POWER SUPPLY DEVICE FOR LOW-VOLTAGE ELECTRONIC RESIDUAL CURRENT CIRCUIT BREAKERS

Abstract: A power supply device for low-voltage electronic residual current circuit breakers, comprising: - an electronic rectifier stage, suitable to receive in input a mains voltage and to generate a first unipolar voltage whose value depends on the value of the mains voltage; and - an electronic adjustment stage, suitable to receive in input the first unipolar voltage and a current and to generate in output a second unipolar voltage of adjustable value. Its particularly consists of the fact that the electronic adjustment stage comprises first electronic means suitable top perform an active adjustment of the current in input to the electronic adjustment stage, so as to keep the second unipolar voltage at a predefined constant value.

Description: POWER SUPPLY DEVICE FOR LOW-VOLTAGE ELECTRONIC RESIDUAL CURRENT CIRCUIT BREAKERS DESCRIPTION The present invention relates to a power supply device for low-voltage electronic residual current circuit breakers (RCCBs) and the like. In particular, the power supply device, according to the present invention, is suitable for use in electronic RCCBs for applications of the single-phase or multiple-phase (two-phase, three-phase, et cetera) with operating voltages around 1000 V or less. Many examples of low-voltage electronic RCCBs are known in the background art. The structure of a low-voltage electronic RCCB of the known type is illustrated schematically with reference to Figure 1. In general, a low- voltage electronic RCCB, designated by the reference numeral 1, comprises a sensor 2, which is suitable to generate a signal 3, indicative of the presence of an imbalance current due to a ground-fault, in an electrical network 4 of the single- or multi-phase type. The signal 3 is received in input by an electronic protection system 5, which generates control signals 6 in order to drive, for example, an electromagnetic release device and/or electronic signaling devices or auxiliary electronic devices (reference 8), aimed at providing signals related to the status of the apparatus or circuit breaker. The electronic protection system 5, the electromagnetic release 7 and the signaling devices 8 must, for their correct operation, be supplied with a given electrical power level P AL> generally provided by an electronic power supply device 9, which has in output a power supply voltage VA L - Traditionally, the electronic power supply device 9 can be realized according to different approaches. According to a first constructive approach, the electronic power supply device 9 is structured, so as to receive electrical power (dashed arrow 10) directly from the sensor 2, which is used to detect the vector imbalance of the currents, between the phases of the electrical network 4. This type of approach, which offers the unquestionable advantage of ensuring power supply (and consequently operation of the RCCB) in a manner virtually independent of the mains voltage, has considerable drawbacks. In fact, the electrical power P AL that can be made available by the power supply device 9 is generally reduced (a few hundred mVA) and allows to supply an electronic protection system 5 or an electromagnetic release 7, which have to be necessarily of the low-power type. It also becomes difficult to supply power to other devices, which are accessories or are of the auxiliary type. Thus, one can say that the power supply devices 9, provided according to the first type of approach described, are often affected by considerable operating limitations. In an alternative constructive approach, the electronic power supply device 9 is structured so as to obtain electric power (dashed arrow 11) directly from the electrical network 4. In order to be able to supply the electric power P AL , voltages and currents (V I and I ΪN ) of the phases of the electric network 4 are made available by means of a rectifier bridge and an appropriate network of resistive and capacitive passive elements (not shown). A network of passive elements of the nonlinear type 12 is generally used in order to widen the available range of the input supply voltage. Practice has shown that also this constructive approach has considerable drawbacks, even though it is inherently very robust and capable of costantly supplying an adequate power level P AL - The use of a network of passive elements makes it difficult to ensure that a stable power supply condition is reached with a low transient period, when supply voltage ranges very different from each other have to be adopted. Furthermore, in this case, it is necessary to dissipate as heat the excess available energy for the higher supply voltage ranges. Moreover, the use of nonlinear passive components is very often critical, since these components generally have relatively large size and considerably high costs, in comparison with the costs of commonly used active or passive circuit elements. Additionally, owing to the need to optimize the working point of the electrical network of passive elements, according to the supplied electric power, it is often necessary to provide a different type of power supply device 9 for each different supply voltage range, which