BACKGROUND

[0001] A multi generator variable speed constant frequency (VSCF) system may include a rotating generator and a power inverter unit (PIU). A no break power transfer (NBPT) mechanism between the generator and/or power inverter units of multiple systems may be desired. During a NBPT, two systems may be briefly connected while one system is turning on or off without power interruption.

BRIEF DESCRIPTION

[0002] According to one aspect, a system for no break power transfer (NBPT) synchronization may include a first bus, a first system, a second bus, a second system, a bus tie contactor, and a generator control unit (GCU). The bus tie contactor may control an electrical connection between the first bus and the second bus. The generator control unit may include a first circuit determining a frequency associated with the first system. The generator control unit may include a second circuit receiving a frequency associated with the second system. The generator control unit may include a logic binning the frequency associated with the second system into one of two or more predetermined frequency bins. The logic may determine a phase offset between the frequencies associated with the first system and the frequency associated with the second system. The logic may adjust the frequency associated with the first system based on the phase offset and the bin associated with the second system.

[0003] According to one aspect, the frequency associated with the first system may be a shore power frequency. According to a different aspect, the frequency associated with the second system may be a shore power frequency. The logic may adjust the frequency associated with the first system incrementally. The logic may generate a synchronized signal when the phase offset is less than or greater than a phase offset threshold. The synchronized signal may drive the bus tie contactor to remove an inhibit between the first bus and the second bus. The logic may bin the frequency associated with the second system based on two or more predetermined frequency ranges. The frequency range associated with the predetermined frequency ranges may range from 59.7 Hz to 61 Hz. The logic may determine the phase offset at a zero crossing of a signal associated with the second system. The logic may adjust the frequency associated with the first system based on a phase of a signal associated with the second system.

[0004] According to one aspect, a system for no break power transfer (NBPT) synchronization may include a first bus, a first system electrically connected to the first bus, a second bus, a second system electrically connected to the second bus, a bus tie contactor controlling an electrical connection between the first bus and the second bus, and a generator control unit (GCU). The generator control unit may include a first circuit determining a frequency associated with the first system. The generator control unit may include a second circuit receiving a frequency associated with the second system. The generator control unit may include a logic binning the frequency associated with the second system into one of two or more predetermined frequency bins. The logic may determine a phase offset between the frequency associated with the first system and the frequency associated with the second system. The logic may adjust the frequency associated with the first system based on the phase offset and the bin associated with the second system. [0005] According to one aspect, the frequency associated with the first system may be a shore power frequency. According to a different aspect, the frequency associated with the second system may be a shore power frequency. The logic may adjust the frequency associated with the first system incrementally. The logic may generate a synchronized signal when the phase offset is less than or greater than a phase offset threshold. The synchronized signal may drive the bus tie contactor to remove an inhibit between the first bus and the second bus. The logic may bin the frequency associated with the second system based on two or more predetermined frequency ranges. The frequency range associated with the predetermined frequency ranges may range from 59.7 Hz to 61 Hz. The logic may determine the phase offset at a zero crossing of a signal associated with the second system.

[0006] According to one aspect, a method for no break power transfer (NBPT) synchronization may include determining a frequency associated with a first system which may be electrically connected to a first bus, determining a frequency associated with a second system which may be electrically connected to a second bus, binning the frequency associated with the second system into one of two or more predetermined frequency bins, determining a phase offset between the frequency associated with the first system and the frequency associated with the second system, adjusting the frequency associated with the first system based on the phase offset and the bin associated with the second system, and controlling a bus tie contactor to remove an inhibit between the first bus and the second bus based on an updated phase offset between the frequency associated with the first system and the frequency associated with the second system.

BRIEF DESCRIPTION OF THE DRAWINGS [0007] FIG. 1 is an exemplary component diagram of a system for no break power transfer (NBPT) synchronization, according to one aspect.

[0008] FIG. 2 is an exemplary binning diagram associated with the system for no break power transfer (NBPT) synchronization of FIG. 1 , according to one aspect.

