Frequency and Voltage Stability Analysis of Grid-Forming Virtual Synchronous Generator Attached to Weak Grid

Abstract

Virtual synchronous generator (VSG) control technique is widely used for the grid-friendly integration of renewable energy. However, when VSG is attached to a weak grid, it is prone to voltage and frequency instability, which aggravates the voltage quality and frequency quality at the point of common coupling (PCC), and in turn, pollutes the supplying quality for the loads. On the one hand, focusing on voltage stability, this paper proposes the impedance modeling for VSG in the synchronously inertial reference coordinates (SIRC) to measure the voltage stability of grid-tied VSG and identify the interaction between VSG and the weak power grid. Studies show that weak grid strength can lead to a wide-band oscillation of VSG. On the other hand, focusing on frequency instability, the motion equation has been put forward to illustrate the oscillation and dynamic deviation of frequency. The relationship between synchronizing ability of VSG and grid stiffness is discussed. Besides, this paper proposes an inertia-damping-strengthened control method to improve frequency stability. Finally, the theoretical analysis is compared with simulations and experiments.

Grid Forming Inverter Modeling, Control, and Applications

“…The authors in [89] propose impedance-based modeling of grid forming VSG in synchronous inertial reference coordinates (SIRC) to measure the voltage stability of weak grids. Moreover, frequency dynamics are also analyzed by proposing a motion equation, where the stiffness is defined to illustrate the synchronizing capability of VSG with weak grids.…”

Effects of clock deviations on the performance of microgrids based on virtual synchronous generators

“…Typical compensators used in [39,40] these equations are listed in Table 1. In the swing equation, the damping effect in the active power is often emulated using a proportional (P) controller of the frequency error [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36]. In some studies, a derivative (D) controller is used to accelerate the transient response of the virtual generator [37,38].…”

“…In some studies, a derivative (D) controller is used to accelerate the transient response of the virtual generator [37,38]. Both P and D compensators introduce a steady-state frequency error when the governor equation is not equipped with an integral compensator [4,[23][24][25][26]. In the governor equation, the basic compensators are considered first, including P, D, integral (I), and proportional-integral (PI) [17][18][19][20][21][22][23][24][25][26].…”

“…Both P and D compensators introduce a steady-state frequency error when the governor equation is not equipped with an integral compensator [4,[23][24][25][26]. In the governor equation, the basic compensators are considered first, including P, D, integral (I), and proportional-integral (PI) [17][18][19][20][21][22][23][24][25][26]. The use of a low-pass filter at the output of a P, PD or PI compensator, hereafter referred to as LPF(P), LPF(PD) or LPF(PI), provides a degree of freedom in the design of these controllers and facilitates the achievements of their dynamic specifications [27][28][29][30][31][32][33][34][35][36][37][38].…”

A New Perspective for Relating Virtual Inertia With Wideband Oscillation of Voltage in Low-Inertia DC Microgrid

“…In some references, a virtual inertia control is used for improving the transient response of the system, i.e., alleviating the RoCoF and FN [23]- [25] or rate of change of voltage (RoCoV) or DC voltage nadir (DCVN) [16], [17]. No matter of RoCoF, FN, RoCoV, or DCVN, it is attributed to the imbalanced active powers which compels the frequency or DC voltage deviate from the nominal value, and thus a RoCoF (RoCoV) and FN (VN) has been emerging.…”