JP4781295B2 - Induction heating cooker - Google Patents

Description

  The present invention relates to an induction heating cooker having a plurality of heating coils.

  Some conventional induction heating cookers have an inner coil and an outer coil arranged substantially concentrically, and the inner coil and the outer coil are each driven by a full-bridge inverter circuit. For small-diameter pans, only the inner coil is driven, and for large-diameter pans, the inner coil and outer coil are alternately driven in a time-sharing manner, and one arm of the full-bridge inverter circuit is used in common. Reduction is aimed at (for example, refer to patent documents 1).

JP 2000-91063 A

  In the conventional induction heating cooker, as described above, only the inner coil or the inner coil and the outer coil are energized according to the pan size, so there is little leakage flux regardless of the pan size, and a full bridge inverter circuit is used. Therefore, the voltage applied to the load circuit such as the inner coil and the outer coil is high, and high thermal power is easily obtained. However, it is difficult to reduce the output to low heating power, and heating is performed by switching the energized state in a time-sharing manner, so that the temperature fluctuation of the pan becomes large and the cooked product may be burnt. Furthermore, when a low-impedance pan made of aluminum or the like is placed, overcurrent tends to flow through the heating coil, and the switching element of the inverter circuit may be destroyed.

  The present invention has been made to solve the above-described problems, and can adjust the heating power from a high heating power to a low heating power regardless of the pan size, and overcurrent is also applied to a low impedance pan such as aluminum. It aims at obtaining the induction heating cooking appliance which can judge a pot safely, without flowing.

In the induction heating cooker according to the present invention, two switching elements are connected in series between the buses of the DC power supply circuit, and three sets of arms each including the two switching elements and three sets of Inverter control means for driving and controlling each switching element of the arm, inner and outer coils arranged concentrically, a resonance capacitor constituting a series resonance circuit with the inner and outer coils, respectively, and input to the DC power supply circuit An input current detecting means for detecting a current to be detected, an inner coil current detecting means for detecting a current flowing in the inner coil, and an outer coil current detecting means for detecting a current flowing in the outer coil. One set is used as a common arm, and a series resonant circuit is connected between the common arm and the other two sets of arms, and an inner coil and an outer coil of the series resonant circuit are connected. Are connected so that the circulation direction of the current flowing out from the common arm is the same direction, and in the inverter control means, the common arm is driven at a high frequency and at least one of the other two arms is driven at a high frequency. And can switch between half-bridge operation to drive at least one of the other two arms at high frequency while fixing one of the two switching elements of the common arm. It is a thing.

  In addition, the inverter control means turns on one of the two switching elements of the common arm at the start of heating to fix the state, and drives at least one of the other two arms at high frequency to drive half The load is determined based on the correlation between the input current detected by the input current detecting means and at least one of the detected currents of the inner coil current detecting means and the outer coil current detecting means.

  In addition, the inverter control means drives the common arm and one of the other two arms at high frequency to perform a full bridge operation when the load judgment made in the half bridge operation is uncertain, and detects the input current. The load determination is performed again based on the correlation between the input current detected by the means and the detected current of either the inner coil current detecting means or the outer coil current detecting means.

  In the induction heating cooker according to the present invention, the inner coil is connected between the common arm and the other set of arms, and the outer coil is connected between the common arm and the other set of arms. It is possible to apply voltage to the coil separately, and the inner coil and the outer coil are connected so that the circulation direction of the current flowing out from the common arm is the same for the inner coil and the outer coil. The currents flowing through each other are suppressed by each other, making it difficult for overcurrent to flow. By enabling the inverter control means to switch between full-bridge operation and half-bridge operation, it can be reduced from high heat power regardless of load pan size. Output control can be performed up to thermal power.

  In addition, at the start of heating, either one of the two switching elements of the common arm is turned on to fix the state, and at least one of the other two sets of arms is driven at a high frequency to perform a half-bridge operation. As a result, the voltage applied to the coil can be reduced to suppress the overcurrent that flows when detecting a low impedance pan, and the pan material to be used can be determined safely and reliably.

  Further, when the load determination performed in the half-bridge operation is indeterminate, the common arm and one of the other two arms are driven at a high frequency to perform a full-bridge operation and detected by the input current detection means. Since the load determination is performed again based on the correlation between the input current and the detected current of either the inner coil current detecting means or the outer coil current detecting means, the load can be accurately applied without causing an overcurrent to flow to each arm. Can be determined.

