JP2018060658A - Electric power unit and induction heating apparatus and control method of electric power unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power unit capable of detecting unbalance of AC output currents from multiple inverse conversion units more flexibly and reliably, while enhancing protection of elements included in these inverse conversion units, and to provide an induction heating apparatus and a control method of the electric power unit.SOLUTION: The electric power unit 2 of an induction heating apparatus 1 includes a forward conversion unit 10, an inverse conversion section 20 including multiple inverse conversion units 21a-21d, a current detector 30 for detecting AC corresponding currents corresponding, respectively, to the AC output currents of the inverse conversion units 21a-21d, a current voltage conversion section 40 for converting the AC corresponding currents of the inverse conversion units 21a-21d, respectively, into DC voltages, and an unbalance detector 50 for detecting unbalance of the AC output currents of the inverse conversion units 21a-21d, respectively, based on the DC voltages of the inverse conversion units 21a-21d, respectively, and the average value of these DC voltages, and outputting a stop signal for stopping operation of the forward conversion unit 10 and the inverse conversion section 20, when unbalance was detected.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a power supply device, an induction heating device, and a control method for the power supply device.

  As a heating method in heat treatment of steel materials, induction heating is used in which high-frequency AC power is supplied to the heating coils and the steel materials are heated by an induction current induced in the steel materials placed in a magnetic field formed by the heating coils. In a power supply device that supplies AC power to the heating coil, generally, low-frequency AC power supplied from a commercial power supply is once converted into DC power, and DC power is converted back into high-frequency AC power, thereby heating High frequency AC power supplied to the coil is generated.

  Depending on the AC power supplied to the heating coil, a plurality of inverse conversion units may be used in parallel.For example, due to differences in the wiring inductance of each of the plurality of inverse conversion units or individual differences in the elements used. Thus, an imbalance may occur in the AC output current of each of the plurality of inverse conversion units. If an imbalance occurs in the AC output current of each of the plurality of inverse conversion units, the elements included in these inverse conversion units may be destroyed.

  In the power supply device described in Patent Document 1, current transformers are installed in the output wirings of the plurality of inverse conversion units, and a plurality of current transformers corresponding to the AC output currents of the plurality of inverse conversion units are provided. The AC corresponding current of each of the inverse conversion units is detected. Then, the AC-compatible currents of each of the plurality of inverse conversion units are passed through a common resistor, and the current imbalance among the AC-compatible currents of each of the plurality of inverse conversion units is such that the combination of the currents flowing through the resistors becomes zero. One of the opposing combinations in a set of detection is passed through the resistor in reverse phase.

  When the AC output current of each of the plurality of inverse conversion units is unbalanced, the synthesis of the current flowing through the resistor does not become zero, and a potential difference occurs between both ends of the resistor. Based on this potential difference, an imbalance of the AC output currents of each of the plurality of inverse conversion units is detected, and when the imbalance is detected, the operation of the power supply device is stopped. As described above, it is avoided that the elements included in these inverse conversion units are destroyed due to the unbalance of the AC output currents of the plurality of inverse conversion units.

Japanese Patent No. 5058748

  In the power supply device described in Patent Document 1, one of the opposing combinations of a pair of combinations that detect current imbalance among the AC-compatible currents of each of the plurality of inverse conversion units so that the combined current flowing through the resistors becomes zero Are flowed through resistors in reverse phase, and the number of inverse conversion units is basically limited to an even number. In addition, even if there is an imbalance in the AC output current of each group of inverse conversion units in which AC-compatible current flows through the resistors in the same phase, the composition of the current flowing through the resistors may be zero. In such a case, there is a possibility that the imbalance of the AC output current of each of the inverse conversion units is not detected.

  The present invention has been made in view of the above-mentioned circumstances, and can detect the imbalance of the AC output current of each of the plurality of inverse conversion units more flexibly and reliably, and protect the elements included in these inverse conversion units. It is an object of the present invention to provide an enhanced power supply device, induction heating device, and power supply device control method.

