H∞ optimal control applied to PWM regenerative sinusoidal converters

PWM regenerative sinusoidal converters are front ends that transfer power in both directions at unity power factor. Although the chosen approach is voltage forced the input and output quantity is current. The primary objectives in either mode (direction of power transfer) is to maintain the DC-link voltage at a predetermined level and to ensure that the line currents are in phase with the respective voltage. Hence, the outputs of the controlled system are DC-link voltage and power factor, while the inputs to the controller are PWM modulation index and phase angle. Ideally, the controller objective is simply to minimise the deviation of the outputs from the desired values. However, this simple objective cannot be achieved because the mathematical models, on which the controller is designed are incomplete. Moreover, disturbance cannot be effectively isolated or modelled. Therefore it is necessary to design a robust controller, one that is able to cope with uncertainty-model error and disturbance. An appropriate technique suitable for the formulation of robust control is H^∞ optimisation. In this paper the authors introduce the technique, formulate the problem and discuss the results