Hereinafter, embodiments of an induction heating cooker according to the present invention will be described in detail with reference to the drawings.
Embodiment 1 FIG.
FIG. 1 is a diagram showing a circuit configuration of an induction heating cooker according to Embodiment 1 of the present invention.
In the figure, the power supplied from the commercial AC power source 1 is converted into DC power by the DC power source circuit 2. The DC power supply circuit 2 includes a rectifier diode bridge 3 that rectifies AC power, a reactor 4, and a smoothing capacitor 5. The input power input to the DC power supply circuit 2 is detected by the input current detector 6 and the input voltage detector 7. The power converted into DC power by the DC power supply circuit 2 is supplied to the inverter circuit 8.

  The inverter circuit 8 includes three sets of two switching elements (IGBT) connected in series between the positive and negative buses of the DC power supply circuit 2 and diodes connected in antiparallel to the switching elements. It consists of an arm. In the following, one of the three arms will be referred to as a common arm 9, and the other two will be referred to as an inner coil arm 10 and an outer coil arm 11. The switching elements on the positive bus side of the arms 9 to 11 are referred to as upper switches 12, 17, 22 and the switching elements on the negative bus side are referred to as lower switches 13, 18, and 23, and the switching elements on the positive bus side of the arms 9 to 11 are referred to. The antiparallel diodes are referred to as upper diodes 14, 19, and 24, and the negative parallel diodes on the negative bus side are referred to as lower diodes 15, 20, and 25.

  The common arm 9 is an arm connected to an inner coil load circuit 30 and an outer coil load circuit 31, which will be described later. The upper switch 12 and the lower switch 13, and the upper diode 14 connected in reverse parallel to the switches 12 and 13, respectively. The connection point of the upper switch 12 and the lower switch 13 is the output point of the common arm 9. A snubber capacitor 16 is connected to the lower switch 13 in parallel. The inner coil arm 10 is an arm to which an inner coil load circuit 30 is connected, and includes an upper switch 17 and a lower switch 18, and an upper diode 19 and a lower diode 20 connected in reverse parallel to the switches 17 and 18. Has been. A snubber capacitor 21 is connected to the lower switch 18 in parallel. The outer coil arm 11 is an arm to which the outer coil load circuit 31 is connected. The upper switch 22 and the lower switch 23, and the upper diode 24 and the lower diode 25 connected in reverse parallel to the switches 22 and 23, respectively. It consists of and. A snubber capacitor 26 is connected to the lower switch 23 in parallel.

  The upper switch 12 and the lower switch 13 of the common arm 9 are ON / OFF driven by a drive signal output from the common arm drive circuit 27, and the upper switch 17 and the lower switch 18 of the inner coil arm 10 are supplied from the inner coil arm drive circuit 28. The on / off drive is performed by the output drive signal, and the upper switch 22 and the lower switch 23 of the outer coil arm 11 are driven on / off by the drive signal output from the outer coil arm drive circuit 29.

  The common arm drive circuit 27 turns off the lower switch 13 while the upper switch 12 of the common arm 9 is turned on, turns the lower switch 13 on while the upper switch 12 is turned off, and turns on and off alternately. Drive signal to output. Similarly, the inner coil arm drive circuit 28 outputs a drive signal for alternately turning on and off the upper switch 17 and the lower switch 18 of the inner coil arm 10, and the outer coil arm drive circuit 29 is similarly output from the outer coil arm drive circuit 29. A drive signal for alternately turning on and off the upper switch 22 and the lower switch 23 of the coil arm 11 is output.

  The above-described snubber capacitors 16, 21, and 26 are switches that delay the fluctuations in the output voltage when the switches 13, 18, and 23 of the common arm 9, the inner coil arm 10, and the outer coil arm 11 are turned off. Is provided to reduce the turn-off loss.

  The inner coil load circuit 30 is a series resonance circuit composed of an inner coil 32 and a resonance capacitor 33, and is connected between the output point of the common arm 9 and the output point of the inner coil arm 10, and is connected to the outer coil load. The circuit 31 is a series resonance circuit including an outer coil 34 and a resonance capacitor 35, and is connected between the output point of the common arm 9 and the output point of the outer coil arm 11. The inner coil 32 is a heating coil having a small outer shape wound in a substantially circular shape, and an annular outer coil 34 is wound around the outer periphery thereof, and the center positions of the inner coil 32 and the outer coil 34 are substantially the same. It arrange | positions so that it may correspond. Note that the inner coil 32 and the outer coil 34 are adjusted so that their inductance values are substantially equal in a state where the large-diameter pan is placed, and the inner coil load circuit 30 and the outer coil load circuit 31 are substantially the same. The resonance frequency is equivalent. The inner coil 32 and the outer coil 34 are wound and connected in the same circumferential direction as viewed from the common arm 9. The inner coil current detector 36 can detect the current flowing through the inner coil 32, and the outer coil current detector 37 can detect the current flowing through the outer coil 34 to detect the magnitude and phase of the current. The outer coil voltage detector 38 detects a voltage generated in the outer coil 34.

