In order to enable the permanent magnet synchronous generator (PMSG)-based wind turbine (WT) to capture more wind energy while providing fast frequency supports effectively during disturbances, this paper proposes a time-sharing frequency coordinated control (TFCC) strategy. Firstly, a rotor virtual inertia control and a DC-link virtual inertia control are presented, and a new adaptive frequency droop control considering frequency deviation is proposed. Secondly, a novel TFCC strategy, which uses the frequency dead-band to coordinate the frequency regulation priority of above three controls, is proposed. With the proposed strategy, the electrostatic energy stored in the DC capacitor is always first utilized for frequency support, while the rotor rotational kinetic energy is only applied when the DC capacitor energy is used up. Finally, the control performance is studied in PSCAD/EMTDC, whose results indicate that the TFCC has better performance in terms of wind energy harvesting and system stability as compared to traditional coordinated control and cascading control, respectively.

High proportion of wind energy in modern power system requires wind turbines (WTs) to provide frequency regulation services. In this context, this paper proposes a comprehensive coordinated control strategy of permanent magnet synchronous generator (PMSG)-based WT for providing inertial response and primary control. Firstly, a DC-link inertia control is proposed for providing virtual inertia by using the electrostatic energy stored in the DC capacitor, and the key parameters that affect the virtual inertia provided by this control are discussed in detail. Moreover, in order to provide more virtual inertia, a virtual capacitor control (VCC) strategy is proposed. With the VCC strategy, the rotor-side converter (RSC) can provide a virtual capacitance much larger than the actual DC capacitance and supply fast and transient extra power support by using the WT’s rotor kinetic energy, in a similar way with the synchronous generator (SG) inertial response. A power-frequency droop control is adopted to allow WT to provide primary control service by using the WT’s rotor kinetic energy. Furthermore, the virtual inertia constant of the proposed strategy is analytically derived. Finally, the simulation results in PSCAD/EMTDC are presented to verify the effectiveness of the proposed control strategy.

State-of-charge (SOC) estimation of lithium-ion (Li-ion) batteries with good accuracy is of critical importance for battery management systems. For the model-based methods, the electrochemical model has been widely used due to its accuracy and ability to describe the internal behaviors of the battery. However, the uncertainty of parameters and the lack of correction from voltage also induce errors during long-time calculation. This paper proposes a particle filter (PF) based method to estimate Li-ion batteries’ SOC using electrochemical model, with sensitive parameter identification achieved using the particle swarm optimization (PSO) algorithm. First, a single particle model with electrolyte dynamics (SPME) is used in this work to reduce the computational burden of the battery electrochemical model, whose sensitive parameters are selected through the elementary effect test. Then, the representative sensitive parameters, which are difficult to measure directly, are adjusted by PSO for a high efficiency. Finally, a model-based SOC estimation framework is constructed with PF to achieve accurate Li-ion battery SOC. Compared with extended Kalman filter and equivalent circuit model, the proposed method shows high accuracy under three different driving cycles.

With the continuous increase of renewable energy generation and high voltage direct current (HVDC) power transmission, the system inertia is declining, thus resulting in greater risks of frequency instability. To solve this issue, a dc‐link inertia control is firstly proposed for a point‐to‐point modular multilevel converter based HVDC (MMC‐HVDC) link, which enables the MMC‐HVDC system to provide emulated inertia support by employing the electrostatic energy stored in the dc capacitors. Moreover, in order to maintain reasonable submodule capacitor size as well as provide more emulated inertia support, a virtual capacitor control for MMC‐HVDC connected an offshore wind farm (OWF) is proposed. With the virtual capacitor control, the OWF is able to provide a large capacity virtual capacitor in dc side of MMC‐HVDC link and supply desired emulated inertia support for onshore power system by utilising the offshore wind turbines’ rotor rotational kinetic energy. Furthermore, a procedure for selecting the appropriate virtual capacitor control parameters is proposed. Finally, the performance of the proposed coordinated control is researched in PSCAD/EMTDC, and the simulation results show that the onshore power system inertia is effectively improved with the coordinated control.

In the low-inertia power system, the lithium-ion (Liion) battery energy storage system (BESS) is expected to provide virtual inertia support to the power system. However, the state-ofthe-art output power boundary evaluation standards have not considered the time-varying feature of inertia emulation profile, based on which the inertia emulation capability of BESS cannot be accurately evaluated. Therefore, this paper firstly proposes the concepts of sustaining power (SP) and SP boundary (SPB) for evaluating the output boundary of BESS in inertia emulation condition. The sustaining current (SC) profile in inertia emulation condition that can opportunely make the response voltage reach the cut-off voltage is identified as the SC boundary (SCB), and the SPB can then be calculated. Then, an offline experimental SPB test method is proposed with improved efficiency, which can provide a predefined reference to the BESS operator and the grid before decision-making regarding frequency control. Applying the SC profiles on the BESS, the response voltage states are classified into three cases. In different cases, the SC profile is adjusted to approach the critical cut-off condition according to the proposed adjustment method. All the cases can achieve the critical cut-off condition with minimum attempts. The proposed SPB test method is validated by experimental tests on the 18650 Li-ion battery at different temperatures and with different state of charge (SOC). The experimental results indicate that the proposed SPB concept significantly increases the output boundary of battery, which can be captured offline with a limited number of trials under the proposed test method. The obtained SPB helps in quantifying the maximum virtual inertia that the BESS can deliver to the grid.

The hybrid high-voltage direct current (HVDC) transmission system with cascaded MMC converters has become a promising alternative for possessing the technical merits of both line-commuted converter (LCC) and voltage source converter (VSC), resulting in favorable characteristics and potential control of good prospect. This paper pays heightened attention to the feasible power and DC voltage control modes of a hybrid HVDC system; characteristics of master–slave control show higher flexibility than the LCC-VSC HVDC system, which demonstrates that the exceptional potential can serve to stability support the AC power grids. To optimize the control effect, besides damping level to attenuate power oscillations, the robustness suitable for various faults is also considered to obtain a multi-objective control problem. A detailed solution is proceeding using the TLS-ESPRIT identification algorithm and H₂/H_∞ hybrid robust control theory. This motivates multi-terminal controllers in the LCC rectifier and MMC inverters, which immensely improve the stability of both sending and receiving girds at the same time. According to the parameters of the actual hybrid HVDC project, the simulation model is established in PSCAD v4.6.2 software, and proposed control methods have been verified to satisfy damping objectives and perform well in multiple operating scenarios.