JP2007012490A - Induction heating cooker - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an increase in loss of a switching element due to an influence of a snubber capacitor connected to the switching element, and to suppress a cost for cooling.
SOLUTION: Inverter means 16, snubber capacitors 18a-19b provided in some or all of switching elements 5a-6b constituting inverter means 16, and the load state of inverter means 16 are detected. Load state detection means 10 and control means 7 for controlling the inverter means 16 to switch to a half-bridge circuit configuration or a full-bridge circuit configuration according to the output of the load state detection means 10 are provided. In the state of the load to switch to the full bridge circuit configuration, switch to the half bridge circuit configuration in the low power range.
[Selection] Figure 1

Description

  The present invention relates to a power control method for heating a metal load (pan) of an induction heating cooker.

  The induction heating cooker generates eddy currents in a metal load (pan) placed in the vicinity of a heating coil through which high-frequency current flows, and the metal load (pan) itself self-heats due to its Joule heat. (Pot) can be heated, and in recent years, the replacement of these is progressing with respect to cooking utensils using gas stoves and electric heaters because of their excellent safety and temperature controllability.

  In such an induction heating cooker, a power control circuit for flowing a high-frequency current to the heating coil is called a so-called resonance inverter, and connects the inductance of the heating coil including a metal load (pan) and a resonance capacitor. A configuration in which the switching element of the power control circuit is on / off controlled at a drive frequency of about 20 to 40 kHz is common. 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.

  Initially, only metal loads (pans) of magnetic materials such as iron could only be heated, but in recent years, metal loads (pans) made of non-magnetic stainless steel can also be heated. Further, a nonmagnetic metal load (pan) made of aluminum that has been considered to be unheatable has been proposed.

  In an induction heating cooker using such a resonance type inverter, when heating a metal load (pan), an inductance (equivalent inductance L) determined by the metal load (pan) and a heating coil, and a resistance component contributing to the heating It has been found that (equivalent resistance R) affects the ease of heat generation.

  That is, when the metal load (pan) is a magnetic metal (iron, magnetic stainless steel, etc.), it is easy to apply power, and when it is a nonmagnetic metal (nonmagnetic stainless steel, aluminum, copper, etc.), it is difficult to apply power. This is because the latter has a small value of the equivalent resistance R, and the eddy current induced in the metal load (pan) does not easily become Joule heat.

  Therefore, the method of switching the number of turns of the heating coil depending on the material of the metal load (pan), that is, the nonmagnetic metal load is solved by increasing the number of turns of the heating coil and increasing the heating efficiency. There are some (see, for example, Patent Documents 1 and 2).

  In addition, when the number of turns of the heating coil is fixed (single heating coil) and the number of turns of the heating coil is increased so that power can be input in a non-magnetic metal load (pan), the magnetic metal For the problem that it is difficult to turn on the power with a load (pan), when a non-magnetic metal load (pan) is detected, the inverter circuit configuration is a half-bridge configuration, and a magnetic metal load (pan) is detected. In this case, there is a proposal that the magnetic metal load (pan) is heated by switching to the full-bridge configuration and applying a voltage twice to the heating coil as compared to the case of the half-bridge circuit method (for example, Patent Literature) 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 high-frequency current does not flow, so the metal load (pan) in that portion does not generate heat, and the metal When the heat distribution of the load (pan) becomes uneven and uneven heating occurs, or when a metal load (pan) with a different diameter is used, the power input level changes depending on the diameter of the metal load (pan) The problem of end up 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 the full bridge circuit configuration or the half bridge circuit configuration depending on whether the metal load (pan) is magnetic or nonmagnetic. Then, in the case of a metal load (pan) characteristically in the middle region, it is switched to an unsuitable inverter circuit configuration and energized, heating efficiency is deteriorated and the inverter circuit is damaged. is there.

  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 applying low power 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. As the temperature increases, the reliability of the switching element deteriorates, and the cost for cooling the switching element increases, resulting in a cost increase.

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

  SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and in claim 1, the inverter means, the snubber capacitor provided in a part or all of the switching elements constituting the inverter means, and the inverter Load state detection means for detecting the load state of the means, and control means for controlling the inverter means to switch to a half-bridge circuit configuration or a full-bridge circuit configuration based on the output of the load state detection means, the control means comprising: In the load state where the full bridge circuit configuration is switched in the high power range, the half bridge circuit configuration is switched in the low power range.

