Fault location of DC distribution systems

Unique systems, methods, techniques and apparatuses of fault location in DC power distribution systems are disclosed. One exemplary embodiment is a DC power distribution system including a plurality of zones each including a DC power distribution line and a protective device. Each protective device structured to sense one or more electrical characteristics of a line and to controllably open a circuit including the line. At least one intelligent electronic device is structured to determine a line inductance based upon electrical characteristics sensed by one or more of the protective devices and to evaluate a location of the line fault based upon the determined line inductance.

BACKGROUND

The present disclosure relates generally to fault location in DC distribution systems, sometimes referred to as DC distribution networks. Recent improvement in energy and power density of power electronic switches has facilitated development of DC power distribution systems. Present efforts at fault location in DC power distribution systems suffer from a number of shortcomings and disadvantages. Existing proposals fail to effectively implement fault current limiting (FCL) functionality and to reduce the adverse impacts of high fault current on equipment within or coupled with the DC power distribution system and on the DC power distribution system itself. There remain unmet needs respecting identification of fault location, speed of fault protection, comprehensive coverage of protected system zones, reliability, minimization of communication delay, and local measurement of fault conditions and fault characteristics. Further unmet needs include enhancing protection selectivity, minimizing fault affected areas, accurate fault location, reducing equipment cost, reduction of fault currents, reducing post-fault over voltages, and fast fault protection. There is a significant need for the unique apparatuses, methods, systems and techniques disclosed herein.

DISCLOSURE

For the purposes of clearly, concisely and exactly describing non-limiting exemplary embodiments of the invention, the manner and process of making and using the same, and to enable the practice, making and use of the same, reference will now be made to certain exemplary embodiments, including those illustrated in the figures, and specific language will be used to describe the same. It shall nevertheless be understood that no limitation of the scope of the invention is thereby created, and that the invention includes and protects such alterations, modifications, and further applications of the exemplary embodiments as would occur to one skilled in the art with the benefit of the present disclosure.

SUMMARY

Exemplary embodiments include unique fault location systems, methods, techniques and apparatuses for DC power distribution systems. Further embodiments, forms, objects, features, advantages, aspects and benefits of the disclosure shall become apparent from the following description and drawings.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

With reference toFIG. 1there is illustrated an exemplary DC power distribution system100. In the illustrated embodiment, DC power distribution system100is structured as a converter-based, tightly-coupled DC power distribution system. In other embodiments, system100may be structured as another type of DC power distribution system. It shall be appreciated that system100may be implemented in a variety of applications, including power distribution systems in naval and marine vessels, land vehicles, construction equipment, mining equipment, aircraft, factories, manufacturing or other industrial facilities, data centers and server farms to name but a few examples.

DC power distribution system100includes AC/DC converter107which is structured to receive AC power from a transmission line or generation source (not illustrated), convert the AC power to DC power, and provide DC power to DC power distribution system100. System100includes a plurality of protection zones101,102and103, and load zones104and105. AC/DC converter107is operatively coupled to protection zone101which includes DC power distribution line113and local protective device111which is operatively coupled with distribution line113.

In certain embodiments local protective device111includes a controllable circuit opening device such as a circuit breaker, relay, contactor or other device that can open and close a circuit including local protective device111. In certain embodiments local protective device111includes devices or equipment which are structured to sense one or more electrical characteristics associated with distribution line113with which local protective device111is coupled, for example, current sensors and/or voltage sensors. In certain embodiments local protective device111includes one or more intelligent electronic devices such as a microcontroller-based control unit structured to receive and process information of electrical characteristics sensed by the sensor electronics of local protective device111. In certain embodiments the intelligent electronic devices may be remote from local protection device111and/or may be operatively coupled with multiple local protective devices. In certain embodiments each local protective device111may include a dedicated associated intelligent electronic device. It shall be appreciated that any or all of the foregoing features may also be present in the other protective devices disclosed herein. In certain embodiments the one or more intelligent electronic devices may be capable of performing some or all of the calculations described below, receiving command signals and/or transmitting command signals.

Zone boundary12defines a boundary between protection zones101and102. Protection zone102includes lines123and124which are coupled with local protective devices121and122, respectively. Lines123and124are also coupled with one another, for example, via a common node or via a DC bus. It shall be appreciated that local protection devices121and122may include some or all of the structural and functional features described above in connection with local protective device111.

Zone boundary23defines a boundary between protection zones102and103. Protection zone103includes lines133and134which are operatively coupled with local protective devices131and132, respectively. Lines133and134are also coupled with one another, for example, via a common node or via a DC bus. It shall be appreciated that local protection devices131and132may include some or all of the structural and functional features described above in connection with local protective device111.