  The control unit 39 controls the entire induction heater. The control unit 39 displays an operation state on the display unit 41 according to an input instruction from the operation input unit 40, and the input current detector 6, the input voltage detector 7, and the inner coil. While taking in the detection values of the current detector 36 and the outer coil current detector 37, the arm drive circuits 27 to 29 are controlled to adjust the heating output. In addition, the drive signal output to each arm 9-11 is a drive frequency higher than the resonance frequency of the inner coil load circuit 30 and the outer coil load circuit 31, and the current flowing through the load circuit is compared with the voltage applied to the load circuit. Then, control is performed so as to flow in a delayed phase.

  Further, the control unit 39 performs a full bridge operation for driving the common arm 9 and the other two sets of arms 10 and 11 at a high frequency, and drives the common arm 9 in a fixed manner and at least of the other two sets of arms 10 and 11. The half-bridge operation for driving one set at high frequency can be switched, and at the start of heating, for example, the lower switch 13 of the upper and lower switches 12 and 13 of the common arm 9 is turned on to fix the state, and the other two sets Based on the correlation between the input current detected by the input current detector 6 and the detected current of the inner coil current detector 36, the inner coil arm 10 is driven at a high frequency among the arms 10 and 11 of the When a load determination (primary determination) is made and this load determination is indeterminate, the common arm 9 and the arm 10 for the inner coil of the other two sets of arms 10 and 11 are raised. Inverter control means that performs full-bridge operation by driving with a wave and performs load determination (secondary determination) again based on the correlation between the input current detected by the input current detector 6 and the detected current of the inner coil current detector 36 It has. This point will be described in detail when explaining the operation.

  Next, operation | movement of the induction heating cooking appliance comprised as mentioned above is demonstrated using drawing of FIGS. 9 to 13 will be described later. FIG. 2 is a flowchart showing a heating control process of the induction heating cooker in the first embodiment, FIG. 3 is a waveform diagram showing an example of a drive signal in a full bridge mode to the inverter circuit, and FIG. 4 is a half bridge mode to the inverter circuit FIG. 5 is a waveform diagram showing an output voltage in the full bridge mode of the inverter circuit, FIG. 6 is a waveform diagram showing an output voltage in the half bridge mode of the inverter circuit, and FIG. FIG. 8 is a diagram showing a determination condition for switching energization only from the inner coil to the inner coil and the outer coil.

  First, the control unit 39 determines whether or not a heating instruction is input from the operation input unit 40 (step 1). When there is an input, the control unit 39 initially determines whether or not the load to be heated is appropriate. A load determination process is performed (step 2). Details of the initial load determination process will be described later. As a result of the initial load determination (step 3), when it is determined that there is no load or pan is unsuitable, the inverter circuit 8 is not driven (step 4), and the fact that the pan is not suitable is displayed on the display unit (step 5). ), Returning to step 1, it is determined whether or not a heating instruction is input.

  On the other hand, if it is determined in step 3 that the pan is appropriate, the heating coil to be energized is set to a mode in which both the inner coil 32 and the outer coil 34 are energized (step 6), and the set thermal power is determined ( Step 7). When the set thermal power is larger than the predetermined value, the inverter circuit 8 is driven in the full bridge mode (step 8), and when the set thermal power is smaller, the inverter circuit 8 is driven in the half bridge mode (step 9).

  In the full bridge mode, as shown in FIG. 3, high-frequency drive signals are output to the upper and lower switches 12 and 13 of the common arm 9, and the upper and lower switches 17 and 18 of the inner coil arm 10 and the outer coil arm 11 A high-frequency drive signal is output to each of the upper and lower switches 22 and 23, and a high-frequency voltage is generated at each output terminal. The voltage applied to the inner coil load circuit 30 constituted by the inner coil 32 and the resonance capacitor 33 is the difference between the output terminal voltage of the inner coil arm 10 and the output terminal voltage of the common arm 9. The difference between the output terminal voltage of the outer coil arm 11 and the output terminal voltage of the common arm 9 is applied to the outer coil load circuit 31 constituted by the resonance capacitor 34. Further, in the half-bridge mode, as shown in FIG. 4, the lower switch 13 of the common arm 9 is turned on to continue (fix) the output terminal voltage thereof is fixed to 0 V, and the inner coil arm 10 and the outer coil The arm 11 is driven at a high frequency, and a high frequency voltage is applied to the inner coil load circuit 30 and the outer coil load circuit 31.

