JP4893120B2 - Induction heating device - Google Patents

Description

  The present invention relates to an induction heating device used in general homes, induction heating cookers, offices, restaurants, factories, and the like.

  Conventionally, in an induction heating apparatus, a control technique for supplying a boosted voltage to an inverter circuit by a booster circuit is known as a method of supplying high-frequency power to a load via a heating coil (see, for example, Patent Document 1).

There is also known a technique in which a power factor correction circuit is incorporated in an induction heating device to suppress harmonic current of an input current (see, for example, Patent Document 2).
Japanese Patent Laid-Open No. 2003-257609 JP-A-1-246683

  However, in the induction heating apparatus using the conventional technique, when the inverter circuit is stopped before the circuit having the boosting function when heating is stopped, the load impedance as viewed from the boosting circuit having the boosting function and the power factor correction circuit suddenly increases. . Since the booster circuit and the power factor correction circuit having a booster function try to maintain the boosting level during heating until an output voltage feedback having a predetermined time constant is applied, the booster circuit over-boosts at the moment when the load impedance becomes high, A voltage exceeding the withstand voltage rating of each element is applied to the output capacitor of the booster circuit and the power factor correction circuit or the switching device of the inverter circuit to which the output voltage is input, resulting in element destruction. Further, if the power factor correction circuit is stopped before the booster circuit, there is a problem that the power factor during the stop process period of the booster circuit is lowered.

  The present invention solves the above-described conventional problems, and does not over-boost the output voltage of a boosting function unit having a boosting function, such as a boosting circuit and a power factor correction circuit having a boosting function, so that the heating operation of the inverter circuit can be performed. It aims at providing the induction heating apparatus which can be stopped.

  In order to solve the above-described conventional problems, the induction heating apparatus of the present invention is configured such that the inverter operation stop timing at the time of heating stop, the boost control unit that controls the boost function unit having the boost function, the output voltage of the boost function unit Boosting operation of the boosting function unit to suppress the boosting width of the voltage boosted by the boosting function unit and output to the inverter by the change in load impedance as seen from the boosting function unit when the operation of the input inverter circuit stops However, the operation is stopped without delaying more than a predetermined amount with respect to the operation stop of the inverter circuit.

  As a result, when the heating operation is stopped, the induction heating device is continuously driven without stopping the inverter circuit as a load before the boosting function unit having the boosting function is stopped, or the boosting function unit is Even if the inverter circuit is stopped before stopping, the boosting circuit stops the boosting operation without delaying more than a predetermined time from the stop, so the load impedance viewed from the boosting function unit is maintained at the boosting function of the boosting function unit. The boosting function unit or the inverter circuit is prevented from suddenly greatly changing when the output voltage is increased, or the boosting operation is stopped before the boosting width of the output voltage due to the boosting function of the boosting function unit becomes large, thereby suppressing the overboost. It is possible to safely stop the heating operation by preventing a voltage exceeding the rating from being applied to the component.

  The induction heating device of the present invention can stop the boosting operation without over-boosting the output voltage when the boosting function unit having the boosting function stops the operation of the inverter circuit that supplies the output voltage when the heating is stopped. It will be.

The first invention includes a boosting function unit that inputs a DC power supply and boosts and outputs a DC voltage having a peak value larger than the peak value by ON / OFF operation of the switching element, and has the heating coil. An inverter circuit that inputs a voltage output from the unit and generates a high-frequency current in the heating coil by an on / off operation of another switching element, a boost control unit that controls the boost operation of the boost function unit, and the inverter circuit An inverter control unit that controls the operation of the inverter circuit, and the boost control unit is boosted by the boost function unit due to a change in load impedance as seen from the boost function unit when the operation of the inverter circuit is stopped, and is supplied to the inverter circuit. in order to suppress the boost width of voltage output below a predetermined value, the driving frequency and the conduction time a predetermined output or less and a predetermined output of the inverter circuit Dohaba set below, by stopping while suppressing the output variation of said inverter circuit, in a state in which the magnitude of the load impedance viewed from the circuit having the boosting function does not change abruptly, the boosting operation of the boosting function unit Is stopped without delaying more than a predetermined delay with respect to the operation stop of the inverter circuit, so that the input voltage of the inverter circuit can be varied with a degree of freedom with respect to the operation of the inverter circuit, and the inverter circuit Can be finely variably controlled, and the boost control unit can boost the voltage output to the inverter after being boosted by the boost function unit due to a change in load impedance as seen from the boost function unit when the operation of the inverter circuit stops. In order to suppress the width below a predetermined value, the boosting operation of the boosting function unit is delayed by a predetermined amount or more with respect to the stop of the inverter circuit Therefore, the boost operation is stopped before the output impedance becomes higher than a predetermined level due to the boosting function of the boosting function unit. Thus, it is possible to suppress the output voltage of the boosting function unit from being excessively boosted.

  According to a second aspect of the invention, in particular, in the first aspect of the invention, the step-up control unit performs the heating operation by stopping the step-up operation of the step-up function unit prior to the operation stop of the inverter circuit by the inverter control unit. When stopping, the inverter circuit, which is the load, is driven at least while the booster circuit is performing the boost operation, so the load impedance seen from the booster circuit suddenly changes greatly and the output voltage of the booster circuit increases excessively. This is an induction heating device that can reliably prevent this from occurring, quickly lower the output voltage, and safely stop the heating operation.

  According to a third invention, in particular, in the second invention, a DC voltage obtained by rectifying an AC power supply is input to output a smoothed DC voltage to the first capacitor, and the power factor of the AC power supply is improved. The boosting function unit includes a boosting circuit control unit that controls the boosting circuit, and stops the boosting operation of the boosting circuit prior to the operation of the inverter circuit. When stopping the operation, since the inverter circuit, which is the load, is driven at least while the booster circuit is performing the boosting operation, the load impedance viewed from the booster circuit changes suddenly and the output voltage of the booster circuit An induction heating apparatus that can reliably prevent over-boosting, quickly reduce the output voltage, and safely stop the heating operation.

