JP2007080752A - Induction heating cooking device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To select an inverter circuit configuration suited for heating and inverter drive conditions by detecting the state of a load. <P>SOLUTION: An induction heating cooking device comprises a power supply means 3; the inverter circuit 50; an input current detection means 10; an inverter current detection means 13; a load state detection means 14 for detecting the state of a load; a voltage detection means 11 for detecting the input voltage of the power supply means 3; and a control means 300 for controlling at least the output voltage of the power supply means 3, and the inverter circuit 50. The inverter circuit 50 can be switched to a half-bridge configuration or a full-bridge configuration. The control means 300 switches to a half-bridge configuration or a full-bridge configuration by the output of the load state detection means 14 and setting power thrown to a metal body to be heated. Either the output voltage of the power supply means 3 or the drive frequency of the inverter circuit 50 is changed to control power thrown to the metal body to be heated. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a power control method for heating a metal body to be heated of an induction heating cooker.

  The induction heating cooker generates an eddy current in a heated metal body arranged in the vicinity of a heating coil that passes a high-frequency current, and the heated metal body itself self-heats due to its Joule heat, thereby efficiently heating the heated metal body. In recent years, the replacement of cooking appliances using gas stoves or electric heaters has been progressing due to their excellent safety and temperature controllability.

  In such an induction heating cooker, the power control circuit for flowing a high-frequency current to the heating coil is called a so-called resonance type inverter, and connects the inductance of the heating coil including the metal to be heated and the resonance capacitor, In general, the switching element of the power control circuit is on / off controlled at a driving frequency of about 20 to 40 kHz. In addition, there are a voltage resonance type and a current resonance type in the resonance type inverter, and the former is often applied for a 100V power source and the latter for a 200V power source.

  At first, only metal pans (loads), which are heated metal bodies made of magnetic materials such as iron, could only be heated, but in recent years, metal pans (loads) made of non-magnetic stainless steel can also be heated. Yes. Further, there has been proposed an aluminum non-heated metal body which can be heated, which can be heated.

  In an induction heating cooker using such a resonance type inverter, when heating a metal body to be heated, an inductance (equivalent inductance L) determined by the metal body to be heated and a heating coil, and a resistance component ( It has been found that the equivalent resistance R) affects the ease of heat generation. That is, when the metal body to be heated is a magnetic metal (iron, magnetic stainless steel, etc.), it is easy to input power, and when it is a nonmagnetic metal (nonmagnetic stainless steel, aluminum, copper, etc.), it is difficult to input power. This is because the latter has a small value of the equivalent resistance R, and the eddy current induced in the metal body to be heated is unlikely to become Joule heat.

  Therefore, a method of switching the number of turns of the heating coil depending on the material of the metal body to be heated, i.e., by increasing the number of turns of the heating coil and increasing the heating efficiency for a non-magnetic metal body to be heated (For example, refer to Patent Documents 1 and 2).

  In addition, the number of turns of the heating coil is fixed (single heating coil), and power can be applied to a non-magnetic metal object to be heated. However, it is difficult to apply power to a magnetic metal object to be heated. When a non-magnetic heated metal body is detected, the inverter circuit configuration is a half-bridge configuration, and when a magnetic heated metal body is detected, a proposal is made to switch to a full-bridge configuration (for example, And Patent Document 3).

JP-A 61-16491 JP-A-61-128493 JP-A-5-251172

  However, in the above prior art, when the number of turns of the heating coil is switched, there is a portion of the heating coil in which the high-frequency current does not flow. Heat distribution of the metal body is not uniform and uneven heating occurs, or when a heated metal body with a different diameter is used, the power input level changes depending on the diameter of the heated metal body. A problem occurs.

  Further, depending on the heating coil tap structure or the lap winding structure provided for switching the number of turns of the heating coil, it may be difficult to secure an insulation distance against a high voltage applied to the heating coil.

  In the latter, the number of turns of the heating coil is fixed (single heating coil), and the inverter circuit configuration is switched to a full bridge circuit configuration or a half bridge circuit configuration depending on whether the metal body to be heated is magnetic or nonmagnetic. Then, in the case of the metal body to be heated which is characteristically in the intermediate region, there is a problem that the inverter circuit configuration is switched to an unsuitable inverter and energized, the heating efficiency is deteriorated and the inverter circuit is damaged.