  Next, in step 10 shown in FIG. 2, the input power is calculated from the input current and the input voltage detected by the input current detector 6 and the input voltage detector 7, and the set thermal power set by the operation input unit 40 is set. Compare with power. When the input power is larger, the drive signals output from the arm drive circuits 27 to 29 are controlled in a direction in which the heating output is reduced (step 11). Specifically, in the case of the full bridge mode, the phase difference of the high-frequency drive signal to the common arm 9 and the inner coil arm 10 or the outer coil arm 11 is reduced, as shown in FIG. As described above, the phase difference of the output terminal voltage is reduced, and the effective value of the AC voltage applied to the inner coil load circuit 30 or the outer coil load circuit 31 is suppressed. In the half-bridge mode, the energization time of the upper switch 17 or 22 of the inner coil arm 10 or the outer coil arm 11 is shortened, and the inner coil load circuit 30 as shown in FIG. Alternatively, the effective value of the AC voltage applied to the outer coil load circuit 31 is suppressed.

  In step 10, when the set power is larger than the input power, control is performed to increase the heating output (step 12). Specifically, in the case of the full bridge mode, the phase difference of the high-frequency drive signal to the common arm 9 and the inner coil arm 10 or the outer coil arm 11 is increased, as shown in FIG. As described above, the phase difference of the output terminal voltage is increased. In the half bridge mode, the energization time of the upper switch 17 or 22 of the inner coil arm 10 or the outer coil arm 11 is lengthened, and as shown in FIG. Alternatively, the effective value of the AC voltage applied to the outer coil load circuit 31 is increased.

  Subsequently, the energization coil mode is determined (step 13). That is, it is determined whether only the inner coil 32 or the inner coil 32 and the outer coil 34 are energized. When both the inner coil 32 and the outer coil 34 are energized, it is determined whether or not the current ratio detected by the inner coil current detector 36 and the outer coil current detection stage 37 is unbalanced (step 14). ). When the size of the pan placed on the heating coil is small, only one of the inner coil 32 and the outer coil 34 has strong magnetic coupling and the other becomes weak, so the load impedance of the inner coil 32 and the outer coil 34 is unbalanced. Thus, the current flowing through each load circuit tends to be unbalanced. Therefore, as shown in FIG. 7, when the current flowing through the inner coil 32 and the current flowing through the outer coil 34 become unbalanced, it is determined that the small-diameter pan is placed, and only the inner coil 32 is placed. The mode is changed to the energized inner coil mode (step 15).

  Further, when only the inner coil 32 is energized, the size of the pan used is large, and if it is placed on both the inner coil 32 and the outer coil 34, a magnetic path spanning the inner coil 32 and the outer coil 34 is formed. As a result, the magnetic coupling between the coils 32 and 34 is strengthened, and the voltage induced in the outer coil 34 is also increased. Therefore, the magnitude of the induced voltage detected by the outer coil voltage detector 38 is determined (step 16), and when an induced voltage exceeding a predetermined value is detected as shown in FIG. It is determined that the medium-diameter pan is placed, and the mode is changed to the inner / outer coil mode in which both the inner coil 32 and the outer coil 34 are energized (step 17).

  Then, it is determined whether or not there is no heating stop instruction input from the operation input unit 40 (step 18). If there is no stop instruction, the process returns to step 7. If there is a heating stop instruction input, the inverter circuit The output of the drive signal to 8 is stopped to stop the heating operation (step 19), and the process returns to step 1 waiting for the heating start instruction.

  Here, the initial load determination processing described above will be described with reference to FIGS. FIG. 9 is a flowchart illustrating the initial load determination process in the first embodiment, FIG. 10 is a waveform diagram illustrating a drive signal for primary determination in the initial load determination process, and FIG. 11 is a diagram illustrating primary determination conditions in the initial load determination process. FIG. 12 is a waveform diagram showing a drive signal for secondary determination in the initial load determination process, and FIG. 13 is a diagram showing secondary determination conditions in the initial load determination process.

