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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,...
A small-signal model based on droop control and utilized in microgrid of photovoltaic (PV) inverters is designed in this paper. The parallel-inverter system composed of two 1kVA PV inverters with no communication line is built on the basis of small-signal model. The influence of droop coefficients on the system stability and dynamic response ability is analyzed by utilizing root locus analysis in...
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...
In the stand-alone brushless doubly fed generator (BDFG)-based shaft power generation system, the stator power winding leakage inductance leads to the strong coupling between load side converter (LSC) and BDFG. In this study, the leakage inductance was used as a part of LCL filter. The difference between LC-L and conventional LCL filter has been analyzed to reveal the damping characteristic that LC-L...
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...
In this paper, it found that the low frequency oscillation phenomenon causing large inductor current and output voltage variations exists in the constant-on-time (COT) controlled boost converter, while the time constant of the output capacitor is below a critical value. The critical value is deduced, which is related to the main circuit parameters such as input voltage, inductance and load current...
The concept of microgrid can integrate large amounts of Distributed Generations (DG) into power system and provide higher reliability, energy security and surety to critical loads. A Virtual Droop Control (VDC) method is proposed for the power management and voltage and frequency regulation and has been applied to the Fort Sill microgrid. The state space models for the microgrid components and systems...
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...
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 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...
Instabilities due to mutual interactions among converters and inverters are sometimes observed. The Lyapunov-based, or an energy-based control is useful to assure stability of parallel-connected power converters. This paper investigates why the Lyapunov-based method can stabilize the system even when linear methods fail in stabilization due to a large line impedance. The analysis is based on the impedance...
Distribution STATic synchronous COMpensators (DSTATCOMs) have been proved an effective approach to correct power quality in distribution network. With reactive component and harmonic component of load current detected independently, selective compensation mode can be realized. To improve the reactive compensation ability and harmonic suppression performance of a cascaded DSTATCOM, the fast-transient...
The application of two control strategies for shunt-connected FACTS devices to enhance the transient stability of a power system will be discussed in this paper. The main focus will be on the use of active power in the FACTS device and therefore a STATCOM with active power injection capability will be considered. The first approach represents the classical cascade controller that consists of an inner...
Hybrid electromagnetic interference (EMI) filters (HEFs) which are composed of an active filter and a passive filter, have been proposed to reduce the size and weight of conventional passive EMI filters. However, accurate models that can be used to predict the stability and performance of HEFs have not been developed. To cope with this, this paper presents a modeling technique for a hybrid common-mode...
This paper analyzes the harmonics emission, propagation, and mitigation issues in an MVDC distribution system. Specifically, the DC current harmonics from a high power NPC DTC motor drive is analyzed. It is found that DC network resonance is a major cause of DC current harmonics amplification and propagation in the MVDC system. As a result, adding a DC-side input filter inductor is proposed to attenuate...
This paper discusses and analyzes the parallel operation of uninterruptible power supplies (UPS) with instantaneous average current sharing control strategy. The analysis demonstrate that the control method introduces a virtual impedance between the inverters. If the impedance configured as resistive, it will simplify the control strategy, the paper analyzes the stability of the control system by...
This paper discusses the dynamic interaction of multi-paralleled inverters within a weak grid. Interactive current and common current models are proposed to explain the interaction among these inverters, which are studied with both open loop and closed loop analysis. An aggregated model is proposed to describe the totality of multi-inverters. Additionally, system stability is explicitly studied and...
In presence of tightly regulated power electronic converters and motor drives in the more electric aircraft (MEA), stability is a great concern for the electrical power system (EPS) in the MEA. The DC electrical power distribution system (EPDS) of the MEA is one of the core architecture for electrical power transmission. DC transmission cables are also taken into account since it cannot be neglected...
This paper deals with the coordinated control of load sharing among multiple sources in DC microgrid with energy storage system. The DC electrical power system (EPS) with parallel sources in the more electric aircraft (MEA) are under study in this paper. Permanent magnet synchronous generators (PMSGs) are the main sources to supply power to meet the load demand on board. An adaptive droop characteristic...
The stability of the cascaded power converters system is an important design consideration, since the interaction among the individual converters in the cascaded system can lead to the degradation of the system stability and dynamical performances, even make the system unstable. In this paper, the stability analysis methods for the cascaded power conversion system are reviewed at the beginning. Following,...
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