  Even if the inverter circuit configuration is switched using a single heating coil, if the impedance of the load of the inverter circuit is large, it is difficult for current to flow through the heating coil that is the load, and it is connected to the switching element of the inverter circuit The snubber capacitor may affect the loss of the switching element, which increases the effect when low power is applied to the load. In other words, when the load impedance is large, the ratio of the charge / discharge current flowing to the switching element due to the charge remaining in the snubber capacitor increases in the control of the low power range, and the switching element loss is caused by excessive current flowing in the switching element. However, there is a problem that the reliability of the switching element is deteriorated due to a temperature rise, and the cost for cooling the switching element is increased, resulting in an increase in cost.

  Moreover, since the charging / discharging current of the snubber capacitor is consumed as electric power that does not contribute to heating of the metal body to be heated, the heating efficiency is lowered.

  The present invention has been made to solve at least one of the above problems.

  The present invention has been made to solve the above-mentioned problem. In claim 1, a high-frequency current is supplied to a power supply means for outputting a DC voltage and a series resonance circuit including a resonance capacitor and a heating coil via the power supply means. An inverter circuit that generates eddy currents in a metal body to be heated disposed near the heating coil and heats it, input current detection means that detects an input current of the power supply means, and current that flows in the series resonance circuit Inverter current detecting means for detecting, load state detecting means for detecting a load state from inputs of the input current detecting means and the inverter current detecting means, voltage detecting means for detecting an input voltage of the power supply means, and at least the power supply Output voltage of the means and control means for controlling the inverter circuit, the inverter circuit being half of the series resonant circuit The control means is configured to be switchable to a ridge configuration or a full-bridge configuration, and the control means switches the inverter circuit to a half-bridge configuration or a full-bridge configuration based on the output of the load state detection means and the set power supplied to the metal body to be heated. The power supplied to the metal body to be heated is controlled by changing either the output voltage of the power supply means or the drive frequency of the inverter circuit.

  According to a second aspect of the present invention, the load state detection means discriminates the impedance of the series resonance circuit or the resonance frequency level in a plurality of stages.

  According to a third aspect of the present invention, when the load state detection means determines that the impedance is low impedance or high resonance frequency, the control means switches the inverter circuit to a half-bridge configuration and substantially fixes the drive frequency of the inverter circuit, The output voltage of the power supply means is controlled to be variable.

  According to a fourth aspect of the present invention, when the load state detection means determines that the impedance is high impedance or low resonance frequency, the control means switches the inverter circuit to a full bridge configuration, and the inverter circuit drive frequency and power supply means The output voltage is controlled to be variable.

  Further, in claim 5, when the load state detection means determines that the impedance is high impedance or low resonance frequency, and when the power to be applied to the metal body to be heated is low power, the half-bridge configuration is switched. The control means controls to vary the drive frequency of the inverter circuit and the output voltage of the power supply means.

  The induction heating cooker according to the present invention is configured as described above, so that the state of the load is determined, and a low-impedance or high-resonance frequency load is a half-bridge inverter circuit. Therefore, an optimum circuit configuration can be selected as a full-bridge inverter circuit, and power control can be performed by a combination of the inverter drive frequency and the DC power supply voltage output, respectively, and the loss of the switching element can be reduced.

  Also, by switching to an inverter circuit configuration that is optimal for the load and adopting a method that makes it easy to control either the drive frequency of the inverter circuit or the output voltage of the power supply means, the inverter circuit has low loss and is resistant to load fluctuations. An induction heating cooker can be provided.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a circuit block diagram for explaining an embodiment of the present invention. In the figure, the AC power supply 1 is converted to DC by the rectifying means 2 and the power supply means 3 outputs a substantially stabilized DC power supply voltage that can be set higher or lower than the effective value voltage of the AC power supply.

  The inverter circuit 50 drives only the switching unit 100 or both switching elements of the switching unit 100 and the switching unit 200 at a high frequency with respect to the series resonant circuit 51 configured by the heating coil 4 and the resonant capacitor 5 or the resonant capacitor 7. Then, a high-frequency current is passed through the heating coil 4 to generate an eddy current in a metal pan (load) that is a metal body to be heated provided in the vicinity of the heating coil 4, and the metal body to be heated itself is heated by Joule heat.

