JP2006202705A - Induction heating cooker and induction heating cooking method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an induction heating cooker improved in controllability so as to smoothly carry out power adjustment in a wide adjustment range of heating power from high heating power to low heating power. <P>SOLUTION: This induction heating cooker is provided with a means having a full-bridge inverter circuit operating as a half-bridge circuit as well, operating with the full bride in outputting the high heating power, operating with the half bridge in outputting the low heating power, and controlling an output current so as to be set nearly equal in operation changeover, whereby the variation of the heating power thereof is reduced. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an induction heating cooker and an induction heating cooking method used in general households.

  A conventional induction heating cooker has a pan material discriminating circuit and an inverter circuit having a full bridge circuit that also functions as a half-bridge circuit, and according to the discrimination result of the pan material discriminating circuit, Switching means for switching the bridge circuit is provided, and both magnetic and non-magnetic cooking pans having different magnetic permeability can be heated (for example, see Patent Document 1).

JP-A-5-251172

  In the above induction heating cooker, the full-bridge circuit and the half-bridge circuit are switched according to the determination result of the pot material determination circuit, so that the operation mode of the inverter circuit is not switched during the heating operation after the pot material determination. . However, when switching between full-bridge circuit and half-bridge circuit to apply a wide range of output adjustment from high heating output to low heating output with high efficiency for the same cooking pot, during the heating operation It is necessary to switch the operation mode of the inverter circuit. Then, when the operation mode of the inverter circuit is switched, there is a problem that the voltage applied to the load circuit fluctuates greatly, the heating output fluctuates greatly, or an overcurrent flows through the inverter circuit.

  The present invention has been made to solve the above-described problems, and provides an induction heating cooker with improved controllability so that a wide range of output adjustment can be smoothly performed from high heating output to low heating output. It is an object.

  The induction heating cooker according to the present invention is a full-bridge type formed by two arms including two switching elements connected in series between output buses of a DC power supply circuit that rectifies an AC power supply and converts it into DC. An inverter circuit, a load circuit including a heating coil and a resonant capacitor connected to the output of the full-bridge inverter circuit, and a drive signal output to the switching element of the full-bridge inverter circuit to adjust the heating output The inverter control means, and the inverter control means drives the two arms forming the full-bridge inverter circuit at high frequency, respectively, and drives one arm at high frequency while It is possible to switch between half-bridge operation modes for fixedly driving the arm. In the induction heating cooker that performs switching between the ridge operation mode and the half-bridge operation mode without stopping the heating operation, before and after the operation mode switching between the full-bridge operation mode and the half-bridge operation mode, the load circuit It has a drive signal adjustment means for setting the drive signal so that the flowing high-frequency alternating current is substantially equal.

  In addition, the induction heating cooking method according to the present invention includes a full-bridge operation mode in which the two arms forming the full-bridge inverter circuit are each driven at a high frequency, and one arm is driven at a high frequency and the other arm is fixedly driven. In the induction heating cooking method in which the switching between the full bridge operation mode and the half bridge operation mode is performed without stopping the heating operation, the full bridge operation mode and the half bridge operation are performed. The drive signal is set so that the high-frequency alternating current flowing in the load circuit is substantially equal before and after the operation mode switching with the mode.

  The present invention relates to a full-bridge inverter circuit formed by two arms including two switching elements connected in series between output buses of a DC power supply circuit that rectifies an AC power supply and converts it into DC. A load circuit including a heating coil and a resonant capacitor connected to the output of the bridge inverter circuit; and an inverter control means for controlling a drive signal output to the switching element of the full bridge inverter circuit in order to adjust the heating output. The inverter control means includes a full-bridge operation mode in which each of the two arms forming the full-bridge inverter circuit is driven at a high frequency, and a half that drives one arm at a high frequency and drives the other arm in a fixed manner. It is possible to switch between the bridge operation mode and the full bridge operation mode. In the induction heating cooker that performs switching to the half-bridge operation mode without stopping the heating operation, the high-frequency alternating current that flows through the load circuit before and after the operation mode switching between the full-bridge operation mode and the half-bridge operation mode. Since there is a drive signal adjusting means for setting the drive signal so as to be substantially equal, the heating output to the cooking pan magnetically coupled to the heating coil of the load circuit is also substantially equal, and the heating adjustment is performed smoothly. be able to. Further, since the output current is equivalent to that before the operation mode is switched, no overcurrent flows through the inverter circuit when the operation mode is switched.

  The present invention also includes a full bridge operation mode in which the two arms forming the full bridge inverter circuit are each driven at a high frequency, and a half bridge operation mode in which one arm is driven at a high frequency and the other arm is fixedly driven. In the induction heating cooking method in which the switching between the full-bridge operation mode and the half-bridge operation mode is performed without stopping the heating operation, the operation mode switching between the full-bridge operation mode and the half-bridge operation mode Since the drive signal is set so that the high-frequency alternating current flowing through the load circuit is approximately equal before and after, the heating output to the cooking pan magnetically coupled to the heating coil of the load circuit is also approximately equal, and smooth It becomes possible to perform heating adjustment.

Hereinafter, an induction heating cooker according to an embodiment of the present invention will be described with reference to the drawings.
Embodiment 1 FIG.
FIG. 1 is a block diagram showing an electrical configuration of induction heating cooker 50 according to the first embodiment. The induction heating cooker 50 is connected to the AC power supply 1, and the power supplied from the AC power supply 1 is converted into DC power by the DC power supply 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 detection means 6 and the input voltage detection means 7. The voltage fluctuation detecting means 8 detects a DC voltage fluctuation synchronized with the AC voltage of the AC power supply 1 and outputs a synchronization signal at a timing when the DC voltage is lowered. The power converted into DC power by the DC power supply circuit 2 is supplied to the inverter circuit 9.

