WO2012169169A1

WO2012169169A1 - Induction heating cooker

Info

Publication number: WO2012169169A1
Application number: PCT/JP2012/003654
Authority: WO
Inventors: 澤田　大輔; 藤井　裕二
Original assignee: パナソニック株式会社
Priority date: 2011-06-07
Filing date: 2012-06-04
Publication date: 2012-12-13
Also published as: JP5895175B2; JPWO2012169169A1

Abstract

An input current detection circuit (13) detects an input current inputted from a direct-current power supply into a resonance circuit including a heating coil (1) and a resonant capacitor (2). A control circuit (9) integrates the input current detected by the input current detection circuit (13) for each duty cycle period, and controls the electrification time of a switching element (4) so that an average value of the input current after the integration corresponds to an input power setting value selected using an input power setting means (16).

Description

Induction heating cooker

The present invention relates to an induction heating cooker that performs power control according to a set value of input power.

Referring to FIG. 15, an induction heating cooker according to the prior art described in Patent Document 1 will be described. FIG. 15 is a circuit diagram showing a configuration of an induction heating cooker according to the prior art. As shown in FIG. 15, the induction heating cooker according to the prior art includes a DC power supply circuit 41, a parallel resonance circuit including a heating coil 44, a resonance capacitor 45 and a load (pan) 60, and a high-frequency current to the heating coil 44. The switching elements 46 and 47 to be supplied and a flywheel diode are provided. The induction heating cooker of FIG. 15 has a circuit configuration of a voltage resonance type inverter, and by turning on and off the switching elements 46 and 47, a resonance current is generated in the parallel resonance circuit, and heating is performed by a high frequency magnetic field generated in the heating coil 44. The load 60 is induction-heated by eddy current loss generated in the load 60 placed on the coil 44. In addition, the power control method used is a frequency at which the current flowing through the heating coil is changed according to the value of the time during which the switching elements 46 and 47 are turned on (on time), and the high-frequency current applied to the pan is controlled to vary the power. Control. According to this method, in the case of a load (pan) 60 having an appropriate impedance, the next energization is performed from a state where the flyback voltage (collector-emitter voltage) due to resonance has completely decreased to 0 V, and the load current (collector) As a current), a negative flywheel current flows through the flywheel diode. However, if the on-time is shortened in order to reduce the output power, the switching element is turned on before the flyback voltage falls below 0V, so that the on-loss is remarkably increased, and the element is deteriorated or destroyed. There was a drawback of inviting.

In order to solve these problems, in Patent Document 1, when the input power set value is greater than a certain value, the operating frequency of the switching element is changed according to the input power set value (a continuous operation control method using frequency control is used). .) When the input power set value is less than a certain value, the ratio of the heating time and the stop time is changed according to the input power set value (intermittent operation control method (hereinafter referred to as “inverter circuit energization and stop”). , Referred to as duty control)).

Japanese Unexamined Patent Publication No. Sho 63-040291

However, the induction heating cooker according to the related art has a problem that, when performing power control by duty control, the difference between the average power of the input power to the load and the set power becomes large depending on the load. is doing. This is due to the following reason. Duty control is an energization operation with a predetermined set power by alternately switching between an energized state and a stopped state according to a predetermined energized time and a stopped time, and an energized time with respect to a predetermined cycle time (energized time + stopped time). This is a control method for obtaining a desired average power by changing the ratio (duty ratio). Here, in the energized state, power control is performed by frequency control so that the input power to the load is equivalent to the set power. However, since the operation state of the switching element at this time varies depending on the load, the switching element is set for each set power. The operating frequency cannot be determined uniquely. For this reason, in general, at the start of operation, the power is operated at an operating frequency far away from the resonant frequency of the resonant circuit (resonance frequency <operating frequency) to set the low power state, and the operating frequency is gradually brought closer to the resonant frequency. Then, a method (soft start control) is used in which the input power is increased to control the power up to the set power. At this time, the time required from the start of operation until the input power reaches the set power level differs depending on the load, and this time is included in the energization time described above. For this reason, the longer the required time, the shorter the remaining energization time (the time for energization corresponding to the set power), and the average power per cycle time also decreases, so the average input power between the average value and the set power The difference increases.

The object of the present invention is to solve the above problems and to provide an induction heating cooker that can reduce the difference between the average input power and the set power as compared with the prior art when performing power control by duty control. It is in.

The induction heating cooker according to the first invention is
A resonance circuit comprising a heating coil for induction heating the pan, and a resonance capacitor connected in parallel to the heating coil;
A switching element connected in series to the resonant capacitor;
An input current detection circuit for detecting an input current input to the resonance circuit from an AC power supply via a rectifier circuit;
Input power setting means for selecting one input power setting value from a plurality of input power setting values to the resonant circuit;
In the induction heating cooker provided with a control circuit for controlling the switching element to repeat the energized state and the stopped state at a predetermined duty cycle,
The control circuit integrates the detected input current in each duty cycle period, and an average value of the input current after the integration of each duty cycle period corresponds to the selected input power setting value. The energization time of the switching element is controlled so as to have a preset value.

The induction heating cooker according to the second invention is
A resonance circuit comprising a heating coil for induction heating the pan, and a resonance capacitor connected in parallel to the heating coil;
A switching element connected in series to the resonant capacitor;
Input power setting means for selecting one input power setting value from a plurality of input power setting values to the resonant circuit;
A pot material determining means for determining the material of the pot;
In the induction heating cooker provided with a control circuit for controlling the switching element to repeat the energized state and the stopped state at a predetermined duty cycle,
The control circuit determines the switching based on the determined material of the pan so that an average value of input power in each duty cycle period is a value corresponding to the selected input power setting value. The energization time of the element is set.

Therefore, when power control is performed by duty control, the difference between the average input power and the set power can be reduced as compared with the prior art, and the usability can be improved by suppressing variations in cooking performance due to load differences.

According to the induction heating cooker according to the present invention, when power control is performed by duty control, the energized state and the stopped state are alternately switched at a predetermined duty cycle, and the switching from the energized state to the stopped state is performed. Since the average value of the input current to the resonance circuit during the duty cycle reaches a preset value corresponding to the input power setting value, the input power average value and the setting corresponding to the input power setting value are set. It is possible to prevent the difference between the power and the load from becoming large depending on the load, and to suppress the variation in the cooking performance due to the load difference, thereby improving the usability.

It is a circuit diagram which shows the structure of the induction heating cooking appliance which concerns on Embodiment 1 of this invention. It is a flowchart of the duty control process which concerns on Embodiment 1 of this invention when an input electric power setting value is set to 1. It is a table which shows the relationship between the input power setting value which concerns on Embodiment 1 of this invention, setting power, and a power control method. It is a graph which shows the relationship between the input power to the pan 3 in Embodiment 1 of this invention, and the voltage level Y of the detection signal from the input current detection circuit 13. It is a graph which shows the time change of the input electric power during duty control in Embodiment 1 of this invention. It is a circuit diagram which shows the structure of the induction heating cooking appliance which concerns on Embodiment 2 of this invention. It is a flowchart of the 1st part of the duty control process which concerns on Embodiment 2 of this invention when an input electric power setting value is set to 1. It is a flowchart of the 2nd part of the duty control process which concerns on Embodiment 2 of this invention when an input power setting value is set to 1. It is a table which shows the relationship between the input power setting value which concerns on Embodiment 2 of this invention, setting power, and a power control method. It is a graph which shows the relationship between the input electric power to the pan 3 in Embodiment 2 of this invention, and the voltage level Y of the detection signal from the input current detection circuit 13. It is a circuit diagram which shows the structure of the induction heating cooking appliance which concerns on Embodiment 3 of this invention. It is a flowchart of the 1st part of the duty control process which concerns on Embodiment 3 of this invention when an input power setting value is set to 1. It is a flowchart of the 2nd part of the duty control process which concerns on Embodiment 3 of this invention when an input electric power setting value is set to 1. It is a table which shows the relationship between the input power setting value which concerns on Embodiment 3 of this invention, setting power, and a power control method. It is a graph which shows the relationship between the input electric power to the pan 3 in Embodiment 3 of this invention, and the voltage level Y of the detection signal from the input current detection circuit 13. It is a graph which shows the time change of the input electric power during duty control in Embodiment 3 of this invention. It is a circuit diagram which shows the structure of the induction heating cooking appliance which concerns on a prior art.

