Power system, control device, and control method

Abstract

This power system comprises: a plurality of power converters that acquire the electrical characteristic value of inputted or outputted power, and control the power conversion characteristics of the power output using the acquired electrical characteristic value as an input value on the basis of a reference function in which the electrical characteristic value of the power output is defined according to the input value, a stored reference function being updated to the acquired reference function; a control device that sets the reference function for each power converter, and outputs the set reference function to the plurality of power converters; and a DC electric line to which the plurality of power converters are connected. For each of the plurality of power converters, the control device calculates the voltage drop in the electric line according to the output power target value and the line impedance of the electric line, and sets the reference function on the basis of the calculated voltage drop.

Description

Technical Field

[0001] The present invention relates to a power system, a control device, and a control method.

Background Art

[0002] As an alternative to large-scale power networks that rely on fossil energy or nuclear energy, power networks using locally produced and consumed electricity have attracted attention. In a power network using locally produced and consumed electricity, various devices such as a photovoltaic (PV) power generation device that generates electricity using renewable energy, a stationary energy storage device, and an electric vehicle (EV) are connected. Since each of the above devices is a DC power source, studies are underway to construct a DC power network (DC grid).

[0003] For example, in the system disclosed in Patent Document 1, each power converter is given a reference function based on its own power (P) and its own voltage (V) and is controlled in an autonomous and decentralized manner to control the DC grid. When a reference function having a droop characteristic is used for the target voltage value according to the amount of power required for the DC bus, that is, when a droop characteristic is provided, this control may be called droop control. By autonomously and decentralizedly controlling each power converter by droop control, it is possible to stabilize the voltage of the DC bus while implementing load sharing of power accommodation for each device according to the amount of power required for the DC bus.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] When performing autonomous decentralized control with each power converter, in an ideal DC grid that does not consider the line length of the DC bus, the voltage levels on the DC bus side are equal for each power converter. Therefore, the power to be exchanged can be accurately grasped, and the target power can be coordinated between the power supply side and the power demand side. However, in an actual DC grid, since there is a line length, the voltage levels are different between the power converter on the power supply side and the power converter on the power demand side due to the voltage drop caused by the resistance of the line. Since autonomous decentralized control is a control in which each power converter measures the voltage level on its own DC bus side and determines power coordination, if the voltage levels are different between the power supply side and the power demand side of the power, it becomes difficult to coordinate the power intended by the reference function.

[0006] The present invention has been made in view of the above, and an object thereof is to perform power coordination of a target power value even when a voltage drop occurs between the power supply side and the power demand side of the power.

Means for Solving the Problems

[0007] In order to solve the above-described problems and achieve the object, a power system according to an aspect of the present invention includes a power conversion unit that converts and outputs input power, a measurement unit that acquires electrical characteristic values of the input or output power, a storage unit that stores a reference function in which the electrical characteristic values of the output of the power conversion unit are defined according to an input value, a characteristic control unit that uses the electrical characteristic values acquired by the measurement unit as input values and controls the power conversion characteristics of the output of the power conversion unit based on the reference function, and an update unit that acquires a reference function and updates the acquired reference function with the reference function stored in the storage unit. The power system further includes a control device having a reference function setting unit that sets a reference function for each of the plurality of power converters, and an output unit that outputs the set reference function to the plurality of power converters, and a DC power line to which the plurality of power converters are connected. The reference function setting unit calculates a voltage drop in the power line based on the power target value of the output of the power conversion unit and the line impedance of the power line for each of the plurality of power converters, and calculates a voltage target value of the self-terminal voltage of the power converter when outputting the power target value within the operating voltage range of the power converter based on the calculated voltage drop. The reference function is set to a reference function in which the electrical characteristic value of the output of the power conversion unit when the self-terminal voltage is the voltage target value is the power target value.

[0008] In the power system according to an aspect of the present invention, when the line impedance changes due to a change in the configuration of the power line, the reference function setting unit calculates a voltage drop in the power line based on the power target value of the output of the power conversion unit and the changed line impedance, and calculates a voltage target value of the self-terminal voltage of the power converter when outputting the power target value within the operating voltage range of the power converter based on the calculated voltage drop. The reference function is updated to a reference function in which the electrical characteristic value of the output of the power conversion unit when the self-terminal voltage is the voltage target value is the power target value, and the output unit may output the updated reference function.

[0009] In the power system according to one aspect of the present invention, when the power demand in the power element connected to the power converter or the power supply from the power element changes, the reference function setting unit calculates the voltage drop in the power line based on the power target value of the output of the power conversion unit corresponding to the change and the line impedance of the power line, and based on the calculated voltage drop, calculates the voltage target value of the self-terminal voltage of the power converter when outputting the power target value within the operating voltage range of the power converter, and may update the reference function to the reference function in which the electrical characteristic value of the output of the power conversion unit when the self-terminal voltage is the voltage target value is defined as the power target value.

[0010] In the power system according to one aspect of the present invention, when the number of power converters connected to the power line increases or decreases, the reference function setting unit calculates the voltage drop in the power line based on the power target value of the output of the power conversion unit of the power converter connected to the power line after the increase or decrease and the line impedance of the power line, and based on the calculated voltage drop, calculates the voltage target value of the self-terminal voltage of the power converter when outputting the power target value within the operating voltage range of the power converter, and may update the reference function to the reference function in which the electrical characteristic value of the output of the power conversion unit when the self-terminal voltage is the voltage target value is defined as the power target value.

[0011] In the power system according to one aspect of the present invention, the power target value may be set based on the power balance in the plurality of power converters, the predicted power balance in the power element connected to the power converter, or the optimization calculation of the output of the power converter.

[0012] In the power system according to one aspect of the present invention, the plurality of power converters may include a power converter to which a power element capable of power supply and charge / discharge is connected, a power converter to which a power element for power supply is connected, and a power converter that consumes power.

[0013] A control device according to one aspect of the present invention includes a power conversion unit that converts and outputs input power, a measurement unit that acquires an electrical characteristic value of the input or output power, a storage unit that stores a reference function in which an electrical characteristic value of the output of the power conversion unit is defined according to an input value, a characteristic control unit that uses the electrical characteristic value acquired by the measurement unit as an input value and controls the power conversion characteristics of the output of the power conversion unit based on the reference function, and an update unit that acquires a reference function and updates the reference function acquired by the storage unit with the acquired reference function. The control device also includes a reference function setting unit that sets a reference function for each of a plurality of power converters, and an output unit that outputs the set reference function to the plurality of power converters. The reference function setting unit calculates a voltage drop in the DC power line to which the plurality of power converters are connected based on a power target value of the output of the power conversion unit and a line impedance of the DC power line for each of the plurality of power converters, and calculates a voltage target value of the self-terminal voltage of the power converter when outputting the power target value within the operating voltage range of the power converter based on the calculated voltage drop. The reference function setting unit sets the reference function to a reference function in which the electrical characteristic value of the output of the power conversion unit when the self-terminal voltage is the voltage target value is defined as the power target value.

[0014] The control method according to one aspect of the present invention includes a power conversion unit that converts and outputs input power, a measurement unit that acquires electrical characteristic values of the input or output power, a storage unit that stores a reference function in which the electrical characteristic values of the output of the power conversion unit are defined according to input values, a characteristic control unit that uses the electrical characteristic values acquired by the measurement unit as input values and controls the power conversion characteristics of the output of the power conversion unit based on the reference function, and an update unit that acquires a reference function and updates the reference function acquired by the storage unit. The control method includes a reference function setting step of setting a reference function for each of a plurality of power converters, and an output step of outputting the set reference function to the plurality of power converters. In the reference function setting step, for each of the plurality of power converters, a voltage drop in the DC power line to which the plurality of power converters are connected is calculated based on a power target value of the output of the power conversion unit and the line impedance of the DC power line, and based on the calculated voltage drop, a voltage target value of the self-terminal voltage of the power converter when outputting the power target value within the operating voltage range of the power converter is calculated. The reference function is set to a reference function in which the electrical characteristic values of the output of the power conversion unit when the self-terminal voltage is the voltage target value are defined as the power target value.

