Power system and method of controlling a power system

Abstract

An electric power system includes: a plurality of electric power converters each having an electric power conversion section that converts and outputs input electric power; a control section that controls the electric power conversion section based on a reference function having a droop characteristic defined in accordance with an input value and a voltage or electric power of a bus to which the electric power conversion section is connected, and performs output control as primary control; and an update section that updates a control method of the output control, and a central control device that performs secondary control of the electric power converters using an update instruction that updates the control method, the update section updating the control method in accordance with the update instruction output from the central control device, the control method being updated so that one electric power converter that performs voltage control is always present among the plurality of electric power converters during the update of the control method by the plurality of electric power converters.

Description

Technical Field

[0001] This invention relates to power systems and control methods for power systems. Background Technology

[0002] As an alternative to large-scale power grids reliant on fossil fuels and nuclear power, power grids utilizing locally generated and consumed electricity are gaining attention. These grids connect a variety of devices that generate electricity using renewable energy sources, such as photovoltaic (PV) power plants, stationary energy storage systems, and electric vehicles (EVs). Since these devices are direct current (DC) power sources, research into constructing DC power grids is progressing.

[0003] One method for controlling a DC power grid involves using power converters connected to the aforementioned machines to perform constant current and constant voltage control on each machine based on instructions from a central control unit, thereby centrally controlling the power supply of the DC bus in the DC power grid. While this centralized control method can easily control the entire DC power grid, it suffers from difficulties in smoothly responding to rapid fluctuations in power supply and demand. Furthermore, this centralized control method, especially when constant voltage control is applied extensively and at multiple locations, can lead to voltage instability and potential fluctuations in the DC bus voltage. Moreover, under constant voltage control at multiple locations, load sharing among the machines cannot be achieved; that is, the machines cannot coordinate their power supply capabilities to supply constant voltage power to the DC bus.

[0004] Therefore, by assigning reference functions based on the power (P) and voltage (V) at the self-terminal to each power converter and autonomously and decentralizedly controlling them, control of the DC power grid is achieved (Patent Documents 1-3). When using a reference function that maintains a droop characteristic for the target voltage value according to the power required by the DC bus, this control is sometimes called droop control. By autonomously and decentralizedly controlling each power converter with droop, load sharing of power transfer between machines is implemented according to the power required by the DC bus, and the voltage of the DC bus can be stabilized.

[0005] Prior art literature

[0006] Patent documents

[0007] Patent Document 1: JP Patent No. 6371603

[0008] Patent Document 2: International Publication No. 2019 / 103059

[0009] Patent Document 3: JP 2018-29408 Summary of the Invention

[0010] The problem that the invention aims to solve

[0011] Among multiple power converters connected to the DC bus, there exists a mixture of two types: those that observe the output voltage to determine the target power and perform feedback control (power control) to make the difference between the target power and the output power zero; and those that observe the output power to determine the target voltage and perform feedback control (voltage control) to make the difference between the target voltage and the output voltage zero. When the method of feedback control is changed according to instructions from the central control unit, for example, if there is a delay in communication from the central control unit to the power converter, a situation may arise where the power converter changing from voltage control to power control completes the change of control method first, while the power converter changing from power control to voltage control is delayed. In this case, the power converter performing feedback control to make the difference between the target voltage and the output voltage zero is absent, and there is a risk of unintentional voltage rises and falls on the DC bus.

[0012] This invention was proposed in view of the above-mentioned problems, and its purpose is to suppress unintentional voltage rises and falls when updating the control method of a power converter.

[0013] Methods for solving problems

[0014] One aspect of the present invention is a power system comprising: a plurality of power converters; a central control unit that performs secondary control of the power converters; a bus connected to the power converters; and power elements connected to the power converters that are capable of supplying, consuming, or charging power. The plurality of power converters each have: a power conversion unit that converts input power and outputs it; a control unit that controls the power conversion unit based on a reference function having a droop characteristic defined according to an input value and the voltage or power of the bus connected to the power conversion unit, and performs output control as primary control; and an update unit that updates the control method of the output. The central control unit performs secondary control of the power converters using an update command that updates the control method, and the update unit updates the control method according to the update command output from the central control unit. During the updating of the control method by the plurality of power converters, the control method is updated such that at least one power converter performing voltage control is always present among the plurality of power converters.

[0015] In one aspect of the present invention, in a power system, primary control of the output can also be performed based on the voltage or current of the bus without being mediated by instructions from a central control device.

[0016] In one aspect of the present invention, in a power system, the power converter performing voltage control among multiple power converters may update the control method after a predetermined time has elapsed since the update instruction was obtained.

[0017] In one aspect of the power system of the present invention, the central control device may output the update command to the power converter that performs voltage control among the plurality of power converters after outputting the update command to the power converter that performs power control among the plurality of power converters.

