WO2016029944A1

WO2016029944A1 - Control of a microgrid

Info

Publication number: WO2016029944A1
Application number: PCT/EP2014/068204
Authority: WO
Inventors: Ritwik MAJUMDER
Original assignee: Abb Technology Ltd
Priority date: 2014-08-28
Filing date: 2014-08-28
Publication date: 2016-03-03

Abstract

The present disclosure relates to a method performed in a first distributed generator (DG) 1 in an electrical microgrid. The method comprises obtaining measurements of at least one parameter in the microgrid local to the first DG. The method also comprises, based on the obtained measurements, determining a first primary control mode of the first DG. The method also comprises instructing a primary control 4 of the first DG that the first DG should be in said first control mode. The method also comprises sending information about that the first DG is in the first control mode, to at least a second DG in the microgrid. The method also comprises receiving information about in which control mode each of said at least a second DG is from each of said at least a second DG, respectively. The method also comprises forwarding said received information to a distributed secondary control 5 of the first DG.

Description

CONTROL OF A MICROGRID

TECHNICAL FIELD

The present disclosure relates to methods and devices for controlling an electrical microgrid BACKGROUND

A microgrid is a localized grouping of electricity generation, energy storage, and loads that normally operates connected to a traditional centralized grid (macrogrid) via a point of common coupling (PCC). This single point of common coupling with the macrogrid can be disconnected, islanding the microgrid. Microgrids are part of a structure aiming at producing electrical power locally from many small energy sources, distributed generators (DGs). In a microgrid, a DG may be connected via a converter which controls the output of the DG, i.e. the output voltage or the current injected into the microgrid. A microgrid (in grid connected mode, i.e. connected to the macrogrid) supplies the optimized or maximum power outputs from the connected DG sites and the rest of the power is supplied by the macrogrid. The microgrid is connected to the macrogrid at a PCC through a controllable switch. This grid connection is lost during grid fault and the microgrid is islanded. In such a microgrid, it is desired that the main system controller (microgrid controller) will be able to monitor system parameters such as voltage at different locations, system frequency, as well as active and reactive power output of the DGs at different locations in the microgrid in order to ensure stable operation, optimize energy usage, improve power quality and minimize loss. This requires each of the components of the microgrid (e.g. DG, storage, loads etc.) to communicate these measured quantities to the microgrid controller after a certain time interval and typically these monitoring time scales can vary from seconds to minutes. The microgrid controller may be regarded as a secondary controller which controls the microgrid on a higher level, based on e.g. local information from primary controllers of each DG, the primary controller controlling the DG based on local measurements. The secondary control is typically centralised, but it may alternatively be distributed such that a distributed part of the secondary controller is co-located in each of the DGs in the microgrid.

The distributed generators in a microgrid can be controlled in different operating modes (control modes). Power control, to inject maximum power; voltage control, to improve the voltage profile; and droop control, to share the loads in the microgrid between the DGs. The control mode of a DG is decided by the primary control of the DG based on local conditions. Each mode contributes to different system stability aspects like power balance, voltage stability and load sharing. On the other hand, the secondary controller, applying secondary control functions, usually implemented in a central controller, coordinates the control mode changes as well as the change in references to ensure improved overall system operation.

US 2010/0318237 discloses the use of a central database storing operational rules for choosing an operating mode of each energy device in a network. An energy management system receives information about the current operating modes of all energy devices and checks whether these modes are the same as those chosen based on the operational rules. If not, the energy device is ordered to change its mode. The operational rules may specify that activation or deactivation of an energy device is to be responsive to one or more of: energy service provider directive or instruction, market price condition, and information specific to an energy device (e.g., whether the device supports energy generation and/or consumption modes, a maximum power consumption and/or maximum power output of the device, a maximum energy storage capacity of the device, a current operational mode of the device (e.g., generate, consume, idle) and operational parameters such as, for example, voltage, current, duty cycle, an amount of energy currently stored by the device, a depth of discharge value, temperature barometric pressure, humidity, dew point, wind direction and wind speed). SUMMARY

It is an objective of the present invention to provide improved control of a DG in a microgrid having a distributed secondary control.

