WO2014044317A1

WO2014044317A1 - Regulated power supply assembly for use in electrical switch

Info

Publication number: WO2014044317A1
Application number: PCT/EP2012/068618
Authority: WO
Inventors: Vijay LIMAYE
Original assignee: Siemens Aktiengesellschaft
Priority date: 2012-09-21
Filing date: 2012-09-21
Publication date: 2014-03-27
Also published as: EP2885804A1; EP2885804B1; CN204696038U

Abstract

The present invention provides a regulated power supply assembly and a method for operating the same suitable for use in an electrical switch. The electrical switch includes an electromagnetic assembly configured to operate said electrical switch in one of an open position and a closed position thereof and effect a transition there between. In accordance with the present invention, an output voltage provided to the electromagnetic assembly is switched based on a switching control signal such that an excitation current is established in the electromagnetic assembly. The excitation current established in the electromagnetic assembly is successively sampled. The switching control signal is generated based on comparing an instantaneous sample of the excitation current with a threshold current reference and/or at least one preceding sample of the excitation current.

Description

Regulated power supply assembly for use in electrical switch The present invention generally relates to an electrical switch used for opening and closing an electrically conduc^¬ tive path between an electric supply and an electric load. In particular, the present invention relates to a regulated power supply assembly suitable for operating such an electri- cal switch.

In conventional electrical switches, at least one movable contact is displaced relative to at least one pair of sta^¬ tionary contacts to establish or interrupt an electrically- conductive path between supply-side and load-side stationary contacts. The supply-side and load side stationary contacts are connected to an electrical supply and an electrical load respectively. An electromagnetic assembly is included to pro^¬ vide a driving force such as to cause desired displacement of the movable contact from an open position to a closed posi^¬ tion to operate the electrical switch.

A typical electromagnetic assembly includes a magnet frame, which includes a stationary portion referred to as 'yoke' and a movable portion referred to as 'armature' (sometimes also referred to as 'anker' ) . The yoke and the armature have com^¬ plementary construction with air gaps in between confronting ends. The yoke is associated with an electromagnetic coil, which is energized using a power supply to establish magnetic flux through the yoke and consequently, through the armature such that the armature moves under the influence of magnetic force. The armature of the electromagnetic assembly is cou^¬ pled to a carrier assembly supporting the movable contacts. The movement of the armature from an unactuated position to an actuated position provides a driving force to displace the movable contact from an open position to a closed position thereof . During a closing stroke, the electromagnetic assembly pro^¬ vides a driving force such that the movable contact is dis^¬ placed from the open position to the closed position. During the closing stroke, the electromagnetic assembly must ini- tially overcome impeding force of biasing springs, which bias the movable contact towards the open position thereof. Thus, the electromagnetic assembly is required to exert a linearly increasing driving force until the movable contact finally reaches the closed position.

When the movable contact is in the closed position, typi^¬ cally, the electromagnetic assembly is required to provide a relatively reduced driving force. Eventually, when it is required to interrupt an electrically- conductive path between supply-side and load-side stationary contacts, the electromagnetic coil is de-energised such that the movable contact reverts to the open position under influ^¬ ence of the biasing springs.

It should be noted that the electrical switch described above is referred to as a normally-open electrical switch; and the present invention will be discussed hereinafter with reference to such configuration. However, it should be noted that the present invention is equally applicable to a normally- closed electrical switch with such modifications as will be apparent to a person skilled in the art.

It is apparent from the preceding description that the driv- ing force required during different stages of electrical switch operation is variable. It is an important considera^¬ tion to optimize the driving force during different stages of operation of the electrical switch. The driving force during the closing stroke should be such that sufficient energy is imparted to swiftly transition from the open position to the closed position such as to reduce arcing phenomenon. However, at the same time, it is highly desirable that the imparted energy is not so high as to cause undesirable mechanical stress due to the closing operation. Such so-called ^xhard' closing operation leads to increased mechanical wear on the pole surfaces of the yoke and the armature. Moreover, such hard closing disadvantageously results in an increased ten- dency for contact bouncing subsequent to the initial engage^¬ ment between the movable and the stationary contacts. Such mechanical stress and contact bouncing lead to deteriorating performance over time and undesirably reduce the operational life of the electrical switch. Thus, it is an important chal- lenge to operate the electromagnetic assembly such that the driving force is efficiently regulated and optimized to sat^¬ isfy the contradictory requirements of reducing arcing and reducing mechanical stress and contact bouncing. In the prior art, it is known to provide control means to supply regulated power to the electromagnetic coil such as to optimize the driving force exerted on the movable contact.

One such system and method is known from US Patent 5,737,172. The patent discloses an electromagnetic contactor, including a coil to which an input voltage is loaded. The electromag^¬ netic contactor includes detector means for detecting a peak voltage value of said input voltage and for detecting an av^¬ erage value of said input voltage, wherein said input voltage is one of a full wave rectified alternating current and a DC voltage; switching means, responsive to an operating signal, for controlling operation of said electromagnetic contactor; and a controller for generating said operating signal and for stabilizing input power supplied to said coil at a constant level by controlling a pulse width of said operating signal based on said peak voltage value and said average value of said input voltage detected by said detector means.

As will be readily apparent, the electromagnetic contactor disclosed in the aforementioned patent is based on voltage regulation based on peak voltage value and average voltage value of an input voltage applied to the electromagnetic coil . Another such voltage-regulation based system and method is known from US Patent 5,914,850. The patent discloses contac^¬ tor equipment for use with an electromagnetic contactor in- eluding, among other components, control means comprising a first means for controlling a voltage level supplied to the operating coil during a closing operation of said contactor such that said voltage level is independent of said current of said operating coil.

