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

Abstract

Disclosed is a power converter electrically connected to a power storage device, the power converter comprising a control unit that refers to a reference function having droop characteristics, which is a control target function, as an output target of the power storage device in accordance with voltage measured by the power converter. The reference function has a constant output / input region over a predetermined voltage range, and the reference function is updated on the basis of a battery state of the power storage device.

Description

Technical Field

[0001] The present invention relates to a power converter electrically connected to an AC commercial power system and electrically connected to a stationary energy storage device capable of supplying power from the commercial power system, which controls the input and output of the stationary energy storage device so as to follow a reference function having a droop characteristic according to the measured voltage and current of the power converter, and updates a reference function having a droop characteristic according to a change in the charge rate of the stationary energy storage device, and a power system including the power converter.

Background Art

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

[0003] Conventionally, as a control method for a DC grid, a power converter connected to a stationary energy storage device or the like performs constant current control or constant voltage control on the stationary energy storage device or the like based on an instruction from a centralized control unit, thereby centrally controlling the amount of power on the DC bus of the DC grid. Although the above centralized control method can easily control the entire DC grid, there is a problem that it is difficult to smoothly respond to rapid power supply and demand fluctuations.

[0004] Therefore, a reference function based on the self-terminal power (P) and the self-terminal voltage (V) is assigned to a stationary energy storage device or the like, and droop control is also performed, which has a droop characteristic that causes the stationary energy storage device or the like to have a droop characteristic with respect to the target voltage value according to the amount of power required for the DC bus. By autonomously and dispersedly controlling the stationary energy storage device or the like through droop control, the input / output amount of the stationary energy storage device or the like can be optimally adjusted according to the amount of power required for the DC bus, and the voltage of the DC bus can be stabilized.

[0005] In the conventional droop control of a stationary energy storage device, in order to stabilize the voltage of the DC bus and the charge state of the stationary energy storage device, according to the change in the charge rate of the stationary energy storage device, the intercept (voltage (V) of the entire DC grid) of the reference function having a droop characteristic is shifted to the high voltage side or the low voltage side, and the reference function is updated. As a reference function updated as described above, for example, a reference function provided with a constant input region in which the target input / output of the energy storage device is maintained at 0 over a predetermined voltage range can be cited (Patent Document 1).

[0006] Further, as a reference function updated as described above, in order to give the energy storage device flexible charge / discharge characteristics, a reference function that does not provide a constant input region where the input / output of the energy storage device is 0 can be cited (Patent Document 2).

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] In Patent Document 1, by providing a constant input region where the input and output are 0 in the reference function, when the DC grid is in steady operation, the power supply of the DC grid can be covered by the power supplied from an external commercial power system or a solar power generation device (PV) without performing charge and discharge of the energy storage device. Therefore, the power efficiency of the entire DC grid is improved. However, in Patent Document 1, even when the charge rate of the energy storage device is low, the operation of the energy storage device remains within the constant input region of the reference function where the input and output of the energy storage device are 0, so there may be cases where the energy storage device cannot maintain a sufficient charge state. If the energy storage device cannot maintain a sufficient charge state, it cannot be utilized as an adjustment force for sudden fluctuations in power supply and demand of the DC grid. Also, in the reference function of Patent Document 2, since the energy storage device is constantly performing charge and discharge, there is a problem that the power loss due to charge and discharge increases and the power efficiency of the DC grid decreases.

[0009] In view of the above circumstances, an object of the present invention is to provide a power converter that performs input / output control according to the battery state of an energy storage device, for example, reduces the output of the energy storage device when the power stored in the energy storage device is low, and can impart excellent adjustment force and power efficiency for sudden fluctuations in power supply and demand, a power system including the power converter, and a control method of the power converter, a control method of the power system, and a program.

Means for Solving the Problems

[0010] The gist of the configuration of the present invention is as follows. [1] A power converter electrically connected to an energy storage device, wherein the power converter refers to a reference function having a droop characteristic as a control target function as an output target of the energy storage device according to the voltage measured by the power converter, the reference function has a constant input region over a predetermined voltage range, and the reference function is updated based on the battery state of the energy storage device. [2] The energy storage device is a stationary energy storage device, The control unit of the power converter executes control based on the reference function having a droop characteristic that generates a target value when self-terminally controlling the stationary energy storage device according to the voltage measured by the power converter. The reference function has a constant input / output region in which the input / output of the stationary energy storage device maintains a constant value over a predetermined voltage range, and the reference function having the constant input / output region is updated based on the battery state of the stationary energy storage device. The power converter according to [1]. [3] The change in the battery state of the energy storage device is a change in the state of charge, a change in the degradation state, or a change in the C-rate. The power converter according to [1] or [2]. [4] When the state of charge of the energy storage device is at a first state of charge and the input / output in the constant input / output region is 0. The power converter according to [3]. [5] When the state of charge of the energy storage device decreases to a second state of charge or less that is lower than the first state of charge due to a decrease in the state of charge of the energy storage device, the constant input / output region shifts to an input region where a charging current is supplied to the energy storage device, and when the state of charge of the energy storage device increases to a third state of charge or more that is higher than the first state of charge due to an increase in the state of charge of the energy storage device, the reference function having the droop characteristic is updated so that the constant input / output region shifts to an output region where the energy storage device discharges. The power converter according to [4]. [6] When the state of charge of the energy storage device decreases from the first state of charge to a predetermined state of charge exceeding the second state of charge, the voltage value at the upper limit of the predetermined voltage range where the input / output in the constant input / output region is 0 shifts to the low voltage side, and when the state of charge of the energy storage device increases from the first state of charge to a predetermined state of charge less than the third state of charge, the reference function having the droop characteristic is updated so that the voltage value at the lower limit of the predetermined voltage range where the input / output in the constant input / output region is 0 shifts to the high voltage side. The power converter according to [5]. [7]When the charging rate of the modular energy storage device decreases from the first charging rate to a predetermined charging rate exceeding the second charging rate, the voltage value at the lower limit of the predetermined voltage range where the input / output in the input / output constant region is 0 remains unchanged. When the charging rate of the energy storage device increases from the first charging rate to a predetermined charging rate less than the third charging rate, the reference function having the droop characteristic is updated so that the voltage value at the upper limit of the predetermined voltage range where the input / output in the input / output constant region is 0 is not changed. The power converter according to [6]. [8]The secondary control for updating the reference function having the droop characteristic is performed based on a command from a central control unit. The power converter according to any one of [1] to [7]. [9]The control unit of the power converter performs control based on the reference function based on the voltage at the self-terminal of the stationary energy storage device without going through the command of the central control unit. The power converter according to [8].

[10] The control period of the secondary control is longer than the control period of the control based on the reference function. The power converter according to [8] or [9].

