Power converter, power system, and power converter control method

Abstract

To stabilize a DC bus with respect to a load variation in a power network.SOLUTION: A power converter 11 comprises: a DC power conversion part 11a for outputting an input power via conversion thereof; a sensor 11b serving as a measurement part for acquiring a measurement value as an electrical property value of the power that is input or output; and a control part 11c for controlling a power conversion property of the power conversion part according to the input value via voltage control or power control, or current control corresponding to a drooping property in which a target value of the electrical property value is defined according to the input value, based on a reference function comprising the drooping property. The control part 11c controls the electrical conversion property based on the target value and a physical quantity of a virtual electrical element to which the power conversion part is connected, and which generates inertial force to a DC bus, wherein the target value is determined, based on the reference function, from the input value being the measurement value.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] Patent Document 1 discloses a multilevel converter, for example, as an invention of a power converter connected to a direct current (DC) power supply network. This multilevel converter converts alternating current (AC) voltage into DC voltage and vice versa. This multilevel converter has a DC section for connection to a DC power supply network and an AC section for connection to an AC power supply network. In the DC section, a virtual capacitor is connected in parallel with the DC power supply network. The virtual capacitor acts to stabilize the inertia of the DC power supply network, and excess power entering the multilevel converter from the DC power supply network is absorbed by the virtual capacitor. Changing the value of the virtual capacitor can affect the voltage of the DC power supply network and the inertia of the DC power supply network. For example, increasing the value of the virtual capacitor increases the inertia of the converter and stabilizes the voltage of the DC power supply network. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6371603 Summary of the Invention [Problem to be solved by the invention]

[0004] In power supply networks, studies are underway to build a direct current power network (DC grid) by connecting a wide variety of DC devices, such as photovoltaic (PV) power generation devices that generate electricity using renewable energy, stationary energy storage devices, and electric vehicles (EVs), to a DC bus via power converters that are DC / DC converters.However, in DC grids where many energy storage devices and EVs have been introduced due to the expansion of renewable energy adoption, when a large load is generated, the network voltage fluctuates significantly, and there is a risk that the grid will operate outside the rated voltage.

[0005] The converter disclosed in Patent Document 1 is an AC / DC converter that converts between AC and DC voltages, and therefore cannot be used as a power converter that transfers power between DC devices and a DC bus. Furthermore, existing power converters that perform DC / DC conversion cannot handle voltage fluctuations in the DC grid, and therefore cannot handle large voltage fluctuations in the DC bus.

[0006] The present invention has been made in view of the above, and has as its object to stabilize a DC bus against load fluctuations in a power network. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems and achieve the object, a power converter according to one aspect of the present invention comprises a DC power conversion unit that converts input power and outputs it; a measurement unit that acquires measured values ​​of an electrical characteristic value of the input or output power; and a control unit that controls the power conversion characteristics of the power conversion unit in accordance with an input value by voltage control, power control, or current control corresponding to a reference function having a drooping characteristic in which a target value of an electrical characteristic value is defined in accordance with an input value, wherein the control unit uses the measured value as the input value and controls the power conversion characteristics of the power conversion unit in accordance with the target value determined from the input value in accordance with the reference function, and imparts virtual inertia to a DC bus to which the power conversion unit is connected.

[0008] In a power converter according to one aspect of the present invention, the state of the bus is determined based on the measurement value, and if it is determined that the bus is in a transient state, the measurement value is used as the input value, and the power conversion characteristics of the power conversion unit are controlled based on the target value determined from the input value based on the reference function, and virtual inertia is imparted to the DC bus to which the power conversion unit is connected, and if it is determined that the bus is in a steady state, the measurement value is used as the input value, and the power conversion characteristics are controlled based on the target value determined from the input value based on the reference function.

[0009] In a power converter according to one aspect of the present invention, the control unit acquires the measurement values ​​at a predetermined cycle, and determines that a transient state is occurring when the absolute value of the difference between the voltage indicated by the latest measurement value and the voltage indicated by the measurement value acquired a predetermined number of times before the latest measurement value is greater than or equal to a threshold value.

[0010] A power system according to one aspect of the present invention includes the power converter, a DC bus connected to the power converter, and a power element connected to the power converter that can supply, consume, or charge power.

