WO2017151057A1

WO2017151057A1 - Electrical energy management apparatus and methods

Info

Publication number: WO2017151057A1
Application number: PCT/SG2017/050088
Authority: WO
Inventors: Xuewei PAN; Peng Wang; Jianfang XIAO; Fook Hoong CHOO
Original assignee: Nanyang Technological University
Priority date: 2016-03-01
Filing date: 2017-02-27
Publication date: 2017-09-08
Also published as: SG11201806279WA; CN108886258B; CN108886258A

Abstract

An electrical energy management apparatus is disclosed. The apparatus comprises: a plurality of interface ports for establishing electrical connections with electrical energy sources and / or electrical energy loads and / or electrical energy storage devices; a plurality of electrical power converters each having input ports and output ports; a relay array comprising a plurality of relay cells arranged to be switchable between connections to input ports and output ports of the plurality of electrical power converters; and a controller configured to generate control signals for the relay cells of the relay array and thereby configure connections between the input ports and output ports of combinations of the electrical power converters.

Description

ELECTRICAL ENERGY MANAGEMENT APPARATUS AND METHODS

FIELD OF THE INVENTION Embodiments of the present invention relate to the management of electrical energy and specifically to the management of conversion of electrical power between different electrical energy sources and loads for microgrid applications.

BACKGROUND OF THE INVENTION

Renewable energy sources (RESs) such as solar photovoltaic (PV), and wind turbines are gaining in popularity. This is in part due to increasing concern over the depletion of fossil fuel based non-renewable energy sources and the carbon emission associated with the use of non-renewable energy sources. The electrical power generation from RESs depends on the actual weather conditions such as wind speed, solar irradiation and temperature. These conditions can vary significantly and rapidly over time. In order to ensure stable energy supply from RESs, energy storage devices such as battery banks and ultra-capacitors, which are direct current (DC) inherent, are often used to compensate for the variations of RESs output power. Further, DC loads like light emitting diodes (LEDs), liquid crystal displays (LCDs), communication devices, computing devices, and motors with variable speed drive, make up a significant portion of electrical power loads. This high penetration of DC-inherent system units results in a requirement for numerous conversions between DC and alternating current (AC) power. Such DC/AC/DC power conversions degrade energy efficiency and system reliability, when integrated in a conventional AC system.

A hybrid AC/DC microgrid, which is comprised of both AC and DC sub-grids, has been demonstrated to be an effective solution for integration of both AC- and DC- inherent system components. It helps reducing the number of power conversions needed.

Figure 1 shows an example of a schematic layout of a hybrid AC/DC microgrid system. The hybrid AC/DC microgrid system 100 comprises an AC bus 110 and a DC bus 120. AC loads 116 and diesel generators 114 are connected to the AC bus 1 0. An Energy storage system (ESS) 124, PV panels 126 and light wind turbine 128 connected to the DC bus 120 are integrated through respective power electronic converters. The ESS 124 is connected to the DC bus 120 via a bi-directional DC/DC converter 132, the PV panels 126 are connected to the DC bus 120 via a unidirectional DC/DC converter 134, and the light wind turbine 128 connected to the DC bus via a 3-Phase AC/DC rectifier 136. A bi-directional Interlinking Converter (BIC) 130 is installed in-between the AC bus 110 and the DC bus 120. The system may be considered as two sub-grids: an AC sub-grid and a DC sub-gird. The bi-directional Interlinking Converter (BIC) 130 maintains power balance in both sub-grids. As shown in Figure 1 , the AC bus 110 may be connected to a utility grid 112. Thus, the hybrid AC/DC microgrid can operate in both grid-tied and islanded modes depending on the availability of the utility grid. A hybrid AC/DC microgrid can be installed in buildings as a fixed installation and tied to the utility grid. It can also be implemented in islanded applications like aircrafts, offshore platforms, etc. Simplicity of installation and operation, especially when the hybrid AC/DC microgrid is deployed for power supply in disaster control and military applications, is a major concern.

Figure 2 shows an example of modularized design of a hybrid AC/DC microgrid. As shown in Figure 2, a hybrid grid module 200 has a number of electric power converters. The hybrid grid module 200 has an AC bus 220 having 3 live phases A, B & C, a neutral line N and a ground line Gnd and a DC bus having positive + negative - and ground Gnd lines. A diesel generator module 212 and a doubly fed induction generator (DFIG) wind generator module 214 are coupled to the AC bus 210. A flywheel AC/DC converter 222, a fuel cell DC/DC converter 224, a battery DC/DC converter 226 and a PV DC/DC converter 228 are connected to the DC bus 220. A bi-directional AC/DC converter 230 connects the AC bus 210 to the DC bus 220. The hybrid grid module 200 is controlled by an energy management system (EMS) 232. The modularized design shown in Figure 2 provides a solution in which all types of power electronic converters are integrated in the hybrid AC/DC microgrid module 200. The advantages of modularized hybrid AC/DC microgrid include: ease of deployment & installation; ease of maintenance; high portability; the system is highly scalable and operation and control are simple. Currently, microgrids are designed on a case-by-case basis taking into considerations of available energy sources, energy storage, and load profiles. Corresponding power conversion modules and system structure must be specially designed. Most of the microgrid components are provided by different vendors, using different technologies, this makes systematic integration a complex and time- consuming task, not easily replicable from one project to the next.

Different types of sources have considerably variant source voltage /current ranges. For example, in a conventional centralized or string configured PV array, a number of PV modules are connected in series resulting in high source voltage/low source current. PV modules can also be connected in parallel to achieve better performance under shaded condition leading to low source voltage/high source current. Similarly, different types of energy storages like Li-ion battery, NiMH battery, Lead-Acid battery, and Supercapacitors, etc. are widely employed in industrial applications. They have different energy density and power density profiles. High power density energy storage can be used to supply or absorb the high transient power for a short time. While high energy density devices are used to supply the energy continuously for sufficiently long time. High power density devices such as supercapacitors are typically low voltage high current energy storage devices. The source voltages of other batteries vary over a wide range depending on the battery type, specific manufacturer, connection of battery modules etc.

