JPH0765943A - Electromagnetic cooking apparatus - Google Patents

Abstract

PURPOSE:To make certain sensing of an improper load in the condition with the input controlled constant from weak to strong flame by furnishing an inverter current sensing part, input current sensing part, frequency sensing part, and maximum sampling value sensing part. CONSTITUTION:An inverter current sensing circuit 19 senses the inverter current flowing through a heater coil 7, while an input current sensing circuit 20 senses the input current fed from AC mains 1. An AC mains frequency sensing circuit 27 senses the frequency of the AC mains 1, while a maximum sampling value sensing part 29 determines the max. value of at least either of the inverter current and input current in the half period of AC voltage on the basis of the frequency sensed by the frequency sensing circuit 27 and feeds the obtained max. value to a microcomputer 24 as a load sensing signal. According to this constitution, the max. value can be obtained at whichever phase the sampling takes place as long as the AC voltage is fed in an amount for half the period, so that it is possible to decrease the sampling time of load sensing signals to a great extent, and a continuous heating with constant input can be achieved even with a low input such as at the time of weak flame heating.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter type electromagnetic cooker, and more particularly to an electromagnetic cooker having a detecting means for detecting an unsuitable load such as an unloaded aluminum pan.

[0002]

2. Description of the Related Art Induction cookers are safe without fire and have excellent thermal efficiency, and are rapidly becoming popular for household use or business use. In such an electromagnetic cooker, if the load is not appropriate, there is a problem that the pan may float and the element parts of the electromagnetic cooker may be damaged, so it is essential to detect an improper load (no load, aluminum pan). It has become. In the conventional electromagnetic cooker, in the case of microcomputer control system,
The load detection is performed by the microcomputer based on the values necessary for load detection, that is, the input current detection signal, the inverter current detection signal, and the on-time signal of the switching element that are AD-converted and averaged. Thus, the AD conversion period is set long so that the average value of the load detection signal does not change even if the commercial power supply frequency changes. This will be described below with reference to the drawings.

FIG. 22 shows a circuit configuration of a conventional microcomputer-controlled electromagnetic cooker. In the figure, a DC power supply (AC / DC converter) 4 is configured by rectifying AC from an AC power supply (commercial power supply) 1 by a full-wave rectifier 2 and smoothing it by a smoothing capacitor 3. Two switching elements 8 and 9 are connected in series between both output terminals of the DC power source 4, and diodes 10 and 11 connected in parallel to the respective switching elements 8 and 9 in opposite directions and two switching elements. Heating coil 7 connected to the connection point of elements 8 and 9
And the resonance capacitors 5 and 6 connected to the heating coil 7 constitute a half-bridge type inverter circuit. Reference numeral 14 is a control circuit that controls on / off of the two switching elements 8 and 9, and includes a reference oscillator 16, an input setting circuit 23 that sets an input, sending an on-time signal V _on based on the setting input, and a load detection signal input. the microcomputer 24 performs load detection based on, PWM oscillator 17 for transmitting a pulse signal of the on time corresponding to the on-time signal V _on, compared with the oscillation signal of the reference oscillator 16 on-time signal V _on, on the basis of the pulse signal driving circuit 15 to turn on the two switching elements 8 and 9 alternately, the load input current detection circuit outputs a voltage V _in corresponding to the input current from the AC power source 1 detected by the current transformer 13 for detecting 20 , An inverter current detector that outputs a voltage V _inv corresponding to the inverter current flowing through the heating coil 7 of the inverter circuit detected by the current transformer 12. Intelligent circuit 19, V _on , V _in , V
An AD converter 21 that samples _inv at a constant interval for a certain period, a sampling value averaging unit 22 that obtains an average value of the sampled values and inputs it to the microcomputer 24, and when the microcomputer 24 detects an inappropriate load, issues a heating stop command. It is composed of an oscillation stop circuit 18 for sending to the PWM oscillator 17.