[0011] A control method for a power converter according to one aspect of the present invention is a control method for a DC power converter that converts and outputs input power, and includes a measurement step of acquiring a measurement value of an electrical characteristic value of the power input to or output from the power converter, and a control step of controlling the power conversion characteristics of the power converter in accordance with an input value by voltage control, power control, or current control corresponding to a reference function having a drooping characteristic in which a target value of the electrical characteristic value is defined in accordance with the input value, wherein the control step uses the measurement value as the input value, controls the power conversion characteristics of the power converter in accordance with the target value determined from the input value in accordance with the reference function, and imparts virtual inertia to a DC bus to which the power converter is connected. [Effects of the Invention]

[0012] According to the present invention, it is possible to stabilize a DC bus against load fluctuations in a power network. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram showing the configuration of a power system according to an embodiment. [Figure 2] FIG. 2 is a diagram illustrating a configuration of the power converter illustrated in FIG. [Figure 3] FIG. 3 is a diagram showing a configuration related to a power conversion function of the control unit shown in FIG. [Figure 4] FIG. 4 is a diagram showing an example of a change in the voltage value of the bus over time. [Figure 5] FIG. 5 is an equivalent circuit diagram of the power conversion unit when performing virtual inertia control. [Figure 6] FIG. 6 is a diagram illustrating an example of power conversion characteristics. [Figure 7] FIG. 7 is a flowchart showing the flow of processing performed by the control unit of the power converter. [Figure 8] FIG. 8 is a graph showing an example of changes in the voltage of the bus 30. [Figure 9] FIG. 9 is a graph showing an example of changes in the current of the bus 30. [Figure 10] FIG. 10 is a sequence diagram showing an example of a control method for a power system. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiment described below. Furthermore, in the description of the drawings, the same parts are appropriately designated by the same reference numerals.

[0015] [Embodiment] <Power system configuration> 1 is a diagram showing the configuration of a power system according to an embodiment. The power system 100 includes a plurality of power converters 11, 12, 13, and 14, a plurality of power elements 21, 22, 23, and 24, and a bus 30. The power system 100 also includes an EMS (Energy Management System) 40. The EMS 40 is an example of a central control device.

[0016] Power converters 11, 12, and 13 are so-called DC / DC converters, and power converter 14 is an AC / DC converter. Power converters 11, 12, 13, and 14 have the function of performing wired or wireless information communication. The configurations and functions of power converters 11, 12, 13, and 14 will be described in detail later.

[0017] Bus 30 is a DC bus in power system 100, and is connected to power converters 11, 12, 13, and 14. Power system 100 configures a power network including a DC grid.

[0018] As an example, power element 21 is a stationary power storage device that can supply, consume, and charge power, and is connected to power converter 11. A stationary power storage device is an example of a permanently installed in-facility power storage device. Power converter 11 has the function of converting the voltage of DC power supplied by power element 21 and outputting it to bus 30, and also converting the voltage of DC power supplied from bus 30 and outputting it to power element 21, causing charging.

[0019] One example of the power element 22 is a solar power generation device capable of generating and supplying electric power, and is connected to the power converter 12. The solar power generation device is an example of a power generation device that generates electric power using renewable energy. The power converter 12 has a function of converting the voltage of the DC power supplied by the power element 22 and outputting it to the bus 30.

[0020] Power element 23 is, for example, an on-board power storage device capable of supplying, consuming, and charging power, and is connected to power converter 13. The on-board power storage device is mounted on an electric vehicle EV and is an example of a mobile, non-stationary power storage device. Power converter 13 has the function of converting the voltage of DC power supplied by power element 23 and outputting it to bus 30, and also converting the voltage of DC power supplied from bus 30 and outputting it to power element 23 for charging. Power converter 13 is provided, for example, in a charging station or residential charging equipment, but may also be mounted on the electric vehicle EV.

[0021] As an example, the power element 24 is a commercial power system and is connected to the power converter 14. The power converter 14 converts the AC power supplied by the power element 24 into DC power and outputs it to the bus 30, and also converts the DC power supplied from the bus 30 into AC power and outputs it to the power element 24. The output of power from the bus 30 to the power element 24 is also called reverse power flow.

[0022] The EMS 40 has a function of comprehensively managing the state of the power system 100. The EMS 40 includes a control unit 41, a storage unit 42, and a communication unit 43.

[0023] The control unit 41 performs various arithmetic processing to realize the functions of the EMS 40, and is configured to include processors such as a CPU (Central Processing Unit), an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), a DSP (Digital Signal Processor), and a GPU (Graphics Processing Unit). The functions of the control unit 41 are realized as functional units by the control unit 41 reading and executing various programs from the storage unit 42.

[0024] The storage unit 42 includes, for example, a ROM (Read Only Memory) that stores various programs and data used by the control unit 41 to perform arithmetic processing. The storage unit 42 also includes, for example, a RAM (Random Access Memory) that is used as a workspace when the control unit 41 performs arithmetic processing and for storing the results of the arithmetic processing of the control unit 41. The storage unit 42 may also include an auxiliary storage device such as an HDD (Hard Disk Drive) or an SSD (Solid State Drive).

[0025] The communication unit 43 includes a communication module that performs wired or wireless information communication and communicates information with the power converters 11, 12, 13, and 14 and the external server 200 via a network NW that includes the Internet, a mobile phone network, etc.