  According to a fourth aspect of the invention, in particular, in the second aspect of the invention, the boosting function unit inputs a DC power source obtained by rectifying the AC power source and boosts the voltage to a voltage having a peak value larger than the peak value. And a power factor improvement circuit that improves the power factor of the AC power supply, and the boost control unit includes a power factor improvement circuit control unit that controls the operation of the power factor improvement circuit, and the power factor improvement circuit control Since the power factor correction circuit has a boosting function by stopping the boosting operation of the power factor improvement circuit prior to stopping the operation of the inverter circuit, the boosting / power factor improvement circuit can be downsized and reduced in cost. In addition, when stopping the heating operation, the load circuit is viewed from the power factor improvement circuit because the inverter circuit, which is the load, is driven at least while the power factor improvement circuit is performing the boosting operation. Sudden An induction heating device capable of reliably preventing the output voltage of the power factor correction circuit from being excessively boosted due to large fluctuations and quickly stopping the heating operation by quickly reducing the output voltage of the power factor improvement circuit; Become.

  According to a fifth aspect of the invention, in particular, in the third aspect of the invention, the power factor correction circuit boosts the voltage to a voltage having a peak value larger than the peak value of the input DC power supply and outputs the boosted voltage to the first capacitor. Since the control unit stops the boosting operation of the power factor correction circuit before stopping the operation of the inverter circuit, the boosting function can be shared between the power factor correction circuit and the boosting circuit. The circuit can be reduced in size and cost, and when the heating operation is stopped, the inverter circuit as a load is driven at least while the power factor correction circuit is performing the boosting operation. The load impedance seen from the power factor correction circuit is suddenly greatly changed and the output voltage of the power factor correction circuit is surely prevented from being excessively boosted. The induction heating device capable of stopping the operation.

  According to a sixth aspect of the invention, in particular, in the fourth or fifth aspect of the invention, the booster circuit control unit stops the boosting operation of the booster circuit prior to the operation stop of the power factor correction circuit by the power factor correction circuit control unit. Thus, it is possible to prevent the inverter circuit from operating in a state where the power factor improvement function of the power factor improvement circuit is lost and affecting the surrounding power supply environment.

  In the ninth invention, in particular, in the third invention, the inverter control is performed after the first drive stop period elapses after the booster circuit controller stops the booster operation of the booster circuit and the voltage of the second capacitor is lowered. When the inverter stops driving the inverter, the booster circuit is in a stable stop state and the load impedance viewed from the booster circuit continues until the voltage of the second capacitor to which the output voltage is applied decreases. Since it can be driven and less fluctuated, the output voltage can be quickly reduced and the booster circuit can be safely stopped without applying a voltage that exceeds the withstand voltage of its output capacitor or switching element of the inverter circuit. It becomes possible.

  According to a tenth aspect of the invention, in particular, in the fourth aspect of the invention, the second drive stop period elapses after the power factor improvement circuit control unit stops the boosting operation of the power factor improvement circuit, and the first capacitor and the second capacitor After the voltage decreases, the inverter control unit stops driving the inverter circuit, so that the power factor correction circuit becomes a stable stop state and the power factor is decreased until the voltage of the first capacitor to which the output voltage is applied decreases. Since the load impedance seen from the improvement circuit can be in a state where fluctuations are small, the output voltage of the power factor correction circuit is quickly reduced and the power factor improvement circuit exceeds the withstand voltage of its output capacitor or switching element of the inverter circuit. It is possible to stop safely without applying an over boosted voltage.

  In an eleventh aspect of the invention, in particular, in the fifth aspect of the invention, after the booster circuit controller stops the boosting operation of the booster circuit, the third drive stop period has elapsed and the voltage of the second capacitor has decreased. The rate control circuit controller stops the boosting operation of the power factor correction circuit, and then the inverter control unit stops driving the inverter circuit after the fourth drive stop period elapses and the voltage of the first capacitor decreases. In addition, the lengths of the third drive stop period and the fourth drive stop period are defined as the second capacitor discharge time after the booster circuit drive stop and the first capacitor after the power factor correction circuit drive stop. The first drive stop period and the second drive stop period necessary to surely enter the drive stop state of the booster circuit and the power factor correction circuit are appropriately set by varying the discharge time corresponding to the magnitude of the discharge time. Secure and It is possible to shorten the total time.

  In a twelfth aspect of the invention, in particular, in the second aspect of the invention, the boosting output voltage detecting unit for detecting the output voltage of the boosting function unit is provided, and the boosting control unit stops the boosting operation of the boosting function unit and then outputs the boosting output. After the output voltage detected by the voltage detection unit falls below a predetermined value, the inverter control unit stops driving the inverter circuit, so that the boosting function unit is in a stable state after stopping the boosting operation or is in a stable state Since the inverter circuit is driving the load impedance as viewed from the boosting function unit until it is detected, the boosting function unit is a component thereof. It is possible to stop safely without over-boosting beyond the withstand voltage of the output capacitor or the switching element of the inverter circuit.

  In a thirteenth aspect of the invention, in particular, in the second aspect of the invention, an input current detection unit that detects an input current is provided, and the boosting control unit stops the boosting operation of the boosting function unit and the input current detected by the input current detection unit is detected. Alternatively, after the input power calculated from the input current becomes equal to or lower than a predetermined value, the inverter control unit stops the operation of the inverter circuit, so that each boosting function unit (if there is a plurality of boosting function units, ) Can stably stop the operation of the inverter circuit after detecting that the step-up operation has been stably stopped, and the step-up function section of the output capacitor that is the component and the switching element that is the component of the inverter circuit It is possible to stop safely without over-boosting beyond the withstand voltage.

  According to a fourteenth aspect of the invention, in particular, in the second aspect of the invention, the boosting function control unit includes a conduction time measuring unit that measures the conduction time of the switching element that determines the boosting level, and the boosting circuit control unit stops the boosting operation. After the conduction time of the switching element becomes equal to or less than a predetermined value, the inverter control unit detects that the boosting function unit has stably stopped the boosting operation by stopping the operation of the inverter circuit. Since the inverter circuit is driven until the boosting operation of the boosting function unit stops, the boosting function unit is able to stop the operation of the inverter circuit. It is possible to stop safely without over-boosting beyond the withstand voltage of the output capacitors and inverter circuit switching elements. It made.

  According to a fifteenth aspect of the invention, in particular, in the first aspect of the invention, the inverter control unit causes the boosting operation of the boosting function unit to stop the operation of the inverter circuit at the time of input power control that changes the drive / stop time ratio of the inverter circuit. By controlling so as to stop without delaying more than a predetermined amount, the booster circuit and the power factor correction circuit can safely stop without over-boosting the output capacitor of each circuit or the switching element of the inverter circuit. It becomes possible.

