KR20010103214A - Power circuit potection method in inverter microwave oven - Google Patents

Abstract

The present invention relates to a power device protection method of an inverter microwave oven, and more particularly, to a power device protection method that can prevent damage to the power device according to temperature. The power element protection method of the present invention monitors the temperature of the power switching element and controls the differential control according to the detected temperature range. 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.

Description

Power device pot protection method in inverter microwave oven

The present invention relates to a power device protection method of an inverter microwave oven, and more particularly, to a power device protection method that can prevent damage to the power device according to temperature.

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 the same temperature, it is very expensive to repair the product itself.

Therefore, the conventional inverter microwave oven is controlled so that the inverter drive itself cannot be made when the temperature rises after a certain period of time in order to prevent damage to the power element. Due to this, the product may not operate normally, and cooking may not be possible at this time. 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 that controls cooking so as to prevent damage to power devices in a product.

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;

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 device of an inverter microwave oven, the method comprising: detecting a temperature of a power device according to driving of an inverter; Controlling the power level by lowering the power level by a predetermined range when the detection temperature is higher than K ° C or the detection temperature continues at higher than K1 ° C in the initial stage of cooking; Stepwise raising the current power level to a predetermined range when the detection temperature is higher than K1 and continues for a predetermined time below K2 占 폚; And when the detection temperature continues for a predetermined time above K3 占 폚, gradually lowering the current power level to a predetermined range.

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.

Inverter microwave oven of the present invention, as shown in Figure 1, includes a rectifier circuit 15 for rectifying the input AC power supply 10, the current rectified in the rectifier circuit 15 is 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 turned 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 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.

When the power switching unit 30 of the IGBT is driven, the microcomputer 35 continuously monitors the IGBT temperature using a separate temperature sensor (not shown), and reads the detected temperature of the temperature sensor ( Step 100). Then, it is determined in which range the temperature of the detected IGBT power switching unit 30 is included.

When the temperature read in step 100 is lower than a predetermined temperature (° C.) (step 103), cooking under normal control is performed (step 106). The normal control in step 106 refers to control by a preset cooking process. That is, at this time, the duty ratio of the power switching unit 30 is controlled based on the amount of current detected from the current transformer 45 to control the driving of the magnetron 40.

After performing step 106, the microcomputer 35 returns to step 100 to continuously monitor the temperature of the power switching unit 30 while controlling the driving of the IGBT power switching unit 30.

Next, after heating for a predetermined time, when the temperature read in the 100th step is higher than the predetermined temperature (K ° C), the microcomputer 35 determines whether the detected temperature is higher than the predetermined temperature (K1 ° C). (Step 109).

When it is determined in step 109 that the detection temperature is not higher than the predetermined temperature (K1 ° C), the temperature range of the detection temperature is higher than K ° C and lower than K1 ° C. It is determined whether the temperature range is the temperature detected at the same time as the start of cooking (step 112).

When the detection temperature is determined to be equal to or higher than K ° C. at the same time as the start of cooking in step 112, the output level of the magnetron 40 is reduced by about 20% to control (step 118). That is, the microcomputer 35 controls the output frequency of the power switching unit 30 by 20%.

However, if it is determined in the step 112 that the cooking state is not the start state and the cooking temperature is determined to be higher than K ° C. during the cooking process, the microcomputer 35 again checks whether the current output state is a full power state. (Step 115).

After the determination of the 115th step, if K ℃ or more continues in the full power state during cooking, the power output level is reduced by 20% and controlled (step 118).

If it is determined that cooking is equal to or greater than K ° C. in step 112 and the current output is not in the full power state in step 115, the microcomputer determines the normal cooking state and performs cooking control using a preset control method. (Step 106).

Next, when the detection temperature is at least K ° C in step 103, the detection temperature is at least K1 ° C in step 109, and the detection temperature reaches at least K3 ° C, whether the temperature reaches K3 ° C or higher for the first time during cooking. Determine (step 121).

When the cooking temperature reaches K3 ° C or higher for the first time in the 121st step, the power level is reduced by about 10% and the flag 1 is set (step 124).