has to be supplied. For these reasons, the practice has shown that, often, the use of power supply devices of this type is scarcely flexible, leading to a consequent increase in production costs, installation costs and operating costs of the electronic RCCB. The aim of the present invention is to provide a power supply device for low- voltage electronic RCCBs, which allows obviating the drawbacks above described. Within the scope of this aim, an object of the present invention is to provide a power supply device for low- voltage electronic RCCBs, which allows using relatively high input supply voltage ranges while maintaining dissipated power at relatively low levels. Another object of the present invention is to provide a power supply device for low-voltage electronic RCCBs, which allows providing an electric power sufficient to supply even relatively high-power electromagnetic release devices. Another object of the present invention is to provide a power supply device for low-voltage electronic RCCBs, which has a reduced transient time before achieving the steady-state condition. Another object of the present invention is to provide a power supply device for low- voltage electronic RCCBs, which is relatively compact, easy to manufacture and at relatively low costs. Thus, the present invention provides a power supply device for low-voltage electronic RCCBs, comprising: - an electronic rectifier stage, suitable to receive in input a mains voltage and to generate a first unipolar voltage, the value of said first unipolar voltage depending on the value of said mains voltage; and - an electronic adjustment stage, suitable to receive in input, from said electronic rectifier stage, said first unipolar voltage and a first current and to generate in output a second unipolar voltage of adjustable value. The power supply device, according to the present invention, is characterized in that said electronic adjustment stage comprises first electronic means, suitable to perform an active adjustment of said first current, so as to keep said second unipolar voltage at a predefined adjustable value. The active adjustment of said first current, in input to said electronic adjustment stage, allows to obtain an output voltage, which can be easily predefined at a chosen value, considerably increasing the operating flexibility of the power supply device, according to the invention. The term "active adjustment" of said first current is used to designate a type of adjustment, which allows to vary the flow of said first current, by using active semiconductor devices. In this manner, the power supply device, according to the present invention, allows to convert a variable mains voltage into a power supply voltage, which can have a predefined adjustable value, preferably constant. The active adjustment of said first current furthermore allows to reduce power dissipation to negligible values, by means of choosing the most appropriate adjustment modes, such as for example a nonlinear adjustment mode of the switching type, in which the flow of said first current is varied according to an ON/OFF mode. Further characteristics and advantages of the power supply device, according to the present invention, are described in greater detail hereinafter with particular reference to the accompanying drawings, wherein: Figure 1 is a schematic view of a low-voltage electronic RCCBs, of a known type; and Figure 2 is a schematic view of a power supply device, according to the present invention; and Figure 3 is a schematic view of a preferred embodiment of a power supply device, according to the present invention; and Figure 4 plots schematically some currents and voltages in the embodiment of the power supply device, according to the present invention, shown in Figure 3. With reference to Figure 2, the power supply device, according to the present invention, generally designated by the reference numeral 20, comprises an electronic rectifier stage 21. The electronic rectifier stage 21 receives in input a mains voltage V NET and generates a first unipolar voltage V IN , whose value depends on the value of the mains voltage V NET - Advantageously, the electronic rectifier stage 21 may comprise a diode bridge, connected so as to obtain a unipolar voltage, which is not necessarily constant. In fact, the first unipolar voltage V I can comprise, for example, a waveform, which varies according to the modulus of one of the phase voltages. Obviously, depending on the available type of mains, the electronic rectifier stage can be adapted to draw voltage from a single-phase or multiple-phase mains. The power supply device 20 furthermore comprises an electronic adjustment stage 24, which is suitable to receive in input the first unipolar voltage V IN and a first current I I . The electronic adjustment stage 24 generates in output a second unipolar voltage V 0 uτ > having an adjustable value (for example an adjustable instantaneous values or an adjustable average value or the like). The second output voltage Vou T constitutes, in practice, the supply voltage, which is provided in output by the power supply device 20. The power supply device 20 comprises first electronic means 27 in order to perform an active