Robust adaptive droop control for DC microgrids (original) (raw)
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Adaptive droop control for high-performance operation in low-voltage DC microgrids
Electrical Engineering, 2019
The most well-known means for the integration of various renewable energy resources is DC microgrids (DCMGs). Different control algorithms have been proposed to regulate the current and voltage of parallel energy sources. Droop control, a method for controlling DC microgrids, does not require a communication link. However, droop control has some constraints, such as not properly sharing the load among parallel converters and deteriorating voltage regulation. This paper proposes an adaptive droop controller to mitigate the problems of conventional droop control. The droop parameters are evaluated online and are adapted utilizing the primary current sharing loops to decrease the deviation in the load current sharing. In addition, the droop lines are shifted by the second loop to eliminate the bus voltage deviation of DCMGs. The proposed algorithm is assessed under various input voltages and load resistances. The simulation and experimental results illustrate the good performance of the introduced technique compared to classic control.
2013 Brazilian Power Electronics Conference, 2013
Currently, the standards of reliability and power quality indicate a new design of the Electric Power Systems (EPS), in which the model of centralized generation gives way to the Distributed Generation (DG). One way to achieve the integration of sources in DG is using DC microgrids, since renewable energy sources can be integrated into systems using DC as well as energy storage and UPS, eliminating conversion stages. The voltage control in these systems is of paramount importance. Therefore, this paper proposes the use of a methodology for nonlinear control associated with the concept of voltage droop control in a grid-connected DC microgrid. Simulation results are presented and the behavior of the system is analyzed.
Distributed Adaptive Droop Control for DC Distribution Systems
IEEE Transactions on Energy Conversion, 2014
A distributed-adaptive droop mechanism is proposed for secondary/primary control of dc Microgrids. The conventional secondary control, that adjusts the voltage set point for the local droop mechanism, is replaced by a voltage regulator. A current regulator is also added to fine-tune the droop coefficient for different loading conditions. The voltage regulator uses an observer that processes neighbors' data to estimate the average voltage across the Microgrid. This estimation is further used to generate a voltage correction term to adjust the local voltage set point. The current regulator compares the local perunit current of each converter with the neighbors' on a communication graph and, accordingly, provides an impedance correction term. This term is then used to update the droop coefficient and synchronize per-unit currents or, equivalently, provide proportional load sharing. The proposed controller precisely accounts for the transmission/distribution line impedances. The controller on each converter exchanges data with only its neighbor converters on a sparse communication graph spanned across the Microgrid. Global dynamic model of the Microgrid is derived, with the proposed controller engaged. A low-voltage dc Microgrid prototype is used to verify the controller performance, link-failure resiliency, and the plug-andplay capability.
a b s t r a c t DC microgrid is one feasible and effective solution to integrate renewable energy resources, as well as to supply reliable electricity. The control objective of DC microgrids is to obtain system stability, low voltage regulation and equal load sharing in per unit. The droop control is an effectively method adopted to implement the control of microgrids with multiple distributed energy units. However in the application of low-voltage DC microgrids, the nominal reference mismatch and unequal cable resistances require a trade-off to be made between voltage regulation and load sharing. In this paper, a unified compensation framework is proposed using the common load condition in local controller, to compensate the voltage drop and load sharing errors. The voltage deviation is compensated with a P controller while the load sharing is compensated through a PI controller. An additional low bandwidth communication is introduced to share the output current information, and the average output current in per unit is generated to represent the common load condition. The performance of the proposed method is analyzed and compared with basic droop control and hierarchical structure method. The large signal stability is analyzed to define the margin of compensation coefficients. Simulations and experiments are carried out to verify the performance of the proposed method.
