JPH07111188A - Inverter device - Google Patents

Abstract

PURPOSE:To realize an inverter device in which an element voltage and an element current to be applied to a switching element can be restricted when an input power supply restores from low voltage abnormality. CONSTITUTION:A heating coil 4 is driven by excitation by a rectifier circuit 2 to rectify a current from an AC power supply into a DC for performing induction heating of a load pot 3. An input power from an AC power supply 1 is detected at an input power detection part 6, an input voltage from the AC power supply 1 is detected at an input voltage detection part 7, and a control part performs on/off of a switching element 8 based on these detected values to regulate current supply to the heating coil 4. When the detected voltage at the input voltage detection part 7 continues to be a specified voltage or less for a specified time, it is detected to be a low voltage, in which case the switching element 8 is turned off.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter device used in an induction heating cooker or the like used in general households.

[0002]

2. Description of the Related Art In recent years, induction heating cookers have become popular in households because of their excellent features of safety, cleanliness, and high efficiency.

Hereinafter, a conventional inverter device will be described as an example when it is used in an induction heating cooker. Figure 9
FIG. 4 is a circuit diagram of a conventional inverter device. In FIG. 9, 1 is an AC power supply, 2 is a rectifier circuit for converting the AC power supply 1 into DC, 3 is a load pan that is a load, 4 is a heating coil magnetically coupled to the load pan 3, and 5 is a parallel connection to the heating coil 4. Resonant capacitor, 6 is an input power detection unit that detects the input power from the AC power supply 1, 7 is an input voltage detection unit that detects the voltage of the AC power supply 1, 8 is a switching element, and 9 is a high-frequency current in the heating coil 4. Is a control unit that controls the on / off of the switching element 8 so that the input power is supplied by the user.

With the above configuration, a high-frequency current is applied to the heating coil 4 so that the input power from the AC power source 1 reaches a predetermined value, and the load pan 3 magnetically coupled to the heating coil 4 is induction-heated. Had been realized.

[0005]

In the above-mentioned conventional configuration, the input power is controlled by increasing or decreasing the ON time of the switching element 8, that is, by increasing the ON time of the switching element 8, the switching element 8 is increased. A large current can be applied to the heating coil 4, and as a result, a large current can be supplied to the heating coil 4 to generate a large magnetic flux.

In such a structure, when the input power source is lowered as shown in FIG. 10A, an operation for extending the ON time of the switching element is performed in order to prevent the input power from being lowered. Due to this operation, when the low voltage continues for a long time, the ON time of the switching element becomes considerably longer than that at the rated input voltage. As a result, when the power failure is restored, excessive element voltage and element current are instantaneously applied to the switching element as shown in FIG.

Therefore, in order to prevent the switching element from being destroyed by the excessive voltage / current generated at this time, the maximum rating of the switching element is to be compared with the voltage / current applied when operating at a normal input voltage. There was a problem that it was forced to have a large margin, resulting in higher costs.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to realize an inverter device capable of suppressing the element voltage and the element current applied to the switching element when the input power supply is restored from a low power abnormality. There is.

[0009]

To achieve the above object, the present invention provides, as a first means, a rectifier circuit for converting a current from an AC power source into a direct current, and a heating coil driven by excitation of the rectifier circuit. A switching element that adjusts the current supply to the heating coil by turning on and off, an input power detection unit that detects the input power from the AC power supply, an input voltage detection unit that detects the voltage of the AC power supply, and the input A low-voltage detection unit that detects low voltage when the voltage detected by the voltage detection unit continues for a certain time and is equal to or lower than a predetermined voltage, and the switching element based on the output from the input power detection unit and the low-voltage detection unit. And a control unit for controlling on / off of the switching element, and the control unit turns off the switching element when the low power detection unit detects low power.

The present invention also provides, as a second means, an element voltage detecting section for detecting an element voltage generated at both ends of a switching element, and an element voltage limiting circuit for outputting according to the detected voltage in the element voltage detecting section. And a control unit that controls the element voltage to a predetermined value or less according to the output of the element voltage limiting circuit, and the element voltage at the time of detecting a low electric current higher than the upper limit of the element voltage when a low electric current is not detected It was decided to lower the upper limit of.

Furthermore, the present invention provides, as a third means, an element current detecting section for detecting an element current generated at both ends of a switching element, and an element current limiting circuit for outputting according to the detected current in the element current detecting section. And a control unit that controls the element current to a predetermined value or less according to the output of the element current limiting circuit, and the element current at the time of detecting a low current lower than the upper limit of the element current when low current is not detected It was decided to lower the upper limit of.

As a fourth means of the present invention, an on-time detection circuit for detecting the on-time of the switching element is provided, and the increase of the on-time is stopped when a low power is detected.

[0013]

According to the present invention, according to the above-mentioned structure, when the AC power source is below the preset voltage and over the predetermined time,
It is possible to stop the oscillation of the switching element and stop the supply of the high frequency current to the heating coil. As a result, the power supply itself is stopped by the low voltage of the AC power source for a predetermined time or longer, and thus it is possible to prevent an excessive element voltage / element current applied at the time of the low voltage recovery.

