JP5612518B2 - Induction heating apparatus, induction heating apparatus control method, and control program - Google Patents

Description

  The present invention relates to an induction heating device including an inverse conversion device that supplies high-frequency power to an induction heating coil, a method for controlling the induction heating device, and a control program.

Before a billet (ingot) is forged, rolled, or extruded to be finished into various products, it is necessary to heat and soften the billet to a settling temperature of 1250 ° C., for example. If you try to keep the rod-shaped billet at the set temperature with a single coil, the temperature distribution will be non-uniform, so there will be wasted fired material that does not reach the specified temperature during transition, such as when shifting from standby to standby to normal heating. There are things to do. Moreover, if it is going to keep both ends to a set temperature, a center part will become high temperature, and the furnace itself may melt | dissolve. In view of this, an induction heating apparatus is used in which the induction heating coil is divided into a plurality of parts, and a high frequency power source (for example, an inverter) is individually connected to each of the divided induction heating coils to perform power control.
However, since the divided induction heating coils are close to each other in order to prevent a temperature drop between the induction heating coils, the mutual inductance M exists and a mutual induction voltage is generated. For this reason, the inverters are in a state of being operated in parallel via the mutual inductance M, and when there is a deviation in the current phase between the inverters, power may be transferred between the inverters. That is, a phase difference occurs in the magnetic field between the divided induction heating coils due to the deviation of the current phase of each inverter. Therefore, the magnetic field is weakened near the boundary between adjacent induction heating coils, and the heat generation density due to the induction heating power is reduced. As a result, temperature unevenness may occur on the surface of the object to be heated (billette or wafer).

  Therefore, even if a mutual inductance M exists between adjacent induction heating coils and a mutual induction voltage is generated, circulating current does not flow between the inverters and heat is generated near the boundary of the divided induction heating coils. The inventors have proposed a “Zone Control Induction Heating (ZCIH)” technique capable of appropriately controlling induction heating power without lowering the density (for example, Patent Documents). 1). According to the ZCIH technology, each power supply unit is configured to include a step-down chopper and a voltage source inverter (hereinafter simply referred to as an inverter). And each power supply unit divided | segmented into the some power supply zone is connected individually to each divided | segmented induction heating coil, and is supplying electric power.

  At this time, each inverter in each power supply unit is subjected to current synchronization control (that is, current phase synchronization control) so that the circulating current does not flow between a plurality of inverters by matching the current phase flowing through each inverter. I have to. In other words, current is not exchanged between a plurality of inverters so that an overvoltage is not generated by regenerative power flowing into the inverters. Moreover, the inverter is configured so that the heat generation density due to the induction heating power does not rapidly decrease near the boundary between the induction heating coils by matching the phase of the current flowing through each of the divided induction heating coils.

  Furthermore, each step-down chopper controls the current amplitude of each inverter by varying the input DC voltage of each inverter, and controls the induction heating power supplied to each induction heating coil. In other words, the ZCIH technology disclosed in Patent Document 1 controls the power of the induction heating coil for each zone by performing current amplitude control for each step-down chopper, and performs a plurality of current synchronization controls for each inverter. The circulation current between the inverters is suppressed, and the heat generation density by the induction heating power near the boundary of each induction heating coil is made uniform. Using such ZCIH technology, the control system of the step-down chopper and the control system of the inverter perform individual control, so that the heat generation distribution on the object to be heated can be arbitrarily controlled. That is, rapid and precise temperature control and temperature distribution control can be performed by the ZCIH technique disclosed in Patent Document 1.

  Patent Document 2 discloses a technique in which DC power is simultaneously supplied to inverters individually connected to a plurality of induction heating coils, and the plurality of induction heating coils are simultaneously operated. Specifically, this technology detects the zero crossing of the output current from each inverter connected to the series resonance circuit, and compares the zero crossing timing at which the output current of each inverter changes from negative to positive with the rising timing of the reference pulse. It is supposed to be. This technique synchronizes the output current of each inverter by adjusting the frequency of the output current so that the phase difference from the reference pulse calculated individually by comparison becomes 0 or approaches 0. . In addition, after the output current of each inverter is synchronized, this technology controls the current flowing through each induction heating coil by increasing or decreasing the output voltage of the inverter, thereby achieving a uniform temperature distribution of the heating object. Is.

The inverters described in Patent Documents 1 and 2 realize a ZVS (Zero Voltage Switching) by connecting a capacitor in series with the heating coil to form a current resonance inverse conversion device and by connecting a chopper to each inverter. The recovery loss of commutation diodes was reduced.

JP 2007-26750 A JP 2004-146283 A

The techniques of Patent Documents 1 and 2 have a problem that the apparatus becomes large because the chopper is provided in the previous stage of each inverter.
Further, the conventional ZCIH is used for semiconductors and is small, so the inductance of the induction heating coil is small and suitable for high frequencies. For this reason, it is difficult to apply to the metal field ZCIH having a relatively low operating frequency and an extremely large capacity.

By the way, the billet has a change from a magnetic material to a non-magnetic material due to a temperature rise exceeding the Curie point, and a phase angle change (phase angle decrease) due to a shape change (gap change) of an object to be heated. The resonance frequency is increased and the resonance current is approximately tripled.
Cold material HOT material Air-core coil equivalent resistance R (ratio) 1 0.3 0.15 (about 7 times)
Inductance L (μH) 118 84 110

  A general induction heating device configured by one zone that does not divide the induction heating coil into a plurality of zones can be operated by following the operation frequency to the natural resonance frequency, and the rising timing of the output rectangular wave voltage of the inverse conversion device By minimizing the phase difference between the resonance current and the zero cross timing, the minimum phase angle operation that improves the power factor could be performed.

