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This paper proposes a new method to suppress frequency variations of power system with large amount of wind power installed by using the kinetic energy of the wind power generators. In recent years, environmental problems have been becoming serious and wind power generation with less environmental impacts has attracted much attention and introduced. Since wind power generation is an unstable power...
Droop control is an effective power sharing control scheme of distributed generation (DG) inverters in islanding AC microgrid, which can stabilize the grid as long as the distributed generation systems have sufficient residual power. On the contrary, many loads have equipped with power conversion circuits in front to improve the operational efficiency, e.g. air conditioners and LED lighting, which...
In this paper, a hierarchical control system based on a novel autonomous current sharing controller for grid-connected microgrids (MGs) is presented. A three-level hierarchical control system is implemented to guarantee the power sharing performance among voltage controlled parallel inverters, while providing the required active and reactive power to the utility grid. A communication link is used...
This paper provides a bridged-T voltage control scheme for a H bridge SiC inverter switching at 150 kHz for generating various waveforms at wide range of frequencies (60 Hz to 10 kHz) which is developed as a core loss test unit. Bridged-T controller attains the advantages of both the open and closed loop controllers. It has the fast dynamic response feature of the open-loop controller and zero steady...
The increase of renewable energy sources and distributed generation may have a negative impact on power systems, specially on weak ones. Therefore, their control systems are acquiring growing importance, with new proposals that aim to contribute to the control and stability of the power system as conventional generating units. This paper studies the effect that a PV system using a synchronous power...
In this paper, an improvement in power sharing for Autonomous Microgrid is well established. All previous studies were based on voltage and frequency droop control to share power between distributed generators. This paper develops a new robust voltage and angle droop control to share power, where its advantage over the common frequency droop is in less frequency variation. The synchronization of Power...
Energy storage systems based on Lithium-ion batteries have been proposed as an environmental friendly alternative to traditional conventional generating units for providing grid frequency regulation. One major challenge regarding the use of Lithium-ion batteries in such applications is their cost competitiveness in comparison to other storage technologies or with the traditional frequency regulation...
This paper proposes a solution for the transient grid frequency drift that occurs when active power transients take place in weak grids. Microgrids (MGs) are by definition weak grids, exhibiting a low inertia and high impedance which make them prone to contingencies that compromise the grid quality and stability. Particularly, the low inertia of the generators coupled to a MG could make the rotor...
This paper presents the comparison of three different fully digital, oversampled, large bandwidth inverter current controllers: a proportional integral controller, a predictive controller, and a non-linear hysteresis controller. The purpose is to determine which one allows to achieve the highest final performance when adopted as the inner current control loop in a microgrid utility interface converter...
The following two types of resonant controllers are mainly employed in stationary reference frame to obtain high performance in voltage-source converters: 1) proportional + resonant (PR) and 2) complex vector proportional + integral (cVPI). The performance analysis and parameter design of these two controllers has been researched in many papers. In this paper, these two groups of resonant controllers...
A DC/DC Modular-Multilevel Converter (MMC) is proposed in this paper, in which two modular multilevel converters are linked by a LCL tank. With the proposed converter, the high power medium frequency transformer can be eliminated to simplify the structure, quasi zero-current-switching operation of both MMCs can be achieved to alleviate the switching loss, the voltage stress of internal LCL tank can...
It is mandatory for grid-connected power converters to synchronize the feed-in currents with the grid. Moreover, the power converters should produce feed-in currents with low total harmonic distortions according to the demands, by employing advanced current controllers, e.g., Proportional Resonant (PR) and Repetitive Controllers (RC). The synchronization is actually to detect the instantaneous grid...
The impact caused by the large scale penetration of renewable energy sources into electrical grid has been given an increasing concern in the past decade. Multiple challenges will occur in the future when the share of the traditional synchronous generators is reduced. One of the main issues is the lack of rotational inertia in the grid, which may cause stability issues. Therefore, the renewable energy...
This paper presents a control scheme that is applied on the shunt-type electric springs (ES), which is used to strictly regulate the grid voltage for ensuring local voltage stability and to mitigate the utility frequency deviation. The operating method of the shunt-type ES is discussed. A laboratory-scale 1 kW experiment has been done to verify the proposed control scheme and to validate the feasibility...
Direct power control (DPC) and model predictive control (MPC) are two well known methods to achieve direct control of active power and reactive power in PWM rectifiers. They both select a voltage vector, according to a switching table or by minimizing a cost function, and then apply it in the next control period. The use of only one voltage vector during one control period leads to high power ripples...
Micro-grids fed with small synchronous generators and intermittent renewable power sources are generally considered as weak power grids unless very large energy storages are incorporated as the energy buffer. Auxiliary techniques are needed to improve their stability when transient interrupts occur. In this paper, the 3-ph Electric Spring (ES) is studied to improve the stability of the micro-grid...
The light load efficiency has drawn more and more attention for the LLC resonant converters. And the high frequency LLC converters are emerging in recent years. The conventional burst mode control cannot fix to the efficiency-optimal state during the burst-on time. Optimal Trajectory Control (OTC) for burst mode can solve this problem by using fixed 3-pulse pattern; however, the burst operation range...
An improved buck-boost + LLC (IBB LLC) cascaded converter appropriate for wide input voltage situation is presented in this paper, which can be used as a constant voltage source or a constant current source charger for battery. The control strategy of dual frequency PWM (DFPWM) is introduced. For the LLC converter, ZVS for MOSFETs and ZCS for diode are achieved. As a result, the switching loss is...
This paper investigates the stability regions of current control for LCL-filtered grid-connected converters, where no active or passive damping is required to stabilize the closed-loop control system. It is already identified in the literature that if the LCL resonance frequency is placed within 1/6 to 1/2 of the system sampling frequency, the grid current control can be directly used without damping...
Three-phase single-switch boost PFC converter operates in discontinuous current mode (DCM) to achieve PFC. If the duty cycle is constant in a line cycle, the average value of the inductor current in a line cycle is not sinusoidal. The PF is low and the input current contains rich 5th and 7th harmonics. Variable switching frequency control can reduce the input current harmonic distortion. However,...
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