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The microgrid with distributed PV and air source heat pump is studied, aim at the problem of controller saturation caused by the lag of the static switch and the mismatch between the operation mode and the control method, droop control is used in island mode and grid-connected mode, an improved pre-synchronization control algorithm is proposed to ensure the smooth transition of the microgrid transient...
This paper proposes a power decoupling solution based on improved single-phase Y-source inverter with no additional power semiconductors. Single-phase inverter would cause voltage and current ripples on the dc link because of double-frequency power ripple. Commonly, large electrolytic capacitors are connected to dc link in H- bridge inverter to accomplish power decoupling. However, electrolytic capacitors...
To broaden the speed range of PMSM (Permanent Magnet Synchronous Motor) for the electric vehicles and to improve the stability in the high speed and small torque operating conditions of the electric vehicles, the control strategy based on flux-weakening control algorithm, using voltage feedback method, combined with SMVSC (Sliding Mode Variable Structure Control) algorithm, using the improved exponential...
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...
A compact 2-terminal, series-pass active damping circuit utilizing semiconductor device is proposed. It is implemented with linearly-operated device such as MOSFET using current feedback control at very low dropout voltage. The damping device features a simple internal structure and is connected in series with a generic switching mode power supply (SMPS). It can damp unwanted oscillation due to the...
For the islanded microgrid which is connected with nonlinear loads, an effective harmonic sharing method should be designed to guarantee the system stable operation. In this paper, a novel method of virtual impedance and PCC voltage compensation are proposed to achieve the harmonic sharing and voltage quality improvement at the point of common coupling (PCC). The fundamental and each harmonic currents...
Modern power grid has already become one of the pillar industry of the national economy. The safety and steady operation of power grid is closely related to the development of all walks of life, national economy guarantee the fundamental interests of people. So it is significant to guarantee the safety of grid in production, operation, and the electric power supply. In this paper, connecting with...
In order to improve fault recovery characteristic of high-voltage direct current transmission system(HVDC), this paper proposes voltage dependent current order limiter(VDCOL), optimizing arc extinguishing angle controlling and adopting SVC reactive power compensator and so on to improve fault recovery feature after analyzing the main factors influencing fault recovery characteristic. This paper makes...
In this paper, we built an experimental platform for the hybrid energy storage system for the ship based on DSP28335. The design of bidirectional DC/DC controller is completed. The PI control algorithm to improve the stability of the control system, and two kinds of operating modes of the half bridge bi-directional DC/DC controller for boost and buck, respectively from the angle of voltage and current...
Traditional droop-controlled systems assume that the generators are able to provide sufficient power as required. This is however not always true, especially in renewable systems, where the energy sources (e.g., photovoltaic source) may not be able to provide enough power (or even loss of power generation) due to the intermittency. In that case, unbalance in active power generation may occur among...
In recent years, with the promotion and application of photovoltaic (PV) technology, research on grid-connected inverters incorporating with weak grid has become a hot field. In general, the large grid impedance will reduce the gain and bandwidth of the control system and slow down the dynamic response, or even lead to resonance and instability of the whole control system. Especially, when the grid...
Multi-port isolated H-bridge converter has the features of high voltage conversion ratio, bidirectional power flow and high-power capacity, which is suitable to be integrated into DC microgrids. This paper uses three-port isolated H-bridge converters as the interfacing converters in power generation units which comprise distributed generation (DG) and energy storage (ES) in DC microgrid. The topology...
The electric arc furnaces (EAFs) are the major disturbances in the medium-voltage level of power system for the low frequency voltage variations, which lead to incandescent lamp flickering. In order to alleviate these voltage variations, the modular multilevel cascaded converter with the topology of single-delta bridge-cell (MMCC-SDBC) is used to the medium-voltage level flicker compensator application...
Photovoltaic (PV) units in DC microgrids (MGs) usually have two operating modes including constant voltage control (CVC) mode and maximum power point tracking (MPPT) mode. When the operating mode of PV units switches between CVC and MPPT, unexpected transient problems of output voltage and current may occur. Droop control applied in DC-MGs can achieve load current sharing at the time when more than...
Low short circuit capacity and high grid impedance are the main electrical characteristics of weak grid, and there are some stability and power quality problems with a large number of PV power generation systems incorporated into weak grid. The increasing penetration of PV power generation easily lead to voltage rise at the end of grid, and it affects the ability of weak grid to accept PV power capacity...
An adaptive controller is designed for three-phase pulse width modulation (PWM) voltage source rectifier with parametric uncertainties based on the dynamic surface control (DSC) technique. The unknown parameters of the system are estimated by applying the adaptive control method. In addition, the problem of “explosion of complexity” in backstepping design procedure is avoided by using the DSC technique...
By analyzing the hybrid property of Microgrid in detail, a mixed logical dynamical model is set up with Hybrid theory. The energy in DC bus capacitor is chosen as state variable, the system functions and constraints with continuous state variables, input control variables, logical variables and auxiliary variables are presented. Based on the MLD model, model predictive control theory is applied for...
This paper will present the modeling and the design of multi-parallel-connected SSSC (MSSSC) with daisy-chained transformers. The advantages of the proposed MSSSC structure include its modularity, scalability, controllability, and flexibility in power transfer, autonomous behavior, and well current-sharing performance. The principle of operation, the steady-state and transient current-sharing characteristics...
Fuel-cell power systems comprising single-phase DC/AC inverters draw low-frequency AC ripple currents at twice the output frequency from the fuel cell. Such a 100/120 Hz ripple current may create instability in the fuel cell system, lowers its efficiency, and shortens the lifetime of fuel cell stack. This paper1 presents a waveform control method that can mitigate such a low-frequency ripple current...
The basic theory and the working principle on quantum secret communication are introduced in this paper, the realization process of protocols of quantum key distribution are analyzed, the key technology of quantum secret communication is discussed. In the resent year, relative experiment and research progress on quantum secret communication are summarized at home and abroad. Finally, the application...
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