According to an aspect of the present invention, there is provided a method performed in a first distributed generator (DG) in an electrical microgrid. The method comprises obtaining measurements of at least one parameter in the microgrid local to the first DG. The method also comprises, based on the obtained measurements, determining a first primary control mode of the first DG. The method also comprises instructing a primary control of the first DG that the first DG should be in said first control mode. The method also comprises sending information about that the first DG is in the first control mode, to at least a second DG in the microgrid. The method also comprises receiving information about in which control mode each of said at least a second DG is from each of said at least a second DG, respectively. The method also comprises forwarding said received information to a distributed secondary control of the first DG.

According to another aspect of the present invention, there is provided a method performed in a first DG in an electrical microgrid. The method comprises obtaining information about in which control mode each of a plurality of DGs in the microgrid are. The method also comprises applying at least one secondary control function based on the obtained information. The method also comprises, as a result of the applying of the secondary control function, determining that the control mode of the first DG should be changed from a first control mode to a second control mode. The method also comprises sending instruction for changing the control mode of the first DG from the first control mode to the second control mode.

According to another aspect of the present invention, there is provided a computer program product comprising computer-executable components for causing a control mode selector of a first DG to perform an embodiment of a method of the present disclosure when the computer-executable components are run on processor circuitry associated with the control mode selector. According to another aspect of the present invention, there is provided a control mode selector for a first DG in an electrical microgrid. The control mode selector comprises processor circuitry, and a storage unit storing instructions executable by said processor circuitry whereby said control mode selector is operative to obtain measurements of at least one parameter in the microgrid local to the first DG. The control mode selector is also operative to, based on the obtained measurements, determine a first primary control mode of the first DG (l). The control mode selector is also operative to instruct a primary control of the first DG that the first DG should be in said first control mode. The control mode selector is also operative to send information about that the first DG is in the first control mode, to at least a second DG in the microgrid. The control mode selector is also operative to receive information about in which control mode each of said at least a second DG is from each of said at least a second DG, respectively. The control mode selector is also operative to forward said received information to a distributed secondary control of the first DG.

According to another aspect of the present invention, there is provided a control arrangement for a DG in an electrical microgrid. The control arrangement comprises a primary control, a distributed secondary control, and an embodiment of the control mode selector of the present disclosure.

According to another aspect of the present invention, there is provided a DG for an electrical microgrid. The DG comprises an electricity generator, and an embodiment of the control arrangement of the present disclosure.

According to another aspect of the present invention, there is provided an electrical microgrid comprising a plurality of DGs of the present disclosure.

According to another aspect of the present invention, there is provided a control system for an electrical microgrid. The control system comprises an embodiment of the control arrangement of the present disclosure in each of a plurality of DGs comprised in the microgrid. According to another aspect of the present invention, there is provided a computer program comprising computer program code which is able to, when run on processor circuitry of a control mode selector in a first DG in an electrical microgrid, cause the control mode selector to obtain measurements of at least one parameter in the microgrid which is local to the first DG. The code is also able to cause the control mode selector to, based on the obtained measurements, determine a first primary control mode of the first DG. The code is also able to cause the control mode selector to instruct a primary control of the first DG that the first DG should be in said first control mode. The code is also able to cause the control mode selector to send information about that the first DG is in the first control mode, to at least a second DG in the microgrid. The code is also able to cause the control mode selector to receive information about in which control mode each of said at least a second DG is from each of said at least a second DG, respectively. The code is also able to cause the control mode selector to forward said received information to a distributed secondary control of the first DG.

According to another aspect of the present invention, there is provided a computer program product comprising an embodiment of a computer program of the present disclosure and a computer readable means on which the computer program is stored.

Since the DG comprising a distributed secondary control, it is an advantage that the DG in accordance with the present invention sends information about its control mode to the other DGs in the microgrid, and

correspondingly receives information about the respective control modes of the other DGs from said other DGs in the microgrid. In this way, all the distributed secondary controls of the DGs of the microgrid are informed about the respective currently used control modes of the DGs, without the need for a central secondary control. Each of the distributed secondary controls may receive the same input of system-wide information/data e.g. from different measurement units or from a central system data unit of the microgrid. Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the element, apparatus, component, means, step, etc." are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated. The use of "first", "second" etc. for different features/components of the present disclosure are only intended to distinguish the features/components from other similar features/components and not to impart any order or hierarchy to the features/components.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will be described, by way of example, with reference to the accompanying drawings, in which: Fig 1 is a schematic block diagram of an embodiment of a DG in accordance with the present invention.

