JP5909402B2 - Power conversion device and induction heating device using the same - Google Patents

Description

  The present invention relates to a power conversion device and an induction heating device using the same, and more particularly to a technique for improving the heating efficiency of an object to be heated.

  In recent years, inverter-type induction heating devices that heat cooking utensils such as pots without using fire have been widely used. The induction heating device is a device that causes a high-frequency current to flow through a heating coil, generates an eddy current in a metal cooking utensil arranged in the vicinity of the heating coil, and generates heat by the electrical resistance of the cooking utensil itself. Generally, a cooking utensil made of a magnetic material such as iron has a large specific resistance, so that it is easy to heat, and a cooking utensil made of a non-magnetic material such as copper or aluminum has a low specific resistance, so that it is difficult to heat.

  As a conventional example for solving this problem, there is an induction heating cooker as disclosed in Patent Document 1. The induction heating cooker of Patent Document 1 is composed of a high frequency inverter of a full bridge circuit that also functions as a half bridge circuit and a single heating coil, and discriminates between a magnetic pot and a non-magnetic pot, and according to the result The high frequency inverter is switched between a full bridge circuit system and a half bridge circuit system, and an object to be heated of different materials is induction heated.

JP 2009-117378 A

  In the induction heating cooker of Patent Document 1, when heating the non-magnetic material, one of the upper and lower arms is in a resting state, and the rested upper and lower arms do not contribute to the heating of the pan at all.

  An object of this invention is to supply a desired electric power efficiently to a cooking appliance by using a switching element effectively, even when heating a nonmagnetic material.

  The above problem is that a converter that converts an AC voltage into a DC voltage by driving a switching element, a first upper and lower arm that connects two main switching elements in series, and a second that connects two main switching elements in series. An inverter that has two upper and lower arms, converts a DC voltage from the converter into an AC voltage and supplies it to a load, and drives the main switching element of the first upper and lower arms, thereby making the inverter a half-bridge circuit Control means for operating the inverter as a full bridge circuit by driving the main switching element of the first upper and lower arms and the main switching element of the second upper and lower arms, and an output terminal of the half bridge circuit A first load circuit connected between the output terminal of the full bridge circuit and the first negative circuit A second load circuit including a part of the circuit, first switch means for connecting the second load circuit and the inverter, one main switching element of the second upper and lower arms, and switching of the converter Second switch means for connecting elements in parallel, and the control means turns off the first switch means and operates the second switch means when the inverter operates as a half-bridge circuit. And when the inverter operates as a full bridge circuit, the first switch means is turned on and the second switch means is turned off.

  ADVANTAGE OF THE INVENTION According to this invention, the conversion efficiency of the converter of an induction heating apparatus can be improved, and the efficiency which supplies electric power to metal cookware can be improved.

The circuit block diagram of the power converter device of Example 1. FIG. The circuit block diagram of the power converter device of Example 2. FIG. The conversion efficiency characteristic graph of a converter. The graph which shows the relationship between the output voltage of a converter, and input electric power. The graph which shows the relationship between the output voltage of a converter, and input electric power. FIG. 9 shows operation waveforms of gate driving in the second embodiment. FIG. FIG. 9 shows operation waveforms of gate driving in the second embodiment. FIG. FIG. 9 shows operation waveforms of gate driving in the second embodiment. FIG. The circuit block diagram of the power converter device of Example 3. FIG. The operation | movement waveform of the power converter device of Example 3. FIG. The circuit block diagram of the power converter device of Example 4. FIG. The operation | movement waveform of the power converter device of Example 4. FIG. The circuit block diagram of the power converter device of Example 5. FIG. The operation waveform of the power conversion measure of Example 5. The operation waveform of the power conversion measure of Example 5. The operation waveform of the power conversion measure of Example 5. The operation waveform of the power conversion measure of Example 5. 6 is a modification of the converter according to the first embodiment. 7 is a modification of the converter according to the second embodiment. 6 is a modification of the inverter according to the third embodiment. 6 is a modification of the inverter according to the third embodiment.

  Embodiments of the present invention will be described below with reference to the drawings.

  The power conversion device according to the first embodiment will be described with reference to FIG. The power converter according to the present embodiment is a device that applies a high-frequency current to the heating coil 14 to inductively heat a metallic object. In FIG. 1, 1 is a commercial power source, 2 is a rectifier circuit, and 20 is a step-up / down voltage. Converters 30 and 40 are upper and lower arms of the inverter.

