METHOD FOR DETECTING AN ELECTRIC ARC IN A RESISTIVE HEATING SYSTEM

Abstract

METHOD FOR DETECTING AN ELECTRIC ARC IN A RESISTIVE HEATING SYSTEM The present description relates to a method for detecting an electric arc in an electric heating system comprising at least one electric heating resistor comprising determining that the number of changes in sign of the filtered time derivative of the electrical power supplied to the electric heating resistor is greater than a first threshold. Figure for abstract: Fig. 1

Description

Title of the invention: METHOD FOR DETECTING AN ELECTRIC ARC IN A RESISTIVE HEATING SYSTEM Technical field

[0001] The present description relates generally to methods for detecting an electric arc in a resistive heating system, in particular for a furnace. Prior art

[0002] A furnace for controlled crystallization of a semiconductor material, in particular silicon used for photovoltaic applications, comprises a crucible containing the semiconductor material and surrounded by electrical heating resistors. The circulation of a current in each electrical resistor causes the emission of heat by the Joule effect.

[0003] Depending on the intended application, the intensity of the current flowing through each electrical heating resistor may be high. There is a risk of an electric arc forming between an electrical heating resistor and another element of the oven. It is desirable to detect the occurrence of an electric arc to stop the current supply to the electrical heating resistor and limit the deterioration of the electrical heating resistor and / or another element of the oven.

[0004] When the electric heating resistors are powered by a three-phase current power supply system, the detection of an electric arc can be carried out from the comparison of the three phases of the current. However, for certain applications, it is desirable for the electric heating resistors to each be powered by a single-phase current. The conventional methods for detecting an electric arc cannot then be implemented. Summary of the invention

[0005] One embodiment overcomes all or part of the drawbacks of known methods for detecting an electric arc in a resistive heating system.

[0006] According to one embodiment, the detection method is compatible with a power supply to the heating system by a single-phase current.

[0007] According to one embodiment, the method allows rapid detection of the electric arc from the start of its formation.

[0008] One embodiment provides a method for detecting an electric arc in an electric heating system comprising at least one electric heating resistor comprising determining that the number of sign changes of the filtered time derivative of the electrical power supplied to the electric resistor heating is greater than a first threshold.

[0009] According to one embodiment, the method comprises interrupting the electrical power supply to the electrical heating resistor when the number of changes in sign of the filtered time derivative of the electrical power supplied to the electrical heating resistor is greater than the first threshold or greater than a second threshold, strictly greater than the first threshold.

[0010] According to one embodiment, the method comprises determining the time derivative of the electrical power supplied to the electrical heating resistor and determining the filtered time derivative by filtering the time derivative.

[0011] According to one embodiment, the method comprises determining values ​​of the electrical power supplied to the electrical heating resistor and determining a new value of the time derivative of the electrical power supplied to the electrical heating resistor from the last two determined values ​​of the electrical power supplied to the electrical heating resistor.

[0012] According to one embodiment, the method comprises determining a new value of the filtered time derivative equal to the last determined value of the time derivative when the last determined value of the time derivative is greater than a derivative value threshold, and equal to 0 when the last determined value of the time derivative is less than the derivative value threshold.

[0013] According to one embodiment, the method comprises determining a new value of a filtered and corrected time derivative equal to the last determined value of the filtered time derivative when the last determined value of the filtered time derivative is different from 0, and equal to the last determined value of the filtered and corrected time derivative when the last determined value of the filtered time derivative is equal to 0.

[0014] According to one embodiment, the method comprises determining a logic value at a first logic state when the product of the last two determined values ​​of the filtered and corrected time derivative is strictly negative and at a second logic state, different from the first logic state, when the product of the last two determined values ​​of the filtered and corrected time derivative is positive or zero.

[0015] According to one embodiment, the method comprises determining a new value of a counter equal to the last determined value of the counter to which is added a first strictly positive increment when the last determined logic value is in the first logic state, possibly a second strictly positive increment and strictly less than the first increment when the last determined logic value is in the second logic state and the last determined value of the filtered time derivative is different from zero, or a third strictly negative increment when the last determined logic value is in the second logic state and the last determined value of the filtered time derivative is equal to zero, and including the detection of an electric arc when the determined value of the counter is greater than the first threshold.

[0016] An embodiment also provides a system for detecting an electric arc in an electric heating system comprising at least one electric heating resistor configured to determine whether the number of changes in sign of the filtered time derivative of the electric power supplied to the electric heating resistor is greater than a first threshold.

