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This paper investigates the fault ride-through (FRT) capability of a hybrid AC/DC microgrid during both AC and DC network faults. In this investigation, commonly proposed FRT strategies for the distributed energy resources and AC and DC microgrids are implemented while the interlinking bidirectional converter is operated in power transfer mode. The investigations have shown that improvement in the...
Droop control is a widely used technique for load sharing in DC microgrids (MGs). However, it has its limitations due to the MG voltage deviating from its rated level and, more importantly, it suffers from possible poor current sharing accuracy. Voltage drops across coupling line impedances is the main factor that causes these limitations, which is further deteriorated by the virtual impedance introduced...
Islanded mixed-source CERTS microgrids that include photovoltaic (PV) microsources and natural gas gensets are vulnerable to the collapse of the dc bus voltage in the CERTS-compatible PV microsources designed with voltage-source characteristics during dynamic overload conditions. Control techniques tailored to prevent the bus voltage collapse are explored. Simulation and experimental verification...
Because of the differences in line impedances, parallel inverters with conventional droop control will have huge circulating current, which does not flow through the loads. To mitigate the circulating current, the research in this paper finds out that parallel-operated inverters should have the impedance in inverse proportion to their capacities, which is difficult to realize in practice. To meet...
A novel control strategy which enables proportional linear and nonlinear loads sharing among paralleled inverters and voltage harmonic suppression is proposed in this paper. The proposed method is based on the autonomous currents sharing controller (ACSC) instead of conventional power droop control to provide fast transient response, decoupling control and large stability margin. The current components...
Harmonic power can be shared by controlling the equivalent harmonic impedance of distributed generation (DG) units in islanded microgrids. This paper firstly reviews several methods for controlling the equivalent harmonic impedance of DGs and adopts the method based on resistive active power filter (R-APF). Then, a droop relationship between the equivalent harmonic impedance of DGs and their remaining...
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...
A hybrid impedance model of Islanded MicroGrid with Paralleled Inverters Controlled by Droop and PQ Strategies (IMG-PICDPS) is derived, in which the PQ-controlled Inverters (PQ-Invs) are equivalent to Norton's circuits, while the DRoop-controlled Inverters (DR-Inv) to Thevenin's circuits in this paper. An impedance-based stability analysis method is further proposed according to the Nyquist criterion...
There is an increasing need to model large networks of inverter-based distributed generation due to the limits of existing simulation tools. A deliberate enforcement of intra-feeder coherency between adjacent droop-controlled inverters is a worthwhile objective, as phase angle coherency will allow for a deliberate partitioning of fast and slow dynamics within the network. This partitioning, in turn,...
Droop control is generally used to realize power sharing without communication lines. VSG (Virtual Synchronous Generator) is a control method that mimics both steady-state droop and dynamic characteristic of SG (Synchronous Generator) to enhance inertia of microgrid. In this paper, the comparison of different damping effect forms in VSG control is given firstly to draw conclusions: For the aspect...
The droop control technology, which can achieve an autonomous power sharing among distributed resources interface converters, provides the advantages of enhanced system reliability and reduced complexity. However, the reactive power sharing accuracy of the conventional Q — V droop method can be degraded due to its dependence on the line impedances. The Q — V droop control method was proposed to reduce...
One of the major feature of DC microgrids is its high penetration of power electronic converters, as a result, the system inertia becomes a problem. In this paper, an admittance-type droop control with additional capability of introducing virtual inertia to the system. With the proposed method, each energy source will also contribute virtual inertia to the system, thus improving transient response...
This paper presents a power-based droop controller for distributed energy resources converters in dc microgrids that are connected to the utility ac grid by a grid-interface converter. Typically, when dc microgrids are interfaced to ac power systems, the microgrid dc bus voltage can be affected by fluctuations caused, for example, by background harmonics present in the ac systems or by fluctuating...
To address the DC link voltage regeneration issue in parallel Uninterruptible Power Supply (UPS) system, a DC link voltage protection (DCVP) method through online virtual resistance regulation is proposed. The proposed control strategy is able to protect the DC link from overvoltage that may trigger the protection mechanism of the UPS system. Moreover, a current sharing control strategy by regulating...
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