Fig 2 is a schematic functional block diagram of an embodiment of a distributed secondary control in accordance with the present invention.

Fig 3 is schematic diagram illustrating triggers for changing between different control modes of a DG, in accordance with the present invention.

Fig 4 is a schematic functional block diagram of an embodiment of a control mode selector in accordance with the present invention.

Fig 5 is a schematic functional block diagram of an embodiment of a distributed secondary control, distributed over a plurality of DGs, in accordance with the present invention.

Fig 6 is a schematic functional block diagram of an embodiment of control mode selectors in a control system of a in a plurality of DGs, in accordance with the present invention. Fig 7 is a schematic illustration of an embodiment of a computer program product in accordance with the present invention.

Fig 8 is a schematic flow chart of an embodiment of a method of the present invention. Fig 9 is a schematic flow chart of an embodiment of another method of the present invention.

DETAILED DESCRIPTION

Embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments are shown.

However, other embodiments in many different forms are possible within the scope of the present disclosure. Rather, the following embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Like numbers refer to like elements throughout the description. Embodiments of the invention relates to a control mode selector. Each Distributed Generator (DG) in a microgrid has a control structure with a primary control, a distributed secondary control and a control mode selector function. Each DG control mode selector chooses control mode based on local measurements, broadcasts its own control mode and receives all the other DGs' control modes. Based on the received control modes of the other DGs, the secondary control can override and change the primary control mode of the DG at the control mode selector. Then, the control mode selector instructs the primary control.

The primary control (also called primary controller herein) is dedicated for controlling a certain DG and is typically locally located in said DG. It is arranged to set/change the control mode, e.g. voltage control, power control or droop control, within a short time frame based on local measurements in the microgrid, e.g. of parameters such as voltage and power flow, and on predetermined reference values or limits for the measured parameters. The secondary control (also called secondary controller herein), on the other hand, controls the DG on a more system-wide (i.e. microgrid-wide) scale and is generally slower than the primary control. Typically, the secondary control will receive system data, e.g. measurements of parameters such as voltage, frequency power flow etc. from different parts of the microgrid, as well as other information about the condition of the microgrid such as whether the microgrid is islanded or has a too small power exchange with the macrogrid for the macrogrid to properly control e.g. the frequency of the microgrid. Typically, the secondary control is centralised and thus obtains

measurements and other system-wide information based on which it decides which DG(s) should change their control mode and instructs the respective primary controls of those DGs accordingly. However, in accordance with the present invention, the secondary control of the microgrid is distributed, i.e. a part of the secondary control is assigned to, and typically located in/co- located with, each of the DGs in the microgrid. Since the secondary control thus comprises a plurality of separate parts, the DG comprising a part of the secondary control (herein also called a distributed secondary controller), the DG sends information about its control mode to the other DGs in the microgrid, and correspondingly receives information about the respective control modes of the other DGs from said other DGs in the microgrid. In this way, all the distributed secondary controls of the DGs of the microgrid are informed about the respective currently used control modes of the DGs, without the need for a central secondary control. Each of the distributed secondary controls may receive the same input of system-wide

information/data e.g. from different measurement units or from a central system data unit of the microgrid.