  The inverter circuit 9 includes two arms (hereinafter referred to as “arms”) formed by two switching elements (IGBTs) 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. The two sets of arms are referred to as a U-phase arm 10 and a V-phase arm 11. The positive bus-side switching element of each arm is referred to as an upper switch, and the negative bus-side switching element is referred to as a lower switch. ing.

  The U-phase arm 10 includes an upper switch 12, a lower switch 13, an upper diode 14 connected in antiparallel with the upper switch 12, and a lower diode 15 connected in antiparallel with the lower switch 13. . The V-phase arm 11 includes an upper switch 16, a lower switch 17, an upper diode 18 connected in antiparallel with the upper switch 16, and a lower diode 19 connected in antiparallel with the lower switch 17. ing.

  The upper switch 12 and the lower switch 13 constituting the U-phase arm 10 are turned on / off by a drive signal output from the U-phase drive circuit 20. Further, the upper switch 16 and the lower switch 17 constituting the V-phase arm 12 are driven to be turned on / off by a drive signal output from the V-phase drive circuit 21. The U-phase drive circuit 20 turns off the lower switch 13 while the upper switch 12 of the U-phase arm 10 is turned on, and turns on the lower switch 13 while the upper switch 12 is turned off. A drive signal for alternately turning on / off the upper switch 12 and the lower switch 13 is output. Similarly, the V-phase drive circuit 21 outputs a drive signal for alternately turning on and off the upper switch 16 and the lower switch 17 of the V-phase arm 11.

  A load circuit 24 including a heating coil 22 and a resonance capacitor 23 is connected between the output points of the two arms in the inverter circuit 9. Although the heating coil 22 and the resonance capacitor 23 form a series resonance circuit and have a resonance frequency, the inverter circuit 9 is driven at a frequency higher than the resonance frequency, so that the load circuit 24 has inductive characteristics. It has become.

  The heating output control means 25 is an inverter control means and functions to control the induction heating cooker 50 as a whole. Based on the heating power instruction set by the user in the heating power setting means 26, the input current detection means 6 and the input voltage detection are detected. In the full bridge operation mode in which the high-frequency drive signal is output from both the U-phase arm drive circuit 20 and the V-phase arm drive circuit 21 using the detection value from the means 7, or one arm is set to the fixed drive. The heating output is controlled in a half-bridge operation mode in which a high-frequency drive signal is output from the other arm.

  The drive signal adjustment means 27 generates the drive signal adjustment value when the operation mode of the inverter circuit 9 is switched from the full bridge operation mode to the half bridge operation mode or when the half bridge operation mode is switched to the full bridge operation mode. It has a function.

  FIG. 2 is a timing chart showing switching and voltage applied to the load circuit 24 in the full bridge operation mode of the inverter circuit 9 of the induction heating cooker 50. In this full-bridge operation mode, the U-phase arm 10 and the V-phase arm 11 of the inverter circuit 9 are 180 degrees out of phase and are driven at a high frequency at a constant frequency. The heating output is controlled by adjusting the energization rate (on time ratio) between the switch 16 and the lower switches 13 and 19. FIG. 2A shows that the energization rates of the upper switches 12 and 16 and the lower switches 13 and 19 of each arm are both about 50% and reach a maximum output state. Moreover, FIG.2 (b) has shown the state which has suppressed the heating output by making the electricity supply rate of the upper switches 12 and 16 smaller than 50%.

  FIG. 3 is a timing chart showing the switching and voltage applied to the load circuit 24 in the half-bridge operation mode of the inverter circuit 9 of the induction heating cooker 50. In this half-bridge operation mode, only the U-phase arm 10 of the inverter circuit 9 is driven at high frequency, and the V-phase arm 11 is fixedly driven (upper switch 16 off, lower switch 19 on). FIG. 3A shows the maximum output state in the half-bridge operation mode in which the energization rates of the upper switch 12 and the lower switch 13 of the U-phase arm 10 are both 50%. FIG. 3B shows a state where the heating output is suppressed by making the energization rate of the upper switch 12 of the U-phase arm 10 smaller than 50% and energizing the lower switch 13 larger than 50%.

  Next, a comparison of applied voltages to the load circuit 24 in the full bridge operation mode and the half bridge operation mode will be described with reference to FIG. In the induction heating cooker 50 driven at a constant frequency, the heating output is substantially proportional to the square of the high-frequency current flowing through the heating coil 22, and the current flowing through the heating coil 22 is proportional to the applied voltage. Then, the voltage applied to the load circuit 24 is adjusted by controlling the energization rate as described above, and the heating output is controlled.

  4A shows a voltage waveform applied to the load circuit 24 in the full-bridge operation mode, where T is the high frequency driving cycle, Δt is the energization time (time per driving cycle) of the upper switches 12 and 16 of each arm. ) And E indicate the voltages between the positive and negative buses of the DC power supply circuit 2, respectively. In the period I (Δt), it is indicated that the voltage E is applied to the load circuit 24 in the period in which the upper switch 12 of the U-phase arm 10 is on and the lower switch 17 of the V-phase arm 11 is on. Yes.

