Power converter and cooking apparatus including the same

A power converter and a cooking apparatus including the same are disclosed. The power converter includes a switching unit to perform switching using a direct current (DC) voltage and to output an alternating current (AC) voltage, a driving unit to output a high-frequency voltage to a magnetron based on the AC voltage, an output voltage detector to detect an output voltage flowing to the magnetron, and a controller to calculate a frequency command value based on the detected output voltage, to generate a frequency command value by avoiding a resonance frequency when the calculated frequency command value corresponds to the resonance frequency, and to output the generated frequency command value to the switching unit. Therefore, it is possible to stably perform oscillation.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Korean Patent Application No. 10-2015-0012984, filed on, 27 Jan. 2015, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a power converter and a cooking apparatus including the same, and, more particularly, to a power converter capable of stably performing oscillation and a cooking apparatus including the same.

2. Description of the Related Art

In general, when an operation button is pressed after putting food into a cooking apparatus using microwaves and closing the cooking apparatus, a voltage is applied to a high-voltage generator and the voltage applied to the high-voltage generator is boosted to apply a voltage to a magnetron for generating microwaves and the microwaves generated by the magnetron are delivered to a cavity via a waveguide.

At this time, the cooking apparatus using microwaves heats the food using frictional heat generated by irradiating microwaves generated by the magnetron to the food to vibrate molecules constituting the food 2.45 billion times per second.

In order to drive the magnetron, high-frequency oscillation should be performed using an AC input voltage. Various attempts to stably drive the cooking apparatus have been made.

SUMMARY OF THE INVENTION

Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a power converter capable of stably performing oscillation and a cooking apparatus including the same.

An object of the present invention is to provide a power converter including a switching unit to perform switching using a direct current (DC) voltage and to output an alternating current (AC) voltage, a driving unit to output a high-frequency voltage to a magnetron based on the AC voltage, an output voltage detector to detect an output voltage flowing to the magnetron, and a controller to calculate a frequency command value based on the detected output voltage, to generate a frequency command value by avoiding a resonance frequency when the calculated frequency command value corresponds to the resonance frequency, and to output the generated frequency command value to the switching unit.

Another object of the present invention is to provide a power converter including a switching unit to perform switching using a direct current (DC) voltage and to output an alternating current (AC) voltage, a driving unit to output a high-frequency voltage to a magnetron based on the AC voltage, an output voltage detector to detect an output voltage flowing to the magnetron, and a controller to control a frequency command value to be constant during at least a portion of a pre-oscillation period in order to heat the magnetron, to control the frequency command value to pulsate during an oscillation stabilization period of an oscillation period, to calculate the frequency command value based on the detected output voltage, to generate a frequency command value by avoiding a resonance frequency when the calculated frequency command value corresponds to the resonance frequency, and to output the generated frequency command value to the switching unit, during the pre-oscillation period or the oscillation stabilization period.

Another object of the present invention is to provide a cooking apparatus including a microwave generator to generate microwaves for heating an object in a cavity, a power converter to supply converted power to the microwave generator, and a microwave transmitter to transmit the generated microwaves to the inside of the cavity, wherein the power converter includes a switching unit to perform switching using a direct current (DC) voltage and to output an alternating current (AC) voltage, a driving unit to output a high-frequency voltage to a magnetron based on the AC voltage, an output voltage detector to detect an output voltage flowing to the magnetron, and a controller to calculate a frequency command value based on the detected output voltage, to generate a frequency command value by avoiding a resonance frequency when the calculated frequency command value corresponds to the resonance frequency, and to output the generated frequency command value to the switching unit.

According to one embodiment of the present invention, a power converter and a cooking apparatus including the same include a switching unit to perform switching using a direct current (DC) voltage and to output an alternating current (AC) voltage, a driving unit to output a high-frequency voltage to a magnetron based on the AC voltage, an output voltage detector to detect an output voltage flowing to the magnetron, and a controller to calculate a frequency command value based on the detected output voltage, to generate a frequency command value by avoiding a resonance frequency when the calculated frequency command value corresponds to the resonance frequency, and to output the generated frequency command value to the switching unit.

In particular, since the magnetron can be driven while avoiding the resonance frequency, it is possible to prevent a circuit element from being damaged by a surge voltage.

The controller changes the frequency command value before oscillation to heat the filament of the magnetron.

