JP3419641B2 - Inverter device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generates a direct current power source from an alternating current power source and energizes a direct current output outputted through a smoothing circuit composed of a reactor and a smoothing capacitor by controlling switching elements of an inverter circuit on and off. The present invention relates to an inverter device that is made to operate by doing so.

[0002]

As an inverter device of this type, an output obtained by converting an alternating current power source into a direct current power source through a rectifying circuit and a smoothing circuit is turned on / off by a switching element of a resonant circuit including a resonant coil and a capacitor. It is provided as an inverter circuit for connecting and disconnecting electricity to resonate, thereby obtaining an AC output. For example, there is one that provides a resonance coil as a heating coil and performs induction heating using a conductive pot as a load.

In such a device, it is common to provide a circuit having a combination of a reactor and a smoothing capacitor in constructing a smoothing circuit for smoothing the rectified output of the rectifier circuit. When adopting such a configuration, reducing the inductance of the reactor can contribute to cost reduction, and thus such a configuration has been adopted.

However, it has been found that the following new problems occur when such a reactor having a small inductance is adopted. That is,
For example, when a commercial power source as an AC power source causes a momentary power failure, or as a phenomenon equivalent to this, playing a power plug with a clatter for a child's mischief causes a momentary AC power source not intended by the user. The withstand capability against a phenomenon that occurs when the power is restored instantaneously, such as when a stopped state occurs, is reduced.

This is because, for example, when the power supply is restored in a short time due to the above-mentioned momentary power failure or the like, the control power supply for controlling the inverter circuit is a cycle of the AC power supply during the suspension period. On the other hand, since several cycles are secured, the control microcomputer continues the control operation. However, the electric charge stored in the smoothing capacitor is discharged as a DC power source when the switching operation is performed several times as the operation of the inverter circuit, so that the electric charge is completely discharged in the meantime.

As a result, when the power supply operation is restored while the microcomputer is not reset,
Since the microcomputer operates while maintaining the duty ratio of the on / off control of the switching element, the load on the reactor with a low inductance increases, and the resonance of the reactor and the smoothing capacitor causes the terminal voltage of the smoothing capacitor to change. Rises sharply. As a result, when a control output is given to the switching element of the inverter circuit to cause a resonance operation, an overvoltage may be applied to the switching element to destroy it.

In other words, instead of reducing the inductance of the reactor, in order to prevent such a problem, it is necessary to take measures such as increasing the capacity of the smoothing capacitor. Therefore, the cost is taken into consideration. Then, the cost reduction as a whole cannot be achieved.

In this case, for example, when a DC power source is obtained from a commercial power source of 100 V and this is switched by a switching element such as an IGBT to oscillate the inverter circuit, in a normal operating state, a smoothing capacitor forming a smoothing circuit. Since the maximum terminal voltage is about 140V, the maximum voltage applied to the IGBT is about 700V when this is switched. Therefore, an IGBT having a withstand voltage of about 900V can be adopted.

However, when the instantaneous power failure occurs as described above, the electric charge of the smoothing capacitor is discharged if the switching operation is performed several times at the time of the power failure, and only the control state to the IGBT continues. Will be done. After this, when the power is restored, charging of the smoothing capacitor starts, but the voltage applied to the smoothing capacitor temporarily rises due to the resonance operation with the reactor, and the charged charge is discharged. Since there is no charge, the battery is charged at a high voltage. When the IGBT is turned on and off in a state where the terminal voltage of the smoothing capacitor is as high as about 250 V, the discharge of the electric charge cannot catch up.
An excessive voltage of, for example, more than 1000 V is applied to the IGBT, and since the withstand voltage is greatly exceeded, it is unavoidable that the IGBT will be destroyed.

The present invention has been made in view of the above circumstances. An object of the present invention is to smooth the recovery from an instantaneous power failure by adopting a simple structure even when the reactor inductance is reduced to reduce the cost. An object of the present invention is to provide an inverter device in which the burden on the capacitor does not increase.

[0011]

According to a first aspect of the present invention, an inverter device has a DC power supply circuit for rectifying an AC power supply with a rectifying circuit and smoothing it with a smoothing circuit including a reactor and a smoothing capacitor to generate a DC power supply, and a resonance. A resonant circuit including a coil and a capacitor, a switching element, and an inverter circuit including a diode connected in anti-parallel thereto, and a control output to the switching element to cause the resonant circuit to perform a resonant operation and the inverter circuit. and control means for driving a time Bei give a charging charge and discharge means for discharging a predetermined time constant of the smoothing capacitor, the power supply state from the previous SL AC power source when it is stopped momentarily, the the power supply is restored If There is a duration in which the control power supply for controlling the inverter circuit is secured, the time or al smoothing Over-charged power to the capacitor
Until between elapses when the can discharge through the discharge means a load having characterized in that have configured the control means so as to stop the control output to the switching element.

