JP2007095345A - Induction heating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an induction heating device in which an output voltage of an active filter is not raised excessively even at a starting time of heating, and an output voltage of the active filter can early be stabilized. <P>SOLUTION: During a period of start up of the active filter 7 from a starting of the active filter 7 till an end of the start up at a starting time of heating, a drive control of an inverter circuit 15 is carried out so that a load impedance of the inverter circuit 15 from the active filter 7 can be stabilized. As a result, a variation of the load impedance of the inverter circuit 15 during a starting period of the active filter is controlled, and the active filter 7 is started up safely and in a short time without excessive rise of the output voltage, and stable operation can be obtained. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an induction heating apparatus such as an induction heating cooker.

Conventionally, in an induction heating apparatus, a control technique using 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). In addition, a technique for suppressing harmonic current by incorporating an active filter in an induction heating device is also known (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 active filter and the inverter circuit are simultaneously started and soft-started at the start of heating, the load impedance of the inverter circuit as viewed from the active filter rapidly changes. The output voltage overshoots, causing breakdown of the breakdown voltage of the component, and the problem that it takes more time than necessary for the active filter to stabilize the output voltage.

  The present invention solves the above-described conventional problems, and provides an induction heating device capable of quickly stabilizing the output voltage of the active filter without over-boosting the output voltage of the active filter even at the start of heating. The purpose is to provide.

  In order to solve the above-mentioned conventional problems, the induction heating device of the present invention has a load impedance of the inverter circuit as viewed from the active filter during the active filter start-up period from the start of start-up until the start-up of the active filter at the start of heating. The inverter circuit is driven and controlled so as to be stable.

  As a result, the amount of fluctuation in the load impedance of the inverter circuit during the active filter start-up period is suppressed, so that the active filter can start up safely and quickly and operate stably without over-boosting the output voltage. It becomes possible.

  The induction heating device of the present invention can be started safely and quickly and stably operated without excessively boosting the output voltage of the active filter at the start of heating.

  A first invention is an active filter that is connected after commercial power supply rectification and improves the power factor by turning on and off the switching element, and an inverter that is connected to the output of the active filter and generates a high-frequency current by turning on and off the switching element Inductive heating that controls the inverter circuit so that the load impedance of the inverter circuit as viewed from the active filter is stable during the active filter start-up period from the start of start-up until the start-up is completed. By using the device, the amount of fluctuation in the load impedance of the inverter circuit during the active filter startup period is suppressed, so the active filter starts up safely and quickly without over-boosting the output voltage and operates stably. Possible to It made.

  In the second invention, in particular, in the first invention, during the active filter activation period, the active filter outputs the same as in the first invention by controlling the inverter circuit operation so that the output power becomes a predetermined value. Without over-boosting the voltage, it is possible to start up safely and quickly and to operate stably.

  The third invention is the same as the first invention, particularly in the first or second invention, by operating the inverter circuit at a predetermined operating frequency and on time during the active filter starting period. The active filter can be safely and quickly started and stably operated without excessively boosting the output voltage.

  In the fourth invention, in particular, in the first invention, during the active filter starting period, the inverter circuit operation is controlled so that the output power is equal to or less than the predetermined fluctuation range, so that the active circuit is active as in the first invention. The filter can be safely and quickly started and stably operated without excessively boosting the output voltage.

  The fifth invention is the same as the first invention particularly in the first or fourth invention, by operating the inverter circuit at an operating frequency and an on-time that are equal to or less than a predetermined fluctuation range during the active filter activation period. The active filter can be safely and quickly started and stably operated without excessively boosting the output voltage.

  According to a sixth aspect of the present invention, in the first aspect of the invention, in the first aspect, the active filter is controlled by driving the inverter circuit so that the output power changes with a predetermined fluctuation amount even during the active filter starting period. The output power can be increased even during the start-up period, and the predetermined output power can be reached more quickly.

  According to a seventh aspect of the invention, in the first or sixth aspect of the invention, in the inspection, the operating frequency and on-time of the inverter circuit are changed by a predetermined fluctuation amount even during the active filter activation period. As in the sixth aspect of the invention, the output power can be increased even during the active filter activation period, and the predetermined output power can be reached more quickly.

  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 an induction heating apparatus according to an embodiment of the present invention.

  In FIG. 1, a commercial power source 1 is a 200V 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 used for power factor improvement is connected to an output terminal on the cathode side of the rectifier circuit 2. A switching element 4 is connected between the choke coil 3 and the output terminal on the anode side of the rectifier circuit 2. Furthermore, the diode 5 is disposed so as to be connected to the high potential side terminal (collector) of the switching element 4. A smoothing capacitor 6 is connected between the cathode side terminal of the diode 5 and the low potential side terminal (emitter) of the switching element 4, and a voltage obtained by boosting the input voltage to an arbitrary voltage is supplied to the smoothing capacitor 6. The choke coil 3, the switching element 4, the diode 5, and the smoothing capacitor 6 constitute an active filter 7. However, in this embodiment, a MOSFET with a high switching speed is used to operate the active filter 7 at a high frequency, but even if there is no reverse diode attached to the MOSFET, the operation is not affected. Not listed.

