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The increasing use of grid-connected inverters to connect renewable energy sources to a power grid will have globally important effect on grid performance. A mismatch between the grid and inverter impedance may cause harmonic resonances, which can lead to instability of the grid and disruption of inverter operation. The grid dynamics vary over time, so the inverter should adapt to the varying conditions...
For the control of electric motors, conventional inverters have utilized position and current sensors, but they undesirable in terms of cost and maintenance effort. For this reason, approaches without the sensors are developed by applying back electromotive force or signal injection-based method which also has some problems related to the the deterioration of control performance in low speed range...
This paper discusses the harmonics compensation of the constant dc-capacitor voltage-control (CDCVC)-based strategy of smart charger (SC) for electric vehicles (EVs) in single-phase three-wire distribution feeders (SPTWDFs) under the distorted source voltage and load currents conditions. The basic principle of the CDCVC-based harmonics compensation strategy under the distorted source voltage and load...
Problems with power quality in the grid have gained a lot of attention recently due to rapid increase in the amount of grid-connected power converters. The converter should produce sinusoidal currents also during abnormal conditions, such as unbalanced grid voltages. Several methods, like the delayed signal cancellation-based method (DSC), have been proposed to alleviate the detrimental effect of...
The well-known droop control and master-slave control methods are two dominant coordinative control schemes for inverter interfacing parallel distributed energy resources (DERs) in islanded AC microgrids. However, both these two control methods have some drawbacks and inherent limitations in practical application. After analyzing their complementary strengths and weaknesses, this paper proposed a...
In large power electronic systems like a wind farm, the mutual interactions between the control systems of the power converters can lead to various stability and power quality problems. In order to predict the system dynamic behavior, this paper presents an approach to model a wind farm as a Multi-Input Multi-Output (MIMO) dynamic system, where the current control loops with Phase-Locked Loops (PLLs)...
In order to enable a more wide-scale utilization of PV systems, the cost of PV energy has to be comparable with other energy sources. Oversizing the PV array is one common approach to reduce the cost of PV energy, since it increases the PV energy yield during low solar irradiance conditions. However, oversizing the PV array will increase the loading of PV inverters, which may have undesired influence...
The increase in renewable energy penetration in the past few years has led to grave power quality issues in the utility grid. This has ushered in the need for a robust and stable control system for reference tracking and disturbance rejection with respect to grid connected converters. Typically, a simple proportional integrator (PI) controller is used in the synchronous reference frame (dq) for current...
With rapid increase of photovoltaic (PV) penetration in distribution system, and the fact that distributed generators may involve in voltage regulation according to IEEE standard 1547, it is necessary to check the stability of PV generator integration, especially utility PV farms. To apply generalized Nyquist Criteria (GNC) based on impedances on D-Q frame, output impedances of PV farm is derived...
To avoid the stability problem of grid connected inverter caused by the conventional phase locked loop (PLL), the direct power control of voltage source inverter in virtual synchronous reference frame without PLL is investigated considering grid voltage disturbance in the paper. Based on the small signal analysis methods, comparison between conventional PLL and no PLL is made. It can be found that...
Embedded grids have been increasingly adopted into applications such as More Electric Aircraft where different power converters are interconnected to each other. Interactions between the grid components poses the risk of instability to the system, more so when in the presence of reduced passive filters. An approach of automated and scalable tuning of such embedded grids with consideration for the...
This paper highlights the power limited nature of the Distributed Generation inverter and demonstrates the practical way to integrate them into the microgrid. Since the energy source of Distributed Generation inverters is power limited in nature, they constrain the operation of inverters to which they are coupled. If the power demanded from these inverters is beyond their capability, their DC-link...
In this paper, a guide for the admittance shaping is introduced for PWM converters tied to the grid using outer power control loop. To obtain intuitive tuning factor, the design method for the power control loop is proposed. The proposed design method could be applied to the power control of PWM converter regardless of system capacity and grid voltage. Instead of directly varying proportional or integral...
Brushless doubly-fed induction generator (BDFIG) is a new type of ac induction machine and can be used for both grid-connected and stand-alone power generation. The conventional control methods for the BDFIG almost all rely on the encoder, which brings many limitations in terms of cost, complexity, reliability, and so on. This paper presents a new rotor speed observer (RSO) for the encoderless operation...
The popularly used current controlled architecture for grid connected converter systems needs a phase locked loop (PLL) for its operation. The PLL generates the unit vectors required for desired current reference generation. This paper proposes to eliminate the grid voltage sensor and presents a method to estimate the unit vectors and grid frequency without a dedicated grid voltage sensor. The estimation...
For a grid-connected Voltage-Source Converter (VSC), dynamics of the grid synchronization plays an important role in affecting the converter performances and stability. Due to its significance, this paper gives a comparative analysis about some basic grid synchronization schemes, through viewpoint of dynamic performances, which appeared as the impacts of voltage perturbation on the estimated angle...
Phase-locked loops (PLLs) are very important in power and energy areas. Many PLLs have been proposed in recent literatures, and all these methods are to design a robust filter and let them be as a preprocessing tool before the synchronous reference frame PLL (SRF-PLL) input. Among these PLLs, a interesting PLL is Least-Error Squares (LES) Filter-Based PLL (LES-PLL), which is composed of a LES filter...
The accurate and fast detection of the grid voltage attributes (e.g. frequency and amplitude) are gaining more attention in microgrids due to the new stringent amendments to the microgrid standards. In this paper, two novel observer based techniques are introduced; one for estimating the frequency and another for the amplitude of the grid voltage. The proposed observer techniques offer superior performance...
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