Estimation-based Consensus Approach for Decentralized Frequency Control of AC Microgrids (original) (raw)
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Decentralized Frequency Control of AC Microgrids: an Estimation-Based Consensus Approach
IEEE Journal of Emerging and Selected Topics in Power Electronics, 2020
In this paper, a decentralized secondary control (SC) based on the active power estimation (APE) is presented. This achievement is realized by employing the unique feature of frequency as a global variable in autonomous AC microgrids (MGs). The APE is merely based on the droop coefficient of P −ω characteristics. The decentralized SC, utilizing a consensus protocol, restores the MG frequency to the nominal value while maintaining accurate power-sharing of the droop mechanism. The consensus protocol is estimation-based and does not require communication infrastructure. In addition to the proposition of stability analysis method, experimental results with four distributed generation units (DGUs) also verify the effectiveness of the proposed SC structure.
Cooperative frequency control for autonomous AC Microgrids
2015 IEEE Eindhoven PowerTech, 2015
Distributed secondary control strategies have been recently studied for frequency regulation in droop-based AC Microgrids. Unlike centralized secondary control, the distributed one might fail to provide frequency synchronization and proportional active power sharing simultaneously, due to having different control parameters. This paper introduces a cooperative algorithm that regulates the system frequency while maintaining the power sharing properties of droop control. Dynamic consensus protocol is used to estimate the average of normalized active powers in the entire MG. This estimation is then added to primary control, compensating the frequency drop caused by the droop mechanism. The proposed controller is fully distributed, meaning that each source exchange information with only its direct neighbors through a sparse communication network. This controller has a unique feature that it does not require measuring the system frequency as compared to the other presented methods. An ac Microgrid with four sources is used to verify the performance of the proposed control methodology.
2019 IEEE 28th International Symposium on Industrial Electronics (ISIE), 2019
In this paper, a novel decentralized control structure is proposed to compensate voltage and frequency deviations of an ac microgrid (MG) with higher bandwidth compared to the conventional control structure with no need for a communication network. This approach is realized by firstly employing finite control set model predictive control of voltage source converter at the primary control level. Then, an adaptive droop control is presented to keep the voltage and frequency of the MG stable in steady state and serve as a secondary level of hierarchical control. Therefore, the MG voltage and frequency are restored to the nominal value with a decentralized communicationfree control structure. Simulation results verify the accurate frequency and voltage restoration as well as fast power-sharing during the transient and steady-state performance with no need for communication infrastructure.
Decentralized Optimal Frequency Control in Autonomous Microgrids
This paper proposes a decentralized optimal secondary controller for frequency regulation and accurate active power sharing in autonomous microgrids. This optimal controller does not require any communication network. Unlike most of the existing works, a systematic approach of secondary controller design is introduced based on a quadratic cost function in the form of a linear quadratic regulator (LQR) solution. The design procedure only depends on the cut-off frequency of the power calculation filter. Decentralized behavior, simplicity, optimality based on a quadratic cost function, and straight forward design procedure are the main advantages of this approach. Using the proposed solution, frequency can be restored immediately following any disturbance in the system, without need of any event-driven and time-dependent protocol. Experimental results validate the effectiveness of the proposed controller.
Droop-free Distributed Control for AC Microgrids
IEEE Transactions on Power Electronics, 2015
A cooperative distributed secondary/primary control paradigm for AC microgrids is proposed. This solution replaces the centralized secondary control and the primary-level droop mechanism of each inverter with three separate regulators: voltage, reactive power, and active power regulators. A sparse communication network is spanned across the microgrid to facilitate limited data exchange among inverter controllers. Each controller processes its local and neighbors' information to update its voltage magnitude and frequency (or, equivalently, phase angle) set points. A voltage estimator finds the average voltage across the microgrid, which is then compared to the rated voltage to produce the first voltage correction term. The reactive power regulator at each inverter compares its normalized reactive power with those of its neighbors, and the difference is fed to a subsequent PI controller that generates the second voltage correction term. The controller adds the voltage correction terms to the microgrid rated voltage (provided by the tertiary control) to generate the local voltage magnitude set point. The voltage regulators collectively adjust the average voltage of the microgrid at the rated voltage. The voltage regulators allow different set points for different bus voltages and, thus, account for the line impedance effects. Moreover, the reactive power regulators adjust the voltage to achieve proportional reactive load sharing. The third module, the active power regulator, compares the local normalized active power of each inverter with its neighbors' and uses the difference to update the frequency and, accordingly, the phase angle of that inverter. The global dynamic model of the microgrid, including distribution grid, regulator modules, and the communication network, is derived, and controller design guidelines are provided. Steady-state performance analysis shows that the proposed controller can accurately handle the global voltage regulation and proportional load sharing. An AC microgrid prototype is set up, where the controller performance, plug-and-play capability, and resiliency to the failure in the communication links are successfully verified.
