System and method for a shared hybrid transfer switch system with integrated relay self-test

Abstract

The present disclosure relates to a shared transfer switch system with built-in relay testing capability for converting power received by a load from a preferred AC power source to an alternative AC power source, or converting power received by a load from an alternative AC power source to a preferred AC power source. The system selectively controls individual relays of the relays used to apply power from the preferred power source or the alternative power source to the load, so that the relays switch from an open state to a closed state at a controlled time, while making voltage measurements at selected positions between the relays. The system can identify which specific relays of a plurality of relays associated with each of the preferred power source and the alternative power source have been correctly opened and closed, and thus verify that all relays required to switch between the preferred power source and the alternative power source are operating correctly.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Patent Application No. 17 / 459,837, filed on August 27, 2021. The subject matter of this application is also related to U.S. Application No. 16 / 867,306, filed on May 5, 2020, which itself claims the benefit of U.S. Provisional Application No. 62 / 843,884, filed on May 6, 2019. The entire disclosures of the above-referenced applications are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to transfer switches used in data centers and other facilities for converting power supplied to one or more loads from one power source to a different power source, and more particularly, to a shared hybrid transfer switch system that enables significantly reduced switching time when converting a load from a first power source to a second power source. Background Art

[0004] This section provides background information related to the present disclosure which is not necessarily prior art.

[0005] In various types of facilities, and particularly in modern data centers, transfer switches are used to reliably facilitate the switching of downstream power distribution infrastructure between two independent power sources (e.g., a utility or "preferred" power source and a backup or "alternate" power source) so that uninterrupted operation of connected equipment (e.g., servers, routers, etc.) is maintained. The transfer can occur automatically when suboptimal power quality conditions are detected on the active source. The transfer can also be manually initiated by workers at the facility when maintenance is required on the active power source.

[0006] Transfer switches are manufactured in a variety of physical forms, performance capabilities, and ampacity ranges for single-phase and three-phase power distribution. In data center applications, transfer switches are preferably located within the equipment rack (i.e., within the rack "space"). The transfer switch provides input directly to IT equipment via its own receptacles or to other rack power distribution devices (e.g., power outlets).

[0007] The electrical switching of a transfer switch uses the contacts of electromechanical relays electrically interconnected in series and parallel combinations. During transfer, these relays are precisely controlled to open the circuit between the previously active source and the load, and quickly close the new circuit for the new active source, while ensuring that the two sources remain electrically isolated from each other. The sequence can be "break before make", where the active contacts are opened before the new contacts are closed (also called "open transfer"), or the sequence can be "make before break", where the new contacts are closed before the previous contacts are opened (also called "close transfer"). The voltage phases of the new source and the load may not be synchronized for an open transfer, or must be synchronized in the case of a close transfer.

[0008] The Information Technology Industry Council (“ITIC”) Computer and Business Equipment Manufacturers Association (“CBEMA”) curve describes the AC input voltage envelope that IT loads can withstand without interruption of functionality. Transfer switch performance should at least meet the maximum limit of this curve, i.e., faster than 20 ms at 70% voltage. To be more market competitive, transfers should be completed within half a line cycle, i.e., less than or equal to 8 ms at a line frequency of 60 Hz. However, typical electromechanical relay contacts operate at release and close times, which cannot achieve such performance for closed transfers. In addition, reliable detection of power quality conditions and transfer management to prevent cross conduction of the source or component failures typically incur additional incremental delays, which makes it difficult or impossible to meet such a half-line cycle transfer time range.

[0009] In order to achieve faster switching times, the switching performance of the relay contacts can be improved by using solid-state switching devices such as TRIAC (bidirectional / bidirectional triode thyristor), anti-parallel SCR (silicon controlled rectifier) ​​pairs or IGBT (insulated gate bipolar transistor). Solid-state relays have previously been combined with electromechanical relays for use in hybrid switching configurations. In these hybrid solutions, the terminals of the solid-state switch are permanently electrically connected in parallel with the relay contacts, so that both the first power supply and the second power supply require dedicated solid-state switches. However, solid-state switches require more components and expensive isolation drive circuits. Therefore, circuit designs that reduce the number of solid-state switches will reduce costs and simplify conversion circuits.

[0010] It is also known that the internal power supplies of some IT equipment can cause large inrush currents to flow through the conversion circuitry during cold starts (i.e., during power cycling) due to capacitor discharge and low input capacitive reactance. The magnitude of the inrush current can exceed the rating of the relay contacts by orders of magnitude and, if the magnitude of the inrush current is not properly reduced, the relay contacts may be damaged or destroyed and may pose an energy hazard. Therefore, a circuit design feature that enables a "soft start" to momentarily reduce or limit the inrush current through the conversion switching circuitry when switching from one power source to another would be extremely valuable in protecting the electronic components of the conversion circuitry.

[0011] Still further, for a system such as that described above, it would be highly desirable to be able to check the various relays associated with the preferred power source and the alternate power source to verify that each relay is opening and closing properly. It would also be highly desirable to be able to perform the desired tests if the various relays could be checked without the need to add additional switching elements, dummy loads, etc. Still further, it would be highly desirable if the tests on the relays associated with the alternate power source could be performed without interrupting the preferred power source while the preferred power source is powering the load. Likewise, it would be highly desirable if the relays associated with the preferred power source could be checked while the load is being powered from the alternate power source, and without interrupting power from the alternate power source to the load. Summary of the invention

[0012] This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.

