Shared resonant shutdown circuit

Abstract

Various embodiments of the present disclosure relate to a shared resonant shutdown circuit. A static transfer switch is provided for alternating power supply from two different power sources to a load. Switching between the two power sources can occur within a fraction of an electrical cycle. In response to sensing performance degradation of the power source supplying the load, the main circuit is shut down using the resonant shutdown circuit. The resonant shutdown circuit is shared between the main circuits of the two different power sources, such that the resonant shutdown circuit is connected to the main circuit of the power source currently supplying power to the load.

Description

Technical Field

[0001] The present invention generally relates to a static transfer switch for transferring electrical power from one power source to another power source to power an electrical load. Background Art

[0002] Static transfer switches are used in industry to control the power supply to critical electrical components. Specifically, static transfer switches are used for electrical loads such as data centers that require a constant, high-quality electrical supply.

[0003] Figure 1 An example of a static transfer switch 10 is shown. As shown, two different power sources 12A, 12B are coupled to the static transfer switch 10. The output of the static transfer switch 10 is coupled to an electrical load 14. Typically, the output is directly connected to a power distribution unit (PDU) 14 that includes a transformer 16. The final electrical load may be a computer server 30 ( Figure 2 However, it should be understood that the static transfer switch 10 can also be used to power other types of electrical loads.

[0004] The static transfer switch 10 may include a variety of sensors 18A, 18B, 20A, 20B to monitor the electrical characteristics and power output of the first electrical power source 12A and the second electrical power source 12B. For example, it may be desirable to monitor the voltage 18A, 18B of each of the power sources 12A, 12B and monitor the output current 20A and voltage 20B. The static transfer switch 10 also includes one or more switches 22A, 22B associated with each of the power sources 12A, 12B. This allows the static transfer switch 10 to supply power to the output from either power source 12A, 12B. For example, the first electrical power source 12A may be a preferred power source 12A (e.g., the grid), while the second electrical power source 12B may be a backup power source 12B (e.g., a generator). During normal use, power can be supplied from the first electrical power source 12A to the load 14 by closing the first switch 22A and opening the second switch 22B (to isolate the second electrical power source 12B). In the event that the first electrical power source 12A experiences a performance degradation (e.g., a voltage drop) as determined by one or more of the sensors 18A, 18B, 20A, 20B, power can be delivered to the second electrical power source 12B by opening the first switch 22A and closing the second switch 22B. Thus, the electrical load 14 has a constant power supply despite the performance degradation event that may occur in one of the power sources 12A, 12B. Summary of the Invention

[0005] A static transfer switch is described for increasing the speed of switching from one power source to another. The system senses a performance degradation of a power source supplying power to a load. In response to sensing the performance degradation, the system shuts off a gate signal of a first switch coupled between the power source and the load. The system also includes a resonant turn-off circuit that forces the first switch to open during a switching event. The resonant turn-off circuit is shared between a first switch associated with a first electrical power source and a second switch associated with a second electrical power source. Depending on which power source is supplying power to the load, the resonant turn-off circuit can be selectively connected to the first switch or the second switch. The present invention may also include any other aspects described below in the written description or accompanying drawings, and any combination thereof. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The present invention may be more fully understood by reading the following description in conjunction with the accompanying drawings, in which:

[0007] Figure 1 is a schematic diagram of a static transfer switch;

[0008] Figure 2 is a schematic diagram showing a static transfer switch for a three-phase power supply and a three-phase load;

[0009] Figure 3 is a schematic diagram of a switching circuit coupled between one phase of a power supply and a load;

[0010] Figure 4 is a series of graphs illustrating electrical characteristics of a switching circuit during an off period of a switch between a power source and a load;

[0011] Figure 5 is a schematic diagram of the charging circuit of the energy storage;

[0012] Figure 6 is another schematic diagram of a static transfer switch;

[0013] Figure 7 is a flow chart illustrating the transfer of power from one power source to another power source to power a load;

[0014] Figure 8 is a schematic diagram of a digital signal processor for controlling power via a static transfer switch;

[0015] Figure 9 is another schematic diagram of a digital signal processor for controlling power via a static transfer switch;