[0026] The external server 200 is a server provided outside the power system 100. The external server 200 is, for example, an information processing device configured to function as an EMS in another power system, or an information processing device that includes a database and functions as a data server for the EMS 40. The external server 200 stores various types of information that may affect the operation of the power system 100.

[0027] <Power converter configuration> Next, a specific configuration of the power converter 11 will be described. Fig. 2 is a diagram showing the configuration of the power converter 11. The power converter 11 has a power conversion unit 11a, a sensor 11b, a control unit 11c, and a communication unit 11d.

[0028] The power conversion unit 11a performs DC / DC conversion, converting the voltage of DC power input from the discharging power element 21 and outputting the converted power to the bus 30. The power conversion unit 11a can also convert the voltage of DC power input from the bus 30 and output the converted power to the power element 21 for charging. The power conversion unit 11a is configured with an electric circuit including, for example, a coil, a capacitor, a diode, a switching element, and the like. The switching element is, for example, a field effect transistor or an insulated gate bipolar transistor. The power conversion unit 11a can control the power conversion characteristics by, for example, PWM (Pulse Width Modulation) control.

[0029] The sensor 11b measures the electrical characteristic values ​​of the power on the bus 30 side of the power conversion unit 11a. Therefore, the sensor 11b measures the electrical characteristic values ​​of the power input from the bus 30 to the power converter 11 or output from the power converter 11 to the bus 30. The sensor 11b can measure current values, voltage values, power values, etc. The sensor 11b is an example of a measurement unit that acquires measurement values. The sensor 11b outputs the measurement values ​​of the electrical characteristic values ​​to the control unit 11c.

[0030] The control unit 11c includes a processor and a storage unit that perform various arithmetic operations to control the operation of the power conversion unit 11a, primarily to realize the power conversion function of the power converter 11. The processor and storage unit may use the configurations exemplified for the control unit 41 and storage unit 42, respectively. The functions of the control unit 11c are realized as a functional unit by the processor reading and executing various programs from the storage unit. For example, the control unit 11c is assigned a reference function based on the power (P) or current (I) and voltage (V) of its own terminal, and controls the power conversion characteristics of the power conversion unit 11a based on the assigned reference function. Specifically, the control unit 11c outputs a PWM signal including information on a manipulated variable (e.g., a duty ratio) for PWM control to the power conversion unit 11a, thereby performing PWM control of the power conversion unit 11a. The control unit 11c may output the manipulated variable to the power conversion unit 11a directly or via another functional unit (e.g., a loop control unit) (not shown).

[0031] When a reference function that gives a droop characteristic to the target voltage value according to the amount of power or current required for the DC bus is used, this control is sometimes called droop control. By each power converter performing droop control in an autonomous and decentralized manner, the DC bus voltage can be stabilized while carrying out load sharing of power interchange among each device according to the amount of power required for the DC bus.

[0032] The communication unit 11d includes a communication module that communicates information via a wired or wireless connection, and a communication control unit that controls the operation of the communication module. The communication unit 11d communicates information with the EMS 40 via the network NW. The communication unit 11d receives, for example, information and commands from the EMS 40 and outputs them to the control unit 11c. The communication unit 11d also transmits, for example, information related to the power status input from the control unit 11c to the EMS 40. Note that if the information related to the power status is a measurement value of the sensor 11b, the communication unit 11d may transmit, for example, the measurement value input from the sensor 11b to the EMS 40.

[0033] 3 is a diagram showing the configuration of the control unit 11c, mainly related to the power conversion function. The control unit 11c includes an operation amount setting unit 11ca, a determination unit 11cb, an update unit 11cc, which are functional units realized by software through the execution of a program, and a storage unit 11cd.

[0034] The update unit 11cc stores the reference function information and control method information included in the update command input from the communication unit 11d in the memory unit 11cd, and updates the reference function information and control method information stored in the memory unit 11cd. Here, the reference function information is various information for identifying the droop function that constitutes the reference function, and will be described in detail later.

[0035] The determination unit 11cb determines the feedback control method to be performed by the manipulated variable setting unit 11ca based on the control method information stored in the storage unit 11cd, and outputs the determination result as determination information. The feedback control methods include feedback control (hereinafter referred to as droopP control) in which a target power Pref (an example of a target value) is determined based on the voltage measurement value Vo by the sensor 11b and reference function information, and the manipulated variable is set so that the difference between Pref and the power measurement value Po (an example of a control target value) by the sensor 11b is within an allowable range, feedback control (hereinafter referred to as droopV control) in which a target voltage Vref (an example of a target value) is determined based on the power measurement value Po by the sensor 11b and reference function information, and the manipulated variable is set so that the difference between Vref and the voltage measurement value Vo (an example of a control target value) by the sensor 11b is within an allowable range, and feedback control (hereinafter referred to as droopV control) in which a target voltage Vref (an example of a target value) is determined based on the power measurement value Po by the sensor 11b and reference function information, and the manipulated variable is set so that the difference between Vref and the voltage measurement value Vo (an example of a control target value) by the sensor 11b is within an allowable range. o and the reference function information and the target current I ref (Example of target value) is determined, and I ref and the current measurement value I by the sensor 11b. o and feedback control (hereinafter referred to as droop I control) in which an manipulated variable is set so that the difference between the droop P control and the droop V control (an example of a control target value) is within an allowable range. Droop P control, which is an example of power control, droop V control, which is an example of voltage control, and droop I control, which is an example of current control, are examples of control methods for controlling the output of the power conversion unit 11a. The control method information described above is information representing droop P control, droop V, or droop I control, and the determination unit 11cb determines the feedback control method based on the control method information stored in the storage unit 11cd, and outputs the determination result of performing droop P control, the determination result of performing droop V control, or the determination result of performing droop I control as determination information.