[0009] FIG. 3 is an exemplary binning diagram associated with the system for no break power transfer (NBPT) synchronization of FIG. 1 , according to one aspect.

[0010] FIG. 4 is an exemplary flow diagram of a method for no break power transfer (NBPT) synchronization, according to one aspect.

[0011] FIG. 5 is an exemplary flow diagram of a method for no break power transfer (NBPT) synchronization, according to one aspect.

DETAILED DESCRIPTION

[0012] The following includes definitions of selected terms employed herein. The definitions include various examples and/or forms of components that fall within the scope of a term and that may be used for implementation. The examples are not intended to be limiting. Further, one having ordinary skill in the art will appreciate that the components discussed herein, may be combined, omitted or organized with other components or organized into different architectures.

[0013] A “logic”, as used herein, processes signals and performs general computing and arithmetic functions. Signals processed by the logic may include digital signals, data signals, computer instructions, processor instructions, messages, a bit, a bit stream, or other means that may be received, transmitted, and/or detected. Generally, the logic may include a variety of circuitry. The logic may include various modules to execute various functions.

[0014] A “bus”, as used herein, refers to an interconnected architecture that is operably connected to other components and may distribute power to one or more systems or subsystems.

[0015] A "database", as used herein, may refer to a table, a set of tables, and a set of data stores (e.g., disks) and/or methods for accessing and/or manipulating those data stores.

[0016] FIG. 1 is an exemplary component diagram of a system 100 for no break power transfer (NBPT) synchronization, according to one aspect. The system 100 for NBPT synchronization may include a first system and a second system to be synchronized. According to one aspect, the first system may be electrically connected to a first bus 132. The second system may be electrically connected to a second bus 134. The first bus 132 and the second bus 134 may be selectively electrically connected via a bus tie connector 130. The first system may be one of a system 112 or system 114. The second system may be one of a system 122 or system 124. According to other aspects, the systems to be synchronized may be tied to the same bus, such as system 112 and system 114 and controlled via respective line contactors. In this way, any of the four systems 112, 114, 122, 124 may power both buses 132, 134 or split to power merely a single bus. For example, any one of shore power (e.g., external power) or power from CSG1 , APU1 , CSG2, or APU2 may be used to power any combination of bus 132 and/or bus 134. [0017] For example, the system 112 may include an engine, a constant speed generator, a power inverter unit, a generator control unit (GCU) controlling a line contactor which controls an electrical connection between the system 112 and the first bus 132. Similarly, the system 114 may include an auxiliary power unit turbine, an auxiliary power unit, a power inverter unit, a GCU controlling a line contactor which controls an electrical connection between the system 114 and the first bus 132.

[0018] Continuing on with the above discussed example, the system 122 may include an engine, a constant speed generator, a power inverter unit, a GCU controlling a line contactor which controls an electrical connection between the system 112 and the second bus 134. Similarly, the system 124 may include an auxiliary power unit turbine, an auxiliary power unit, a power inverter unit, a GCU controlling a line contactor which controls an electrical connection between the system 114 and the second bus 134. The bus tie contactor 130 may control the electrical connection between the first bus 132 and the second bus 134. [0019] Generally, the system that is turning on or off to/from an external source (e.g., either one of the CSG/APU units or shore power) may use a zero crossing detector on the external source, compare the time difference to an internal signal and adjust its internal frequency based on the algorithm to achieve a minimum phase difference between the internal and external signals. After synchronizing, the system that is turning on enables a corresponding line contactor and applies OIS, thereby bridging the two systems. After the inhibit is removed, depending on whether a same bus transfer, bus1/bus2 transfer, transfer to shore power, the appropriate contactor inhibit is applied or released.