  The AC voltage supplied from the commercial power source 1 is rectified by the rectifier circuit 2 and supplied to the step-up / step-down converter 20. The step-up / step-down converter 20 boosts or steps down the input voltage and outputs it. A series circuit of the IGBT 3 and the diode 4 arranged on the input side, a series circuit of the diode 6 and the IGBT 7 arranged on the output side, The choke coil 5 is arranged between a connection point (point a) between the emitter terminal of the IGBT 3 and the cathode terminal of the diode 4 and a connection point (point b) between the anode terminal of the diode 6 and the collector terminal of the IGBT 7. Of the output points of the buck-boost converter 20, the output point on the cathode terminal side of the diode 6 is designated as p point, and the output point on the emitter terminal side of the IGBT 7 is designated as n point.

  Inverters 30, 40 and a smoothing capacitor 15 are connected in parallel between the output points (p point, n point) of the step-up / down converter 20.

  Inverter 30 includes a series connection of IGBTs 8a and IGBTs 8b, which are main switching elements, and a diode 9a is connected in reverse parallel to IGBT 8a, and a diode 9b is connected in reverse parallel to IGBT 8b.

  The inverter 40 includes a series connection of IGBTs 8c and IGBTs 8d which are main switching elements. A diode 9c is connected in antiparallel to the IGBT 8c, and a diode 9d is connected in antiparallel to the IGBT 8d. A snubber capacitor 10c is connected in parallel to the IGBT 8c, and a snubber capacitor 10d is connected in parallel to the IGBT 8d. The snubber capacitors 10c and 10d are charged or discharged by a cut-off current when the IGBT 8c or IGBT 8d is turned off, and the change in voltage applied to both IGBTs is reduced, thereby suppressing turn-off loss.

  A series circuit of the relay 11, the resonance capacitor 12, and the heating coil 14 is connected between the connection point (point o) between the IGBT 8a and the IGBT 8b and the connection point (point q) between the IGBT 8c and the IGBT 8d. A series circuit of the heating coil 14 and the resonance capacitor 13 is connected between the n points. A relay 16 is connected between point b of the buck-boost converter 20 and point o of the inverter 30. By switching the relays 11 and 16 arranged in this way, the resonance frequency and the inverter circuit system can be changed according to the object to be heated.

  Next, a driving method according to the material of the object to be heated will be described. Since the heating coil 14 and the object to be heated are magnetically coupled, when the object to be heated is converted into an equivalent circuit viewed from the side of the heating coil 14, the equivalent resistance and equivalent inductance of the object to be heated are connected in series. The equivalent resistance and equivalent inductance of the object to be heated vary depending on the material, and both are large for a magnetic material such as iron, and both are small for a non-magnetic material such as copper and aluminum. Therefore, when the object to be heated is a magnetic material such as iron, the relay 16 is turned off and the relay 11 is turned on, and heating is performed in a full bridge circuit using both the inverters 30 and 40.

  On the other hand, when the object to be heated is a non-magnetic material such as copper or aluminum, the relay 16 is turned on, the relay 11 is turned off, and the SEPP (Single Ended Push Pull) composed of the inverter 40, the heating coil 14, and the resonant capacitor 13. Heating is performed with an inverter of the type. At this time, the IGBT 7 and the IGBT 8b are connected in parallel, and the diode 6 and the diode 9a are also connected in parallel. When the IGBTs 7 and 8b are driven in synchronization, the currents flowing through the IGBTs 7 and 8b and the diodes 6 and 9a are halved, so that conduction loss and switching loss can be reduced. On the other hand, when the IGBTs 7 and 8b are driven in a complementary manner, the driving frequency of each IGBT can be halved, so that the switching loss can be halved. In this way, the amount of heat generated by each element can be reduced, and the radiating fin can be miniaturized.

  FIG. 18 shows a modification of the first embodiment. A difference from FIG. 1 is that a boost converter 100 is used instead of the buck-boost converter 20 of FIG. In the boost converter 100, the IGBT 3 and the diode 4 are omitted from the step-up / down converter 20, and one end of the choke coil 5 is connected to the output terminal of the rectifier circuit 2. Since the operation and effect are the same as those in the first embodiment, description thereof is omitted.

  In the above, an example in which an IGBT is used as the voltage-driven semiconductor element has been described. However, a power MOSFET suitable for high-frequency driving may be used in place of the IGBT, and a wide-range capable of ultrahigh-frequency / high-temperature operation. A band gap element SiC or GaN MOSFET or JFET may be used.

