JP5183563B2 - Induction heating cooker - Google Patents

Description

  The present invention relates to an induction heating cooker.

  In recent years, induction cooking devices having two or more heating ports incorporated in a system kitchen or the like have been widely used. Such an induction heating cooker requires a power conversion circuit that converts a large current, such as a rectifier circuit or an inverter circuit, for each heating port, so that the circuit configuration of the induction heating cooker as a whole becomes large and the circuit board is accommodated. Need a big space to do. On the other hand, in order to improve the design, it is required to reduce the size and thickness of the device.

  In the conventional induction heating cooker, for example, “a switching element temperature detection circuit for detecting the switching element temperature, a heating coil current limiting circuit for limiting the heating coil current to an N-stage limit value corresponding to the switching element temperature,” And a control unit that controls on and off of the switching element so that an input current from the AC power source becomes a predetermined value within a range limited by a heating coil current limiting circuit has been proposed (for example, Patent Document 1).

  Further, for example, “one heat dissipating member that dissipates heat generated by the positive and negative switching elements forming the plurality of inverters” is provided, and “the temperature sensor 17 installed on the heat dissipating plate 3 does not exceed the heat dissipating capacity of the heat dissipating plate 3. In this way, the driving of the two inverters 15 and 16 is controlled. "(For example, see Patent Document 2).

JP-A-4-277488 (Claim 3) JP 2008-153244 A (paragraph numbers [0006], [0015])

  In recent years, induction heating cookers are required to further reduce the size and thickness of equipment, so the heat dissipation capability is limited, and the total amount of heat generated by the switching elements thermally coupled to one heat dissipation member is Often the amount of heat dissipation is exceeded. In order to suppress the heat generation amount of the switching element, it is necessary to suppress the output of the inverter circuit.

However, among the plurality of inverter circuits, even if the heating output is suppressed, the heating output of the inverter circuit in which the amount of heat generated by the switching element is not reduced may be weakened.
Even if the output of such an inverter circuit that does not need to suppress the heating output is weakened, the effect of suppressing the amount of generated heat is small, and the heating output is suppressed, so that the user's usability is deteriorated. There was a point.

  The present invention has been made to solve the above-described problems, and can suppress the suppression of the output of the inverter circuit having a small effect of suppressing the heat generation amount, and can suppress the temperature rise of the inverter circuit and can be used. It aims at obtaining the induction heating cooking appliance which can improve a user's usability.

The induction heating cooker according to this invention is
A plurality of inverter circuits;
Circuit temperature detecting means for detecting temperatures of the plurality of inverter circuits;
Output current detection means for detecting current flowing in each inverter circuit;
Overcurrent protection means for setting an output current limit value as an upper limit of the current flowing through the inverter circuit for each inverter circuit;
Control means for controlling the drive of each inverter circuit so that the current flowing through the inverter circuit does not exceed the output current limit value;
The overcurrent protection means includes
When the temperature detected by the circuit temperature detection means exceeds a predetermined temperature,
At least one of the output current limit values of each inverter circuit is reduced.

The present invention controls the drive of each inverter circuit so that the current flowing through the inverter circuit does not exceed the output current limit value, and when the temperature detected by the circuit temperature detection means exceeds a predetermined temperature, At least one of the output current limit values is reduced.
For this reason, it is possible to avoid the suppression of the output of the inverter circuit that has a small effect of suppressing the heat generation amount, thereby suppressing the temperature rise of the inverter circuit and improving the user-friendliness.

It is a circuit block diagram of the induction heating cooking appliance which concerns on Embodiment 1. FIG. It is a figure which shows the drive signal example of the inverter circuit of the induction heating cooking appliance which concerns on Embodiment 1. FIG. It is a figure which shows the example of the output current limiting value of the inverter circuit of the induction heating cooking appliance which concerns on Embodiment 1. FIG. It is a figure which shows the example of the relationship between the output electric current with respect to the pan of the various materials of the induction heating cooking appliance which concerns on Embodiment 1, and input electric power. It is a flowchart explaining the heating control processing operation | movement of the induction heating cooking appliance which concerns on Embodiment 1. FIG. It is a figure explaining the process which adjusts the output current limiting ratio of the induction heating cooking appliance which concerns on Embodiment 1. FIG. It is a figure which shows the example of the other output current limiting value of the inverter circuit of the induction heating cooking appliance which concerns on Embodiment 1. FIG. It is a circuit block diagram of the induction heating cooking appliance which concerns on Embodiment 2. FIG. It is a figure which shows the drive signal example of the inverter circuit of the induction heating cooking appliance which concerns on Embodiment 2. FIG. It is a figure which shows the example of the output current limiting value of the inverter circuit of the induction heating cooking appliance which concerns on Embodiment 2. FIG. It is a figure which shows the example of IPM used as a switching element of the inverter circuit of an induction heating cooking appliance.

