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Photovoltaic units that are connected to the grid through dc/dc converters and inverters in distributed generation, are controlled via a synchronous-generator-like voltage control mechanism. While other control schemes such Synchronverters are used to control the inverter frequency and power at a fixed dc link voltage, the proposed approach considers both the dc-link voltage dynamics and the inverter...
Conservation Voltage Reduction (CVR) schemes and renewable energy based distributed generation (DG) can be coordinated to maintain lower node voltages for reducing load consumption and line losses in distribution systems. In addition, smart inverter interfaced DGs are significant resources to maintain the lowest possible voltages at the loading points and adjacent nodes. This paper describes a method...
The problems associated with the harmonics needs more attention as more number of distributed generators like PV and wind are integrated into a distribution system. Although the integration presents a lot of benefits, satisfying the needs of local load requirements by reducing the line losses and facilitating congestion management, the problems of power quality that impact the distribution system...
This paper presents the dynamic performance analysis of grid connected Z-source inverter (ZSI) based distributed generation (DG). ZSI provides a single stage buck boost conversion which reduces the switching losses and becomes an economical option for DG systems. The standards set by the utility is met by the ZSI even during variable input conditions by regulation of shoot through duty ratio. The...
Commonly used 3-leg inverter interfaces in a microgrid are not capable of maintaining balanced and sinusoidal voltage at their terminals with unbalanced and nonlinear loads. Additional compensating circuits are required to take care of such loads. Simulation and experimental results of 4-leg inverter with nonlinear and unbalanced load justify its use from power quality improvement point of view in...
This paper introduces a methodology to model and control a single-phase tri state integrated Buck-Boost inverter suitable for low power distributed generation with the capability to operate in grid connected and island modes. The tri-state modulation is adopted in order to achieve power decoupling by means of average inductor current. This way it is possible to control the DC/AC conversion independently...
This paper presents the control of a photovoltaic distributed generation system based on dual-stage topology of three level DC-DC boost converter (3LBC) and three-level neutral-point-clamped (NPC) voltage source inverter (VSI). Decoupling control strategy of three-level VSI is proposed to control the current injected into the grid, reactive power compensation, and DC-link voltage. The resulting system...
This paper presents a 5-level Cascaded H-Bridge Multilevel Inverter (CHMI) able to perform several tasks and applicable to a microgrid with multiple local power sources. The current control strategy is based on the conservative power theory (CPT) generating references for different modes of operation. The primary merits of multilevel cascade voltage source inverters are the possibility of having independent...
This paper introduces a new inverter topology called a “quasi-Y-source inverter”. The proposed inverter inherits all the advantages of the original Y-source inverter. In addition, the new topology draws continuous current from the source which is required for many renewable sources. It also has dc-current-blocking capacitors, which avoids saturation in the transformer core. Simulations and experimental...
Increased penetration levels of Distributed Generation (DG) can cause steady state and transient voltage issues and possible overloading conditions. This paper aims to verify the overvoltage and overloading issues caused by DG at high penetration levels. A typical utility distribution feeder was selected using cluster analysis for simulations. DG at various penetration levels was interconnected at...
This paper proposes a unified grid current control for grid-interactive distributed generation inverters. In the approach, the grid-side current, instead of inverter-side current, is controlled as an inner loop, while the filter capacitor voltage is indirectly regulated through a virtual admittance in the outer loop. It, therefore, provides several superior features over traditional control schemes:...
Applications of 4-leg inverter are found not only in active and unbalanced load compensators but also as an interface for transferring power generated by renewable energy sources in distributed generation system and microgrids. However existing distributed generation systems commonly use 3-leg inverters. In this paper, the possibility of using a 4-leg inverter interface along with the existing units...
This paper presents the control of a photovoltaic distributed generation system based on dual-stage topology of DC-DC boost converter and three-level neutral-point-clamped (NPC) voltage source inverter (VSI). Decoupling control strategy of three-level VSI is proposed to control the current injected into the grid, reactive power compensation, and DC-link voltage. The resulting system is able to extract...
The distributed generation (DG) should supply continuous power to the local critical load, even in the condition of utility outage. And many efforts have been made for the three-phase inverter in the DG to transfer between the islanding mode and the grid-tied mode seamlessly. This paper proposes a transfer strategy based on indirect current control for the three-phase inverter in the DG, which is...
In grid connected DC-AC systems, low pass filters are utilized to reduce injected current harmonics. LCL filters have recently drawn attention for system grid interfaces due to its small size and have shown better attenuation to switching harmonics than simple L filters. However, the LCL filter causes resonance resulting in oscillation and instability of the current controller. In order to stabilize...
Distributed generation (DG) is being increasingly embedded in electric four-wire distribution systems which commonly feed three/single phase linear and/or nonlinear loads. This has an impact on power quality of the utility in terms of low power factor, grid current harmonics and unbalance, and neutral current. Conventionally, the DG unit is connected to the grid via a coupling inverter. This inverter...
This paper presents a study for determining the maximum amount of PV solar generation that can be connected in a 27.6 kV feeder of a distribution utility - London Hydro. Various factors such as steady state voltage rise, Temporary Over Voltage (TOV), short circuit current and harmonic contributions, that could potentially constrain DG connectivity are investigated. Load flow studies with PSS/E and...
The current deregulation trend in the electric power industry has led to the utilities trying to adapt Distributed Generation (DG) into their existing infrastructure. In this paper, 12.47 kV distribution feeders of American Electric Power (AEP) are modeled in OpenDSS to investigate the impacts of PV integration. With increasing PV penetration reverse power may flow on the grid which is associated...
Grid-connected solar photovoltaic distributed generation (PV-DG) units offer many benefits such as clean energy, reduced emissions and creation of new green jobs. A combination of supportive legislation, incentives, technology developments and costs decrease have favored the proliferation of PV-DG plants of different capacities, ranging from a few kVA (small-scale) to several MVA (large-scale). Due...
A low voltage (LV) distribution level unified power flow controller (UPFC) is shown capable of regulating the positive sequence voltage with a network while simultaneously correcting phase unbalance voltages that can be produced by high levels of distributed photovoltaic (PV) generation. Instantaneous reactive power theory shows that DC-bus capacitor power will fluctuate at twice mains frequency during...
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