[0017] An embodiment also provides an oven comprising an electric heating system comprising at least one electric heating resistor and a system for detecting an electric arc in the electric heating system as defined previously.

[0018] According to one embodiment, the oven comprises a system for supplying electricity to the electric heating resistor by a single-phase current. Brief description of the drawings

[0019] These characteristics and advantages, as well as others, will be explained in detail in the following description of particular embodiments given without limitation in relation to the attached figures among which:

[0020] [Fig.l] represents, in a partial and schematic manner, an embodiment of a crystallization furnace;

[0021] [Fig.2] represents, in the form of a block diagram, an embodiment of a method for detecting an electric arc;

[0022] [Fig.3] represents a curve of the evolution of the electrical power supplying an electrical heating resistor of the oven of [Fig.l] as a function of time;

[0023] [Fig.4] represents a curve of the evolution of the time derivative of the electrical power of [Fig.3] as a function of time;

[0024] [Fig.5] represents a curve of the evolution of the time derivative of the electrical power of [Fig.3] as a function of time after filtering; and

[0025] [Fig.6] represents an evolution curve of a counter used during the implementation of the embodiment of the method illustrated in [Fig.2]. Description of the embodiments

[0026] The same elements have been designated by the same references in the different figures. In particular, the structural and / or functional elements common to the different embodiments may have the same references and may have identical structural, dimensional and material properties.

[0027] For the sake of clarity, only the steps and elements useful for understanding the modes of embodiments described have been shown and are detailed. In particular, the structure of an oven comprising an electric heating system is known and is not described in detail.

[0028] In the following description, when reference is made to absolute position qualifiers, such as the terms "front", "back", "top", "bottom", "left", "right", etc., or relative position qualifiers, such as the terms "above", "below", "upper", "lower", etc., or to orientation qualifiers, such as the terms "horizontal", "vertical", etc., reference is made unless otherwise specified to the orientation of the figures or to an oven in a normal position of use.

[0029] Unless otherwise specified, the expressions "about", "approximately", "substantially", and "of the order of" mean to within 10%, preferably to within 5%.

[0030] [Fig.l] shows, in a partial and schematic manner, an embodiment of a crystallization furnace 10. The furnace 10 comprises an enclosure 12 in which a crucible 14 is arranged. The enclosure 12 may be a water-cooled enclosure in which a controlled atmosphere can be maintained. The crucible 14 may be arranged in a support 16 which is a good conductor of heat. The furnace 10 further comprises electrical heating resistors 18 surrounding the crucible 14, in particular above the crucible 14, below the crucible 14, and around the side wall of the crucible 14. Thermally insulating walls 20 delimit, in the enclosure 12, a heating zone 22 containing the crucible 14 and the heating resistors 18.

[0031] The oven 10 comprises an electrical power supply system 24 for the heating resistors 18. The electrical power supply system 24 comprises in particular electrical transformers connected to the mains and switches for activating or interrupting the power supply to each heating resistor 18 independently of one another. The electrical power supply system 24 further comprises sensors, in particular current intensity sensors and voltage sensors for determining the instantaneous electrical power supplied to each heating resistor 18. The oven 10 further comprises a processing module 26 configured to control the operation of the oven 10. The processing module 26 comprises, for example, a processor.The processing module 26 is connected to the electrical power supply system 24 and is notably configured to control the activation or interruption of the power supply of each heating resistor 18 by the electrical power supply system 24.

[0032] In operation, an electric arc may form between the heating resistors 18 and components of the oven 10 normally connected to a low reference potential, for example the earth. This may be the case for example when there is not enough space between a heating resistor 18 and the thermally insulating walls 20, when there is contact between two components of the heating resistor 18, or when the charge placed in the crucible 15 is incorrectly positioned in the furnace and comes close to one of the heating resistors 18. When an electric arc forms, it can cause damage to parts of the furnace 10. In addition, when the electric arc is self-sustaining, the damage to the furnace 10 can be significant, or even lead to a compromise in the operational safety of the furnace 10.

[0033] There is therefore a need to quickly detect the formation of an electric arc, in particular to interrupt the electrical supply to the heating resistors.

[0034] According to one embodiment, the electrical power supply system 24 is configured to supply each heating resistor 18 with a single-phase current. According to one embodiment, the electrical power supply system 24 comprises a single-phase output electrical transformer connected to each heating resistor 18. A single-phase output transformer advantageously has a reduced size and a reduced cost compared to a two-phase output or three-phase output transformer.

