In a DC distributed power system, the interaction between individually designed modules/subsystems may cause instability of whole system. small-signal sense, system level stability is determined by impedance ratio Z/sub o//Z/sub i/. Here, o/ output source module/subsystem, and i/ input load module/subsystem. As result, an effective way to prevent defining specifications for modules/subsystems. This paper briefly summarizes existing works introduces authors' contribution in specifications. A...

In this paper, a generalized droop control (GDC) is proposed for grid-supporting inverter based on comparison between traditional and virtual synchronous generator (VSG) control. Both the VSG have their own advantages, but neither nor can meet demand different dynamic characteristics in grid-connected (GC) stand-alone (SA) modes at same time. Rather than using proportional controller with low-pass filter, as control, or fully mimicking conventional parameters active power loop of GDC be...

The coupling between the active and reactive power of droop-controlled inverter is critical in low-voltage microgrid. conventional virtual power-based control strategy can decouple inverter, whereas load probably not equally shared among parallel inverters To tackle this issue, paper proposes an improved method for with a unified rotation angle transformation. Meanwhile, optimal value rigorously derived through investigating relative stability system by innovatively adopting Routh Stability...

To address the unbalanced and harmonic power sharing issue among parallel inverters caused by feeder impedance mismatch in islanded microgrids, an adaptive virtual control method is proposed based on injection of extra small ac signal (SACS) output voltage each inverter. Similar to principle active power-frequency droop, frequency injected droops with power, while produced SACS detected adjust at fundamental negative sequence selected frequencies, which will tune distribution system. When...

The distributed generation (DG) should supply continuous power to the local critical load, even in condition of utility outage. And many efforts have been made for three-phase inverter DG transfer between islanding mode and grid-tied seamlessly. This paper proposes a strategy based on indirect current control DG, which is composed mainly two cascaded feedback loops, i.e., capacitor voltage loop external grid loop, synchronous reference frame. In mode, controlled by regulating voltage. When...

This paper presents a unified control strategy that enables both islanded and grid-tied operations of three-phase inverter in distributed generation, with no need for switching between two corresponding controllers or critical islanding detection. The proposed composes an inner inductor current loop, novel voltage loop the synchronous reference frame. is regulated as source just by operation, controller automatically activated to regulate load upon occurrence islanding. Furthermore,...

This paper presents a stability criterion for three-phase AC distributed power system (DPS). While the source output impedance and load input admittance under synchronous reference frame are generally investigated to predict of DPS, infinity-norms innovatively adopted in proposed improve computational complexity conservatism. Meanwhile, conservatism analyzed compared with existing ones. Furthermore, terminal characteristics studied DPS composed an LC filter boost rectifier, which cover...

Stability issues in hybrid energy storage systems (HESSs) are the major concern, addition to control design challenges of individual modules. In this paper, stability <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$Z + Z$</tex></formula> type cascade HESS focused. The have been studied for many years. Impedance ratio criterions form xmlns:xlink="http://www.w3.org/1999/xlink"><tex...

Parallel droop-controlled inverters with renewable energy sources are widely employed in islanded ac microgrids, where dynamic interactions among them may cause small-signal stability issues. Since the active power-frequency droop scheme is applied, exist not only bus voltage and transmitted current, but also variable system fundamental frequency. This paper introduces a novel terminal characteristic model for inverter. Besides conventional impedance admittance, new set of characteristics...

LCL resonance complicates the design of a current control loop and can even threaten its stability. Extensive approaches have been proposed to deal with this resonance, among which active damping (AD) schemes based on feedback single filter variable shown be effective cost-efficient. This paper presents study such AD techniques, where generalized approach developing an controller by relating diagram equivalent circuit is proposed. Based approach, forms any one four commonly used variables...

