KR101445386B1 - Micro-electromechanical system based arc-less switching with circuitry for absorbing electrical energy during a fault condition - Google Patents

Abstract

A system according to the present invention is disclosed herein (Fig. 10). The system includes a micro-electromechanical system switch (20). The system also includes a balanced diode bridge 28 configured to suppress arc formation between the contacts of the micro-electromechanical switch system. The pulse circuit 52 is connected to a balanced diode bridge to form a pulse signal in response to the fault condition. The energy-absorbing circuit 200 is connected in parallel with the pulse circuit and absorbs the electrical energy generated by the fault state without affecting the formation of the pulse signal by the pulse circuit.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a micro-electromechanical system switch and a system including a balanced diode bridge,

1 is a block diagram of an exemplary MEMS based switching system, in accordance with an aspect of the present invention;

Figure 2 is a schematic diagram illustrating an exemplary MEMS based on the switching system shown in Figure 1;

3-5 are schematic flow diagrams illustrating exemplary operation of a MEMS based switching system shown in FIG. 2,

Figure 6 is a schematic diagram illustrating a serial-parallel array of MEMS switches,

Figure 7 is a schematic diagram illustrating a gated MEMS switch,

FIG. 8 is a flowchart showing an operation sequence of a system including a MEMS based on the switching system shown in FIG. 1; FIG.

Figure 9 is a graph of experimental results showing the turn-off of the switching system,

Figure 10 is a schematic diagram illustrating an exemplary MEMS-based switching system, in accordance with an aspect of the present invention;

Figs. 11 and 12 are graphs showing simulation results of an exemplary circuit signal representing the details of the switching operation of the switching system of Fig. 10 according to aspects of the present invention;

DESCRIPTION OF THE REFERENCE NUMERALS

10: Arc-free micro-electromechanical system switch (MEMS) based switching system

12: MEMS-based switching circuit

14: arc suppression circuit

16: Single package

18: Schematic of an arc-free micro-electromechanical system switch (MEMS) based switching system

20: MEMS switch 22: first contact

24: second contact 26: third contact

28: Balanced Diode Bridge

29: First Branch of Balanced Diode Bridge

30: first diode D1

31: Second branch of balanced diode bridge

32: second diode D2 33: voltage snubber circuit

34: third diode D3 36: fourth diode D4

38: single package 40: load circuit

44: voltage source V _BUS 46: load inductance

48: Load resistance R _LOAD 50: Load circuit current

52: Pulse circuit 54: Pulse switch

56: Pulse capacitor C _PULSE 58: Pulse inductance L _PULSE

60: first diode D _P 62: pulse circuit current I _PULSE

64: Schematic of a process for triggering a pulse circuit

66, 68: direction of pulse circuit current

70, 72: current vector 74, 76: current vector

78: Schematic showing initiation of MEMS switch opening

84, 88: Inductance 86: Load current direction

94: Schematic of circuit elements

96: Exemplary Embodiment of Switching Circuit

98, 100, 102: MEMS switch 104: Gated switch circuit

106: MEMS switch 108: Grading resistance

110: grading capacitor 112: flowchart of exemplary logic

114: sense block 116: decision block

118: Switch condition creation block 120: Trigger block

122: current conversion block 124: open block without arc

130: graph of experimental results

132: Change in amplification 134: Change in time

136, 138, 140: a reference number indicating the first, second and third sections of the graph 130

142: reaction curve 144: reaction curve

146: reaction curve 148: reaction curve

152: area of the response curve 142 representing the switching open process

154: area of the response curve 142 indicating the open state of the switch

200: Energy-absorbing circuit

This patent application is a continuation in part of U.S. Patent Application 11 / 314,336, filed December 20, 2005, which is incorporated herein by reference in its entirety.

Embodiments of the present invention relate generally to switching devices that switch off current in a current path, and more particularly to micro-electromechanical systems based on switching devices.

Circuit breakers are electrical devices designed to protect electrical equipment from damage caused by defects in the circuit. Typically, the most common circuit breakers include bulky electromechanical switches. Unfortunately, these conventional circuit breakers are so large that it has been required to use a great deal of force to activate the switching mechanism. In addition, the switches of such circuit breakers generally operate at relatively low speeds. Moreover, such a circuit breaker is complex to design in a disadvantage and thus has a high manufacturing cost. Further, when the contacts of the switching mechanism in the conventional circuit breaker are physically disconnected, an arc is generally formed between them to continue to deliver current until the current flow in the circuit stops. In addition, the energy associated with the arc can seriously damage the contact and / or cause damage such as a fire.

As an alternative to slow electromechanical switches, fast solid state switches have been used in high speed switching applications. As will be appreciated, this solid state switch switches between conduction and non-conduction states through applications of controlled voltage or bias. For example, by reverse biasing a solid state switch, the switch can be converted to a non-conductive state. However, solid state switches exhibit leakage currents because they do not form the physical spacing between the contacts when they are switched to a non-conducting state. Further, the internal resistance shows a voltage drop when the solid state switch operates in the conduction state. Both voltage drop and leakage current contribute to generating excess heat under normal operating conditions, which is detrimental to switching performance and lifetime. Also, at least in part, due to inherent leakage current associated with solid state switches, may not be usable in circuit breaker applications.