According to the above construction, when the AC power supply is momentarily stopped, the control means determines that the time point when the power supply is restored is during the period when the control power supply for controlling the inverter circuit is secured. to, to the point in time whether we smoothing capacitor
Discharging an overcharged charge through a discharge means
Because until between elapses when it stops a control output to the switching device, in a state of excessive voltage to the smoothing capacitor resonant circuit of the reactor and a smoothing capacitor is formed immediately after feeding restoration is applied Also, it becomes possible to discharge the charge charged at that time through the discharging means, and to provide the control output of the switching element when the terminal voltage of the smoothing capacitor falls to the same level as in the normal operating state. As a result, an excessive voltage is not applied to the switching element, element destruction can be prevented, and it is not necessary to set the allowable amount of the reactor or the smoothing capacitor to an excessive value.

According to another aspect of the present invention, an inverter device includes a DC power supply circuit that rectifies an AC power supply with a rectifier circuit and smoothes it with a smoothing circuit including a reactor and a smoothing capacitor to generate a DC power supply, and a resonance coil including a resonance coil and a capacitor. An inverter circuit composed of a circuit, a switching element, and a diode connected in antiparallel to the circuit, and a control means for driving the inverter circuit by giving a control output to the switching element to cause the resonant circuit to perform a resonant operation. When the power supply state from the AC power supply is momentarily stopped, the control means controls the inverter circuit when the power supply is restored.
When the power source is being secured , the control output to the switching element is started from that point in a state where the duty ratio is low.

According to the above configuration, the time when the power supply is restored
A control power supply for controlling the inverter circuit is secured.
If the control means outputs the control output to the switching element at a low duty ratio when the power supply is restored, the ON / OFF control should be performed from a state where the load on the switching element is lightened. As a result, the switching element can be prevented from being destroyed by the application of an overvoltage, and during this period, the electric charge of the smoothing capacitor can be gradually discharged to return its terminal voltage to the normal level. It becomes possible to shift the on / off duty ratio of the switching element to a normal control state.

Further, in the above structure, a power supply monitoring means for monitoring the voltage of the AC power supply is provided, and the control means includes:
Instead of performing the control operation when the power supply state from the AC power supply is momentarily stopped, when the power supply monitoring means detects that the voltage of the AC power supply drops below a certain level. Can be configured to perform the control operation (the invention of claim 3).

Thus, the control of the switching element of the inverter circuit can be promptly performed as described above in response to the voltage drop of the AC power supply due to the momentary power failure or the like, which also prevents the overvoltage breakdown of the switching element. You will be able to protect it.

Further, in the above construction, detection means for detecting a change in the terminal voltage of the smoothing capacitor is provided, and instead of the control means, when the power supply state from the AC power supply is momentarily stopped. Then, the control operation may be performed when the detecting means detects that the terminal voltage of the smoothing capacitor has changed by a predetermined level or more (the invention of claim 4). The effect of can be obtained.

Further, in the above structure, a power supply monitoring means for monitoring the voltage of the commercial power supply used as the AC power supply is provided, and the control means is operated when the power supply state from the AC power supply is momentarily stopped. Alternatively, when the power supply monitoring means detects that the voltage of the commercial power supply has dropped below a certain level, the control operation can be performed within a half cycle of the commercial power supply from that point (claim). According to this, the power supply monitoring means monitors the voltage of the commercial power supply, and when the voltage drops below a certain level, the control means stops the switching element within a half cycle of the commercial power supply. In order to prevent overvoltage breakdown of the switching element due to overcharging of the smoothing capacitor when returning in a short time such as That.

Further, in the above configuration, when the control output to the switching element is started from a stopped state, the control means may be controlled to return to the control output in the state before the stop ( Invention of claim 6). According to this configuration, when the control means starts the control output to the switching element after the control of the inverter circuit is stopped due to the occurrence of an instantaneous power failure or the like, the duty ratio is started from a low state and before the stop. Since the control output is returned to the control output in the control state, the inverter circuit can be driven in the same state before and after the stop, and the usability is improved for the user.

Further, a display means for indicating a control state is provided, and when the control output to the switching element is started from a state where the duty ratio is low, the control means outputs the control output before the stop. It can be configured to maintain a corresponding display state (the invention of claim 7).
According to this configuration, even when the control means starts the control output to the switching element from the low state, the display state on the display means is maintained in the same manner as the state before the stop. It will be possible to use it without any discomfort until it returns to the normal state before the stop.

Then, a display means for indicating the control state is provided,
The control means may be configured to display the state of the control output before the stop even when the control output to the switching element is stopped (the invention of claim 8). According to this configuration, the display means keeps the display state on the display means even during the period in which the control is stopped. Since the display state is not stopped due to the occurrence of, it can be used without a feeling of strangeness.

Further, the control means holds the control state before the stop when the power supply stop detection state by the power source monitoring means is within a predetermined time, and resets the control state when the predetermined time is exceeded. It may be configured as described above (the invention of claim 9). According to this configuration, when the power supply stop state is restored within the predetermined time, the control means
Since the control state before the stop is held, for example, in the case of momentary power failure, it is possible to hold the control state as it is and drive and control the inverter circuit.