[11] The reference function having the droop characteristic is configured to change the input / output amount of power or current in response to a change in voltage. The power converter according to any one of [1] to

[10] .

[12] The power converter according to any one of [1] to

[11] , which is a DC / DC converter.

[13] A power element is provided that includes a power converter and a stationary energy storage device electrically connected to the power converter. The power converter is a power system that refers to a reference function having a droop characteristic, which is a control target function, as an output target of the energy storage device according to the measured voltage of the power converter. The reference function has an input / output constant region over a predetermined voltage range, and the reference function is updated based on the state of charge of the energy storage device. The power system.

[14] The energy storage device is a stationary energy storage device. A power system comprising a control unit that executes control based on a reference function that generates a target value when self-terminally controlling the stationary energy storage device according to the voltage measured by the power converter. The reference function has a constant input / output range in which the input / output of the stationary energy storage device maintains a constant value over a predetermined voltage range, and the reference function having the constant input / output range is updated based on the battery state of the stationary energy storage device. The power system according to

[13] .

[15] The change in the battery state of the energy storage device is a change in the state of charge, a change in the degradation state, or a change in the C-rate. The power system according to

[13] or

[14] .

[16] The power system according to

[15] , wherein the state of charge of the energy storage device is at a first state of charge and the input / output in the constant input / output range is 0.

[17] When the state of charge of the energy storage device decreases to a second state of charge that is lower than the first state of charge due to a decrease in the state of charge of the energy storage device, the constant input / output range shifts to an input range in which a charging current is supplied to the energy storage device. When the state of charge of the energy storage device increases to a third state of charge that is higher than the first state of charge due to an increase in the state of charge of the energy storage device, the reference function having the droop characteristic is updated so that the constant input / output range shifts to an output range in which the energy storage device discharges. The power system according to

[16] .

[18] When the state of charge of the energy storage device decreases from the first state of charge to a predetermined state of charge exceeding the second state of charge, the voltage value at the upper limit of the predetermined voltage range where the input / output in the constant input / output range is 0 shifts to the low voltage side. When the state of charge of the energy storage device increases from the first state of charge to a predetermined state of charge less than the third state of charge, the reference function having the droop characteristic is updated so that the voltage value at the lower limit of the predetermined voltage range where the input / output in the constant input / output range is 0 shifts to the high voltage side. The power system according to

[17] .

[19] When the charging rate of the energy storage device decreases from the first charging rate to a predetermined charging rate exceeding the second charging rate, the voltage value at the lower limit of the predetermined voltage range where the input / output in the input / output constant region is 0 is not changed. When the charging rate of the energy storage device increases from the first charging rate to a predetermined charging rate less than the third charging rate, the reference function having the droop characteristic is updated so that the voltage value at the upper limit of the predetermined voltage range where the input / output in the input / output constant region is 0 is not changed, in the power system described in

[18] .

[20] The power system further includes a central control unit that controls the power converter, and the secondary control for updating the reference function having the droop characteristic is performed based on a command from the central control unit, in the power system according to any one of

[13] to

[19] .

[21] The control unit performs control based on the reference function based on the voltage at the self-terminal of the energy storage device without going through a command from the central control unit, in the power system described in

[20] .

[22] The control period of the secondary control is longer than the control period of the control based on the reference function, in the power system described in

[20] or

[21] .

[23] The reference function having the droop characteristic is configured to change the input / output amount of power or current in response to a change in voltage, in the power system according to any one of

[13] to

[22] .

[24] The line to which the power element is electrically connected is a DC bus, in the power system according to any one of

[13] to

[23] .

[25] A control method for a power converter electrically connected to an energy storage device, a step in which the power converter refers to a reference function having a droop characteristic, which is a control target function, as an output target of the energy storage device according to the voltage measured by the power converter; a step in which the reference function is updated based on the battery state of the energy storage device; comprising: the reference function having an input / output constant region over a predetermined voltage range A control method for a power converter.

[26] A control method for a power system provided with a power element including a power converter and a stationary energy storage device electrically connected to the power converter, comprising: a step in which the power converter refers to a reference function having a droop characteristic, which is a control target function, as an output target of the energy storage device according to a voltage measured by the power converter; a step in which the reference function is updated based on a battery state of the energy storage device; and the reference function has an input / output constant region over a predetermined voltage range A control method for a power system.

[27] A control method for a power system provided with a power element including a power converter and a stationary energy storage device electrically connected to the power converter, and further including a central control device capable of information communication with the power converter and an external server holding demand information of power, comprising: a step in which the power converter refers to a reference function having a droop characteristic, which is a control target function, as an output target of the energy storage device according to a voltage measured by the power converter; a step of acquiring the demand information from the external server; a step in which the reference function is updated based on a battery state of the energy storage device; and the reference function has an input / output constant region over a predetermined voltage range A control method for a power system.

[28] A program for causing a processor to execute a control method for a power converter electrically connected to an energy storage device, comprising: a step of referring to a reference function having a droop characteristic, which is a control target function, as an output target; a step in which the reference function is updated based on a battery state of the energy storage device; and the reference function has an input / output constant region over a predetermined voltage range A program.

[29] A program for causing a processor to execute

[29] A program for causing a processor to execute A program for executing a control method of a power system provided with an AC power converter and a power element provided with a stationary energy storage device electrically connected to the power converter, a step in which the power converter refers to a reference function having a droop characteristic, which is a control target function, as an output target of the energy storage device according to a voltage measured by the power converter; a step in which the reference function is updated based on the battery state of the energy storage device; comprising; the reference function having a constant input / output region over a predetermined voltage range Program.

Effect of the Invention

[0011] According to the aspect of the power converter and the power system including the power converter of the present invention, a droop control function based on a reference function having a droop characteristic for generating a target value when self-terminally controlling the energy storage device according to the voltage measured by the power converter is provided. The reference function having a droop characteristic has a constant input / output region in which the target input / output of the energy storage device maintains a constant value over a predetermined voltage range. Based on the change in the battery state of the energy storage device, the reference function having a droop characteristic with a constant input / output region is updated, so that input / output control is performed according to the battery state of the energy storage device. For example, when the power stored in the energy storage device is low, the output of the energy storage device is restricted, thereby imparting excellent adjustment power to the energy storage device against rapid power supply and demand fluctuations and improving the power efficiency of the power system.

[0012] According to an aspect of the power converter and the power system including the power converter of the present invention, due to a decrease in the charge rate of the energy storage device, the charge rate of the energy storage device drops to a second charge rate that is lower than a first charge rate at which the input and output in the constant input-output range are 0. As a result, the constant input-output range shifts to an input range where a charging current is supplied to the energy storage device. Due to an increase in the charge rate of the energy storage device, the charge rate of the energy storage device rises to a third charge rate that is higher than the first charge rate. By updating the reference function having droop characteristics so that the constant input-output range shifts to an output range where the energy storage device discharges, the charge rate of the energy storage device can be maintained within an appropriate range. Therefore, it is possible to more surely impart an excellent adjustment force to the energy storage device against rapid fluctuations in power demand and supply.