  Further, in claim 2, the snubber capacitor capacity connected to each switching element in a load state that switches to a full bridge circuit configuration in a high power region is the same as that in a load state that switches to a half bridge configuration in a high power region. It is controlled by the control means so as to be smaller than the capacity of the snubber capacitor connected to each switching element.

  The induction heating cooker of the present invention is configured as described above, so that it does not require switching of the number of turns of the heating coil, and uses a single heating coil to detect the state of the metal load (pan). Switching from the detection means so that the circuit configuration of the inverter means (half-bridge circuit configuration or full-bridge circuit configuration) becomes an optimal circuit configuration, making it difficult to input power to heat the metal load (pan). Because there is no heat and the metal load (pan) is heated with high efficiency, the load can be switched to the full-bridge circuit configuration in the high power range and switched to the half-bridge circuit configuration in the low power range, It further reduces the loss of the switching element in the low power range, suppresses the temperature rise of the switching element, improves reliability, and improves the switching element and heating coil It is possible to suppress the cost of the retirement.

  In addition, the snubber capacitor capacity in a load state having a full bridge circuit configuration in a high power range is connected in parallel to the series body of each switching element in a load state having a half bridge configuration in a high power range. By controlling the total capacity to be smaller than the total capacity in the case of the half-bridge configuration, the loss of the switching element can be further reduced, and the cost for cooling the switching element and the heating coil can be suppressed. .

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 is a main part circuit block diagram of an induction heating cooker showing an embodiment of the present invention. In FIG. 1, 1 is an AC power source. A rectifying means 2 converts the AC power source 1 into a DC voltage and outputs it.

  Reference numerals 5a, 5b, 6a and 6b denote switching elements, and a diode 14 is connected in antiparallel to each of the switching elements 5a to 6b.

  Reference numerals 18a, 18b, 19a and 19b are snubber capacitors, which are connected in parallel to the switching elements 5a to 6b, and prevent the switching elements 5a to 6b from being destroyed by a surge voltage or a transient voltage. In this embodiment, the snubber capacitors 18a to 19b are connected to all of the switching elements 5a to 6b. However, either the switching element 5a or the switching element 5b and either the switching element 6a or the switching element 6b are used. It is also effective to connect to one of them, whereby it can be prevented from being destroyed by a surge voltage.

  3 is a heating coil, and 4 is a resonance capacitor, which are connected in series to form a resonance circuit 15. This resonance circuit 15 is an intermediate connection point between the switching elements 5a and 5b and an intermediate connection point between the switching elements 6a and 6b. Connected between the dots.

  Reference numeral 16 denotes an inverter means, which includes a switching element 5a-6b, a diode 14 connected in antiparallel to each switching element 5a-6b, a snubber capacitor 18a-19b connected in parallel, and a resonance circuit 15. The DC voltage that is the output of the rectifying means 2 is converted, a high-frequency current is passed through the heating coil 3, an eddy current is generated in the metal load (pan) 17 disposed in the vicinity of the heating coil 3, and the metal load is generated by the Joule heat. (Pot) 17 itself is heated by self-heating. Further, the inverter means 16 can switch the current to the resonance circuit 15 to be either a half-bridge circuit configuration or a full-bridge circuit configuration by combining the operations of the switching elements 5a to 6b.

  7 is a control means, 8 is an input means operated by a user, 9 is an input voltage detection means for detecting the voltage of the AC power source 1 which is an input of the rectification means 2, and 12 is an input current for detecting an input current of the rectification means 2. The control means 7 detects the input power by inputting the outputs of the input voltage detection means 9 and the input current detection means 12, and the value of the input power and the metal load set by the user with the input means 8 ( The drive signal applied to the switching elements 5a to 6b of the inverter means 16 is controlled by the drive means 11 to be described later so as to coincide with the target heating power that is the electric power for heating the pot 17). Apply the set target heating power.

  Reference numeral 13 denotes inverter current detecting means for detecting a current flowing through the resonance circuit 15.