In period III (Δt), voltage (−E) is applied to the load circuit 24 while the lower switch 13 of the U-phase arm 10 is on and the upper switch 16 of the V-phase arm 11 is on. I will show you. Period II and period IV are periods in which the lower switches 13 and 17 are on in both the U-phase arm 10 and the V-phase arm 11 and indicate that no voltage is applied to the load circuit 24 ( The applied voltage of the load circuit 24 indicates the output point potential of the U-phase arm 10 with reference to the output point potential of the V-phase arm 11). Therefore, the effective voltage value (Vfb) applied to the load circuit 24 is expressed by the following equation (1).

このように、フルブリッジ動作モードでは、最大Ｅ（正負母線間電圧）の電圧印加が可能となっている。 Here, when the energization rate is maximized (50%), Δt is half of T, and therefore the maximum voltage effective value (maxVfb) can be expressed by the following equation (2).

As described above, in the full-bridge operation mode, a maximum voltage E (positive / negative bus voltage) can be applied.

4B and 4C show voltage waveforms applied to the load circuit 24 in the half-bridge operation mode (the U-phase arm 10 is driven at high frequency and the V-phase arm 11 is fixed), and ΔT is The energization time (time per drive cycle) of the upper switch 12 of the U-phase arm 10 and Vav indicate the DC component of the applied voltage. The applied voltage direct current component Vav is proportional to the energization rate (formula (3)) of the U-phase arm 10 and can be represented by the following formula (4).

In the period V (formula (3)), the high frequency (alternating current) voltage applied to the load circuit 24 in a state where the upper switch 12 of the U-phase arm 10 is on and the lower switch 17 of the V-phase arm 11 is on. The component is represented by the formula (5).

In the period VI (formula (6)), the high frequency (alternating current) voltage component applied to the load circuit 24 in the state where the lower switches 13 and 17 are turned on for both the U-phase arm 10 and the V-phase arm 11 is expressed by the formula (6). 7). Therefore, the effective voltage value (Vhb) applied to the load circuit 24 can be expressed by Expression (8).

このように、ハーフブリッジ動作モードでは、最大でＥの２分の１の電圧印加が可能となっている。 Here, when the energization rate is maximized (50%), ΔT is one half of T, and therefore the maximum voltage effective value (maxVhb) can be expressed by the following equation (9).

Thus, in the half-bridge operation mode, a voltage application of a half of E at maximum is possible.

The relationship between the energization rate at which the load circuit applied voltage (Vfb) in the full bridge operation mode and the load circuit applied voltage (Vhb) in the half bridge operation mode are equal is expressed by the following equations (1) and (8). (10). Then, the relationship of Formula (11) is materialized.

  Therefore, as shown in FIG. 5, in the full-bridge operation mode, an equivalent applied voltage is applied to the load circuit 24 if the energization rate in the full-bridge operation mode is set to 1/4 to 1/2 times the energization rate in the half-bridge operation mode. be able to. On the contrary, in the half-bridge operation mode, an equivalent applied voltage can be applied to the load circuit 24 by increasing the energization rate by 2 to 4 times the full-bridge operation mode.

  FIG. 6 is a flowchart showing an example of the flow of the heating output control process for switching between the full bridge operation mode and the half bridge operation mode according to the set thermal power. The flow of the heating output control process will be described based on FIG. First, it is determined whether the full-bridge operation mode or the half-bridge operation mode is set (step S101). When it is the full bridge operation mode (step S101; full bridge), the set thermal power set by the user in the thermal power setting means 26 is compared with the half bridge operational mode switching thermal power (HB switching thermal power) (step S102). ).

  When the set thermal power is equal to or less than the HB switching thermal power (step S102; ≦), the operation mode is switched to the half bridge operation mode (step S103). Then, the upper switch energization rate is set to A times (however, the upper switch energization rate after A times is 50% or less) (step S104). A is a drive signal adjustment value generated by the drive signal adjustment means 27 so as to be a value of 2 to 4 and approximately satisfying the relationship of the expression (11). FIG. 7A shows a timing chart showing the switching at the time of switching the inverter operation state in step S103 and step S104 and the change in the voltage applied to the load circuit 24. FIG.

  On the other hand, when the operation mode is the half-bridge operation mode (step S101; half-bridge), the set heating power and the full-bridge operation mode switching heating power (FB switching heating power) are compared (step S105). If the set thermal power is equal to or greater than the FB switching thermal power (step S105; ≧), the operation mode is switched to the full bridge operation mode (step S106). Then, the upper switch energization rate is set to B times (step S107). B is a drive signal adjustment value generated by the drive signal adjustment means 27 so as to be a value that satisfies the relationship of the expression (11) in a number of 1/4 to 1/2. FIG. 7B shows a timing chart showing the switching of the inverter operation state from the half-bridge operation mode to the full-bridge operation mode and the change in the applied voltage to the load circuit 24 in steps S106 and S107.

  When the operation mode is determined by the above steps, the set thermal power is compared with the input power obtained from the detection values of the input current detection means 6 and the input voltage detection means 7 (step S108). If the input power is small (step S108;>), it is determined whether the upper switch energization rate is less than the upper limit value (50%) (step S109). If the energization rate is less than the upper limit value (step S109; <), the upper switch energization rate is increased (step S110). When the input power is larger than the set thermal power (step S108; <), the upper switch energization rate is compared with the lower limit value (step S111). If it is larger than the lower limit (step S111;>), the upper switch energization rate is decreased (step S112).

  Note that the switching timing of the inverter circuit operation mode by the heating output control means 25 is switched in synchronization with the output signal from the voltage fluctuation detection means 8. By doing so, it is possible to switch the inverter circuit operation mode at the timing when the output voltage of the DC power supply circuit 2 that fluctuates in synchronization with the AC voltage of the AC power supply 1 decreases.

