JP2009099324A - Induction heating cooker - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an induction heating cooker capable of reducing switching loss and capable of obtaining a desired input voltage without varying an output of a booster circuit while maintaining an output of the booster circuit and simplifying a circuit configuration. <P>SOLUTION: The induction heating cooker includes a heating coil 71 for heating an object to be heated, an inverter 100 having a switching element, for supplying an alternating current to the heating coil 71, the booster circuit 20 for boosting an input voltage to a constant voltage and supplying to the inverter 100, a control part 81 for controlling drive of the switching element, and a load detection part 84 for detecting a type of the object to be heated and outputting a detection result to the control part 81. The control part 81 switches a drive control system of the switching element depending on the detection result of the load detection part 84. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an induction heating cooker.

  Conventionally, regarding an induction heating apparatus, “the voltage of the smoothing means when heating is stopped is quickly reduced, and the time until restart is shortened. As a technique for the purpose of "after the control means 30 has lowered the output of the boosting means 35 so as to make the voltage of the smoothing means 22 immediately after stopping the inverter 21 equal to or lower than a predetermined voltage before stopping the heating," Induction heating device that stops heating. Is proposed (Patent Document 1).

  “To reduce the size and cost of the filter, and improve the operational reliability of the product and surrounding equipment. As a technology aiming at “resonance comprising a rectifier circuit 3 for rectifying the AC power source 1 and converting it to a DC power source, and a DC coil that converts the DC power source into a high-frequency current by a switching element 8 and comprising a heating coil 5 and a resonant capacitor 4. An inverter 9 for heating the load 7 disposed in the vicinity of the circuit 6; power setting means 12 for setting the on / off duty of the switching element 8 to vary the heating power; and on / off of the switching element 8 An induction heating cooker including an oscillating means 14 for determining a frequency includes a frequency changing means 13 for changing and controlling the oscillation frequency of the oscillating means 14, and the frequency changing means 13 is based on the oscillation frequency of the oscillating means 14. The change control is performed almost periodically in the range of the frequency (f0 ± Δf) that is slightly changed up and down around the frequency (f0). Is proposed (Patent Document 2).

JP 2004-171934 A (summary) Japanese Unexamined Patent Publication No. 2004-55312 (Abstract)

In the conventional induction heating apparatus such as the above-mentioned Patent Document 1, when the input power is controlled, the commercial power supply voltage may be boosted by a boosting circuit (the boosting means 35 in the above-mentioned Patent Document 1) and supplied to the inverter. .
Therefore, it is necessary to control the output voltage of the booster circuit in accordance with the required input power, which complicates the circuit configuration and control procedure related to the output control of the booster circuit.

  Moreover, in the technique of the said patent document 2, since electric power control is performed by duty control of a switching element, there exists a subject which a switching loss increases at the time of low input electric power at the time of low frequency operation like the time of iron pan heating.

  The present invention has been made in order to solve the above-described problems. The output voltage of the booster circuit is reduced by reducing the switching loss while simplifying the circuit configuration by keeping the output voltage of the booster circuit constant. It is an object of the present invention to obtain an induction heating cooker that can obtain a desired input power without being varied.

  An induction heating cooker according to the present invention includes a heating coil for heating an object to be heated, an inverter having a switching element for supplying an alternating current to the heating coil, and boosting an input voltage to a constant voltage to the inverter. A booster circuit to supply; a control unit that drives and controls the switching element; and a load detection unit that detects a type of an object to be heated and outputs a detection result to the control unit, and the control unit includes the load The drive control method of the switching element is switched according to the detection result of the detection unit.

According to the induction heating cooker according to the present invention, the output voltage of the booster circuit is configured to be constant to simplify the circuit configuration, and the drive control method of the switching element is switched, so that the type of the object to be heated is changed. Necessary input power.
In addition, by switching the drive control system of the switching element according to the detection result of the load detection unit, the switching loss can be suppressed by using a control system with a small switching loss at the time of low frequency operation such as when heating the iron pan. Can do.

Embodiment 1 FIG.
FIG. 1 is a circuit diagram of an induction heating cooker according to Embodiment 1 of the present invention.
The induction heating cooker of FIG. 1 includes a booster circuit 20, a control circuit 81, an operation unit 82, a display unit 83, a load detection unit 84, and a high frequency power supply module 100.
The AC power supply 11 is a power supply supplied from the outside of the induction heating cooker, such as a commercial AC power supply. Here, for convenience of description, it is also shown in the circuit diagram of FIG.