  Reference numeral 10 denotes a load state detection means, which receives the outputs of the input current detection means 12 and the inverter current detection means 13, and detects the state (equivalent inductance L and equivalent resistance R) of the resonance circuit 15 which is the load of the switching elements 5a to 6b. By inputting the output of the load state detection means 10 to the control means 7, the control means 7 controls the combination of the operations of the switching elements 5a to 6b to change the circuit configuration of the inverter means 16 to a half bridge circuit. Control to switch to either the configuration or the full bridge circuit configuration.

  Reference numeral 11 denotes drive means which is controlled based on the output signal of the control means 7 and outputs drive signals to the switching elements 5a to 6b for operation. That is, when the circuit configuration of the inverter means 16 is a half-bridge circuit configuration, it can be realized by exclusively driving the switching elements 5a and 5b and driving the switching element 6b to be in an ON state. Moreover, when it is set as a full bridge circuit structure, it can implement | achieve by driving exclusively the combination of switching element 5a and 6b and 5b and 6a.

  FIG. 2A is an equivalent circuit diagram showing the resonance circuit 15 of the heating coil 3 and the metal load (pan) 17 disposed in the vicinity of the heating coil 3, and the resistance R1 of the heating coil 3 itself is connected to the inverter power source 100. FIG. And a state in which the inductance L1 and the capacitance C of the resonant capacitor 4 are connected in series, and an equivalent resistance R2 and an equivalent inductance L2 of the metal load (pan) 17 disposed in the vicinity of the heating coil 3 are connected in series. Represents the state of being coupled to the heating coil 3 with the coupling degree M of the inductance.

  FIG. 2B is an equivalent circuit diagram obtained by modifying (simplifying) the equivalent circuit of FIG. 2A, and the entire equivalent resistance R, equivalent inductance L, and resonant capacitor 4 with respect to the inverter power source 100. Is represented by a circuit connected in series. The equivalent resistance R and the equivalent inductance L can be expressed by the following equations.

  FIG. 3 is a diagram showing measurement results of the equivalent resistance R and the equivalent inductance L viewed from the heating coil 3 when the metal load (pan) 17 is actually arranged in the vicinity of the heating coil 3. 17 was measured for four types: a magnetic stainless steel pan (I), a non-magnetic stainless steel pan (B), an aluminum pan (C), and a pan (d) in which magnetic stainless steel was bonded to aluminum. The measurement frequency at this time is 20 kHz to 100 kHz. As described above, the values of the equivalent resistance R and the equivalent inductance L are not constant depending on the type of the metal load (pan) 17, and actually, various types of metal loads (pans) 17, the heating coil 3, and the like. The values of the equivalent resistance R and the equivalent inductance L are dispersed due to variations in the position where the metal load (pan) 17 is placed.

  By the way, the electric power consumed by the load of the inverter means 16 by the operation of the inverter means 16 can be expressed by the following equation by the equivalent resistance R and the current I flowing through the equivalent resistance R shown in FIG.

Accordingly, since the equivalent resistance R contributes to the heat generation of the metal load (pan) 17, the same current flows through the heating coil 3 as the metal load (pan) 17 has a smaller value of the equivalent resistance R in FIG. 3. It becomes difficult to generate heat. However, as can be seen from FIG. 3, since the value of the equivalent resistance R increases when the frequency of the high-frequency current flowing through the heating coil 3 is set to a high frequency, even a metal load (pot) 17 that does not easily generate heat at a low frequency is high. It can be heatable at the frequency.

  Further, the ease of high-frequency current flowing through the heating coil 3 is also affected by the equivalent resistance R and the equivalent inductance L. That is, if the value of the equivalent resistance R is large, the high frequency current does not flow unless the voltage of the inverter power source 100 of the inverter means 16 is high.

  Further, if the equivalent resistance R is smaller than the value of the equivalent inductance L, the selectivity Q of the resonance circuit 15 in which the equivalent inductance L is connected in series increases, so that almost no high-frequency current flows unless it is near the resonance frequency of the resonance circuit 15. No state.

  When both the equivalent resistance R and the equivalent inductance L are small, a high-frequency current is likely to flow but it is difficult to generate heat.