The induction heating cooker according to the first aspect is
A resonance circuit comprising a heating coil for induction heating the pan, and a resonance capacitor connected in parallel to the heating coil;
A switching element connected in series to the resonant capacitor;
An input current detection circuit for detecting an input current input to the resonance circuit from an AC power supply via a rectifier circuit;
Input power setting means for selecting one input power setting value from a plurality of input power setting values to the resonant circuit;
In the induction heating cooker provided with a control circuit for controlling the switching element to repeat the energized state and the stopped state at a predetermined duty cycle,
The control circuit integrates the detected input current in each duty cycle period, and an average value of the input current after the integration of each duty cycle period corresponds to the selected input power setting value. The energization time of the switching element is controlled so as to have a preset value.

Therefore, even if there is a difference in the average power during the required time from the start of energization until the input power reaches the set power, the energization time can be varied according to the load. Therefore, the difference between the average input power and the set power can be reduced as compared with the prior art regardless of the load.

The induction heating cooker according to the second aspect is the heating cooker according to the second aspect,
It further comprises a pan material judging means for judging the material of the pan,
The control circuit controls an energization time of the switching element according to the determined material of the pan.

Accordingly, the load current has a length from the start of operation until the input current reaches a predetermined integrated input power for switching between the energized state and the stopped state from the start of energization, and occurs during the required time. Even when there is a difference in average power or when the input power itself in the energized state varies depending on the power control method during continuous operation, the energization time can be varied according to the load. For this reason, the difference between the average input power and the set power can be reduced as compared with the prior art regardless of the load.

The induction heating cooker according to the third aspect is
A resonance circuit comprising a heating coil for induction heating the pan, and a resonance capacitor connected in parallel to the heating coil;
A switching element connected in series to the resonant capacitor;
Input power setting means for selecting one input power setting value from a plurality of input power setting values to the resonant circuit;
A pot material determining means for determining the material of the pot;
In the induction heating cooker provided with a control circuit for controlling the switching element to repeat the energized state and the stopped state at a predetermined duty cycle,
The control circuit determines the switching based on the determined material of the pan so that an average value of input power in each duty cycle period is a value corresponding to the selected input power setting value. The energization time of the element is set.

Accordingly, depending on the material of the pan, the input power itself when performing the duty control operation changes, and even when a difference occurs between the set power and the actual average input power, this corresponds to the set power. Since the time ratio (ratio of energization time to duty cycle time) at which the average input power can be obtained can be set according to the material of the load, the average input power The difference from the set power can be reduced.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
FIG. 1 is a circuit diagram showing a configuration of an induction heating cooker according to Embodiment 1 of the present invention.

In FIG. 1, the induction heating cooker according to the present embodiment includes a heating coil 1, a resonant capacitor 2, a switching element 4, a flyhole diode 5, a rectifying element 6, a choke coil 7, and a smoothing capacitor 8. And a control circuit 9, which is a microcomputer, a switching element drive circuit 10, a power supply circuit 11, a zero volt pulse detection circuit 12, an input current detection circuit 13, and an input power setting means 16. The control circuit 9 includes a pulse number adding circuit 14 and an input current adding circuit 15.

The heating coil 1 and the resonance capacitor 2 connected in parallel to the heating coil 1 constitute a resonance circuit. The pan 3 as a load is disposed in the vicinity of the heating coil 1. The switching element 4 is connected in series to the resonance circuit, and supplies a high-frequency current to the resonance circuit together with the flywheel diode 5 connected in parallel to the switching element 4. The power rectified by the rectifying element 6 that rectifies the AC power from the AC power supply is smoothed by a smoothing circuit including the choke coil 7 and the smoothing capacitor 8 and supplied to the resonance circuit and the switching element 4. Here, the rectifier element 6, the choke coil 7, and the smoothing capacitor 8 constitute a rectifier circuit. Further, the control circuit 9 controls the entire induction heating cooker, and the switching element driving circuit 10 drives the switching element 4 at a high speed according to a command from the control circuit 9. Furthermore, the power supply circuit 11 supplies a DC stabilized power supply to the entire induction heating cooker. The zero volt pulse detection circuit 12 detects the zero volt timing of the AC voltage from the AC power supply, generates a zero volt pulse at the detection timing, and outputs the zero volt pulse to the pulse number adding circuit 14. The input current detection circuit 13 uses a current transformer to detect an input current input to the resonance circuit from the AC power supply via the rectifier circuit, and inputs a detection signal having a voltage level corresponding to the detected input current. This is output to the current adding circuit 15. The pulse number adding circuit 14 counts the zero volt pulse from the zero volt pulse detecting circuit 12, and stores data indicating the count result as stored data. Further, the input current adding circuit 15 adds (accumulates) the input current detected by the input current detecting circuit 13 by accumulating values corresponding to the voltage levels of the detection signals from the input current detecting circuit 13, and integrates them. Data indicating the result is stored as stored data. The current detected by the input current detection circuit 13 corresponds to the input power, and the stored data of the input current integration circuit 15 corresponds to the integration power. The user operates the input power setting means 16 to select and set one input power setting value from among a plurality of input power setting values to the resonance circuit.

The operation and action of the induction heating cooker configured as described above will be described below. Note that the difference between the induction heating cooker according to the present embodiment and the induction heating cooker according to the prior art described in Patent Document 1 described with reference to FIG. 15 is set by the input power setting means 16. The control method in the case where the set input power value is less than the predetermined value, that is, the heating operation and the stop of the pan 3 are repeated at a predetermined duty cycle (that is, the switching element 4 is switched at a predetermined switching cycle sufficiently shorter than the duty cycle). The energization state for driving and the stop state for turning off the switching element 4 are repeated at a predetermined duty cycle.) Only the control method by duty control (intermittent operation) is used. In other cases, for example, when the input power set value set by the input power setting means 16 is a predetermined value or more, and the control method during the heating operation during duty control is the same as that of the induction heating cooker according to the prior art. is there. Specifically, using a voltage resonance type inverter, the pan 3 is induction-heated by eddy current loss generated in the pan 3 placed on the heating coil 1 by a high-frequency magnetic field generated in the heating coil 1. Further, the power control method used is a frequency at which the current flowing through the heating coil 1 is changed according to the value of the time (on time) when the switching element 4 is turned on, and the high frequency current applied to the pan 3 is controlled to vary the power. Control. Furthermore, the determination method of the input power set value when the control method is switched between frequency control and duty control is the same as the determination method according to the prior art. Specifically, for the purpose of preventing the occurrence of a significant increase in the on-loss of the switching element 4 in the low power state, based on the minimum input power that can avoid the destruction of the switching element 4 by the cooling configuration, The range of the input power set value for frequency control is determined. Hereinafter, detailed description of the same configuration, operation, and setting method as those of the induction heating cooker according to the prior art will be omitted, and the induction heating cooker according to the present embodiment and the induction heating cooker according to the prior art will be omitted. Only the differences will be described.

A control method when the input power set value set by the input power setting means 16 is less than a predetermined value will be described with reference to FIGS. FIG. 2 is a flowchart of the duty control process according to Embodiment 1 of the present invention when the input power set value is set to 1. FIG. 3 is a table showing a relationship among the input power set value, the set power, and the power control method according to Embodiment 1 of the present invention. FIG. 4 is a graph showing the relationship between the input power to the pan 3 and the voltage level Y of the detection signal from the input current detection circuit 13 in Embodiment 1 of the present invention.

According to the induction heating cooker according to the first embodiment of the present invention, the user uses the input power setting means 16 to select among the input power setting values in five stages from the input power setting values “1” to “5”. Select and set the desired input power setpoint. Here, as shown in FIG. 3, the set power corresponding to the input power set value “1” is 100 W, the set power corresponding to the input power set value “2” is 300 W, and the input power set value “3”. Is set to 600 W, the set power corresponding to the input power set value “4” is 900 W, and the set power corresponding to the input power set value “5” is 1200 W. Further, the control circuit 9 performs continuous operation by frequency control in the input power set value range from “3” to “5”, and in the input power set value range of “1” and “2”, the input power set value “ With the set power (600 W) corresponding to “3”, the duty cycle time is set to 6 seconds and the duty control operation is performed.

In FIG. 2, when the input power setting value is set to “1” by the input power setting means 16, the control circuit 9 receives a signal including the input power setting value “1” from the input power setting means 16 (S1). ). In response to this, the control circuit 9 first resets the stored data of the pulse number adding circuit 14 and the input current adding circuit 15 in the control circuit 9 to 0 (in S2 and S3, the initial value 0 is set). set).

Next, the control circuit 9 sets 720 to the period time reachability determination value of the stored data of the pulse number adding circuit 14 (S4), and sets 15120 to the energization time reachability determination value of the stored data of the input current adding circuit 15. Set (S5). A method for setting the period time reachability determination value and the energization time reachability determination value will be described later.

Next, the control circuit 9 transmits a drive signal to the switching element drive circuit 10 to drive the switching element 4 at a predetermined switching cycle sufficiently shorter than the duty cycle, shifts to an energized state, and heats the pan 3 Is started (S6).

The zero volt pulse detection circuit 12 detects the zero volt timing of the AC voltage from the AC power source, that is, the inversion timing of the positive / negative voltage, and generates a zero volt pulse at the detection timing. For example, when the AC power source is a single-phase three-wire 200 V / 60 Hz commercial frequency power source, the zero volt pulse detection circuit 12 has one cycle of AC voltage from the AC power source (1 / (60 × 2) = about 16 Detect zero volt timing twice in milliseconds.

The zero volt pulse detection circuit 12 transmits a zero volt pulse to the control circuit 9 when the zero volt timing is detected. When detecting the zero volt pulse (YES in S7), the control circuit 9 adds 1 to the stored data immediately before the pulse number adding circuit 14 in the control circuit 9 (S8). For example, when the immediately preceding stored data is 0, 1 is set in the pulse number adding circuit 14 after the addition.

The input current detection circuit 13 detects an input current (power supply current) from an AC power source using a current transformer, converts the detected input current into a detection signal having a voltage level corresponding to the input current, and controls the control circuit. Output to 9. The control circuit 9 (microcomputer) converts the detection signal from the input current detection circuit 13 into a digital value of 0 to 255 digits according to the voltage level (analog value). As described above, since the maximum input power set value of the induction heating cooker in this embodiment is “5”, that is, the maximum set power is “1200 W”, the control circuit 9 is in a heating stop state (input power 0 W = input). The voltage level of the detection signal from the input current detection circuit 13 at current 0A) is converted to 0 digits, and the voltage level of the detection signal from the input current detection circuit 13 at the maximum set value “5” (input power 1200 W) is Convert to 255 digits. Further, in the input power from 0 W to 1200 W, when the input power is X and the voltage level of the detection signal from the input current detection circuit 13 is Y, the linearity is Y = 0.2125X. The relationship between the input power to the pan 3 and the voltage level Y is set (see FIG. 4).

After detecting the zero volt pulse, the control circuit 9 receives the detection signal from the input current detection circuit 13 and sets a value (digit) corresponding to the voltage level of the detection signal to the stored data immediately before the input current addition circuit 15. (S9). Here, when starting the heating operation, the operation is performed at an operating frequency far away from the resonance frequency of the resonance circuit (resonance frequency <operating frequency) to achieve a low power state (soft start control). When the input power at that time is set to 200 W, the voltage level of the detection signal from the input current detection circuit 13 is Y = 0.2125 × 200≈43 digits according to the above-described line format, and the immediately preceding stored data is 0. Therefore, 43 is set in the input current adding circuit 15.

The control circuit 9 adds a value corresponding to the voltage level of the detection signal from the input current detection circuit 13 to the storage data of the input current addition circuit 15, and then the storage data of the input current addition circuit 15 determines whether or not the energization time has been reached. It is determined whether or not (15120) has been reached (S10).

Hereinafter, a method for setting the period time reachability determination value of the stored data of the pulse number adding circuit 14 and the energization time reachability determining value of the stored data of the input current adding circuit 15 will be described. As described above, the set power corresponding to the input power set value “1” is 100 W, the set power corresponding to the input power set value “2” is 300 W, and the input power set values “1” and “2” The duty control operation is performed by setting the duty cycle time to 6 seconds with the set power (600 W) corresponding to the input power set value “3”. In short, for example, when the input power set value is “1”, the control is performed such that the average power is set to 100 W by setting the input power to 600 W, energizing for 1 second, and stopping energization for 5 seconds. . In other words, the average power every 6 seconds is exactly the same as the average power when operated continuously at an input power of 100 W (the average power under duty control is 600 × 1/6 = 100 W, The average power is 100 × 6/6 = 100 W.)

The cycle time reachability determination value of the stored data of the pulse number adding circuit 14 is set to a value corresponding to the duty cycle time (6 seconds) of repeated energization and deenergization. Specifically, the period time reachability determination value of the stored data of the pulse number adding circuit 14 is equal to the number of occurrences of zero volt timing in 6 seconds, and is set to 2 × 60 Hz × 6 seconds = 720 times. Further, the energization time reachability determination value of the stored data of the input current adding circuit 15 corresponds to the (energization) time of the switching element 4, and is the set power corresponding to the input power set value, and only the above-described repetitive duty cycle time. It is set to the value of the stored data of the input current adding circuit 15 when energized continuously. Specifically, as described above, since the control circuit 9 performs the addition process to the stored data of the input current adding circuit 15 after detecting the zero volt pulse, the addition process to the stored data of the input current adding circuit 15 in 6 seconds is performed. The total number of times is equal to the number of occurrences of zero volt timing in 6 seconds, which is 2 times × 60 Hz × 6 seconds = 720 times. When the input power is 100 W, the reception voltage level Y of the detection signal from the input current detection circuit 13 is Y = 0.2125 × 100≈21 digits, and the input power is set to 100 W and is continuously operated for 6 seconds. In this case, the result of adding the stored data of the input current adding circuit 15 is 21 × 720 = 15120 digits. Therefore, even when duty control is performed with the input power set to 600 W, if the addition result of the stored data of the input current adder circuit 15 when 6 seconds have elapsed from the start of energization is 15120 digits, the average power is 100 W. Become. Accordingly, when the input power set value is “1”, 15120 is set as the energization time reachability determination value of the stored data of the input current adding circuit 15. Also in the case of the input power set value “2”, 45360 is set as the energization time reachability determination value of the stored data of the input current adding circuit 15 as in the case of the input power set value “1” (see FIG. 3). ).

In FIG. 2, the control circuit 9 determines whether or not the data stored in the input current adding circuit 15 has reached the energization time reachability determination value (15120) (S10), and if it has reached the energization time reachability determination value. If not (NO in S10), the energized state is continued according to the flowchart of FIG. 2, while if the energization time reachability determination value is reached (YES in S10), the energized state is shifted to the stopped state, that is, the switching element is driven. A stop signal is transmitted to the circuit 10 to stop the switching element 4, and the heating operation to the pan 3 is stopped (S11).

When the zero volt pulse detection circuit 12 detects the zero volt timing after stopping the heating operation, a zero volt pulse is transmitted from the zero volt pulse detection circuit 12 to the control circuit 9. When detecting the zero volt pulse (YES in S12), the control circuit 9 adds 1 to the stored data immediately before the pulse number adding circuit 14 (S13). After the addition to the stored data of the pulse number adding circuit 14, the control circuit 9 determines whether or not the stored data of the pulse number adding circuit 14 has reached the period time reachability determination value (720) (S14). The period time reachability determination value of the stored data of the pulse number adding circuit 14 is set to a value corresponding to 6 seconds, which is the period time of the duty control. As described above, the number of occurrences of zero volt timing in 6 seconds is 2 times × 60 Hz × 6 seconds = 720 times, and the stored data of the pulse number adding circuit 14 is incremented by 1 each time the zero volt timing is detected. Therefore, the addition result for 6 seconds is 720. Therefore, the period time reachability determination value of the stored data of the pulse number adding circuit 14 is set to 720. The control circuit 9 determines whether or not the data stored in the pulse number adding circuit 14 has reached the cycle time arrival determination value, and if it has not reached the cycle time arrival determination value (NO in S14), is shown in FIG. The stop state is continued according to the flowchart. On the other hand, if the stored data of the pulse number adding circuit 14 has reached the cycle time reachability determination value (YES in S14), the stored data of the pulse number adding circuit 14 and the input current adding circuit 15 are reset to 0. (Initial value 0 is set in S2 and S3), transition from the stopped state to the energized state, that is, a drive signal is transmitted to the switching element drive circuit 10 to switch the switching element 4 at a predetermined switching cycle sufficiently shorter than the duty cycle It drives, it transfers to an energization state and the heating operation | movement to the pan 3 is started (S6). Hereinafter, the series of operations (S2 to S14) described so far are repeated until the end of the heating operation is selected using the input power setting means 16.

Therefore, according to the process of FIG. 2, when the control circuit 9 controls the switching element 4 to repeat the energization state and the stop state at a predetermined duty cycle, the input current detected by the input current detection circuit 13 is determined. Integration is performed in each duty cycle period, and the average value of the input current after integration in each duty cycle period is set to a value set in advance so as to correspond to the input power setting value selected using the input power setting means 16. Thus, the energization time (corresponding to the energization time reachability determination value) of the switching element 4 is controlled.

