FIELD OF THE INVENTION

The present invention relates to a microgrid system, and more specifically to a system and a method for providing uninterrupted power in a microgrid system.

BACKGROUND OF THE INVENTION

Microgrids are power systems that are able to generate and distribute electric power, where power generation, power storage and power distribution means are physically close to each other. This is in contrast to classical power grids where the same means are typically separated by long distances.

The microgrid usually comprises one or more controllers that coordinate the operation of various equipment/components used in power generation, power storage and power distribution, while in some cases also carrying out supervising, coordinating and some protection functions for the equipment/components. In a microgrid, the generation means can include renewable and non-renewable sources or a combination thereof. Further, the supplied loads are also placed geographically close to the power sources in the microgrid system. The energy storage might be part of the system in the form of batteries, which may be combined with supercapacitors and managed with battery management subsystem.

A power source in a microgrid system can work in parallel with an electrical public/main grid supply to avail the power supply available through the grid. The status of such operations of the microgrid system when the electrical main grid is utilized is being referred as On grid' status, and when the microgrid is supplying power solely using other power generation sources connected with it i.e. when the grid supply is not available, the status is referred as Off grid' status.

Loads are typically supplied with AC voltage/current, whereas the power supplied by a photovoltaic generator is typically DC. Therefore a DC/AC inverter is provided to allow the system to carry out the electrical inversions and supply power from the photovoltaic generator to AC loads. In a prior-art configuration used for utilizing solar power, a DC/AC inverter, referred herein as solar inverter is used in parallel to the grid i.e. feeding an electrical bus for providing power to a load.

In absence of any other power sources connected in the electrical bus e.g. in a scenario having only the grid supply and solar power source and the grid supply not available (off grid status), the solar inverter, specially a grid tied solar inverter may not operate and go into a blocking state for lack of power reference in the electrical bus or for safety reasons. Therefore, most of the solar inverters, especially the grid tied solar inverters used with solar sources require a voltage to be imposed on their respective AC output to function. For uninterrupted power supply (UPS) to the load, a microgrid system would need a power storage device to also work along with its power sources. The operation of power storage device needs to be coordinated with the grid and solar power sources.

There is a need for a method and system which would allow effective operation of a microgrid with solar inverters for uninterrupted power with ability to supply power to the loads in all operating conditions i.e., both on grid and off grid. It is also desirable that such a system be compact and efficient for deploying and usage for uninterrupted power to connected loads. SUMMARY

The above-mentioned shortcomings, disadvantages and problems are addressed herein which will be understood by reading and understanding the following specification.

The present invention provides an electrical subsystem in a microgrid system connected with a plurality of power sources. The plurality of power sources include at least one direct current (DC) power generating source. The electrical subsystem comprises a converter and charging module, an inverter and a controller. The controller and charging module is for providing uninterrupted power supply to a microgrid bus. The converter and charging module is also connected to a power line from a public grid and a storage device. The power from the public grid through the power line and the storage device are power sources from the plurality of power sources.

The inverter provided in the electrical subsystem is for converting power from the at least one DC power generating source to supply electrical power in the microgrid bus. The controller provided in the electrical subsystem is for controlling the inverter and also controlling the operation of the converter and charging module with one or more switches. This controlling is based on detection of status of the supplied power in the microgrid bus which also includes determination of availability of power (in view of loads connected to the system and expected variations in the load i.e. load profile over time) and power variations in the plurality of the power sources.

In an embodiment, the components/modules of electrical subsystem as mentioned above i.e. specifically the converter and charging module, the controller, the inverter along with components for electrical connection and communication/networking components are included in (assembled within) an enclosure. In an embodiment, the power line of the public grid is electrically separated (electrically isolated) from the microgrid bus with the converter and charging module. Thereby, the power line of the public grid and the microgrid bus are different lines and are not connected together (or share same power line/bus).

