In this paper, a nonlinear current-limiting droop controller is proposed to achieve accurate power sharing among parallel operated DC-DC boost converters in a DC micro-grid application. In particular, the recently developed robust droop controller is adopted and implemented as a dynamic virtual resistance in series with the inductance of each DC-DC boost converter. Opposed to the traditional approaches that use small-signal modeling, the proposed control design takes into account the accurate nonlinear dynamic model of each converter and it is analytically proven that accurate power sharing can be accomplished with an inherent current limitation for each converter independently using input-to-state stability theory. When the load requests more power that exceeds the capacity of the converters, the current-limiting capability of the proposed control method protects the devices by limiting the inductor current of each converter below a given maximum value. Extensive simulation results of two paralleled DC-DC boost converters are presented to verify the power sharing and current-limiting properties of the proposed controller under several changes of the load.
A novel droop controller for DC microgrid systems, consisting of multiple paralleled sources feeding a constant power load (CPL), is proposed to achieve the desired voltage regulation and accurate load power distribution, while ensuring an overvoltage protection for each source. CPLs are well-known to exhibit negative impedance characteristic due to their nonlinear behaviour, which may cause instability to a DC microgrid if the necessary impedance inequality criteria are not satisfied. In this paper, a new droop control scheme is proposed to limit the voltage of each source below a desired bound, achieve tight voltage regulation and power sharing, and guarantee closed-loop system stability with the existence of a CPL. The upper limit of the voltage of each source is rigorously proven using ultimate boundedness theory, while after a suitable manipulation of the admittance matrix of the microgrid, analytic conditions of stability are obtained to guide the control parameters design. To validate the theoretical design and analysis, a detailed simulation is performed of a DC microgrid equipped with the proposed controller.
This paper looks into the voltage stability and network scalability of self-contained converter-based dc mg under an innovative control approach, namely a nonlinear adaptive droop-based controller with overcurrent protection, devised for hea applications. Apart from guaranteeing tight voltage regulation and accurate adaptive distribution of load power across parallel batteries proportional with their current soc, the controller features an inherent overcurrent protection. Notably, the applied nonlinear adaptive droop-based controller introduces a virtual voltage and a constant virtual resistance, placed in series with the inductance and parasitic resistance of each dc/dc bidirectional boost converter. Moreover, the voltage stability for the $n$ -dimensional system is subsequently investigated, providing valuable insights into the voltage dynamic behaviour, followed by a network scalability study based on the system's passivity properties. Finally, numerical simulations replicating various in-flight scenarios align with and validate our theoretical developments in the pursuit of minimising emissions, environmental impact, and operational costs.
In this paper, an adaptive nonlinear droop-based control approach is proposed for converter-based self-contained electrical power systems (EPS) designed for electric aircraft applications to ensure tight voltage regulation and accurate load power distribution among parallel sources. By taking into account the accurate nonlinear dynamic models of the power converters, we mathematically prove an upper bound for the input current of each converter separately by means of Lyapunov methods and ultimate boundedness theory. In particular, the adopted nonlinear droop-based controller introduces a virtual voltage and a virtual resistance in series with the inductance and parasitic resistance of each DC/DC boost converter. To verify the proposed controller performance and its underlying developed theory, simulation results of the low-voltage bus dynamics have been presented for an onboard aicraft DC microgrid (MG).
A novel distributed power consensus control approach with overvoltage protection is proposed and analysed for meshed direct current (DC) microgrids (MGs) with constant power loads (CPLs). The DC MG considered herein consists of source and load nodes connected over an undirected weighted graph induced by the electrical circuit network, namely the conductance matrix. When deploying, the proposed controller features a second graph, that models the communication network over which the source nodes exchange information such as the instantaneous powers, and which is used to adjust the power injection accordingly to achieve power sharing. Additionally, one aims to maintain the voltage at each source below operator-set limits. This feature is critical given the power and voltage dependency. By addressing the occurrence of abnormal voltage values at different nodes in the network, one would guarantee a relatively safer power consensus policy and microgrid operation. To accommodate both objectives, we developed a nonlinear power consensus-based control system, with a voltage-limiting component, by means of Lyapunov analysis and ultimate boundedness theory. Asymptotic closed-loop stability is also established around a set of equilibria. Finally, numerical simulations align with and validate our theoretical findings.
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