During the heating period, when the level of the frequency command value reaches the first level after the first time by change of the frequency command value, the controller controls the frequency command value to become an oscillation frequency. Therefore, it is possible to shorten an oscillation time.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

The terms “module” and “unit” attached to describe the names of components are used herein to aid in the understanding of the components and thus should not be considered as having specific meanings or roles. Accordingly, the terms “module” and “unit” may be used interchangeably.

FIG. 1is a partial perspective view of a cooking apparatus according to an embodiment of the present invention, andFIG. 2is a cross-sectional view of the cooking apparatus ofFIG. 1.

Referring to the figure, in the cooking apparatus100according to the embodiment of the present invention, a door106having a cooking window104attached thereto is openably and closably coupled to a front surface of a main body102and an operation panel108is coupled to a portion of the front surface of the main body102.

The door106opens and closes a cavity134. Although not shown, a door choke (not shown) for shielding microwaves may be placed in the door106.

The operation panel108includes an operation unit107for operating the cooking apparatus and a display unit105for displaying operation of the cooking apparatus.

The cavity134having a space having a predetermined size is provided in the main body102such that an object to be heated140, for example, food is held and heated by microwaves.

A microwave generator110for generating microwaves is provided on an outer side surface of the cavity134and a microwave transmitter112for guiding the microwaves generated by the microwave generator110into the cavity134is provided on the output side of the microwave generator110.

The microwave generator110may include a magnetron. The magnetron may generate and output a high frequency of 2450 MHz.

The microwave transmitter112transmits the microwaves generated and output by the microwave generator110to the cavity134. The microwave transmitter112may include a waveguide or a coaxial line. In order to transmit the generated microwaves to the microwave transmitter112, as shown in the figure, a feeder142may be connected.

Although the microwave transmitter112may have an opening145leading to the cavity134as shown in the figure, the present invention is not limited thereto and an antenna may be connected to an end of the microwave transmitter. The opening145may have various shapes such as a slot shape. Through the opening145or the antenna, the microwaves are radiated to the cavity134.

Although one opening145is provided at the upper side of the cavity134in the figure, the opening145may be provided at the lower side or the lateral side of the cavity134or a plurality of openings may be provided. The same is true when the antenna is provided instead of the opening145.

The power conversion unit for supplying a voltage to the microwave generator110is provided below the microwave generator110.

The power conversion unit may boost the voltage input to the cooking apparatus100to a high voltage and supply the high voltage to the microwave generator110. The power conversion unit may include a high-voltage transformer or an inverter for supplying a high voltage of about 3500 V generated by switching operation of one or more switching elements to the microwave generator110.

A cooling fan (not shown) for cooling the microwave generator110may be provided around the microwave generator110.

Although not shown, a resonance mode converter (not shown) for converting a resonance mode of the cavity134may be provided. An example of the resonance mode converter (not shown) may be at least one of a stirrer, a rotation table or a sliding table. The rotation table or the sliding table may be provided at the upper side of the cavity134and the stirrer may be provided at various positions of the cavity, that is, the lower side, the lateral side or the upper side of the cavity.

The cooking apparatus100using the microwaves operates when a user opens the door106, puts the object to be heated140in the cavity134and presses a cooking selection button (not shown) and a start button (not shown) of the operation panel108, more particularly, the operation unit107, with the door106closed.

That is, the power conversion unit of the cooking apparatus100boosts the input AC voltage to a high DC voltage and supplies the high DC voltage to the microwave generator110, the microwave generator110generates and outputs microwaves, and the microwave transmitter112transmits and radiates the generated microwaves to the cavity134. Therefore, the object to be heated140held in the cavity134, for example, food, is heated.

The power conversion unit ofFIG. 1is hereinafter referred to as a power converter.

FIG. 3is a block diagram showing an example of a power converter according to an embodiment of the present invention.

Referring to the figure, the power converter200according to one embodiment of the present invention may convert an input AC voltage. In particular, the power converter200may convert the input AC voltage into a DC voltage, boost the DC voltage and output a high voltage.

The power converter200may include a rectifier405, a dc end capacitor C, a switching unit420, a driving unit425and a controller415.

The rectified voltage is stored in the dc end capacitor C and may be smoothed.

Unlike the figure, a converter including a switching element may be used instead of the rectifier.

An input voltage detector A may detect the input voltage Vin input to the rectifier405. The input voltage detector A may include a resistor, an amplifier or a voltage transformer. The detected input voltage Vin may be input to the controller415.

An input current detector D may detect input current Iin. Although input current Iin flowing between the rectifier405and the dc end is shown as being detected in the figure, input current Iin flowing in a previous stage of the rectifier405may be detected.