[0036] Furthermore, when the determination unit 11cb determines that the feedback control method is droop I control, it determines whether the bus 30 is in a steady state or a transient state based on the measurement values ​​output from the sensor 11b, and outputs this determination result as determination information. Specifically, the determination unit 11cb acquires measurement values ​​from the sensor 11b at predetermined intervals. The determination unit 11cb stores the acquired measurement values ​​in the memory unit 11cd. The determination unit 11cb determines whether the bus 30 is in a steady state or a transient state based on the voltage values ​​of the bus 30 included in the measurement values ​​stored in the memory unit 11cd, and outputs the determination result as determination information.

[0037] FIG. 4 shows an example of the change over time in the voltage value of the bus 30 included in the measurement value. In FIG. 4, the vertical axis represents the voltage of the bus 30, and the horizontal axis represents the number of steps in obtaining the measurement value. For example, the determination unit 11cb determines the voltage value (V obsv [n]) and the voltage value obtained at the nkth step (V obsv The determination unit 11cb calculates the absolute value of the difference between V obsv [n] and V obsv The absolute value of the difference with [nk] is small, and |V obsv [n]-V obsv If [nk]|<threshold, it is determined that the steady state is present. obsv [n] and V obsv The absolute value of the difference with [nk] is large, and |V obsv [n]-V obsv If [nk]|≧threshold, it is determined that the state is transient. The sampling frequency for acquiring the measured values ​​is, for example, 10 kHz, and the value of k is 200, but the sampling frequency for acquiring the measured values ​​and the value of k are not limited to these frequencies and values, and other frequencies and values ​​may also be used. In addition, the threshold for determining whether the state is steady or transient is determined by the power conversion unit and power elements connected to the bus 30.

[0038] The manipulated variable setting unit 11ca sets the feedback control method in accordance with the determination information input from the determination unit 11cb, sets the manipulated variable based on the measurement value input from the sensor 11b, the reference function information acquired from the storage unit 11cd, and the state of the bus 30 indicated by the determination information, and outputs the manipulated variable to the power conversion unit 11a. For example, when the feedback control method is set to droopI control, the manipulated variable setting unit 11ca performs steady control when the state of the bus 30 indicated by the determination information is a steady state, and performs virtual inertia control when the state of the bus 30 indicated by the determination information is a transient state.

[0039] 5 is an equivalent circuit diagram of the power conversion unit 11a when performing virtual inertia control. Virtual inertia control is a control in which the power conversion unit 11a simulates the operation of a virtual capacitor with respect to the current source IA, and generates a virtual inertial force, which is the same as the inertial force of an actual capacitor, for the voltage of the bus 30, thereby suppressing sudden voltage fluctuations on the bus 30. Here, the inertial force is a force that tries to suppress fluctuations in voltage and a force that withstands instantaneous changes in voltage. Specifically, when performing virtual inertia control, the operation amount setting unit 11ca sets the current output value I from the power conversion unit 11a to out is calculated using the following formula (1), and the calculated output value I out In equation (1), the manipulated variable is set to be I o is the target current value for droopI control, V obsv is the measured voltage of the bus 30, R is the resistance of the virtual resistor R of the bus 30, C is the capacitance of the virtual capacitor C of the bus 30, and T s is the control period, and n is the number of control steps. The resistance value of the virtual resistor R and the capacitance of the virtual capacitor C are determined by the power conversion unit and power elements connected to the bus 30. Note that the formula (1) is an example, and I out The equation for setting is not limited to equation (1), but may be any other equation as long as it can simulate the operation of the virtual resistor R and the virtual capacitor C.

[0040]

number

[0041] In addition, when performing steady-state control, the manipulated variable setting unit 11ca sets the current output value I out is calculated using the following formula (2), and the calculated output value I out The manipulated variable is set so that: Steady-state control is a control in which the component of virtual capacitor C is removed from virtual inertia control.

[0042]

number

[0043] The feedback control performed by the manipulated variable setting unit 11ca can be performed using a known method, such as PID control, which is performed by reading out parameters such as proportional gain, integral time, and differential time stored in the memory unit 11cd.