  First, the inner coil 32 is energized by half-bridge driving (step 21). For example, like the drive signal shown in FIG. 10, the lower switch 13 of the common arm 9 is turned on, the output terminal voltage is set to 0 V, the inner coil arm 10 is driven at a high frequency, and the output terminal voltage of the inner coil arm 10 is set. A high-frequency voltage is generated, the upper and lower switches 22 and 23 of the outer coil arm 11 are turned off, and the output terminal of the outer coil arm 11 is set to an indefinite potential from 0 V to + V (positive bus potential). Only a high frequency voltage is generated (step 21). Then, using the current values detected by the input current detector 6 and the inner coil current detector 36, primary determination is performed based on, for example, FIG. 11 (step 22). In FIG. 11, when the output current is large or when the output current is large with respect to the input current, it is determined that the pot is not suitable for heating with low resistance such as an aluminum pan. In addition, when the input current is small or the output current is small, it is determined that the pan is not placed on the coil (no load), or a small object such as a fork or knife is placed. Further, when the input current and the output current are within the predetermined range, it is determined that the determination cannot be made accurately, and the process proceeds to the secondary determination.

  When the secondary determination is made, the inner coil 32 is energized by full bridge drive (step 23). For example, the drive signal shown in FIG. 12 is output, the common arm 9 and the inner coil arm 10 are driven at a high frequency to generate a high frequency voltage at the output terminal of the inner coil arm 10, The switches 22 and 23 are turned off, the output terminal of the arm 11 for the outer coil is set to an indefinite potential from 0 V to + V (positive bus potential), and a high frequency voltage is generated only in the inner coil load circuit 30 (step 23). Then, using the current values detected by the input current detector 6 and the inner coil current detector 36, for example, secondary determination is performed based on FIG. 13 (step 24). In FIG. 13, when the output current is large, or when the output current is large relative to the input current, it is determined that the pot is not suitable for low resistance heating such as an aluminum pan. Further, when the input current is small or the output current is small, it is determined that the pan is not placed on the heating coil, or a small object such as a fork or knife is placed (step 24). If the load is determined to be an inappropriate pan or accessory in the primary determination (step 22) or the secondary determination (step 24), an inappropriate pan is set as the detected load data (step 25), and an appropriate pan is detected. If so, aptitude pot is set as the load data (step 26), and the initial load determination process is terminated.

  As described above, according to the first embodiment, only the inner coil 32 or the inner coil 32 and the outer coil 34 are energized and heated according to the pan size, so that the leakage magnetic flux is small regardless of the pan size. In addition, heating operation can be performed in a wide output range from high output by full bridge operation to low output by half bridge operation. Moreover, since the initial load determination process is performed only on the inner coil 32 by the half-bridge operation at the start of heating, the pot determination can be performed safely and reliably regardless of the pot size or pot material. In the half-bridge operation, since the output terminal of the common arm 9 is a fixed voltage, the output can be adjusted independently by the inner coil 32 and the outer coil 34, and only the inner coil 32 or the outer coil 34 can be adjusted. Even in the case of one-side drive in which only the current is supplied and the other coil is not supplied, the potential of one end of the load circuit that is not supplied with current is fixed, so that the induced current hardly flows.

In the first embodiment, the output control in the full bridge operation is performed by controlling the phase difference between the drive signal to the common arm 9 and the drive signal to the inner coil arm 10 or the outer coil arm 11. However, output control may be performed by controlling the energization ratio and drive frequency of the upper switch and lower switch of each arm. Further, output control in the half-bridge operation may be performed by controlling the drive frequency.
Further, in the first embodiment, when operating in the inner / outer coil mode, the switching elements of the three sets of arms are set by the drive signals shown in FIG. 3 or FIG. 4 so that the inner coil 32 and the outer coil 34 are energized simultaneously. Although the driving operation is shown, the inner coil 32 and the outer coil 34 may be operated so as to be alternately energized in a time division manner. FIG. 14 (full bridge operation) and FIG. 15 (half bridge operation) show examples of drive signals when the inner coil 32 and the outer coil 34 are alternately energized.

Embodiment 2. FIG.
As shown in the flowchart of FIG. 9, the initial load determination of the first embodiment is such that only the inner coil load circuit 30 is energized by half-bridge driving, and the pan material is determined regardless of the pan size. In the second embodiment, the initial load determination is performed by simultaneous energization of the inner coil 32 and the outer coil 34 or full bridge drive.

