阅读说明：本技术 接地故障检测 (Ground fault detection ) 是由 S·伊莱森 于 2019-02-04 设计创作，主要内容包括：在配电系统中提供了一种接地故障检测方法。该方法包括：检测(30)配电系统中的接地故障；向第一切换设备发送指令以将第一能量存储单元(1)与能量存储系统断开连接(31),而其余的能量存储单元仍然并联连接到DC总线,以能够继续向配电系统供电；以及再次测试(32)接地故障。再次实施对接地故障的测试,并且重复断开连接、测试和重新连接的步骤,直到接地故障已经被识别(36、37)或者所有能量存储单元已经被测试为止。(A method of ground fault detection is provided in an electrical distribution system. The method comprises the following steps: detecting (30) a ground fault in the power distribution system; sending an instruction to the first switching device to disconnect (31) the first energy storage unit (1) from the energy storage system, while the remaining energy storage units remain connected in parallel to the DC bus to be able to continue to supply power to the power distribution system; and testing (32) the ground fault again. The testing for ground faults is performed again and the steps of disconnecting, testing and reconnecting are repeated until a ground fault has been identified (36, 37) or all energy storage cells have been tested.)

1. A method of ground fault detection in an electrical distribution system, the electrical distribution system comprising an energy storage system, a system controller, and a ground fault detection system, the energy storage system comprising a plurality of energy storage units, each energy storage unit of the plurality of energy storage units connected together in parallel to a DC bus of the electrical distribution system; each energy storage unit comprises a plurality of energy storage modules connected together in series; the method comprises the following steps:

detecting a ground fault in the power distribution system;

sending instructions to a first switching device to disconnect a first energy storage unit from the energy storage system while remaining plurality of energy storage units remain connected in parallel to the DC bus to enable continued power supply to the power distribution system;

testing the earth fault again;

providing an indication of the ground fault in the first energy storage unit if the ground fault is no longer present; sending an instruction from a controller to reconnect the first energy storage unit if the ground fault is still present;

sending an instruction from the controller to disconnect a next energy storage unit;

testing the earth fault again; and

repeating the steps of disconnecting, testing and reconnecting until the ground fault has been identified or all energy storage units have been tested.

2. The method of claim 1, wherein if the ground fault persists after all energy storage units have been tested, providing an indication that the ground fault is in a portion of the power distribution system other than the energy storage system.

3. The method of claim 1 or claim 2, wherein the method further comprises:

connecting a removable ground fault detection unit to the disconnected energy storage unit, which has identified the ground fault, and

a process is implemented to identify a faulty one of the energy storage modules within the energy storage unit.

4. The method according to any of the preceding claims, wherein the process comprises:

isolating the first module at the two terminals;

checking the remaining plurality of modules for a ground fault;

removing and replacing the isolated module if there is no ground fault; if the ground fault is still present; reconnecting the isolated module;

isolating the next module;

checking the ground fault in the cabinet again;

if the ground fault is still present, the steps of isolating and checking are repeated until a faulty module is determined.

5. The method according to any one of the preceding claims, wherein the method further comprises: reconnecting the cabinet to the energy storage system after removing and replacing the failed module and determining that no additional failed modules exist.

6. The method according to any of the preceding claims, wherein the steps of isolating, checking and reconnecting are performed automatically under the control of one local cabinet controller, isolating the module by sending a control signal to one module switching device to test for a ground fault in the remaining plurality of modules, and if a ground fault is not found, reconnecting the module.

7. An electrical power distribution system comprising an energy storage system, a system controller, and a ground fault detection system; wherein the energy storage system comprises a plurality of energy storage units, each of the plurality of energy storage units connected together in parallel to one DC bus of the power distribution system; each energy storage unit comprises a plurality of energy storage modules connected together in series; wherein the ground fault detection system comprises a ground fault detection module and a control module; wherein each energy storage unit includes a switching device to connect or disconnect one energy storage unit from the DC bus under control of the control module, while the remaining plurality of energy storage units remain connected in parallel to the DC bus to enable continued power to the power distribution system.