Although not shown in the figure, a dc end voltage detector (not shown) may be further included. The dc end voltage detector (not shown) may detect a voltage Vdc across the dc end. The dc end voltage detector (not shown) may include a resistor, an amplifier or a voltage transformer. The detected voltage Vdc across the dc end may be input to the controller415.

The switching unit420includes a plurality of switching elements and may perform switching operation using a dc voltage to output an AC voltage.

In particular, the switching unit420may perform switching operation using the DC voltage Vdc across the dc end capacitor C to output an AC voltage.

The switching unit420may include an upper-arm switching element Sa and a lower-arm switching element S′a. At this time, the upper-arm switching element Sa and the lower-arm switching element S′a may complimentarily operate.

A pulse signal Scc from the controller415may be input to the upper-arm switching element Sa and the lower-arm switching element S′a. At this time, the pulse signal Scc may be generated based on a frequency command value Fref generated by the controller415.

The driving unit425may output a high-frequency voltage to the magnetron250using the AC voltage output by the switching operation of the switching unit420.

The magnetron250may be a diode vacuum tube for oscillating microwaves in a magnetic field. The magnetron250may include an anode, a cathode and a grid. A filament (FM ofFIG. 4) may be connected to the cathode in order to heat the magnetron250.

An output voltage detector E may detect an output voltage Vout across the magnetron250. That is, the output voltage Vout supplied to the magnetron250may be detected. The output voltage detector E may include a resistor, an amplifier or a voltage transformer. The detected output voltage Vout may be input to the controller415.

The output current detector F may detect output current Iout flowing in the magnetron250. In the figure, output current Iout flowing in the output end of the magnetron250is detected.

The controller415may calculate the frequency command value Fref based on the detected output voltage Vout and output a generated frequency command value Fref while avoiding a resonance frequency when the changed frequency command value Fref corresponds to the resonance frequency.

The controller415may calculate consumed power P of the magnetron250based on the detected output voltage Vout.

The controller415may calculate the consumed power of the magnetron250based on the detected output voltage Vout and output current Iout.

The controller415may generate a current command value Iref based on the calculated output power P and generate a frequency command value Fref based on the current command value Iref.

The controller415may control the calculated output power P to follow a power command value pref.

The controller415may control the detected input current Iin to follow the current command value Iref generated by a current command generator411.

The controller415may calculate output power P based on the detected output current Iout and output voltage Vout during a filament heating period of the magnetron250before oscillation of the magnetron250, change the frequency command value Fref based on the calculated output power P, and output the generated frequency command value Fref while avoiding the resonance frequency when the changed frequency command value Fref corresponds to the resonance frequency.

When the level of the frequency command value Fref reaches a first level within a first time by change of the frequency command value Fref, the controller415may control the level of the frequency command value Fref to become a second level greater than the first level.

When the level of the frequency command value Fref reaches the first level after the first time by change of the frequency command value Fref, the controller415may control the frequency command value Fref to become an oscillation frequency.

The controller415may generate a pulsating frequency command value Fref based on the detected input current and current command value Iref, in order to increase the output voltage Vout applied to the magnetron250, and the switching unit420may perform switching operation based on a pulse signal corresponding to the pulsating frequency command value Fref.

Operation of the controller415will be described below in detail with reference toFIGS. 4 to 5.

FIG. 4is a circuit diagram showing an example of the power converter according to the embodiment of the present invention.

Referring to the figure, the circuit diagram of the power converter200ofFIG. 4is similar to that ofFIG. 3, except that the switching unit420and the driving unit425ofFIG. 3are shown in greater detail.

Therefore, the switching unit420and the driving unit425will be focused upon.

The switching unit420may include the upper-arm and lower-arm switching elements Sa and S′a and an LLC filter. The driving unit425may include a transformer. In particular, the driving unit425may include a high-voltage transformer (HVT).

More specifically, the upper-arm and lower-arm switching elements Sa and S′a are connected in series across the dc end. A first inductor L1, a second inductor L2and a capacitor C1may be connected to the lower-arm switching element S′a in parallel.

One end of the first inductor L1may be connected between the upper-arm and lower-arm switching elements Sa and S′a, a primary input of the transformer HVT may be connected between the other end of the first inductor L1and one end of the second inductor L2, and a primary output of the transformer HVT may be connected between the other end of the second inductor L2and the capacitor C1.

The magnetron250may be connected across the secondary side of the transformer HVT.

