Design-Oriented Transient Stability Analysis of Grid-Connected Converters With Power Synchronization Control

Abstract

The power synchronization control (PSC) has been increasingly used with voltage-source converters (VSCs) connected to the weak ac grid. This paper presents an in-depth analysis on the transient stability of the PSC-VSC by means of the phase portrait. It is revealed that the PSC-VSC will maintain synchronization with the grid as long as there are equilibrium points after the transient disturbance. In contrast, during grid faults without any equilibrium points, the critical clearing angle (CCA) for the PSC-VSC is identified, which is found equal to the power angle at the unstable equilibrium point of the post-fault operation. This fixed CCA facilitates the design of power system protection. Moreover, it is also found that the PSC-VSC can still re-synchronize with the grid after around one cycle of oscillation, even if the fault-clearing angle is beyond the CCA. This feature reduces the risk of system collapse caused by the delayed fault clearance. These findings are corroborated by simulations and experimental tests.Index Terms-Transient stability, phase portrait, weak grid, power synchronization control.

Reference-Feedforward Power-Synchronization Control

“…Its properties have been studied in detail over the years. Two recent examples are the large-signal transient stability analysis presented in [3] and the analytic selection of the power-control gain derived in [4]. In addition, in [4] an empirical selection recommendation for the so-called active resistance (which resembles the proportional gain of a current controller) is given.…”

Transient Stability of Vdc – Q Control-Based PV Generator With Voltage Support Connected to Grid Modelled as Synchronous Machine

“…The need to develop new stability assessment methods for grid tied VSCs is also highlighted in [6]. Transient stability analysis of grid connected converters equipped with various control strategies has been reported in the recent works [7]- [16]. The transient stability of grid connected converter with Power Synchronization Control (PSC) is analyzed through phase portraits in [7].…”

“…Transient stability analysis of grid connected converters equipped with various control strategies has been reported in the recent works [7]- [16]. The transient stability of grid connected converter with Power Synchronization Control (PSC) is analyzed through phase portraits in [7]. The risk of transient stability due to Loss Of Synchronization (LOS) of grid connected VSC with PSC is carried out in [8] considering nonlinear model of PLL.…”

“…Transient stability analysis of grid connected VSCs during Low Voltage Ride Through (LVRT) is presented in [9]. However, the current control dynamics are not considered in [7]- [9]. The work carried out in [10] has incorporated Lyapunov functions to investigate the stability of Inverter-Interfaced Distributed Generator (IIDG).…”

“…The dynamics of converters are mainly dictated by the control strategy. In [7]- [16] the V dc − Q control has not been analyzed. The small signal stability analysis of dc link voltage control based converters is carried out in [18], [19].…”