The booster circuit 20 is supplied with an AC voltage from the AC power supply 11, boosts the voltage to a constant voltage, and supplies the voltage to the high-frequency power supply module 100. Although not shown in FIG. 1, a rectifier circuit that rectifies AC power supplied from the AC power supply 11 into DC is provided.
The rectifier circuit may be configured separately from the booster circuit 20, but here it has been described integrally from the viewpoint of simplicity of explanation.

The high-frequency power supply module 100 has arms 30 and 40 composed of two switching elements connected in series.
The arm 30 includes switching elements 31 and 32, and the arm 40 includes switching elements 41 and 42, respectively. The arms 30 and 40 constitute a full bridge inverter circuit.
The full bridge circuit supplies an alternating current to a heating coil 71 described later.

A heating coil 71 and a resonance capacitor 61 are connected between the arms 30 and 40. The resonant capacitor 61 may be configured with variable capacitance.
The heating coil 71 and the resonance capacitor 61 constitute a resonance circuit.

The control circuit 81 performs drive control of the switching elements 31, 32, 41, 42, receives detection results of the load detection unit 84, and transmits / receives signals to / from the operation unit 82 and the display unit 83.
The control circuit 81 can be configured by an arithmetic device such as a CPU or a microcomputer, software for defining the operation thereof, a switching element drive circuit, and the like.
In FIG. 1, the connection between the control circuit 81 and each device is omitted.

The operation unit 82 includes an operation panel that transmits a user operation to the control circuit 81.
The display unit 83 displays the operating state of the induction heating device based on an instruction from the control circuit 81.
The load detection unit 84 detects the size and type (magnetic material or nonmagnetic material, etc.) of the heated object using a known method, and outputs the result to the control circuit 81. The determination of the size of the object to be heated may be performed by the load detection unit 84 itself, or only the detection result such as current may be output to the control circuit 81 and the control circuit 81 may determine.

  Note that a snubber capacitor may be provided in parallel with each of the switching elements 32 and 42 so as to delay the output voltage fluctuation when each switching element is turned off, thereby reducing the turn-off loss of each switching element.

FIG. 2 is a circuit configuration example of the booster circuit 20.
The booster circuit 20 includes a coil 21, a switching element 22, a diode 23, and a capacitor 24.
The coil 21 is supplied with a DC voltage output from the rectifier circuit.
The switching element 22 is driven ON / OFF based on an instruction from the control circuit 81.
The diode 23 prevents the electric charge accumulated in the capacitor 24 from being discharged through the switching element 22.
The capacitor 24 receives the voltage supplied to the booster circuit 20 and accumulates electric charges.

Next, the operation of the booster circuit 20 of FIG. 2 will be briefly described.
When the switching element 22 is turned on, a current flows in the order of the coil 21-> the switching element 22, and electromagnetic energy is accumulated in the coil 21.
When the switching element 22 is turned OFF, the electromagnetic energy accumulated in the coil 21 is added to the DC voltage and flows to the capacitor 24 and the output terminal. The voltage output at this time is boosted from the DC voltage applied to the booster circuit 20.
By controlling the ON / OFF interval of the switching element 22, the output voltage of the booster circuit 20 can be varied.

In general, a non-magnetic material to be heated, such as aluminum or copper, having a low specific resistance has a smaller resistance value and less likely to generate Joule heat compared to a magnetic material to be heated such as iron. Need to increase. In order to increase the current of the heating coil, the capacitance of the resonant capacitor 61 is reduced by known means such as a capacitor switching circuit using a relay to reduce the impedance of the load circuit, and the output voltage of the booster circuit 20 is increased. It is necessary to increase the input voltage of the inverter.
On the other hand, when an object to be heated of a magnetic material such as an iron pan is induction-heated, since the resistance value of the object to be heated is large, the current of the heating coil can be reduced, so that the output voltage of the booster circuit 20 is reduced. Thus, the input voltage of the inverter can be reduced.
Further, the cooking heat setting means provided in the operation unit 82 increases the output voltage of the booster circuit 20 when a large heating power is set, and decreases the output voltage of the booster circuit 20 when a low heating power is set. Thus, the input power of the inverter can be increased or decreased.

