Modeling, analysis and control of buck type PWM converter by circuit DQ transformation

Abstract

The buck type PWM rectifier and current source type static var compensator (SVC) are completely analyzed using circuit DQ transformation. Exact LTI DC and AC equivalent circuits in unified forms are induced and full set of equations are derived in explicit form. From the DC circuit, various characteristics such as possible operating range, gain, powers, power factor, unity power factor condition and the practical behavior including component and load variations are analyzed clearly. From the AC perturbation circuits, the system dynamic characteristic equations of small signal dynamic model and simplified output model are fully derived. These circuit models are verified through computer simulations and experiments with good agreement, so it is very useful to estimate all the electrical values of the designed converter and to design the controller. Such analyses is not possible or very difficult in other modeling techniques, so the results contribute in the research area of the converter analysis and the easy controller design with sufficient accuracy. But it is noted that the model is based on the averaging concept, which may result in some time delay in control process, so the need of instantaneous model for real time control is also important. New modeling method by vector transformed circuit theory is proposed with theory and applications. The proposed method is general because the variables need not be sinusoidal, and has simple but full informed circuit forms, moreover the method is equivalent and easily converted to contemporary per phase analysis and DQ transformation analysis. The method is valid for any instantaneous variation of voltage and current, and adequately describes the performance of the converter under both steady stage and transient operation with simplicity and clear physical picture. As examples of applications, three- phase buck type PWM rectifier and single phase boost type PWM converter are modeled. From this model, full steady state a...