Advantages of the Invention

[0015] According to the present invention, even if a voltage drop occurs between the power supply side and the demand side of the power, it is possible to supply power with a target power value.

Brief Description of the Drawings

[0016]

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[0017] Embodiments of the present invention will be described below with reference to the drawings. Note that the present invention is not limited to the embodiments described below. Further, in the description of the drawings, the same parts are appropriately denoted by the same reference numerals.

[0018] Embodiment <Configuration of Power System> FIG. 1 is a diagram showing the configuration of a power system according to an embodiment of the present invention. The power system 1 includes a plurality of power converters 11 to 14, power elements 21 to 24, and a bus 30. Further, the power system 1 includes an EMS (Energy Management System) 40. The EMS 40 is an example of a central control device.

[0019] The bus 30 is a DC bus in the power system 1 and is connected to the power converters 11 to 14. The bus 30 is an electric wire line that transmits DC power. The power converters 11, 12, and 13 are DC / DC converters that convert DC voltage, and the power converter 14 is an AC / DC converter that converts alternating current (AC) to DC. The power converters 11 to 14 have a function of performing information communication by wire or wirelessly. The configuration and functions of the power converters 11 to 14 will be described in detail later.

[0020] The power element 21 is, as an example, a stationary energy storage device capable of charging and discharging electric power, and is connected to the power converter 11. The stationary energy storage device is an example of an in-facility energy storage device that is permanently installed. 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 converting the voltage of the DC power supplied from the bus 30 and outputting it to the power element 21 to charge the power element 21.

[0021] The power element 22 is, as an example, 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 power using renewable energy. The power converter 12 has a function of converting the voltage of the DC power supplied by the power element 22 and outputting it to the bus 30.

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

[0023] The power element 24 is, as an example, 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 converts the DC power supplied from the bus 30 into AC power and outputs it to the power element 24. The output of power from the bus 30 to the power element 24 is also called reverse power flow.

[0024] The EMS 40 has a function of integrally managing the state of the power system 1. The EMS 40 includes a control unit 41, a storage unit 42, and a communication unit 43.

[0025] FIG. 2 is a block diagram showing the configuration of the control unit 41. The control unit 41 is configured by connecting a processor 401, a memory 402, a storage 403, an input / output I / F 404, and a communication I / F 405 to a bus 406. The memory 402 is, for example, a RAM, and is composed of a volatile memory or a non-volatile memory. The memory 402 serves as a work space when the processor 401 performs arithmetic processing, and stores the results of the arithmetic processing of the processor and the like. The storage 403 is composed of a ROM (Read Only Memory) and an auxiliary storage device such as an HDD (Hard Disk Drive) or an SSD (Solid State Drive). The storage 403 stores programs and data used by the processor 401 to perform arithmetic processing. The input / output I / F 404 is connected to the storage unit 42, and writes information to the storage unit 42 and reads information from the storage unit 42. The communication I / F 405 is connected to the communication unit 43 and controls the communication unit 43. The processor 401 is, for example, a CPU (Central Processing Unit), reads a program from the storage 403, and executes it using the memory 402 as a work space. The processor 401 may be an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), a DSP (Digital Signal Processor), or a GPU (Graphics Processing Unit). By the processor 401 executing the program, the functions of the EMS 40 are realized.

[0026] The storage unit 42 includes, for example, an HDD or an SSD, and stores various data and the like used by the control unit 41 to perform arithmetic processing. The storage unit 42 stores, for example, as various data, data indicating the line impedance of the bus 30, data indicating the wiring topology of the bus 30, data indicating the operating voltage range of voltage conversion of the power converters 11 to 14, and the like.

[0027] The communication unit 43 is configured to include a communication module that performs information communication by wire or wirelessly. The communication unit 43 performs information communication with each power converter and the external server 200 included in the power system 1 via a network NW composed of an Internet line network, a mobile phone line network, or the like.

[0028] FIG. 3 is a diagram showing a functional unit according to the present invention realized in the control unit 41 when the processor 401 executes a program. The reference function setting unit 411 sets the respective reference functions of the power converters 11 to 14. The output unit 412 outputs an update command including the reference functions set by the reference function setting unit 411 to the power converters 11 to 14.

[0029] Note that the external server 200 is a server provided outside the power system 1. 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 having a database and functioning 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 1.

[0030] <Configuration of Power Converter> Next, the specific configuration of the power converter 11 will be described. FIG. 4 is a diagram showing the configuration of the power converter 11. The power converter 11 includes a power conversion unit 110, a sensor 120, a control unit 100, and a communication unit 130.

[0031] The power conversion unit 110 performs DC / DC conversion that converts the voltage of the DC power input from the discharging power element 21 and outputs it to the bus 30. The power conversion unit 110 can also convert the voltage of the DC power input from the bus 30 and output it to the power element 21 to charge the power element 21. The power conversion unit 110 is composed of an electric circuit including, for example, a coil, a capacitor, a diode, a switching element, etc. The switching element is, for example, a field effect transistor or an insulated gate bipolar transistor. The power conversion unit 110 can control the power conversion characteristics, for example, by PWM (Pulse Width Modulation) control.

[0032] The sensor 120 measures the electrical characteristic values of the power on the bus 30 side of the power conversion unit 110. Therefore, the sensor 120 measures the electrical characteristic values of the power input to or output from the power converter 11. The sensor 120 can measure current values, voltage values, power values, etc. The sensor 120 is an example of a measurement unit that acquires electrical characteristic values. The sensor 120 outputs the measured electrical characteristic values to the control unit 100.

[0033] The control unit 100 includes a processor and a storage unit that perform various arithmetic processes for controlling the operation of the power conversion unit 110 mainly for realizing the power conversion function of the power converter 11. The processor can use the one exemplified as the configuration of the processor 401, and the storage unit can use the one exemplified as the configuration of the storage 403. The functions of the control unit 100 are realized as functional units by the processor reading various programs from the storage unit and executing them. For example, the control unit 100 controls the power conversion characteristics of the power conversion unit 110 according to a reference function based on the self-terminal power (P) and the self-terminal voltage (V). Specifically, the control unit 100 outputs a PWM signal including information on an operation amount (for example, a duty ratio) for PWM control to the power conversion unit 110 to perform PWM control on the power conversion unit 110. Note that the control unit 100 may directly output the operation amount to the power conversion unit 110, or may output it to the power conversion unit 110 via another functional unit (for example, a loop control unit) not shown in the figure.

[0034] The communication unit 130 includes a communication module that performs information communication by wire or wirelessly, and a communication control unit that controls the operation of the communication module. The communication unit 130 performs information communication with the EMS 40 via the network NW. The communication unit 130 receives information and commands from the EMS 40, for example, and outputs them to the control unit 100. Also, the communication unit 130 transmits information regarding the power status input from the control unit 100 to the EMS 40, for example. Note that when the information regarding the power status is the measurement value of the sensor 120, the communication unit 130 may transmit the measurement value input from the sensor 120 to the EMS 40, for example.

[0035] FIG. 5 is a diagram showing a functional unit according to the present invention realized in the control unit 100. The control unit 100 includes an operation amount setting unit 100a, an information providing unit 100b, and an update unit 100c, which are functional units realized software-wise by executing a program. The information providing unit 100b acquires the electrical characteristic value output from the sensor 120 and outputs the acquired electrical characteristic value to the communication unit 130.

[0036] The operation amount setting unit 100a, which is an example of the characteristic control unit, controls the power conversion characteristics of the power conversion unit 110. Specifically, the operation amount setting unit 100a sets a target value of the output of the power conversion unit 110 based on the electrical characteristic value measured by the sensor 120 and the reference function information stored in the storage unit 102 provided in the control unit 100. The target value is an electrical characteristic value, for example, a voltage value or a power value. Also, the operation amount setting unit 100a performs feedback control to set an operation amount (for example, a duty ratio) for PWM control so that the difference between the electrical characteristic value measured by the sensor 120 and the set target value is within a predetermined range. The feedback control performed by the operation amount setting unit 100a can be executed using a known method such as PID control in which parameters such as a proportional gain, an integral time, and a differential time stored in advance in the storage unit 102 of the control unit 100 are read out and executed. The operation amount setting unit 100a outputs information on the set operation amount to the power conversion unit 110 and controls the power conversion unit 110.