The operation of the conventional half-bridge type inverter type electromagnetic cooker configured as described above will be described. The two switching elements 8 and 9 are alternately turned on and off with respect to the DC power source 4. A high-frequency current, that is, an inverter current is supplied to the heating coil 7 and the resonance capacitors 5 and 6 of the inverter circuit to heat the load close to the heating coil 7. At this time, the control circuit 14 compares the reference oscillation signal of the constant frequency sent from the reference oscillator 16 by the PWM oscillator 17 with the on-time signal V _on output from the microcomputer 24 to set the on-time, and the drive circuit 15 The drive pulse having a constant frequency having the ON time set by is alternately sent to the two switching elements 8 and 9. In such an electromagnetic cooker of the half-bridge type inverter system, the input increases when the ON time of the switching elements 8 and 9 is increased, and the input can be continuously changed from zero.

Among the above heating operations, in the microcomputer-controlled electromagnetic cooker, the load is detected by the following method. First, in the AD converter 21, as shown in FIG.
As shown in FIG. 24, the input current detection signal V _in and the inverter current detection signal V _inv are fixed at a fixed interval (Δ
Sampling is performed at t), and these are averaged by the sampling value averaging unit 22. Similarly, the on-time signal is averaged.
Even if the commercial power frequency changes during the sampling period T ₁ ,
Further, it is set to 300 msec, which is long enough so that the average value becomes the same no matter which phase of the load detection signal the sampling starts. FIG. 25 is a diagram showing the relationship between the on-time and the input current detection signal average value V _in , but the characteristics differ between when the load is appropriate and when there is no load, and the load judgment line f as shown in FIG. _Since no load can be detected by ₁ (function related to on-time signal average value V _on ), f ₁ (V _on ) is calculated by the microcomputer after sampling and averaging, and this is compared with V _in The load is being detected. At the same time, FIG.
6 is a diagram showing the relationship between the on-time and the average value V _inv of the inverter current detection signal. The characteristics are different depending on whether the load is appropriate or the aluminum pot, and the load judgment line f ₂ as shown in the figure. Since the aluminum pot can be detected by (function related to ON time signal average value V _on ), f can be detected by the microcomputer.
₂ (V _on ) is calculated and compared with V _inv to detect the aluminum pot. If an unsuitable load is detected, the ON time is set to 0 to stop heating, and if an unsuitable load is detected, thereafter, inverter control such as constant input control is performed for a certain time T ₂ (5 msec). Sampling is started to detect the load again.

By the way, as can be seen from FIGS. 25 and 26, it is difficult to make a clear distinction between the proper load and the non-appropriate load when the on-time has a relationship which is similar to each other. What has been described so far is a case where constant input continuous heating is performed for a minimum on time (discrimination on time, indicated by T _up in the figure) capable of detecting an inappropriate load in both relationships.
When the ON time is less than T _up and continuous heating is performed, load detection is performed by the following method. That is, FIG. 27 and FIG.
As shown in 8, instantly increase the discrimination on-time T _up ,
Wait until the load detection signal is a steady state (T ₃ ~6ms
ec), then sampling and averaging are performed to detect an improper load (T ₁ = 300 msec). If an improper load is detected, the on-time is set to 0 and heating is stopped, and an improper load is detected. If it returns to the original on time. This operation is repeated with a fixed interval (T ₀ = 3 sec). As a result, continuous heating can be performed while detecting the load even when the on-time is short, but the ratio of the time T ₃ + T ₁ until the on-time is raised to T _up and the load is detected during the interval period T _0. Is not constant because it is large. FIG. 29 shows how the input fluctuates as the on-time changes in the case of an appropriate load, but even if the period T _{0 of} 100 W of input is long, the actual input will be 137 W on average. Since the sampling period T ₁ is fixed in the conventional load detection method, the interval period T ₀ can only be lengthened in order to bring the input close to a constant _value , but since the detection of an inappropriate load is delayed, it can be set longer. Can not.

[0007]

As described above, in the conventional microcomputer-controlled electromagnetic cooker, if the on-time is short, in other words, if the input is low, it is not possible to perform constant-input continuous heating. , It is not possible to realize an electromagnetic cooker capable of constant input control from low heat to high heat. In addition, the aluminum pan has a characteristic that repulsive force is generated between it and the heating coil when the input is increased, and when the pan is lightweight, AD
Since the conversion period is long, there is a problem that the pot may float or slip sideways.

[0008] Therefore, an object of the present invention is to provide an electromagnetic cooker which can reliably detect an improper load from a low heat to a high heat in a constant input control state and is safe.

