State-Space Control of Electric Vehicle Charging

Sammanfattning

The increasing adoption of high-voltage battery systems in electric vehicles presentschallenges when interfacing with legacy charging infrastructure designed for lowerbattery voltage levels. This is because the charging voltage must exceed the batteryvoltage to drive current into the battery pack. To address this, the stator windingsof the electric machine are utilised as inductive elements within a DC–DC boostconverter, thereby reducing additional hardware requirements and enabling effectivevoltage boosting.However, employing the stator windings introduces significant control challengesdue to nonlinear dynamics, rotor-angle-dependent inductance, magnetic coupling,and eddy current effects. These characteristics lead to phase coupling, parametervariation, and the risk of unintended torque generation. To overcome these issues, astate-space-based cascade control strategy is developed, comprising an inner currentcontrol loop and an outer voltage control loop, both incorporating integral actionto ensure accurate tracking and elimination of steady-state error.The charging system is modelled and controlled in Continuous Conduction Mode(CCM), which represents the dominant operating regime during charging.The charging system is fundamentally control-affine with a state-dependent inputmatrix, which introduces nonlinear behaviour. The nonlinear system is linearisedaround a stable operating point using a first-order Taylor expansion and the Jacobianmatrix, enabling controller synthesis. The inner-loop controller is designedusing Linear Quadratic Regulator (LQR) techniques, while the outer-loop controlleris tuned via pole placement. Model accuracy is validated through comparison withanalytical transfer functions and independent circuit simulations, including verificationof transient behaviour using resonance-based peak-to-peak analysis.The proposed control framework is evaluated under varying operating conditions, includingchanges in supply voltage, load, and rotor position. The results demonstratestable and reliable voltage boosting, effective current regulation, and robustness tosystem nonlinearities. Furthermore, the state-space formulation provides a flexibleand adaptable control structure, supporting efficient integration into evolvingsystem designs and reducing development effort for the OEM.