  A choke coil 8 is connected between the output terminals of the smoothing capacitor 6 on the high potential side. A parallel connection body of a snubber capacitor 9, a diode (reverse conducting element) 10, and a switching element 11 is connected between the output terminal of the choke coil 8 and the low potential side terminal of the smoothing capacitor 6. Further, the diode (reverse conducting element) 12 is connected to the high potential side terminal (collector) of the switching element 11. Further, a smoothing capacitor 13 is connected between the cathode side terminal of the diode 12 and the low potential side terminal (emitter) of the switching element 11. The smoothing capacitor 6, choke coil 8, snubber capacitor 9, diode 10, switching element 11, diode 12, and smoothing capacitor 13 constitute a booster circuit 14. The smoothing capacitor 13 supplies a voltage obtained by boosting the voltage of the smoothing capacitor 6 to the inverter circuit 15.

  The inverter circuit 15 is connected to the output terminal of the booster circuit 14, that is, both ends of the smoothing capacitor 13. The ends of the smoothing capacitor 13 are connected to the switching elements 16 and 17 connected in series. Diodes (reverse conducting elements) 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 of the diode are connected). 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 to face a load 23 such as a pan that is a heated object.

  The induction heating apparatus shown in FIG. 1 has a current detection unit 24 that detects an input current from a current transformer (output detection means) 40, and a thermal power setting that is set by the microcomputer 26 based on the operation content when the user operates the operation unit 39. A signal output from the reference current setting unit 25 that outputs a corresponding current reference value is compared by a microcomputer 26 (hereinafter referred to as a microcomputer), and a signal is sent from the microcomputer 26 to the variable conduction ratio setting unit 27 so that a predetermined input is obtained. Is output. The variable continuity ratio setting unit 27 sets the continuity ratio of the switching elements 16 and 17 at the drive frequency set by the microcomputer 26 and exclusively controls the continuity between the switching element 16 and the switching element 17. The inverter circuit control means 28 includes the current detection unit 24, the reference current setting unit 25, the microcomputer 26, and the variable conduction ratio setting unit 27.

  The signal output from the voltage detection unit 29 that detects the voltage of the smoothing capacitor 13 as the input voltage of the inverter circuit 15 is compared with the reference voltage setting unit 30 by the microcomputer 26, and the microcomputer 26 outputs a predetermined smoothing capacitor 13. A signal is output to the variable continuity ratio setting unit 31 so as to obtain the above voltage. 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 control means 32 includes the microcomputer 26, the voltage detection part 29, the reference voltage setting part 30, and the variable conduction ratio setting part 31, and shares the microcomputer 26 with the inverter circuit control means 28, thereby simplifying the circuit and control. Make it possible.

  The active filter control means 33 that controls the driving of the switching element 4 of the active filter 7 includes an input current detection unit 34 that detects an input current of the induction heating device with a current transformer 40, and an output of the input current detection unit 34. And the output of the reference sine wave detection unit 35 are compared by the active filter drive control IC 36, and a signal is output from the active filter drive control IC 36 to the conduction ratio setting unit 37, and the conduction ratio setting unit 37 outputs the reference sine wave voltage waveform. The conduction ratio of the switching element 4 is set at the drive frequency set by the oscillating unit 38 so that an input current waveform equivalent to the above is obtained, and the conduction control of the switching element 4 is performed. Further, the active filter drive control IC 36 has a communication port with the microcomputer 26 included in the inverter circuit control means 28 and the booster circuit control means 32, and the microcomputer 26 can control the active filter drive control IC 36 at any timing. It is possible to control the drive / stop timing. The active filter control means 33 includes these input current detection unit 34, reference sine wave detection unit 35, active filter drive control IC 36, conduction ratio setting unit 37, and oscillation unit 38. However, the active filter drive control IC 36 is set so as not to operate at any time when there is no operation permission signal from the microcomputer 26, and the microcomputer 26 can control the drive / stop timing of the active filter 7. is there.

  The induction heating apparatus shown in FIG. 1 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.