[0009]

In order to solve the above-mentioned problems, the present invention provides, firstly, an AC / DC converter for rectifying an AC voltage from an AC power source to obtain a DC voltage, a switching element,
An inverter circuit configured to include a heating coil and a resonance capacitor, the switching element being periodically turned on and off to convert the direct current voltage to a high frequency and supply the heating voltage to the heating coil to heat a load, and a setting input. In an electromagnetic cooker having a microcomputer that performs load detection by inputting a load detection signal while setting the on-time of the switching element based on, an inverter current detection unit that detects an inverter current flowing in the heating coil, and the AC An input current detection unit that detects an input current from a power supply, a frequency detection unit that detects the frequency of the AC power supply, and the inverter current in a half cycle of the AC voltage based on the frequency detected by the frequency detection unit or The maximum value of at least one of the input currents is calculated and the maximum value is input to the microcomputer as a load detection signal. And summarized in that and a maximum sampling value detecting unit for.

Second, it comprises an AC / DC converter for rectifying an AC voltage from an AC power source to obtain a DC voltage, a switching element, a heating coil and a resonance capacitor, and the switching element is periodically turned on / off. An inverter circuit that converts the DC voltage into a high frequency and supplies it to the heating coil to heat a load, and sets the ON time of the switching element based on a setting input and also inputs a load detection signal to detect the load. In an electromagnetic cooker having a microcomputer for performing an inverter current detection unit that detects an inverter current flowing in the heating coil, an input current detection unit that detects an input current from the AC power supply, and a frequency of the AC power supply. Frequency detecting section, and the frequency in the half cycle of the AC voltage based on the frequency detected by the frequency detecting section. And summarized in that and a sampling value averaging unit for inputting the average value calculated at least one of the average value of over motor current or the input current to the microcomputer as a load detection signal.

Thirdly, an AC / DC converter for rectifying an AC voltage from an AC power source to obtain a DC voltage, a switching element, a heating coil and a resonance capacitor are included, and the switching element is periodically turned on / off. An inverter circuit that converts the DC voltage into a high frequency and supplies it to the heating coil to heat a load, and sets the ON time of the switching element based on a setting input and also inputs a load detection signal to detect the load. In an electromagnetic cooker having a microcomputer for performing an inverter current detection unit that detects an inverter current flowing in the heating coil, an input current detection unit that detects an input current from the AC power supply, and a frequency of the AC power supply. Frequency detector, a zero-cross detector that detects the zero voltage value of the AC voltage, and a detector that detects the frequency. The average value of at least one of the inverter current and the input current in a quarter cycle of the AC voltage from the zero voltage value is obtained based on the determined frequency and the average value is input to the microcomputer as a load detection signal. The gist is to have a sampling value averaging part.

[0012]

In the above structure, firstly, the relationship characteristic between the ON time of the switching element and the maximum value of the input current detection signal differs between the case where the load is proper and the case where there is no load, and the load judgment line is set. It is possible to detect no load. In addition, the relationship between the ON time and the maximum value of the inverter current detection signal is different between when the load is appropriate and when the aluminum pan is used, and it is possible to detect the aluminum pan by setting the load judgment line. . The maximum value of the input current signal or the inverter current signal, which is the load detection signal, corresponds to one cycle of each signal, that is, a half cycle of the AC voltage from the AC power supply (10 msec at 50 Hz, 8.3 mse at 60 Hz).
If there is c), it can be obtained by sampling from any phase. Therefore, the sampling time of the load detection signal can be significantly reduced. When continuous heating such as simmering fire is performed within the minimum on-time capable of non-appropriate load detection, the on-time is instantly determined after a certain interval period and increased to the on-time. Sampling. Since the sampling time is very short compared to the interval period, it is possible to realize continuous heating with a constant input even when the input is low, such as simmering heating. This makes it possible to reliably detect an improper load in a constant input control state from low heat to high heat.

Secondly, no load or an unsuitable load such as an aluminum pot can be detected by using the average value of the input current detection signal or the inverter current detection signal. Similar to the above, the average value of these load detection signals is the same no matter which phase is started, as long as it takes only one cycle of each signal, that is, a half cycle of the AC voltage from the AC power supply. Therefore,
Similarly to the above, it is possible to reliably detect an improper load in the constant input control state from low heat to high heat, and in addition to this, it is possible to reduce the influence of noise and improve reliability against noise. Become.