  The switching unit 100 connects the damper diodes 103 and 104 in antiparallel to the series body of the switching elements 101 and 102, respectively. Further, snubber capacitors 105 and 106 are connected to the switching elements 101 and 102 as necessary. One end of a series resonance circuit 51 (a series body of the heating coil 4 and the resonance capacitor 5 or the resonance capacitor 7), which is a load, is connected to the midpoint of the series body of the switching elements 101 and 102.

  The switching unit 200 has the same configuration as the switching unit 100.

  The circuit configuration of the inverter circuit 50 is a series resonant circuit 51 that is a load in the switching relay 6 and the switching relay 8 so that both a half-bridge configuration (including a single-ended push-pull (SEPP) circuit configuration) and a full-bridge configuration can be taken. Switch the connection destination of.

  Specifically, by connecting the switching relay 6 and disconnecting the switching relay 8, the series resonance circuit 51 as a load is connected to the midpoint of the switching unit 100 and the reference potential side of the power supply means 3, and a half-bridge configuration ( Or, it is a SEPP) type inverter circuit configuration. If the switching relay 6 is connected to the high voltage side of the power supply means 3 and the resonance capacitor 5 is also connected, a half-bridge configuration is obtained. Since the basic operation is the same in the SEPP and the half-bridge configuration, the following description will be made as the circuit configuration of the SEPP.

  By driving the switching elements 101 and 102 alternately and exclusively, a high-frequency current having the frequency of the driving frequency of the switching elements 101 and 102 flows through the series resonance circuit 51 that is a load.

  In order to obtain a full bridge configuration, the switching relay 6 is disconnected, the switching relay 8 is connected, and the series resonant circuit 51 as a load is connected to the midpoint of the series body of the switching elements 201 and 202 of the switching unit 200. By alternately driving the combinations of the switching elements 101 and 202 and 102 and 201 alternately, a high-frequency current having a frequency of the driving frequency flows through the series resonance circuit 51 that is a load.

  The control means 300 sets the target power to be input to the metal body to be heated according to the setting of the operation unit 18 operated by the user, and accordingly the setting of the circuit configuration of the inverter circuit 50, the switching elements 101, 102, 201, The setting of the driving frequency 202 and the setting of the DC power supply voltage output of the power supply means 3 are performed. Further, the drive signals to the switching elements 101, 102, 201, 202 are converted into appropriate signal levels by the gate drive means 15. Moreover, it has a prevention means so that switching element 101,102 and switching element 201,202 may not be short-circuited. In addition, the drive signals of the switching relays 6 and 8 are converted to an appropriate signal level by the relay drive means 16, and a prevention means is provided so that the switching relays 6 and 8 are not driven simultaneously.

  In order to detect the operation of the inverter circuit 50, the control means 300 detects the input current of the power supply means 3 flowing to the AC power supply 1 side by the current detection element 9, and converts the detected current into a voltage. Then, the voltage detection means 11 for detecting the voltage of the AC power supply 1 and the current detected by the current detection element 12 for detecting the current (inverter current) flowing through the series resonance circuit 51 which is the load of the inverter circuit 50 are converted into a voltage. Inverter current detection means 13 is provided.

  The load state detection means 14 estimates the material and shape of the metal body to be heated from the inputs of the input current detection means 10 and the inverter current detection means 13, and specifically, the input current detection means 10 and the inverter. From the two inputs of the current detection means 13, whether the load state of the inverter circuit 50 is high impedance or low impedance, and whether the resonance frequency of the load of the inverter circuit 50 is high or low is discriminated. The result is determined in several stages and output to the control means 300.

  The phase difference detection means 17 detects the phase difference of the inverter current with respect to the drive timing of the switching elements 101, 102, 201, 202. This is to prevent the inverter current from leading and becoming in phase with respect to the drive timing of the switching elements 101, 102, 201, 202. The switching elements 101, 102 output from the inverter current detection means 13 and the control means 300 are output. , 201, 202 are input, and when the phase difference is equal to or smaller than a predetermined phase difference, a detection signal is generated and output to the control means 300.

  The reason why the phase difference of the inverter current becomes small with respect to the drive timing of the switching elements 101, 102, 201, 202 is that the drive frequency of the switching elements 101, 102, 201, 202 is close to the resonance frequency of the load of the inverter circuit 50. When the control means 300 detects this signal, it can be avoided by setting the frequency setting of the drive signal of the switching elements 101, 102, 201, 202 higher than the preset value.