As will be readily understood, in various voltage-regulation based control mechanisms, the operation of the electrical switch essentially becomes independent of main supply volt^¬ age. However, it is important to note that the driving force is a function of, among other factors, the excitation current supplied to the electromagnetic coil and not the voltage ap^¬ plied across the electromagnetic coil. In other words, the excitation current does not de facto depend only on the ap^¬ plied voltage but also the effective impedance of the elec- tromagnetic coil. The effective impedance, in turn, is de^¬ pendent, among other factors, on geometrical construction of the electromagnetic assembly, air gap between the armature and the yoke, which is continually changing during the clos^¬ ing stroke, and also, temperature of the electromagnetic coil. Therefore, even though voltage-regulation control mechanisms ensure that a constant voltage is applied across the electromagnetic coil, yet such methods fail to provide satisfactory regulation of the driving force generated by the electromagnetic assembly.

In particular, the operational temperature of the electromag^¬ netic coil is bound to vary depending upon the ambient tem^¬ perature and thus, location of the installation; and also, during different instances of use of the electrical switch in a particular installation. It is a general practice to configure the device based on the maximum operating temperature stipulated for the electrical switch. However, when the ac^¬ tual temperature is lower than the maximum operating tempera- ture, the impedance of the electromagnetic coil is much less and accordingly, the driving force generated during the clos^¬ ing stroke becomes undesirably high. An alternative control mechanism known in the art is based on current regulation. One such solution is known from US Patent 5,910,890. The patent discloses a control circuit for an electrical switching device having a set of contacts which are operated by an electromagnetic coil. The control circuit applies a first level of current to the electromagnetic coil during a defined period of time and thereafter, a second level of current to the electromagnetic coil, where the first level is greater than the second level. In such current-regulation based control mechanisms, one of the important challenges is to regulate rate of energy trans^¬ fer to the electromagnetic coil under varying voltage condi^¬ tions. Thus, when the main supply voltage becomes higher, the current build-up in the electromagnetic coil is faster. This essentially leads to much higher gain of energy during the closing stroke. Owing to aforementioned inherent problem in current-regulation based control mechanisms, such mechanisms are less preferred compared to voltage-regulation based con^¬ trol mechanisms.

In light of the above, there is a need for an improved power supply suitable for use in electrical switches. It is desir^¬ able that the improved power supply provides optimum driving force produced using an electromagnetic assembly within the electrical switch such as to optimize closing time required for transitioning the electrical switch from an open position to a closed position and closing velocity imparted to movable components, such as one or more movable contacts, an arma^¬ ture, and so on, within the electrical switch.

Accordingly, an object of the present invention is to provide a regulated power supply assembly suitable for use in elec^¬ trical switches such that driving force produced using an electromagnetic assembly is effectively regulated and opti^¬ mized.

The object of the present invention is achieved by a regu- lated power supply assembly suitable for use with an electri^¬ cal switch according to claim 1, a method for providing a regulated power supply suitable for use with an electrical switch according to claim 11, and an electrical switch according to claim 21. Further embodiments of the present in- vention are addressed in the dependent claims.

In a first aspect of the present invention, a regulated power supply assembly suitable for use in an electrical switch is provided. The electrical switch comprises an electromagnetic assembly configured to operate said electrical switch in one of an open position and a closed position thereof and effect a transition there between. The regulated power supply assembly comprises switching means, sampling means, and control^¬ ling means. The switching means are operable for switching an output voltage provided to the electromagnetic assembly such that an excitation current is established therein. The switching means are operated based on a switching control signal. The sampling means are configured for successively sampling the excitation current established in the electro- magnetic assembly. The controlling means are configured for generating the switching control signal based on comparing an instantaneous sample of the excitation current with a thresh^¬ old current reference and/or at least one preceding sample of the excitation current.

In a second aspect of the present invention, a method for providing a regulated power supply suitable for use in an electrical switch is provided. The electrical switch com^¬ prises an electromagnetic assembly configured to operate said electrical switch in one of an open position and a closed po^¬ sition thereof and effect a transition there between. In accordance with the method of the present invention, an output voltage provided to the electromagnetic assembly is switched based on a switching control signal such that an excitation current is established in the electromagnetic assembly. The excitation current established in the electromagnetic assem^¬ bly is successively sampled. The switching control signal is generated based on comparing an instantaneous sample of the excitation current with a threshold current reference and/or at least one preceding sample of the excitation current.

In a third aspect of the present invention, an electrical switch comprising a regulated power supply assembly in accordance with the first aspect of the present invention and op^¬ erated in accordance with the second aspect of the present invention is provided. Thus, the present invention provides a regulated power supply assembly suitable for use with an electric switch, a method for providing a regulated power supply suitable for use with an electric switch, and an electric switch comprising said regulated power supply assembly and operated in accordance with said method.

The present invention facilitates an effective control over energy delivered to an electromagnetic assembly within the electric switch, and hence best optimizes the driving force generated during closing operation. The energy delivered to the electromagnetic assembly is advantageously independent of an input voltage and temperature of the electromagnetic as^¬ sembly, in particular, an electromagnetic coil within the electromagnetic assembly. Thus, a consistent performance is achieved under all operating conditions.

