Research On Fractional-order Control Strategies Of Buck Converter

DC-DC converter is a kind of DC power converter of the power electronic devices,it is widely used in industry and civilian area, etc. In practice, there are usually theinfluence of load parameters, DC power supply input voltage fluctuations and otherfactors and will lead to the output voltage of converter performance becomes poor. Toimprove the dynamic and static performance of converter, and make it have a wide rangeof input voltage, good load capacity and strong anti-interference, select the appropriatecontrol method is very important.So far, people have proposed a lot of control methods about DC-DC converter, but itseach have advantages and disadvantages, in complex working conditions, the controlperformance is not satisfactory. In recent years, many studies found that the fractionalorder controller can achieve better control effect and robustness than the integer ordercontroller, and greatly promoted the application of mathematical theory of fractionalcalculus in the field of control. However, the studies of fractional order control aboutDC-DC converter are rare. Therefore, to explore fractional-order control strategies aboutDC-DC converter is a new idea and a method to improve output performance of theconverter. In this paper, the Buck converter as an example, put forward two kinds ofinnovative fractional-order control methods based on mathematical model of the Buckconverter, the analysis of integer order control, the fractional-order calculus and thetheory of fractional-order system:(1) Fractional-order lead-lag compensation control scheme for Buck convertermethodThis paper based on loop transfer function of closed loop control system of Buckconverter, using frequency domain analysis method, designed a fractional-order activelead-lag compensation network. The fractional-order compensation network has moreflexible structures. To get the control performance and stability that an integer-ordercompensation control can not achieve, it is necessary to choose an appropriate fractionalorder which can make control system get better gain margin and phase margin nearcross-over frequency. Simulation results show that even if the Buck converter changes inload, expected output voltage jump and working conditions, such as the input DC powersupply voltage fluctuation, fractional-order lead-lag compensation network control alsocan obtain more satisfactory voltage output performance and robustness compared withthe integer order control.(2) An adaptive fractional-order PI?D?control method for Buck converterStudy first from the state space model of the Buck converter, analysis kpand kiparameters in PI?D?controller with sliding mode control theory, and then proposed the kpand kiparameters adaptive control law, and give out adaptive PI?D?controller designmethod. Because the method is based on the design of integer-order PID controller, only to search order parameters of fractional calculus, and at the same time in the kpand kicontrol parameters according to the adaptive law is set by change, compared with theexisting traditional PI?D?controller design method, parameter design is more simple andflexible. The simulation results show that compared with the traditional integer order PIDcontroller and PI?D?controller, the adaptive fractional-order PI?D?controller can getbetter output voltage tracking control performance, can obviously enhance the systemload and input voltage perturbation ability, control has better robustness.The results of the study to explore the Buck converter control strategy, improve theconverter output performance and robustness provides a useful reference.