FIG. 5 is a graph showing the time change of the input power during duty control in Embodiment 1 of the present invention, and shows the time change of the input power when the heating operation control according to the flowchart of FIG. 2 is performed. As shown in FIG. 5, according to the present embodiment, the length of the period from when the stored data of the pulse number adding circuit 14 and the input current adding circuit 15 is reset to zero until the input power becomes 600 W Regardless, the integrated input power (area A in FIG. 5) within the duty control period (6 seconds) when the input power set value is “1” corresponds to the input power set value “1”. It is equal to the integrated input power (area B in FIG. 5) when the set power (100 W) is continuously energized for the duty control cycle time. That is, the average input power when the input power set value is “1” is equal to the average input power when the power is continuously energized with the set power of 100 W.

As described above, in the present embodiment, together with the rectifying element 6 that converts AC power from an AC power source into DC power, the heating coil 1 that generates a high-frequency magnetic field and heats the pan 3, and the heating coil 1 A resonance capacitor 2 constituting a resonance circuit, a switching element 4 connected to the resonance circuit to generate a resonance current, an input current detection circuit 13 for detecting an input current to the resonance circuit, and a detection result by the input current detection circuit 13 The input current adding circuit 15 is configured to add, the control circuit 9 for arbitrarily changing the ON time of the switching element 4 to output predetermined power, and the input power setting means 16. Here, the control circuit 9 continuously heats the pan 3 when the input power set value set by the input power setting means 16 is greater than or equal to a predetermined value, while when the input power set value is less than the predetermined value. Performs an intermittent operation in which the heating operation and the stop are repeated at a predetermined duty cycle, and in the intermittent operation, the stored data of the addition result by the input current adding circuit 15 is set to a predetermined energization time reachability determination value for each input power setting value. When it reaches, the state is changed from the heating operation to the stop.

In the present embodiment, the duty control when the input power set value is less than a predetermined value (3 in the present embodiment) is based on the data stored in the pulse number adding circuit 14 and the duty cycle time is 6 seconds. Done. Further, switching from the energized state to the stopped state at the time of duty control is performed by a predetermined energization corresponding to the integrated current when the stored data of the input current adding circuit 15 is energized for 6 seconds with the set power corresponding to the input power set value. This is performed when the time reachability determination value is reached. For this reason, even if there is a difference in the average power during the required time from the start of energization until the input power reaches the set power, the energization time can be varied according to the load. Therefore, the difference between the average input power and the set power can be reduced as compared with the prior art regardless of the load.

In the present embodiment, the input power set value has five stages from “1” to “5”, the set power corresponding to the input power set value “1” is 100 W, and the input power set value “2”. ”Is 300 W, the set power corresponding to the input power set value“ 3 ”is 600 W, the set power corresponding to the input power set value“ 4 ”is 900 W, and the input power set value“ The set power corresponding to “5” was 1200 W. Further, the control circuit 9 performs continuous operation by frequency control in the input power set value range from “3” to “5”, and in the input power set value range of “1” and “2”, the input power set value “ Although the duty control operation was performed with the set power (600 W) corresponding to “3” and the duty cycle time set to 6 seconds, the present invention is not limited to this. Needless to say, the same effects as those of the present embodiment can be obtained without being limited to the number of steps of the input power set value and the set power corresponding thereto.

In the present embodiment, in the input power set value range of “1” and “2”, the duty cycle time is set to 6 seconds with the set power (600 W) corresponding to the input power set value “3”. The number of pulses for performing duty control operation, setting the energization time reachability determination value of the stored data of the input current adding circuit 15 for determining switching from the energized state to the stopped state to 15120, and detecting the cycle time of 6 seconds Although the period time reachability determination value of the stored data of the adder circuit 14 is set to 720, the present invention is not limited to this. Needless to say, the same effect as the present embodiment can be obtained without being limited to the energization time reachability determination value and the cycle time reachability determination value described above.

In the present embodiment, continuous operation is performed by frequency control in the input power setting value range of setting values “3” to “5”. However, the input power can be changed by changing the conduction ratio while the operating frequency is fixed. It goes without saying that the same effect as in the present embodiment can be obtained even when the conduction ratio control for controlling the above is performed.

(Embodiment 2)
FIG. 6 is a circuit diagram showing a configuration of an induction heating cooker according to Embodiment 2 of the present invention.

6, the induction heating cooker according to the present embodiment includes a heating coil 1, a resonant capacitor 2, a switching element 4, a flyhole diode 5, a rectifying element 6, a choke coil 7, and a smoothing capacitor 8. A control circuit 9, which is a microcomputer, a switching element drive circuit 10, a power supply circuit 11, a zero volt pulse detection circuit 12, an input current detection circuit 13, an input power setting means 16, and a resonance voltage detection circuit 17. It is configured with. The control circuit 9 includes a pulse number adding circuit 14, an input current adding circuit 15, and a pan material determining circuit 18.

The heating coil 1 and the resonance capacitor 2 connected in parallel to the heating coil 1 constitute a resonance circuit. The pan 3 as a load is disposed in the vicinity of the heating coil 1. The switching element 4 is directly connected to the resonance circuit, and supplies a high-frequency current to the resonance circuit together with the flywheel diode 5 connected in parallel to the switching element 4. The power rectified by the rectifying element 6 that rectifies the AC power from the AC power supply is smoothed by a smoothing circuit including the choke coil 7 and the smoothing capacitor 8 and supplied to the resonance circuit and the switching element 4. Here, the rectifier element 6, the choke coil 7, and the smoothing capacitor 8 constitute a rectifier circuit. Further, the control circuit 9 controls the entire induction heating cooker, and the switching element driving circuit 10 drives the switching element 4 at a high speed according to a command from the control circuit 9. Furthermore, the power supply circuit 11 supplies a DC stabilized power supply to the entire induction heating cooker. The zero volt pulse detection circuit 12 detects the zero volt timing of the AC voltage from the AC power supply, generates a zero volt pulse at the detection timing, and outputs the zero volt pulse to the pulse number adding circuit 14. The input current detection circuit 13 uses a current transformer to detect an input current input to the resonance circuit from the AC power supply via the rectifier circuit, and inputs a detection signal having a voltage level corresponding to the detected input current. It outputs to the current addition circuit 15 and the pan material determination circuit 18. Further, the pulse number adding circuit 14 counts the zero volt pulse from the zero volt pulse detecting circuit 12, and stores data indicating the count result as stored data. Further, the input current adding circuit 15 adds (accumulates) the input current detected by the input current detecting circuit 13 by accumulating values corresponding to the voltage levels of the detection signals from the input current detecting circuit 13, and integrates them. Data indicating the result is stored as stored data. The current detected by the input current detection circuit 13 corresponds to the input power, and the stored data of the input current integration circuit 15 corresponds to the integration power. Further, the resonance voltage detection circuit 17 detects the resonance voltage generated in the resonance capacitor, and the pot material determination circuit 18 uses the detection results of the input current detection circuit 13 and the resonance voltage detection circuit 17 to determine the material of the pot 3. Determine. The input current detection circuit 13, the resonance voltage detection circuit 17, and the pot material determination circuit 18 constitute a pot material determination unit that determines the material of the pot 3. The user operates the input power setting means 16 to select and set one input power setting value from among a plurality of input power setting values to the resonance circuit.

The operation and action of the induction heating cooker configured as described above will be described below. Note that the difference between the induction heating cooker according to the present embodiment and the induction heating cooker according to the prior art described in Patent Document 1 described with reference to FIG. 15 is set by the input power setting means 16. The control method in the case where the set input power value is less than the predetermined value, that is, the heating operation and the stop of the pan 3 are repeated at a predetermined duty cycle (that is, the switching element 4 is switched at a predetermined switching cycle sufficiently shorter than the duty cycle). The energization state for driving and the stop state for turning off the switching element 4 are repeated at a predetermined duty cycle.) Only the control method by duty control (intermittent operation) is used. In other cases, for example, when the input power set value set by the input power setting means 16 is a predetermined value or more, and the control method during the heating operation during duty control is the same as that of the induction heating cooker according to the prior art. is there. Specifically, using a voltage resonance type inverter, the pan 3 is induction-heated by eddy current loss generated in the pan 3 placed on the heating coil 1 by a high-frequency magnetic field generated in the heating coil 1. Further, the power control method used is a frequency at which the current flowing through the heating coil 1 is changed according to the value of the time (on time) when the switching element 4 is turned on, and the high frequency current applied to the pan 3 is controlled to vary the power. Control. Furthermore, the determination method of the input power set value when the control method is switched between frequency control and duty control is the same as the determination method according to the prior art. Specifically, for the purpose of preventing the occurrence of a significant increase in the on-loss of the switching element 4 in the low power state, based on the minimum input power that can avoid the destruction of the switching element 4 by the cooling configuration, The range of the input power set value for frequency control is determined.

Furthermore, the pot material determination circuit 18 determines the material of the pot 3 based on the detection results of the input current detection circuit 13 and the resonance voltage detection circuit 17 using a known technique. Specifically, the pan material determination circuit 18 uses, for example, that the input current detected by the input current detection circuit 13 and the resonance voltage detected by the resonance voltage detection circuit 17 differ greatly depending on the material of the pan 3. Then, it is determined whether the material of the pan 3 is iron or nonmagnetic stainless steel. Hereinafter, detailed description about the same structure, operation | movement, and setting method as the induction heating cooking appliance which concerns on a prior art is abbreviate | omitted, and only a difference with the induction heating cooking appliance which concerns on a prior art is demonstrated.

A control method when the input power set value set by the input power setting means 16 is less than a predetermined value will be described with reference to FIGS. 7A, 7B, 8 and 9. FIG. 7A and 7B are flowcharts of the duty control process in the second embodiment of the present invention when the input power set value is set to 1. FIG. 8 is a table showing the relationship between the input power set value, the set power, and the power control method according to Embodiment 2 of the present invention. FIG. 9 is a graph showing the relationship between the input power to the pan 3 and the voltage level Y of the detection signal from the input current detection circuit 13 in Embodiment 2 of the present invention.

According to the induction heating cooker according to the second embodiment of the present invention, the user uses the input power setting means 16 to select among the input power setting values in five stages from the input power setting values “1” to “5”. Select and set the desired input power setpoint. Here, as shown in FIG. 3, the set power corresponding to the input power set value “1” is 100 W, the set power corresponding to the input power set value “2” is 300 W, and the input power set value “3”. Is set to 600 W, the set power corresponding to the input power set value “4” is 900 W, and the set power corresponding to the input power set value “5” is 1200 W. Further, the control circuit 9 performs continuous operation by frequency control in the input power set value range from “3” to “5”, and in the input power set value range of “1” and “2”, the input power set value “ With the set power (600 W) corresponding to “3”, the duty cycle time is set to 6 seconds and the duty control operation is performed.

7A, when the input power setting value is set to “1” by the input power setting means 16, the control circuit 9 receives a signal including the input power setting value “1” from the input power setting means 16 (S1). ). In response to this, the control circuit 9 first resets the stored data of the pulse number adding circuit 14 and the input current adding circuit 15 in the control circuit 9 to 0 (in S2 and S3, the initial value 0 is set). set).

Next, the control circuit 9 sets 720 to the period time reachability determination value of the stored data of the pulse number adding circuit 14 (S4). A method for setting the period time reachability determination value will be described later.

Next, the control circuit 9 receives the detection signal from the input current detection circuit 13 and the detection signal from the resonance voltage detection circuit 17, and determines the material of the pot 3 by the pot material determination circuit 18 in the control circuit 9. (S21), the energization time reachability determination value of the stored data of the input current adding circuit 15 is set according to the determination result (S22 and S32).

Hereinafter, a method for setting the period time reachability determination value and the energization time reachability determination value will be described.

The input current detection circuit 13 detects an input current (power supply current) from an AC power supply using a current transformer, converts the detected input current into a voltage corresponding to the input current, and peaks the peak voltage of the voltage. A detection signal detected by the hold circuit and having a voltage level as a detection result is output to the control circuit 9. The control circuit 9 (microcomputer) converts the detection signal from the input current detection circuit 13 into a digital value of 0 to 255 digits according to the voltage level (analog value). As described above, the maximum input power set value of the induction heating cooker according to the embodiment of the present invention is “5”, that is, the maximum set power is “1200 W”. Hereinafter, when the iron enamel pan is called the enamel pan, the voltage level of the detection signal from the input current detection circuit 13 in the heating stopped state (input power 0 W = input current 0 A) is 0 digit. And the voltage level of the detection signal from the input current detection circuit 13 at the maximum set value “5” (input power 1200 W) is converted into 255 digits. Further, in the input power from 0 W to 1200 W, when the input power is X and the voltage level of the detection signal from the input current detection circuit 13 is Y, the linearity is Y = 0.2125X. The relationship between the input power to the pan 3 and the voltage level Y is set (see FIG. 9).

The set power corresponding to the input power set value “1” is 100 W, the set power corresponding to the input power set value “2” is 300 W, and the input power set values “1” and “2” The duty control operation is performed by setting the duty cycle time to 6 seconds with the set power (600 W) corresponding to the value “3”. In short, for example, when the input power set value is “1”, the control is performed such that the average power is set to 100 W by setting the input power to 600 W, energizing for 1 second, and stopping energization for 5 seconds. . In other words, the average power every 6 seconds is exactly the same as the average power when operated continuously at an input power of 100 W (the average power under duty control is 600 × 1/6 = 100 W, The average power is 100 × 6/6 = 100 W.) As will be described later, since the control circuit 9 performs the addition process to the storage data of the input current addition circuit 15 after detecting the zero volt pulse, the total number of addition processes to the storage data of the input current addition circuit 15 in 6 seconds is: Equivalent to the number of occurrences of zero volt timing in 6 seconds.

Here, the zero volt pulse detection circuit 12 detects the zero volt timing of the alternating voltage from the alternating current power source, that is, the inversion timing of the positive / negative voltage, and generates the zero volt pulse at the detection timing. For example, when the AC power supply is a single-phase three-wire 200 V / 60 Hz commercial frequency power supply, the zero volt timing is set in one cycle of AC voltage from the AC power supply (1 / (60 × 2) = about 16 milliseconds). Detect twice. Therefore, the number of occurrences of zero volt timing in 6 seconds is 2 times × 60 Hz × 6 seconds = 720 times.

When the enamel pan is heated with the input power set to 100 W, the voltage level Y of the detection signal from the input current detection circuit 13 is Y = 0.2125 × 100≈21 digits, and the input power is set to 100 W. The result of adding the stored data of the input current adding circuit 15 when continuously operating for 6 seconds is 21 × 720 = 15120 digits. Therefore, even when duty control is performed with the input power set to 600 W, the average power is 100 W if the stored data of the input current addition circuit 15 when 6 seconds have elapsed from the start of energization is 15120 digits. Therefore, when the input power set value is set to “1” and the material of the pan 3 is determined to be iron, 15120 is set as the energization time reachability determination value of the stored data of the input current adding circuit 15 (S22). ). In the case of the input power set value “2”, 45360 is set as the energization time reachability determination value of the stored data of the input current adding circuit 15 as in the case of the input power set value “1” (FIG. 8). reference.).

However, the input power is originally obtained based on the effective value and phase of the input current and the effective value and phase of the input voltage. Even if the maximum value of the input current is the same, the effective value of the input current is different. In some cases, the input power will not be the same. For example, a nonmagnetic stainless steel (nonmagnetic SUS (Steel Use Stainless)) pan (hereinafter referred to as a nonmagnetic stainless steel pan), which is a typical nonmagnetic material pan, is set to “3”. When set and heated so that the voltage level of the detection signal from the input current detection circuit 13 is 128 digits, the actual input power is 640 W, and the set power 600 W corresponding to the input power set value “3” 1.06 times as much power is input (see FIG. 9). Accordingly, as shown in FIG. 9, the relationship between the input power to the pan 3 represented by Y = 0.2125X in the iron enamel pan and the voltage level Y of the detection signal from the input current detection circuit 13. Is represented by Y = 0.2X in a non-magnetic stainless steel pan (0.2≈0.2125 / 1.06).

On the other hand, when the input power is set to 600 W and the enamel pan is heated, the reception voltage level of the detection signal from the input current detection circuit 13 by the control circuit 9 is Y = 0.2125 × 600≈127 digits, The energization time is 6 × (15120/127) /720≈0.99 seconds for a time of 6 seconds. When heating a non-magnetic stainless steel pan, using the energization time reachability determination value of the stored data of the input current addition circuit 15 made of iron is equivalent to energizing the energization time when heating the enamel pan. The average power is 640 × 0.99 / 6≈106 W, and a difference from the set power (100 W) occurs. In order to prevent this, the energization time reachability determination value may be changed between the case of the nonmagnetic stainless steel pan and the case of the enamel pan. When the non-magnetic stainless steel pan is heated with the input power set to 100 W, the voltage level Y of the detection signal from the input current detection circuit 13 is Y = 0.2 × 100≈20 digits, so the input power is set to 100 W. Then, the result of adding the stored data of the input current adding circuit 15 when continuously operating for 6 seconds is 20 × 720 = 14400 digits. Therefore, when the input power set value is set to “1” and the material of the pan 3 is determined to be nonmagnetic stainless steel, 14400 is set as the energization time reachability determination value (S32). In this case, the average power is 640 × (14400/127) / 720≈101 W, and the difference between the average input power and the set power (100 W) can be substantially eliminated. In the case of the input power set value “2”, 43200 is set as the energization time reachability determination value of the stored data of the input current adding circuit 15 as in the case of the input power set value “1” (FIG. 8). reference.).