8. The power distribution system of claim 7, wherein each energy storage module comprises a plurality of energy storage devices connected together in series.

9. The power distribution system of claim 8, wherein the plurality of energy storage devices comprise one of electrochemical cells or batteries.

10. The power distribution system of any of claims 7-9, wherein the power distribution system is an isolated power system that can continue to operate in the presence of a ground fault condition.

Technical Field

The present invention relates to ground fault detection systems and methods for energy storage modules, particularly modules comprising electrochemical cells or batteries that provide electrical energy to an end user.

Background

Various types of stored electrical energy modules or stored electrical energy power units are becoming increasingly common in many applications, particularly where there are environmental or public health issues related to emissions in sensitive environments. Stored electrical energy power units are commonly used to provide electrical energy to operate equipment to avoid emissions while in use, although stored energy may have been generated in many different ways. The stored electrical energy may also be used to provide peak shaving in systems that are otherwise powered from the electrical grid or from various types of power generation systems, including diesel generators, gas turbines, or renewable energy sources. Aircraft, vehicles, ships, offshore drilling rigs, or drilling rigs in remote locations and other power plants are examples of users who store electrical energy on a large scale. The vehicle driver may use the stored energy power unit in city centres and charge from the internal combustion engine on the main road to reduce harmful emissions in towns and cities, or the vehicle driver may charge from the electricity supply. Ferries that make most voyages relatively close to populated areas or in sensitive environments are designed with hybrid or all-electric drive systems. The ferry can use the stored energy to power the vessel when near shore and use a diesel generator to recharge the battery when offshore. In some countries, the availability of power from renewable energy sources for charging the stored energy unit means that fully electric ships can be used, without using diesel or other non-renewable energy sources at all, as long as the stored energy unit is reliable enough for the covered distance. At a stop, whether hybrid or fully electric, the stored energy unit can be charged onshore. In order to obtain a sufficiently reliable stored energy unit for long-term use as a main power supply, certain technical problems have to be solved in the development of the technology.

Disclosure of Invention

According to a first aspect of the invention, a ground fault detection method in an electrical distribution system, the electrical distribution system comprising an energy storage system, a system controller, and a ground fault detection system, wherein the energy storage system comprises a plurality of energy storage units, each of the plurality of energy storage units being connected together in parallel to a DC bus of the electrical distribution system; each energy storage unit comprises a plurality of energy storage modules connected together in series; the method comprises the following steps: detecting a ground fault in the power distribution system; sending instructions to the first switching device to disconnect the first energy storage unit from the energy storage system while the remaining energy storage units remain connected in parallel to the DC bus to enable continued power supply to the power distribution system; testing the earth fault again; providing an indication of the ground fault in the first energy storage unit if the ground fault is no longer present; sending an instruction from the controller to reconnect the first energy storage unit if the ground fault is still present; sending a command from the controller to disconnect the next energy storage unit; testing the earth fault again; and repeating the steps of disconnecting, testing and reconnecting until a ground fault has been identified or all energy storage cells have been tested.

If the ground fault persists after all of the energy storage units have been tested, an indication of the ground fault in a portion of the power distribution system other than the energy storage system may be provided.

When a faulty cabinet has been identified, the system may continue to operate without the cabinet-in some cases the fault may be in the cabinet rather than in a module of the cabinet-or an operator may replace all battery modules in the cabinet without looking for the exact location of the fault, but preferably the method further comprises: the method includes connecting a removable ground fault detection unit to a disconnected energy storage unit that has identified a ground fault, and implementing a process of identifying a faulty energy storage module within the energy storage unit.