However, in the case of the techniques of Patent Documents 1 and 2 in which the induction heating coil is divided into a plurality, the phase angle increases due to the mutual induction voltage, and therefore the minimum phase angle control cannot be performed in all zones. That is, in the zone where the maximum output power must be output, there is a problem that the phase difference becomes larger than necessary and the predetermined output power cannot be output.
Since the natural resonance frequency changes, there is a problem in that the phase changes and the minimum phase angle that always becomes the phase lag mode cannot be obtained.

  In addition, a single billet that performs rapid heating has a large power peak value because of the characteristic that the resonance current is about three times higher. In the configuration in which the inverters are provided on a one-to-one basis in the inverter, there is a problem that the capacity of the forward converter, the reactor, and the capacitor becomes large and the cost is increased.

  Then, an object of this invention is to provide the induction heating apparatus which can output a maximum output in the zone which should output a maximum output, the control method of an induction heating apparatus, and a control program.

In order to solve the above-mentioned problem, the present invention targets the maximum output zone (for example, 2 zones) and the phase between the rising timing of the output rectangular wave voltage (high frequency voltage) of the inverse converter and the zero cross timing of the resonance current. Control the angle to be the minimum value.
This minimum phase angle is obtained when the output voltage of the inverse conversion device of the central zone (2 zones), which is the maximum output zone, is adjacent when the mutual induction voltages (Vm12, Vm32) are received from the adjacent zones (for example, 1 and 3 zones). It is set to be a value (Vinv> (Vm12 + Vm32)) larger than the sum of the mutual induction voltages coming from the zone.
In the adjacent zones (zones 1 and 3), the capacitance of the capacitor is set so that the natural resonance frequency above the Curie point is equal to or lower than the natural resonance frequency at the time of the cold material (maximum power zone (2 zones)). . That is, when a mutual induction voltage (Vm21, Vm31, respectively) is received from the central zone, the output voltage (Vinv) of the inverse conversion device in the adjacent zone is higher than the mutual induction voltage arriving from the maximum output zone (Vinv> The capacitance of the capacitor is set so that Vm21 or Vinv> Vm31). By doing so, the resonance current phase delay mode can be set while the frequency is the same and the current is synchronized.

  According to the present invention, the maximum output can be output in the zone where the maximum output should be output. For this reason, when a plurality of induction heating coils and a plurality of inverse conversion devices are used, the substantially resonant current flowing through each induction heating coil can be set to the phase delay mode by following the natural resonance frequency. Note that an inverse conversion device that supplies maximum power can reduce the converter capacity by performing minimum phase angle control.

It is sectional drawing of the billet heater used for the induction heating apparatus which is one Embodiment of this invention. It is the equivalent circuit schematic and vector diagram for demonstrating operation | movement of the induction heating apparatus which is one Embodiment of this invention. It is a block diagram of the induction heating apparatus which is one Embodiment of this invention. It is a frequency characteristic figure for demonstrating the resonance characteristic which is different with a cold material and a HOT material. It is explanatory drawing for demonstrating an equivalent sine wave voltage and average value control. It is a block block diagram of the control unit which controls an inverse converter. It is a circuit diagram of a 2nd embodiment using an IPM module. It is a circuit diagram of a 3rd embodiment using an IPM module. It is a circuit diagram of a 4th embodiment using a high order resonance prevention reactor. It is a wave form diagram for demonstrating operation | movement when a rectangular wave voltage is used.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Each figure is only schematically shown so that the present invention can be fully understood. Therefore, the present invention is not limited to the illustrated example. Moreover, in each figure, the same code | symbol is attached | subjected about the common component and the same component, and those overlapping description is abbreviate | omitted.

(First embodiment)
(overall structure)
FIGS. 1A and 1B are structural diagrams of a billet heater used in an induction heating apparatus according to an embodiment of the present invention, and FIG. 2 is an equivalent circuit diagram and operation of the billet heater. FIG. 3 is a circuit configuration diagram of the induction heating apparatus.
As shown in FIGS. 1 (a) and 1 (b), a billet heater 10 is provided with a concentric refractory material and a heat insulating material around a columnar billet (ingot) 1 to be heated, and the outer periphery of the heat insulating material. An induction heating coil is wound around the surface. The refractory material and the heat insulating material avoid heat dissipation of the billet heated to a high temperature and prevent the coil wire from fusing. The billet 1 has a diameter of 55 mm.
In the sectional view in the axial direction of FIG. 1A, the induction heating coil is divided into three zones from the first zone to the third zone through a gap, and is composed of the divided induction heating coils 11, 12, and 13. . The induction heating coil 12 may be referred to as an induction heating central coil, and the induction heating coils 11 and 13 may be referred to as induction heating adjacent coils.

  When the billet 1 is induction-heated, eddy current loss occurs, so the induction heating coils 11, 12, and 13 are equivalently expressed by a series circuit of an equivalent inductor and an equivalent resistor (FIG. 2 (a)). . Moreover, as shown in FIG. 3, the induction heating coils 11, 12, and 13 are respectively connected to capacitors 21, 22, and 23 in series. Therefore, the series circuit of the induction heating coils 11, 12, 13 and the capacitors 21, 22, 23 is equivalently expressed as an RLC series resonance circuit, and the inverter power supply Einv of the output voltage Vinv is connected to one end thereof, and the other end is connected. And an AC power supply Em having a mutual induction voltage Vm is connected to the circuit (FIG. 2A). Thereby, the inverter current Iinv (solid arrow) flows, and the mutual induction current Im (broken arrow) flows in the reverse direction. In order not to flow reverse current, the output voltage Vinv of the reverse converters 30, 35, 31 (FIG. 3) must be higher than the mutual induction voltage Vm.