Further, the control means is configured to hold the control state before the stop when the power supply state is restored with the control power source being valid, and to reset the control state when the power is restored thereafter. It is possible (the invention of claim 10). According to this configuration, when the power supply state is restored with the control power supply being valid, the control unit can maintain the control state before the stop. Therefore, for example, in the case of an instantaneous power failure, the control is performed as it is. The inverter circuit can be driven and controlled while holding the state.

The discharging means may be a resistance element connected as a discharging element between both terminals of the smoothing capacitor (the invention of claim 11). This allows
With a simple configuration, it becomes possible to discharge the excess charge charged in the smoothing capacitor.

Further, when the control means detects that the voltage of the AC power source has returned to a predetermined level or higher, the control means returns the control output to the switching element to the state before the stop. It is possible (the invention of claim 12).

Further, when the control output to the switching element is stopped for a fixed stop period, a stop control circuit for stopping the control output to the switching element for a fixed time is provided, and the control means is controlled by the stop control circuit. When the stop period does not end even after a fixed time of stopping the control output to the switching element, a timer function is provided until the stop period ends, and the stop state is held by the timer function. It is possible (the invention of claim 13).

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION A first embodiment in which the present invention is applied to an electromagnetic cooker will be described below with reference to FIGS. 1 to 4. FIG. 1 shows a schematic electrical configuration of a direct current power supply circuit 2 that constitutes the power supply of an inverter circuit 1.
Rectifies the output Vi of the AC power supply circuit 3 by the full-wave rectification circuit 4 as a rectification circuit, and outputs the rectified output VD.
Through the smoothing reactor 5 to the DC power supply lines 2a, 2
power supply line 2a,
A smoothing capacitor 6 is connected between 2b, and the smoothing capacitor 6 is used as a DC power supply VC to supply power to the inverter circuit 1. A discharging resistor 7 as a discharging means is connected in parallel to the smoothing capacitor 6, and when the smoothing capacitor 6 is fully charged by this, for example, when the smoothing capacitor 6 has an electrostatic capacity of 9 μF, the discharging resistor 7 is discharged. When the resistance value of No. 7 is about 240 kΩ, the discharge time constant becomes about 2 seconds.

The AC power supply circuit 3 is an output V of the commercial AC power supply.
i is a power plug 8, a power switch 9 and a fuse 10
AC power supply lines 3a and 3b for receiving via the power supply lines 3a and 3b, and a varistor 11 and a noise prevention capacitor 12 are connected between the power supply lines 3a and 3b.

The inverter circuit 1 is of a single-end type, and includes a heating coil 13 as a resonance coil and a collector / emitter of an IGBT 14 as a switching element connected in series between the DC power supply lines 2a and 2b, and rectified. A flywheel diode 15 as an element is connected to the IGBT 14 in an antiparallel state, and a resonance capacitor 16 is connected in parallel to the heating coil 13. The heating coil 13 is for interlinking a high-frequency magnetic field with the pan P as a conductive load.

Next, the structure of the control circuit 17 for controlling the drive of the inverter circuit 1 will be described. The oscillation control circuit 18 PWMs the IGBT 14 of the inverter circuit 1.
ON / OFF control is performed based on a signal, and is composed of a timing circuit 19, an oscillation circuit 20, an output control circuit 21, and a gate drive circuit 22.

The timing circuit 19 described above is the IGBT 1
4 is generated based on the secondary side output of the current transformer 19a interposed in the energization path to the resonance capacitor 16, and the timing signal for performing the on / off operation with the minimum switching loss. To the oscillation circuit 20 to control the oscillation timing.
The oscillator circuit 20 is configured to generate a sawtooth wave signal which is a carry signal of a PWM signal, and the output control circuit 21 includes an output sawtooth wave signal described above and an output reference level from a microcomputer 23 as a control means described later. A square wave PWM signal is generated based on comparison with the signal. The gate drive circuit 22 amplifies the PWM signal and supplies it to the gate of the IGBT 14 to perform switching control by a pulse width modulation method.

The input current detection circuit 24 is the AC power supply circuit 3
Is provided with a current transformer 24a interposed in a power supply line 3a therein, and detects an input current of the entire device based on a secondary side output of the current transformer 24a, and inputs a voltage level corresponding to the detected current value. The current detection signal is supplied to the microcomputer 23.

The operation section 25 has a function of issuing an operation start command for the inverter circuit 1 and setting an output, and is configured to give an output setting signal having a voltage level corresponding to the output setting to the microcomputer 23. ing.
The microcomputer 23 has a program stored therein in advance so as to control the inverter circuit 1 as described later.

The terminal voltage detection circuit 26 as a detection means for detecting a change in the terminal voltage VC of the smoothing capacitor 6 has a series circuit of a detection capacitor 26a and a detection resistor 26b connected between both terminals of the smoothing capacitor 6. The common connection point of the detection capacitor 26a and the detection resistor 26b is used as an output terminal, and a detection signal corresponding to a change in the terminal voltage VC of the smoothing capacitor 6 is output.