[0018] One aspect of the present invention is a control method for a power system, the power system comprising: a plurality of power converters, each having a power conversion unit connected to a bus for converting and outputting input power; power elements connected to the power converters for supplying, consuming, or charging power; and a central control device for controlling the power converters. The control method of the power system comprises the following steps: the power conversion unit converts and outputs input power; based on a reference function having a droop characteristic defined according to the input value, and the voltage or power of the bus connected to the power conversion unit, the power conversion unit is controlled to perform output control as a primary control; the central control device performs secondary control on the power converters using an update instruction to update the control method; and the power converters update the output control method according to the update instruction, wherein during the updating of the control method by the plurality of power converters, the control method is updated such that at least one of the plurality of power converters always performs voltage control.

[0019] Invention Effects

[0020] According to the power system of the present invention, a plurality of power converters include: a power conversion unit that converts and outputs input power; a control unit that controls the power conversion unit and executes the output control as a primary control based on a reference function having a droop characteristic defined according to the input value and the voltage or power of the bus connected to the power conversion unit; and an update unit that updates the control method of the output. For the plurality of power converters, a central control device that performs secondary control of the power converters uses an update instruction to update the control method to perform secondary control on the power converters. The update unit updates the control method according to the update instruction output from the central control device. During the update of the control method by the plurality of power converters, the control method is updated such that at least one power converter that performs voltage control is always present among the plurality of power converters. Therefore, when the control method is updated, the voltage of the bus connected to the power converters is controlled by at least one power converter that performs voltage control, suppressing unintentional voltage rises and falls in the bus.

[0021] According to the power system control method of the present invention, the power system includes: a plurality of power converters, each having a power conversion unit connected to a bus for converting and outputting input power; power elements connected to the power converters for supplying, consuming, or charging power; and a central control device for controlling the power converters. The power system control method executes the following steps: the power conversion unit converts and outputs the input power; based on a reference function having a droop characteristic defined according to the input value, and the voltage or power of the bus connected to the power conversion unit, the power conversion unit is controlled to perform output control as a primary control; the central control device performs secondary control on the power converters using an update instruction to update the control method; and the power converters update the output control method according to the update instruction. During the update of the control method by the plurality of power converters, the control method is updated such that at least one power converter performing voltage control is always present among the plurality of power converters. Therefore, when updating the control method, the voltage of the bus connected to the power converters is controlled by at least one power converter performing voltage control, suppressing unintentional voltage rises and falls in the bus. Attached Figure Description

[0022] Figure 1 A diagram illustrating the structure of the power system related to the first embodiment.

[0023] Figure 2 To indicate Figure 1 The diagram shows the structure of the power converter.

[0024] Figure 3 To indicate Figure 2 A diagram showing the structure of the control unit.

[0025] Figure 4A This is a diagram illustrating an example of power conversion characteristics.

[0026] Figure 4B This is a diagram illustrating an example of power conversion characteristics.

[0027] Figure 4C This is a diagram illustrating an example of power conversion characteristics.

[0028] Figure 4D This is a diagram illustrating an example of power conversion characteristics.

[0029] Figure 5 A flowchart illustrating the processing flow performed by the control unit of a power converter.

[0030] Figure 6 A timing diagram illustrating an example of a control method for a power system.

[0031] Figure 7 A flowchart illustrating the processing flow performed by the control unit of a power converter.

[0032] Figure 8A A diagram illustrating the timing of updating reference function information and feedback control methods in a power converter.

[0033] Figure 8B A diagram illustrating the timing of updating reference function information and feedback control methods in a power converter.

[0034] Figure 9 This diagram illustrates the structure of the control unit of the power converter related to the second embodiment.

[0035] Figure 10 This is a flowchart illustrating the processing flow performed by the control unit of the power converter related to the second embodiment.

[0036] Figure 11 A timing diagram illustrating an example of a control method for a power system related to the second embodiment.

[0037] Figure 12 This is a diagram illustrating the timing of updating reference function information and the feedback control method in the power converter related to the second embodiment. Detailed Implementation

[0038] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited by the embodiments described below. Furthermore, in the accompanying drawings, the same reference numerals are appropriately used for the same parts.

[0039] (First Embodiment)

[0040] <Structure of Power Systems>

[0041] Figure 1 This diagram illustrates the structure of the power system related to the first embodiment. The power system 100 includes multiple power converters 11, 12, 13, and 14, multiple power elements 21, 22, 23, and 24, and a bus 30. Furthermore, the power system 100 includes an EMS (Energy Management System) 40. The EMS 40 is an example of a central control device.

[0042] Power converters 11, 12, and 13 are DC / DC converters, and power converter 14 is an AC / DC converter. Power converters 11, 12, 13, and 14 have the function of wired or wireless information communication. The structure and function of power converters 11, 12, 13, and 14 will be described in detail later.

[0043] Bus 30 is a DC bus in power system 100 and is connected to power converters 11, 12, 13, and 14. Power system 100 constitutes a power network including a DC power grid.