  FIG. 16 is a flowchart showing an initial load determination process in the second embodiment, FIG. 17 is a waveform diagram showing a drive signal for primary determination in the initial load determination process, and FIG. 18 is a drive signal for secondary determination in the initial load determination process. FIG. Note that the circuit configuration in the second embodiment is the same as that in FIG. 1 described in the first embodiment, and a description thereof will be omitted.

  The inverter control means of the control unit 39 in the second embodiment fixes the state by turning on the lower switch 13 among the upper and lower switches 12 and 13 of the common arm 9 at the start of heating, and the other two sets of arms 10 and 11 is driven at a high frequency to perform a half-bridge operation, and the input detected by the input current detector 6 when the ratio of the current detected by the inner coil current detector 36 and the outer coil current detector 37 is within a predetermined range. A load determination (primary determination) is performed based on the correlation between the current and the sum of the detected currents of the inner coil current detector 36 and the outer coil current detector 37. When this load determination is uncertain, the common arm 9 and the other two arms 10 and 11 are driven at a high frequency to perform a full bridge operation, and are detected by the inner coil current detector 36 and the outer coil current detector 37. When the ratio of the detected currents is within the predetermined range, again based on the correlation between the input current detected by the input current detector 6 and the sum of the detected currents of the inner coil current detector 36 and the outer coil current detector 37. Perform load determination (secondary determination).

  Further, when the ratio of the detected currents of the inner coil current detector 36 and the outer coil current detector 37 during the half-bridge operation is outside a predetermined range, the lower switch 13 of the upper and lower switches 12 and 13 of the common arm 9 is turned on. In addition to fixing the state, the inner coil arm 10 of the other two arms 10 and 11 is driven at a high frequency to perform a half-bridge operation, and the input current detected by the input current detector 6 and the inner coil current A load determination (primary determination) is performed based on the correlation with the detection current of the detector 36. Further, when this load determination is uncertain, the common arm 9 and the inner coil arm 10 out of the other two sets of arms 10 and 11 are driven at a high frequency to perform a full bridge operation and detected by the input current detector 6. The load determination (secondary determination) is performed again based on the correlation between the input current and the detected current of the inner coil current detector 36.

Next, the operation of the second embodiment will be described with reference to FIGS.
In the present embodiment, drive signals as shown in FIG. 17 are output from the common arm drive circuit 27, the inner coil arm drive circuit 28, and the outer coil arm drive circuit 29, and the lower switch 13 of the common arm 9 is turned on. The output terminal voltage is fixed at 0V. The upper switches 17 and 22 and the lower switches 18 and 23 of the inner coil arm 10 and the outer coil arm 11 are alternately turned on and off alternately to output a high frequency voltage, and the inner coil load circuit 30 and the outer coil load circuit 31 A high frequency voltage is applied by half-bridge driving (step 101).

  Then, it is determined whether the ratio of the current flowing through the inner coil 32 and the current flowing through the outer coil 34 detected by the inner coil current detector 36 and the outer coil current detector 37 is within a predetermined range (step 102). If the difference is not large, it is possible that a large-diameter or medium-diameter pan is placed, and it is detected by the input current detector 6 using the relationship shown in FIG. 11 as in the first embodiment. A primary determination is made from the input current and the sum of the output currents flowing through the inner coil 30 and the outer coil 32 (step 103). When the output current is large relative to the input current, or when the output current is absolutely large, it is judged that the pan has a low electrical resistance (low resistance pan) that is not suitable for induction heating, such as an aluminum pan, and the output current and input current are If it is small, it is determined that there is no load or a small load such as a knife or fork is placed. Further, when the input current and the output current are within a predetermined range and are large to some extent, it is determined that the medium diameter or large diameter is an appropriate pan (medium diameter / large diameter pan).