[0037] The update unit 100c stores the reference function information included in the update command input from the communication unit 130 in the storage unit 102 of the control unit 100, and updates the reference function information stored in the storage unit 102. The update command is a command transmitted from the EMS 40. Here, the reference function information is various information for specifying the reference function, which will be described in detail later.

[0038] Note that the other power converters 12, 13, and 14 may have the same configuration as the power converter 11. However, the power conversion unit 110 of the power converter 14 performs AC / DC conversion that converts the AC power supplied from the power element 24 into DC power and outputs it to the bus 30, and DC / AC conversion that converts the DC power supplied from the bus 30 into AC power and outputs it to the power element 24.

[0039] <Characteristics of the reference function> Next, the reference function that serves as the basis for the control unit 100 to control the power conversion characteristics of the power conversion unit 110 will be described. FIG. 6A is a diagram showing an example of the reference function indicated by the reference function information. The reference function information is various information for specifying the reference function. In FIG. 6A, the vertical axis is the voltage V and the horizontal axis is the power P. The reference function indicated by the line DL1 in FIG. 6A shows the V-P characteristic, which is the relationship between the power P on the bus 30 side and the voltage V of the power conversion unit 110 included in the power converter 11, and shows the power conversion characteristics of the power conversion unit 110. The reference function indicated by the line DL3 in FIG. 6A shows the power conversion characteristics of the power conversion unit 110 included in the power converter 13. Note that the power P is a positive value when the power conversion unit 110 supplies power to the bus 30, that is, when the power element 21 is in the discharging state, and is a negative value when the power is supplied from the bus 30, that is, when the power element 21 is in the charging state. Also, the state where the power P = 0 is a state where neither charging nor discharging is occurring.

[0040] The reference function represented by line DL1 is composed of functions defined according to the intervals of input values. The reference function represented by line DL3 is composed of a plurality of functions with different drooping characteristics, which are defined according to the intervals of input values and are connected to each other. These line DL1 and line DL3 are specified by reference function information. Note that the reference function may be in a bent linear or curved shape and may be composed of a plurality of functions with different drooping characteristics, which are defined according to the intervals of input values and are connected to each other. The reference function information includes, for example, the coordinate information of the boundaries of the function, the intercept information of the function, the information of the slope (i.e., the drooping coefficient), and the information of the shape (linear, curved, etc.) in the coordinates with the horizontal axis as P and the vertical axis as V.

[0041] The control unit 100 of the power converter 11 controls the power conversion characteristics of the power conversion unit 110 so that they become the characteristics of the reference function indicated by line DL1. That is, the control unit 100 of the power converter 11 controls the power conversion unit 110 so that the operating point defined by the value of V and the value of P is located on line DL1. Note that the reference function is not limited to a function with a drooping characteristic, and may be other functions as long as it is a function in which the target value of the electrical characteristic value is defined according to the input value.

[0042] As control methods for the power conversion unit 110 executed by the control unit 100, for example, there are droop P control and droop V control. The droop P control determines a target power value, which is a target value, based on a voltage value, which is an electrical characteristic value measured by the sensor 120, and a reference function, and is a control method that makes the difference between the measured power value by the sensor 120 and the target power value fall within an allowable range. The droop V control determines a target voltage value, which is a target value, based on a power value or a current value, which is an electrical characteristic value measured by the sensor 120, and a reference function, and is a control method that makes the difference between the measured voltage value by the sensor 120 and the target voltage value fall within an allowable range. Note that as the electrical characteristic values such as the measured value and the target value, a current value may be used instead of the power value. In this case, for example, the reference function is defined as a V-I characteristic, which is the relationship between the current (I) on the horizontal axis and the voltage (V) on the vertical axis. Also, for example, the control unit 100 determines a target current value, which is a target value of the current value, based on the measured voltage value by the sensor 120 and the reference function information, and sets the operation amount so that the difference between the target current value and the measured current value by the sensor 120 falls within an allowable range. The feedback control is also called droop I control and is executed instead of the droop P control.

[0043] Note that also for the power converters 12, 13, and 14, reference function information corresponding to each power converter is stored in the storage unit 102, and control is performed so as to have the characteristics of the reference function specified by the stored reference function information.

[0044] <Control Method> Next, the control methods for the power converters 11 to 14 and the control method for the power system 1 will be described. In the power system 1, so-called distributed control in which the power converters 11 to 14 perform control individually and autonomously in a decentralized manner, and centralized control in which the EMS 40 performs cooperative control of the power converters 11 to 14 according to the power situation of the power system 1 can be executed. Note that, for example, the distributed control is repeatedly executed at a relatively short cycle, and the centralized control is executed at an interval longer than the cycle of the distributed control. The distributed control is also called primary control, and the centralized control is also called secondary control. These control methods are executed, for example, by a processor executing a program in each power converter or the EMS 40.

[0045] <Central Control> First, the central control will be described. In the example shown below, each storage unit 102 of the power converters 11 to 14 stores the reference function information in an updatable manner. The EMS 40 executes central control by updating the reference functions used by the power converters 11 to 14 according to commands. Updating the reference function according to a command means that the command sent from the EMS 40 to the power converters 11 to 14 includes the reference function information regarding the reference function, and it means that part or all of the reference function information stored in the power converters 11 to 14 is updated by the command. As described above, the reference function information is the coordinate information of the function boundary, the section information of the function, the information of the slope (i.e., the droop coefficient), and the information of the shape (such as a straight line or a curve). The reference function information used for updating is stored in the storage unit 42 of the EMS 40, and the control unit 41 reads and uses it as appropriate.

[0046] Next, an example of the operation of the central control in the power system 1 will be described with reference to the sequence diagram of FIG. 7. In the power system 1, the processes shown in FIG. 7 are performed at a predetermined cycle. First, the EMS 40 requests the self-terminal measurement information from each of the power converters 11 to 14 (step S101). The self-terminal measurement information is an example of the information regarding the power status of the power system 1 and includes the electrical characteristic values measured by the respective sensors 120 of the power converters 11 to 14 and the measurement times of the electrical characteristic values.

[0047] Next, the power converters 11 to 14 transmit the self-terminal measurement information they have acquired to the EMS 40 (step S102). The EMS 40 stores the respective self-terminal measurement information in the storage unit 42. Next, as an example of information regarding the power situation of the power system 1, the EMS 40 requests various information that may affect the operation of the power system 1 from the external server 60 (step S103). In this example, the EMS 40 requests power generation amount and demand prediction information from the external server 60. The power generation amount and demand prediction information includes prediction information on the power generation amount and power demand prediction information in the power system 1, and may include information such as the season and current weather of the area where the power system 1 is installed, and future weather forecasts. Also, when the external server 60 functions as an EMS of another power system, if the operation state of the other power system may affect the operation of the power system 1, the power generation amount and demand prediction information may include prediction information on the power generation amount and power demand prediction information in the other power system. Next, the external server 60 transmits the power generation amount and demand prediction information to the EMS 40 (step S104). The EMS 40 stores the power generation amount and demand prediction information in the storage unit 42.

[0048] Next, the control unit 41 of the EMS 40 reads out the transmitted information, that is, information regarding the power situation of the power system 1, etc. from the storage unit 42, and based on this, generates reference functions for the power converters 11 to 14 (step S105). FIG. 8 is a flowchart showing the flow of the process of generating the reference function. This process is a process performed by the reference function setting unit 411 and is an example of a reference function setting step.

[0049] First, the control unit 41 sets power supply or demand power target values for the power converters 11 to 14 from the power generation amount and demand prediction information stored in the storage unit 42 (step S201). These power target values may be set by performing an operation optimization calculation of the power system 1, or an operator may set the power target values from the power generation amount and demand prediction information in the EMS 40. Also, the power target values may be set from the self-terminal measurement information acquired from the power converters 11 to 14.

