Method of controlling an electric power distribution system including a microgrid

Abstract

A method (300) for controlling a power distribution network (1) and a microgrid controller (8) suitable for the method. The power distribution network (1) comprises assets (3‑7) in a first part (1a) and a second part (1b), wherein the parts (1a, 1b) are selectively connected to each other at a connection point (PCC) in an interconnected state. The method comprises monitoring (301, 306) and controlling (310) the assets (3‑7) of the power distribution network (1). In a first control mode (310A), the first part (1a) is controlled by a power distribution network controller (9) and the second part is controlled by a microgrid controller (8). In particular, the method comprises selecting (303) between controlling (310) the distribution network (1) in an interconnected state according to a first control mode (310A) and controlling (310) the distribution network (1) in an interconnected state according to a second control mode (310B), in which the assets (3‑7) of both the first part (1a) and the second part (1b) are controlled by a distribution network controller (9).

Description

Technical Field

[0001] The present invention relates to a power system, and more particularly to control of a power distribution system including a microgrid. According to one aspect of the present invention, a microgrid controller is provided. Background Art

[0002] A typical power system includes a generator at a power plant that produces electrical energy. The power system also includes a transmission system with transmission lines at a high voltage, such as above 140 kV, for transmitting the generated electricity to the distribution side of the power system for power consumption. The transmission system will generally include high voltage lines, and the power is converted down for use in a medium voltage (above 1 kV and below 100 kV, for example, between 15 kV and 45 kV) power distribution system. Therefore, the distribution system can start with a transformer at a substation and include distribution lines in a grid or network for transmitting power at medium and low voltages to loads for consumption.

[0003] Power distribution systems including microgrids

[0004] In addition to loads, the distribution system may also include other assets, such as distributed generators, energy storage devices, and voltage source converters. Therefore, the distribution system may include power production facilities, while providing a net consumption of electricity. The distribution system network may also include parts that both produce and consume electricity and can operate separately, i.e., microgrids. Therefore, the distribution network may include a first part connected to the transmission system and a second part that can provide a net production of electrical energy, such as a microgrid, which is arranged downstream of the first part in the direction from the transmission system and the second part can be disconnected from the first part and operated separately by a distributed generator arranged in the second part (i.e., in the microgrid), but the second part is (usually) not connected to the transmission grid. The second part or microgrid can be connected to the first part or disconnected from the first part by a circuit breaker arranged at the so-called PCC (point of common coupling). Therefore, the microgrid can be connected to the transmission grid via the first part of the distribution network.

[0005] Controlling power distribution systems and microgrids

[0006] In order to control the power in the distribution grid, the distribution grid may be provided with a network control system or a distribution network controller, such as a distribution network controller using a distribution management system (DMS). The DMS includes software for analyzing, measuring and controlling the network, and the DMS generally provides the functions of monitoring the distribution network and controlling the distribution network. The DMS appropriately includes Volt-VAR control (VVC), which monitors and controls the voltage level and reactive power in the distribution network, for example by controlling tap changers and series capacitors. The DMS also appropriately includes a load shedding application (LSA) to disconnect the load from the distribution system in the event of an undesirable electrical condition in the distribution network. In addition, the DMS can provide power flow control and fault management. The DMS can provide automated network control and provide network data to operators through a GUI (graphical user interface).

[0007] The distribution network controller can use the DMS to monitor the distribution network between the transformer connecting the distribution network to the transmission network and the PCC connecting the distribution network to the microgrid, that is, monitor the first part of the distribution network. Based on the monitoring of the first part of the distribution network, the assets of the first part of the distribution network, such as energy storage devices, controllable loads, tap-changing transformers, distributed generators, and controlled series capacitors, are controlled.

[0008] The microgrid is typically provided with a microgrid controller, which is a central controller or a controller distributed between the assets of the microgrid. The microgrid controller typically monitors a second portion of the distribution network that is downstream from the PCC, such as monitoring the voltage level and power flow at the PCC, and monitors electrical entities at multiple locations within the microgrid or the second portion, such as the voltage and current in the transmission lines or cables, at the generators, at the loads, and at the transformers within the microgrid. The microgrid controller can provide voltage level control, reactive power control, load shedding, power flow control, and active power balancing within the microgrid network when the microgrid is connected to the grid and when the microgrid is disconnected from the rest of the distribution network (i.e., when the microgrid is isolated).

[0009] Thus, a typical distribution network including a microgrid may typically include a distribution network controller configured to monitor and control assets in a first portion of the distribution network located upstream from a PCC, while a microgrid controller is configured to monitor a second portion of the distribution network located downstream from the PCC (i.e., the microgrid). The microgrid controller may be used to control power flow at the PCC (i.e., between the microgrid and the first portion of the distribution network).

[0010] A microgrid typically optimizes its own operation and does not fluctuate with the overall operation of the distribution system. US2017 / 016071 (E1) aims to address the problem of microgrids not interoperating with distribution management systems (DMS), see §0004 and §0005 of E1. The idea in E1 is that microgrids should contribute to “overall power grid optimization” (§0025). E1 shows examples of what should be achieved with microgrids, such as contributing to reactive power in the distribution grid (§0012, §0036), volt / VAR control (§0023, §0032), and “energy and cost optimization” (§0024). To achieve these goals, E1’s microgrid has been adapted to operate in a so-called “VPP mode” (referring to “virtual power plant” in §0030), where the microgrid is used to inject active and reactive power and support voltage and frequency (§0036 in E1).