  In the first embodiment, an example in which the effective value of the voltage applied to the load circuit 24 is controlled to be substantially equal when the inverter circuit operation mode is switched is shown. Since the circuit 9 is driven, the load circuit 24 has an inductive load characteristic, and the high-frequency component of the applied voltage hardly flows through the load circuit 24. Therefore, the applied voltage waveform is expanded in the Fourier series at the drive frequency. The primary component may be controlled so as to have substantially the same effective value.

  Further, in the first embodiment, when switching from the full bridge operation mode to the half bridge operation mode, the upper switch energization rate is increased by 2 to 4 times, and when switching from the half bridge operation mode to the full bridge operation mode, the upper switch energization is performed. Although the rate is ¼ to 1/2 times, the energization rate is not changed when switching from the full bridge operation mode to the half bridge operation mode, and the energization rate is not changed when switching from the half bridge operation mode to the full bridge operation mode. The output current may not increase when the operation mode is switched to prevent the occurrence of overcurrent.

  As described above, when switching between the full-bridge operation mode and the half-bridge operation mode, the applied voltage to the load circuit 24 is adjusted to be approximately the same, thereby preventing the occurrence of overcurrent when switching the inverter circuit operation mode. Smooth thermal power adjustment from heating output to low heating output can be performed. In addition, by switching between the full-bridge operation mode and the half-bridge operation mode when the DC power supply voltage drops in synchronization with the AC voltage of the commercial AC power supply, the DC component of the resonant capacitor 23 of the load circuit 24 is small at the time of switching. It is possible to obtain a device that does not generate a stable operating state.

Embodiment 2. FIG.
The induction heating cooker 50a according to the second embodiment performs heating output control by arm phase difference control in the full-bridge operation mode of the inverter circuit 9, and by energization rate control in the half-bridge operation mode of the inverter circuit 9. Is what you do. Since the induction heating cooker 50a is the same as the circuit configuration of the induction heating cooker 50 according to Embodiment 1, the description of the circuit configuration is omitted.

  FIG. 8 is a timing chart showing switching and voltage applied to the load circuit 24 in the full bridge operation mode of the inverter circuit 9 of the induction heating cooker 50a. The induction heating cooker 50a controls the heating output by adjusting the drive phase difference between the U-phase arm 10 and the V-phase arm 11 with the energization rate of the upper and lower switches of each arm of the inverter circuit 9 being 50%. ing. FIG. 8A shows that the maximum output state is obtained when the phase difference between the U-phase arm 10 and the V-phase arm 11 is approximately 180 degrees. FIG. 8B shows a state where the heating output is suppressed by reducing the inter-arm phase difference. The half-bridge operation mode is the same as that shown in FIG.

  FIG. 9 is a flowchart showing an example of the flow of the heating output control process performed by the heating output control means 26 of the induction heating cooker 50a. The flow of this heating output control process will be described based on FIG. First, it is determined whether the full bridge operation mode or the half bridge operation mode is selected (step S201). When the operation mode is the full bridge operation mode (step S201; full bridge), the set thermal power set by the user in the thermal power setting means 26 and the detection values of the input current detection means 6 and the input voltage detection means 7 Is compared with the input power obtained from (step S202). If the input power is small (step S202;>), it is determined whether the phase difference between the arms is less than the upper limit (180 degrees (half cycle)) (step S203). If the inter-arm phase difference is less than the upper limit (step S203; <), the inter-arm phase difference is increased (step S204).

  When the input power is larger than the set thermal power (step S202; <), it is determined whether the inter-arm phase difference is larger than the lower limit value (step S205). The lower limit value of the inter-arm phase difference is set to a level at which an excessive current does not flow into the switching element and is destroyed due to the phase of the current flowing through the load circuit 24 at the time of turn-on. If the inter-arm phase difference is larger than the lower limit (step S205;>), the inter-arm phase difference is reduced (step S206). If the inter-arm phase difference has reached the lower limit (step S205; ≦), the operation mode is switched to the half-bridge operation mode, the upper switch 16 of the V-phase arm 11 is turned off, and the lower switch 17 is turned on. It is fixed (step S207). Then, the energization rate of the upper switch 12 of the U-phase arm 10 is set to twice the inter-arm phase difference (however, the upper limit of the energization rate is 50%) (step S208).

  Even when the operation mode is the half-bridge mode (step S201; half-bridge), it is obtained from the set thermal power set by the user in the thermal power setting means 26 and the detection values of the input current detection means 6 and the input voltage detection means 7. The input power is compared (step S209). If the input power is small (step S209;>), it is determined whether the upper switch energization rate is less than the upper limit (50%) (step S210). If the energization rate is less than the upper limit (step S210; <), the upper switch energization rate is increased (step S211). When the upper switch energization rate has reached the upper limit (step S210; ≧), the operation mode is switched to the full bridge operation mode (step S212), and the inter-arm phase difference is ¼ times the upper switch energization rate. (Step S213).

  If the input power is larger than the set thermal power (step S209; <), it is determined whether the upper switch energization rate is greater than the lower limit (step S214). The lower limit value of the upper switch energization rate is the same as the lower limit value of the phase difference between the arms, because an excessive current flows in the switching element in relation to the phase of the current flowing in the load circuit 24 when the upper switch of the U-phase arm 10 is turned on. The level should not be destroyed. If the upper switch energization rate is greater than the lower limit (step S214;>), the upper switch energization rate is decreased (step S215).

