Research Of Mid-frequency Magnetron Sputtering Power Supply Based On All Digital Control System

Mid-frequency magnetron sputtering power supply(MFMSPS) is the preferredselection for large-area magnetron sputtering production line. The technologydevelopment status for MFMSPS and influence on process for different operatingmodes are introduced. The advantages and disadvantages of coating process withdifferent output waves are analyzed, and hence the bipolar rectangular wave isadopted as the output mode. Compared with analog controlled power supply, thedigital controlled power supply has various advantages, which is a development trendfor switching mode power supply. FPGA is hereby used to build all digital controlsystem. Based on FPGA, man-machine interface circuit and protection circuit are alsodesigned and programed.With the AC-DC-AC two-level converter applied to main circuit, the theorydesign of MFMSPS and the calculation and choosing of parameter are researchedwith simulation software SABER. Digital pulse width modulation signal issynthesized by FPGA via frequency divider and counter. IGBT driver modulesM57962L is used to control the switches’ on and off, achieving the purpose ofregulating power transmission. With the current sensor to real time sample outputcurrent, via signal filter circuit, A/D transform circuit and PID closed-loop controlarithmetic, corresponding DPWM is outputted to regulate forward Buck choppercircuit’s driving duty cycle, and cause corresponding change of bus voltage afterinverter input. Hence loading current is regulated and the MFMSPS with constantcurrent characteristic is achieved. Arc is detected or interrupted with software method.Over current, over heat and other protections are designed. Output wave parameter isregulated by using key press to set full-bridge inverter circuit driving signal’sfrequency and duty cycle, so that coating process is satisfied. The designed mid-frequency power supply’s frequency can range from20kHz to40kHz, duty cyclefrom10%to80%. The maximum output voltage is600V and the maximum outputcurrent is10A.Time delay in digital control, A/D conversion resolution, the DPWM resolutionand sampling and holding that impact on the digital controller performance wasanalyzed. Every module is programed with VHDL and its validity is verified throughsimulation. With the mathematical model of system analyzed and the control model ofsystem designed, the parameter of digital PID controller is set by using MATLAB andits validity is verified through simulation as well. The controller meeting therequirements can be seen from the Bode diagram and step response. The experimenton a prototype machine verified the feasibility and validity of the design scheme.