[0044] The storage unit 11cd or the manipulated variable setting unit 11ca outputs information such as information on the power situation, reference function information, and control method information to the communication unit 11d.

[0045] The other power converters 12, 13, and 14 may have the same configuration as the power converter 11. However, the power conversion unit 11a of the power converter 14 is a so-called inverter that converts AC power input from the power element 24 into DC power and outputs it to the bus 30, or converts DC power input from the bus 30 into AC power and outputs it to the power element 24.

[0046] <Characteristics of reference functions> Next, a reference function that is the basis for the control unit 11c to control the power conversion characteristics of the power conversion unit 11a will be described. Fig. 6 is a diagram showing an example of the power conversion characteristics.

[0047] 6(a) is a diagram showing the VI characteristic, which is the relationship between the current (I) and voltage (V) on the bus 30 side of the power conversion unit 11a of the power converter 11, and shows the power conversion characteristic of the power conversion unit 11a of the power converter 11. Note that I is a positive value when the power conversion unit 11a supplies power to the bus 30, i.e., when the power element 21 is in a discharging state, and is a negative value when power is supplied from the bus 30, i.e., when the power element 21 is in a charging state.

[0048] The line DL1 shown in FIG. 6(a) is a straight or curved line that is bent halfway. The reference function represented by this line DL1 is composed of five droop functions with different droop characteristics defined according to the range of input values. Specifically, the line DL1 is composed of lines representing the five droop functions and is identified by reference function information. The reference function information includes, for example, coordinate information of the boundaries of the droop functions in a coordinate system with I as the horizontal axis and V as the vertical axis, information on the intercept of the droop function, information on the slope (i.e., droop coefficient), and information on the shape (straight line, curve, etc.). In the power converter 11, the control unit 11c controls the power conversion characteristics of the power conversion unit 11a so that they become the characteristics of the reference function represented by the line DL1. That is, the control unit 11c of the power converter 11 controls the power conversion unit 11a so that an operating point defined by the values ​​of V and I is located on the line DL1.

[0049] 6(b) is a diagram showing the VP characteristic, which is the relationship between power (P) and voltage (V) on the bus 30 side of the power conversion unit 11a of the power converter 12, and shows the power conversion characteristic of the power conversion unit 11a of the power converter 12. Note that P is a positive value when the power conversion unit 11a supplies power to the bus 30, i.e., when the power element 21 is in a discharging state, and is a negative value when power is supplied from the bus 30, i.e., when the power element 21 is in a charging state.

[0050] Line DL2 shown in FIG. 6(b) is a straight or curved line that is bent halfway. The reference function represented by this line DL2 is configured by connecting lines representing five droop functions, each with a different droop characteristic, defined according to an input value interval. Line DL2 is identified by reference function information, similar to line DL1. This reference function information includes, for example, coordinate information of the boundary of the droop function in a coordinate system with P as the horizontal axis and V as the vertical axis, information on the intercept of the droop function, information on the slope (i.e., droop coefficient), and information on the shape (straight line, curve, etc.). In power converter 12, control unit 11c controls power conversion characteristics of power conversion unit 11a so that they conform to the characteristics of the reference function represented by line DL2. That is, control unit 11c of power converter 12 controls power conversion unit 11a so that an operating point defined by the values ​​of V and P is located on line DL2.

[0051] Figure 6(c) is a diagram showing the VP characteristics, which are the relationship between power (P) and voltage (V) on the bus 30 side of the power conversion unit 11a of the power converter 13, and shows the power conversion characteristics of the power conversion unit 11a of the power converter 13.

[0052] The line DL3 shown in FIG. 6(c) is a straight or curved line that is bent halfway. The reference function represented by this line DL3 is configured by connecting lines representing nine droop functions that are defined according to the range of input values ​​and have different droop characteristics, and the line DL3 is also identified by the reference function information. In the power converter 13, the control unit 11c controls the power conversion characteristics of the power conversion unit 11a so that they become the characteristics of the reference function indicated by the line DL3. That is, the control unit 11c of the power converter 13 controls the power conversion unit 11a so that the operating point defined by the value of V and the value of P is located on the line DL3.

[0053] Figure 6(d) is a diagram showing the VP characteristics, which are the relationship between power (P) and voltage (V) on the bus 30 side of the power conversion unit 11a of the power converter 14, and shows the power conversion characteristics of the power conversion unit 11a of the power converter 14.

[0054] Line DL4 shown in FIG. 6(d) is a straight or curved line that is bent halfway. The reference function represented by this line DL4 is configured by connecting lines representing three droop functions that are defined according to the range of input values ​​and have different droop characteristics, and line DL4 is identified by reference function information, similar to line DL1. In power converter 14, control unit 11c controls power conversion characteristics of power conversion unit 11a so that they become the characteristics of the reference function indicated by line DL4. That is, control unit 11c of power converter 14 controls power conversion unit 11a so that an operating point defined by the values ​​of V and P is located on line DL4.