[0013] In one aspect, the present disclosure relates to a shared transfer switch system with built-in relay testing capability, which is used to convert power received by a load from a preferred AC power source to an alternative AC power source, or to convert power received by a load from an alternative AC power source to a preferred AC power source. The shared transfer switch system may include a first primary relay and a first secondary relay, the first primary relay and the first secondary relay are coupled in series, and are connected in series with the preferred power source and the load so that the load can be powered by the preferred power source. The system may also include a second primary relay and a second secondary relay, the second primary relay and the second secondary relay are coupled in series, and are also connected in series with the alternative power source and the load, for providing power to the load from the alternative power source when the preferred power source cannot be used to power the load. The system may also include a switch subsystem and a controller for controlling the operation of the second primary relay and the second secondary relay. The switch subsystem may be connected to the controller and the first primary relay, the first secondary relay, the second primary relay, the second secondary relay, and the load. The switch subsystem may be configured to be controlled by the controller to control switching from one or the other of the preferred power source or the alternative power source to the load. The system may also include a relay test subsystem including a relay test software module and a voltage detection subsystem operably associated with the controller for performing a relay test process. The relay test process includes performing a plurality of voltage tests by selectively opening and closing the second primary relay and the second secondary relay to verify proper operation of the second primary relay and the second secondary relay.

[0014] On the other hand, the present disclosure relates to a shared transfer switch system with built-in relay testing capability, which is used to convert power received by a load from a preferred AC power source to an alternative AC power source, or to convert power received by a load from an alternative AC power source to a preferred AC power source. The shared transfer switch system may include a first primary relay and a first secondary relay, the first primary relay and the first secondary relay are coupled in series, and are connected in series with the preferred power source and the load so that the load can be powered by the preferred power source. The system may also include a second primary relay and a second secondary relay, the second primary relay and the second secondary relay are coupled in series, and are also connected in series with the alternative power source and the load to provide power to the load from the alternative power source when the preferred power source cannot be used to power the load. The system may also include a switch subsystem and a controller for controlling the operation of the second primary relay and the second secondary relay. The switch subsystem may be connected to the controller and the first primary relay, the first secondary relay, the second primary relay, the second secondary relay, and the load. The switch subsystem may be configured to be controlled by the controller to control switching from one or the other of the preferred power source or the alternative power source to the load. The system may also include a relay test subsystem including a relay test software module and a voltage detection subsystem operably associated with the controller for performing a relay test process. The relay test process includes performing a plurality of voltage tests by selectively opening and closing the second primary relay and the second secondary relay to verify proper operation of the second primary relay and the second secondary relay.

[0015] In yet another aspect, the present disclosure relates to a method for testing a plurality of relays associated with a system for converting power from one or the other of a preferred AC power source or an alternative power source to a load. The method may include using a first primary relay and a first secondary relay, the first primary relay and the first secondary relay are coupled in series, and are connected in series with the preferred power source and the load, so that the load can be powered by the preferred power source. The method may also include using a second primary relay and a second secondary relay, the second primary relay and the second secondary relay are coupled in series, and are also connected in series with the alternative power source and the load, to provide power to the load from the alternative power source when the preferred power source cannot be used to power the load. The method may also include using a switch subsystem, the switch subsystem is connected to the first primary relay, the first secondary relay, the second primary relay and the second secondary relay, and the load, and the switch subsystem is configured to be controlled to switch from one or the other of the preferred power source or the alternative power source to the load. The method may also include performing a relay test process, the relay test process including performing a plurality of voltage tests by selectively opening and closing the second primary relay and the second secondary relay to verify the correct operation of the second primary relay and the second secondary relay.

[0016] Further areas of applicability will become apparent from the description provided herein.The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The drawings described herein are only for the purpose of illustrating selected embodiments rather than all possible implementations, and are not intended to limit the scope of the present disclosure. In the drawings:

[0018] Figure 1 is a diagram of one embodiment of a shared hybrid transfer switch system coupled to a first (preferred) power source and a second (alternative) power source. The switching topology is symmetrical on both sides of the load, so as not to clutter the diagram, only one side is shown;

[0019] Figure 2 Shows Figure 1 a system wherein the respective relay contacts are in positions that they assume when the system is in a stable operating state receiving power from a first power source;

[0020] Figure 3 shows how a particular relay is controlled to momentarily interrupt power to a load during a first intermediate step of a switching sequence that switches a load from a first power source to a second power source for an off transition in which one of the relay contacts associated with the preferred power source is initially open;

[0021] Figure 4 showing how a particular relay of the system is further controlled during a second intermediate step in which an anti-parallel SCR circuit is switched on to provide an alternate current path from an alternate power source to a load;

[0022] Figure 5 shows how a particular relay of the system is further controlled during another intermediate step in which one of the relay contacts associated with the alternative power source is closed, wherein the anti-parallel SCR circuit forms an alternative current path to the load;

[0023] Figure 6 The positions of the contacts of the various relays of the system are shown when the system is operating in a steady state after having switched to using the second power source and after the anti-parallel SCR circuit has been disconnected.

[0024] Figure 7 is a diagram showing the timing of the transitions that occur when switching from a preferred power source to an alternate power source;

[0025] Figure 8 An embodiment of a system configured to process single-phase AC power is shown;

[0026] Fig. 9 An embodiment of a system configured to process a three-phase delta AC power source is shown;

[0027] Fig.10 An embodiment of a system configured to process AC power in a three-phase wye configuration is shown;

[0028] Fig.11 Shows Figure 1 Another embodiment of the system includes a relay test feature to test various relays of the system without interrupting power from the preferred power source;

[0029] Fig.12 Shows Fig.11 system, but during one phase of the test, one of the relays is closed (indicated by the dotted line);

[0030] Fig.13 is a schematic diagram of various waveforms that help illustrate voltages detected at various stages of a relay test performed under the control of a controller; and

[0031] Fig.14 Shows Fig.11 A flow chart of various operations that a system may perform when checking various relays associated with alternative power sources.

[0032] Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. DETAILED DESCRIPTION

[0033] Example embodiments will now be described more fully with reference to the accompanying drawings.