The process may include: isolating the first module at the two terminals; checking the remaining modules for a ground fault; removing and replacing the isolated module if there is no ground fault; if the ground fault is still present; reconnecting the isolated module; isolating the next module; checking the ground fault in the cabinet again; if the ground fault is still present, the steps of isolating and checking are repeated until a faulty module is determined.

The method may further comprise: after removing and replacing the failed module and determining that no additional failed modules exist, the rack is reconnected to the energy storage system.

The steps of isolating, checking and reconnecting may be performed automatically under the control of the local cabinet controller, isolating the module by sending a control signal to the module switching device to test for a ground fault in the remaining modules, and if a ground fault is not found, reconnecting the module.

According to a second aspect of the invention, a power distribution system comprises: an energy storage system, a system controller, and a ground fault detection system; wherein the energy storage system comprises a plurality of energy storage units, each of the plurality of energy storage units connected together in parallel to a DC bus of the power distribution system; each energy storage unit comprises a plurality of energy storage modules connected together in series; the ground fault detection system comprises a ground fault detection module and a control module; wherein each energy storage unit includes a switching device to connect or disconnect each energy storage unit from the DC bus under control of the control module, while the remaining energy storage units remain connected in parallel to the DC bus to enable continued power supply to the power distribution system.

There may be one energy storage device in the cabinet, or there may be multiple energy storage devices in the cabinet. For a plurality of energy storage devices, the energy storage devices are connected in parallel or in a combination of series and parallel, but preferably each energy storage module comprises a plurality of energy storage devices connected together in series.

The energy storage device may comprise one of an electrochemical cell or a battery.

The power distribution system may be an isolated power system capable of continuing to operate in the presence of a ground fault condition.

Drawings

Examples of ground fault detection systems and methods for energy storage modules in an electrical distribution system according to the present invention will now be described with reference to the accompanying drawings, in which:

FIG. 1 is a block diagram illustrating an example of a modular stored energy system in which the present invention may be applied;

FIG. 2 is a block diagram illustrating the present invention; and is

Fig. 3 is a flow chart illustrating a method according to the present invention.

Detailed Description

Early large batteries were lead-acid, but recently, lithium ion batteries have been developed for large applications for electrical energy storage. Lithium ion batteries are typically pressurized and the electrolyte is flammable, thus requiring care in using and storing the lithium ion batteries. A problem that may occur with lithium ion batteries is thermal runaway, which may be caused by internal short circuits generated in the battery cells during manufacturing. Other causes such as mechanical damage, overcharging, or uncontrolled current flow may also cause thermal runaway, but battery system designs are generally adapted to avoid these conditions. Manufacturing problems of the unit cannot be completely eliminated and therefore precautions are required to minimize the effects of thermal runaway occurring. In large lithium ion battery systems, limiting the amount of energy released during thermal runaway is a challenge. The thermal event may raise the temperature in a single unit from a standard operating temperature in the range of 20 ℃ to 26 ℃ up to 700 ℃ to 1000 ℃. The safe operating temperature is below 60 ℃, and therefore this is a serious problem.

In the marine and offshore industries, there are strict regulations on the risk of a vessel or drilling rig, one requirement being that no excess temperature must be transferred from one unit to another. If overheating occurs, the overheating should be limited to a single cell and not allowed to diffuse. In addition, for marine and offshore applications, the weight and volume of any equipment is severely limited, resulting in a compact, lightweight system that is preferred. It is a challenge to produce a compact, lightweight system that achieves the required thermal isolation and quickly and efficiently cools units that experience overheating.

In lithium ion battery systems, it is very important that the temperature of the battery cells not exceed a specified operating temperature and that the cell temperature is uniform throughout the system. Continued operation outside of the specified operating temperature window may severely impact the life of the battery cell and increase the risk of thermal runaway.

