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The resonant stability problems of LCL filter have become big challenges for grid-connected inverter in weak grid. This paper takes the effect of non-minimum phase time delay on the ratio between resonance frequency and sampling frequency into account and use it to design the LCL filter. Both LCL resonance frequency and inverter-side inductor and filter capacitor related L1C resonance frequency are...
This paper explores the impact of the output impedance on the power-sharing stability between parallelized microgrid inverters (MGIs) operating with virtual synchronous generator (VSG) method. In these systems, a virtual output impedance is usually added to the control loop of each MGI to improve the power sharing, regardless of line impedance unbalances. The time derivative of the MGI output current...
This paper presents a state of charge (SOC) based control strategy for virtual synchronous generator (VSG) when connecting to the grid. The VSG is operated in voltage source mode, the output frequency of VSG is calculated by considering the virtual inertial and the power reference together. The power reference is acquired by adding the SOC control module and the frequency control module, the proportion...
Due to the large adjust inertia of the diesel generator set (DGS), the quality of power supply would decline when a large load disturbance occurs to the diesel generator system. This paper aims to improve the stability of the diesel generator system voltage amplitude and frequency under impact load conditions using a virtual synchronous generator (VSG) method. Firstly, a mathematical model of DGS...
With increasing penetration of renewable energy sources into modern power systems, multi-parallel inverters are commonly employed in the interface to the utility grid, giving rise to potential resonance problems. Firstly, 2-parallel inverters equivalent circuit model is established based on its control. In order to decouple inverter output current, the components characteristics of inverter output...
This paper concentrates on the load disturbance in three phase microgrid inverter (MGI) with an isolated transformer based on virtual synchronous generator (VSG) control. The transformer can provide the VSG with inductive output impedance when placed behind the LC filter. But the load disturbance may lead to steady-state error and poor dynamic performance with only capacitor voltage feedback control...
This paper proposes a novel seamless transfer method for microgrid connected fuel cell inverters (FCIs) between voltage source and current source modes. In order to protect the fuel cell, the FCI output power should be restricted when the microgrid frequency is greatly disturbed. In this sense, the FCI is transfered from voltage source mode to constant current source mode. Meanwhile, the FCI is transfered...
China Machinery Industry Standard (CMIS) GB/T 12326-2008 prescribed in the islanded operation mode, microgrid inverter (MGI) output voltage dynamic transient range is less than 10% when the resistive load is switched rapidly between 0% and 100%. The three-loop power virtual synchronous generator (VSG) control methods are commonly used in MGI units to share the loads among the parallel MGIs. However,...
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...
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...
The three-loop power virtual synchronous generator (VSG) control methods are commonly used in microgrid inverter (MGI) units to share the loads among the parallel MGI units. In order to achieve stable operation of the MGI units under paralleled or grid-connected mode, a droop synchronization controller is designed in this paper. The difference of phase and amplitude between different MGI units is...
For the problem that paralleled inverters cannot share reactive power proportional to their power capacity in islanding microgrid. Originally, the effect of inverter output impedance and line impedance to reactive power sharing with conventional droop control is analyzed. Following, a method adjusting the output reactive power by paralleling capacitor at the inverter output is proposed, and the relationship...
Microgrid should be operated in both grid-connected and islanded mode to ensure high voltage quality and reliability. In the case of continuous uninterrupted power supply, seamless transfer is important between the two modes,and synchronization of the voltage of the point of common coupling (PCC) and utility grid should be finished first to achieve the goal. In this paper varies of synchronization...
In this paper, a general active damping method based on capacitor voltage detection for stable control of LCL-filter grid-connect inverter is proposed. Three active damping methods are derived from the general form. Root locus and bode diagrams are used to analysis these three active damping methods. And in the case of different control delay, robustness of three active damping methods are compared...
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