JP6486983B2 - Abnormality detection apparatus and abnormality detection method for induction melting furnace - Google Patents

Description

  The present invention relates to an abnormality detection apparatus and an abnormality detection method for an induction melting furnace that melts a material to be melted stored in the furnace by supplying electric power to a heating coil provided on the outer periphery of the furnace wall through an electric power supply means. About.

  Conventionally, in this type of induction melting furnace, as shown in Patent Document 1 below, the melt temperature is set so that the material to be melted is in a shelf-suspended state, and heating is continued to prevent the furnace wall from being damaged. There has been known a detection device that detects a rise by a temperature sensor embedded in a refractory material having a furnace body structure, and further detects a leakage accident by connecting the temperature sensor to a leakage detection antenna.

JP-A-6-82170

  Here, in the induction melting furnace, the inside of the refractory material where the temperature sensor is installed has a coil holding lining, and the coil holding lining is provided with a water-cooled heating coil.

  Therefore, in such a conventional detection device, the temperature sensor and the vicinity thereof are cooled, so that it is difficult to detect an excessive temperature rise caused by hanging the shelf.

  In particular, in recent years, the combination of a voltage source inverter and a series resonant load has been applied more than the conventional combination of a current source inverter and a parallel resonant load. Full power can be applied. For this reason, the combination of such voltage source inverter and series resonant load is effective in that only the periphery of the furnace wall of the melted material is melted and the center of the melted material is not melted and it is easy to generate a shelf-hanging case. New solutions are desired.

  In view of the above circumstances, an object of the present invention is to provide an abnormality detection device and an abnormality detection method for an induction melting furnace of an induction melting furnace that can easily and reliably detect an abnormality such as a shelf hanging state. To do.

An abnormality detection apparatus for an induction melting furnace according to a first aspect of the present invention is a resonant circuit in which a forward converter and an inverse converter in which first and second switching elements operate alternately are provided in a heating coil provided on the outer periphery of the furnace wall. The power to be melted stored in the furnace by supplying power through a power supply means comprising a power conversion unit that constitutes a control signal generation unit that generates control signals for the first and second switching elements. An apparatus for detecting an abnormality in an induction melting furnace for melting a material,
A load impedance calculation unit for calculating a load impedance from a supply state of power to the heating coil;
A load resonance frequency calculation unit that calculates a load resonance frequency from a supply state of power to the heating coil, and the load impedance time-dependent change calculated by the load impedance calculation unit and the load resonance frequency calculation unit. The case where there is no change with time of the load resonance frequency is detected as an abnormality.

  According to the abnormality detection apparatus for the induction melting furnace of the first invention, the inventors of the present invention, who are pioneers and experts of the induction melting furnace, repeat the diligent test research, and when the shelf hanging state proceeds, the induction melting furnace As the leakage inductance, which is the inductance of the reactor, does not change, the resonance frequency is fixed, and the molten material at the bottom of the furnace and the melted material at the shelf at the top of the furnace do not change, so that the load impedance is almost fixed.

  Based on this knowledge, paying attention to the change with time of load impedance and the change with time of load resonance frequency, by detecting that there is no change in both of these as abnormal, without using a temperature sensor that is difficult to detect, etc. Abnormalities such as a shelf hanging state can be reliably detected with a simple configuration.

The abnormality detection device for an induction melting furnace of the second invention is the first invention,
The load resonance calculated by the load resonance frequency calculation unit at a constant sampling cycle when the previous value and the current value of the load impedance calculated by the load impedance calculation unit at a constant sampling cycle are within the load impedance determination threshold value An abnormality is detected when the previous value of the frequency and the current value are within the load resonance frequency determination threshold value, and the change with time of the load impedance and the change with time of the load resonance frequency are not both. To do.

  According to the abnormality detection apparatus for an induction melting furnace of the second invention, the previous value and the current value of the load impedance in a constant sampling period (for example, every one minute) are within the load impedance determination threshold value, and the constant sampling period If the previous value and current value of the load resonance frequency (for example, in increments of 1 minute) are within the load resonance frequency determination threshold, it is abnormal if there is no change in load impedance over time and change in load resonance frequency over time By detecting this, it is possible to easily and reliably detect an abnormality such as a shelf hanging condition.

The abnormality detection apparatus for an induction melting furnace of the third invention is the first invention,
The amount of change over time of the load impedance calculated by the load impedance calculation unit is within a load impedance determination threshold, and the amount of change over time of the load resonance frequency calculated by the load resonance frequency calculation unit is the load. An abnormality is detected when the change in the load impedance and the change in the load resonance frequency with time are not detected when the resonance frequency is within the resonance frequency determination threshold value.