[0044] Power element 21 is, for example, a stationary energy storage device capable of supplying, consuming, and charging electricity, and is connected to power converter 11. The stationary energy storage device is an example of a permanently installed in-equipment energy storage device. Power converter 11 has the following functions: it converts the voltage of the DC power supplied to power element 21 and outputs it to bus 30; it also converts the voltage of the DC power supplied from bus 30 and outputs it to power element 21, thus charging power element 21.

[0045] Power element 22 is, for example, a solar power generation device capable of generating and supplying electricity, and is connected to power converter 12. The solar power generation device is an example of a power generation device that uses renewable energy to generate electricity. Power converter 12 has the function of converting the voltage of the DC power supplied by power element 22 and outputting it to bus 30.

[0046] Power element 23 is an example of an on-board energy storage device capable of supplying, consuming, and charging electricity, and is connected to power converter 13. The on-board energy storage device is mounted on an electric vehicle (EV) and is an example of a mobile, non-stationary energy storage device. Power converter 13 has the following functions: it converts the voltage of the DC power supplied to power element 23 and outputs it to bus 30, and it converts the voltage of the DC power supplied from bus 30 and outputs it to power element 23, thus charging power element 23. Power converter 13 can be installed, for example, in charging stations or residential charging equipment, but it can also be mounted on an electric vehicle (EV).

[0047] Power element 24, exemplified by a commercial power system, is connected to power converter 14. Power converter 14 converts the AC power supplied to power element 24 into DC power and outputs it to bus 30, and also converts the DC power supplied from bus 30 into AC power and outputs it to power element 24. The power output from bus 30 to power element 24 is also referred to as reverse current.

[0048] EMS40 has the function of comprehensively managing the status of power system 100. EMS40 includes a control unit 41, a storage unit 42, and a communication unit 43.

[0049] The control unit 41 performs various computational processes to implement the functions of the EMS 40, and is configured with processors such as CPUs (Central Processing Units), ASICs (Application Specific Integrated Circuits), FPGAs (Field-Programmable Gate Arrays), DSPs (Digital Signal Processors), and GPUs (Graphics Processing Units). The functions of the control unit 41 are implemented as functional units by reading various programs from the storage unit 42 and executing them.

[0050] The storage unit 42 includes, for example, ROM (Read Only Memory) for storing various programs and data used by the control unit 41 for computational processing. Furthermore, the storage unit 42 includes, for example, RAM (Random Access Memory) for storing workspace during computational processing by the control unit 41 and the results of computational processing by the control unit 41. The storage unit 42 may also include auxiliary storage devices such as HDD (Hard Disk Drive) or SSD (Solid State Drive).

[0051] The communication unit 43 is configured to include a communication module for information communication via wired or wireless means. The communication unit 43 communicates with the power converters 11, 12, 13, 14 and the external server 200 via a network NW consisting of an Internet line network, a mobile telephone line network, etc.

[0052] Furthermore, the external server 200 is a server located outside the power system 100. The external server 200 may include, for example, an information processing device and a database configured to function as an EMS in other power systems, and may function 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.

[0053] <Structure of Power Converter>

[0054] Next, the specific structure of the power converter 11 will be described. Figure 2 This diagram illustrates the structure of a power converter 11. The power converter 11 includes a power conversion unit 11a, a sensor 11b, a control unit 11c, and a communication unit 11d.

[0055] The power conversion unit 11a performs DC / DC conversion, transforming the voltage of the DC power input from the discharging power element 21 and outputting it to the bus 30. The power conversion unit 11a can also transform the voltage of the DC power input from the bus 30 and output it to the power element 21 for charging. The power conversion unit 11a is, for example, composed of an electrical circuit including coils, capacitors, diodes, and switching elements. Switching elements include, for example, field-effect capacitors and insulated-gate bipolar transistors. The power conversion characteristics of the power conversion unit 11a can be controlled, for example, by PWM (Pulse Width Modulation) control.

[0056] Sensor 11b measures the electrical characteristics of the power supplied to or from the power converter 11a via bus 30. Therefore, sensor 11b measures the electrical characteristics of the power input to or output from the power converter 11. Sensor 11b can measure current, voltage, and power values. Sensor 11b is an example of a measuring unit that acquires measured values. Sensor 11b outputs the measured electrical characteristic values ​​to the control unit 11c.

[0057] The control unit 11c is configured to perform various arithmetic operations for controlling the operation of the power converter 11a in order to realize the main power conversion function of the power converter 11a. The processor and the storage unit can adopt the structures exemplified as control unit 41 and storage unit 42, respectively. The function of the control unit 11c is implemented as a functional unit by the processor reading various programs from the storage unit and executing them. For example, the control unit 11c controls the power conversion characteristics of the power converter 11a based on a reference function. Specifically, the control unit 11c outputs a PWM signal, including information on the operating quantity (e.g., duty cycle) for PWM control, to the power converter 11a and performs PWM control on the power converter 11a. Alternatively, the control unit 11c can output the operating quantity directly to the power converter 11a, or it can output it to the power converter 11a through other functional units (e.g., loop control units) not shown.