Briefly, a system according to aspects of the present technique is disclosed herein. The system includes a micro-electromechanical system switch. The balanced diode bridge is configured to suppress arc formation between the contacts of the micro-electromechanical system switch. The pulse circuit is connected to the balanced diode bridge. The pulse circuit includes a pulse capacitor that forms a pulse signal that causes a flow of the pulse current through the balanced diode bridge. The pulse signal is generated in response to a fault condition in the load circuit connected to the micro-electromechanical system switch. The energy-absorbing circuit is connected in parallel with the pulse circuit. The energy-absorbing circuit comprises an energy-absorbing capacitor which absorbs the electrical energy generated by the fault condition without affecting the formation of the pulse signal by the pulse circuit.

A system according to another aspect of the present technique is disclosed herein. The system includes a switching element including a micro-electromechanical system switch configured to switch the system from a first switching state to a second switching state. An arc suppression circuit is coupled to the switching element, wherein the arc suppression circuit is configured to suppress arc formation between the contacts of the micro-electromechanical system switch. A detection circuit is coupled to the arc suppression circuit and is configured to detect the presence of a fault condition. The pulse circuit is connected to an arc suppression circuit and a detection circuit, wherein the pulse circuit is configured to form a pulse signal responsive to the fault condition, the pulse signal being associated with an arc suppression circuit associated with initiating the opening of the micro- . The energy-absorbing circuit is connected in parallel with the pulse circuit. The energy-absorbing circuit absorbs the electrical energy generated by the fault condition without affecting the formation of the pulse signal by the pulse circuit.

These and other features, aspects, and advantages of the present invention will be better understood from the following detailed description with reference to the accompanying drawings, wherein like reference numerals are used to refer to like parts throughout.

According to one or more embodiments of the present invention, systems and methods for arc-free switching based on micro-electromechanical systems are described herein. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of various embodiments of the invention. However, those skilled in the art will appreciate that embodiments of the invention may be practiced without these specific details, and that the invention is not limited to the embodiments shown, but that the invention may be practiced in various other embodiments. In other instances, well known methods, procedures, and components have not been described in detail.

In addition, various operations may be described as a plurality of discontinuous execution steps to aid in understanding embodiments of the present invention. However, the order of description should not be construed as to imply that such operations must be performed in the order shown, nor should they be construed as dependent on the order. Also, the recursive use of the phrase "in one embodiment" does not necessarily refer to the same embodiment. Finally, the terms " comprising, "" comprising, "" having ", and the like, as used herein, have the same meaning as well as different representations.

1 is a block diagram of an exemplary arc-free micro-electromechanical system switch (MEMS) based switching system 10, in accordance with an aspect of the present invention. In recent years, MEMS have been generally used in micron-scale devices capable of integrating a plurality of functionally distinct elements such as mechanical elements, electromechanical elements, sensors, actuators and electronic devices on a common substrate through micro- Lt; / RTI > However, it is anticipated that various technologies and structures currently available in MEMS devices will use nanotechnology-based devices, such as structures that may be less than 100 nm in size, for example, after several years. Thus, while an exemplary embodiment described throughout this specification refers to a MEMS-based switching device, the inventive aspects of the present invention should be broadly interpreted and should not be limited to micron-scale devices.

1, an arc-free MEMS-based switching system 10 is shown to include a MEMS-based switching element 12 and an arc suppression circuit 14, And is connected to the MEMS-based switching device 12 as a reference. In this embodiment, the entire MEMS-based switching circuit 12 may be integrated with the arc suppression circuit 14, for example, in a single package 16. In another embodiment, only a portion or component of the MEMS-based switching circuit 12 may be integrated with the arc suppression circuit 14.

2-5, the MEMS-based switching circuit 12 may include one or more MEMS switches. The arc suppression circuit 14 may also include a balanced diode bridge and a pulse circuit. The arc suppression circuit 14 may also be configured to facilitate suppression of arc formation between the contacts of one or more MEMS switches. The arc suppression circuit 14 may be configured to facilitate suppression of arc formation in response to alternating current (AC) or direct current (DC).

Referring to FIG. 2, a schematic 18 of an exemplary arcless MEMS based switching system shown in FIG. 1 is shown in accordance with one embodiment. As described with reference to FIG. 1, the MEMS-based switching circuit 12 may include one or more MEMS switches. In the illustrated embodiment, the first MEMS switch 20 is shown to include a first contact 22, a second contact 24, and a third contact 26. In one embodiment, the first contact 22 can be configured as a drain, the second contact 24 can be configured as a source, and the third contact 26 can be configured as a gate. 2, the voltage snubber circuit 33 may be connected in parallel with the MEMS switch 20 and may limit voltage overshoot during fast contact disconnections as described in more detail below. ≪ RTI ID = 0.0 > . In certain embodiments, the snubber circuit 33 may include a snubber capacitor (not shown) in series with a snubber resistor (not shown). The snubber capacitor can facilitate the transient voltage gain enhancement during open sequencing of the MEMS switch 20. [ In addition, the snubber resistors can suppress any current pulses generated by the snubber capacitors during the closing operation of the MEMS switch 20. In certain other embodiments, the voltage snubber circuit 33 may include a metal oxide varistor (MOV) (not shown).