Further, when the AC power supply is below a preset voltage and for a predetermined time or longer, the limit value of the element voltage generated across the switching element is lowered or the element current applied to the switching element is limited. By lowering the value, it is possible to prevent excessive device voltage and device current at the time of low voltage recovery. According to this method, the element voltage or the element current can be reliably reduced to a predetermined value or less without stopping heating and by appropriately setting the amount of decrease in the limit value.

Further, when the AC power supply is at a voltage lower than a preset voltage and for a predetermined time or longer, the ON time of the switching element is increased by making the ON time of the switching element no longer increase. Therefore, it is possible to prevent excessive device voltage and device current applied to the switching device at the time of recovery from low power.

[0016]

【Example】

(Embodiment 1) An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, 1 is an AC power supply, 2 is a rectifying circuit for converting the AC power supply 1 into DC, 3 is a load pan as a load, 4 is a heating coil magnetically coupled to the load pan 3, and 5 is a heating coil 4. A resonance capacitor connected in parallel with the input voltage detector 6, an input power detection unit for detecting the input power from the AC power supply 1, a input voltage detection unit 7 for detecting the voltage of the AC power supply 1, and a preset voltage of the AC power supply 1 for 10 When the voltage is lower than or equal to the predetermined voltage and is longer than a predetermined time, a low-power detection unit that detects low power, 8 is a switching element, and 9 is a high-frequency current supplied to the heating coil 4 so that the input power is set by the user. The control unit controls ON / OFF of the switching element 8 and turns OFF the switching element 8 to stop heating when the low electric power detection unit 10 detects a low electric power.

Next, the operation of the inverter device of this embodiment will be described with reference to FIG. FIG. 2A shows how the input power is reduced, where it is reduced by 30% of the rated power. The ON time of the switching element starts to increase with the decrease of the input power, but when the decrease of the input power continues for a predetermined time, the heating is stopped. That is, the on-time once becomes zero here and the oscillation / heating operation is stopped. Therefore, when the input voltage returns to the rated voltage thereafter, the switching element is turned off, so that an excessive element voltage / element current does not occur. Needless to say, the oscillation / heating operation is started after the input power is restored.

(Second Embodiment) A second embodiment of the present invention will be described below with reference to the drawings.

In FIG. 3, 1 is an AC power supply, 2 is a rectifying circuit for converting the AC power supply 1 into DC, 3 is a load pan as a load, 4 is a heating coil magnetically coupled to the load pan 3, and 5 is a heating coil 4. A resonance capacitor connected in parallel with the input voltage detector 6, an input power detection unit for detecting the input power from the AC power supply 1, a input voltage detection unit 7 for detecting the voltage of the AC power supply 1, and a preset voltage of the AC power supply 1 for 10 When the voltage is lower than or equal to the predetermined voltage and is longer than a predetermined time, a low-power detection unit that detects low power, 8 is a switching element, and 9 is a high-frequency current supplied to the heating coil 4 so that the input power is set by the user. A control unit for controlling ON / OFF of the switching element 8, 11 is an element voltage detection unit for detecting an element voltage generated at both ends of the switching element 8, and 12 is a function for lowering a control value from a normal value at the time of low power detection. Had Is a child voltage limiting circuit.

Next, the operation of the inverter device of this embodiment will be described with reference to FIG. FIG. 4A shows how the input power is reduced, where it is reduced by 30% of the rated power. FIG. 4B shows the limit value of the element voltage, which is lowered when the low voltage continues for a predetermined time or longer. As a result, the element voltage during the low power period is limited to a value smaller than that at the rated voltage, and the ON time of the switching element is also limited. Therefore, the heating operation can be continued without applying an excessive element voltage even when returning from the low voltage.

(Embodiment 3) A third embodiment of the present invention will be described below with reference to the drawings.

In FIG. 5, 1 is an AC power supply, 2 is a rectifying circuit for converting the AC power supply 1 into DC, 3 is a load pan as a load, 4 is a heating coil magnetically coupled to the load pan 3, and 5 is a heating coil 4. A resonance capacitor connected in parallel with the input voltage detector 6, an input power detection unit for detecting the input power from the AC power supply 1, a input voltage detection unit 7 for detecting the voltage of the AC power supply 1, and a preset voltage of the AC power supply 1 for 10 When the voltage is lower than or equal to the predetermined voltage and is longer than a predetermined time, a low-power detection unit that detects low power, 8 is a switching element, and 9 is a high-frequency current supplied to the heating coil 4 so that the input power is set by the user. A control unit for controlling ON / OFF of the switching element 8, 13 is an element current detection unit for detecting an element current applied to the switching element 8, and 14 has a function of lowering a limit value from a normal value at the time of low power detection. Element It is a flow-limiting circuit.