  Therefore, in order to heat the metal load (pan) 17, the inverter power source 100 of the appropriate inverter means 16 is combined with the combination of the equivalent resistance R and the equivalent inductance L that change depending on the type and arrangement of the metal load (pan) 17. And the drive frequency of the inverter means 16 in the vicinity of the resonance frequency of the resonance circuit 15 are required.

  Therefore, in this embodiment, the load state detection means 10 for detecting the load state of the inverter means 16 with respect to the metal load (pan) 17 estimates the equivalent impedance of the load of the inverter means 16 so that the metal load (pan) 17 In order to be heated appropriately, when the impedance is low, the circuit configuration of the inverter means 16 is set to a half-bridge circuit configuration set to drive in a high frequency range, and when the impedance is high, set to drive in a low frequency range. The drive means 11 is controlled by the control means 7 so as to obtain the full bridge circuit configuration, and the voltage of the power source 100 of the inverter means 16 and the drive frequency range of the inverter means 16 are set.

  In other words, by changing the circuit configuration of the inverter means 16 having the resonance circuit 15 as a load from the half-bridge circuit configuration to the full-bridge circuit configuration, it is possible to apply a substantially double voltage to the resonance circuit 15. About four times as much power can be applied to the metal load (pan) 17. That is, for a metal load (pan) 17 such as a non-magnetic metal having a large equivalent resistance R, a high voltage can be applied to generate heat even when the equivalent resistance R is large by adopting a full bridge circuit configuration. I did it.

  FIG. 4 is a diagram for explaining the operation of the load state detection means 10, FIG. 4 (a) is a diagram for explaining the operation of the load state detection means 10 when the inverter means 16 has a full bridge circuit configuration, and FIG. 4 (b). These are figures explaining operation | movement of the load state detection means 10 in case the inverter means 16 is a half bridge circuit structure. The load state detection means 10 uses the output of the input current detection means 12 and the output of the inverter current detection means 13 as parameters, and tries to grasp the impedance state of the load by each combination. The load state is grasped by classifying into regions A ′, B, B ′, C, C ′, D, and D ′. That is, the relationship between the output of the input current detection means 12 and the output of the inverter current detection means 13 is mapped and prepared in the form of a table in the memory. For example, the output of each of the input current detection means 12 and the inverter current detection means 13 is prepared. Are converted into address information as address information, and the areas A, A ′, B, B ′, C, C ′, D, and D ′ are uniquely determined by the respective input values. What should I do?

  For example, in FIG. 4A, a region A is a case where the input current hardly flows or the inverter current flows extremely. This is when the equivalent resistance R of the load of the inverter means 16 is extremely small or too large. This corresponds to the case where the equivalent inductance L is extremely large or small, specifically, the case where the shape of the metal load (pan) 17 disposed in the vicinity of the heating coil 3 is extremely small, or the inverter means. This corresponds to a case where 16 is out of order.

  Region B is a case where a sufficient input current flows even if the inverter current is not so large, and corresponds to a combination in which the equivalent resistance R is large and the equivalent inductance L is appropriate.

  Region D corresponds to a case where the input current is relatively small but the inverter current is large, and corresponds to a case where the equivalent resistance R is small and the equivalent inductance L is also relatively small.

  The region C is an intermediate region between the region B and the region D, and the region C and the region C ′ are set as hysteresis regions. That is, when the user moves the metal load (pan) 17 during heating and the positional relationship with the heating coil 3 changes, the user replaces the metal load (pan) 17 and the metal load (pan) 17 changes. When the type changes, it may be necessary to change the circuit configuration of the inverter unit 16, but in the case of a load detected at the boundary between the region B and the region D, the circuit configuration of the inverter unit 16 is frequently switched. If this occurs, an abnormal current or voltage is generated at the timing of switching, or it takes time for switching, and power is not applied during that time, resulting in a decrease in actual power. Therefore, it is necessary to provide an allowable range for deviation from a certain area and reduce such switching frequency. For this reason, an area C is provided, and if it is detected that the area C is present, it is frequently necessary. Control is performed by the control means 7 so that the inverter circuit configuration is not switched.

  Note that the threshold values for determining the regions A, B, C, D, A ′, B ′, C ′, and D ′ in FIGS. 4A and 4B are suitable for appropriate heating in each circuit configuration. It is sufficient that the circuit configuration corresponding to the state of the metal load (pot) 17 to be heated can be appropriately determined and switched.