When the magnetron250is driven using the power converter200, the frequency command value needs to be changed in order to heat the magnetron.

The switching unit420includes an L (inductor) component and a C (capacitor) component, by which the resonance frequency is determined.

When the resonance frequency is reached upon changing the frequency command value, a surge high voltage is applied to the magnetron250by resonance. For example, the surge high voltage of about 8 kV is instantaneously applied.

To this end, a probability that not only the magnetron250but also the various circuit elements of the power converter200are damaged increases.

In the present invention, the controller415may calculate the frequency command value based on the detected output voltage and outputs the generated frequency command value while avoiding the resonance frequency when the calculated frequency command value corresponds to the resonance frequency, thereby stably performing oscillation. In particular, the magnetron250may be driven while avoiding the resonance frequency, thereby preventing the circuit elements from being damaged by the surge voltage.

Operation of the power converter200according to the embodiment of the present invention will be described in greater detail with reference toFIG. 5.

FIG. 5is a block diagram showing an example of the controller ofFIG. 3 or 4.

Referring to the figure, the controller415may include a power calculator409, a current command value generator411and a frequency command value generator412.

The power calculator409may calculate output power P based on the output voltage Vout. In particular, the output power P may be calculated based on the output voltage Vout and the output current Iout.

The current command value generator411may generate the current command value Iref based on the calculated output power P. In particular, the current command value generator411may generate the current command value Iref based on the calculated output power P and the power command value Pref.

The current command value generator411may include a calculator419for calculating a difference between the power command value Pref and the calculated output power P and a proportional integral (PI) controller419for controlling the calculated output power P to follow the power command value Pref based on such difference.

For example, as the difference between the power command value Pref and the calculated output power P increases, the level of the current command value Iref may increase. As the difference between the power command value Pref and the calculated output power P decreases, the level of the current command value Iref may decrease.

As a result, the current command value generator411may generate and output the current command value Iref.

Next, the frequency command value generator412may generate the frequency command value Fref based on the input current Iin detected by the input current detector D and the current command value Iref generated by the current command value generator411. The controller415may output the pulse signal Scc based on the frequency command value Fref to the switching unit420.

The frequency command value generator412may include a calculator413for calculating a difference between the current command value Iref and the detected input current Iin and a proportional integral (PI) controller414for controlling the detected input current Iin to follow the current command value Iref based on such difference. The frequency command value generator412may output the frequency command value Fref.

For example, as the difference between the current command value Iref and the detected input current increases, the level of the frequency command value Fref may increase. As the difference between the current command value Iref and the detected input current Iin decreases, the level of the frequency command value Fref may decrease.

The frequency command value generator412may further include a limiter417for limiting the resonance frequency when the generated frequency command value Fref is the resonance frequency.

Accordingly, the frequency command value generator42calculates the frequency command value Fref and outputs the generated frequency command value Fref while avoiding the resonance frequency when the calculated frequency command value Fref is the resonance frequency.

The controller415may calculate the output power P based on the detected output current Iout and output voltage Vout during the filament heating period of the magnetron250before oscillation of the magnetron250, change the frequency command value Fref based on the calculated output power P, and output the generated frequency command value Fref while avoiding the resonance frequency when the changed frequency command value Fref corresponds to the resonance frequency.

When the level of the frequency command value Fref reaches a first level within a first time by change of the frequency command value Fref, the controller415may control the level of the frequency command value Fref to become a second level greater than the first level.

When the level of the frequency command value Fref reaches the first level after the first time by change of the frequency command value Fref, the controller415may control the frequency command value Fref to become an oscillation frequency.

The controller415may generate a pulsating frequency command value Fref based on the detected input current and current command value Iref, in order to increase the output voltage Vout applied to the magnetron250, and the switching unit420may perform switching operation based on a pulse signal corresponding to the pulsating frequency command value Fref.

FIG. 6is a view referred to for describing operation of the controller ofFIG. 5.

The controller415may control the switching unit420to sequentially increase the power applied to the magnetron250.

Referring to the figure, the period may be divided into a first period T1for soft-switching the switching unit420, a heating period for heating the magnetron250, an oscillation stabilization period T3, an output acceleration period T4and a normal operation period T5. The first and second periods correspond to a pre-oscillation period and the third to fifth periods correspond to a post-oscillation period.

During the first period T1, the output power applied to the magnetron250sequentially increases up to P1. The soft starting unit416in the frequency command value generator412may sequentially increase the frequency command value.

