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This paper proposes an enhanced distributed generation (DG) unit with an adaptive virtual impedance control approach in order to solve the inaccurate reactive power sharing problem. The proposed method can adaptively regulate DG units with the aid of the equivalent impedance, and the mismatching problem of the feeder impedance is compensated by sharing the reactive power accurately. The proposed control...
This paper presents a Linear Quadratic Regulator (LQR) based bumpless transfer controller for achieving seamless transition between the grid connected and the islanded modes of operation in microgrids. During the grid connected mode, the inverter based Distributed Generators (DGs) operate in current controlled mode where they supply a constant active and reactive power. During the islanded mode, the...
Appropriate control strategies for power sharing between multiple generation units operating in parallel are required to create a stable AC microgrid bus. In this paper, we explore the droop control strategy, implemented by power electronics units, to maintain a stable AC bus voltage without the need for a separate (central) communication layer. In particular, our suggested control method is based...
A droop-Lyapunov based control technique using direct-quadrature (d-q) rotating frame dynamic model is presented in this paper for the frequency and voltage magnitude regulation of a stand-alone single-phase voltage-source inverter (SPVSI). Steady-state and dynamic performance of the controller are analyzed based on the d-q frame model and direct Lyapunov method respectively to satisfy control aims...
The paper presents the energetic performances of a system used for drying of current transformer from 110 kV Ciungetu power station. In fact, the drying process is based on an induction heating system that contains a half-controlled rectifier and a voltage source inverter that operates with resonant load. Two frequencies are taken into consideration for the inverter control. The former is the resonance...
Achieving a high-level of stability represents one major concern in autonomous microgrids (MGs) with high penetration levels of renewable energy sources. The aim of this paper is to study how photovoltaic (PV) power plants can provide dynamic frequency support in an MG, in order to obtain an improved stability for the entire power system. On the PV side an energy storage subsystem is added, which...
Sampling points in one cycle of 400 Hz inverter are 8 times less than that of 50 Hz inverter, resulting in lower control accuracy and larger static error in 400 Hz power supply system. This paper set up a mathematical model for single-phase solid-static power supply system. The transformer leakage inductance and load can be regarded as uncertainties. A robust controller based on the principle of mixed...
This paper presents a Solid State Transformer (SST) interface for grid connected Photovoltaic (PV) system. A new method is proposed for Maximum Power Point Tracking (MPPT) through a single phase inverter with phase displacement control. The inverter control variable is redefined such that it can be used for MPPT. Due to this control technique one converter stage for power tracking is eliminated, leading...
In modern power systems and especially in autonomous distributed generation (DG), the frequency and voltage regulation should be continuously controlled. Hence the analysis of such a DG system is essential for the reliable operation of the local grid, with the voltage source inverter to play a key role as a controlled interface between the energy sources and the loads. In this frame, the complete...
In this paper, we proposed an improved calculating method of repetitive control, in the light of the output voltage jump caused by the traditional calculating method during the periodic transition of output voltage. In the improved model, the zero crossing information of phases outputted by the controller is used to judge the start of learning cycle of repetitive control loop and calculate the actuating...
This manuscript presents modified scheme of synchronous space-vector modulation allowing providing nonlinear dependences between the fundamental voltage and fundamental frequency of dual three-phase open-winding ac drive with four modulated inverters. Behavior of the system with six control modes (characterized by different dc-voltages and switching frequencies of inverters) and two nonlinear Voltage/Frequency...
This paper presents the control method of an LCL filter implemented for a three-phase, voltage-source, grid-connected inverter for not only offering better attenuation of switching harmonics but also for highly damping the resonance. A discrete-time deadbeat current controller with tuned state-feedback gains is proposed to realize the time optimum responses with high control accuracy. In addition,...
Inversion-based control for modular high frequency (MHF) inverters in a two-degree-of-freedom structure is presented in this paper. This establishes a state-space average model of MHF inverters. The results of this paper are illustrated using simulation and experiment based on an MHF3P inverter with four submodules.
This paper presents a frequency control strategy for networked micogrids. Applying a hierarchical control structure, the usual droop-control for AC microgrids is replaced by a droop-free paradigm that acts as a first and second level control. To control the frequency of the networked microgrid system, a third control level is introduced to control the frequency for the whole system in a distributed...
The recently proposed small-AC-signal droop based secondary control is very attractive for microgrids to restore the voltage and frequency of overall system and to share the output power between paralleled distributed generations (DGs). However, the previous work has not discussed the system stability of the novel secondary control method. This paper presents a small-signal model for the microgrids...
The distributed generator based on power electronic converters has no inherent inertial response like that from the rotating mass of the conventional synchronous generator. The control scheme of Virtual Synchronous Generator (VSG) is anticipated to improve the distributed generator system stability by imitating the behavior of the synchronous generator including the system inertia. Unlike a real synchronous...
Controlled Power Converters are extensively used in industrial applications as they can adapt the electrical energy as required by the application. However, these devices must be properly commutated in order to control voltages and currents. Indeed, power converters are known to be multivariable, coupled, and nonlinear systems; therefore, the control technique needs to be chosen carefully. There are...
Severe distortion will occur in the output current of inverter when grid voltage is unbalanced with harmonics contained. In this paper a scheme of repetitive control for three-phase grid-connected inverters with LCL filter under stationary frame is proposed. The THD of the injected grid current is decreased obviously with the proposed scheme. Two separate decoupled control systems can be achieved...
The asymmetry of the inherent distributed capacitances causes the rise of neutral-to-ground voltage in ungrounded system or high resistance grounded system. Overvoltage may occur in resonant grounded system if Petersen coil is resonant with the distributed capacitances. Thus, the restraint of neutral-to-ground voltage is critical for the safety of distribution networks. An active grounding system...
This paper presents a novel active synchronization control strategy of multi-bus microgrid based on distributed cooperation technology. The method can reconnect microgrid back to utility grid (UG) seamlessly with sparse communication channels. Through the cross product of voltage vectors in the synchronizer, the frequency and phase of microgrid can track the main grid simultaneously. The voltage differences...
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