The comparison circuit 27 is adapted to receive the detection signal of the terminal voltage detection circuit 26, and when the magnitude of the detection signal, that is, the amount of change in the terminal voltage VC of the smoothing capacitor 6 exceeds a predetermined level, the micro circuit is used. Computer 23
And a detection signal is output to the output control circuit 21. In this case, in the comparison circuit 27, as shown in FIG. 2, the signal input from the input terminal I is applied to the inverting input terminal of the comparator 27a, and the non-inverting input terminal has a reference potential of a predetermined level. Connected to a battery 27b that provides The output terminal of the comparator 27a is a resistor 27c.
It is connected to the DC power supply VDD via the and is grounded via the capacitor 27d.

The display device 28 is the microcomputer 2
The control state of the inverter circuit 1 by 3 is displayed, and for example, the set heating output level is digitally displayed.

FIG. 3 shows a control power supply circuit 29 for supplying power to the microcomputer 23. A step-down transformer 29a is connected between power supply lines connected to the power plug 8 and its secondary side output is provided. The terminal is connected to the AC input terminal of the full-wave rectifier circuit 29b. The DC output terminal of the full-wave rectifier circuit 29b is connected to the microcomputer 23 via an IC that constitutes the constant voltage circuit 29c and capacitors 29c and 29d provided on the input / output side. The microcomputer 23 is adapted to be supplied with a predetermined operating voltage VCC by the operation of the constant voltage circuit 29c.

Further, even when the AC power supply is stopped by the set capacity of the capacitor 29e, the microcomputer 23 continues to operate at the terminal voltage due to the charged electric charge for a certain period of time. Then, when the power supply voltage drops below a predetermined level, the microcomputer 23 stops the progress of the program and resets itself.

Next, the operation of this embodiment will be described with reference to FIG. First, when the pan P is placed on the heating coil 12, the power switch 9 is turned on, and when the operation start of the inverter circuit 1 is commanded through the operation unit 25, the microcomputer 23 outputs a control signal to the IGBT 14. Then, the IGBT 14 is switched through the output control circuit 21 and the gate drive circuit 22. At this time, the microcomputer 23 causes the display device 28 to display the set heating output.

Now, the microcomputer 23 first executes a material determination program for determining the material of the pot P placed on the heating coil 13, and according to the material of the pot P determined by the program, The heating control pattern stored is read and a control output is given. Further, when performing the heating operation, when executing the above-described material determination program, control is performed in a state where the heating output is weak, and subsequently, the heating output is gradually raised to a set level. The heating operation is performed by soft start.

Now, the principle of the heating operation will be briefly described. First, when the IGBT 14 is turned on, the heating coil 13 is supplied with power from the DC power supply circuit 2, and when the IGBT 14 is turned off thereafter, the current supplied from the DC power supply circuit 2 depends on the nature of the coil. Since it does not suddenly become zero, the resonance current flows through the resonance capacitor 16 side forming the resonance circuit.

Then, when the terminal voltage of the resonance capacitor 16 becomes high and the current from the heating coil 13 becomes zero,
After that, when the current starts to flow from the resonance capacitor 16 side toward the heating coil 13 and the terminal voltage of the resonance capacitor 16 becomes zero, the IGBT 14 is in the off state, so that the flywheel diode 15 moves forward. Is applied, the terminal voltage of the resonance capacitor 16 does not drop further, and the current flowing from the resonance capacitor 16 to the heating coil 13 becomes zero. In the heating coil 13, since the resonance current does not suddenly become zero, the smoothing capacitor 6 of the DC power supply circuit 2 is connected via the flywheel diode 15.
Current will flow from the side.

On the other hand, in the timing circuit 19, the inter-terminal voltage VCE when the IGBT 14 is off becomes equal to or less than the set value based on the detection signal of the change in the resonance current of the resonance capacitor 16 output from the secondary side of the current transformer 19a. Since the period is determined and the on-timing of the IGBT 14 is set within that period, the output control circuit 21 controls the on-off of the IGBT 14 with the on-time corresponding to the set on-timing and a predetermined oscillation frequency. This causes the IGBT 14 to generate the inter-terminal voltage V based on the resonance current.
The inverter circuit 1 is turned on every time when CE is minimized, and the inverter circuit 1 is caused to perform a resonant operation by control so as to prevent breakdown due to overvoltage.

Next, the inverter circuit 1 is operated as described above.
The figure shows the operation when a momentary power failure or a similar situation (for example, a situation where a power plug is momentarily stopped due to a child's mischief, etc.) occurs while the drive control is being performed. This will be described with reference to FIG.

If the commercial power source instantaneously loses power, the output voltage VD of the rectifying circuit 4 and the terminal voltage VC of the smoothing capacitor 6 decrease (see FIGS. 4A to 4C). At this time, while the control power supply VCC of the microcomputer 23 continues, the IGBT 23 of the inverter circuit 1 is controlled to be turned on and off by the microcomputer 23 (see (d) in the same figure). The charged charges of 6 are almost completely discharged when the on / off operation is performed several times.

