An increased number of microgrids (MGs) will exist in future active distribution systems (ADSs); however, these MGs belong to multiple operators and cannot simply be controlled as a public grid in the electricity market environment. For multimicrogrids (MMGs) which have multiple coexisting beneficiaries, it will be unfeasible to realize a cooperative control among them. Hence, we propose a game theoretic non-cooperative distributed coordination control (NCDCC) scheme to address multi-operator energy trading and facilitate a powerful control structure for MMGs. The proposed NCDCC coordinates the individual benefits of each MG and achieves a global objective, based on differential game theory (DGT). Furthermore, it simplifies the implementation of many ADS control functions, including global coordination, local autonomy, and self-healing, by reconsidering an ADS as MMGs and every MG as an agent. Moreover, the NCDCC reduces the control dimension and number of agents by obviating the requirements for a central controller and complex communication topologies. We investigate the effectiveness, adaptability, and fairness of this scheme by means of several representative cases studies.

To overcome the real-time problem of maximum power point tracking (MPPT) for partially shaded photovoltaic (PV) systems, a novel nature-inspired MPPT controller with fast convergence and high accuracy is proposed in this paper. The proposed MPPT controller is achieved by combining salp swarm algorithm (SSA) with grey wolf optimizer (GWO) (namely, SSA-GWO). The leader structure of the GWO algorithm is introduced into the basic SSA algorithm to enhance the global search capability. Numerical simulation on 13 benchmark functions was done to evaluate the proposed SSA-GWO algorithm. Finally, the MPPT performance on PV system with the proposed SSA-GWO algorithm under static and dynamic partial shading conditions was investigated and compared with conventional MPPT algorithms. The quantitative and simulation results validated the effectiveness and superiority of the proposed method.

Accurate fault location reduces operating cost and outage time. This paper proposes a time-domain method to accurately locate faults in transmission lines, which only requires a very short data window (several milliseconds) during faults. First, the voltage distribution through the line during faults is accurately obtained by solving the matrix form partial differential equations using the proposed numerical scheme. The proposed numerical scheme is mathematically validated for the transmission line fault location problem, with the optimal selection of time and distance intervals to ensure stability and minimum solution error. Afterwards, the fault location is obtained via the extremum value of the voltage distribution. The method fully considers distributed parameters as well as asymmetry of the line. Extensive numerical experiments validated that (a) the proposed numerical scheme demonstrates advantages towards other numerical schemes; (b) the proposed method presents higher fault location accuracy compared to the existing method, independent of fault types, locations and impedances; and (c) the fault location accuracy is not sensitive towards fault inception angles, loading conditions, measurement errors and parameter errors. The proposed method works with relatively low sampling rates (80 samples per cycle) and is compatible with IEC 61850 standard in present digital substations.

Large scale wind farms (WFs) are gradually required to participate in power system frequency regulation especially in a weak grid. Corresponding ancillary frequency control functionalities and the contribution of the WF to system frequency stability are well studied. However, the impact of WF ancillary frequency control on wind turbine generators (WTGs) is rarely considered. It is found in this paper that the ancillary frequency control deteriorates drive-train torsional oscillation of the WTG, which restricts application of the ancillary control. To overcome this problem, this paper proposes an adaptive damping control scheme based on reactive power modulation of the WTG to suppress drive-train torsional oscillation, which can assist the WF to meet the grid code requirements. Superior to the traditional active power modulation method, the proposed adaptive control scheme can achieve satisfactory damping improvement with less control effort. Furthermore, the adaptive scheme with a torsional frequency updating mechanism can effectively counteract torsional damping deterioration caused by parameter uncertainties, operating condition or control mode variations. Feasibility and effectiveness of the proposed damping control are validated by simulations and real-time experiments.

This paper analyzes the influence of the doubly fed induction generator (DFIG) based wind farm (WF) participating in the frequency response (FR) on the oscillation modes of the power system and proposes a hybrid modulated active damping scheme to mitigate the potential power oscillations. The FR control would excite additional lightly damped electro-mechanical oscillation mode and deteriorate the damping for the primary interarea oscillation mode inside the power system. Moreover, the internal damping effect on the turbine torsional oscillation would be weakened resulting shaft damage risk if FR is required by the WF. The frequencies of those modes are usually close to each other. By integrated hybrid multiple active damping loops into the active and reactive power controller of the WF respectively, the damping control on all the oscillation modes can be improved at the same time. The analysis and effectiveness of the proposed scheme in this paper are verified by the time-domain simulations.

Equivalent inertia of the power system is reducing with the increasing wind power penetration. To alleviate this issue, more and more countries have put forward grid codes which require wind farms (WFs) to provide inertial response as traditional synchronous generation does. It is found in this paper that the synthetic inertial control of the WF in a weak grid deteriorates drive-train torsional oscillation of wind turbine generators (WTGs). Furthermore, the WF emulating inertial response is involved in power system oscillations and induces a new critical low frequency oscillation. The above oscillations threaten small-signal stability of the WF and the power system, which restricts the WF to fulfill grid code requirements. To overcome this problem, this paper proposes a two-level damping control scheme consisting of a WTG level torsional oscillation damping control and a WF level low frequency oscillation adaptive damping control to enhance damping characteristic of the WF. Simulation results show that the two-level damping control can simultaneously counteract these concerned multiple oscillations under various operating conditions, which facilitates the WF to meet grid code requirements and improves dynamic stability of the WF and the power system.