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Hybrid AC/DC microgrid (MG) has attracted more and more attention due to its advantages such as better power sharing, improved system dynamics, and optimal management. But the complicated structure brings a great challenge to the modeling and stability analysis. In recent years, dynamic phasor model has been well applied in the modeling of AC MGs. Dynamic phasor tranforms sinusoidal quantities to...
Dead-time effect of dual active bridge (DAB) DC-DC converter is usually out of consideration in traditional optimized strategies, causing the deviation of the theoretical and actual results. In this paper, the current stress model of DAB with dead-time effect is given, and combining the transmission power model, a current-stress-optimized strategy is proposed. Meanwhile, the corresponding control...
Parallel three-level T-type inverters (3LT2Is) can increase power rating and reliability, but the circulating current problem will arise. Unbalanced conditions including unbalanced filter inductances and unbalanced grid voltage have negative effects on the operation of parallel 3LT2Is. This paper presents an improved repetitive control scheme for circulating current suppression in parallel 3LT2Is...
Paralleled inverters have the merits of high power rating, improved reliability and convenient maintenance, but zero-sequence circulating current (ZSCC) will occur and lead to current distortion and system loss. The ZSCC control is more complicated when adopting three-level topology and increasing paralleled number. This paper addresses the suppression of ZSCC in multi-paralleled three-level T-type...
The voltage droop control technology is commonly adopted to control the power sharing between parallel energy storage units in island dc microgrid for its low cost on the control and communication system, but a large number of voltage and current sensors are needed in the traditional droop control method. An improved droop control method for reducing current sensors is proposed. To achieve voltage...
This paper gives a detailed analysis about the causes of the voltage distortion caused by dead time in dual active bridge (DAB) DC-DC converter. The zero-crossing point of the equivalent leakage inductor's current is the definitive factor for various voltage distortion phenomena, which is determined by dead time and phase-shift ratios. Based on the switching characterization of DAB in dual-phase-shift...
The modular multilevel converter (MMC) is considered to be the state of the art in medium- and high-voltage application. The nearest level modulation (NLM) method is one of the most popular modulations, however, when applied to MMC with small number of sub-modular (SM), the output waveforms contain large harmonic components. This paper proposes a modified NLM method. By changing the traditional rounding...
Supercapacitors (SCs) are widely utilized as energy storage units (ESUs) to compensate the transient power fluctuations. In this paper, an improved virtual impedance based coordinated control strategy for distributed SCs is proposed to achieve accurate power distribution. Unlike the existed strategy which can hardly adjust the output power of each SC if the energy storage system contains several distributed...
To balance the state-of-charge (SoC) of distributed energy storage units (ESUs) in dc microgrid, it is necessary to adjust the output power of each ESU according to its SoC, but the traditional SoC-based adaptive droop control methods can't adjust output power and suppress output ripple current simultaneously when there are several single-phase inverters connected to the dc bus. A SoC balancing method...
Microgrid(MG) system black start restoration is an integral part in providing power to traditional grid and stable operation of MG. Aiming at choosing the black start power supply, information entropy theory is used in assessment of distributed generation(DG)'s black start capacity. As the process of pre-synchronous is the key of maintaining steady state in top-down restoration, rapidity and accuracy...
Energy management is the core of economical and efficient operation for hybrid AC/DC microgrid. In this paper, renewable energy sources are forecast by using BP neural network based on modified particle swarm optimization (MPSO-BP). Compared with traditional algorithm, the modified algorithm performs better in both search ability and speed. After forecasting, with the objectives of minimum total cost...
Selective harmonic elimination pulse-width modulation (SHEPWM) is a well-known switching technique applied in power electronics field for eliminating low order harmonics. According to symmetrical pulse patterns over the quarter of the period in SHEPWM, the neutral-point voltage could be balance naturally in a certain range. However, the neutral-point voltage fluctuation would be enlarging as the output...
Parallel three-level T-type inverters (3LT2Is) can increase the capacity of the distributed generation system. In this situation, the zero-sequence circulating currents (ZSCCs) will occur in the common dc-link voltage of parallel 3LT2Is. This paper presents a novel ZSCC reduction method based on the developing selective harmonic elimination pulse-width modulation (SHEPWM) for parallel 3LT2Is. And...
This paper presents a predictive current control strategy with active damping method applied to a current source inverter. This control strategy uses a discrete-time model of the system to predict the future value of the grid current for all possible current vectors generated by the inverter. According to a cost function that minimizes the errors of the predicted grid current and the reference grid...
In this paper, the Z-source three-level T-type converter (3LT2C) is proposed for low-voltage applications. The Z-source 3LT2C basically combines the positive aspects of the Zsource two-level converter with the advantages of the Z-source neutral point clamped (NPC) converter. The traditional space vector modulation (SVM) technique for Z-source 3LT2C produces the desired voltage transfer gain with minimized...
In this paper, a new modulation method is proposed for a $Z$-source three-level T-type inverter $(3\mbox{LT}^2{I})$. The $Z$-source $3\mbox{LT}^2{I}$ combines the merits of the $Z$-source two-level inverter and the advantages of the $Z$-source neutral-point-clamped inverter. Although the previous literature has proved that the space vector modulation (SVM) technique for $Z$-source $3\mbox{LT}^2{I}$...
Gird-connected photovoltaic (PV) inverters with the function of active power filter (APF) not only inject the active power into the electric network, improve the power quality, but also make full use of their capacity, especially in the cloudy day or the night. An improved implementation of the amplitude limiting control of the three-phase grid-connected PV inverters is presented. To achieve the optimally...
A new high-efficiency transformless photovoltaic generation system, which is based on singlephase hybrid clamped three-level inverter, is proposed in this paper. The leakage current problem in transformless photovoltaic generation systems is solved. The elimination of the transformer can not only reduce the cost, size and weight of the conversion stage, but also increase the system efficiency. Comparing...
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