[0050] The operation optimization calculation is executed to be applicable to various conditions. For example, assume that the power system 1 is controlled so that the bus 30 operates at a predetermined voltage operating point. In this state, based on the power generation amount and demand prediction information, the EMS 40 predicts that the weather in the area where the power element 22, which is a solar power generation device, is installed will be sunny in the future and the power generation amount will increase, and determines from the self-terminal measurement information obtained from the power converter 12 connected to the power element 22 that there is a margin in power supply to the power element 22. 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 energy storage device, is charged at the said operating point. Also, simultaneously with the said update, the EMS 40 determines to update the reference function of the power converter 14 connected to the power element 24 so that no power is supplied from the power element 24, which is a commercial power system. Also, the operation optimization calculation can be executed with conditions set from viewpoints such as not exceeding the contract power of the power element 24, which is a commercial power system, such as peak cut and utilization of nighttime power, and optimization of electricity charges.

[0051] Next, the control unit 41 sets the shapes of the reference functions of the power converters 11 to 14 (step S202). For example, when the power target value of the power converter 13 set in step S201 is a negative value and the power element 23 is to be charged, the control unit 41 sets the shape of the reference function of the power converter 13 to the shape of the line DL3 shown in FIG. 6A so that the power converter 13 charges the power element 23. Also, when the power target value of the power converter 11 set in step S201 is a positive value and the power element 23 is to be charged by the power supply from the power element 21, the control unit 41 sets the shape of the reference function of the power converter 11 to the shape of the line DL1 shown in FIG. 6A so that the power converter 11 supplies power.

[0052] Next, the control unit 41 calculates the voltage drop in the circuit of the bus 30 by using the power target value set in step S201, the data indicating the line impedance of the bus 30 stored in the storage unit 42, the data indicating the wiring topology of the bus 30 stored in the storage unit 42, the data indicating the operating voltage range of the power converters 11 to 14 stored in the storage unit 42, etc., and based on the calculated voltage drop, sets the voltage target value, which is the target value of the terminal voltage of the power converters 11 to 14 when outputting the power target value set in step S201 (step S203).

[0053] FIG. 9 is a diagram showing an example of the relationship between power supply and demand in the power system 1. For example, assuming that the power element 23 is charged by the power supply from the power element 21 as shown in FIG. 9, if the power target value of the power converter 11 is P + and the target value of the terminal voltage of the power converter 11 is V + , the power target value of the power converter 13 is P - , the target value of the terminal voltage of the power converter 13 is V - , and when the line impedance related to the power converter 11 is R1 and the line impedance related to the power converter 13 is Rev, the control unit 41 sets P + = P - , and sets V + so that it falls within the operating voltage range of the power converter 11 and V - so that it falls within the operating voltage range of the power converter 13, and sets V + and V - .

[0054] Next, the control unit 41 optimizes the reference function of the shape set in step S202 so that the power value of the output of the power converter when the terminal voltage is the voltage target value becomes the power target value based on the target value of the terminal voltage set in step S203 (step S204). Here, an example of the process of step S204 will be described with reference to FIGS. 6A and 6B. The dashed-dotted line shown in FIGS. 6A and 6B indicates the voltage drop between the power converter 11 and the power converter 13. FIG. 6A is an example of the reference function before optimization in step S204.

[0055] When there is no voltage drop in bus 30, for example, if the terminal voltages of power converters 11 and 13 are Va as shown in Fig. 6A, power converter 11 supplies power to bus 30 at 50 kW, which is the power target value when the terminal voltage on line DL1 is Va, and power converter 13 charges power element 23 at -50 kW, which is the power target value when the terminal voltage on line DL3 is Va. However, when a voltage drop occurs between power converter 11 and power converter 13 as shown by the dashed line in Fig. 6A, the operating point of power converter 11 is at the position of Po1 shown in Fig. 6A, and the operating point of power converter 13 is at the position of Po3 shown in Fig. 6A. When the operating point of power converter 13 is at the position of Po3, it performs constant voltage control according to line DL3 and charges power element 23 at -30 kW. Also, when the operating point of power converter 11 is at the position of Po1, it suppresses the output from power element 21 to 30 kW according to line DL1.

[0056] Therefore, the control unit 41 performs an optimization process in step S204, changes the slope information of line DL1 and shifts it upward to obtain line DL1a shown in Fig. 6B. Also, the control unit 41 changes the slope information of line DL3 and shifts it downward to obtain line DL3a shown in Fig. 6B. When this optimization is performed, the operating point of power converter 11 is at the position of Po1a shown in Fig. 6B, and the operating point of power converter 13 is at the position of Po3a shown in Fig. 6B. When the operating point of power converter 13 is at the position of Po3a, it performs constant power control according to line DL3a and charges power element 23 at -50 kW. Also, when the operating point of power converter 11 is at the position of Po1, it sets the output from power element 21 to 50 kW according to line DL1a. Thus, even when a voltage difference is caused by a voltage drop between power converter 11 and power converter 13, power flow is not suppressed, and power can be supplied from power converter 11 at 50 kW and power element 23 can be charged at -50 kW. Note that the control unit 41 may change the slope instead of changing the slope information of line DL1 so as to obtain the target power value.

[0057] Returning to FIG. 7, the EMS 40 that has generated the reference function outputs an update command including the generated reference function information (step S106). The output of the update command is performed by the output unit 412. Step S106 is an example of an output step. Next, among the power converters 11 to 14, the power converter to be updated acquires the update command of the reference function and updates the reference function information (step S107). The power control device that has finished updating the reference function information executes decentralized control (step S108).

[0058] Note that when the wiring topology is changed, when there is an increase or decrease in the power converters connected to the bus 30, when there is a change in the self-terminal measurement information of the power converters, or when it is detected from the self-terminal measurement information sent from the power converters that there is a suppression in the power supply and demand power of the power converters, the control unit 41 may execute the process shown in FIG. 8.

[0059] <Decentralized control> Next, regarding the control method of decentralized control in the power converters 11 to 14, the power converter 11 will be described as an example. Note that in the other power converters 12 to 14, the same control method as the following description may be appropriately executed.

[0060] In the control method of the power converter 11, the control unit 100 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 110, based on the reference function. An example of the content of this control step will be specifically described with reference to FIG. 10. FIG. 10 is a flowchart showing the flow of processing performed by the control unit 100.

[0061] The control unit 100 executes the process shown in FIG. 10, for example, at a predetermined cycle. First, the control unit 100 acquires the electrical characteristic value measured by the sensor 120 (step S301). Next, the control unit 100 acquires the reference function information from the storage unit 102 (step S302).

[0062] Next, the control unit 100 sets a target value for the output of the power converter 11 (step S303). Here, when the control unit 100 performs droop P control, the power value of the reference function that intersects when a line is drawn along the horizontal axis from the voltage value measured by the sensor 120 is set as the target value. Also, when the control unit 100 performs droop V control, if the reference function is a V - P characteristic, the voltage value of the reference function that intersects when a line is drawn along the vertical axis from the power value measured by the sensor 120 is set as the target value, and if the reference function is a V - I characteristic, the voltage value of the reference function that intersects when a line is drawn along the vertical axis from the current value measured by the sensor 120 is set as the target value.

[0063] Next, the control unit 100 sets an operation amount for PWM control so that the difference between the electrical characteristic value measured by the sensor 120 and the target value set in step S203 is within a predetermined range, and outputs the set operation amount to the power conversion unit 110 (step S304). Thereby, the control of the power conversion unit 110 is executed.

[0064] [First Embodiment] Next, a first embodiment of the optimization of the aforementioned reference function will be described. FIG. 11 is a diagram showing power elements and a power converter included in the first embodiment. Note that the same components as those in the aforementioned embodiment are denoted by the same reference numerals and the description thereof is omitted. In the first embodiment, power elements 21A, 21B, 21C, power element 23, power converters 11A, 11B, 11C, and power converter 13 are included in the power system 1. Power elements 21A, 21B, 21C are the same stationary type energy storage devices as power element 21. Power element 21A is connected to power converter 11A, power element 21B is connected to power converter 11C, and power element 21C is connected to power converter 11C.