Thirdly, the average value of the above load detection signals is
By starting the sampling from the phase where the AC voltage from the AC power source becomes zero voltage, the value is always the same if only one quarter cycle of the AC voltage is taken. Therefore, the sampling time can be further shortened, and an inappropriate load can be reliably detected in the constant input control state from low heat to high heat, and the noise resistance can be further improved.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 7 are views showing a first embodiment of the present invention. Note that, in FIG. 1 and FIGS. 8 and 13 showing a second embodiment and a third embodiment to be described later, the same or equivalent parts as the devices and elements in FIG. 22 are designated by the same reference numerals and are duplicated. The description is omitted.

First, the structure of the electromagnetic cooker will be described. In this embodiment, as shown in FIG.
Maximum sampling value detecting section 29 inputs the sampled on-time signal V _on the converter 21, the voltage V _in corresponding to the input current, the maximum value required for the microcomputer for each value of the voltage V _inv corresponding to the inverter current, the commercial power supply A commercial frequency detection circuit 27 that detects the frequency of 1 and a sampling interval switching unit 28 that switches the sampling interval of the AD converter 21 based on the commercial frequency detection signal are provided. Reference numerals 25 and 26 denote voltage dividing resistors, and the voltage dividing resistors 25 and 26 appropriately divide the AC voltage from the commercial power source 1 and input it to the commercial frequency detection circuit 27.

Next, the operation of the half bridge type inverter type electromagnetic cooker configured as described above will be described.
By alternately turning on / off the two switching elements 8 and 9 with respect to the DC power source 4, high-frequency DC, that is, inverter current is supplied to the heating coil 7 and the resonance capacitors 5 and 6 of the inverter circuit, and the heating coil 7 is supplied to the heating coil 7. Heat nearby loads. At this time, in the control circuit 14, the reference oscillator signal of the constant frequency sent from the reference oscillator 16 in the PWM oscillator 17 and the on-time signal V output from the microcomputer 24.
_{The on} time is set by comparing _on, and the drive pulse having the constant frequency having the on time set by the drive circuit 15 is set to 2
The signals are alternately sent to the individual switching elements 8 and 9.

Among the above heating operations, in this embodiment,
The load is detected by the following method. That is, the maximum value of the input current detection signal and the inverter current detection signal is detected, and this is compared with the value calculated based on the maximum value of the on-time signal (which can be called an average value because the on-time signal is direct current). Then, the improper load is detected. The maximum value of the load detection signal can be obtained regardless of which phase the sampling is started as long as there is one cycle of the load detection signal. Therefore, the sampling period is significantly reduced as compared with the conventional load detection method.

Therefore, first, before the heating is started, the commercial frequency detection circuit 27 detects whether the commercial power supply frequency is 50 Hz or 60 Hz, and the sampling switching unit 28 sets the sampling interval Δt to a half cycle of the commercial power supply (50 Hz). Then 1
AD converter 21 so as to switch the time from 0 msec to 8.3 msec at 60 Hz at predetermined equal intervals.
Command. For example, in this embodiment, the sampling interval Δ
t is a time obtained by dividing a half cycle time of the commercial power source into 10 equal parts, 1 msec at 50 Hz and 0.
Switch to 83 msec. The AD converter 21 performs sampling at a predetermined equal interval number + 1 times. As a result, the sampling period is one cycle of the load detection signal regardless of whether the commercial power supply frequency is 50 Hz or 60 Hz.

During continuous heating, as shown in FIGS. 2 and 3, the input current detection signal V _in and the inverter current detection signal V
_Inv is sampled at intervals of 10 equal intervals for one period, and the maximum sampling value is detected by the maximum sampling value detection unit 29 from among these. The on-time signal similarly detects the maximum sampling value. FIG. 4 is a diagram showing the relationship between the on-time and the maximum value S _in of the input current detection signal. The characteristics differ depending on whether the load is appropriate or unloaded, and the load judgment line f as shown in the figure is used. _Since no load can be detected by ₁ (function related to on-time signal maximum value S _on ), f ₁ (S _on ) is calculated by the microcomputer after detecting the maximum sampling value, and this is compared with S _in. Detect no load. At the same time, FIG. 5 shows the ON time and the maximum value S of the inverter current detection signal.
_Although it is a diagram showing the relationship of _inv , the characteristics are different between when the load is appropriate and when the aluminum pan is used, and the load judgment line f ₂ (function relating to the maximum on-time signal S _on ) shown in the figure Since the aluminum pan can be detected, the microcomputer calculates f ₂ (S _on ) and compares it with S _inv to detect the aluminum pan. If an unsuitable load is detected here, the on-time is set to 0 to stop heating, and if an unsuitable load is detected, then a constant time T ₂ (5 mse for 50 Hz).
In the case of c and 60 Hz, 4.15 msec) is applied to perform inverter control such as constant input control, and sampling is started to perform load detection again.

