As the wind-integrated power system is a strongly nonlinear system with uncertain operating conditions that vary with time, it is difficult to guarantee the effectiveness of the conventional model-based sub-synchronous damping control (SSDC). To solve this problem, a model-free adaptive control (MFAC) method for static synchronous compensator (STATCOM) is proposed to realize sub-synchronous oscillation (SSO) mitigation. The method is driven by a limited number of online input/output (I/O) data rather than full technical and operational details of the system. First, the structure of the proposed MFAC is described in detail with control algorithms of all modules. Particularly, a new form of one-step-ahead weighted predictive control algorithm of MFAC for SSO mitigation is proposed. Then, the convergence of tracking error along with the stability of the closed-loop system with the improved MFAC are analyzed. Finally, the performance of the proposed MFAC for STATCOM is demonstrated and compared with that of the conventional SSDC under various operating conditions. Time domain simulation results validate the effectiveness of the proposed MFAC and demonstrate its better adaptability than the conventional SSDC.

The strong nonlinearity, time-varying structure, and complex operating conditions in interconnected power systems with the wind farm deteriorate the control performance of widearea damping control (WADC) designed by conventional modelbased methods. In this paper, an improved model-free adaptive control (MFAC), which employs the pseudo-partial derivative (PPD) to linearize the nonlinear power system dynamically, considering WADC requirements and system disturbances is proposed to damp out the inter-area oscillation for wind farm. In addition, to compensate for communication delays in a wide-area measurement system (WAMS), an adaptive delay compensator (ADC) is employed to reimbursed both constant and variable delays. The proposed controller depends only on online I/O data, which avoids the complicated system modeling process and can adapt to variations of system operating conditions and delay scenarios. Moreover, compared to existing MFAC damping approaches, the proposed approach provides additional advantages for wind farm on managing initial values and the stability region of PPD. The communication delays are compensated, which is not considered in other MFAC-based methods. Finally, case studies with various uncertainties and disturbances are conducted to validate the proposed control strategy.

Truck-mounted mobile emergency resources (MERs) play a significant role in microgrid formation and regulation for power system resilience enhancement. This paper proposes a distributed fixed-time secondary control (DFSC) scheme to regulate the frequency and active power sharing in islanded microgrids with MERs. The proposed DFSC scheme is designed based on a general directed communication graph which considers MER characteristics (e.g., mobility, flexibility, and potential cyber threats). Each DER receives data from its neighbors through directional communication links. The proposed pinning control strategy selects only a small number of DERs for pinning, which have access to the reference frequency information and would guide the operation of remaining local DERs and MERs. In addition, the guaranteed convergence time is determined by control parameters and communication graph without applying the initial operation states. The paper demonstrates that the desired control performances (i.e., frequency restoration and accurate active power sharing) are realized in a timely fashion considering frequent operations of MERs. Case studies are tested and discussed for load variations, different control parameters, communication link failures, and MER operations through time-domain simulations in PSCAD/EMTDC platform.

Incorporating subsynchronous damping controllers (SSDCs) into the control loops of doubly-fed induction generators (DFIGs) is one of the most cost-effective methods to suppress subsynchronous oscillation (SSO). However, it is difficult to achieve satisfactory control performance of SSDCs due to the time-varying structure and operating conditions of wind integrated power systems. In this paper, an improved model-free adaptive control (MFAC) method is developed for DFIGs to overcome the limitations of conventional methods for SSO mitigation. First, the structure of the MFAC-based SSDC (M-SSDC) for DFIGs is designed. Then, an improved MFAC predictive control algorithm is proposed to achieve SSO mitigation. Moreover, the stability of the closed-loop system with the proposed M-SSDC is analyzed, which provides some guidelines for determining controller parameters. Additionally, the input-output signal pair of M-SSDC is selected by using geometric measure for the optimum damping performance. Case studies under various operating conditions of the test power system validate the effectiveness of the proposed M-SSDC as well as its superior damping performance over conventional approaches.

With the integration of renewable energy resources and variable loads into power grid, power oscillations caused by persistent external fluctuating forces are becoming more prevalent. Termed as “forced oscillations (FO)”, such phenomena could happen even when the grid is with good damping characteristics. Therefore, conventional mitigation methods based on improving damping are rendered less effective. By leveraging the new control capability offered by static synchronous compensator with energy storage (E-STATCOM), a novel approach to mitigating FOs is proposed in this paper. A control strategy based on resonant controllers is adopted to modulate active and reactive power supplied by E-STATCOM. It is theoretically shown that FOs propagating from the disturbed area to other areas can be effectively eliminated by this method. Besides, we derived the analytical relationship among the location, the capacity of E-STATCOM and the suppression performance. Case studies demonstrate the effectiveness of the proposed method.

The most effective countermeasure against forced oscillations (FOs) is to locate and isolate external disturbances from power systems. However, it is challenging for existing location identification schemes to meet real-time computation and communication requirements in central data concentrators. To solve this problem, we propose a distributed cooperative scheme for locating FO sources. Phasor data collectors (PDCs) located at local control centers are utilized to calculate local energy flows embedded in low frequency oscillations (LFOs). We apply an average-consensus algorithm for exchanging the energy flow information among local PDCs which detects the cut-set energy and locate the FO source in a distributed manner. We also propose an adaptive minimum cut-set division method based on graph theory. By implementing the proposed method on the central PDC, the auxiliary control data are updated automatically, which makes the location scheme adaptive to changes in grid and communication network topologies. The effectiveness of the distributed cooperative location scheme is verified using the results for IEEE 39-bus power system.