  Further, at the settling temperature (1250 ° C.), since the Curie point (740 ° C. to 770 ° C.) is exceeded, the billet 1 changes from a magnetic material to a non-magnetic material. For this reason, the natural resonance frequency is increased and the resonance current is approximately tripled. Since the phase of the mutual induction voltage Vm changes by 360 ° depending on the frequency and shows a circular locus (FIG. 2B), the output voltage (inverter voltage Vinv) of the inverter (inverter 35) is delayed at any frequency. In order to prevent the phase (that is, the resonance current from leading), the output voltage (inverter voltage Vinv) is larger than the sum of the mutual induction voltages Vm12 and Vm32 coming from the adjacent zones (1, 3 zones). (Vinv> (Vm12 + Vm32)) is set. When the mutual induction voltages Vm12 and Vm32 coming from the first and third zones are equal, Vinv> 2 | Vm |, and the phase angle when Vinv = 2 | Vm | is 30 ° (a in FIG. 2C). point).

  In the circuit configuration diagram of FIG. 3, an induction heating apparatus 100 according to an embodiment of the present invention includes two sets of billet heaters 10 (10 a and 10 b), two sets of capacitor units 20 (20 a and 20 b), and two sets. Inverse conversion devices 30 (30a, 30b), 35 (35a, 35b), 31 (31a, 31b), a forward conversion device 40, and a control unit 50 are configured.

  As described with reference to FIG. 1, the billet heater 10 includes induction heating coils 11, 12, and 13 having inductances L1, L2, and L3, the mutual inductance of the induction heating coils 11 and 12 is M12, and the induction heating coil. The mutual inductance of 12 and 13 is M23. In addition, since the distance between the induction heating coils L1 and L3 is long, the mutual inductance is ignored.

The capacitor unit 20 includes three capacitors 21, 22 and 23 having capacitances C ₀₁ , C ₀₂ and C ₀₃ . The capacitors 21, 22, and 23 are connected in series with the induction heating coils 11, 12, and 13, respectively, and constitute an LC resonance circuit.

  FIG. 4 is a frequency-current characteristic diagram of each zone showing frequency characteristics that change between the billet cold material and the HOT material. FIG. 4 (a) shows the characteristics of the 1 and 3 zone cold material, FIG. 4 (b) shows the characteristics of the 1 and 3 zone HOT material, and FIG. 4 (c) shows the property of the 2 zone cold material. FIG. 4 (d) shows the characteristics of the two-zone HOT material. As can be seen from the figure, the current of the HOT material is three times that of the cold material.

As shown in FIGS. 4B and 4C, the HOT natural resonance frequency (350 Hz) in the first and third zones is lower than the cold natural resonance frequency (400 Hz) in the maximum power zone (two zones). Are set to capacitances C ₀₁ , C ₀₂ , C ₀₃ of capacitors 21, 22, 23 (FIG. 3).
In other words, when the mutual induction voltages (Vm21 and Vm31, respectively) are received from the second and third zones in one zone, the output voltage (inverter voltage Vinv) of the reverse conversion device 30 in one zone comes from the second and third zones. The capacitances of the capacitors 21 and 22 are set so as to be higher than the mutual induction voltage (Vinv> Vm21 or Vinv> Vm31). Similarly, the capacitor 22 is set so that the output voltage (inverter voltage Vinv) of the three-zone inverse converter 31 is higher than the mutual induction voltage coming from the second and first zones (Vinv> Vm23 or Vinv> Vm13). , 23 is set.

In addition, since the resonance frequency of the HOT material is higher than that of the cold material, as shown in FIGS. 4 (c) and 4 (d), the inverter voltage Vinv is kept the same and the change in the natural resonance frequency is followed in each zone. By performing the control, the resonance currents of the zones can be made equal.
That is, in the two zones, when a cold material having a natural resonance point of 400 Hz is heated to become a HOT material, the resonance current increases three times and the natural resonance point rises to 550 Hz. By following the natural resonance point of 550 Hz, the resonance current is reduced, and the resonance current can be controlled to be equal to the resonance current of the cold material. At this time, although the natural resonance frequency is set low at 350 Hz in the first and third zones, the resonance current is further reduced because it is driven at 550 Hz, which is the same frequency as the second zone. That is, since the mutual induction voltage received from the 2nd zone to the 1st and 3rd zones does not change, the output voltage (inverter voltage Vinv) of the inverse conversion devices 30 and 31 is reduced.

The inverse conversion device 30 (31) shown in FIG. 3 includes electrolytic capacitors C _F1 and C _F2 connected in series, and two IGBTs (Insulated Gate Bipolar Transistors) Q11 and Q12 (Q31 and Q32), and is a half bridge. A circuit is configured and power is supplied to the induction heating coils 11 and 13 via the capacitors 21 and 23.

In the inverse conversion device 30 (31), the emitter end of the transistor Q11 and the collector end of the transistor Q12 are connected, and a DC voltage Vdc is applied between the collector end of the transistor Q11 and the emitter end of the transistor Q12, so that they are connected in series. The DC voltage Vdc is applied to the electrolytic capacitors C _F1 and C _F2 .
In the induction heating device 100, a connection point between the emitter end of the transistor Q11 and the collector end of the transistor Q12 and one end of the capacitor 21 are connected, and the other end of the capacitor 21 and one end of the induction heating coil 11 are connected. The other end of the heating coil 11 and the connection point P of the electrolytic capacitors C _F1 and C _F2 are connected.