Such effective control in turn, results in eliminating of undue mechanical stress, contact bounce, and related adverse affects on performance over a period of time, thereby in- creasing an operational life of the electric switch. Further^¬ more, the present invention advantageously regulates energy required to operate the electromagnetic assembly and hence, provides improved energy efficiency. The present invention is further described hereinafter with reference to illustrated embodiments shown in the accompany^¬ ing drawings, in which:

FIG 1 illustrates a schematic view of a regulated

power supply assembly suitable for use with an electric switch in accordance with an embodiment of the present invention,

FIG 2 illustrates a schematic view of controlling

means in accordance with an embodiment of the present invention,

FIGS 3A-3C illustrate a schematic diagram of a control

logic, and variation of two control parameters for operating the regulated power supply assembly based on a rate-based current regulation technique in accordance with an embodiment of the present invention,

FIGS 4A-4B illustrate a schematic diagram of a control

logic, and variation of a single control parame^¬ ter for operating the regulated power supply as^¬ sembly based on a threshold-based current regu^¬ lation technique in accordance with an embodi^¬ ment of the present invention,

FIG 5 illustrates a flowchart depicting a method for providing regulated power supply suitable for use with an electric switch in accordance with an embodiment of the present invention,

FIG 6 illustrates a flowchart depicting a method for generating a switching control signal based on a rate-based current regulation technique in ac^¬ cordance with an embodiment of the present in^¬ vention, and

FIG 7 illustrates a flowchart depicting a method for generating a switching control signal based on a threshold-based current regulation technique in accordance with an embodiment of the present in^¬ vention . Various embodiments are described with reference to the draw^¬ ings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purpose of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more embodiments. It may be evident that such embodiments may be practiced without these specific details. Referring to FIG 1, a partial schematic view of an electric switch 100 is provided. The electric switch 100 includes an electromagnetic assembly 102 and a regulated power supply as^¬ sembly 104. The regulated power supply assembly 104 includes switching means 106, sampling means 108, and controlling means 110. In addition, the regulated power supply assembly

104 includes free-wheeling means 112 and full-wave rectifica^¬ tion means 114.

The electric switch 100 includes various other components in addition to the electromagnetic assembly 102 and the regu^¬ lated power supply assembly 104. However, these additional components are not shown in the adjoining figure for sake of clarity . The electric switch 100 includes at least one pair of sta^¬ tionary contacts and corresponding at least one movable con^¬ tact, which is displaceable between an open position and a closed position. In the closed position, the movable contact establishes an electrical flow path between the stationary contacts in a bridge-like manner.

The electromagnetic assembly 102 is operably coupled to the movable contact and is configured to operate the electrical switch 100 in one of an open position and a closed position thereof and effect a transition there between. In particular, when a voltage is provided to an electromagnetic coil C within the electromagnetic assembly 102, the electromagnetic assembly 102 generates a driving force to displace the mov- able contact from an open position to a closed position. The electromagnetic assembly 102 continues to provide a driving force during the closed position of the electric switch 100 to maintain the closed position. Eventually, when the elec- trie switch 100 is required to be transitioned to the open position, the voltage to the electromagnetic assembly 102 is removed such that the movable contact returns to the open po^¬ sition. The operation of the electric switch 100, as de^¬ scribed in the foregoing description, is generally known in the art.

As noted earlier, it is essential to provide a regulated power supply to the electromagnetic assembly 102 such that the electromagnetic assembly 102 provides an optimum driving force. This is achieved through the regulated power supply assembly 104, which will now be described in detail.

The regulated power supply assembly 104 includes input termi^¬ nals Tl, T2 across which, an input voltage Vin is applied. The input terminals Tl, T2 are connected to the full-wave rectification means 114.

The regulated power supply assembly 104 further includes out^¬ put terminals T3, T4. The output from the full-wave rectifi- cation means 114 is connected to the output terminals T3, T4 through a series connection of the switching means 106 and the sampling means 108. In addition, the free-wheeling means 112 are connected across the output terminals T3, T4. The controlling means 110 are operatively coupled to the input terminals Tl, T2, the switching means 106, the sampling means 108, and the free-wheeling means 112.

The output terminals T3, T4 are coupled to respective input terminals of the electromagnetic assembly 102 to provide an output voltage Vout thereto. In various embodiments of the present invention, the input voltage Vin is one of a direct-current voltage and an alter^¬ nating-current voltage. The input voltage Vin is applied to the full-wave rectifica^¬ tion means 114 to achieve a unidirectional voltage. The full- wave rectification means 114 may be implemented using any suitable technique known in the art. In one exemplary embodi^¬ ment of the present invention a bridge rectifier is used. As will be apparent, the full-wave rectification means 114 ad^¬ vantageously enable the regulated power supply assembly 104 to be operated using an alternating-current voltage as well as a direct-current voltage as the input voltage Vin. The switching means 106 are operable for switching the output voltage Vout provided to the electromagnetic assembly 102 such that an excitation current is established in the elec^¬ tromagnetic assembly 102, and in particular, in the electro^¬ magnetic coil C. The switching means 106 are operated based on a switching control signal received from the controlling means 110, as will be explained later in the following de^¬ scription. In an exemplary embodiment of the present invention, a transistor Ql is used to implement the switching means 106. The switching control signal is applied to gate terminal of the transistor Ql, while a current path is estab^¬ lished from source to drain of the transistor Ql .

The sampling means 108 are configured for successively sam^¬ pling the excitation current established in the electromag- netic assembly 102. In an exemplary embodiment of the present invention, the sampling means 108 include a resistor R connected in series with the switching means 106. The voltage drop across the resistor R is sampled by the controlling means 110 and the excitation current is derived therefrom.