  According to the abnormality detection apparatus for an induction melting furnace of the third aspect of the invention, the amount of change with time of the load impedance in the predetermined time is within the load impedance determination threshold, and the amount of change with time of the load resonance frequency in the predetermined time is the load resonance frequency determination threshold. If there is no change with time in the load impedance and change with time in the load resonance frequency, an abnormality is detected easily and reliably, such as a shelf-suspended condition. can do.

According to a fourth aspect of the present invention, there is provided a method for detecting an abnormality in an induction melting furnace comprising a heating coil provided on an outer periphery of a furnace wall, a forward converter and an inverse converter in which the first and second switching elements are alternately operated. The power to be melted stored in the furnace by supplying power through a power supply means comprising a power conversion unit that constitutes a control signal generation unit that generates control signals for the first and second switching elements. An abnormality detection method for an induction melting furnace for melting a material,
A change in load impedance with time calculated by a load impedance calculation unit that calculates a load impedance from a power supply state to the heating coil, and a load resonance frequency calculation that calculates a load resonance frequency from the power supply state to the heating coil The case where there is no change with time of the load resonance frequency calculated by the unit is detected as an abnormality.

  According to the abnormality detection method for the induction melting furnace of the fourth invention, when the shelf hanging state proceeds, the leakage inductance that is the inductance of the induction melting furnace does not change, so that the resonance frequency is fixed, and the molten metal and furnace at the bottom of the furnace Based on the knowledge that the load impedance is almost fixed because the melted material in the top shelf does not change, paying attention to the change over time of the load impedance and the change over time of the load resonance frequency, both of which do not change By detecting as an abnormality, it is possible to reliably detect an abnormality such as a shelf suspended state with a simple configuration without using a temperature sensor that is difficult to detect.

The whole block diagram which shows the structure of the induction melting furnace of this embodiment. Explanatory drawing which shows the content of the abnormality detection process in the induction melting furnace of FIG. Explanatory drawing which shows the content of the abnormality detection process in the induction melting furnace of FIG.

  With reference to FIG. 1, the control apparatus of the induction melting furnace in which the abnormality detection apparatus of this embodiment is mounted will be described. The induction melting furnace is for melting the material to be melted X stored in the melting furnace.

  Specifically, the induction melting furnace control device includes a power source 1, a high-voltage power receiving panel 2, a converter transformer 3, a power converter 4, a high-frequency matching device 5, an induction heating device 6, and a control circuit. 10 and a control device (controller) 100 having a function as the abnormality detection device of the present invention.

  The power conversion device 4 and the high frequency matching device 5 correspond to the power conversion unit of the present invention.

  The power source 1 is a rated AC power source and is connected to the high voltage power receiving panel 2.

  The high-voltage power receiving panel 2 is a device for energizing / stopping the power supply to the induction heating device and shutting off the power supply when a failure occurs, and includes a power fuse 2a and a circuit breaker 2b. The power fuse 2a is a means for interrupting current in the event of a short circuit accident, and the circuit breaker 2b performs an opening / closing operation associated with energization and stop of the power source.

  The transformer for converter 3 is connected to the high voltage power receiving panel 2 and adjusts so that the input voltage to the power converter 4 becomes a predetermined value.

  The power conversion device 4 is a device for generating an arbitrary high-frequency current from a commercial power supply of 50 Hz or 60 Hz, connected to the transformer 3 for the conversion device, and is a forward converter 41a, 41b that is an AC / DC converter. And inverse converters 42a and 42b, which are DC / AC converters, are controlled by an output control signal from the control circuit 10.

  Specifically, the power conversion device 4 includes diode-type forward converters 41a and 41b on the input side, IGBT-type reverse converters 42a and 42b on the output side, and each of the forward converters 41a and 41b is smoothed in series. Reactors 43a and 43b are connected, and smoothing capacitors 44a and 44b are connected in parallel to forward converters 41a and 41b.

  Further, the power conversion device 4 detects a DC voltage on the output side of the forward converters 41a and 41b and outputs a DC voltage signal (a); and a DC current signal ( b), and output values of the DC voltage detector 45 and the DC current detector 46 are output to the control circuit 10.

  Details of the control content of the power conversion device 4 by the control circuit 10 will be described later.

  The high-frequency matching device 5 is provided between the power conversion device 4 and the induction heating device 6 and improves the load power factor because the induction heating device 6 has a low power factor.

  Specifically, the high-frequency matching device 5 detects and outputs the resonance capacitors 51a and 51b, the current detector 52 that detects the output current of the high-frequency matching device 5 and outputs the output current signal (d), and the output voltage. The voltage detector 53 is configured to output a voltage signal (e).

  The induction heating device 6 generates an eddy current in the material X to be melted accommodated in the melting furnace body by energizing the heating coil 61 with a high-frequency current supplied from the power conversion device 4 and the high-frequency matching device 5. The melted material X is heated and melted by Joule heat generated between the metal materials by the eddy current.