[0055] <Control method> Next, a control method for the power converters 11, 12, 13, and 14 and a control method for the power system 100 will be described. In the power system 100, so-called local-end control, in which the power converters 11, 12, 13, and 14 individually control each other in an autonomous and decentralized manner, and centralized control, in which the EMS 40 cooperatively controls the power converters 11, 12, 13, and 14 depending on the power status of the power system 100, can be performed. Note that, for example, the local-end control is repeatedly performed at relatively short intervals, and the centralized control is performed at intervals longer than the cycle of the local-end control. The local-end control is also called primary control, and the centralized control is also called secondary control. These control methods are executed, for example, by a program executed by a processor in each power converter or the EMS 40.

[0056] <Self-end control> First, a control method for power converters 11, 12, 13, and 14 in self-end control will be described using power converter 11 as an example. A control method similar to that described below may also be executed appropriately for the other power converters 12, 13, and 14. If power element 22 is an element that does not control the amount of power generated from the viewpoint of efficiency, such as a solar power generation device, power converter 12 may execute MPPT (Maximum Power Point Tracking) control, which operates when power corresponding to the amount of power generated from power element 22 is input so that the output power to bus 30 is maximized at that amount of power generated. For example, FIG. 4(b) shows an example of a reference function used when executing MPPT control.

[0057] In the control method for power converter 11, control unit 11c executes a control step of controlling the power conversion characteristics of power converter 11, i.e., the power conversion characteristics of power conversion unit 11a, based on a reference function. An example of the content of this control step will be described in more detail with reference to Fig. 7. Fig. 7 is a flowchart showing the flow of processing performed by control unit 11c.

[0058] First, in the control unit 11c, the operation amount setting unit 11ca and the judgment unit 11cb acquire the latest measurement value from the sensor 11b (step S101). Next, in the control unit 11c, the judgment unit 11cb acquires the measurement value acquired and stored k times before from the storage unit 11cd (step S102). Subsequently, in the control unit 11c, the judgment unit 11cb calculates the voltage value (V obsv [n]) and the voltage value (V obsv [nk]) (V obsv [n]-V obsv [nk]) is calculated (step S103).

[0059] Next, in the control unit 11c, the determination unit 11cb determines whether the absolute value of ΔV is equal to or greater than a predetermined threshold (step S104). If the absolute value of ΔV is equal to or greater than the predetermined threshold (Yes in step S104), the determination unit 11cb outputs determination information indicating a transient state to the manipulated variable setting unit 11ca, and sets the control performed by the manipulated variable setting unit 11ca to virtual inertia control (step S105). If the absolute value of ΔV is less than the predetermined threshold (No in step S104), the determination unit 11cb outputs determination information indicating a steady state to the manipulated variable setting unit 11ca, and sets the control performed by the manipulated variable setting unit 11ca to steady control (step S106).

[0060] Next, in the control unit 11c, the manipulated variable setting unit 11ca acquires reference function information from the storage unit 11cd (step S107). Next, in the control unit 11c, the determination unit 11cb determines the feedback control method based on the control method information stored in the storage unit 11cd (step S108). Next, in the control unit 11c, the manipulated variable setting unit 11ca acquires the determination information output from the determination unit 11cb, sets the manipulated variable for executing feedback control using the control method based on the acquired determination information based on the measured value and the reference function information, and outputs it to the power conversion unit 11a (step S109). This executes control of the power conversion unit 11a.

[0061] 8 is a graph showing changes in the voltage of the bus 30 when the determination unit 11cb determines that the bus 30 is in a transient state and the manipulated variable setting unit 11ca performs virtual inertia control using droop I control. In FIG. 8, the change in the voltage of the bus 30 when virtual inertia control is performed is shown by a solid line, and for comparison, the change in voltage when virtual inertia control is not performed is shown by a dashed line. When the voltage of the bus 30 changes, if virtual inertia control is not performed, the voltage of the bus 30 fluctuates significantly, as shown by the dashed line in FIG. 8. On the other hand, if virtual inertia control is performed when the voltage of the bus 30 changes, the voltage of the bus 30 can be suppressed, as shown by the solid line in FIG. 8.

[0062] Fig. 9 is a graph showing changes in the current value of bus 30. Specifically, Fig. 9(a) shows changes in the current value of bus 30 when virtual inertia control is not performed under droop I control, and Fig. 9(b) shows changes in the current value of bus 30 when virtual inertia control is always performed under droop I control. Also, Fig. 9(c) shows changes in the current value of bus 30 when virtual inertia control is performed when droop I control is performed when bus 30 is in a transient state, and steady-state control is performed when droop I control is performed when bus 30 is in a steady state, according to the flowchart shown in Fig. 7.