The controlling means 110 has at least two input ports PI, P2, and at least two output ports SI, S2. The controlling means 110 samples the input voltage Vin at the input port PI. In addition, the controlling means 110 continuously samples the excitation current to obtain successive samples thereof through the input port P2. Further, in one embodiment, the controlling means 110 store at least one preceding sample of the excitation current. The controlling means 110 are configured for generating the switching control signal based on comparing an instantaneous sample of the excitation current with a threshold current reference and/or at least one pre^¬ ceding sample of the excitation current. The switching con- trol signal is output through the output port SI. Addition^¬ ally, the controlling means provide a free-wheeling control signal to control the free-wheeling means 112 at the output port S2. In an exemplary embodiment of the present invention, the controlling means 110 are implemented using a microcon- troller. Various logical modules within the microcontroller relevant to the present invention are illustrated in FIG 2.

Referring to FIG 2, a schematic view of controlling means in accordance with an exemplary embodiment of the present inven- tion is illustrated. The controlling means 110 include a mul^¬ tiplexer 202, an analog-to-digital converter 204, a logic module 206, a counter 208, and a comparator 210.

The two input ports PI, P2 are connected to the multiplexer 202. As explained earlier, the input voltage Vin is sampled through the input port PI and the excitation current is sam^¬ pled through the input port P2. The multiplexer 202 receives a signal select signal from the logic module 206 based on which one of the input voltage Vin and the excitation current is sampled, and provided to the analog-to-digital converter

204. The analog-to-digital converter 204 in turn converts the analog signals to digital signals and provide to the logic module 206. It should be noted that the logic module 206 is configured to provide sampling triggers to the analog-to- digital converter 204 in a suitable manner.

In the exemplary embodiment depicted in the adjoining figure, the controlling means 110 are such that the switching control signal is a pulse-width modulated signal. In this embodiment, the counter 208 generates a saw-tooth shaped carrier signal, and the logic module 206 generates a duty-regulation signal. The signals from the counter 208 and the logic module 206 are provided to the comparator 210, which produces a pulse-width modulated signal. The pulse-width modulated signal is output through the output port SI and acts as the switching control signal . In addition, the logic module 206 directly outputs the free^¬ wheeling control signal through the output port S2.

It should be noted that various techniques to generate pulse- width modulated signals are well known in the art and while one technique has been illustrated for exemplary purpose, any suitable technique may be used and all such techniques are well within the scope of the present invention.

Referring back to FIG 1, as mentioned earlier, the free^¬ wheeling means 112 are connected across the output terminals T3, T4. Thus, the free-wheeling means 112 are effectively coupled across the electromagnetic assembly 102 and there^¬ fore, provide a free-wheeling current flow path for the exci^¬ tation current.

The free-wheeling means 112 include a transistor Q2, a diode D connected in series with the transistor Q2, and a varistor VAR connected across the source and drain of the transistor Q2. The gate of transistor Q2 is connected to the output port S2 provided by the controlling means 110 and receives the free-wheeling control signal therefrom.

When the transistor Q2 is switched-on, a low-impedance freewheeling current flow path is established through the tran- sistor Q2 and the diode D. On the other hand, when the transistor Q2 is switched-off, a high-impedance free-wheeling current flow path is established through the varistor VAR and the diode D. Thus, the free-wheeling means 112 are operable in one of a high-impedance mode and a low-impedance mode based on a free-wheeling control signal received from the controlling means 110. In accordance with the techniques of the present invention, the regulated power supply assembly 104 is operable in accor^¬ dance with two distinct techniques, namely, a rate-based cur^¬ rent regulation technique and a threshold-based current regu^¬ lation technique. Each of these two techniques will now be described in detail with reference to FIGS 3A-3C and FIGS 4A- 4B respectively.

Referring to FIGS 3A through 3C, a schematic diagram showing control logic implemented in the logic module 206, and varia- tion of two control parameters for operating the regulated power supply assembly based on a rate-based current regula^¬ tion technique is illustrated in accordance with an embodi^¬ ment of the present invention. In accordance with the rate-based current regulation tech^¬ nique, the excitation current established in the electromag^¬ netic assembly 102 is regulated through monitoring the rate of change of the excitation current. In this technique, two control parameters, namely, a thresh^¬ old current reference and a desired rate of change of excita^¬ tion current are defined.

One exemplary variation of the threshold current reference during operation of the electric switch 100 is shown in FIG 3B . As shown in FIG 3B, the threshold current reference

I (ref) is configured such that the threshold current refer^¬ ence I (ref) is maintained at a first value I (c) and subse^¬ quently, and is reduced to a second value I (h) .

In an exemplary embodiment of the present invention, such variation of threshold current reference I (ref) is based on elapsed time subsequent to initiation of transition from the open position to the closed position. In an alternative embodiment, spatial position of the movable contact is tracked through suitable means and threshold current reference I (ref) varies based on spatial position of the movable contact.

In effect, the threshold current reference I (ref) is main^¬ tained at the first value I (c) during transition from the open position to the closed position, and is reduced to a second value I (h) subsequent to transition to the closed po- sition.

It is important to note that the threshold current reference I (ref) is reduced to the second value I (h) only after elapse of sufficient time period subsequent to initial engagement (depicted as Xc in FIG 3B) between the movable and the sta^¬ tionary contacts to facilitate reaching a stable state such that effect of contact bouncing and so on is minimized. Fur^¬ ther, it should be noted that the second value I (h) of threshold current reference is such that it is sufficient to maintain the closed position of the electric switch 100.

Similarly, one exemplary variation of the desired rate of change of the excitation current during operation of the electric switch 100 is shown in FIG 3C. As shown in FIG 3C, the desired rate of change of excitation current

di/dt (desired) is configured such that a constant rate of change of excitation current is achieved during transition from the open position to the closed position. It should be noted that the variation of desired rate of change of excitation current di/dt (desired) as shown in FIG 3C is exemplary in nature and any desired variation function may be defined. In one embodiment of the present invention, such variation of desired rate of change of excitation current di/dt (desired) is based on elapsed time subsequent to initiation of transi^¬ tion from the open position to the closed position. In an al- ternative embodiment, spatial position of the movable contact is tracked through suitable means and desired rate of change of excitation current di/dt (desired) varies based on spatial position of the movable contact.