[0034] In various embodiments discussed below, the present disclosure achieves significantly faster switching times, which are generally possible for current electromechanical relays. In various embodiments, the switching performance of the relay is improved by using a solid-state switching device such as a bidirectional / bidirectional triode thyristor (TRIAC), an anti-parallel silicon controlled rectifier (SCR) pair, or an insulated gate bipolar transistor (IGBT). The selected solid-state switching device is connected to the contacts of the relay and can close the circuit two or three orders of magnitude faster than can be achieved using only conventional electromechanical relays. In addition, the solid-state switching device is configurably connected between any of the corresponding poles of the relay contacts of the circuits of the two power supplies, so that the solid-state switching device is shared between the circuits of the two power supplies. Therefore, the same solid-state switching circuit can be configured on the active power supply side to provide soft start during power-on (cold start), or on the passive power supply side to facilitate fast switching. In various embodiments discussed below, the solid-state device remains activated until the relay contacts have stabilized to a closed state. During steady-state operation of the active source, the solid-state switch can be switched to connect to the relay contacts of the passive source circuit to reduce the turn-on time conversion. Importantly, various embodiments provide a soft-start feature that helps limit the inrush current through components of the system when switching from one power source to another.

[0035] Reference Figure 1 , shows a shared hybrid switching system 10 according to one embodiment of the present disclosure. In this embodiment, the system 10 includes a controller 12 for controlling the switching of a plurality of relays 14a and 14b, 16, 18, 20, 22 and an anti-parallel SCR pair 24 to control the switching of power to the load from one or the other of a "preferred" or primary AC power source 26 and an "alternative" or secondary AC power source 28. It should be understood that the switching topology is symmetrical on both sides of the load, and in order to avoid cluttering the figure, the switching topology is shown in FIG. Figure 1 Only one side is shown in FIG. 1 . The common sides of the relay contacts 14a and 14b are coupled to each other at a first common connection point 14c, and one side (the "tail") of the anti-parallel SCR pair 24 is also coupled to the first connection point 14c. The purpose of the relays 14a and 14b is to "swing" the shared SCR circuit tail between power sources to achieve fast switching. The opposite side of the anti-parallel SCR pair 24 is coupled to a second common connection point 17 along with the common sides of the primary relays 16 and 18. The load is also in communication with the second connection point 17.

[0036] Thermistor 30 (in this example, an NTC thermistor) is coupled between one side of the SCR pair 24 and the first common connection point 14c, and forms a current limiter to relieve contact current overload when the anti-parallel SCR pair 24 is turned on during switching operations. The load can be one or more devices or subsystems that require AC power to operate, such as one or more servers, network switches, power distribution units (PDUs), or virtually any other component that requires AC power to operate. The system 10 can be located in a suitable housing (not shown) and mounted in a data center equipment rack, and can include one or more AC outlets (not shown) for supplying AC power directly to other devices and components.

[0037] Relay 14a may be part of a first Form A double pole normally open (DPNO) relay assembly having another similar relay (the similar relay being Figure 1 ). Similarly, relay 14 b may be part of a second form ADPNO relay assembly used in the mirrored portion of system 10. Alternatively, relays 14 a and 14 b may include form C single pole double throw (SPDT) bistable relays. Both implementations are possible, although it is believed that configuring relays 14 a and 14 b as parts of separate form ADPNO relays would be a more preferred implementation.

[0038] The primary relays 16 and 18 may be Form A single-pole normally open (SPNO) relay contacts (conventional snubber circuits not shown). The secondary relays 20 and 22 may include Form ADPNO relay contacts to provide source isolation for predictable startup conditions and operation in diagnostic mode (conventional snubber circuits not shown). By diagnostic mode, it is meant that when the circuit is closed on the opposite side, relay 20 or relay 22 may be disconnected so that the primary relay 16 or 18 may be closed instantaneously in sequence without causing cross conduction between sources. By sensing the voltage change across the contacts of the primary relay 16 or 18, the controller 12 may determine whether the relay 16 or relay 18 may be closed or opened. For each secondary relay 20 and 22, its contacts are connected in series with a voltage sensing resistor ( Figure 1 The anti-parallel SCR pair 24 is connected in parallel (not shown) so that each voltage sensing resistor string bridges the secondary relay contact, and when the secondary relay is closed, the voltage sensing resistor string is partially shunted. The anti-parallel SCR pair 24 includes SCR24a and SCR 24b, and the gates 24a1 and 24b1 of the two SCRs are connected to the controller 12. Likewise, the anti-parallel SCR pair 24 preferably includes a snubber circuit and a series fail-safe fuse, which are not shown to avoid cluttering the figure.

[0039] Will refer to Figures 2 to 5 The operation of system 10 is described. Figure 2 System 10 is shown in a steady state operation state powered by preferred power source 26. Relay contact 14a is open, relay contact 14b is closed, the SCRs of anti-parallel SCR pair 24 are both open, relay 16 is closed, and relay 18 is open. Current flows from preferred power source 26 through relay contacts 20 and 16 to the load according to the dashed arrows.

[0040] Figure 3 A first operation of switching to power from the alternative power source 28 is shown. Again, in this example, the system 10 is configured as a "break before make" system, although the system 10 can be controlled so that it operates as a "make before break" switching system. However, it is contemplated that a "break before make" control scheme will be a more preferred control configuration.

[0041] Using the "break before make" switching control method, the relay 16 is initially open. The relay contacts 14a and 14b, the relay contact 18 and the relay contact 22 are maintained as shown in FIG. Figure 2 Same location as shown.

[0042] Figure 4 The next operation of the controller 12 subsequently triggering SCR 24a or SCR 24b of the SCR pair 24 is shown. It should be understood that when triggered by the controller 12, the two SCRs in the SCR pair 24 are not turned on at the same time. One of the SCRs is turned on during the positive quadrant of the sinusoid, while the other of the SCRs is turned on during the negative quadrant of the sinusoid. Therefore, as the sinusoid alternates between positive and negative, SCRs 24a and 24b are turned on alternately. All relay contacts 14a, 14b, 16, 18, 20 and 22 remain as shown. Figure 3 In the event that either SCR 24a or SCR 24b is triggered, current now flows from the alternate power source 28 through the relay contacts 14b and through either SCR 24a or SCR 24b to the load. For convenience, the alternating operation of SCRs 24a and 24b will be described hereinafter as the operation of an "anti-parallel SCR pair 24".