  When the drive timing of the switching elements 101, 102, 201, 202 is equal to or less than a predetermined phase difference, when the load condition of the inverter circuit 50 changes (such as a change in the relative position of the metal body to be heated with respect to the heating coil 4), The switching element 101, 102, 201, 202 drive frequency may coincide with the resonance frequency of the load of the inverter circuit 50, or the switching element 101, 102, 201, 202 drive frequency may be lower, resulting in overcurrent. Otherwise, a voltage exceeding the withstand voltage of the switching elements 101, 102, 201, 202 may be generated, leading to destruction of the switching elements 101, 102, 201, 202 and a failure of the inverter circuit 50.

  As a normal operation, the inverter circuit 50 is driven as a circuit configuration of either a full bridge or a half bridge, and the control unit 300 selects the configuration of the inverter circuit 50 according to the output of the load state detection unit 14 and continues driving. Will do.

  FIG. 2 is a diagram for explaining the operation of the load state detection means 14. In the figure, the horizontal axis is the output of the input current detection means 10, and the vertical axis is the output of the inverter current detection means 13. And it utilizes that the combination of the output of the input current detection means 10 and the output of the inverter current detection means 13 changes according to the state of the load. Specifically, by converting each input output voltage into a digital value by an AD converter and using it as address information, the state of the load can be taken out as data for two inputs.

  For example, region A in FIG. 2 is a characteristic exhibited by a metal body to be heated that is most suitable for induction heating, such as iron or magnetic stainless steel (SUS430). Since it is a magnetic material and has a certain degree of resistivity, the magnetic flux generated by the heating coil 4 tends to concentrate, and an eddy current can be efficiently generated and self-heated. Since the equivalent resistance component of the load impedance of the inverter circuit 50 is large, large power can be obtained with a small inverter current.

  Region B is made of non-magnetic stainless steel (SUS304) or the like, and shows characteristics in the case of a metal body to be heated with a thin plate thickness. In non-magnetic stainless steel, the magnetic flux generated by the heating coil 4 is not concentrated on the bottom of the pan, and the resistivity of the material itself is low (about one-fourth that of iron), so the energy transmission efficiency is reduced. However, since the resistance component of the generated eddy current path is increased by reducing the plate thickness at the bottom of the pan, it is a region that generates heat sufficiently if the inverter current is increased, although not as much as in region A.

  Region C is made of nonmagnetic stainless steel or the like, and shows characteristics in the case of a heated metal body having a large plate thickness. Unlike the load in the region B, since the resistance component of the eddy current path is low, sufficient heat cannot be generated unless more inverter current is supplied.

  Region D is a case of a non-magnetic metal pan (load), especially a metal pan (load) using aluminum or copper having a low resistivity, and heat cannot be generated unless an inverter current is passed further than region C. .

For example, although an inverter current hardly flows in a high-impedance metal pan (load), since the equivalent resistance of the load of the inverter circuit 50 tends to be high, a large input current flows with respect to a small inverter current. If the inverter current is I and the equivalent resistance component of the load impedance of the inverter circuit 50 is R, the power W input to the metal pan (load) is W = I, ignoring the loss generated in the heating coil 4 itself. ² xR.

  The power W is maximized when a high-frequency current having a resonance frequency determined by the load impedance and the capacitance of the resonance capacitors 5 and 7 flows. The resonance frequency is expressed by the following equation when the inductance component of the load impedance is L and the resonance capacitor capacitance is C.

  Therefore, even if the equivalent resistance value is the same level in a high impedance load, the resonance frequency is different if the equivalent inductance is different. Therefore, the current flowing through the heating coil 4 varies depending on the inverter frequency to be driven.

  Similarly, in a low impedance load, a low equivalent inductance inherent to a nonmagnetic metal pan (load) is originally affected, and the resonance frequency becomes high.

  In order to heat the metal body to be heated in the region D, it is necessary to increase the load impedance of the inverter circuit 50. As the method, the number of turns of the heating coil 4 is increased to increase the magnetic coupling with the heated metal body to increase the equivalent resistance and the equivalent inductance, or the inverter current frequency is set to a low frequency suitable for the region A. There is a method of increasing the frequency from a band (20 to 40 kHz or the like) to a higher frequency band (60 to 90 kHz).

  Some products have already been put to practical use by the combination of the above methods, but the maximum input power and heating efficiency have not reached those of iron and magnetic stainless steel.