  A power supply device according to one aspect of the present invention includes a forward conversion unit that converts alternating current power supplied from an alternating current power source into direct current power, and a plurality of reverses that respectively reversely convert direct current power supplied from the forward conversion unit into alternating current power. A reverse conversion unit including a conversion unit; a current detection unit that detects an AC-compatible current of each of the plurality of reverse conversion units corresponding to an AC output current of each of the plurality of reverse conversion units; and a plurality of the reverse conversion units. A current-voltage converter for converting the AC-compatible current into a DC voltage; the DC voltage of each of the plurality of inverse conversion units; and the AC output current of each of the plurality of inverse conversion units based on an average value of these DC voltages When an imbalance is detected, an stop signal for stopping the operation of the forward conversion unit and the reverse conversion unit is output. Comprises a balance detector, the.

  Moreover, the induction heating apparatus of 1 aspect of this invention is equipped with the said power supply device and the heating coil which induction-heats a to-be-heated part with the alternating current power supplied from the said reverse conversion part of the said power supply device.

  The control method of the power supply device according to one embodiment of the present invention includes a forward conversion unit that converts alternating current power supplied from an alternating current power source into direct current power, and reverses the direct current power supplied from the forward conversion unit to alternating current power. And a reverse conversion unit including a plurality of reverse conversion units to be converted, and a method for controlling a power supply apparatus, wherein each of the plurality of reverse conversion units corresponds to an AC output current corresponding to an AC output current of each of the plurality of reverse conversion units. And converting the AC corresponding current of each of the plurality of inverse conversion units into a DC voltage, and the plurality of inverse conversions based on the DC voltage of each of the plurality of inverse conversion units and an average value of these DC voltages. When detecting an unbalance of the AC output current of each unit, and detecting an imbalance of the AC output current of each of the plurality of inverse conversion units, Serial forward transform unit and stops the operation of the inverse transform unit.

  According to the present invention, it is possible to more flexibly and reliably detect an imbalance of the AC output currents of each of the plurality of reverse conversion units, and to enhance the protection of elements included in these reverse conversion units. A method for controlling a power supply device can be provided.

It is a block diagram of an example of a power supply device and an induction heating device for explaining an embodiment of the present invention. It is a block diagram of the unbalance detection part of the power supply device of FIG. It is a flowchart of the process which the unbalance detection part of FIG. 2 performs.

  FIG. 1 shows an example of a power supply device and an induction heating device for explaining an embodiment of the present invention.

  An induction heating device 1 shown in FIG. 1 includes a power supply device 2 and a heating coil 3. The power supply device 2 includes a forward conversion unit 10 that converts AC power supplied from a commercial AC power source 4 into DC power, and an inverse conversion unit 20 that converts DC power supplied from the forward conversion unit 10 back into AC power. Have The heating coil 3 is connected to the inverse conversion unit 20 via the matching circuit 5 and the transformer 6, and inductively heats the article to be heated W with AC power supplied from the inverse conversion unit 20. The article to be heated W is a conductor, and is made of a metal such as steel.

  There are various combinations of the forward conversion unit 10. For example, there are a method in which phase control is performed by a thyristor and conversion into DC power smoothed by an LC filter, or a method in which diode rectification is performed and smoothing is performed by an LC filter by a chopper.

  The inverse transform unit 20 includes a plurality of inverse transform units, and includes four inverse transform units 21a to 21d in the illustrated example. Each of the inverse conversion units 21a to 21d includes one or more unit inverse conversion circuits of the same number.

  The unit inverse conversion circuit is configured by, for example, a full bridge circuit mainly including four power semiconductor elements capable of switching operation, and high-frequency AC power is generated by a predetermined switching operation of the four power semiconductor elements.