  Next, an equivalent impedance of the load of the inverter unit 16 is estimated by the load detection unit 10, and the circuit configuration of the inverter unit 16 is a half bridge circuit configuration or a full bridge circuit so that the metal load (pan) 17 is appropriately heated. Details of the control for switching to the configuration will be described.

  First, the number of turns of the heating coil 3 is increased so as to be suitable for heating an aluminum nonmagnetic metal load (pan) 17 having a small equivalent resistance R and a relatively small equivalent inductance L, and FIG. By increasing the degree of coupling M shown in a), the equivalent resistance R shown in Equation 1 and the equivalent inductance L are increased, and the frequency of the high-frequency current flowing in the heating coil 3 is set to a high frequency. The inverter means 16 is operated. Then, the threshold value is set so that the detection region of the load state detection means 10 shown in FIG. 4B at this time is in an energized state with respect to the load of the inverter means 16 corresponding to the regions D ′ to C ′.

  And if the magnetic load (pan) 17 of magnetism (iron, magnetic stainless steel, etc.) is heated under the same conditions, the equivalent resistance R becomes too large and the energized state becomes the regions B ′ and A ′ of FIG. 4B. When the voltage of the half bridge circuit configuration and the high driving frequency are kept as they are, sufficient power is not applied to the magnetic metal load (pan) 17 so that heating power is not obtained and heating is not performed. Therefore, in such a case, if the inverter circuit configuration is switched to the full-bridge circuit configuration and energized, it is possible to apply a voltage substantially doubled to the resonance circuit 15 and obtain about four times the power. it can. That is, by setting the energized state corresponding to the region B in FIG. 4A, electric power for heating the metal load (pan) 17 of magnetism (iron, magnetic stainless steel, etc.) can be obtained and heated. .

  Control is performed so as to switch to a half-bridge circuit configuration for a load determined to be in region D when energized with a full-bridge circuit configuration. Similarly, control is performed so that the load determined to be in the region B when energized with the half-bridge circuit configuration is switched to the full-bridge circuit configuration.

  When the equivalent resistance R of the non-magnetic metal load (pan) 17 is low, the inverter means 16 is switched to the half-bridge circuit configuration, the drive frequency of the inverter means 16 is set to a high frequency, and the load of the inverter means 16 is set. Is controlled so as to heat the metal load (pot) 17 efficiently.

  In this way, if the load detection means 10 as shown in FIG. 4 is configured, the equivalent inductance and equivalent resistance of the load can be estimated. Therefore, even if the metal load (pan) 17 is a load made of a single material, Even a load combining a plurality of materials can be determined appropriately. The metal load (pan) 17 is not distinguished depending on whether the material is magnetic or non-magnetic. Instead, the impedance of the load equivalent circuit itself is estimated and judged. Needless to say, the circuit configuration of the inverter means 16 can always be selected.

  In order to change the drive frequency of the inverter means 16, the resonance capacitor 4 of the resonance circuit 15 is changed. That is, when the drive frequency is set in the vicinity of 50 KHz in the case of the half bridge circuit configuration, when the value of the equivalent inductance L including the metal load (pan) 17 is, for example, 125.62 uH, the capacity of the resonant capacitor 4 is 0.08 uF. Set to. Further, when the drive frequency is set near 20 KHz in the case of the full bridge circuit configuration, when the value of the equivalent inductance L including the metal load (pan) 17 is, for example, 247.85 uH, the capacitance of the resonant capacitor 4 is 0.35 uF. Set to.

  Thus, the capacity of the resonant capacitor 4 is switched between the case where the inverter unit 16 has a half-bridge circuit configuration and the case where the inverter unit 16 has a full-bridge circuit configuration, so that the drive frequency of the inverter unit 16 is close to the resonant frequency of the resonant circuit 15. Thus, in the case of a metal load (pan) 17 made of a material having low skin resistance and a metal load (pan) 17 containing a non-magnetic material, the impedance of the load of the inverter means 16 can be increased, and the metal load (pan) ) It was not difficult to turn on the electric power for heating 17, and the inverter means 16 was not overloaded and an abnormal oscillation state was not generated, so that the reliability could be improved.