By the way, as can be seen from FIGS. 4 and 5,
In both relations, if the on-time is less than a certain value, the characteristics of the aptitude load and the aptitude load are similar, and it is difficult to make a clear distinction.
What has been described so far is the minimum on-time (discrimination on-time, indicated by T _up in the figure) that allows unsuitable load detection in both relationships.
The above is the case of performing constant input continuous heating, and the load detection in the case of continuous heating when the on-time is less than T _up is performed by the following method. That is, 50 in FIGS.
As shown in the example of Hz, the discrimination on-time T _up is instantly increased to wait until the load detection signal reaches a steady state (T ₃ ~
6 msec), and then sampling / maximum value detection to detect an improper load (T ₁ = 10 at 50 Hz).
At msec, 60 Hz, T ₁ = 8.3 msec). If an unsuitable load is detected, the on-time is set to 0 to stop heating, and if an appropriate load is detected, the original on-time is restored. This operation is repeated with a fixed interval (T ₀ = 3 sec).

As described above, in the present embodiment, the ratio of the time T ₃ + T ₁ until the load detection is performed by raising the on-time to T _up for the interval period T ₀ is lower than that of the conventional load detection method. Greatly reduced. The input fluctuates with the change of the on-time, but since this period is minute with respect to the interval period, it can be regarded as an almost constant input. For example, considering FIG. 29 showing how the input fluctuates according to the change of the ON time shown in the conventional example, T ₁ is 10 msec at 50 Hz, and the actual input is 102 W even on average.
Then, it can be regarded as a constant input of almost 100 W. Also, when detecting an aluminum pan, the period during which the input is raised is greatly reduced, so there is no risk of the pan floating or slipping sideways. Therefore, it is possible to provide a safe electromagnetic control cooker of a microcomputer control type capable of constant input control from low heat to high heat.

8 to 12 show a second embodiment of the present invention. In the present embodiment, in addition to the circuit configuration described in the first embodiment, the maximum sampling value detection unit 29 that finds the maximum sampling value output from the AD converter and inputs the maximum sampling value to the microcomputer is used as the sampling output from the AD converter. The sampling value averaging unit 22 for calculating the average value of the values and inputting it to the microcomputer is replaced.

To explain the operation, the sampling method of the load detection signal is the same as that of the first embodiment, but in this embodiment, the average value of the sampling values is obtained as a microcomputer input.
At this time, since the phase of the load detection signal at the start of sampling and the phase at the end of sampling always match, the average value is the same regardless of which phase of the load detection signal the sampling starts. Further, this value is equal to the average value in the case of the conventional load detection method.

At the time of continuous heating, as shown in FIGS. 9 and 10, the input current detection signal V _in and the inverter current detection signal V _inv are sampled at equal intervals, and these are averaged by the sampling value averaging unit 22. Similarly, the on-time signal is averaged. As described above, since the average value obtained here is equal to that in the conventional load detection method, the relationship between the ON time and the load detection signal average value V _in , and the ON time and the inverter current detection signal average value V _inv . The relationships are the same as those shown in FIGS. 25 and 26 shown in the conventional example. The no-load and aluminum pan detection methods based on these characteristics and the subsequent inverter control are the same as in the first embodiment. Load detection method in the case of continuous heating at lower than the determination on time T _up is also the same as in the first embodiment, FIG. 11, as shown in the example of 50Hz in FIG. 12, momentarily raised to determine the on-time T _up, Wait until the load detection signal reaches a steady state (T _{3 to} 6 msec), then perform sampling and averaging to detect an inappropriate load (T ₁ = 10 msec at 50 Hz, T ₁ = 8.3 msec at 60 Hz), If an unsuitable load is detected, the ON time is set to 0 to stop heating, and if an appropriate load is detected, the original ON time is restored. This operation is repeated with a fixed interval (T ₀ = 3 sec).