  The commercial power source 1 is full-wave rectified by the rectifier circuit 2 and supplied to the active filter 7. In the active filter 7, when the commercial power source 1 is smaller than the voltage of the smoothing capacitor 6, the diode 5 included in the active filter 7 and the bridge diode of the rectifier circuit 2 cannot be turned on, the input current waveform is distorted, and the power factor becomes significantly low. At this time, in the active filter control means 33, the current waveform detected by the current detection unit 34 by the active filter driving IC 36 becomes equal to the detection waveform of the reference sine wave detection unit 35, and the voltage detection means 42 detects the active filter 7. The smoothing capacitor 6 that is an output voltage is detected, and a signal is output to the variable conduction ratio setting unit 37 so that the voltage of the smoothing capacitor 6 becomes the target voltage. The variable conduction ratio setting unit 37 is based on the signal, and the switching element 4 The on / off signal is output.

  By turning the switching element 4 on and off, an input current flows from the commercial power source 1 via the choke coil 3 and a distorted input current is prevented from flowing to the commercial power source 1 side. In addition, when the first switching element 4 is turned on, energy is stored in the choke coil 3 from the commercial power source 1, and after that, when the conduction time set by the variable conduction ratio setting unit 37 elapses, the switching element 4. Is turned off, and the energy stored in the choke coil 3 is supplied to the smoothing capacitor 6 via the diode 5, so that the voltage of the smoothing capacitor 6 is boosted to a voltage higher than that of the commercial power supply 1, and then passed through the smoothing capacitor 13. It is supplied to the inverter circuit 15. FIG. 3 shows an operation waveform of one cycle of the active filter 7.

  The active filter drive control IC 36 is designed not to operate unless it receives an operation permission signal transmitted from the microcomputer 26. As a result, the microcomputer 26 can drive and stop the active filter 7 at an arbitrary timing.

  The voltage of the commercial power source 1 is boosted by the active filter 7 as shown in FIG.

  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. Further, since the switching element 11 has the diode 12 and the snubber capacitor 9 connected in parallel, when the switching element 11 is turned off, the snubber capacitor 9 starts charging with an inclination, and the switching element 11 realizes the ZVS turn-off operation.

  If the snubber capacitor 9 becomes the same voltage as the smoothing capacitor 6 during the period when the switching element 11 is off, the voltage equal to that of the smoothing capacitor 6 is fixed. After that, when the voltage of the smoothing capacitor 6 becomes higher than that of the snubber capacitor 9. The snubber capacitor 9 starts discharging, and 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. In addition, the snubber capacitor 9 can be operated 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, in the present embodiment, 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 shown in FIG. The smoothing capacitor 6 corresponding to the output of the active filter 7 is boosted by the boosting circuit 14 and output to the smoothing capacitor 13 as shown in FIG. The voltage value of the smoothing capacitor 13 is adjusted so that the power set by the user in the operation unit 39 is input to the object to be heated. FIG. 4 shows an operation waveform of one cycle of the booster circuit 14.

  The voltage of the smoothing capacitor 13 boosted by the booster circuit 14 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 off from the on state, the snubber capacitor 20 is discharged with an inclination, so that the switching element 16 realizes a ZVS turn-off operation. When the snubber capacitor 20 is completely discharged, the diode 19 is turned on. When an on signal is applied to the gate of the switching element 17 while the diode 19 is on, the diode 19 is turned off and current is commutated to the switching element 17. The switching element 17 realizes a ZVS & ZCS turn-off operation. When the switching element 17 is turned off from the on state, the snubber capacitor 20 is charged with an inclination, so that the switching element 17 realizes a ZVS turn-off operation. When the snubber capacitor 20 is charged to the same voltage as the smoothing capacitor 13, the diode 18 is turned on. When an on signal is applied to the gate of the switching element 16 while the diode 18 is on, the diode 18 is turned off. Thus, a 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 shown in FIG. FIG. 5 shows an operation waveform of one cycle 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 about 2 μs so as not to short-circuit the smoothing capacitor 13. Further, in the present embodiment, the high frequency power is controlled by varying the drive frequency and conduction time of the switching elements 16 and 17.

  In the induction heating apparatus shown in FIG. 1, since the load 23 (pan, frying pan, etc.) of various materials is used by the user for a to-be-heated body, the load impedance seen from the active filter 7 is various. That is, when the active filter 7 and the inverter circuit 15 are simultaneously activated / soft-started when heating is started, the load impedance of the inverter circuit 15 is changed when the operating frequency and on-time of the inverter circuit 15 are changed by predetermined values. Since the amount of variation varies depending on the material and structure of the load 23, the best matching between the control amount of the active filter 7 and the control amount of the inverter circuit 15 cannot be uniquely determined. Therefore, if the active filter 7 and the inverter circuit 15 are simultaneously activated and soft-started, and the amount of change in the load impedance of the inverter circuit 15 viewed from the active filter 7 and the control amount of the active filter 7 are mismatched, The output voltage (voltage of the smoothing capacitor 6) overshoots, and breakdown breakdown of components (smoothing capacitor 6, switching element 4, etc.) occurs.