[0013] According to an aspect of the power converter and the power system including the power converter of the present invention, as the charge rate of the energy storage device decreases from the first charge rate to a predetermined charge rate exceeding the second charge rate, the voltage value at the upper limit of a predetermined voltage range where the input and output in the constant input-output range are 0 shifts to the low voltage side. As the charge rate of the energy storage device increases from the first charge rate to a predetermined charge rate less than the third charge rate, the voltage value at the lower limit of a predetermined voltage range where the input and output in the constant input-output range are 0 shifts to the high voltage side. By updating the reference function having droop characteristics in this way, while utilizing the power supplied from an external commercial power system, the charge rate of the energy storage device can be maintained within an appropriate range. Therefore, while more surely imparting an excellent adjustment force to the energy storage device against rapid fluctuations in power demand and supply, the power efficiency of the power system can be further improved.

[0014] According to an aspect of the power converter and the power system including the power converter of the present invention, secondary control for updating a reference function having droop characteristics is performed based on a command from a central control unit, and droop control based on the reference function is performed based on the voltage at the local end of the energy storage device without going through the command of the central control unit. As a result, the amount of power required that varies with time in the entire power network including the energy storage device can be accurately reflected in the input / output control of the energy storage device. Therefore, the control of the entire power network including the energy storage device is optimized, and power required for the entire power network can be efficiently supplied.

[0015] According to an aspect of the control method of the power converter, the control method of the power system, and the program of the present invention, it is possible to improve the power efficiency of the power system while imparting excellent adjustment power to the energy storage device against rapid power supply / demand fluctuations.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0017] <Embodiment> A power system including a power converter according to an embodiment of the present invention will be described. Note that FIG. 1 is an explanatory diagram showing an overview of an entire power network constituting the power system including the power converter according to the embodiment of the present invention. FIG. 2 is an explanatory diagram of a reference function having droop characteristics given to devices used in the power network constituting the power system including the power converter according to the embodiment of the present invention. FIG. 3 is an explanatory diagram showing a state in which the reference function given to devices used in the power system including the power converter according to the embodiment of the present invention is updated. FIG. 4 is an update example of a reference function having droop characteristics given to a stationary energy storage device used in the power system including the power converter according to the embodiment of the present invention. FIG. 5 is a sequence diagram showing an example of a control method of the power system.

[0018] As shown in FIG. 1, in a power system 1 including a power converter according to an embodiment of the present invention, a bidirectional DC / DC converter 12, which is electrically connected to an AC commercial power system 100 and is capable of supplying power from the AC commercial power system 100, is provided. Specifically, an AC / DC converter 11 that is connectable to the AC commercial power system 100 and converts AC power input from the AC commercial power system 100 into DC power and outputs it, a DC bus 19 connected to the output of the AC / DC converter 11, a first DC / DC converter 13 connected to the DC bus 19 and converting DC power input from the DC bus 19 into a charging voltage of a storage battery to be charged and outputting it, a charger (EV charger 17 in the power network 10) connected to the first DC / DC converter 13 and connectable to the storage battery to be charged, a bidirectional DC / DC converter 12 connected to the DC bus 19 and converting DC power input from the DC bus 19 into a charging voltage of a stationary energy storage device 14 and outputting it, and a photovoltaic power generation device (PV) 15, which is a power generation device that generates power using renewable energy and is connected to the DC bus 19 via a second DC / DC converter 16, are provided.

[0019] From the above, the power network 10 that constitutes the power system 1 is a DC grid. In the power network 10, the storage battery is, for example, an in-vehicle storage battery mounted on an electric vehicle (EV) 18 that is a load. The output of the DC bus 19 is connected to the EV charger 17, and the in-vehicle storage battery of the electric vehicle 18 is connected to the EV charger 17 to charge the in-vehicle storage battery. The stationary energy storage device 14 is an in-facility energy storage device of the power network 10.

[0020] Each power converter has, as an example, a power conversion unit, a sensor, a control unit, and a communication unit.

[0021] The power conversion unit is a part having a power conversion function that is AC / DC conversion or DC / DC conversion in each power converter, and is composed of 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 can control the power conversion characteristics, for example, by PWM (Pulse Width Modulation) control.

[0022] The sensor is used in each power converter to measure the electrical characteristic values at its own end, such as current value, voltage value, and power value. The sensor outputs the measured value to the control unit.

[0023] In the power system 1 equipped with the power network 10, the power reception amount from the commercial power system 100 is controlled by the control unit. Further, the control unit controls the charge and discharge of the stationary energy storage device 14, the discharge of the solar power generation device 15, and the charging of the in-vehicle storage battery of the electric vehicle 18 connected to the EV charger 17.

[0024] Each control unit is configured to include a processor that performs various arithmetic processes for controlling the power conversion function and a storage unit. The processor is, for example, a CPU (Central Processing Unit), ASIC (Application Specific Integrated Circuit), FPGA (Field-Programmable Gate Array), DSP (Digital Signal Processor), GPU (Graphics Processing Unit), or the like. The storage unit stores various programs and data used by the processor to perform arithmetic processes, and includes, for example, a ROM (Read Only Memory). Further, the storage unit is used to store a work space when the processor performs arithmetic processes and the results of the processor's arithmetic processes, and includes, for example, a RAM (Random Access Memory). The storage unit may include an auxiliary storage device such as an HDD (Hard Disk Drive) or an SSD (Solid State Drive). The function of each control unit is realized as a functional unit by the processor reading out and executing various programs from the storage unit. For example, each control unit outputs a PWM signal including information on an operation amount (for example, a duty ratio) for PWM (Pulse Width Modulation) to the power conversion unit and performs PWM control on each power converter. Note that each control unit may directly output the operation amount to the power conversion unit, or may output it to the power conversion unit via another functional unit (for example, a loop control unit) not shown in the figure.

[0025] The communication unit is configured to include 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 performs information communication with a central control unit 110, which will be described later, via a network NW composed of, for example, an Internet line network or a mobile phone line network. The communication unit receives a command from the central control unit 110, for example, and outputs it to the control unit. The communication unit transmits information regarding the power status input from the control unit to the central control unit 110, for example. When the information regarding the power status is a measurement value of the sensor, the communication unit may transmit the measurement value input from the sensor to the central control unit 110, for example.

[0026] An example of the central control unit 110 will be described. The central control unit 110 includes a control unit, a storage unit, and a communication unit. The configurations of the control unit, the storage unit, and the communication unit can use those exemplified as the configurations of the control unit, the storage unit, and the communication unit of the power converter, respectively.

[0027] The functions of the control unit are realized as functional units by the control unit reading and executing various programs from the storage unit.

[0028] The communication unit performs information communication with each power converter and the external server 200 via the network NW.

[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 energy management system (EMS) in another power system, or an information processing device having a database and functioning as a data server for the central control unit 110. The external server 200 stores various information that may affect the operation of the power system 1.

[0030] In the power system 1, the bidirectional DC / DC converter 12 has a function of performing droop control so as to follow a reference function having a droop characteristic, which is a control target function for generating a target value when performing so-called local control for controlling the stationary energy storage device 14 according to the measured voltage (V) at its own end of the bidirectional DC / DC converter 12. That is, it has a function of performing control based on a reference function having a droop characteristic. Such control is executed by the control unit of the bidirectional DC / DC converter 12.

[0031] The bidirectional DC / DC converter 12 connected to the stationary energy storage device 14 has a function of performing droop control on the operation of the stationary energy storage device 14 so that the relationship between the voltage (V) at its own end and the power (P) at its own end, that is, the relationship between the voltage (V) at its own end and the power (P) charged and discharged from the stationary energy storage device 14 follows a reference function having a predetermined droop (dropping) characteristic. That is, the bidirectional DC / DC converter 12 controls so that the relationship between the voltage (V) at its own end and the power (P) at its own end maintains a reference function having a predetermined droop (dropping) characteristic at a predetermined control period. Note that the "droop characteristic" means a dropping characteristic, and it is a characteristic having a relationship other than a relationship in which the power input / output amount is constant over a predetermined voltage range or a relationship in which the voltage is constant over a predetermined range of the power input / output amount.

[0032] The reference function having a droop characteristic for controlling the stationary energy storage device 14 provided in the bidirectional DC / DC converter 12 has a constant input / output region in which the target input / output of the stationary energy storage device 14 maintains a constant value over a predetermined voltage range.

[0033] As a specific example, as shown in FIG. 2, in the case of a first charge rate where the battery state of the stationary power storage device 14 (here, the charge rate of the stationary power storage device 14) is recognized as a steady state that is neither high nor low, in the normal operation zone of the power network 10, an input / output constant region is provided in the reference function so that there is no charge / discharge of the stationary power storage device 14 (that is, power (P) = 0). That is, in the reference function, a region is provided where the charge rate of the stationary power storage device 14 is at the first charge rate and the power input / output in the input / output constant region is 0. When the charge rate of the stationary power storage device 14 is the first charge rate and the power network 10 is in the normal operation zone, the input / output constant region of the reference function is the dead zone of the input / output of the stationary power storage device 14.

[0034] On the other hand, when the charge rate of the stationary power storage device 14 is the first charge rate and the power network 10 is in a semi-normal operation zone with high power demand, the bidirectional DC / DC converter 12 performs droop control on the stationary power storage device 14 so as to discharge with a reference function that maximizes the droop characteristic. Also, when the charge rate of the stationary power storage device 14 is the first charge rate and the power network 10 is in a semi-normal operation zone with low power demand, the bidirectional DC / DC converter 12 performs droop control on the stationary power storage device 14 so as to charge with a reference function that maximizes the droop characteristic.

[0035] In the power system 1, other power converters other than the bidirectional DC / DC converter 12 also have a function of controlling the operation of the device so as to follow a reference function that generates a target value when controlling the device connected to the other power converter according to the voltage at its own end measured by the other power converter. Such control is executed by the control unit of the power converter.

[0036] In the power system 1, the AC / DC converter 11 that converts the AC power input from the AC commercial power system 100 into DC power and outputs it has a function of primary control such that the relationship between the voltage (V) at its own end and the power (P) at its own end, that is, the relationship between the voltage (V) at its own end and the power (P) output to the DC bus 19 has a predetermined droop characteristic. That is, the AC / DC converter 11 performs droop control on the input and output from the commercial power system 100 so that the relationship between the voltage (V) at its own end and the power (P) input to and output from the DC bus 19 follows a reference function having a predetermined droop characteristic at a predetermined control period.

[0037] As a specific example, as shown in FIG. 2, the AC / DC converter 11 connected to the commercial power system 100 performs droop control on the input from the commercial power system 100 using a reference function that maximizes the droop characteristic in the normal operation zone so that power can be stably supplied to the power network 10 centered on the power supply from the commercial power system 100 during the normal operation of the power network 10. On the other hand, when the power network 10 is in a quasi-normal operation zone or a transient operation zone with low power demand (in FIG. 2, the upper quasi-normal operation zone and the transient operation zone where the value of the voltage (V) is high), the power supply from the commercial power system 100 is cut off. Also, when the power network 10 is in a quasi-normal operation zone or a transient operation zone with high power demand (in FIG. 2, the lower quasi-normal operation zone and the transient operation zone where the value of the voltage (V) is low), an input / output constant region (the vertical zone in FIG. 2) is provided so that the power supply from the commercial power system 100 does not exceed the contract power, respectively.

[0038] The first DC / DC converter 13, which converts the DC power input from the DC bus 19 into the charging voltage of the in-vehicle battery of the electric vehicle 18 to be charged and outputs it, has a function of performing primary control so that the relationship between the voltage (V) at its own terminal and the power (P) at its own terminal, that is, the relationship between the voltage (V) at its own terminal and the power (P) input from the DC bus 19, constitutes a predetermined characteristic. That is, the first DC / DC converter 13 has a function of controlling the output of the EV charger 17 so that the relationship between the voltage (V) at its own terminal and the power (P) input from the DC bus 19 follows a reference function having a predetermined characteristic at a predetermined control period.

[0039] As a specific example, as shown in FIG. 2, the first DC / DC converter 13 connected to the EV charger 17 performs control of the output of the EV charger 17 when the power network 10 is in a transient operation zone with high power demand, and does not perform control of the output of the EV charger 17 when the power network 10 is in a quasi-normal operation zone, a normal operation zone, a quasi-normal operation zone with low power demand, or a transient operation zone with low power demand.

[0040] The second DC / DC converter 16 connected to the photovoltaic power generation device (PV) 15 has a function of performing primary control so that the relationship between the voltage (V) at its own terminal and the power (P) at its own terminal, that is, the relationship between the voltage (V) at its own terminal and the power (P) output to the DC bus 19, constitutes a predetermined characteristic. That is, the second DC / DC converter 16 has a function of controlling the photovoltaic power generation device (PV) 15 so that the relationship between the voltage (V) at its own terminal and the power (P) output to the DC bus 19 follows a reference function having a predetermined characteristic at a predetermined control period.

[0041] As a specific example, as shown in FIG. 2, the second DC / DC converter 16 connected to the photovoltaic power generation device (PV) 15 performs output control of the photovoltaic power generation device (PV) 15 when the power network 10 is in a transient operation zone with low power demand, and performs maximum power point tracking control (MPPT) on the photovoltaic power generation device (PV) 15 in other operation zones.