[0035] According to one embodiment, the processing module 26 is configured to determine the evolution of the electrical power supplied by the electrical power supply system 24 to each heating resistor 18 as a function of time, in particular from the signals supplied by the sensors of the electrical power supply system 24. The processing module 26 is further configured to determine the evolution of the time derivative of the electrical power supplied by the electrical power supply system 24 to each heating resistor 18 as a function of time.

[0036] [Fig.2] represents, in the form of a block diagram, an embodiment of a method for detecting an electric arc implemented by the processing module 26. According to one embodiment, the detection method is implemented by the processing module 26 for each heating resistor 18.

[0037] In step 30, the processing module 26 determines a new value Pn of the electrical power P supplied by the electrical power system 24 to the heating resistor 18, where n is an integer greater than 1. According to one embodiment, the processing module 26 is connected to a sensor of the voltage supplied by the electrical power system 24 and to a sensor of the intensity of the current supplied by the electrical power system 24 and determines the successive values ​​of the electrical power Pn at a sampling period Tsamp. The sampling period Tsamp can be between 0.1 s and 10 s, and is for example equal to 1 s. The lower the sampling period Tsamp, the better the detection, but the greater the computing power of the processing module 26 must be. The method continues in step 32.At the first execution of step 30, the method continues at step 32 when two successive values ​​of the electrical power P are determined. At each subsequent execution of step 30, the method continues at step . 32 as soon as a new value Pn of the electric power P is determined.

[0038] In step 32, the processing module 26 determines a new value P'n of the time derivative P' of the electrical power supplied by the electrical power system 24 to the heating resistor 18. According to one embodiment, the new value P'n of the time derivative P' is determined from the last value Pn of the electrical power and the penultimate Pn i value of the electrical power determined in step 30. According to one embodiment, the new value P'n of the time derivative P' is equal to the difference between the last determined value Pn of the electrical power P and the penultimate determined value Pn4 of the electrical power P divided by the sampling period Tsamp. The method continues in step 34.

[0039] In step 34, the processing module 26 determines a filtered time derivative P'f obtained by filtering the time derivative P' of the electrical power supplied by the electrical power supply system 24 to the heating resistor 18. According to one embodiment, the absolute value of the new value P'n of the time derivative P' determined in step 32 is compared to a threshold TH_P' of the derivative value. In the case where the absolute value of the new value P'n of the time derivative P' is less than the threshold TH_P' of the derivative value, the new value P'fn of the filtered time derivative P'f is equal to 0. In the case where the absolute value of the new value P'n of the time derivative P' is greater than the threshold TH_P' of the derivative value, the new value P'fn of the filtered time derivative P'f is equal to the new value P'n of the time derivative P' determined in step 32.According to one embodiment, the derivative value threshold TH_P' is in the range from 0.01 kW / s to 100 kW / s, and is for example equal to 0.4 kW / S. According to one embodiment, the derivative value threshold TH_P' can be parameterized in particular as a function of the power of the furnace. Step 34 advantageously makes it possible to discard values ​​of the filtered time derivative P'f which correspond to normal variations in the electrical power P. The method continues at step 36.

[0040] In step 36, the processing module 26 determines a filtered and corrected time derivative P'f2 obtained from the filtered time derivative P'f of the electrical power supplied by the electrical power supply system 24 to the heating resistor 18. According to one embodiment, if the new value P'fn of the filtered time derivative P'f is different from zero, then the new value P'f2n of the filtered and corrected time derivative P'f2 is equal to the new value P'fn of the filtered time derivative P'f determined in step 34. If the new value P'fn of the filtered time derivative P'f is equal to zero, then the new value P'f2n of the filtered and corrected time derivative P'f2 is equal to the previous value P'I,, । of the intermediate time derivative P'f2 determined in the previous execution of step 36. Step 36 allows to prevent the new value P'f2n of the filtered and corrected time derivative P'f2 from being equal to 0 as soon as a previously determined value of the filtered time derivative P'f is different from 0. The method continues at step 38.

[0041] In step 38, the processing module 26 determines whether the filtered time derivative P'f has changed sign. According to one embodiment, the processing module 26 determines a new logical value Detectn of a logical data item Detect. The processing module 26 sets the new logical value Detectn to the logical value "True" when the filtered time derivative P'f has changed sign and sets the logical data item Detectn to the logical value "False" when the filtered time derivative P'f has not changed sign. According to one embodiment, if the product between the last value P'f2n of the filtered and corrected time derivative P'f2 and the penultimate value P'f2n_i of the filtered and corrected time derivative P'f2 is positive, then the processing module 26 sets the new logical value Detectn to the logical value "False", and, if the product between the last value P'f2n of the filtered and corrected time derivative P'f2 and the penultimate value P'f2n.i of the filtered and corrected time derivative P'f2 is negative, then the processing module 26 sets the new logical value Detectn to the logical value "True". The method continues at step 40.