Suggested New Voltage and Frequency Control Framework for Autonomous Operation of Microgrids
2013
Decentralized control strategies are popular candidates in microgrids control because of their reliability and performance. Conventionally, droop control (as a main decentralized strategy) is been utilized in order to prevent permanent droop of voltage and frequency after change in loads and also to share generated power between distributed generation units. In this paper, a new droop control strategy was introduced to control the voltage and frequency of autonomous microgrids. Following a review of the basic droop equations, it was concluded that the new form of droop equations enhanced the voltage and frequency control performance better than conventional droop equations. The voltage control behavior in the proposed method was within the acceptable range, and the frequency also returned to the nominal value after a change in loads. The simplicity and accurateness of the proposed method is a unique characteristic compared with the other recent control methods. Simulation studies sh...
A Multi-Functional Fully Distributed Control Framework for AC Microgrids
This paper proposes a fully distributed control methodology for secondary control of AC microgrids. The control framework includes three modules: voltage regulator, reactive power regulator, and active power/frequency regulator. The voltage regulator module maintains the average voltage of the microgrid distribution line at the rated value. The reactive power regulator compares the local normalized reactive power of an inverter with its neighbors' powers on a communication graph and, accordingly, fine-tunes Q-V droop coefficients to mitigate any reactive power mismatch. Collectively, these two modules account for the effect of the distribution line impedance on the reactive power flow. The third module regulates all inverter frequencies at the nominal value while sharing the active power demand among them. Unlike most conventional methods, this controller does not utilize any explicit frequency measurement. The proposed controller is fully distributed; i.e., each controller requires information exchange with only its neighbors linked directly on the communication graph. Steadystate performance analysis assures the global voltage regulation, frequency synchronization, and proportional active/reactive power sharing. An AC microgrid is prototyped to experimentally validate the proposed control methodology against the load change, plug-and-play operation, and communication constraints such as delay, packet loss, and limited bandwidth.
An improved decentralised coordinated control scheme for microgrids with AC-coupled units
—Microgrids composed of solemnly AC-coupled distributed energy resources can be found in many real-life applications while their control has not been researched nearly enough to address some fundamental challenges, the most important of which is overall system reliability and fault tolerance. This paper proposes a droop-based coordinated control scheme for microgrids with AC-coupled units, a method that enables distributed energy resources units to hot swap between current source and voltage source grid-supporting control modes for satisfying load demand and ensuring energy storage systems will constantly be able to form the grid during islanded operation. The proposed control scheme has been realised in MATLAB/Simulink simulation model of a small-scale microgrid of AC-coupled units that corresponds to a real testbed in Northern Greece. Preliminary simulation results, in islanded mode, demonstrate the effectiveness of the proposed control scheme regarding power-sharing accuracy among the resources and state-of-charge balancing among storage units. Keywords—microgrids, hybrid power systems, maximum power point tracking, energy storage, droop control
Team-oriented Adaptive Droop Control for Autonomous AC Microgrids
2014
This paper proposes a distributed control strategy for voltage and reactive power regulation in ac Microgrids. First, the control module introduces a voltage regulator that maintains the average voltage of the system on the rated value, keeping all bus voltages within an acceptable range. Dynamic consensus protocol is used to estimate the average voltage across the Microgrid. This estimation is further utilized by the voltage regulator to elevate/lower the voltage-reactive power (Q-E) droop characteristic, compensating the drop caused by the droop mechanism. The second module, the reactive power regulator, dynamically fine-tunes the Q-E coefficients to handle the proportional reactive power sharing. Accordingly, locally supplied reactive power of any source is compared with neighbor sources and the local droop coefficient is adjusted to mitigate and, ultimately, eliminate the load mismatch. The proposed controllers are fully distributed; i.e., each source requires information exchange with only a few other sources, those in direct contact through the communication infrastructure. A Microgrid test bench is used to verify the proposed control methodology, where different test scenarios such as load change, link failure, and inverter outage are carried out.
2015 17th European Conference on Power Electronics and Applications (EPE'15 ECCE-Europe), 2015
Microgrid, as a promising technology to integrate renewable energy resources in the distribution system, is gaining increasing research interests recently. Although many previous works have been done based on the droop control in a microgrid, they mainly focus on achieving proportional power sharing based on the power rating. With various types of distributed generator (DG) units in the system, factors that closely related to the operation cost, such as fuel cost and efficiencies of the generator should be taken into account in order to improve the efficiency of the whole system. In this paper, a multiagent based distributed method is proposed to minimize operation cost of the AC microgrid. Each DG is acting as an agent which regulates the power individually using proposed frequency scheduling method. Optimal power command is obtained through carefully designed consensus algorithm with only light communication between neighboring agents. Case studies verified that the proposed control strategy can effectively reduce the operation cost.