[0042] From the above, in the power system 1, the power system 1 is configured to follow a reference function having a droop characteristic so as to change the power input / output amount of devices such as the stationary energy storage device 14 according to the change in the voltage of the entire power system 1. Further, in the power system 1, each power element (each device and each power converter connected to each said device) performs decentralized primary control based on the voltage at its own end and the power at its own end. That is, the droop control is primary control, and the primary control is implemented by the control unit of each power converter based on the voltage at the own end of each device connected to the power converter.

[0043] Also, in the power system 1, the bidirectional DC / DC converter 12 is configured such that a reference function having a droop characteristic with a constant input / output range is updated based on the change in the battery state of the stationary energy storage device 14 (in the power system 1, the change in the charge rate of the stationary energy storage device 14). That is, the reference function having a droop characteristic with a constant input / output range is appropriately updated according to the change in the charge rate of the stationary energy storage device 14. Note that the change in the battery state of the stationary energy storage device 14 is measured, for example, by a known BMS (Battery Management System). The BMS is configured to include, for example, a sensor, a microcomputer, and an input / output interface. The BMS may be provided outside the stationary energy storage device 14, or may be provided in the stationary energy storage device 14. The BMS may be provided in the bidirectional DC / DC converter 12. The BMS transmits information regarding the measured battery state to the bidirectional DC / DC converter 12 via a communication line.

[0044] Based on the change in the state of charge of the stationary energy storage device 14, by updating the reference function having a droop characteristic with a constant input-output range, the state of charge of the stationary energy storage device 14 can be stably maintained at a predetermined level or higher. Therefore, an excellent adjustment force can be imparted to the stationary energy storage device 14 against rapid fluctuations in power supply and demand in the power network 10. Also, by setting the reference function having a droop characteristic such that the input-output in the constant input-output range becomes zero when the state of charge of the stationary energy storage device 14 reaches a predetermined value, it becomes possible to mainly use the power of the external commercial power system 100 or the solar power generation device (PV) 15. Thus, the charge-discharge loss of the stationary energy storage device 14 can be prevented and the power efficiency of the power system 1 can be improved.

[0045] For example, as shown in FIG. 3, in the power system 1, the reference function having a droop characteristic of the stationary energy storage device 14 is updated by secondary control. The secondary control for updating the reference function having a droop characteristic is implemented, for example, based on a command from the central control unit 110. Therefore, the power system 1 further includes a central control unit 110 that controls a power converter such as the bidirectional DC / DC converter 12.

[0046] On the other hand, the droop control for making the operation of the stationary energy storage device 14 follow the reference function having a droop characteristic is implemented based on the voltage at the local end of the stationary energy storage device 14 as described above without going through the command of the central control unit 110.

[0047] By implementing the secondary control for updating the reference function having a droop characteristic based on a command from the central control unit 110 and implementing the droop control based on the voltage at the local end of the stationary energy storage device 14 without going through the command of the central control unit 110, the amount of power required that varies with time for the entire power network 10 equipped with the stationary energy storage device 14 can be accurately reflected in the input-output control of the stationary energy storage device 14. Therefore, the control of the entire power network 10 equipped with the stationary energy storage device 14 is optimized, and it is possible to efficiently supply the required power to the entire power network 10.

[0048] For example, when the power network 10 of the power system 1 is in the normal operation zone, as shown in FIG. 4, due to the decrease in the charge rate of the stationary energy storage device 14, the charge rate of the stationary energy storage device 14 drops to a second charge rate or lower than the first charge rate (in FIG. 4, for illustrative purposes, the state of charge (SoC) is 50%) (in FIG. 4, for illustrative purposes, the state of charge (SoC) is 30%). By doing so, the input-output constant region of the reference function with droop characteristics controlled by the bidirectional DC / DC converter 12 shifts to the input region where the charging current is supplied to the stationary energy storage device 14 (in FIG. 4, the region where the self-terminal power (P) is negative), and the reference function with droop characteristics is updated. On the other hand, due to the increase in the charge rate of the stationary energy storage device 14, the charge rate of the stationary energy storage device 14 rises to a third charge rate or higher than the first charge rate (in FIG. 4, for illustrative purposes, the state of charge (SoC) is 70%). By doing so, the input-output constant region of the reference function with droop characteristics controlled by the bidirectional DC / DC converter 12 shifts to the output region where the stationary energy storage device 14 discharges (in FIG. 4, the region where the self-terminal power (P) is positive), and the reference function with droop characteristics is updated. As shown in FIG. 4, when the charge rate of the stationary energy storage device 14 is the first charge rate, the input and output in the input-output constant region are controlled to be 0.

[0049] From the above, when the power network 10 of the power system 1 is in the normal operation zone, as shown in FIG. 4, as the charging rate of the stationary energy storage device 14 increases from a charging rate equal to or lower than the second charging rate (in FIG. 4, for illustrative purposes, the state of charge (SoC) is 30%) to the first charging rate (in FIG. 4, for illustrative purposes, the state of charge (SoC) is 50%), the input / output constant region of the reference function having the droop characteristics controlled by the bidirectional DC / DC converter 12 shifts from the input region where the charging current is supplied to the stationary energy storage device 14 (in FIG. 4, the region where the local power (P) is negative) to the input / output 0 direction, and the reference function having the droop characteristics is updated. On the other hand, as the charging rate of the stationary energy storage device 14 decreases from a charging rate equal to or higher than the third charging rate (in FIG. 4, for illustrative purposes, the state of charge (SoC) is 70%) to the first charging rate, the input / output constant region of the reference function having the droop characteristics controlled by the bidirectional DC / DC converter 12 shifts from the output region where the stationary energy storage device 14 discharges (in FIG. 4, the region where the local power (P) is positive) to the input / output 0 direction, and the reference function having the droop characteristics is updated.

[0050] By updating the reference function having the droop characteristics as described above, the charging rate of the stationary energy storage device 14 can be stably maintained within an appropriate range, so that the stationary energy storage device 14 can be more surely provided with excellent regulating power against sudden fluctuations in power supply and demand of the power network 10.

[0051] For example, when the power network 10 of the power system 1 is in the normal operation zone, as shown in FIG. 4, as the charging rate of the stationary energy storage device 14 decreases from the first charging rate to a predetermined charging rate exceeding the second charging rate (in FIG. 4, for illustrative purposes, the state of charge (SoC) is 40%), the voltage value at the upper limit of a predetermined voltage range where the input / output in the constant input / output region is 0 shifts to the low voltage side, and the reference function having droop characteristics is updated. On the other hand, as the charging rate of the stationary energy storage device 14 increases from the first charging rate to a predetermined charging rate less than the third charging rate (in FIG. 4, for illustrative purposes, the state of charge (SoC) is 60%), the voltage value at the lower limit of a predetermined voltage range where the input / output in the constant input / output region is 0 shifts to the high voltage side, and the reference function having droop characteristics is updated.