On the other hand, DC grid voltage varies in a wide range to adapt to: i) different DC load requirements including high voltage DC load (800V/400V/200V) and low voltage load (48V/24V); and ii) different AC grid voltage. For example, for 230V/400V AC grids, the DC grid voltage should be higher than 650V while for 110V/200V AC grids, a DC grid voltage around 400V is sufficient. AC girds of different countries and territories are not standardized. The voltage and frequency of AC grid, corresponding major appliances and AC power sources vary widely. In such circumstances, a low frequency transformer can be utilized to match the voltage difference. However, such devices are bulky, heavy and uneconomical.

Therefore, microgrid applications require a prohibitive amount of expertise and customization. Thus, there exists a need in the art to design an integrated hybrid microgrid module that adapts to various energy sources, energy storage, and loads provided by different vendors of different countries and territories.

US Patent application publication US2013/0099581 describes an energy storage system which comprises a plurality of storage mediums having substantially different energy and power density that are each connected to a DC bus via a respective bidirectional isolated DC-DC converter; and a controller configured to independently determine a current demand for each storage medium based on a control mode. The converters can be reconnected in different configurations using external terminals and removable jumper cables or using insulated bus-bars.

US Patent application publication US2012/0175955 describes a system and method for providing reconfigurable AC interfaces for AC power systems. US Patent US9373965 describes an electric power router with multiple power supply modes. Customized power converters are required before renewable energy sources can be connected to the electric power router.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, an electrical energy management apparatus comprises: a plurality of interface ports for establishing electrical connections with electrical energy sources and / or electrical energy loads and / or electrical energy storage devices; a plurality of electrical power converters each having input ports and output ports; a relay array comprising a plurality of relay cells arranged to be switchable between connections to input ports and output ports of the plurality of electrical power converters; and a controller configured to generate control signals for the relay cells of the relay array and thereby configure connections between the input ports and output ports of combinations of the electrical power converters.

Embodiments of the present invention facilitate plug-and-play operation for end users. Plug-and-play implies that the external device including different renewable energy sources (PV, wind turbine, fuel cell etc.), fossil energy sources (diesel generators), energy storages, and loads can be automatically detected and managed without user intervention. The plug-and-play concept aims to simplify the integration, accelerate the deployment and lower the cost of hybrid AC/DC microgrid.

In an embodiment the controller is operable to configure the relay cells of the relay array to establish series and / or parallel connections between the input and output ports of the electrical power converters. The apparatus may further comprise one or more DC and / or DC buses. The relay cells of the relay array are configured to establish connections between the input and / or output ports of the electrical power converters and the DC buses and / or AC buses. In an embodiment, a further relay array is provided to allow configuration of connections between the interface ports and the input ports of the plurality of power converters.

In an embodiment the plurality of electrical power converters comprises bidirectional DC/DC converters and / or bidirectional AC/DC converters.

The relay cells may be implemented as single pole double throw switches.

In order to provide adaptability the plurality of electrical power converters may be detachably connected to the energy management apparatus.

To facilitate plug and play operation, in some embodiments the apparatus further comprises a communication bus coupled to the controller, the interface ports comprising a connection to the communication bus to provide a communication link between the controller and interfaces of the electrical energy sources and / or electrical energy loads and / or electrical energy storage devices.

In an embodiment the controller is configured to select a configuration for the relay cells using information received over the communication link. The electrical power converters may be coupled to the communication bus and the controller may be configured to generate control signals for the electrical power converters and to send the control signals over the communication bus. In an embodiment this is implemented by each of the electrical power converters having an interface component having a memory storing setting information and the controller is configured to generate control signals to update the setting information.

According to a second aspect of the present invention a method in a controller of a an energy management apparatus is provided. The method comprises: receiving signals indicative of electrical energy sources and / or electrical energy loads and / or electrical energy storage devices coupled to the energy management apparatus; determining a microgrid structure for the of electrical energy sources and / or electrical energy loads and / or electrical energy storage devices coupled to the energy management apparatus; and generating control signals for relay cells of the energy management apparatus to configure connections between the of electrical energy sources and / or electrical energy loads and / or electrical energy storage devices coupled to the energy management apparatus and electrical power converters according to the microgrid structure. BRIEF DESCRIPTION OF THE DRAWINGS

In the following, embodiments of the present invention will be described as non- limiting examples with reference to the accompanying drawings in which:

Figure 1 shows an example of a schematic layout of a hybrid AC/DC microgrid system;

Figure 2 shows an example of modularized design of a hybrid AC/DC microgrid; Figure 3 shows an electrical energy management system according to an embodiment of the present invention; Figure 4 shows the structure of a relay cell of an embodiment of the present invention;

Figures 5a to 5d illustrate the basic principle of achieving electronically reconfigurable connections of input ports for two converters with the proposed relay cell;

Figures 6 to 8 illustrate a two-level electronically reconfigurable connection of input ports of four converters with corresponding two level relay cells according to an embodiment of the present invention;

Figure 9 is a table showing the voltage rating, current rating, and power rating for possible configurations of power converter modules in embodiments of the present invention; Figures 10a to 10c show the output ports of four bidirectional isolated DC/DC converter with reconfigurable connections;

Figure 11 shows reconfigurable structure with multiple AC and DC buses according to an embodiment of the present invention;

Figure 12 illustrates reconfigurable interfaces of an embodiment of the proposed hybrid microgrid module with external sources/storages/loads;

Figure 13 shows an overview diagram of an electronically reconfigurable structure of a hybrid AC/DC microgrid module according to an embodiment of the present invention;