  The switching operation of the power semiconductor element in each unit inverse conversion circuit of each of the inverse conversion units 21a to 21d is synchronously controlled by the inverse conversion control unit 22, and basically currents having the same phase and the same amplitude are converted into the inverse conversion units 21a to 21a. 21d.

  Examples of power semiconductor elements include various power semiconductors capable of switching operation such as IGBTs (Insulated Gate Bipolar Transistors) and MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors). An element can be used, and as a semiconductor material, for example, there are a material using Si (silicon) and a material using SiC (silicon carbide).

  The power supply device 2 further includes a current detection unit 30, a current-voltage conversion unit 40, and an unbalance detection unit 50.

  The current detection unit 30 includes current transformers 31a to 31d, and detects the AC corresponding currents ia to id of the reverse conversion units 21a to 21d corresponding to the AC output currents Ia to Id of the reverse conversion units 21a to 21d.

  The current transformer 31a is provided on the output wiring 23a of the reverse conversion unit 21a. The output current 23a is used as the primary side of the current transformer 31a, and the current transformer 31a converts the AC output current Ia of the reverse conversion unit 21a flowing in the output wiring 23a. A current multiplied by the current transformation ratio of 31a flows to the secondary side of the current transformer 31a. The current flowing on the secondary side of the current transformer 31a is detected as the AC corresponding current ia of the inverse conversion unit 21a.

  In addition, when a plurality of unit inverse conversion circuits are included in the inverse conversion unit 21a, a combination of currents output from these unit inverse conversion circuits may flow on the primary side of the current transformer 31a. Alternatively, a current output from any one unit inverse conversion circuit may flow.

  Similarly, the AC corresponding current ib of the reverse conversion unit 21b is detected by the current transformer 31b provided in the output wiring 23b of the reverse conversion unit 21b, and the current transformer 31c provided in the output wiring 23c of the reverse conversion unit 21c. The AC corresponding current ic of the reverse conversion unit 21c is detected, and the AC corresponding current id of the reverse conversion unit 21d is detected by the current transformer 31d provided in the output wiring 23d of the reverse conversion unit 21d.

  The current-voltage conversion unit 40 converts the AC corresponding currents ia to id of the inverse conversion units 21 a to 21 d into DC voltages Va to Vd. The conversion from the AC-compatible current to the DC voltage is performed for each AC-compatible current. For example, the AC-compatible current may be rectified and passed through the resistor, and the voltage across the resistor may be smoothed by the capacitor. The obtained DC voltages Va to Vd of the inverse conversion units 21 a to 21 d are input to the unbalance detection unit 50.

  The unbalance detection unit 50 determines the AC output currents Ia to Id of the inverse conversion units 21a to 21d based on the DC voltages Va to Vd of the inverse conversion units 21a to 21d and the average value Vavg of these DC voltages Va to Vd. Detect imbalance.

  FIG. 2 shows a configuration of the unbalance detection unit 50.

  The unbalance detection unit 50 includes a calculation unit 51 and a comparison unit 52, and the calculation unit 51 includes an average value calculation unit 53, an upper limit value calculation unit 54, and a lower limit value calculation unit 55.

  The DC voltages Va to Vd of the inverse conversion units 21 a to 21 d obtained by the current voltage conversion unit 40 are input to the average value calculation unit 53. The average value calculator 53 calculates an average value Vavg = (Va + Vb + Vc + Vd) / 4 of the input DC voltages Va to Vd.

  The average value Vavg obtained by the average value calculation unit 53 is input to the upper limit value calculation unit 54 and the lower limit value calculation unit 55. The upper limit value calculation unit 54 and the lower limit value calculation unit 55 are allowable ranges for the DC voltages Va to Vd, and the upper limit values of ranges in which the AC output currents Ia to Id of the inverse conversion units 21a to 21d can be regarded as balanced. And a lower limit value.