  In addition, you may comprise an induction heating apparatus using the power converter device of a present Example demonstrated above. As an example of the induction heating device, there is an induction heating device in which a glass plate is provided above the heating coil 14 and induction heating is performed on a metallic pan placed on the glass plate.

  The power converter device of Example 2 is demonstrated using FIG. The same components as those in the first embodiment are denoted by the same reference numerals, and redundant description is avoided. The difference from the first embodiment is that the inverter 30 connected to the buck-boost converter 20 in the first embodiment is connected to the rectifier circuit 2 and the relay 16 connected to the b point in the first embodiment is a point. It is a connected point.

  First, the case where the object to be heated is non-magnetic will be described. In this case, the relay 16 is turned on, the relay 11 is turned off, and heating is performed by an SEPP type inverter including the inverter 40, the heating coil 14, and the resonance capacitor 13. At this time, the IGBT 3 and the IGBT 8a are connected in parallel, and the diode 4 and the diode 9b are connected in parallel. When the IGBTs 3 and 8a are driven in synchronization, the currents flowing through the IGBTs 3 and 8a and the diodes 4 and 9b are halved, so that conduction loss and switching loss can be reduced. On the other hand, by driving the IGBTs 3 and 8a in a complementary manner, the driving frequency of each IGBT can be halved, so that the switching loss can be halved. As a result, the amount of heat generated by each element can be reduced, and the size of the radiating fin can be reduced.

  Next, the case where the cooking utensil is magnetic will be described. In this case, the relay 16 is turned off, the relay 11 is turned on, and heating is performed in a full bridge circuit using both the inverters 30 and 40. In this embodiment, the inverter 30 is connected to the output part of the rectifier circuit 2, and the inverter 40 is connected to the output part of the buck-boost converter 20. Accordingly, the output voltage of the rectifier circuit 2 is applied to the inverter 30 as it is, and the voltage boosted or lowered by the step-up / down converter 20 is input to the inverter 40. Since the input voltage to the inverter 30 is the output voltage of the rectifier circuit 2, it becomes a pulsating voltage obtained by rectifying the commercial voltage. On the other hand, since the input voltage to the inverter 40 is the output voltage of the buck-boost converter 20, a smoothed voltage is applied.

FIG. 3 shows the output voltage and conversion efficiency of the buck-boost converter 20, and FIG. 4 shows the relationship between the converter output voltage and the inverter output power. As shown in FIG. 4 , the inverter output power can be reduced by lowering the output voltage of the buck-boost converter 20. However, as shown in FIG. 3, when the output voltage of the buck-boost converter 20 is set to 150 V or less, the conversion efficiency of the buck-boost converter 20 when the output voltage is 300 V is lowered. Therefore, when the output voltage of the buck-boost converter 20 exceeds 150V, the power is controlled by the output voltage of the buck-boost converter 20, and when the output voltage of the buck-boost converter 20 is 150V or less, the inverter 30 or 40 is duty controlled. To control.

  Next, a method for controlling the output power of the inverter at a converter output voltage of 150 V or less will be described. FIG. 5 shows the relationship between the duty of IGBTs 8a and 8d (ratio of conduction time of drive cycle) and inverter output power. At this time, the converter voltage applied to the inverter is constant at 150V. As shown here, the inverter output power can be controlled by changing the duty of the IGBTs 8a and 8b. As a result, the converter voltage can be operated at a constant 150V, so that the inverter output power can be controlled without reducing the efficiency.

  The operation waveforms of each IGBT will be described with reference to FIGS. 6 and 7, the IGBTs 8a and 8b and the IGBTs 8c and 8d operate in a complementary manner, the IGBTs 8a and 8d are synchronized, and the IGBTs 8b and 8c are synchronized.

  FIG. 6 is an operation waveform of each IGBT used when the inverter output is maximum. After IGBTs 8a and 8d having a duty of PW (PW ≦ T / 2) are turned on synchronously, IGBTs 8b and 8c having a duty of PW are synchronized. And turn on.

  On the other hand, FIG. 7 shows operation waveforms of the IGBTs used when the inverter output is reduced. After the IGBTs 8a and 8d with the Duty of PW1 are turned on synchronously, the IGBTs 8b and 8c with the Duty of PW2 (PW1 <PW2). Are turned on synchronously. By using these operation waveforms, the current flowing through the IGBTs 8a and 8d can be suppressed, and the inverter output power can be reduced. Although the above has been described with reference to the IGBTs 8a and 8b, the same effect can be obtained even with the IGBTs 8b and 8c as a reference.