According to another aspect of the technique, the load circuit 40 may be connected in series with the first MEMS switch 20. The load circuit 40 includes a voltage source V _BUS (44). In addition, the load circuit 40 may also include a load inductance L _LOAD (46), wherein the load inductance L _LOAD (46) represents a combined load inductance and a bus inductance shown in the load circuit 40. The load circuit 40 may also include a load resistance R _LOAD 48 that represents the combined load resistance shown by the load circuit 40. Reference numeral 50 denotes a load circuit current I _LOAD that can flow through the load circuit 40 and the first MEMS switch 20.

Further, as shown with reference to FIG. 1, the arc suppression circuit 14 may include a balanced diode bridge. In the illustrated embodiment, the balanced diode bridge 28 is shown as having a first branch 29 and a first branch 31. The term "balanced diode bridge " as used herein is used to denote a diode bridge configured such that the voltage drop across the first and second branches 29, 31 is substantially equal. The first branch 29 of the balanced diode bridge 28 may include a first diode D1 30 and a second diode D2 32 coupled together to form a first series circuit. In a similar manner, the second branch 31 of the balanced diode bridge 28 may include a third diode D3 34 and a fourth diode D4 36 that are effectively interconnected to form a second series circuit .

In one embodiment, the first MEMS switch 20 may be parallel connected across the midpoint of the balanced diode bridge 28. The midpoint of the balanced diode bridge may include a first midpoint located between the first and second diodes 30 and 32 and a second midpoint located between the third and fourth diodes 34 and 36 . In addition, the first MEMS switch 20 and the balanced diode bridge 28 are tightly packaged to facilitate minimization of the parasitic inductance generated by the connection of the balanced diode bridge 28 and, in particular, the MEMS switch 20 . According to an exemplary aspect of the present technique, the first MEMS switch 20 and the balanced diode bridge 28 are positioned next to each other to form a diode bridge (not shown) during the turn-off of the MEMS switch 20, The inherent inductance between the first MEMS switch 20 and the balanced diode bridge 28 is less than a few percent of the voltage across the drain 22 and source 24 of the MEMS switch 20, Thereby generating a small di / dt voltage. In one embodiment, the first MEMS switch 20 may be integrated with the balanced diode bridge 28 in a single package 38 or alternatively may be integrated with the MEMS switch 20 and the diode bridge 28 Lt; RTI ID = 0.0 > inductance. ≪ / RTI >

The arc suppression circuit 14 may also include a pulse circuit 52 that is effectively connected in connection with the balanced diode bridge 28. The pulse circuit 52 may be configured to detect the switch state and to start opening the MEMS switch 20 in response to the switch state. As used herein, the term "switch state" refers to a state that triggers a change in the current operating state of the MEMS switch 20. For example, the switch state may change the first closed state of the MEMS switch 20 to the second open state or the first open state of the MEMS switch 20 to the second closed state. The switch condition may occur in response to a number of operations including but not limited to circuit fault or switch on / off requests.

The pulse circuit 52 may include a pulse switch 54 and a pulse capacitor C _pulse 56 connected in series to the pulse switch 54. [ In addition, the pulse circuit may include a pulse inductance L _PULSE 58 and a first diode D _p (60) serially connected to the pulse switch 54. The pulse inductance L _PULSE 58, the diode D _p 60, the pulse switch 54 and the pulse capacitor C _pulse 56 may be connected in series to form the first branch of the pulse circuit 52, The components of one branch may be configured to facilitate pulse current formation and timing. Reference numeral 62 denotes a pulse circuit current I _PULSE that can flow through the pulse circuit 52.

According to aspects of the present invention, as described below, the MEMS switch 20 can be quickly switched from the first closed state to the second open state while delivering current even at around 0 V (e.g., , Approximately a few picoseconds or a few nanoseconds). This can be obtained through the combined operation of the load circuit 40 and the pulse circuit 52 includes a balanced diode bridge 28 connected in parallel across the contacts of the MEMS switch 20.

3-5 are schematic flow diagrams illustrating exemplary operation of the arc-free MEMS-based switching system 18 shown in FIG. Referring to FIG. 2, an initial state of an exemplary operation of an arc-free MEMS based switching system 18 is shown. The MEMS switch 20 has been shown to start in the first closed state. Further, as shown, there is a load current I _LOAD 50 having substantially the same value as V _BUS / R _{LOAD in the} load circuit 40.

Further, for the description of the exemplary operation of the arc-free MEMS-based switching system 18, the resistance associated with the MEMS switch 20 is determined by the voltage generated by the load current passing through the resistance of the MEMS switch 20 Is sufficiently small to have only a negligible effect on the voltage near zero between the midpoints of the diode bridge 28 when pulsed. For example, it can be assumed that the resistance associated with the MEMS switch 20 is sufficiently small to produce a voltage drop of less than a few millivolts due to the expected maximum load current.

