KR20010102728A - Power circuit potection method in inverter microwave oven - Google Patents

Abstract

The present invention relates to a method for protecting a power device of an inverter microwave oven, and more particularly, to a power device protection method capable of preventing damage to a power device due to a change in an input power source. The present invention monitors the external input power frequency at the beginning of cooking, and monitors the fluctuation of the input power, and changes the input power by the fluctuation value of the inverter output voltage generated by the power switching unit 30 during cooking. It monitors and prevents damage of a power element. Therefore, the present invention can drive the microwave oven in a stable state while preventing damage to the power device due to variations in the input power source, thereby increasing the reliability of the product and at the same time having the advantage of being economically effective.

Description

Power device pot protection method in inverter microwave oven

The present invention relates to a method for protecting a power device of an inverter microwave oven, and more particularly, to a power device protection method capable of preventing damage to a power device due to a change in an input power source.

The inverter microwave oven controls the magnetron which is a drive source by the inverter system. The inverter method can vary the amount of high frequency output of the magnetron as a driving source.

The magnetron oscillates a high frequency output until current flows to the anode of the magnetron only after the internal heater generates heat. The current generated at this time is called a positive current, and the product of the positive current and the positive voltage is the power P applied to the magnetron. When the power is multiplied by the efficiency of the magnetron, a high frequency output amount is generated according to the magnitude.

Therefore, the amount of current flowing through the magnetron corresponds to the output amount of the high frequency, and when the current flows a lot, the output increases, and when the current flows low, the high frequency output decreases.

The biggest feature of such electronics for inverters is the use of expensive power switching devices, such as IGBTs, to generate very high voltages and use them as driving sources of products. Therefore, when the IGBT is damaged due to a change in temperature or input power, it is very expensive to repair the product itself.

Therefore, in order to prevent damage of the power element, the conventional inverter microwave oven shuts off the power for about 500 msec in the inverter circuit itself in the event of a change in the input power. However, when the 500 msec elapses, the microwave oven is restarted again.

Therefore, when the input power is continuously generated for 500 msec or more controlled by the inverter circuit, the power element in the inverter circuit may be damaged by the unstable input power. Due to this, a case in which the product does not operate normally occurs, and in particular, a case in which the microwave oven can no longer be used due to breakage of the power device occurs. Due to these problems, conventional inverter microwave ovens have instability in use, resulting in a problem of lowering the reliability of the product.

Accordingly, an object of the present invention is to provide a power device protection method of an inverter microwave oven capable of performing optimal control according to a change in input power.

In addition, another object of the present invention is to provide a method for protecting a power element of an inverter microwave oven which can prevent the breakage of the power element by processing the fluctuation of the input power by software.

1 is a configuration diagram of an inverter microwave oven according to the present invention;

2 is an operation flowchart showing a power device protection method of the inverter microwave oven according to the present invention;

3 to 5 are flowcharts showing sub operations required when performing the operation flowchart illustrated in FIG. 2.

Explanation of symbols on the main parts of the drawings

10: power supply 15,50: rectifier

20: inductor 25: transformer

30: power switching unit 40: magnetron

45: current transformer 55: inverter drive unit

35: microcomputer R1, R2: resistance

According to an aspect of the present invention, there is provided a method for protecting a power element of an inverter microwave oven, the method comprising: detecting an external input power frequency at an initial stage of operation of the microwave oven; ; Determining a change value of the input power from the detected external input power frequency and driving the inverter when the input power is stable; Feedbacking an inverter output value generated from driving the inverter; And determining the variation value of the input power from the inverter output value and controlling the drive of the inverter.

Hereinafter, a power device protection method of an inverter microwave oven according to the present invention will be described in detail with reference to the accompanying drawings.

1 is a block diagram of an inverter microwave oven according to the present invention.