  According to a sixteenth aspect of the invention, in particular, in the third or fourth aspect of the invention, the power factor correction circuit includes a first choke coil whose input end is connected to a DC power source and a high potential side at the output end of the first choke coil. A first switching element that accumulates energy in the first choke coil by connecting and turning on the terminal, and supplies the energy to the first capacitor on the output side via the first diode by turning off the first switching element; The power factor of the input power source is improved by turning on and off the first switching element and boosted to a voltage higher than the DC power source, and the booster circuit is connected to the output terminal of the power factor correction circuit. When the high-potential side terminal is connected to the output terminals of the second choke coil and the second choke coil and is turned on, energy is stored in the second choke coil and turned off. And a second switching element that supplies the energy to the second capacitor on the output side via the second diode, and the output voltage of the power factor correction circuit is turned on and off by the second switching element. A configuration in which the voltage is increased to a large voltage may be employed.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment)
FIG. 1 shows a circuit diagram of an induction heating apparatus according to an embodiment of the present invention. As shown in the figure, the induction heating apparatus in the embodiment of the present invention includes a power factor correction circuit 7, a booster circuit 14, an inverter control unit 28, a booster circuit control unit 32, a power factor correction circuit control unit 33, and an operation unit 39. The configuration of these circuit blocks will be described below.

  First, the configuration of the power factor correction circuit 7 will be described. The commercial power source 1 is a 200 V commercial power source that is a low-frequency AC power source, and is connected to an input terminal of a rectifier circuit 2 including a bridge diode and an input filter. A choke coil 3 that is a first choke coil, a switching element 4 that is a first switching element (a MOSFET in the present embodiment), a diode 5 that is a first diode, and a smoothing capacitor 6 that is a first capacitor are: A power factor improvement circuit 7 for improving the power factor of the commercial power source 1 is configured. The input side terminal of the choke coil 3 is connected to the high potential side (positive electrode side) output terminal of the rectifier circuit 2. Further, the high potential side terminal (drain) of the switching element 4 is connected to the connection point between the output side terminal of the choke coil 3 and the anode side terminal of the diode 5. The low potential side terminal (source) of the switching element 4 and the low potential side terminal of the smoothing capacitor 6 are connected to the low potential side (negative electrode side) output terminal of the rectifier circuit 2, and the high potential side terminal of the smoothing capacitor 6 is the diode 5. Are connected to the cathode side terminal. At both ends of the smoothing capacitor 6, the output voltage of the rectifier circuit 2, which is a DC power source input by the power factor correction circuit 7, has a DC value that has a peak value larger than the peak value due to the on / off operation of the choke coil 3 and the switching element 11. A voltage boosted to an arbitrary voltage is supplied and smoothed. However, in the present embodiment, a MOSFET having a high switching speed is used as the switching element 4 in order to operate the power factor improvement circuit 7 at a high frequency and enhance the power factor improvement effect. Usually, a protective diode is attached to the MOSFET in the reverse direction, but it is not shown in the figure because it does not affect the description of the basic operation of the present embodiment without this protective diode.

  Next, the configuration of the booster circuit 14 will be described. A smoothing capacitor 6 that is a second capacitor, a choke coil 8 that is a second choke coil, a snubber capacitor 9, a diode 10, a switching element 11 that is a second switching element (IGBT in the present embodiment), a second The diode 12 and the smoothing capacitor 13 are the booster circuit 14. The input side terminal of the choke coil 8 is connected to the connection point between the cathode side terminal of the diode 5 and the high potential side output terminal of the smoothing capacitor 6. A snubber capacitor 9 is connected between the output side terminal of the choke coil 8 and the low potential side terminal of the smoothing capacitor 6, and in parallel with the snubber capacitor 9, a diode (reverse conduction element) 10 and a parallel connection body of the switching element 11 are connected. Connected. The anode side terminal of a diode (reverse conducting element) 12 is connected to the high potential side terminal (collector) of the switching element 11, and a smoothing capacitor is connected between the cathode side terminal of the diode 12 and the low potential side terminal (emitter) of the switching element 11. 13 is connected. The voltage of the smoothing capacitor 13 is a voltage obtained by boosting the voltage of the smoothing capacitor 6 to a DC voltage having a peak value larger than the peak value, and is supplied between the input terminals of the inverter circuit 15.

  The input terminal of the inverter circuit 15 is connected to the output terminal of the booster circuit 14, that is, both ends of the smoothing capacitor 13. A series connection body of switching elements 16 and 17 is connected to both ends of the smoothing capacitor 13. Diodes 18 and 19 are connected to switching elements 16 and 17 in antiparallel (so that the high potential side terminal (collector) of the switching element and the cathode side terminal of the diode are connected), respectively. A snubber capacitor 20 is connected in parallel to the switching element 17 (which may be the switching element 16). Further, a series connection body of the heating coil 21 and the resonance capacitor 22 is connected in parallel to the switching element 17 (which may be the switching element 16). The heating coil 21 is disposed so as to face the bottom surface of a heated object 23 such as a pot as a load.

  Next, the configuration of the inverter control unit 28 will be described. Output from the reference current setting unit 24 that outputs the signal output from the input current detection unit 25 that detects the input current of the induction heating device shown in the figure and the current reference value according to the input setting determined by the operation content of the user. These signals are compared by a microcomputer 26 (hereinafter referred to as a microcomputer), and a signal is output from the microcomputer 26 to the variable conduction ratio setting unit 27 so that a set input can be obtained. The variable conduction ratio setting unit 27 sets the conduction ratio of the driving time of the switching elements 16 and 17 at the driving frequency set by the microcomputer 26 and exclusively controls the switching element 16 and the switching element 17. The inverter control unit 28 includes the reference current setting unit 24, the input current detection unit 25, the microcomputer 26, and the variable conduction ratio setting unit 27.

