WO2016055084A1

WO2016055084A1 - A microgrid communication system including a wireless communication network for improving microgrid operation and reliability

Info

Publication number: WO2016055084A1
Application number: PCT/EP2014/071284
Authority: WO
Inventors: Gargi Bag; Ritwik MAJUMDER; Zhibo PANG; Morgan Johansson
Original assignee: Abb Technology Ltd
Priority date: 2014-10-06
Filing date: 2014-10-06
Publication date: 2016-04-14

Abstract

A wireless communication network is used in a microgrid communication system for improving microgrid operation, wherein the wireless communication network is adapted to communicate non-time critical data aspoint-to-point during normal operation and broadcast time critical data to all the receiving nodes in the network during islanding.

Description

A MICROGRID COMMUNICATION SYSTEM INCLUDING A WIRELESS

COMMUNICATION NETWORK FOR IMPROVING MICROGRID OPERATION AND RELIABILITY

TECHNICAL FIELD

The present invention relates to the technical field of energy distribution. In particular, it concerns improving microgrid operation and reliability.

BACKGROUND

A microgrid is a localised grouping of electricity generation, energy storage, and loads that normally operates connected to a traditional centralised grid via a point of common coupling. Microgrids are part of the structure for so called distributed generation aiming at producing electrical power locally from many small energy sources which are called distributed generators (DGs) or micro sources. Power balance between the energy sources and loads at all time, grid connected or islanded, is required for stable voltage and frequency. The main aim of the DGs in a microgrid is to provide maximum real power to fulfil the load demands .

Islanding refers to a condition of a microgrid, where the distributed generator continues powering a part of a distribution network even though power from an electric utility is no longer present .

A microgrid can operate in an islanding mode or grid connected mode. In the grid connected mode, the difference between the total load consumption in the microgrid (P_L) and total power generation (P_G) in the microgrid is provided by or sent back to the grid (P_GRID) · In the islanded mode, load shedding, or storage action, may be required to maintain power balance as well as to ensure power supply to some loads for a defined time. Depending on the operation mode, the control of the microgrid changes. The various types of control actions from DGs and the microgrid controller within a microgrid require measurements and switch status. The operational performance of the microgrid, together with components such as DGs, storage, loads etc., as well as the microgrid controller, can be improved with efficient and reliable communication of this information from the measured point to the individual controllers.

Use of communication technology can be done to improve microgrid operation, stability and reliability as well as to achieve an optimal use of power generated in the micro sources. There are many communication technologies available, both wired and wireless, that can be considered for the information exchange. Wired communication technologies provide fast and reliable communication. However cost of installation and the effort can be high, especially if the media is fiber optics and a large area is considered. On the other hand wireless technologies in general are easier and more cost effective to install especially where the terrain is difficult and wired infrastructure is either not available or difficult to set up. Some of the wireless technologies can also provide high speed communication. However there can be some drawbacks such as reliability (due to interference, lossy nature of the links) and security threats which needs to be addressed . US20120283890 relates to a microgrid system and communications unit in a local controller and describes communication during islanding . US20130187454 relates to detecting and communicating islanding conditions in power networks.

SUMMARY

It is an object of the present invention to provide an improved alternative to the above techniques and prior art. More specifically, the present invention introduces how a communication infrastructure can be used in a microgrid system for reliable and efficient information exchange. The proposed invention can be used for normal as well as critical system operation ensuring data exchange among the required components only. The proposed method for information exchange can be achieved with available communication technologies. To achieve these and other objects, a system and a method in accordance with the independent claims are provided. Further developments of the invention are the subject of the dependent claims . The invention is based on the insight that one of the key challenges with microgrids is to improve the operation and reliability during islanding. This can be obtained with proper change of microgrid control mode and that relates to change in control of the microgrid components, such as distributed generators, energy storage, loads, etc. A cost effective and reliable communication infrastructure can ensure that. On the other hand, normal operation of the microgrid can also be improved in terms of regulation and reactive support with exchange of relevant measurements. A communication infrastructure to achieve both the purposes while ensuring high reliability can offer an improved microgrid operation. The communication scheme must be able to act based on priority of information and particularly ensure fast and reliable communication of islanding information to the microgrid components.

According to a first aspect of the invention, a microgrid communication system for improving microgrid operation and reliability is provided as defined in claim 1.

According to a second aspect of the invention, a method for improving microgrid operation and reliability in a microgrid communication system is provided as defined in claim 8.