Embodiment 1 FIG.
<Configuration>
1 is a circuit configuration diagram of an induction heating cooker according to Embodiment 1. FIG.
As shown in FIG. 1, the induction heating cooker in the present embodiment includes a first DC power supply circuit 2, a first inverter circuit 3, a second DC power supply circuit 4, a second inverter circuit 5, and a load circuit. 6, a load circuit 7, and a heat dissipation member 36.

The first inverter circuit 3 and the second inverter circuit 5 correspond to the “inverter circuit” in the present invention.
Hereinafter, when the first inverter circuit 3 and the second inverter circuit 5 are not distinguished from each other, they are also simply referred to as “inverter circuits”.

The first DC power supply circuit 2 includes a rectifier diode bridge 14, a choke coil 16, and a smoothing capacitor 18.
The first DC power supply circuit 2 converts commercial AC power from the commercial AC power supply 1 into DC power.

The second DC power supply circuit 4 includes a rectifier diode bridge 15, a choke coil 17, and a smoothing capacitor 19.
The second DC power supply circuit 4 converts commercial AC power from the commercial AC power supply 1 into DC power.

The first inverter circuit 3 converts DC power that is the output of the first DC power supply circuit 2 into high-frequency power.
The first inverter circuit 3 includes an upper switching element 24, a lower switching element 25, an upper diode 28, a lower diode 29, and a drive circuit 32.
The upper switching element 24 and the lower switching element 25 are connected in series between the output buses of the first DC power supply circuit 2 serving as a DC power supply.
The upper diode 28 is connected in antiparallel with the upper switching element 24.
The lower diode 29 is connected in antiparallel with the lower switching element 25.
The drive circuit 32 drives the upper switching element 24 and the lower switching element 25 (hereinafter also referred to as “switching element”).

The second inverter circuit 5 converts the DC power that is the output of the second DC power supply circuit 4 into high-frequency power.
The second inverter circuit 5 includes an upper switching element 26, a lower switching element 27, an upper diode 30, a lower diode 31, and a drive circuit 33.
The upper switching element 26 and the lower switching element 27 are connected in series between the output buses of the second DC power supply circuit 4 serving as a DC power supply.
The upper diode 30 is connected in antiparallel with the upper switching element 26.
The lower diode 31 is connected to the lower switching element 27 in antiparallel.
The drive circuit 33 drives the upper switching element 26 and the lower switching element 27 (hereinafter also referred to as “switching element”).

The load circuit 6 is connected to the output of the first inverter circuit 3.
The load circuit 6 includes a heating coil 8, a resonant capacitor 10, and a diode 12.
The heating coil 8 is constituted by an induction heating coil wound in a spiral shape. The heating coil 8 induction-heats a container to be heated such as a pan placed on the induction heating cooker when a high-frequency current is supplied.
The resonant capacitor 10 is connected to the heating coil 8 in series. A resonance circuit is formed by the heating coil 8 and the resonance capacitor 10.
The diode 12 is connected in parallel with the resonant capacitor 10.

The load circuit 7 is connected to the output of the second inverter circuit 5.
The load circuit 7 includes a heating coil 9, a resonant capacitor 11, and a diode 13.
The heating coil 9 is constituted by an induction heating coil wound in a spiral shape. The heating coil 9 induction-heats a heated container such as a pan placed on the induction heating cooker when a high-frequency current is supplied.
The resonant capacitor 11 is connected to the heating coil 8 in series. A resonance circuit is formed by the heating coil 9 and the resonance capacitor 11.
The diode 13 is connected in parallel with the resonant capacitor 11.

The heat dissipation member 36 has, for example, a hollow or fin structure.
The heat radiating member 36 includes the upper switching element 24 and the lower switching element 25 of the first inverter circuit 3, and the upper switching element 26 and the lower switching element 27 (hereinafter also referred to as “each switching element”) of the second inverter circuit 5. Are thermally coupled to each other.
That is, the heat radiating member 36 is shared by the first inverter circuit 3 and the second inverter circuit 5, and generates heat generated by the switching elements constituting the first inverter circuit 3 and the second inverter circuit 5. It dissipates heat.

  The upper switching element 24, the lower switching element 25, the upper switching element 26, and the lower switching element 27 correspond to the “switching element” in the present invention.

  Furthermore, the induction heating cooker in the present embodiment includes an input current detection circuit 20, an input current detection circuit 21, an input voltage detection circuit 22, an input voltage detection circuit 23, an output current detection circuit 34, an output current detection circuit 35, a temperature A sensor 37, an operation input unit 38, and a control unit 39 are provided.

The output current detection circuit 34 and the output current detection circuit 35 correspond to “output current detection means” in the present invention.
The temperature sensor 37 corresponds to “circuit temperature detection means” in the present invention.
The control unit 39 corresponds to the “control unit” in the present invention.