[0011] One disadvantage of the virtual power plant proposed in E1 is that the control scheme of E1 tends to be complex and operation may become unstable if the microgrid is subjected to sudden topological or electrical changes, which may cause the microgrid to blackout or disconnect. In addition, it is a simplification to view a microgrid as a virtual power plant because a microgrid is typically more complex than a power plant. A microgrid may also include multiple distributed generators, for example including distributed generators with different power outputs from renewable energy plants such as solar photovoltaic plants or wind power plants, and viewing a microgrid as a VPP may result in the microgrid being used in a far less optimized manner than can be provided by conventional control through a dedicated microgrid controller. VPP operation is intended to support the distribution grid by implementing the set points of the microgrid at the PCC, and such operation helps provide optimization functions for the distribution network upstream of the PCC, but may have negative effects on the microgrid. Summary of the invention

[0012] It is an object of the present invention to provide an alternative solution for controlling a microgrid that does not have the disadvantages of the prior art.For the purpose, aspects of the present invention provide a means of extending the control of a power distribution network into a microgrid connected to the power distribution network.

[0013] According to a first aspect, the present invention provides a method for controlling assets in a distribution network, the distribution network comprising a first part and a second part, the first part and the second part comprising assets, such as generators and loads. The first part and the second part of the distribution network are selectively connected to each other in an interconnected state. The distribution network also includes a network controller and a microgrid controller. The method includes monitoring the distribution network (including monitoring electrical entities in the distribution network) and controlling the assets of the distribution network based on the monitoring. The control also includes controlling the assets of the distribution network according to a first control mode in the interconnected state, wherein the assets of the first part are controlled by the distribution network controller and the assets of the second part are controlled by the microgrid controller. .

[0014] In particular, the method of the first aspect includes selecting between controlling the assets of the distribution network according to a first mode in the interconnected state and controlling the assets of the distribution network according to a second control mode in the interconnected state, in which the assets of the first part and the assets of the second part are both controlled by the distribution network controller.

[0015] By means of the second mode, wherein the second portion is controlled by the distribution network controller, this helps to achieve better performance in the control of the distribution network. In the first mode, the control of the second portion by the microgrid controller provides an alternative for controlling the second portion in a grid-connected state. Inappropriate control of the second portion or microgrid can be more easily avoided than in prior art systems.

[0016] In an embodiment of the first aspect, the selecting is performed by the microgrid controller.

[0017] Since the microgrid controller can provide major functions when adding a microgrid to the power distribution network, enabling the microgrid controller to implement mode switching helps facilitate implementation in different power distribution network control systems.

[0018] In an embodiment of the first aspect, the selecting comprises evaluating at least one electrical entity in a second portion of the power distribution network and switching from the second mode to the first mode when any electrical entity violates a threshold bandwidth of the electrical entity.

[0019] In yet another embodiment, the evaluated at least one electrical entity of the second portion comprises at least one of the following:

[0020] - the voltage level at the connection (PCC) between the distribution network and the microgrid,

[0021] - a reactive power flow between a first part of the electricity distribution network and a second part of the electricity distribution network,

[0022] - an active power flow between a first part of the electricity distribution network and a second part of the electricity distribution network,

[0023] - a voltage level at an asset within the second part of the distribution network, and

[0024] - an electric current from an asset in a second part of the electricity distribution network.

[0025] An embodiment of the first aspect comprises

[0026] - selecting a specific control function for the distribution network controller, for example a so-called DMS function (Distribution Management System), and

[0027] - controlling the assets in said first portion according to said control function in said first mode, or

[0028] - controlling assets in the electricity distribution network, ie the first part and the second part, according to the control function in the second mode.

[0029] In this embodiment, the first mode and / or the second mode may also include informing the microgrid controller which specific control function the distribution network controller is currently using. In this way, the microgrid controller may be adapted to facilitate the execution of the selected DMS function when controlling the second portion so that the second portion or microgrid can support the first portion of the distribution network. For example, when informed that the distribution network controller in the second mode provides DMS functions such as voltage control, the second portion may facilitate the DMS function after switching to the first mode by supporting the voltage level at the PCC, thereby still controlling the microgrid based on measurements in the microgrid.

[0030] In an embodiment of the first aspect, a circuit breaker is provided at the PCC and monitoring of the second portion of the power distribution network comprises monitoring a state of the circuit breaker, and the method further comprises switching to a third control mode when the circuit breaker is open, in which the second portion is controlled by the microgrid controller as an islanded microgrid.