Figure 14 shows a hybrid AC/DC microgrid module according to an embodiment of the present invention connected to a plurality of devices; Figure 15 illustrates the local communication network of a hybrid AC/DC microgrid module according to an embodiment of the present invention; Figure 16 illustrates Flash programming options for the digital signal processor of a power converter;

Figure 17 illustrates the procedure of plug-and-play incorporating live identification and live reprogramming in an embodiment of the present invention; and

Figure 18 shows a diagram of the integrated hybrid AC/DC microgrid module mechanical structure according to an embodiment of the present invention

DETAILED DESCRIPTION

Figure 3 shows an electrical energy management system according to an embodiment of the present invention. The energy management system forms a hybrid AC/DC microgrid that can be electronically reconfigured. As shown in Figure 3, the electrical energy management system comprises an adaptive integrated plug-and-play hybrid AC/DC microgrid module 300 which is coupled to a plurality of energy sources (both AC and DC); a plurality of energy storage devices; and a plurality of loads (both AC and DC). As shown in Figure 3, a wind turbine (or several wind turbines) 310 are coupled via a smart interface 312 to the AC/DC microgrid module 300. The smart interface 312 comprises a local controller 312a; a local communication bus interface 312b which may be implemented as a controller area network (CAN) bus interface; a memory 312c which may be implemented as a flash memory; a power interface 312d and a communication device 312e which may be implemented as a wireless antenna. The communication device 312e allows the smart interface 312 to communicate with a control module 350 of the AC/DC microgrid module 300. In some embodiments, the energy sources such as the wind turbines 310 may be located a distance from the AC/AC microgrid module 300 therefore wireless communication may allow flexibility.

A photovoltaic (PV) cell array 314 is coupled to the AC/DC microgrid module 300 via a smart interface 316. An energy storage device 318 is coupled to the AC/DC microgrid module 300 via a smart interface 320. A diesel generator 322 is coupled to the AC/DC microgrid module 300 via a smart interface 324. A number of electrical loads 326 are coupled to the AC/DC microgrid module 300 via a smart interface 328. The smart interfaces 316 320 324 & 328 are configured in an analogous manner to the smart interface 312 which couples the wind turbines 310 to the AC/DC microgrid module 300.

A plurality of electrical power converters are coupled to the AC/DC microgrid module 300. As shown in Figure 3, a first DC/DC converter 330 is connected to the AC/DC microgrid module 300 via a smart interface 332. The smart interface 332 comprises a local controller 332a; a local communication bus interface 332b which may be implemented as a controller area network (CAN) bus interface; a memory 332c which may be implemented as a flash memory; and a power interface 332d.

A second DC/DC converter 334 is connected to the AC/DC microgrid module 300 via a smart interface 336. A first AC/DC converter 338 is connected to the AC/DC microgrid module 300 via a smart interface 340. A second AC/DC converter 342 is connected to the AC/DC microgrid module 300 via a smart interface 344. The smart interfaces 336 340 & 344 are configured in an analogous manner to the smart interface 332 which couples the first DC/DC converter 330 to the AC/DC microgrid module 300.

The AC/DC microgrid module 300 comprises a control module 350 which has a local central controller 352. The local central controller 352 may be implemented using the ARM reduced instruction set computing (RISC) architecture. The local central controller 352 is coupled to a local communication bus 534, which may be implemented as a controller area network (CAN) bus. As shown in Figure 3, the local communication bus 534 includes connections 355 which allow data transfer between the local central controller 352 and the smart interfaces 312 316 320 324 328 332 336 340 & 344.

As described above, a smart interface comprising a power interface, a communication interface for example a communication bus interface, and a local controller has been proposed to bridge the connections between the main body of the AC/DC microgrid module 300 and the external devices. The information stored in the smart interface of the external devices can be transferred to the local central controller 352 of the AC/DC microgrid module 300 through the local communication bus 354 to facilitate the live identification of devices.

The power interfaces of the connected devices, for example, the power interface 312d of the smart interface 312 of the wind turbines 310, are connected to power terminals 356 of the AC/DC microgrid module 300.

Sensor devices 392 and protection / fault isolation devices 394 are connected to the power terminals 356. The protection/ fault isolation devices 394 comprise relays and contactors. The sensor devices 392 monitor the voltage and current of sources/loads/buses/ambient. The sensor devices 392 provide analogue signals which are sent to the local controller 350.

The AC/DC microgrid module 300 further comprises a first relay array 360 which comprises a plurality of relay cells 362, a second relay array 365 which comprises a plurality of relay cells 367, a third relay array 370 which comprises a plurality of relay cells 372; and a fourth relay array 375 which comprises a fourth plurality of relay cells 377.

The AC/DC microgrid module 300 further comprises a first DC bus 380; a second DC bus 382; a first AC bus 385 and a second AC bus 387. By selectively switching the relays of the relay arrays, connections between energy sources, power converters and energy loads can be established via the AC and / or DC buses. In some embodiments connections 384 allow connections between the energy sources and the energy loads to be directly established. Energy sources, energy storage, loads, and power converters are defined as external devices. Based on energy sources and load requirements, the module structure can be electronically reconfigured by controlling selected cells of relay array in ON or OFF states. The control firmware embedded in the power converter can be online reprogrammed accordingly. The plug-and-play feature of the proposed microgrid module are achieved through the above mentioned live reconfigurable structure, live identification of devices, and live reprogramming.

Power Electronics Building Block (PEBB) is a broad concept of designing modular power electronic systems incorporating the integration of power devices, gate drives, and other components to functional blocks. The adoption of functional building blocks simplifies the design, testing, onsite installation, and maintenance work for different specific microgrid applications. With the standardization of interfaces of the building blocks, control, and protection requirements, the value of PEBBs can be enhanced.

Two types standard PEBBs including bidirectional DC/DC converters and bidirectional AC/DC converters may be used in embodiments of the present invention. As described above, in order to satisfy the variable source voltage/current rating and different AC/DC loads requirements, the connections of proposed PEBBs should be able be reconfigured.