In the initial condition of the MEMS based switching system 18, the pulse switch 54 is in the first open state. In addition, there is no pulse circuit current in the pulse circuit 52. Further, in the pulse circuit 52, the capacitor C _PULSE 56 may be pre-charged with the voltage V _PULSE, where V _PULSE is significantly greater than the expected load current I _LOAD 50 during the propagation of the load current Is a voltage capable of generating a 1/2 sinusoidal curve of a pulse current having a maximum value (for example, twice). C _Pulse 56 and L _Pulse 58 may be selected to resonate together.

FIG. 3 is a schematic diagram 64 illustrating the process of triggering the pulse circuit 52. FIG. A detection circuit (not shown) may be connected to the pulse circuit 52. The detection circuit may comprise, for example, a sense circuit (not shown) configured to sense the level of the load circuit current I _LOAD 50 and the voltage level of the voltage source V _BUS 44. Further, the detection circuit can be configured to detect the switch condition as described above. In one embodiment, the switch condition may be caused by a current level and / or a voltage level that exceeds a predetermined threshold.

The pulse circuit 52 may be configured to detect switching conditions and facilitate switching the current closed state of the MEMS switch 20 to the second open state. In one embodiment, the switch condition may be a voltage level exceeding a predetermined threshold level or an error condition caused by a load current in the load circuit 40. However, as will be appreciated, the switch condition may also include monitoring the ramp voltage to obtain a given system-dependent ON time in the MEMS switch 20.

In one embodiment, the pulse switch 54 may generate a sinusoidal pulse in response to the received trigger signal as a result of the detected switching condition. Triggering of the pulse switch 54 may initiate a sinusoidal current resonance in the pulse circuit 52. The current direction of the pulse circuit current can be represented by reference numerals 66 and 68. The current direction and the relative magnitude of the pulse circuit current passing through the first diode 30 and the second diode 32 of the first branch 29 of the balanced diode bridge 28 are also determined by the current vectors 72 and 70 ). Similarly, the current vectors 76 and 74 represent magnitudes relative to the current direction of the pulse circuit current through the third diode 34 and the fourth diode 36, respectively.

The peak value of the sinusoidal bridge pulse current may be determined by the value of the initial voltage, and the pulse capacitor C _PULSE (56) value and a pulse inductance L _PULSE (58) on the pulse capacitor C _PULSE (56). The values for the pulse inductance L _PULSE 58 and the pulse capacitor C _PULSE 56 determine the pulse width of the 1/2 sine curve of the pulse current. The bridge current pulse width can be adjusted to meet the load current change rate (V _BUS / L _LOAD ) during the fault condition and the system load current turn-off requirement based on the desired peak-through current. In accordance with an aspect of the present invention, the pulse width 54 may be configured to be in a conducting state prior to opening of the MEMS switch 20.

The triggering of the pulse switch 54 controls the timing of the pulse circuit current I _PLUSE 62 through the balanced diode bridge 28 so that it is lower than the impedance of the path through the contacts of the MEMS switch 20 during the open interval And facilitating the generation of an impedance path. The pulse switch 54 is also triggered to cause a desired voltage drop across the contact of the MEMS switch 20 to appear.

In one embodiment, the pulse switch 54 may be a solid state switch that may be configured to have a switching speed in the range of, for example, a few nanoseconds to a few microseconds. The switching speed of the pulse switch 54 must be relatively fast compared to the expected rise time of the load current in the fault condition. The current speed of the MEMS switch 20 depends on the rising speed of the load current depending on the inductance L _LOAD 46 in the load circuit 40 and the bus supply voltage V _BUS 44 as described above. If, when the load current I _LOAD (50) is able to rise rapidly compared to the possible speed of the bridge pulse circuit, MEMS switch 20 may have a suitable speed so as to adjust the larger load current I _LOAD (50).

The pulse circuit current I _PULSE 62 increases from zero and is equally divided between the first and second branches 29, 31 of the balanced bridge 28. As described above, according to one embodiment, the difference in voltage drop across the branches 29, 31 of the balanced diode bridge 28 can be designed to be negligible. Also, as discussed above, the diode bridge 28 is balanced so that the voltage drop across the first and second branches of the diode bridge 28 is substantially equal. Also, as the resistance of the current closed MEMS switch 20 is relatively low, the voltage drop across the MEMS switch 20 is relatively small. However, if the voltage drop across the MEMS switch 20 is greater (e. G., By the inherent design of the MEMS switch), balancing of the diode bridge 28 will cause the diode bridge 28 to contact the MEMS switch 20 ≪ RTI ID = 0.0 >).≪ / RTI > According to aspects of the present invention, if the resistance of the MEMS switch 20 causes a distinct voltage drop across the MEMS switch 20, the diode bridge 28 will increase the magnitude of the maximum bridge pulse current, Imbalance can be accommodated.

Referring to FIG. 4, a schematic 78 is shown when the opening of the MEMS switch 20 is started. The pulse switch 54 in the pulse circuit 52 is triggered prior to opening of the MEMS switch 20, as described above. As the pulse current I _PULSE 62 increases, the voltage across the pulse capacitor C _PULSE 56 decreases due to the resonance action of the pulse circuit 52. In the on-state where the switch is closed and conducts, the MEMS switch 20 exhibits a path of low impedance relative to the load circuit current I _LOAD 50.

