# Resonant Power Supply for Plasma Cleaning Based on Fuzzy Logic Power Tracking
## 3 Resonant Power Supply Control Method for Plasma Cleaning
Its control flow chart is shown in Figure 6.  
The actual output power \(\mathrm{P_{CUR}}\) is calculated according to the sampled output voltage and current, and the power change value E is obtained by comparing it with the power  
Figure 5: Flow chart of PSPWM-PFM mixed modulation control program. Figure 6: Flow chart of maximum power tracking program based on PFM. at the last moment. Based on this, the disturbance step length \(\alpha\) is calculated. Firstly, judge whether the current actual power \(\mathrm{P_{CUR}}\) increases or decreases compared with the last power \(\mathrm{P_{LAST}}\). If it increases, the direction of disturbance is correct, and keep the direction of disturbance; otherwise, the disturbance will reverse. The increase or decrease of the frequency is determined according to the relationship between the current frequency \(\mathrm{F_{CUR}}\) and the frequency \(\mathrm{F_{LAST}}\) at the last time. Finally, judge whether the adjusted dead zone, duty cycle and frequency exceed the limit value. If not, the system will execute the adjusted frequency and update the power \(\mathrm{P_{LAST}}\) and frequency \(\mathrm{F_{LAST}}\) for the next calculation; otherwise, the frequency before the adjustment will be executed [14]. Although the PFM perturbation method has the advantages of being simple and efficient, it is difficult to achieve accurate and efficient power tracking for such a nonlinear time-varying system as a plasma discharge power supply. However, the fuzzy controller does not need an accurate mathematical model for the controlled object, so it is very suitable for this system. Therefore, the maximum power tracking algorithm based on fuzzy PFM is adopted in this paper to ensure that the system works near the resonant frequency point [15]. Figure 7 shows the working principle of the fuzzy controller. The system errors E and EC are obtained by the quantitative calculation of input and feedback, which are used as the input of the fuzzy controller. Control variables were fuzzified, fuzzy domains and corresponding membership functions were determined, and E and EC were obtained. Then, according to the pre-established fuzzy control rules, the decision is made, and the fuzzy output C is obtained. The fuzzy output C is de-fuzzified to obtain the actual control quantity C, which is sent to the control mechanism to complete the whole control process [16]. The control variables of the algorithm are system output power and frequency, respectively. The input \(e\) and \(ec\) of the fuzzy controller are their corresponding changes, namely:  
\[e=P(k)-P(k-1) \tag{1}\]  
\[ec=F(k)-F(k-1) \tag{2}\]  
The output parameter \(c\) is the disturbance amount to the driving signal frequency of the full-bridge switch tube, namely:  
\[c=\Delta F_{\mathrm{D}} \tag{3}\]  
The fuzzy theory domain of input \(e\), \(ec\), and output \(c\) is set as \(E=EC=C=[-1,\,-0.8,\,\ldots,\,0.8,\,1]\), with a total of 11 grades. The value of parameter variation and control quantity can be expressed by fuzzy subsets. The fuzzy subsets of power variable e and output control variable \(c\) are represented by seven fuzzy languages: \"positive big (PB), positive median (PM), positive small (PS), zero (ZE), negative small (NS), negative medium (NM), and negative big (NB)\". EC, the fuzzy subset of frequency variation, is expressed by six fuzzy languages: \"PB, PM, PS, NS, NM, NB\". The relationship between each input quantity and each fuzzy subset is represented by membership function. Membership curves of \(E\), \(EC\), and \(C\) are shown in Figure 2:0  
Figure 2:1 Fuzzy control principle. After the fuzzy processing is completed, the corresponding fuzzy control rules can be formulated. They are formulated according to human experience. The design idea is: when the power change is positive, the disturbance direction is proved to be correct, and the direction of output control quantity and frequency change quantity should be consistent, otherwise, the reverse operation should be carried out.