[0016] Figure 10 is another schematic diagram of a static transfer switch;

[0017] Figure 10A It is a schematic diagram of a double-throw switch;

[0018] Figure 11 is a schematic diagram of a resonant shutoff circuit shared between two main circuits;

[0019] Figure 12 is another schematic diagram of a static transfer switch;

[0020] Figure 13 is another schematic diagram of a static transfer switch;

[0021] Figures 14A to 14E is a schematic diagram of the operation of the resonant shut-off circuit; and

[0022] Figure 15 It shows Figures 14A to 14E A series of graphs showing the electrical characteristics of a switching circuit. DETAILED DESCRIPTION

[0023] Figure 2 An example of a three-phase static transfer switch 10 is shown in FIG. Typically, the static transfer switch 10 is designed to complete a switching event between the two power sources 12A, 12B within one electrical cycle of the power sources 12A, 12B. This is desirable in order to provide a high-quality, constant power supply with minimal impact on the electrical loads 14, 30. To achieve such a rapid switching event, solid-state switches 22A, 22B (first switch 22A and second switch 22B) are typically used to perform the switching event, since the solid-state switches 22A, 22B can be turned on and off in less than one electrical cycle. Preferably, the switches 22A, 22B are silicon-controlled rectifiers (SCRs). Various types of thyristors can be used for the solid-state switches 22A, 22B, such as integrated gate-commutated thyristors (IGCTs), reverse-blocking integrated gate-commutated thyristors (RB-IGCTs), or gate-turn-off thyristors (GTOs). In the case of a multi-phase static transfer switch 10, each of the main switches 22A, 22B will be composed of multiple individual switches 26, with at least one switch 26 for each phase A, B, and C. Anti-parallel thyristor pairs 26 are particularly suitable for each switch 26 associated with phases A, B, and C. Because the power sources 12A, 12B are AC power sources, each switch 26 typically includes two switches 26A, 26B arranged in anti-parallel. However, each anti-parallel thyristor pair 26A, 26B is often considered a single switch 26 because they are typically turned on and off together. The static transfer switch 10 may also include a series of manual switches 28, which are primarily used to isolate various sections of the circuit during maintenance.

[0024] It is generally preferred that the first power source 12A and / or the second power source 12B include an uninterruptible power supply (UPS) 32 to provide control over the electrical characteristics of the original power sources 12A, 12B and manage power dips or losses in the original sources 12A, 12B. As noted, the output is typically coupled to the transformer 16 of the PDU 14, and the final electrical load 30 is typically a rack of computer servers 30 in a data center.

[0025] The present invention is an improvement herein in that it uses a resonant turn-off topology that is tuned to force commutate a three-phase power system and is operated by an embedded digital processor that uses software intelligence and algorithmic control signals to enable autonomous and sub-millisecond transfer switching.

[0026] The shutdown circuit 40 with RTO topology is as follows: Figure 3 As shown, the circuit 40 includes a main circuit 42 and a resonant circuit 44. The main thyristors 26A, 26B (first switches) are S m1 and S m2 The resonant circuit includes four auxiliary thyristor switches 34 (third switches) S r1 、S r2 、S r3 、S r4 , resonant capacitor C (energy storage) 36 and resonant inductor L 38. Capacitor C36 is precharged to provide a resonant current to produce the zero current crossing of the main thyristor 26. Inductor L38 limits the di / dt of the main thyristor 26 during turn-off. During normal conduction, only the main thyristor S m1 (or S m2 ) 26A, 26B are conducting and all auxiliary switches 34 are off. Therefore, the pre-charged resonant capacitor 36 is isolated from the main thyristor switch 26. During the resonant off operation, the auxiliary switches 34S r1,2 (or S r3,4 The inductor 38L is triggered to turn off by sending a gate signal to it (depending on the direction of the current). As a result, the energy stored in the resonant capacitor 36 is discharged. When the resonant current through the inductor 38L exceeds the load current, the current through the main thyristor 26 is commutated to the resonant circuit. At the same time, the capacitor 36 voltage provides a negative bias voltage to help the main thyristor 26 turn off (i.e., open and stop conducting). When the main thyristor 26 current reaches zero, it begins to turn off by the reverse bias voltage from the resonant capacitor 36. In the RTO topology, there are three possible design options to control performance: the resonant capacitor value C, the pre-charged initial capacitor voltage V c0 , and the resonant inductance value L. These parameters can be used to determine how much and how fast the main thyristor current can be turned off, as well as the size and cost of the auxiliary resonant circuit.

[0027] Figure 4 The voltage and current waveforms for the resonant turn-off operation of the main thyristor 26 and the auxiliary switch 34 are shown. As shown in the bottom graph, at time 0.1 seconds, a gate signal is sent to turn off the main thyristor 26, and a gate signal is sent to turn on the auxiliary thyristor 34. This occurs due to performance degradation identified by sensors 18 and 20. Because the second switch 22B cannot close to switch power to the second power source 12B until the first switch 22A has opened, it may be beneficial to be able to stop conducting current through the first switch 22A more quickly than with a conventional static transfer switch. That is, once the gate-on signal is applied to the SCR, current continues to conduct through the SCR even after the gate-off signal is applied. However, after the gate-off signal is applied to the SCR, the SCR stops conducting current after the current drops below a threshold. This typically occurs in AC current when the current waveform crosses zero. However, it may take up to half an AC cycle for the power waveform to cross zero (i.e., 8 ms). It may be beneficial to be able to stop the first switch 26A more quickly so that the second switch can be closed more quickly to transfer power from the first power source 12A to the second power source 12B as quickly as possible. Figure 4 As shown in the top graph of FIG, the current flowing to the loads 14 and 16 through the main thyristor 26 and the auxiliary thyristor 34 stops within less than 0.18 ms after the gate signal is applied to the main thyristor 26 and the auxiliary thyristor 34, preferably within 0.5 ms. Therefore, the turn-off speed is greatly improved.

[0028] refer to Figure 4 After the auxiliary resonant thyristor 34 is triggered, resonance begins and the resonant current through L 38 increases rapidly. Once the resonant current exceeds the load 14, 16 current, the main thyristor 26 current decreases to zero and begins to turn off. Simultaneously, the load 14, 16 current is commutated or bypassed to the auxiliary circuit 44 (34, 36, 38). The resonant capacitor 36 is recharged by the load 14, 16 current, but with the opposite voltage polarity. After the resonant capacitor 36 voltage is sufficiently high and the load 14, 16 current is interrupted, the auxiliary thyristor 34 is turned off. As a result, the RTO has disconnected the first power supply 12A, and the loads 14, 16 are ready to transfer to the alternative power supply 12B.

[0029] Figure 5A resonant circuit 44 is shown (one resonant circuit per phase). As shown, a pre-charge circuit 46 is coupled to the resonant circuit 44 via a DC bus 48. Preferably, the DC bus 48 is slowly pre-charged via a single bridge rectifier diode 50 having a resistor 52 to prevent capacitor inrush current. In addition, in the event that the DC bus 48 operates above a set limit, a bleeder resistor 54 can be used to adjust the DC level to a desired value. A pre-charge relay 56 and a bleeder relay 58 are used to turn pre-charge and bleed on or off. Preferably, a fourth switch 60 is provided between the pre-charge circuit 46 and the capacitor 36 to separate the pre-charge circuit 46 from the capacitor. In response to a switching event, the fourth switch 60 is preferably disconnected to stop charging the capacitor. If desired, a fourth switch 60 can be provided for each resonant circuit 44 to separate the corresponding circuit 44 from the DC bus 48.

[0030] Phase-locked loop (PLL) 62 (see Figure 9 ) is used to determine the frequency and phase angle of the AC waveform of power source 12A. Because switches 34 need to be fired with the correct polarity, PLL 62 can be used to determine the firing order of auxiliary switches 34. Since this is a three-phase system, the polarity of phase A, phase B, and phase C will not be the same at the same time. The firing order is determined by the following algorithm:

[0031] IF 0<=PLL_RADIAN[PHASE_A]<=IT

[0032] Turn ON OUT_RTO_PLUS_A

[0033] Turn OFF OUT_RTO_MINUS_A

[0034] ELSE

[0035] Turn ON OUT_RTO_MINUS_A

[0036] Turn OFF OUT_RTO_PLUS_A

[0037] The same algorithm is applied to the remaining phases to complete the firing sequence if necessary. In other words, only two of the auxiliary switches 34 are turned on to release current from the capacitor 36, with one switch 34 coupled to the input of the main thyristor 26 and the other switch 34 coupled to the output 26 of the main thyristor. The two auxiliary switches 34 that are turned on depend on the current flow of the AC current through the main switch 26. Thus, when the current is positive, one switch pair 34 is turned on (while the other remains off), and when the current is negative, the other switch pair 34 is turned on (and likewise, the other remains off). Preferably, in the static transfer switch 10, all main switches 22A, 26 are turned off (i.e., opened) and the auxiliary switches 34 are turned on (closed) simultaneously. Because some phases A, B, C will have positive current and some will have negative current at the switching moment, the auxiliary switch pair 34 that is closed in each phase resonant circuit 44 differs depending on the current of the particular phase A, B, C.

[0038] Figure 6 The main circuit 42 is shown. The following table lists the Figures 5 and 6 The names of the signals of the main circuit 42 and the resonant circuit 44 are explained below. Figure 2 and Figures 8 and 9 ) can be used to generate control signals used by the main circuit 42 and the resonant circuit 44.

[0039]

[0040]

[0041] Figure 7A flow chart illustrates a method for transferring power supply to a load 14 from one power source 12A to another power source 12B in a static transfer switch 10. As will be appreciated, this method can be implemented by a controller 64, which can take the form of a DSP 64. In steps 66 through 68, the energy storage (capacitor 36) is precharged by the charging circuit 46. The voltage of the DC bus 48 between the charging circuit 46 and the resonant circuit 44 is monitored and controlled to maintain a desired charge on the capacitor 36. That is, the relays 56 and 58 open and close as needed to supply voltage and discharge voltage to charge the capacitor 36. In step 70, the quality of the power supplied by the power source 12A connected to the load 14 is monitored for performance degradation events. When such a condition is identified, in steps 72 through 78, the main switch 26 of the first power source 12A is opened to disconnect the first power source 12A from the load 14. In other words, in step 72, a gate-off signal is sent to the main switch 26. Then, in step 74, the auxiliary switches 34 that must be switched on in each resonant circuit 44 are determined by the phase locked loop 62 (see OUT_RTO_MINUS, OUT_RTO_PLUS algorithm above). The auxiliary switches 34 that have been determined in step 74 are then switched on in step 76 using the gate signal.

[0042] In step 78, the DSP 64 verifies that the preferred power source 12A is fully decoupled by confirming that the net current and voltage across the primary switches 22A, 26 of each phase of the preferred power source 12A are zero or negligible enough to confirm that the resonant circuit 44 has in fact reversed the bias of each of the primary circuits 42. Finally, the DSP 64 may initiate a turn-on command to the backup power source 12B in step 80. Due to power quality considerations such as inrush current and soft start, as well as the preferred turn-on conditions, the method for turning on the secondary power source 12B may vary while still utilizing the improved method of turning off the primary switches 26 of the first power source 12A. After the primary switches 22B, 26 of the backup power source 12 have been turned on, power transfer is complete in step 82.

[0043] Figures 8 and 9 A control system is shown that can be used to control the resonant circuit 44 and the associated charging circuit 46. It should be understood that this control system can also be used to control the main circuit 42. A digital signal processor (DSP) 64 can be used to control all relays, sense voltages for PLL synchronization, and control the main switches 26, 42 and RTO thyristors 34, 44. As shown, a scaling processor 84 can be provided to adjust the input for use by the DSP 64. Also as shown Figure 9 As shown, the DSP 64 may include a PLL element 62 and a phase decoder element 86 to evaluate the current direction of each phase and generate a gate signal for the auxiliary switch 34 .