When the amplification of the pulse circuit current I _PULSE 62 is greater than the amplification of the load circuit current I _LOAD 50 (e.g., by the resonance action of the pulse circuit 52), the gate contact 26 Is suitably biased to change the current operating state of the MEMS switch 20 from a first closed and a conductive state to a resistance-raised state where the MEMS switch 20 begins to turn off (the contact is still closed, The contact pressure is reduced by the open process), which causes the switch resistance to rise and the switch resistance to rise, causing the load current to diverge from the MEMS switch 20 to the diode bridge 28.

In this current condition, the balanced diode bridge 28 exhibits a relatively low impedance path to the load circuit current I _LOAD 50 as compared to the path through the MEMS switch 20, which represents an increase in contact resistance. Direction change of such a MEMS switch load circuit current I _LOAD (50) through (20) is a much faster process to load circuits compared to the rate of change of current I _LOAD (50). The values of the inductance L ₁ 84 and inductance L ₂ 88 associated with the connection between the MEMS switch 20 and the balanced diode bridge 28 are very low Small may be desirable.

The current transfer process from the MEMS switch 20 to the pulse bridge continues to increase the current in the first diode 30 and the fourth diode 36 while simultaneously increasing the current in the second diode 32 and the third diode 34 . The transfer process is completed when the mechanical contacts 22, 24 of the MEMS switch 20 are separated to form a physical gap and all load current is delivered by the first diode 30 and the fourth diode 36.

Continuing to switch the load circuit current I _LOAD from the MEMS switch 20 to the diode bridge 28 in the direction 86 causes an imbalance across the first and second branches 29 and 31 of the diode bridge 28 . In addition, as the pulse circuit current decreases, the voltage across the pulse capacitor C _PULSE 56 is constantly reversed (e.g., acting as a "counter electromotive force ") resulting in a substantial reduction of the load circuit current I _LOAD to zero . The second diode 32 and the third diode 34 in the diode bridge 28 are reverse biased such that the load circuit includes the pulse inductor L _PULSE 58 and the bridge pulse capacitor C _PULSE 56, .

Referring to FIG. 5, a schematic 94 for connected circuit elements is shown for a load current reduction process. As described above, when the contacts of the MEMS switch 20 are disconnected, an infinite contact resistance is obtained. In addition, the diode bridge 28 no longer maintains a voltage close to zero across the contacts of the MEMS switch 20. In addition, the load circuit current I _LOAD is now equal to the current through the first diode 30 and the fourth diode 36. The current does not pass through the second diode 32 and the third diode 34 of the diode bridge 28, as described above.

The apparent switch contact voltage difference from the drain 24 to the source 26 of the MEMS switch 20 is also _{dependent on the} pulse inductor L _PULSE 58, the pulse capacitor C _PULSE 56, the load circuit inductor L _LOAD 46, Can be raised to a maximum value that is approximately twice the V _BUS voltage, at a rate determined by a net resonant circuit that includes a resistor R _LOAD 48 and damping by circuit loss. In addition, the pulse circuit current I _PULSE 62, which is equal to the load circuit current I _LOAD 50, can be resonantly reduced to a value of zero and can be reduced to zero by the reverse blocking action of the diode bridge 28 and the diode DP 60 Lt; / RTI > The voltage across the pulse capacitor C _PULSE 56 will resonate inversely with the negative peak and maintain the negative peak value until the pulse capacitor C _PULSE 56 is recharged.

The diode bridge 28 may be configured to maintain a voltage close to zero at both ends of the MEMS switch 20 until the contacts are disconnected to open the MEMS switch 20 so that the MEMS switch 20 is open Thereby preventing the damage by suppressing the arc that is to be formed between the contacts of the MEMS switch 20. In addition, the contacts of the MEMS switch 20 approach the open state with much reduced contact current through the MEMS switch 20. In addition, the circuit inductance, the load inductance, and the energy stored in the source may be absorbed through a voltage dissipation circuit (not shown). The voltage snubber circuit 33 may be configured to limit the voltage overshoot during fast contact isolation by the induced energy remaining in the interface inductance between the bridge and the MEMS switch. In addition, the rate of increase or decrease in the voltage across the contacts of the MEMS switch 20 during opening can be controlled through the use of a snubber circuit (not shown).

A gap is also formed between the contacts of the MEMS switch 20 when in the open state, nevertheless current leakage may be present between the load circuit 40 and the diode bridge circuit 28 of the MEMS switch 20. This current leakage can be suppressed by introducing a secondary mechanical switch (not shown) connected in series within the load circuit 40 to create a physical gap. In this embodiment, the mechanical switch may include a second MEMS switch.

FIG. 6 illustrates an exemplary embodiment 96 of a switching circuit 12 (see FIG. 1) that may include, for example, a plurality of MEMS switches arranged in a series or series-parallel array. 6, the MEMS switch 20 may be replaced by two or more first set MEMS switches 98, 100 electrically connected to the series circuit. In one embodiment, at least one of the first set of MEMS switches 98, 100 may be further coupled to a parallel circuit, wherein the parallel circuit includes two or more second set MEMS switches (e.g., 100, 102) can do. According to an aspect of the present invention, a static grading resistor and a dynamic grading capacitor may be connected in parallel with at least one first set or second set MEMS switch.