[0065] The power converters 11A, 11B, and 11C are the same as the power converter 11. The power converter 11A has a function of converting the voltage of the DC power supplied by the power element 21A and outputting it to the bus 30, and converting the voltage of the DC power supplied from the bus 30 and outputting it to the power element 21A to charge the power element 21A. The power converter 11B has a function of converting the voltage of the DC power supplied by the power element 21B and outputting it to the bus 30, and converting the voltage of the DC power supplied from the bus 30 and outputting it to the power element 21B to charge the power element 21B. The power converter 11C has a function of converting the voltage of the DC power supplied by the power element 21C and outputting it to the bus 30, and converting the voltage of the DC power supplied from the bus 30 and outputting it to the power element 21C to charge the power element 21B.

[0066] In the first embodiment, the line impedance related to the power converter 13 is Rev, the line impedance related to the power converter 11A is R1, the line impedance related to the power converter 11B is R2, the line impedance related to the power converter 11C is R3, and Rev = R1 = R2 = R3.

[0067] FIG. 12A is a diagram showing an example of a reference function set in step S202 in the first embodiment. For example, when the control unit 41 charges the power element 23 with the power supply from the power elements 21A, 21B, and 21C, the shape of the reference function of the power converter 11A is set to the shape of the line DL11a shown in FIG. 12A, the shape of the reference function of the power converter 11B is set to the shape of the line DL11b shown in FIG. 12A, and the shape of the reference function of the power converter 11C is set to the shape of the line DL11c shown in FIG. 12A. Also, when the control unit 41 charges the power element 23 with the power supply from the power elements 21A, 21B, and 21C, the shape of the reference function of the power converter 13 is set to the shape of the line DL31a shown in FIG. 12A.

[0068] When there is no voltage drop in bus 30, for example, if the self-terminal voltage of each power converter is V1 shown in FIG. 12A, power converter 11A supplies power to bus 30 at 5 kW, which is the power target value when the self-terminal voltage is V1 on line DL11a, power converter 11B supplies power to bus 30 at 15 kW, which is the power target value when the self-terminal voltage is V1 on line DL11b, and power converter 11C supplies power to bus 30 at 30 kW, which is the power target value when the self-terminal voltage is V1 on line DL11c. Also, power converter 13 charges power element 23 at -50 kW, which is the power target value when the self-terminal voltage is V1 on line DL31a.

[0069] The dashed line shown in FIG. 12A is a line approximating the voltage drop in bus 30. In other figures showing reference functions as well, the dashed line is a line approximating the voltage drop in the bus to which the power converter is connected. When a voltage drop occurs along the dashed line shown in FIG. 12A between power converters 11A, 11B, 11C and power converter 13, power converter 13 performs power control for charging so that the power value at the intersection of the dashed line and line DL31a is reached, and charges power element 23 at -21 kW. Also, power converter 11A performs power control so that the power value at the intersection of the dashed line and line DL11a is reached, suppressing the output to bus 30 to 1 kW, power converter 11B performs power control so that the power value at the intersection of the dashed line and line DL11b is reached, suppressing the output to bus 30 to 5 kW, and power converter 11C performs power control so that the power value at the intersection of the dashed line and line DL11c is reached, suppressing the output to bus 30 to 15 kW.

[0070] Therefore, control unit 41 optimizes lines DL11a, DL11b, and DL11c in step S204 described above. Specifically, control unit 41 changes the slope of line DL11a to line DL11aa shown in FIG. 12B, changes the slope of line DL11b to line DL11ba shown in FIG. 12B, and changes the slope of line DL11c to line DL11ca shown in FIG. 12B. Also, control unit 41 changes the intercept information of line DL31a and shifts it downward to obtain line DL31aa shown in FIG. 12B.

[0071] Thus, even if a voltage difference is generated due to a voltage drop in the bus 30, power sharing is not suppressed, the output of the power converter 11A is set to 5 kW, the output of the power converter 11B is set to 15 kW, the output of the power converter 11C is set to 30 kW, and the power element 23 can be charged at -50 kW. Note that when optimizing the lines DL11a, DL11b, and DL11c, the control unit 41 may change the slope information of the reference function so that the output from the power converter 11A becomes 5 kW, the output from the power converter 11B becomes 15 kW, and the output from the power converter 11C becomes 30 kW.

[0072] [Second Embodiment] Next, a second embodiment of the optimization of the aforementioned reference function will be described. In the second embodiment, similar to the first embodiment, the power converters 11A, 11B, 11C, the power converter 13, the power elements 21A, 21B, 21C, and the power element 23 are included in the power system 1. In the second embodiment, the line impedance related to the power converter 13 is Rev, the line impedance related to the power converter 11A is R1, the line impedance related to the power converter 11B is R2, the line impedance related to the power converter 11C is R3, and Rev = R1 = R2 < R3.

[0073] FIG. 13A is a diagram showing an example of the reference function set in step S202 in the second embodiment. For example, when the control unit 41 charges the power element 23 with the power supplied from the power elements 21A, 21B, 21C, the shape of the reference function of the power converter 11A is set to the shape of the line DL12a shown in FIG. 13A, the shape of the reference function of the power converter 11B is set to the shape of the line DL12b shown in FIG. 13A, and the shape of the reference function of the power converter 11C is set to the shape of the line DL12c shown in FIG. 13A. Also, when the control unit 41 charges the power element 23 with the power supplied from the power elements 21A, 21B, 21C, the shape of the reference function of the power converter 13 is set to the shape of the line DL32a shown in FIG. 13A.

[0074] When there is no voltage drop in bus 30, for example, if the self-terminal voltage of each power converter is V2 shown in Fig. 13A, the power converter 11A supplies power to bus 30 at 5 kW, which is the power target value when the self-terminal voltage is V2 on line DL12a. The power converter 11B supplies power to bus 30 at 15 kW, which is the power target value when the self-terminal voltage is V2 on line DL12b. The power converter 11C supplies power to bus 30 at 30 kW, which is the power target value when the self-terminal voltage is V2 on line DL12c. Also, the power converter 13 charges the power element 23 at -50 kW, which is the power target value when the self-terminal voltage is V2 on line DL32a.

[0075] The dashed line and the long-dashed line shown in Figs. 13A and 13B are lines approximating the voltage drop in bus 30. When a voltage drop occurs along the dashed line shown in Fig. 13A between the power converters 11A, 11B and the power converter 13, and a voltage drop occurs along the long-dashed line shown in Fig. 13A between the power converter 11C and the power converter 13, the power converter 13 performs power control for charging so that the power value is at the intersection of the dashed line, the long-dashed line, and line DL32a, and charges the power element 23 at -9 kW. Also, the power converter 11A performs power control so that the power value is at the intersection of the dashed line and line DL12a, suppressing the output to bus 30 to 1 kW. The power converter 11B performs power control so that the power value is at the intersection of the dashed line and line DL12b, suppressing the output to bus 30 to 5 kW. The power converter 11C performs power control so that the power value is at the intersection of the long-dashed line and line DL12c, suppressing the output to bus 30 to 3 kW.

[0076] Therefore, the control unit 41 optimizes the lines DL12a, DL12b, and DL12c in the aforementioned step S204. Specifically, for example, with respect to the line DL12a, the control unit 41 changes the intercept information and shifts it upward to obtain the line DL12aa shown in FIG. 13B, for the line DL12b, changes the intercept information and shifts it upward to obtain the line DL12ba shown in FIG. 13B, and for the line DL12c, changes the intercept information and shifts it upward to obtain the line DL12ca shown in FIG. 13B. Also, the control unit 41 changes the intercept information of the line DL32aa and shifts it downward to obtain the line DL32aa shown in FIG. 13B.