The reverse conversion device 35 includes a single electrolytic capacitor CF3 and four transistors Q21, Q22, Q23, and Q24, constitutes a full bridge circuit, and is connected to the induction heating coil 12 via the capacitor 22 with the reverse conversion device. Electric power larger than 30, 31 is supplied.
In the inverse conversion device 35, the emitter end of the transistor Q21 and the collector end of the transistor Q22 are connected, the emitter end of the transistor Q23 and the collector end of the transistor Q24 are connected, and the collector ends of the transistors Q21 and Q23 and the transistors Q22 and Q24. A DC voltage Vdc is applied to the emitter end of the capacitor, and a DC voltage Vdc is applied to the electrolytic capacitor CF3. A connection point between the emitter end of the transistor Q23 and the collector end of the transistor Q24 and one end of the capacitor 22 are connected, and the other end of the capacitor 22 and one end of the induction heating coil 12 are connected.
The connection point between the emitter end of the transistor Q21 and the collector end of the transistor Q22 and the other end of the induction heating coil 12 are connected.

The inverse conversion device 31 has the same configuration as the inverse conversion device 30, and the inverse conversion devices 30b, 35b, 31b have the same configuration as the inverse conversion devices 30a, 35a, 31a.
The forward conversion device 40 is configured by a diode bridge, generates a DC voltage Vdc using a commercial power supply AC, and generates a first reverse conversion device aggregate (inverse conversion devices 30a, 35a, 31a) and a second reverse conversion. Power is supplied to the device assembly (inverse conversion devices 30b, 35b, 31b). The forward conversion device 40 does not use a chopper, and the same fixed DC voltage Vdc is applied to the reverse conversion devices 30a, 35a, and 31a.

As described above with reference to FIG. 4, the capacitors 21, 22, and 23 have the HOT natural resonance frequency in the 1 and 3 zones lower than the cold natural resonance frequency in the maximum power zone (2 zones). The capacitances C ₀₁ , C ₀₂ and C ₀₃ are set as follows.

(Function of control unit)
The control unit 50 generates a gate signal for controlling the gates of the transistors (IGBT) in the inverse converters 30, 31, and 35, and includes a ROM (Read Only Memory), a RAM (Random Access Memory), and a CPU (Central The following functions are realized when the CPU executes a predetermined program.

1) All zones are operated with the same frequency and current synchronization.
Since the divided induction heating coils 11, 12, and 13 are close to each other, the mutual induction inductances M12 and M23 exist, and the mutual induction voltage Vm is generated. In order to avoid the phase difference of the magnetic field between the induction heating coils generated by the exchange of power generated between the inverters, the 1, 2 and 3 zones are the same frequency and are synchronized with a sine wave current. drive. As a result, a phenomenon in which the amount of heat generation locally decreases and uneven heat generation occurs can be avoided.

  2) The control unit 50 causes the inverse conversion devices 30, 35, and 31 to function as a PWM resonance inverter. Specifically, since the inverse conversion devices 30, 35, and 31 need to realize ZVS, a rectangular wave shape obtained by PWM-modulating a rectangular wave voltage having a predetermined carrier frequency with a sine wave signal (Sinωt) having a predetermined operating frequency. Equivalent sine wave voltage (in FIG. 5 (a) in the case of the inverse conversion device 35 which is a full bridge circuit). The equivalent sine wave voltage is averaged by the LR time constant ((L1-C01) R time constant), and a coil current having a substantially sine waveform flows through the induction heating coils 11, 12, and 13. The control unit 50 performs average value control that makes the synchronous control time constant longer than the resonance time constant (T = 2L / R) (see FIG. 5B), and the frequency of the coil current is the target operating frequency and the target The equivalent sine wave voltages of the inverse conversion devices 30, 35, and 31 are feedback-controlled so as to be in phase. The target phase is a phase between a zero cross point where a sine wave signal for generating an equivalent sine wave makes a transition from negative to positive and a zero cross point where a coil current having a substantially sine waveform makes a transition from negative to positive. In this way, the control unit 50 generates an equivalent sine wave signal with an operating frequency of 1 kHz using a triangular wave signal with a carrier frequency of 8 kHz by PWM control, and controls the gates of the IGBTs in the inverse conversion devices 30, 35, and 31. I have control.

3) Minimum Phase Angle Control The two-zone inverse converter 35 that outputs maximum power performs minimum phase angle control while following the natural resonance frequency. Hereinafter, the minimum phase angle control will be described.
Control is performed so that the minimum phase angle (for example, 30 °) of the maximum output zone (2 zones) is obtained.
Specifically, as described above, the minimum phase angle is larger than the sum of the mutual induction voltages Vm12 and Vm32 in which the output voltage (inverter voltage Vinv) comes from the adjacent zones (1, 3 zones) (Vinv> ( Vm12 + Vm32)). When the mutual induction voltages Vm12 and Vm32 coming from the first and third zones are equal, Vinv> 2 | Vm | (FIG. 2 (c)), and the minimum phase angle at this time is 30 °.

Even if there is a change in the natural resonance frequency, it is also conceivable to operate at a fixed frequency with a sufficiently large phase angle in order to always output the inverter voltage Vinv that exceeds the mutual induction voltage Vm coming from another zone. However, the following problems arise.
a) Since the phase angle is sufficiently large, high power factor operation cannot be performed.
b) Since the inverter voltage Vinv exceeding the mutual induction voltage Vm is generated, a margin is required for the voltage / current rating (effective power Vdc × Idc).