[0042] In step 40, the processing module 26 determines a new value CPTn of a CPT counter from the last value CPTn i of the CPT counter determined in the previous execution of step 40. The CPT counter is initially set to zero. If the new logic value Detectn determined in step 38 is "True", the last value CPTn i of the CPT counter is increased by a positive increment ACPT1. According to one embodiment, the increment ACPT1 is in the range from 1 to 100, and is for example equal to 10. Furthermore, if the new value P'fn of the filtered time derivative P'f determined in step 34 is different from zero, a positive increment ACPT2, strictly less than the increment ACPT1, is added to the last value CPT„ । of the counter CPT, and if the new value P'fn of the filtered time derivative P'f determined in step 34 is equal to zero, a negative increment ACPT3 is added to the last value CPT„ । of the counter CPT.The new value CPTn of the counter CPT is therefore equal to the last value CPTn i of the counter CPT determined at the previous execution of step 40 to which the increment ACPT1 is possibly added and to which the increment ACPT2 or the increment ACPT3 is added. However, if the result is negative, then the new value CPTn of the counter CPT is equal to zero. According to one embodiment, the increment ACPT2 is strictly less than the increment ACPT1 and is in the range from 0 to 10, and is for example equal to 0. According to one embodiment, the increment ACPT3 is in the range from -10 to -1, and is for example equal to -1. The use of the negative increment ACPT3 makes it possible to bring the counter CPT back to 0 at a slow rate, in particular in the case where the counter CPT has been increased by one-off events. not corresponding to an electric arc. The use of the positive increment ACPT2, strictly lower than the increment ACPT1, allows the CPT counter to continue increasing at a slow rate when there is no change in sign of the time derivative P' but the value P'n of the time derivative remains higher than the threshold TH_P' of the derivative value.

[0043] The method continues at step 42.

[0044] In step 42, the processing module 26 determines whether the new value CPTn of the CPT counter determined in step 40 has exceeded a first counter threshold TH1_CPT. According to one embodiment, the first counter threshold TH1_CPT is in the range from 10 to 1000, and is for example equal to 40. If the new value CPTn of the CPT counter has exceeded the first counter threshold TH1_CPT (Y), the method continues in step 44. If the new value CPTn of the CPT counter has not exceeded the first counter threshold TH1_CPT (N), the method returns to step 30.

[0045] In step 44, the processing module 26 determines whether the new value CPTn of the counter CPT determined in step 40 has exceeded a second counter threshold TH2_CPT, strictly greater than the first counter threshold TH1_CPT. According to one embodiment, the second counter threshold TH2_CPT is in the range from 10 to 2000, and is for example equal to 200. If the new value CPTn of the counter CPT has not exceeded the second counter threshold TH2_CPT (N), the method continues in step 46. If the new value CPTn of the counter CPT has exceeded the second counter threshold TH2_CPT (Y), the method continues in step 48.

[0046] In step 46, which corresponds to the case where the new value CPTn of the counter CPT has exceeded the first counter threshold TH1_CPT but has not exceeded the second counter threshold TH2_CPT, the processing module 26 performs an action corresponding to a risk of formation of an electric arc. According to one example, the processing module 26 issues an alert on a human-machine interface. The method returns to step 30.

[0047] In step 48, which corresponds to the case where the new value CPTn of the counter CPT has exceeded the second counter threshold TH2_CPT, the processing module 26 performs an action corresponding to the detection of the occurrence of an electric arc. According to one example, the processing module 26 controls the electrical power supply system 24 to interrupt the electrical power supply to the heating resistor 18. According to one example, the processing module 26 issues an alert on a human-machine interface. The method returns to step 30.

[0048] Alternatively, the method may implement only one counter threshold. In this case, step 44 is replaced by step 46 and step 48 is not present.