As described above, the present embodiment can obtain exactly the same effects as the first embodiment, but the present embodiment is superior to the first embodiment in the following points. That is, in the first embodiment, since the load detection is performed using only one maximum sampling value, if noise is superimposed on the maximum value of the load detection signal, it may be erroneously determined. On the other hand, in the present embodiment, since all the sampling values are averaged, the influence of noise is reduced. Therefore, the reliability with respect to noise resistance is higher than that in the first embodiment.

13 to 21 show a third embodiment of the present invention. In this embodiment, in addition to the circuit configuration described in the second embodiment, a zero cross detection circuit 30 for detecting a place where the commercial power supply voltage becomes 0 is added in the control circuit 33.

The operation will be described. In this embodiment, when sampling the load detection signal, the zero-cross detection circuit 3 is used.
Based on the synchronization signal from 0, the phase of the load detection signal at the start of sampling is always the same. By doing so, the average value is always the same regardless of the length of the sampling period. That is, the zero-cross detection circuit 30 detects the place where the commercial power source becomes 0 V, and AD the synchronization pulse signal V _ac .
It is sent to the converter 21. The AD converter 21 waits for _a predetermined time ta after receiving the synchronizing pulse signal V _ac and starts sampling the load detection signal. Setting the sampling interval and switching according to the commercial power frequency are the first and second
Is the same as in Example, the number of sampling times c is previously set such that t _a + sampling period is within a half cycle of the load detection signal. In this embodiment, t _a = 0 and c = 6.

In the continuous heating, as shown in FIGS.
As shown in FIG. 17, the AD converter 21 samples the input current detection signal V _in and the inverter current detection signal V _inv 6 times at the same time when the synchronization pulse signal V _{ac is} generated, and these are averaged by the sampling value averaging unit 22. To do. Similarly, the on-time signal is averaged. FIG. 18 is a diagram showing the relationship between the on-time and the synchronous input current detection signal average value V ′ _in . The characteristics differ between the case where the load is proper and the case where there is no load, and as shown in the figure. Since no load can be detected by the load judgment line f ₁ (a function related to the synchronous on-time signal average value V ′ _on ), f ₁ (V ′ _on ) is calculated by the microcomputer after sampling and averaging, This is to detect the no-load compared to the V _'in. At the same time, FIG. 19 is a diagram showing the relationship between the ON time and the maximum value V ′ _inv of the synchronous inverter current detection signal. The characteristics are different between when the load is appropriate and when the aluminum pot is used, and are shown in the figure. Such load judgment line f
₂ it is possible to detect the aluminum pan with (function relating to on-time signal maximum value V _'on), f by the microcomputer
₂ ( _V'on ) is calculated and compared with _V'inv to detect the aluminum pot. If an unsuitable load is detected here, the on-time is set to 0 to stop heating, and if an unsuitable load is detected, then a constant time T ₂ (5 mse for 50 Hz).
In the case of c and 60 Hz, 4.15 msec) is applied to perform inverter control such as constant input control, and sampling is started to perform load detection again. The load detection method in the case of continuous heating for less than the determination on-time T _up is the same as in the first and second embodiments, and as shown in the example of 50 Hz in FIGS.
Instantly raise the discrimination on-time T _up , wait until the synchronous pulse signal is generated after the load detection signal becomes steady (T _{3 to} 6 to 10 msec), and then perform sampling /
Unsuitable load is detected by averaging (T ₁ = 5 msec at 50 Hz, T ₁ = 4.15 mse at 60 Hz).
c) If the improper load is detected, the on-time is set to 0 to stop the heating, and if the improper load is detected, the original on-time is restored. This operation is performed at fixed intervals (T ₀ = 3 sec)
And repeat.

As described above, the present embodiment can obtain the same effect as the second embodiment, but in this embodiment, the sampling period of the load detection signal can be shorter than one cycle of the load detection signal. Therefore, load detection can be made faster than in the second embodiment.