During the second period T2, the output power applied to the magnetron250may be maintained at P1. The frequency command value generator412may output a constant frequency command value. Alternatively, the frequency command value generator412may output the pulsating frequency command value.

The consumed power P2applied to the magnetron250may increase to P2such that oscillation is performed at a time Tgs.

During the third period T3, the output power applied to the magnetron250may be maintained at P2. The frequency command value generator412may output a pulsating frequency command value based on pulse frequency modulation (PFM).

During the fourth period T4, the output power applied to the magnetron250sequentially increases up to P3. The frequency command value generator412may sequentially increase the frequency command value.

During the fifth period T5, the output power applied to the magnetron250may be maintained at P3.

(b) ofFIG. 6shows the output voltage Vout applied to the magnetron, which has a first voltage level Vout1in the second period T2and has a second voltage level Vout2or more in the third period T3.

FIGS. 7A to 8are views referred to for describing operation of the power converter ofFIG. 3 or 4.

First,FIG. 7Ashows an example of a frequency command value Fm generated by the frequency command value generator412of the controller415. In particular, the frequency command value Fm during the first period T1to the third period T3is shown.

The frequency command value Fm shown in the figure may correspond to the frequency command value Fref ofFIG. 5.

The controller415may increase the frequency command value such that soft starting is performed during the first period T1which is the pre-oscillation period.

The controller415may control the frequency command value to be constant during the second period T2which is the pre-oscillation period, in order to heat the magnetron. Unlike the figure, the frequency command value may increase.

The controller415may control the frequency command value to pulsate during the oscillation stabilization period T3which is the oscillation period.

The controller415may control the generated frequency command value Fref while avoiding the resonance frequency when the calculated frequency command value Fref corresponds to the resonance frequency, during the second period T2or the oscillation stabilization period T3.

FIG. 7Bshows an example of the output voltage Vout applied across the magnetron.

Although the command value Vout_ref of the output voltage Vout has a constant value, the output voltage Vout is not constant during actual operation.

In particular, during the second period T2or the oscillation stabilization period T3, the output voltage Vout is not constant.

During the second period T2or the oscillation stabilization period T3, when the generated frequency command value Vref corresponds to the resonance frequency, as shown in the figure, a surge voltage is generated at a first point Po1, a second point Po2and a third point Po3.

In order to prevent the surge voltage, as described above, the controller415may output the generated frequency command value Fref while avoiding the resonance frequency when the calculated frequency command value Fref corresponds to the resonance frequency.

In particular, the frequency command value may be generated while avoiding the frequencies corresponding to the first point Po1, the second point Po2and the third point Po3.

The frequency command value generator412of the controller415may include the limiter417for limiting the resonance frequency.

FIG. 8shows the frequency command value S excluding the resonance frequency according to the embodiment of the present invention.

Referring to the figure, in the frequency command value S, a specific frequency is excluded in a first period Poa and a second period Pob.

The frequency command value S of the figure may correspond to the frequency command value Fref ofFIG. 5.

FIG. 9is a flowchart illustrating a method of operating a power converter according to an embodiment of the present invention.

Referring to the figure, the controller415of the power converter200calculates the output power P based on the output voltage Vout upon heating the filament of the magnetron250(S810).

Next, the controller415of the power converter200calculates the frequency command value based on the output power P (S815).

Next, the controller415of the power converter200determines whether the calculated frequency command corresponds to the resonance frequency according to the circuit configuration (S820). When the calculated frequency command corresponds to the resonance frequency, the controller415of the power converter200outputs the generated frequency command value Fref while avoiding the resonance frequency (S825).

Next, the controller415of the power converter200drives the magnetron250based on the frequency command value Fref (S830).

As described above, the controller for outputting the generated frequency command value to the switching unit while avoiding the resonance frequency when the calculated frequency command value corresponds to the resonance frequency may be included to stably perform oscillation.

In particular, the magnetron may be driven while avoiding the resonance frequency to prevent the circuit element from being damaged by the surge voltage.

The controller may change the frequency command value before oscillation to heat the filament of the magnetron.

The controller may control the frequency command value to become the oscillation frequency when the level of the frequency command value reaches the first level after the first time by change of the frequency command value, thereby shortening the oscillation time.

The power converter and the cooking apparatus including the same according to the foregoing embodiments are not restricted to the embodiments set forth herein. Therefore, variations and combinations of the exemplary embodiments set forth herein may fall within the scope of the present invention.