For marine applications, it is of particular interest to use energy storage modules, such as batteries, at their maximum charge or discharge rate due to the installation costs and the weight and space occupied by the modules on a ship or offshore platform. Furthermore, maintenance and repair or replacement is complex and expensive compared to land-based use of the stored energy system, and therefore extending the life of the stored energy module is particularly important. Taking a lithium ion battery as an example, a lithium ion battery is sensitive to high temperatures, and therefore it is important to ensure that the operating temperature and ambient temperature are controlled for all cells of the lithium ion battery system to ensure that the design life is reached. Local variations or hot spots on the individual cells may also impair the achievable overall lifetime.

An example of an energy storage system to which the present invention may be applied is illustrated in fig. 1. The system includes an energy storage unit (e.g., a cabinet or cabinet 1) in which a plurality of energy storage modules 10 are electrically connected together in series by a bus 2a to a cabinet controller 28 and to a central controller 3 by a bus 2 b. Typically, the module includes enough battery cells of about 3V that are electrically connected in series to form a battery module of at least 78V, and in some cases, up to 120V. Within a single cabinet or cabinet of about 1kV, the battery modules are electrically connected in series. For the entire system, there are multiple cabinets in parallel in the battery compartment.

Each of the energy storage modules is cooled by a cooling fluid which circulates from the cooling system 5 through an inlet duct 6 and an outlet duct 7. The cooling systems may be fluidly connected in series or in parallel. The parallel connection simplifies providing the same temperature of cooling fluid to each module. The cooling fluid is typically water, which is less expensive than synthetic coolants and is easier to obtain and dispose of. Each energy storage module 10 includes a plurality of energy storage devices, e.g., a plurality of battery cells, electrically connected together in series. This type of modular system, including cooling, is particularly suitable for lithium ion cells.

Within the module 10, on one side of each cell, a battery cell cooler is provided through which cooling fluid from the cooling system 5 passes to cool the battery cells via an inlet pipe 6 and an outlet pipe 7. The cell cooler comprises a conduit through which the cooling fluid flows, which may be a metal conduit, but more typically is a synthetic material such as a polymeric plastic (e.g., polyethylene), a polyamide (such as PA66 plastic), or a thermoplastic (such as TCE2, TCE5) or other suitable material that can be molded or extruded into a desired shape and that is capable of withstanding the normal operating temperatures of the energy storage module 10.

US20160336623 describes a monitoring and regulating system for energy storage devices comprising a battery management system capable of opening a relay or contactor when the measured current exceeds a predetermined threshold when charging, discharging or idle, and may also include monitoring ground fault or leakage current conditions in the unit.

Ground faults in electrical systems are undesirable and may cause safety problems, and there is therefore a need to eliminate them as soon as possible in practical situations. There are many standardized grounding systems that can be used in power distribution networks. The TT system is a system in which the points of the power supply equipment are directly grounded and the consumers are locally directly grounded; TN systems are systems in which the power supply is grounded and all exposed conductive parts are connected to a neutral conductor; and IT systems are systems without a connection to ground, the IT systems are isolated or there is a high impedance ground connection.

For grounded power systems (such as TN systems), a ground fault can result in a fault current that can be very large and the system must be designed to eliminate the fault current through a fuse, circuit breaker, or equivalent. However, isolated power systems (IT systems) are generally able to continue operating under ground fault conditions, although IT is desirable to eliminate ground faults as quickly as possible by disconnecting faulty equipment from the power system. If the fault is not timely cleared, maintaining operation in the presence of a ground fault condition in the IT system may result in a voltage to ground that rises, which may cause damage to equipment or pose a threat to personnel. An unremoved ground fault may also make IT systems more susceptible to a second ground fault. In this case, the second ground fault generally causes a fault current in the TN system similar to the first ground fault.

For critical operations, such as for marine and offshore power systems, e.g. for hospital equipment to be kept on a drilling vessel or at an onshore location, it is generally considered that in the presence of a ground fault, maintaining operation is better than risking disconnecting the necessary equipment. For marine and offshore power systems, ground faults typically cause the opening of a bus tie, isolation of the two power systems onboard the vessel, so that if a second ground fault occurs, only half of the power systems are shut down. This is not an ideal situation and should still disconnect the malfunctioning equipment if possible.