[0043] Figure 5 The next operation is shown, where, while the controller 12 holds the anti-parallel SCR pair 24 in the "on" state, the controller closes the relay contact 18. This places the anti-parallel SCR pair 24 in parallel with the relay contact 18. Thus, current is able to flow to the load through the relay contacts 18 and 22 and through the combination of the relay contact 14b and the anti-parallel SCR pair 24. It should be understood that in Figure 5, the anti-parallel SCR pair 24 substantially enables power to be provided until the relay contacts 18 close, thereby overcoming the delay time that would otherwise be experienced in waiting for the relay contacts 18 to respond and fully close.

[0044] Figure 6 The next operation is shown, wherein the anti-parallel SCR pair 24 is no longer triggered by the controller 12 and naturally commutates off, the relay contact 14b opens and the relay contact 14a closes. With the preferred power source 26 reselected as the power source for the system 10, Figure 6 This final configuration of relays 14a and 14b shown in FIG. 1 prepares system 10 for the next transition.

[0045] Figure 7 A number of graphs are shown illustrating the timing of the above-described transition from the preferred power source 26 to the alternative power source 28. It should be understood that Figure 7 Idealized (simulated) waveforms are depicted; as shown here, in actual circuits, when the contacts are commanded to open, they cannot open instantaneously. Curve 100 represents the current through relay contacts 20 and 16 and the load when the preferred power source is activated; curve 102 represents the voltage across the load; line 104 represents the current through relay contacts 22 and 18 and the load when the alternative power source is activated; curve 106 represents the preferred power supply voltage before relay contact 20; curve 108 represents the alternative power supply voltage before relay contact 22. A fault occurs at point 110 located at the 19.0 ms point on the graph. The current to the load drops to zero, and the controller 12 commands the relay contacts 16 to open. At point 112 on the graph timeline at 23 ms (i.e., 4 ms after the fault occurs), the relay contacts 16 finally open after their inherent delay. At point 114 at 24 ms (i.e., 5 ms after the fault occurs) on the graph timeline, the anti-parallel SCR pair 24 is triggered and the controller 12 commands the relay contacts 18 to close. This action occurs only 5 ms after the fault is detected. At point 116 at 31 ms on the graph timeline, the relay contacts 18 finally open after their inherent delay. At point 118 at 50 ms on the graph, the anti-parallel SCR pair 24 is no longer triggered by the controller and naturally switches off. Arrow 120 represents the total time duration during which one of the SCRs of the anti-parallel SCR pair 24 is turned on and supplies current to the load, while arrow 122 indicates the total overlap time during which one of the SCRs of the anti-parallel SCR pair 24 is connected in parallel with the relay contacts 18. In this example, the total time that the load experiences no power is only 5 ms, which is well within the expected time period of 8 ms or less at a 60 Hz line frequency as specified by the ITIC curve developed by the Information Technology Industry Council.

[0046] Figure 8 A system 200 configured to implement a single phase topology according to the present disclosure is shown. In this embodiment, essentially two iterations of the system 10 are included, wherein each pair of relays 14a, 14b, 20 and 22 are controlled together, respectively.

[0047] Fig. 9 A system 300 configured to implement a three-phase delta topology according to the present disclosure is shown. An example of the system 10 is used to control the conversion from each of the X-phase, Y-phase, and Z-phase 26x / 26y / 26z of the preferred power source to the X-phase, Y-phase, and Z-phase 28x / 28y / 28z of the alternate power source.

[0048] Fig.10 A system 400 configured to implement a three-phase Y topology according to the present disclosure is shown. In this implementation, four instances of the system 10 are used to control the transition from each of the preferred power phases X, Y, and Z (labeled 26x, 26y, 26z) and the neutral line to each of the alternative power phases X, Y, and Z (labeled 28x, 28y, and 28z) and the neutral line. In this implementation, the relay contacts 20 of the two instances of the system 10 associated with the X phase and the Y phase are switched together, and the relay contacts 20 of the two instances of the system 10 associated with the Y phase and the neutral line are switched together. The relay contacts 14a, 14b, and 22 are treated in the same manner.

[0049] The various embodiments of the system 10 presented herein may also be implemented in a "make before break" ("closed switching") configuration. The source voltage phasing may be asynchronous or synchronous, where a synchronous condition is required for the "closed switching" configuration.

[0050] Although the various embodiments described herein show an anti-parallel SCR pair 24 as the solid-state switching component, it should be understood that other solid-state components such as but not limited to insulated gate bipolar transistors (IGBTs) or TRIACs may be used as the solid-state switching devices with little or no modification to the system 10.

[0051] Another advantage of the present system 10 is that because the anti-parallel SCR pair 24 need only carry current for brief time intervals until the relay contacts 16 and 18 stabilize during a switching operation, the duty rating of the SCRs of the anti-parallel SCR pair 24 can be lower than would otherwise be required to handle the current from the preferred power source 26 or the alternate power source 28.

[0052] The system 10 also provides a significant "soft start" benefit because at startup, the anti-parallel SCR pair 24 is gradually triggered at a larger conduction angle until it is fully turned on. This causes the voltage to ramp up, effectively ramping up the current flowing into the load. This soft start benefit also reduces the inrush current during cold starts when power is initially applied to a reactive load that is in a fully discharged state.

