A comprehensive study of orthogonal signal generation schemes for single phase systems

Single phase dq (park) transformation finds widespread application in grid interfaced converter current control, phase locked loop, reference current generation and active/reactive power calculation. The method requires additional signal to create orthogonal set and transform it to rotating frame. This is generally achieved using orthogonal signal generation(OSG) unit. As park transformation is instantaneous, associated dynamic and steady state performance depends on how fast and accurately OSG can generate orthogonal signal set while eliminating noises and disturbance signal. Moreover, power calculation in stationary frame also necessitates orthogonal sets of voltage and current signal. This paper presents a comprehensive comparative study of several OSG mechanisms reported in literature and applied to single phase systems. Various aspects of OSGs are assessed including dynamic response, accuracy, disturbance rejection feature, frequency adaptability and implementation. Moreover, issues in complex coefficient filter based OSG are identified and a generalized time delay transformation with reduced computation is also suggested. The discussions presented are substantiated via simulation results.