| Induction heating power has been used widely in industrial areas. The control method for inverter is crucial to determine whether induction heating power can work safely and efficiently. In traditional method which uses analog control circuit, some disadvantages such as difficult debugging and aging component, are unavoidable. Digital control method is not mature now. With the development of Field Programmable Gate Arrays (FPGA), people gradually dedicate to develop all digital phase locked loop (ADPLL). ADPLL based on FPGA has a lot of advantage such as agility to design, convenient to amend and easy to realize. In this paper, a digital control strategy of inverter based on ADPLL is designed to realize the digital control of parallel inverter.Firstly, the operating principle, load character and operating states of resonance parallel inverter are investigated in this paper. Traditional analog phase locked loop(PLL) is analyzed, after analysis, a mathematical model for a proportional-integral control strategy ADPLL is put forward. Then the condition to stability, dynamic characteristic of ADPLL and the influence of parameter to the performance are discussed.Afterwards, all the logic design for the ADPLL is completed by the hardware description language, with two different modulus counters to implement the proportional-integral control strategy. The simulation wave and experimental results show that this ADPLL can not only implement frequency tracking, but is also smart to debug and can be applied to a wide-range of loads, compared with analog PLL.Finally, in order to complete the digital control of inverter with ADPLL, the digital start circuit and overlapping angle strategy is designed, With swept–frequency start circuit and fixed angle control principle. This paper use Verilog and VHDL language and top to down method to complete the design. The simulation results in QuartusII show that this design can complete the requirement of inverter controller. |
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