Referring now to the control diagram shown in FIG 3A, at summing junction 302, threshold current reference I (ref) and in^¬ stantaneous sample S (i) are compared, and difference there between is calculated. Similarly, difference between instan- taneous sample S (i) and a preceding sample S(i-l) is calcu^¬ lated at summing junction 304. The outputs from summing junctions 302 and 304 are provided to the control block 306, which implements a desirable control function, as described below .

When the instantaneous sample S (i) of the excitation current is equal to or more than the threshold current reference I (ref) , the duty-regulation signal output from logic module 206 corresponds to a low duty cycle. Accordingly, the switch- ing control signal available at the output port SI of the controlling means 110 is configured to operate the switching means 106 with a low duty cycle.

On the other hand, when the instantaneous sample S (i) of the excitation current is less than the threshold current refer^¬ ence I (ref) , control block 306 determines the actual rate of change of excitation current di/dt (actual) based on the com^¬ paring between the instantaneous sample S (i) and the at least one preceding sample S(i-l) .

The actual rate of change of excitation current di/dt (actual) is compared with the desired rate of change of excitation current di/dt (desired) . When the actual rate of change of excitation current

di/dt (actual) is equal to or more than the desired rate of change of excitation current di/dt (desired) , the duty- regulation signal output from logic module 206 corresponds to a low duty cycle. Accordingly, the switching control signal available at the output port SI of the controlling means 110 is configured to operate the switching means 106 with a low duty cycle.

On the other hand, when the actual rate of change of excita^¬ tion current di/dt (actual) is less than the desired rate of change of excitation current di/dt (desired) , the duty- regulation signal output from logic module 206 corresponds to a high duty cycle. Accordingly, the switching control signal available at the output port SI of the controlling means 110 is configured to operate the switching means 106 with a high duty cycle. Referring to FIGS 4A and 4B, a schematic diagram showing control logic implemented in the logic module 206, and variation of a single control parameter for operating the regulated power supply assembly based on a threshold-based current regulation technique is illustrated in accordance with an em- bodiment of the present invention.

In accordance with the threshold-based current regulation technique, the excitation current established in the electro^¬ magnetic assembly 102 is regulated through comparing the ex- citation current with a varying threshold current reference.

In this technique, a single control parameter, namely, a threshold current reference is defined. One exemplary variation of the threshold current reference during operation of the electric switch 100 is shown in FIG 4B. As shown in FIG 4B, the threshold current reference

I (ref) is configured such that the threshold current refer^¬ ence I (ref) increases from an initial value I (i) to a final value I (f) during at least a part of transition from the open position to the closed position of the electric switch 100, and is reduced from the final value I (f) to a holding value 1(h) subsequent to transition to said closed position. In the exemplary embodiment shown in FIG 4B, the threshold current reference I (ref) achieves the final value I (f) before an initial engagement between the movable and the stationary contacts, and remains constant thereafter till the electric switch 100 stably transitions to the closed position.

In one embodiment of the present invention, such variation of threshold current reference I (ref) is based on elapsed time subsequent to initiation of transition from the open position to the closed position. In an alternative embodiment, spatial position of the movable contact is tracked through suitable means and threshold current reference I (ref) varies based on spatial position of the movable contact.

It is important to note that the threshold current reference I (ref) is reduced to the holding value I (h) only after elapse of sufficient time period subsequent to initial engagement (depicted as Xc in FIG 4B) between the movable and the sta- tionary contacts to facilitate reaching a stable state such that effect of contact bouncing and so on is minimized. Fur^¬ ther, it should be noted that the second value I (h) of threshold current reference is such that it is sufficient to maintain the closed position of the electric switch 100.

Referring now to the control logic shown in FIG 4A, at summing junction 402, instantaneous value of threshold current reference I (ref) and instantaneous sample S (i) are compared, and a difference there between is calculated. The output from summing junctions 402 is provided to the control block 404, which implements a desirable control function, as described below .

When the instantaneous sample S (i) of the excitation current is equal to or more than the threshold current reference

I (ref) , the duty-regulation signal output from logic module 206 corresponds to a low duty cycle. Accordingly, the switch^¬ ing control signal available at the output port SI of the controlling means 110 is configured to operate the switching means 106 with a low duty cycle.

On the other hand, when the instantaneous sample S (i) of the excitation current is less than the threshold current refer^¬ ence I (ref) , the duty-regulation signal output from logic module 206 corresponds to a high duty cycle. Accordingly, the switching control signal available at the output port SI of the controlling means 110 is configured to operate the switching means 106 with a high duty cycle.

It should be noted that the control parameters namely, threshold current reference I (ref) and desired rate of change of excitation current di/dt (desired) as explained in conjunc- tion with FIG 3B and FIG 3C; and threshold current reference I (ref) explained in conjunction with FIG 4B are configured based on various mechanical and electrical parameters associ^¬ ated with the electromagnetic assembly 102. Referring back to FIG 1, as described in conjunction with FIGS 3A through 4B, the controlling means 110 generate the switching control signal based on comparing an instantaneous sample of said excitation current with a threshold current reference and/or at least one preceding sample of said exci- tation current.

It should be noted that the sampling of excitation current and modification in the switching control signal in accordance with the techniques described in the preceding descrip- tion are performed at a sufficiently high frequency to pro^¬ vide stringent control and negligible deviation in the actual excitation current from the required excitation current.