In an embodiment, the storage device is electrically charged through the converter and charging module. The power for charging the storage device is sourced from the at least one DC power generating source (which can be the solar power source).

In an embodiment, the inverter is a grid-tied solar inverter for providing electrical power to the microgrid bus to power the loads connected in the microgrid bus or/and the public grid.

In an embodiment, the controller comprised in the electrical subsystem is configured to operate the electrical subsystem in coordination with a server of the microgrid system. Also the controller can be configured to operate the electrical subsystem in coordination with at least one other controller associated with a power source connected directly to the microgrid bus. Here, this power source directly connected to the microgrid bus is a power source remote to the electrical subsystem i.e. is not the power source connected through the electrical subsystem.

The present invention also provides for a method for providing uninterrupted power supply in a microgrid system. The method comprises provisioning a converter and charging module comprised in the electrical subsystem for providing uninterrupted power supply to a microgrid bus. The converter and charging module is capable of being connected or disconnected to power sources derived from a power line bus from a public grid and a power storage device. The method also comprises provisioning an inverter comprised in the electrical subsystem for converting power from the at least one DC power source to supply electrical power in the microgrid bus. The method further comprises detecting status of power supply from the power sources with a controller comprised in the electrical subsystem. The status of power supply includes determination of availability of power and power variations in the power sources. Finally, the method comprises operating one or more switches with the controller based on the detected status of power supply for controlling supply of power from the power sources and providing uninterrupted power supply in the microgrid bus.

In an embodiment, the controller based on the detected status of power regulates charging of the storage device and provides power to the public grid.

In an embodiment, the method mentioned herein above further comprises having the controller comprised in the electrical subsystem operate in coordination with a remote device (other controllers of the microgrid system located outside the electrical subsystem e.g. remote controller and server).

BRIEF DESCRIPTION OF DRAWINGS

Figure 1 illustrates a compact microgrid system;

Figure 2 illustrates a converter and charging block for supplying uninterrupted power in the microgrid system;

Figure 3 illustrates an embodiment of the microgrid system with power being provided from the public grid;

Figure 4 illustrates an embodiment of the microgrid system with power being provided from a storage device; Figure 5 illustrates an embodiment of the microgrid system with power being provided from a solar power source in a microgrid bus;

Figure 6 illustrates an embodiment of the microgrid system with a power source connected in a microgrid bus and managed with a respective controller in coordination with a controller comprised in a compact electrical subsystem; and

Figure 7 illustrates a method for providing uninterrupted power in a microgrid system.

DETAILED DESCRIPTION

The present invention is related to a method and a system for providing uninterrupted power supply in a compact microgrid environment. As mentioned earlier, conventional solar inverters work in parallel with the main public grid and go off operation when the grid is not available.

The present invention discloses an electrical subsystem comprising a plurality of converters provided in a converter and charging module (UPS module) together with a solar inverter, to be operated with a controller and configured with switches for allowing unrestricted operation of the generation/ distribution in the microgrid environment in both off grid and on grid conditions.

In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific embodiments, which may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments, and it is to be understood that other embodiments may be utilized. The following detailed description is, therefore, not to be taken in a limiting sense. Figure 1 illustrates a microgrid system 100 in accordance to an exemplary embodiment of the present invention. The microgrid system 100 comprises exemplary power sources like power supply connection through a power line bus 110a from a public grid 110 or a DC generating source like Solar/Photo Voltaic panels 114 and power supply from power storage system (e.g. battery) 112 providing power to electrical load(s) 118 connected in the microgrid system. The power sources, power storage means (e.g. batteries) and the loads of the microgrid are connected to an electrical subsystem 116.

As it may be appreciated by a person skilled in the art, there may be more than one power generating source of each type, storage subsystems, electrical loads and electrical subsystems for an exemplary embodiment of the present invention.