The input current detection circuit 20 detects a current (hereinafter referred to as “input current”) supplied to the first inverter circuit 3.
The input voltage detection circuit 22 detects a voltage (hereinafter referred to as “input voltage”) supplied to the first inverter circuit 3.
The output current detection circuit 34 detects a current (hereinafter referred to as “output current”) that flows from the first inverter circuit 3 to the load circuit 6 as a current that flows through the first inverter circuit 3.

The input current detection circuit 21 detects a current (hereinafter referred to as “input current”) supplied to the second inverter circuit 5.
The input voltage detection circuit 23 detects a voltage (hereinafter referred to as “input voltage”) supplied to the second inverter circuit 5.
The output current detection circuit 35 detects a current (hereinafter referred to as “output current”) flowing from the second inverter circuit 5 to the load circuit 7 as a current flowing through the second inverter circuit 5.

The temperature sensor 37 detects the temperature of the heat dissipation member 36.
As described above, the heat dissipation member 36 is thermally coupled to each switching element. For this reason, the temperature sensor 37 detects the temperature of the first inverter circuit 3 and the second inverter circuit 5 by detecting the temperature of the heat dissipation member 36.

  The temperature sensor 37 is composed of, for example, a thermistor, and detects the temperature of the heat radiating member 36 by contacting the side surface of the heat radiating member 36. The configuration of the temperature sensor 37 is not limited to this, and any configuration that can detect the temperature of the heat radiating member 36 may be used. For example, the temperature of the heat radiating member 36 may be detected in a non-contact manner by detecting infrared rays emitted from the heat radiating member 36 using an infrared sensor.

  The temperature sensor 37 may be any sensor that detects the temperatures of the first inverter circuit 3 and the second inverter circuit 5. For example, a temperature sensor may be provided for each inverter circuit or each switching element, and the total amount of heat generation may be obtained from the temperature detected by each temperature sensor.

  The operation input unit 38 causes the control unit 39 to input operation settings of the induction heating cooker by an operation of a user or the like.

The control unit 39 controls the entire operation of the induction heating cooker.
The control unit 39 has detection values from the input current detection circuit 20, the input current detection circuit 21, the input voltage detection circuit 22, the input voltage detection circuit 23, the output current detection circuit 34, the output current detection circuit 35, and the temperature sensor 37. Entered.
The control unit 39 controls the drive circuit 32 and the drive circuit 33.

The control unit 39 supplies power (hereinafter referred to as “input power”) supplied to the load circuit 6 from the input current value detected by the input current detection circuit 20 and the input voltage value detected by the input voltage detection circuit 22. Is calculated.
The controller 39 supplies power (hereinafter referred to as “input power”) supplied to the load circuit 7 from the input current value detected by the input current detection circuit 21 and the input voltage value detected by the input voltage detection circuit 23. Is calculated.
The control unit 39 controls the drive circuits 32 and 33 so that the calculated input power value becomes a power value corresponding to the heating power set by the operation input unit 38, and the first inverter circuit 3 and the first inverter circuit 3 are controlled. The heating output of the second inverter circuit 5 (hereinafter also referred to as “each inverter circuit”) is adjusted.

The control unit 39 includes overcurrent protection means 40.
The overcurrent protection means 40 sets an output current limit value (Ip1 × α) as an upper limit of the current flowing through the first inverter circuit 3, and an output current limit value as an upper limit of the current flowing through the second inverter circuit 5 (Ip2 × α) is set.
Here, Ip1 and Ip2 are output current upper limit values. α is an output current limiting ratio. Details will be described later.

The control unit 39 controls the drive circuit 32 of the first inverter circuit 3 so that the output current detected by the output current detection circuit 34 does not exceed the output current limit value (Ip1 × α).
The control unit 39 controls the drive circuit 33 of the second inverter circuit 5 so that the output current detected by the output current detection circuit 35 does not exceed the output current limit value (Ip2 × α).
Details will be described later.

When the temperature detected by the temperature sensor 37 exceeds a predetermined protection temperature by the operation described later, the overcurrent protection means 40 outputs the output current limit value (Ip1 × α) of the first inverter circuit 3 and the second The output current limit value (Ip2 × α) of the inverter circuit 5 is reduced.
Thereby, it is possible to suppress energy loss that occurs in each switching element, and to suppress the temperature of each switching element from excessively rising and breaking the switching element. Details of the operation will be described later.

  The control unit 39 and the overcurrent protection means 40 can be realized by hardware such as a circuit device that realizes these functions, or can be realized as software executed on an arithmetic device such as a microcomputer or CPU. You can also.

FIG. 2 is a diagram illustrating an example of a drive signal of the inverter circuit of the induction heating cooker according to the first embodiment.
FIG. 2A shows an example of a drive signal at the time of high output. FIG. 2B shows an example of a drive signal at the time of low output.
As shown in FIG. 2, the adjustment of the heating output of each inverter circuit in the present embodiment is performed by duty control performed by adjusting the conduction ratio of each switching element at a constant driving frequency.