[0077] As a result, even if a voltage difference occurs due to voltage drop in the bus 30, power flow is not suppressed, the output of the power converter 11A can be set to 5 kW, the output of the power converter 11B can be set to 15 kW, the output of the power converter 11C can be set to 30 kW, and the power element 23 can be charged at -50 kW. Note that when optimizing the lines DL12a, DL12b, and DL12c, the control unit 41 may change the slope of the reference function so that the output from the power converter 11A is 5 kW, the output from the power converter 11B is 15 kW, and the output from the power converter 11C is 30 kW.

[0078] [Third Embodiment] Next, a third embodiment of the optimization of the aforementioned reference function will be described. FIG. 14 is a diagram showing power elements and power converters included in the third embodiment. Note that the same components as those in the aforementioned embodiments in the third embodiment are denoted by the same reference numerals, and the description thereof is omitted. The third embodiment includes power elements 21A, 21B, 21C, power elements 23A, 23B, power converters 11A, 11B, 11C, and power converters 13A, 13B in the power system 1. The power converters 13A, 13B are the same power converters as the power converter 13. Also, the power elements 23A, 23B are the same power elements as the power element 23. The power converter 13A has a function of converting the voltage of the DC power supplied by the power element 23A and outputting it to the bus 30, and converting the voltage of the DC power supplied from the bus 30 and outputting it to the power element 23A to charge the power element 23A. The power converter 13B has a function of converting the voltage of the DC power supplied by the power element 23B and outputting it to the bus 30, and converting the voltage of the DC power supplied from the bus 30 and outputting it to the power element 23B to charge the power element 23B.

[0079] In the third embodiment, the line impedance related to the power converter 13A is Rev1, the line impedance related to the power converter 13B is Rev2, the line impedance related to the power converter 11A is R1, the line impedance related to the power converter 11B is R2, the line impedance related to the power converter 11C is R3, and Rev1 = Rev2 = R1 = R2 = R3.

[0080] FIG. 15A is a diagram showing an example of the reference function set in step S202 in the third embodiment. For example, when the control unit 41 charges the power elements 23A, 23B with the power supplied from the power elements 21A, 21B, 21C, the shape of the reference function of the power converter 11A is set to the shape of the line DL13a shown in FIG. 15A, the shape of the reference function of the power converter 11B is set to the shape of the line DL13b shown in FIG. 15A, and the shape of the reference function of the power converter 11C is set to the shape of the line DL13c shown in FIG. 15A. Also, the control unit 41 sets the shape of the reference function of the power converter 13A to the shape of the line DL33a shown in FIG. 15A, and the shape of the reference function of the power converter 13B to the shape of the line DL33b shown in FIG. 15A.

[0081] When there is no voltage drop in bus 30, for example, if the self-terminal voltage of each power converter is V3 shown in FIG. 15A, the power converter 11A supplies power to bus 30 at 5 kW, which is the power target value when the self-terminal voltage is V3 on line DL13a. The power converter 11B supplies power to bus 30 at 25 kW, which is the power target value when the self-terminal voltage is V3 on line DL13b. The power converter 11C supplies power to bus 30 at 50 kW, which is the power target value when the self-terminal voltage is V3 on line DL13c. Also, the power converter 13A charges the power element 23A at -50 kW, which is the power target value when the self-terminal voltage is V3 on line DL33a. The power converter 13B charges the power element 23B at -30 kW, which is the power target value when the self-terminal voltage is V3 on line DL33b.

[0082] However, when a voltage drop occurs along the dashed-dotted line shown in FIG. 15A between the power converters 11A, 11B, 11C and the power converters 13A, 13B, the power converter 13A performs charging power control so that the power value at the intersection of the dashed-dotted line and line DL33a is obtained, and charges the power element 23A at -15 kW. The power converter 13B performs charging power control so that the power value at the intersection of the dashed-dotted line and line DL33b is obtained, and charges the power element 23B at -20 kW. Also, the power converter 11A performs power control so that the power value at the intersection of the dashed-dotted line and line DL13a is obtained, and suppresses the output to bus 30 to 3 kW. The power converter 11B performs power control so that the power value at the intersection of the dashed-dotted line and line DL13b is obtained, and suppresses the output to bus 30 to 12 kW. The power converter 11C performs power control so that the power value at the intersection of the dashed-dotted line and line DL13c is obtained, and suppresses the output to bus 30 to 20 kW.

[0083] Therefore, the control unit 41 optimizes the lines DL13a, DL13b, and DL13c in the aforementioned step S204. Specifically, for example, with respect to the line DL13a, the control unit 41 changes the section information and shifts it upward to obtain the line DL13aa shown in FIG. 13B, for the line DL13b, changes the section information and shifts it upward to obtain the line DL13ba shown in FIG. 13B, and for the line DL13c, changes the section information and shifts it upward to obtain the line DL13ca shown in FIG. 13B. Also, the control unit 41 changes the section information of the line DL33a and shifts it downward to obtain the line DL33aa shown in FIG. 15B, and for the line DL33b, changes the section information and shifts it downward to obtain the line DL33ba shown in FIG. 15B.

[0084] As a result, even if there is a voltage drop in the bus 30, power transfer is not suppressed, the output of the power converter 11A is set to 5 kW, the output of the power converter 11B is set to 25 kW, the output of the power converter 11C is set to 50 kW, the power element 23A can be charged at -50 kW, and the power element 23B can be charged at -30 kW. Note that when optimizing the lines DL13a, DL13b, and DL13c, the control unit 41 may change the slope so that the output from the power converter 11A becomes 5 kW, the output from the power converter 11B becomes 25 kW, and the output from the power converter 11C becomes 50 kW.

[0085] [Fourth Embodiment] Next, a fourth embodiment of the optimization of the aforementioned reference function will be described. FIG. 16 is a diagram showing the power elements and power converters included in the fourth embodiment. Note that the same components as those in the embodiment or the previous embodiments in the fourth embodiment are denoted by the same reference numerals and the description thereof is omitted. In the fourth embodiment, the buses 30A, switches 31, power elements 21, 22, power elements 23A, 23B, power element 24, power converters 11, 12, 13A, 13B, and power converter 14 are included in the power system 1.

[0086] In the fourth embodiment, the power system 1 has a bus 30A instead of the bus 30. The bus 30A is a bus with a ring-type wiring topology. The switch 31 is a device that opens and closes the circuit of the ring-type bus 30A. In the fourth embodiment, the switch 31 is in the closed state. Also, in the fourth embodiment, the bus side of the power converter 13A and the bus side of the power converter 13B are connected before being connected to the bus 30A.

[0087] FIG. 17A is an example of a reference function set in step S202 in the fourth embodiment. For example, when the control unit 41 charges the power elements 23A and 23B with the power supplied from the power elements 21, 22, and 24, the shape of the reference function of the power converter 11 is the shape of the line DL14a shown in FIG. 17A, the shape of the reference function of the power converter 12 is the shape of the line DL24a shown in FIG. 17A, and the shape of the reference function of the power converter 14 is the shape of the line DL44a shown in FIG. 17A. Also, the control unit 41 sets the shape of the reference function of the power converter 13A to the shape of the line DL34a shown in FIG. 17A, and the shape of the reference function of the power converter 13B to the shape of the line DL34b shown in FIG. 17A.

[0088] When there is no voltage drop in the bus 30A, for example, if the self-terminal voltage of each power converter is V4 shown in FIG. 17A, the power converter 11 supplies power to the bus 30 at a power target value of 20 kW when the self-terminal voltage is V4 on the line DL14a, the power converter 12 supplies power to the bus 30 at a power target value of 20 kW when the self-terminal voltage is V4 on the line DL24a, and the power converter 14 supplies power to the bus 30 at a power target value of 40 kW when the self-terminal voltage is V4 on the line DL44a. Also, the power converter 13A charges the power element 23A at a power target value of -50 kW when the self-terminal voltage is V4 on the line DL34a, and the power converter 13B charges the power element 23B at a power target value of -30 kW when the self-terminal voltage is V4 on the line DL34b.

