Frequency-domain analysis of three-phase linear current regulators

Stationary frame proportional plus integral (PZ) current-regulated voltage-source inverters are conventionally regarded as unsatisfactory for ac systems because they cannot eliminate steady-state errors. This paper presents a technique for interpreting the stationary/rotating frame transformations as modulation processes in the Laplace domain, which move the control function from one part of the frequency spectrum to another. The technique is used to compare stationary and synchronous frame PI regulators on a common basis to better understand the advantages of a synchronous frame regulator. A new form of stationary frame resonant regulator is then derived which achieves zero steady-state error without requiring the complex transformations of a synchronous frame regulator. The performance of this new regulator is evaluated and found to be similar to that of the synchronous frame PI regulator.