JP2006331662A - Induction heating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an induction heating device capable of surely carrying out response, when power is fluctuated, in relation to an induction heating device. <P>SOLUTION: This induction heating device 10 is so structured that a power voltage V of a power source 1 is detected via a detection means 17 connected to both ends of the power source 1; and a control means 16 controls to stop a drive signal S1 to a drive element 4, when the power voltage V fluctuates outside of normal voltage. Thereby, the inexpensive induction heating device, capable of responding to the fluctuation of the power voltage by a simple structure, can be provided. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an induction heating apparatus such as an induction heating cooker or an induction heating rice cooker (hereinafter referred to as a rice cooker) used in general households or restaurants.

  In recent years, induction heating devices have been widely used because heating to cooking containers is a heating method that does not use thermal power, and is excellent in convenience.

  Such a conventional induction heating apparatus will be described with reference to FIG. 5 mainly using a rice cooker as an example.

  FIG. 5 is a configuration diagram of a conventional induction heating apparatus. In FIG. 5, reference numeral 1 denotes a power source, which is supplied with a DC power source voltage V obtained from an AC power source (not shown) through a rectifier or a smoother.

  Further, 2 is a heating coil, 3 is a resonance capacitor, and the heating coil 2 and the resonance capacitor 3 are connected in parallel to form a resonance circuit 11, which is connected in series with the power source 1 together with the drive element 4 that drives the resonance circuit 11. .

  Then, an object to be heated such as a pot of a cooking container (not shown) is placed on the heating coil 2.

  Here, the drive element 4 uses an IGBT which is a semiconductor switching element whose collector loss is significantly smaller than that of a bipolar transistor or the like. For example, a rated breakdown voltage between its collector and emitter (hereinafter referred to as CE). Vk is 900V and the rated current is 60A.

  Reference numeral 5 denotes a reverse conducting diode connected in parallel to the driving element 4, and reference numeral 6 denotes a control means comprising a microcomputer.

  Here, the control means 6 detects the power supply voltage V of the power supply 1 at the port P1 by the back-electromotive voltage Vce between CE of the drive element 4, and determines the energization time to the drive element 4 according to the counter-electromotive voltage Vce. The induction heating device 30 is configured so as to be controlled.

  In the above configuration, the control means 6 generates a drive signal S1 for energizing the drive element 4 at an oscillation frequency (several tens KHz outside the audible region) of an oscillation circuit (not shown) provided inside.

  A high-frequency current (hereinafter referred to as current) Ic is generated in the resonance circuit 11 by the drive signal S1, and an eddy current is induced in the object to be heated by the current Ic to be induction-heated.

  Here, in order to control the object to be heated with constant power, the control means 6 detects the fluctuation of the power supply voltage V of the power supply 1 with the counter electromotive voltage Vce. For example, the fluctuation of the power supply voltage is reduced, that is, the counter electromotive voltage Vce. When the voltage decreases, the ON time of the drive signal S1 is lengthened, and the energization time to the drive element 4 is lengthened.

  When it is determined that the back electromotive voltage Vce may exceed the rated withstand voltage Vk of the drive element 4, the control means 6 stops the next drive signal S1.

As prior art document information related to the invention of this application, for example, Patent Document 1 is known.
Japanese Patent Laid-Open No. 11-204242

  However, in the above-described conventional induction heating device 30, when the control means 6 determines that the back electromotive voltage Vce may exceed the rated withstand voltage Vk of the drive element 4, the next drive signal S1 is stopped. It is difficult to cope with the case where the fluctuation of the power supply voltage V is faster than the processing speed.

  For this reason, the drive element 4 having a high rated withstand voltage Vk is used. However, increasing the rated withstand voltage Vk causes a problem that the cost increases and the shape of the drive element 4 increases and the induction heating device becomes expensive.

  The present invention solves such a conventional problem, and an object of the present invention is to provide an induction heating apparatus that can cope with fluctuations in the power supply voltage V without increasing the rated withstand voltage Vk of the drive element 4.

  In order to achieve the above object, an induction heating apparatus of the present invention has the following configuration.

  According to the first aspect of the present invention, when the power supply voltage fluctuates outside the steady voltage, the control means is configured to stop energization of the drive element for a predetermined time. It is possible to obtain an inexpensive induction heating apparatus that can cope with fluctuations in

  According to a second aspect of the present invention, in the first aspect of the invention, when the power supply voltage returns from outside the steady voltage to within the steady voltage, the control means controls the energization time to the drive element stepwise from a predetermined time. The back electromotive force generated in the drive element can be made lower than the rated breakdown voltage of the drive element.

  According to a third aspect of the present invention, in the first aspect of the present invention, when there is a predetermined number of times of response when the power supply voltage fluctuates, the control means notifies the outside and It has the effect that it can notify the fluctuation of the power supply voltage.

  According to a fourth aspect of the present invention, in the first aspect of the present invention, the detection means is formed by a surge absorbing element and a resistor, and the detection rate of fluctuations in the power supply voltage is increased by the capacitor component of the surge absorbing element. Has the effect of being able to.

