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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...
Fatigue and destruction in the shafts of a wind turbine caused by sub-synchronous oscillations during power system faults is critical for wind turbine reliability. This paper investigates a three-mass shaft model according to a MW class doubly-fed wind generator shaft mechanical structure and obtains the electromagnetic torque of a wind turbine by PSCAD simulation when sub-synchronous oscillation...
A major concern for wind farm connection to power systems is large variation of power output caused by the variability and unpredictability of wind speed. For a power system with high wind power penetration, the frequency control process of conventional generators (CGs) to match load and wind power variation becomes an important operation issue. Energy storage systems play an important role in solving...
Voltage stability analysis has been highly concerned by researchers. However, probabilistic techniques cannot handle fuzzy factors in power system. In this paper, a voltage stability analysis method based on adaptive fuzzy logic with consideration of random factors of loads is proposed. System states are classified, fuzzy mathematical model and fuzzy voltage indexes are established, and voltage stability...
Distributed generators and micro-grid connection in distribution network has changed power flow from unidirectional to bidirectional. Therefore, it is necessary to install directional components to locate the fault position accurately when there is a short circuit fault in distribution network. However, voltage information is not available because there are no voltage transformers in most of the current...
This paper proposes an advanced non-harmonic detection control strategy for three-phase four-wire Active Power Filter (APF) based on improved Vector-Resonant Control (VRC). The mathematical model of the split-capacitor configuration is established with the source currents and the DC bus voltage as state variables. The proposed control scheme detects and regulates the source currents directly, without...
In a DC microgrid (MG) with droop control system only, there exists an inherent deviation between DC bus voltage and its rated value during the steady-state operations. In order to eliminate the inherent deviation, a secondary voltage regulation system (SVRS) based on vanadium redox battery (VRB) storages is proposed in this paper. It adopts double closed loop control strategy coordinating with the...
In this paper, a new coordination photovoltaic/battery micro-grid control strategy is proposed to improve the micro-grid fault ride-through capability. Under normal condition, the proposed strategy can restrain the influence of load fluctuations. When symmetrical grid fault happens, the micro-grid can ride through it by the proposed strategy. The DC-link bus voltage and AC current could be kept stable...
This paper proposes a novel control approach which integrates optimal operation and direct torque control (DTC) for motors in a building lift system. The optimal control and operation of lifts is based on fuzzy logic based on the real time data inputs such as original level, destination level, call level, etc. The DTC is used in the motor controller. The fuzzy PID controller in DTC is designed to...
Two-level energy management system is proposed and developed for coordination control of practical microgrid with distributed renewable sources and energy storages. A SCADA system has been developed to provide real time information of network information and individual components and to control operation of individual inverters and converters in order to achieve smooth and quick system operating mode...
In this paper, we investigate energy-efficient hybrid precoding for the Millimeter Wave (mmWave) multi-input multi-output (MIMO) systems. The considered multivariate optimization problem is hard to tackle because of the non-convex objective function and constraints. To solve the intractable problem, we propose a two-step optimization algorithm to obtain a near-optimal solution. The original multivariate...
Aiming at stabilizing the DC bus voltage and optimizing energy storage, this paper presents a control strategy of hybrid energy storage systems in DC micro-grid based on voltage droop method. The control strategy makes use of the super capacitor not only to compensate the high-frequency components of bus power according to the DC bus voltage, but also indirectly to compensate low-frequency components...
Three phase AC/DC converter based on the traditional double loop control may act as a link bridge in hybrid micro-grid due to its bidirectional power flow with unit power factor on AC side. When the AC/DC converter works on the condition of unbalanced voltage on the AC side, a second order ripple voltage will be generated in the DC-link and some amount of third harmonic current will exist in the AC...
In an autonomous micro grid or a power system with high renewable power penetration, the intermittency of renewable energy resources becomes major concern of system operation. Dynamic process of frequency response and control due to unit failures and resource variation may have significant impacts on system operational reliability because the outputs of committed conventional generators have to be...
A dynamic voltage restorer (DVR) based on photovoltaic (PV) generation/battery units is proposed to improve voltage quality in a microgrid. The restorer is connected with the grid by a rectifier, which is in series with the point of common coupling (PCC). Using energy management system (EMS), the proposed apparatus could be operated under dynamic voltage restorer mode, uninterrupted power supply mode...
With high wind power penetration, power system operators require accurate wind power output from wind farms for system operation. A more accurate four dimension wind speed model is proposed in this paper to simulate the effects of terrain and time delay of wind speed. Two coordinate transformation matrixes are proposed to easily incorporate wind direction in wind speed simulation. The effects of random...
Three equivalent drive train models of a wind turbine generator (WTG) are presented in this paper. The flexibility of the blades bending and the drive train are considered to analyze its transient stability under a three-phase fault. The simulations show that the fifth order lumped-mass model provides too optimistic estimation while the ninth order three-mass model can observe the motion of shaft...
The weakest bus in a network is the first point where voltage collapses in a severe contingency. The weakest bus may change with system configurations and operating conditions. This paper proposes a technique to evaluate the weakest bus and system reliability based on system voltage stability under various system contingencies and operation conditions. A power system is divided into safety, margin,...
The wake effect of a wind turbine generator (WTG) may affect output of a wind farm. Wake effect depends on wind speed, and the size and location of WTGs in a wind farm. When one or more WTGs fail in a wind farm, the wind speed distribution in the farm will change, which may lead to different wind power output from the farm. This paper proposes a Monte Carlo simulation technique is used to evaluate...
With the development of wind power, the inherent characteristics of randomness and uncertainty of wind energy would have an impressive effect on power system frequency, it is necessary for wind farm to participate in frequency regulating in order to share the burden with the frequency-regulating power plants, and to improve power system stability. Two operation modes of the wind farm are proposed...
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