  In ZCIH, the zone that outputs at the maximum ratio with respect to the rated power has the minimum phase angle, so that the natural resonance point (350 Hz) of the HOT material in the first and third zones is the natural resonance point (400 Hz) of the cold material in the two zones. The capacitance is set so as to be lower than that (FIG. 2A). In the first and third zones, the coil voltage is low, so there is no need for a capacitor.

(Configuration of control unit)
Next, the configuration of the control unit 50 for controlling the inverse conversion devices 30, 31, and 35 will be specifically described.
FIG. 6 is a block configuration diagram of the control unit 50a that controls the inverse converters 30, 31, and 35. FIG. 6 shows a configuration diagram of the control unit that controls the first and third zones. It is the same. The control unit 50a includes an A / D converter to the outside, to detect the coil current _{i L.}

The control unit 50a includes an amplitude calculator 201, a target current generator 202, an adder 203, PI controllers 204 and 208, a zero cross detector 205, a current synchronization reference phase signal generator 206, and a synchronization shift. Detector 207, voltage command value calculator 209, triangular wave comparator 210, frequency setter 211, phase angle comparator 215, 30 ° reference value generator 216, comparators 217 and 219, and PI controller 218.

Amplitude calculator 201 calculates the amplitude of the converted value _{I L} to the coil current _{i L} converted A / D. Target current generator 202 generates a target value of the coil current i _L. The adder 203 subtracts the output value of the amplitude calculator 201 from the output waveform of the target current generator 202 and outputs an error signal. The PI controller 204 performs a proportional integral operation on the error signal output from the adder 203.

Zero-crossing detector 205, the coil current i _L by using the converted value I _L obtained by converting A / D, to calculate the zero-cross point when the coil current i _L is changed from negative to positive. The current synchronization reference phase signal generator 206 outputs a reference value of a phase difference from the target current generator 202 in order to synchronize the coil currents flowing through the induction heating coils 11, 12, and 13. This reference value is set to a minimum phase angle of 30 ° in the case of two zones, and may be a value larger than the minimum phase angle in the case of the first and third zones because power consumption is small.
The synchronization shift detector 207 detects a difference (synchronization shift) between the output value of the current synchronization reference phase signal generator 206 and the output value of the zero cross detector 205. PI controller 208 is proportional integral operation using the output deviation of the synchronization shift detector 20 7.

The voltage command value calculator 209 generates a voltage command value Vinv ^* indicating a sine waveform with an operation frequency of 1 kHz based on the output signals of the PI controllers 204 and 208 and the frequency command value f ^* . The frequency setter 211 outputs a value having a carrier frequency of 8 kHz. The triangular wave comparator 210 compares the voltage command value Vinv ^* with the triangular wave signal having the carrier frequency set by the frequency setting unit 211, and generates a PWM control signal. PWM control signal is input to the inverters 30,35,31, by the coil current _{i L} flowing through the inductive heating coil 11, 12, 13 is fed back as _{I L,} the amplitude of the coil current _{i L} is the operating frequency And the phase when the coil current i _L changes from negative to positive coincides in each zone. Further, the zero cross point of the voltage command value Vinv ^* indicating a sine waveform coincides with the inversion timing of the triangular wave signal. As a result, the output voltage Vinv of the inverse converters 30, 35, and 31 is obtained by inverting the positive and negative of the rectangular wave voltage when the voltage command value Vinv ^* is zero-crossed, the transition timing before and after the positive and negative inversion at the origin 0, and the zero-cross point. The time periods T1 and T2 (FIG. 5A) coincide with each other.

The phase angle comparator 215 compares the output phase of the zero cross detector 205 with the phase of the voltage command value Vinv ^* output from the voltage command value calculator 209. That is, the phase angle comparator 215 calculates the phase difference between the sine wave signal and the coil current i _L of the voltage command value Vinv ^*, voltage - output current phase difference .theta.v ^*. The 30 ° generator 216 outputs a value of 30 ° which is the minimum phase angle.

The comparator 217 compares the voltage-current phase difference θv ^* output from the phase angle comparator 215 with a value of 30 °. When the value of the voltage-current phase difference θv ^* is larger than 30 °, the comparator 217 When the value of the voltage-current phase difference θv ^* is smaller than 30 °, a positive constant value is output. At this time, the comparator 217 also compares the voltage-current phase difference from the other zones (2, 3 zones) with the value of 30 °. The PI controller 218 performs a proportional-integral operation on the output signal of the comparator 217 and outputs a frequency command value f ^* having an operation frequency of about 1 kHz to the voltage command value calculator 209. As a result, when the value of the voltage-current phase difference θv ^* is larger than 30 °, feedback control is performed so that the frequency command value f ^* decreases, and the value of the voltage-current phase difference θv ^* is smaller than 30 °. Sometimes feedback control is performed so that the frequency command value f ^* increases.

The comparator 219 compares the voltage command value Vinv ^* with twice (2 Vm) the mutual induction voltage Vm from another zone, and outputs the comparison result to the voltage command value calculator 209. Here, when the voltage command value Vinv ^* is smaller than 2 Vm from another zone, the voltage command value calculator 209 performs control in a minor loop so as to increase the value of the voltage command value Vinv ^* . Note that the mutual induction voltage Vm received from the first and second zones is calculated by Vm = (M ₁₂ i ₂ + M ₁₃ i ₃ ).