[0052] From the above, when the power network 10 of the power system 1 is in the normal operation zone, as shown in FIG. 4, as the charging rate of the stationary energy storage device 14 increases from a predetermined charging rate exceeding the second charging rate (in FIG. 4, for illustrative purposes, the state of charge (SoC) is 40%) to the first charging rate, the voltage value at the upper limit of a predetermined voltage range where the input / output in the constant input / output region is 0 shifts to the high voltage side, and the reference function having droop characteristics is updated. On the other hand, as the charging rate of the stationary energy storage device 14 decreases from a predetermined charging rate less than the third charging rate (in FIG. 4, for illustrative purposes, the state of charge (SoC) is 60%) to the first charging rate, the voltage value at the lower limit of a predetermined voltage range where the input / output in the constant input / output region is 0 shifts to the low voltage side, and the reference function having droop characteristics is updated.

[0053] By updating the reference function having droop characteristics as described above, while using the power supplied from the external commercial power system 100, the charging rate of the stationary energy storage device 14 can be maintained within a more appropriate range. Therefore, it is possible to more surely impart excellent regulating power to the stationary energy storage device 14 against sudden fluctuations in power demand and supply in the power network 10, and further improve the power efficiency of the power system 1.

[0054] In FIG. 4, as the charge rate of the stationary energy storage device 14 decreases from the first charge rate to a predetermined charge rate exceeding the second charge rate (in FIG. 4, for example, the charge rate (SoC) is 40% as an illustration), the reference function having a droop characteristic is updated so that the voltage value at the lower limit of the predetermined voltage range where the input / output in the input / output constant region is 0 is not changed. Further, as the charge rate of the stationary energy storage device 14 increases from the first charge rate to a predetermined charge rate less than the third charge rate (in FIG. 4, for example, the charge rate (SoC) is 60% as an illustration), the reference function having a droop characteristic is updated so that the voltage value at the upper limit of the predetermined voltage range where the input / output in the input / output constant region is 0 is not changed.

[0055] The specific numerical values of the first charge rate, the second charge rate, and the third charge rate of the stationary energy storage device 14, the determination of the charge rate of the stationary energy storage device 14, and the degree of each of the above-described shifts can be performed by the central control unit 110.

[0056] As shown in FIG. 3, in the power system 1, for the reference functions of the primary control provided in the AC / DC converter 11, the first DC / DC converter 13, and the second DC / DC converter 16, which are power converters other than the bidirectional DC / DC converter 12, the secondary control comprehensively determines and optimally updates the reference functions of the primary control provided in each of the power converters of the AC / DC converter 11, the first DC / DC converter 13, and the second DC / DC converter 16.

[0057] For updating the reference functions of the primary control provided in each power converter, including the bidirectional DC / DC converter 12, for example, a computer such as AI (artificial intelligence) can be used.

[0058] In the power system 1, the central control unit 110 performs secondary control on a plurality of power converters (in the power system 1, the AC / DC converter 11, the bidirectional DC / DC converter 12, the first DC / DC converter 13, and the second DC / DC converter 16), including the bidirectional DC / DC converter 12. The central control unit 110 is connected to each of the power converters, namely the AC / DC converter 11, the bidirectional DC / DC converter 12, the first DC / DC converter 13, and the second DC / DC converter 16, via communication means. Therefore, the secondary control by the central control unit 110 is in the form of centralized control. The central control unit 110 is an EMS. Note that the primary control and the secondary control are executed by a program on a processor in, for example, each power converter or the central control unit 110.

[0059] For example, in secondary control, when the information communication between the central control unit 110 and each power converter follows the TCP / IP protocol, function information is included in the data part of the IP packet of the command signal for performing function update. The function information is, for example, the coordinate information of the boundary of the function (droop function) representing the droop characteristics, the intercept information of the droop function, the information of the slope (i.e., the droop coefficient), and the information of the shape (straight line, curve, etc.). The function information also includes the information of the constant input / output range. These information are, for example, the information defined in the P-V coordinates. The data part of the IP packet includes, as a data sequence, the information to be updated among these information. The function information used for update is stored in the storage unit of the central control unit 110, and the control unit reads and uses it as appropriate.

[0060] In the power system 1, the control cycle of the primary control (droop control) that causes the operation of devices such as the stationary energy storage device 14 to follow the reference function is different from the control cycle of the secondary control that updates the reference function. The primary control (droop control) controls the operation of devices such as the stationary energy storage device 14 so that the relationship between the local voltage and the local power follows a predetermined reference function. Therefore, the control cycle of the primary control is, for example, 1 second or less. On the other hand, since the secondary control is a control that optimally updates the reference function based on the overall power supply and demand situation of the entire power system 1, the control cycle of the secondary control is, for example, several tens of minutes to several hours. Therefore, the control cycle of the secondary control is longer than the control cycle of the droop control.

[0061] Next, an example of a control method for a power system as centralized control will be described with reference to the sequence diagram of FIG. 5.

[0062] First, in step S201, the central control unit 110 calls the timer of its own device and starts timing. Subsequently, in step S202, the central control unit 110 requests the local measurement information from each power converter. The local measurement information is an example of information regarding the power situation of the power system 1 and includes measurement values measured by sensors of each power converter and the measurement time.

[0063] Subsequently, in step S203, each power converter transmits the local measurement information to the central control unit 110. The central control unit 110 stores the respective local measurement information in the storage unit.

[0064] Next, in step S204, as an example of information regarding the power situation of the power system 1, the central control unit 110 requests various information that may affect the operation of the power system 1 from the external server 200. In this example, the central control unit 110 requests power generation amount and demand prediction information from the external server 200. 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 200 functions as an EMS for 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.

[0065] Next, in step S205, the external server 200 transmits the power generation amount and demand prediction information to the central control unit 110. The central control unit 110 stores the power generation amount and demand prediction information in the storage unit.

[0066] Next, in step S206, the control unit of the central control unit 110 reads out the transmitted information, that is, information regarding the power situation of the power system 1, etc. from the storage unit, and based on this, executes an operation optimization calculation for the power system 1.

[0067] The operation optimization calculation is executed to be applicable to various conditions. For example, it is assumed that the power system 1 is controlled such that the DC bus 19 operates at a predetermined voltage operating point. In this state, the central control unit 110, based on the power generation amount and demand prediction information, predicts that the future weather in the area where the solar power generation device 15 is installed will be sunny and the power generation amount will increase, and determines that there is a margin in power supply to the solar power generation device 15 from the self-terminal measurement information obtained from the second DC / DC converter 16 connected to the solar power generation device 15. In this case, the central control unit 110 determines to update the reference function of the bidirectional DC / DC converter 12 connected to the stationary energy storage device 14 so that the stationary energy storage device 14 is charged at the operating point. Also, the central control unit 110 determines to update the reference function of the AC / DC converter 11 so that power is not supplied from the commercial power system 100 simultaneously with the update. Note that the reference function may be switched instead of updated.