Figure 1 is a schematic block diagram of an embodiment of a DG 1 in accordance with the present invention. The DG 1 comprises an electricity generator 6 e.g. a wind turbine, solar panel, flywheel or the like, and a control arrangement 2 for controlling the power inputted into the microgrid from the electrical generator 6, typically via a converter. The control arrangement 2 comprises a primary control 4 as well as a distributed secondary control 5. In accordance with the present invention, the control arrangement also comprises a control mode selector 3. The control mode selector 3 may be a separate part/unit of the control arrangement 2 or it may be a function run in the control arrangement e.g. integrated in the primary control 4 and/or the distributed secondary control 5. Also, the primary control 4 and the distributed secondary control 5 may be separate units within the control arrangement 2, or they may be integrated with each other, e.g. be manifested by the same processor circuitry running appropriate software. The figure also schematically shows some functionality of the control arrangement 2. The distributed secondary control 5 sets, determines or calculates reference values for the primary control 4, e.g. for voltage at the DG 1 and/or power output of the DG. Measurement results are provided to the control mode selector 3, and/or to the primary control (local measurements) and the distributed secondary control 5 (system measurements) as discussed above. In accordance with the present invention, and as shown by arrows in figure 1, the DG e.g. by means of the control mode selector 3 sends (e.g. broadcasts) information about in which control mode the DG currently is to other DG(s) in the microgrid, and receives information from said other DGs about in which control mode each of them currently is. The information about in which control mode the DG 1 is as well as in which control mode each of the other DGs are, is inputted to the distributed secondary control 5. The distributed secondary control 5 may then determine whether the control mode of the DG 1 is proper or should be overridden based on the information about the control modes of the DGs and on other system information

(measurements in relation to references, islanding etc.). If the distributed secondary control 5 determines to override the control mode set by the primary control 4, it instructs the primary control to change the control mode, e.g. via the control mode selector 3.

Figure 2 is a schematic functional block diagram of an embodiment of a distributed secondary control 5 in accordance with the present invention. As illustrated in the figure, the distributed secondary control 5 may consider any of a plurality of different secondary control functions, such as stability and load sharing, power balance, and voltage profile. For instance, the DG 1 may be used for improving the power balance in the microgrid when needed. In that case, if the secondary control 5 realises, typically based on power measurements in the microgrid as compared with reference values, that there is a problem with the power balance in the microgrid, the secondary control may decide that the DG 1 should be in power control mode, especially if the information from the other DGs in the microgrid indicate that too few other DGs are in power control mode. If the DG 1 is not already in power control mode, the distributed secondary control 5 thus decides to override the control mode (e.g. droop control, frequency control or voltage control) currently used by the DG 1, as set by the primary control, to force the DG 1 into power control mode. Similarly, if the distributed secondary control 5 determines that there is a problem with stability and load sharing, it may force the DG into droop control, or if it determines that there is a problem with the voltage profile it may force the DG into voltage control. Additionally, if the

distributed secondary control 5 e.g. realises that the microgrid has been islanded, it may force at least some of the DGs in the microgrid, e.g. the DG 1, into frequency control since the frequency is no longer controlled by the macrogrid.

Figure 3 illustrates how a DG may change between different control modes and examples are given to the reasons for changing from one control mode to another control mode by the primary control 4 based on local measurements. MPPT stands for maximum power point tracking.

Figure 4 is a schematic functional block diagram of an embodiment of a control mode selector 3 in accordance with the present invention. The control mode selector receives local measurements of voltage and frequency which are checked for whether they are within their predetermined limits. Other received information may include system status such as whether the microgrid is islanded and/or whether the distributed secondary control has decided to override the control mode. The control mode selector 3 is a part of the control arrangement 2 which may take control mode decisions based on local measurements and possibly other system information. It may thus be separate from the distributed secondary control 5 which generally works slower. The secondary control 5 may also get this information and compute something based on system-wide information on a more general level to decide the control mode of the DG 1 more slowly than the control mode selector 3 and pass override instructions via the control mode selector 3. Typically, the control mode selector determines to change the primary control mode based on local measurement as shown in figures 3 and 4. The slow acting secondary control 5 may override the control mode selector decisions. The primary control 4, in this embodiment of the DG 1, follows the instruction from control mode selector 3 to steer the converter via which power from the electricity generator 6 is inputted into microgrid. Logic in the control mode selector 3 is used to determine the control mode (as also in figure 3) for the DG and the primary control 4 is instructed to change the (primary) control mode. The control mode may then be changed (overridden) by the distributed secondary control, as discussed herein. Figure 5 is a schematic functional block diagram of an embodiment of control mode selectors 3 in a control system 7 in a plurality of DGs 1, in accordance with the present invention. In the figure, six DGs 1 (DG la, DG lb, DG lc, DG id, DG le and DG if) are schematically indicated, each comprising a corresponding control mode selector 3 (3a, 3b, 3c, 3d, 3e and 31). Each DG 1 comprises a primary control 4, and as illustrated to the left in the figure, the primary control 4 may switch its respective DG 1 between the control modes droop control, power control and voltage control. These primary control modes are corresponded by secondary control functions in the distributed secondary control 5 in each DGi, i.e. the secondary control functions stability and load sharing, power balance and voltage profile illustrated to the right in the figure. It is schematically indicated in the figure in which control mode each of the DGs la-f currently in, and arrows indicate that each of the DGs can switch between the three different control modes, either based on primary control and local measurements or du to override by the distributed secondary control 5. Thus, DG la is currently in droop control, DG lb is in power control, DG lc is also in power control, DG id is in voltage control, DG le is in droop control and DG if is also in droop control. As mentioned herein, the primary control 4 switches control mode based on local