Next, when the zero volt pulse detection circuit 12 detects the zero volt timing, it transmits a zero volt pulse to the control circuit 9. When detecting the zero volt pulse (YES in S23 or S33), the control circuit 9 adds 1 to the stored data immediately before the pulse number adding circuit 14 in the control circuit 9 (S24 and S34). For example, when the immediately preceding stored data is 0, 1 is set in the pulse number adding circuit 14 after the addition.

After detecting the zero volt pulse, the control circuit 9 receives the detection signal from the input current detection circuit 13 and sets a value (digit) corresponding to the voltage level of the detection signal to the stored data immediately before the input current addition circuit 15. Are added (S25 and S35). Here, when starting the heating operation, the operation is performed at an operating frequency far away from the resonance frequency of the resonance circuit (resonance frequency <operating frequency) to achieve a low power state (soft start control). When the input power at that time is set to 200 W, the voltage level of the detection signal from the input current detection circuit 13 is Y = 0.2125 × 200≈43 digits according to the above-described line format, and the immediately preceding stored data is 0. Therefore, 43 is set in the input current adding circuit 15.

Next, the control circuit 9 determines that the stored data of the input current adding circuit 15 is the energization time reachability determination value (15120 when the material of the pan 3 is iron, and 14400 when the material of the pan 3 is nonmagnetic stainless steel. (S26 and S36). If the energization time reachability determination value has not been reached, the energization state is continued according to the flowchart of FIG. 7A, while the energization time arrival determination value is reached. If it has reached, it shifts from the energized state to the stopped state, that is, a stop signal is transmitted to the switching element drive circuit 10 to stop the switching element 4, and the heating operation to the pan 3 is stopped (S11).

When the zero volt pulse detection circuit 12 detects the zero volt timing after stopping the heating operation, a zero volt pulse is transmitted from the zero volt pulse detection circuit 12 to the control circuit 9. When detecting the zero volt pulse (YES in S12), the control circuit 9 adds 1 to the stored data immediately before the pulse number adding circuit 14 (S13). After the addition to the stored data of the pulse number adding circuit 14, the control circuit 9 determines whether or not the stored data of the pulse number adding circuit 14 has reached the period time reachability determination value (720) (S14). The period time reachability determination value of the stored data of the pulse number adding circuit 14 is set to a value corresponding to 6 seconds, which is the period time of the duty control. As described above, the number of occurrences of zero volt timing in 6 seconds is 2 times × 60 Hz × 6 seconds = 720 times, and the stored data of the pulse number adding circuit 14 is incremented by 1 each time the zero volt timing is detected. Therefore, the addition result for 6 seconds is 720. Therefore, the period time reachability determination value of the stored data of the pulse number adding circuit 14 is set to 720. The control circuit 9 determines whether or not the data stored in the pulse number adding circuit 14 has reached the period time reachability determination value, and if it has not reached the period time reachability determination value (NO in S14), FIG. 7A. And the stop state is continued according to the flowchart of FIG. 7B. On the other hand, if the stored data of the pulse number adding circuit 14 has reached the cycle time reachability determination value (YES in S14), the stored data of the pulse number adding circuit 14 and the input current adding circuit 15 are reset to 0. (Initial value 0 is set in S2 and S3), transition from the stopped state to the energized state, that is, a drive signal is transmitted to the switching element drive circuit 10 to switch the switching element 4 at a predetermined switching cycle sufficiently shorter than the duty cycle It drives, it transfers to an energization state and the heating operation | movement to the pan 3 is started (S6). Hereinafter, the series of operations (S2 to S14) described so far are repeated until the end of the heating operation is selected using the input power setting means 16.

Therefore, according to the processing of FIGS. 7A and 7B, the control circuit 9 is detected by the input current detection circuit 13 when controlling the switching element 4 to repeat the energized state and the stopped state at a predetermined duty cycle. The input current is integrated in each duty cycle period, and the average value of the input current after the integration of each duty period is set in advance so as to correspond to the input power setting value selected using the input power setting means 16 The energization time of the switching element 4 (corresponding to the energization time reachability determination value) is controlled so as to be a value. Furthermore, the control circuit 9 controls the energization time of the switching element 4 according to the material of the pan 3.

When the heating operation control according to the flowcharts of FIGS. 7A and 7B is performed, the input power changes with time as shown in FIG. 5 as in the first embodiment.

As described above, in the present embodiment, the rectifying element 6 that converts AC power from an AC power source into DC power, the heating coil 1 that generates a high-frequency magnetic field and heats the pan 3, and the heating coil 1. And a resonance capacitor 2 constituting a resonance circuit, a switching element 4 connected to the resonance circuit to generate a resonance current, an input current detection circuit 13 for detecting an input current to the resonance circuit, and the resonance capacitor 2 From the resonance voltage detection circuit 17 that detects the generated resonance voltage, the input current addition circuit 15 that adds the detection results of the input current detection circuit 13, and the detection results of the input current detection circuit 13 and the resonance voltage detection circuit 17 The pot material determination circuit 18 which is a pot material determination means for determining the pot material, and the on-time of the switching element 4 to output predetermined power And a control circuit 9 to change, and and an input power setting means 16. Here, the control circuit 9 continuously heats the pan 3 when the input power set value set by the input power setting means 16 is a predetermined value or more, while the input power set value is less than the predetermined value. In this case, an intermittent operation is performed in which the heating operation and the stop are repeated at a predetermined duty cycle. In addition, in the intermittent operation, the storage data of the addition result by the input current addition circuit 15 is determined for each input power set value and the pan material determination circuit The state is changed from the heating operation to the stop when the energization time reachability determination value which is a different value depending on the determination result by 18 is reached.

In the present embodiment, the duty control when the input power set value is less than a predetermined value (3 in the present embodiment) is based on the data stored in the pulse number adding circuit 14 and the duty cycle time is 6 seconds. Do more. Further, switching from the energized state to the stopped state at the time of duty control is performed by a predetermined energization corresponding to the integrated current when the stored data of the input current adding circuit 15 is energized for 6 seconds with the set power corresponding to the input power set value. This is performed when the time reachability determination value is reached, and further, the arrival determination condition for the average power (energization time reachability determination value) is changed even with the same set power according to the material (type) of the load. Therefore, according to the present embodiment, the length of time required from the start of operation until the input current reaches the predetermined integrated input power for switching between the energized state and the stopped state from the start of energization is increased or decreased depending on the load. Even if there is a difference in the average power generated during the required time, or when the input power itself in the energized state varies depending on the power control method during continuous operation, the energization time can be varied according to the load. Can respond. For this reason, the difference between the average input power and the set power can be reduced as compared with the prior art regardless of the load.

In the present embodiment, in the input power set value range of “1” and “2”, the duty cycle time is set to 6 seconds with the set power (600 W) corresponding to the input power set value “3”. In the enamel pan (iron), the reachability determination value of the stored data of the input current adding circuit 15 for determining the switching from the energized state to the stopped state is set to 15120, and the nonmagnetic stainless steel pan (nonmagnetic (Made of stainless steel) was set to 14400. Furthermore, the reachability determination value of the stored data of the pulse number adding circuit 14 for detecting the cycle time of 6 seconds is set to 720. However, the present invention is not limited to this. Needless to say, the same effect as the present embodiment can be obtained without being limited to the energization time reachability determination value and the cycle time reachability determination value described above.

Moreover, in this Embodiment, although the pan material determination circuit 18 determined whether the material of the pan 3 is either two types of materials, iron and nonmagnetic stainless steel, this invention is not limited to this. . For example, in the case of an induction heating cooker capable of heating an aluminum pan, it may be further determined that it is aluminum, and the same effect as this embodiment can be obtained regardless of the determination contents of the pot material determination circuit 18. It goes without saying that it is possible.

(Embodiment 3)
FIG. 10 is a circuit diagram showing a configuration of an induction heating cooker according to Embodiment 3 of the present invention.

10, the induction heating cooker according to the present embodiment includes a heating coil 1, a resonant capacitor 2, a switching element 4, a flyhole diode 5, a rectifying element 6, a choke coil 7, and a smoothing capacitor 8. A control circuit 9, which is a microcomputer, a switching element drive circuit 10, a power supply circuit 11, a zero volt pulse detection circuit 12, an input current detection circuit 13, an input power setting means 16, and a resonance voltage detection circuit 17. It is configured with. The control circuit 9 includes a pulse number adding circuit 14 and a pan material determining circuit 18.

