Study On Robust Control For ICPT System Based On μ-synthesis

Inductively coupled power transfer (ICPT) technology can be defined as atechnology where power is transferred in wireless way between two electrical isolationsides by a high-frequency alternating magnetic-field. This novel technology involveselectromagnetic coupling, power electronics, automatic control and other field. Due tothe vital components including resonant network, high-frequency converter and coupledmagnetic circuit, ICPT systems have represented some complicated mathematicalproperties such as autonomous oscillating property, high dimensional nonlinearity,uncertainty, etc. These system properties lead to a significant increase in the complexityand difficulty for system modeling and synthesis. From the literature review, it can befound that there isn’t such one effective method so far to solve the problems ofuncertain nonlinear behaviors modelling and robust synthesis for ICPT systems.Aiming at the complex dynamical behavior characteristics of ICPT systems, thispaper is devoted to proposing a robust synthesis method which can be universallyapplied to the modeling, control, analyses of stability and performance for this kind ofuncertain nonlinear systems, and further researching a practical ICPT system in order toverify the validity of the proposed method. The main works of this paper are listed asfollows:1． Proposed an improved generalized state-space averaging (GSSA) modellingmethodTo model the complex dynamical behaviors such as autonomous oscillatingproperty, high dimensional nonlinearity and uncertainty for ICPT systems, an improvedGSSA method is proposed by taking into account the system dynamic uncertainty(high-frequency unmodeled part), parameter uncertainty and external disturbances.Based on the system model described by traditional GSSA method, the system uncertainpart is first separated from the nominal part by means of the linear fractionaltransformation, and then the performance weighting functions are attached to the systemmodel for reflecting the spectrum characteristics of all the perturbations, and theimproved GSSA model is finally established to describe this augmented object.2. Studied and analyzed the robust synthesis control problem for ICPT system withstructured uncertaintyBased on the design indexes of system robust stability and robust performance, the robust synthesis problem caused by all the perturbations in ICPT system is firsttransformed into a minimization problem of the structured singular values so that ahigh-order and continuous μ synthesis robust controller can be solved by D-K Iterativealgorithm. In order to make μ synthesis robust controller easy in implementation ofpractical engineering, the optimal Hankel-norm approximation and discrete similarmethod are given in the paper which are respectively used to reduce the order anddiscrete the algorithm for μ synthesis robust controller.3．Studied the stability and performance analysis problems for the perturbed ICPTsystem, and proposed a robust optimization method for circuit parametersTo investigate the performance of closed-loop perturbed system, the nominalperformance, robust stability and robust performance are all tested and analyzed. Thenthe boundary condition of uncertain parameters to maintain the system robust stabilityand robust performance is further derived. On this basis, a robust optimization strategyof circuit parameters for the purpose of improving the system robustness is proposed.The core idea of robust optimization strategy is to reduce the system sensitivity tocircuit parameter perturbations by increasing the stability margin of closed-loop system,i.e. the reciprocal of structured singular value.4．Verified the validity of the proposed synthesis method via a practical ICPTsystemAccording to the improved GSSA model and circuit parameters obtained from therobust optimization for LCL type ICPT system, a robust controller is designed on thebasis of μ synthesis theory, and further the simulation model and experimental platformfor the μ synthesis control system are respectively established. From analyzing thesystem transient responses to external disturbances, load perturbations and referencevoltage changes, the simulation and experimental results can not only illustrate thevalidity of μ synthesis control, but also can verify the correctness of theoreticalresearch.The main contributions of the paper are as follows:1. Aiming at the modeling problem for a class of systems with autonomous oscillatingproperty, high dimensional nonlinearity and uncertainty such as ICPT systems, thevarious uncertainties and external disturbances have been innovatively taken intoaccount in the process of GSSA modeling and analysis, so that the complexdynamical behaviors of such systems can be described more objectively andaccurately. 2. Aiming at the robust synthesis problem of ICPT systems caused by all theperturbations, a robust control strategy based on the structured singular values hasbeen proposed. This control strategy that uses the system robust stability and robustperformance as the design indexes can guarantee the closed-loop system operationaccording to the predetermined performance.3. Aiming at the stability and performance analysis problem for ICPT systems withthe perturbations, the boundary condition of uncertain parameters to maintain thesystem robust stability and robust performance is derived. According to theboundary condition, a robust optimization method of circuit parameters has beenproposed for the sake of improving the system robustness.