[0063] If the control unit 11c does not perform virtual inertia control when performing droop I control, the current value of the bus 30 will change significantly as shown in Fig. 9(a) in response to changes in the voltage of the bus 30. However, in this case, when the current value changes significantly, the voltage of the bus 30 will fluctuate significantly as shown by the dashed line in Fig. 8.

[0064] Furthermore, if the control unit 11c always performs virtual inertia control when performing droop I control, the sensor 11b will pick up small voltage changes due to noise on the bus 30, and the output value I of the current from the power conversion unit 11a will be out will vibrate as shown in FIG. 9(b).

[0065] On the other hand, when the control unit 11c performs the virtual inertia control when the bus 30 is in a transient state under the droop I control according to the flowchart shown in FIG. 7, and performs the steady state control when the bus 30 is in a steady state under the droop I control, the output value I out suppresses oscillation, and the output value I out can be converged.

[0066] <Centralized control> Next, centralized control will be explained. In the example shown below, an EMS 40 provided outside the power converters 11, 12, 13, and 14 performs centralized control by updating the reference function and feedback control method used by the power converters 11, 12, 13, and 14 for control by commands. Updating the reference function and feedback control method by commands means that the commands include reference function information related to the reference function and control method information related to the feedback control method, and that part or all of the reference function and the feedback control method are updated by the commands. The memory unit 11cd of each of the power converters 11, 12, 13, and 14 stores the reference function information and control method information in an updatable manner.

[0067] For example, in information communication between EMS 40 and power converters 11, 12, 13, and 14, a command signal for updating the reference function includes reference function information and control method information. As described above, the reference function information is coordinate information of the boundary of the droop function, information on the intercept of the droop function, information on the slope (i.e., droop coefficient), and information on the shape (straight line, curve, etc.). The control method information is information representing droopP control, droopV control, or droopI control. The reference function information used for updating is stored in memory unit 42 of EMS 40, and is read out and used by control unit 41 as appropriate.

[0068] Next, an example of a control method for the power system 100 as centralized control will be described with reference to the sequence diagram of FIG.

[0069] First, the EMS 40 calls its own timer and starts timing (step S201). Next, the EMS 40 requests local measurement information from each of the power converters 11, 12, 13, and 14 (step S202). The local measurement information is an example of information related to the power status of the power system 100, and includes measurements taken by the sensors 11b of each of the power converters 11, 12, 13, and 14, as well as the time of measurement.

[0070] Next, the power converters 11, 12, 13, and 14 each transmit their own-end measurement information to the EMS 40 (step S203). The EMS 40 stores the respective own-end measurement information in the storage unit .

[0071] Next, the EMS 40 requests various types of information that may affect the operation of the power system 100 from the external server 200, as an example of information related to the power status of the power system 100 (step S204). In this example, the EMS 40 requests power generation and demand forecast information from the external server 200. The power generation and demand forecast information includes forecast information on the amount of power generated in the power system 100 and forecast information on the demand for power, and may include, for example, information on the season, current weather, and future weather forecast for the area in which the power system 100 is installed. Furthermore, if the external server 200 functions as an EMS for another power system, and the operational status of the other power system may affect the operation of the power system 100, the power generation and demand forecast information may include forecast information on the amount of power generated and demand for power in the other power system.

[0072] Next, the external server 200 transmits the power generation amount and demand forecast information to the EMS 40 (step S205). The EMS 40 stores the power generation amount and demand forecast information in the storage unit .

[0073] Next, the control unit 41 of the EMS 40 reads out the transmitted information, i.e., information relating to the power status of the power system 100, from the memory unit 42, and performs an operational optimization calculation for the power system 100 based on this information (step S206).

[0074] The operational optimization calculation is performed to adapt to various conditions. For example, suppose that the power system 100 is controlled so that the bus 30 is at a predetermined voltage operating point. In this state, suppose that the EMS 40 determines, based on power generation and demand forecast information, that the weather in the area where the power element 22, a solar power generation device, is installed is expected to be sunny in the future, resulting in an increase in power generation, and that, based on local measurement information acquired from the power converter 12 connected to the power element 22, the power element 22 has a surplus in terms of power supply. In this case, the EMS 40 determines to update the reference function of the power converter 11 connected to the power element 21, a stationary energy storage device, so that the power element 21 is charged at the operating point. Simultaneously with this update, the EMS 40 also determines to update the reference function of the power converter 14 connected to the power element 24 so that power is not supplied from the power element 24, a commercial power grid.

[0075] In addition, the operational optimization calculation can be performed with conditions set from the perspective of not exceeding the contracted power of the power element 24, which is the commercial power system, such as peak cutting and utilization of nighttime power, and from the perspective of optimizing electricity rates.