The heating coil 1 and the resonance capacitor 2 connected in parallel to the heating coil 1 constitute a resonance circuit. The pan 3 as a load is disposed in the vicinity of the heating coil 1. The switching element 4 is connected in series to the resonance circuit, and supplies a high-frequency current to the resonance circuit together with the flywheel diode 5 connected in parallel to the switching element 4. The power rectified by the rectifying element 6 that rectifies the AC power from the AC power supply is smoothed by a smoothing circuit including the choke coil 7 and the smoothing capacitor 8 and supplied to the resonance circuit and the switching element 4. Here, the rectifier element 6, the choke coil 7, and the smoothing capacitor 8 constitute a rectifier circuit. Further, the control circuit 9 controls the entire induction heating cooker, and the switching element driving circuit 10 drives the switching element 4 at a high speed according to a command from the control circuit 9. Furthermore, the power supply circuit 11 supplies a DC stabilized power supply to the entire induction heating cooker. The zero volt pulse detection circuit 12 detects the zero volt timing of the AC voltage from the AC power supply, generates a zero volt pulse at the detection timing, and outputs the zero volt pulse to the pulse number adding circuit 14. The input current detection circuit 13 uses a current transformer to detect an input current input to the resonance circuit from the AC power supply via the rectifier circuit, and generates a detection signal having a voltage level corresponding to the detected input current. This is output to the material judgment circuit 18. Further, the pulse number adding circuit 14 counts the zero volt pulse from the zero volt pulse detecting circuit 12, and stores data indicating the count result as stored data. Further, the resonance voltage detection circuit 17 detects the resonance voltage generated in the resonance capacitor, and the pot material determination circuit 18 uses the detection results of the input current detection circuit 13 and the resonance voltage detection circuit 17 to determine the material of the pot 3. Determine. The input current detection circuit 13, the resonance voltage detection circuit 17, and the pot material determination circuit 18 constitute a pot material determination unit that determines the material of the pot 3. The user operates the input power setting means 16 to select and set one input power setting value from among a plurality of input power setting values to the resonance circuit.

A control method when the input power set value set by the input power setting means 16 is less than a predetermined value will be described with reference to FIGS. 11A, 11B, 12 and 13. 11A and 11B are flowcharts of the duty control process in the third embodiment of the present invention when the input power set value is set to 1. FIG. 12 is a table showing the relationship between the input power set value, the set power, and the power control method according to Embodiment 3 of the present invention. FIG. 13 is a graph showing the relationship between the input power to the pan 3 and the voltage level Y of the detection signal from the input current detection circuit 13 in Embodiment 3 of the present invention.

According to the induction heating cooker according to the third embodiment of the present invention, the user uses the input power setting means 16 to select among the input power setting values in five stages from the input power setting values “1” to “5”. Select and set the desired input power setpoint. Here, as shown in FIG. 3, the set power corresponding to the input power set value “1” is 100 W, the set power corresponding to the input power set value “2” is 300 W, and the input power set value “3”. Is set to 600 W, the set power corresponding to the input power set value “4” is 900 W, and the set power corresponding to the input power set value “5” is 1200 W. Further, the control circuit 9 performs continuous operation by frequency control in the input power set value range from “3” to “5”, and in the input power set value range of “1” and “2”, the input power set value “ With the set power (600 W) corresponding to “3”, the duty cycle time is set to 6 seconds and the duty control operation is performed.

11A, when the input power setting value is set to “1” by the input power setting means 16 (S1), the control circuit 9 receives a signal including the input power setting value “1” from the input power setting means 16. To do. In response to this, the control circuit 9 first resets the stored data of the pulse number adding circuit 14 and the input current adding circuit 15 in the control circuit 9 to 0 (sets the initial value 0 in S2). .

Next, the control circuit 9 receives the detection signal from the input current detection circuit 13 and the detection signal from the resonance voltage detection circuit 17, and determines the material of the pot 3 by the pot material determination circuit 18 in the control circuit 9. (S21) The energization time reachability determination value of the stored data of the pulse number adding circuit 14 is set according to the determination result (S41 and S43).

The input current detection circuit 13 detects an input current (power supply current) from an AC power supply using a current transformer, converts the detected input current into a voltage corresponding to the input current, and peaks the peak voltage of the voltage. A detection signal detected by the hold circuit and having a voltage level as a detection result is output to the control circuit 9. The control circuit 9 (microcomputer) converts the detection signal from the input current detection circuit 13 into a digital value of 0 to 255 digits according to the voltage level (analog value). As described above, the maximum input power set value of the induction heating cooker according to the embodiment of the present invention is “5”, that is, the maximum set power is “1200 W”. Hereinafter, when the iron enamel pan is called the enamel pan, the voltage level of the detection signal from the input current detection circuit 13 in the heating stopped state (input power 0 W = input current 0 A) is 0 digit. And the voltage level of the detection signal from the input current detection circuit 13 at the maximum set value “5” (input power 1200 W) is converted into 255 digits. Further, in the input power from 0 W to 1200 W, when the input power is X and the voltage level of the detection signal from the input current detection circuit 13 is Y, the linearity is Y = 0.2125X. The relationship between the input power to the pan 3 and the voltage level Y is set (see FIG. 13).

However, the input power is originally obtained based on the effective value and phase of the input current and the effective value and phase of the input voltage. Even if the maximum value of the input current is the same, the effective value of the input current is different. In some cases, the input power will not be the same. For example, when the nonmagnetic stainless steel pan is heated so that the input power setting value is set to “3” and the voltage level of the detection signal from the input current detection circuit 13 is 128 digits, the actual input power Becomes 640 W, and 1.06 times the set power 600 W corresponding to the input power set value “3” is input (see FIG. 9). Accordingly, as shown in FIG. 9, the relationship between the input power to the pan 3 represented by Y = 0.2125X in the iron enamel pan and the voltage level Y of the detection signal from the input current detection circuit 13. Is represented by Y = 0.2X in a non-magnetic stainless steel pan (0.2≈0.2125 / 1.06). The same applies to the case of duty control.

As described above, the set power corresponding to the input power set value “1” is 100 W, the set power corresponding to the input power set value “2” is 300 W, and the input power set values “1” and “2” The duty control operation is performed by setting the duty cycle time to 6 seconds with the set power (600 W) corresponding to the input power set value “3”. In short, for example, when the input power set value is “1”, the control is performed such that the average power is set to 100 W by setting the input power to 600 W, energizing for 1 second, and stopping energization for 5 seconds. .

At this time, in the case of a non-magnetic stainless steel pan, since duty control is actually performed with an input power of 640 W, the average power is 640 / 6≈107 W, and there is a difference between the actual input power and the set power. Will occur. In order to prevent this, the energization time reachability determination value may be changed between the case of the nonmagnetic stainless steel pan and the case of the enamel pan. Specifically, the energization time in the case of a non-magnetic stainless steel pan is a time considering the input power ratio of 1.06 with respect to the optimal energization time of 1 second in the case of an enamel pan. .94 seconds should be set.

Here, the zero volt pulse detection circuit 12 detects the zero volt timing of the alternating voltage from the alternating current power source, that is, the inversion timing of the positive / negative voltage, and generates the zero volt pulse at the detection timing. For example, when the AC power supply is a single-phase three-wire 200 V / 60 Hz commercial frequency power supply, the zero volt timing is set in one cycle of AC voltage from the AC power supply (1 / (60 × 2) = about 16 milliseconds). Detect twice. Therefore, the number of occurrences of zero volt timing per second is 2 × 60 Hz × 1 second = 120 times, and the stored data of the pulse number adding circuit 14 is incremented by 1 each time the zero volt timing is detected. The addition result for one second is 120. Similarly, the addition result in 0.94 seconds is 2 times × 60 Hz × 0.94 seconds = 113 times. Therefore, when the input power set value is “1”, when the pot material determination circuit 18 determines that the material of the pot 3 is iron, the energization time reachability determination value of the stored data of the pulse number adding circuit 14 is determined. 120 is set (S41), and if it is determined to be nonmagnetic stainless steel, 113 is set to the energization time reachability determination value of the stored data of the pulse number adding circuit 14 (S43). When the input power set value is “2”, as in the case where the input power set value is “1”, when it is determined that the material of the pan 3 is iron, the stored data of the pulse number adding circuit 14 is stored. The energization time reachability determination value is set to 360, and if it is determined to be non-magnetic stainless steel, 338 is set to the energization time reachability determination value of the data stored in the pulse number adding circuit 14 (see FIG. 12). .

