A Type-3 PLL for Single-Phase Applications

Different structures of single-phase PLL have been widely developed for the synchronization of single-phase grid-connected power electronic-based equipments. These PLLs mostly employ proportional-integral (PI) controller as loop filter, thereby resulting in a type-2 control system. Hence, they are able to achieve zero steady-state phase error following step changes in frequency and phase of a single-phase input signal. However, when the input signal varies continuously over time in a linear manner, these PLLs exhibit a finite steady-state phase error. Thus, they may not be suitable for applications that require accurate estimation of phase angle when a ramp change in frequency occurs. To overcome this problem without compromising the benefits of type-2 PLLs, a type-3 PLL for single-phase applications is developed in this paper. Through experimental validation and comparison with an advanced single-phase type-2 PLL, the effectiveness of developed type-3 PLL is demonstrated.