  In the present embodiment, the inverter circuit 15 is driven so that the load impedance of the inverter circuit 15 viewed from the active filter 7 is stable during the active filter activation period from the start of activation to the completion of activation at the start of heating. By controlling, it becomes possible to start and soft start in a state where the fluctuation amount of the load impedance of the inverter circuit 15 viewed from the active filter 7 during the active filter starting period is suppressed, and the output voltage (voltage of the smoothing capacitor 6) It is possible to start up safely and quickly without over-boosting and to operate stably. The inverter circuit 15 drives and controls the switching elements 16 and 17 by changing the operating frequency and the ON time by a predetermined control amount until the microcomputer 26 reaches a predetermined output power after the activation of the active filter 7 is completed. In the inverter circuit 15 during the active filter activation period, the microcomputer 26 uses the input current detected by the current transformer 40 and the input current detection unit 24 as a feedback constant so that the output power becomes a predetermined value or less than a predetermined fluctuation range. By controlling the operating frequency or on-time of 17 and 17 to be a predetermined value or controlled within a predetermined fluctuation range, the fluctuation amount of the load impedance of the inverter circuit 15 viewed from the active filter 7 can be suppressed to a constant value or less than the predetermined fluctuation amount. And

  In the induction heating apparatus shown in FIG. 1, when the enamel pan is heated, the waveforms when the switching elements 16 and 17 are activated with the on-time fixed at 3 μs and the operating frequency fixed at about 23 kHz are shown in FIG. As shown in FIG. 6, since the on-time of the switching elements 16 and 17 of the inverter circuit 15 is fixed during the active filter starting period, the inverter load impedance as viewed from the active filter 7 becomes stable, and the active filter 7 becomes the output voltage. It can be seen that the smoothing capacitor 6 can be started up without excessively boosting the voltage of the smoothing capacitor 6.

  As described above, in the present embodiment, the active filter is activated to activate the active filter 7 in a state where the inverter circuit 15 is driven and controlled so that the load impedance of the inverter circuit 15 viewed from the active filter 7 becomes stable at the start of heating. By providing the period, the active filter 7 can be started and soft-started while the fluctuation amount of the load impedance of the inverter circuit 15 is suppressed, and the output voltage (the voltage of the smoothing capacitor 6) is not excessively boosted. It can be started safely and quickly and can operate stably.

  Further, in the present embodiment, at the time of inspecting the substrate to check whether the substrate operates correctly in the factory, the output power of the inverter circuit 15 changes with a predetermined fluctuation amount even during the active filter activation period. By controlling the operating frequency and on-time of the inverter circuit 15 with a predetermined control amount, it is possible to quickly reach a predetermined output power, and it is possible to shorten the substrate inspection time.

  As described above, the induction heating apparatus according to the present invention can be started safely and quickly and stably operated without excessively boosting the output voltage of the active filter at the start of heating. 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 apparatus.

Circuit diagram of induction heating apparatus in an embodiment of the present invention Waveform diagram of voltage and current in each part of the induction heating device Waveform diagram of voltage and current in the active filter of the same induction heating device Waveform diagram of voltage and current in the booster circuit of the induction heating device Waveform diagram of voltage and current in the inverter circuit of the same induction heating device Waveform diagram at the start of enamel pan heating in the same induction heating device

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Commercial power supply 7 Active filter 14 Booster circuit 15 Inverter circuit 21 Heating coil 23 Load 28 Inverter circuit control means 32 Booster circuit control means 33 Active filter control means 40 Current transformer (output detection means)

Claims (7)

An active filter that is connected after commercial power rectification and improves the power factor by turning on and off the switching element, and an inverter circuit that is connected to the output of the active filter and generates high-frequency current by turning on and off the switching element An induction heating apparatus that drives and controls the inverter circuit so that the load impedance of the inverter circuit as viewed from the active filter is stable during the active filter activation period from the start of activation to the completion of activation at the start. The induction heating apparatus according to claim 1, wherein the inverter circuit operation is controlled so that the output power becomes a predetermined value during the active filter activation period. The induction heating apparatus according to claim 1 or 2, wherein the inverter circuit is operated while being fixed at a predetermined operating frequency and on-time during the active filter activation period. The induction heating apparatus according to claim 1, wherein the inverter circuit operation is controlled so that the output power is equal to or less than a predetermined fluctuation range during the active filter activation period. 5. The induction heating apparatus according to claim 1, wherein the inverter circuit is operated at an operating frequency and an on-time that are equal to or less than a predetermined fluctuation range during an active filter activation period. The induction heating device according to claim 1, wherein at the time of inspection, the inverter circuit is driven and controlled so that the output power changes with a predetermined fluctuation amount even during the active filter activation period. The induction heating apparatus according to claim 1 or 6, wherein at the time of inspection, the operating frequency and on-time of the inverter circuit are changed by a predetermined fluctuation amount even during the active filter activation period.