[0031]

As described above, according to the present invention,
First, a frequency detection unit that detects the frequency of the AC power supply,
Based on the detected frequency, find the maximum value of at least one of the inverter current in the half cycle of the AC voltage from the AC power supply or the input current from the AC power supply, and input the maximum value to the microcomputer as a load detection signal Maximum sampling Since the value detection unit is provided, the sampling time of the load detection signal can be significantly reduced, and an unsuitable load can be reliably detected in a constant input control state from low heat to high heat.

Secondly, the average value of at least either the inverter current or the input current in a half cycle of the AC voltage of the AC power supply is calculated based on the frequency detected by the frequency detection unit,
Since the sampling value averaging unit for inputting the average value to the microcomputer as the load detection signal is provided, in addition to the first effect, the influence of noise is further reduced and the noise resistance can be improved.

Third, a zero-cross detector for detecting the zero voltage value of the AC voltage from the AC power source, and a quarter cycle of the AC voltage from the zero voltage value based on the frequency detected by the frequency detector. Since a sampling value averaging unit for calculating an average value of at least one of the inverter current and the input current in the above and inputting the average value to the microcomputer as a load detection signal is provided, it is possible to further shorten the sampling time of the load detection signal. In this way, an inappropriate load can be reliably detected in a constant input control state from low heat to high heat, and noise resistance can be improved in the same manner as described above.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of an electromagnetic cooker according to the present invention.

FIG. 2 is a diagram for explaining a sampling operation of an input current detection signal during continuous heating in the first embodiment.

FIG. 3 is a diagram for explaining a sampling operation of an inverter current detection signal during continuous heating in the first embodiment.

FIG. 4 is a characteristic diagram showing the relationship between the ON time for each load and the maximum value of the input current detection signal in the first embodiment.

FIG. 5 is a characteristic diagram showing the relationship between the on-time for each load and the maximum value of the inverter current detection signal in the first embodiment.

FIG. 6 is a diagram for explaining a load detection operation at the time of heating an appropriate load when the on-time is less than the minimum on-time capable of detecting an unsuitable load in the first embodiment.

FIG. 7 is a diagram for explaining an aluminum pan detection operation during heating when the on-time is less than the minimum on-time capable of detecting an improper load in the first embodiment.

FIG. 8 is a circuit diagram showing a second embodiment of the present invention.

FIG. 9 is a diagram for explaining a sampling operation of an input current detection signal during continuous heating in the second embodiment.

FIG. 10 is a diagram for explaining the sampling operation of the inverter current detection signal during continuous heating in the second embodiment.

FIG. 11 is a diagram for explaining the load detection operation when the appropriate load is heated when the on-time is less than the minimum on-time capable of detecting an unsuitable load in the second embodiment.

FIG. 12 is a diagram for explaining an aluminum pan detection operation during heating when the on-time is less than the minimum on-time capable of detecting an improper load in the second embodiment.

FIG. 13 is a circuit diagram showing a third embodiment of the present invention.

FIG. 14 is an AC power supply frequency of 5 in the third embodiment.
It is a figure for demonstrating the sampling operation of the input current detection signal at the time of continuous heating at 0 Hz.

FIG. 15 shows an AC power supply frequency of 5 in the third embodiment.
It is a figure for demonstrating the sampling operation of the inverter current detection signal at the time of continuous heating at 0 Hz.

FIG. 16 shows an AC current frequency of 6 in the third embodiment.
It is a figure for demonstrating the sampling operation of the input current detection signal at the time of continuous heating at 0 Hz.

FIG. 17 shows an AC power supply frequency of 6 in the third embodiment.
It is a figure for demonstrating the sampling operation of the inverter current detection signal at the time of continuous heating at 0 Hz.

FIG. 18 is a characteristic diagram showing the relationship between the on-time for each load and the input current detection signal average value in the third embodiment.

FIG. 19 is a characteristic diagram showing the relationship between the on-time for each load and the average value of the inverter current detection signal in the third embodiment.

FIG. 20 is a diagram for explaining a load detection operation at the time of heating an appropriate load when the on-time is less than the minimum on-time capable of detecting an inappropriate load in the third embodiment.

FIG. 21 is a diagram for explaining an aluminum pan detection operation during heating when the on-time is less than the minimum on-time capable of detecting an inappropriate load in the third embodiment.