measurements, but this control mode made be changed by the secondary control 5 overriding the control mode selection by the primary control. Each DG 1 may be associated with one or more of the secondary control functions, such that if e.g. the DG la is associated with the voltage profile function, then the distributed secondary control 5 of the DG la will override (if needed) the primary control mode if it determines that there is a problem with the voltage profile in the microgrid. Thus, the distributed secondary control 5 may override the currently used control mode (droop control) and instruct the primary control 4 to change to voltage control. In some embodiments, there may be a predetermined hierarchy between the different DGs of the microgrid in case of e.g. a problem with the voltage balance in the microgrid, such that first e.g. the distributed secondary control 5 of DG la overrides the primary control mode to change the control mode of DG la to voltage control. If the voltage profile is still not kept within its predetermined limits, then e.g. the distributed secondary control 5 of DG lb overrides the primary control mode to change the control mode of DG lb to voltage control etc. In accordance with the present invention, each DG is informed about the currently used control modes of the other DGs in the microgrid. Figure 6 illustrates an embodiment of a control arrangement 2 in a DG 1. The control arrangement 2 comprises a control mode selector 3, either as a discrete part thereof or integrated with other parts of the control

arrangement 2. The control mode selector 3 comprises processor circuitry 61 e.g. a central processing unit (CPU). The processor circuitry 61 may comprise one or a plurality of processing units in the form of microprocessor(s).

However, other suitable devices with computing capabilities could be comprised in the processor circuitry 61, e.g. an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or a complex programmable logic device (CPLD). The processor circuitry 61 is configured to run one or several computer program(s) or software (SW) 71 (see also figure 7) stored in a data storage 62 of one or several storage unit(s) e.g. a memory. The storage unit is regarded as a computer readable means 72 (see figure 7) as discussed herein and may e.g. be in the form of a Random Access Memory (RAM), a Flash memory or other solid state memory, or a hard disk, or be a combination thereof. The processor circuitry 61 may also be configured to store data in the storage 62, as needed. The control mode selector may also comprise a communication interface 63, e.g. for sending and receiving information to/from other DGs in the microgrid. The communication interface may, if needed, also be used for communicating with other parts of the control arrangement 2 (especially if discrete parts) and/or as a control interface sending control signals for steering the converter controlling the power input from the electricity generator 6. If the control mode selector 3 is integrated with other parts of the control arrangement 2, e.g. the primary control 4 and/or the distributed secondary control 5, the processor circuitry, the data storage 62 and/or the

communication interface 63 may be shared with these other part(s). Thus, the same processor circuitry 61, data storage 62 and communication interface 63 may be regarded as comprised also in e.g. the distributed secondary control 5 of the DG 1.

Figure 7 illustrates a computer program product 70. The computer program product 70 comprises a computer readable medium 72 comprising a computer program 71 in the form of computer-executable components 71. The computer program/computer-executable components 71 may be configured to cause a device, e.g. the control mode selector 3 and/or the distributed secondary control 5 as discussed herein, to perform an