FIG. 3 is a diagram illustrating an example of an output current limit value of the inverter circuit of the induction heating cooker according to the first embodiment.
In each switching element of each inverter circuit, the loss of the switching element, that is, the amount of heat generated increases as the current flowing during conduction or switching increases. For this reason, it becomes possible to suppress the emitted-heat amount of each switching element by providing a restriction | limiting in the electric current sent through each switching element.
In FIG. 3, Ip is an upper limit value of current at which the loss of the switching element does not become excessive. Hereinafter, Ip is referred to as an output current upper limit value.
Ip × 1.0 indicates the output current limit value in a state where the output current limit value is not suppressed due to the temperature rise of the switching element (normal time).
When the temperature of the switching element rises, the output current limit value is successively reduced to Ip × 0.9, Ip × 0.8, and Ip × 0.7 in order to suppress the heat generation amount.
Hereinafter, Ip × α is referred to as an output current limit value, and α is referred to as an output current limit ratio.

As for the heating output of each inverter circuit, the output current flowing through the heating coils 8 and 9 (also the current flowing through each switching element) becomes larger as it increases.
Even with the same output current, the heating output (input power to the inverter circuit) is large due to the material of the container to be heated (hereinafter referred to as “pan”) that is induction-heated by the heating coils 8 and 9. Different.

FIG. 4 is a diagram illustrating an example of the relationship between the output current and the input power with respect to the pots of various materials of the induction heating cooker according to the first embodiment.
As in the example shown in FIG. 4, a large input power can be obtained with a small output current in a magnetic SUS pan having a large resistance value, compared to a nonmagnetic SUS pan having a small resistance value.
Therefore, in the example shown in FIG. 4, even if the output current limit value of the inverter circuit for induction heating the magnetic SUS pan is reduced to Ip × 0.9, Ip × 0.8, and Ip × 0.7, the input power is reduced. Is not limited.
On the other hand, when the output current limit value of the inverter circuit for induction heating the nonmagnetic SUS pan is lowered to Ip × 0.9, Ip × 0.8, and Ip × 0.7, the input current is about 70% respectively. , About 50%, about 40%.

In the following description, the output current upper limit value of the first inverter circuit 3 is referred to as “Ip1”. Further, the output current upper limit value of the second inverter circuit 5 is referred to as “Ip2”.
The output current upper limit values Ip1 and Ip2 are set to a level at which the switching element loss does not become excessive in each inverter circuit.

  In the present embodiment, the output current limiting ratio α assumes a value of 0.7 to 1.0, with the lower limit value being “0.7” and the upper limit value being “1.0”.

<Operation>
Next, operation | movement of the heating control process of the induction heating cooking appliance in this Embodiment is demonstrated.

FIG. 5 is a flowchart for explaining the heating control processing operation of the induction heating cooker according to the first embodiment.
Hereinafter, description will be given based on each step of FIG.
In the initial state, both the first inverter circuit 3 and the second inverter circuit 5 are in a driving state (an operating state in which heating is performed).
In the initial state, the output current limiting ratio α is “1.0”.

(Step 1)
First, the control unit 39 uses the input current detection circuits 20 and 21, the input voltage detection circuits 22 and 23, and the output current detection circuits 34 and 35 to input currents and inputs of the first inverter circuit 3 and the second inverter circuit 5. The voltage and output current are detected.

(Step 2)
The control unit 39 compares the output current value (Io1) of the first inverter circuit 3 with the output current limit value (Ip1 × α) of the first inverter circuit 3 set in the overcurrent protection means 40.
When the output current (Io1) of the first inverter circuit 3 is larger than the output current limit value (Ip1 × α), the process proceeds to step 5.

(Step 3)
On the other hand, when the output current (Io1) of the first inverter circuit 3 is less than or equal to the output current limit value (Ip1 × α), the control unit 39 detects the input current value of the first inverter circuit 3 detected in step 1 above. Then, the input power value (Po1) is calculated from the input voltage value and compared with the power value of the set thermal power for the load circuit 6 set by the operation input unit 38.
If the calculated input power value (Po1) is equal to the power value of the set thermal power, the process proceeds to step 6.

(Step 4)
When the calculated input power value (Po1) is smaller than the power value of the set thermal power, the control unit 39 controls the drive circuit 32 of the first inverter circuit 3 to increase the heating output by a predetermined amount, and to step 6 move on.

(Step 5)
On the other hand, when the input power value (Po1) calculated in step 3 is larger than the power value of the set thermal power, or in step 2, the output current (Io1) of the first inverter circuit 3 is the output current limit value (Ip1). If it is determined that it is larger than xα), the control unit 39 controls the drive circuit 32 of the first inverter circuit 3 to decrease the heating output by a predetermined amount, and proceeds to Step 6.