  FIG. 5 shows an example of a method for switching the capacitance of the resonance capacitor 4 described above. In FIG. 5A, the resonance capacitor 4 is configured in parallel connection and switched using a relay or the like. In FIG. 5B, the resonance capacitor 4 is configured in series and is switched using a relay or the like.

  FIG. 6 shows the relationship between the drive frequency and the inverter power (power for heating the metal load (pan) 17) when it is determined that the load is suitable for heating with the full bridge circuit configuration. Characteristic A is a full bridge circuit configuration, and characteristic B is a characteristic when switching to a half bridge circuit configuration.

  In the case of the same load, the power obtained by the full bridge circuit configuration is four times the power obtained by the half bridge circuit configuration in principle. Conversely, in the half-bridge circuit configuration, the power is 1/4 times that of the full-bridge circuit configuration.

Therefore, as shown in FIG. 6, the maximum and minimum drive frequencies of the set power (inverter power) defined in the full bridge circuit configuration are f _FL and f _FH , and the drive frequency f _{HL in the} half bridge circuit configuration The power obtained at ˜f _HH is the same as the power in the low power range obtained at the drive frequencies f _FM ˜f _FH of the full bridge circuit configuration.

That is, the inverter power when the drive frequency is f _FM of the full bridge circuit configuration will be the same as the inverter power when the driving frequency f _HL of the half-bridge circuit configuration, the driving frequency in a half-bridge circuit configuration to increase from f _HL If so, it can be realized at a driving frequency lower than the driving frequency for setting the low power range in the full bridge circuit configuration.

In the present embodiment, the switching power value for switching from the full-bridge circuit configuration to the half-bridge circuit configuration is 20% of the maximum set power. At this time, the drive frequencies f _FM and f _HH are close to each other. Since the switching point between the high power range and the low power range corresponds to the power input capacity of each bridge circuit configuration, it corresponds to 1/4 of the rated power, and actually between 1/3 and 1/8 of the rated power. An appropriate value may be selected. Further, it is necessary to provide hysteresis for the switching operation so that frequent switching operation does not occur in the vicinity of the switching point.

  Thereby, since the drive frequency of the inverter means 16 in the low power region can be shifted to a low frequency region, the number of switching times of the switching elements 5a and 5b due to charging / discharging of the snubber capacitors 18a and 18b is reduced, so that the loss is also reduced. Thus, thermal stress on the switching elements 5a and 5b can be reduced and reliability can be increased (in this case, since the operation is based on a half-bridge circuit configuration, the switching element 6a is turned off and the switching element 6b is turned on). State.)

  FIG. 7 is a diagram illustrating a circuit example in the case of switching the capacitances of the snubber capacitors 18a to 19b. In the figure, it is constituted by snubber capacitors 18c, 18d connected in series to the switching devices 5a, 5b and the snubber capacitors 18a, 18b that are always connected and the switch means S1, S2 whose contact state is switched by the control of the control means 7. .

  The load state in which the full bridge circuit configuration is suitable in the high power range is that the load impedance of the inverter means 16 is large and the inverter current can efficiently transmit power to the metal load (pan) 17, but the snubber capacitor 18 a Electric charges are likely to remain in .about.19b, and the charge / discharge current of the switching elements 5a to 6b is increased to increase the loss.

  This phenomenon increases relative to the operation in a load state in which a single heating coil 3 is used and a half-bridge circuit configuration is suitable in a high power range.

  Therefore, in a load state in which a full bridge circuit configuration is suitable in a high power region, the charge / discharge current applied to the switching elements 5a to 6b is reduced by reducing the capacity of the snubber capacitors 18a to 19b as a whole and reducing the residual charge itself. It is effective to suppress the loss and reduce the loss.

  Therefore, in the case of a half bridge circuit configuration, the switch means S1 and S2 are connected and the snubber capacitors 18c and 18d are added to increase the capacity. In the case of a full bridge circuit configuration, the switch means S1 and S2 Both or one of them is disconnected to reduce the capacity.

  It goes without saying that the effect is increased by setting the capacitance of the snubber capacitor connected in parallel to the series body of the switching elements 5a to 6b at this time as compared with the case of the half-bridge circuit configuration.