[0031] According to a second aspect, the present invention provides a microgrid controller for controlling a portion of a power distribution network, in particular a microgrid. The power distribution network comprises a first portion and a second portion, each of the first portion and the second portion comprising an asset, and wherein the first portion and the second portion are selectively connected to each other in an interconnected state at a connection point (PCC). The power distribution network further comprises a network controller. The microgrid controller comprises:

[0032] - a monitoring function or a monitoring device configured to monitor a second part of the electricity distribution network,

[0033] - a controller configured to control assets in a second part of the distribution network based on monitoring of the second part, and the control is performed according to the first control mode in the interconnected state. In particular, the microgrid controller comprises:

[0034] a mode selector configured to select between controlling the assets of the second portion of the distribution network according to the first mode in the interconnected state and controlling the assets of the second portion of the distribution network according to a second control mode in the interconnected state, in which the assets of the second portion are controlled by the distribution network controller, and

[0035] - a monitoring data communicator configured to communicate the monitoring data in the second control mode to the power distribution network controller.

[0036] Thus, the microgrid controller is configured to select a control mode based on monitoring of the second portion by the monitoring function and to communicate data retrieved during monitoring of the second portion to the distribution network controller in the second control mode.

[0037] In an embodiment of the second aspect, the microgrid controller further comprises an evaluator configured to evaluate at least one electrical entity of a second portion of the power distribution network based on a corresponding threshold bandwidth for each evaluated electrical entity, wherein the mode selector is adapted to switch from the second control mode to the first control mode when the electrical entity violates the threshold bandwidth for the electrical entity.

[0038] In an embodiment of the second aspect, the evaluated at least one electrical entity in the second portion includes at least one of the following:

[0039] - a voltage level at a connection (PCC) between the first part of the electricity distribution network and the second part of the electricity distribution network,

[0040] - a reactive power flow between a first part of the electricity distribution network and a second part of the electricity distribution network,

[0041] - an active power flow between a first part of the electricity distribution network and a second part of the electricity distribution network,

[0042] - a voltage level at an asset in a second part of the distribution network, or

[0043] - Electricity from an asset in a second part of the electricity distribution network.

[0044] In an embodiment of the second aspect, the mode selector is adapted to switch from the first control mode back to the second control mode when the assessed electrical entity has again entered a threshold bandwidth for the electrical entity and preferably stayed within the bandwidth for a predetermined time.

[0045] Thus, the microgrid controller is configured to switch back when the monitored and evaluated electrical entity no longer violates the threshold and preferably has remained within the bandwidth and stabilized for a preset period of time.

[0046] In an embodiment of the second aspect, the monitoring device is adapted to monitor a state of a circuit breaker provided at the PCC for interconnecting the first part and the second part of the power distribution network. In this embodiment, the mode selector is adapted to switch to a third control mode when the circuit breaker is open, and the microgrid controller is configured to control the second part as an islanded microgrid according to the third control mode.

[0047] In an embodiment of the second aspect, the microgrid controller further comprises a control signal communicator configured to communicate control settings from the distribution network controller to assets of a second part of the distribution network, in particular distributed generators, voltage source converters and / or energy storage devices of the second part. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 A power distribution network including a microgrid is shown;

[0049] Figure 2A Figure C shows three control modes;

[0050] Figure 3 An embodiment of a method of controlling a microgrid and a power distribution network is shown;

[0051] Figure 4 Embodiments of a microgrid controller and a network controller are shown. DETAILED DESCRIPTION

[0052] Figure 1A distribution network 1 consisting of two parts is shown, namely a first part 1a, which is connected to the transmission grid via a transformer 10, and a second part 1b, which is a microgrid, which is connected to the first part at a PCC (point of common coupling). The distribution network 1 includes a plurality of assets 3-7, such as loads 3, voltage source converters 4, distributed generators 5, series capacitors 6 and energy storage devices 7. The energy storage device 7 and the distributed generators 5 can be connected to the distribution network grid 1 voltage source converter 4. The assets 3-7 are arranged in the first part 1a and in the microgrid 1b. The first part 1a includes a distribution network controller 9, which is operably connected to the assets 3-7 of the first part 1a and is arranged to monitor the first part 1a of the distribution network 1, including monitoring the PCC. The microgrid 1b includes a microgrid controller 8, which is arranged to monitor the microgrid 1b (including monitoring the PCC) and is operably connected to the assets 3-7 of the microgrid to control these assets 3-7 (such as connecting and disconnecting assets) or adjust the settings of the control of the distributed generators 5. The power distribution network controller 9 and the microgrid controller 8 are communicatively connected to each other.

[0053] Controlling the first part 1a of the distribution network by a distribution network controller 9 monitoring the first part 1a of the distribution network starting from the PCC and located upstream is similar to a conventional prior art system. Controlling the second part 1b of the distribution network by a microgrid controller monitoring the second part 1b of the distribution network starting from the PCC and located downstream or a microgrid is similar to a conventional prior art system. Therefore, an embodiment of the present invention can provide control of a microgrid (second part 1b) in a grid-connected state in a manner similar to an existing control system, in which the second part 1b is connected to the first part 1a.

[0054] However, according to an embodiment of the present invention, the distribution network controller 9 is configured to monitor and control the assets 3-7 of the second part 1b (i.e., the microgrid) of the distribution network 1 in addition to monitoring and controlling the assets 3-7 of the first part 1a. In an embodiment of the present invention, such monitoring and control of the assets 3-7 in the second part 1b can be performed by the distribution network controller 9 via the microgrid controller 8. Therefore, an embodiment of the present invention provides an additional mode for controlling the assets of the microgrid (i.e., the second part 1b) in a grid-connected state. In addition, an embodiment provides a method for switching between these control modes so that the two control modes of the grid-connected state can be selectively used.