When the commercial power supply is restored while the microcomputer 23 is obtaining the control power supply VCC, the output voltage VD of the rectifier circuit 4 is restored and the smoothing capacitor 6 is supplied to the smoothing capacitor 6 via the reactor 5. The charging operation of is started. At this time, if the inductance of the reactor 5 is small, as shown in FIG.
By configuring a resonance circuit with the smoothing capacitor 6,
The charging voltage to the smoothing capacitor 6 becomes excessive and the terminal voltage VC rises sharply (for example, in this case, rises to about 250V).

The charge of the smoothing capacitor 6 is blocked by the diode of the rectifier circuit 4 in the discharge path to the side of the rectifier circuit 4 via the reactor 5, so that it is discharged rapidly unless the IGBT 14 of the inverter circuit 1 is turned on. There is no route to do. However, when the IGBT 14 is turned on by the control output before stopping, an overvoltage (1000 V or more) is applied between the collector and the emitter of the IGBT 14, so that overvoltage breakdown cannot be avoided in the conventional configuration (see the same figure). (D) is indicated by a broken line.

Therefore, in the present embodiment, when the terminal voltage VC of the smoothing capacitor 6 suddenly rises, this change is detected by the terminal voltage detection circuit 26, and the comparison circuit 2
When the amount of change is equal to or greater than a predetermined level in 7, the detection signal is given to the output control circuit 21 and the microcomputer 23. As a result, the output control circuit 2
1 stops the control output to the IGBT 14, and the microcomputer 23 controls the stopped state to be held for a predetermined time, for example, for 3 seconds.

Then, during this period, the excessively charged charge of the smoothing capacitor 6 is discharged through the discharging resistor 7, and after the time constant of about 2 seconds elapses, a normal charge is generated. When 3 seconds have passed after returning to the state, the stable state can be achieved. After that, the microcomputer 23 sets the control signal for the IGBT 14 in the same manner as in the state before the stop, to the output control circuit 21.
To restart the operation. At this time, I
Since the overvoltage is not applied to the GBT 14, it can be operated as usual. In addition, the microcomputer 23 starts the control power supply VC from the time when the power failure occurs.
As long as C is obtained, the state of the heating output before the power failure is displayed on the display device 28 is maintained.

It should be noted that the power failure time is long and the control power supply VCC of the microcomputer 23 cannot be secured (6
0 msec or more), the microcomputer 23
Are reset by a reset circuit (not shown) when the control power supply voltage VCC decreases. Therefore, in this case, when the power is restored, a soft start is started from the material determination program as described above and the control output is gradually increased as in the case of normal power-on, so that the IGBT 14 is protected against overvoltage breakdown. It never arrives.

According to the present embodiment as described above, the terminal voltage detection circuit 26 detects a change in the terminal voltage VC of the smoothing capacitor 6 and, when the changing level is not less than a predetermined level, the comparison circuit 27 detects it. A signal is output to stop the operation of the inverter circuit 1, and thereafter, the microcomputer 23 holds the stopped state for a predetermined time (for example, 3 seconds) to discharge excess charge through the discharging resistor 7, Since the control output similar to that before the stop is given to the IGBT 14 from the state of returning to the state, even when the capacity of the reactor 5 and the smoothing capacitor 6 is used to a necessary extent in a normal use state, an instantaneous power failure or When the power plug 8 is cluttered by a child's mischief and a situation similar to a momentary power failure occurs and an overvoltage occurs in the smoothing capacitor 6, I BT14 is able to be prevented from reaching the overvoltage breakdown, it is possible to reduce the cost of the reactor by simply adding a simple and inexpensive configuration.

FIGS. 5 to 7 show a second embodiment of the present invention, and the portions different from the first embodiment will be described below. As shown in FIG. 5, the present embodiment is different in that a DC voltage detection circuit 30 and a comparison circuit 31 are provided in place of the terminal voltage detection circuit 26 and the comparison circuit 27. The DC voltage detection circuit 30 is formed by connecting a series circuit of resistors 30a and 30b between the DC output terminals of the rectification circuit 4, and obtains a detection signal Vd obtained by dividing the output voltage VD of the rectification circuit 4.

In the comparison circuit 31, as shown in FIG. 6, the input detection signal Vd is given to the base of the transistor 32. The collector of the transistor 32 is connected to the DC power supply terminal VDD via the resistor 33, the emitter is grounded via the Zener diode 34 with the polarity shown, and is connected to the non-inverting input terminal of the comparator 36 via the diode 35. . A protective diode 37 is connected between the emitter and the base of the transistor 32.

The non-inverting input terminal of the comparator 36 is grounded via the capacitor 38 and the resistor 39. The inverting input terminal of the comparator 36 is connected to a battery 40 that provides a voltage for comparison reference. The output terminal of the comparator 36 is the output control circuit 21.
It is also connected to the microcomputer 23 and provides a detection signal.