[0058] The communication unit 11d comprises a communication module for wired or wireless information communication and a communication control unit for controlling the operation of the communication module. The communication unit 11d communicates with the EMS 40 via a network NW. For example, the communication unit 11d receives information and commands from the EMS 40 and outputs them to the control unit 11c. Furthermore, the communication unit 11d, for example, sends information related to the power status input from the control unit 11c to the EMS 40. Additionally, if the power status related information is a measurement value from the sensor 11b, the communication unit 11d may also send the measurement value input from the sensor 11b to the EMS 40.

[0059] Figure 3 This diagram illustrates the structure primarily related to the power conversion function of the control unit 11c. The control unit 11c includes: an operation quantity setting unit 11ca, a decision unit 11cb, an update unit 11cc, and a storage unit 11cd, all implemented via software through program execution.

[0060] 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 storage unit 11cd, and updates the reference function information and control method information stored in the storage unit 11cd. Here, the so-called reference function information refers to various information used to determine the drooping function constituting the reference function, which will be described in detail later.

[0061] The determination unit 11cb makes a determination based on control method information stored in the storage unit 11cd regarding the feedback control method performed by the operation amount setting unit 11ca, and outputs the determination result as determination information. Furthermore, as a feedback control method, there are two types: one where a target power Pref (an example of a target value) is determined based on the measured voltage value Vo obtained from the sensor 11b and reference function information, and the operation amount is set so that the difference between Pref and the measured power value Po (an example of a controlled object value) obtained from the sensor 11b is within an allowable range (hereinafter referred to as droopP control); and another where a target voltage Vref (an example of a target value) is determined based on the measured power value Po obtained from the sensor 11b and reference function information, and the operation amount is set so that the difference between Vref and the measured voltage value Vo (an example of a controlled object value) obtained from the sensor 11b is within an allowable range (hereinafter referred to as droopV control). The droopP control, as an example of power control, and the droopV control, as an example of voltage control, are examples of control methods for controlling the output of the power conversion unit 11a. The aforementioned control method information refers to information indicating droopP control or droopV control. The determination unit 11cb makes a determination based on the control method information that stores the feedback control method in the storage unit 11cd, and outputs the determination result of performing droopP control or the determination result of performing droopV control as determination information.

[0062] The operation quantity setting unit 11ca sets the feedback control method according to the decision information input from the decision unit 11cb. It sets the operation quantity based on the measured value input from the sensor 11b and the reference function information obtained from the storage unit 11cd, and outputs it to the power conversion unit 11a. Furthermore, the feedback control performed by the operation quantity setting unit 11ca can be executed using known methods, such as PID control, which reads parameters stored in the storage unit 11cd, including proportional gain, integral time, and derivative time.

[0063] The storage unit 11cd or the operation setting unit 11ca outputs information related to power conditions, reference function information, etc., to the communication unit 11d.

[0064] Alternatively, other power converters 12, 13, and 14 may have the same structure as power converter 11. However, the power conversion section 11a of power converter 14 is a so-called inverter that converts AC power input from power element 24 into DC power and outputs it to bus 30, and converts DC power input from bus 30 into AC power and outputs it to power element 24.

[0065] <Properties of Reference Functions>

[0066] Next, the reference function based on the power conversion characteristics of the power conversion unit 11a controlled by the control unit 11c will be explained. Figures 4A to 4D This is a diagram illustrating an example of power conversion characteristics.

[0067] Figure 4A This diagram illustrates the VP characteristic, representing the relationship between power (P) and voltage (V) on the bus 30 side of the power conversion section 11a, which is part of the power converter 11. It shows the power conversion characteristics of the power conversion section 11a. P is positive when the power conversion section 11a supplies power to the bus 30, i.e., when the power element 21 is discharging, and negative when power is supplied from the bus 30, i.e., when the power element 21 is charging.

[0068] Figure 4A The line DL1 shown is a straight line or a curve that bends midway. The reference function represented by this line DL1 is constructed by connecting multiple droop functions with different droop characteristics, defined according to the interval of the input value. Specifically, line DL1 is constructed by connecting five droop functions with different droop characteristics, and is determined by reference function information. The reference function information includes, for example, the coordinate information of the boundary of the droop function in an coordinate system with the horizontal axis set to P and the vertical axis set to V, the slice 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.). In the power converter 11, the control unit 11c controls the power conversion characteristics of the power conversion unit 11a to be the characteristics of the reference function represented by line DL1. That is, the control unit 11c of the power converter 11 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 line DL1.

[0069] Figure 4B The diagram shows the VP characteristics of the power (P) and voltage (V) relationship on the bus 30 side of the power conversion section 11a of the power converter 12, which is a power conversion unit 11a of the power converter 12.