adjustment of the first current l w in input to the electronic adjustment stage 24, so as to keep the second unipolar voltage V OUT at a predefined constant value. The first electronic means 27 perform an active adjustment of the first current I IN n input to the electronic adjustment stage 24. This allows providing, in output from the first electronic means 27, a second current I OUT , which has an adjustable average value. Preferably, the first electronic means 27 perform an active adjustment of the first current l m> according to a nonlinear adjustment mode and particularly according to a switching-type adjustment mode. In particular, the first current I IN is preferably varied according to an ON/OFF mode. In this case, the second current I 0 uτ can therefore have a pulsed-type waveform with an easily adjustable pulse width and repetition period. Again with reference to Figure 2, the electronic adjustment stage 24 advantageously comprises a charge accumulation circuit 23, which is electrically connected to the first electronic means 27. The charge accumulation circuit 23 receives in input the second current I 0 uτ and generates in output the second unipolar voltage V OUT - Thus, the value of the second unipolar voltage V OUT is adjustable, according to the average value of the second current I OUT - Preferably, the electronic adjustment stage 24 comprises second electronic means 26, which are electrically connected to the first electronic means 27 and generate control signals V COM in order to keep the second current I 0 uτ below a predefined maximum threshold. In particular, the second electronic means 26 are suitable to limit the amplitude of the pulses of the second current I 0 uτ- In this manner, sudden variations of the voltage V I , caused by sudden changes in the mains voltage, are prevented from causing high current pulses of the current Iouτ > which may happen since the second current I 0 τjτ trends intrinsically to charge, in the shortest possible time, the charge accumulation circuit 23. This fact implies that in the power supply device 20, the voltage V OUT remains at a substantially constant value despite the occurrence of sudden mains voltage variations. This is particularly advantageous, since it prevents the possibility of damage to the electronic components connected downstream the power supply device 20. Preferably, the electronic adjustment stage 24 comprises third electronic means 28, which are electrically connected to the first electronic means 27 and are suitable to increase the stability of the adjustment stage 24. Advantageously, the third electronic means 28 send a feedback signal V FREQ to the first electronic means 27 in order to adjust the slope of the rising/falling edges related to the pulses of the second current I 0 uτ- In this manner it is possible to reduce the onset of electromagnetic noise. A preferred embodiment of the electronic adjustment stage 24, regarding the power supply device 20, according to the invention, is now described schematically with reference also to Figure 3. According to this embodiment, the first electronic means 27 comprise an electronic interruption circuit 41, which is advantageously suitable to enable/interrupt, following the reception of an enable/disable signal V AB , the first current I IN , in input to the adjustment stage 24. Advantageously, the first electronic means 27 also comprise an electronic control circuit, which comprises a comparator circuit block 44 and an enabling circuit block 45. The comparator circuit block 44 is suitable to generate a control signal 47 if the voltage V OUT assumes values below or above a predefined range. The enabling circuit block 45 is suitable to generate, following the reception of the control signal 47, an enable/disable signal V AB for the electronic interruption circuit 41. Advantageously, the electronic interruption circuit 41 comprises one or more active electronic semiconductor devices Qi, such as for example transistors of the MOSFET, BJT or IGBT types, active electronic semiconductor devices Qj . can be connected, for example by means of an appropriate bias network schematically represented by the element R P , at the input terminal of the electronic adjustment stage 24 which is assumed to have a voltage potential which is positive (terminal T or equal to zero (terminal T 2 ). The chosen type of connection is important for the choice of the active semiconductor devices Qi comprised within the electronic interruption circuit 41. For example, if the connection occurs at the terminal T 1? the electronic interruption circuit 41 can include MOSFET transistors of the N type or BJT transistors of the NPN type, whereas if the connection occurs at the terminal T 2 , the electronic circuit 41 can include MOSFET transistors of the P type or BJT transistors of the PNP type. Preferably, the comparator circuit block 44 comprises a hysteresis comparator 46, which is suitable to receive in input a signal V 0 uτι > indicative of the second unipolar voltage V Θ uτ and a reference signal V REF . The reference voltage V REF can be used to adjust the amplitude of the variation range of the voltage V 0 uτ- Advantageously, the enabling circuit block 45 comprises one