[0053] Of course, the use of solid-state anti-parallel SCR pairs 24 in parallel with the contacts facilitates rapid switching, and the shunting action of the SCRs means that the relay contacts can naturally bounce to a final closed position without causing arcing, wear and erosion of the contact surfaces of each of the relays, which often occurs with conventional power conversion circuits when switching suddenly from one power source to another. Significant reduction and / or elimination of contact bounce can extend the life of the relay contacts and reduce stress on various other components of the system 10 caused by large inrush currents.

[0054] Reference Fig.11 and Fig.12 , shows a system 500 according to another embodiment of the present disclosure, which includes a relay test software module ("RTSM") 12b and a relay voltage detection subsystem 12c that can be accessed by the controller 12. The voltage detection subsystem 12c utilizes a voltage sensing resistor string ("VSRS") subsystem 12d, which is a conventional voltage sensing circuit composed of series and parallel coupled resistors and is coupled at a node (node ​​N1) and also grounded. The construction of the VSRS subsystem 12d is well known in the art, and the subsystem can form part of the voltage detection subsystem 12c, or it can form a stand-alone circuit. Moreover, although in Fig.11 VSRS 12d is shown as being coupled only across secondary relay 22, but it should be understood that an additional VSRS identical to VSRS 12d would also be coupled across secondary relay 20 for monitoring the voltage at node N2 and also in communication with controller 12, but this has been omitted to avoid cluttering the diagram. Alternatively, a suitable switch subsystem may be used to controllably decouple VSRS subsystem 12d from node N1 and place it at node N2, across secondary relay 20 relative to ground.

[0055] Optionally, but preferably, a load voltage sensing resistor string ("LVSRS") subsystem 12e is also included in the system 500. The LVSRS subsystem 12e is composed of resistors coupled in series and parallel, with the load and ground coupled across, and is capable of monitoring the voltage across the load in real time or at a selected time commanded by the controller 12. The RTSM 12b, the voltage detection subsystem 12c, and the VSRS subsystem 12d can be collectively considered to form a "relay test subsystem." If the LVSRS subsystem 12e is included, the component can also form part of the voltage detection subsystem 12c. In addition, although the RTSM 12b is shown to be stored in the non-volatile memory 12a associated with the controller 12, it should be understood that the RTSM 12b can alternatively be stored in a separate non-volatile memory component that can be accessed by the controller 12.

[0056] The system 500 also includes a user interface 13 having a human machine interface ("HMI") health button 13a. The HMI health button 13a enables a user to initiate a relay test operation using the RTSM 12b, which will be described in detail in the following paragraphs. The HMI health button 13a, or alternatively, a separate dedicated controller, can enable a user to also initiate a check of the voltage across the load using the LVSRS subsystem 12e, which will be described in more detail in the following paragraphs. In a preferred implementation, the voltage sensing subsystem 12c can simultaneously use both the VSRS subsystem 12d and the LVSRS subsystem 12e to capture sample waveforms.

[0057] The RTSM 12b functionality of system 500 provides a number of important benefits without the need to add additional electrical components (e.g., additional relays, dummy loads, etc.) to system 500 to check the functionality of relays 18 / 22 and 16 / 20. Thus, except for non-volatile memory 12a, RTSM 12b, VSRS 12d, and user interface 13, the physical components and interconnections of system 500 may be the same as those of system 10.

[0058] The RTSM 12b enables the testing of relays 18 and 22 when the load is being powered by the preferred power source 26. Conversely, the RTSM 12b allows the testing of relays 16 and 20, respectively, when the load is being powered by the alternate power source 28. The sequence of operations performed by the controller 12 using the RTSM 12b is the same in both cases, and therefore the following description will only describe the operation of testing relays 18 and 22, it being understood that the same operations are performed in testing relays 16 and 20 when the alternate power source 28 is being used and the preferred power source is not being used. It will also be understood that Fig.11 and Fig.12 The system 500 shown in FIG. Figure 1As with the system 10 in FIG. 1 , only half of the components required to perform system operation are shown. It will be appreciated that the switching topology is symmetrical on both sides of the load and is controlled in the same manner using the RTSM 12b. To avoid cluttering the diagram, the FIG. Fig.11 and Fig.12 Only one side is shown.

[0059] exist Fig.11 , it will be appreciated that when the preferred power source 26 is powering the load, both secondary relays 20 and 22 are closed, primary relay 16 is closed, primary relay 18 is open, relay 14b is closed, and SCR 24 is open. When the contacts of secondary relay 22 are closed and the resistor of VSRS 12d is partially shunted (shorted) by the action of the relay contacts, the voltage between the primary relay 18 and the secondary relay 22 in series will match the input voltage at the alternative (passive) power source 28. Thus, in Fig.11 In the case where the primary relay 18 is open and the secondary relay 22 is closed, the voltage at the node N1 detected by the voltage detection subsystem 12c using the VSRS 12d will be the input voltage provided by the alternative power source 28. Fig.13 , the voltage at the input of the alternative power source 28 is identified by waveform 602 , and the voltage between the primary relay 18 and the secondary relay 22 (at node N1 ) is identified by waveform 604 .

[0060] When the system is operating in its normal automatic transfer detection state and the preferred power source 26 is powering the load, the user can press the HMI health button 13a. Fig.12 As shown, assuming relays 22 and 14b operate correctly, this action will disconnect the alternate source secondary relay 22 and relay 14b. When the contacts of secondary relay 22 are open (i.e., the relay is open), the number of "active" resistors in VSRS 12d increases, so that the change in the voltage drop across VSRS 12d effectively causes the measured voltage level at node N1 to decrease relative to the input voltage at the alternate power source 28. As shown by Fig.13 As indicated by the difference between waveform 602 and waveform 604 at point 602a in FIG. 1 , the voltage measured at node N1 drops significantly (typically by 15% or slightly more). Therefore, when RTSM 12b commands secondary relay 22 to open and its contacts actually open, the voltage measured by voltage sensing subsystem 12c at node N1 using VSRS 12d will drop significantly.