[0044] The static transfer switch 10 is designed to deliver power to a load 14 between a preferred electrical power source 12A and an alternate electrical power source 12B in response to power quality disturbances. Traditionally, thyristors 26 are commonly used in conventional static transfer switches 10 due to their high current handling capabilities. As semi-controlled devices, thyristors 26 cannot be turned off by simply removing the gate signal to the thyristor 26 because the conduction current through the thyristor 26 commutates below its minimum holding current (typically less than 1A) or the voltage applied to the thyristor 26 is reversed, which can take up to half a cycle of the fundamental frequency of the power source 12 (e.g., 8.3 ms in a 60 Hz AC system). To accelerate the commutation of the thyristor 26, a resonant turn-off (RTO) circuit 44 can be used, as described above and below, where the resonant turn-off circuit 44 is added in parallel with the thyristor 26. During the turn-off period of the thyristor 26, the resonant turn-off circuit 44 injects a reverse current to force the thyristor 26 current to quickly commutate to zero. Thus, the resonant shutoff circuit 44 can interrupt current flow in 1 ms, or preferably less than half a cycle of the power source 12, which significantly reduces the time it takes to disconnect the electrical power source 12. Typically, each phase A, B, and C of each power source 12 has a separate resonant shutoff circuit 44 to quickly shut down each phase during transfer and allow for rapid transfer back and forth between the power sources 12 in both directions. Thus, a two-source static transfer switch 10 requires six resonant shutoff circuits 44. Similarly, a three-source static transfer switch 10 may require nine resonant shutoff circuits 44.

[0045] like Figures 10 and 11 As shown, the number of resonant turn-off circuits 44 can be reduced by sharing the resonant turn-off circuits 44 between phases A, B, and C of different power supplies 12A and 12B. This can be used to reduce the cost and complexity of the static transfer switch 10. As shown, an AC contactor or relay 90 can be used to select which power supply 12A and 12B the resonant turn-off circuit 44 is connected to. Although electromechanical switches 90 may be preferred due to their low cost, high capacity, and good reliability, various types of switches 90 (i.e., fourth and fifth switches) can be used to connect the resonant turn-off circuit 44 to the selected power supply 12A and 12B. Because the contactor 90 is not directly involved in the actual switching event of turning off the thyristor 26A of one power supply 12A and turning on the thyristor 26B of the other power supply 12B, the switching time of the contactor 90 is not important, so a contactor 20 with a switching time shorter than the switching time of the main thyristor 26A and / or the auxiliary thyristor 34 can be used. Although separate contactors 90A, 90B may be used, with each contactor 90A, 90B corresponding to one of the power sources 12A, 12B and one of the phases A, B, C, as shown in FIG. Figure 10AThe illustrated single double-throw switch 90 can combine two switches 90A, 90B (i.e., the fourth and fifth switches) into one physical switch 90. In use, the contactors 90A, 90B connect the shared resonant shutoff circuit 44 to the main circuit 42 of the power source 12A, 12B currently supplying power to the electrical load 14. As a result, the resonant shutoff circuit 44 is connected and ready to quickly shut off the current through the operating main circuit 42 when a power transfer switching event is initiated. For example, when the thyristor 26 of the first electrical power source 12A is closed so that power is being supplied from the first power source 12A to the load 14, the first contactor 90A is closed to connect the shared resonant shutoff circuit 44 to the first thyristor 26, while the second contactor 90B is opened to disconnect the shared resonant shutoff circuit 44 from the second thyristor 26. Conversely, when the thyristor 26 of the second electrical power source 12B is closed so that power is being supplied from the second electrical power source 12B to the load 14, the second contactor 90B is closed to connect the shared resonant turn-off circuit 44 to the second thyristor 26, while the first contactor 90A is opened to disconnect the shared resonant turn-off circuit 44 from the second thyristor 26. Due to the shared arrangement of the resonant turn-off circuits 44, the number of resonant turn-off circuits 44 can be reduced to three instead of the six required in a conventional two-source static transfer switch 10. Similarly, in a three-source system, the number of resonant turn-off circuits 44 can be reduced from nine to three. The contactor 90 can also be used to protect the resonant turn-off circuit 44 and / or the isolation circuit 44 during a fault condition (e.g., a fault of the thyristors 26, 34 or the IGBT 96).