or more active electronic semiconductor devices Q 2 (for example of the previously described type), which are advantageously connected at the input terminal Ti or T 2 . According to the embodiment shown in Figure 3, the charge accumulation circuit 23 comprises one or more capacitive elements 51, which are advantageously connected between the output terminals T 3 and T 4 of the adjustment stage 24. Preferably, the second electronic means 26 comprise a network of resistive elements 53 (elements R F ι and R F2 ), which is suitable to generate a feedback signal V F , indicative of the value of the second current I 0 uτ- Advantageously, the second electronic means 26 also comprise one or more active semiconductor devices Q 3 (for example of the above described type) which are suitable to generate, according to the feedback signal V F , a control signal V COM for the first electronic means 27. In particular, the active semiconductor devices 55 generate the control signal V COM (which can be an enable/disable signal) for the electronic interruption circuit 41. Preferably, the third electronic means 28 comprise a network of capacitive and/or resistive elements (elements R F3 and C F3 ), which is connected between one of the output terminals (T 3 or T 4 ) and the first electronic means 27. The waveforms of some voltages and currents inside the adjustment stage 24 are now illustrated schematically with reference to Figure 4 in order to make easier to understand the operation of the preferred embodiment illustrated in Figure 3. With reference also to Figure 4, the waveform 60 schematically plots the voltage related to the node "A" of the adjustment stage 24. The peaks 61, related to the waveform 60, represent the enable/disable signals V AB sent by the electronic enabling circuit 45. In particular, the rising/falling edges (Fi and F 2 ) of each peak 61 respectively represent an enable/disable signal for the electronic interruption circuit 41. The waveform 62 instead plots the second current I 0 uτ- It is clearly noticeable that at each peak 61 of the waveform 60 there is a current pulse 63 which is used to charge the charge accumulation circuit 23. The slope of the rising/falling edges F 3 and F 4 related to each current pulse 63 is adjusted by the third electronic means 28 by sending the feedback signal V FREQ to the first electronic means 27. Considering the waveform 65, which plots the voltage V OUT , it can be noted that the second current I 0 uτ charges the charge accumulation circuit 23. As shown, after an initial transient 66, the voltage V OUT can remain substantially constant by virtue of the action of the pulsed second current I 0 uτ, which keeps charged, by virtue of successive pulses 63, the charge accumulation circuit 23. When the voltage V OUT drops below a threshold value Vsi, a rising edge Fi of the waveform 60 intervenes, causing the onset of the rising edge F 3 of the second current I 0 uτ, which reaches a value corresponding to the value of the first current 1^. This causes a ramp-like increase Ri of the voltage V OUT - As soon as the voltage V 0 uτ exceeds a threshold value V S2 , a rising edge Fi of the waveform 60 intervenes and causes the onset of the rising edge F 3 of the second current I 0 uτ, which returns to zero. In this manner, the voltage V OUT decreases, according to an exponential behavior R2, which corresponds to the natural discharge transient of the charge accumulation circuit 23. The voltage V 0 uτ therefore has a ripple 67 whose maximum value can be adjusted by acting on the reference voltage V REF of the hysteresis comparator 46. In practice it has been found that the power supply device 20, according to the present invention, achieves the intended aim and objects. In particular, the power supply device 20 allows to supply an electric power level, which is sufficient to supply electromagnetic release devices, including release devices having relatively high power consumption, while limiting power dissipation. An adjustment of the first current Iι N , for example according to a switching-type mode, allows to limit power dissipation only to the transients which correspond to a rising/falling edge F 3 and F 4 of each pulse 63 of the second current I 0 uτ- Moreover, by virtue of the adjustment of the first current I IN , the steady-state condition of the voltage V 0 uτ is possible after a relatively short transient period. Moreover, it has been found that the power supply device 20 can be realized in a relatively compact size. Furthermore, it has been found to be easy to manufacture, allowing achieving a considerable reduction in manufacturing costs, installation costs and operating costs. Owing to its flexibility and operating characteristics, the power supply device 20 has proved itself useful for very wide input voltage ranges. The power supply device, according to the present invention, thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the inventive concept. All the details may furthermore be replaced with other technically equivalent elements. In practice, the materials used, so long as they are compatible with the specific use, as well as the dimensions, may be any according to the requirements and the state of the art.