Also, it should be noted that a frequency of the switching control signal may be much higher than a frequency of the sampling the excitation current. In one example, the switch^¬ ing control signal has a frequency of 16 KHz while the exci^¬ tation current is sampled at 1.6 KHz. In general, the sam^¬ pling frequency should be such that a sufficient time inter- val is provided between two successive samples of the excita^¬ tion current for a perceptible change therein based on elec^¬ trical inertia of the electromagnetic assembly 102. Also, as stated earlier, in an exemplary embodiment, the switching control signal is a pulse-width modulated signal. When the switching control signal is applied to the switching means 106, during the ^λΟΝ' period of the switching control signal, the excitation current flows through the transistor Ql and the resistor R whereas during the ^xOFF' period of the switching control signal the free-wheeling means 112 provide the free-wheeling current flow path to maintain continuity of current and avoid sudden voltage surges and other undesirable effects due to sudden breakage of excitation current in the electromagnetic coil C.

During transition from the open position to the closed position and during the closed position, it is desirable that the free-wheeling means 112 provide a low-impedance current flow path for the excitation current. On the hand, when it is re^¬ quired to switch-off the electric switch 100, or in other words, effect a transition from the closed position to the open position in the electric switch 100, it is desirable that the free-wheeling means 112 provide a high-impedance path to quickly decay the excitation current.

Accordingly, the controlling means 110 provide the free^¬ wheeling control signal at the output port S2 such that the free-wheeling means operate in the low-impedance mode during transition from the open position to the closed position and during the closed position, and further such that the freewheeling means operate in the high-impedance mode during transition from the closed position to the open position. In particular, during transition from the open position to the closed position and also, during the closed position, the free-wheeling control signal is such that transistor Q2 remains in conducting state and hence, a low-impedance path is established through transistor Q2 and diode D. On the other hand, during transition from the closed position to the open position, the free-wheeling control signal keeps the transis^¬ tor Q2 in non-conducting state, and hence, a high-impedance path through the varistor VAR and diode D is established and consequently, the excitation current is quickly decayed.

As will be apparent, when the electric switch 100 is to be switched-off, the input voltage Vin is withdrawn. The con- trolling means 110 sense this change and accordingly, set the switching control signal to such value that transistor Ql is turned-off. At the same time, the free-wheeling control sig^¬ nal is also set to such value that transistor Q2 is also turned-off. This ensures that the established excitation cur- rent in the electromagnetic assembly 102 is quickly decayed and the electric switch 100 transitions from the closed posi^¬ tion to the open position.

Referring now to FIG 5, a flowchart depicting a method for providing regulated power supply suitable for use with an electric switch is illustrated in accordance with an embodi^¬ ment of the present invention. The electric switch includes an electromagnetic assembly configured to operate the elec^¬ trical switch in one of an open position and a closed posi- tion thereof and effect a transition there between.

At step 502, one or more control parameters are configured. As explained in conjunction with FIGS 3A-3C and FIGS 4A-4B, the present invention provides two distinct techniques, namely, a rate-based current regulation technique and a threshold-based current regulation technique. The control pa^¬ rameters are configured in accordance with the desired tech^¬ nique to be followed. In a first embodiment, in accordance with the rate-based cur^¬ rent regulation technique, the excitation current established in the electromagnetic assembly is regulated through monitor^¬ ing the rate of change of the excitation current. In this technique, two control parameters, namely, a threshold cur^¬ rent reference and a desired rate of change of excitation current are defined. The threshold current reference is configured such that the threshold current reference is maintained at a first value during transition from the open position to the closed position, and is reduced to a second value subsequent to transi^¬ tion to the closed position. At the same time, the desired rate of change of the excitation current during transition from the open position to the closed position is also configured .

In a second embodiment, in accordance with the threshold- based current regulation technique, the excitation current established in the electromagnetic assembly is regulated through comparing the excitation current with a varying threshold current reference. In this technique, a single con^¬ trol parameter, namely, a threshold current reference is de- fined.

In this case, the threshold current reference is configured such that the threshold current reference increases from an initial value to a final value during at least a part of transition from the open position to the closed position, and is reduced from the final value to a holding value subsequent to transition to the closed position.

At step 504, an output voltage provided to the electromag- netic assembly is switched such that an excitation current is established therein, wherein the output voltage is switched based on a switching control signal.

In an embodiment of the present invention, this step further includes receiving an input voltage as a direct current sup^¬ ply and/or an alternating current supply and generating the output voltage therefrom such that the output voltage is uni^¬ directional . In an embodiment of the present invention, this step further includes providing a free-wheeling current flow path for the excitation current. As explained in detail in the foregoing description, the free-wheeling current flow path is operable in one of a high-impedance mode and a low-impedance mode based on a free-wheeling control signal. The free-wheeling current flow path is configured in the low-impedance mode during transition from the open position to the closed posi- tion and during the closed position, and further configuring the free-wheeling current flow path in the high-impedance mode during transition from the closed position to the open position . At step 506, the excitation current is successively sampled.

At step 508, the switching control signal is generated based on comparing an instantaneous sample of the excitation current with a threshold current reference and/or at least one preceding sample of the excitation current.

The steps 504 through 508 are performed iteratively starting from initiation of transition from the open position to the closed position until the electric switch transitions back to the open position based on withdrawal of input voltage or any other suitable switch-off signal therefor.

The control logic for generation of switching control signal for the rate-based and the threshold-based current regulation techniques is explained in conjunction with FIG 6 and FIG 7 respectively .