[0068] Also, the operation optimization calculation can be set and executed from the viewpoints of not exceeding the contract power of the commercial power system 100, such as peak shaving and utilization of nighttime power, and optimization of electricity charges.

[0069] Also, the storage unit of the central control unit 110 stores a learned model, and the central control unit 110 may execute the operation optimization calculation using the learned model. The learned model can use, for example, a learned model generated by deep learning using a neural network, with information on the power status of the power system 1 and the results of updating the reference functions for each power converter corresponding thereto as teacher data.

[0070] Subsequently, in step S207, the central control unit 110 outputs an update command for the reference function to the power converter to be updated among the power converters, and executes the step of updating. Subsequently, in step S208, the central control unit 110 resets the timer. Subsequently, in step S209, each power converter executes its own terminal control. These own-terminal controls are own-terminal controls that reflect the power situation of the power system 1, and all the power converters will be cooperatively controlled.

[0071] Next, other embodiments of the power converter and the power system of the present invention will be described. In the power converter and the power system of the above embodiment, the reference function was configured to change the amount of power input and output at the own terminal according to the change in the voltage at the own terminal. Instead of this, it may be configured to change the amount of current input and output at the own terminal according to the change in the voltage at the own terminal.

[0072] Also, as a method of making the relationship between the voltage at the own terminal and the power at the own terminal follow a reference function having predetermined characteristics, for example, the power converter may observe the voltage at the own terminal and set the target power from the reference function, and make the power follow the target power. Or, the power converter may observe the power at the own terminal and set the target voltage from the reference function, and make the voltage follow the target voltage.

[0073] In the power system of the above embodiment, other power converters other than the bidirectional DC / DC converter connected to the stationary energy storage device also follow the reference function that generates the target value when controlling the devices connected to the other power converters according to the voltages measured by the other power converters. However, the control by other power converters other than the bidirectional DC / DC converter connected to the stationary energy storage device does not have to be control based on the reference function.

[0074] Also, in the power system of the above embodiment, a central control unit was separately provided, and the central control unit implemented secondary control in a concentrated manner. Instead of this, at least one of the plurality of power converters may be configured to have a function as a central control unit that controls the plurality of power converters.

[0075] Also, in the power system of the above embodiment, as the battery state of the stationary energy storage device, the reference function was updated based on the change in the state of charge. Instead of this, the reference function may be updated based on the change in the deterioration state or the change in the C-rate.

Industrial Applicability

[0076] The power converter and the power system of the present invention can impart excellent adjustment power and power efficiency to sudden power supply and demand fluctuations, so they have high utility value in the field of DC grids having a local production and local consumption power network.

Explanation of Signs

[0077] 1 Power system 10 Power network 11 AC / DC converter 12 Bidirectional DC / DC converter 13 First DC / DC converter 14 Stationary energy storage device 15 Solar power generation device 16 Second DC / DC converter 17 EV charger 19 DC bus 100 Commercial power system 110 Central control unit

Claims

1. A power converter electrically connected to an energy storage device, wherein the power converter refers to a reference function having a droop characteristic as a control objective function as an output target of the energy storage device according to the voltage at its own terminal measured by the power converter, the reference function having a constant input / output region over a predetermined voltage range, the reference function being updated based on the state of charge of the energy storage device, controlling the energy storage device based on the voltage at its own terminal and the reference function, wherein the change in the state of charge of the energy storage device is a change in the charge rate, a change in the degradation state, or a change in the C-rate, wherein the charge rate of the energy storage device is at a first charge rate and the input / output in the constant input / output region is 0 Power converter.

2. wherein the energy storage device is a stationary energy storage device, the control unit of the power converter executes control based on the reference function to generate a target value when self-terminally controlling the stationary energy storage device according to the voltage measured by the power converter, the reference function having a constant input / output region in which the input / output of the stationary energy storage device maintains a constant value over a predetermined voltage range, The power converter according to claim 1, wherein the reference function having the constant input / output region is updated based on the state of charge of the stationary energy storage device.

3. When the charge rate of the energy storage device decreases due to a decrease in the charge rate of the energy storage device to a second charge rate or less that is lower than the first charge rate, the constant input / output region shifts to an input region where a charging current is supplied to the energy storage device, and when the charge rate of the energy storage device increases due to an increase in the charge rate of the energy storage device to a third charge rate or more that is higher than the first charge rate, the constant input / output region shifts to an output region where the energy storage device discharges, and the reference function having the droop characteristic is updated. The power converter according to claim 1 or 2.

4. When the charge rate of the energy storage device decreases from the first charge rate to a predetermined charge rate exceeding the second charge rate, the voltage value at the upper limit of the predetermined voltage range where the input / output in the constant input / output region is 0 shifts to the low voltage side, and when the charge rate of the energy storage device increases from the first charge rate to a predetermined charge rate less than the third charge rate, the voltage value at the lower limit of the predetermined voltage range where the input / output in the constant input / output region is 0 shifts to the high voltage side, and the reference function having the droop characteristic is updated. The power converter according to claim 3.

5. When the charging rate of the energy storage device decreases from the first charging rate to a predetermined charging rate exceeding the second charging rate, the voltage value at the lower limit of the predetermined voltage range where the input / output in the input / output constant region is 0 is not changed. When the charging rate of the energy storage device increases from the first charging rate to a predetermined charging rate less than the third charging rate, the reference function having the droop characteristic is updated so that the voltage value at the upper limit of the predetermined voltage range where the input / output in the input / output constant region is 0 is not changed. The power converter according to claim 4.

6. The secondary control for updating the reference function having the droop characteristic is performed based on a command from a central control unit. The power converter according to any one of claims 1 to 5.

7. The control unit of the power converter performs control based on the reference function based on the voltage at the self-terminal of the energy storage device without going through the command of the central control unit. The power converter according to claim 6.

8. The control period of the secondary control is longer than the control period of the control based on the reference function. The power converter according to claim 6 or 7.

9. The reference function having the droop characteristic is configured to change the input / output amount of power or current in response to a change in voltage. The power converter according to any one of claims 1 to 8.