  Next, the configuration of the booster circuit control unit 32 will be described. The signal output from the boosted output voltage detection unit 29 that detects the voltage of the smoothing capacitor 13 that is the input voltage of the inverter circuit 15 is compared with the reference voltage set by the reference voltage setting unit 30 by the microcomputer 26, and is output from the microcomputer 26. A signal is output to the variable conduction ratio setting unit 31 so that a predetermined voltage of the smoothing capacitor 13 is obtained. The variable conduction ratio setting unit 31 sets the conduction ratio of the switching element 11 at the drive frequency set by the microcomputer 26 and controls the conduction of the switching element 11. The booster circuit controller 32 driven by the booster circuit 14 includes the microcomputer 26, the boosted output voltage detector 29, the reference voltage setting unit 30, and the variable conduction ratio setting unit 31, and shares the microcomputer 26 with the inverter controller 28. In addition, the circuit configuration and the control method can be simplified.

  Next, the configuration of the power factor correction circuit control unit 33 will be described. The power factor correction circuit control unit 33 that controls the driving of the switching element 4 of the power factor improvement circuit 7 includes an input current detection unit 34 that detects the input current of the induction heating device. The reference sine wave voltage waveform output from the sine wave detection unit 35 is compared by the power factor improvement circuit drive control IC 36, and a signal is output from the power factor improvement circuit drive control IC 36 to the conduction ratio setting unit 37. The setting unit 37 sets the conduction ratio of the switching element 4 at the drive frequency set by the oscillation unit 38 so as to obtain an input current waveform equivalent to the reference sine wave voltage waveform, and controls the conduction of the switching element 4. Further, the power factor improvement circuit drive control IC 36 has a communication port with the microcomputer 26 included in the inverter control unit 28 and the booster circuit control unit 32, and the microcomputer 26 is used for power factor improvement circuit drive control at an arbitrary timing. The operation of the IC 36 can be controlled. The power factor correction circuit control unit 33 includes the input current detection unit 34, the reference sine wave detection unit 35, the power factor improvement circuit drive control IC 36, the conduction ratio setting unit 37, and the oscillation unit 38.

  In addition, the induction heating device has an operation unit 39, and the operation unit 39 transmits the operation content of the user to the microcomputer 26. The microcomputer 26 performs heating start, heating power adjustment, and heating stop based on the content received from the operation unit 39.

  The operation of the induction heating apparatus configured as described above will be described below.

  FIG. 2 shows a voltage or current waveform of each part of the induction heating device in the present embodiment. FIG. 2A shows an AC voltage waveform of the commercial power source 1. FIG. 2B shows the output voltage waveform of the DC power supply, that is, the output voltage waveform of the rectifier circuit 2. This voltage is input to the power factor correction circuit 7, boosted and output to the smoothing capacitor 6. FIG. 4C shows a waveform applied to the smoothing capacitor 6, that is, an output voltage waveform of the power factor correction circuit 7 and an input voltage waveform of the booster circuit 14. FIG. 4D shows a waveform applied to the smoothing capacitor 13, that is, an output voltage waveform of the booster circuit 14 and an input voltage waveform of the inverter circuit 15. FIG. 4E shows a high frequency current waveform generated in the heating coil 21.

  First, the operation of the power factor correction circuit 7 will be described. The commercial power source 1 shown in FIG. 2A is full-wave rectified by the rectifier circuit 2, and a DC power source is formed as shown in FIG. This DC power supply is supplied between the input terminals of the power factor correction circuit 7. The power factor correction circuit 7 cannot turn on the diode 5 included in the power factor correction circuit 7 and the bridge diode of the rectifier circuit 2 when the magnitude of the instantaneous value of the DC power supply voltage is smaller than the voltage of the smoothing capacitor 6. The input current waveform is distorted and the power factor is significantly reduced. At that time, the power factor correction circuit control unit 33 changes the output of the conduction ratio setting unit 37 so that the current waveform detected by the input current detection unit 34 becomes equal to the detection waveform of the reference sine wave detection unit 35, and switching is performed. The element 4 is turned on / off. In the state where the first switching element 4 is turned on, energy is stored in the choke coil 3 from the commercial power source 1, and then the switching element 4 is turned off when the conduction time set by the conduction ratio setting unit 37 elapses. The energy stored in the choke coil 3 is supplied to the smoothing capacitor 6 via the diode 5. As a result, an input current flows from the commercial power source 1 through the choke coil 3 and a distorted input current is prevented from flowing to the commercial power source 1 side. In the present embodiment, the power factor correction circuit 7 has not only a power factor correction function but also a boosting function at the same time. For this reason, as shown in FIG. 2 (c), the voltage of the smoothing capacitor 6 has a peak value higher than the peak value of the input voltage of the power factor correction circuit 7, which is the peak value of the commercial power source 1, that is, the peak value of the DC power source. It becomes a voltage and is supplied to the inverter circuit 15 through the smoothing capacitor 13.

  Next, the operation of the booster circuit 14 will be described. The booster circuit 14 stores energy in the choke coil 8 while the switching element 11 is turned on. When the switching element 11 is turned off, the energy stored in the choke coil 8 charges the smoothing capacitor 13 via the diode 12. Thus, a boosting operation is performed. In the present embodiment, the operating frequency and conduction time of the switching element 11 are variable, and the voltage of the smoothing capacitor 13 is adjusted. Since the diode 12 is provided between the smoothing capacitor 13 and the high potential side terminal of the switching element 11 and the snubber capacitor 9 is connected to the switching element 11 in parallel, the snubber is turned off when the switching element 11 is turned off. The capacitor 9 starts charging with a slope due to resonance of the choke coil 8 and the snubber capacitor 9, and the switching element 11 realizes a so-called ZVS turn-off operation. Further, when the voltage of the snubber capacitor 9 becomes the same voltage as that of the smoothing capacitor 13 while the switching element 11 is turned off, the diode 12 is turned on and is fixed to a voltage equivalent to that of the smoothing capacitor 13. When the voltage becomes higher than that of the snubber capacitor 9, the diode 12 is turned off and the snubber capacitor 9 starts discharging. When the snubber capacitor 9 is completely discharged, the diode 10 is turned on.

  In the present embodiment, a continuous drive mode in which the switching element 11 is turned on within a predetermined time after the completion of the discharge of the snubber capacitor 9 is used. However, after a predetermined time or more has elapsed after the snubber capacitor 9 has been discharged, the switching element 11 is turned on. There is no problem even if 11 is turned on. The snubber capacitor 9 can operate even if the switching element 11 is turned on before the discharge is completed. In this case, the current flowing in the choke coil 8 suddenly flows into the switching element 11 and the loss increases. Therefore, after the snubber capacitor 9 is completely discharged, the switching element 11 is turned on within a predetermined time. The above is the operation of the booster circuit 14.