[0020] Each of the above discussed GCU’s 116, 118, 126, and 128 may include a first circuit determining a frequency associated with the first system (e.g., a local frequency), a second circuit receiving a frequency associated with the second system (e.g., a frequency of a system to be synchronized to), a logic, a storage drive, etc. According to one aspect, the second circuit may sample the frequency associated with the second system. As described herein with respect to FIG. 1 , the system 112 may be synchronized with the system 122, although other variations are contemplated (e.g., the system 112 may be synchronized with the system 124, the system 114 may be synchronized with the system 122, the system 114 may be synchronized with the system 124, etc.).

[0021] In any event, the logic (e.g., of GCU 116) may bin the frequency associated with the second system into one of two or more predetermined frequency bins. There may be a finite number of frequencies that may be used during NBPT to facilitate speedy synchronization. The logic may bin the frequency associated with the second system based on two or more predetermined frequency ranges, although four exemplary bins are described herein with respect to FIGS. 2-3. According to one aspect, the frequency range associated with the predetermined frequency ranges may range from 59.7 Flz to 61 Hz, for example. The logic may determine a phase offset between the frequency associated with the first system and the frequency associated with the second system. The phase offset may be determined, for example, at a zero crossing of a signal associated with the second system, a zero crossing of a signal associated with the first system, at a rising edge, falling edge, etc.

[0022] The logic may adjust the frequency associated with the first system based on the phase offset and the bin associated with the second system. The logic may adjust the frequency in an incremental fashion. The logic may adjust the frequency associated with the first system based on a phase of a signal associated with the second system. According to one aspect, the frequency associated with the first system may be a shore power frequency. According to another aspect, the frequency associated with the second system may be the shore power frequency. Thus, the system 100 may monitor the frequency of the two power systems and make small corrections or adjustments to the PIO output frequency to synchronize the frequencies of the two systems.

[0023] In any event, after the incremental adjustments for the frequencies of respective systems (or not if incremental adjustments are not required), when the phase offset is less than or greater than a phase offset threshold, the logic may generate a synchronized signal which may be fed to the bus tie contactor 130. In this way, the synchronized signal may drive the bus tie contactor 130 to remove an inhibit between the first bus 132 and the second bus 134 once the phase offset becomes less than a phase offset threshold, thereby enabling the no break power transfer to occur between the first system and the second system when the frequencies of AC voltage of respective systems are synchronized. It will be appreciated that according to another aspect, the synchronization may occur along a single bus, where system 112 and system 114 act as the first system and the second system from the example described herein.

[0024] In addition to the output regulation and protection functions, the inverter controller or GCU may control the NBPT functionality. This may include the synchronization function that can operate in coming online or offline regimes. The PCU may employ a seamless synchronization method, where the phase/frequency synchronization happens gradually, in up to 100 cycles, without disturbing the power bus. After NBPT mode, the inverter controller may change the voltage loop gain, making the system less stiff, effectively increasing its output impedance. Such a scheme may drastically reduce the circulating currents between the parallel systems.

[0025] In this way, the NBPT synchronization system may enable synchronization to the other power source to occur. Rather than using an instant synchronization upon detecting the other source voltage zero crossing, the NBPT synchronization system slowly (e.g., 100ms - 2s) adjusts the output phase angle until two phases coincide within 1 °. At that time, the synchronization control may be switched to the other source. Such synchronization allows for a seamless operation for the electro-magnetic loads (e.g., motors and transformers). The NBPT synchronization system may operate in both directions. In other words, when the system is coming online and when the system relinquishes the network power or goes offline.

[0026] According to one aspect, the gain of the voltage control loop is significantly reduced after the NBPT process, effectively increasing the system output impedance, while the reference voltage level is increased. This reduces the circulating currents between two systems by means of currents gaining greater authority in controlling the output voltage. The regulation level increase serves two purposes: voltage droop compensation at high loads that happens due to the increased output impedance and to accommodate the sources (e.g., external power) that don’t have tight output regulation levels.