Figure 4 shows the structure of a relay cell of an embodiment of the present invention. The relay cell 400 comprises two single-pole double-throw (SPDT) relays or other electromagnetic switching devices: a first relay 410 and a second relay 420. The relay cell further comprises a coil 430. As shown in Figure 4, the first relay 410 and the second relay 420 share the same coil 430 resulting in the action of two SPDT simultaneously. Figure 4 shows two states: a relay 400 in the ON state and a relay 400' in the OFF state. The default state, two SPDT relays within the relay cell are connected to the terminals of B and B' respectively which is defined as the OFF state. When two SPDT relays are connected to the terminals of A and A', it is defined as the ON state. Figures 5a to 5d illustrate the basic principle of achieving electronically reconfigurable connections of input ports for two converters with the proposed relay cell. A bidirectional isolated DC/DC converter such as dual active bridge (DAB) converter is used in embodiments of the present invention. The converter is isolated by a high frequency transformer, which allows series or parallel connections at both sides of the converter.

As shown in Figures 5a and 5c, the relay cell 500' 500 is connected to input ports of two bidirectional DC/DC converters 502 504. Figure 5a shows the configuration when the relay cell 500' is in the OFF state. This is caused by the application of a control signal 532' causing the coil 530 of the relay cell 500' to be in the OFF state. Figure 5b shows the equivalent circuit between the bidirectional DC/DC converters 502 504. As shown in Figures 5a and 5b, when the relay cell is in the OFF state, the input ports of the two converters are in series connection.

Figure 5c shows the configuration when the relay cell 500 is in the ON state. This is caused by the application of a control signal 532 causing the coil 530 of the relay cell 500 to go to the ON state. Figure 5d shows the equivalent circuit between the bidirectional DC/DC converters 502 504. As shown in Figures 5c and 5d, when the relay cell is in the ON state, the input ports of the two converters are in parallel connection.

The above-described principle can be extended to more levels of relay cells, allowing the reconfigurable connections of more converters.

Figures 6 to 8 illustrate a two-level electronically reconfigurable connection of input ports of four converters with corresponding two level relay cells according to an embodiment of the present invention. As shown in Figures 6 to 8, the connections of a first isolated bidirectional DC/DC converter 602; a second isolated bidirectional DC/DC converter 604; a third isolated bidirectional DC/DC converter 606; and a fourth isolated bidirectional DC/DC converter 608 can be configured by three relay devices. The relay devices may be considered as a first level relay cell 610 comprising a first relay device 612 and a second relay device 614, and a second level relay cell comprising a third relay device 622. Each of the relay devices comprises two SPDT relays as described above in relation to Figure 4. In the configuration shown in Figure 6a, the first relay device 612 receives a control signal 613' which causes the first relay device 612 to be in the OFF state. In Figure 6a, the first relay device in the OFF state is denoted as 612'. Similarly, the second relay device 614 receives a control signal 615' which causes the second relay device 614 to be in the OFF state (denoted as 614') and the third relay device 622 receives a control signal 623' which causes the third relay device to be in the OFF state (denoted as 622').

Figure 6b shows the equivalent circuit of the first isolated bidirectional DC/DC converter 602; the second isolated bidirectional DC/DC converter 604; the third isolated bidirectional DC/DC converter 606; and the fourth isolated bidirectional DC/DC converter 608 with the relay devices of the first relay cell 610 and the second relay cell in the OFF state. As shown in Figure 6b, in this state, the first isolated bidirectional DC/DC converter 602; the second isolated bidirectional DC/DC converter 604; the third isolated bidirectional DC/DC converter 606; and the fourth isolated bidirectional DC/DC converter 608 are connected in series.

Figure 7a shows a configuration when the relay devices are all in the ON state. As shown in Figure 7a, the first relay device 612 receives a control signal 613 which causes the first relay device 612 to be in the ON state (denoted as 613). Similarly, the second relay device 614 receives a control signal 615 which causes the second relay device 614 to be in the ON state (denoted as 614) and the third relay device 622 receives a control signal 623 which causes the third relay device to be in the ON state (denoted as 622). Figure 7b shows the equivalent circuit of the first isolated bidirectional DC/DC converter 602; the second isolated bidirectional DC/DC converter 604; the third isolated bidirectional DC/DC converter 606; and the fourth isolated bidirectional DC/DC converter 608 with the relay devices of the first relay cell 610 and the second relay cell in the ON state. As shown in Figure 7b, in this state, the first isolated bidirectional DC/DC converter 602; the second isolated bidirectional DC/DC converter 604; the third isolated bidirectional DC/DC converter 606; and the fourth isolated bidirectional DC/DC converter 608 are connected in parallel.

Figure 8a shows a configuration when first relay device 612 and the second relay device 614 of the first level relay cell are in the ON state and the third relay device 622 in the second level relay cell is in the OFF state. In the configuration shown in Figure 8a, the first relay device 612 receives a control signal 613 which causes it to be in the ON state; the second relay device 614 receives a control signal 615 which causes it to be in the ON state and the third relay device 622' receives a control signal 623' which causes it to be in the OFF state.

Figure 8b shows the equivalent circuit of the first isolated bidirectional DC/DC converter 602; the second isolated bidirectional DC/DC converter 604; the third isolated bidirectional DC/DC converter 606; and the fourth isolated bidirectional DC/DC converter 608 when the relay devices are in the configuration shown in Figure 8a. As shown in Figure 8b, the first isolated bidirectional DC/DC converter 602 and the second isolated bidirectional DC/DC converter 604 are connected in parallel, and the third isolated bidirectional DC/DC converter 606; and the fourth isolated bidirectional DC/DC converter 608 are connected in series.