embodiment of a method of the present disclosure. The computer

program/computer-executable components may be run on the processor circuitry 61 of the device for causing the device to perform the method. The computer program product 70 may e.g. be comprised in a storage unit or memory 62 comprised in the device and associated with the processor circuitry 61. Alternatively, the computer program product 70 may be, or be part of, a separate, e.g. mobile, storage means, such as a computer readable disc, e.g. CD or DVD or hard disc/drive, or a solid state storage medium, e.g. a RAM or Flash memory. Figure 8 is a schematic flow chart of an embodiment of a method of the present invention. The method is performed in a first DG 1, e.g. by the control mode selector 3 comprised therein. Measurements of at least one parameter, e.g. a voltage or frequency, in the microgrid, which measurement is local to the first DG 1, are obtained Si, e.g. received from the primary control 4 of the DG 1. Based on the obtained Si measurements, a first primary control mode of the first DG 1 is determined S2. Then, the primary control 4 of the first DG 1 is instructed S3 that the first DG should be in said first control mode.

Information about that the first DG 1 is in the first control mode is sent S4 to at least a second DG 1 in the microgrid, typically to all other DGs in the same microgrid as the first DG. The DG may periodically or continually send the information about its control mode, or the DG may send the information only when the control mode is changed. Correspondingly, the DG receives S5 information about in which control mode each of said at least a second DG 1 is from each of said at least a second DG, respectively. Typically, all DGs in a microgrid reports its control mode to the other DGs in accordance with the present invention. Then, the DG forwards S6 said received S5 information to the distributed secondary control 5 of the first DG 1. Optionally, the first DG 1 also receives S7 instructions from the distributed secondary control 5 that the first DG 1 should be in a second control mode, based on said forwarded S6 information, i.e. the control mode is overridden by the distributed secondary control 5 as discussed herein. Then, the fist DG instructs S8 the primary control 4 to change the control mode of the first DG 1 from the first control mode to the second control mode. In some embodiments, the received S7 instructions are based on at least one secondary control function associated with the first DG 1 evaluated by the secondary control 5. In some embodiments, the at least one secondary control function is any one of voltage profile, power balance and/or load sharing. In some embodiments, the first DG 1 receives a deactivation command (e.g. automatically manually inputted by an operator), instructing the first DG 1 to no longer allow changing of the control mode based on instructions from the distributed secondary control 5. The DG is then opted out of the possibility of overriding the primary control mode in the way described herein in accordance with some other embodiments of the present invention.

In some embodiments, the sending S4 information comprises broadcasting the information about that the first DG 1 is in the first control mode to the other DG(s) 1 in the microgrid including the second DG.

In some embodiments, the at least one locally measured parameter comprises at least one of voltage, power and frequency.

Figure 9 is a schematic flow chart of an embodiment of another method of the present invention. The method is performed in a first DG 1, e.g. by the distributed secondary control 5 therein. The first DG obtains S11 information about in which control mode each of a plurality of DGs 1 in the microgrid currently are. Then, the first DG applies S12 at least one secondary control function based on the obtained S11 information, i.e. the obtained mode information is used as (part of) the ingoing data when applying the secondary control function. As a result of the applying S12 of the secondary control function, the first DG 1 determines S13 that the control mode of the first DG should be changed from a first control mode to a second control mode. Then, the first DG sends (e.g. forwards) S14 instructions (e.g. to the primary control 4) for changing the control mode of the first DG from the first control mode to the second control mode.

In some embodiments, the first DG 1 has been pre-associated with the at least one secondary control function, e.g. the voltage profile function as

exemplified above in relation to figure 5. In some embodiments, the at least one secondary control function is any one of voltage profile, power balance and/or load sharing.

In some embodiments of the present invention, the first and second control modes are any two different control modes chosen from the group consisting of power control, voltage control, frequency control and droop control. Below follow some other aspects of the present invention.

According to an aspect of the present invention, there is provided a distributed secondary control 5 for a first DG in an electrical microgrid. The distributed secondary control comprises processor circuitry 61, and a storage unit 62 storing instructions 71 executable by said processor circuitry 61 whereby said distributed secondary control 5 is operative to obtain S11 information about in which control mode each of a plurality of DGs 1 in the microgrid are. The distributed secondary control 5 is also operative to apply S12 at least one secondary control function based on the obtained S11 information. The distributed secondary control 5 is also operative to, as a result of the applying S12 of the secondary control function, determine S13 that the control mode of the first DG should be changed from a first control mode to a second control mode. The distributed secondary control 5 is also operative to send S14 instruction for changing the control mode of the first DG from the first control mode to the second control mode.