[0055] Figure 2A-C illustrates the first operation mode, the second operation mode and the third operation mode of the microgrid controller. In the first operation mode and the second operation mode, the first part 1a is connected to the second part 1b (i.e., the microgrid) at the connection point (i.e., PCC), and the first mode and the second mode constitute the optional operation modes of the microgrid controller 8 in this grid-connected state.

[0056] In the first operating mode, the microgrid controller 8 monitors the microgrid (including monitoring the PCC) and controls the assets 3-7 of the microgrid, such as Figure 2A The monitoring and control is shown in dashed lines. The distribution network controller 9 monitors and controls the first part 1a of the distribution network 1, including monitoring the PCC. The microgrid controller 8 is configured to control the distribution network 1 downstream of the PCC (i.e., the second part 1b), and the distribution network controller 9 is configured to control the distribution network upstream of the PCC (i.e., the first part 1a). Both power flow and voltage are monitored at the PCC by both the distribution network controller 9 and the microgrid controller 8. In addition, the connection status at the PCC (e.g., the status of the interconnection circuit breaker (not shown)) is also monitored by controllers 8 and 9.

[0057] exist Figure 2C In the third operation mode shown, the first part 1a and the second part 1b of the distribution network 1 are disconnected from each other at the PCC, and the microgrid controller 8 is arranged to control the distribution network downstream of the PCC (i.e., the microgrid, which is also referred to as the second part 1b), and the distribution network controller 9 is arranged to control the distribution network upstream of the PCC (i.e., the first part 1a). In this case, there is no power flow at the PCC and only the voltage is monitored on both sides of the PCC.

[0058] Figure 2B A second operating mode is illustrated, in which the microgrid controller 8 is arranged to communicate monitoring and control signals between the microgrid 1b (including the assets 3-7 of the microgrid 8) and the distribution network controller 9. The distribution network controller 9 is arranged to monitor the first part 1a and the microgrid 1b (the second part) and also control the assets 3-7 of both the first part 1a and the second part 1b of the distribution network 1. In this second operating mode, the microgrid controller 8 is arranged to monitor and evaluate the electrical entities in the microgrid 1b and switch the control mode when any electrical entity violates the corresponding threshold value for the entity. Therefore, the microgrid controller 8 is configured to provide monitoring functions and regain control of the second part 1b when the electrical entity violates the threshold value, for example for safety or stability purposes or to avoid power loss.

[0059] Figure 3A control method 300 for controlling a distribution network 1, in particular assets 3-7 of the distribution network 1, in an embodiment of the present invention is presented. The method 300 comprises monitoring 306 a first portion 1a of the distribution network 1, monitoring 301 a second portion 1b of the distribution network, and controlling 310 the first portion 1a and the second portion 1b of the distribution network 1. In more detail, the distribution network controller 9 monitors and controls 310A the first portion 1a, and the microgrid controller 8 monitors and controls the second portion 1b, the control 310 being performed in a "first" control mode. These monitoring 301, 306 and controls 310, 310A are similar to conventional controls of a distribution network 1 including or connected to a microgrid (second portion 1b). Therefore, in the first control mode (310A), control of the distribution network 1 is performed by both controllers 8 and 9, each controller 8 or 9 controlling a respective portion 1a or 1b of the distribution network 1.

[0060] The control method 300 further comprises selecting 303 a control mode. In short, the selection 303 of the control mode is based on the monitoring 301 of the second portion 1 b and, in the grid-connected state, the first control mode 310A or the second control mode 310B is selected. In the second control mode 310B, the control 310 of both the first portion 1 a and the second portion 1 b of the distribution network 1 is performed by the distribution network controller 9 based on the monitoring 306 of the first portion 1 a and the monitoring 301 of the second portion 1 b. Thus, the distribution network controller 9 monitors the entire distribution network 1 and controls the assets 3-7 in the entire distribution network 1, i.e. the assets 3-7 downstream of the PCC as well as the assets 3-7 upstream.

[0061] In the island mode, the microgrid (e.g., the second part 1b of the distribution network 1) can also be disconnected and controlled. The control method 300 also includes this island mode or a third control mode 310C. Islanding can be planned or an unexpected event. In order to prepare for unexpected events, the monitoring 301 of the second part 1b includes monitoring 302 of the connection at the PCC, in particular, the state of the circuit breaker set at the PCC for selectively connecting and disconnecting the first part 1a and the second part 1b. If the circuit breaker is disconnected, the method includes selecting the third control mode (i.e., island mode) 310C, wherein the distribution network controller controls the first part 1a and the microgrid controller 8 controls the second part 1b. Planned islanding can include receiving an islanding message from a control system such as a distribution network controller 9 via the microgrid controller 8.

[0062] Figure 3The embodiment of the control method 300 also shows some optional but preferred control measures shown within the dashed lines. Preferably, the selection 302 of the control mode includes evaluating 305 electrical entities, such as those monitored 301 in the second part 1b. The evaluation 305 can include comparing the electrical entities using criteria including a threshold bandwidth, and selecting a first control mode 310A when a violation is detected. Each evaluated electrical entity has its corresponding bandwidth, such as a certain range, a minimum level or a maximum level, and the microgrid controller 8 is configured to select the first control mode 310A when a violation of the allowed bandwidth is detected.