  As described above, the load impedance of the inverter circuit 50 can be estimated to some extent from the combination of the input current and the inverter current. Further, by combining with the drive frequency setting of the control means 300, the level of the load impedance and the level of the resonance frequency of the inverter circuit 50 can be estimated.

  FIG. 3 is a circuit block diagram for explaining the operation when it is determined that the load of the inverter circuit 50 is a load having a low impedance or a high resonance frequency. This figure is an excerpt of a circuit block portion that needs to be operated only when it is determined that the load is in FIG.

  The switching coil 6 is turned on and the switching relay 8 is turned off and the resonance capacitor 5 is connected to the heating coil 4.

  In FIG. 3, when the power control of the load of the inverter circuit 50 is performed, the selectivity Q of the series resonance circuit 51 composed of the heating coil 4 and the resonance capacitor 5 is increased particularly in a low impedance load. When trying to control the power of the load, the operation width is narrow and the change in power is abrupt, which makes it very difficult to control. Therefore, in the case of such a load, a method in which the inverter drive frequency is brought close to the resonance frequency in advance and the power of the load is controlled by changing the power supply voltage applied to the inverter circuit 50 is advantageous.

  For a load having a low impedance or a high resonance frequency, an inverter circuit 50 having a half bridge (or SEPP) configuration is used as shown in FIG. This is because, with respect to the inverter circuit 50 having the full bridge configuration, if the power supply voltage is the same, the voltage applied to the load corresponds to half, so that the inverter current is halved and the power input under the driving conditions of the same switching elements 101 and 102 Becomes about 1/4. Thereby, the overcurrent resulting from low impedance can be suppressed.

  In order to bring the inverter drive frequency close to the resonance frequency of the series resonance circuit 51 composed of the heating coil 4 and the resonance capacitor 5, the output of the phase difference detection means 17 is monitored, and the drive signal of the switching elements 101 and 102 and the inverter current The inverter drive frequency may be controlled so that the phase does not fall within a predetermined value. For this reason, if the load is in a stable state, the inverter drive frequency is substantially fixed.

  In this state, the control means 300 outputs a signal for controlling the output voltage to the power supply means 3, calculates the input power from the input current detection means 10 and the voltage detection means 11, and sets the target load power. The setting of the DC power supply voltage output of the power supply means 3 is adjusted so as to be within a predetermined range.

  Therefore, the control means 300 is a half-bridge inverter circuit 50 by the operation of the switching relays 6 and 8 in a load having a low impedance or a high resonance frequency, and the power control of the load is performed with the inverter drive frequency substantially fixed. This is done by varying the output voltage of the means 3.

  Even during this operation, the load state detection unit 14 is operating, and when the load state changes during heating, the determination result is output to the control unit 300 to change the operation state of the inverter circuit 50 in a timely manner. Is.

  FIG. 4 is an example of load power control by the above method. In FIG. 4, the horizontal axis represents the target power W to be input to the metal pan (load) set by the operation unit 18, and the vertical axis represents the inverter drive frequency f and the output voltage V of the power supply means 3.

  The inverter drive frequency f is substantially fixed, and only the output voltage V of the power supply means 3 is changed according to the target power W. Thereby, electric power control from the low electric power thrown into a metal pan (load) to the maximum electric power is attained.

  FIG. 5 is a circuit block diagram for explaining the operation when it is determined that the load has a high impedance or a low resonance frequency. This figure is an excerpt of a circuit block portion that needs to be operated only in the case of the load in FIG.

  In the case of performing load power control in FIG. 5, since the selectivity Q of the series resonance circuit 51 composed of the heating coil 4 and the resonance capacitor 5 is low in a high impedance load, the metal object to be heated is not affected by changes in the inverter drive frequency. Since the change in the input power is gradual, it is common to control the inverter drive frequency. However, if the above-described low-impedance load is shared with the heating coil 4, the heating coil 4 needs to have a number of turns that can handle the low-impedance load. When power is applied to the metal body, a high power supply voltage must be applied to the inverter circuit 50.

  For example, for a high impedance load, a heating coil 4 that can apply a power supply voltage of 200 V to the inverter circuit 50 and supply 2 kW to the metal body to be heated is increased to 500 W under the same conditions by increasing the number of turns of the heating coil 4. In this case, it is necessary to boost the applied voltage to 400V.

  For such a load, the inverter circuit 50 has a full bridge configuration. This is because the full-bridge inverter circuit 50 can apply a voltage twice as high as the voltage applied to the inverter circuit 50 to the load with respect to the half-bridge inverter circuit 50.