  Another method is phase shift control. The phase shift control is a method of controlling the power by fixing the duty of the IGBT and shifting the phases of the inverter 30 and the inverter 40. As shown in FIG. 8, the delay time (shift) is provided from the IGBT 8a on, and the IGBT 8d is set. In addition to turning on, a delay time (shift) is provided from turning on the IGBT 8b to turn on the IGBT 8c. As the shift amount is increased, the simultaneous ON period of the IGBTs 8a and 8d and the simultaneous ON period of the IGBTs 8b and 8c are shortened. Therefore, the energization period between the oq points in FIG. It becomes low and can reduce the electric power which the heating coil 14 gives to a cooking appliance. In the phase shift control, the maximum power can be obtained when the shift amount is zero, and the operation waveform of each IGBT at that time is the same as that shown in FIG.

  FIG. 19 shows a modification of the second embodiment. A difference from FIG. 2 is that a step-down converter 110 is used instead of the step-up / step-down converter 20 of FIG. In step-down converter 110, diode 6 and IGBT 7 are omitted from step-up / down converter 20, and one end of choke coil 5 is connected to inverter 40. Since the operation and effect are the same as those in the second embodiment, description thereof is omitted.

  A power conversion apparatus according to the third embodiment will be described with reference to FIG. The same components as those in the first embodiment are denoted by the same reference numerals, and redundant description is avoided. The difference from the first embodiment is that an auxiliary inductor 62 magnetically coupled to the choke coil 5 is connected between the point b and the relay 16, and a snubber capacitor 10a parallel to the IGBT 8a and a snubber capacitor 10b parallel to the IGBT 8b are provided. Is a point. Since the inverter operation is the same as that of the first embodiment, a description thereof will be omitted.

  The converter operation during aluminum heating will be described with reference to FIG. When the aluminum is heated, the relay 16 is turned on and the relay 11 is turned off. Here, the current flowing through the IGBT 8b is Im, the voltage is Vm, the current flowing through the IGBT 7 is Is, the collector-emitter voltage is Vs, the current flowing through the diode 9a is Id1, the current flowing through the diode 6 is Id2, and the choke coil 5 flows. Let the current be IL. In Example 3, since soft switching is performed during the boosting operation, only the boosting operation will be described.

  Prior to time t0, no drive signal is applied to the gates of IGBT 8b and IGBT 7, and both IGBTs are off. When the drive signal of the IGBT 7 is turned on at time t0, the current that has been flowing through the diode 6 flows into the IGBT 7. Thereafter, the electric charge charged in the snubber capacitor 10b is discharged through the path of the snubber capacitor 10b, the relay 16, the auxiliary inductor 62, and the IGBT 7, and the electric charge is extracted. When the electric charge of the snubber capacitor 10b is extracted, the energy stored in the auxiliary inductor 62 causes the current Is to flow through the path of the auxiliary inductor 62, the IGBT 7, and the diode 9b. For this reason, if a drive signal is applied to IGBT8b at the time t1 immediately after that, IGBT8b will be turned ON in the period when the diode 9b is energized. That is, the IGBT 8b can perform zero voltage switching (hereinafter referred to as ZVS) and zero current switching (hereinafter referred to as ZCS). Therefore, switching loss due to the turning on of the IGBT 8b does not occur.

  Next, at time t2, current begins to flow through the IGBT 8b, and at time t3, current in the path of the auxiliary inductor 62, IGBT 7, diode 9b, and relay 16 stops flowing, and from the commercial power source 1 through the rectifier circuit 2, the IGBT 3, choke A current flows through the path of the coil 5, the auxiliary inductor 62, and the IGBT 8b.

  At time t4, the gate drive signals of IGBT 8b and IGBT 7 are turned off. When the current of the IGBT 8b is cut off, the current flows from the commercial power source 1 to the IGBT 3, the choke coil 5, the auxiliary inductor 62, and the snubber capacitor 10b from the commercial power source 1 through the rectifier circuit 2 from time t4 to time t5. The voltage between the emitters rises by dv / dt determined by the capacity of the snubber capacitor 10b and the cutoff current value. That is, by making the dv / dt of the collector-emitter voltage of the IGBT 8b moderate by the snubber capacitor 10b, ZVS can be achieved and the turn-off loss can be reduced. On the other hand, since no current flows through the IGBT 7 after time t3, no turn-off loss occurs at the time of turn-off at time t4.