According to the above configuration, in the case where a power failure of the commercial power source occurs or a situation similar to the momentary power failure that occurs when the power plug 8 is unplugged and unplugged due to mischief of a child occurs, The output voltage VD of the rectifier circuit 4 also decreases. In the DC voltage detection circuit 30, when the output voltage VD of the rectifier circuit 4 is in a normal state, the rectified output V that is input according to a half cycle of the commercial power source.
With the detection voltage Vd obtained by D, the transistor 32,
Since the state in which the capacitor 38 is charged via the diode 35 is maintained, the comparator 36 outputs a high level detection signal.

When the power supply is stopped as described above, the level of the detection voltage Vd input to the comparison circuit 31 decreases, and when the zener voltage VZ of the zener diode 34 becomes equal to or lower than the zener voltage VZ, the transistor 32 does not turn on and the capacitor Charging to 38 is stopped. Then,
The charge of the capacitor 38 is reduced and the charge is discharged through the resistor 39. As a result, the level of the input signal to the comparator 36 decreases, and when the level is below a predetermined level, the comparator 36 outputs a low level detection signal. Like

The output control circuit 21 receives the low level detection signal from the comparison circuit 31 and immediately outputs the IGBT1.
The control output to 4 is stopped, and this state is maintained in the state where the low level detection signal is applied thereafter. In addition,
In the comparison circuit 31, since the terminal voltage of the capacitor 38 does not immediately rise at the time point when the instantaneous power failure is restored, the comparator 36 outputs a high-level detection signal after delaying for a certain time.

On the other hand, when the low level detection signal is applied from the comparison circuit 31, the microcomputer 23 responds to this by stopping the control output to the output control circuit 21, and immediately after the power is restored. The control stop state is held only for a predetermined time so as not to allow it. During this predetermined time (for example, 3 seconds), the electric charge excessively charged in the smoothing capacitor 6 is discharged through the discharging resistor 7, and when the terminal voltage VC of the smoothing capacitor 6 returns to the normal state, the microcomputer 23 IGBT14
The control output to is restarted to be the same as the state before the stop.

According to the second embodiment as described above, the instantaneous power failure is quickly detected to stop the operation of the inverter circuit 1, and the operation is restarted after a predetermined time has elapsed after the recovery from the instantaneous power failure. The charge can be discharged until the terminal voltage VC of the smoothing capacitor 6 returns to the normal level, and therefore the same effect as that of the first embodiment can be obtained.

FIG. 7 shows a third embodiment of the present invention. Hereinafter, parts different from the first or second embodiment will be described. In this embodiment, instead of holding the control output to the IGBT 14 stopped for a predetermined time after the momentary power failure is restored, a soft start is performed by the microcomputer 23 from the time of restoration. What you did is different. That is, when the terminal voltage detection circuit 26 in the configuration of the first embodiment is adopted, the control output is given to the IGBT 14 by soft start when it is detected that the momentary power failure is restored.

As a result, the IGBT 14 is controlled so as to gradually increase the duty ratio from the low state, and the IGBT 14 is controlled.
It is possible to discharge the excessive charge of the smoothing capacitor 6 while reducing the load on T14 (FIG. 7 (d)).
reference). After that, the microcomputer 23 returns the duty ratio to the control state before the occurrence of the power failure and drives and controls the inverter circuit 1. Even in this case,
The microcomputer 23 retains the display state on the display device 28 before the power failure occurs, and even if the user changes the control state due to the occurrence of the instantaneous power failure, the display does not change and the failure occurs. It can be used as it is without feeling the occurrence of, and does not cause a feeling of strangeness.

Further, also in the case of the structure in which the DC voltage detection circuit 30 and the comparison circuit 31 in the second embodiment are adopted, the electric charge of the smoothing capacitor 6 is reduced by performing the soft start after the power failure recovery in the same manner as described above. IGBT1
It becomes possible to discharge the battery 4 without burdening it and return it to the normal control state.

According to the third embodiment as described above, by performing the soft start after the recovery from the instantaneous power failure,
Smoothing capacitor 6 without burdening the IGBT 14
Since the charged electric charges can be discharged, and the discharge can be simultaneously performed through the discharging resistor 7 to return to the normal state, the same effect as that of the first and second embodiments can be obtained.

In this embodiment, the discharging resistor 7 is used as it is, but as described above, by performing the soft start, the excessive charge of the smoothing capacitor 6 is gradually discharged while the IGBT 14 is being discharged. Since the overvoltage breakdown can be prevented, the discharge resistor 7 is not an indispensable configuration, and the same effect can be obtained by providing the discharge means as needed.

The present invention is not limited to the above embodiment, but can be modified or expanded as follows. The control power may be supplied from a battery or the like. As the switching element, an FET, a bipolar transistor, or the like can be used instead of the IGBT. The inverter circuit can be applied not only to the single end type but also to a half bridge type. As the discharging means, a varistor or the like can be adopted in addition to the discharging resistor.