[0063] Some examples of monitored and assessed electrical entities are given below.

[0064] Criteria for mode switching in grid-connected state may include:

[0065] - monitoring the power balance within the microgrid (second part 1b) and switching to a first operation mode 310A of the microgrid when the power balance of the microgrid (1b) violates a first threshold, which is a power balance threshold. The first operation mode 310A may preferably include power balance of the microgrid (1b).

[0066] Criteria for mode switching in grid-connected state may include:

[0067] - Monitoring the voltage level within the microgrid (1 b) and switching to the first operation mode 310A when a second threshold is reached, the second threshold being a voltage level threshold. The first operation mode 310A preferably comprises voltage control in the microgrid 1 b.

[0068] Criteria for mode switching in grid-connected state may include:

[0069] - Monitoring reactive power and switching to the first operation mode 310A when a third threshold is reached, which is a reactive power threshold. The first operation mode 310A preferably comprises reactive power control in the microgrid 1 b.

[0070] Criteria for mode switching in grid-connected state may include:

[0071] -Monitoring the voltage level and reactive power within the microgrid 1b and switching to the first mode 310A when the second threshold and / or the third threshold are reached. The first mode 310A may preferably include VVC (Volt-VAR control) of the microgrid 1b and / or the first portion 1a. The first mode 310A may include Volt-VAR optimization in the microgrid (1b) or the first portion 1a, which includes VCC and, for example, simultaneously keeps system losses or voltage drops to a minimum.

[0072] Criteria for mode switching in grid-connected state may include:

[0073] - Monitoring harmonics in the microgrid 1 b and switching to the first operation mode 310A when a fourth threshold is reached, the fourth threshold being a harmonic threshold. The first operation mode 310a may preferably comprise cancelling harmonics in the microgrid.

[0074] The microgrid controller 8 may also be configured to switch back to the first operating mode when the criteria (eg the first, second, third and fourth criteria) have re-entered and preferably stabilized again into an acceptable bandwidth or have ceased to violate the threshold in question.

[0075] Figure 3 Other suitable control measures of an embodiment of comprises informing 307 the distribution network controller 9 of the selected control mode. The selection 303 of the control mode is performed by the microgrid controller 8 which suitably informs 307 the distribution network controller 9 of the selection.

[0076] The distribution network controller 9 is suitably selected or configured to adopt a control function, preferably a so-called DMS function, in the distribution network 1. The distribution network controller 9 preferably selects 308 a specific control function to be adopted. In addition, the distribution network controller 9 is preferably configured to notify 309 the microgrid controller 8 of the selected control function (e.g. the selected DMS function). The distribution network controller 9 will then adopt the selected DMS function when controlling 310A the first part 1a according to the first mode. The distribution network controller 9 will adopt the selected DMS function when controlling 310B the first part 1a and the second part 1b according to the second mode. In the first mode, the microgrid controller can support 312A the selected DMS function based on the indication of the received (at 309) DMS function. The distribution network controller 9 can notify 309 the microgrid controller 8 of the selected DMS function in both the first mode and the second mode and also in the third mode, so that the microgrid controller 8 is ready to support 312A the DMS function in the first mode 310A.

[0077] The distribution network controller 9 may be configured with direct communication for monitoring and controlling the second part 1b. Figure 3 A preferred embodiment is shown in which the microgrid controller 8 communicates 313B the monitoring (eg, measurement) of the electrical entities in the second portion 1b. In addition, Figure 3A preferred embodiment in which the microgrid controller 8 communicates 314B control signals (e.g., control settings) for the assets 3-7 of the second portion 1b is shown in FIG. Thus, the microgrid controller 8 is configured to communicate 313B measured electrical entities and communicate 314B control settings between the second portion 1b and the distribution network controller 9 when executing the second control mode 310B.

[0078] In another embodiment ( Figure 3 ), the microgrid controller 8 is configured to monitor at least one location in the first part 1a of the distribution network 1, such as an asset 3-7, a wire or a circuit breaker in the distribution network. The distribution network controller 9 can be configured to communicate such monitoring, including communicating one or more measured electrical entities in the distribution network 1. When supporting 312A the DMS function performed by the distribution network controller 9 in the first part 1a, such monitoring can be applicable to the microgrid controller 8 and the support 312A for the DMS function can be based on monitoring electrical entities at a location away from the second part 1b in the first part 1a, for example. Therefore, the distribution network controller 9 and the microgrid controller 8 can be adapted to communicate measurements of electrical entities to each other, wherein the distribution network controller 9 transmits data of electrical entities in the first part 1a to the microgrid controller 8 and the microgrid controller 8 transmits data of electrical entities in the second part 1b to the distribution network controller 9. In addition to the measurements, such an exchange can also include status information of the monitored devices in the respective parts 1a, 1b of the distribution network 1.