[0070] Figure 4B The line DL2 shown is a straight line or a curve that bends midway. The reference function represented by line DL2 is constructed by connecting five droop functions with different droop characteristics, defined according to the interval of the input value. Line DL2, like line DL1, is determined by the reference function information. In the power converter 12, the control unit 11c controls the power conversion characteristics of the power conversion unit 11a to be the characteristics of the reference function represented by line DL2. That is, the control unit 11c of the power converter 12 controls the power conversion unit 11a so that the operating point defined by the values ​​of V and P is located on line DL2.

[0071] Figure 4C The diagram shows the VP characteristics of the power (P) and voltage (V) relationship on the bus 30 side of the power conversion section 11a of the power converter 13, which is a power conversion unit 11a of the power converter 13.

[0072] Figure 4C The line DL3 shown is a straight line or a curve that bends midway. The reference function represented by line DL3 is constructed by connecting nine droop functions with different droop characteristics, defined according to the interval of the input value. Line DL3, like line DL1, is determined by reference function information. In the power converter 13, the control unit 11c controls the power conversion characteristics of the power conversion unit 11a to be the characteristics of the reference function represented by 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 values ​​of V and P is located on line DL3.

[0073] Figure 4D The diagram shows the VP characteristics of the power (P) and voltage (V) relationship on the bus 30 side of the power conversion section 11a of the power converter 14, which is a power conversion unit 11a of the power converter 14.

[0074] Figure 4D The line DL4 shown is a straight line or a curve that bends midway. The reference function represented by line DL4 is constructed by connecting three droop functions with different droop characteristics, defined according to the interval of the input value. Line DL4, like line DL1, is determined by reference function information. In the power converter 14, the control unit 11c controls the power conversion characteristics of the power conversion unit 11a to be the characteristics of the reference function represented by line DL4. That is, the control unit 11c of the power converter 14 controls the power conversion unit 11a so that the operating point defined by the values ​​of V and P is located on line DL4.

[0075] <Control Methods>

[0076] Next, the control methods for power converters 11, 12, 13, and 14, as well as the control method for the power system 100, will be described. In the power system 100, there are two control methods: self-end control, which allows for individual and autonomous decentralized control of power converters 11, 12, 13, and 14, and centralized control, which coordinates the control of power converters 11, 12, 13, and 14 according to the power conditions of the power system 100. Furthermore, for example, self-end control is repeatedly executed with a shorter cycle, while centralized control is executed at intervals longer than the self-end control cycle. Self-end control is also called primary control, and centralized control is also called secondary control. These control methods involve, for example, having a processor execute a program in each power converter or the EMS 40.

[0077] <Automatic Control>

[0078] First, the control methods for power converters 11, 12, 13, and 14 in the self-controlled system will be explained using power converter 11 as an example. The same control methods described below can also be appropriately implemented in the other power converters 12, 13, and 14. Furthermore, if power element 22 is an element whose power generation is not controlled from the perspective of efficiency, such as a solar power generation device, and if power corresponding to its power generation is input from power element 22, power converter 12 can also perform MPPT (Maximum Power Point Tracking) control to operate in a way that maximizes the output power to bus 30 based on its power generation. For example... Figure 4B This is an example of a reference function used when performing MPPT mode control.

[0079] In the control method of the power converter 11, the control unit 11c executes a control step that controls the power conversion characteristics of the power converter 11, i.e., the power conversion characteristics of the power conversion unit 11a, based on a reference function.

[0080] Reference Figure 3 as well as Figure 5 A specific example of the contents of this control step is given. Figure 5 A flowchart illustrating the processing flow performed by the control unit 11c.

[0081] First, in the control unit 11c, the operation quantity setting unit 11ca obtains a measurement value from the sensor 11b (step S101). Next, in the control unit 11c, the operation quantity setting unit 11ca obtains reference function information from the storage unit 11cd (step S102). 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 S103). Next, in the control unit 11c, the operation quantity setting unit 11ca obtains the determination information output from the determination unit 11cb, sets the operation quantity for executing the feedback control based on the obtained determination information based on the measurement value and the reference function information, and outputs it to the power conversion unit 11a (step S104). Control of the power conversion unit 11a is then executed.

[0082] Centralized control

[0083] Next, centralized control will be explained. In the example shown below, the reference function and feedback control method used in the control of power converters 11, 12, 13, and 14 are updated via instructions, thereby enabling centralized control to be performed on the EMS40 externally installed on power converters 11, 12, 13, and 14. Updating the reference function and feedback control method via instructions means that the instructions include reference function information related to the reference function and control method information related to the feedback control method, updating part or all of the reference function and the feedback control method. The respective storage units 11cd of power converters 11, 12, 13, and 14 can update the reference function information and control method information.

[0084] For example, in the information communication between EMS40 and power converters 11, 12, 13, and 14, the instruction signal for updating the reference function includes reference function information and control method information. The reference function information, as described above, includes the coordinates of the droop function boundary, the slice information of the droop function, the slope (i.e., the droop coefficient) information, and the shape (straight line, curve, etc.) information. The control method information indicates either droopP control or droopV control. The reference function information used in the update is stored in the storage unit 42 of EMS40, and the control unit 41 reads and uses it appropriately.