[0027] The NBPT synchronization system takes advantage of the PIU synthesis functions for use in modifying the output frequency until the PIU is locked, or synchronized to another PIU. Phase detection circuits of the GCU or of the respective systems 112, 114, 122, 124, along with the ability to change the output frequency may be used in the synchronization. The system may detect the time difference of AC output phases and adjust the PIU output frequency at regular intervals until the PIU is within acceptable limits for connecting the PIU to the other PIU. In addition, communication channels between the PIUs may be facilitated to ensure that each applies output impedance softening (OIS) prior to and/or after the PIU bridging to limit circulating currents between the two PIUs.

[0028] In FIG. 1 , the multi-generator VSCF system may use NBPT to seamlessly switch between generators/P I Us to provide an interrupted power. The PIU-PIU communication link enables each PIU to communicate its system state between other PIUs and to indicate when a NBPT should be initiated and terminated. In addition to inter-PIU communication, PIUs are sensing the power buses for the power quality and synchronization during NBPT.

[0029] FIG. 2 is an exemplary binning diagram 200 associated with the system for no break power transfer (NBPT) synchronization of FIG. 1 , according to one aspect. As seen in FIG. 2, this figure is described with reference to four exemplary frequency bins. For example, there is a first bin 202, a second bin 204, a third bin 206, and a fourth bin 208. The first bin 202 may be referred to as bin A, the second bin 204 may be referred to as bin B, the third bin 206 may be referred to as bin C, and the fourth bin 208 may be referred to as bin D. In FIG. 2, a range is illustrated which may represent the possible frequency range that is being synchronized to. [0030] Each bin may be associated with a P_index_max value and a P_index_min value. For example, for the first bin 202 or bin A, P_index_max = 2, for the second bin 204 or bin B, P_index_max = 3, for the third bin 206 or bin C, P_index_max = 3, and for the fourth bin 208 or bin D, P_index_max = 3. For the first bin 202 or bin A, P_index_min value = 0, for the second bin 204 or bin B, P_index_min value = 1, for the third bin 206 or bin C, P_index_min value = 2, and for the fourth bin 208 or bin D, P_index_min value = 3. It will be appreciated that if additional or fewer bins are utilized in a different implementation, that the P_index_max value and the P_index_min value for each bin may be assigned differently. Further, it can be seen that the first bin 202, the second bin 204, the third bin 206, and the fourth bin 208 range across a frequency range defined by a first nominal frequency tolerance and a second nominal frequency tolerance. [0031] According to one aspect, the first bin 202 may be associated with a determined frequency less than the nominal frequency of the system, the second bin 204 may be associated with a value equal to the nominal frequency of the system, the third bin 206 may be associated with a value larger than the nominal frequency of the system, and the fourth bin 208 may be associated with a value larger than the frequency of the third bin 206. These four preset frequencies may correspond to a P_index_min and a P_index_max count. For example, a P_index_min of 1 may mean that the minimum frequency to be selected is the value at preset 1 and never preset 0. Likewise, a P_index_max of 2 may limit a maximum selectable frequency of what as defined by preset 2.

[0032] Upon initialization, the NBPT synchronization system may determine the frequency of the system it will to transfer to by capturing multiple zero crossing events of the second system to synchronize to and measuring this value. This frequency will fall into one of the four bins. The NBPT synchronization system may then determine the proper set of steps and what presets can be utilized in order to achieve synchronization. This is indicated by the P_index_min and P_index_max variables in FIG. 2. For example, if the frequency to switch to is just to the right of the preset 0 frequency, then the frequency to synchronize to would be in area “B.” This frequency value sets the P_index_min to 1 and the P_index_max to 3, which means preset 0 frequency will not be utilized in this synchronization event. This is because the smallest preset is too close of an offset change and may cause delays in the synchronization.

[0033] FIG. 3 is an exemplary binning diagram 300 associated with the system for no break power transfer (NBPT) synchronization of FIG. 1 , according to one aspect. It can be seen that for a first portion of the second bin 204 or bin B, P_index_max = 3 and P_index_min = 3 and for a second portion 304 of the second bin 204 or bin B, P_index_max = 2 and P_index_min = 3.