  In the second embodiment, when the inverter circuit 9 is switched from the full bridge operation mode to the half bridge operation mode, the upper switch energization rate is doubled (FIG. 10A), and the half bridge operation mode is changed to the full bridge. When switching to the operation mode, the upper switch energization ratio is set to ¼ (FIG. 10B). However, when the operation mode of the inverter circuit 9 is switched, the effective value of the applied voltage to the load circuit 24 before and after the switching is changed. Equation (11) may be established so as to be substantially equivalent. Thus, if the upper switch energization rate and the inter-arm phase difference are set, it is possible to reduce the output power fluctuation at the time of operation mode switching.

  In addition, the effective value of the applied voltage to the load circuit 24 is not controlled substantially equally when the operation mode is switched, but the applied voltage waveform is Fourier-series-expanded with the driving frequency so that the effective value of the primary component becomes substantially equal. You may control.

  As described above, in the induction heating cooker 50a that performs the heating output control by the full bridge operation mode and the phase difference control between the arms at the high heating output, and controls the heating output by the half bridge operation mode and the energization rate control at the low heating output. Since the control is performed so as not to increase the voltage applied to the load circuit 24 when the operation mode of the inverter circuit 9 is switched, an output overcurrent does not flow at the time of switching, and a device that operates stably can be obtained. In addition, when the applied voltage of the load circuit 24 is controlled to be approximately the same when the operation mode is switched, the heating output is also the same before and after the operation mode switching, and a device capable of smoothly adjusting the heating power from the high heating output to the low heating output. Obtainable.

Embodiment 3 FIG.
The induction heating cooker 50b according to Embodiment 3 performs heating output control by frequency control of the inverter circuit 9. FIG. 11 is a block diagram showing an electrical configuration of the induction heating cooker 50b. Based on FIG. 11, the structure of the induction heating cooking appliance 50b is demonstrated. In addition, the same code | symbol is attached | subjected about the same part as Embodiment 1, or an equivalent part, and description shall be abbreviate | omitted.

  The output current detection means 28 detects the current flowing through the load circuit 24 composed of the heating coil 22 and the resonance capacitor 23. The data storage means 29 stores operation mode switching data for obtaining a drive frequency that provides an output current equivalent to that before the operation mode switching when switching between the full bridge operation mode and the half bridge operation mode. This data is generated in advance in the full-bridge operation mode and half-bridge operation mode using various cooking pans at various frequencies, and is generated from the measured values of the drive frequency, input current, and output current. The material and size of the cooking pot used are determined from the values of the drive frequency, the input current detected by the input current detection means 6 and the output current detection means 28, and the output current, and substantially the same output when the operation mode is switched. The drive frequency that becomes the current can be referred to.

  In the frequency control, the inverter circuit 9 is driven at a frequency higher than the resonance frequency of the load circuit 24 constituted by the heating coil 22 and the resonance capacitor 23, but the drive frequency is brought close to or away from the resonance frequency of the load circuit 24. The output current is adjusted to control the heating output. The loss generated in the inverter circuit 9 includes an on-loss at the time of switch conduction and a switching loss at the time of turn-on / turn-off. When the drive frequency is increased to achieve a low heating output, the number of switching operations As a result, the switching loss increases and the efficiency deteriorates. Therefore, in the case of a low heating output, the driving frequency is not so high by switching to the half-bridge operation mode.

  FIG. 12 is a timing chart showing switching and voltage applied to the load circuit 24 in the full-bridge operation mode of the inverter circuit 9 of the induction heating cooker 50b. In the third embodiment, the U-phase arm 10 and the V-phase arm 11 of the inverter circuit 9 are 180 degrees out of phase, and the high-frequency drive is performed with the energization rate of the upper and lower switches of each arm being 50%. The heating output is controlled by adjusting the driving frequency. FIG. 12A shows a maximum output state in which the driving frequency of the upper switches 12 and 16 and the lower switches 13 and 17 of each arm is set to the lower limit frequency. Moreover, FIG.12 (b) has shown the state which makes the drive frequency higher than a minimum frequency and has suppressed the heating output.

  FIG. 13 is a timing chart showing switching and voltage applied to the load circuit 24 in the half-bridge operation mode of the inverter circuit 9. In this operating state, only the U-phase arm 10 of the inverter circuit 9 is driven at high frequency, and the V-phase arm 11 is fixedly driven (upper switch off, lower switch on). FIG. 13A shows the maximum output state in the half-bridge operation mode in which the drive frequency of the U-phase arm 10 is the lower limit frequency. Moreover, FIG.13 (b) has shown the state which raised the drive frequency of the U-phase arm 10 and suppressed the heating output.

  FIG. 14 is a flowchart showing an example of the flow of the heating output control process performed by the frequency control while the heating output control means 25 switches between the full bridge operation mode and the half bridge operation mode. The flow of the heating output control process will be described based on FIG. First, it is determined whether the operation mode is the full bridge operation mode or the half bridge operation mode (step S301). In the case of full-bridge operation mode driving (step S301; full-bridge), it is obtained from the set thermal power set by the user in the thermal power setting means 26 and the detection values of the input current detection means 6 and the input voltage detection means 7. The input power is compared (step S302).

  If the input power is smaller than the set thermal power (step S302;>), it is determined whether the inverter drive frequency is higher than the lower limit drive frequency (step S303). If the inverter drive frequency is higher than the lower limit drive frequency (step S303;>), the inverter drive frequency is lowered (step S304). If the input power is greater than the set thermal power (step S302; <), it is determined whether the inverter drive frequency is lower than the upper limit drive frequency (step S305).

