# Resonant Power Supply for Plasma Cleaning Based on Fuzzy Logic Power Tracking
## 3 Resonant Power Supply Control Method for Plasma Cleaning  
This section proposes a PSPWM-PFM hybrid modulation control mode, aiming to combine the characteristics of PSPWM and PFM control modes, so that the system can adjust the output power quickly and accurately, and ensure that the system has a wide enough power tuning range. It can also adjust the working frequency of the system to prevent the system from deviating from the resonant frequency point due to changes in the external environment such as air pressure, temperature, or load, and maintain a higher output efficiency. Figure 3: Main circuit diagram of resonant power supply for plasma cleaning. Figure 2: Cross section of plasma torch: (**a**) Lateral section; (**b**) Frontal section; (**c**) Real figure. Figure 4 shows the PSPWM-PFM mixed modulation closed-loop control diagram of the system. Firstly, the output voltage signal U and current signal I of the system are sampled. The voltage signal is obtained from the secondary winding of the power transformer and sampled by the secondary voltage detection circuit. The current signal is sampled by a secondary current detection circuit. After the signal is sampled and calculated by the master chip, the actual output power P of the system is obtained. The functions of over voltage protection (OVP), over current protection (OCP), and over power protection (OPP) are also set for the sampled and calculated signals. The actual output power P is compared with the user's set power PSET, and the power deviation E is obtained. After the PID modulation of bias E and mixed modulation of PSPWM-PFM, the driving signal with variable pulse width and period is obtained, and then the corresponding IGBT tube in the phase-shifting full-bridge circuit is driven to achieve the modulation of the output power [10; 11]. The program of the mixed modulation part of the main control chip is executed according to the flow chart shown in Figure 5. After the system is powered on, soft start is carried out first. After arcing successfully, the system allocates an initial duty cycle and frequency to the driver according to the set power. Then the operation according to the deviation between the actual power value and the set power value is selected. If the deviation is greater than 100 W, the system adopts PSPWM modulation. The adjustment time of the system is reduced by using the characteristics of PSPWM rapid power adjustment, so as to ensure that the system has a larger power adjustment range. If the deviation is less than or equal to 100 W, the system adopts fuzzy PFM modulation and carries out maximum power tracking to ensure that the system works at the maximum power point under the current duty cycle, namely the resonant frequency point, to ensure that the system has a high-power factor and work efficiency. There are many ways to judge whether the system works near the resonant frequency point. One is to use the zero-crossing detection circuit to detect the zero-crossing of the secondary current of the transformer, and to ensure that the output current and voltage are in the same phase through the phase-locked loop, so as to ensure that the system works in the resonant state. However, for the plasma with a nonlinear working state, its load is always in a dynamic equilibrium state with large fluctuation, which is easy to cause the false zero-crossing detection and make the calculation result wrong [12]. Another simple and effective method is to continuously disturb the working frequency of the system, and record the corresponding working voltage and current, so as to find the working frequency corresponding to the maximum output power of the resonant power supply system for plasma cleaning. According to the simulation results, when the  
Figure 4: System mixed modulation closed-loop control diagram. system works near the resonant frequency, the active power output reaches the maximum value [13].