Referring to FIG. 7, an exemplary embodiment 104 of a graded MEMS switch circuit is shown. Graded switch circuitry 104 may include at least one MEMS switch 106, a grading resistor 108, and a grading capacitor 110. Graded switch circuitry 104 may include a plurality of MEMS switches arranged in a series or series-parallel array, for example, as shown in FIG. The grading resistor 108 may be connected in parallel with the at least one MEMS switch 106 to provide voltage grading for the switch array. In an exemplary embodiment, the grading resistor 108 may be sized to provide adequate leakage for a particular application while at the same time providing adequate steady-state voltage balancing (division) between the series switches. Grading capacitor 110 and grading resistor 108 may also be provided in parallel with each MEMS switch 106 of the array to provide dynamic sharing during switching and fixed sharing in the off state. Additional grading resistors or grading capacitors or both can be added to each MEMS switch in the switch array.

8 is a flow diagram of exemplary logic 112 for switching a MEMS based switching system from a current operating state to a second state. According to an exemplary aspect of the present technique, a switching method is disclosed. As described above, the detection circuit can be effectively connected to the arc suppression circuit and configured to detect the switch condition. In addition, the detection circuit may comprise a sensing circuit configured to sense a current level and / or a voltage level.

As shown in block 114, the current level and / or voltage level in the load circuit, such as load circuit 40 (see FIG. 2), may be sensed, for example, via a sensing circuit. It may also be determined as to whether the sensed current level or sensed voltage level, as indicated by the sensing block 116, is different from the expected value or exceeds the expected value. In one embodiment, it may be determined (e.g., via a detection circuit) whether the sensed current level or sensed voltage level exceeds a predetermined threshold level. Alternatively, voltage or current ramp rates may be monitored to detect the switch condition without substantial fault occurrence.

The switch condition may be generated as indicated by block 118 if the sensed current level or sensed voltage level is different from or a distance from the expected value. As discussed above, the term "switch condition" refers to a condition that triggers a change in the current operating state of the MEMS switch. In this embodiment, the switch condition can be generated in response to a fault signal and can be used to facilitate the start of MEMS switch opening. Blocks 114-118 are representative examples of switch conditions. However, as will be appreciated, other switch condition generation methods may also be conceived in accordance with aspects of the present invention.

As shown in block 120, the pulse circuit may be triggered to start the pulse circuit current in response to the switch condition. By the resonance operation of the pulse circuit, the pulse circuit current level can continuously increase. A voltage drop close to zero at both ends of the contact of the MEMS switch can be maintained, at least in part, by the diode bridge 28 if the instantaneous amplification of the pulse circuit current is significantly greater than the instantaneous amplification of the load circuit current.

Also, as shown in block 122, the load circuit current through the MEMS switch can be switched from a MEMS switch to a pulse circuit. As described above, the diode bridge exhibits a relatively low impedance path, contrary to the path through the MEMS switch, where the relatively high impedance increases as the contacts of the MEMS switch begin to separate. The MEMS switch can then be opened without an arc, as shown in block 124.

As discussed above, a voltage drop close to zero at both ends of the contact of the MEMS switch can be maintained while the instantaneous amplification of the pulse circuit current is significantly greater than the instantaneous amplification of the load circuit current, thereby facilitating the opening of the MEMS switch Thereby suppressing the formation of an arc at both ends of the contact of the MEMS switch. Thus, as described above, a MEMS switch can be opened at a voltage condition close to zero across the contacts of the MEMS switch, with a greatly reduced current passing through the MEMS switch at this time.

9 is a graph 130 of experimental results showing the current operating state switching of a MEMS switch of a MEMS based switching system, in accordance with an aspect of the present invention. As shown in FIG. 9, a change 132 of the amplification is shown for a change in time 134. Reference numerals 136, 138, and 140 also denote first, second, and third sections of graph 130.

The response curve 142 represents the change in amplification of the load circuit current as a function of time. The change in amplification of the pulse circuit current as a function of time is illustrated by the response curve 144. In a similar manner, a change in the amplification of the gate voltage as a function of time was implemented in the response curve 146. The response curve 148 represents the zero gate voltage reference and the response curve 150 represents the reference level for the load current prior to turn-off.

Reference numeral 152 also indicates an area on the response curve 142 where the switching-over process occurs. Similarly, reference numeral 154 represents the area on the response curve 142 where the contacts of the MEMS switch are disconnected and the switch is in an open state. Also, as can be seen from the second section 138 of the graph 130, the gate voltage has a low value to facilitate the opening start of the MEMS switch. In addition, as can be seen from the third section 140 of the graph 130, the load circuit current 142 and the pulse circuit current 144 in the 1/2 conductive section of the balanced diode bridge decrease.

A further aspect of the present invention includes an additional energy-absorbing circuit 200, shown in FIG. 10, which provides electrical energy during a switched load current interruption of a protected load circuit, such as may occur in response to a fault condition (E. G., Trapped or < / RTI > taken up). This circuit is connected to a parallel circuit with a balanced diode bridge 28. This addition can optimize the load current interruption due to a fault condition that can occur in the load circuit and is advantageous over the reduced amount of let-through current in the switching circuitry employing aspects of the present invention. will be. In addition, aspects of the present invention further provide for the optimization of circuit elements in a MEMS-based switching system, such as simplifying the circuit design process, enabling appropriate circuit selection for a given application, and reducing the cost of the weight and switching system .