  As the inverter drive frequency is increased, switching loss increases and efficiency decreases, so an upper limit value is set in advance. If the inverter drive frequency is lower than the upper limit drive frequency (step S305; <), the inverter drive frequency is increased (step S306). If the inverter drive frequency has reached the upper limit drive frequency (step S305; ≧), the operation mode is switched to the half-bridge operation mode, and the operation mode is switched from the values of the input current detection means 6 and the output current detection means 28. The drive frequency is changed with reference to the data 29 (step S307).

  FIG. 15 (a1) shows the switching at the time of switching the inverter operation state from the full-bridge operation mode to the half-bridge operation mode and the change in the applied voltage to the load circuit 24 at this time. FIG. 15 (a2) shows a case where the full bridge operation mode is switched to the half bridge operation mode. As described above, when switching without changing the inverter drive frequency or the like, the output current decreases and no overcurrent flows through the output of the inverter circuit 9.

  On the other hand, even when the operation mode is the half-bridge operation mode (step S301; half-bridge), the set thermal power set by the user in the thermal power setting means 26 and the detection of the input current detection means 6 and the input voltage detection means 7 are detected. The input power obtained from the value is compared (step S308). If the input power is smaller than the set thermal power (step S308;>), it is determined whether the inverter drive frequency is higher than the lower limit drive frequency (step S309). When the frequency is higher than the lower limit driving frequency (step S309;>), the inverter driving frequency is lowered (step S310).

  When the inverter drive frequency has reached the lower limit drive frequency (step S309; ≦), the drive frequency is switched to the full bridge operation mode, and the drive mode is referred to the operation mode switching data 29 from the values of the input current and the output current. Is changed (step S311). FIG. 15B shows switching and switching of the voltage applied to the load circuit 24 when switching the inverter operation state from the half-bridge operation mode to the full-bridge operation mode.

  If the input power is greater than the set thermal power (step S308; <), it is determined whether the inverter drive frequency is lower than the upper limit drive frequency (step S312). If the inverter drive frequency is lower than the upper limit drive frequency (step S312; <), the inverter drive frequency is increased (step S313).

  As described above, when heating output control is performed by frequency control, heating is performed at a relatively low driving frequency even at low heating output by switching to full bridge operation mode at high heating output and half bridge operation mode at low heating output. Output control can be performed, and a device with reduced switching loss can be obtained. In addition, the cooking pan material and pan diameter are determined from the inverter drive frequency, input current, and output current, and converted to a frequency that does not cause large output current fluctuations when the operation mode is switched. A device capable of adjusting the heating output with high efficiency and smoothness up to the heating output can be obtained.

Embodiment 4 FIG.
The induction heating cooker 50c according to Embodiment 4 starts the inverter determination process in the half-bridge operation mode at the start of heating, starts the pan determination process, and then switches to the full-bridge operation mode. FIG. 16 is a block diagram showing an electrical configuration of the induction heating cooker 50c. In addition, the same code | symbol shall be attached | subjected about the same or equivalent part as the induction heating cooking appliance 50 or the induction heating cooking appliance 50b, and description shall be abbreviate | omitted.

  The pan determination control data storage means 30 stores inverter circuit drive data at the time of pan determination performed at the start of heating (FIGS. 18 and 19) and data used for pan determination (FIGS. 20 and 21). . The output heating control means 25 is configured to execute a pot determination process based on inverter circuit drive data stored in the pot determination control data storage means 30 and data used for pot determination.

  FIG. 17 is a flowchart illustrating an example of the flow of the pot determination process of the induction heating cooker 50c. FIG.18 and FIG.19 is a timing chart which shows the state of switching in the inverter circuit 9 at the time of pot determination. FIG.20 and FIG.21 is explanatory drawing which shows the data used for pot determination. Based on these figures, the pan determination process will be described.

  FIG. 18A shows a switching state at the time of activation. The operation mode at this time is the half-bridge operation mode, and the drive frequency is f1. FIG. 18B shows a switching state when the pan determination is first performed in the half-bridge operation mode. The driving frequency at this time is f2, and is lower than f1. FIG. 18C shows a switching state when performing the second pan determination in the half-bridge operation mode. The driving frequency at this time is set to f3, which is lower than f2.

  FIG. 19A shows a switching state when switching from the half-bridge operation mode to the full-bridge operation mode. The drive frequency at this time remains the same as f3. Then, the phase difference between the arms is adjusted so that the output current does not fluctuate greatly. The phase difference between the arms at this time is Ph1. FIG. 19B shows a switching state when performing the third pan determination in the full bridge operation mode. At this time, the phase difference between the arms is set to Ph2, which is wider than Ph1. FIG.19 (c) has shown the switching state when making the last pan determination. At this time, the phase difference between the arms is set to Ph3 which is wider than Ph2.

  FIGS. 20 (a), (b) and FIGS. 21 (a), (b) show the first to fourth pan determination data, respectively, and the input current and output current detected at each time point. From the above values, it is impossible to heat with low-efficiency materials such as aluminum pans (inappropriate pan 1), small items such as forks and spoons that should not be heated (inappropriate pan 2), magnetic pans to heat and It is for discriminating non-magnetic pans.

  The flow of the pan determination process will be described based on FIG. At the start of heating, the inverter circuit 9 is activated in the half-bridge operation mode and the frequency f1 (step S401). Thereafter, the drive frequency is lowered to frequency f2 (step S402). Based on the input current and output current detected by the input current detection means 6 and the output current detection means 28 and the data (FIG. 20 (a)) stored in the pot determination control data storage means 30 (FIG. 20 (a)). Is determined (step S403).