[0066]

As described above, according to the inverter device of the present invention, the following effects can be obtained.
According to the inverter device of claim 1, the control means causes
When the control power supply for the time the power supply is restored to control the inverter circuit is in the period that is secured, discharge hand excessively charge charged in that time or al smoothing capacitor
Because until between elapses when the can discharge through the stage stops the control output for the switching elements, a resonance circuit of a reactor and a smoothing capacitor immediately after feeding the return is formed excessive voltage to the smoothing capacitor Even in the applied state, the electric charge charged at that time can be discharged through the discharging means, and switching is performed when the terminal voltage of the smoothing capacitor falls to the same level as in the normal operating state. By giving the control output of the element, the excessive voltage is not applied to the switching element, the element destruction can be prevented, and it is not necessary to set the allowable amount of the reactor and the smoothing capacitor to an excessive value. .

According to the second aspect of the inverter device, the control for controlling the inverter circuit is performed when the power supply is restored.
When the power supply is being secured , the control output to the switching element starts from the state where the duty ratio is low from that point, so the load on the switching element is lightened and the overvoltage is applied. It is possible to gradually discharge the electric charge of the smoothing capacitor and return the terminal voltage to the normal level while preventing the destruction due to the damage.

According to the third aspect of the inverter device, the control output to the switching element is stopped for a predetermined time when the power supply monitoring means detects that the voltage of the AC power supply has dropped below a certain level, or Since the control output starts from the state where the duty ratio is low,
In response to a drop in the AC power supply voltage due to a momentary power failure, etc., the switching element of the inverter circuit can be quickly controlled as described above, which also prevents overvoltage breakdown of the switching element and protects it. Will be able to.

According to the fourth aspect of the inverter device, the detecting means for detecting the change in the terminal voltage of the smoothing capacitor is provided, and the above control is performed when the detecting means changes the terminal voltage of the smoothing capacitor by a predetermined level or more. By quickly detecting a power supply stoppage such as an instantaneous power failure and controlling the switching element, overvoltage breakdown can be prevented.

According to the inverter device of the fifth aspect, when the power supply monitoring means detects that the voltage of the commercial power supply has dropped to a certain level or lower, the control means switches within a half cycle of the commercial power supply from that point. Since the above-described control is performed on the element, it is possible to prevent overvoltage breakdown of the switching element due to overcharging of the smoothing capacitor when the device is restored in a short time such as an instantaneous power failure.

According to the sixth aspect of the inverter device, when the control output to the switching element is started by the control means after the control of the inverter circuit is stopped due to the occurrence of an instantaneous power failure or the like, the duty ratio becomes low. Since the control is started so as to return to the control output in the control state before the stop, the inverter circuit can be driven in the same state before and after the stop, and the usability is improved for the user.

According to the seventh aspect of the inverter device, even when the control means starts the control output to the switching element from a low state, the display state on the display means is maintained in the same manner as the state before the stop. The user can use the control state without feeling uncomfortable until the control state returns to the normal state before the stop.

According to the eighth aspect of the inverter device, since the display state of the display means is maintained by the control means even during the period in which the control is stopped, the display state continues in the case of an instantaneous power failure. Therefore, for the user, there is no stop of the display state due to the occurrence of a power failure,
You will be able to use it without any discomfort.

According to the ninth aspect of the inverter device, when the power supply stop state is restored within the predetermined time, the control means holds the control state before the stop, so that, for example, in the case of an instantaneous power failure. Can hold the control state as it is and drive-control the inverter circuit. According to the eleventh aspect of the present invention, when the power supply state is restored with the control power supply being effective, the control means causes
Since the control state before the stop can be held, for example, in the case of momentary power failure, the inverter circuit can be drive-controlled while holding the control state as it is. Further, according to the inverter device of the twelfth aspect, it becomes possible to discharge the excess charge charged in the smoothing capacitor with a simple configuration.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an electrical configuration showing a first embodiment of the present invention.

FIG. 2 is an electrical configuration diagram of a comparison circuit.

FIG. 3 is an electrical configuration diagram of a control power supply.

FIG. 4 is a diagram showing a temporal change in voltage of each part.

FIG. 5 is a view corresponding to FIG. 1 showing a second embodiment of the present invention.

FIG. 6 is a view corresponding to FIG.

FIG. 7 is a view corresponding to FIG. 4, showing a third embodiment of the present invention.

[Description of Reference Signs] 1 is an inverter circuit, 2 is a DC power supply circuit, 3 is an AC power supply circuit, 4 is a full-wave rectification circuit (rectification circuit), 5 is a reactor,
6 is a smoothing capacitor, 7 is a discharging resistor (discharging means), 8
Is a power plug, 11 is a varistor, 13 is a heating coil (resonance coil), 14 is an IGBT (switching element), 1
5 is a flywheel diode, 16 is a resonance capacitor, 17 is a control circuit, 18 is an oscillation control circuit, 19 is a timing circuit, 20 is an oscillation circuit, 21 is an output control circuit, 2
2 is a gate drive circuit, 23 is a microcomputer (control means), 26 is a terminal voltage detection circuit (detection means), 26
Reference numeral a is a detection capacitor, 27 is a comparison circuit, 28 is a display device (display means), 29 is a control power supply circuit, 30 is a DC voltage detection circuit (detection means), and 31 is a comparison circuit.