  Otherwise, the process proceeds to the secondary determination. In this case, a drive signal as shown in FIG. 18 is output from the common arm drive circuit 27, the inner coil arm drive circuit 28, and the outer coil arm drive circuit 29 (step). 104). Then, it is determined whether the output current detected by the inner coil current detector 36 and the output current detected by the outer coil current detector 37 are within a predetermined ratio range (step 105). If it is out of the predetermined range, the small-diameter pan may be placed, and the process proceeds to Step 111 described later. If it is within the predetermined range, secondary determination of the pan is performed as in the first embodiment as shown in FIG. (Step 106). That is, when the sum of the output currents exceeds a predetermined value or when the output current is large with respect to a small input current, it is determined that the pot is not suitable for induction heating with a low electrical resistance (low resistance pan), When the output current or input current is small, it is determined that there is no load on which the pan is not placed, or a small load where heating of the fork, knife, etc. should be stopped. Otherwise, a large or medium diameter pan is placed. It is determined that it is placed. If it is determined in the primary determination in step 103 and the secondary determination in step 106 that the pan is a low resistance pan, no load, or a small load, the load determination result is an inappropriate pan (step 107), and a medium diameter suitable for heating or If it is determined that the pan is a large-diameter pan, the load determination result is set as an inner / outer coil energizing pan (step 108). Note that the threshold values of FIG. 11 used for the primary determination and FIG. 13 used for the secondary determination are values adjusted according to the operating conditions such as the driving conditions of each arm and the input voltage.

  In step 102, when the ratio of the current flowing through the inner coil 32 and the current flowing through the outer coil 34 detected by the inner coil current detector 36 and the outer coil current detector 37 is not within the predetermined range, the inner coil 32 is detected. 10 is output from the common arm drive circuit 27 and the inner coil arm drive circuit 28, and it is determined that there is a high possibility that the small-diameter pan magnetically coupled to the arm is placed. Then, only the inner coil 32 is half-bridge driven (step 109), and the pot is determined from the output current detected by the inner coil current detector 36 and the input current detected by the input current detector 6 in the same manner as in step 103. (Step 110). However, the determination threshold is different from that in step 102. If the output current is excessive, or if the input current or output current is small, it is judged as an inappropriate pan, and if the input current and output current are within a certain range, and if it is somewhat large, it is judged as a small-diameter pan (small pan) ), Otherwise, the drive signal shown in FIG. 12 is output from the common arm drive circuit 27 and the inner coil arm drive circuit 28 to shift to the secondary determination process, and the output of the outer coil arm 11 is released. Then, a high frequency voltage is output from the common arm 9 and the inner coil arm 10, and the high frequency voltage is applied only to the inner coil load circuit 30 by full bridge driving (step 111). Then, the secondary determination is performed using the output current and the input current detected by the inner coil current detector 36 and the input current detector 6 (step 112). When it is determined that the low-resistance pan, the no-load state, or the small load is determined by the primary determination in step 110 and the secondary determination in step 112, the load determination result is set as an inappropriate pan (step 107), and a small-diameter pan suitable for heating When it is determined, the load determination result is set as the inner coil energizing pan (step 113).

  In the second embodiment, the means for detecting the current flowing in the inner heating coil 32 and the outer heating coil 34 is provided, and the heating pot is heated from the ratio of the detected inner heating coil current and the outer heating coil current. An example of switching the heating coil to be energized by judging the size has been shown, but means for detecting the voltage generated in the inner heating coil 32 and the outer heating coil 34 or the voltage generated in the resonant capacitors 33 and 35 is provided. The heating coil to be energized may be switched by judging the size of the pot being heated from the ratio of the detected voltage.

  As described above, according to the second embodiment, when the heating is started, the lower switch 13 of the common arm 9 is turned on to fix the state, and the other two arms 10 and 11 are driven at a high frequency to be half-bridged. When the ratio of the currents detected by the inner coil current detector 36 and the outer coil current detector 37 is within a predetermined range, a high frequency voltage is applied to only the inner coil 32 by a half-bridge operation as in the first embodiment. Since the determination process of the initial load is performed by applying, the pot determination can be performed safely and reliably regardless of the pot size and pot material. Further, when the inner coil 32 and the outer coil 34 are in a half-bridge operation, when the load is uncertain in the primary determination, the inner coil 32 and the outer coil 34 are set in a secondary determination by a full-bridge operation. Therefore, it is possible to accurately determine the load without causing an overcurrent to flow through the arms 9 to 11.

