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This paper addresses the stability challenges that exist in a bidirectional grid connected electric vehicle (EV) charger. The EV charger under consideration comprises of an ac-dc single phase active rectifier stage followed by a dc-dc dual active bridge (DAB) stage. small-signal models suited for stability analysis of this charger are derived. Controller design considerations are discussed in order...
With increasing flexible AC transmission system (FACTS) devices in operation, like the most versatile unified power flow controller (UPFC), the AC/DC transmission flexibility and power system stability have been suffering unprecedented challenge. This paper introduces the user-defined modeling (UDM) method into the UPFC dynamic modeling process, to deal with the challenging requirements of power system...
A model control and a filter suppressing oscillation of the output voltage that can obtain the stable output voltage of a dc-dc converter have been proposed previous. Although there is a problem that the condition on the input side of dc-dc converter is changed when it connects the load equipment to renewable energy generators through the DC bus, since the renewable energy generators are sometimes...
Small signal stability of inverter based droop controlled microgrid is a major problem from past decade. In this work, an optimal state feedback controller is designed to improve the stability of the two inverter based test microgrid. The detailed full order small signal model of the test microgrid is developed in state space considering network and load dynamics. Eigen value and sensitivity analysis...
Hybrid AC/DC microgrid (MG) has attracted more and more attention due to its advantages such as better power sharing, improved system dynamics, and optimal management. But the complicated structure brings a great challenge to the modeling and stability analysis. In recent years, dynamic phasor model has been well applied in the modeling of AC MGs. Dynamic phasor tranforms sinusoidal quantities to...
Voltage phase control is a novel field-weakening scheme for PMSM which was reported as more stable in high speed region. This paper provides a current ripple reduce method and a frequency-compensation method. The current ripple reduce method deals with the problem that the voltage phase control has bigger current ripple compared to the tradition method. The frequency-compensation method decreases...
In this paper, a wireless modular control strategy for input-series output-parallel (ISOP) inverter system is proposed to ensure equal sharing of input voltage and output current among the constituent inverters. Compared with existing control strategies for the ISOP inverter system, such as centralized control which restricts the modularity of the system and distributed control which realizes voltage...
Solid state transformers (SSTs) can be interconnected with each other through a distribution feeder to form a smart grid. When the main grid is disconnected, SSTs form an islanded microgrid. With available communications, master-slave microgrid control structure can be adopted. The system-level stability analysis can be simplified by considering only the grid interface stage of the SST. The loop feeder...
In DC microgrids, constant power loads (CPLs) would lead to a destabilizing effect that may cause the main bus voltage oscillation. Hence, most researcher are exploring the stabilization methods for DC/DC buck converters feeding CPLs. In practical applications, buck converters are always cascaded with LC input filters to prevent the switching harmonics from returning into the source. With the addition...
This paper analyzes an effect of voltage feedforward control in order to improve stability of BESS which is connected to diesel generator in stand-alone microgrid. In the stand-alone microgrid, BESS can be charged from the diesel generator when SOC of battery bank is insufficient, where BESS operates as CC-CV control. In this case, although LCL filter is designed to put a resonance point greater than...
A novel approach to evaluate asymptotic stability of current-mode control for DC-DC power converters is given based on the singular perturbations (time-scale separation) approach. The small parameter ε which separates time scales is related to the physical values of inductances and capacitances through the LC matrix M = εS. Our approach also results in asymptotic stability of a simple robust integral...
Flux-Weakening (F-W) based on feedback voltage regulation is commonly adopted in Interior Permanent Magnet Synchronous Motor (IPMSM) drive systems. Voltage vector magnitude is controlled in closed-loop by modifying the current reference space vector, following a reference value related to the inverter limitations. Stable and fast voltage control allows to operate with lower voltage margin, which leads...
This paper deals with a newly conceived control topology based on the Repetitive action in 4-leg VSI for stand-alone Ground Power Unit (GPU) applications. In such mode of operation, a dedicated controller has to regulate the inverter output voltages, which are measured at the output of the power filter. The proposed Repetitive Control can provide the required harmonic compensation capabilities that...
Because of the differences in line impedances, parallel inverters with conventional droop control will have huge circulating current, which does not flow through the loads. To mitigate the circulating current, the research in this paper finds out that parallel-operated inverters should have the impedance in inverse proportion to their capacities, which is difficult to realize in practice. To meet...
To avoid the stability problem of grid connected inverter caused by the conventional phase locked loop (PLL), the direct power control of voltage source inverter in virtual synchronous reference frame without PLL is investigated considering grid voltage disturbance in the paper. Based on the small signal analysis methods, comparison between conventional PLL and no PLL is made. It can be found that...
In this paper, first, the existing frequency and voltage amplitude restoration control strategies are reviewed. Moreover, the proposed second order washout filter control strategy is proposed to enhance the dynamic response under load disturbance. The physical parameter of the proposed method is derived, and system stability for the system parameter is discussed. Finally, extensive simulation results...
This paper develops a distributed cooperative control scheme for DC microgrids with time-varying coupling delays in noisy environments. The proposed distributed cooperative control, consisting of distributed primary control and secondary control, will regulate the voltage of microgrids to the desired values and through a sparse communication network with asymmetric communication delays and noise disturbances...
The paper proposes a hybrid droop control strategy to enhance the stability and increase maximum constant power loads (CPLs) capability of DC microgrids in a realistic scenario. By capturing the detailed model of inner control loops and hybrid droop control and general dc MG topology, a thorough comparative study is conducted between traditional droop control and hybrid droop control. Enhanced control...
In this paper, a new control approach is proposed for PV system with hybrid energy storage system (HESS) in isolated DC grid application. The proposed control approach solves the current controller conflict problem in HESS and provides faster DC link voltage restoration. In the proposed control approach a predictive term is used to control the battery current and the supercapacitor (SC) current. In...
This paper focuses on regulation regimes of the transformer's secondary voltage. Automatic transformer's voltage regulation circuit is studied and upgraded.
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