[0049] Figures 3, 4, 5, and 6 were obtained for a real operating phase of the furnace 10 during which an electric arc formed in a heating resistor 18 of the furnace 10 between times t1, equal to 17707 s, and t2 equal to 19420 s. method for detecting an electric arc according to the embodiment illustrated previously in relation to [Fig.2] has been implemented. The derivative value threshold TH_P' is equal to 0.4. The increment ACPT1 is equal to 10. The increment ACPT2 is equal to 0. The increment ACPT3 is equal to -1. The first counter threshold TH1_CPT is equal to 40 and the second counter threshold TH2_CPT is equal to infinity so as not to cause the power supply to the heating resistor 18 to be stopped.

[0050] [Fig. 3] represents a curve of evolution as a function of time of the electrical power P supplied by the electrical supply system 24 to the heating resistor 18 during an operating phase of the furnace 10 during which an electric arc occurred.

[0051] [Fig.4] represents a curve of evolution as a function of time of the time derivative P' corresponding to the curve of evolution of the power P of [Fig.3].

[0052] [Fig.5] represents a curve of evolution as a function of time of the filtered time derivative P'f obtained from the curve of evolution as a function of time of the time derivative P' of [Fig.4].

[0053] [Fig.6] represents a curve of evolution of the CPT counter used during the implementation of the embodiment of the method illustrated in [Fig.2]. As can be seen in [Fig.6], the CPT counter exceeds the first counter threshold TH1_CPT shortly after tl, precisely at 17715 s. The detection of the formation of an electric arc is therefore rapid. Furthermore, if the second counter threshold TH2_CPT were taken equal to 200, the electrical supply of the heating resistor 18 would have been interrupted shortly after time tl, precisely at 17737 s.

[0054] Various embodiments and variations have been described. Those skilled in the art will understand that certain features of these various embodiments and variations could be combined, and other variations will occur to those skilled in the art. Finally, the practical implementation of the described embodiments and variations is within the ability of those skilled in the art from the functional indications given above.

Claims

Claims

1. A method of detecting an electric arc in an electric heating system comprising at least one electric heating resistor (18) comprising determining that the number of changes in sign of the filtered time derivative of the electrical power supplied to the electric heating resistor (18) is greater than a first threshold.

2. A method according to claim 1, comprising interrupting the power supply to the electric heating resistor (18) when the number of changes in sign of the filtered time derivative of the electric power supplied to the electric heating resistor (18) is greater than the first threshold or greater than a second threshold, strictly greater than the first threshold.

3. A method according to claim 1 or 2, comprising determining the time derivative of the electrical power supplied to the electrical heating resistor (18) and determining the filtered time derivative by filtering the time derivative.

4. A method according to any one of claims 1 to 3, comprising determining values ​​of the electrical power supplied to the electrical heating resistor (18) and determining a new value of the time derivative of the electrical power supplied to the electrical heating resistor (18) from the last two determined values ​​of the electrical power supplied to the electrical heating resistor (18).

5. The method of claim 4, comprising determining a new value of the filtered time derivative equal to the last determined value of the time derivative when the last determined value of the time derivative is greater than a derivative value threshold, and equal to 0 when the last determined value of the time derivative is less than the derivative value threshold.

6. The method of claim 5, comprising determining a new value of a filtered and corrected time derivative equal to the last determined value of the filtered time derivative when the last determined value of the filtered time derivative is different from 0, and equal to the last determined value of the filtered and corrected time derivative when the last determined value of the filtered time derivative is equal to 0.

7. A method according to claim 6, comprising determining a logical value to a first logical state when the product of the last two determined values ​​of the filtered and corrected time derivative is strictly negative and to a second logical state, different from the first logical state, when the product of the last two determined values ​​of the filtered and corrected time derivative is positive or zero.

8. Method according to claim 7, comprising the determination of a new value of a counter equal to the last determined value of the counter to which is added a first strictly positive increment when the last determined logic value is in the first logic state, possibly a second strictly positive increment and strictly less than the first increment when the last determined logic value is in the second logic state and the last determined value of the filtered time derivative is different from zero, or a third strictly negative increment when the last determined logic value is in the second logic state and the last determined value of the filtered time derivative is equal to zero, and comprising the detection of an electric arc when the determined value of the counter is greater than the first threshold.

9. System for detecting (26) an electric arc in an electric heating system comprising at least one electric heating resistor (18) configured to determine whether the number of changes in sign of the filtered time derivative of the electric power supplied to the electric heating resistor (18) is greater than a first threshold.

10. Oven comprising an electric heating system comprising at least one electric heating resistor (18) and a system (26) for detecting an electric arc in the electric heating system according to claim 9.

11. Oven according to claim 10, comprising an electrical power supply system (24) of the electrical heating resistor (18) by a single-phase current.

Images