To eliminate the earth fault, a means of disconnecting the faulty equipment, usually a circuit breaker, is required and the location of the earth fault must be known in order to disconnect the correct equipment. A ground fault detection system for an isolated system may be used to detect ground faults, and a current transformer connected to the detection system may provide an indication of which part of the system a fault occurs. An energy storage system may include several battery cells connected in parallel, and if a ground fault occurs in one of the battery cells, a large number of current transformers are required for accurate positioning.

Typically, ground fault detection is provided only at the system level, which gives an indication that a ground fault has occurred, but no indication as to which part of the system the fault is located. This requires extensive manual troubleshooting, which is time consuming and in most cases requires operation on a powered system. Once the ground fault has been located, the relevant part of the system can be disconnected. Conventional approaches require a current transformer for each branch if ground fault detection is to be performed more accurately. In the event of a ground fault in an energy storage system, it is desirable to be able to locate the fault in a more efficient manner in order to determine which cabinet is faulty and then determine all of the modules within the cabinets that are to be replaced, without having to use a large number of current transformers to obtain more detailed information. While it is possible to locate a current transformer on each cabinet to give a more precise location of the ground fault and isolate it, it is still bulky and expensive and the design of the present disclosure overcomes these problems.

The present invention utilizes the built-in features of conventional energy storage systems to effectively locate and eliminate faults without requiring many current transformers to locate ground faults. On a coarser level, this can also be implemented without manual troubleshooting. Fig. 2 and 3 illustrate the system of the present invention and the processes involved in handling ground faults using the method of the present invention. A plurality of cabinets 1 are connected in parallel by DC buses 41, 42. A current transformer 43 is provided for both phases. Within each cabinet is a controller 3, which controller 3 comprises a switching device, such as a circuit breaker 40, which switching device can be activated upon receiving a control instruction via a control signal from a central controller 44. There is no power flow from the central controller. Both phases are disconnected and the battery string is completely electrically isolated from the rest of the system. The controller can open or close the circuit breaker in each cabinet at a time to disconnect that cabinet. At the same time, all other cabinets are still connected to the system and can provide energy.

When a ground fault is detected 30 in the energy storage system, for each of the plurality of cabinets 1 containing energy storage modules 10, the switching device 40 located in the cabinet may be used to disconnect one cabinet at a time. The process can be automated by using Programmable Logic Controller (PLC) circuit breakers or other suitable means of providing electrical isolation. The circuit breakers may be selected and disconnected under the control of a central system controller. Starting from the first of the n cabinets 1, in response to an instruction to disconnect that cabinet, the cabinet n-1 is disconnected 31 by opening the breaker of that cabinet. A test 32 is made to see if a ground fault is still present. If there is still a ground fault 33 after the cabinet 1 has been disconnected, the cabinet is reconnected 34 by closing the circuit breaker in response to an instruction from the controller. The next cabinet (n ═ n +1) is selected 35 and the connection 31 is then disconnected in the same way. This process is repeated until the effect of disconnecting a particular cabinet 1 is that the ground fault detector indicates 36 that there is no longer a ground fault. The ground fault detector may be provided by the current transformer 43 of fig. 2 together with a data processing unit, which is typically part of the system controller 43. The indication that there is no longer a ground fault means that the ground fault has been successfully located 37 and that the particular cabinet that was disconnected, which resulted in the ground fault being removed, is kept disconnected.

This method is suitable for locating a single ground fault and is therefore not suitable for TN systems with "ground faults" in design. If there are two ground faults in the system (e.g., the first actual ground fault in a TN system or the first and second ground faults in an IT system), a large fault current of the same order of magnitude as the short circuit will flow, and therefore one of the circuit breakers in the system operates due to this high current at this time to prevent the flow of the large fault current. Eliminating the first ground fault as soon as possible avoids entering this phase. When the circuit breaker has been operated, the circuit breaker has actually isolated one of the ground faults, so the method of the invention can be used to locate and eliminate a second ground fault.