When the flag 1 is set in the step 124 (step 127), it is determined whether the detection temperature continues for more than a predetermined time (N seconds) above K3 ° C (step 130).

When the detection temperature is greater than or equal to K3 ° C in step 121, but the detection temperature is not continued for more than a predetermined time (N seconds) in K130 or more in step 130, the process proceeds to step 142 and the detection temperature is greater than or equal to K2 ° C. It is determined whether the predetermined time (N1 second) is maintained.

When the condition of step 142 is satisfied, it is determined whether the current power level reaches 90% (step 145). When the condition of step 145 is not satisfied, the power level is increased by one step. Adjust (step 148).

In step 142, when the detection temperature is maintained at a predetermined time (N1 second) above K2 ° C, and in step 145, the current power level reaches 90%. The cooking control of the microwave oven according to the drive of the inverter is terminated (step 151).

On the other hand, when the cooking temperature reaches K3 ° C, the flag 1 is set (step 127), and if the detection temperature is maintained at the K3 ° C or higher for more than N seconds in step 130, the power switching unit 30 The output level of the magnetron 40 by the control is lowered by 10% and controlled (step 133).

When the output level by the adjustment of the step 133 falls below 50%, the microcomputer 35 determines that cooking cannot be performed in the current output state and stops the operation of the inverter driver 55 (S139). step).

That is, the present invention monitors the temperature of the power switching unit 30 according to the driving of the microwave oven, and determines the range of the temperature of the power switching unit 30 to reduce or increase the inverter output level. To perform the control.

Therefore, in the present invention, the specific temperature (K ° C) for adjusting the output level of the power switching unit 30 is set. And a first temperature K1 ° C. higher than the specific temperature K ° C., a second temperature K2 ° C. higher than the first temperature K2 ° C., based on the specific temperature K ° C. A third temperature (K3 ° C) higher than the second temperature (K2 ° C) is set, and appropriate control is performed accordingly.

The determination of whether the detected temperature in step 103 is equal to or lower than K ° C is for controlling cooking by a cooking method preset in the initial operation.

The determination of whether the detection temperature in step 109 is equal to or higher than K ° C and equal to or lower than K1 ° C is for determining whether the detection temperature is a detection temperature after heating for a predetermined time or an abnormal high temperature state in the initial state by continuous heating or the like. Therefore, after determining the temperature in the step 109, it is determined in the step 112 whether the initial operation or not, and in step 115 whether it is in the full power state, the normal operating state or the state to lower the power level by about 20%, etc. It is determined by the control.

In addition, even when the detection temperature in step 121 is higher than K1 ° C and below K3 ° C, the output level of the magnetron 40 is adjusted according to the determination of steps 112 and 115 above.

When the detection temperature rises above K3 ° C. in step 121, it is determined whether the detection temperature is continuously maintained for a predetermined time (N seconds) (step 130), and when the condition of step 130 is not satisfied. In step 142, it is determined whether the detection temperature continues for a predetermined time (N1 second) above K2 占 폚.

When the condition of step 142 is satisfied, it is determined whether the current power level is 90% or less, and control is performed to raise the power level step by step.

When the power level is increased while the control is performed as described above, if the detection temperature is continuously maintained for more than a predetermined time (N seconds) at K3 ° C or higher, the control is performed to step down the power level by step 133 again. . Even when such a control does not lower the temperature of the power switching unit and when the power level is lowered to 50% or less, the microcomputer 35 determines that normal cooking is difficult to perform the control to stop driving the inverter.

As described above, the power element protection method of the inverter microwave oven according to the present invention monitors the temperature of the power switching element and controls the differential control according to the detected temperature range. 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.

Claims (1)

Detecting a temperature of the power device according to the drive of the inverter; Controlling the power level by lowering the power level by a predetermined range when the detection temperature is higher than K ° C or the detection temperature continues at higher than K1 ° C in the initial stage of cooking; Stepwise raising the current power level to a predetermined range when the detection temperature is higher than K1 and continues for a predetermined time below K2 占 폚; And gradually lowering the current power level to a predetermined range when the detection temperature continues at a temperature above K3 占 폚 for a predetermined time.