Protection zone103is coupled with load zone104. Protection zone106is coupled with load zone105. More specifically, line133is coupled with load zone104which includes loads141-144coupled with line133by way of local protective devices145-148, respectively. Line134is operatively coupled with load zone105which includes loads151-154and local protective devices155-158. Loads151-154are connected to line134by way of local protective devices155-158, respectively. Each load151-154,141-144may be fed by a DC/DC converter (not illustrated) or may be driven directly by the DC line or DC bus with which it is coupled.

In the illustrated embodiment, system100is a converter-based tightly coupled DC power distribution system. In another embodiment, system100may be structured as a variety of other types of DC power distribution systems.

With reference toFIG. 2there is illustrated DC power distribution system200. It shall be appreciated that system200and the features and components thereof may include any or all of the structural and functional features and attributes described above in connection with system100. System200includes four zones210,220,230and240. Zone210includes line213and local protective device211and is defined in part by zone boundary212which also defines in part adjacent zone220. Local protective device211is operatively coupled to line213which may receive DC power from a DC power transmission system, an AC/DC converter, and/or a DC/DC converter, which may, in turn, be coupled with a power generation or transmission system as applicable. For clarity of illustration these features have not been depicted inFIG. 2, it being appreciated that a variety of configurations and combinations of these features are contemplated.

Zone220is bounded by zone boundaries212and223. Zone220includes local protective device222, line224and inductor221which is positioned in line with local protective device222and line224. Local protective device222and inductor221are operatively coupled to line224in a series relationship in the illustrated embodiment, it being appreciated that other operative coupling relationships are also contemplated. It shall be further appreciated that other types of functionally equivalent inductance affecting devices may be utilized to adjust line inductance in accordance with the principles disclosed herein. It shall be further appreciated that such potential variations may also be utilized for the other inductors disclosed herein Zone220is operatively coupled with and adjacent to zones210and230.

Zone230is bounded in part by zone boundary223. Zone230includes local protective device231, line233and inductor232. Local protective device231and inductor232are operatively coupled to line233in a series relationship in the illustrated embodiment, it being appreciated that other operative coupling relationships are also contemplated.

Load zone240includes local protective device241, inductor242and load245. Load245is operatively coupled to line233of zone230by way of local protective device241and inductor242. Local protective device241and inductor242are operatively coupled to line233in a series relationship in the illustrated embodiment, it being appreciated that other operative coupling relationships are also contemplated.

With continuing reference toFIG. 2, it shall be appreciated that inductors221,232, and242are provided at or proximate the boundaries separating zones210,220,230and240. In certain preferred forms, placement of inductors is selected to be as close as possible to a zone boundary without adversely affecting the operation of local protective devices in adjacent zones. The zone boundary inductance are preferably large enough to overcome the neighboring protection zone overlapping caused by measurement errors as described in further detail herein. By way of example, if all estimated measurement errors contribute to ˜10% error in calculated inductance, then the zone boundary inductance should be ˜10% of inductance plus a margin of error. In certain embodiments, the zone boundary inductances are large enough to discriminate different distribution lines. It shall be further appreciated that in certain preferred forms the inductances of inductors221,232and242are much smaller than system equivalent inductance such that they have little to no impact on noannual operation of system200.

With reference toFIG. 3there are illustrated graphs301and302which depict inductance values observable at the protective devices of system200during normal operation both before and after the addition of inductor242to zone240. The inductance values include inductance310of zone210; inductance320of zone220; inductance330of zone230; and inductance340of zone240. Inductances310,320,330and340are representative of the inductances which can be determined by local protective devices211,222,231and241, respectively, during normal, non-fault operation of system200when system200is on line.

Protective devices211,222,231and241are capable of protecting one or more protection zones. When a fault such as a line-to-line short circuit fault, line-to-ground fault or other type of fault occurs in system200, the fault current limiting (FCL) function of one or more converters which may be coupled with system200can be initiated. Due to communication delay and inherent FCL control time constants, fault currents normally are uncontrolled for a certain time before limited to a fixed value. Transient voltages and currents during an uncontrolled period can be measured by local protective devices211,222,231and241. The measured voltages and currents can be used to determine the inductance between a protective device and the fault location. If the derived inductance is less than already known line inductance for a given zone, then the fault is within the protected zone and the corresponding protective device will open to isolate the faulted part. The remaining portion of the DC power distribution system can continue normal operation. These operations can occur in advance of the time required to achieve the steady state current by the FCL function of a converter coupled with system200. This allows for either redundant protection schemes, or elimination of the converter-based FCL functionality. With this inductance based fault location technique, fast and selective protection schemes of DC power distribution systems can be readily achieved.