  If the output current is large, it is determined that the pan is a low impedance improper pan 1 such as an aluminum pan, and if the input current is small, there is no load or a small object such as a fork (improper pan 2). Judge (step S403; improper pan) and stop heating. When the input current or the output current falls within a predetermined range, it is determined that the magnetic pan (large) or the nonmagnetic SUS pan (large) (hereinafter, the nonmagnetic SUS pan is referred to as a nonmagnetic pan) (step S403). ; Magnetic pot / non-magnetic pot), the process proceeds to the heating output control process. If the input current or output current is a relatively small value, the process proceeds to the next pan determination process as undecided (step S403; undecided).

  If the pan type is not determined in the first pan determination (step S403), the drive frequency is lowered to the frequency f3 (step S404). Then, the second pan determination is performed from the input / output current detected at this time and the data (FIG. 20B) stored in the pan determination control data storage means 30 (step S405). In this determination, when the output current is large, it is determined as an improper pan 1 having a low impedance such as an aluminum pan, and when the input current or output current is small, a small object such as a no-load state or a fork (improper pan) 2) (step S405; improper pan) and heating is stopped. If the input current or output current falls within a predetermined range, it is determined as a magnetic pan (large) or a non-magnetic pan (medium / large) (step S405; magnetic pan / non-magnetic pan), and heating output control is performed. Transition to processing.

  If the input current or output current is a relatively small value, the process proceeds to the next pan determination process as undecided (step S405; undecided). When the pan type is not determined in the second pan determination (step S405), the half-bridge operation mode is switched to the full-bridge operation mode, and the drive frequency is not changed as shown in FIG. In addition, the phase difference between the arms is set to Ph1 so that the output current is substantially the same before and after switching (step S406). Thereafter, the phase difference between the arms is expanded to Ph2 (step S407). Then, the third pan determination is performed based on the input / output current detected at this time point and the data (FIG. 21A) stored in the pan determination control data storage means 30 (step S408).

  As a result of the determination, in the case of an improper pan (step S408; improper pan), heating is stopped. In the case of a heatable magnetic pan or a non-magnetic pan (small / medium) (step S408; magnetic pan / non-magnetic pan), the process proceeds to a heating output control process. If the type of pan is not determined even in the third pan determination (step S408; undecided), the inter-arm phase difference is expanded to Ph3 (step S409). Then, the final pan determination is performed based on the input / output current detected at this time and the data (FIG. 21B) stored in the pan determination control data storage means 30 (step S410). And in the case of an improper pan (step S410; improper pan), heating is stopped. In the case of a heatable magnetic pan or non-magnetic pan (step S410; magnetic pan / non-magnetic pan), the process proceeds to a heating output control process.

  When a pan made of a low impedance material such as aluminum is used, the impedance of the load circuit 24 becomes small, and an excessive output current easily flows through the inverter circuit 9. However, since the voltage applied to the load circuit 24 is lowered in the half-bridge operation mode and the operation is started at a high drive frequency, it is possible to make a pan determination stably without flowing an excessive current. For pans that can be used but have a small magnetic coupling with the heating coil 22 such as small-diameter pans, the pans are accurate if the input current and output current do not flow very much in half-bridge operation mode or high-frequency drive. Cannot judge. However, when the inter-arm phase difference is expanded to Ph3 in the full-bridge operation mode, a predetermined current can be passed through the load circuit 24, so that accurate pan determination can be performed.

  As described above, it is possible to safely make a pan judgment even for a pan having a small load impedance and a large load current, and distinguish small-sized pans and small items such as knives and forks that should not be heated. When determining the load, it is possible to accurately determine the size of the load by driving in the full-bridge operation mode and accurately determine whether or not to heat.

It is a block diagram which shows the electric constitution of the induction heating cooking appliance which concerns on Embodiment 1. FIG. It is a timing chart which shows the voltage in the switching and load circuit in a full bridge operation mode. It is a timing chart which shows the applied voltage to switching and a load circuit in a half-bridge operation mode. It is explanatory drawing which shows the voltage waveform applied to the load circuit of a full bridge operation mode and a half bridge operation mode. It is explanatory drawing which shows the relationship between the electricity supply rate of a half bridge operation mode, and the electricity supply rate of a full bridge operation mode. It is a flowchart which shows an example of the flow of a heating output control process. It is a timing chart which shows the change at the time of an inverter circuit operation state switching, and the change of the applied voltage to a load circuit. It is a timing chart which shows the voltage in the switching and load circuit in a full bridge operation mode. It is a flowchart which shows an example of the flow of a heating output control process. It is a timing chart which shows the change at the time of an inverter circuit operation state switching, and the change of the applied voltage to a load circuit. It is a block diagram which shows the electric constitution of the induction heating cooking appliance which concerns on Embodiment 3. FIG. It is a timing chart which shows the voltage in the switching and load circuit in a full bridge operation mode. It is a timing chart which shows the applied voltage to switching and a load circuit in a half-bridge operation mode. It is a flowchart which shows an example of the flow of a heating output control process. It is a timing chart which shows the change at the time of an inverter circuit operation state switching, and the change of the applied voltage to a load circuit. It is a block diagram which shows the electric constitution of the induction heating cooking appliance which concerns on Embodiment 4. It is a flowchart which shows an example of the flow of a heating output control process. It is a timing chart which shows the state of switching in an inverter circuit at the time of pan judgment processing. It is a timing chart which shows the state of switching in an inverter circuit at the time of pan judgment processing. It is explanatory drawing which shows the data used for pot determination. It is explanatory drawing which shows the data used for pot determination.