FIG 6 illustrates a flowchart depicting a method for provid^¬ ing generating a switching control signal based on a rate- based current regulation technique in accordance with an em^¬ bodiment of the present invention. At step 602, an instantaneous sample of the excitation cur^¬ rent is compared with the threshold current reference.

When the instantaneous sample of the excitation current is equal to or more than the threshold current reference then, at step 610, the switching control signal is configured to provide a low duty cycle.

On the other hand, when the instantaneous sample of the exci- tation current is less than the threshold current reference then, at 604, an actual rate of change of the excitation cur^¬ rent is determined. The actual rate of change of the excita^¬ tion current is determined based on the comparing between the instantaneous sample and the at least one preceding sample of the excitation current.

Subsequently, at step 606 the actual rate of change of the excitation current is compared with the desired rate of change of the excitation current.

When the actual rate of change of excitation current is equal to or more than the desired rate of change of excitation cur^¬ rent then, at step 610, the switching control signal is con^¬ figured to provide a low duty cycle.

On the other hand, when the actual rate of change of excita^¬ tion current is less than the desired rate of change of exci^¬ tation current then, at step 608, the switching control sig^¬ nal is configured to provide a high duty cycle.

Referring now to FIG 7, a flowchart depicting a method for providing generating a switching control signal based on a threshold-based current regulation technique is illustrated in accordance with an embodiment of the present invention.

At step 702, an instantaneous sample of the excitation cur^¬ rent is compared with threshold current reference. When the instantaneous sample of the excitation current is equal to or more than an instantaneous value of the threshold current reference then, at step 706, the switching control signal is configured to provide a low duty cycle.

On the other hand, when the instantaneous sample of the exci^¬ tation current is less than an instantaneous value of the threshold current reference, the switching control signal is configured provide a high duty cycle.

It should be noted that during various steps mentioned in FIG 6 and FIG 7, the value of threshold current reference I (ref) corresponds to the instantaneous value thereof obtained from the variation of threshold current reference I (ref) shown if FIG 3B and FIG 4B respectively.

As will now be understood in light of the description pro^¬ vided herein, the present invention facilitates an effective control over energy delivered to an electromagnetic assembly within the electric switch through an effective regulation of excitation current established in the electromagnetic assem^¬ bly. Therefore, the present invention optimizes kinetic en^¬ ergy gain provided to the movable contact during closing op^¬ eration. The energy delivered to the electromagnetic assembly is advantageously independent of an input voltage and tem^¬ perature of the electromagnetic assembly, in particular, an electromagnetic coil within the electromagnetic assembly. Thus, a consistent performance is achieved under all operat^¬ ing conditions.

Such effective control in turn, results in eliminating undue mechanical stress, contact bounce, and related adverse af^¬ fects on performance over a period of time, thereby increas^¬ ing an operational life of the electric switch. Furthermore, the present invention advantageously regulates energy re^¬ quired to operate the electromagnetic assembly and hence, provides improved energy efficiency. While the present invention has been described in detail with reference to certain embodiments, it should be appreciated that the present invention is not limited to those embodi^¬ ments. In view of the present disclosure, many modifications and variations would present themselves, to those of skill in the art without departing from the scope and spirit of this invention. The scope of the present invention is, therefore, indicated by the following claims rather than by the forego^¬ ing description. All changes, modifications, and variations coming within the meaning and range of equivalency of the claims are to be considered within their scope.

Claims

Claims :

A regulated power supply assembly (104) suitable for use in an electrical switch (100), said electrical switch (100) comprising an electromagnetic assembly (102) con^¬ figured to operate said electrical switch (100) in one of an open position and a closed position thereof and effect a transition there between, said regulated power supply assembly (104) comprising:

- switching means (106) operable for switching an output voltage (Vout) provided to said electromagnetic assem^¬ bly (102) such that an excitation current is estab^¬ lished therein, wherein said switching means (106) are operated based on a switching control signal,

- sampling means (108) configured for successively sam^¬ pling said excitation current, and

- controlling means (110) configured for generating said switching control signal based on comparing an instantaneous sample (S (i) ) of said excitation current with a threshold current reference (I(ref)) and/or at least one preceding sample (S(i-l)) of said excitation cur^¬ rent .

The regulated power supply assembly (104) according to claim 1, wherein said threshold current reference

(I(ref)) is configured such that said threshold current reference (I(ref)) is maintained at a first value (1(c)) during transition from said open position to said closed position, and is reduced to a second value (1(h)) subse^¬ quent to transition to said closed position, and wherein a desired rate of change of said excitation current dur^¬ ing transition from said open position to said closed position is configured. The regulated power supply assembly (104) according to claim 2, wherein when said instantaneous sample (S (i) ) of said excitation current is equal to or more than said threshold current reference (I(ref)), said switching con^¬ trol signal is configured to operate said switching means (106) with a low duty cycle.

The regulated power supply assembly (104) according to claim 2 or 3, wherein said controlling means (110) are further configured for determining an actual rate of change of said excitation current when said instantaneous sample (S (i) ) of said excitation current is less than said threshold current reference (I(ref)), wherein said actual rate of change of said excitation current is de^¬ termined based on said comparing between said instantane^¬ ous sample (S (i) ) and said at least one preceding sample (S(i-l)) of said excitation current, and comparing said actual rate of change of said excitation current with said desired rate of change of said excitation current, and wherein

- when said actual rate of change of excitation current is equal to or more than said desired rate of change of excitation current, said switching control signal is configured to operate said switching means (106) with a low duty cycle, and

- when said actual rate of change of excitation current is less than said desired rate of change of excitation current, said switching control signal is configured to operate said switching means (106) with a high duty cy^¬ cle .

