RU1830642C - Procedure of output power control in induction heating apparatus - Google Patents

Description

the latter is connected to the output of the voltage sensor. 11 on the compensating capacitor, and the output with the control electrode of the key element, the voltage sensor 12 at the output of the rectifier, the output of which is connected to the first input of the comparator 13, the second input of the comparator is connected to the output of the device for setting the output power level 14 of the device, and the output is with the second input of the control unit.

A method for controlling the output power of an induction heating device is implemented by the following steps. The time of the conductive state of the key element in the period of the inverter output frequency is controlled. Due to this, the time interval during which the inductor (load) is connected to the power source during the period of the output frequency is changed. Additionally, the output voltage of the rectifier is measured. The output power level is set by setting the voltage level. Two voltages are compared: the rectifier measured at the output and the target. An inhibition signal is generated to turn on the key element of the inverter if the signal proportional to the voltage at the output of the rectifier, if the signal proportional to the voltage at the output of the rectifier is less than the reference voltage (reference signal). Measurement (regulation) of the output power of the device is carried out by changing the reference signal.

A device for implementing the control method operates as follows. The rectifier converts the alternating voltage of the generator 5 into a constant voltage with a ripple equal to twice the frequency of the network. At the output of the rectifier, taking into account the operation of filter 6, we have the voltage in the form shown in Fig. 2 (first diagram). The key element 7 (transistor) is turned on by a signal from the control unit 10 with a frequency equal to the resonant frequency of the load circuit from elements 8 and 9. The moment of switching on of the element 7 is synchronized by the signal of the voltage sensor 11. Thus, the inverter operates on the principle of self-excited. A negative half-cycle in the operation of the inverter is generated in the form of free oscillation.

To control the output power, the conduction interval of the key element is changed over the period (positive half period) of the output frequency. Voltage sensor 12 measures the voltage at the output of the rectifier. The output level reference device 14 generates a constant reference voltage. Two voltages: from the output of the sensor 12 and the device 1.4, are compared in the comparator 13. When the voltage exceeds the reference from the output of the device 14 from the output of the sensor 12, the comparator 13 generates a switch-on signal of the key element 7 for the control unit 10. As soon as the voltage at the output of the sensor 12 will exceed the voltage at the output of the device 14

0, the comparator 13 is activated and the supply of a control signal to enable the key element 7 is enabled. Thus, by changing the level of the reference signal from output 14 from each half-cycle of the supply

5 voltages cut out the interval during which the load (8, 9) is not connected to the power source. The duration of the interval varies with the level of the reference signal. As a result,

0 regulation of power output. The above is illustrated by the diagrams of Fig. 2 (second - fifth).

The second diagram shows the signal from the output of the device 14. In the third diagram, 5 the envelope voltage on the load circuit 8, 9 (the diagrams correspond to the maximum output power of the induction heating device). The fourth diagram shows an enlarged signal from the output of the device 14. The fifth diagram illustrates a decrease in the output power level of the induction heating device to increase the signal from the output of the device 14. The envelope curve appears

5 intervals when element 7 is not turned on. The voltage sensors 11 and 12 are implemented according to any of the known schemes. Comparator 13 is an integrated circuit. The output power level setting device 14 is implemented as a reference voltage source and can be implemented on any of the known circuits. The control unit 10 is implemented similarly to the control unit of the prototype.

5

Compared with the prototype, the range of control of the output power of the induction heating device when controlling by the claimed method can be increased by 1.5-2.0 times.

When regulated according to the prior art, due to the deterioration of the filtering conditions and the protection of the supply network against the ingress of high-frequency components 5 current, the control range is limited to 45-50% of the maximum power.

With the control according to the claimed method, the control range can be expanded up to 90% of the maximum power.

Claims (1)

SUMMARY OF THE INVENTION A method for controlling the output power of an induction heating device comprising a single-phase rectifier with a capacitive filter and an inverter in the form of a series circuit of a key element and an inductor shunted by a compensating capacitance, with a key element control unit in which the time of the conductive state of the key element is controlled by period of the inverter output frequency, I distinguish u and with the fact that. In order to expand the range of regulation of the output power, the voltage at the output of the rectifier is measured. generating a reference signal of the output power level by setting the voltage level, comparing the measured voltage and the reference signal, generating a prohibition signal to turn on the key element when the voltage at the output of the rectifier is lower than the reference signal, and changing the output power level by changing the reference signal. 2 as J Ј .Ht g Fig .-. 1  Figure 2 V H