JP2822560B2 - Induction heating cooker - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an induction heating cooker used in ordinary households.

2. Description of the Related Art In recent years, induction heating cookers have been widely used in ordinary households as safe, clean and high-heat cookers. The heating principle of this induction heating cooker is performed by passing a high-frequency current through a heating coil by a switching element that switches between high frequency and high voltage and large current, but in order to operate this switching element safely, conventional induction heating cooking is performed. The vessel had the configuration shown in FIG.

In FIG. 3, reference numeral 21 denotes a power supply abnormality detection circuit, reference numeral 22 denotes a high-frequency power supply, which includes a switching element 22a for generating a high-frequency power supply, a rectifying stack 22b, capacitors 22c and 22e, a coil 22d, and a resonance capacitor 22f constituting a filter unit. It is configured. 23 is a heating coil, 24 is a control means, 25 is a commercial AC power supply, and 26 is a pot as a load.

Here, when the power supply abnormality detection circuit 21 detects that an abnormality has occurred in the voltage of the commercial AC power supply 25 due to an instantaneous power failure or lightning strike, the control means 24 controls the high-frequency power supply 22 to stop the output voltage, and the heating coil This is to prevent the coil current to 23 from flowing. This prevents the switching element 22a from being damaged by applying an excessive voltage and current to the heating coil 23.

Problems to be Solved by the Invention In the conventional induction heating cooker, with the above configuration, the switching element 22a of the high-frequency power supply 22 is prevented from being destroyed by a high voltage and a large current generated due to an instantaneous power failure or lightning strike. Although protected, in this configuration, the power supply abnormality detection circuit 21 must have very high accuracy and high speed, and therefore the circuit configuration is very complicated and expensive. There has been a problem that if the detection is performed with too high speed and high accuracy, the device becomes too sensitive to other external noises, and the device frequently and unnecessarily repeatedly stops and returns.

The present invention solves such a problem, and an object of the present invention is to provide an induction heating cooker that operates safely and stably.

Means for Solving the Problems In order to solve the above object, an induction heating cooker according to the present invention includes a high-frequency power supply that generates a high-frequency voltage from a commercial AC power supply, a heating coil connected to the high-frequency power supply,
Current detection means for detecting the amount of coil current flowing through the heating coil; A / D conversion means for receiving the output of the current detection means and converting the coil current amount into a digital amount;
When the output of the / D conversion means is between a predetermined digital amount L1 and a digital amount L2 larger than the digital amount L1, the high-frequency power source is controlled to maintain the coil current, and from this digital amount L2, When the digital amount L2 is larger than the digital amount L2, the high-frequency power source is controlled so that the output of the A / D converter is between the digital amount L1 and the digital amount L2, thereby reducing the coil current. Control means for controlling the high frequency power supply to stop the coil current when the digital amount exceeds the digital amount L3.

Further, when the coil current stops because the output of the A / D conversion means exceeds the digital amount L3, the coil current is controlled by controlling the high-frequency power supply only for a predetermined time T2 for each predetermined cycle T1, and the A A return means for detecting that the output of the / D conversion means is equal to or less than the digital amount L3 is provided.

Further, after receiving the output of the return means and detecting that the output of the A / D conversion means has become equal to or less than the digital amount L3, after a predetermined time T3, the high-frequency power supply is controlled to release the stop of the output. , A return delay means for providing a normal coil current.

Operation According to the above configuration, even when an abnormal voltage is generated due to an instantaneous power failure or lightning strike in the commercial AC power supply, and an excessive coil current is about to flow through the heating coil, the operation of the control means causes
The coil current IL converted to a digital amount at a predetermined resolution by the A / D conversion means When the predetermined digital amount between L2 and L3 is reached, the output of the high-frequency power supply is first controlled to limit the coil current. The coil current IL converted to a digital amount by the A / D conversion means increases to a predetermined digital amount L3.
Is exceeded, the output of the high frequency power supply is stopped to prevent the coil current IL from flowing.

After stopping, the high-frequency power source is output only for a predetermined time T2 every predetermined period T1 by the function of the return means, and at this time, the coil current IL converted to a digital amount by the A / D conversion means is converted to a predetermined digital value. When the amount becomes equal to or less than L3, the output stop of the high-frequency power supply is released.

