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As negative incremental resistance caused by constant power behavior of power converters may bring stability problem to distributed systems, stability of PV integration to distributed system attracts more and more attention. Compared to the widely used positive impedance method, D-Q Frame impedance matrix method is more accurate for integration of PV generator that has non-symmetrical control in DQ...
Droop-based control methods are used for operation of different inverters in the converter-interfaced AC microgrids. To ensure accurate power sharing among multiple inverters with fast dynamics and enhance stability in a stand-alone AC microgrid with constant impedance and constant power loads, this paper proposes a modified droop-based controller. The performance of the proposed controller is verified...
The traditional DG (distributed generation) wireless droop control base on “power-voltage-current” close loop is widely used. The power sharing performance of this method is significantly affected by the feeder impedance, mismatch inverter parameters, and unbalanced local load. Due to the affection of mismatched line impedance, the traditional droop method cannot make the reactive power shared accurately...
In single-phase power converters, passive power pulsation decoupling buffers (capacitors or LC circuits) have been widely adopted to reduce the twice-line frequency voltage and current ripple. With constant demands for higher power density and efficiency, active implementations of power pulsation buffers have always been an attractive prospect. While various implementations of active buffers have...
The Hilbert transform (HT) is widely used in signal processing and it has been found as a good tool to understand some physical phenomena in electrical systems. This paper presents a methodology to derive the input impedance of a power electronic converter with the application of the Hilbert transform. The results in the frequency domain based on the Fourier transform are compared with the HT calculations...
The growing number of renewable energy sources and power electronic participants are increasingly endangering the quality of supply at distribution grid level. A modular shunt-connected power conditioning system featuring uninterruptible power supply capability is proposed to locally increase power quality and supply reliability. This paper proposes an operation-mode-adaptive cascaded control strategy...
A series transistor array-based linear AC regulator was developed in the past and this technique is very fast-responding compared to the popular servo-transformer based AC voltage regulator. It has similar efficiency levels to the ferro-resonant types, but does not have waveform defects or power factor dependency. This patented technique is efficient when the input line voltage is at its lowest possible...
Direct current (DC) power technology, is well-established as a fully controlled power link between different ac grids. Nowadays, distributed generation (DG) has substantially changed the traditional power grid structure, with the high penetration of the renewable energy systems (RES) playing a key role on the system performance. The stochastic and intermittent nature of the power injected by the RES...
In this paper, an improved control strategy for three-phase inverter is proposed, which ensures three-phase output voltage symmetry under unbalanced grid voltage. Firstly, the positive and negative sequence separation module is used to obtain unbalance output voltage and current during the grid faults. By calculating output power of the inverter, an improved P-ƒ, Q-U and Q-G droop control strategy...
This paper presents a division-summation (D-Σ) digital controlled three-phase four-leg voltage source inverter with load impedance estimation for uninterruptible power supply applications. The D-Σ digital control developed for current tracking can accommodate wide filter inductance variation, which has been successfully adopted in grid-tied applications. This paper proposes a load impedance estimation...
This paper shows the development of a strategy to connect multiple different types of converters in parallel in an isolated single-phase microgrid harmoniously. First, the droop control strategy for microgrids and the particularities of the microgrid operation are explained, such as controlling the voltage and current of the battery to maintain its integrity. Then three different types of converters...
Various fault scenarios have been analyzed by running a number of differently combined 380 VDC microgrid tests. These tests represented a common grid topology with low system impedance at grid resonance points within the single- or lower double-digit kHz range. At serial arc faults, self-excited resonant modes of the arc plasma column have been observed. They lead to an increased arc column stability...
The Performance of battery packs is highly affected by imbalances between the series connected cells that provide the required string voltage. A modular battery implementation based on cascaded converters can have advantages over traditional centralized battery systems with add-ons active/passive balancing techniques. This paper investigates the use of a modular battery integrated within a cascaded...
The closed-loop (CL) impedances of each connected microgrid device (generator, sto rage or load) are key elements in stability studies of DC microgrids from the point of view of the DC common bus. The calculation of the CL impedance of standard DC/DC converters is widely described in the literature. The application of this method to a three-phase AC/DC converter connecting DC microgrids to the utility...
In this paper we present a counter/reference control based potentiostat architecture including the analysis and experimental results. Then, a comparison between different potentiostat architectures was achieved in order to study the effect of counter/reference (CR) voltage control in potentiostats instead of working/reference (WR) electrodes. Reported results are obtained with (Fe(CN)6)4− with a concentration...
This paper investigates the impact of the Fault Ride-Through (FRT) capability and the dynamic reactive power support of large-scale PhotoVoltaic (PV) systems according to the newly proposed German Grid Code (GGC) on short-term voltage stability. The PV system is based on a generic model and realistic parameters are used that are determined in consultation with a manufacturer. In this context, improvements...
This paper proposes the use of structural equation modelling (SEM) to assess the contributions of on-load tap changer (OLTC) on voltage controlled demand response (VCDR) in future power systems. For the development of a VCDR scheme, optimal deployment of the available resources is necessary. Thus, understanding the contributions of voltage controlled devices such as OLTCs to VCDR will assist the optimal...
DC power distribution gains popularity in future residential, renewable energy, transportation and data centers. Such dc system can be connected to ac system through bidirectional interface converter. Compared with isolated converters, transformerless solutions have the advantages of higher power density, efficiency, and lower cost. One concern about the non-isolated connection is the coupled common-mode...
Inverters in voltage control mode including droop control and virtual synchronous generator (VSG) are promising for interconnecting the renewable energy to the grid, which are both emulating the frequency and voltage regulating functions of synchronous generators through droop method. However, improper transient impact current and reactive power output are observed for inverters in voltage control...
A significant factor for properly designing the protection scheme of a microgrid is the fault current contribution from the converter-interfaced distributed energy resources (CI-DERs). The fault current direction and magnitude is difficult to be defined, since the currents injected by the CI-DERs affect it considerably. The fault situation is even more complicated, considering the case of islanded...
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