As shown in FIG. 1, the inverter microwave oven of the present invention includes a rectifier circuit 15 for rectifying the AC power input 10, and the current rectified by the rectifier circuit 15 is an inductor 20. ) To be applied to the primary side of the transformer 25. On the secondary side of the transformer 25, a magnetron 40 for generating microwaves is mounted. That is, the magnetron 40 is driven by the voltage induced on the secondary side of the transformer 25 to generate a microwave.

On the other hand, the primary side voltage of the transformer 25 is controlled by the power switching unit 30. The power switching unit 30 is controlled on / off by the PWM control signal output from the inverter driver 55 to control the high voltage applied to the transformer 25. The inverter driver 55 operates under the control of the microcomputer 35. The power switching unit 30 is the IGBT power device described above.

The current flowing through the magnetron 40 is detected by the current transformer 45, and the detected current is output through the rectifying circuit 50. The current amount signal flowing through the magnetron 40 detected by the current transformer 45 is applied to the microcomputer 35.

On the other hand, the magnetron 40 is in a state where only a high voltage is applied from the transformer 25 without current flowing to the anode of the magnetron until the heater inside is heated to release the hot electrons. The state at this time is called a non-oscillation region, and it takes about 2 seconds for the heater of the magnetron 40 to normally emit hot electrons and generate a high frequency wave.

That is, the current flows to the anode of the magnetron 40 only after the normal oscillation of the magnetron 40 is performed by the heater. The current at this time is called an anode current, and the product of the anode current and the anode voltage is the power P applied to the magnetron 40. When the power P is multiplied by the efficiency of the magnetron 40, high frequency is generated according to the magnitude.

Therefore, the current flowing in the magnetron 40 corresponds to the output of the high frequency, and when the current is operated to flow a lot, the output is high, and when operated to flow less, the high frequency output is lowered. That is, the amount of current detected by the current transformer 45 is applied to the microcomputer 35 to control the amount of current flowing through the magnetron 40 and used to control the generated high frequency output.

Inverter control of the IGBT power element in the inverter microwave oven of the present invention having the above configuration is made as follows.

FIG. 2 is an operation flowchart for protecting a power device of an inverter microwave oven according to the present invention, and FIGS. 3 to 5 are sub operation flowcharts required for the operation of the operation flowchart of FIG.

In the initial operation of supplying power to the inverter microwave oven or at the beginning of operation of cooking, power input from the outside into the microwave oven may be in a very unstable state. In addition, the inverter microwave oven suddenly requires a lot of power to drive the magnetron 40 at the beginning of cooking. Therefore, even in this case, the input power of the microwave oven has an unstable state.

Therefore, when the unstable power is supplied, the present invention controls the power element of the microwave oven not to be driven, and controls the power element to be driven after the power is stabilized to perform stable operation of the inverter microwave oven.

First, the microcomputer 35 monitors whether a cooking start command is input by a user command, and performs an initial operation for cooking when the cooking start command is input (step 100).

At this time, the microcomputer 35 inputs an external input power and performs the external power interrupt 200 shown in FIG. 3 to check the frequency of the input power. That is, the external power frequency is checked at the external power interrupt 200 at the beginning of the operation of the microwave oven (step 200).

When performing an interrupt for checking the external power frequency by the external power interrupter 200, internal timer count data described later is initialized (step 210).

After the external power frequency is checked by the external power interrupt 200, the microcomputer 35 performs the internal timer interrupt 300 shown in FIG. The internal timer interrupt 300 counts the external power frequency in units of predetermined time by the internal timer (step 310). The external power frequency count in a predetermined time unit in step 310 is performed after a predetermined time elapses after the external power frequency is checked by the external power interrupt 200.

When the external power frequency of the predetermined time unit checked in step 310 is increased by a predetermined number or more, the internal timer interrupt sets flag 1 to temporarily stop the inverter (step 320). That is, in this case, it is determined that the power frequency input into the microwave oven is not normal.

Through the above process, the microcomputer 35 determines that the external power source frequency is not normally input, and sets the flag 1. Therefore, in step 110, the microcomputer 35 confirms that the value of the flag 1 is set, and cuts off the power supplied to the inverter for a predetermined time (N seconds) (step 120).