  The control circuit 10 controls the operation / stop of the induction melting furnace, the output adjustment, and the like, and also controls the power factor detection unit that detects the output power factor as a control device of the induction melting furnace, and the IGBT inverse converters 42a and 42b. It has a function as a control signal generation part which performs.

  Specifically, the control circuit 10 includes, for example, a power factor detection unit and a PLL control unit, and the power factor detection unit outputs an output current signal (d) of the high-frequency matching device 5 that is an output value of the current detector 52. From the output voltage signal (e) of the high frequency matching device 5 that is the output value of the voltage detector 53, the output power factor of the alternating current / voltage output from the high frequency matching device 5 is calculated. In addition, the PLL control unit generates a control signal for controlling the IGBT inverse converters 42a and 42b based on the output power factor calculated by the power factor detection unit.

  The control device 100 mainly performs operations such as operation / stop of the induction furnace, adjustment of power supplied to the material X to be melted, protection to prevent damage / failure of components, etc. An anomaly is detected.

Specifically, the control device 100 has a function as a load impedance calculation unit. Load impedance [% R], in the control apparatus 100, is calculated from the output power Po and the output voltage Vo of the power converter ^{4 (% R = Vo 2 /} Po).

  Moreover, the control apparatus 100 has a function as a load resonance frequency calculation part. The load resonance frequency f is calculated as a resonance frequency in a resonance circuit formed between the matching device 5 and the heating coil 61 {f = 1 / [2π√ (LC)]}.

  Then, the control device 100 repeatedly executes the load impedance calculation process and the load resonance circuit calculation process at a constant processing cycle.

  Here, the control device 100 accumulates the calculated load impedance and load resonance frequency in chronological order.

  FIG. 2 shows time series data of the load impedance and the load resonance frequency accumulated by the control device 100.

  In FIG. 2, the horizontal axis represents the progress of dissolution, that is, the elapsed time [t], and the vertical axis represents the load impedance [% R] of the load impedance and the frequency characteristic [Hz] of the load resonance frequency.

  In FIG. 2, the circuit configuration (see FIG. 1) of the induction melting furnace of the present embodiment is a case where a resonance capacitor (51a, 51b) and a heating coil 61 are connected in series, and this is a series resonance load. It is shown as (solid line). In this case, the high frequency power is supplied from the voltage source inverter, and the load impedance in this case is r.

  On the other hand, the case where the resonance capacitors (51a, 51b) are connected in parallel to the heating coil 61 is shown as a reference in FIG. 2 as a parallel resonance load (broken line). In this case, the configuration is such that high-frequency power is supplied from the current source inverter, and the load impedance in this case is indicated as R.

  As shown in FIG. 2, normally, when there is no abnormality such as a shelf hanging state, the load resonance frequency characteristic (dashed line) is a characteristic that gradually increases from the initial stage of dissolution, and the load impedance characteristic is a parallel resonant load (dashed line). ), Low impedance (equivalent to 50% R) at the beginning of melting, high impedance (equivalent to 200% R) of the material X to be melted near the magnetic transformation point, and rated impedance (equivalent to 100% R) near the molten metal The amplitude greatly fluctuates around 100% R depending on the temperature of the melting material X.

  On the other hand, in the case of a series resonant load (solid line), it is generally 3 to 4 times larger than the rated impedance (100% r) in the vicinity of the rated molten metal at the initial stage of melting, and is increased by the temperature rise of the melted material X as the melting progresses. This is a characteristic that the impedance gradually decreases.

  Thus, normally, when there is no abnormality such as a shelf hanging state, the load resonance frequency characteristic and the load impedance characteristic (both in the case of a parallel resonance load and in the case of a series resonance load) both change continuously.

  On the other hand, according to the earnest test research conducted by the inventors of the present application, as shown in FIG. 3, when there is an abnormality such as a shelf hanging state, these continuities are impaired.

  Specifically, in contrast to the case where there is no abnormality such as a shelf hanging state shown by thin lines in FIG. 3, as shown by a thick line, when the shelf is suspended, magnetic flux concentrates on the melted portion, and the shelf hanging portion Since the effective magnetic flux does not act on the material, the load characteristic change accompanying the progress of dissolution is stagnant. That is, when the shelf is suspended, the leakage inductance, which is the inductance of the furnace, does not change, so that the resonance frequency is fixed. .

  Therefore, the control apparatus 100 for the induction melting furnace according to the present embodiment detects a case where there is no change with time in the load impedance and change with time in the load resonance frequency as abnormal.