In one embodiment, the energy-absorbing circuit 200 is connected across the DC side of the balanced diode bridge 28 connected in parallel with the pulse circuit 52, as shown in FIG. The circuit 200 may comprise an energy-absorbing element such as a resistor Rt, a diode Dt and a capacitor Ct. In order to account for the operating interference exhibited by the circuit 200, the opening of the MEMS switch 20 into the non-conducting state and the opening of the two diagonal bridges, which can shedding current during the process of limiting the fault current, Let's start with the turn-off of the diodes (e.g., diodes 32 and 34). The diode bridge voltage quickly rises above the initial voltage value VtIni stored on the capacitor Ct and the diode Dt is turned on. As the fault occurs, the electrical energy stored in the capacitor Ct can be quickly discharged by a suitable discharge resistance (not shown in FIG. 10).

The inventors of the present invention have discovered innovative and structured and / or operational relationships that allow independent optimization of the pulse circuit 52 and the energy-absorbing circuit 200 for a given circuit breaker application. Such optimization may indicate a selection of suitable components and / or a reduction in substantial cost for a given application. For example, the value of the pulse capacitor Cp and the initial voltage VpIni are preferably selected (e.g., by selecting a capacitor value that is small enough for the capacitor Cp) to provide an optimal peak pulse current and / Or the pulse width. That is, the independence of the energy trapping requirement is implemented by the pulse capacitor C _PULSE in addition to the pulse-forming requirement. Similarly, the value of the energy-absorbing capacitor Ct and its initial voltage (VtIni) can be independently selected for fast absorption of the fault energy during the fault interval (e.g., a capacitance large enough for the energy-absorbing capacitor Ct ). That is, the independence of the pulse-forming requirement is implemented by the capacitor Cp.

Circuit arrays using aspects of the present invention should exhibit a reduced amount of pole-thru current and lower blocking energy dissipation. As discussed above, the diode bridge 28 and MEMS switch 20 can be packaged to be closely integrated with one another to reduce parasitic inductance in the diode bridge and each interconnect to the MEMS switch (e.g., ). This increases the amount of electrical energy that can be stored in such an interconnect. Otherwise, during the opening of the MEMS switch, the additional interconnection to the snubbers 33 by a protection circuit (e.g., snubber 33) connected across the MEMS switch 20 when the contacts are disconnected. Because the inductance reduces the effective protection action, the corresponding incremental amount of electrical energy is dissipated by the open contact of the MEMS switch. One important function of the snubber 33 is to maintain the voltage across the MEMS switch during the open operation of the contact until a complete isolation and voltage hold-off capability is obtained to prevent arcing by excess voltage ramp formation. It is retarding the rise (for example, reducing the speed).

In operation, a reliable and substantially quick turn-off of the load current (in response to a fault that may occur in the load circuit) can be performed in a MEMS-based switching system using aspects of the present invention , Is achieved through an exemplary sequence in the following case: the capacitors C _PULSE and Ct can be initially charged with the initial voltages VPInit and VtInit, respectively, with the respective exemplary voltage polarities shown in Fig. The MEMS switch 20 will initially be in the ON (e.g., conductive) state in response to the gating signal applied through the contact gate 26. With the occurrence of a fault, the load current will rise at a relatively fast rate (e.g., a high value of di / dt). For example, when the magnitude of the load current exceeds a predetermined threshold and / or when the rate of change of the load current (di / dt) exceeds a predetermined value, the pulse switch 54 is triggered do. The value of the I _PULSE current will increase to a predetermined reasonable (design) value that exceeds the fault current value. As discussed above, the pulsed diode bridge 28 is configured to generate a voltage drop close to zero across the MEMS switch 20. Immediately before reaching the peak value of the I _PULSE current, the MEMS switch 20 will be gated to the off-state (non-conducting state).

As the MEMS switch contact pressure decreases in response to the decreasing gating signal, the increasing contact resistance causes current to flow from the load circuit to the diode bridge 28. [ The current flow through the switch contacts 22, 24 is essentially reduced to zero before such contacts are disconnected. The contacts 22 and 24 will open under voltage conditions close to zero. The fault current will be delivered by the diode bridge 28. The value of the I _PULSE current will decrease after it reaches the peak value (for example, with a sinusoid). When the value of the I _PULSE current decreases to a value corresponding to the instantaneous value of the increasing fault current, the diodes D2 and D3 will stop conducting. At this time, the diodes D1 and D4 will conduct the fault current from the load circuit. The pulse capacitor C _PULSE also decreases in voltage until its voltage polarity reverses. The increase in the magnitude of the reverse voltage stored on the capacitor C _PULSE by the fault current is in opposition to the bus source voltage 44 and reduces the rising speed di / dt of the fault current.