─────────────────────────────────────────────────── --- Continuation of the front page (56) References JP-A-7-327377 (JP, A) JP-A-61-189191 (JP, A) Practical application Sho-62-51986 (JP, U) (58) Field (Int.Cl. ⁷ , DB name) H02M 7/48

Claims (13)

(57) [Claims] 1. A DC power supply circuit for rectifying an AC power supply with a rectifier circuit and smoothing it with a smoothing circuit composed of a reactor and a smoothing capacitor to generate a DC power supply, a resonance circuit composed of a resonance coil and a capacitor, and a switching element, and An inverter circuit formed of diodes connected in anti-parallel, a control unit that gives a control output to the switching element to cause the resonance circuit to perform a resonance operation and drive the inverter circuit, and a charge stored in the smoothing capacitor. And a discharging means for discharging at a predetermined time constant, wherein the control means controls the inverter circuit when the power supply is restored when the power supply state from the AC power supply is momentarily stopped. when the power supply is in the period that is secured, the time or al the smoothing capacitor
Discharges the excessively charged electric charge through the discharging means.
The inverter device until between elapses when it is Rukoto, characterized in that it is configured to stop the control output to the switching element. 2. A DC power supply circuit for rectifying an AC power supply with a rectifier circuit and smoothing it with a smoothing circuit composed of a reactor and a smoothing capacitor to generate a DC power supply, a resonance circuit composed of a resonance coil and a capacitor, and a switching element, and An inverter circuit composed of diodes connected in anti-parallel, and a control means for applying a control output to the switching element to cause the resonance circuit to perform a resonance operation and drive the inverter circuit, wherein the control means is , when the power supply state from the AC power supply is stopped momentarily, it when the power supply is restored the in-
A control power supply for controlling the burner circuit is secured
An inverter device characterized in that, during the period , the control output to the switching element is started from that point in a state in which the duty ratio is low. 3. A power supply monitoring means for monitoring the voltage of the AC power supply is provided, and the control means performs the control operation when the power supply state from the AC power supply is momentarily stopped. 3. The power supply monitoring means is configured to perform when the voltage of the AC power supply is detected to have dropped to a certain level or lower.
Inverter device according to. 4. A detection means for detecting a change in the terminal voltage of the smoothing capacitor is provided, and the control means performs the control operation when the power supply state from the AC power supply is momentarily stopped. Alternatively, the inverter device according to claim 1 or 2, wherein the detecting device is configured to perform it when it is detected that the terminal voltage of the smoothing capacitor has changed by a predetermined level or more. 5. A power supply monitoring means for monitoring the voltage of a commercial power supply used as the AC power supply is provided, and the control means performs the control operation when the power supply state from the AC power supply is momentarily stopped. Alternatively, when it is detected by the power supply monitoring means that the voltage of the commercial power supply has dropped to a certain level or lower, the operation is performed within a half cycle of the commercial power supply from that point. The inverter device according to claim 1 or 2. 6. The control means, when starting the control output to the switching element from a stopped state, controls so as to return to the control output in the state before the stop. The inverter device according to any one of claims. 7. A display means for indicating a control state is provided, wherein when the control output to the switching element is started from a low duty ratio state, the control means outputs a control output before the stop to the display means. 7. The inverter device according to claim 6, which holds a corresponding display state. 8. A display means for indicating a control state is provided, and the control means is configured to display a state of the control output before the stop even during the stop of the control output to the switching element. Claims 1 to 7
The inverter device according to any one of 1. 9. The control means holds the control state before the stop when the power supply stop detection state by the power supply monitoring means is within a predetermined time, and resets the control state when the predetermined time is exceeded. The inverter device according to any one of claims 1 to 8, wherein the inverter device is configured as described above. 10. The control means is configured to hold the control state before the stop when the power supply state is restored with the control power supply being valid, and to reset the control state when the power is restored after that. The inverter device according to any one of claims 1 to 9, wherein the inverter device is provided. 11. The inverter device according to claim 1, wherein the discharging means is a resistance element connected as a discharging element between both terminals of the smoothing capacitor. . 12. The control means is configured to, when the power supply monitoring means detects that the voltage of the AC power supply has returned to a predetermined level or higher, return the control output to the switching element to the state before the stop. The inverter device according to claim 3, wherein the inverter device is provided. 13. A stop control circuit for stopping the control output to the switching element for a fixed time when the control output to the switching element is stopped for a fixed stop period, the control means is configured to operate by the stop control circuit. When the stop period does not end even after a fixed time of stopping the control output to the switching element, a timer function is provided until the end of the stop period, and thereby the stop state is held. The inverter device according to any one of claims 1 to 12, wherein the inverter device is provided.