  Whether there is a change with time is based on the fluctuation characteristics of the resonance frequency and load impedance in the normal state, comparing the stagnation status of the resonance frequency and load impedance every unit time, and the discontinuity of fluctuation characteristics of the resonance frequency and load impedance. Although it may be actually connected by detection, it is desirable to detect by any of the following processes.

  As a first detection processing method, the induction melting furnace control device 100 has the same value as the previous value and the current value of the load impedance in a certain sampling period (for example, every one minute), that is, within the load impedance determination threshold value. In addition, a case where the previous value and the current value of the load resonance frequency in a certain sampling period (for example, every one minute) are equal, that is, within the load resonance frequency determination threshold is detected as an abnormality.

  As a result, it is possible to easily and reliably detect an abnormality such as a shelf hanging state. As a second detection processing method, a case where the amount of change with time of the load impedance in the predetermined time is within the load impedance determination threshold value and the amount of change with time of the load resonance frequency in the predetermined time is within the load resonance frequency determination threshold. Detect as abnormal.

  Also in this case, an abnormality such as a shelf hanging state can be specifically and easily detected.

  As described above in detail, according to the abnormality detection apparatus for the induction melting furnace of the present embodiment, paying attention to the change with time of the load impedance and the change with time of the load resonance frequency, the case where both of them do not change is regarded as abnormal. By detecting, it is possible to reliably detect an abnormality such as a shelf hanging state with a simple configuration without using a temperature sensor that is difficult to detect.

  In this embodiment, the shelf hanging state is described as an example as described above, but the abnormality is not limited to this, and both the change with time of the load impedance and the change with time of the load resonance frequency change. If there is not, for example, the control device 100 stores the load impedance change collected in the normal melting work, and if this is compared with the current load impedance change, Anomaly detection may be performed.

DESCRIPTION OF SYMBOLS 1 ... Power supply, 2 ... High voltage receiving board, 3 ... Transformer for conversion devices, 4 ... Power conversion device, 5 ... High frequency matching device, 6 ... Induction heating device, 10 ... Control circuit (control signal production | generation part), 16 ... (gamma) Control circuit (phase difference detection unit), 41a, 41b ... diode type forward converter, 42a, 42b ... IGBT type reverse converter, 61 ... heating coil, 100 ... control device (abnormality detection device, load impedance calculation unit, resonance frequency) Calculation part), X ... material to be dissolved.

Claims (4)

The heating coil provided on the outer periphery of the furnace wall includes a power converter in which a forward converter and an inverse converter in which the first and second switching elements operate alternately constitute a resonant circuit, the first and first 2 An abnormality detection apparatus for an induction melting furnace that melts a material to be melted housed in a furnace by supplying power via a power supply means that includes a control signal generation unit that generates a control signal for a switching element. And
A load impedance calculation unit for calculating a load impedance from a supply state of power to the heating coil;
A load resonance frequency calculation unit for calculating a load resonance frequency from a supply state of power to the heating coil,
An induction melting furnace that detects a case where there is no change with time in the load impedance calculated by the load impedance calculation unit and change with time in the load resonance frequency calculated by the load resonance frequency calculation unit. Anomaly detection device. In the induction melting furnace abnormality detection device according to claim 1,
The load resonance calculated by the load resonance frequency calculation unit at a constant sampling cycle when the previous value and the current value of the load impedance calculated by the load impedance calculation unit at a constant sampling cycle are within the load impedance determination threshold value An abnormality is detected when the previous value of the frequency and the current value are within the load resonance frequency determination threshold value, and the change with time of the load impedance and the change with time of the load resonance frequency are not both. An abnormality detection device for induction melting furnace. In the induction melting furnace abnormality detection device according to claim 1,
The amount of change over time of the load impedance calculated by the load impedance calculation unit is within a load impedance determination threshold, and the amount of change over time of the load resonance frequency calculated by the load resonance frequency calculation unit is the load. An abnormality detection apparatus for an induction melting furnace, wherein an abnormality is detected when the change in the load impedance and the change in the load resonance frequency with time are both absent when the resonance frequency is within a resonance frequency determination threshold. The heating coil provided on the outer periphery of the furnace wall includes a power converter in which a forward converter and an inverse converter in which the first and second switching elements operate alternately constitute a resonant circuit, the first and first 2 An abnormality detection method for an induction melting furnace that melts a material to be melted stored in the furnace by supplying power via a power supply means that includes a control signal generation unit that generates a control signal for the switching element. And
A change in load impedance with time calculated by a load impedance calculation unit that calculates a load impedance from a power supply state to the heating coil, and a load resonance frequency calculation that calculates a load resonance frequency from the power supply state to the heating coil An abnormality detection method for an induction melting furnace, wherein a case where there is no change with time in the load resonance frequency calculated by the unit is detected as an abnormality.