Supervisory Control of an Adaptive-Droop Regulated DC Microgrid With Battery Management Capability
IEEE Transactions on Power Electronics, 2000
DC power systems are gaining an increasing interest in renewable energy applications because of the good matching with dc output type sources such as photovoltaic (PV) systems and secondary batteries. In this paper, several distributed generators (DGs) have been merged together with a pair of batteries and loads to form an autonomous dc microgrid (MG). To overcome the control challenge associated with coordination of multiple batteries within one stand-alone MG, a double-layer hierarchical control strategy was proposed. 1) The unit-level primary control layer was established by an adaptive voltage-droop method aimed to regulate the common bus voltage and to sustain the states of charge (SOCs) of batteries close to each other during moderate replenishment. The control of every unit was expanded with unit-specific algorithm, i.e., finish-of-charging for batteries and maximum powerpoint tracking (MPPT) for renewable energy sources, with which a smooth online overlap was designed and 2) the supervisory control layer was designed to use the low-bandwidth communication interface between the central controller and sources in order to collect data needed for adaptive calculation of virtual resistances (VRs) as well as transit criteria for changing unit-level operating modes. A small-signal stability for the whole range of VRs. The performance of developed control was assessed through experimental results.
Advances in Engineering and Intelligence Systems, 2023
Today, DC microgrids provide the possibility to provide proper management and control for energy storage systems, generation sources, consumers, and other power components. The droop control method is one of the most common methods used in DC microgrids. One of the main challenges in the droop control method is that it is not possible to share the current and regulate the voltage at the same time in this method. To overcome the weaknesses of the voltage drop control method, the paper presents an adaptive control method that can be used to share the current and adjust the voltage accordingly based on the load condition. When the load in the microgrid is low, the output current is lower than the maximum limit and so current sharing is not a difficult challenge. When the load increases to the point where the output current exceeds the maximum limit then current sharing becomes very important. Using this method, this problem is solved by increasing the total gain decrease. For more accuracy, a gray-wolf algorithm has been used to optimize the droop gains. The performance of the proposed method has been verified through a set of simulations, and the results confirm the effectiveness of the proposed method for the DC microgrid.
International Journal of Power Electronics and Drive Systems (IJPEDS), 2024
To ensure the stable and accurate operation of "rural areas", a reliable power source is necessary, and voltage issues must be carefully considered in power system design to ensure patient safety. Remote DC microgrids provide a viable option for transferring energy across power sources while assuring stability and high efficiency. In this paper, an adaptive droop control approach is developed and compared to the standard droop control method. The suggested technique recommends a dynamic modification of droop coefficients intending to effectively limit the buildup of mistakes in current sharing and departures from the preset voltage setpoints. Through the implementation of the adaptive droop control method, the remote DC microgrid not only enhances current balancing performance but also contributes to a substantial improvement in voltage stability, thereby increasing the overall operational efficiency of the system. Simulation and experimental results on a small-scale remote DC microgrid validate the proposed adaptive droop control approach, proving its effectiveness in the small-scale microgrid system.
Optimal, Nonlinear, and Distributed Designs of Droop Controls for DC Microgrids
In this paper, the problem of optimal voltage and power regulation is formulated for distributed generators (DGs) in DC microgrids. It is shown that the resulting control is optimal but would require the full information of the microgrid. Relaxation of information requirement reduces the optimal control into several controls including the conventional droop control. The general setting of a DC microgrid equipped with local sensing/communication network calls for the design and implementation of a cooperative droop control that uses the available local information and coordinates voltage control in a distributed manner. The proposed cooperative droop control is shown to include other controls as special cases, its performance is superior to the conventional droop control, and it is robust with respect to uncertain changes in both distribution network and sensing/communication network. These features make the proposed control an effective scheme for operating a DC microgrid with intermittent and distributed generation.
Distributed Control for DC Microgrid Based on Optimized Droop Parameters
IETE Journal of Research, 2018
The droop control approach is widely used in case of parallel operation of DC sources. The conventional droop control method is realized by linearly reducing the load voltage as the load current increases. This droop control is unable to achieve effective equal load sharing as well as the bus voltage regulation. The load sharing error is enhanced when cable line parameters of parallelconnected DC sources are not equal. The droop gain and nominal voltage reference of source converters are the key parameters to achieve the bus voltage deviation within the permissible limits and effective load sharing. In this paper, the droop parameters of the proposed distributed control scheme are optimized with the help of the Particle Swarm Optimization technique for the aforementioned control objectives of the DC microgrid for unequal cable line resistances. The performance of the proposed control scheme based on optimal droop parameters is verified through MATLAB/Simulink environment and validated by a hardware-in-the-loop real-time simulator based on the dSPACE 1202 platform.