It is a figure which shows the circuit structure of the induction heating cooking appliance in Embodiment 1 of this invention. 3 is a flowchart showing a heating control process of the induction heating cooker in the first embodiment. It is a wave form diagram which shows an example of the drive signal in the full bridge mode to an inverter circuit. It is a wave form diagram which shows an example of the drive signal in the half bridge mode to an inverter circuit. It is a wave form diagram which shows the output voltage of the full bridge mode of an inverter circuit. It is a wave form diagram which shows the output voltage of the half bridge mode of an inverter circuit. It is a figure which shows the judgment conditions which switch electricity only to an internal heating coil from internal heating coil electricity supply and external heating coil electricity supply. It is a figure which shows the determination conditions which switch electricity supply to the inner coil and the outer coil from electricity supply only of an inner heating coil. 3 is a flowchart showing an initial load determination process in the first embodiment. It is a wave form diagram which shows the drive signal for primary determination in an initial load determination process. It is a figure which shows the primary determination conditions in an initial stage load determination process. It is a wave form diagram which shows the drive signal for secondary determination in an initial load determination process. It is a figure which shows the secondary determination conditions in an initial load determination process. It is a waveform diagram of the output voltage showing another example of the full bridge mode of the inverter circuit. It is a waveform diagram of the output voltage showing another example of the half bridge mode of the inverter circuit. 10 is a flowchart illustrating an initial load determination process in the second embodiment. It is a wave form diagram which shows the drive signal for primary determination in an initial load determination process. It is a wave form diagram which shows the drive signal for secondary determination in an initial load determination process.

Explanation of symbols

1 commercial AC power supply, 2 DC power supply circuit, 8 inverter circuit, 9 common arm,
10 arm for inner coil, 11 arm for outer coil, 27 common arm drive circuit,
28 Inner coil arm drive circuit, 29 Outer coil arm drive circuit, 32 Inner coil, 33 Resonant capacitor for inner coil, 34 Outer coil, 35 Resonant capacitor for outer coil, 39 Control unit, 40 Operation input unit, 41 Display section.

Claims (6)

Two switching elements are connected in series between the buses of the DC power supply circuit, and three sets of arms each including the two switching elements,
Inverter control means for driving and controlling each switching element of the three sets of arms;
An inner coil and an outer coil arranged on concentric circles;
A resonance capacitor that constitutes a series resonance circuit with each of the inner coil and the outer coil;
Input current detection means for detecting a current input to the DC power supply circuit;
An inner coil current detecting means for detecting a current flowing through the inner coil;
An outer coil current detecting means for detecting a current flowing through the outer coil;
One of the three sets of arms is a common arm, and the series resonance circuit is connected between the common arm and the other two sets of arms, and the inner coil and the outer coil of the series resonance circuit are connected to the common arm. Connect so that the direction of current flowing out of
In the inverter control means, the common arm is driven at a high frequency and at least one of the other two sets of arms is driven at a high frequency, and one of the two switching elements of the common arm is turned on. And the other is turned off to fix the state, and the half-bridge operation for driving at least one of the other two arms at high frequency can be switched.   The inverter control means turns on one of the two switching elements of the common arm at the start of heating to fix the state, and drives one of the other two arms at high frequency. Half-bridge operation is performed, and load determination is performed based on the correlation between the input current detected by the input current detection means and the detected current of either the inner coil current detection means or the outer coil current detection means. The induction heating cooker according to claim 1, wherein   The inverter control means turns on one of the two switching elements of the common arm at the start of heating to fix the state, and drives the other two arms at high frequency to perform a half-bridge operation. When the ratio of the current detected by the inner coil current detecting means and the outer coil current detecting means is within a predetermined range, the input current detected by the input current detecting means and the inner coil current detecting means and the outer coil The induction heating cooker according to claim 1, wherein load determination is performed based on a correlation with a sum of detected currents of the current detecting means.   When the load determination performed by the half-bridge operation is uncertain, the inverter control unit drives the common arm and the other two sets of arms at a high frequency to perform a full-bridge operation, and the internal coil current detection unit and the When the ratio of the current detected by the outer coil current detecting means is within a predetermined range, the sum of the input current detected by the input current detecting means and the detected currents of the inner coil current detecting means and the outer coil current detecting means The induction heating cooker according to claim 3, wherein the load determination is performed again based on the correlation with the induction heating cooker. When the ratio of the detected currents of the inner coil current detecting means and the outer coil current detecting means during half-bridge operation is outside a predetermined range, the inverter control means is one of the two switching elements of the common arm. Is turned on and the state is fixed, and the arm connected to the series resonance circuit of the inner coil of the other two sets of arms is driven at a high frequency to perform a half-bridge operation, and is detected by the input current detecting means induction heating cooker according to claim 3, characterized in that the load determined based on the correlation of the input current and the detected current in said coil current sensing hand stage.   When the load determination performed in the half-bridge operation is uncertain, the inverter control means drives the common arm and one of the other two arms at a high frequency to perform a full-bridge operation, and the input current 6. The load determination is performed again based on a correlation between an input current detected by a detecting means and a detected current of either the inner coil current detecting means or the outer coil current detecting means. The induction heating cooker described.

Images