(effect)
According to the present embodiment, the inverse conversion device 35 targeted for the maximum output zone (2 zones) includes the rising timing of the rectangular wave voltage of the inverse conversion device output and the zero crossing timing when the coil current transitions from negative to positive. Is controlled so that the phase angle between is minimum.
This minimum phase angle is obtained when the mutual induction voltages (Vm12, Vm32) are received from the adjacent zones (1, 3 zones), and the output voltage (inverter voltage) of the reverse conversion device 35 in the central zone (2 zones) which is the maximum output zone. Vinv) is set to a value (Vinv> (Vm12 + Vm32)) larger than the sum of the mutual induction voltages (Vm12, Vm32) coming from the first and third zones.
Further, in the adjacent zones (1, 3 zones), the capacitors 21, 22, so that the natural resonance frequency during HOT above the Curie point is equal to or lower than the natural resonance frequency during cold material (of the maximum power zone (2 zones)). 23 capacitance is set.
That is, when a mutual induction voltage (Vm21, Vm31) is received from two or three zones, the output voltage Vinv of the inverse conversion device 30 in one zone is higher than the mutual induction voltages Vm21, Vm31 (Vinv> Vm21 or Vinv> The capacitances C ₀₁ , C ₀₂ , C ₀₃ of the capacitors 21, 22, 23 are set so as to be Vm 31).

  The inverse converters 30, 35, 31 generate an equivalent sine wave voltage that is PWM-modulated at a predetermined carrier frequency, and this equivalent sine wave voltage is averaged by the LR time constant, and the induction heating coils 11, 12, A coil current having a substantially sinusoidal waveform flows through 13. Thereby, since the inverters 30, 35, and 31 can be set to ZVS, the commutation diode does not change from the on state to the off state, and no recovery current is generated. Then, the inverse conversion devices 30, 35, and 31 are generated so that the synchronous control time constant is longer than the resonance time constant (T = 2L / R) and the frequency of the coil current becomes the target operating frequency and the target phase. The equivalent sine wave voltage is PWM controlled. That is, the inverse conversion devices 30, 35, and 31 function as a PWM resonance type inverter. As a result, high power factor operation becomes possible, thereby improving the efficiency and reducing the capacity of the inverse conversion device.

(Second embodiment)
In the first embodiment, a half bridge circuit is used for the inverters 30 and 31 and a full bridge circuit is used for the inverter 35 to form an independent circuit. (Intelligent Power Module) Modules can be connected in parallel.
FIG. 7 is a circuit diagram of an inverse conversion device using an IPM module and a billet heater.
The IPM module is a generalized module in which six IGBTs and six commutation diodes are modularized for the purpose of driving a three-phase motor. The IPM module 60 includes power supply terminals V +, V−, output terminals U, V, W, and a gate terminal.

The induction heating apparatus 101 is a three-bridge configuration of a half bridge circuit using one IPM module 60 for each of the three induction heating coils 11, 12, 13 and includes power supply terminals V +, Electrolytic capacitors C _F1 and C _F2 connected in series are connected to both ends of V−, and a DC voltage Vdc is applied. The output terminals U, V, and W are connected to one ends of capacitors 24, 25, and 26, respectively, and the other ends of the capacitors 24, 25, and 26 are connected to one ends of induction heating coils 11, 12, and 13, respectively. The other ends of the capacitors 11, 12, and 13 are connected to one ends of the capacitors 27, 28, and 29, and the other ends of the capacitors 27, 28, and 29 are collectively connected to the connection point P of the electrolytic capacitors C _F1 and C _F2. Yes. The capacitances of the capacitors 24, 25, 26, 27, 28, and 29 are twice the capacitances of the capacitors 21, 22, and 23 (FIG. 2).

  By using the IPM module 60, a simple and small-sized ZCIH can be realized, which is suitable for use in heating a semiconductor substrate.

(Third embodiment)
Although the second embodiment uses one IPM module, it is possible to increase the capacity by connecting two or more IPM modules in parallel.
FIG. 8 is a circuit diagram around the inverse converter using the IPM module of the third embodiment and the billet heater.
The induction heating device 102 includes two IPM modules 60a and 60b, electrolytic capacitors C _F1 and C _F2 , capacitors 24a, 25a and 26a, capacitors 27, 28 and 29, capacitors 24b, 25b and 26b, and induction heating. Coils 11, 12, and 13 are provided.

Electrolytic capacitors C _F1 and C _F2 connected in series are connected to both ends of power supply terminals V + and V− of the IPM modules 60a and 60b, and a DC voltage Vdc is applied. The output terminals U1, V1, and W1 of the IPM module 60a are connected to one ends of the capacitors 24a, 25a, and 26a, the other ends of the capacitors 24a, 25a, and 26a are the one ends of the induction heating coils 11, 12, and 13, and the capacitor 24b. 25b, 26b, the other ends of the induction heating coils 11, 12, 13 are connected to one ends of the capacitors 29, 28, 27, and the other ends of the capacitors 29, 28, 27 are collectively electrolyzed. It is connected to a connection point P between the capacitors C _F1 and C _F2 . The other ends of the capacitors 24b, 25b, and 26b are connected to the output terminals U2, V2, and W2 of the IPM module 60b.

  According to the induction heating device 102 of the present embodiment, the output power of each inverse conversion device using the IPM modules 60a and 60b is added, so that the output can be increased.