Further, after a lapse of a predetermined time T3 from the time when the suspension of the output of the high-frequency power supply is released, the high-frequency power supply is set to a normal output by the function of the return delay means.

FIG. 1 shows the configuration of an induction heating cooker according to an embodiment of the present invention, and FIG. 2 shows the operation timing of the induction heating cooker according to the embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes a high-frequency power supply that generates a high-frequency voltage from a commercial AC power supply, and a switching element that performs high-frequency switching.
1a, a rectifying stack 1b, filter units 11c, 1d, 1e, a resonance capacitor 1f, and the like.

Reference numeral 2 denotes a heating coil connected to the high-frequency power supply 1, reference numeral 3 denotes current detecting means for detecting the amount of coil current IL flowing through the heating coil 2 by a current transformer and an analog circuit, and reference numeral 4 denotes an output of the current detecting means 3. A / D conversion means for converting the received coil current amount into an 8-bit digital amount with a resolution of 256 divisions.

5 is to maintain the output of the high frequency power supply 1 when the output of the A / D conversion means 4 is between a predetermined digital amount L1 and a digital amount L2 larger than the digital amount L1, and from the digital amount L2, Digital quantity L3 larger than this digital quantity L2
The output of the high-frequency power supply 1 is limited so that the output of the A / D conversion means 4 is between L1 and L2, and the output of the high-frequency power supply 1 is stopped when the output exceeds L3. Means.

6: When the output of the high frequency power supply 1 is stopped because the output of the A / D conversion means 4 exceeds the digital amount L3, the high frequency power supply 1 is output only for a predetermined time T2 every predetermined period T1, and A / D conversion is performed. It is a return means for detecting that the output of the means 4 has become equal to or less than L3 and releasing the output stop of the high frequency power supply 1.

7 outputs the high-frequency power supply 1 a predetermined time T3 after the suspension of the output of the high-frequency power supply 1 is released by the return means 6,
This is a return delay means for allowing a normal coil current to flow.

Here, the A / D conversion means 4, the control means 5, the return means 6, and the return delay means 7 are realized by a control circuit 8 including a microcomputer.

 9 is a commercial AC power supply, and 10 is a pot as a load.

Next, the operation of the induction heating cooker according to one embodiment of the present invention,
This will be described with reference to FIG. 1 and FIG.

In FIG. 2, after the power is turned on at time 0 and the high-frequency power is turned on at point A, the predetermined power set by the control means 5 is maintained. At this time, the commercial AC power supply 9
Is stable, the coil current IL is also stable, and A /
The input of the current detection means 3 A / D converted by the D conversion means 4 is between a predetermined digital amount L1 and L2.

At the point B, when an abnormality occurs due to a momentary power failure or lightning strike in the commercial AC power supply 7, a large current starts flowing through the heating coil 2,
When the input of the IL detector 3 converted by the A / D converter 4 exceeds a predetermined digital amount L2, the heating coil 2
In order to prevent the excessive coil current IL from flowing through the switching element 1a and destroying the switching element 1a, the output of the high-frequency power supply 1 is gradually suppressed from the point B to the point C.

At the point C, when the input of the current detection means 3 converted by the A / D conversion means 4 returns to less than the predetermined digital amount L2, it is determined that the commercial AC power supply 9 has returned to normal, and the output of the high-frequency power supply 1 is stabilized again. Have maintained.

Next, from point D to point E, the input of the current detection means 3 converted by the A / D conversion means 4 is converted into a predetermined digital amount L3.
Is exceeded, the output of the high-frequency power supply 1 is stopped at the point E by the operation of the control means 5.

After the point E, the stop of the output of the high-frequency power supply 1 is released for a predetermined time T2 every predetermined period T1 by the operation of the return means 6, and the input of the current detection means 3 converted by the A / D conversion means 4 is input. Is taken into the control means 5, and when it is still equal to or more than the predetermined digital amount L3, the output of the high frequency power supply 1 is stopped again, and the IL detection means 3 converted by the A / D conversion means 4 is output.
Confirmation of the input is repeated at the cycle T1.

Then, at the point F, when the input taken into the control means 5 becomes less than the predetermined digital amount L3, it is considered that the commercial AC power supply 9 has returned to normal, and the stop of the output of the high-frequency power supply 1 is released.