This paper presents a transformerless static synchronous compensator (STATCOM) system based on hybrid multilevel H-bridge converter with delta configuration. STATCOM is characterized by per-phase series connection of high-voltage operating at fundamental frequency and low-voltage 5 kHz without any other circuit for dc voltage control. A new control strategy proposed in this focus regulation. Clustered balancing realized injecting zero-sequence current to the delta-loop, while individual...

This paper presents a three-phase transformerless structure of modular multilevel converters based on cascaded pulsewidth-modulated chopper cells in medium-voltage D-STATCOM application. It is suggested for installation unbalanced power-supply systems to achieve higher performance improving power quality. proposes new control strategy power-flow analysis with focus dc capacitor voltage that insulated from the source fault. enables system compensate nonlinear load even under asymmetrical grid...

Compared with conventional power transformer, the electronic transformer (PET) or solid-state has many attractive additional features. This paper focuses on an H-bridge-based three-phase three-stage modular PET, which consists of input stage series-connected H-bridge converters, isolation several independent dual-active-bridge and output parallel-connected converters. PET suffers dc-link capacitor voltage unbalancing issue, module current sharing issue. In this paper, a system control...

In an islanded microgrid composed of droop-controlled parallel inverters, the system frequency endures deviations as load changes. To compensate for deviation without involving communication infrastructures among distributed generators (DGs), proportional-integral regulator based secondary control (PI-SFC) method has been proposed in literature. However, PI-SFC may incur real power-sharing errors because integrator accumulates disturbances and noise each DG, leading to different compensation...

Extensive solutions have been proposed to damp <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> filter resonance. However, the time delay caused by computation and modulation process aggravates complexity of current loop analysis. In this article, a generalized virtual impedance model for six kinds commonly used active damping methods is proposed, physical meaning established introducing metric "damping factor." To ensure system...

Grid-forming inverters, which are represented by droop control and virtual synchronous generator control, have been widely studied applied because of their excellent grid-supporting ability smooth off-grid switching. When a grid-forming inverter is connected to microgrid or utility grid, the loops active power reactive will be coupled voltage phase difference, affect performance. This paper first derives small-signal linearized model system, based on frequency feedforward an amplitude...

The series active power filter (APF) is suitable for compensating a voltage type harmonics-producing load, whereas the control approach it adopts may directly influence its compensation characteristics. This paper first discusses of detecting source current in terms basic operation principle APF, then developing load voltage. On basis these, hybrid proposed. In this approach, reference signal needed by APF obtained both and Thus, has advantages second approaches and, at same time, can...

Reactive power control through the static compensator (STATCOM) has gained wide attentions due to its outstanding performance. But for a STATCOM with traditional strategies, unbalanced utility voltages will greatly affect performance of and, in severe cases, may even cause shutdown overcurrent protection. This paper proposes novel strategies ensure normal operation three-phase three-wire systems when system voltage unbalance occurs furthermore, mitigate at point common coupling (PCC) whether...

The three-phase four-leg inverter is very suitable for the high-power uninterruptible power supply application, and load neutral point voltage (LNPV) should meet requirement. In this paper, two factors influencing LNPV were revealed first, which are switching states ratio of inductance to phase ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> ). Then, 16 can be classified into four groups, ones in first second group come minimum amplitude...

This paper presents a novel modulation and capacitor voltage control method for the modular multilevel converter (MMC) allowing fixed switching frequency of 50 Hz. In proposed method, angles are calculated through new approach with reference to nearest level control. And then, every four pulse patterns grouped together averaging dc fundamental ac components in output individual submodules. Accordingly, absorbed power each submodule could be self-balanced during few line periods simply by...

A shunt active power filter (APF) with current detection at the source side is considered as a closed-loop system from view of whole distribution system, which expected better harmonics filtering performance compared one load detection. The conventional control scheme can be mainly grouped into two types: 1) current-source-based (CS) and 2) power-balance-based (PB) scheme. As introduced in this paper, CS has good dc-voltage regulation, but it bears inevitable conflict between stability,...