According to another aspect of the present invention, there is provided a computer program product 70 comprising computer-executable components 71 for causing a distributed secondary control 5 of a first DG 1 to perform an embodiment of a method of the present disclosure when the computer- executable components are run on processor circuitry 61 associated with the distributed secondary control 5.

According to another aspect of the present invention, there is provided a computer program 71 comprising computer program code which is able to, when run on processor circuitry 61 of a distributed secondary control 5 in a first DG 1 in an electrical microgrid, cause the distributed secondary control 5 to obtain S11 information about in which control mode each of a plurality of DGs 1 in the microgrid are. The code is also able to cause the distributed secondary control 5 to apply S12 at least one secondary control function based on the obtained S11 information. The code is also able to cause the distributed secondary control 5 to, as a result of the applying S12 of the secondary control function, determine S13 that the control mode of the first DG should be changed from a first control mode to a second control mode. The code is also able to cause the distributed secondary control 5 to send S14 instruction for changing the control mode of the first DG from the first control mode to the second control mode.

According to another aspect of the present invention, there is provided a control mode selector 3 for a first DG 1 in an electrical microgrid. The control mode selector comprises means (e.g. the processor circuitry 61, possibly in cooperation with the communication interface 63) for obtaining Si measurements of at least one parameter in the microgrid local to the first DG 1. The control mode selector also comprises means (e.g. the processor circuitry 61) for, based on the obtained Si measurements, determining S2 a first primary control mode of the first DG 1. The control mode selector also comprises means (e.g. the processor circuitry 61, possibly in cooperation with the communication interface 63) for instructing S3 a primary control 4 of the first DG 1 that the first DG should be in said first control mode. The control mode selector also comprises means (e.g. the processor circuitry 61, typically in cooperation with the communication interface 63) for sending S4 information about that the first DG 1 is in the first control mode, to at least a second DG 1 in the microgrid. The control mode selector also comprises means (e.g. the processor circuitry 61, typically in cooperation with the communication interface 63) for receiving S5 information about in which control mode each of said at least a second DG 1 is from each of said at least a second DG, respectively. The control mode selector also comprises means (e.g. the processor circuitry 61, possibly in cooperation with the

communication interface 63) for forwarding S6 said received S5 information to a distributed secondary control 5 of the first DG 1.

According to another aspect of the present invention, there is provided a distributed secondary control 5 for a first DG in an electrical microgrid. The distributed secondary control comprises means (e.g. the processor circuitry 61, possibly in cooperation with the communication interface 63) for l8 obtaining S11 information about in which control mode each of a plurality of DGs 1 in the microgrid are. The distributed secondary control also comprises means (e.g. the processor circuitry 61) for applying S12 at least one secondary control function based on the obtained S11 information. The distributed secondary control also comprises means (e.g. the processor circuitry 61) for, as a result of the applying S12 of the secondary control function, determining S13 that the control mode of the first DG should be changed from a first control mode to a second control mode. The distributed secondary control also comprises means (e.g. the processor circuitry 61, possibly in cooperation with the communication interface 63) for sending S14 instructions for changing the control mode of the first DG from the first control mode to the second control mode.

The present disclosure has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the present disclosure, as defined by the appended claims.

Claims

1. A method performed in a first distributed generator, DG, (1) in an electrical microgrid, the method comprising: obtaining (Si) measurements of at least one parameter in the microgrid local to the first DG (1); based on the obtained (Si) measurements, determining (S2) a first primary control mode of the first DG (1); instructing (S3) a primary control (4) of the first DG (1) that the first DG should be in said first control mode; sending (S4) information about that the first DG (1) is in the first control mode, to at least a second DG (1) in the microgrid; receiving (S5) information about in which control mode each of said at least a second DG (1) is from each of said at least a second DG, respectively; and forwarding (S6) said received (S5) information to a distributed secondary control (5) of the first DG (1).

2. The method of claim 1, further comprising: receiving (S7) instructions from the distributed secondary control (5) that the first DG (1) should be in a second control mode, based on said forwarded (S6) information; and instructing (S8) the primary control (4) to change the control mode of the first DG (1) from the first control mode to the second control mode.