  In the above-described example, instead of increasing the applied voltage from 200 V to 400 V, the inverter circuit configuration is changed from a half bridge (or SEPP) to a full bridge configuration, so that power can be supplied.

  In addition, it is clear that the power supply means 3 has a boosting function, so that it is possible to supply more power, and such a power supply means 3 is general.

  When performing power control, there are a method of changing the inverter drive frequency by setting the output voltage of the power supply means 3 to a predetermined voltage, and a method of changing the output voltage of the power supply means 3 while substantially fixing the inverter drive frequency. I can take it.

  In the former method, the input power increases when the inverter driving frequency is set low, and the input power decreases when the inverter driving frequency is set high. The output voltage needs to be able to set a voltage sufficient to supply the maximum power.

  In the latter method, the input power is low if the output voltage of the power supply means 3 is set low, and high if it is set high. It is necessary that the inverter drive frequency can be set to a frequency sufficient to supply the maximum power.

  Needless to say, power control can be performed using only one of the above two methods, but by using both in combination, the loss of the power supply means 3 itself and the loss of the inverter circuit 50 can be kept low. The power can be controlled. Specifically, the latter method can be used when setting low power, and the former method can be used when setting high power, or both intermediate regions can be used.

  FIG. 6 is an example of power control by the above method. In FIG. 6, the horizontal axis represents the target power W to be set, and the vertical axis represents the inverter drive frequency f and the output voltage V of the power supply means 3.

  6A shows the former method, FIG. 6B shows the latter method, and FIG. 6C shows a combination of both methods.

  In the method of FIG. 6C, the methods of (a) and (b) are switched in a predetermined power setting between the maximum power setting and the minimum power setting. Only one of the inverter driving frequency f and the output voltage setting V of the power supply means 3 is changed with an arbitrary power setting value Wx as a boundary.

  FIG. 7 is a circuit block diagram for explaining the operation when it is determined that the load has a high impedance or a low resonance frequency and when the low power region is set as the target power. This drawing is an excerpt of a circuit block portion that needs to be operated only in the case of the load in FIG. 1, and a description thereof is omitted here.

  In a high impedance or low resonance frequency load, as described in the explanation of FIG. 5, if the number of turns of the heating coil 4 is increased to share the load with a low impedance or high resonance frequency, a high impedance or high resonance frequency is obtained. With a load having a resonance frequency, it is possible to heat the metal body to be heated with a low inverter current. However, when outputting low power, since the inverter current is low, the charge / discharge current for the snubber capacitors 105, 106, 205, and 206 connected to the switching elements 101, 102, 201, and 202 for suppressing the transient voltage is large. Therefore, since the loss of the switching elements 101, 102, 201, 202 increases, the switching element rises in temperature and is damaged, and the thermal efficiency is extremely deteriorated.

  In FIG. 7, in order to solve the above-described problem, in the circuit configuration of FIG. 5, the switching element 201 is fixed in the off state and the switching element 202 is fixed in the on state to operate as a half bridge (SEPP) configuration. .

  Because of the half-bridge configuration, the same power supply voltage is applied as compared to the full-bridge configuration, and in the case of the same drive frequency, the former is supplied with about 1/4 of the latter power. At this time, since the state of the snubber capacitors 205 and 206 connected in parallel to the switching elements of the switching unit 200 is fixed, no charging / discharging current flows, and no loss of the switching elements 201 and 202 is caused thereby.

  Moreover, since it is possible to apply low power at a lower driving frequency than in the case of the full bridge configuration, charging of the snubber capacitors 105 and 106 connected in parallel to the switching elements 101 and 102 of the switching unit 100 is possible. The number of discharges is reduced, and the loss of the switching elements 101 and 102 can be reduced.

  In order to perform power control, a method of changing the inverter drive frequency by setting the output voltage of the power supply means 3 to a predetermined voltage as in the case of FIG. 5 and a power supply means with the inverter drive frequency substantially fixed. 3 can be used.

  It is effective to use this control in combination or switching as a method of lower loss and higher heating efficiency in the low power range included in the power control range that can be set in the inverter configuration of FIG.

  FIG. 8 is an example of power control by the above method. In FIG. 8, the horizontal axis represents the target power to be set, and the vertical axis represents the inverter drive frequency f and the output voltage V of the power supply means 3.