As described above in relation to Figures 6 to 8, each of the 1st-level relay cell selectively connects the input ports of two converters either in parallel or series connections. The 2nd-level relay cell controls the routing between 1st-level relay, resulting in the series (Fig. 6) and parallel connections (Fig. 7) and the mixture of both connections (Fig. 8) of four isolated bidirectional DC/DC converters.

As described above in relation to Figures 5 to 8 the connections between power converters can be configured by the relays of the relay arrays. Those of skill in the art will appreciate that although an even number of converters are shown to be connected by relay devices in the Figures, it should be understood that any number of converters can be connected by the relay devices in alternative embodiments of the resent invention. For instance, three converters can be connected in the way that two converters are connected in parallel with the third converter in series connection. Further, although the DC/DC converters having a rated output power voltage of 200V are shown as examples, it should be understood that the DC/DC converter having other rated output power voltage (e.g. 100V) can be used. Moreover, DC/DC converters having different rated output power voltages can be used in combination.

Figure 9 is a table showing the voltage rating, current rating, and power rating for possible configurations of power converter modules in embodiments of the present invention. As shown in Figure 9, with the proposed reconfigurable structure, the modular power converters (PEBBs) can be dynamically recombined together based on the specific sources' requirement like voltage rating, current rating, and power rating as shown in the table. For low voltage high current applications like supercapacitors, parallel connections can be configured. For high voltage low current like conventional centralized or string configured array, series connections can be configured.

In Figures 5 to 8 described above the reconfigurable routing at the input side of bidirectional DC/DC converter is discussed. The same principle can be applied to the output side. This could generate a variable DC grid voltage. For example, if the rated output voltage of DC/DC converter is 200V, different typical DC grid voltage can be created with series/parallel/ series-parallel combinations of output ports of the DC/DC converter.

Figures 10a to 10c show the output ports of four bidirectional isolated DC/DC converter with reconfigurable connections. As mentioned above, in this example the rated output of each DC/DC converter is 200V.

In the configuration shown in Figure 10a, a first bidirectional isolated DC/DC converter 1002; a second bidirectional isolated DC/DC converter 1004; a third bidirectional isolated DC/DC converter 1006; and a fourth bidirectional isolated DC/DC converter 1004 are connected in series. Thus a DC grid voltage of 800V can be created. In the configuration shown in Figure 10b, the first bidirectional isolated DC/DC converter 1002 and the second bidirectional isolated DC/DC converter 1004 are connected in parallel. The third bidirectional isolated DC/DC converter 1006 and the fourth bidirectional isolated DC/DC converter 1008 are also connected in parallel. The two parallel connected pairs are connected in series. Thus a DC grid voltage of 400V can be created.

In the configuration shown in Figure 10c, the first bidirectional isolated DC/DC converter 1002; the second bidirectional isolated DC/DC converter 1004; the third bidirectional isolated DC/DC converter 1006 and the fourth bidirectional isolated DC/DC converter 1008 are all connected in parallel. Thus a DC grid voltage of 200V can be created.

Correspondingly, different AC grid output can be generated to adapt to a wide range of AC sources' or AC loads' specifications.

Figure 1 shows reconfigurable structure with multiple AC and DC buses according to an embodiment of the present invention. The structure in Figure 11 has dual AC and DC buses.

The structure shown in Figure 11 comprises a first AC/DC converter 1102 and a second AC/DC converter 1104. A first DC bus 1110 and a second DC bus 1112 can be selectively coupled to the DC terminals of the first AC/DC converter 1102 and the second AC/DC converter 1104 by a first relay array 1120. The first relay array 1120 comprises a first relay device 1222 and a second relay device 1224.

A first AC bus 1130 and a second AC bus 1132 can be selectively coupled to the AC terminals of the first AC/DC converter 1102 and the second AC/DC converter 1104 by a second relay array 1140 and a third relay array 1150. The second relay array comprises a first relay device 1142 and a second relay device 1144. The third relay array comprises a first relay device 1152 and a second relay device 1154.

As described above with reference to Figure 11 , the first AC bus 1130 and the second AC bus 1132 are connected selectively connected to the AC ports of the AC/DC converters via relay arrays having two relay devices. Those of skill in the art will appreciate that additional AC buses may be added with corresponding additional relay devices added to the relay arrays. In such embodiments the number of relay devices in the relay array may depend on the number of AC buses. For instance, if there are three AC buses, each relay array may comprise three relay devices.

Bidirectional AC/DC converters may be employed to interconnect between the DC buses and AC buses. The specifications (bus voltage, frequency) of dual buses can be set individually to different value or the same value depending on the source and load requirements. As described above the interconnections between DC bus and AC bus can be reconfigured using the proposed relay cells.

The multiple bus design concept described herein boosts the overall redundancy, compatibility, and reliability of the system. In case of failure of part of the system, the proposed hybrid microgrid module can continue operation after reconfiguring the structure. The proposed hybrid microgrid module is capable of supplying power for loads of different standards and interconnecting with DC grids of different standards simultaneously. The proposed hybrid microgrid module is capable of powering AC loads of different standards, connecting with AC sources of different standards, and interconnecting with AC grids of different standards simultaneously. The technical challenges associated with AC sources/grids synchronization, transitions between islanded and grid connected operating modes can also be addressed.

Figure 12 illustrates the reconfigurable interfaces of an embodiment of the proposed hybrid microgrid module with external sources/storages/loads.

As shown in Figure 12, an interface component 1210 comprises three DC interfaces: a first DC interface 1212; a second DC interface 1214; and a third DC interface 1216. Each of the DC interfaces is implemented as, for example, a power socket which is both load and source compatible. In the example shown in Figure 12, a low voltage DC load 1213 is coupled to the first DC interface 1212; a high voltage DC load 1215 is coupled to the second DC interface 1214; and a DC source 1217 is coupled to the third DC interface 1216. The interface component 1210 comprises a plurality of relay cells. A first relay cell 1222 is coupled to the first DC interface 1212; a second relay cell 1224 is coupled to the second DC interface 1214; and a third relay cell 1226 is coupled to the third DC interface 1216.