Next, the control circuit 9 determines that the stored data of the pulse number adding circuit 14 is an energization time reachability determination value (120 when the material of the pan 3 is iron and 113 when the material of the pan 3 is nonmagnetic stainless steel. 11) (S42 and S44). If the energization time reachability determination value has not been reached, the energization state is continued according to the flowchart of FIG. 11A, while the energization time reachability determination value is reached. If it has reached | attained, it will transfer to a stop state from an energized state, ie, a stop signal will be transmitted to the switching element drive circuit 10, the switching element 4 will be stopped, and the heating operation to the pan 3 will be stopped (S11).

When the zero volt pulse detection circuit 12 detects the zero volt timing after stopping the heating operation, a zero volt pulse is transmitted from the zero volt pulse detection circuit 12 to the control circuit 9. When detecting the zero volt pulse (YES in S12), the control circuit 9 adds 1 to the stored data immediately before the pulse number adding circuit 14 (S13). After the addition to the stored data of the pulse number adding circuit 14, the control circuit 9 determines whether or not the stored data of the pulse number adding circuit 14 has reached the period time reachability determination value (720) (S14). The period time reachability determination value of the stored data of the pulse number adding circuit 14 is set to a value corresponding to 6 seconds, which is the period time of the duty control. As described above, the number of occurrences of zero volt timing in 6 seconds is 2 times × 60 Hz × 6 seconds = 720 times, and the stored data of the pulse number adding circuit 14 is incremented by 1 each time the zero volt timing is detected. Therefore, the addition result for 6 seconds is 720. Therefore, the period time reachability determination value of the stored data of the pulse number adding circuit 14 is set to 720. The control circuit 9 determines whether or not the data stored in the pulse number adding circuit 14 has reached the period time reachability determination value (S14). If it has not reached the period time reachability determination value (NO in S14). ) The stop state is continued according to the flowcharts of FIGS. 7A and 7B. On the other hand, if the data stored in the pulse number adding circuit 14 has reached the cycle time reachability determination value (YES in S14), the stored data in the pulse number adding circuit 14 is reset to 0 (initial value 0 in S2). Set), the transition from the stop state to the energized state, that is, the drive signal is transmitted to the switching element drive circuit 10 to drive the switching element 4 at a predetermined switching cycle sufficiently shorter than the duty cycle, the transition to the energized state, The heating operation to the pan 3 is started (S6). Hereinafter, the series of operations (S2 to S14) described so far are repeated until the end of the heating operation is selected using the input power setting means 16.

Therefore, according to the processing of FIG. 11A and FIG. 11B, when the control circuit 9 controls the switching element 4 to repeat the energized state and the stopped state at a predetermined duty cycle, each duty is determined based on the material of the pan 3. The energization time of the switching element 4 (the energization time reachability determination value is determined in advance) so that the average value of the input power in the cycle period becomes a value corresponding to the input power setting value selected using the input power setting means 16. Corresponding).

FIG. 14 is a graph showing a time change of input power during duty control in the third embodiment of the present invention, and shows a time change of input power when the heating operation control according to the flowcharts of FIGS. 11A and 11B is performed. . As shown in FIG. 14, according to the present embodiment, the input power setting is performed regardless of the length of the period from when the stored data of the pulse number adding circuit 14 is reset to zero until the input power reaches 600 W. The integrated input power (area A in FIG. 14) within the duty control period (6 seconds) when the value is “1” is the duty at the set power (100 W) corresponding to the input power set value “1”. It is equal to the integrated input power (area B in FIG. 14) when energized continuously for the control cycle time. That is, the average input power when the input power set value is “1” is equal to the average input power when the power is continuously energized with the set power of 100 W.

As described above, in the present embodiment, together with the rectifying element 6 that converts AC power from an AC power source into DC power, the heating coil 1 that generates a high-frequency magnetic field and heats the pan 3, and the heating coil 1 A resonance capacitor 2 constituting a resonance circuit, a switching element 4 connected to the resonance circuit to generate a resonance current, an input current detection circuit 13 for detecting an input current to the resonance circuit, and a resonance voltage generated in the resonance capacitor 2 A resonance voltage detection circuit 17 for detecting the pot, a pan material determination circuit 18 for determining the pot material from the detection results of the input current detection circuit 13 and the resonance voltage detection circuit 17, and the switching element 4 being turned on to output predetermined power The control circuit 9 is formed by arbitrarily changing the time, and the input power setting means 16 is provided. Here, the control circuit 9 continuously heats the pan 3 when the input power set value set by the input power setting means 16 is greater than or equal to a predetermined value, while when the input power set value is less than the predetermined value. Performs an intermittent operation in which the heating operation and the stop are repeated at a time ratio according to the input power set value, and in the intermittent operation, the time ratio is changed at the same input power set value according to the determination result by the pan material determination circuit 18.

According to the present embodiment, depending on the material of the pan, the input power itself when performing the duty control operation changes, and there is a difference between the set power and the actual average input power. Compared to the conventional technology regardless of the load, the time ratio (ratio of energization time to duty cycle time) that can obtain the average input power equivalent to the set power can be set according to the material of the load. Thus, the difference between the average input power and the set power can be reduced.

In the present embodiment, in the present embodiment, in the input power set value range of “1” and “2”, the duty cycle time is set at the set power (600 W) corresponding to the input power set value “3”. Set to 6 seconds, perform duty control operation, set the energization time when the input power setting value is “1” to 1 second for enamel pan (iron material), and nonmagnetic stainless steel pan (nonmagnetic material) Then, in order to set to 0.94 seconds, the energization time reachability determination value of the stored data of the pulse number adding circuit 14 is set to 120 and 113, respectively. Furthermore, the reachability determination value of the stored data of the pulse number adding circuit 14 for detecting the cycle time of 6 seconds is set to 720. However, the present invention is not limited to this. Needless to say, the same effect as the present embodiment can be obtained without being limited to the energization time reachability determination value and the cycle time reachability determination value described above.

As described above, according to the induction heating cooker according to the present invention, when power control is performed by duty control, the energized state and the stopped state are alternately switched at a predetermined duty cycle, and the energized state is stopped. Is switched when the average value of the input current to the resonance circuit for each duty cycle period reaches a preset value corresponding to the input power setting value. It is possible to prevent the difference between the set power corresponding to the set value from becoming large depending on the load, and to suppress the variation in the cooking performance due to the load difference, thereby improving the usability. Therefore, the induction heating cooker according to the present invention can be applied not only to the induction heating cooker but also to all devices that perform induction heating and perform a duty control operation.

1 Heating coil 2 Resonant capacitor 3 Load (pan)
4 Switching element 5 Flywheel diode 6 Rectifier 7 Choke coil 8 Smoothing capacitor 9 Control circuit (microcomputer)
DESCRIPTION OF SYMBOLS 10 Switching element drive circuit 11 Power supply circuit 12 Zero volt pulse detection circuit 13 Input current detection circuit 14 Pulse frequency addition circuit 15 Input current addition circuit 16 Input power setting means 17 Resonance voltage detection circuit 18 Pot material judgment circuit

Claims

A resonance circuit comprising a heating coil for induction heating the pan, and a resonance capacitor connected in parallel to the heating coil;
A switching element connected in series to the resonant capacitor;
An input current detection circuit for detecting an input current input to the resonance circuit from an AC power supply via a rectifier circuit;
Input power setting means for selecting one input power setting value from a plurality of input power setting values to the resonant circuit;
In the induction heating cooker provided with a control circuit for controlling the switching element to repeat the energized state and the stopped state at a predetermined duty cycle,
The control circuit integrates the detected input current in each duty cycle period, and an average value of the input current after the integration of each duty cycle period corresponds to the selected input power setting value. An induction heating cooker characterized by controlling an energization time of the switching element so as to have a preset value.
It further comprises a pan material judging means for judging the material of the pan,
The induction heating cooker according to claim 1, wherein the control circuit controls an energization time of the switching element according to the determined material of the pan.
A resonance circuit comprising a heating coil for induction heating the pan, and a resonance capacitor connected in parallel to the heating coil;
A switching element connected in series to the resonant capacitor;
Input power setting means for selecting one input power setting value from a plurality of input power setting values to the resonant circuit;
A pot material determining means for determining the material of the pot;
In the induction heating cooker provided with a control circuit for controlling the switching element to repeat the energized state and the stopped state at a predetermined duty cycle,
The control circuit determines the switching based on the determined material of the pan so that an average value of input power in each duty cycle period is a value corresponding to the selected input power setting value. An induction heating cooker characterized in that the energization time of the element is set.