The operator may then be directed to the failed energy storage unit to test for the failure within the cabinet. Once a faulty enclosure has been identified, the fault can be narrowed down to the module level. This relies on disconnecting the modules, thus requiring that the individual modules can be isolated. For example, each module may have a circuit breaker disposed within the module to isolate the module at two terminals. The circuit breaker can also be operated remotely. This process may be implemented by an operator on that particular cabinet using a removable or handheld ground fault detection system in a similar manner to the process of fig. 3, but within the cabinet with the ground fault, isolating one module at a time until the fault disappears. The failed energy storage module may then be disconnected, removed from the cabinet and replaced, and the cabinet reconnected to the energy storage system. In practice, the cost of having a circuit breaker in each module and the relatively low number of modules in a cabinet or string means that it may be preferable to manually disconnect one module at a time by removing power cables or the like connected to the modules.

The method of the present invention can be implemented without the need for additional hardware, enabling automatic localization of ground faults in the energy storage system without the need for current transformers on each battery pack. Circuit breakers controlled via programmable logic controllers or other similar devices installed in each cabinet can be easily integrated into the energy storage system. The method allows the following quick checks to be made: when a ground fault is detected on the power distribution system level, whether the fault is located in the energy storage system, and if the fault is located in the battery system, whether the fault is eliminated is this check; or the method indicates that there is no fault in the energy storage system, then manual troubleshooting of other portions of the power distribution system may be performed. The power distribution system includes all portions of the power system that are electrically connected to the energy storage unit. A portion of the power circuit may be separated from another portion of the power circuit by using a transformer, so all portions of the same power system as the energy storage unit, which do not have a transformer in between, are included in the power distribution system.

The method of the present invention is particularly suitable for energy storage systems compared to other parts of the power system, since there are multiple power sources or loads electrically connected together in parallel in the battery system, i.e. the cabinet shown in fig. 2. Each cabinet is not important to the system individually, so the cabinets can be disconnected temporarily without losing any functionality compared to disconnecting motors operating specific loads that should not be interrupted. The time each cabinet is disconnected is typically in the range of 5 seconds to 20 seconds, and during this interval the other cabinets may increase or decrease their state of charge compared to the disconnected cabinet. However, the interval is short enough that the difference in state of charge between the reconnected battery pack and the other packs is very limited, meaning that this can be done safely.

The energy storage system is able to handle operation with a temporary reduction in maximum power associated with disconnecting one of the racks containing battery modules, for example in the example illustrated in fig. 2, four of the five racks remain connected throughout the test. Disconnecting a battery pack only represents a temporary reduction in power, but the available energy is not reduced for a long time, since once a fault has been identified, a healthy battery pack can be reconnected after a short time.

In the event of a ground fault being detected in the energy storage system, the system is arranged to automatically implement troubleshooting to determine which cabinet is faulty, avoiding many manual troubleshooting. This reduces maintenance costs because the man-hours required for troubleshooting can be limited to the time it takes to identify and replace one or more modules in the cabinets that the system has identified as faulty without having to traverse each cabinet before this step can begin. Reducing the use of personnel in troubleshooting reduces the risk of injury during troubleshooting of the failed power system. This method makes it possible to significantly reduce the time for which the system must continue to operate in the presence of a ground fault, thus minimizing the risk of a serious second ground fault occurring. No current transformers are required in each cabinet to pinpoint faults, which reduces assembly time, cost, and space requirements.

Although detailed examples have been given for electrochemical units, such as batteries, e.g. lithium ion, alkaline or NiMh batteries or other batteries, the invention is applicable to other types of stored energy units, in particular non-cylindrical capacitors, supercapacitors or supercapacitors, fuel cells or other types of energy storage.