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Distributed control methods generally implemented with droop control have been widely applied in the energy management of microgrids. However, the robustness and stability of distributed control has been influenced by the size and diversity of the microgrid structure and compositions. Meanwhile, centralized control has been considered lack of flexibility and expansibility. In this paper, a novel control...
A large amount of distributed generation is connected to the grid, reducing rotational inertia of the power system. Based on the Static Synchronous Generator Model, inertia controller is introduced on outer voltage loop in this paper to enhance grid inertia. The developed inertia controller can generate inertial current superposed in conventional current reference. The inertial current can be adjusted...
This paper discussed the tuning process of the power system stabilizer (PSS) for a nuclear turbine-generator excitation system. By measuring the non-compensated phase-frequency characteristic of the excitation without PSS, and through calculation and critical gain test, the PSS parameters are determined. Through step response and anti-regulation experiment, the effectiveness of the PSS is verified.
STATCOMs provide grid with not only reactive power compensation but auxiliary stability support through exerting influence on the dynamic behavior of Synchronous Generator (SG) during grid power oscillations. In this paper, method of electrical torque analysis is utilized to analyze the mechanism of STATCOM affecting the transient performance of SG when operates in power oscillations suppression mode,...
The integration of Distributed Energy Resources (DER), μ-grids, Electric Vehicle (EV) charging, aggregated demand response and customer participation in the power market, has led to unprecedented dynamic behaviors and complication in the electric power system operations. With the introduction of Phasor Measurement Units (PMU), wide area monitoring and controls are feasible. In this paper, a stochastic...
This paper proposes a frequency scanning-based impedance analysis for stability assessment of grid-connected inverter system, which is able to perform stability assessment without using system mathematical models and inherit the superior feature of impedance-based stability criterion with consideration of the inverter nonlinearities. Small current disturbance is injected into grid-connected inverter...
For high PV penetration, grid ancillary services such as dynamic voltage support and low-voltage ride-through (LVRT) operation are recommended by network operators. This paper proposes an integrated controller for LVRT capability of a three-phase grid-tied PV system connected to a LV grid. Generally X/R ratio is low for LV grids, therefore the active power injection is given higher priority than the...
Due to the high frequency nature and constant power load characteristics, stability issue exists widely in contemporary power electronic systems. Impedance-based criteria can be used in stability prediction. Thus, the accurate extraction of impedance becomes significantly important. For AC systems, impulse injection method has been proposed for its short measurement duration, but the accuracy needs...
The recently proposed concept virtual synchronous generator (VSG) has been intensively researched. Its core idea is to add a segment in traditional inverter control to simulate synchronous generator's rotor motion characteristic so that the distributed energy resources (DER) can have virtual inertia. VSG control usually contains output current amplitude limiting part to avoid too large current from...
Distributed static series compensator (DSSC) is a new type of distributed FACTS devices that can realize accurate control of power flow and enhance voltage stability. Thus, it could be installed in stability-limited transmission systems widely. This paper presents a new capacity control model for DSSCs and deduces the corresponding power flow equations. To illustrate the effect on system power voltage...
Power electronic converters may interact with the grid, thereby influencing dynamic behavior and resonances. Impedance and passivity based stability criteria are two useful methods that allow for studying the grid-converter system as a feedback system, whose behavior is determined by the ratio of grid and converter impedances. In this paper, the ac-side admittance of the modular multilevel converter...
Cascaded DC converters are becoming widely used in DC distributed power system. When a DC converter is tightly regulated, it operates as a constant power load (CPL). In a cascaded system, instability problems usually occurs due to the negative incremental impedance characteristic caused by a CPL. In order to mitigate instability, this paper proposes a new approach by adding an additional stabilizer...
Load frequency control in an islanded microgrid is challenging due to the low system inertia and random power variations resulting from renewable energy sources and loads. The traditional droop control mechanism may become unstable under some conditions. To overcome this problem a new control algorithm is proposed in this paper. The necessary condition derived to ensure the frequency stability is...
This paper investigates the dispatch of diesel generators in Kinmen Island power system with wind power generators. Because wind conditions are somewhat unpredictable, it is difficult to provide a stable base load of power to the grid from wind energy. To ensure an adequate supply of energy at all times, wind energy needs to be combined with other sources. To know the dynamic behavior of the system,...
A bidirectional integrated bus voltage conditioner (IBVC) is proposed for isolated phase shifted full bridge (PSFB) DC-DC converter to improve the DC bus voltage stability in cascaded power converter system. In this method, the load converter is controlled tightly with high control bandwidth. Unlike those separate converter based DC bus voltage stabilization methods with auxiliary switches, multiplexing...
The LCL-filter is one of the methods to reduce the size of the filter inductor but it leads to resonance in the system. The resonance usually results in unstable system and triggers the over-current protection. An active damping technique based on the virtual resistor is provided in this paper. The concept and the mathematical analysis of the proposed method are explained, and then the stability of...
Multistage systems are highly prone to issues of instability due to the interaction between converters. In this paper, the operation principles of a novel triple-phase-shift based dual active bridge converter are elaborated. Additionally, the impedance model of the cascaded system based on small signal analysis is proposed and applied for analyzing the stability of the cascaded system. The theoretical...
This paper presents an eigenvalue-based impedance stability analytical method of multiple paralleled grid-connected inverter system. Different from the conventional impedance-based stability criterion, this work first built the state-space model of paralleled grid-connected inverters. On the basis of this, a bridge between the state-space-based modelling and impedance-based stability criterion is...
When designing a controller in DC Microgrid, normally the communication delay, which may cause system instability, has not been taken into account. In this paper, the effect of communication delay on system stability is studied based on a distributed control strategy, and a novel delay-independent stability criterion for the system with time-varying delays is proposed. To obtain a less conservative...
Power electronic converters and electric motor drives in advanced automotive systems, when they are tightly regulated, behave as constant power loads (CPLs) at the input terminals and usually cause negative impedance instability problems. Especially in a DC microgrid system with multiple parallel-connected buck converters, which is loaded by CPLs, the improper parameter settings of the buck converters...
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