[0085] Next, as a reference for centralized control Figure 6 The timing diagram illustrates an example of the control method for power system 100.

[0086] First, EMS40 calls the timer of the self-device to start timing (step S201). Next, EMS40 requests self-terminal metering information from power converters 11, 12, 13, and 14 respectively (step S202). The so-called self-terminal metering information is an example of information related to the power status of the power system 100, including the measured values ​​and measurement times measured by the sensors of power converters 11, 12, 13, and 14 respectively.

[0087] Next, power converters 11, 12, 13, and 14 send their self-metering information to EMS40 (step S203). EMS40 stores their respective self-metering information in storage unit 42.

[0088] Next, as an example of information related to the power status of power system 100, EMS 40 requests various information from external server 200 that may affect the operation of power system 100 (step S204). In this example, EMS 40 requests power generation and demand forecast information from external server 200. Power generation and demand forecast information includes forecast information on power generation in power system 100 and power demand forecast information, and may also include information such as the season, current weather, and future weather forecasts for the region where power system 100 is located. Furthermore, when external server 200 functions as an EMS for another power system, and the operating status of that other power system may affect the operation of power system 100, the power generation and demand forecast information may also include forecast information on power generation and power demand forecasts in that other power system.

[0089] Next, the external server 200 sends power generation and demand forecast information to the EMS 40 (step S205). The EMS 40 stores the power generation and demand forecast information in the storage unit 42.

[0090] Next, the control unit 41 of the EMS40 reads the transmitted information from the storage unit 42, namely information related to the power status of the power system 100, and performs the power system 100 utilization optimization calculation based on this (step S206).

[0091] The optimization calculation is applied to various conditions. For example, the power system 100 is configured to operate at a predetermined voltage on the bus 30. In this state, the EMS 40 anticipates, based on power generation and demand forecast information, that the area where the power element 22, which is installed as a solar power generation device, is located will experience sunny weather and increased power generation in the future. Based on self-metering information obtained from the power converter 12 connected to the power element 22, it determines that there is a margin for supplying power to the power element 22. In this case, the EMS 40 determines to update the reference function of the power converter 11 connected to the power element 21 so that the power element 21, which is a fixed-type energy storage device, is charged at this operating point. Furthermore, the EMS 40 determines to update the reference function of the power converter 14 connected to the power element 24 simultaneously with this update, so that power is not supplied from the power element 24, which is part of a commercial power system.

[0092] Furthermore, by using optimization calculations, conditions can be set and executed from the perspectives of peak cutoff, effective utilization of nighttime electricity, contracted electricity not exceeding 24 of the electricity elements in a commercial power system, and appropriate electricity costs.

[0093] Furthermore, the storage unit 42 of the EMS40 stores the learned model, and the EMS40 can also use the learned model to perform application optimization calculations. The learned model can be generated using deep learning with neural networks, for example, by using information related to the power status of the power system 100, the switching and updating results of the reference functions of the corresponding power converters 11, 12, 13, and 14 as teaching data.

[0094] Next, based on the results of optimization calculations, EMS40 sets reference function information and control method information suitable for the power converters 11, 12, 13, and 14 that are being updated, and outputs update instructions for the reference function (droop function) and feedback control method, including the set reference function information and control method information (step S207). Then, EMS40 resets the timer (step S208).

[0095] Next, the power converters of the updating objects in power converters 11, 12, 13, and 14 obtain the update instructions for the reference function and the feedback control method, and perform the update of the reference function and the feedback control method (step S209).

[0096] Figure 7This is a flowchart illustrating the process of updating the reference function and feedback control method performed by the power converter. Upon receiving the update command, the control unit 11c of the power converter refers to the control method information stored in the storage unit 11cd and determines whether the feedback control method before the update is droopV control (step S301).

[0097] If the control method indicated in the control method information before the update is droopP control ("No" in step S301), the control unit 11c proceeds to step S303. If the control method indicated in the control method information before the update is droopV control ("Yes" in step S301), the control unit 11c determines whether a predetermined time has elapsed since the update command was obtained (step S302). If no predetermined time has elapsed since the update command was obtained ("No" in step S302), the control unit 11c repeats step S302 until the predetermined time has elapsed. If a predetermined time has elapsed since the update command was obtained ("Yes" in step S302), the control unit 11c updates the reference function information and control method information stored in the storage unit 11cd using the reference function information and control method information reported by the received update command (step S303).

[0098] Return to Figure 6 Next, power converters 11, 12, 13, and 14 respectively execute self-end control (step S210). Here, the power converters 11, 12, 13, and 14 that have obtained update instructions use the updated reference function and feedback control method to perform self-end control. These self-end controls are self-end controls that reflect the power status of the power system 100, and thus power converters 11, 12, 13, and 14 are coordinated under control.