[0046] like Figure 12As shown, the number of resonant shutoff circuits 44 can also be reduced by eliminating the resonant shutoff circuit 44 from one phase C of the three-phase system. Thus, as shown, the resonant shutoff circuit 44 can be directly connected to the main circuits 42 of two of the phases A and B. In this arrangement, when two main circuits 42 are shut down using the respective resonant shutoff circuits 44, the current flow from the third phase C is automatically forced to zero through the delta input side 92 of the transformer 16 between the main circuits 42 and the electrical load 14. For example, in a power transfer switching event where power is initially being supplied by the first power source 12A, the resonant shutoff circuits 44 directly connected to the main circuits 42 for phases 12A-A and 12A-B (i.e., phases A and B of source 12A) are activated. This causes the respective main circuits 42 to be disconnected and phases 12A-A and 12A-B to be separated from the load 14. Then, one or more of the two resonant shutoff circuits 44 forces the remaining main circuits 42 of phases 12A-C to disconnect through the delta side 92 of transformer 14, thereby isolating the remaining main circuits 42 from load 14. Even though third phase C may not have its own resonant shutoff circuit 44, the current discharged by the two resonant shutoff circuits 44 and the current conducted by all three main circuits 42 can stop flowing to transformer 16 within 0.5 ms of the gate signal sent to the main circuits 42, or less than half a cycle of power supply 12. The main circuits 42 for phases 12B-A, 12B-B, and 12B-C are then closed to connect the second electrical power source 12B to load 14. Preferably, the two resonant shutoff circuits 44 are activated simultaneously by simultaneously closing the corresponding auxiliary switches 34, so that the current from the two resonant shutoff circuits 44 forces the remaining main circuits 42 to disconnect through the delta side 92 of transformer 16. Preferably, the output side of transformer 16 is a star-side output 94. Therefore, whereas a conventional static transfer switch 10 has a separate resonant shutdown circuit 44 for each phase A, B, and C of the three-phase electrical power source 12, the present embodiment can be used to eliminate the resonant shutdown circuit 44 from one of the phases C, such that no resonant shutdown circuit 44 is directly connected to the main circuit 42 of the one phase C. Due to the delta-connected resonant shutdown circuits 44, the number of resonant shutdown circuits 44 can be reduced to four instead of the six required for the conventional dual-source static transfer switch 10. Similarly, in a three-source system, the number of resonant shutdown circuits 44 can be reduced from nine to six.

[0047] like Figure 13 As shown, it can also be combined Figure 10 and Figure 12to further reduce the number of resonant turn-off circuits 44. Thus, the static transfer switch 10 may share the resonant transfer circuit 44 between two corresponding phases A, B of the power sources 12A, B, and may have one phase C connected through the delta side 92 of the transformer 16 without its own resonant transfer circuit 44. As a result, the number of resonant turn-off circuits 44 may be reduced from six to two in a two-source system and from nine to two in a three-source system.

[0048] Figures 14A to 14E Pictured Figure 11 The operation of the resonant shut-off circuit 44 (see the detailed reference numerals for details) Figure 11 ),and Figure 15 However, it should be understood that any type of resonant shutoff circuit 44 may be used, including Figure 3 and Figure 5 The resonant turn-off circuit 44 is provided. The capacitor 36 can be precharged to a relatively low voltage (40V to 50V) and provides a resonant current to produce a zero current crossing of the main circuit 42. A precharge circuit 46 can be provided for precharging the capacitor 36. The resonant inductor 38 limits the current change to provide a relatively soft commutation. Figure 14A As shown, before t1, the main thyristor 26 conducts current to the load 14. Figure 14B In FIG. 1 , at t1 , when a switching event is initiated, the gate signal of at least one of the main thyristors 42 is turned off according to the load current direction, and the corresponding auxiliary thyristor 34 and IGBT 96 are closed using the gate signal. For example, Figure 14A In the case of Sm1, the load current is conducted. Figure 14B In the process, from t1 to t2, the load current is forced to commutate from the main thyristor 26 to the resonant turn-off circuit 44. Figure 14C In FIG. 2 , at t2 , the reverse bias voltage from the capacitor 36 is applied to the anode of the main thyristor 26 to accelerate its turn-off. Figure 15 As shown, during this period, capacitor 36 is discharged and the voltage of capacitor 36 drops. The energy stored in capacitor 36 is preferably large enough to maintain the voltage polarity and reverse the bias to main thyristor 26. The time period between t2 and t3 allows the main thyristor 26 to have sufficient time to commutate. Figure 14D In the example, at t3, the main thyristor 26 completely blocks the forward voltage, and the auxiliary thyristor 34 and the IGBT 96 are commanded to turn off. Figure 14D In the process, from t3 to t4, the voltage of the resonant capacitor 98 increases until it reaches the clamping voltage. Figure 14EIn the embodiment of FIG4 , the loop energy has been absorbed by the snubber circuit 100, and the load current is zero and completely interrupted at t4. It should be understood that a variety of resonant shutdown circuits 44 may be used herein, with additional examples provided in U.S. patent application Ser. No. 16 / 795,988, which is incorporated herein by reference.