As shown in Figure 1, the electrical subsystem 116 comprises solar inverter 116c, and converter & charging module/block 116a for providing power to the electrical load 118 by the power sources (110, 112, 114) when configured so with help of controller 116b and with operation of various switches 116d. The function of converter & charging module is to provide an uninterrupted power supply with the help of battery 112, the battery being charged by supply from public grid 110 when available or with the solar power supply 114 (DC power generating source) and solar inverter 116c.

Figure 2 is an expanded view of the components comprised within the converter and charging block 116a. The converter and charging block 116a comprises multiple converters (210, 220 and 230) and also an optional bypass 200. An AC/DC converter 210 is provided for connection with AC supply from the public grid. The AC/DC converter 210 converts AC to DC while drawing power from the public grid. Additionally it can also be operated for converting a DC supply to AC while providing power to the public grid. A DC/ AC 220 converter is provided for connection with the electrical load 118 wherein the electrical load 118 is an AC load and the DC/ AC 220 converter can be operated to power the AC load with DC as the input, and a DC/DC 230 converter for connection with the battery 112 for charging the battery 112 or for drawing power from the battery 112 (or other dc source / energy storage) to provide power to the AC load 118 or to the public grid 110.

Thus, when the public grid 110 is available, power is supplied to the converter and charging section 116a, wherein the AC power is converted to DC and further converted to AC for supply to the load 118. Alternately, the AC power from the public grid maybe converted to DC for charging the battery 112. Further, power supply connection to the load (microgrid bus, 116e having the load and solar power supply supplied through solar inverter) can also take place via the optional bypass 200. It is to be noted that all connection to the load or to the supplies or to the storage system can be provided with switches (116d) to operate/isolate any of the connections to the load or power source/battery to suit the various operation of the electrical subsystem 116.

One would recognize that electrical supply in the microgrid bus being derived from the converter and charging section is different from that of the public grid i.e. the electrical supply in the microgrid bus can be configured to be produced for any specified voltage and frequency as per the configuration of the converter and charging section. Such electrical configuration can also be provided to the converter and charging section through the controller 116b. Thus, the microgrid bus (116e) is electrically separated (isolated) from the power line (110a) of the public grid (110). The electrical reference to other power sources can thus be provided by the uninterrupted power supply generated with the converter and charging section.

For uninterrupted power, the battery 112 can be used as a power source, the DC power is supplied to the converter and charging section 116a, wherein the DC power is converted to AC and supplied to the load 118. Alternately, the power from the battery 112 may also be used to provide power to the public grid. When the solar photovoltaic source 114 (DC power generating source) is used in the microgrid as a power source, the DC power from the solar photovoltaic source 114 is provided to the solar inverter 116c wherein the DC is converted to AC and for performing the conversion from DC to AC. The solar inverter for effective operation can include a DC to DC converter to first convert the DC from the photovoltaic source to a suitable level before converting the DC to AC to provide power in the microgrid bus (116e) connecting the AC load. In this configuration, the solar inverter 116c can be a grid-tied solar inverter 116c as that can function without being blocked out because of availability of uninterrupted power at the microgrid bus (116e) to supply to the electrical loads. Also, the solar inverter can extract a reference voltage from the output of the converter and charging block 116a (UPS) to synchronize and supply AC power.

DC generation sources can supply power to the load 118 in addition to the grid supplied power not only when the public grid is totally not available, but also in a scenario when the power from the public grid is insufficient.

The operation of the electrical subsystem 116 is managed with the controller 116b for operating the converter and charging 116a and for connecting and disconnecting the power sources to the electrical load through the switches 116d. A person skilled in the art can easily recognize that switches 116d provided in the electrical subsystem can be configured for safety and for various combinations for powering from the different power sources and to provide power to the load/grid. The controller 116b can provide for such configurations of combination according to the required operations and also can be configured to change configurations automatically to provide uninterrupted power to the AC loads and for effective usage of the available power sources. A change in configuration can be initiated based on detection of a power variation event in any one of the power sources. It may be known to the person skilled in the art that more than one controller may be used and the several controllers may be coordinated with help of a server of the microgrid and with provision of communication networks for communications (wired/wireless digital communication) as may be needed for coordination with the one or more controllers.