However, when the output voltage of the booster circuit 20 is controlled according to the type of the object to be heated, the output control of the booster circuit 20 must be performed in addition to the drive control of each switching element of the high frequency power supply module 100. Since the number of objects to be controlled increases, the configuration and control procedure of the control circuit 81 are complicated.
Therefore, in the present invention, the output voltage of the booster circuit 20 is made constant, and control is performed so as to obtain a necessary heating output only by driving control of each switching element of the high frequency power supply module 100.

However, since the switching loss characteristic varies depending on the frequency region, the drive frequency of the switching element is varied according to the type of the object to be heated, and a drive control method suitable for the switching loss characteristic is used.
There are two types of drive control methods here: phase control of the switching element and duty control. Hereinafter, the outline of these drive control systems will be described with reference to FIGS. 3 to 4, and then the application in the present invention will be described.

FIG. 3 shows a current change in duty control and an ON / OFF time chart of the switching element. (1) to (4) in the time chart correspond to one cycle of the inverter circuit. Hereinafter, each section in FIG. 3 will be described.
3 shows a circuit configuration in which a snubber capacitor 91 connected in parallel to the switching element 32 and a snubber capacitor 92 connected in parallel to the switching element 42 are provided. Further, description of the control circuit 81 and the like is omitted.

(1) The control circuit 81 turns on the switching elements 31 and 42. In this section, current is supplied to the heating coil 71 via the switching element 31.
(2) The control circuit 81 turns off the switching element 31 and turns on the switching element 32. In this section, the switching elements 32 and 42 form a closed circuit, and a current flows between them.

(3) The control circuit 81 turns off the switching element 42 and turns on the switching element 41. In this section, current is supplied to the heating coil 71 via the switching element 41.
(4) The control circuit 81 turns off the switching element 41 and turns on the switching element 42. In this section, the switching elements 32 and 42 form a closed circuit, and a current flows between them.

As described above, the current direction is reversed in the sections (1) to (2) and the sections (3) to (4), and the alternating current is supplied to the heating coil 71.
By varying the on-time ratio of the upper switching elements 31 and 41 and the lower switching elements 32 and 42, the energization time of the heating coil 71 changes, thereby controlling the AC power supplied to the heating coil 71. can do.
Such a method of controlling power by controlling the on-time ratio (on-duty ratio) of the switching element is called duty control.

  FIG. 4 shows a current change in phase control and an ON / OFF time chart of the switching element. (1) to (4) in the time chart correspond to one cycle of the inverter circuit. Hereinafter, each section in FIG. 4 will be described. The circuit configuration is the same as that shown in FIG.

(1) The control circuit 81 turns on the switching elements 31 and 42. In this section, current is supplied to the heating coil 71 via the switching element 31.
(2) The control circuit 81 turns off the switching element 42 and turns on the switching element 41. In this section, the switching elements 31 and 41 form a closed circuit, and a current flows between them.

(3) The control circuit 81 turns off the switching element 31 and turns on the switching element 32. In this section, current is supplied to the heating coil 71 via the switching element 41.
(4) The control circuit 81 turns off the switching element 41 and turns on the switching element 42. In this section, the switching elements 32 and 42 form a closed circuit, and a current flows between them.

As described above, the current direction is reversed in the sections (1) to (2) and the sections (3) to (4), and the alternating current is supplied to the heating coil 71.
If the phase difference between the switching elements 31 and 41 is opened, the time of the sections (1) and (3) in FIG. 4 is widened, the energization time of the heating coil 71 is increased, the input power is increased, and the phase difference is reduced ( 1) The time of (3) is shortened and the electric power supplied to the heating coil 71 is reduced.
Such a method of controlling electric power by controlling the phase of the switching element is called phase control. In the phase control, the switching element is controlled with the on-time ratio of the switching element fixed at 50%.

The outline of duty control and phase control has been described above with reference to FIGS.
Next, the proper use of these control methods will be described from the viewpoint of the type of the object to be heated.

When the object to be heated is aluminum or copper, which is a low resistance metal, the low resistance metal can be heated by increasing the drive frequency of the inverter arm (30, 40) and increasing the resistance by the skin effect.
When the object to be heated is a high resistance metal such as iron, the loss is reduced by driving the inverter arm (30, 40) at a frequency lower than the driving frequency for heating the low resistance metal. It becomes possible.

Since the characteristics of the switching loss vary depending on the frequency region, when the driving frequency of the switching element is varied according to the type of the object to be heated as described above, the switching loss varies depending on the frequency region.
Therefore, consider using a drive control method that can effectively reduce the switching loss in each frequency region.