Based on the average value Vavg, the upper limit calculator 54 calculates the upper limit Vhigh by multiplying the average value Vavg by a predetermined ratio, for example, as shown in the following equation.
Vhigh = Vavg × 1.2 (1)
In Formula (1), the predetermined ratio “1.2” that is applied to the average value Vavg is an example, and the ratio that is applied to the average value Vavg can be set as appropriate.

The lower limit calculator 55 also calculates the lower limit Vlow by multiplying the average value Vavg by a predetermined ratio based on the average value Vavg, for example, as shown in the following equation.
Vlow = Vavg × 0.8 (2)
In Formula (2), the predetermined ratio “0.8” to be applied to the average value Vavg is an example, and the ratio to be applied to the average value Vavg can be set as appropriate.

  The upper limit value Vhigh obtained by the upper limit value computation unit 54 and the lower limit value Vlow obtained by the lower limit value computation unit 55 are input to the comparison unit 52. The comparison unit 52 further receives DC voltages Va to Vd of the inverse conversion units 21 a to 21 d.

  The comparison unit 52 compares each of the DC voltages Va to Vd with the upper limit value Vhigh and the lower limit value Vlow, and at least one of the DC voltages Va to Vd is greater than the upper limit value Vhigh or less than the lower limit value Vlow. In this case, a stop signal is output on the assumption that the AC output currents Ia to Id of the inverse conversion units 21a to 21d are unbalanced.

  The stop signal output from the comparison unit 52 is input to the forward conversion control unit 11 and the reverse conversion control unit 22. The inverse conversion control unit 22 stops the switching operation of the power semiconductor element in the unit inverse conversion circuit of each of the inverse conversion units 21a to 21d based on the input stop signal. Thereby, the driving | operation of the reverse conversion part 20 is stopped. The operation of the forward conversion unit 10 is also stopped by the forward conversion control unit 11 to which a stop signal is input.

  As described above, when the imbalance of the AC output currents Ia to Id of the inverse conversion units 21a to 21d is detected and the imbalance of the AC output currents Ia to Id is detected, the operation of the forward conversion unit 10 and the inverse conversion unit 20 is performed. Can be prevented from destroying the power semiconductor elements of some of the inverse conversion units through which a relatively excessive current flows among the inverse conversion units 21a to 21d. The destruction of the power semiconductor element due to the destruction of the power semiconductor element of the unit can be prevented from spreading to other inverse conversion units, and the protection of the element can be enhanced.

  Preferably, each of the inverse conversion units 21a to 21d includes one unit inverse conversion circuit, in other words, preferably detects an imbalance of the AC output current of each unit inverse conversion circuit. The protection of the element can be further strengthened by detecting the imbalance of the AC output current more precisely.

  Then, by directly detecting the imbalance of the AC output currents Ia to Id of the inverse conversion units 21a to 21d based on the AC output currents Ia to Id, the imbalance of the AC output currents Ia to Id is accurately detected. can do.

  Further, the AC corresponding currents ia to id of the inverse conversion units 21a to 21d corresponding to the AC output currents Ia to Id of the inverse conversion units 21a to 21d are converted into the DC voltages Va to Vd, and the AC output currents Ia to Id are converted. By detecting the imbalance based on the DC voltages Va to Vd and the average value Vavg of the DC voltages Va to Vd, the AC output currents Ia to Id of the inverse conversion units 21a to 21d are detected for each of the inverse conversion units 21a to 21d. Can be determined to be relatively over or under. Thereby, the imbalance of the AC output current of each of the plurality of inverse conversion units can be detected flexibly without restriction on the number of inverse conversion units.

  The calculation unit 51 calculates the average value Vavg, the upper limit value Vhigh, and the lower limit value Vlow of the DC voltages Va to Vd, and the comparison unit 52 compares the DC voltages Va to Vd with the upper limit value Vhigh and the lower limit value Vlow, respectively. Are preferably processed in real time, and as long as they are processed in real time, the calculation unit 51 (average value calculation unit 53, upper limit value calculation unit 54, lower limit value calculation unit 55) and comparison unit 52 are configured by analog circuits. It may be configured by a digital circuit.