As shown in Figure 12, the microgrid module comprises a DC bus 1230; a first DC/DC converter 1250; a second DC/DC converter 1252; and a third DC/DC converter 1254. A first relay array 1240 is coupled to the output ports of the DC/DC converters and is arranged to selectively connect the output ports with the DC bus to establish series or parallel connections between the output ports of the DC/DC converters as described above.

A second relay array 1242 is connected to the input ports of the DC/DC converters and is arranged to selectively connect the input ports of the DC/DC converters in series or parallel connections.

As shown in Figure 12, first relay cell 1222; the second relay cell 1224; and the third relay cell 1226 of the interface component 1210 can selectively connect the DC interfaces with either the DC bus 1230 or the input of the DC/DC converters. When the high voltage DC load is plugged into the socket, the corresponding relay switches to connect the DC bus. When the DC source 217 such as a PV or battery is plugged into the socket (the third DC interface 1216), the correspondingthird relay cell 1226 switches to the connection to the input ports of the second DC/DC converter 1252. When the low voltage DC load 1213 (48V/24V) is plugged into the socket (the first DC interface 1212), the first relay cell 1222 switches to the connection to the input ports of the first DC/DC converter 1250. Since all the converters are bidirectional, the power will transfer from high voltage DC grid to the low voltage DC load. On the AC side, the interface component 1210 comprises an AC interface 1262. For the AC side, both the source and load can be plugged into the same socket of the interface 1262. This is illustrated by AC source load 1264 shown in Figure 12. the microgrid module comprises a first AC bus 1280 and a second AC bus 1282. The interface component 1210 comprises a pair of AC relay cells 1270 which can selectively switch the AC source or load 1264 between the first AC bus 1280 and the second AC bus 1282. Thus, the relay cells 1270 can select the routing between the dual AC buses according to the requirements of AC source or AC load 1264. Figure 13 shows an overview diagram of an electronically reconfigurable structure of a hybrid AC/DC microgrid module according to an embodiment of the present invention. As shown in Figure 13, the hybrid AC/DC microgrid module 1300 comprises a controller 1310 which is coupled to a local communication bus 1312. The controller 1310 controls four relay arrays via the local communication bus 1312. A first relay array 1320 comprises relay cells which control connections to input ports of DC/DC converters 1360. The relay cells may be considered as first level relay cells 1322 and second level relay cells 1324 as described above in relation to Figures 6 to 8. A second relay array 1330 comprises relay cells which control connections to the output ports of the DC/DC converters 1360 and also relay cells 1336 which control connections to the DC ports of AC/AC converters 1370. The relay cells which control connections to the output ports of the DC/DC converters 1360 may be considered as first level relay cells 1332 and second level relay cells 1334. A third relay array 1340 comprises pairs of relay cells 1342 which can selectively couple the AC ports of the AC/DC converters 1370 to a first AC bus 1396 and a second AC bus 1398. The pairs of relay cells comprise combination of two relay cells for 4-wire AC interfaces. These relay cells comprise four relay arrays.

A fourth relay array 1350 comprises DC relay cells 1352 which can selectively connect DC interfaces 1382 with a first DC bus 1392; a second DC bus 1394 and the input ports of the DC/DC converters 1360. The fourth relay array 1350 further comprise AC relay cell pairs 1354 each comprising a pair of relay cells which can selectively connect AC interfaces with the first AC bus 1396 and the second AC bus 1398. The controller 1310 generates control signals for the relay arrays. The first relay array 1320 controls the connections of input ports of DC/DC PEBB 1360 to accommodate variable source voltage range/current range. The second relay array 1330 controls the connections of output ports of DC/DC PEBB 1360 and input ports of AC/DC PEBB 1370 resulting in variable DC grid voltage/current range. The third relay array 1340 controls the connections between output ports of AC/DC PEBB 1370 and dual AC buses. The routing of fourth relay array 1350 can be selectively controlled allowing load and source compatible interfaces. As a result, the overall structure of microgrid module can be electronically reconfigured subject to the actual states of four relay arrays.

As shown in Figure 13, each of the AC/DC converters 1370 and the DC/DC converters 1360 may comprise a digital signal processor (DSP) which communicates with the controller 1310 via the local communication bus 1312.

For the proposed hybrid AC/DC microgrid modules, the external devices comprise energy sources, energy storages, loads, and power converters. In order to achieve the "plug and play" function, the first step is the live identification of external devices. As described above in relation to Figure 3, a smart interface comprising power interface, communication interface, local controller has been proposed to connect the microgrid main body and external devices. The information modelling of these external devices is critical to realize fast identification. The International Standard IEC 6 850 defines the information models to be used in the exchange of information with distributed energy resources (DER). IEC 61850-7-420 provides the information model and logical nodes (LNs) for typical DERs, including electrical connection points (ECPs), controllers, generators, power converters, and auxiliary systems (such as measurement devices, protection devices). Other standards including IEC 61850 7-1 , 7-2, 7-3, and 7-4 provide the model principles of physical equipment. Those IEC 61850 models are defined generally based on relatively preliminary and rigid microgrid structure. For the proposed reconfigurable structure microgrid, information modelling of external devices may be improved based on previously mentioned standards.

The information processing in a proposed hybrid AC/DC microgrid module will now be described with reference to Figure 14.

Figure 14 shows a hybrid AC/DC microgrid module according to an embodiment of the present invention connected to a plurality of devices. The external devices can be categorized into two types: 1) core device: energy sources, energy storage, and loads); 2) auxiliary device: power converters.

The configuration of the AC/DC microgrid module 300 is as described above in relation to Figure 3.