[0099] Figure 8A This diagram illustrates the timing of the update of reference function information and feedback control method in a power converter that receives an update command. Furthermore, for comparison with this embodiment, the power converter being updated was not... Figure 7 In the case of handling Figure 8B The reference function information and the timing at which the feedback control method is updated are shown in the diagram.

[0100] like Figure 8B As shown, for example, if the update of the power converter 11 from droopP control to droopV control is delayed compared to the update of the power converter 14 from droopV control to droopP control due to communication delay, during the delay period, the power converter performing droopV control is not present, and there is a risk of unintentional voltage rise or fall in the bus 30.

[0101] In contrast, in this embodiment, the power converter that receives the update command performs the update. Figure 7 The processing, therefore, since the power converter 14, which updates from droopV control to droopP control, updates the control method after a predetermined time has elapsed since receiving the update command, thus, as Figure 8A As shown, even if there is a delay in the update from droopP control to droopV control in the power converter 11, the power converter performing droopV control is still in a state where it exists, and in the bus 30, unintentional voltage rises and falls can be suppressed.

[0102] (Second Implementation)

[0103] The second embodiment of the present invention will now be described. The power system related to the second embodiment differs from that of the first embodiment in the method of centralized control, the reference function, and the method for updating the feedback control method. Other structures are the same as those in the first embodiment; therefore, the same reference numerals are used for structures identical to those in the first embodiment, and descriptions are omitted. In the following description, the differences from the first embodiment will be explained.

[0104] Figure 9 This diagram illustrates the structure related to the power conversion function of the control unit 11c, which is mainly associated with the second embodiment. The control unit 11c associated with the second embodiment differs from the control unit 11c associated with the first embodiment in that it outputs information indicating that the update unit 11cc has completed the update of the reference function and the feedback control method to the communication unit 11d.

[0105] Figure 10 This is a flowchart illustrating the process of updating the reference function and feedback control method of the power converter being updated in the second embodiment. Furthermore, the processes of steps S301 to S303 are the same as in the first embodiment, and therefore their description is omitted. After completing the process in step S303, the control unit 11c outputs update completion information indicating that the update process of the reference function and feedback control method has ended to the communication unit 11d (step S304). This update completion information is then sent from the communication unit 11d to the EMS40.

[0106] Next, use Figure 11 The timing diagram illustrates the centralized control in the second embodiment. Furthermore, in the centralized control of the second embodiment, in... Figure 11 Before step S401 shown Figure 6 The processing of steps S201 to S206 shown is completed.

[0107] After performing the optimization calculation, EMS40 outputs an update command to the power converter that is the target of the update of the reference function and feedback control method. Specifically, EMS40 stores information indicating the feedback control method executed by power converters 11 to 14 in the storage unit 42, and determines the feedback control method executed by the target power converter by referring to this information (step S401). Here, for example, it is determined that power converters 11 and 13 perform droopP control, and power converter 14 performs droopV control.

[0108] Next, EMS40 first outputs an update command for the reference function (droop function) and the feedback control method to the power converter 11 executing droopP control (step S402). During this process, EMS40 does not output update commands to other power converters that are being updated until it receives an update completion message from power converter 11. Upon receiving the update command, power converter 11 executes... Figure 10 The power converter 11 processes and updates the reference function and feedback control method (step S403). If the update of the reference function and feedback control method is completed, the power converter 11 sends the update completion information to the EMS40 (step S404) and executes self-end control (step S405).

[0109] Upon receiving the update completion information from power converter 11, EMS 40 outputs an update command for the reference function (droop function) and feedback control method to power converter 13, which performs the same droop control (step S406). During this process, EMS 40 does not output update commands to other power converters that are being updated until it receives the update completion information from power converter 11. Power converter 13, upon receiving the update command, executes... Figure 10 The process involves updating the reference function and feedback control method (step S407). If the update of the reference function and feedback control method is completed, the power converter 13 sends the update completion information to the EMS40 (step S408) and executes self-end control (step S409).

[0110] Upon receiving the update completion message from power converter 13, EMS40 outputs an update command to the power converter executing droopP control. Then, it outputs update commands for the reference function (droop function) and feedback control method to power converter 13 executing droopV control (step S410). Power converter 14, upon receiving the update command, executes... Figure 10The process involves updating the reference function and feedback control method (step S411). If the power converter 14 finishes updating the reference function and feedback control method, it sends an update completion message to the EMS 40 (step S412) and executes self-end control (step S413). Then, upon receiving the update completion message from the power converter 14, the EMS 40 resets the timer (step S414).

[0111] Figure 12 This diagram illustrates the timing of the update of reference function information and feedback control method in a power converter that receives an update command. In the second embodiment, after the power converter 11, which performs droopP control, finishes updating to droopV control, the EMS40 outputs an update command to droopP control to the power converter 14, which performs droopV control. This becomes a necessary state for the power converter performing droopV control, and in the bus 30, unintentional voltage rises and falls can be suppressed.