3. The method of claim 2, wherein the received (S7) instructions are based on at least one secondary control function associated with the first DG (1) evaluated by the secondary control (5).

4. The method of claim 3, wherein the at least one secondary control function is any one of voltage profile, power balance and/or load sharing.

5. The method of any preceding claim 2-4, further comprising receiving a deactivation command, instructing the first DG (1) to no longer allow changing of the control mode based on instructions from the distributed secondary control (5).

6. The method of any preceding claim, wherein the method is performed by a control mode selector (3) in a control arrangement (2) of the first DG (1).

7. The method of any preceding claim, wherein the sending (S4) information comprises broadcasting the information about that the first DG (1) is in the first control mode to the other DG(s) (1) in the microgrid including the second DG (1).

8. The method of any preceding claim, wherein the at least one locally measured parameter comprises at least one of voltage, power and frequency.

9. A method performed in a first distributed generator, DG, (1) in an electrical microgrid, the method comprising: obtaining (S11) information about in which control mode each of a plurality of DGs (1) in the microgrid are; applying (S12) at least one secondary control function based on the obtained (S11) information; as a result of the applying (S12) of the secondary control function,

determining (S13) that the control mode of the first DG should be changed from a first control mode to a second control mode; and sending (S14) instructions for changing the control mode of the first DG from the first control mode to the second control mode.

10. The method of claim 9, wherein the method is performed by a

distributed secondary control (5) in the first DG (1).

11. The method of claim 9 or 10, wherein the first DG (1) has been pre- associated with the at least one secondary control function.

12. The method of any one of claims 9-11, wherein the at least one secondary control function is any one of voltage profile, power balance and/or load sharing.

13. The method of any one of claims 9-12, wherein the first and second control modes are any two different control modes chosen from the group consisting of power control, voltage control, frequency control and droop control.

14. A computer program product (70) comprising computer-executable components (71) for causing a control mode selector (3) of a first DG (1) to perform the method of any one of claims 1-8 when the computer-executable components are run on processor circuitry (61) associated with the control mode selector.

15. A control mode selector (3) for a first DG (1) in an electrical microgrid, the control mode selector comprising: processor circuitry (61); and a storage unit (62) storing instructions (71) executable by said processor circuitry (61) whereby said control mode selector (3) is operative to: obtain measurements of at least one parameter in the microgrid local to the first DG (1); based on the obtained measurements, determine a first primary control mode of the first DG (1); instruct a primary control (4) of the first DG (1) that the first DG should be in said first control mode; send information about that the first DG is in the first control mode, to at least a second DG (1) in the microgrid; receive information about in which control mode each of said at least a second DG (1) is from each of said at least a second DG, respectively; and forward said received information to a distributed secondary control (5) of the first DG (1).

16. A control arrangement (2) for a DG (1) in an electrical microgrid, comprising: a primary control (4); a distributed secondary control (5); and the control mode selector (3) of claim 15.

17. A DG (1) for an electrical microgrid, comprising: an electricity generator (6); and the control arrangement (2) of claim 16.

18. An electrical microgrid comprising a plurality of DGs (1) according to claim 17.

19. A control system for an electrical microgrid, comprising a control arrangement (2) according to claim 16 in each of a plurality of DGs (1) in the microgrid.

20. A computer program (71) comprising computer program code which is able to, when run on processor circuitry (61) of a control mode selector (3) in a first DG (1) in an electrical microgrid, cause the control mode selector (3) to: obtain (Si) measurements of at least one parameter in the microgrid local to the first DG (1); based on the obtained (Si) measurements, determine (S2) a first primary control mode of the first DG (1); instruct (S3) a primary control (4) of the first DG (1) that the first DG should be in said first control mode; send (S4) information about that the first DG (1) is in the first control mode, to at least a second DG (1) in the microgrid; receive (S5) information about in which control mode each of said at least a second DG (1) is from each of said at least a second DG, respectively; and forward (S6) said received (S5) information to a distributed secondary control (5) of the first DG (1).

21. A computer program product (70) comprising a computer program (71) according to claim 20 and a computer readable means (72) on which the computer program is stored.