In order to wait for the commercial AC power supply 9 to be sufficiently stabilized, the output of the high-frequency power supply 1 is returned to the normal state by the operation of the return delay means 7 and the coil current IL flows after a lapse of time T3.

In the present embodiment, an example is described in which the switching element of the high-frequency power supply 1 is a single switching element, but the same applies to a half-bridge or push-pull high-frequency power supply circuit using two switching elements. Needless to say.
Further, in the present embodiment, the coil current IL is divided into digital quantities of 256 divided into 8 bits for control, but it is clear that any number of bits or resolution may be used according to each device.

Effect of the Invention According to the above configuration, in the induction heating cooker of the present invention, an abnormality occurs in a general commercial AC power supply due to an instantaneous power failure, lightning strike, or the like, and an excessive coil current flows in the heating coil, thereby switching the high frequency power supply. Even when the element is destroyed, the A / D conversion means continues to monitor the coil current with the input that has been decomposed into the required resolution digital value. The output of the power supply is suppressed so as not to apply an excessive coil current or an excessive voltage that may cause the destruction of the switching element. When the excessive coil current continues to flow, the output of the high-frequency power supply is stopped to protect the switching element.

Also, once the high-frequency power supply is stopped, the high-frequency power supply is periodically output for a short time to monitor the coil power supply, and if the coil current returns to normal at that time, the output of the high-frequency power supply is returned to normal. Normal operation is performed, and furthermore, by providing a delay time after the coil current returns to normal, the commercial AC power supply is sufficiently stabilized and the high-frequency power supply is output. In addition, the induction heating cooker can be used safely. Further, since the heating coil current is directly detected, it is possible to obtain a great effect that necessary and sufficient protection can be performed without unnecessary stoppage due to noise superimposed on a commercial AC power supply as in the related art. Things.

[Brief description of the drawings]

FIG. 1 is a block diagram of an induction heating cooker according to one embodiment of the present invention, FIG. 2 is a time chart showing the operation of the induction heating cooker according to one embodiment of the present invention, and FIG. It is a block diagram of a cooking appliance. DESCRIPTION OF SYMBOLS 1 ... High frequency power supply, 1a ... Switching element, 1b ... Rectification stack, 1c-1e ... Filter part, 1f ... Resonant capacitor, 2 ... Heating coil, 3 ... Current detection means, 4 ...
... A / D conversion means, 5 ... control means, 6 ... return means, 7
...... Return delay means, 8 ... Control circuit using microcomputer, 9 ... Commercial AC power supply, 10 ... Pot, 21 ... An abnormal voltage detection circuit.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H05B 6/12

Claims (3)

(57) [Claims] 1. A high-frequency power supply for generating a high-frequency voltage from a commercial AC power supply, a heating coil connected to the high-frequency power supply, current detection means for detecting a coil current flowing through the heating coil, and A / D conversion means for receiving the output and converting the coil current amount into a digital amount, and this A / D
When the output of the conversion means is between a predetermined digital amount L1 and a digital amount L2 larger than the digital amount L1, the high-frequency power supply is controlled to maintain the coil current, and from the digital amount L2, the L2 When the digital amount L3 is larger than the digital amount L3, the high-frequency power supply is controlled so that the output of the A / D conversion means is between the digital amount L1 and the digital amount L2 to limit the coil current. Digital quantity L3
And a control means for controlling the high-frequency power supply to stop the coil current when the temperature exceeds the limit. 2. When the output of the A / D conversion means exceeds the digital amount L3 and the control means controls the high-frequency power supply to stop the coil current, the high-frequency power supply is turned off only for a predetermined time T2 every predetermined time T1. Output the coil current and take the output of the A / D conversion means into the control means, and when this input is less than the digital amount L3, control the high frequency power supply to release the stop of the coil current. 2. The induction heating cooker according to claim 1, further comprising a return means for setting a normal coil current. 3. The output of the A / D conversion means exceeds the digital amount L3, and the control means controls the high frequency power supply to control the coil current IL.
Is stopped, by the return means, the high-frequency power supply is output only for a predetermined time T2 for each predetermined cycle T1, a coil current is passed, and the output of the A / D conversion means is taken into the control means. A return delay means for controlling the output of the high-frequency power supply to release the stop of the coil current and to return the output voltage to a normal output voltage after a predetermined time T3 from the detection of the digital amount L3 or less. An induction heating cooker as described.