[0089] However, when there is a voltage drop in bus 30A, if the operating point of power converter 11 is OP1, the operating point of power converter 12 is OP2, the operating point of power converter 13A is OP31, the operating point of power converter 13B is OP32, and the operating point of power converter 14 is OP4 in the figure, the positions of the respective operating points will be the positions shown in Fig. 17A. When the positions of the respective operating points are the positions shown in Fig. 17A, power converter 13A does not charge power element 23A, and power converter 13B charges power element 23B at -30 kW. Also, when the positions of the respective operating points are the positions shown in Fig. 17A, power converter 11 sets the output to the bus 30A to 0 kW, power converter 12 sets the output to the bus 30A to 20 kW, and power converter 14 suppresses the output to the bus 30A to 10 kW.

[0090] Therefore, control unit 41 optimizes line DL14a and line DL44a in the aforementioned step S204. Specifically, for example, control unit 41 changes the intercept information of line DL14a and shifts it upward to obtain line DL14aa shown in Fig. 17B, and changes the intercept information of line DL44a and shifts it upward to obtain line DL44aa shown in Fig. 17B. Also, control unit 41 changes the intercept information of line DL34a and shifts it downward to obtain line DL34aa shown in Fig. 17B, and changes the intercept information of line DL34b and shifts it downward to obtain line DL34ba shown in Fig. 17B.

[0091] As a result, even if a voltage difference is generated due to a voltage drop in bus 30A, power flow is not suppressed, the output of power converter 11 can be set to 20 kW, the output of power converter 12 can be set to 20 kW, the output of power converter 14 can be set to 40 kW, power element 23A can be charged at -50 kW, and power element 23B can be charged at -30 kW. Note that when optimizing line DL14a and line DL44a, control unit 41 may change the slope so that the output from power converter 11 becomes 20 kW and the output from power converter 14 becomes 40 kW.

[0092] [Fifth Embodiment] Next, a fifth embodiment of the optimization of the aforementioned reference function will be described. FIG. 18 is a diagram showing power elements and a power converter included in the fifth embodiment. In the fifth embodiment, the same components as those in the embodiment or the aforementioned embodiments are denoted by the same reference numerals and the description thereof is omitted. The fifth embodiment is different from the fourth embodiment in that the switch 31 is in an open state.

[0093] When the switch 31 is in the closed state, the reference functions of the power converters 11, 12, 13A, 13B, and 14 are as shown in FIG. 17B. When the switch 31 changes from the closed state to the open state, the line impedance of the bus 30A changes due to the change in the wiring topology from the ring type to the bus type, and the voltage drop between the power converters increases. For example, between the power converter 14 and the power converters 13A and 13B, when the switch 31 is in the closed state, they are connected in parallel, but when the switch 31 is in the open state, they are connected in series, and the configuration of the bus 30A changes and the line impedance increases, so the voltage drop increases.

[0094] As a result, the positions of the operating points of the power converters 11, 12, 13A, 13B, and 14 become the positions shown in FIG. 19A. As shown in FIG. 19A, the power converter 11 supplies power to the bus 30A at 20 kW, the power converter 12 supplies power to the bus 30A at 20 kW from the power element 22, and the power converter 14 supplies power to the bus 30A at 25 kW from the power element 24. Also, the power converter 13A charges the power element 23A at -35 kW, and the power converter 13B charges the power element 23B at -30 kW, making it difficult to perform the target power flow.

[0095] Therefore, when the data indicating the wiring topology stored in the storage unit 32 is changed due to the state change of the switch 31, the control unit 41 executes the processes shown in FIGS. 7 and 8 to optimize the reference functions of the respective power converters. Specifically, the control unit 41 changes the slope information of the line DL44aa and shifts it upward to obtain the line DL45aa shown in FIG. 19B. Also, the control unit 41 changes the slope information of the line DL34aa and shifts it downward to obtain the line DL35aa shown in FIG. 19B.

[0096] Thus, even if a voltage difference is generated due to a voltage drop in bus 30A, power transfer is not suppressed. The output from power converter 11 is set to 20 kW, the output from power converter 12 is set to 20 kW, the output from power converter 14 is set to 40 kW, power element 23A can be charged at -50 kW, and power element 23B can be charged at -30 kW. Note that when optimizing line DL44aa, control unit 41 may change the slope so that the output from power converter 14 becomes 40 kW.

[0097] [Sixth Embodiment] Next, a sixth embodiment of the optimization of the aforementioned reference function will be described. The sixth embodiment is an example in which the output of power element 22 decreases when each power converter operates with the reference function shown in FIG. 17B in the fourth embodiment.

[0098] For example, when the output of power element 22 becomes 0 kW, the reference function of power converter 12 is updated to line DL26a shown in FIG. 20A. Also, when the output of power element 22 becomes 0 kW, the voltage drop between power converter 14 and power converters 13A and 13B decreases. When the voltage drop between power converters decreases, the operating point positions of power converters 11, 12, 13A, 13B, and 14 become the positions shown in FIG. 20A. Here, in power converters 11 and 14, the terminal voltage drops. As shown in FIG. 20A, power converter 11 supplies power to bus 30A at 30 kW, and power converter 14 supplies power to bus 30A at 50 kW. Also, power converter 13A charges power element 23A at -50 kW, and power converter 13B charges power element 23B at -30 kW, and the power supply from power element 24, which is a commercial power system, increases.

[0099] Therefore, when the output of the power element 22 decreases, the control unit 41 optimizes the reference functions of each power converter. Specifically, the control unit 41 changes the intercept information for the line DL44aa and shifts it downward to obtain the line DL46aa shown in FIG. 20B. Further, the control unit 41 changes the intercept information for the line DL14aa and shifts it upward to obtain the line DL16aa shown in FIG. 20B. As a result, even if a voltage difference is generated due to voltage drop between the power converters 11 and 14 and the power converters 13A and 13B, the power supply from the power element 24 is suppressed, the output of the power converter 11 is set to 40 kW, the output from the power converter 14 is suppressed to 40 kW, the power element 23A can be charged at -50 kW, and the power element 23B can be charged at -30 kW. Note that when optimizing the lines DL14aa and DL44aa, the control unit 41 may change the slope so that the output from the power converter 11 becomes 40 kW and the output from the power converter 14 becomes 40 kW.

[0100] [Seventh Embodiment] Next, a seventh embodiment of the optimization of the reference function described above will be described. FIG. 21 is a diagram showing power elements and power converters included in the seventh embodiment. Note that the same components as those in the embodiment or the previous embodiments are denoted by the same reference numerals and the description thereof is omitted. The seventh embodiment is an example in which a power converter 11D and a power element 21D are added to the fourth embodiment. The power element 21D is the same stationary energy storage device as the power element 21, and the power converter 11D is the same power converter as the power converter 11.

[0101] When the power converter 11D to which the power element 21D is connected is connected to the bus 30A at the position shown in FIG. 21 from the state shown in FIG. 16, the reference functions of the respective power converters before being updated by the central control are, as shown in FIG. 22A, the reference function of the power converter 11 is the line DL14aa, the reference function of the power converter 12 is the line DL24a, the reference function of the power converter 13A is the line DL34aa, the reference function of the power converter 13B is the line DL34ba, the reference function of the power converter 14 is the line DL24a, and the reference function of the power converter 11D is the line DL17d.

[0102] When the power element 21D and the power converter 11D are added to the power system 1, the power supplied to the bus 30A increases. For this reason, the voltage drop between the power converters becomes large in the bus 30A, and the positions of the operating points of each of the power converters 11, 11D, 12, 13A, 13B, and 14 become the positions shown in FIG. 22A. Note that the operating point of the power converter 11D in the figure is OP12.

[0103] Here, in the power converters 11, 11D, 12, and 14, the terminal voltage rises. As shown in FIG. 22A, the output of the power converter 11 becomes 0 kW, the power converter 11D supplies power to the bus 30A at 10 kW, the power converter 12 supplies power to the bus 30A at 20 kW, and the power converter 14 supplies power to the bus 30 at 40 kW. Further, the power converter 13A charges the power element 23A at -40 kW, and the power converter 13B charges the power element 23B at -30 kW, so that the charging power is suppressed.