In the circuit configuration associated with graph302, the derived inductance values can be used to indicate the faults within most zones of system200even considering measurement errors. This can be accomplished because the fault inductances311,321and331of zones210,220and230(which are lower than the normal, non-fault inductances310,320and330) do not extend into adjacent zones or overlap. However, in the absence of inductors221,232,242this is not the case for zones220,230and240. Since there is overlap between the inductances of these zones due to measurement errors, it is not practicable to reliably differentiate between faults in the neighboring two zones. The addition of inductor242to zone240alleviates this overlap by providing an offset non-fault inductance343and an offset fault inductance345as illustrated graph302. The amount of added inductance is denoted by offset inductance342. Similar offset occurs for zone220and230. After the added inductances, the location of faults in any of zones210,220,230and240can be uniquely distinguished. It shall be further appreciated that in certain embodiments, the insertion of inductors can be extended to each protection zone not only to differentiate faults between neighboring zones but also to increase fault location accuracy for the full range of a protected zone. It shall be appreciated that similar methodology may be utilized to select the parameters and locations of inductors or other impedance altering components for other protection zones of a DC power distribution system.

With reference toFIG. 4there is illustrated equivalent circuit400representing a portion of system100or system200between a protective device and a short circuit fault. Equivalent circuit400includes line resistance R, line inductance L, and fault resistance RF.

The state space equation of the equivalent circuit400can be expressed as:

The voltage, current and di/dt are sampled or calculated at different time steps. (R+RF) and L can be estimated from data sampled at multiple time instants, for example, using least squares method. The voltage at N sampling time instants can be expressed as:

Based on the least square method, the unknown parameters L and R+RFcan be determined by

At least two samples are preferred to identify parameters L and R+RF. In certain embodiments, an online moving-window least square method is implemented to identify the equivalent inductance from the protective device to fault. The number of samples for the moving-window is defined by the user. It shall be appreciated that the one or more intelligent electronic devices disclosed herein may be configured to perform inductance calculations or determinations in accordance with the foregoing equations and techniques.

With reference toFIG. 5there is illustrated an exemplary process500for calculating inductance values performed by an intelligent electronic device. Process500generally includes fault detection and fault location functionalities. Process500may be implemented in whole or in part in one or more of the intelligent electronic devices disclosed herein. In certain forms the fault detection and fault location functionalities may be performed by separate intelligent electronic devices. In certain forms both functionalities may be performed by the same intelligent electronic device. Furthermore, as noted above, the intelligent electronic devices disclosed herein may be dedicated to a respective local protective device or may be structured to serve multiple local protective devices.

Process500begins at start operation501and proceeds to conditional503which evaluates whether a fault is present. Conditional503may perform this evaluation using a variety of techniques such as a limit, threshold or trigger point established for line-to-line or line-to-ground voltage, line current or line current time rate of change. If a fault is not detected, process500proceeds to operation505which causes process500to proceed to the next time interval and then return to conditional503. If conditional503detects a fault condition, process500proceeds to operation507where a counter value k is set to zero.

From operation507, process500proceeds to operation511where an intelligent electronic device receives measurements of voltage, current, and di/dt which may be calculated by the intelligent electronic device based on line current measurement information or determined independently and provided to the intelligent electronic device.

From operation511, process500proceeds to conditional513which evaluates whether counter value k is less than a user defined counter threshold M. If counter value k is less than a user defined value M, process500advances to operation517where matrices A and B from Equation 3 above are calculated or determined using all k samples. If counter value k is not less than user defined value M, the logic advances to operation515where matrices A and B from Equation 3 above are calculated or determined using the M most recent samples.

From either operation515or517process500proceeds to operation519where a line inductance L and optionally a sum of line resistance and fault resistance R+RFare calculated using Equation 4 above and matrices A and B. From operation519, process500proceeds to conditional520where the calculated line inductance is compared to a normal, non-fault line inductance. If the calculated inductance is less than the non-fault line inductance, process500advances to the operation522to send a trip signal to open the protective device and then proceeds to end operation525which terminates the process500. If the calculated inductance is larger than the non-fault line inductance, process500advances to conditional521where the time duration of the process500beginning at operation511is compared to a user defined value Tmax. If the time duration is less than Tmax, process500advances to operation523where the counter value k is incremented by one before the logic advances to operation511. If the time duration is not less than Tmax, the logic advances to end operation525which may terminate process500allowing for it to be re-initiated at a later time.