  Next, the operation of the inverter circuit 15 will be described. The voltage generated in the smoothing capacitor 6 connected between the output terminals of the power factor correction circuit 7 shown in FIG. 2C is boosted as shown in FIG. 2D by the boosting circuit 14 and output to the smoothing capacitor 13. Is done. The voltage value of the smoothing capacitor 13 is adjusted by increasing / decreasing so that the power set by the user in the operation unit 39 is input to the heated object 23. The smoothed DC voltage output to both ends of the smoothing capacitor 13 is supplied to the inverter circuit 15. The inverter circuit 15 causes the heating coil 21 to generate a high-frequency current having a predetermined frequency as shown in FIG. 2E by turning on and off the switching elements 16 and 17. When the switching element 16 is turned on when the switching element 16 is turned off, the snubber capacitor 20 discharges with a gentle slope due to the resonance of the heating coil 21 and the snubber capacitor 20, so that the switching element 16 realizes a zero volt switching (ZVS) turn-off operation. . When the snubber capacitor 20 is completely discharged, the diode 19 is turned on. When the diode 19 is on, an on signal is applied to the gate of the switching element 17 and when the diode 19 is on standby, the direction of the resonance current of the heating coil 21 is reversed. Is turned off and a current is commutated to the switching element 17, and the switching element 17 realizes a ZVS & zero current switching (ZCS) turn-on operation. When the switching element 17 is turned on from the on state, the snubber capacitor 20 is charged with a gentle slope due to the resonance of the heating coil 21 and the snubber capacitor 20, so that the switching element 17 realizes a ZVS turn-off operation. When the snubber capacitor 20 is charged to the same voltage as that of the smoothing capacitor 13, the diode 18 is turned on. When the diode 18 is turned on, an on signal is applied to the gate of the switching element 16, and the heating coil 21 is turned on. The direction of the resonance current is reversed, the diode 18 is turned off, the current is commutated to the switching element 16, and the switching element 16 realizes a ZVS & ZCS turn-on operation. The above is the operation of the inverter circuit 15.

  In the present embodiment, the switching elements 16 and 17 are alternately turned on and off at intervals of a dead time of 2 μs so as not to short-circuit the smoothing capacitor 13. Further, the driving frequency of the switching elements 16 and 17 is fixed, and the high frequency power is controlled by changing the conduction time. By making the driving frequency of the booster circuit 14 and the inverter circuit 15 the same, the booster circuit 14 and the inverter are controlled. The generation of audible sound due to the drive frequency difference of the circuit 15 is suppressed. However, it goes without saying that high-frequency power can be controlled even if the drive frequency of the inverter circuit 15 is varied.

  Next, the stop timing of the power factor correction circuit 7, the booster circuit 14, and the inverter circuit 15 when stopping the heating operation of the induction heating device will be described. In the induction heating apparatus of the present embodiment, when the user performs a heating stop operation on the operation unit 39, the operation unit 39 transmits a heating stop command to the microcomputer 26. Receiving the heating stop command, the microcomputer 26 fixes the drive frequency and conduction time of the inverter circuit 15 to be equal to or less than the predetermined fluctuation width, suppresses fluctuations in the output of the inverter circuit 15, and increases the boost voltage width from the power factor improvement circuit 7. A signal for stopping the boosting operation of the booster circuit 14 is output to the variable conduction ratio setting unit 31 of the booster circuit 14 having a large value. The microcomputer 26 stops the operation of the power factor correction circuit 7 in the power factor correction circuit control IC 36 when the third drive stop period elapses after the boost operation stop signal of the boost circuit 14 is output to the variable conduction ratio setting unit 31. Output a signal. The microcomputer 26 outputs a signal for stopping the operation of the power factor correction circuit 7 to the power factor improvement circuit control IC 36, and then the variable conduction ratio setting means 27 operates the inverter circuit 15 when the fourth drive stop period elapses. Output a signal to stop. Thus, the operation of the power factor correction circuit 7 is stopped after stopping the operation of the booster circuit 14 with priority over the inverter circuit 15, and finally the heating operation of the inverter circuit 15 is stopped. When only the booster circuit 14 has the boosting function, the microcomputer 26 outputs the boosting operation stop signal of the booster circuit 14 to the variable conduction ratio setting unit 31 and then the variable conduction ratio when the first drive stop period elapses. A signal for stopping the operation of the inverter circuit 15 may be output to the setting means 27. When only the power factor correction circuit circuit 14 has the boosting function, the microcomputer 26 outputs a signal for stopping the operation of the power factor correction circuit 7 to the power factor correction circuit control IC 36 and then stops the second drive. When the period has elapsed, a signal for stopping the operation of the inverter circuit 15 may be output to the variable conduction ratio setting means 27.

  With this configuration, the booster circuit 14 and the power factor improving circuit 7 having a boost function are preferentially stopped over the inverter circuit 15, so that the load impedance as viewed from the circuit having the boost function, that is, the heating coil 21 and The circuit having the boosting function can be stopped in a state where the magnitude of the output value of the inverter circuit 15 including the object to be heated 23 does not change abruptly, and the output voltages of the power factor correction circuit 7 and the boosting circuit 14 are excessively boosted. It will not be. Therefore, it is possible to suppress the application of voltages exceeding the respective withstand voltages to the output capacitor of the circuit having the boosting function and the switching elements 16 and 17 of the inverter circuit 15.

  The inverter circuit 15 can obtain the same effect by stopping at a timing that satisfies at least one of the following conditions (1) to (4).

  (1) Power factor improvement circuit control for controlling the elapsed time after the microcomputer 26 outputs the boost operation stop signal to the boost circuit control unit 32 that controls the boost operation of the boost circuit 14 or the boost operation of the power factor improvement circuit 7 The elapsed time from the output of the boosting operation stop signal to the unit 33 is measured and determined in advance in consideration of the delay time required for the booster circuit 14 and the power factor correction circuit 7 to stop and become stable. The specified drive stop period elapses. As the predetermined drive stop period, for example, the booster circuit 14 is necessary for the voltage of the smoothing capacitor 13 to fall below a predetermined voltage after the boost operation stop signal is output to the booster circuit control unit 32. For the power factor correction circuit 7, the time required for the voltage of the smoothing capacitor 6 or the smoothing capacitor 13 to fall below a predetermined voltage after the drive stop signal is output to the power factor correction circuit control unit 33 is set. You may make it set.