Explanation of symbols

1 AC power supply, 2 DC power supply circuit, 3 rectifier diode bridge, 4 reactor, 5 smoothing capacitor, 6 input current detection means, 7 input voltage detection means, 8 voltage fluctuation detection means, 9 inverter circuit, 10 U-phase arm, 11 V Phase arm, 12 Upper switch, 13 Lower switch, 14 Upper diode, 15 Lower diode, 16 Upper switch, 17 Lower switch, 18 Upper diode, 19 Lower diode, 20 U phase drive circuit, 21 V phase drive circuit, 22 Heating coil , 23 resonance capacitor, 24 load circuit, 25 heating output control means (inverter control means), 26 heating power setting means, 27 drive signal adjustment means, 28 output voltage detection means, 29 data storage means, 30 pan determination control data storage means 50 induction heating cooker, 50a induction heating cooker, 50b induction heating cooker, 50 Induction heating cooker.

Claims (7)

A full-bridge inverter circuit formed by two arms including two switching elements connected in series between output buses of a DC power supply circuit that rectifies and converts AC power into DC;
A load circuit including a heating coil and a resonant capacitor connected to the output of the full-bridge inverter circuit;
Inverter control means for controlling a drive signal output to the switching element of the full-bridge inverter circuit in order to adjust the heating output;
The inverter control means includes
A full bridge operation mode in which each of the two arms forming the full bridge inverter circuit is driven at a high frequency;
It is possible to switch between half-bridge operation mode in which one arm is driven at high frequency and the other arm is fixedly driven,
In the induction heating cooker that performs switching between the full bridge operation mode and the half bridge operation mode without stopping the heating operation,
Drive signal adjusting means for setting the drive signal so that the high-frequency alternating current flowing in the load circuit is substantially equal before and after the operation mode switching between the full-bridge operation mode and the half-bridge operation mode. Induction heating cooker. A full-bridge inverter circuit formed by two arms including two switching elements connected in series between output buses of a DC power supply circuit that rectifies and converts AC power into DC;
A load circuit including a heating coil and a resonant capacitor connected to the output of the full-bridge inverter circuit;
Inverter control means for controlling a drive signal output to the switching element of the full-bridge inverter circuit in order to adjust the heating output;
The inverter control means includes
A full bridge operation mode in which each of the two arms forming the full bridge inverter circuit is driven at a high frequency;
It is possible to switch between half-bridge operation mode in which one arm is driven at high frequency and the other arm is fixedly driven,
In the induction heating cooker that performs switching between the full bridge operation mode and the half bridge operation mode without stopping the heating operation,
Induction heating cooking, characterized by comprising drive signal adjustment means for setting the drive signal so that a high-frequency alternating current flowing in the load circuit does not increase when the operation mode is switched between the full-bridge operation mode and the half-bridge operation mode. vessel. The inverter control means includes
The operation mode switching between the full-bridge operation mode and the half-bridge operation mode is performed when the output voltage of the DC power supply circuit that fluctuates in synchronization with an AC voltage of a commercial power supply decreases. The induction heating cooking appliance in any one of. A full-bridge inverter circuit formed by two arms including two switching elements connected in series between output buses of a DC power supply circuit that rectifies and converts AC power into DC;
A load circuit including a heating coil and a resonant capacitor connected to the output of the full-bridge inverter circuit;
Inverter control means for controlling a drive signal output to the switching element of the full-bridge inverter circuit in order to adjust the heating output;
The inverter control means includes
A full bridge operation mode in which each of the two arms forming the full bridge inverter circuit is driven at a high frequency;
It is possible to switch between half-bridge operation mode in which one arm is driven at high frequency and the other arm is fixedly driven,
In the induction heating cooker that performs switching between the full bridge operation mode and the half bridge operation mode without stopping the heating operation,
An induction heating cooker characterized by starting a heating operation in the half-bridge operation mode. A full-bridge operation mode in which each of the two arms forming the full-bridge inverter circuit is driven at a high frequency;
It is possible to switch between half-bridge operation mode in which one arm is driven at high frequency and the other arm is fixedly driven,
In the induction heating cooking method for performing switching between the full bridge operation mode and the half bridge operation mode without stopping the heating operation,
The induction heating cooking method, wherein the drive signal is set so that the high-frequency alternating current flowing through the load circuit is substantially equal before and after the operation mode switching between the full-bridge operation mode and the half-bridge operation mode. A full-bridge operation mode in which each of the two arms forming the full-bridge inverter circuit is driven at a high frequency;
It is possible to switch between half-bridge operation mode in which one arm is driven at high frequency and the other arm is fixedly driven,
In the induction heating cooking method for performing switching between the full bridge operation mode and the half bridge operation mode without stopping the heating operation,
The induction heating cooking method, wherein the drive signal is set so that a high-frequency alternating current flowing in the load circuit does not increase when the operation mode is switched between the full-bridge operation mode and the half-bridge operation mode. A full-bridge operation mode in which each of the two arms forming the full-bridge inverter circuit is driven at a high frequency;
It is possible to switch between half-bridge operation mode in which one arm is driven at high frequency and the other arm is fixedly driven,
In the induction heating cooking method for performing switching between the full bridge operation mode and the half bridge operation mode without stopping the heating operation,
A heating operation is started in the half-bridge operation mode.

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