[0049] Although preferred embodiments of the present invention have been described, it will be understood that the present invention is not limited thereto and may be modified without departing from the present invention herein. Although each embodiment described herein may refer only to certain features and may not specifically refer to each feature described with respect to other embodiments, it will be appreciated that, unless otherwise stated, the features described herein are interchangeable even without reference to a particular feature. It will also be understood that the advantages described above are not necessarily the only advantages of the present invention; and it should be expected that all described advantages may not necessarily be achieved by each embodiment of the present invention. The scope of the present invention is defined by the appended claims, and all devices and methods that fall within the meaning of the claims (whether literally or by equivalents) are intended to be encompassed therein.

Claims

1. A static transfer switch comprising: a first electrical power source; a second electrical power source; Electrical loads; a first switch between the first electrical power source and the electrical load; a second switch between the second electrical power source and the electrical load; Resonant shutdown circuit; a fourth switch between the resonant turn-off circuit and the first switch; a fifth switch between the resonant turn-off circuit and the second switch; wherein when the first switch is closed and connects the first electrical power source to the electrical load, the fourth switch is closed to connect the resonant shutoff circuit to the first switch; as well as Wherein when the second switch is closed and connects the second electrical power source to the electrical load, the fifth switch is closed to connect the resonant off circuit to the second switch. 2 . The static transfer switch of claim 1 , wherein the fourth switch and the fifth switch have slower switching times than the first switch and the second switch. 3 . The static transfer switch of claim 1 , wherein the fourth switch and the fifth switch are electromechanical switches.

4. The static transfer switch of claim 1 , wherein the resonant turn-off circuit comprises an energy reservoir and a third switch, the third switch closing during a switching event to connect the energy reservoir to one of the first and second switches to force the one of the first and second switches to open. The static transfer switch of claim 4 , wherein the third switch comprises a thyristor.

6. The static transfer switch according to claim 4, further comprising two third switches of the third switches coupled to the first switch and the second switch, one of the third switches being coupled to inputs of the first switch and the second switch, and the other of the third switches being coupled to outputs of the first switch and the second switch, the energy storage being arranged between the two third switches.

7. The static transfer switch of claim 4 , further comprising two of the third switches coupled to the first switch and the second switch, the two third switches each being arranged between the energy storage and an input or an output of the first switch and the second switch, wherein if a positive current is being conducted through the first switch or the second switch, one of the two third switches is closed, and if a negative current is being conducted through the first switch or the second switch, the other of the two third switches is closed.

8. The static transfer switch of claim 4 , further comprising four of the third switches coupled to the first and second switches, two of the third switches coupled to inputs of the first and second switches, and two of the third switches coupled to outputs of the first and second switches, the energy reservoir being arranged between two of the third switches on one side and two of the third switches on the other side, wherein if a positive current is being conducted through the first or second switch, two of the third switches on the opposite side of the energy reservoir are closed, and if a negative current is being conducted through the first or second switch, different two of the third switches on the opposite side of the energy reservoir are closed. 9 . The static transfer switch of claim 4 , further comprising an inductor coupled between inputs or outputs of the first and second switches and the third switch.

10. The static transfer switch of claim 4, wherein the energy storage is a capacitor.

11. The static transfer switch of claim 4, further comprising a charging circuit to maintain a predetermined charge of the energy storage.