  As described above, according to the present invention, it is possible to obtain an advantageous effect that it is possible to obtain an inexpensive induction heating apparatus that can cope with fluctuations in the power supply voltage with a simple configuration.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS.

  In addition, the same code | symbol is attached | subjected to the part of the structure same as the structure demonstrated in the term of the prior art, and detailed description is simplified.

(Embodiment)
FIG. 1 is a configuration diagram of an induction heating apparatus according to an embodiment of the present invention, in which a heating coil 2 and a resonant capacitor 3 are connected in parallel to a power source 1 having a power source voltage V to form a resonant circuit 11. It is the same as the conventional configuration that it is formed, and that the drive element 4 and the reverse conducting diode 5 that drive the resonance circuit 11 together with the resonance circuit 11 are connected in series to the power source 1.

  Reference numeral 17 denotes detection means. The detection means 17 is a serial connection body of a surge absorbing element and a resistor connected in parallel to both ends of the power supply 1 and is formed so that the power supply voltage V of the power supply 1 can be detected at its midpoint. ing.

  Here, the surge absorbing element of the detecting means 17 is formed of a gap type discharge element or a bidirectional Zener diode in which an opposing electrode is provided in a case such as glass and a set voltage can be set by a gap between the electrodes. A semiconductor junction element, a varistor made of a zinc oxide material, or the like can be used.

  Of these, there are many types of varistors, which are more preferable because they can easily cope with 100V and 200V AC power supplies.

  Next, 16 is a control means, 18 is a notification means, and the control means 16 comprising a microcomputer detects the power supply voltage V of the power supply 1 at the port P1 by the detection means 17, and comprises the drive element 4, a buzzer, an LED, and the like. The induction heating device 10 is configured to control the notification means 18.

  In the above configuration, the control means 16 generates a drive signal S1 for energizing the drive element 4 at an oscillation frequency (several tens of KHz outside the audible region) of an oscillation circuit (not shown) provided therein.

  Then, a current Ic is generated in the resonance circuit 11 by the drive signal S1, and an eddy current is induced in a heated object (not shown) placed on the heating coil 2 by this current Ic to be induction-heated.

  2 is a schematic diagram of the fluctuation of the power supply voltage, FIG. 3 is an operation explanatory diagram when the fluctuation of the power supply voltage is steady, and FIG. 4 is an explanatory diagram of the operation when the power supply voltage fluctuates. Next, the operation at the time of fluctuation will be described with reference to FIG.

  Here, the steady state means that the power source voltage V at T1 and T3 shown in FIG. 2 is within the steady state voltage, that is, the power source voltage V is within the range of the lower limit voltage VL to the upper limit voltage VU, for example, ± 10% with respect to the rated voltage Va. Is within.

  On the other hand, the time of fluctuation means that the power supply voltage V at T2 is outside the steady voltage, that is, until the power supply voltage V fluctuates beyond the steady voltage range and returns to the rated voltage Va again.

  First, the steady state operation is performed at times ta and tc shown in FIG. 2, and the control means 16 detects that the power supply voltage V at the time of the previous generation of the drive signal S1 is the rated voltage Va within the steady state voltage. Also outputs the drive signal S1 of the on-time t1 shown in FIG.

  Then, in the resonance circuit 11, a current Ic1 shown in FIG. 3B corresponding to the drive signal S1 is generated, and the object to be heated is controlled to be heated at a constant power by the current Ic1.

  Thereafter, when the drive signal S1 is turned off, the current Ic1 is suddenly turned off from the on state. As a result, the heating coil 2 causes the previous power supply voltage V shown in FIG. 3C to be the back electromotive voltage having the same value as the rated voltage Va. Vce1 is generated between CE of the drive element 4.

  Here, when the power supply voltage V decreases within the steady voltage from the time ta to the time tb1 shown in FIG. 2, the control means 6 lengthens the on-time of the drive signal S1 by the amount that the power supply voltage V has decreased. As shown in FIG. 3C, the control is configured such that the back electromotive voltage Vce becomes a value corresponding to the steady voltage of the power supply voltage V.

  As described above, the back electromotive voltage Vce does not exceed the rated withstand voltage Vk of the drive element 4 in a steady state.

  Next, the operation at the time of fluctuation will be described. The factor that the power supply voltage V fluctuates is that external noise such as lightning surge and instantaneous power failure is superimposed on the AC power supply in the home. It appears as a sudden voltage fluctuation of V.

  On the other hand, the rice cooker needs about 1 hour or more of cooking time, and since it operates with heat insulation for 24 hours after cooking, it is necessary to control heating and heat insulation with constant power against fluctuations in the power supply voltage during rice cooking or during heat insulation. It is necessary to deal with fluctuations in the power supply voltage.

  The operation when the power supply voltage fluctuates is shown in FIG. 4A when the control means 16 detects that the power supply voltage V exceeds the steady voltage range and becomes the voltage Vb1 at the time tb1 in FIG. As shown, when the drive signal S1 is controlled to stop for a predetermined time toff1 from time tb1, and when the time until the power supply voltage V returns to the steady voltage is longer than toff1, the stop control is continued to maintain the steady voltage. Stop control is released after toff2 returned to the inside.