(Step 6)
Next, the control unit 39 determines the output current value (Io2) of the second inverter circuit 5 and the output current limit value (Ip2 × α) of the second inverter circuit 5 set in the overcurrent protection means 40. Compare.
When the output current (Io2) of the second inverter circuit 5 is larger than the output current limit value (Ip2 × α), the process proceeds to Step 9.

(Step 7)
On the other hand, when the output current (Io2) of the second inverter circuit 5 is less than or equal to the output current limit value (Ip2 × α), the control unit 39 detects the input current value of the second inverter circuit 5 detected in step 1 above. Then, the input power value (Po2) is calculated from the input voltage value and compared with the power value of the set thermal power for the load circuit 7 set by the operation input unit 38.
When the calculated input power value (Po1) is equal to the power value of the set thermal power, the process proceeds to step 10.

(Step 8)
When the calculated input power value (Po2) is smaller than the power value of the set thermal power, the control unit 39 controls the drive circuit 33 of the second inverter circuit 5 to increase the heating output by a predetermined amount, and to step 10 move on.

(Step 9)
On the other hand, when the input power value (Po2) calculated in Step 7 is larger than the power value of the set thermal power, or in Step 6, the output current (Io2) of the second inverter circuit 5 is the output current limit value (Ip2). If it is determined that it is larger than xα), the control unit 39 controls the drive circuit 33 of the second inverter circuit 5 to decrease the heating output by a predetermined amount, and proceeds to Step 10.

(Step 10)
Next, the control unit 39 determines whether or not it is a predetermined timing for adjusting the output current limit value based on the detection value of the temperature sensor 37.
If it is not the predetermined timing, the process returns to Step 1.

  The predetermined timing is set to an arbitrary time interval according to the heat capacity of the heat radiating member 36 or the like. This is because the change in the detection value of the temperature sensor 37 is slower than the input / output current and the input voltage, so that the temperature of the switching element and the like is determined at a predetermined time interval.

(Step 11)
When it is determined in step 10 that the predetermined timing is reached, the control unit 39 detects the temperature (Tc) of the heat radiating member 36 thermally coupled to each switching element by the temperature sensor 37.

(Step 12)
Next, the control unit 39 compares the temperature (Tc) detected by the temperature sensor 37 with a predetermined protection temperature.
The predetermined protection temperature is set to a value lower than, for example, the heat radiation amount of the heat radiating member 36 or the temperature of thermal destruction of the switching element.

(Step 13)
When the temperature (Tc) detected by the temperature sensor 37 is equal to or lower than a predetermined protection temperature, it is determined whether or not the output current limit ratio α is an upper limit value (for example, 1.0).
If the output current limit ratio α is the upper limit value, the process returns to step 1.

(Step 14)
On the other hand, if the output current limit ratio α is not the upper limit value, the overcurrent protection means 40 increases the output current limit ratio α and then returns to step 1. Details will be described later.

(Step 15)
In step 12, when the temperature (Tc) detected by the temperature sensor 37 is higher than the predetermined protection temperature, it is determined whether or not the output current limiting ratio α is a lower limit value (for example, 0.7).
When the output current limit ratio α is the lower limit value, the process proceeds to step 17.

(Step 16)
On the other hand, if the output current limit ratio α is not the lower limit value, the overcurrent protection means 40 decreases the output current limit ratio α and then returns to step 1. Details will be described later.

  As described above, the overcurrent protection means 40 reduces the output current limit ratio α when the temperature detected by the temperature sensor 37 exceeds a predetermined temperature, thereby reducing the output current limit value (Ip × α) is reduced at approximately the same ratio.

(Step 17)
If it is determined in step 15 that the output current limiting ratio α is the lower limit value, the control unit 39 determines that the circuit is abnormal and stops driving each inverter circuit.

  Next, details of the processing of step 14 and step 16 will be described.

FIG. 6 is a diagram illustrating a process of adjusting the output current limit ratio of the induction heating cooker according to the first embodiment.
First, the process of increasing the output current limit ratio α in step 14 will be described with reference to FIG.

(Step 14-1)
First, the overcurrent protection means 40 adds a predetermined value to the output current limit ratio α.
Here, for example, “0.1” is added.
Not limited to this, the output current limit ratio α may be multiplied by a predetermined value (for example, “1.1”).

(Step 14-2)
Next, the overcurrent protection means 40 determines whether or not the output current limit ratio α is greater than “1.0”.
If the output current limit ratio α is not greater than “1.0”, the process of step 14 is terminated.

(Step 14-3)
On the other hand, if the output current limit ratio α is greater than “1.0”, the overcurrent protection means 40 sets “1.0” as the value of the output current limit ratio α, and the process of step 14 is ended.

  Next, the process for reducing the output current limiting ratio α in step 16 will be described with reference to FIG.