  FIG. 5 is an example showing the relationship between the power control method and the switching element loss when the switching element is driven at a driving frequency of 23 kHz. The drive frequency of 23 kHz corresponds to the drive frequency when heating a heated object made of a magnetic material such as an iron pan.

In FIG. 5, when the duty control and the phase control are compared, the phase control can be controlled with the on-duty ratio of the upper switching elements (31, 41) and the lower switching elements (32, 42) fixed to 50%. However, since the inrush current to the snubber capacitors 91 and 92 at the low input power is small, the loss at the low input power is small as compared with the duty control.
When heating an iron pan or the like, the input power may be relatively small, so it is preferable to use phase control with a low input power.

  FIG. 6 shows an example of the relationship between the power control method and the switching element when the switching element is driven at a driving frequency of 70 kHz. The driving frequency of 70 kHz corresponds to the driving frequency when heating an object to be heated made of a low-resistance nonmagnetic material such as an aluminum pan.

In FIG. 6, when the duty control and the phase control are compared, the inrush current to the snubber capacitors 91 and 92 is small when the input power is low, as in the case of the frequency 23 kHz driving state. Therefore, the phase control is compared with the duty control. The loss at low input power is small.
However, in the high input power state, the switching element loss is larger in the phase control than in the duty control.
This is because an excessive current flows between the closed circuits of the switching elements 31 to 41 in the section (2) in the time chart of FIG. 4, so that the switching element loss increases at an accelerated rate as the input power increases. . In particular, when heating an aluminum pan or the like, a large current is input, so this tendency appears more remarkably.
Therefore, it is preferable to use duty control when heating an aluminum pan or the like.

As described above, the control circuit 81 switches the drive control method of the switching element as follows according to the detection result of the load detection unit 84.
(1) When the load detection unit 84 detects that the object to be heated is of a magnetic material, the drive control method of the switching element is switched to phase control.
(2) When the load detector 84 detects that the object to be heated is made of a non-magnetic material, the drive control method of the switching element is switched to duty control.

As described above, in the induction heating cooker according to the first embodiment, at the time of heating an iron pan that requires high-precision thermal power control, by performing power control by phase control, switching element loss at low thermal power is achieved. Is suppressed and the output range on the low thermal power side is expanded.
Thereby, the convenience in stew cooking, heat insulation cooking, etc. is aimed at.

  On the other hand, when heating the aluminum pan, by controlling the power by duty control, switching element loss in the high input state is suppressed, and by expanding the output range on the high thermal power side, such as hot water cooking when using the aluminum pan Convenient.

  In this way, by switching the power control method depending on the type of pot, there is no need to increase the allowable loss rating of the switching element, the amount of heat generated by the switching element due to the switching loss is suppressed, the cooling structure is simplified, and the cost is reduced. Reduction can be achieved.

As described above, a large current is required when heating a non-magnetic material such as an aluminum pan, and a small current is required when heating a magnetic material such as an iron pan. .
Therefore, the required power value varies depending on the pan type, so that the same effect can be achieved by switching the power control method based on the power value supplied to the heating coil instead of switching the power control method depending on the pan type. can do.
Specifically, means for detecting input power or load power may be provided as appropriate, and power control may be performed by phase control when the power is smaller than the threshold, duty control when the power is greater than or equal to the threshold, and the like.

Embodiment 2. FIG.
FIG. 7 is a circuit diagram of an induction heating cooker according to Embodiment 2 of the present invention.
The circuit configuration of FIG. 7 includes a new arm 50 in the high frequency power supply module 100 in addition to the configuration described in FIG. 1 of the first embodiment.
The arm 50 includes switching elements 51 and 52.
Each of the arm 30 and the arm 40 and the arm 40 and the arm 50 constitutes a full bridge inverter circuit. The arm 40 is shared by both full bridge circuits.
Each full-bridge circuit is independently driven and controlled, as will be described later.

A large-diameter outer heating coil 71 and a resonance capacitor 61a are connected between the arms 30 and 40. A resonance capacitor 61b is connected in parallel to the resonance capacitor 61a.
The switch 62 is configured by a relay, for example, and switches the connection of the resonance capacitor 61b. When the switch 62 is closed, the resonant capacitors 61a and 61b are connected in parallel. When the switch 62 is opened, the resonant capacitor 61b is disconnected from the circuit.
The outer heating coil 71 and the resonance capacitors 61a to 61b constitute a resonance circuit.

