthermore, the present invention is not limited to the above-described embodiments. The present invention also includes configurations in which the above-described components are appropriately combined. Furthermore, further effects and modifications can be easily derived by those skilled in the art. Therefore, the broader aspects of the present invention are not limited to the above-described embodiments, and various modifications are possible. [Industrial Applicability]

[0102] The present invention can be used in a power converter, a control method for a power converter, a power system, and a control method for a power system. [Explanation of symbols]

[0103] 11, 12, 13, 14: Power converters 11a: Power conversion section 11b: Sensor 11c, 41: Control section 11ca: Operation amount setting section 11cb: Judgment part 11cc, 42: Storage section 11d, 43: Communications Department 21, 22, 23, 24: Power elements 30: Bus 40:EMS 100: Power Systems 200: External server DL1, DL11, DL12, DL13: Lines EV: Electric vehicle NW: Network

Claims

1. a power conversion unit that converts input power and outputs the converted power; a measurement unit that acquires a measurement value of an electrical characteristic value of input or output power; a control unit that controls the power conversion characteristics of the power conversion unit based on a reference function; Equipped with the reference function is configured by connecting a plurality of droop functions defined according to input values ​​and having different droop characteristics; The control unit controlling the power conversion characteristics using different control methods according to the droop characteristics of the droop function and 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; Selecting types of electrical characteristic values ​​of the measurement value, the control target value, and the target value according to the droop characteristic of the droop function Power converter.

2. When the absolute value of the droop coefficient of the droop function is smaller than a predetermined value, the control unit selects a power value or a current value as the measurement value and selects a voltage value as the control object value and the target value, and performs feedback control of the voltage value; when the absolute value of the droop coefficient is equal to or greater than a predetermined value, the control unit selects a voltage value as the measurement value and selects a power value or a current value as the control object value and the target value, and performs feedback control of the power value or the current value. The power converter of claim 1 .

3. The reference function is switched or updated based on an external command.

3. The power converter according to claim 1 or 2.

4. A storage unit for storing the reference function in a switchable or updatable manner is provided. The power converter according to any one of claims 1 to 3.

5. A power converter according to any one of claims 1 to 4; a bus connected to the power converter; a power element connected to the power converter and capable of supplying, consuming, or charging power; A power system comprising:

6. A plurality of the power converters; a central control unit 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. The power system of claim 5 .

7. The central control device outputs the command based on information acquired from the plurality of power converters. The power system of claim 6.

8. A method for controlling a power converter, comprising: a control step of controlling a power conversion characteristic of the power converter based on a reference function; and an acquisition step of acquiring a measured value of an electrical characteristic value of power input to or output from the power converter, the reference function is configured by connecting a plurality of droop functions defined according to input values ​​and having different droop characteristics; In the control step, controlling the power conversion characteristics using different control methods according to the droop characteristics of the droop function and 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; Selecting types of electrical characteristic values ​​of the measurement value, the control target value, and the target value according to the droop characteristic of the droop function A method for controlling a power converter.

9. A control method for a power system including a plurality of power converters, a bus connected to the plurality of power converters, and a power element connected to each of the plurality of power converters and capable of supplying, consuming, or charging power, the method comprising: a control step of controlling a power conversion characteristic of the power converter based on a reference function; an acquisition step of acquiring a measurement value of an electrical characteristic value of the power input to or output from the power converter; acquiring information about the power status of the power system; switching or updating a reference function of at least one of the plurality of power converters based on information about the power situation; Equipped with the reference function is configured by connecting a plurality of droop functions defined according to input values ​​and having different droop characteristics; In the control step, controlling the power conversion characteristics using different control methods according to the droop characteristics of the droop function and 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; Selecting types of electrical characteristic values ​​of the measurement value, the control target value, and the target value according to the droop characteristic of the droop function Power system control methods.

10. The processor A program for executing a control method for a power converter, a control step of controlling a power conversion characteristic of the power converter based on a reference function; and an acquisition step of acquiring a measured value of an electrical characteristic value of power input to or output from the power converter, the reference function is configured by connecting a plurality of droop functions defined according to input values ​​and having different droop characteristics; In the control step, controlling the power conversion characteristics using different control methods according to the droop characteristics of the droop function and 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; Selecting types of electrical characteristic values ​​of the measurement value, the control target value, and the target value according to the droop characteristic of the droop function program.

11. The processor A program for executing a control method for a power system including a plurality of power converters, a bus connected to the plurality of power converters, and power elements that are connected to each of the plurality of power converters and are capable of supplying, consuming, or charging power, the program comprising: a control step of controlling a power conversion characteristic of the power converter based on a reference function; an acquisition step of acquiring a measurement value of an electrical characteristic value of the power input to or output from the power converter; acquiring information about the power status of the power system; switching or updating a reference function of at least one of the plurality of power converters based on information about the power situation; Equipped with the reference function is configured by connecting a plurality of droop functions defined according to input values ​​and having different droop characteristics; In the control step, controlling the power conversion characteristics using different control methods according to the droop characteristics of the droop function and 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; Selecting types of electrical characteristic values ​​of the measurement value, the control target value, and the target value according to the droop characteristic of the droop function program.

12. A control method for a power system including a plurality of power converters, a bus connected to the plurality of power converters, power elements connected to each of the plurality of power converters and capable of supplying, consuming, or charging power, and a central control device capable of communicating with an external server that holds information on the plurality of power converters and power demand, the method comprising: a control step of controlling a power conversion characteristic of the power converter based on a reference function; an acquisition step of acquiring a measurement value of an electrical characteristic value of the power input to or output from the power converter; acquiring information about the power status of the power system; acquiring the demand information from the external server; switching or updating a reference function of at least one of the plurality of power converters based on the information about the power situation and the demand information; Equipped with the reference function is configured by connecting a plurality of droop functions defined according to input values ​​and having different droop characteristics; In the control step, controlling the power conversion characteristics using different control methods according to the droop characteristics of the droop function and 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; Selecting types of electrical characteristic values ​​of the measurement value, the control target value, and the target value according to the droop characteristic of the droop function Power system control methods.

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