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In this paper, an improved control strategy for three-phase inverter is proposed, which ensures three-phase output voltage symmetry under unbalanced grid voltage. Firstly, the positive and negative sequence separation module is used to obtain unbalance output voltage and current during the grid faults. By calculating output power of the inverter, an improved P-ƒ, Q-U and Q-G droop control strategy...
Distributed control methods generally implemented with droop control have been widely applied in the energy management of microgrids. However, the robustness and stability of distributed control has been influenced by the size and diversity of the microgrid structure and compositions. Meanwhile, centralized control has been considered lack of flexibility and expansibility. In this paper, a novel control...
In this paper, a positioning method of distributed power system is proposed to minimize average voltage variation of DC microgrid through voltage sensitivity. Power flow analysis is performed to derive voltage sensitivity, and droop bus is introduced to improve the accuracy of voltage sensitivity. In addition, the averaged voltage sensitivity according to the position of the distributed power system...
In microgrids, photovoltaic (PV) and storage are integrated as a droop-controlled ideal source, which is not practical and challenges the system efficiency. Instead, PV-storage can be allocated separately. This PV-storage independent system is more flexible and easier to optimize. But, the conventional PQ-controlled PVs rely on master voltage-controlled storage sources. In this paper, a novel operation...
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...
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...
Inverters in voltage control mode including droop control and virtual synchronous generator (VSG) are promising for interconnecting the renewable energy to the grid, which are both emulating the frequency and voltage regulating functions of synchronous generators through droop method. However, improper transient impact current and reactive power output are observed for inverters in voltage control...
In order to stabilize the power fluctuation caused by distributed energy in the bipolar-type DC micro-grid, a new hybrid energy storage system (HESS) coordination control strategy is proposed in this paper. First, in order to take advantage of lithium battery and super capacitor complementary performances, a cascade structure of the lithium battery and the super capacitor is adopted. Meanwhile, voltage...
The microgrid can operate in grid-connected mode and islanded mode, and the parallel operation of inverters will be involved in both modes. However, due to the differences of output characteristic among various inverters, the load power can't be shared equally. As a result, some methods without communication lines such as droop control and VSG (virtual synchronous generator) control have been proposed...
Due to different initial state of charge (SoC) of distribution energy storage system (DESS) and mismatched line impedance, the SoC of DESS is unbalanced in microgrid. The conventional P-f droop, used to obtain accuracy load sharing, cannot balance the SoC. To overcome the drawback, this paper proposes a unified SoC based droop control method with distributed communication lines. In this scheme, the...
Droop control method has been widely applied to achieve equal power sharing among distributed generations in microgrids. In practice, low-pass filters are usually required to mitigate the harmonics and noises in the calculated instantaneous power and obtain the average power used for the generation of frequency and voltage references. Unfortunately, the design of low-pass filters has not been studied...
A bipolar dc microgrid features three voltage levels and is capable of transmitting power more efficiently than a unipolar system. This paper proposes a droop control to achieve load sharing and voltage balancing in such a microgrid system. Droop control is adopted to ensure that autonomous sharing of load power can be realized without communication. Moreover, the positive and negative pole voltages...
In order to address the economical dispatch problem in islanding microgrids, this paper proposes a criterion and a decentralized economical-sharing scheme. The criterion is to judge the optimal economical-sharing whether can be realized via the decentralized approach. Then an optimal decentralized economical-sharing scheme is proposed. This overcomes the limitations of traditional centralized control,...
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