The server(s) are communicatively connected with the one or more controllers in the electrical subsystem and can be remotely located i.e. not provided with the electrical subsystem but supports coordination amongst controllers and for interactions related with electrical/physical parameter information or any operation related information (e.g. converter operation, switch positions, grid availability, power tariffs, environment related information affecting solar operation or other renewable power sources etc.) for effective operation of the electrical subsystem through the controllers in coordination with the remote servers that are enabled with additional inputs/information from related systems/subsystems or by an user/operator. The remotely located controller(s) can be part of a digital platform or virtual computing system supporting cloud based services.

The one or more controller used in the electrical subsystem can receive inputs (analog/digital) from one or more sensors (not shown in the figure) to detect an electrical/physical parameters (voltage, current, power, temperature etc.) from the power sources connected to the electrical subsystem and at the microgrid bus (power for AC loads) for the purpose of coordination and operation of the electrical subsystem to supply uninterrupted power to the AC loads or to the grid on requirement. It would be apparent for the person skilled in the art, that for the purpose of coordination and operation including protection of the electrical subsystem, power sources/loads suitable arrangements with devices/networks e.g. protection relays, network devices, communication network or bus can be provided and coordinated/configured for operation with help of the one or more controllers. In compact electrical subsystem such arrangements can be managed with one controller.

In an embodiment of the invention, the controller 116b can detect availability of the public grid 110, and accordingly control power supply from the power sources 112 and 114 to the load(s) 118.

In an embodiment of the present invention, the controller 116b can also perform various power management functions. For example, excess power generated from the DC source 114 can be used to charge the battery 112 while concurrently supplying the electrical loads/AC load 118 in the off-grid mode. The controller 116b can also regulate charging of the battery 112 according to the power conditions of the microgrid.

As shown in Figure 1, the electrical subsystem 116 is provided with three main electric connection points to the outside environment such as the public grid 110, the photovoltaic or other DC generating source 114, and the load 118 and a connection to batteries for storage and UPS purposes.. Thus, the electrical subsystem is positioned in series between the grid 110/ the photovoltaic 114 or other DC source, and the load(s) 118. It should be noted that the subsystem 116 can be connected to multiple power sources and / or loads, and may accordingly have more electric connection points with the outside environment, or may be connected to several other electrical equipment which are typically used in grids / electrical networks. .

The power components and the controller of the system are designed such that available power from the photovoltaic source or other DC source and/or the battery can supply both the electric load(s) and the public grid. For example, in a scenario when a solar power source is used for supplying the available power to the public grid, a grid-tied solar inverter may provide AC power to the public grid via the converter & charging block through the converters and also via the optional bypass contained in the converter and charging block 116a that bypasses the converters in the converter & charging block and provides for direct connection of the public grid to the microgrid bus having AC loads and solar power source as per the exemplary embodiment described with Figure 1.

Figure 3, illustrates an exemplary scenario when power is available from the public grid 110. The controller 116b detects the availability of grid power and operates a combination of switches connecting the public grid 110 to the electrical loads via the converter and charging modules 116a and hence power is being provided from the public grid 110 to the electrical load 118 in this state. The dotted lines 300 shown in the figure represents signaling and communication channels between the controller and the switches to operate the switches. The switches 116d- 1 , 116-d-4, 116-d5 are operated to connect and the switches 116d-2 associated with the Battery 112 and the switch 116d-3 associated with the solar inverter 116c are kept disconnected to illustrate one possibility of operation of the electrical subsystem in the microgrid.

The controller 116b can be configured to ensure optimal energy usage in the microgrid by detecting electrical/physical parameters and manages use of power sources including batteries for efficient and improved reliability (life) of the power sources and batteries. In an embodiment, the controller can profile and manage power balance among grid, load, DC source and battery for optimal energy use.