  FIG. 3 shows processing of the unbalance detection unit 50.

  The average value calculation unit 53 of the unbalance detection unit 50 calculates the average value Vavg of the DC voltages Va to Vd when the DC voltages Va to Vd of the inverse conversion units 21a to 21d are input (step S1).

  The average value Vavg obtained by the average value calculation unit 53 is input to the upper limit value calculation unit 54 and the lower limit value calculation unit 55, and the upper limit value calculation unit 54 calculates the upper limit value Vhigh (step S2a). Thus, the lower limit value Vlow is calculated (step S2b).

  The average value calculation unit 53, the upper limit value calculation unit 54, and the lower limit value calculation unit 55 are configured by analog circuits, and the upper limit value calculation unit 54 and the lower limit value calculation unit 55 are connected to the average value calculation unit 53 in parallel. Assuming that the calculation of the upper limit value Vhigh and the calculation of the lower limit value Vlow are performed in parallel, the average value calculation unit 53, the upper limit value calculation unit 54, and the lower limit value calculation unit 55 include a microprocessor, a sequencer, etc. In the case of a digital circuit using the above, the calculation of the upper limit value Vhigh and the calculation of the lower limit value Vlow may be performed sequentially.

  Next, the comparison unit 52 determines whether or not the DC voltages Va to Vd of the inverse conversion units 21a to 21d are larger than the upper limit value Vhigh and smaller than the lower limit value Vlow (steps S3a to S3d). .

  If it is determined in step S3a that the DC voltage Va is greater than the upper limit value Vhigh or less than the lower limit value Vlow (step S3a-Yes), the DC voltage Vb is greater than the upper limit value Vhigh or less than the lower limit value Vlow in step S3b. Is determined (step S3b-Yes), the DC voltage Vc is determined to be higher than the upper limit value Vhigh or lower than the lower limit value Vlow in step S3c (step S3c-Yes), or the DC voltage Vd is determined in step S3d. Is determined to be larger than the upper limit value Vhigh or smaller than the lower limit value Vlow (step S3d-Yes), the comparison unit 52 outputs a stop signal (step S4).

  On the other hand, when it is determined in steps S3a to S3d that all of the DC voltages Va to Vd are not less than the lower limit value Vlow and not more than the upper limit value Vhigh (step S3a-No, step S3b-No, step S3c-No, step S3d-No ) Returns to step S1.

  Assuming that the comparison unit 52 is composed of an analog circuit, the comparison of the DC voltages Va to Vd with the upper limit value Vhigh and the lower limit value Vlow in the comparison unit 52 is performed in parallel, and further, for each DC voltage Va to Vd. The determination whether or not the upper limit value Vhigh is greater than the lower limit value Vlow is performed in parallel, but the comparison unit 52 is configured by a digital circuit using a microprocessor, a sequencer, or the like. For example, the above comparison and determination may be performed sequentially.

  By executing the above processing in real time, even if an imbalance occurs in the AC output currents Ia to Id of the inverse conversion units 21a to 21d during a transitional period, the unbalance of the AC output currents Ia to Id is achieved. The balance can be detected, and the protection of the element can be further strengthened.