12. The static transfer switch of claim 1 , wherein during a corresponding switching event, within 0.5 ms of turning off gate signals to the first switch and the second switch, current discharged by the resonant turn-off circuit and current conducted through the first switch and the second switch stop flowing to the electrical load.

13. The static transfer switch of claim 1, wherein the fourth switch and the fifth switch comprise double-throw switches.

14. The static transfer switch of claim 1, wherein the resonant turn-off circuit forces the first switch and the second switch to open in less than half an electrical cycle of the first electrical power source and the second electrical power source, respectively.

15. The static transfer switch of claim 1, wherein the first switch and the second switch comprise silicon controlled rectifiers. 16 . The static transfer switch of claim 1 , wherein the first switch and the second switch comprise an integrated gate-commutated thyristor (IGCT), a reverse-blocking integrated gate-commutated thyristor (IGCT), or a gate-turn-off thyristor (GTO).

17. The static transfer switch of claim 1, further comprising a transformer between the first and second switches and the electrical load.

18. The static transfer switch of claim 1, wherein the electrical load comprises a data center.

19. The static transfer switch of claim 1, wherein one of the first electrical power source and the second electrical power source comprises an uninterruptible power supply (UPS).

20. A static transfer switch comprising: a first set of power inputs coupled to a first three-phase electrical power source, each of the first power inputs being coupled to one phase of the first three-phase electrical power source; a second set of power inputs coupled to a second three-phase electrical power source, each of the second power inputs being coupled to one phase of the second three-phase electrical power source; a set of power outputs coupled to a three-phase electrical load, each of the power outputs being coupled to one phase of the three-phase electrical load; a first set of switches coupled between the first set of power inputs and the set of power outputs; a second set of switches coupled between the second set of power inputs and the set of power outputs; a third set of switches coupled between a set of energy reservoirs and the first set of switches, and between the energy reservoirs and the second set of switches, each third switch coupled between one of the energy reservoirs and a corresponding first switch and a corresponding second switch; a fourth switch set coupled between the third switch set and the first switch set, each fourth switch coupled between a corresponding third switch and a corresponding first switch; a fifth switch set coupled between the third switch set and the second switch set, each fifth switch coupled between a corresponding third switch and a corresponding second switch; a sensor for determining an electrical characteristic of the first three-phase electrical power source; a power transfer controller, the sensor being an input to the power transfer controller, and the first set of switches and the second set of switches being outputs of the power transfer controller; wherein during normal operation, the power transfer controller closes one of the first and second switch sets to electrically connect the first power input set or the second power input set, respectively, to the power output set, and opens the other of the first and second switch sets to electrically isolate the first power input set or the second power input set from the power output set, the first three-phase electrical power source, or the second three-phase electrical power source, respectively, thereby supplying power to the three-phase electrical load; wherein during normal operation, when the first set of switches is closed, the fourth set of switches remains closed and the fifth set of switches remains open, and when the second set of switches is closed, the fifth set of switches remains closed and the fourth set of switches remains open; wherein when the sensor identifies that the performance of the first three-phase electrical power source or the second three-phase electrical power source connected to the three-phase electrical load is degraded, the power transmission controller initiates a switching event, comprising: turning off a gate signal of each of the first switch or the second switch that is closed during normal operation; After the gate signal of the corresponding first switch or the corresponding second switch has been turned off, closing at least one third switch between each first switch and the second switch and each corresponding energy storage, the energy storage assembly thereby releasing current to the input or the output of the corresponding first switch or the corresponding second switch to force the current conducted through the corresponding first switch or the corresponding second switch to decrease, the current decrease causing the corresponding first switch or the corresponding second switch to open and stop conducting current therethrough between the corresponding first three-phase electrical power source or the second three-phase electrical power source and the three-phase electrical load; closing the other of the first and second sets of switches to supply power to the three-phase electrical load from the other of the first or second three-phase electrical power sources; and After the first switch set and the second switch set are opened and closed, when the first switch set is opened and the second switch set is closed during the switching event, the fourth switch set is opened and the fifth switch set is closed, and when the second switch set is opened and the first switch set is closed during the switching event, the fifth switch set is opened and the fourth switch set is closed.

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