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A highly flexible and reliable control strategy is proposed to achieve bounded voltage and precise current sharing, which is implemented in a reverse-droop-based dc Micro-Grid. To acquire the fast-dynamic response, the reverse droop control is used to replace the V-I droop control in the primary level. In the secondary level, the containment-based controller is proposed to bound the bus voltages within...
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...
Accelerated developments of renewable energy production technologies and their integration to existing AC microgrids have led to the emergence of several new inverters control schemes. The recently introduced proportional resonant (PR) controllers have the ability to precisely track AC quantities and are increasingly used in grid supporting inverters, especially for current control loops which are...
In this paper, a bidirectional buck-boost converter for connecting energy storages to a DC microgrid is presented. The integration of energy storages into the microgrid allows an enhanced utilization of renewable energy sources. Therefore, an efficient control of energy storages and corresponding power converters is required. Two operating modes of the converter are considered: current control mode...
In the case of sensitive and critical load, the distributed generation (DG) should supply continuous power, even in the condition of utility outage. This paper proposes a novel seamless transfer control strategy, which based on special master and slave DGs. The master DG unit is controlled by a novel control strategy, which combines indirect current control and droop control. A part of slave DGs are...
Whereas bipolar DC microgrid has several advantages over monopolar DC grid [1], [2], its disadvantages cannot be underestimated. The currents in the pole lines can become asymmetric, and the neutral conductor carries non-zero current. To eliminate the current imbalance caused by unipolar loads/generators in bipolar DC microgrids, different types of current redistributor have been proposed and implemented...
The distributed generation (DG) should supply continuous power to local critical load, even in the condition of utility outage. This paper proposes a novel seamless transfer control strategy, which combines indirect current control and droop control. A microgrid structure of multi-masters and multi-slaves is also proposed, which based on the master-slave control and droop control. The master DGs are...
There has been a gradual increase in generation of power from renewable energy resources interfaced to existing utility grid to increase its reliability. Tapping of these resources is done in multiple ways like standalone wind generators or photovoltaic plants, microgrids etc. Interfacing DC sources like photovoltaic cells, battery, fuel cells with AC systems requires tie line inverter with robust...
In this paper, a renewable energy based wind-PV microgrid is investigated for seamless transfer between the grid connected and isolated modes according to the grid availability. The VSC (Voltage Source Converter) based voltage and current controls are used to provide smoothness in both the operations. A battery bank is connected at the DC bus of VSC for load leveling during low power generations or...
This paper proposes a central control framework to coordinate proportionate charging of batteries based on their capacity in an autonomous DC microgrid. This serves the purpose of longevity and reliability issues in an autonomous microgrid. The uneven distribution of power based on a preferential charging/discharging approach is implemented using a multi-input single output(MISO) mamdani based fuzzy...
The decoupling of the capacitor voltage and inductor current has been shown to improve significantly the dynamics performance of voltage source inverters in isolated microgrids. However, still the computation and PWM delays limit the achievable bandwidth. A technique based on a lead compensator structure is proposed to overcome this limitation. It is shown how a widen bandwidth for the current loop...
In stand-alone microgrids based on voltage source inverters state feedback coupling between the capacitor voltage and inductor current degrades significantly the dynamics performance of voltage and current regulators. The decoupling of the controlled states is proposed, considering the limitations introduced by system delays. Moreover, a proportional resonant voltage controller is designed according...
Grid-connected photovoltaic systems are usually designed to provide active powers. The statutory standards or the grid-code does not allow the injection of reactive power. However, many countries have relaxed or are in process of relaxing the standards. Hence, it is highly desirable that the capacity of the inverters to control reactive power be utilized. The reactive power that a PV can supply is...
In this paper, two charging modes of battery energy storage system (BESS) for a stand-alone microgrid are analyzed. The stand-alone microgrid system consists of 50kW BESS, 50kW diesel generator (DG) and controllable loads, where BESS is composed of 115kWh battery bank and 50kW DC-AC inverter. The operation modes of the stand-alone microgrid system are divided into four modes, and BESS is connected...
This paper presents the comparison of three different fully digital, oversampled, large bandwidth inverter current controllers: a proportional integral controller, a predictive controller, and a non-linear hysteresis controller. The purpose is to determine which one allows to achieve the highest final performance when adopted as the inner current control loop in a microgrid utility interface converter...
This paper proposes a new control strategy for the Voltage Source Converter based Distributed Generation units operating in a Microgrid under unbalanced load conditions. The objective of the proposed control strategy is to control the positive sequence components and the negative sequence components of the Voltage at the Point of Common Coupling (PCC) in dq — frame, so that the Voltage will be controlled...
DC Microgrids (MGs) are increasingly popular in recent years to support distributed generation based power systems. This paper focuses on the improvement of the load sharing control strategy and presents a decentralized control scheme, namely improved digital average current sharing (IDACS). Compared to the conventional hierarchical droop control scheme, the IDACS shows the structural difference and...
Connection of Distributed Power Generators (DPGs) to a utility grid requires the synchronization between the DPG and the grid voltages with the goal of controlling the power flow and limiting the currents at instant that the switch or breaker closes. Synchronization methods typically match the positive sequence voltage component of the two systems being connected, the connection being realized when...
In this paper a transition control strategy for parallel voltage source inverters (VSIs) operating in a microgrid system is presented. In the proposed control method, VSIs regulate the power flow in standalone (SA) and grid connected (GC) modes through a hybrid control architecture without needing of an external communication link between them. The hybrid controller uses the current control in GC...
This paper proposes a smooth transition control strategy for voltage source inverters between standalone (SA) and grid connected (GC) modes of operation. During transition both current control and droop control will participate in formulating the inverter output voltage but with different weights or coefficients. In transition mode the controller varies the output coefficients of the current and droop...
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