Impact of Synchronization Phase Dynamics on DQ Impedance Measurement

Abstract

Small-signal stability assessment of the threephase system can be performed using the measured impedances of the load and source. To obtain the dc steadystate operation point, the impedances are measured in the rotating dq-frame, and the phase angle is needed for the coordinate transformation used in both the perturbation injection and the impedance calculation. However, the phase estimation may introduce additional dynamics, affecting the accuracy of impedance measurement. This paper investigates the impact of phase synchronization dynamics on the measured impedance results. It is revealed that the phase variations in the perturbation injection has little effect on the measured impedance, while the phase dynamics introduced in the impedance calculation may have a significant impact. Based on impedance transformation, a new impedance calculation method is proposed, which can reduce the errors caused by the phase dynamics. Finally, the simulation and experiment results verify the accuracy of the analytical results and the effectiveness of the proposed method.

Impedance-Based Interactions in Grid-Tied Three-Phase Inverters in Renewable Energy Applications

“…As discussed in Reference [89], the multivariable impedance measurements are extremely difficult to be performed due to the grid-impedance effect on the synchronization [90] as well as the highly varying nature of the grid impedance [91,92], and therefore, the accuracy of the measurements may be questionable. The same applies also to the measurements of the feedback-loop gains.…”

Single stationary domain equivalent inverter admittance for three‐phase grid‐inverter system considering the interaction between grid and inverter

“…Combining the models of power stage circuit (14), (15) and current controller (16), (17) through Park transformation model (10), (11), self-admittance Y SA and accompanying-admittance Y AA for the inverter itself can be derived as shown in (18) and (19).…”

“…For the measurement of dq and modified sequence domain impedance, the PLL and Park transformations are required [7, 10]. These parts introduce additional dynamics, which may affect the accuracy of impedance measurement [11].…”

Self-Synchronized Grid Impedance Estimation Unit Using Interpolated DFT Technique

“…Estimation of the impedance can be done in different reference frames: abc-frame [21]- [24], αβ (stationary) reference frame or dq (synchronous) reference frame. In this last case, voltages and currents acquired are transformed in the dq-frame first, using an estimated grid angle, typically obtained with a phase-locked loop (PLL) computed by the PIC [15], [20], [25]- [27], or by one featured in the impedance measurement unit (IMU) [18], [28]. The PLL effect on the grid impedance computation has been extensively described in the literature [25], [28], [29].…”

“…In this last case, voltages and currents acquired are transformed in the dq-frame first, using an estimated grid angle, typically obtained with a phase-locked loop (PLL) computed by the PIC [15], [20], [25]- [27], or by one featured in the impedance measurement unit (IMU) [18], [28]. The PLL effect on the grid impedance computation has been extensively described in the literature [25], [28], [29]. Because the grid angle estimator (GAE) tracks the angle based on the voltages, perturbations on the grid voltages result in a distorted angle, impacting the grid impedance estimation, especially for low frequencies.…”