[0034] The NBPT synchronization system, using the set of preset frequencies, may adjust the frequency of its output to align the two power system zero crossing events. The NBPT synchronization system based upon the initial offsets in these zero crossings and the frequency of the system to align to will either determine the fastest way to reach synchronization by either speeding up the frequency or slowing it down in order to match the zero crossings by selecting the appropriate preset frequency. This adjustment of the frequency and calculating the offsets occurs at every zero crossing event. The NBPT synchronization system continues to makes adjustments by selecting the right preset frequency until the two system zero crossings are aligned within a specific offset tolerance range. Once this occurs, the NBPT synchronization system indicates to the system that it is aligned and to initialize the power transfer request if aligned to an external system.

[0035] FIG. 4 is an exemplary flow diagram of a method 400 for no break power transfer (NBPT) synchronization, according to one aspect. The method may include an initialization 402 where different variables may be initialized. For example, variables may include P_index_min (e.g., a minimum allowed frequency), P_index_max (e.g., a maximum allowed frequency), and PJndex (e.g., a current frequency). At 404, shore power frequency may be calculated or determined. According to another aspect, at 404, the frequency of another system (e.g., the second system) to be synchronized with the first system may be determined, along with the frequency of the first system. Further, the systems to be synchronized may be identified, as well as relays or bus ties (e.g., line contactors, bus contactors, etc.) which, if an inhibit is removed, would electrically connect respective first and second systems. Based on the determined frequency associated with the first system and the determined frequency associated with the second system, P_index_min, P_index_max, and the direction or phase offset may be set. In other words, the determined frequency associated with the second system may be binned into one of two or more bins. Depending on the assigned bin, different P_index_min and P_index_max values may be initialized.

[0036] Often, the two systems will have frequencies that are extremely close to one another and after synchronization, and the system returns to nominal. Even if the two systems have slightly different frequencies, they will only be bridged (with OIS) for a short amount of time and any differences will not create excess circulating currents. Safeguards may be built in to other parts of control circuits to protect the PIU if out of range voltages and or currents are detected.

[0037] Additionally, at 408, the phase offset may be calculated or the direction determined (i.e. , whether the first frequency associated with the first system should be incremented or decremented to synchronize the respective frequencies of the first and second systems). In this way, the frequency associated with the second system may be binned into one of two or more predetermined frequency bins by the logic of the corresponding GCU (e.g., one of 116, 118, 126, and 128).

[0038] At 410, a check may be made to determine whether the phase offset is less than or greater than a phase offset threshold. If yes, the phase offset is less than the phase offset threshold, a synchronized signal may be generated and sent 412 to control the previously discussed relays (which, if an inhibit is removed, would electrically connect respective first and second systems), bus ties, line contactors, bus contactors, thereby electrically connecting the first system and the second system. As discussed above, the first system may be any one of the system 112, the system 114, the system 122, the system 124, etc. of FIG. 1. Similarly, the second system may be any one of the system 112, the system 114, the system 122, the system 124, etc. of FIG. 1. In this way, the second system may synchronize to the first system and vice versa.

[0039] At 416, a check is made to determine whether the phase offset is greater than a lo_threshold. The lo_threshold or low threshold is a calculated number or predetermined number and associated with enabling the synchronization to occur within a desired time frame, such as two seconds, for example. At 418, the polarity or direction associated with the phase offset is checked. If the frequency associated with the second system is leading (e.g., the path associated with 420), the frequency associated with the first system, the frequency associated with the first system may be incremented for synchronization, in general. If the frequency associated with the second system is lagging (e.g., the path associated with 432) behind the frequency associated with the first system, the frequency associated with the first system may be decremented for synchronization, in general. However, different circumstances may result where these are not necessarily followed.

