The use of supplementary controllers for mitigating subsynchronous control interaction (SSCI) in doubly-fed induction generator based wind parks is quite promising due to their low investment costs. These SSCI damping controllers are typically designed and tested using an aggregated wind turbine (WT) model that represents the entire wind park (WP). However, no research has been reported on their implementations in a realistic WP. This paper, first presents various implementation schemes for a linear-quadratic regulator based SSCI damping controller, and discusses the corresponding practical challenges. Then, an implementation scheme that obviates the need for high rate data transfer between the WTs and the WP secondary control layer is proposed. In the proposed implementation, the SSCI damping controller receives only the WT outage information updates from the WP controller, hence it is not vulnerable to the variable communication network latency. The SSCI damping controller parameters are also modified when there is a change in WT outage information for the ultimate performance. The effectiveness of the proposed implementation scheme is confirmed with detailed electromagnetic transient simulations, considering different wind speeds at each WT and WT outages due to sudden decrease in wind speeds.
Large-scale PV power plant (LS-PVPP) projects are generally carried out by engineering, procurement, and construction methods. In addition to designing different parts of the power plant with the classification of engineering documents, it is necessary for the design team to be familiar with the design methodology of an LS-PVPP. Due to its importance, this chapter presents more details of engineering documents and their classification. Due to the scale of construction of LS-PVPP, the volume of documents is high and the process producing documents is complicated. The classification of LS-PVPP engineering certificates, in general, is divided into four main categories, namely feasibility study; basic design; detailed design and shop drawing; and as-built and final documentation. The chapter introduces a method for roadmap and optimal design of PV plant equipment.
Wireless communications can facilitate transfer of synchrophasor data between spatially separated phasor measurement units (PMUs) and phasor data concentrators (PDCs). However, such communication systems may impose random access delay and failure on PMU channels that lead to missing synchrophasor data frames at the output of the PDC. This paper presents a new approach for online reliability assessment and improvement of synchrophasor data communications. The proposed approach involves elaborate estimation and probabilistic prediction algorithms that trigger a prioritized handover mechanism in order to minimize the number of synchrophasor data frames that are missing over successive time stamps. Extensive simulations based on the LTE communications in a low-voltage distribution feeder confirm significant performance improvement and fast fault detection under the communication link failures. This non-intrusive approach can be adopted by network operators to ensure reliable transmission of synchrophasor data to monitoring, control, and protection applications in smart grids.
A novel filter for use in three-phase power systems is introduced. When the input to the filter is a three-phase balanced set of signals, the filter suppresses noise and distortions and extracts a smooth version of the fundamental components. When the input signal to the filter is unbalanced, it extracts the positive-sequence components of the input signal. The filter also estimates the magnitude, phase-angle and frequency of the input signal while adaptively accommodates variations in all these three variables. Characteristics of the filter including its mathematical equations as well as steady-state and dynamic responses are discussed in this paper. Structural simplicity and robustness of the filter make it desirable for power system application. It can specifically be used as an adaptive anti-aliasing filter
This article presents a controller in stationary frame for enhanced performance of voltage source converters (VSCs) under weak and unbalanced grid conditions. The controller incorporates a nested multiloop structure consisting of an inner phase-locked loop-integrated current controller as well as an outer dc-link voltage control loop based on integral-resonant control mechanism. The controller neutralizes double-frequency oscillations of the dc-link voltage as well as third-order harmonics in the output currents under voltage imbalance while improving system performance and stability under weak grid conditions. First, the dc-link dynamics of a VSC under unbalanced grid conditions are revisited. It is shown that in the power balance equation, there are nonlinear coupling terms between different mechanisms of the dc-link control loop. Second, this article proposes an approach to surpass these terms by separating dc voltage dynamics. Finally, using a robust multivariable control approach, system performance, and stability under weak grid conditions are significantly improved. Software simulations and hardware-in-the-loop tests are carried out to validate the enhanced performance of the proposed controller.
Microgrids are prone to network-wide disturbances such as voltage and frequency deviations. Detection of disturbances by a microgrid central controller is therefore necessary for improving the network operation. Motivated by this application, this paper presents a new structure for the centralized detection of disturbances with noisy synchrophasor data and packet delay/dropouts. We build the proposed structure starting from the analysis of noise-delay tradeoff in synchrophasor networks and developing a new phasor data concentrator for compensation of data losses. The statistical performance metrics of the disturbance detector are numerically evaluated in the case of islanding detection, corroborating that the centralized detector counteracts the measurement noise and lowers the detection time. Numerical results show that the proposed structure significantly mitigates the probability of false detection. Moreover, it can achieve the lower bound of average detection time in a wide range of packet drop rates. This paper is useful to network designers who need to employ data acquisition systems for reliable and robust microgrid control applications.
The employment of DC-Microgrids based on renewable power generation has shown to be a really good option for the decentralization of the conventional power grid and its modernization. However, the intermittent nature of renewable energy sources and the large variations of power demand caused by variable loads still represent a challenge from the control point of view, where the usual approach for the control strategy of DC-Microgrids still relies on linear PI-controllers and their simplicity. Recent literature has shown that the employment of such controllers, usually employing a linearized model designed for a specific operating point, represent a major factor on the underperformance and inefficiency of DC-Microgrids. To deal with these limitations, nonlinear controllers capable of providing a much broader operating region have been used to assure robust and stable operation for DC-Microgrids. The drawback of such controllers, and the main reason to still prevent their use on a larger scale, is that they usually present more complex models and a heavy mathematical approach is necessary in order to determine the control law, This paper will present in detail the analysis, modelling, and control design of a multi-variable nonlinear controller based on input-output feedback linearization for a 5-switch bidirectional DC-DC converter. The performance of the nonlinear controller is verified by means of simulation results for a case study concerning the connection of a Supercapacitor (SC) to a controlled DC-Microgrid.
This paper proposes an improved phase-locked loop (PLL) for estimation of frequency and phasors of three-phase voltage and current signals in power systems. It works for balanced and unbalanced inputs amd offers highly robust performance against wide range of input signal attitudes including its amplitude, and angle. Therefore, it can be reliably applied to different signals in power systems such as fault currents and short-circuit voltages. The parameters of the proposed system are conveniently reduced to the selection of two damping ratios based on developing a linear mathematical model. The simulation results confirm that the system is capable of tracking wide range of changes in frequency, amplitude and phase angle with excellent robustness and short transient time. The proposed system not only reduces the computations compared to its counterparts, but also improves a wide range of applications including grid-synchronization of distributed generation units, power quality monitoring, and measurement of synchrophasors.
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