FIG. 22 is a circuit diagram of a conventional electromagnetic cooker.

FIG. 23 is a diagram for explaining a sampling operation of an input current detection signal during continuous heating in the above conventional example.

FIG. 24 is a diagram for explaining a sampling operation of an inverter current detection signal during continuous heating in the above conventional example.

FIG. 25 is a characteristic diagram showing the relationship between the on-time for each load and the average value of the input current detection signal in the above conventional example.

FIG. 26 is a characteristic diagram showing the relationship between the on-time for each load and the average value of the inverter current detection signals in the conventional example.

FIG. 27 is a diagram for explaining a load detection operation when an appropriate load is heated when the on-time is shorter than the minimum on-time capable of detecting an unsuitable load in the conventional example.

FIG. 28 is a diagram for explaining an aluminum pan detection operation during heating when the on-time is less than the minimum on-time capable of detecting an improper load in the conventional example.

FIG. 29 is a diagram for explaining how the input fluctuates as the on-time is changed in the case of an appropriate load in the conventional example.

[Explanation of symbols]

 1 AC power supply 2 Full-wave rectifier 4 DC power supply (AC / DC converter) 5,6 Resonant capacitor 7 Heating coil 8,9 Switching element 19 Inverter current detection circuit 20 Input current detection circuit 21 AD converter 22 Sampling value averaging unit 23 Input setting circuit 24 Microcomputer 27 Commercial frequency detection circuit (frequency detection unit) 28 Sampling interval switching unit 29 Maximum sampling value detection unit 30 Zero-cross detection circuit 31, 32, 33 Control circuit

Claims (3)

[Claims] 1. An AC / DC converter for rectifying an AC voltage from an AC power source to obtain a DC voltage, a switching element, a heating coil, and a resonance capacitor, and the switching element is periodically turned on / off. Inverter circuit for converting the DC voltage to high frequency and supplying it to the heating coil to heat the load, and setting the ON time of the switching element based on the setting input and inputting the load detection signal to detect the load. In an electromagnetic cooker having a microcomputer, an inverter current detection unit that detects an inverter current flowing in the heating coil, an input current detection unit that detects an input current from the AC power supply, and a frequency that detects the frequency of the AC power supply. A detection unit and the inverter power supply in the half cycle of the AC voltage based on the frequency detected by the frequency detection unit. An electromagnetic cooker comprising: a maximum sampling value detection unit that obtains a maximum value of at least one of a flow and an input current and inputs the maximum value to the microcomputer as a load detection signal. 2. An AC / DC converter for rectifying an AC voltage from an AC power source to obtain a DC voltage, a switching element, a heating coil, and a resonance capacitor, and the switching element is periodically turned on / off. Inverter circuit for converting the DC voltage to high frequency and supplying it to the heating coil to heat the load, and setting the ON time of the switching element based on the setting input and inputting the load detection signal to detect the load. In an electromagnetic cooker having a microcomputer, an inverter current detection unit that detects an inverter current flowing in the heating coil, an input current detection unit that detects an input current from the AC power supply, and a frequency that detects the frequency of the AC power supply. A detection unit and the inverter power supply in the half cycle of the AC voltage based on the frequency detected by the frequency detection unit. An electromagnetic cooker, comprising: a sampling value averaging unit that obtains an average value of at least one of a flow and an input current and inputs the average value to the microcomputer as a load detection signal. 3. An AC / DC converter for rectifying an AC voltage from an AC power source to obtain a DC voltage, a switching element, a heating coil, and a resonance capacitor, and the switching element is periodically turned on / off. Inverter circuit for converting the DC voltage to high frequency and supplying it to the heating coil to heat the load, and setting the ON time of the switching element based on the setting input and inputting the load detection signal to detect the load. In an electromagnetic cooker having a microcomputer, an inverter current detection unit that detects an inverter current flowing in the heating coil, an input current detection unit that detects an input current from the AC power supply, and a frequency that detects the frequency of the AC power supply. The detection unit, the zero-cross detection unit that detects the zero voltage value of the AC voltage, and the frequency detection unit A sampling value for obtaining an average value of at least one of the inverter current or the input current in a quarter cycle of the AC voltage from the zero voltage value based on the frequency and inputting the average value to the microcomputer as a load detection signal. An electromagnetic cooker having an average part.