The Research of Buck Converter Sliding Mode Algorithm based on Power Function Exponential Reaching Law

Abstract

The article designs a new kind of power function exponential reaching law based on exponential reaching law. It associates the speed of the trajectory and the distance of velocity to the sliding mode surface and uses intelligence features of the exponential function. The reaching law suppresses the chattering phenomenon and overcomes the exponential reaching law through a switch sliding mode surface. The power function exponential reaching law is applied to the Buck converter, and presents a specific Matlab/Simulink module, the simulation verified the effectiveness of this method. Introduction Sliding mode control is a kind of variable structure control method, it is not sensitive to the internal parameters and external disturbance, and has good robustness. Dynamic response is relatively excellent, suitable for engineering practice. Under ideal conditions, the switching frequency is infinite and won't produce the chattering. But in the real cases, chattering is unable to avoid. Chattering can cause high frequency oscillation in the system, it also put forward a great challenge for its application in the engineering practice. Scholars at home and abroad focus on a lot of problem of chattering on the sliding mode control method. Our scientists founded near rate method to reduce the chattering in the sliding mode movement problems and got the ideal effect . The literature [2] proposed variable speed reaching law for the first time. It produced the fan switch area, gived the fan switch area and the mathematical model of quasi sliding mode. The literature [3] combined fuzzy control with sliding mode control, adjusted the coefficient of exponential reaching law through the fuzzy rules. It settled the input fuzzy rules to the absolute value s of the switch function, the output of the fuzzy rules for coefficient and the exponential reaching law e and k , which could further improve the dynamic performance of the sliding mode, reduced the high frequency vibration of the system. The literature [4] designed a kind of adaptive variable speed reaching law in front of the track to sliding mode, used the adaptive exponential reaching law. It reached the sliding mode surface and used variable speed reaching law, effectively reduced the chattering. The literature [5] was based on power frequency approach Rate and integral reaching law. It designed a number of power points near rate and power frequency near rate index of integral sliding mode observer. The simulation results showed that the sliding mode observer had played a very good effect on inhibition of jitter. The literature [6] proposed a double exponential reaching law and increased the convergence speed of the system, the system had better dynamic quality. The literature [7] proposed a new discrete reaching law for the uncertain part of the system. Disturbance predictor was designed and made the system stable in the origin, had very high estimation precision, wreaked the chattering effectively. The literature [8] used fuzzy control for International Conference on Information Sciences, Machinery, Materials and Energy (ICISMME 2015) © 2015. The authors Published by Atlantis Press 962 on-line estimation in view of the uncertainties in the system, fuzzed adaptive adjustment of the switch gain and reduced the switch gain as far as possible, in order to reduce chattering. This paper designs a new kind of sliding mode reaching law the exponential function on the second order the Buck converter, the reaching law is based on sliding mode variable index reaching law. It adapts the design of the exponential function of symbols instead of sliding mode variable structure control switch function and a larger scale has the effect of adaptive adjustment, effectively suppress the chattering phenomenon. The mathematical model of Buck converter Buck converter is a DC Buck converter. It is also known as DC chopper, it is a kind of output voltage which is less than or equal to the average of the input voltage of the switch tube DC voltage converter. Fig.1 Buck converter topology structure diagram Fig.1 is Buck converter topology structure. U1 stands for input DC voltage, Vg stands for switch tube which is responsible for the entire circuit on and off, D stands for the fly-wheel diode, L, C stands for inductance and capacitance, RL stands for the load resistance. When the switch tube Vg conducts, charges current through the inductor L load; when switch tube Vg shuts off, the load current through the inductor L discharge. Buck converter maintains the stability of the load voltage by rapid on-off switch tube. Keeping the switch tube Vg on and off cycle can adjust the size of the load on both ends of the output current and voltage. If load is the impedance load, we consider iL inductor current and capacitor voltage vc as state variables, ignore the inductance and capacitance of the parasitic resistance. We can get the state space equation of the Buck converter: