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This paper presents the role of Distribution Static Synchronous Compensator (DSTATCOM) in the domain of reactive power sharing and harmonics mitigation in distribution systems under distorted grid condition. Extraction of reference current is done using Synchronous Reference Frame (SRF) based strategy which greatly influences the performance of the DSTATCOM. A modified SRF PLL is used for unit vector...
In three-phase grid-tied inverter, grid voltage feedforward is helpful to improve grid-tied power quality for strong grid condition. This paper found that the voltage feedforward had different effect on power quality under weak grid condition compared with that in ideal grid condition. And recent reported studies show that grid voltage feedforward has negative effect for grid-inverter system stability...
The accurate and fast detection of the grid voltage attributes (e.g. frequency and amplitude) are gaining more attention in microgrids due to the new stringent amendments to the microgrid standards. In this paper, two novel observer based techniques are introduced; one for estimating the frequency and another for the amplitude of the grid voltage. The proposed observer techniques offer superior performance...
The well-known droop control and master-slave control methods are two dominant coordinative control schemes for inverter interfacing parallel distributed energy resources (DERs) in islanded AC microgrids. However, both these two control methods have some drawbacks and inherent limitations in practical application. After analyzing their complementary strengths and weaknesses, this paper proposed a...
This paper highlights the power limited nature of the Distributed Generation inverter and demonstrates the practical way to integrate them into the microgrid. Since the energy source of Distributed Generation inverters is power limited in nature, they constrain the operation of inverters to which they are coupled. If the power demanded from these inverters is beyond their capability, their DC-link...
In order to enable a more wide-scale utilization of PV systems, the cost of PV energy has to be comparable with other energy sources. Oversizing the PV array is one common approach to reduce the cost of PV energy, since it increases the PV energy yield during low solar irradiance conditions. However, oversizing the PV array will increase the loading of PV inverters, which may have undesired influence...
The increasing use of grid-connected inverters to connect renewable energy sources to a power grid will have globally important effect on grid performance. A mismatch between the grid and inverter impedance may cause harmonic resonances, which can lead to instability of the grid and disruption of inverter operation. The grid dynamics vary over time, so the inverter should adapt to the varying conditions...
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...
As a basic building block, the phase-locked loop (PLL) has been widely used in the grid-connected voltage source inverter (VSI). But it has been shown recently that PLL has adverse impact on stability of grid-inverter system. In a weak grid, the PLL may cause unexpected harmonic, or even instability. In order to overcome this problem, this paper proposes a q-axis voltage feedforward control method...
In this paper, a virtual synchronous generator with photovoltaic energy storage hybrid system (VSG-PV) is adopted. VSG-PV can not only output the maximum power of photovoltaic, but also can maintain a stable voltage and frequency of the point of common coupling when system worked in the island model comparing to the conventional photovoltaic generation system. The small signal model of the hybrid...
An increased deployment of distributed generation in recent years has contributed to creation of meshed power networks usually seen as a way to improve power flow management capability. Also, power electronics converters have been commonly used to interface distributed resources to the grid, yet their impact on the network stability has not been sufficiently explored. In this paper the stability of...
In this paper a current-limiting droop control of grid-tied inverters that introduces virtual inertia and operates without a phase locked loop unit is proposed. The proposed controller inherits a self-synchronization function and can guarantee tight bounds for the inverter frequency. In addition, using nonlinear Lyapunov theory, it is analytically proven that the inverter current never violates a...
The asymmetric inverter controller structure or parameters result in frequency coupling in phase domain for the three-phase grid-connected inverter system. And it is difficult to measure the inverter admittance matrix in engineering practice due to the coupling term. What's more, applying the coupled admittance matrix to analyze the system stability, the generalized Nyquist criterion (GNC) has to...
This paper presents a multi-PLL clock architecture used in a 4-lane multi-protocol serial link applications. The clock architecture consists of one public LC PLL and four standalone ring PLLs placed within each lane. A swtich capacitor array based LC VCO is used in the LC PLL to enlarge the frequency tuning range and decrease the VCO gain. A two stage pseudodifferential inverter based ring VCO with...
Considering the new challenges in the energetic scenario around the world, this paper proposes the implementation of a micro-grid with photovoltaic generation and local accumulation, considering its capability to operate connected or islanded from the utility grid. The system will supply power to utility grid and local loads through six single-phase inverters in wye configuration, three of them operating...
With the advent of distributed generation, single-phase rooftop solar photovoltaic (PV) generators of small rating, feeding power to the utility grid has become popular. Cost and performance of the inverters used to integrate such systems to the grid depends upon the topology of the inverter used, modulation scheme employed, and the efficiency of auxiliary functions like maximum power point tracking...
Grid-connected inverter's output electric energy could trace the power flow, this is the prerequisite for the parallel operation of the photovoltaic power generation systems and the power grid systems operation. In order to achieve the parallel operation between the single phase photovoltaic system and The Grid, this paper presents a Grid-Connected control strategy of Grid connected inverter output...
Grid synchronisation plays a vital role in grid tied inverters where the phase, frequency and voltage amplitude of grid is a critical information. In order to extract this information accurately, an improved technique of single-phase synchronous reference frame phase locked loop (SRF-PLL) is used in grid tied inverters. This method uses a transport delay block and a changed Park transform in such...
Synchronous machines have traditionally acted as the foundation of large-scale electrical infrastructures and their physical properties have formed the cornerstone of system operations. However, with the increased integration of distributed renewable resources and energy-storage technologies, there is a need to systematically acknowledge the dynamics of power-electronics inverters — the primary energy-conversion...
In this paper, a new control strategy for seamless mode transfer of grid-connected single-phase inverter is proposed. Generally, power flow between DC side and AC side is controlled by current reference of grid-connected inverter in d-q synchronous rotating frame. Therefore, it is general to reverse the current reference if the direction of power flow is changed. However, it causes a rapid change...
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