  As a result, in the case of a load state having a full bridge circuit configuration in a high power region, the residual charge amount of the snubber capacitors 18a to 19b is reduced, and the discharge current is reduced, so that the loss of the switching element can be reduced. As a result, the thermal stress on the switching element is reduced and the reliability can be further increased.

  Furthermore, even in a load state that takes a full-bridge circuit configuration in a high-power range, a snubber can be used in combination with a method that shifts the operating frequency range to the low-frequency side by using a half-bridge circuit configuration in the low-power range. In addition to reducing the number of charge / discharge cycles with respect to the residual charge of the capacitors 18a to 19b and the snubber capacitors 19a and 19b becoming inoperative, the residual charge itself is reduced and the effect is increased, and the loss of the switching elements 5a to 6b is reduced. It will be greatly reduced.

  Next, the operation according to the above configuration will be described.

  First, when a metal load (pan) 17 is placed in the vicinity of the heating coil 3 of the induction heating cooker and heating is started, control is performed so that the circuit configuration of the inverter means 16 becomes a preset half-bridge circuit configuration. The drive means 11 is controlled by means 7, and the capacity of the resonant capacitor 4 is switched to 0.08 uF, and the drive means is controlled so as to drive the inverter means 16 near 50 kHz, so that the heating coil 3 has a high frequency current. Apply.

  Next, the control means 7 determines the area of the areas A ′, B ′, C ′, and D ′ from the input from the load state detection means 10 in the graph of FIG. The equivalent inductance L and equivalent resistance R are estimated.

  If it is determined that the control means 7 is in the D ′ region, for example, it is determined that the metal load (pan) 17 can be heated efficiently, and is heated as it is in a half-bridge circuit configuration.

  If it is determined that it is in the region B ′, it is determined that the metal load (pan) 17 cannot be heated efficiently, and the drive means 11 is immediately controlled to switch to the full bridge circuit configuration. The capacity is switched to 0.35 uF, and the drive means is controlled to drive the inverter means 16 at around 20 kHz so that a high-frequency current flows through the heating coil 3.

  If it is determined that it is in the region A ′, it is determined that the metal load (pan) 17 is a small load that is not suitable for heating, or that the inverter means 16 is out of order, and the operation of the drive means 11 is immediately stopped. Stop heating.

  Similarly, when the circuit configuration of the inverter means 16 is energized in a full bridge circuit configuration, any of the areas A, B, C, and D in the graph of FIG. 4A from the input of the load state detection means 10 If it is determined that it is in the region B, it is determined that the metal load (pan) 17 can be efficiently heated, and is heated as it is with a full bridge circuit configuration. If it is determined that the load is in the region D, it is determined that the metal load (pan) 17 cannot be heated efficiently, and the drive means 11 is immediately controlled to switch to the half-bridge circuit configuration. The capacity is switched to 0.08 uF, and the drive means is controlled to drive the inverter means 16 in the vicinity of 50 kHz so that a high-frequency current flows through the heating coil 3. If it is determined that the load is in the area A, it is determined that the metal load (pan) 17 is a small load that is not suitable for heating, or that the inverter means 16 has failed, etc. To stop.

  And when the control means 7 operates the inverter means 16 and is supplying the high frequency current to the heating coil 3, it always monitors the detection output from the load state detection means 10, for example, a user is the metal load (pan) 17 When the positional relationship with the heating coil 3 is changed by moving the plate or when another metal load (pan) 17 is placed, the drive means 11 is immediately detected by the detection output from the load state detection means 10. To control the circuit configuration of the inverter means 16 or stop the operation of the inverter means 16.

  In this way, a single heating coil 3 that does not require switching of the number of turns of the heating coil 3 is used, which is caused by an impedance change due to the material and shape of the metal load (pan) 17 or the positional relationship with respect to the heating coil 3. Electric power that heats the metal load (pan) 17 by switching the circuit configuration (half-bridge circuit configuration or full-bridge circuit configuration) of the inverter means 16 from the state of the input current and the inverter current so that the circuit configuration is optimal. The metal load (pan) 17 is heated with high efficiency without reducing the circuit loss of the inverter means 16, and the switching elements 5a, 5b, 6a, 6b and the heating coil 3 The cost for cooling can be suppressed.