[0061] If the peak voltage detected at node N1 is equal to or less than 85% of the nominal peak reference voltage, it can be determined that the secondary relay 22 has been successfully disconnected. The nominal peak reference voltage is established during steady state operation as the nominal AC output of the preferred power source 26 before the conditions that trigger the automatic transfer operation. Under normal operating conditions, the input voltage available from the alternative power source 28 will be almost equal to the nominal peak reference voltage.

[0062] Next, during the second phase of the operation, as Fig.12 1 , the RTSM 12b closes the primary relay 18 associated with the alternative power source 28, as indicated by the line 18' in FIG. 1 . This connects the preferred power source 26 to the primary relay 18. More specifically, the preferred power source 26 is connected to the node N1. The peak voltage is again measured at the serial connection of the primary relay and the secondary relay of the passive source (i.e., at the node N1). If the peak voltage is restored to within a few percent margin of the nominal voltage (i.e., the main power source 26 voltage), it can be determined that the primary relay 18 has been successfully closed.

[0063] The final operation is to restore the controller 12 to the normal relay state, that is, commanding the passive source primary relay 18 to open, and commanding the relay 14b and the secondary relay 22 to close. After these operations, the system 500 returns to normal automatic detection operation.

[0064] Brief reference Fig.14 Flowchart 700 summarizes the above-described operations for checking the primary relay 18 and the secondary relay 22 when the system 500 uses the preferred power source 26 to power the load. Fig.14 The operations in flowchart 700 are performed when the system is initially in its normal automatic transition detection state (ie, Fig.11 It will be appreciated that when the system uses the alternative power source 28 to power the load, the relays 16 and 20 may be checked using Fig.14 The corresponding operations shown in .

[0065] At operation 702, the controller 12 determines whether a command to initiate a relay test process has been received from a user (i.e., typically from the HMI health button 13a). If such a command is received, at operation 704, the controller 12 begins disconnecting the relay 14b and the secondary relay 22 using the RTSM 12b. Then, as indicated at operation 706, the voltage detection subsystem 12c and the VSRS 12d are used to perform voltage measurements at the node N1. The voltage reading may be recorded in the memory 12a. Then, as indicated at operation 708, the RTSM 12b causes the controller 12 to check whether the voltage present at the node N1 is equal to or less than 85% of the nominal peak reference voltage. If the check at operation 708 produces a "no" answer, this indicates that the secondary relay 22 has failed to disconnect, and at operation 722, the RTSM 12b causes the controller 12 to report that the secondary relay test has failed, and at operation 724, the RTSM 12b causes the controller 12 to abort the relay test process and close the relay 14b to resume the normal automatic transfer detection state. If the test at operation 708 produces a "yes" answer, the secondary relay 22 has been successfully opened, and at operation 710, the RTSM 12b causes the controller 12 to report that the secondary relay test has passed. Then, as indicated at operation 712, the RTSM 12b causes the controller 12 to close the primary relay 18. Then, as indicated at operation 714, the RTSM 12b causes the controller 12 to perform another voltage check at node N1. Then, as indicated at operation 716, the RTSM 12b causes the controller 12b to determine whether the voltage just measured at node N1 is at or near the nominal peak reference voltage. As indicated at operation 718, if the test produces a "yes" answer, the controller 12 can report / record that the primary relay 18 has been successfully closed and the primary relay test has passed. If the check at operation 716 produces a "no" answer, then at operation 726, the RTSM 12b causes the controller 12 to report that the primary relay failed to close and the primary relay test has not passed. After the relay test is complete and the test results have been reported, at operation 720 the RTSM 12b causes the controller 12 to restore the relay state for normal automatic transfer detection and ends the relay test process.

[0066] will understand, Fig.14 The specific order of operations shown in flowchart 700 may vary, and thus system 500 is not necessarily limited to Fig.14 The exact order of operations is shown in .

[0067] A significant advantage of the system 500 and RTSM 12b is that the above-described voltage tests can be completed within only a few line cycles of the AC signal, for example, within only six line cycles of the AC input signal from the main power supply 26. Another significant benefit is that the above-described relay voltage tests can all be performed without interrupting the power supply to the load from the preferred power supply 26. Similarly, if the system 500 is operated using power from the alternate power supply 28, the relays associated with the preferred power supply (i.e., relays 16 and 20) can all be checked without interrupting the power supply to the load from the alternate power supply 28. Therefore, the controller 12 can be programmed to perform the above-described voltage tests, for example, on a predetermined schedule, such as weekly, through the controlled opening / closing of various relays, without the need to switch the load to a different power supply before performing the relay tests.

[0068] If the LVSRS subsystem 12e is included, the system 500 can be commanded to perform a voltage check on the voltage across the load. As described above, this check can be performed simultaneously with the check performed by the VSRS subsystem 12d. The LVSRS subsystem 12e sensing capability provides redundancy and can help determine whether an internal or external fault occurred during normal operation that caused the transfer; for example, the primary relay (relay 16 or relay 18) of the active power source accidentally disconnected. For example, if the active power source is the preferred AC power source 26, and the primary relay 16 accidentally disconnects, this will mean that the output voltage reading will be invalid, but the input voltage from the preferred AC power source 26 will still exist. Otherwise, if the LVSRS subsystem 12e detects a voltage loss or unqualified voltage during the test, the system 500 will automatically transfer to another power source (i.e., the preferred power source 26 or the alternate power source 28). The voltage loss may occur due to a source fault or an internal hardware fault such as a secondary relay or primary relay contact that spontaneously disconnects. If the internal hardware fault is a permanent condition, the self-test will reveal the internal fault as the root cause.

[0069] Thus, LVSRS subsystem 12e provides a valuable subsystem that aids in evaluating the health of primary relays 16 and 18. Importantly, the testing performed using LVSRS subsystem 12e and VSRS subsystem 12d may be performed without interrupting power to the load.