In some embodiments control signals (ON and OFF commands) are sent to the relays of the relay arrays directly from the control module 350 of the AC/DC microgrid module 300.

As shown in figure 14, the smart interfaces of the core devices 312 316 320 324 & 328 process data which can be divided into four types: Control Signals; Status Information; Setting Information; and Measured Values. The smart interfaces of the auxiliary devices also comprise a firmware control component. The measured values may include metering information. The relay controllers may send control relay relative status information (CREL RSTA) to the control module 350. Table I and II give two specific examples of the information models of both core devices (battery energy storage) and auxiliary devices (power converter).

Table I: The information modelling example of battery energy storage

Battery voltage low or undercharged, Initial state of charge, State of health, Others.

Source type (Battery type); Operational authority ; Amp-hour capacity rating;

Minimum resting amp-hour capacity rating allowed; Nominal battery voltage;

Number of cells in series; Number of cells in parallel; Charge/discharge

Settings curve; Charge/discharge curve by time (Schedule); Self-discharge rate; Information Maximum battery charge/discharge current; Maximum battery charge/discharge voltage; High battery voltage alarm level; Low battery voltage alarm level ;Others.

Cycle life data vs depth of discharge curve; Actual amp-hour capacity vs discharge rate curve; Unit cost; Installation cost.

Table II: The information modelling example of power converter

Information

Details of each type

type

Measured input/output voltage/current/frequency/power; Power flow

Measured direction

Values Accumulated input/output energy; Measured heat sink temperature, enclosure temperature, and humidity; Others.

ON/OFF command; Converter functionality; Operating modes command; Economic dispatch parameters; Operating references of active/reactive

Controls

power; voltage level/current/frequency; Energy and ancillary service Signal

schedule; Operational characteristics; Relay/Contactor control signal; Protection signal; Others.

ON/OFF status; Relay/Contactor /circuit breaker status; Operating mode

Status

status;

Information

Fault signal; Others. Converter type; Power rating, input/output voltage & current & frequency range; Voltage & current & frequency thresholds for protection;

Settings

Operating range of heat sink temperature, enclosure temperature, and Information

humidity; Conditions of the converter including functional status, using time, life span; Others.

The information model of external devices can be divided into four types: Measured Values, Control Signal, Status Information and Settings Information. Measured Values refer to analogue data measured from the process or calculated in the functions such as currents, voltages, power, and physical measurements of temperature, irradiance, etc. Control Signals of core devices are mainly to control the ON/OFF and operating modes, while for auxiliary device more functionality like ON/OFF command, operating modes command, operating references, operational characteristics etc. should be defined. Status Information reflects the operating status and states of key index and key elements. For the Measured values, Control signal, Status information, the real time data will be exchanged with local central controller regularly. The Setting Information is the most important part of information model to identify the external devices. The Setting Information of core devices should include device type, operational authority, detailed device rating, specific characteristics of device provided by the manufactures. Similarly, through the Setting Information of power converter, the converter type and detailed converter ratings can be identified by the local central controller. Device rating information can be utilized to electronically reconfigure the system structure to adapt to newly added devices. Operational authority and device characteristics will be used in online management and optimization of energy management system (EMS) of the local central controller. Based on the above discussion, the proposed PEBBs are employed to accommodate a wide range of renewable energy sources, fossil energy sources, energy storages, and loads with electronically reconfigure structure. Therefore, the control firmware embedded in each PEBB should be able to reprogrammed correspondingly. On the other hand, if the EMS algorithm of the hybrid microgrid module has been updated, the control firmware also need to be updated accordingly. In embodiments of the present invention, a live reprogramming technique based on local communication bus (CAN bus) is proposed to avoid human intervention. Figure 15 illustrates the local communication network of a hybrid AC/DC microgrid module according to an embodiment of the present invention. The predesigned control firmware 1512 for different energy sources/loads will be stored in the memory storage of local central controller 1510. As shown in Figure 15, the smart interfaces 1530 devices (energy sources, energy storages and loads) are connected to the communication bus 1520. The smart interfaces 1540 of PEBBs (converters) are also connected to the communication bus 1520. Once a new device is identified, the device information will be collected through the communication bus 1520, which may include corporate characteristics, operational authority, operational characteristics, operating modes, economic dispatch parameters, etc. Under the control of local central controller 1510, the system structure will be electronically reconfigured to accommodate the newly added device. The collected device information will be merged into the existing program and written to flash of DSP 1542 of each PEBB on line. Figure 16 illustrates Flash programming options for the digital signal processor of a power converter. As shown in Figure 16, the Digital Signal Processor (DSP) 1600 may be implemented as a F2810, F2811 or F2812 DSP. The DSP comprises A central processing unit (CPU) 1602; Single Access Random Access Memory (SARAM) 1604; and Boot ROM 1606; Normally, for DSP controlled customized power module, the user's application codes can be predesigned and programmed to the Flash Array of DSP through JTAG communication interface 1608 (Option A as shown in Figure 16) or Serial-based (SCI/SPI) flash programming of the Boot ROM 1606 (Option B as shown in Figure 16). The JTAG communication interface 1608 implements serial communications according to the Joint Test Action Group (JTAG) standard.

Compared with these methods, CAN bus flash programming is a fast and popular method to program devices in-circuit and compatible with local CAN communication bus of the proposed hybrid microgrid module. The basic procedure of CAN bus live flash programming is:

1) Write the Communication Kernel and Flash Application program interface (CKFA) into one-time programmable (OTP) memory 1610 or in a protected sector of

Flash of DSP through JTAG Emulator.

2) The CKFA is automatically loaded into the DSP RAM upon reset under Boot ROM control.

3) The application code 1612 is transferred to the RAM and programmed into Flash under CKFA control through CAN bus.

Figure 17 illustrates the procedure of plug-and-play incorporating live identification and live reprogramming in an embodiment of the present invention.