DESCRIPTION OF SYMBOLS 1 Induction heating apparatus 2 Power supply device 3 Heating coil 4 AC power supply 5 Matching circuit 6 Transformer 10 Forward conversion part 11 Forward conversion control part 20 Reverse conversion part 21a-21d Reverse conversion unit 22 Reverse conversion control part 23a-23d Output wiring 30 Current Detectors 31a to 31d Current transformer 40 Current voltage converter 50 Unbalance detector 51 Calculator 52 Comparator 53 Average value calculator 54 Upper limit calculator 55 Lower limit calculator Ia to Id AC output currents ia to id AC compatible Current Va to Vd DC voltage Vavg Average value Vhigh Upper limit value Vlow Lower limit value W Object to be heated

Claims (9)

A forward converter that converts AC power supplied from an AC power source into DC power;
An inverse conversion unit including a plurality of inverse conversion units for inversely converting DC power supplied from the forward conversion unit into AC power;
A current detection unit for detecting an AC-compatible current of each of the plurality of inverse conversion units corresponding to an AC output current of each of the plurality of inverse conversion units;
A current-voltage converter that converts the AC-compatible current of each of the plurality of inverse conversion units into a DC voltage;
When detecting the imbalance of the AC output current of each of the plurality of inverse conversion units based on the DC voltage of each of the plurality of inverse conversion units and an average value of the DC voltage, An unbalance detector that outputs a stop signal for stopping the operation of the converter and the inverse converter; and
A power supply device comprising: The power supply device according to claim 1,
Each of the plurality of inverse conversion units is a power supply device including one unit inverse conversion circuit. The power supply device according to claim 1 or 2,
The unbalance detector is
An arithmetic unit that calculates an average value of the DC voltage of each of the plurality of inverse conversion units, and calculates an upper limit value and a lower limit value of an allowable range for the DC voltage based on the obtained average value;
The DC voltage of each of the inverse conversion units is compared with the upper limit value and the lower limit value, and the DC voltage of one or more of the inverse conversion units is greater than the upper limit value or less than the lower limit value. A comparator that outputs a stop signal;
A power supply unit having The power supply device according to claim 3,
Calculation of the average value, the upper limit value, and the lower limit value of the DC voltage of each of the plurality of inverse conversion units by the calculation unit, and the DC voltage of each of the plurality of inverse conversion units by the comparison unit A power supply apparatus in which the comparison between the upper limit value and the lower limit value is executed in real time. A power supply device according to any one of claims 1 to 4,
A heating coil for inductively heating the heated portion with AC power supplied from the inverse conversion portion of the power supply device;
An induction heating device comprising: A forward conversion unit that converts AC power supplied from an AC power source into DC power, and an inverse conversion unit that includes a plurality of reverse conversion units that reversely convert DC power supplied from the forward conversion unit into AC power, respectively. A method for controlling a power supply device comprising:
Detecting the AC corresponding current of each of the plurality of inverse conversion units corresponding to the AC output current of each of the plurality of inverse conversion units;
Converting the AC-compatible current of each of the plurality of inverse conversion units into a DC voltage;
Detecting an imbalance of the AC output current of each of the plurality of inverse conversion units based on the DC voltage of each of the plurality of inverse conversion units and an average value of the DC voltages;
The control method of the power supply device which stops the operation | movement of the said forward conversion part and the said reverse conversion part, when the imbalance of the said alternating current output current of each of these reverse conversion units is detected. A method of controlling a power supply device according to claim 6,
Each of the plurality of inverse conversion units is a method for controlling a power supply apparatus including one unit inverse conversion circuit. It is a control method of the power supply device according to claim 6 or 7,
An average value of the DC voltage of each of the plurality of inverse conversion units is calculated, and an upper limit value and a lower limit value of an allowable range for the DC voltage are set based on the obtained average value.
When the DC voltage of each of the plurality of inverse conversion units is compared with the upper limit value and the lower limit value, and the DC voltage of one or more of the inverse conversion units is greater than the upper limit value or less than the lower limit value And a control method of the power supply apparatus for detecting an unbalance of the AC output current of each of the plurality of inverse conversion units. A control method for a power supply device according to claim 8,
Calculation of the average value, the upper limit value, and the lower limit value of the DC voltage of each of the plurality of inverse conversion units, and comparison of the DC voltage, the upper limit value, and the lower limit value of each of the plurality of inverse conversion units And a method of controlling the power supply apparatus that executes the process in real time.

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