This paper presents a novel fast frequency and voltage regulation method for battery energy storage system (BESS) based on the amplitude-phase-locked-loop (APLL). In the proposed method, the primary frequency regulation and inertia emulating control are designed based on grid frequency deviation ( ${\Delta }f$ ) and its differential $(df/dt)$ signals detected by APLL, avoiding complicated and sensitive differential operation to get better dynamic support performance. Moreover, unlike the traditional voltage control only using grid voltage deviation ( ${\Delta }V$ ), the proposed method also uses the voltage differential control ( $dV/dt$ -control) to improve dynamic performance of traditional voltage control and behaviors of grid voltage based on the $dV/dt$ signal from APLL. Finally, simulations and experiments are implemented to validate the effectiveness of the proposed APLL-based BESS on improving the dynamic behaviors of grid frequency and voltage.

Virtual synchronous control (VSynC) in DFIG -based wind turbines (WTs) was studied. This paper mainly studies the fault ride through strategy of the VSynC-based DFIG under symmetrical grid fault. The fault current is limited and the dynamic reactive power support to help grid voltage recovery are studied. Firstly, the transient behavior of the VSynC-based DFIG is analyzed and the influence of the originally existing virtual resistance is studied. In the proposed method, the virtual resistance just works in the forced current component to limit the forced component of the fault current and accelerate the attenuation of the natural flux. Then the dynamic feedforward compensation is employed to trade-off to limit the natural component of the fault current and decay the natural flux component aroused by grid faults. In addition, the fast dynamic reactive power support of during grid faults according to grid codes. On the post-fault, the coordination control of active power is also implemented to limit steady-state rotor current. Finally, simulation and experiment results demonstrate the feasibility and correctness of the proposed fault ride through strategy for the VSynC

The grid voltage modulated direct power control (GVM-DPC)-based inverter is an attractive solution to regulate the instantaneous real and reactive powers injected into power grids. However, the power coupling in GVM-DPC, i.e., interactions between the real and reactive power loops, may deteriorate its transient performance. In this paper, a power decoupling strategy for GVM-DPC is proposed based on a dynamic feedforward power compensation (DFPC) algorithm. It is proved that the proposed strategy has better decoupling performance than that of the traditional virtual impedance method (VIM). Firstly, power coupling characteristics in GVM-DPC are analyzed, indicating that the ignorance of voltage angle variation at the point of common coupling (PCC) will result in severe power coupling. Then, power coupling magnitudes are derived according to relationships among the real power, reactive power and PCC voltage. Next, the coupling magnitudes are compensated into the power control loop of the GVM-DPC for the better decoupling performance. The transient performance of inverter using DFPC is studied based on the impedance analysis. Also, the relationship between coupling magnitude and grid side impedance is studied, which indicates the limited power decoupling capability of VIM. Finally, the proposed method is validated by the simulations and a hardware-in-loop system.

This paper establishes an instantaneous voltage model to illustrate the dynamic characteristics of grid voltage in electromagnetic time scale affected by power-electronic interfaced voltage regulatory devices with two typical categories of control systems, i.e., power-current cascading control and power synchronization control, exemplified by the STATCOM and virtual synchronous condenser (VSCON) respectively. In this paper, a linearized instantaneous voltage model is firstly established to analyze the impact paths of control loops in the STATCOM and VSCON. Based on the model, the dynamic process of grid voltage is divided into three stages. Various factors on the dynamic process of grid voltage are analyzed, especially cascading control loops prior to the functioning of AC voltage control. Moreover, stiffness characteristic is proposed to evaluate the effects of power electronic interfaced voltage regulatory devices with different control structures. In addition, the effectiveness of the stiffness compensation based on the VSCON is validated by the study cases.

With the rapid development of wind power generation, the inertial response of wind turbines (WTs) has become a topic of wide concern recently, due to its influence on grid frequency dynamics and stability. This paper proposes and defines the inner potential to summarize and understand the inertia control methods and inertial response of type-3 and type-4 WTs, which is analogous to typical synchronous generators (SGs), to make it more easy to understand by system operators and engineers with a traditional power system background. The dynamics of the defined inner potential of the wind turbine without any inertia control is different from SGs, thus the electromechanical inertia is completely hidden. The rapid power control loop and synchronization control loop are the major reasons that the WT’s inertial response is disenabled. On the basis of the defined inner potential’s dynamic, the existing inertia control method for WTs are reviewed and summarized as three approaches, i.e., optimizing the power control or synchronization control or both. At last, the main challenges and issues of these inertia controls are attempted to explain and address.

This paper presents an improved virtual synchronous control (VSynC) for the grid-connected voltage source converter (VSC) so as to continuously operate under the grid voltage with steady unbalance. The improved VSynC introduces the negative sequence power controls on basis of conventional VSynC. The improved VSynC is capable of regulating the negative sequence internal voltage to reduce the negative-sequence injected currents and oscillated powers of the VSC aroused by the negative-sequence grid voltage. Three alternative local control objectives for the VSC itself under steady state unbalanced grid conditions and their corresponding power references are deduced and computed. Simulated and experimental results are presented to validate the correctness and effectiveness of the proposed improved VSynC to enhance the continuous operation performance of VSynC-based VSCs during grid voltage steady-state unbalance.