As noted above, process500may be implemented in one or more intelligent electronic devices such as those disclosed herein. In certain embodiments a plurality of intelligent electronic devices each corresponding to a particular protection zone may execute process500at a separation location for each zone. In certain embodiments one or more central or clustered intelligent electronic devices may execute process500at one location for a plurality of protection zones. It shall be further appreciated that a number of variations and modifications to process500are contemplated including, for example, the omission of one or more aspects of process500, the modification of the inductance calculation mathematics, the addition of further conditionals and operations and/or the reorganization or separation of operations and conditionals into separate processes.

A number of further exemplary embodiments shall now be described. One embodiment is a DC power distribution system comprising: a plurality of DC power distribution zones bounded by one or more zone boundaries, each of said zones including at least one DC power distribution line and at least one protective device operatively coupled with the DC power distribution line, each protective device structured to sense one or more electrical characteristics associated with the DC power distribution line with which it is operatively coupled and to controllably open a circuit including said DC power distribution line based upon detection and location of a line fault; at least one intelligent electronic device structured to determine one or more line inductance values based upon the one or more electrical characteristics sensed by one or more of the protective devices and to evaluate a location of the line fault based upon the determined line inductance values; and at least one inductor coupled with a DC distribution line of one of the plurality of zones, the inductor having an inductance value such that line inductances of each of the plurality of zones when no fault is present differ in magnitude such that the line inductance values determined by the at least one intelligent electronic device during a line fault uniquely identify one of the plurality of DC power distribution zones as containing the line fault.

In certain forms of the exemplary system the intelligent electronic device is structured to determine a line inductance using linear regression analysis based on a number of samples of the one or more electrical characteristics. In certain forms the number of samples used to determine line inductance is one of the total number of samples taken as of a first time interval following detection of the line fault and a predetermined number of most recent samples' as of a second time interval. In certain forms the one or more electrical characteristics comprise line-to-line or line-to-ground voltage, line current, and the first derivative of line current. In certain forms the line inductance is determined based upon a first matrix including a plurality of line-to-line or line-to-ground voltage values and a second matrix including a plurality of line current values and a plurality of first derivatives of line current values. Certain forms further comprise a plurality of intelligent electronic devices each associated with a respective protective device. In certain forms the DC power distribution system is a converter-based tightly-coupled DC power distribution system.

One exemplary embodiment is a method of locating faults in a DC power distribution network, the method comprising: defining a plurality of protection zones of the DC power distribution network; detecting a fault within the DC power distribution network; after detecting the fault sampling one or more electrical characteristics of each of the protection zones of the DC power distribution network; determining a plurality of line inductance values each associated with a respective protection zone; and locating the fault as being within one of the protection zones based upon the determined line inductance values.

In certain forms of the exemplary method the one or more electrical characteristics comprise voltage, current and current time rate of change. In certain forms the sampling of one or more electrical characteristics occurs while the DC power distribution network is online. In certain forms the locating the fault includes evaluating the determined line inductance values relative to corresponding predetermined inductance threshold values. In certain forms said predetermined inductance threshold values are based upon the inductance of respective protection zones under non-fault operating conditions plus a margin of error. In certain forms at least one protection zone includes an inductor having an inductance value selected such that line inductances of each of the plurality of zones when no fault is present differ in magnitude such that the line inductance values determined during a line fault uniquely identify a particular one of the plurality of DC power distribution zones as containing the fault. In certain forms the line inductance value is determined based upon a first matrix including a plurality of line-to-line or line-to-ground voltage sample values and a second matrix including a plurality of line current sample values and a plurality of first derivatives of line current sample values.

One exemplary embodiment is a method comprising: monitoring a plurality of protection zones of a DC power distribution system, the zones being demarcated by one or more boundaries; storing non-fault inductance values for each protection zone, the values reflective of inductance values during non-fault operation of the DC power distribution system detectable at a plurality of local protective devices each of which is associated with a respective protection zone; detecting a fault in the DC power distribution system; calculating a fault condition inductance value using information of one or more electrical characteristics sensed by one or more of the local protective devices; and determining which of the protection zones contains the fault based upon the calculated fault condition inductance value and the non-fault inductance values.

Certain forms of the exemplary method further comprise after the determining which of the protection zones contains the fault transmitting to the local protective device of the protection zone containing the fault a command to open a circuit including said local protective device. In certain forms the detecting the fault is based upon one or more of a current value exceeding a current threshold, a voltage value exceeding a voltage threshold, and a current time rate of change value exceeding a current time rate of change threshold. In certain foul's the calculating an inductance value is based upon a plurality of sensed voltage values, a plurality of sensed current values and a plurality of current time rate of change values. In certain forms the calculating an inductance value is based upon a linear regression utilizing the plurality of sensed voltage values, the plurality of sensed current values and the plurality of current time rate of change values. In certain forms each of the local protective devices includes intelligent electronics which calculate the inductance of its respective protection zone.