[0040] For example, at 420, a check may be made to determine whether the offset is greater than a hi_threshold and whether P_index_max is 2. In this scenario, if P_index_max = 2, and according to the four bin example of FIG. 2, this would mean that the signal associated with the second system is slower than the signal associated with the first system, and if P_index_min is less than PJndex at 436, then the current signal may be decremented in frequency at 438. If P_index_min is not less than PJndex at 436, then the current signal is already at a point where decrementing may not be possible or necessary, for example. In other words, if the offset > hi hreshold and PJndex_max = 2, or the condition at 420 is true, then the first signal associated with the first system is close to synchronization with the second signal from the second system. The decrementing at 438 may be implemented to ensure that no overshoot occurs and so the frequency synchronization may occur more slowly to ensure accurate synchronization.

[0041] On the other hand, if PJndex < PJndex_max is true at 422, PJndex may be incremented at 440 to speed up the frequency and synchronize as quickly as possible. If PJndex < PJndex_max is not true, then the current frequency is already at the maximum allow frequency, and thus, no incrementing may occur. [0042] Returning to the check on direction at 418, if the frequency associated with the second system is lagging behind the frequency associated with the first system, the frequency associated with the first system may be decremented for synchronization, in general. At 432, a check may be performed to determine if PJndex is a non-zero value. If this is true that PJndex is a non-zero value, the frequency associated with the first system may be decremented at 434. If PJndex is zero, nothing is decremented.

[0043] Returning to 416 where the check is made to determine whether the phase offset is greater than a lo hreshold, if the phase offset is not greater than the low threshold, a check may be performed at 424. The check at 424 may be to determine whether P index < P index min. If it is true that P index < P_index_min, PJndex may be incremented at 428. If it is not true that PJndex < P_index_min, a check may be performed at 426. The check at 426 may be to determine whether P_index_min < PJndex. If it is true that PJndex_min < PJndex, PJndex may be decremented at 430. If it is not true that PJndex_min < PJndex, no action may be performed. At 442, any incrementing or decrementing may have been performed, and the cycle may be repeated at the next falling edge 444 and the phase offset recalculated at 408.

[0044] FIG. 5 is an exemplary flow diagram of a method 500 for no break power transfer (NBPT) synchronization, according to one aspect. The method 500 for NBPT synchronization may include determining 502 a frequency associated with a first system which may be electrically connected to a first bus, determining 504 a frequency associated with a second system which may be electrically connected to a second bus, binning 506 the frequency associated with the second system into one of two or more predetermined frequency bins, determining 508 a phase offset between the frequency associated with the first system and the frequency associated with the second system, adjusting 510 the frequency associated with the first system based on the phase offset and the bin associated with the second system, and controlling 512 a bus tie contactor to remove an inhibit between the first bus and the second bus based on an updated phase offset between the frequency associated with the first system and the frequency associated with the second system.

[0045] Although the subject matter has been described in language specific to structural features or methodological acts, it is to be understood that the subject matter of the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example aspects.

[0046] Various operations of aspects are provided herein. The order in which one or more or all of the operations are described should not be construed as to imply that these operations are necessarily order dependent. Alternative ordering will be appreciated based on this description. Further, not all operations may necessarily be present in each aspect provided herein.

[0047] As used in this application, "or" is intended to mean an inclusive "or" rather than an exclusive "or". Further, an inclusive “or” may include any combination thereof (e.g., A, B, or any combination thereof). In addition, "a" and "an" as used in this application are generally construed to mean "one or more" unless specified otherwise or clear from context to be directed to a singular form. Additionally, at least one of A and B and/or the like generally means A or B or both A and B. Further, to the extent that "includes", "having", "has", "with", or variants thereof are used in either the detailed description or the claims, such terms are intended to be inclusive in a manner similar to the term "comprising”.

[0048] Further, unless specified otherwise, “first”, “second”, or the like are not intended to imply a temporal aspect, a spatial aspect, an ordering, etc. Rather, such terms are merely used as identifiers, names, etc. for features, elements, items, etc. For example, a first channel and a second channel generally correspond to channel A and channel B or two different or two identical channels or the same channel. Additionally, “comprising”, “comprises”, “including”, “includes”, or the like generally means comprising or including, but not limited to. [0049] It will be appreciated that various of the above-disclosed and other features and functions, or alternatives or varieties thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.