Figure 4 illustrates a scenario wherein the power is supplied from the battery 112 and the solar photovoltaic source 114 via the solar inverter 116c. In this configuration, the controller 116a may provide for an off grid status and operates the switch 116d-l for disconnecting the provision of power from the public grid 110 and connecting the switches 116d-2 associated with the battery 112. Alternately, the controller 116b may after disconnecting the power from the public grid 110 operate the switch 116d-3 associated with solar photovoltaic power source 114 for providing power from the solar photovoltaic power source 114. As shown in Figure 3, in such a configuration, the controller 116b can have the power supplied to the load 118 through the battery 112 and the solar inverter 116c. Also, in this configuration depending on the status of the power supply, battery may be charged through the power from the solar power source.

In an embodiment, the storage device i.e. the battery bank 112 is charged or discharged according to an energy balance profiled for the battery management subsystem in the microgrid system with help of the controller 116b.

The embodiments of the present invention can be designed to operate with sources (e.g. diesel generator (DG)) having different power generation capacities. For example, a DG of capacity lesser than that of the AC load can be used. In such cases when the load is greater than DG, the deficit power can be taken from solar power source and/or batteries. The controller can control the supply from the power sources to the AC loads, in such a configuration.

The present invention provides for embodiments designed to take and suppress variations, which may occur during operation in the various power generation sources connected to the electrical subsystem 116 and can deliver clean, quality power to the connected load(s). Such control can be done with the controller 116b of the microgrid system. In one embodiment, when off grid, the controller detects and accounts for load variations and/or DC source power variations, while keeping stable voltage supply to the load(s). In an embodiment of the present invention, the microgrid system components are containerized such that outdoor operation as well as unmanned operation via remote communication, monitoring and control are possible. The controller can be enabled to operate with remote connectivity by having a network connection (e.g. a static IP internet).

Figure 5 illustrates an embodiment of the microgrid system explicitly showing the microgrid bus 116e having plurality of power sources and a load connected to the microgrid bus. The configuration for microgrid operation shown in the figure is the configuration allowing power to be supplied from the solar power source. In this configuration, depending on the status of power supply with the storage power source (power availability and power profile of the batteries), the storage device (batteries) may be charged with the solar power source or discharged to supplement power provided in the microgrid bus.

In a compact installation of a microgrid system, the microgrid bus can be located within the electrical subsystem enclosure (shown in Figure 3 with a box 116) and can be formed with a bus bar. The power supply from the power sources and battery is provided to the load via the microgrid bus 116e.In an embodiment of the present invention, the power line bus 110a and the microgrid bus 116e are electrically separated (isolated) or connected with the electrical subsystem 116a.

Figure 6 illustrates an embodiment of the present invention showing a microgrid bus 610 being located outside the enclosure of the electrical subsystem and having an additional power source 620 connected to the microgrid bus 610. In this exemplary embodiment, the microgrid bus 610 can be a distribution power line (e.g. power cable, overhead transmission line) and allows for connection of multiple power sources and loads. In this microgrid system, the electrical subsystem is shown connected to the microgrid bus 610, where the electrical subsystem is a power source providing uninterrupted power supply, sourced from solar power source, public grid and power storage device. A controller 630 is provided for coordination of power source 620 in the microgrid system.

A person skilled in the art can readily associate such coordination enabled through suitable provision of communication between the controller and the power source or a circuit breaker electrically connecting/disconnecting the power source for providing power. Also, it is to be understood that coordination of a power source with other power sources in the microgrid system is enabled through suitable communication between controllers as per the programs in the various controllers or one or more servers gathering data from the power sources/controllers. Also Figure 6 illustrates the microgrid system having multiple loads 118,118a connected to the microgrid bus 610.