The procedure is implemented by the central controller 1710 which comprises a local energy management system (EMS) 1720, a CAN bus processing module; and a database module 1740. The database module 1740 stores logical nodes 1742 corresponding to devices connected to the hybrid AC/DC microgrid module. The CAN bus processing module 1130 receives measured values, status information and setting information from smart interfaces 1760 of devices connected to the local communication bus 1750 and sends control signals to the smart interfaces 1760 of the devices over the local communication bus 1750.

The procedure is as follows:

Step 1 : When the external core device is plugged in, auxiliary power supply is established.

Step 2: Establish the CAN bus communication link between the external device and local central controller. Step 3: The external device uploads its information model through CAN bus 1750. A logical node 1742 is created in the database 1740 following a defined standard according to detected device type and corresponding memory resource is allocated. The logical node 1742 obtains the Measured Values, Status Information and Settings Information from CAN processing module.

The scale of logical nodes is dynamically expandable based on actual available microgrid resources. The logical node also serves as the Application Programming Interface (API) between EMS and local database.

Step 4: Operational data processing block 1722 of EMS obtains/updates data from logical nodes.

Step 5: Based on the analysis of available sources and load requirements, the microgrid structure is electronically reconfigured 1724. The Relay Array nodes states will change and send out the control signals to auxiliary systems to alter the states of physical Relay Array correspondingly through CAN bus 1750. While individual converter nodes can merge together to accommodate newly added device and source-sensitive application codes can be reprogrammed to the associated converter through CAN bus 1750.

Step 6: The On-line management and optimization block 1726 of EMS generates the control signals for external devices under the related optimization objective and constraints.

Step 7: Real time control signals 1728 transfer to the corresponding logical nodes and update their control signals settings. Finally the updated control signals will take effect after being delivered to the external devices through CAN bus communication. Figure 18 shows a diagram of the integrated hybrid AC/DC microgrid module mechanical structure according to an embodiment of the present invention. As shown in Figure 18, Modularized DC/DC converters 1802 and modularized DC/AC converters 1804 can be added and removed from the front panel of microgrid module 1800. When the converters are plugged in, both electrical and communicational connections with the main body are established. The human machine interface (HMI) 1810 is installed for display of microgrid module operation status in real time. User commands or operation preferences can also be configured through the HMI. AC and DC sockets 1820 with water splash resistance are installed on the front and back panels for integration of external devices including energy sources, storages, loads, etc. Sockets for interconnection among microgrid modules, which forms a scalable power park, are reserved to enhance system flexibility.

The proposed plug-and-play design described above can be implemented to enhance the flexibility, scalability and adaptability of the microgrid modules. The applications of the proposed microgrid modules covers electricity supply for remote villages, islands, stand-alone weather stations, signal towers, off-shore platforms, etc. Military application and disaster control in case of earthquake, flood, etc. which have high requirement of system reliability and flexibility are also the potential applications areas.

Whilst the foregoing description has described exemplary embodiments, it will be understood by those skilled in the art that many variations of the embodiments can be made within the scope and spirit of the present invention.

Claims

1. An electrical energy management apparatus comprising:

a plurality of interface ports for establishing electrical connections with electrical energy sources and / or electrical energy loads and / or electrical energy storage devices;

a plurality of electrical power converters each having input ports and output ports;

a relay array comprising a plurality of relay cells arranged to be switchable between connections to input ports and output ports of the plurality of electrical power converters; and

a controller configured to generate control signals for the relay cells of the relay array and thereby configure connections between the input ports and output ports of combinations of the electrical power converters.

2. An apparatus according to any preceding claim wherein the controller is operable to configure the relay cells of the relay array to establish series and / or parallel connections between the input and output ports of the electrical power converters.

3. An apparatus according to any preceding claim, further comprising a DC bus, wherein the relay cells of the relay array are configured to establish connections between the input and / or output ports of the electrical power converters and the DC bus.

4. An apparatus according to any preceding claim, further comprising an AC bus, wherein the relay cells of the relay array are configured to establish connections between the input and / or output ports of the electrical power converters and the AC bus.

5. An apparatus according to any preceding claim, further comprising a second relay array comprising a plurality of relay cells, the relay cells of the second relay array being coupled to the interface ports and switchably connected to the input ports of the plurality of power converters.

6. An apparatus according to any preceding claim wherein the plurality of electrical power converters comprises bidirectional DC/DC converters and / or bidirectional AC/DC converters.

7. An apparatus according to any preceding claim wherein the relay cells comprise single pole double throw switches.

8. An apparatus according to any preceding claim wherein the plurality of electrical power converters are detachably connected to the energy management apparatus.

9. An electrical energy management apparatus according to any preceding claim, further comprising a communication bus coupled to the controller, the interface ports comprising a connection to the communication bus to provide a communication link between the controller and interfaces of the electrical energy sources and / or electrical energy loads and / or electrical energy storage devices.

10. An electrical energy management apparatus according to claim 9 wherein the controller is configured to select a configuration for the relay cells using information received over the communication link.

11. An apparatus according to claim 9 or claim 10, wherein the electrical power converters are coupled to the communication bus and the controller is configured to generate control signals for the electrical power converters and to send the control signals over the communication bus.

12. An apparatus according to claim 11 wherein each of the electrical power converters comprises an interface component having a memory storing setting information and the controller is configured to generate control signals to update the setting information.

13. A method in a controller of an energy management apparatus, the method comprising: receiving signals indicative of electrical energy sources and / or electrical energy loads and / or electrical energy storage devices coupled to the energy management apparatus;

determining a microgrid structure for the of electrical energy sources and / or electrical energy loads and / or electrical energy storage devices coupled to the energy management apparatus; and

generating control signals for relay cells of the energy management apparatus to configure connections between the of electrical energy sources and / or electrical energy loads and / or electrical energy storage devices coupled to the energy management apparatus and electrical power converters according to the microgrid structure.