(Step 16-1)
First, the overcurrent protection means 40 includes the ratio (Io1 / Ip1) between the output current Io1 of the first inverter circuit 3 and its output current upper limit value Ip1, the output current Io2 of the second inverter circuit 5 and its output current upper limit. The ratio of the value Ip2 (Io2 / Ip2) is compared.

(Step 16-2)
The ratio (Io1 / Ip1) of the output current Io1 of the first inverter circuit 3 and its output current upper limit value Ip1 is the ratio of the output current Io2 of the second inverter circuit 5 and its output current upper limit value Ip2 (Io2 / Ip2). If it is smaller, the overcurrent protection means 40 performs the following processing.
The overcurrent protection means 40 outputs a value obtained by subtracting a predetermined value (for example, “0.1”) from the ratio (Io2 / Ip2) between the output current Io2 of the second inverter circuit 5 and the output current upper limit value Ip2. The current limit ratio α is set, and the process of step 16 is terminated.
However, the present invention is not limited to this, and Io2 / Ip2 may be multiplied by a predetermined value (for example, “0.9”).

(Step 16-3)
On the other hand, the ratio (Io1 / Ip1) between the output current Io1 of the first inverter circuit 3 and its output current upper limit value Ip1 is equal to the ratio (Io2 / Ip1) of the output current Io2 of the second inverter circuit 5 and its output current upper limit value Ip2. In the case of Ip2) or more, the overcurrent protection means 40 performs the following processing.
The overcurrent protection means 40 outputs a value obtained by subtracting a predetermined value (for example, “0.1”) from the ratio (Io1 / Ip1) between the output current Io1 of the first inverter circuit 3 and the output current upper limit value Ip1. The current limit ratio α is set, and the process of step 16 is terminated.
Not limited to this, Io1 / Ip1 may be multiplied by a predetermined value (eg, “0.9”).

  As a result, the output current limit values (Ip1 × α, Ip2 × α) are lowered from the current output current levels (Io1, Io2) to suppress the output in at least one of the inverter circuits and reduce the loss in the switching element. Can be suppressed.

For example, let us consider a case where the pan that is the load of one inverter circuit is the nonmagnetic SUS pan in FIG. 4 and the load of the other inverter circuit is the magnetic SUS pan of FIG.
In this case, if the temperature sensor 37 detects a temperature higher than the protection temperature and reduces the output current limit ratio α to 0.7 to 0.9, the output current of the inverter circuit for induction heating the nonmagnetic SUS pan is suppressed. Thus, loss in the switching element can be suppressed.
On the other hand, the output current of the inverter circuit for induction heating the magnetic SUS pan is driven by a current smaller than Ip1 × 0.7, so even if the output current limit ratio α is reduced to 0.7 to 0.9. The heating output of the inverter circuit is maintained.
Therefore, even in such a high heating output state, the heating output of the magnetic SUS pan with little loss in the switching element is maintained, and the heating output is not unnecessarily weakened.

<Effect>
As described above, in the present embodiment, when the temperature detected by the temperature sensor 37 exceeds a predetermined temperature, the output current limiting ratio α is decreased, and the first inverter circuit 3 and the second inverter circuit are reduced. The output current limit value (Ip × α) of 5 is reduced at a substantially equal ratio.
As a result, it is possible to avoid the suppression of the output of the inverter circuit that has a small effect of suppressing the heat generation amount, to suppress the temperature rise of each inverter circuit, and to improve the user-friendliness.

In addition, the ratio of the output current and the output current upper limit value, whichever is larger, of the two inverter circuits is obtained, and the output current limit ratio α is set to a value smaller than this ratio.
As a result, among the inverter circuits in operation, the output of the inverter circuit that has little energy loss and suppresses the heating output can be maintained without being suppressed as much as possible. Further, the energy loss of the switching element is large, and the output of the inverter circuit having a large effect of suppressing the heat generation amount of the switching element can be suppressed by limiting the output.
Therefore, the heating output is not suppressed unnecessarily, the thermal destruction of the inverter circuit can be prevented, and the user-friendliness can be improved.

The heat dissipation member 36 is shared by the first inverter circuit 3 and the second inverter circuit 5 and dissipates heat generated by the switching elements constituting the first inverter circuit 3 and the second inverter circuit 5. To do.
For this reason, the cooling structure of the circuit of the whole induction heating cooker can be reduced in size, and the cost can be reduced by sharing the temperature sensor 37 that detects the temperature of the switching element.
Further, since the heat dissipating member 36 is shared by a plurality of inverter circuits, when only one inverter circuit is operated, the heat dissipating capacity of the heat dissipating member 36 can be used.

In the present embodiment, the case where there are two inverter circuits has been described. The present invention is not limited to this, and two or more inverter circuits may be provided.
In this case, for example, the maximum value of the ratio of the current flowing through the inverter circuit with respect to each output current limit value of the plurality of inverter circuits is obtained, and the output current limit ratio α is set to a value smaller than the maximum value of this ratio. Then, the output current upper limit value Ip of each inverter circuit is multiplied by the output current limit ratio α to reduce each output current limit value (Ip × α).
The effect similar to the said effect can be acquired also by such a structure and operation | movement.