[0104] Therefore, when the power element 21D and the power converter 11D are added to the power system 1, the control unit 41 optimizes the reference functions of the respective power converters. Specifically, the control unit 41 changes the intercept information for the line DL44aa and shifts it upward to obtain the line DL47aa shown in FIG. 22B. Further, the control unit 41 changes the intercept information for the line DL14aa and shifts it upward to obtain the line DL17aa shown in FIG. 22B. Further, the control unit 41 changes the intercept information for the line DL34aa and shifts it downward to obtain the line DL37aa shown in FIG. 22B.

[0105] Thereby, even if a voltage difference is generated due to a voltage drop in the bus 30A, power flow is not suppressed, the output of the power converter 11 can be set to 10 kW, the output of the power converter 14 can be set to 40 kW, the power element 23A can be charged at -50 kW, and the power element 23B can be charged at -30 kW. Note that when optimizing the lines DL14aa and DL44aa, the control unit 41 may change the slope so that the output from the power converter 11 becomes 10 kW and the output from the power converter 14 becomes 40 kW.

[0106] [Modification Example] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and can be implemented in various other forms. For example, the present invention may be implemented by modifying the above-described embodiments as follows. Note that the above-described embodiments and the following modification examples may be combined with each other. The present invention also includes those configured by appropriately combining the components of the above-described embodiments and each modification example. Further, additional effects and modification examples can be easily derived by those skilled in the art. Therefore, a broader aspect of the present invention is not limited to the above-described embodiments and modification examples, and various changes are possible.

[0107] In the above-described embodiment, for example, even when the demand for power in the power element 23 decreases, the EMS 40 may update the reference function.

[0108] In the above-described embodiment, the power converter to which the power element that consumes power is connected may be connected to the bus 30 or the bus 30A. The power element that consumes power is, for example, a device that converts power into kinetic energy or thermal energy.

[0109] In the present invention, the EMS 40 may send an update command only to the power converter that updates the reference function. In this case, the EMS 40 may notify the power converter that does not update the reference function that it will not be updated.

Industrial Applicability

[0110] The present invention can be used in a power system, a control device, and a control method.

Explanation of Reference Numerals

[0111] 1 Power system 11 to 14, 11A, 11B, 11C, 11D, 13A, 13B Power converters 21A, 21B, 21C, 21D, 22, 23, 23A, 23B, 24 Power elements 30, 30A Buses 31 Switch 40 EMS 41 Control Unit 42, 102 Memory Unit 43, 130 Communication Unit 60 External Server 100 Control Unit 110 Power Conversion Unit 120 Sensor 100a Operation Quantity Setting Unit 100b Information Provision Unit 100c Update Unit 411 Reference Function Setting Unit 412 Output Unit NW Network

Claims

1. A power conversion unit that converts and outputs the input power; A measurement unit that acquires the electrical characteristic value of the input or output power; A storage unit that stores a reference function in which the electrical characteristic value of the output of the power conversion unit is defined according to the input value; A characteristic control unit that uses the electrical characteristic value acquired by the measurement unit as an input value and controls the power conversion characteristic of the output of the power conversion unit based on the reference function; An update unit that acquires a reference function and updates the reference function acquired with the reference function stored in the storage unit; A plurality of power converters having; A reference function setting unit that sets the reference function of each of the plurality of power converters; An output unit that outputs the set reference function to the plurality of power converters; A control device having; A DC power line to which the plurality of power converters are connected; comprising, For each of the plurality of power converters, the reference function setting unit calculates the voltage drop in the power line based on the power target value of the output of the power conversion unit and the line impedance of the power line, and based on the calculated voltage drop, calculates the voltage target value of the self-terminal voltage of the power converter when outputting the power target value within the operating voltage range of the power converter, and sets the reference function to a reference function in which the electrical characteristic value of the output of the power conversion unit when the self-terminal voltage is the voltage target value is defined as the power target value Power system.

2. When the line impedance changes due to a change in the configuration of the power line, the reference function setting unit calculates the voltage drop in the power line based on the power target value of the output of the power conversion unit and the changed line impedance, and based on the calculated voltage drop, calculates the voltage target value of the self-terminal voltage of the power converter when outputting the power target value within the operating voltage range of the power converter, and updates the reference function to a reference function in which the electrical characteristic value of the output of the power conversion unit when the self-terminal voltage is the voltage target value is defined as the power target value, The output unit outputs the updated reference function. The power system according to claim 1.

3. When the power demand in the power element connected to the power converter or the power supply from the power element changes, the reference function setting unit calculates the voltage drop in the power line according to the change, based on the power target value of the output of the power conversion unit corresponding to the change and the line impedance of the power line, and calculates the voltage target value of the self-terminal voltage of the power converter when outputting the power target value within the operating voltage range of the power converter, and updates the reference function to the reference function defined by the electrical characteristic value of the output of the power conversion unit when the self-terminal voltage is the voltage target value being the power target value. The power system according to claim 1.

4. When the number of the power converters connected to the power line increases or decreases, the reference function setting unit calculates the voltage drop in the power line according to the increase or decrease, based on the power target value of the output of the power conversion unit of the power converter connected to the power line after the increase or decrease and the line impedance of the power line, and calculates the voltage target value of the self-terminal voltage of the power converter when outputting the power target value within the operating voltage range of the power converter, and updates the reference function to the reference function defined by the electrical characteristic value of the output of the power conversion unit when the self-terminal voltage is the voltage target value being the power target value. The power system according to claim 1.

5. The power target value is set based on the power balance of the plurality of power converters, the predicted power supply and demand in the power element connected to the power converter, or the optimization calculation of the output of the power converter. The power system according to claim 1.

6. The plurality of power converters include a power converter connected to a power element capable of power supply and charge and discharge, a power converter connected to a power element for power supply, and a power converter for consuming power. The power system according to claim 1.

7. A power conversion unit that converts and outputs the input power, a measurement unit that acquires the electrical characteristic values of the input or output power, a storage unit that stores a reference function in which the electrical characteristic values of the output of the power conversion unit are defined according to the input value, a characteristic control unit that uses the electrical characteristic values acquired by the measurement unit as input values and controls the power conversion characteristics of the output of the power conversion unit based on the reference function, an update unit that acquires a reference function and updates the acquired reference function with the reference function stored in the storage unit, and a reference function setting unit that sets the reference function for each of a plurality of power converters; An output unit that outputs the set reference function to the plurality of power converters; having For each of the plurality of power converters, the reference function setting unit calculates a voltage drop in the DC power line to which the plurality of power converters are connected based on the power target value of the output of the power conversion unit and the line impedance of the DC power line, and based on the calculated voltage drop, calculates a voltage target value of the self-terminal voltage of the power converter when outputting the power target value within the operating voltage range of the power converter, and sets the reference function to a reference function in which the electrical characteristic value of the output of the power conversion unit when the self-terminal voltage is the voltage target value is defined as the power target value. Control device.

8. A power conversion unit that converts and outputs the input power, a measurement unit that acquires the electrical characteristic values of the input or output power, a storage unit that stores a reference function in which the electrical characteristic values of the output of the power conversion unit are defined according to the input value, a characteristic control unit that uses the electrical characteristic values acquired by the measurement unit as input values and controls the power conversion characteristics of the output of the power conversion unit based on the reference function, an update unit that acquires a reference function and updates the acquired reference function with the reference function stored in the storage unit, a reference function setting step of setting the reference function for each of a plurality of power converters; An output step of outputting the set reference function to the plurality of power converters; having The reference function setting step calculates, for each of the plurality of power converters, a voltage drop in the DC power line to which the plurality of power converters are connected based on a power target value of the output of the power conversion unit and a line impedance of the DC power line, and calculates, based on the calculated voltage drop, a voltage target value of the self-terminal voltage of the power converter when outputting the power target value within the operating voltage range of the power converter, and sets the reference function to a reference function in which an electrical characteristic value of the output of the power conversion unit when the self-terminal voltage is the voltage target value is defined as the power target value. Control method.

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