  (2) After the microcomputer 26 outputs the drive stop signal to the booster circuit control unit 32 and the power factor correction circuit control unit 33, the boosted output voltage detection unit 29 that detects the output voltage of the booster circuit 14 has a predetermined voltage or less. Detect voltage level. However, it is preferable to determine the predetermined voltage within a range equal to or lower than the voltage peak value of the commercial power source 1.

  (3) After the microcomputer 26 outputs a drive stop signal to the booster circuit control unit 32 and the power factor improvement circuit control unit 33, the input current value or the input current value detected by the input current detection unit 25 of the induction heating device is calculated. The input power thus obtained becomes equal to or less than a predetermined input current input power. However, the predetermined input power may be determined from the power factor calculated from the input filter included in the rectifier circuit 2, the voltage of the commercial power source 1, the fixed drive frequency of the inverter circuit 15, and the conduction time.

  (4) After the microcomputer 26 outputs a drive stop signal to the booster circuit control unit 32 and the power factor improvement circuit control unit 33, the booster circuit control unit 32 and the power factor improvement circuit control unit 33 are configured of the switching elements constituting each of them. The fact that the continuity time has become a predetermined time or less is transmitted to the microcomputer 26, and the microcomputer 26 completes receiving the signal.

  Furthermore, in the present embodiment, an input power region that is uncontrollable or difficult to control by the conduction time ratio of the switching elements 16 and 17 of the inverter circuit 15 is controlled by providing a time ratio for driving and stopping the inverter circuit 15. To do. In the case of the control method, when the inverter circuit 15 is stopped from driving, the same effect can be obtained by stopping the inverter circuit 15 in the same procedure as the heating stop method already described.

  Even at the time of input power control by PDM (pulse density control) that changes the time ratio of driving / stopping of the switching elements 16 and 17 of the inverter circuit 15, the booster circuit 14 is stopped before the inverter circuit 15 is temporarily stopped. Next, the power factor improvement circuit 7 is stopped, and then the inverter circuit 1 is stopped. The load impedance viewed from the booster circuit 14 and the power factor improvement circuit 7 is driven by the inverter circuit 15, and therefore the fluctuation is As a result, the booster circuit 14 and the power factor correction circuit 7 can be safely stopped without over-boosting more than the withstand voltage of the output capacitors of the circuits and the switching elements 16 and 17 of the inverter circuit 15.

  Further, by stopping the booster circuit 14 before the power factor correction circuit 7, it is possible to suppress the power factor decrease during the stop processing period of the booster circuit 14, and to shorten the period during which the power factor operates in a low state. Is possible.

  In the above-described embodiment, the booster circuit 14 is stopped before the inverter circuit 15 stops. However, even if the inverter circuit 15 stops before the booster circuit 14, a predetermined time has passed since the inverter circuit 15 stopped. Even if the operation of the booster circuit 15 is stopped before the output voltage exceeds a predetermined voltage due to the boosting action of the booster circuit 14, the same effect can be obtained.

  As described above, the induction heating device according to the present embodiment (hereinafter, this induction heating device) has a power function as a boosting function unit that boosts and outputs a DC voltage having a peak value larger than the peak value of the input DC power supply. A rate improving circuit 7 and a booster circuit 14 are provided. The power factor correction circuit 7 boosts the voltage by the on / off operation of the switching element 4 (first switching element), and the booster circuit 14 boosts the voltage by the on / off operation of the switching element 11 (second switching element). In addition, the induction heating apparatus includes an inverter circuit 15 that generates a high-frequency current in the heating coil 21. The inverter circuit 15 receives the voltage boosted by the power factor correction circuit 7 and the booster circuit 14 and generates a high-frequency current by the on / off operation of the other switching elements 16 and 17.

  In addition, the induction heating apparatus controls the boosting operation of the power factor correction circuit control unit 33 and the boosting circuit 14 that control the boosting operation of the power factor improvement circuit 7 as a boosting control unit that controls the boosting operation of the boosting function unit. A booster circuit control unit 32 and an inverter control unit 28 for controlling the operation of the inverter circuit 15 are provided. With this configuration, the induction heating apparatus can finely variably control the output of the inverter circuit by varying the boost value of the input voltage of the inverter circuit 15 with a degree of freedom with respect to the operation of the inverter circuit 15.

  In addition, in this induction heating apparatus, the power factor improvement circuit 7 (step-up function unit) and the step-up circuit 14 (step-up function unit) change in load impedance as seen from the step-up function unit that occurs when the operation of the inverter circuit 15 is stopped. Therefore, the boosting operation of the power factor correction circuit 7 and the boosting circuit 14 is delayed by a predetermined amount or more with respect to the stop of the operation of the inverter circuit 15 in order to suppress the boosting width of the voltage boosted and output by the boosting function unit to a predetermined value or less. Stop without doing. With this configuration, when the operation of the inverter circuit 15 is stopped, the boosting operation is stopped before the output voltage becomes higher than a predetermined level, so that the output voltages of the power factor correction circuit 7 and the boosting circuit 14 are prevented from being excessively boosted. can do.

  Further, in the present induction heating apparatus, the power factor correction circuit control unit 33 (boost control unit) and the boost circuit control unit 32 (boost control unit) have a power factor prior to the operation of the inverter circuit 15 being stopped by the inverter control unit 28. The boosting operation of the improvement circuit control unit 33 and the boosting circuit control unit 32 is stopped. With this configuration, when the heating operation is stopped, since the inverter circuit 15 as a load is driven at least while the boosting circuit 14 is performing the boosting operation, the load impedance as viewed from the boosting circuit 14 fluctuates greatly. Thus, it is possible to reliably prevent the output voltage of the booster circuit 14 from being excessively boosted, to quickly reduce the output voltage and to safely stop the heating operation.