  Next, an operation for preventing an increase in loss of the switching element due to the influence of the snubber capacitors 18a to 19b will be described.

In a load that operates with the circuit configuration of the inverter means switched to the full bridge circuit configuration, when the set target heating power is in the high power range, the control means 7 switches to the full bridge circuit configuration, and as shown in FIG. Is controlled in the range of f _{FL to} f _FM .

When the set target thermal power is in the low power range, the circuit is switched to the half bridge circuit configuration, and the drive frequency is controlled in the range of f _{HL to} f _HH . At the same time, the switch means S1 and S2 are both disconnected to reduce the capacity. As a result, the discharge current flowing through the switching element is reduced, and the loss of the switching element is reduced. As a result, the thermal stress on the switching element is reduced and the reliability can be increased.

  In this way, the circuit configuration of the inverter unit 16 is changed from the load state detection unit 10 that detects the state of the metal load (pan) 17 using the single heating coil 3 that does not require switching of the number of turns of the heating coil 3. (Half-bridge circuit configuration or full-bridge circuit configuration) is switched to an optimum circuit configuration, and it is not difficult to turn on the power to heat the metal load (pan) 17, and the metal load is highly efficient. Since the (pan) 17 is heated and the load is switched to the full bridge circuit configuration in the high power region and energized, it can be switched to the half bridge circuit configuration in the low power region. The loss of 5a to 6b is further reduced, the temperature rise of the switching elements 5a to 6b is suppressed, the reliability is improved, and the switching elements 5a to 6b are added. It is possible to suppress the cost of cooling the coil 3.

  Further, in the case of a load that switches to a full bridge circuit configuration in a high power region, the capacity of the snubber capacitors 18a to 19b is made smaller than the capacity of the snubber capacitors 18a and 18b when switched to the half bridge circuit configuration in a low power region. By switching to, the loss of the switching elements 5a to 6b can be further reduced, and the cost for cooling the switching elements 5a to 6b and the heating coil 3 can be suppressed.

It is a principal part circuit block diagram of the induction heating cooking appliance which shows one Example of this invention. (A) is an equivalent circuit diagram showing a resonance circuit of a heating coil and a metal load (pan) arranged in the vicinity of the heating coil, and (b) is an equivalent circuit diagram obtained by modifying (simplifying) the equivalent circuit of (a). is there. It is a figure which shows the measurement result of the equivalent resistance R and the equivalent inductance L which were seen from the heating coil when the metal load (pan) was actually arranged in the vicinity of the heating coil. (A) is a figure explaining operation | movement of the load state detection means when an inverter means is a full bridge circuit structure, (b) is a figure explaining operation | movement of the load state detection means when an inverter means is a half bridge circuit structure. is there. (A) is a circuit which switches the value of a resonance capacitor by parallel connection, (b) is a circuit diagram which switches the value of a resonance capacitor by series connection. It is a figure explaining the relationship between the drive frequency of an inverter means, and the inverter electric power applied to a metal load (pan). It is a circuit diagram which shows the circuit example which switches the capacity | capacitance of a snubber capacitor.

Explanation of symbols

5a, 5b, 6a, 6b Switching element 7 Control means 10 Load state detection means 16 Inverter means 18a, 18b, 19a, 19b Snubber capacitors.

Claims (2)

An inverter means (16), a snubber capacitor (18a-19b) provided in a part or all of the switching elements (5a-6b) constituting the inverter means (16), and the inverter means (16) Load state detection means (10) for detecting the load state, and control means for controlling the inverter means (16) to switch to the half-bridge circuit configuration or the full-bridge circuit configuration based on the output of the load state detection means (10). (7) The induction heating cooker characterized in that the control means (7) switches to a half-bridge circuit configuration in a low power region in a state of a load that switches to a full-bridge circuit configuration in a high power region. The snubber capacitor capacity connected to each switching element (5a, 5b) when the load is switched to the full bridge circuit configuration in the high power range is the switching when the load is switched to the half bridge configuration in the high power range. The induction heating cooker according to claim 1, wherein the control means (7) controls the snubber capacitor capacity to be smaller than that of the snubber capacitor connected to the element (5a, 5b).

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