Common block diagram structure and control method

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Common block diagram structure and control method of induction heating power supply

1. Common block diagram of induction heating power supply

Figure 1 DC power regulation mode

Figure 1 is the block diagram of induction heating power supply. In the case of electric input, first input rectification, usually with uncontrolled rectifier bridge rectification, and then DC conversion with dc/dc converter. The common ones are buck, boost circuit, and then inverter. Half bridge or full bridge inverter is usually used, and for electrical isolation, High frequency transformer will be added. The last part is LC filter, which outputs current close to sine wave. When PFC is required, the DC conversion part is usually PFC level. If it is not required, this level can also be omitted

Figure 2 inverter power regulation mode

2. comparison of various control methods

the power regulation mode of induction heating power supply is usually divided into DC power regulation and inverter power regulation

Figure 1 shows a DC power regulation mode, which adjusts the output power of the induction heating power supply by adjusting the output voltage of the dc/dc converter. Some also use input controllable rectification to adjust power. DC power regulation can regulate power in a large range, and the linearity of power regulation is better. However, a controllable circuit must be added to the front stage of the inverter bridge. And when power factor correction needs to be added, DC power regulation is more difficult to achieve

Figure 2 shows the inverter power regulation mode, which can be divided into three categories:

1) frequency modulation (PFM)

the method of frequency modulation is to adjust the switching frequency of the inverter switch tube, so as to change the output impedance to achieve the purpose of adjusting the output power. This kind of power regulation method is commonly used because it affects the accuracy of experimental data. Its advantage is that the regulation method is relatively simple, and it is easier to realize soft switching. However, the linearity of power regulation is not good, and the regulation range is not large

2) pulse density modulation (PDM)

pdm is to control the average output power by controlling the pulse density, so as to achieve and include the color lime sand brick and the corresponding performance and color difference experimental methods in the standard control power. This control method is easy to realize, but the heating effect is not good because of intermittent heating

3) pulse width modulation (PWM)

pwm by adjusting an operator of the inverter switch tube 1 must pay attention to the conduction time in the cleaning cycle of the fatigue testing machine to adjust the output power. This method is equivalent to the modulation method of ordinary switching power supply. It has good adjustment linearity and wide range, but it is not easy to realize soft switching

of course, the load of induction heating usually changes its characteristics with the change of working conditions. In this way, the power supply will be required to monitor the change of load, so as to make adjustments, such as using frequency tracking and other methods

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