5. The regulated power supply assembly (104) according to claim 1, wherein said threshold current reference

(I(ref)) is configured such that said threshold current reference (I(ref)) increases from an initial value (I(i)) to a final value (1(f)) during at least a part of transi^¬ tion from said open position to said closed position, and is reduced from said final value (1(f)) to a holding value (1(h)) subsequent to transition to said closed po^¬ sition.

6. The regulated power supply assembly (104) according to claim 5, when said instantaneous sample (S (i) ) of said excitation current is equal to or more than an instanta^¬ neous value of said threshold current reference (I(ref)), said switching control signal is configured to operate said switching means (106) with a low duty cycle.

7. The regulated power supply assembly (104) according to claim 5 or 6, wherein when said instantaneous sample

(S (i) ) of said excitation current is less than an instan^¬ taneous value of said threshold current reference

(I(ref)), said switching control signal is configured to operate said switching means (106) with a high duty cy^¬ cle .

8. The regulated power supply assembly (104) according to any of the preceding claims further comprising freewheeling means (112) coupled across said electromagnetic assembly (102) for providing a free-wheeling current flow path for said excitation current, and wherein said free^¬ wheeling means (112) are operable in one of a high- impedance mode and a low-impedance mode based on a free^¬ wheeling control signal. The regulated power supply assembly (104) according to claim 8, wherein said controlling means (110) are further configured for providing said free-wheeling control sig^¬ nal to said free-wheeling means (112) such that said free-wheeling means (112) operate in said low-impedance mode during transition from said open position to said closed position and during said closed position, and further such that said free-wheeling means (112) operate in said high-impedance mode during transition from said closed position to said open position.

The regulated power supply assembly (104) according to any of the preceding claims further comprising a full- wave rectification means (114) configured for receiving an input voltage (Vin) as a direct current supply and/or an alternating current supply and generating said output voltage (Vout) therefrom such that said output voltage (Vout) is unidirectional.

A method for providing a regulated power supply suitable for use in an electrical switch, said electrical switch comprising an electromagnetic assembly configured to op^¬ erate said electrical switch in one of an open position and a closed position thereof and effect a transition there between, said method comprising:

- switching (504) an output voltage (Vout) provided to said electromagnetic assembly such that an excitation current is established therein, wherein said output volt age (Vout) is switched based on a switching control sig^¬ nal,

- successively sampling (506) said excitation current, and - generating (508) said switching control signal based on comparing an instantaneous sample (S (i) ) of said exci^¬ tation current with a threshold current reference

(I (ref) ) and/or at least one preceding sample (S(i-l)) of said excitation current.

The method according to claim 11 further comprising:

- configuring (502) said threshold current reference

(I (ref) ) such that said threshold current reference

(I (ref) ) is maintained at a first value (1(c)) during transition from said open position to said closed position, and is reduced to a second value (1(h)) subse^¬ quent to transition to said closed position, and

- configuring (502) a desired rate of change of said ex^¬ citation current during transition from said open position to said closed position.

The method according to claim 12, wherein when said instantaneous sample (S (i) ) of said excitation current is equal to or more than said threshold current reference (I (ref)), said switching control signal is configured to provide a low duty cycle (610) .

The method according to claim 12 or 13 further comprising determining (604) an actual rate of change of said exci^¬ tation current when said instantaneous sample (S (i) ) of said excitation current is less than said threshold cur^¬ rent reference (I (ref)), wherein said actual rate of change of said excitation current is determined based on said comparing between said instantaneous sample (S (i) ) and said at least one preceding sample (S(i-l)) of said excitation current, and comparing (606) said actual rate of change of said excitation current with said desired rate of change of said excitation current, wherein - when said actual rate of change of excitation current is equal to or more than said desired rate of change of excitation current, said switching control signal is configured to provide a low duty cycle (610), and

- when said actual rate of change of excitation current is less than said desired rate of change of excitation current, said switching control signal is configured to provide a high duty cycle (608) . 15. The method according to claim 11 further comprising configuring (502) said threshold current reference (I(ref)) such that said threshold current reference (I(ref)) in^¬ creases from an initial value (I(i)) to a final value (1(f)) during at least a part of transition from said open position to said closed position, and is reduced from said final value (1(f)) to a holding value (1(h)) subsequent to transition to said closed position.

16. The method according to claim 15, when said instantaneous sample (S (i) ) of said excitation current is equal to or more than an instantaneous value of said threshold cur^¬ rent reference (I(ref)), said switching control signal is configured to provide a low duty cycle (706) . 17. The method according to claim 15 or 16, wherein when said instantaneous sample (S (i) ) of said excitation current is less than an instantaneous value of said threshold cur^¬ rent reference (I(ref)), said switching control signal is configured provide a high duty cycle (704) .

18. The method according to any of the preceding claims fur^¬ ther comprising providing (504) a free-wheeling current flow path for said excitation current, wherein said freewheeling current flow path is operable in one of a high- impedance mode and a low-impedance mode based on a free^¬ wheeling control signal.

19. The method according to claim 18 further comprising configuring said free-wheeling current flow path in said low-impedance mode during transition from said open posi^¬ tion to said closed position and during said closed posi^¬ tion, and further configuring said free-wheeling current flow path in said high-impedance mode during transition from said closed position to said open position.

20. The method according to any of the preceding claims fur^¬ ther comprising receiving (504) an input voltage (Vin) as a direct current supply and/or an alternating current supply and generating said output voltage (Vout) there^¬ from such that said output voltage (Vout) is unidirec^¬ tional .

21. An electrical switch (100) comprising a regulated power supply assembly (104) in accordance with any of claims 1 to 10, wherein said regulated power supply assembly (104) is operated in accordance with any of claims 11 to 20.