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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...
In distribution network, with the installed of photovoltaic (PV), bought many problems. One of the most concerned problems is the overvoltage in the terminal bus of distribution network. It is caused by the reverse power flow which brought out by the increase of the PV sources penetration. In this paper, an improved PQ-Q (V) control strategy is proposed to alleviate such problem. The economic performance...
With increasing penetration of renewable energy sources into modern power systems, multiparallel inverters are commonly employed in the interface to the utility grid, giving rise to potential resonance problems. In order to better understand the issue, resonance of multiparallel inverters is analyzed under an asynchronous carrier. First, multiparallel inverter equivalent circuits are modeled within...
In this paper, a 5kW wireless electric vehicles (EV) charger is introduced and modeled in time-frequency domain. Base on the function of the charging current, two current control methods are discussed. It is found that the DC-link voltage control can make the voltage source inverter (VSI) work under soft switching mode but the adjustable range of the charging current is limited. The phase shift control...
The application of reduced common mode voltage pulse width modulation methods bring much high order harmonics to the variable speed drive system, which causes considerable iron loss inside the electric motor. In this paper, an improved iron loss model considering those high order harmonics is proposed. Iron loss coefficients are obtained based on experimental data by utilizing multiple linear regression...
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,...
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...
This paper presents a new topology of higher order power filter for grid-tied voltage-source inverters, named the LCL-LC filter, which inserts an extra capacitor connected in parallel to the Lf-Cf series resonant circuit of LLCL filter Particularly, it can strongly attenuate the harmonic currents around the switching frequency, and the attenuation rate become -60dB at high frequency which leading...
In micro grid, the voltage and frequency will fluctuate with the switching of large-power electric load. With inverter control of energy storage systems,both active and reactive power pumped into the utility grid can be controlled which could achieve the stabilizing effect of voltage and frequency. This paper addresses active and reactive power control strategies used in energy storage system to eliminate...
The single-mode overmodulation strategy of matrix converter is put forward for the lower voltage transfer ratio. Single-mode overmodulation strategy and its effect on increasing voltage transfer ratio are analyzed theoretically, and the simulation model of the strategy is set up. Theoretical analysis and simulation results show that the proposed strategy can make the voltage transfer ratio rise to...
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