  In FIG. 8A, the full bridge configuration and the half bridge configuration are switched with the target power Wx in the low power range as a boundary. In the case of the region F that is greater than or equal to Wx, the full bridge configuration is used, and in the region H that is less than the region F, the half bridge configuration is used. In region H, the output voltage V of the power supply means 3 is fixed, and the power control is performed by changing only the inverter drive frequency f. In region F, the output voltage V of the power supply means 3 is fixed, and the inverter drive frequency f is changed to perform power control. Even if the same frequency is set, higher power can be input in the region F.

  FIG. 8B shows a method in which the full bridge configuration and the half bridge configuration are switched with the target power Wx in the low power range as a boundary, and the power control method in the case of the full bridge configuration with a higher target power Wy is switched. It is.

  In this way, the state of the load is discriminated, and an optimum circuit configuration is selected as a half-bridge inverter circuit for a low impedance or high resonance frequency load, and as a full bridge inverter circuit for a high impedance or low resonance frequency load. In addition, power control can be performed by a combination of the inverter drive frequency f and the output voltage V of the power supply means 3, respectively, and the loss of the switching elements 101, 102, 201, 202 can be reduced.

  In addition, since it is possible to switch to the configuration of the inverter circuit 50 that is optimal for the load and to easily control either the drive frequency of the inverter circuit 50 or the output voltage of the power supply means 3, it is low loss and is resistant to load fluctuations. An induction cooking device having the inverter circuit 50 can be provided.

It is a principal part circuit block diagram of one Example of this invention. It is a figure explaining operation | movement of a load condition detection means similarly. It is a circuit block diagram for low impedance or high resonance frequency load in the same manner. It is a figure explaining the electric power control method of the circuit block for a low impedance thru | or high resonance frequency load similarly. It is a circuit block diagram for high impedance or low resonance frequency load. It is a figure explaining the electric power control method of the circuit block for a high impedance thru | or low resonance frequency load similarly. FIG. 6 is a circuit block diagram for controlling a low power range in the same high impedance or low resonance frequency load. It is a figure explaining the electric power control method similarly including the low electric power range control in a high impedance thru | or low resonant frequency load.

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 Power supply means 4 Heating coil 5, 7 Resonance capacitor 10 Input current detection means 11 Voltage detection means 13 Inverter current detection means 14 Load state detection means 50 Inverter circuit 51 Series resonance circuit 300 Control means

Claims (5)

A high-frequency current is passed through a power supply means for outputting a direct current voltage and a series resonance circuit including a resonance capacitor and a heating coil via the power supply means, and an eddy current is generated in a metal body to be heated arranged near the heating coil From the input of the inverter circuit for heating, the input current detection means for detecting the input current of the power supply means, the inverter current detection means for detecting the current flowing through the series resonance circuit, and the input current detection means and the inverter current detection means A load state detection means for detecting a load state; a voltage detection means for detecting an input voltage of the power supply means; and a control means for controlling at least the output voltage of the power supply means and the inverter circuit, The control can be switched to a half-bridge configuration or a full-bridge configuration for the series resonant circuit, and the control The stage switches the inverter circuit to a half-bridge configuration or a full-bridge configuration according to the output of the load state detection means and the set power supplied to the metal body to be heated, An induction heating cooker characterized by controlling power supplied to a metal body to be heated by changing either one of them. 2. The induction heating cooker according to claim 1, wherein the load state detection unit determines an impedance of the series resonance circuit or a resonance frequency level in a plurality of stages. When the load state detection means determines that the impedance is low impedance or high resonance frequency, the control means switches the inverter circuit to a half-bridge configuration, substantially fixes the drive frequency of the inverter circuit, and sets the output voltage of the power supply means. The induction heating cooker according to claim 1 or 2, wherein the induction heating cooker is controlled to be variable. When the load state detection means determines that the impedance is high impedance or low resonance frequency, the control means switches the inverter circuit to a full bridge configuration and changes the drive frequency of the inverter circuit and the output voltage of the power supply means. The induction heating cooker according to claim 1 or 2, wherein the induction heating cooker is controlled. When the load state detecting means determines that the impedance is high impedance or low resonance frequency, and the power to be applied to the metal body to be heated is low power, the control means switches to the inverter circuit. The induction heating cooker according to claim 1 or 2, wherein the drive frequency and the output voltage of the power supply means are controlled to be variable.

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