A small-diameter inner heating coil 72 and a resonance capacitor 63a are connected between the arms 40 and 50. A resonance capacitor 63b is connected in parallel with the resonance capacitor 63a.
The switch 64 is configured by a relay, for example, and switches the connection of the resonance capacitor 63b. When the switch 64 is closed, the resonant capacitors 63a and 63b are connected in parallel, and when the switch 64 is opened, the resonant capacitor 63b is disconnected from the circuit.
The inner heating coil 72 and the resonance capacitors 63a to 63b constitute a resonance circuit.

The control circuit 81 controls the driving of the switching elements 31, 32, 41, 42, 51, 52, controls the operation of the switches 62 and 64, receives the detection result of the load pan detection unit 84, and controls the operation unit 82 and the display unit 83. Send and receive signals.
By controlling the operation of the switches 62 and 64, the resonance frequency of the resonance circuit is switched according to the type of the object to be heated, and each switching element is driven and controlled at a frequency according to this.

  In the circuit configuration as shown in FIG. 7 as well, the switching loss is effectively suppressed by switching the drive control method of the switching element according to the type of the object to be heated, similar to that described in the first embodiment. Can do.

In particular, the circuit configuration of FIG. 7 has a larger number of switching elements than the circuit configuration of FIG. 1, so that the heat generation of the switching elements due to switching loss increases accordingly.
Therefore, it is effective to suppress the switching loss by switching the control method as described in the first embodiment.

  It should be noted that the same effect can be achieved by switching the control method as described in the first embodiment not only in the circuit configurations of FIGS. 1 and 7 but also in other circuit configurations.

3 is a circuit diagram of the induction heating cooker according to Embodiment 1. FIG. 2 is a circuit configuration example of a booster circuit 20. The change of the electric current in duty control and the ON / OFF time chart of a switching element are shown. The current change in phase control and the ON / OFF time chart of a switching element are shown. It is an example which shows the relationship between a power control system and a switching element loss at the time of driving a switching element with the drive frequency of 23 kHz. It is an example which shows the relationship between a power control system and a switching element at the time of driving a switching element with the drive frequency of 70 kHz. It is a circuit diagram of the induction heating cooking appliance which concerns on Embodiment 2. FIG.

Explanation of symbols

  11 AC power supply, 20 booster circuit, 21 coil, 22 switching element, 23 diode, 24 capacitor, 30 arm, 31-32 switching element, 40 arm, 41-42 switching element, 50 arm, 51-52 switching element, 61a- 61b resonance capacitor, 62 switch, 63a to 63b resonance capacitor, 64 switch, 71 to 72 heating coil, 81 control circuit, 82 operation section, 83 display section, 84 load detection section, 100 high frequency power supply module.

Claims (4)

A heating coil for heating an object to be heated;
An inverter having a switching element and supplying an alternating current to the heating coil;
A boosting circuit that boosts the input voltage to a constant voltage and supplies the boosted voltage to the inverter;
A control unit that drives and controls the switching element;
A load detection unit that detects the type of the object to be heated and outputs a detection result to the control unit;
With
The controller is
The induction heating cooker characterized by switching the drive control system of the switching element according to the detection result of the load detection unit. The load detector is
Detect whether the object to be heated is made of magnetic material or non-magnetic material,
The controller is
When the load detection unit detects that the object to be heated is of a magnetic material,
By controlling the drive phase difference of the switching element to control the input power,
When the load detection unit detects that the object to be heated is of a non-magnetic material,
The induction heating cooker according to claim 1, wherein the input power is controlled by varying an on-duty ratio of the switching element. A heating coil for heating an object to be heated;
An inverter having a switching element and supplying an alternating current to the heating coil;
A boosting circuit that boosts the input voltage to a constant voltage and supplies the boosted voltage to the inverter;
A control unit that drives and controls the switching element;
With
The controller is
When the power supplied to the heating coil is smaller than a predetermined value,
By controlling the drive phase difference of the switching element to control the input power,
When the power supplied to the heating coil is not less than the predetermined value,
An induction heating cooker, wherein input power is controlled by varying an on-duty ratio of the switching element. The heating coil is
It consists of two coils, an inner coil and an outer coil.
The inverter is
Having three arms in which the two switching elements are connected in series;
1 arm as a shared arm,
The other two arms and the shared arm constitute two inverters,
The induction heating cooker according to claim 2 or 3, wherein the two inverters supply an alternating current to the inner coil and the outer coil.

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