[0079] Figure 4 An embodiment of a microgrid controller 8 and a distribution network controller 9 for executing the control method of the present invention is illustrated. Figure 4 It is a simplified diagram of the structure of the controllers 8 and 9 and mainly discloses the control functions for executing the control method, and discloses the microgrid controller 8 and the distribution network controller 9 in cooperation to execute Figure 3 The microgrid controller 8 and the distribution network controller 9 include a combination of hardware and software selected and configured to perform different functions for controlling the distribution network. These different functions are shown as Figure 4 The microgrid controller 8 and the distribution network controller 9 comprise respective communication interfaces 89, 99 for communicating with each other. The communication interfaces for monitoring and controlling the parts 1a, 1b of the distribution network 1 are not shown in FIG. Figure 4 However, such communication may be provided by the same communication interfaces 89, 99, such as Figure 4 The control system is shown by the horizontal arrows in FIG. 1 (which represent inputs and outputs) and is executed by a control system network (e.g., a SCADA system or similar system).

[0080] As main functional blocks, the microgrid controller 8 includes:

[0081] a controller 80 configured to control the second part 1 b of the power distribution network 1 , in particular the microgrid,

[0082] a monitoring function or monitor 81 configured to monitor the second part 1 b of the power distribution network,

[0083] - a mode selector 82 for selecting a control mode for the power distribution network, and

[0084] A communication interface 89 configured to exchange information with the power distribution network controller 9 .

[0085] The controller 80 for the second part is configured in the first control mode and the third control mode (ie, according to Figure 3 The controller 80 preferably comprises a support function 86 configured to support 312A a DMS function in the first mode 310A, the DMS function being employed by the distribution network controller 9. Figure 4 As shown, the communication interface 89 is preferably used to receive a “DMS function indication” from the distribution network controller 9 via the communication interface 99 of the distribution network controller 9. The controller 80 for the second part 1b of the microgrid controller 8 preferably includes a control signal communicator 85, which is configured to communicate 314B control signals (e.g., settings) for the assets 3-7 of the second part 1b during the second control mode 310B. The communicator 85 is configured to transmit control signals received from the distribution network controller 9 to the second part 1b of the distribution network 1 during the second control mode 310B. The controller 80 is configured to receive control signals (e.g., including settings) for the assets 3-7 (e.g., distributed generators 5) of the second part 1b from the distribution network controller 9 through the communication interfaces 89 and 99, as Figure 4 The microgrid controller 8 may also receive measurement and status information of the first part 1a of the distribution network from the distribution network controller 9 via the communication interface 89. The DMS support function 86 may preferably be adapted to provide support 312A for the DMS function based on the measurement and status information received from the distribution network controller 9 in the first control mode 310A.

[0086] The monitoring function 81 comprises a communicator 83 of monitoring data, in particular status and measurement information, from monitoring 301 the second part 1b of the distribution network 1, which is configured to communicate 313B the monitoring data, in particular electrical entities, of the second part 1b to the distribution network controller 9 during the second control mode 310B.

[0087] The monitoring function 81 is preferably further configured to monitor 302 the connections at the PCC, in particular the status of the interconnection breaker at the PCC.In the unexpected islanding of the second part 1b, the microgrid controller 8 is preferably configured to select 304 the third control mode 310C, for example based on the status of the interconnection breaker.

[0088] The mode selector 82 is configured to perform a selection 303 of a control mode based on monitoring 301 of the second portion 1b of the power distribution network 1. The mode selector 82 preferably includes an evaluator 84 configured to evaluate 305 one or more monitored electrical entities in the second portion 1b, the evaluation 305 being performed based on range thresholds, minimum and / or maximum levels, as referred to herein. Figure 3 The microgrid controller 8 is preferably configured to notify 307 the distribution network controller 9 of the mode selection via the communication interface 89, 99, such as Figure 4 shown.

[0089] The mode selector 82 is preferably further configured to select 304 a third control mode 310C (ie, island mode) based on monitoring 302 the PCC state, such as Figure 3 As shown ( Figure 4 ). Therefore, the mode selector 82 may be adapted to select 304 the third control mode 310C when the state of the circuit breaker at the PCC changes to “open”.

[0090] The distribution network controller 9 includes the main functional blocks:

[0091] - a controller 90 configured to control 310 assets 3-7 in the power distribution network 1, in particular

[0092] - controlling the assets 3-7 in the first part 1a in the first mode 310A and the third control mode 310C, and

[0093] - controlling the assets 3-7 in both the first part 1a and the second part 1b in the second control mode 310B,

[0094] a monitoring function 91 configured to monitor the first portion 1a of the electricity distribution network 1,

[0095] - A DMS selector configured to select 308 a control function for controlling 310 the power distribution network, in particular to select 308 the following control functions:

[0096] - controlling 310 the first portion 1a in a first mode 310A, and

[0097] - controlling 310 the first part 1a and the second part 1b in a second mode 310B, and

[0098] - A communication interface 99 configured for communicating with the microgrid controller 8 and preferably also for monitoring 306 the first part 1 a of the distribution network 1 and controlling 310 the assets 3 - 7 of the first part 1 a of the distribution network.

[0099] like Figure 4 As further shown, the distribution network controller 9 is preferably configured to receive a control mode indication from the microgrid controller 8 (see Figure 3 307 in the figure) and the measurement and status indication about the second part 1b of the distribution network 1. In addition, as shown in the figure, the distribution network controller 9 is configured to indicate the DMS function in the second control mode 310B (see Figure 3 309 in the first part 1a), measurement and status information and control signals (see Figure 3 314B) is transmitted to the microgrid controller 8.