  Next, at time t <b> 5, the diode 9 a is turned on by the energy stored in the auxiliary inductor 62, and energy enters the path of the auxiliary inductor 62, the diode 9 a, the smoothing capacitor 15, the commercial power supply 1, the rectifier circuit 2, the IGBT 3, and the choke coil 5. Flows. The energy stored in the choke coil 5 flows through the choke coil 5, the diode 6, the smoothing capacitor 15, the commercial power supply 1, the rectifier circuit 2, and the IGBT 3 to charge the smoothing capacitor 15. When the energy of the auxiliary inductor 62 runs out at time t6, the current in the path of the auxiliary inductor 62, the diode 9a, the smoothing capacitor 15, the commercial power supply 1, the rectifier circuit 2, the IGBT 3, and the choke coil 5 stops flowing.

  As described above, by providing the auxiliary inductor 62 and turning on the IGBT 8b after turning on the IGBT 7, a soft switching operation can be performed and the switching loss of the IGBT 8b can be reduced. The timing for turning on the IGBT 7 and the IGBT 8b may be within about 1/10 of the drive cycle.

FIG. 20 shows a modification of the third embodiment. A difference from FIG. 9 is that a boost converter 120 is used instead of the step-up / step-down converter 20 of FIG. In the boost converter 120, the IGBT 3 and the diode 4 are omitted from the step-up / down converter 20, and one end of the inductor 62 is connected to the output terminal of the rectifier circuit 2. Note that the operation and effect are the same as those in the third embodiment, and thus the description thereof is omitted.

  The power converter of Example 4 is demonstrated using FIG. The same components as those of the second embodiment are denoted by the same reference numerals, and redundant description is avoided. The difference from the second embodiment is that an auxiliary inductor 62 magnetically coupled to the choke coil 5 is connected between the point a and the relay 16, a snubber capacitor 10a parallel to the IGBT 8a, and a snubber capacitor 10b parallel to the IGBT 8b. It is a point. Since the inverter operation is the same as that of the second embodiment, a description thereof will be omitted.

  The converter operation during aluminum heating will be described with reference to FIG. When the aluminum is heated, the relay 16 is turned on and the relay 11 is turned off. Here, the current flowing through the IGBT 8a is Im, the voltage is Vm, the current flowing through the IGBT 3 is Is, the voltage is Vs, the current flowing through the diode 9b is Id1, the current flowing through the diode 4 is Id2, and the current flowing through the choke coil 5 is IL. To do. In Example 4, since soft switching is performed during the step-down operation, only the step-down operation will be described.

  Prior to time t0, no drive signal is applied to the gates of IGBT 8a and IGBT 3, and both IGBTs are off. When the driving signal of the IGBT 3 is turned on at time t0, the electric charge charged in the snubber capacitor 10a flows through the path of the snubber capacitor 10a, IGBT 3, auxiliary inductor 62, and relay 16, and the electric charge is extracted. The current flowing at this time becomes ZCS with a gentle di / dt due to the leakage inductance of the choke coil 5 and the auxiliary inductor 62, and the turn-on loss of the IGBT 8a can be reduced. When the electric charge of the snubber capacitor 10a is extracted, the current Is flows through the path of the auxiliary inductor 62, the relay 16, the diode 9a, and the IGBT 3 by the energy stored in the auxiliary inductor 62. For this reason, if a drive signal is applied to the IGBT 8a at time t1 immediately after that, the IGBT 8a is turned on during the period in which the diode 9a is energized. That is, the IGBT 8a can perform ZVS and ZCS. Therefore, the switching loss due to the turning on of the IGBT 8a does not occur.

  Next, at time t2, current begins to flow through the IGBT 8a, and at time t3, current in the path of the auxiliary inductor 62, relay 16, diode 9a, and IGBT 3 stops flowing, and from the commercial power source 1 through the rectifier circuit 2, the IGBT 3 and choke A current flows through the path of the coil 5, the diode 6 and the smoothing capacitor 15 and the path of the IGBT 8 a, the relay 16, the auxiliary inductor 62, the choke coil 5, the diode 6 and the smoothing capacitor 15.