  In addition, the induction heating apparatus inputs a DC power source obtained by rectifying the AC power source, boosts the voltage to a peak value larger than the peak value, outputs the voltage to the smoothing capacitor 6, and improves the power factor of the AC power source. A power factor improvement circuit 7 (a boosting function unit) and a power factor improvement circuit control unit 33 (a boosting control unit) for controlling the operation of the power factor improvement circuit 7 are provided. As a result, the power factor correction circuit 7 is provided with the boosting function and the power factor improvement function at the same time, so that the boosting / power factor correction circuit can be reduced in size and cost. Also, by stopping the boosting operation of the power factor correction circuit 7 prior to the stop of the operation of the inverter circuit 15, when stopping the heating operation, at least during the boosting operation of the power factor correction circuit 7, Since the inverter circuit 15 is driven, the load impedance viewed from the power factor improvement circuit 7 is suddenly greatly changed and the output voltage of the power factor improvement circuit 7 is reliably prevented from being excessively boosted. The induction heating device can quickly stop the heating operation by quickly reducing the output voltage of the rate improvement circuit 7.

  Further, the booster circuit control unit 32 stops the boosting operation of the booster circuit 14 prior to the operation of the power factor correction circuit 7 being stopped by the power factor improvement circuit control unit 33. As a result, the induction heating apparatus prevents the inverter circuit 15 from operating in a state where the power factor improvement function of the power factor improvement circuit 7 is lost and affecting the surrounding power supply environment.

  In addition, according to the instruction of the microcomputer 26, the induction heating device is configured so that the fluctuation range of the output value of the inverter circuit 15 is less than a predetermined value by the inverter control unit 28 in order to stabilize the load impedance as viewed from the power factor correction circuit 7 and the booster circuit 14. Thus, fluctuations in the conduction time of the switching elements 16 and 17 that drive the inverter circuit 15 are limited. While the limited state is maintained (for example, when the operation frequency or the drive time ratio is operated within a predetermined fluctuation range), the power factor correction circuit control unit 33 and the booster circuit control unit 38 are connected to the power factor improvement circuit 7. And the boosting operation of the booster circuit 14 is stopped. As a result, the fluctuation amount of the load impedance is suppressed in the process in which the boosting operation of the power factor improving circuit 7 and the boosting circuit 14 is stopped, and the output voltages of the power factor improving circuit 7 and the boosting circuit 14 It is possible to stop safely without over-boosting beyond the withstand voltage of the output capacitors (smoothing capacitors 6 and 13) and the switching elements 16 and 17) of the inverter circuit 15.

  Further, according to the instruction of the microcomputer 26, the induction heating device is configured such that the variable conduction ratio setting means 27 is activated after the first drive stop period elapses after the boost operation of the boost circuit 14 is stopped and the voltage of the smoothing capacitor 9 decreases. An instruction is given to stop the drive of the inverter circuit 15. The load impedance viewed from the booster circuit 14 is continuously driven by the inverter circuit 15 until the voltage of the smoothing capacitor 13 to which the output voltage is applied decreases until the booster circuit 14 is in a stable stop state, and the fluctuation is small. Therefore, the output voltage can be quickly reduced and the booster circuit 14 can be safely stopped without applying a voltage that is excessively boosted beyond the withstand voltage of the switching capacitor of the smoothing capacitor 13 or the inverter circuit 15 as its output capacitor. It becomes possible.

  In addition, the induction heating apparatus performs the second drive after the power factor correction circuit control unit 33 stops the boosting operation of the power factor correction circuit 7 in accordance with an instruction from the microcomputer 26 that receives a signal from the power factor correction circuit control unit 33. After the stop period elapses and the voltages of the smoothing capacitor 6 and the smoothing capacitor 13 decrease, the inverter control unit 28 stops driving the inverter circuit 15. As a result, the load impedance viewed from the power factor correction circuit 7 can be in a state of little fluctuation until the power factor improvement circuit 7 is in a stable stop state and the voltage of the smoothing capacitor 6 to which the output voltage is applied decreases. The output voltage of the power factor correction circuit 7 can be quickly reduced and the power factor improvement circuit 7 can be safely stopped without applying a voltage that is excessively boosted beyond the breakdown voltage of its output capacitor or the switching element of the inverter circuit 15. It becomes possible.

  Further, according to an instruction from the microcomputer 26, the induction heating apparatus is configured to operate after the third drive stop period elapses after the booster circuit control unit 32 stops the booster operation of the booster circuit and the voltage of the smoothing capacitor 13 decreases. After the improvement circuit control unit 33 stops the boosting operation of the power factor improvement circuit 7 and then the fourth drive stop period elapses and the voltage of the smoothing capacitor 6 decreases, the inverter control unit 28 drives the inverter circuit 15. The smoothing capacitor 6 after the stop of driving of the smoothing capacitor 13 and the power factor improvement circuit 7 after the stop of driving of the booster circuit 14 is compared with the length of the third driving stop period and the fourth driving stop period. The discharge time varies depending on the discharge time. As a result, the third drive stop period and the fourth drive stop period necessary for reliably driving the booster circuit 14 and the power factor correction circuit 7 are ensured and the total time is shortened. Can do.

  Further, the induction heating apparatus includes a boosted output voltage detection unit 29 that detects an output voltage of the power factor correction circuit 7 or the boosting circuit 14 that is a boosting function unit. Then, after the power factor correction circuit control unit 33 or the boost circuit control unit 32 which is the boost control unit stops the boost operation, it detects that the output voltage detected by the boost output voltage detection unit 29 has become a predetermined value or less. After that, the inverter control unit 28 stops driving the inverter circuit 15 to detect that the power factor correction circuit 7 or the booster circuit 14 is in a stable state after the boosting operation is stopped or is approaching a stable state. Until the detection, the load impedance viewed from the boosting function unit is driven by the inverter circuit 15 and is in a state of little fluctuation. Therefore, the boosting function unit includes the output capacitor and the inverter circuit as its components. It is possible to stop safely without over-boosting beyond the withstand voltage of the switching element.

  As described above, the induction heating apparatus according to the present invention is capable of stopping the driving without over-boosting the boosting circuit or the power factor correction circuit having a boosting function when heating is stopped. Of course, it is also useful as an induction heating type copy roller, induction heating type melting furnace, induction heating type jar rice cooker, or other induction heating type heating device.