[0076] Furthermore, the memory unit 42 of the EMS 40 may store a trained model, and the EMS 40 may execute an operation optimization calculation using the trained model. The trained model may be, for example, a trained model generated by deep learning using a neural network, using information on the power status of the power system 100 and the corresponding results of switching or updating reference functions for the power converters 11, 12, 13, and 14 as training data.

[0077] Next, based on the result of the operation optimization calculation, EMS 40 sets reference function information and control method information suitable for the power converter to be updated among power converters 11, 12, 13, and 14, and outputs an update command for the reference function (droop function) and feedback control method including the set reference function information and control method information (step S207). Next, EMS 40 resets the timer (step S208).

[0078] Next, the power converter to be updated among power converters 11, 12, 13, and 14 receives a command to update the reference function and the feedback control method, and updates the reference function and the feedback control method (step S209).

[0079] [Variations] 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 above-described embodiments may be modified as follows to implement the present invention. The above-described embodiments and the following modifications may be combined with each other. The present invention also includes configurations in which the components of the above-described embodiments and modifications are appropriately combined. Furthermore, further effects and modifications can be easily derived by those skilled in the art. Therefore, the broader aspects of the present invention are not limited to the above-described embodiments and modifications, and various modifications are possible.

[0080] In the above-described embodiment, the control unit 11c may perform virtual inertia control when the bus 30 is in a transient state, and may perform steady-state control when the bus 30 is in a steady state, even when performing droopP control. When the power converter 11 performs droopP control, the reference function referred to by the manipulated variable setting unit 11ca is configured, for example, by replacing the horizontal axis of the characteristics shown in Fig. 6(a) with power (P) and using a droop function with drooping characteristics defined according to the range of the input value.

[0081] The manipulated variable setting unit 11ca may change the resistance value of the virtual resistor R and the capacitance of the virtual capacitor C in the formulas (1) and (2) in response to an instruction from the EMS 40. Furthermore, the EMS 40 may set the resistance value of the virtual resistor R and the capacitance of the virtual capacitor C in the formulas (1) and (2) based on information acquired from the power converters 11, 12, 13, and 14, and instruct the power converters 11, 12, 13, and 14 to set the set resistance value and capacitance. [Industrial Applicability]

[0082] The present invention can be used in a power converter, a power system, and a control method for a power converter. [Explanation of symbols]

[0083] 11, 12, 13, 14: Power converters 11a: Power conversion section 11b: Sensor 11c, 41: Control section 11ca: Operation amount setting section 11cb: Judgment part 11cc: Update section 11cd, 42: Storage section 11d, 43: Communications Department 21, 22, 23, 24: Power elements 30: Bus 40:EMS 100: Power Systems 200: External server DL1, DL2, DL3, DL4: Lines EV: Electric vehicle NW: Network

Claims

1. a DC power conversion unit that converts input power and outputs the converted power; a measurement unit for acquiring a measurement value of an electrical characteristic value of the input or output power; a control unit that controls the power conversion characteristics of the power conversion unit according to an input value by voltage control, power control, or current control corresponding to a reference function having a drooping characteristic that defines a target value of an electrical characteristic value according to the input value; Equipped with The control unit uses the measurement value as the input value, controls the power conversion characteristics of the power conversion unit based on the target value determined from the input value based on the reference function, and imparts virtual inertia to a DC bus to which the power conversion unit is connected. Power converter.

2. The control unit determines the state of the bus based on the measurement value, and when it is determined that the bus is in a transient state, it uses the measurement value as the input value and controls the power conversion characteristics of the power conversion unit based on the target value determined from the input value based on the reference function, imparts virtual inertia to the DC bus to which the power conversion unit is connected, and when it is determined that the bus is in a steady state, it uses the measurement value as the input value and controls the power conversion characteristics based on the target value determined from the input value based on the reference function. The power converter of claim 1 .

3. The control unit acquires the measurement value at a predetermined cycle, and determines that the voltage is in a transient state when the absolute value of the difference between the voltage indicated by the latest measurement value and the voltage indicated by the measurement value acquired a predetermined number of times before the latest measurement value is equal to or greater than a threshold value. The power converter according to claim 2 .

4. The power converter according to any one of claims 1 to 3; a DC bus connected to the power converter; a power element connected to the power converter and capable of supplying, consuming, or charging power; A power system comprising:

5. A control method for a DC power converter that converts input power and outputs the converted power, a measuring step of acquiring a measured value of an electrical characteristic value of the power input to or output from the power converter; a control step of controlling a power conversion characteristic of the power converter according to an input value by voltage control, power control, or current control corresponding to a reference function having a drooping characteristic in which a target value of an electrical characteristic value is defined according to the input value; Equipped with In the control step, the measured value is used as the input value, and the power conversion characteristics of the power converter are controlled based on the target value determined from the input value based on the reference function, and virtual inertia is applied to a DC bus to which the power converter is connected. A method for controlling a power converter.

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