[0070] Perhaps the most significant benefit of the system 500 is its ability to perform the above-described comprehensive relay testing operations on all relays associated with the preferred power source and the alternate power source without requiring the addition of any additional hardware components (e.g., one or more additional relays, switches, dummy loads, etc.) to the system 500, or requiring any modifications to the overall hardware design of the system. The above-described relay testing can be completed in only a few milliseconds, which virtually eliminates any concern about whether a switch to the alternate power source 28 is required to handle an emergency situation in which power is suddenly lost from the preferred power source 26 (or vice versa).

[0071] It will also be appreciated that although system 500 has been described as being in conjunction with Figure 1 , but RTSM 12b may be included for use with any other implementation described herein.

[0072] The foregoing description of the embodiments is provided for the purpose of illustration and description. The description is not intended to be exhaustive or limit the present disclosure. Even if not specifically shown or described, each element or feature of a particular embodiment is usually not limited to the particular embodiment, but can be interchanged and can be used for selected embodiments when applicable. Each element or feature of a particular embodiment can also be modified in many ways. Such modification is not considered to depart from the present disclosure, and all such modifications are intended to be included in the scope of the present disclosure.

[0073] Example implementations are provided so that the present disclosure will be thorough and will fully convey the scope to those skilled in the art. Many specific details, such as examples of specific components, devices, and methods, are set forth to provide a thorough understanding of the embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example implementations may be implemented in many different forms, and that neither specific details nor example implementations should be construed as limiting the scope of the present disclosure. In some example implementations, well-known processes, well-known device structures, and well-known techniques are not described in detail.

[0074] The terms used herein are for the purpose of describing specific example embodiments only and are not intended to be limiting. Unless the context clearly indicates otherwise, as used herein, the singular forms "a", "an", and "the" may also be intended to include plural forms. The terms "comprises", "comprising", "including", and "having" are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and / or parts, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, parts, and / or groups thereof. Unless specifically identified as an order of execution, the method steps, processes, and operations described herein should not be interpreted as necessarily requiring them to be performed in the specific order discussed or shown. It should also be understood that additional or alternative steps may be adopted.

[0075] When an element or layer is referred to as being "on", "engaged to", "connected to" or "coupled to" another element or layer, the element or layer may be directly on, directly engaged to, directly connected to or directly coupled to another element or layer, or there may be an intervening element or layer. In contrast, when an element is referred to as being "directly on", "directly engaged to", "directly connected to" or "directly coupled to" another element or layer, there may be no intervening element or layer. Other words used to describe the relationship between elements (e.g., "between" and "directly between", "adjacent" and "directly adjacent", etc.) should be interpreted in a similar manner. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0076] Although the terms first, second, third, etc. can be used herein to describe various elements, components, regions, layers and / or parts, these elements, components, regions, layers and / or parts should not be limited by these terms. These terms can only be used to distinguish an element, component, region, layer or part from another region, layer or part. Unless the context clearly indicates, the terms such as "first", "second" and other numerical terms used herein do not imply order or sequence. Therefore, the first element, component, region, layer or part discussed below can be referred to as the second element, component, region, layer or part, without departing from the teaching of exemplary embodiments.

[0077] In this article, for ease of description, spatial relative terms such as "inside", "outside", "below", "below", "below", "above", "above", etc. can be used to describe the relationship between an element or feature as shown in the figure and another (one or more) elements or (one or more) features. Spatially relative terms may be intended to cover different orientations of the device when in use or operation in addition to the orientation depicted in the drawings. For example, if the device in the drawings is turned over, the elements described as being "below" or "below" other elements or features will be oriented to be "above" other elements or features. Therefore, the example term "below" can cover both the upper orientation and the lower orientation. The device can be oriented in other ways (rotated 90 degrees or in other orientations), and the spatial relative descriptors used in this article are interpreted accordingly.

Claims

1. A shared transfer switch system with built-in relay testing capability, the shared transfer switch system being used to transfer power received by a load from a preferred power source to an alternative power source, or to transfer power received by the load from the alternative power source to the preferred power source, the shared transfer switch system comprising: a first primary relay and a first secondary relay, the first primary relay and the first secondary relay being coupled in series and connected in series with the preferred power source and the load so that the load can be powered by the preferred power source; a second primary relay and a second secondary relay, the second primary relay and the second secondary relay coupled in series and also in series with the alternative power source and the load for providing power from the alternative power source to the load when the preferred power source is unavailable for powering the load; a voltage sensing resistor string coupled across the second secondary relay; a controller for controlling operation of the second primary relay and the second secondary relay; a switch subsystem in communication with the controller and the first primary relay, the first secondary relay, the second primary relay, the second secondary relay, and the load, the switch subsystem being configured to be controlled by the controller to control switching from one or the other of the preferred power source or the alternative power source to the load; and a relay test subsystem, the relay test subsystem comprising a relay test software module and a voltage detection subsystem, the relay test software module and the voltage detection subsystem being operably controlled by the controller for performing a relay test process, the relay test process comprising performing a plurality of voltage tests by: opening the second secondary relay when the first primary relay and the first secondary relay are closed and when the second primary relay is open, and using power from the alternative power source to help verify that the second secondary relay has opened by taking a first voltage measurement using the voltage sensing resistor string without interrupting power to the load; opening the second secondary relay without interrupting power to the load; The second primary relay is closed while the second secondary relay remains open and while both the first primary relay and the first secondary relay remain closed, and a second voltage measurement is obtained using the voltage sensing resistor string while using power from the preferred power source and without interrupting power to the load to verify that the second primary relay has been successfully closed.

2. The shared transfer switch system according to claim 1, wherein: The voltage sensing resistor string of the voltage detection subsystem is configured to facilitate voltage measurement at a node between and in series with the second primary relay and the second secondary relay.

3. The shared transfer switch system of claim 2, further comprising a user interface having a control for enabling the relay testing process.