  At time t4, the gate drive signals for IGBT 8a and IGBT 3 are turned off. First, when the current of the IGBT 8a is interrupted, the snubber capacitor 10a, the relay 16, the auxiliary inductor 62, the choke coil 5, the diode 6, and the smoothing capacitor 15 are passed from the commercial power source 1 through the rectifier circuit 2 from time t4 to t5. A current flows through the path, and the collector-emitter voltage of the IGBT 8a increases by dv / dt determined by the capacity of the snubber capacitor 10a and the cutoff current value. That is, by making the dv / dt of the collector-emitter voltage of the IGBT 8a moderate by the snubber capacitor 10a, ZVS can be achieved and the turn-off loss can be reduced. On the other hand, since no current flows in the IGBT 3 after the time point t3, no turn-off loss occurs at the time of turn-off at the time point t4.

  Next, when Vm rises at time t5, the voltage between the IGBTs 8b decreases, the diode 9b turns on, and the auxiliary inductor 62, choke coil 5, diode 6 and smoothing capacitor 15 are turned on by the energy stored in the auxiliary inductor 62. The current flows through the path of the diode 9b and the relay 16. At time t6, the energy of the auxiliary inductor 62 disappears, and the energy stored in the choke coil 5 causes the choke coil 5, the diode 6, the smoothing capacitor 15, the diode 4 path, the choke coil 5, the diode 6, the smoothing capacitor 15, A current flows through the path of the diode 9b, the relay 16, and the auxiliary inductor 62, and charges the smoothing capacitor 15.

  As described above, by providing the auxiliary inductor 62 and turning on the IGBT 8a after turning on the IGBT 3, a soft switching operation can be performed and the switching loss of the IGBT 8a can be reduced. The timing for turning on the IGBT 3 and the IGBT 8a may be within about 1/10 of the driving cycle.

  FIG. 21 shows a modification of the fourth embodiment. A difference from FIG. 11 is that a step-down converter 130 is used instead of the step-up / step-down converter 20 of FIG. The step-down converter 130 is obtained by omitting the diode 6 and the IGBT 7 from the step-up / down converter 20 and connecting one end of the choke coil 5 to the inverter 40. Since the operation and effect are the same as those in the second embodiment, description thereof is omitted.

  A power conversion apparatus according to a fifth embodiment that realizes power factor correction control (PFC control) will be described with reference to FIG. The same components as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted.

  First, voltage / current detection points necessary for controlling each IGBT in the present embodiment will be described.

  In order to detect the power input from the AC power source AC and the material of the object to be heated, it is necessary to detect the AC current flowing from the AC power source AC. In this embodiment, the AC current flowing from the AC power source AC is converted into a voltage by the current sensor 70 and then detected by the AC current detection circuit 71.

  Further, in order to improve the power factor by generating the waveform of the AC current according to the voltage of the AC power supply AC, a signal that is a reference for the current waveform is required. In this embodiment, the output voltage of the rectifier circuit 2, that is, the rectified DC voltage is detected by the input voltage detection circuit 72. In order to reduce the number of components, it is also possible to obtain a reference waveform inside the control circuit without detecting the input voltage and generate an AC current waveform. In this case, the input voltage detection circuit 72 can be deleted. .

  The generation of the AC current waveform can be realized by controlling the current waveform flowing through the choke coil 5 for the converter. In this embodiment, the current flowing through the converter is converted into a voltage by the current sensor 73 and then detected by the input current detection circuit 74. It is also possible to generate the waveform of the AC current by detecting the currents of the IGBTs 3 and 7 without detecting the current of the choke coil 5. In this case, there is no problem if the position of the current sensor 73 is changed.

  In order to control the input power and to detect the material and state of the object to be heated, it is necessary to detect the current flowing through the heating coil 14. In this embodiment, the current flowing through the heating coil 14 is converted into a voltage by the current sensor 75 and then detected by the coil current detection circuit 76.

  Further, in order to control the output power of the load, it is necessary to perform feedback control by detecting the output voltage of the converter, that is, the power supply voltage of the inverter. In the present embodiment, the voltage of the smoothing capacitor 15 is detected by the inverter voltage detection circuit 77. The control circuit 80 generates a drive signal for each switching element based on the detection value of each detection circuit and the power command value from the input power setting unit 90.

  When the power conversion device of this embodiment is used for an induction heating device, in order to control power by an inverter circuit, a PFM (pulse frequency control) that varies the frequency by utilizing the fact that the impedance of the resonant load circuit changes depending on the frequency. ) Easy to control. In this embodiment, power can be controlled by performing PFM control on the upper and lower arms of the IGBTs 8c and 8d. However, PAM (pulse amplitude control) control in which the power supply voltage amplitude of the inverter is variable is desirable under a load condition where the power change with respect to the frequency is large, that is, a high Q representing the sharpness of resonance. In this embodiment, power control can be performed by controlling the power supply voltage of the inverter by PWM control of the converter composed of IGBTs 3, 7, and 8b. The IGBTs 3, 7, and 8 b are driven by a drive circuit 78 based on a control signal from the control circuit 80, and the IGBTs 8 c and 8 d are driven by a drive circuit 79 based on a control signal from the control circuit 80.