In the present embodiment, the output current upper limit value Ip of each inverter circuit is multiplied by the output current limit ratio α, respectively, and the output current limit value (Ip × α) of each inverter circuit is reduced at a substantially equivalent ratio. It was.
The present invention is not limited to this, and at least one of the output current limit values (Ip × α) of the plurality of inverter circuits may be reduced.

For example, among the output current limit values of the plurality of inverter circuits, the output current limit value having the largest ratio of the current flowing through the inverter circuit to the output current limit value may be decreased.
For example, the output current limit ratio α may be set for each inverter circuit, and only the output current limit ratio α for the inverter circuit having the largest Io / Ip may be decreased.
Thereby, even if it suppresses a heating output among the inverter circuits in operation | movement, the output of the inverter circuit with a small calorific value suppression effect of a switching element is not restrict | limited. On the other hand, the output of the inverter circuit having a large effect of suppressing the amount of heat generated by the switching element can be suppressed.

  In the first embodiment, the output current upper limit value Ip1 of the first inverter circuit 3 and the output current upper limit value Ip2 of the second inverter circuit 5 are set to the same current level (Ip = Ip1 = Ip2). The present invention is not limited to this, and different current levels may be set depending on the heating coil and switching element to be used, the drive frequency of the load circuit and the inverter circuit, and other operating conditions. FIG. 7 shows an example where the output current upper limit value Ip1 and the output current upper limit value Ip2 are at different current levels.

Embodiment 2. FIG.
In the first embodiment, the driving frequency of each inverter circuit is constant, the heating output is controlled by duty control, and the output current upper limit value is constant regardless of the heating output level.
In the second embodiment, a description will be given of a mode in which the heating output is controlled by the drive frequency of each inverter circuit, and the output current upper limit value is varied according to the drive frequency of the inverter circuit.

<Configuration>
FIG. 8 is a circuit configuration diagram of the induction heating cooker according to the second embodiment.
As shown in FIG. 8, the induction heating cooker in the present embodiment has a configuration in which the diode 12 of the load circuit 6 and the diode 13 of the load circuit 7 are not provided in place of the configuration of the first embodiment.
Other configurations are the same as those of the first embodiment (FIG. 1), and the same parts are denoted by the same reference numerals.

FIG. 9 is a diagram illustrating an example of a drive signal of the inverter circuit of the induction heating cooker according to the second embodiment.
FIG. 9A shows an example of a drive signal at the time of high output. FIG. 9B shows an example of a drive signal at the time of low output.
As shown in FIG. 9, the adjustment of the heating output of each inverter circuit in the present embodiment is performed by frequency control in which the switching conduction ratio is constant and the drive frequency of each switching element is changed.

FIG. 10 is a diagram illustrating an example of the output current limit value of the inverter circuit of the induction heating cooker according to the second embodiment.
The loss (heat generation amount) of each switching element of each inverter circuit increases as the current flowing during conduction or switching increases. Also, the switching loss increases as the frequency of driving increases with the number of times of switching per unit time.
For this reason, it becomes possible to suppress the emitted-heat amount of each switching element by reducing the output current upper limit Ip, so that the drive frequency of each switching element becomes high.

Even when the inverter circuit is driven and heated at the same frequency for the same size pan, the current flowing through the inverter circuit varies greatly depending on the material of the pan to be heated.
For this reason, it becomes possible to suppress the emitted-heat amount of each switching element by providing a restriction | limiting in the electric current sent through each switching element.

  In FIG. 10, Ip × 1.0, Ip × 0.9, Ip × 0.8, and Ip × 0.7 indicate that the output current limiting ratio α is set as the temperature detected by the temperature sensor 37 increases. It is a line which shows the output current limit value at the time of restrict | limiting with 1.0, 0.9, 0.8, 0.7.

As shown in FIG. 10, the overcurrent protection means 40 in the present embodiment changes each output current upper limit value (Ip) according to the drive frequency of the first inverter circuit 3 and the second inverter circuit 5. .
When the temperature detected by the temperature sensor 37 exceeds a predetermined temperature, the output current upper limit values (Ip) of the first inverter circuit 3 and the second inverter circuit 5 are the same as in the operation of the first embodiment. ) Is multiplied by the output current limit ratio α to reduce the output current limit value (Ip × α).

Also in the present embodiment, as in FIG. 4 of the first embodiment, a pot made of a material such as magnetic SUS having a large resistance value has a smaller output current (heating) than a pot made of a material such as non-magnetic SUS having a small resistance value. A large heating output (input power) can be obtained with a coil current and a switching element current.
For this reason, even if the output current is suppressed and the loss caused by the switching element is reduced, the output of the pan of a high resistance material such as magnetic SUS is not easily suppressed, and high heat power can be maintained, so the induction heating cooker is easy to use. Can be obtained.