In a compact microgrid installation i.e. the electrical subsystem connected with its power sources, storage devices and loads as shown in Figure 1, the operation of the microgrid can be managed with a single controller. Thus, this configuration is simple and can be device efficient (less number of devices). The installation also supports optional connectivity with remote system (e.g. servers, and other controllers if any) and extended electrical connectivity to connect additional power sources in the microgrid system for availing advantages of a microgrid system.

The operation of the microgrid system especially the electrical subsystem is illustrated with Figure 7 that provides a method 700 to construct and provide uninterrupted power in a microgrid system using the electrical subsystem 116. An uninterrupted power supply is provided with an electrical subsystem in a microgrid system. As described earlier, a converter and charging module comprised in the electrical subsystem is used. The method provides for provisioning the converter and charging module 116a for providing uninterrupted power supply to the microgrid bus (step 710) along with provision of a solar inverter (grid-tied solar inverter) connected to a solar source (step 720) to make use of the solar power to power the load, store power in the storage device i.e. charge the batteries, and provide power to the public grid (based on a configuration managed by a controller in the electrical subsystem).

The converter and charging module 116a is capable of being connected or disconnected to the power sources derived from a power line bus 110a from a public grid 110 and a power storage device 112. In step 720, the method provides for provisioning the inverter comprised in the electrical subsystem for converting power from a DC power generating source, for example a solar power source to supply electrical power in the microgrid bus. As the microgrid bus is provided with an uninterrupted power supply through the converter and charging module, a conventionally available grid-tied solar inverter can be used that can function irrespective of the status of power in the powerline of the public grid (no block out due to unavailability of power in the power line of the public grid).

In step 730, status of provided power of the power sources are detected with a controller provided in the electrical subsystem. The status of provided power includes determination of availability of the power sources e.g. whether the public grid 110 is available or not, or the status of solar power 114 (availability/capability), or the status of storage device to supply power (capability and availability as per charging/discharging profile), or the status of power (loading effect) determined from the microgrid bus.

For example, the controller 116b may detect that power is available from the public grid. In this scenario, the controller co-ordinates the operation of the switches 116d- 1, 116d-4 and 116d-5 (refer Figure 3) to enable power supply from the public grid 110 to the load 118 via the converter and charging block 116a (this is one example of configuration for operating the electrical subsystem). In step 740 the controller 116b operates the switches for connecting and disconnecting the plurality of converters comprised in the electrical subsystem based on the status and operation requirements (programmed configurations). Finally, as shown in step 750 the controller 116b provides uninterrupted power from the power sources to the loads based on the detected status of power in the connected power sources, load requirements and operation of switches and converters in the electrical subsystem including operations to charge the battery bank 112 to store power or provide power to public grid when excess power is available from the solar power source.

The status of provided power of the power sources may also include checking for power variations in the power sources. The available power may be insufficient for the AC loads hence along with detecting the availability of power the power variations are also detected. Hence based on the detected status of the provided power in the power sources further action can be taken by the controller 116b for ensuring uninterrupted power to the AC loads 118.

As described earlier, the controller can be programmed for various configurations example charging of battery when solar power is available or providing power to the public grid. As appreciated by a person skilled in the art, a microgrid system consists of several controllers and one or more servers to co-ordinate operation of the microgrid system. The controller comprised in the electrical subsystem is configured to function/co-ordinate with other controllers provided in the microgrid system. Also, the controller comprised in the electrical subsystem can function in coordination with the one or more servers of the microgrid to carry out a function of the microgrid or to operate effectively. These other controllers and servers can be located remotely (remote devices) including as a virtual device in a digital platform/cloud based systems.

While the invention has been described in relation to microgrids, the invention is not limited to microgrids and is extendable to other types of power grids such as minigrids, nanogrids etc. This written description uses examples to describe the subject matter herein, including the best mode, and also to enable any person skilled in the art to make and use the subject matter. The patentable scope of the subject matter is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.