The voltage across the DC input to the diode bridge 28 will increase rapidly and when its value reaches the initial voltage CtInit stored on the capacitor Ct the diode Dt begins to conduct and the circuit 200 starts I will come. As the capacitor Ct is charged, it produces a counter-electromotive force that reverses the rate of rise of the fault current (e. G., Negative di / dt). For example, when the voltage on capacitor Ct reaches the bus source voltage, the fault current decreases to zero. In the above description, it is understood that the energy-absorbing capacitor Ct absorbs electrical energy representing a fault regardless of the pulse circuit, and reduces its load current very rapidly to zero through its resonance action with load and pulse inductance will be.

The circuit arrangement using aspects of the present invention preferably isolates the functions provided by the capacitors Ct and C _PULSE . Further, the circuit branch with the energy-absorbing capacitor Ct is not limited to absorbing the energy of the load / source system as well as the "gain " of the diode bridge in terms of control (e.g., suppression) Quot; snubber ". This can be achieved in an exemplary embodiment with adjustable pre-charge on the capacitor Ct.

Figure 11 summarizes the concept of operation described above in the form of a graph through the expected circuit signal, shown as a function of time for the MEMS based switching system shown in Figure 10. This signal may be used during an exemplary time interval of 10 [micro] s (since it may be useful to understand the operational details regarding the exemplary initial transient response of the switching system) during the switched turn-off of the load current in response to the fault condition , And Figure 12 shows these expected circuit signals (operating details in a longer time interval and operational details regarding the exemplary response of the switching system in series with the turn-off of the load current) Lt; RTI ID = 0.0 > 120 < / RTI >

The signal plots of FIGS. 11 and 12 are distinguished with reference to the system shown in FIG. 10 as follows: I _d1 and I _d2 represent currents conducted by bridge diodes D1 and D2, respectively. I _PULSE represents the pulse current. And Isw_in represents the current flowing through the contacts 22 and 24 of the MEMS switch 20. Itrap represents the current flowing through the energy-absorbing circuit 200. The load current represents the load current in response to the fault condition, and this current is effectively limited by the system shown in FIG. V_C _PULSE represents the voltage across the pulse capacitor 56. Vbridge represents the voltage across the diode bridge 28. And Vd2 represents the voltage across the diode D2. Vsw represents the voltage across the contacts 22, 24 of the MEMS switch 20. Vtrap represents the voltage across the energy-absorbing capacitor Ct.

While such features of the invention are shown and described herein, those skilled in the art will appreciate that various modifications and changes are possible. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.

SUMMARY OF THE INVENTION In accordance with the present invention, a system is provided that includes a balanced-diode bridge configured to suppress arc formation between a micro-electromechanical system switch and its contacts.

Claims (11)

A micro-electromechanical system switch 20, A balanced diode bridge (28) configured to inhibit arc formation between the contacts of the micro-electromechanical system switch, A pulse circuit (52) coupled to the balanced diode bridge, the pulse circuit comprising a pulse capacitor, the pulse capacitor configured to form a pulse signal causing a flow of a pulse current through the balanced diode bridge, Is generated in response to a fault condition in a load circuit connected to the micro-electromechanical system switch, And an energy-absorbing circuit (200) connected in parallel with the pulse circuit, The energy-absorbing circuit (200) comprises an energy-absorbing capacitor (Ct) that absorbs electrical energy resulting from the fault condition without affecting the formation of a pulse signal by the pulse circuit, The energy-absorbing capacitor is configured to limit the rate of change of the voltage across the balanced bridge bridge as the fault condition occurs system. The method according to claim 1, The capacitance value of the pulse capacitor is selected to control one or more pulse signal characteristics of the pulse signal irrespective of the capacitance value of the energy-absorbing capacitor system. 3. The method of claim 2, Wherein the one or more pulse signal characteristics of the pulse signal are selected from the group consisting of a width of the pulse signal, a peak of the pulse signal, and combinations thereof system. The method according to claim 1, The capacitance value of the energy-absorbing capacitor is selected to control the amount of electrical energy absorbed by the energy-absorbing capacitor irrespective of the capacitance value of the pulse capacitor system. The method according to claim 1, The energy-absorbing circuit further comprises a diode (Dt) connected in series with the energy-absorbing capacitor, The diode being connected to be in a conductive state when a voltage across the balanced bridge bridge is equal to an initial voltage value stored in the energy-absorbing capacitor, The conduction state of the diode causes the energy-absorbing circuit to receive a fault current system. The method according to claim 1, Wherein the balanced diode bridge comprises a first branch and a second branch, The first branch comprising a first diode and a second diode connected to a first series circuit, Wherein the second branch includes a third diode and a fourth diode connected to a second series circuit system. The method according to claim 6, The micro-electromechanical system switch is connected in parallel across the midpoints of the balanced diode bridge, Wherein a first midpoint is located between the first diode and the second diode and a second midpoint is located between the third diode and the fourth diode system. The method according to claim 1, The micro-electromechanical system switch is integrated with the balanced diode bridge in a single package system. The method according to claim 1, The pulse circuit is configured to detect a fault condition and to initiate opening of the micro-electromechanical system switch in response to the fault condition system. The method according to claim 1, The micro-electromechanical system switch 20 includes a plurality of first micro-electromechanical switches electrically coupled in series with each other system. 11. The method of claim 10, At least one of the plurality of first micro-electromechanical switches is further connected to a parallel circuit comprising a plurality of second micro-electromechanical switches system.

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