  Next, in the induction heating apparatus of this embodiment, a method for controlling the converter when the object to be heated is copper or aluminum will be described. As described in the first embodiment, when the object to be heated is aluminum, the relay 16 is turned on and the relay 11 is turned off and driven by the SEPP inverter. The IGBTs 3, 7, and 8b operate as IGBTs for step-down, step-up, and step-up / step-down choppers, and perform power factor correction control and output voltage control that generate an input current waveform according to the voltage of the AC power supply AC.

  A control method of the IGBTs 3, 7, and 8b according to the present embodiment will be described with reference to FIGS. 14 and 15, the voltage of the AC power supply AC is indicated by Vac, and the voltage of the smoothing capacitor 15 is indicated by V15. In order to make the explanation easy to understand, it is assumed that the AC power supply Vac has a positive voltage period. First, in FIG. 14, when Vac is higher than V15, the IGBTs 7 and 8b are turned off, and the IGBT 3 is turned on / off to enable the step-down mode chopper operation. Conversely, when Vac is lower than V15, the IGBT 3 is turned on, and the IGBTs 7 and 8b are controlled to be turned on / off, thereby enabling the chopper operation in the boost mode. Thus, by switching the chopper operation according to the change in the AC power supply voltage Vac, that is, the voltage change within the commercial cycle, the number of switching of each switching element can be reduced, switching loss can be reduced, and the IGBTs 7 and 8b can be reduced. Since the parallel operation is performed, the current flowing through each IGBT is halved and the loss can be reduced. When Vac is a negative voltage, the voltage is converted to a positive voltage via the rectifier circuit 2, so that the operation is the same as that of the positive voltage period described above.

  Further, as shown in FIG. 15, when Vac is smaller than V15 (in the boost mode), the IGBTs 7 and 8b can be driven in a complementary manner so that the driving frequency of the IGBTs 7 and 8b can be halved. Can be halved. As a result, the amount of heat generated by each element can be reduced, and the size of the radiating fin can be reduced.

  Further, as shown in FIG. 16, the chopper operation in the step-up / step-down mode can be performed by simultaneously controlling on / off of the IGBTs 3, 7, 8b regardless of the voltage change within the commercial cycle.

  In addition, as shown in FIG. 17, the chopper operation in the step-up / step-down mode is possible by controlling on / off of IGBTs 3, 7, and 8b and driving IGBTs 7 and 8b in a complementary manner regardless of a voltage change within a commercial cycle. In addition, since the drive frequency of the IGBTs 7 and 8b can be halved, the switching loss can be halved. As a result, the amount of heat generated by each element can be reduced, and the size of the radiating fin can be reduced.

DESCRIPTION OF SYMBOLS 1 Commercial power supply 2 Rectifier circuit 3, 7, 8a, 8b, 8c, 8d IGBT
4, 6, 9a, 9b, 9c, 9d Diode 5 Choke coil 10a, 10b, 10c, 10d Snubber capacitor 11, 16 Relay 12, 13 Resonant capacitor 14 Heating coil 15 Smoothing capacitor 20 Buck-boost converter 30, 40 Inverter 62 Auxiliary inductor 70, 73, 75 Current sensor 71 AC current detection circuit 72 Input voltage detection circuit 74 Input current detection circuit 76 Coil current detection circuit 77 Inverter voltage detection circuit 78, 79 Drive circuit 80 Control circuit 90 Input power setting unit 100 Step-up converter 110 Step-down converter

Claims (14)