4. The shared transfer switch system according to claim 1, wherein: The relay test software module performs the relay test process by opening the second secondary relay when the second primary relay is open and performing a voltage test at a node representing a midpoint between the second primary relay and the second secondary relay, and then closing the second primary relay when the second secondary relay is open and performing a voltage test at the node.

5. The shared transfer switch system according to claim 4, wherein: The relay test software module is configured to perform the relay test process by opening the first secondary relay and performing a voltage test at the node when the first primary relay is open, and then closing the first primary relay and performing a voltage test at the node when the first secondary relay is open.

6. The shared transfer switch system of claim 1 further comprises a load voltage sensing resistor string connected to the controller for monitoring the voltage across the load to help evaluate the condition of one or more of the first primary relay or the second primary relay.

7. The shared transfer switch system according to claim 1, wherein: The switch subsystem includes an additional relay and a solid-state switching device, wherein the additional relay and the solid-state switching device are configured to: during a switching operation from the preferred power source to the alternative power source, when the additional relay is in a closed state and the solid-state switching device is turned on, operate in series to provide a temporary current path between the alternative power source and the load; as well as Wherein, when the relay test process is started, the additional relay is disconnected.

8. A shared transfer switch system with built-in relay testing capability, the shared transfer switch system for transferring power received by a load from a preferred power source to an alternate power source, or transferring power received by the load from the alternate power source to the preferred power source, the shared transfer switch system comprising: a first primary relay and a first secondary relay, the first primary relay and the first secondary relay being coupled in series and also being connected in series with the preferred power source and the load so that the load can be powered by the preferred power source; a second primary relay and a second secondary relay, the second primary relay and the second secondary relay coupled in series and also in series with the alternative power source and the load, for providing power from the alternative power source to the load when the preferred power source is unavailable for powering the load; a voltage sensing resistor string coupled across the second secondary relay; a controller for controlling operation of the first and second primary relays and the first and second secondary relays; a switch subsystem in communication with the controller and the first and second primary relays and the first and second secondary relays, the switch subsystem being configured to be controlled by the controller to control switching from one or the other of the preferred power source or the alternate power source to the load; and a relay test subsystem, the relay test subsystem comprising a relay test software module and a voltage detection subsystem, both of which are controlled by the controller to perform a relay test process, the relay test process comprising performing a plurality of voltage tests by: selectively opening the second secondary relay when the first primary relay and the first secondary relay are closed and when the second primary relay is open, and using the alternative power source to facilitate performing a first voltage test to obtain a first voltage measurement using the voltage sensing resistor string without interrupting power to the load to verify that the second secondary relay has opened; opening the second secondary relay without interrupting power to the load; The second primary relay is closed while the second secondary relay remains open and while both the first primary relay and the first secondary relay remain closed, and a second voltage measurement is obtained using the voltage sensing resistor string while using power from the preferred power source and without interrupting power to the load to verify that the second primary relay has been successfully closed.

9. The shared transfer switch system according to claim 8, wherein: The second primary relay and the second secondary relay are tested by the controller while power is being provided by the preferred power source.

10. The shared transfer switch system according to claim 8, wherein: The first primary relay and the first secondary relay are tested while power is being provided by the alternative power source.

11. The shared transfer switch system according to claim 8, wherein: The controller uses the relay test software module to close the second primary relay when the second secondary relay is open, and uses the voltage detection subsystem to measure the voltage at a node representing an intermediate series connection point between the second primary relay and the second secondary relay when power is being provided by the preferred power source to verify correct operation of the second primary relay.

12. The shared transfer switch system according to claim 8, wherein: The controller uses the relay test software module to close the first primary relay when the first secondary relay is open, and uses the voltage detection subsystem to measure the voltage at a node representing an intermediate series connection point between the first primary relay and the first secondary relay when power is being provided by the alternative power source to verify correct operation of the first primary relay.

13. The shared transfer switch system of claim 8, further comprising a user accessible control for initiating the relay testing process.

14. The shared transfer switch system of claim 13, further comprising a user interface subsystem, and wherein: The user accessible control includes a button operably associated with the user interface subsystem to enable a user to initiate the relay testing process.

15. A method for testing a plurality of relays associated with a system for transferring power from one or the other of a preferred power source or an alternate power source to a load, the method comprising: using a first primary relay and a first secondary relay, the first primary relay and the first secondary relay being coupled in series and connected in series with the preferred power source and the load so that the load can be powered by the preferred power source; using a second primary relay and a second secondary relay, the second primary relay and the second secondary relay coupled in series and also in series with the alternative power source and the load, for providing power from the alternative power source to the load when the preferred power source is unavailable for powering the load; a voltage sensing resistor string coupled across the second secondary relay; using a switch subsystem in communication with the first primary relay, the first secondary relay, the second primary relay, and the second secondary relay and the load, the switch subsystem being configured to be controlled to switch from one or the other of the preferred power source or the alternate power source to the load; as well as A relay testing process controlled by a controller is performed, the relay testing process comprising performing a plurality of voltage tests by: selectively opening the second secondary relay and performing a first voltage measurement using the alternative power source in conjunction with the voltage sensing resistor string and without interrupting power to the load to verify that the second secondary relay has moved to an open position when the first primary relay and the first secondary relay are both closed and the second primary relay is open; opening the second secondary relay without interrupting power to the load; The second primary relay is closed while the second secondary relay remains open and while both the first primary relay and the first secondary relay remain closed, and a second voltage measurement is obtained using the voltage sensing resistor string while using power from the preferred power source and without interrupting power to the load to verify that the second primary relay has been successfully closed.

16. The method of claim 15, further comprising performing the first voltage measurement at a node defining an intermediate point between a series connection of the second primary relay and the second secondary relay; and The second voltage measurement is then performed at the node after the second primary relay has opened and the second secondary relay has closed.

Images