That is, the microcomputer 35 does not operate the inverter driver 55 during the initial operation time when a predetermined time has elapsed after the power is input into the product, and thus the operation of the power switching unit 30 is also kept off. Will be.

Next, even while the power supply of the inverter is cut off for the predetermined time (N seconds), the internal timer interrupt 300 counts the external power frequency and monitors whether power at the normal power frequency is being input (310). In step 320, the value of the flag 1 is cleared at the normal power frequency input (step 320).

After a predetermined time (N seconds) has elapsed, the microcomputer 35 confirms that the value of the flag 1 is cleared (step 110), and outputs a signal for reoperation of the inverter driver 55. In this way, when the inverter driver 55 is driven, the power switching unit 30 performs an on / off switching operation (step 130).

When the 130th step is performed, the high pressure generated by the on / off pupil of the power switching unit 30 is induced in the transformer 25 and supplied to the magnetron 40 to proceed with cooking.

On the other hand, when the inverter power is supplied to the magnetron 40, the microcomputer 35 receives a voltage generated by the on / off operation of the power switching unit 30 and feeds back a predetermined time (N1 second) unit. The inverter output voltage is updated (step 140).

The inverter output voltage is performed by the analog input data lead 400 shown in FIG. That is, after power is supplied to the microwave oven, the microcomputer 35 receives the inverter output voltage generated by the power switching unit 30. The inverter output voltage fed back as described above is input through the analog input terminal of the microcomputer 35, and the value thereof is recognized (step 410).

In this way, the inverter output voltage updated in step 140 is compared with the data before a predetermined time (N1 second), and the two values compare the difference and the absolute value K to compare whether the difference between the two values is greater than the absolute value K. (Step 150). That is, step 150 is to check the variation of the input power using the inverter output voltage. For example, when the duty cycle of the power switching unit 30 is the same, the inverter output voltage changes according to the magnitude of the input voltage. Accordingly, in step 150, a comparison is performed by setting a predetermined value K corresponding to the fluctuation range of the inverter output voltage in order to monitor the fluctuation range of the input voltage.

If the difference between the two values is greater than the absolute value K in step 150, the microcomputer 35 determines that the input power is very irregular and performs the control to turn off the inverter power (step 160).

In operation 150, when the difference between the two values is smaller than the absolute value K, the microcomputer 35 determines that the power input state is normal (operation 170).

In operation 160, the operation of the inverter driving unit 55 is interrupted to turn off the power switching unit 30, and in operation 170, the power switching unit 30 is controlled by the inverter driving unit 55. ) Is on.

In the normal control operation of step 170, the high voltage generated by the on / off operation of the power switching unit 30 is induced in the transformer 25 and supplied to the magnetron 40, whereby cooking is performed (180). step). In addition, by turning off the power switching unit 30 in step 160, the supplied inverter power is temporarily cut off.

As described above, the present invention monitors the external input power frequency at the beginning of cooking, and monitors the change of the input power, and the input power by the change of the inverter output voltage generated by the power switching unit 30 while the cooking is in progress. It is characterized in that to monitor the fluctuation of the to prevent damage to the power device. Control by this process is repeated until the end of cooking (step 190).

As described above, the power element protection method of the inverter microwave oven according to the present invention continuously monitors the change in the input voltage while the cooking is in progress, so that the power switching element for controlling the high output is not damaged by the change in the input voltage. Do not Therefore, the present invention is capable of driving the microwave oven in a stable state while preventing damage to the power device, thereby increasing the reliability of the product and at the same time having the advantage of being economically effective.

Claims (1)

In an inverter microwave oven that generates high power by inverter control: Detecting an external input power frequency at an initial stage of operation of the microwave oven; Determining a change value of the input power from the detected external input power frequency and driving the inverter when the input power is stable; Feedbacking an inverter output value generated from driving the inverter; And determining the variation value of the input power from the inverter output value and controlling the drive of the inverter.