The DGs in a microgrid try to provide maximum real power to fulfil the load demands. The system voltage is maintained by the main grid. However, in weak grid or off grid operation, reactive support from the DGs is required in many scenarios. A weak grid operation could be a grid with low short circuit ratio and an off grid operation is when the microgrid is islanded. One option for reactive support is centralised control, where the objective functions from the energy management system are set out to control the resources. However, in a distributed control scenario, the reactive support from the distributed sources must come in a decentralised manner and the exchange of information related to reactive power injection and voltages among the DGs may be required to improve the voltage profiling under normal operation.

In accordance with an embodiment of the invention a wireless communication network is included in a microgrid communication system for improving the operation and reliability of the system. The microgrid communication system further includes a controller, a switch and microgrid components. The wireless communication network supports quality of service related to non-time critical data (e.g. power, voltage, etc.) and time critical data (e.g. grid connection failure) . The wireless communication network is configured to communicate non-time critical data using point-to- point connection between the microgrid components and the controller during normal operation and to broadcast time critical data to all the receiving nodes in the wireless mesh network during islanding. Thereby, when a wireless communication network is used, the operation of the microgrid can be improved both during normal operation and islanding and, moreover, data communication only among the required components can be achieved which improves the reliability of the microgrid.

In accordance with another embodiment of the invention the microgrid communication system is adapted to act based on priority of data. Based on the requirement of the measured signal different priorities are set and different quality of services are provided by the communication network.

In accordance with another embodiment of the invention time critical data broadcasted during islanding is given the highest priority .

In accordance with another embodiment of the invention the microgrid communication system comprises a wired backbone communications network. One advantage and benefit with the concept of the present invention is that the reliability of the communication is increased as the mesh network provides alternative routes to the destination. This offer an effective microgrid operation in islanding which is one of the key challenges.

Another advantage and benefit with the concept of the present invention is improved power quality with coordinated voltage profiling and higher reliability with secured and fast islanding based action for the microgrid.

Another advantage and benefit is a more efficient communication scheme to support improved microgrid operation in different applications .

Another advantage and benefit is that the wireless mesh network is easier to configure especially where the terrain is difficult and wired infrastructure is either not available or difficult to set up. At the same time it incurs low installation costs as devices discover each other and sets up routes to destination automatically . BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the present invention will emerge more clearly to a person skilled in the art from the following non-limited detailed description when considered in connection with the attached drawings, wherein:

Figure 1 shows a schematic drawing of conditions during islanding and normal operation in accordance with an exemplifying embodiment of the present invention.

Figure 2 shows a schematic drawing of how a communication network is used to propagate islanding information in accordance with an example of the present invention.

Figure 3 shows a schematic drawing in accordance with another exemplifying embodiment of the present invention.

Figure 4 shows a schematic drawing in accordance with another exemplifying embodiment of the present invention.

DETAILED DESCRIPTION

An embodiment for improving microgrid operation and reliability, according to the present invention, is shown in figure 1. During normal operation conditions 11, point-to-point connection is used to communicate non-time critical data, such as power, voltage, etc. Voltage profiling, i.e. how the voltage varies over the microgrid network, is needed, during normal operation 11 to maintain the voltage in the microgrid within an acceptable range. There is always a maximum and minimum limit on the acceptable voltage which creates the bandwidth within which the network should operate. Also based on the voltage profile the power flow and the loss changes. During islanding 12, the microgrid loses connectivity to the main grid 10 and a static transfer switch 13 broadcasts this information to the microgrid components 14-19. A static transfer switch is a switch based on semiconductors technology which operates much faster than a normal switch. A mesh communication network is used for communication within the microgrid. Such networks are considered self-organizing, self- healing and highly scalable so that routers automatically discover each other and find multiple alternative routes to destination in case one path fails. The present invention uses mesh network support variety of applications ranging from Automatic Meter Reading (AMR) to microgrid related applications such as islanding, voltage profiling, reactive power support etc.

In order to differentiate between different types of applications, virtual local area network (VLAN) tagging is used, whereby a VLAN ID is appended in the packet. VLAN is used in the mesh communication network to logically segment the network based on different applications. Thus in this case, islanding can have a different VLAN ID than the applications, such as voltage profiling, AMR etc. Therefore, by using VLAN tags, it is possible to differentiate which VLAN a frame belongs to. Each node can be a part of one or more VLANs . Using VLAN IDs will also limit the amount of broadcast in the network as the nodes that are not a member of a VLAN will not receive broadcast messages from other nodes .