Circuit diagram of induction heating apparatus in an embodiment of the present invention Voltage or current waveform diagram of each part in the same induction heating device

Explanation of symbols

1 Commercial power supply 3 Choke coil (first choke coil)
4 Switching element (first switching element)
5 Diode (first diode)
6 Smoothing capacitor (first capacitor)
7 Power factor correction circuit (step-up function unit)
8 Choke coil (second choke coil)
11 Switching element (second switching element)
12 Diode (second diode)
13 Smoothing capacitor (second capacitor)
14 Booster circuit (Boost function part)
15 Inverter circuit 21 Heating coil 23 Heated object (load)
25, 34 Input current detection unit 26 Microcomputer (boost circuit control unit, inverter control unit)
28 Inverter control section 29 Boost output voltage detection section 32 Boost circuit control section (boost control section)
33 Power factor correction circuit controller

Claims (14)

A boosting function unit that inputs a DC power source and boosts and outputs a DC voltage having a peak value larger than the peak value by ON / OFF operation of the switching element, and a voltage that has a heating coil and is output by the boosting function unit An inverter circuit that inputs and generates a high-frequency current in the heating coil by ON / OFF operation of another switching element, a boost control unit that controls the boost operation of the boost function unit, and an inverter that controls the operation of the inverter circuit A booster that boosts a voltage that is boosted by the booster function unit and output to the inverter circuit due to a change in load impedance as seen from the booster function unit when the operation of the inverter circuit is stopped. in order to suppress the width less than a predetermined, the output drive frequency and the conduction time of a predetermined inverter circuit or less and less than the predetermined output variation width Set by stopping while suppressing the output variation of said inverter circuit, in a state in which the magnitude of the load impedance viewed from the circuit having the boosting function does not change abruptly, the boosting operation of the boosting function unit, the inverter An induction heating apparatus that stops without delaying more than a predetermined amount with respect to the circuit operation stop. The induction heating apparatus according to claim 1, wherein the boosting control unit stops the boosting operation of the boosting function unit prior to the operation stop of the inverter circuit by the inverter control unit. A DC power source obtained by rectifying the AC power source is input and a smoothed DC voltage is output to the first capacitor and a power factor improving circuit for improving the power factor of the AC power source is provided. A booster circuit that receives the DC voltage output from the rate improving circuit, boosts the DC voltage to a DC voltage having a peak value larger than the peak value, and outputs the boosted voltage to the second capacitor, and the boost controller controls the booster circuit The induction heating apparatus according to claim 2, further comprising a circuit control unit, wherein the boosting circuit control unit stops the boosting operation of the boosting circuit prior to stopping the operation of the inverter circuit. The step-up function unit receives a DC power source obtained by rectifying the AC power source, boosts the voltage to a voltage having a peak value larger than the peak value, outputs the voltage to the first capacitor, and improves the power factor of the AC power source. A boosting control unit including a power factor correction circuit control unit that controls the operation of the power factor correction circuit, and the power factor correction circuit control unit precedes the operation stop of the inverter circuit. The induction heating apparatus according to claim 2, wherein the boosting operation of the power factor correction circuit is stopped. The power factor correction circuit boosts the voltage to a peak value larger than the peak value of the input DC power supply and outputs the boosted voltage to the first capacitor. The power factor correction circuit control unit performs the operation before the operation of the inverter circuit is stopped. The induction heating apparatus according to claim 3, wherein the boosting operation of the power factor correction circuit is stopped. 6. The induction heating device according to claim 4, wherein the booster circuit control unit stops the boosting operation of the booster circuit prior to the stop of the boosting operation of the power factor correction circuit by the power factor correction circuit control unit. 4. The inverter control unit stops driving the inverter circuit after the first drive stop period elapses after the boost circuit control unit stops the boost operation of the boost circuit and the voltage of the second capacitor decreases. The induction heating apparatus described. After the power factor improvement circuit control unit stops the boosting operation of the power factor improvement circuit, the inverter control unit controls the inverter circuit after the second drive stop period elapses and the voltages of the first capacitor and the second capacitor decrease. The induction heating apparatus according to claim 4, wherein the driving is stopped. After the boosting circuit control unit stops the boosting operation of the boosting circuit, the power factor correction circuit control unit performs the boosting operation of the power factor improvement circuit after the third drive stop period has elapsed and the voltage of the second capacitor has dropped. After the fourth drive stop period has elapsed and the voltage of the first capacitor has dropped, the inverter control unit stops driving the inverter circuit, and the third drive stop period and the fourth drive stop period The length of the drive stop period of the second capacitor is made to differ depending on the magnitude of the discharge time of the second capacitor after the booster circuit drive stop and the discharge time of the first capacitor after the drive stop of the power factor correction circuit, respectively. Item 6. The induction heating apparatus according to Item 5. A boost output voltage detection unit for detecting the output voltage of the boost function unit is provided, and after the boost control unit stops the boost operation of the boost function unit, the output voltage detected by the boost output voltage detection unit becomes a predetermined value or less. The induction heating device according to claim 2, wherein the inverter control unit stops driving the inverter circuit. An input current detection unit that detects an input current is provided, the boost control unit stops driving the boost function unit, and the input current detected by the input current detection unit or the input power calculated from the input current becomes a predetermined value or less. The induction heating apparatus according to claim 2, wherein the inverter control unit stops the operation of the inverter circuit. A conduction time measuring unit configured to measure a conduction time of the switching element that constitutes the boosting function unit and determines the boosting level, and the boosting control unit stops the boosting operation of the boosting function unit and the conduction time of the switching element is a predetermined value; The induction heating device according to claim 2, wherein after the following, the inverter control unit stops the operation of the inverter circuit. When the inverter control unit performs input power control that changes the drive / stop time ratio of the inverter circuit, the boost operation of the boost function unit stops without delaying more than a predetermined delay with respect to the stop of the operation of the inverter circuit. The induction heating device according to claim 1, wherein the induction heating device is controlled. The power factor correction circuit has a first choke coil whose input terminal is connected to a DC power source, and a high potential side terminal connected to the output terminal of the first choke coil and is turned on to turn on energy to the first choke coil. And a first switching element that supplies the energy to the first capacitor on the output side via the first diode by storing and turning off the power, and the power supply is input by turning on and off the first switching element And boosting the voltage to a voltage larger than the DC power source, and the booster circuit has a second choke coil connected to the output terminal of the power factor correction circuit and a high voltage at the output terminal of the second choke coil. When the potential side terminal is connected and turned on, energy is accumulated in the second choke coil and turned off, and the energy is output via the second diode. And a second switching element to be supplied to the second capacitor, wherein the voltage is boosted to a voltage higher than the output voltage of the power factor correction circuit by turning on and off the second switching element. The induction heating device described in 1.