  That is, when the detecting means 17 detects that the power supply voltage V has become the voltage Vb3 within the steady voltage at tb2 in FIG. 2, the control means 16 cancels the stop control and generates the drive signal S1 again.

  Here, as shown in FIG. 4A, the on-time of the drive signal S1 after canceling the stop control starts from a short time t2, t3, t4,... Control is performed so that the time is always t1.

  As an example of gradually increasing the time, the shortest time t2 is set to 5 μs, and t3, t4... Are increased by adding 0.25 μs to the previous on-time, or every time synchronized with the frequency of the AC power supply. It may be longer.

  As a result, the power source voltage V rapidly changes from Vb2 to Vc from before the time tb2 shown in FIG. The breakdown voltage Vk can be prevented from exceeding.

  Further, when it is detected a predetermined number of times or more that the power supply voltage V has fluctuated outside the steady voltage, the control means 16 drives the notification means 18 to notify the outside by a buzzer sound, LED blinking, or the like.

  As is apparent from the above description, the response to fluctuations in the power supply voltage of the induction heating apparatus 10 can be dealt with even if the power supply voltage V suddenly returns from outside the steady voltage to within the steady voltage in the increasing direction or decreases from the increase. The counter electromotive voltage Vce does not exceed the rated withstand voltage Vk of the drive element 4 even if it suddenly returns in the direction.

  As described above, according to the present embodiment, when the power supply voltage V of the power supply 1 fluctuates outside the steady voltage, the control means 16 stops the energization of the drive element 4 for a predetermined time toff1, or the power supply voltage V is outside the steady voltage. When the predetermined time toff1 elapses during the return from the normal voltage to the steady voltage, the control means 16 continues to stop energization until the normal voltage returns to the normal voltage, thereby causing a voltage fluctuation with a long transient characteristic such as an instantaneous power failure or a lightning surge. Can respond.

  Further, when the power supply voltage V returns from outside the steady voltage to inside the steady voltage, the control means 16 increases the control of the energization time to the drive element 4 stepwise from a predetermined time, thereby causing the reverse generated in the drive element 4. The electromotive voltage Vce can be made lower than the rated withstand voltage Vk of the drive element 4.

  Further, when the response when the power supply voltage V fluctuates is performed a predetermined number of times or more, the control means 16 drives the notification means 18 to notify the outside, thereby notifying the user of the fluctuation of the power supply voltage V. Can do.

  Furthermore, by forming the detection means 17 with a surge absorbing element and a resistor, a simple circuit configuration can be achieved, and the detection speed of fluctuations in the power supply voltage V can be increased by the capacitor component of the surge absorbing element.

  Here, the detection means 17 can be implemented even if formed by two resistors, but the surge absorbing element is more useful because it can increase the detection speed of the fluctuation of the power supply voltage.

  In the present embodiment, the fluctuation of the power supply voltage V has been described as a decreasing direction that generally occurs. However, the present invention is not limited to this, and the present invention can be implemented in a higher direction.

  In addition, it is preferable to use the rate of change from the rated voltage Va instead of using a voltage value (absolute value) such as the lower limit voltage VL value for the determination of the fluctuation of the power supply voltage V.

  Thus, for example, if the rated voltage Va is 100% and the fluctuation range of the power supply voltage V, that is, the steady voltage is ± 10% of the rated voltage Va, even when the AC power supply is changed from the 100V system to the 200V system. Since the same% value can be used, there is no need to change the program of the control means 16.

  The induction heating device according to the present invention has an effect that when a power supply voltage fluctuates due to an instantaneous power failure or the like, it can reliably cope with this with a simple configuration, and is useful for an induction heating device or the like.

The block diagram of the induction heating apparatus by one embodiment of this invention Schematic diagram of fluctuations in power supply voltage Illustration of operation during normal identification Operation explanatory diagram at the time of the change Configuration diagram of conventional induction heating device

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Power supply 2 Heating coil 3 Resonance capacitor 4 Drive element 5 Reverse conducting diode 10 Induction heating device 16 Control means 17 Detection means 18 Notification means Ic Current S1 Drive signal Vce Back electromotive voltage

Claims (4)

A resonance circuit formed of a heating coil and a resonance capacitor connected to a power source, a drive element for driving the resonance circuit, and a control means for controlling the energization time to the drive element,
Detection means for detecting the power supply voltage at both ends of the power supply is provided, and when the detection means detects that the power supply voltage has fluctuated outside the steady voltage, the control means stops energizing the drive element for a predetermined time. Induction heating device. 2. The induction heating apparatus according to claim 1, wherein when the power supply voltage returns from outside the steady voltage to within the steady voltage, the control means lengthens the control of the energization time to the drive element stepwise from a predetermined time. The induction heating apparatus according to claim 1, wherein when the control outside the steady voltage has occurred a predetermined number of times or more, the control means notifies the outside. The induction heating apparatus according to claim 1, wherein the detection means is formed of a surge absorbing element and a resistor.

Images