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In this paper a unified Impedance-based Stability Criterion (UIBSC) has been proposed for paralleled grid-tied inverters. Compared to the traditional Impedance-based Stability Criterion (IBSC) which needs to evaluate all minor loop gains (MLGs) of each individual inverter, the UIBSC only checks the derived global minor loop gain (GMLG) once to determine system stability. As a result, the computation...
Detecting the load currents is a basic control method of paralleled active power filter (PAPF). The stability and compensation effect of the system would be influenced by the interactions of the load, weak grid and the paralleled active power filter (PAPF), when the load can't be equivalent to an ideal harmonic current source. The impedance models are established to analyze the stability of the system,...
In this paper, a radial-chordal decomposition (RCD) technique is proposed to decouple the power angle and voltage control of a smart load based on the use of electric springs (ES). The paper gives a highlight of the decoupling feature and the merit of achieving multiple functionalities within a single ES. This RCD control method has been tested on a 2 kW small-scale power system. Experimental results...
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...
With power converters integrated to the weak power grid, the influences of the voltage feed-forward and the current decoupling on the stability of the current control loop become obvious and need to be considered. Complex transfer functions are applied to analyze the effects of the feed-forward and cross decoupling compensation on the stability of the current control loop. Negative influences of the...
When multiple stable systems are combined into one system, the newly formed hybrid system has a certain possibility to be unstable. Such a natural phenomenon has been verified in the fields of chemistry and biology over the last century. The use of electric springs (ES), which must be implemented in large quantity over the power grids, can also suffer from the same issue if specified design are not...
The interaction between STATCOM and voltage-source inverter (VSI) may cause instability in an islanded micro-grid. Impedance models of storage battery power convert system (PCS) and cascaded multilevel static synchronous compensator (STATCOM) are established based on which the interaction mechanism between PCS and STATCOM is studied. Using Nyquist stability criterion and admittance ratio analysis,...
Due to intermittence and randomness, renewable energy distributed generations (e.g. wind or photovoltaic power) can cause a serious influence on the operation of the Microgrid, such as frequency and voltage fluctuations. Superconducting Magnetic Energy Storage (SMES) is probably a preferred technology to overcome these fluctuations. This paper proposes a multi-module current-source power conditioning...
In highly microgrid (MG) integrated distribution systems, problems such as a sudden cut out of the MGs due to grid faults may lead to adverse effects to the grid. As a consequence, ancillary services provided by MGs are preferred since it can make the MG a contributor to ride through the faults. In this paper, a voltage support strategy based on negative sequence droop control, which regulate the...
In most modern power electronics systems constant power loads (CPL) exist, which could have a severe influence on system stability. Conventionally two modelling tools for a system qualitative study are considered — generalized state-space averaging (GSSA) and DQ modelling methods. In this paper their strict mathematical equivalence in the balanced three-phase system is shown and areas of GSSA application...
The continuous integration of renewable energy sources into power systems has led to the construction of large power plants based on power electronics, with power ratings up to hundreds of megawatts, in order to accomodate technologies like solar PV and wind energy. Due to the size of these plants, they must provide support services for the grid and it is necessary to analyze the impact they have...
The interactions of more and more power electronics-interfaced power systems can worsen the power quality and the system stability in distribution networks. System stability can be addressed analyzing the source and load impedances at the interaction section and well-established approaches exist for DC and three-phase AC networks. Some papers focus also on single-phase AC systems, whose study is generally...
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...
Transient stability analysis (TSA) of power system is gaining importance given the dwindling gap of power generation and demand as well as increasing penetration of intermittent renewable energy sources. Current approaches to TSA are primarily based on time-domain, energy-function, and common-Lyapunov-function based analyses. This paper outlines a transient-stability-analysis approach based on polynomial...
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...
In this paper, we present an unstable phenomenon in cascaded systems that the source converter might become unstable after connected with the load converter though it can work stably individually. However, by staggering the switches' turn-on time between the source converter and load converter, it can become stable. Analysis in this paper shows that the essential reason for this phenomenon is that...
Predictive current control (PCC) methods have been widely implemented for grid-connected voltage source inverters (VSIs) recently to achieve better output performance, however, facing the challenge of high sensitivity to uncertain system disturbances and inevitable time delay. In this paper, a new PCC scheme has been proposed for a single-phase VSI to improve the quality of the current fed to the...
This work proposes the usage of a repetitive-based control to dynamically restore the voltage applied to grid sensitive loads. The control is able to wipe off harmonic distortion and relies on simple transfer function. As a consequence, there is no need to apply harmonic selective filters. Moreover, the filter is able to work on sinusoid references and avoids employment of the dq transform. The design...
As the share of photovoltaic (PV) generation is growing worldwide, so is the concerns about its stochastic nature that can complicate the operation and planning of energy systems. With this paper we give an overview on the topic, analyzing and quantifying the stochasticity of PV and its impact on energy systems, with a main focus on the generation sector. The impact is analyzed in terms of ability...
Power converter operation on high-impedance grids can result in oscillatory behavior as a result of “self-synchronization” of an inverter's phase detection unit (PDU). This phenomenon is particularly of concern in renewable energy applications and it occurs when the converter's injected current changes the voltage angle at the point-of-common coupling (PCC) and synchronizes to itself through its PDU...
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