(Fourth embodiment)
In the first embodiment, only the electrolytic capacitor C _F1 is connected to the power source side of the inverter, but in order to prevent a high-order current component from flowing back to the power source, a low frequency is provided for each inverter. A pass filter can be provided.
FIG. 9 is a circuit diagram of a fourth embodiment using a high-order resonance preventing reactor.
Similarly to the first embodiment, the induction heating device 103 includes inverse conversion devices 30, 35, 31, capacitors 21, 22, 23, and induction heating coils 11, 12, 13, and further includes the inverse conversion devices 30, 35 and 31 are provided with a high-order resonance reactor 73 and a capacitor 74 constituting an LC low-pass filter on each power supply side, and one end of three high-order resonance reactors 73 is connected to one end of an electrolytic capacitor 72 and a choke. Connected to one end of the coil 71. A DC voltage Vdc is applied to the other end of the choke coil 71, and the other end of the electrolytic capacitor 72 and the other end of the capacitor 74 are grounded.

The high-order resonance prevention reactor 73 sets the inductance so that the resonance frequency f0 determined by the capacitor 74 (for example, 1000 μF) is lower than the high-order resonance frequency 2f0 by adding to the wiring inductance (several μH). To do.
Thereby, it is possible to prevent the component of the high-order resonance frequency 2f0 of the mutual induced electromotive force Vm from circulating to the power source side of the inverse conversion devices 30, 35, and 31.

(Fifth embodiment)
In each of the above embodiments, in all zones (1, 2, 3 zones), the control unit 50 causes the inverse converters 30, 35, 31 to function as a PWM resonance inverter, and a rectangular wave voltage (high frequency voltage) of the carrier frequency. Was modulated with a sine wave of the operating frequency and an equivalent sine wave was output. Since the supply power increases in the two heating center zones, the control unit 50 can reduce the loss by causing the inverse converter 35 to function as a current resonance type inverter that outputs a rectangular wave voltage having an operation frequency (Japanese Patent Laid-Open No. 2005-260707). 2010-287447).
That is, the control unit 50 sets the pulse width to the inverse conversion device 35 so that the zero cross timing at which the sine wave current zero crosses from negative to positive is in the resonance current phase delay mode in which the rising timing of the rectangular wave drive voltage is delayed. I have control. Thereby, the reverse recovery loss of the commutation diode in the reverse conversion device 35 is prevented from occurring. In this case, the control unit 50 also functions as a PWM resonance inverter for the inverse conversion devices 30 and 31.

FIG. 10 is a waveform diagram for explaining the operation when a rectangular wave voltage is used. This waveform diagram shows the output voltage Vinv (rectangular wave voltage waveform) of the inverse conversion device 35, its fundamental wave voltage waveform and the coil current waveform, the vertical axis is the voltage / current, and the horizontal axis is the phase (ωt). It is. The output voltage Vinv of the inverse conversion device 35 is a positive / negative symmetrical odd function waveform (rectangular wave voltage waveform) indicated by a solid line, and the fundamental wave is shown as a broken line fundamental wave voltage waveform. The maximum amplitude of the output voltage Vinv is ± Vdc, and the phase angle of the control angle δ is set with respect to the zero cross point of the fundamental wave voltage waveform. That is, both the rising timing and falling timing of the output voltage Vinv of the inverse converter 35 and the zero cross timing of the fundamental voltage waveform have a phase difference of the control angle δ. At this time, the amplitude of the fundamental voltage waveform is (4Vdc / π) · cosδ, and the frequency is the operating frequency (1 kHz).
The coil current waveform i _L shown by a solid line is a sine wave that has been delayed by the phase difference θ than zero-cross timing of the fundamental wave voltage waveform.

(Modification)
The present invention is not limited to the embodiments described above, and various modifications such as the following are possible.
(1) In the first embodiment, the capacitors 2 1 , 2 2 , and 2 3 are connected in series to the induction heating coils 11, 12, and 13. The capacitors 2 1 and 2 3 can be directly connected without being connected.
That is, since the supplied power is small in the first and third zones, it can function as a PWM non-resonant inverter by adding a capacitor. This is because in the first and third zones, it is not necessary to lower the output voltage Vinv to lower the power factor or the capacity of the inverse conversion device.
(2) In the first embodiment, the inverse converters 30, 35, and 31 are directly connected to the series circuits of the capacitors 2 1 , 2 2 , 2 3 , and the induction heating coils 11, 12, 13. Can be connected through a matching transformer.
For example, when the output voltage Vinv = 200 Vac is sufficient when the power supply voltage is 400 Vdc, it is effective in that the output current of the inverter can be reduced by the matching transformer.

(3) Although each of the above embodiments has described a circuit for supplying power to a billet heater (FIG. 1) that burns a single billet, it can also be used in a vertical furnace or a pancake spiral coil.
In the vertical furnace, the lowest zone where the temperature is likely to drop is set to the maximum output, so the target of the minimum phase angle control is the lowest zone. In the upper zone, the capacitance of the capacitor is set so that the natural resonance point is lower than the natural resonance point of the lowest zone.
In the pancake-type spiral coil, the outermost peripheral zone has the maximum output, and therefore, the outermost peripheral zone is the target of the phase angle constant control. In other zones, the capacitance is set such that the natural resonance point is lower than the natural resonance point of the outermost peripheral zone. The operating frequency of the center coil (singular point) is 200 kHz, and the others are 40 kHz.

(4) In each of the above embodiments, the metal billet is directly induction-heated. However, the semiconductor wafer or the like can be indirectly heated by induction-heating graphite as a nonmagnetic material.
The zone that outputs the maximum output is subjected to the minimum phase angle control, and the capacitances of the capacitors in other zones are set so that the natural resonance point is lower than the natural resonance point of the lowest zone.
Used for heating vertical graphite tube by solenoid coil and disk-shaped graphite heating by pancake coil.
In this case, it is preferable to use a chopper + resonance type inverter at a heating frequency of about 20 kHz to 50 kHz.