10. The power converter according to any one of claims 1 to 9, which is a DC / DC converter.

11. A power element is provided, which includes a power converter and a stationary energy storage device electrically connected to the power converter. The power converter includes a control unit that refers to a reference function having a droop characteristic, which is a control target function, as an output target of the energy storage device according to the voltage measured at the self-terminal of the power converter. The reference function has an input / output constant region over a predetermined voltage range, and the reference function is updated based on the state of charge of the energy storage device. The power converter controls the energy storage device based on the voltage at the self-terminal and the reference function. The change in the state of charge of the energy storage device is a change in the charging rate, a change in the degradation state, or a change in the C-rate. The charging rate of the energy storage device is at a first charging rate, and the input / output in the input / output constant region is 0. Power system.

12. The energy storage device is a stationary energy storage device. A power system comprising a control unit that executes control based on a reference function for generating a target value when self-terminally controlling the stationary energy storage device according to the voltage measured by the power converter. The reference function has a constant input / output range in which the input / output of the stationary energy storage device maintains a constant value over a predetermined voltage range. The power system according to claim 11, wherein the reference function having the constant input / output range is updated based on the battery state of the stationary energy storage device.

13. The power system according to claim 11 or 12, wherein the change in the battery state of the energy storage device is a change in the state of charge, a change in the degradation state, or a change in the C-rate.

14. The power system according to claim 13, wherein when the state of charge of the energy storage device is at a first state of charge, the input / output in the constant input / output range is 0.

15. The reference function having the droop characteristic is updated such that when the state of charge of the energy storage device decreases to a second state of charge or less that is lower than the first state of charge due to a decrease in the state of charge of the energy storage device, the constant input / output range shifts to an input range in which a charging current is supplied to the energy storage device, and when the state of charge of the energy storage device increases to a third state of charge or more that is higher than the first state of charge due to an increase in the state of charge of the energy storage device, the constant input / output range shifts to an output range in which the energy storage device discharges.

16. The reference function having the droop characteristic is updated such that when the state of charge of the energy storage device decreases from the first state of charge to a predetermined state of charge exceeding the second state of charge, the voltage value at the upper limit of the predetermined voltage range where the input / output in the constant input / output range is 0 shifts to the low voltage side, and when the state of charge of the energy storage device increases from the first state of charge to a predetermined state of charge less than the third state of charge, the voltage value at the lower limit of the predetermined voltage range where the input / output in the constant input / output range is 0 shifts to the high voltage side.

17. When the charging rate of the energy storage device decreases from the first charging rate to a predetermined charging rate exceeding the second charging rate, the voltage value at the lower limit of the predetermined voltage range where the input / output in the input / output constant region is 0 is not changed. When the charging rate of the energy storage device increases from the first charging rate to a predetermined charging rate less than the third charging rate, the reference function having the droop characteristic is updated so that the voltage value at the upper limit of the predetermined voltage range where the input / output in the input / output constant region is 0 is not changed. The power system according to claim 16.

18. The power system further includes a central control unit that controls the power converter, and secondary control for updating the reference function having the droop characteristic is performed based on a command from the central control unit. The power system according to any one of claims 11 to 17.

19. The control unit performs control based on the reference function based on the voltage at the self-terminal of the energy storage device without going through a command from the central control unit. The power system according to claim 18.

20. The control period of the secondary control is longer than the control period of the control based on the reference function. The power system according to claim 18 or 19.

21. The reference function having the droop characteristic is configured to change the input / output amount of power or current in response to a change in voltage. The power system according to any one of claims 11 to 20.

22. The line to which the power elements are electrically connected is a DC bus. The power system according to any one of claims 11 to 21.

23. A control method for a power converter electrically connected to an energy storage device, The step of the power converter referring to a reference function having a droop characteristic, which is a control target function, as an output target of the energy storage device according to the voltage measured at the self-terminal of the power converter; The step of updating the reference function based on the battery state of the energy storage device; The step of controlling the energy storage device based on the voltage at the self-terminal and the reference function; Comprising, The reference function has an input / output constant region over a predetermined voltage range, The change in the battery state of the energy storage device is a change in charging rate, a change in deterioration state, or a change in C-rate, The charging rate of the energy storage device is at the first charging rate, and the input / output in the input / output constant region is 0 Control method of the power converter.

24. A control method for a power system provided with a power element including a power converter and a stationary energy storage device electrically connected to the power converter, comprising: The power converter refers to a reference function having a droop characteristic as a control target function as an output target of the energy storage device according to a voltage at its own terminal measured by the power converter; Updating the reference function based on the battery state of the energy storage device; Controlling the energy storage device based on the voltage at its own terminal and the reference function; Comprising: The reference function has a constant input / output region over a predetermined voltage range; The change in the battery state of the energy storage device is a change in the state of charge, a change in the state of deterioration, or a change in the C rate; When the state of charge of the energy storage device is at a first state of charge, the input / output in the constant input / output region is 0 A control method for a power system.

25. A control method for a power system provided with a power element including a power converter and a stationary energy storage device electrically connected to the power converter, and including a central control device capable of information communication with the power converter and an external server holding demand information of the power, comprising: The power converter refers to a reference function having a droop characteristic as a control target function as an output target of the energy storage device according to a voltage at its own terminal measured by the power converter; Obtaining the demand information from the external server; Updating the reference function based on the battery state of the energy storage device; Controlling the energy storage device based on the voltage at its own terminal and the reference function; Comprising: The reference function has a constant input / output region over a predetermined voltage range; The change in the battery state of the energy storage device is a change in the state of charge, a change in the state of deterioration, or a change in the C rate; When the state of charge of the energy storage device is at a first state of charge, the input / output in the constant input / output region is 0 A control method for a power system.

26. A program for causing a processor to execute a control method for a power converter electrically connected to an energy storage device, comprising: The power converter refers to a reference function having a droop characteristic as a control target function as an output target of the energy storage device according to a voltage at its own terminal measured by the power converter; Updating the reference function based on the battery state of the energy storage device; Controlling the energy storage device based on the voltage at its own terminal and the reference function; Comprising: The reference function has a constant input / output region over a predetermined voltage range; The reference function has a constant input / output region over a predetermined voltage range; The change in the battery state of the energy storage device is a change in the state of charge, a change in the degradation state, or a change in the C-rate, wherein the input / output in the constant input / output range is 0 when the state of charge of the energy storage device is at a first state of charge Program. **Claim 27** A program that causes a processor to execute a control method for a power system provided with a power element including a power converter and a stationary energy storage device electrically connected to the power converter, the power converter referring to a reference function having a droop characteristic as a control target function as an output target of the energy storage device according to the voltage at its own terminal measured by the power converter; updating the reference function based on the battery state of the energy storage device; controlling the energy storage device based on the voltage at its own terminal and the reference function; wherein the reference function has a constant input / output range over a predetermined voltage range, the change in the battery state of the energy storage device is a change in the state of charge, a change in the degradation state, or a change in the C-rate, wherein the input / output in the constant input / output range is 0 when the state of charge of the energy storage device is at a first state of charge Program. ​ ​

Images