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In cascade AC systems, the impedance interaction between the source module and the load module may cause overall system instability. The generalized Nyquist stability criterion can be applied to characterize the stability of cascade three-phase AC systems. But it is usually very complicated and cannot directly reveal effective control strategy to alleviate the interaction problem. Based on three-phase...
Since low voltage ride-through (LVRT) was proposed, its improvements have never been stopped, especially the improvements for operation under unbalanced faults. In this paper, an overall control strategy is proposed to solve the problem that the output current quality and dc-link voltage quality cannot be guaranteed at the same time. For this propose, a current control method is employed to guarantee...
With high power Virtual Synchronous Generator (VSG)-based Voltage Source Converter (VSC) and low switching frequency, time delay has become a big issue affecting VSC stability and dynamic response in islanded mode. In this paper, effect of time delay on output impedance is analyzed and a hybrid derivative feedback control is proposed to improve system stability and dynamic response. First step, derivative...
This paper investigates the dynamic interactions of current controllers for multi-paralleled, grid-connected inverters. The consequent harmonics instability phenomena, which features with oscillations above the fundamental frequency, are evaluated by the impedance-based stability criterion. The frequency range of effective impedance-based stability analysis is first identified. The effect of each...
Multiple resonances may result in instability of a LCL filter based multiple grid connected converter (MGCC) system. This paper investigates the critical factors of multiple resonances in MGCC system. It is found that, closed-loop output admittance of the grid connected converter can be configured to meet the requirements of resonances suppression, by properly designing control method and parameters...
DC microgrid will be the main power supply system for the future sustainable homes and buildings due to the advantages of the low converter cost and easy control with no reactive power concern. The system-level stability is an important issue in the design of the DC power supply system. The overlap between the output impedance of paralleled converter and load input impedance causes the system instability...
The number of high voltage direct current transmission (HVDC) installations is growing rapidly nowadays, and network operators are working to define grid codes that regulate behaviors of HVDC system to operate under different conditions. This paper presents implementation of a small-scale HVDC lab prototype, which aims at studying the characteristics of the VSC-HVDC system and meeting the requirements...
The adoption of virtual synchronous generation (VSG) control can maintain the stability of voltage and frequency in power electronic interfaced mircogrid. In this paper virtual impedance is added to the VSG control strategy in order to improve the system control performance in resistive-inductive line impedance, the influence of virtual impedance on VSG system stability and dynamic performance is...
Renewable energy generation is widely used to solve energy shortage and environment problem. Since the output power of the solar cell and the wind turbine will change with the sunlight irradiation and the wind flow, the power of the solar cell and the wind turbine are not stable, so there is a need of a storage equipment connected to the micro-grid system. With the characteristics of high efficient...
This paper describes the design principles of damped proportional-resonant (PR) controllers used for the grid-connected inverters. Previous works focused on the frequency domain analysis to select parameters, which can't reflect the time domain performance directly. This paper presents a mathematical model of grid-connected inverter connected with a LC filter and isolation transformer in the stationary...
Normally, photovoltaic (PV) power system can be considered as a disturbance of power system. But in proposed paper that when power fluctuation occurs, high permeability PV system can suppress power grids low frequency oscillation because of its large capacity and quick response. If high penetration PV system has the ability of power system energy balance, it is sure to get more extensive applications...
The use of LCL-filter for reducing current harmonics has been commonly used for converters connected to the power grid. However, under non-ideal power grid condition, a converter using an LCL-filter may interact with other converters connecting to the grid. In this paper, a three-phase voltage source converter using an LCL-filter is studied. Simulations show that resonant oscillation occurs in the...
A stability or resonance analysis of a micro-grid consisting of multiple grid-connected-converters (GCC) with LCL filter is important but complicated, because it is influenced by many factors such as LCL filters of the GCC, the grid impedance and various (nonlinear or even time-variable) loads. It is necessary to construct a framework for revealing and analyzing the main unstable factors and then...
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