As described above, in the present embodiment, each output current upper limit value (Ip) is changed according to the drive frequency of the first inverter circuit 3 and the second inverter circuit 5.
Therefore, similarly to the effect of the first embodiment, when the inverter circuit is driven by frequency control, it is possible to avoid the suppression of the output of the inverter circuit that has a small effect of suppressing the heat generation amount, and the temperature of each inverter circuit While suppressing the rise, the user-friendliness can be improved.

  Note that, instead of the configuration of the first and second embodiments, the first inverter circuit 3 and the second inverter circuit 5 include a plurality of switching components that constitute the first inverter circuit 3 and the second inverter circuit 5. You may make it have a power module with which the element was enclosed with the common package.

For example, as shown in FIG. 11, an IPM (Intelligent Power Module) enclosed in one package is used as a switching element constituting a plurality of inverter circuits.
The temperature sensor 37 may detect the temperature of the IPM package or the temperature of the member thermally coupled to the package as the temperature of the first inverter circuit 3 and the second inverter circuit 5. .

  DESCRIPTION OF SYMBOLS 1 Commercial AC power source, 2 First DC power circuit, 3 First inverter circuit, 4 Second DC power circuit, 5 Second inverter circuit, 6 Load circuit, 7 Load circuit, 8 Heating coil, 9 Heating coil DESCRIPTION OF SYMBOLS 10 Resonant capacitor, 11 Resonant capacitor, 12 Diode, 13 Diode, 14 Rectifier diode bridge, 15 Rectifier diode bridge, 16 Choke coil, 17 Choke coil, 18 Smoothing capacitor, 19 Smoothing capacitor, 20 Input current detection circuit, 21 Input current Detection circuit, 22 Input voltage detection circuit, 23 Input voltage detection circuit, 24 Upper switching element, 25 Lower switching element, 26 Upper switching element, 27 Lower switching element, 28 Upper diode, 29 Lower diode, 30 Upper diode, 31 Lower Diode, 32 driving circuit, 33 a driving circuit, 34 an output current detection circuit, 35 output current detection circuit, 36 the heat radiating member, 37 temperature sensor, 38 operation input unit, 39 control unit, 40 overcurrent protection means.

Claims (7)

A plurality of inverter circuits;
Circuit temperature detecting means for detecting temperatures of the plurality of inverter circuits;
Output current detection means for detecting current flowing in each inverter circuit;
Overcurrent protection means for setting an output current limit value as an upper limit of the current flowing through the inverter circuit for each inverter circuit;
Control means for controlling the drive of each inverter circuit so that the current flowing through the inverter circuit does not exceed the output current limit value;
The overcurrent protection means includes
When the temperature detected by the circuit temperature detection means exceeds a predetermined temperature,
An induction heating cooker that reduces at least one of the output current limit values of the inverter circuits. The overcurrent protection means includes
When the temperature detected by the circuit temperature detection means exceeds a predetermined temperature,
The induction heating cooker according to claim 1, wherein the output current limit value of each inverter circuit is reduced at a substantially equal ratio. The overcurrent protection means includes
When the temperature detected by the circuit temperature detection means exceeds a predetermined temperature,
2. The induction heating cooker according to claim 1, wherein, among the output current limit values of the respective inverter circuits, the output current limit value having the largest ratio of the current flowing through the inverter circuit to the output current limit value is reduced. . The overcurrent protection means includes
When the temperature detected by the circuit temperature detection means exceeds a predetermined temperature,
Obtain the maximum value of the ratio of the current flowing through the inverter circuit to the output current limit value of each inverter circuit,
4. The output current limit value is decreased by multiplying the output current limit value of each inverter circuit by a ratio smaller than the maximum value of the ratio, respectively. 5. Induction heating cooker. The overcurrent protection means includes
According to the drive frequency of each inverter circuit, each output current limit value is changed,
When the temperature detected by the circuit temperature detection means exceeds a predetermined temperature,
The induction heating according to any one of claims 1 to 4, wherein the output current limit value is reduced by multiplying at least one of the output current limit values of each inverter circuit by a predetermined ratio. Cooking device. A heat dissipating member that dissipates heat generated by the switching elements composing the plurality of inverter circuits, and is made common to the plurality of inverter circuits;
The circuit temperature detecting means includes
The induction heating cooker according to any one of claims 1 to 5, wherein a temperature of the heat radiating member is detected as a temperature of the plurality of inverter circuits. The plurality of inverter circuits are:
A power module in which a plurality of switching elements constituting the plurality of inverter circuits are enclosed in a common package,
The circuit temperature detecting means includes
6. The induction according to claim 1, wherein a temperature of a package of the power module or a temperature of a member thermally coupled to the package is detected as a temperature of the plurality of inverter circuits. Cooker.

Images