Next, the operation of the inverter device of this embodiment will be described with reference to FIG. FIG. 6A shows how the input power is reduced, where the input power is reduced by 30% with respect to the rated power. FIG. 6B shows the limit value of the element current, which is reduced when the low voltage continues for a predetermined time or longer. As a result, the element current during the low power period is limited to a value smaller than that at the rated voltage, and the ON time of the switching element is also limited. Therefore, the heating operation can be continued without applying an excessively large element current even when returning from the low voltage.

(Embodiment 4) A fourth embodiment of the present invention will be described below with reference to the drawings.

In FIG. 7, 1 is an AC power supply, 2 is a rectifying circuit for converting the AC power supply 1 into DC, 3 is a load pan as a load, 4 is a heating coil magnetically coupled to the load pan 3, and 5 is a heating coil 4. A resonance capacitor connected in parallel with the input voltage detector 6, an input power detection unit for detecting the input power from the AC power supply 1, a input voltage detection unit 7 for detecting the voltage of the AC power supply 1, and a preset voltage of the AC power supply 1 for 10 When the voltage is lower than or equal to the predetermined voltage and is higher than a predetermined time, a low-current detecting unit, 8 is a switching element, 15 is an on-time detection circuit that detects the on-time of the switching element 8, and 9 is a high frequency in the heating coil 4. The on / off of the switching element 8 is controlled so that the current is supplied so that the input power is set by the user, and the low power detection unit 1 is provided.
This is a control unit that does not increase the on-time when low power is detected by 0.

Next, the operation of the inverter device of this embodiment will be described with reference to FIG. FIG. 8A shows how the input power is reduced, where it is reduced by 30% of the rated power. FIG. 8B shows changes in the ON time of the switching element 8. The on-time starts increasing at the same time as the start of low voltage,
When the low voltage detection is performed after a predetermined time, the operation is continued without increasing the on time. Therefore, the increase in the element voltage and the element current that occur when the low voltage is restored can be suppressed to a relatively small value as shown in FIG.

[0028]

As described above, according to the inverter device of the present invention, when the oscillation and heating are temporarily stopped in the case of the low power abnormality of the relatively long input power source with a small drop amount, the power supply is restored from the low power state. It is possible to prevent excessive device voltage and device current applied to the switching device. Further, by preventing the limit value of the element voltage or the element current from decreasing at the time of the low electric power or increasing the ON time, the oscillation and heating are not stopped, and the excessive element voltage and the element current at the time of returning to the low electric power are prevented. be able to.
As a result, the maximum rating required for the switching element can be significantly reduced compared to the conventional one, and the cost of the switching element can be reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an inverter device according to a first embodiment of the present invention.

FIG. 2 is a characteristic diagram illustrating the operation of the device.

FIG. 3 is a circuit diagram of an inverter device according to a second embodiment of the present invention.

FIG. 4 is a characteristic diagram illustrating the operation of the device.

FIG. 5 is a circuit diagram of an inverter device according to a third embodiment of the present invention.

FIG. 6 is a characteristic diagram illustrating the operation of the device.

FIG. 7 is a circuit diagram of an inverter device according to a fourth embodiment of the present invention.

FIG. 8 is a characteristic diagram illustrating the operation of the device.

FIG. 9 is a circuit diagram of a conventional inverter device.

FIG. 10 is a characteristic diagram illustrating the operation of the device.

[Explanation of symbols]

 1 AC power supply 2 Rectifier circuit 4 Heating coil 6 Input power detection unit 7 Input voltage detection unit 8 Switching element 9 Control unit 10 Low power detection unit

Claims (4)

[Claims] 1. A rectifying circuit for rectifying a current from an AC power supply into a DC current, a heating coil driven by excitation of the rectification circuit, a switching element for adjusting current supply to the heating coil by turning on and off, and the AC power supply. Input power detection unit that detects the input power from the AC power supply, an input voltage detection unit that detects the voltage of the AC power supply, and a low power supply when the detection voltage at the input voltage detection unit continues for a certain period of time or less. A low-power detection unit that detects the low-power detection by the low-power detection unit, and a control unit that controls the on / off of the switching element based on the output from the input-power detection unit and the low-power detection unit. The inverter device in which the control unit turns off the switching element when being turned off. 2. An element voltage detection unit for detecting an element voltage generated at both ends of a switching element, an element voltage limiting circuit for outputting according to a detection voltage in the element voltage detection unit, and an output of the element voltage limiting circuit. And a control unit that controls the element voltage to be equal to or lower than a predetermined value in accordance with the above, and lowers the upper limit of the element voltage when the low voltage is detected than the upper limit of the element voltage when the low voltage is not detected. Inverter device. 3. An element current detection section for detecting an element current generated at both ends of a switching element, an element current limiting circuit for outputting according to a detection current in the element current detection section, and an output of the element current limiting circuit. 2. A control unit that controls the element current to a predetermined value or less in accordance with the above, and lowers the upper limit of the element current when the low current is detected than the upper limit of the element current when the low current is not detected. Inverter device. 4. The inverter device according to claim 1, further comprising an on-time detection circuit that detects an on-time of the switching element, and stops increasing the on-time when a low electric current is detected.