Claims: CLAIMS 1. A power supply device for low- voltage electronic residual current circuit breakers, comprising: - an electronic rectifier stage, suitable to receive in input a mains voltage and to generate a first unipolar voltage, the value of said first unipolar voltage depending on the value of said mains voltage; and - an electronic adjustment stage, which is suitable to receive in input, from said electronic rectifier stage, said first unipolar voltage and a first current and which is suitable to generate in output a second unipolar voltage, which has an adjustable value; characterized in that said electronic adjustment stage comprises first electronic means, suitable to perform an active adjustment of said first current, so as to keep said second unipolar voltage at a predefined adjustable value. 2. The power supply device, according to claim 1, characterized in that said first electronic means perform an active adjustment of said first current, in accordance to an adjustment mode of the non-linear type. 3. The power supply device, according to claim 2, characterized in that said first electronic means perform an active adjustment of said first current, in accordance to an adjustment mode of the switching type. 4. The power supply device, according to one or more of the previous claims, characterized in that said first electronic means perform an active adjustment of said first current, so as to generate in output a second current, which has an adjustable average value. 5. The power supply device, according to claim 4, characterized in that said second current is of the pulsed type, with adjustable pulse width and repetition period. 6. The power supply device, according to one or more of the previous claims, characterized in that said electronic adjustment stage comprises a charge accumulation circuit, which is electrically connected to said first electronic means, said charge accumulation circuit receiving in input said second current and generating said second unipolar voltage, the value of said second unipolar voltage depending on the average value of said second current. 7. The power supply device, according to one or more of the previous claims, characterized in that said first electronic means comprise: - an electronic interruption circuit, which is suitable to enable/interrupt, following the reception of an enable/disable signal, said first current; and - a comparator circuit block, which is suitable to generate a control signal when said second unipolar voltage assumes values above or below a preset range; and - an enabling circuit block, which is suitable to generate, following a control signal from said comparator circuit block, an enable/disable signal for said electronic interruption circuit. 8. The power supply device, according to previous claims, characterized in that said second current of the pulsed type, whose pulse amplitude is equal to the amplitude of said first current and whose pulse duration can be adjusted by said electronic control circuit. 9. The power supply device, according to one or more of the previous claims, characterized in that said electronic adjustment stage comprises second electronic means, which are electrically connected to said first electronic means and are suitable to generate control signals for said first electronic means in order to limit to a predefined maximum threshold the amplitude of the pulses of said second current. 10. A power supply device, according to one or more of the previous claims, characterized in that said electronic adjustment stage comprises third electronic means which are electrically connected to said first electronic means and are suitable to increase the stability of said electronic adjustment stage. 11. The power supply device, according to claim 10, characterized in that said third electronic means are capable to adjust the slope of the rising/falling edges of the pulses of said second current. 12. A low-voltage electronic residual current circuit breaker, characterized in that it comprises a power supply device, according to one or more of claims 1 to 11.

Inventors: BRANDONISIO SALVATORE, BRANDONISIO, SALVATORE
Applicants: ABB SERVICE SRL, BRANDONISIO SALVATORE, ABB SERVICE S.R.L., BRANDONISIO, SALVATORE
Application year: 2001
Main classification: H02H1
IPC codes: H02H1, H02H3