Control Performance Standards-Oriented Event-Triggered Load Frequency Control for Power Systems Under Limited Communication Bandwidth

Abstract : Load frequency control (LFC) of modern power systems tends to employ open communication networks to transmit measurement/control signals. Under a limited network bandwidth, the continuous and high-sampling-rate signal transmission will be prone to degradation of the LFC performance through network congestion. This brief proposes a decentralized control performance standards (CPSs)-oriented event-triggered (ET) LFC scheme for power systems under constrained communication bandwidth. The proposed scheme comprises the ET LFC scheme and the CPSs-oriented regulation scheme. In the CPSs-oriented regulation scheme, regulation rules are designed to adjust the threshold parameter of the ET LFC scheme based on the North American Electrical Reliability Council (NERC)'s CPS1 and CPS2. The rules generate a larger threshold parameter to lower the triggering frequency in order to reduce unnecessary transmission of measurement/control signals, while ensuring the frequency and tie-lie power of the power systems to meet the required CPS1 and CPS2 instead of the asymptotic stability requirement in the existing research. The reduced transmission of these signals lessens the communication burden. In addition, the decentralized control strategy is used to solve the problems of poor large scalability and computational dimension caused by the centralized control strategy. The effectiveness of the proposed scheme is evaluated on an IEEE 39-bus test system with renewable energy sources.
 ? In the previous studies, two typical three-area LFC schemes equipped with non-heat turbines, which are commonly used in the existing researches, have been applied to verify the effectiveness of the proposed method. ? At first, dimension difference caused from different types of turbine/generator is small, such as non-reheated and hydro turbine with 3rd-order and reheated turbine with 4th-order. ? Secondly, the number of equivalent generators contained in one control area is usually no more than four. ? Then the design of the multi-area LFC can be carried out one by one, which means that the total time spent will increase linearly with the number of areas.
 ? This provides the hint to deal with the event-triggering problems. Meanwhile, a novel two-layer structure was proposed to solve the set points compensation problem for industrial processes under network-based environment. ? In this paper, an event-triggered control algorithm is proposed for the LFC scheme of multi-area power systems. It is worth pointing out that, the proposed LFC problem is nontrivial. ? As the time delay will degrade the dynamic performance and cause instability of augmented power system. ? Instability of the LFC scheme denotes the deviation far away from zero which exists in the ACE and frequency.
 • In this paper, a delay-dependent robust method is proposed for analysis/synthesis of a PID-type LFC scheme considering time delays. • Due to the increased complexity and uncertainties of the modern power systems, various advanced control methods were proposed for the LFC scheme, such as genetic algorithm (GA), sliding mode control , and robust control . • Effectiveness of the proposed method is demonstrated by calculation of the RPI and simulation studies. • The controller gains can be optimized when a minimal RPI for a given delay upper bound is obtained by using the ICCL algorithm proposed in and the binary search technique.
 ? In particular, the delay-dependent stability of the LFC has been investigated via calculating delay margins, and the delay margins are used as a performance index to guide the design and operation of the LFC controller. ? The effect of the load disturbances on the augmented output is defined as a robust performance index (RPI) of the augmented LFC scheme. ? By utilizing a time-delayed system design approach, a new model of LFC scheme with delays is formulated where the communication delays and eventtriggered control are integrated for the LFC scheme. ? Due to the inevitable communication time delays such as packet dropouts, disordering and ACE signal updating [7], the control performance suffers severe time delays which may destabilize the power system.

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