[0112] In addition, in the second embodiment, when an update command to droopP control is output to the power converter that performs droopV control, the power converter that performs droopP control ends the update to droopV control and becomes the power converter that performs droopV control. Therefore, it can also be a structure in which the processing of steps S301 and S302 is not performed.

[0113] (Modified Example)

[0114] The embodiments of the present invention have been described above, but the present invention is not limited to the embodiments described above and can be implemented in various other ways. For example, the present invention can also be implemented by modifying the embodiments described above as follows. In addition, the embodiments described above and the following modifications can be combined separately. Cases in which the structural elements of the various embodiments and modifications described above are appropriately combined are also included in the present invention. Furthermore, further effects and modifications can be easily derived by those skilled in the art. Therefore, the present invention is not limited to the embodiments and modifications described above, and various changes can be made.

[0115] In the above embodiments, electrical characteristic values ​​such as measured values, target values, and controlled object values ​​can be represented by current values ​​instead of power values. In this case, for example, the reference function is defined as the VI characteristic, which is the relationship between current (I) and voltage (V). Furthermore, for example, the control unit 11c determines the target power Iref (an example of a target value) based on the measured voltage value Vo obtained from the sensor 11b and the reference function information, and sets the operating quantity so that the difference between Iref and the measured current value Io (an example of a controlled object value) obtained from the sensor 11b is within an allowable range. This feedback control is also called droopI control and is executed as droopP control. Furthermore, in droopV control, the target voltage Vref is determined based on the measured current value Io obtained from the sensor 11b and the reference function information.

[0116] In the above embodiments, different reference function information is stored in the storage unit 11cd, and the reference function information used by the operation quantity setting unit 11ca in the stored reference function information can be switched according to the instructions from the EMS40.

[0117] In the first embodiment described above, similarly to the second embodiment, an update command is first output to the power converter that has executed droopP control, and then an update command is output to the power converter that has executed droopV control.

[0118] In the above embodiments, the feedback control performed by each power converter is not limited to droopV control or droopP control based on a reference function, but may also be constant voltage control to keep the voltage constant or constant power control to keep the power constant. Constant voltage control as an example of voltage control and constant power control as an example of power control are examples of control methods for controlling the output of the power conversion unit 11a.

[0119] Industrial utilization potential

[0120] This invention can be applied to power systems and power system control methods.

[0121] Symbol Explanation

[0122] 11, 12, 13, 14: Power converters

[0123] 11a: Power Conversion Section

[0124] 11b: Sensor

[0125] 11c, 41: Control Unit

[0126] 11ca: Operational quantity setting unit

[0127] 11cb: Decision Unit

[0128] 11cc: Update Department

[0129] 11cd, 42: Storage Department

[0130] 11d, 43: Ministry of Communications

[0131] 21, 22, 23, 24: Electricity Elements

[0132] 30: Bus

[0133] 40: EMS

[0134] 100: Power System

[0135] 200: External Server

[0136] DL1, DL2, DL3, DL4: Lines

[0137] EV: Electric Vehicle

[0138] NW: Network.

Claims

1. An electric power system, comprising: Multiple power converters, each having a power conversion unit, a control unit, and a regeneration unit; The central control unit performs secondary control over the power converter; The bus connected to the power conversion unit; and An electrical element connected to the power converter and capable of supplying, consuming, or charging electricity. The power conversion unit converts the input power and outputs it. The control unit controls the power conversion unit to perform the output control as a primary control based on a reference function having a droop characteristic defined according to the input value and the voltage or power of the bus connected to the power conversion unit. The updating unit updates the control method for the output. The central control device uses update instructions to update the control method to perform secondary control on the power converter. The updating unit updates the control method according to the updating command output from the central control device. During the updating of the control method by the plurality of power converters, the control method is updated such that at least one of the power converters performing voltage control is always present.

2. The power system according to claim 1, wherein, The primary control, which is the output of the control, is executed based on the voltage or current of the bus, without being mediated by instructions from the central control unit.

3. The power system according to claim 1 or 2, wherein, The power converter performing voltage control among the plurality of power converters updates the control method after a predetermined time has elapsed since receiving the update instruction.

4. The power system according to claim 1 or 2, wherein, The central control device. After outputting the update command to the power converter that is performing power control among the plurality of power converters, the update command is output to the power converter that is performing voltage control among the plurality of power converters.

5. A control method for a power system, wherein the power system is equipped with: Multiple power converters, each having a power conversion unit that is connected to a bus and converts and outputs the input power; An electrical element that is connected to the power converter and is capable of supplying, consuming, or charging electricity; and The central control unit controls the power converter. The control method for the power system includes the following steps: The power conversion unit converts the input power and outputs it. Based on a reference function having a drooping characteristic defined according to the input value, and the voltage or power of the bus connected to the power conversion unit, the power conversion unit is controlled to perform control of the output as a primary control; The central control device uses an update command to update the control method to perform secondary control on the power converter; and The power converter updates the output control method according to the update instruction. During the updating of the control method by the plurality of power converters, the control method is updated such that at least one of the power converters performing voltage control is always present.

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