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Recent developments in the design of power electronic elements with higher voltage and power rating and medium/high frequency enable the use of solid state transformer at different voltage levels for microgrid design. In this study, the concept of a Multi-Port Solid State Transformer (MPSST) for distribution network application is introduced to achieve the goal of creating galvanic isolation between...
Droop based autonomous control offers several advantages such as communication independence, plug-n-play capability and enhanced reliability of the system. Despite these advantages, frequency and voltage of droop controlled microgrid varies with the load change which is one of the major drawback of the droop control. Presently, the frequency and voltage restoration in microgrid is achieved through...
Single phase loads, which constitute the majority of low voltage consumers, give rise to unbalanced load currents in microgrids. As a consequence the voltage unbalance might rise beyond the permissible range. The voltage unbalance can be reduced by injecting a negative sequence (NS) compensation signal into the DERs reference voltage. However, such compensation might cause circulating currents between...
This paper addresses load current sharing and circulating current issues of parallel-connected dcdc converters in low-voltage dc microgrid. Droop control is the popular technique for load current sharing in dc microgrid. The main drawbacks of the conventional droop method are poor current sharing and drop in dc grid voltage due to the droop action. Circulating current issue will also arise due to...
A truly distributed and autonomous control strategy is proposed for the FREEDM System-a power electronics based distribution grid. The proposed control strategy requires no communication between and among all grid assets. By utilizing available local quantities (V, f) as a way to communicate among all connected devices, the strategy contains a novel dual droop control loops between the medium voltage...
In this paper, a generalized droop-control scheme for low-voltage microgrid is proposed. The control scheme includes three mutually interacting droop control loops for regulating the power flows between the primary energy sources and the common ac bus. The first droop control is adopted directly from the conventional P/f and Q/V droop control for enabling an automatic power sharing between parallel-connected...
Power flow control is one of the most important issues for operating the inverter-dominated autonomous microgrid. A technical challenge is how to achieve the accurate active/reactive power sharing of inverters. P-F and Q-V droop control schemes have been widely used for power sharing in the past decades. But it suffers from the poor power sharing in the presence of unequal line impedance. In order...
Microgrid is widely accepted as an effective mean of integrating various distributed energy resources (DERs) through their interface converters to provide electric power of high quality and reliability. These distributed resources interface converters (DICs) are required to operate in an autonomous fashion without any communication for enhanced reliability. Conventionally, the real power-frequency...
The VF (voltage and frequency control) droop control techniques are used to set the VF reference value which allows the operation of multiple VSCs in parallel to share the loads and regulate system voltage and frequency separately. In this paper, the characteristics of four VF control strategies which are: open loop VF control; VF control scheme with voltage feedback in abc reference frame; VF control...
Microgrid has become the focus of the researchers around the world because of the more emphasis on the flexibility and reliability of power system and low carbon society. Most of the microsources are connected to the microgrid through inverters, thus the modeling of inverter is quite important to the modeling and analysis of microgrid. Considering only the fundamental component of the input and output...
A new control strategy of grid-connected inverters in microgrid is presented in this paper. Combining the voltage, the frequency, the active power and the reactive power of microgrid, the structure of the grid-connected inverters is analyzed. And then it achieved the V/f-P/Q control strategy of the grid-connected inverters in microgrid. Also, the conventional P/Q control strategy of the grid-connected...
This paper proposes an appropriate control systems aiming at the control demands of distributed generation (DG) unit in the micro-grid. When the micro-grid is connected to the main grid, PQ control with droop characteristic is adopted for the inverter; When micro-grid separates from the main grid, Vf control with droop characteristic is used. Also, the controller can make the conversion between different...
This paper proposes a new method to determine the droop of the inverter-based distribution generations (DGs). Conventionally, inverter-based DGs have droop controller with fixed slope according to their capacity. Some additional control methods have been proposed in order to enforce the maximum or minimum limit of a unit. However, in some severe cases, the frequency deviation during the islanded mode...
Due to the rapid increase in global energy consumption and the diminishing of fossil fuels, the customer demand for new generation capacities and efficient energy production, delivery and utilization keeps rising. Utilizing distributed generation, renewable energy and energy storage can potentially solve such problems as energy shortage and global warming. A promising structure to interconnect these...
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