[0100] The present invention has been described with reference to embodiments of aspects of the invention: a method 300 for controlling a distribution network 1 and a microgrid controller 8 suitable for the method. The distribution network 1 comprises assets 3-7 in a first part 1a and a second part 1b, which are selectively connected to each other in an interconnected state at a connection point (PCC). The method comprises monitoring 301, 306 and controlling 310 the assets 3-7 of the distribution network 1. In a first control mode 310A, the first part 1a is controlled by a distribution network controller 9 and the second part is controlled by a microgrid controller 8. In particular, the method comprises selecting 303 between controlling 310 the distribution network 1 in an interconnected state according to a first control mode 310A and controlling 310 the distribution network 1 in an interconnected state according to a second control mode 310B, wherein in the second control mode 310B, the assets 3-7 of both the first part 1a and the second part 1b are controlled by the distribution network controller 9.

[0101] The present invention provides a microgrid control system 8 or a microgrid controller, which is configured to extend the DMS monitoring and control function into the microgrid (second part 1b). The microgrid controller 8 is configured to control the microgrid (second part 1b) in an island state and a grid-connected state, wherein there are two operating modes in the grid-connected state: a first operating mode 310A for autonomously controlling the microgrid, and a second operating mode 310B including extending the DMS function into the microgrid. The microgrid controller 8 is configured to extend the DMS monitoring and control in the grid-connected state when at least one standard for the microgrid 8 function is met, and interrupt the DMS monitoring and control and act autonomously when at least one of the at least one standard is violated. The microgrid controller 8 is configured to switch between the first operating mode 310A and the second operating mode 310B according to meeting or violating at least one standard.

[0102] The criteria for abandoning DMS expansion and autonomously controlling the microgrid preferably also include detecting whether the circuit breaker at the PCC is disconnected. Therefore, the microgrid controller 8 is configured to monitor the state of the circuit breaker at the PCC, and the "fifth" criterion for mode switching is when the state of the PCC circuit breaker is disconnected. When the circuit breaker is disconnected, the microgrid controller 8 switches to the island mode, which can be regarded as the third control mode 310C. The third control mode 310C can include an island stage leading from the grid-connected state to the island state.

[0103] The present invention includes a first control mode 310A and a third control mode 310C, wherein the microgrid controller 8 controls the assets of the microgrid in a manner similar to the microgrid controller of the prior art. Thus, the microgrid controller 8 can monitor and control the microgrid (1b) when it is grid-connected (first mode 310A) and when it is islanded (third mode 310C). During the first operating mode 310A and the third operating mode 310C, the distribution network controller 9 monitors and controls the distribution network upstream of the microgrid (i.e., the first part 1a). Both the microgrid controller 8 and the distribution network controller 9 preferably monitor the voltage level and power flow at the PCC.

[0104] Compared with the prior art, the present invention is different in that the microgrid controller 8 and the distribution network controller 9 can operate in the second control mode 310B. The second control mode 310B of the microgrid controller 8 includes serving as an extension of the distribution controller 9 to monitor the microgrid 1b and forwarding monitoring data about electrical entities in the microgrid (i.e., the second part 1b) to the distribution network controller 9. The second control mode 310B of the distribution network controller 9 includes controlling the distribution network 1 including both the first part 1a and the second part 1b, in particular controlling the assets 3-7 of the two parts 1a, 1b, the control being based on the monitoring of the two parts 1a, 1b. In an embodiment of the present invention, when the circuit breaker is disconnected, a change in the operation of the microgrid controller 8 from the second control mode 310B to the third control mode 310C is executed. In an embodiment of the present invention, when at least one predefined standard for an electrical entity deviates (in Figure 3 305) when an acceptable operating bandwidth or a maximum or minimum threshold is violated, a change from the second operating mode 310B to the first operating mode 310C is performed (in Figure 3 303 of ).

[0105] However, the present invention is not limited to the presented embodiments. The scope of the present invention is defined by the appended claims, within which a person skilled in the art may provide the present invention in various forms.

Claims

1. A method (300) for controlling a power distribution network (1), the power distribution network comprising a first part (1a) and a second part (1b), each of the first part (1a) and the second part (1b) comprising an asset (3-7), the first part (1a) and the second part (1b) being selectively connected to each other in an interconnected state at a connection point PCC, the power distribution network (1) further comprising a power distribution network controller (9) and a microgrid controller (8), The method comprises monitoring (301, 306) the power distribution network (1), including monitoring electrical entities of the power distribution network (1); controlling (310) assets (3-7) of the power distribution network (1) based on the monitoring (301, 306); The controlling (310) further comprises controlling (310) the assets (3-7) of the power distribution network (1) according to a first control mode (310A) in the interconnected state, wherein: The assets (3-7) of the first part (1a) are controlled by the distribution network controller (9), and the assets (3-7) of the second part (1b) are controlled by the microgrid controller (8), The method is characterized in that the method comprises: Choose between the following (303): - controlling (310) assets of the power distribution network (1) according to the first control mode (310A) in the interconnected state, and - controlling (310) the assets (3-7) of the distribution network (1) in the interconnected state according to a second control mode (310B), in which the assets (3-7) of the first part (1a) and the assets (3-7) of the second part (1b) are controlled by the distribution network controller (9).