An example of how the mesh communication network is used to propagate islanding information according to the invention is shown in figure 2. In this case all the nodes 20a-20g other than the smart meter 21 belongs to a particular VLAN e.g. VLAN 15, which is reserved for communicating islanding information. When an islanding event occurs, the static transfer switch 27 sends a broadcast in VLAN 15. When an intermediate node or router 20a-20g receives such a broadcast, it checks whether it has an ESSID or IP address. In other words, it checks if a microgrid component 22-26 is associated with the VLAN ID. If yes, then it passes the broadcast to the microgrid component 22-26 and also passes the message to other routers in the network excluding the one from which it is received. If there are no devices interested in the broadcast, it still forwards the broadcast to other routers, other than the one which it received the broadcast from. A timestamp in the message ensures that a time-stamped message is forwarded only once .

As the information is flooded in the network by passing it to all the routers in the network it increases the reliability of the communication. Flooding the information among the routers also saves the time the network needs to react in case of a path or router failure as it does not need the time to reconfigure a new path. This is because when the information is flooded it is sent to all the possible paths making sure that the information reaches on time even if one of the path or router fails.

The self-organizing and self-healing nature of the mesh network allows the routers to route the messages through a new path towards the destination in case one of the routes fails, thus increasing reliability. Using VLAN IDs enables the intermediate routers to differentiate between applications and assign them different priority and bandwidth at the time of forwarding. Figure 3 shows another embodiment according to the present invention. Wireless nodes or routers 30a-30k act as access points for the microgrid components to communicate with each other and the control unit. Since every application ranging from islanding to AMR has individual communication requirements, different Quality of Service (QoS) will be provided to different applications depending on their need. The QoS will provide priority and additional bandwidth to the application traffic at the forwarding node. For example, for time critical data, higher priority and larger bandwidth can be assigned so that the data can be delivered within shorter time and better determinism.

Another embodiment according to the present invention is illustrated in figure 4. Here it is shown how the mesh network can be utilized to support applications such as voltage profile and reactive power support during normal operation. In this case the solar PV 41 and the diesel generator 42 use point-to-point communication. A separate VLAN ID can be used to identify this application at the routers. In this case if the path between one set of routers is broken the messages can be routed though alternative paths in the mesh network. For the microgrid communication system, spanning over large areas will require many wireless routers which will increase the number of hops and ultimately the communication latency. This may not be desirable for applications such as islanding. Therefore the communication network topology should consist of wireless routers and a high speed wired backbone network. The wireless routers will still form a mesh network among them and try to find routes to the nearest point of access to the wired network. The person skilled in the art realises that the present invention is not in any way restricted to the embodiments described above. On the contrary, several modifications and variations are possible within the scope of the invention as defined in the appended claims .

Claims

1. A microgrid communication system for improving microgrid operation and reliability, the system comprising a control unit, a wireless communication network, a switch and microgrid components, and wherein the wireless communication network supports quality of services related to time critical data and non-time critical data, and wherein the wireless communication network is adapted to:

during normal operation, communicate non-time critical data as point-to-point between the microgrid components and the control unit; and

during islanding, broadcast time critical data to all the receiving nodes from the switch by flooding the time critical data to all the receiving routers in the wireless communication network.

2. A microgrid communication system according to claim 1, wherein the system is adapted to act based on priority of data.

3. A microgrid communication system according to claim 2, wherein the time critical data broadcasted during islanding is given the highest priority.

4. A microgrid communication system according to any preceding claim, wherein the control unit is implemented as a central control unit or a distributed control unit.

5. A microgrid communication system according to any preceding claim, wherein the wireless communication network is a mesh network.

6. A microgrid communication system according to any preceding claim, wherein the system further comprises a wired backbone communications network.

7. A microgrid communication system according to any preceding claim, wherein the switch is a static transfer switch.

8. A method for improving microgrid operation and reliability in a microgrid communication system, the system including a control unit, a wireless communication network, a switch and microgrid components, and wherein the wireless communication network supports quality of services related to time critical data and non-time critical data, and wherein the method including:

communicating non-time critical data point-to-point between the microgrid components and the control unit during normal operation, using the wireless communication network; and

broadcasting time critical data to all receiving nodes from the switch during islanding, by using the wireless communication network to flood the data to all the receiving routers.

9. The method according to claim 8, wherein the microgrid communication system is adapted to act based on priority data.

10. The method according to claim 9, wherein the time critical data broadcasted during islanding is given the highest priority.

11. The method according to claim 8-10, wherein the control unit is implemented as a central control unit or a distributed control unit .

12. The method according to any of claims 8-11, wherein the wireless communication network is a mesh network.

13. The method according to any of claims 8-12, wherein the microgrid communication system further includes a wired backbone communication network.

14. The method according to any of claims 8-13, wherein the switch is a static transfer switch.