A converter that converts an AC voltage into a DC voltage by driving a switching element;
It has a first upper and lower arm in which two main switching elements are connected in series and a second upper and lower arm in which two main switching elements are connected in series, and converts a DC voltage from the converter into an AC voltage to load An inverter to supply to
Driving the main switching element of the first upper and lower arms to operate the inverter as a half bridge circuit, and driving the main switching element of the first upper and lower arms and the main switching element of the second upper and lower arms. And control means for operating the inverter as a full bridge circuit;
A first load circuit connected between output terminals of the half-bridge circuit;
A second load circuit connected between output terminals of the full bridge circuit and including a part of the first load circuit;
First switch means for connecting the second load circuit and the inverter;
One main switching element of the second upper and lower arms, and second switch means for connecting the switching element of the converter in parallel;
With
The control means includes
When operating the inverter as a half-bridge circuit, turning off the first switch means and turning on the second switch means,
When the inverter operates as a full bridge circuit, the first switch means is turned on and the second switch means is turned off. In claim 1,
The converter is
A series circuit of a first switching element and a first diode disposed on the input side;
A series circuit of a second diode and a second switching element disposed on the output side;
A choke coil disposed between a connection point of the first switching element and the first diode and a connection point of the second diode and the second switching element;
A power conversion device comprising: In claim 2,
The second switch means includes
Between the connection point of the first switching element and the first diode and the connection point of the two main switching elements of the second upper and lower arms, or
The power conversion device is provided between a connection point of the second switching element and the second diode and a connection point of two main switching elements of the second upper and lower arms. In claim 1,
The converter includes a series circuit of a diode and a switching element disposed on the output side, and a choke coil disposed between a connection point of the diode and the switching element and an input terminal,
The power conversion device, wherein the second switch means is provided between a connection point of the switching element and the diode and a connection point of two main switching elements of the second upper and lower arms. In claim 1,
The converter includes a series circuit of a switching element and a diode disposed on the input side, and a choke coil disposed between a connection point of the diode and the switching element and an output terminal,
The power conversion device, wherein the second switch means is provided between a connection point of the switching element and the diode and a connection point of two main switching elements of the second upper and lower arms. A converter that converts an AC voltage into a DC voltage by driving a switching element;
It has a first upper and lower arm in which two main switching elements are connected in series and a second upper and lower arm in which two main switching elements are connected in series, and converts a DC voltage from the converter into an AC voltage to load An inverter to supply to
Driving the main switching element of the first upper and lower arms to operate the inverter as a half bridge circuit, and driving the main switching element of the first upper and lower arms and the main switching element of the second upper and lower arms. And control means for operating the inverter as a full bridge circuit;
A first load circuit connected between output terminals of the half-bridge circuit;
A second load circuit connected between output terminals of the full bridge circuit and including a part of the first load circuit;
First switch means for connecting the second load circuit and the inverter;
One main switching element of the second upper and lower arms, and second switch means for connecting the switching element of the converter in parallel;
An auxiliary inductor connected to one end of the second switch means;
With
The control means includes
When operating the inverter as a half-bridge circuit, turning off the first switch means and turning on the second switch means,
When the inverter operates as a full bridge circuit, the first switch means is turned on and the second switch means is turned off. In claim 6,
The converter is
A series circuit of a first switching element and a first diode disposed on the input side;
A series circuit of a second diode and a second switching element disposed on the output side;
A choke coil disposed between a connection point of the first switching element and the first diode and a connection point of the second diode and the second switching element;
A power conversion device comprising: In claim 7,
A series circuit of the second switch means and the auxiliary inductor is:
Between the connection point of the first switching element and the first diode and the connection point of the two main switching elements of the second upper and lower arms, or
Between the connection point of the second switching element and the second diode and the connection point of the two main switching elements of the second upper and lower arms;
The choke coil and the auxiliary inductor are magnetically coupled. In claim 6,
The converter includes a series circuit of a diode and a switching element disposed on the output side, and a choke coil disposed between a connection point of the diode and the switching element and an input terminal,
The series circuit of the second switch means and the auxiliary inductor is provided between the connection point of the switching element and the diode and the connection point of the two main switching elements of the second upper and lower arms. A power conversion device. In claim 6,
The converter includes a series circuit of a switching element and a diode disposed on the input side, and a choke coil disposed between a connection point of the diode and the switching element and an output terminal,
The series circuit of the second switch means and the auxiliary inductor is provided between the connection point of the switching element and the diode and the connection point of the two main switching elements of the second upper and lower arms. A power conversion device. In claim 1 or claim 6,
The control means drives the switching element of the converter and one switching element of the second upper and lower arms synchronously to drive the power conversion device.
In claim 1 or claim 6,
The control means drives the switching element of the converter and one switching element of the second upper and lower arms in a complementary manner.
The power conversion device according to any one of claims 1 to 12,
An induction heating device comprising a top plate,
The first load circuit includes a heating coil, wherein the metal pan placed on the top plate is induction-heated by an AC voltage supplied from the inverter to the heating coil. Induction heating device. In claim 6,
One of the switching elements of the second upper and lower arms is turned on after the switching element of the converter is turned on.