2. The method according to claim 1, wherein The selection (303) is performed by the microgrid controller (8).

3. The method according to claim 1 or 2, wherein: The selecting (303) comprises evaluating (305) at least one electrical entity of the second part (1b) of the power distribution network (1) based on a corresponding threshold bandwidth for each evaluated electrical entity, and switching from the second control mode (310B) to the first control mode (310A) when any electrical entity violates the threshold bandwidth for the electrical entity.

4. The method according to claim 3, wherein: The at least one electrical entity evaluated in the second part (1b) includes at least one of the following: - a voltage level at a connection point PCC between the first part (1a) of the distribution network and the second part (1b) of the distribution network (1), - a reactive power flow between a first part (1a) of the power distribution network and a second part (1b) of the power distribution network (1), - an active power flow between a first part (1a) of the power distribution network and a second part (1b) of the power distribution network (1), - the voltage level at an asset (3-7) in the second part (1b) of the distribution network (1), or - Electricity from assets (3-7) in the second part (1b) of the electricity distribution network (1).

5. The method according to claim 1 or 2, comprising: - selecting (308) a specific control function for the distribution network controller (9), and - controlling (310) assets (3-7) in said first portion (1a) in a first mode (310A), and controlling (310) assets (3-7) in said distribution network (1) according to said control function in a second mode (310B), The first mode (310A) or the second mode (310B) further includes notifying (311) the microgrid controller (8) of which specific control function the distribution network controller (9) is currently using.

6. The method according to claim 1 or 2, wherein: A circuit breaker is arranged at the connection point and monitoring (301) of the second part of the distribution network (1) includes monitoring (302) the state of the circuit breaker, and the method also includes switching (304) to a third control mode (310C) when the circuit breaker is disconnected, in which the second part (1b) is controlled as an island microgrid by the microgrid controller (8).

7. A microgrid controller (8) for controlling a portion of a distribution network (1), the distribution network (1) comprising a first portion (1a) and a second portion (1b), the second portion comprising assets (3-7), the first portion (1a) and the second portion (1b) being selectively connected to each other in an interconnected state at a connection point PCC, and the distribution network (1) further comprising a distribution network controller (9), the microgrid controller (8) comprising: - a monitoring function (81) configured to monitor (301) a second part (1b) of the power distribution network (1), a controller (80) configured to control (310) assets (3-7) in the second part (1b) of the distribution network (1) based on monitoring (301) of the second part (1b), the control (310) being performed according to a first control mode (310A) in the interconnected state, The invention is characterized by comprising: - a mode selector (82) configured to select (303) between: - controlling (310) assets (3-7) of the second part (1b) of the electricity distribution network (1) according to a first mode (310A) in the interconnected state, and - controlling (310) assets (3-7) of a second part (1b) of the distribution network (1) in the interconnected state according to a second control mode (310B), in which the assets (3-7) of the second part (1b) are controlled by the distribution network controller (9), and - a monitoring data communicator (83) configured to communicate (313B) monitoring data to the distribution network controller (9) in the second control mode (310B).

8. The microgrid controller (8) of claim 7, further comprising an evaluator (84) configured to evaluate (305) at least one electrical entity of the second portion (1b) of the power distribution network (1) based on a respective threshold bandwidth for each evaluated electrical entity, wherein The mode selector (82) is adapted to switch from the second control mode (310B) to the first control mode (310A) when any electrical entity violates a threshold bandwidth of the electrical entity.

9. The microgrid controller (8) according to claim 8, wherein: The at least one electrical entity evaluated in the second part (1b) includes at least one of the following: - a voltage level at a connection point PCC between the first part (1a) of the distribution network and the second part (1b) of the distribution network (1), - a reactive power flow between a first part (1a) of the power distribution network and a second part (1b) of the power distribution network (1), - an active power flow between a first part (1a) of the power distribution network and a second part (1b) of the power distribution network (1), - the voltage level at an asset (3-7) in the second part (1b) of the distribution network (1), or - Electricity from assets (3-7) in the second part (1b) of the electricity distribution network (1).

10. The microgrid controller (8) according to claim 8, wherein: The mode selector (82) is adapted to switch back from the first control mode (310A) to the second control mode (310B) when the assessed electrical entity has again entered a threshold bandwidth for the electrical entity.

11. The microgrid controller (8) according to any one of claims 7 to 10, wherein: The monitoring function (81) is adapted to monitor (302) the state of a circuit breaker arranged at the connection point for interconnecting a first part (1a) with a second part (1b) of the distribution network (1), and wherein the mode selector (82) is adapted to switch (304) to a third control mode (310C) when the circuit breaker is disconnected, and wherein the microgrid controller (8) is configured to control (310) the second part (1b) as an island microgrid according to the third control mode (310C).

12. The microgrid controller (8) according to any one of claims 7 to 10, further comprising a control signal communicator (85), which is configured to communicate control settings from the distribution network controller (9) to the assets (3-7) of the second part (1b) of the distribution network (1) in the second control mode (310B).

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