10 Billet heater 11, 12, 13 Induction heating coil 20 Capacitor unit 21, 22, 23, 24a, 24b, 25a, 25b, 26a, 26b Capacitor 30, 30a, 30b, 31, 31a, 31b, 35, 35a, 35b, Inverse converter 40 Forward converter 41 Diode bridge 42 Electrolytic capacitor 45 Chopper 50, 50a, 50b Control unit 55, 56, 57 A / D converter 60, 60a, 60b IPM module 71, 73 Reactor 72, 74 Capacitor 100, 101 , 102, 103 Induction heating device 201 Amplitude calculation unit 202 Target current generator 203 Adder 204, 208, 218 PI controller 205 Zero cross detection unit 206 Current reference phase signal generator 207 Synchronization deviation detection unit 209 Voltage finger Value calculator 210 triangular wave comparator 211 frequency setter 215 phase angle comparator 216 30 ° setter 217, 219 comparator

Claims (11)

A plurality of induction heating coils arranged close to each other, a capacitor connected in series to each of the induction heating coils, and a high frequency voltage converted from a DC voltage to each of the induction heating coil and a series resonance circuit of the capacitor An induction device comprising: a plurality of inverse conversion devices applied to the control circuit; and a control circuit for controlling the plurality of inverse conversion devices so as to align the phases of coil currents flowing through the plurality of induction heating coils while performing voltage width control on the high-frequency voltage. A heating device,
The capacitor is one in which the capacitance of the adjacent zone is set so that the natural resonance frequency above the Curie point of the material to be heated is equal to or lower than the natural resonance frequency at the time of the cold material in the maximum power zone,
The control circuit synchronizes the plurality of inverters with the same frequency and current-synchronizes the high-frequency voltage generated by a specific inverter that supplies maximum power to the plurality of induction heating coils and the series resonance circuit. An induction heating apparatus, wherein control is performed such that a phase difference with a flowing coil current is minimized. The high-frequency voltage exhibits a rectangular wave voltage obtained by comparing a sine wave signal and a triangular wave signal,
The induction heating apparatus according to claim 1, wherein the phase difference is a phase difference between a zero cross timing of the sine wave signal and a zero cross timing of the coil current.   The induction heating device according to claim 2, wherein the zero cross timing of the coil current is delayed from the zero cross timing of the sine wave signal. The high-frequency voltage exhibits a rectangular wave voltage whose time integration value changes to a sine wave shape,
The induction heating apparatus according to claim 1, wherein the phase difference is a phase difference between a zero cross timing of the sine wave and a zero cross timing of the coil current.   5. The high frequency voltage according to claim 1, wherein the high frequency voltage has a value larger than a sum of mutual induction voltages caused by adjacent coil currents flowing through the plurality of induction heating coils arranged close to each other. The induction heating device according to Item. The plurality of inverse conversion devices are connected to a power source that supplies DC power,
6. The induction heating device according to claim 1 , wherein each of the inverse conversion devices has an LC low-pass filter inserted between the reverse power device and the power source . The induction heating coil, the capacitor, and the inverse conversion device are provided in three sets,
The specific reverse conversion device is an reverse conversion device that supplies high-frequency power to an induction heating central coil disposed in the center,
The high-frequency voltage generated by the specific inverse converter is larger than the sum of mutual induction voltages generated by two induction heating adjacent coils arranged adjacent to the induction heating central coil. The induction heating apparatus according to any one of claims 1 to 6.   The induction heating apparatus according to any one of claims 2 to 4, wherein the phase difference is approximately 30 degrees. The induction heating device according to any one of claims 1 to 8 , wherein the reverse conversion device is configured by any one of a full bridge circuit and a half bridge circuit. A plurality of induction heating coils arranged close to each other, a capacitor connected in series to each of the induction heating coils, and a high frequency voltage converted from a DC voltage to each of the induction heating coil and a series resonance circuit of the capacitor A plurality of inverse conversion devices applied to the induction heating device, and a method for controlling the plurality of inverse conversion devices to control the voltage width of the high-frequency voltage and to align the phases of coil currents flowing through the plurality of induction heating coils Because
The capacitor is one in which the capacitance of the adjacent zone is set so that the natural resonance frequency above the Curie point of the material to be heated is equal to or lower than the natural resonance frequency at the time of the cold material in the maximum power zone,
The plurality of inverters have the same frequency and current synchronization, and the high-frequency voltage generated by a specific inverter that supplies maximum power to the plurality of induction heating coils and the coil current flowing through the series resonance circuit A control method for an induction heating device, wherein the control is performed so that the phase difference is minimized. A plurality of induction heating coils arranged close to each other, a capacitor connected in series to each of the induction heating coils, and a high frequency voltage converted from a DC voltage to each of the induction heating coil and a series resonance circuit of the capacitor And a control program for controlling the plurality of inverse converters so that the phases of the coil currents flowing through the plurality of induction heating coils are aligned while controlling the voltage width of the high-frequency voltage. There,
The capacitor is one in which the capacitance of the adjacent zone is set so that the natural resonance frequency above the Curie point of the material to be heated is equal to or lower than the natural resonance frequency at the time of the cold material in the maximum power zone,
The plurality of inverters have the same frequency and current synchronization, and the high-frequency voltage generated by a specific inverter that supplies maximum power to the plurality of induction heating coils and the coil current flowing through the series resonance circuit A control program for a control circuit that is executed by a computer so that the phase difference is minimized.

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