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Capacitor-current-feedback active damping method is commonly used in LCL-filtered grid-connected inverters, which attenuates the resonance peak by emulating a virtual resistor in parallel with the filter capacitor. Taking the digital control delay into account, the emulation component becomes frequency-dependent, and it will turn negative when the filter resonance frequency becomes higher than one-sixth...
Since the capacitor equivalent series resistance (ESR) above 1kHz almost stays constant, dc-link current root-mean-square (RMS) closed form equation is an easy way to evaluate the capacitor losses from the switching harmonic currents (SHCs). But when the ac current contains multiple low order harmonics (LOHs), their impacts on the dc-link has not been systematically studied. In this paper, a straightforward...
This paper presents a unified selective harmonic compensation strategy using DG-interfacing inverter with LCL filter in the presence of nonlinear local loads for both grid-connected and islanded microgrid. Compared with the existing harmonic compensation methods in the literature, the proposed strategy consists of a triple-control-loop in the grid-connected mode to compensate the grid current harmonics...
A novel control strategy which enables proportional linear and nonlinear loads sharing among paralleled inverters and voltage harmonic suppression is proposed in this paper. The proposed method is based on the autonomous currents sharing controller (ACSC) instead of conventional power droop control to provide fast transient response, decoupling control and large stability margin. The current components...
This paper proposes a capacitor-less inverter for AC motor driving system. The proposed converter consists of a single-phase diode rectifier, a small film capacitor at the DC bus, a three-phase voltage-source inverter, and a permanent magnet synchronous motor (PMSM). Since the DC bus capacitor is quite small, the input current of the AC source will be affected directly by the three-phase inverter...
To address the active power feeding issue in the parallel Uninterruptible Power Supply (UPS) system, a DC-link Voltage Protection (DCVP) control strategy is proposed in this paper. The proposed control method only relies on local load information, which increases the system reliability and robustness. Moreover, virtual resistance based regulation strategies are proposed for solving the active power...
Harmonic resonance issues have been attracted more and more attention due to a large number of power electronic inverters being used in power systems. In this paper, in order to have a deep insight into resonances, the singular value sensitivities with respect to component parameters of the network and the control parameters of inverters are used for harmonic resonance analysis based on Singular Value...
This paper deals with a newly conceived control topology based on the Repetitive action in 4-leg VSI for stand-alone Ground Power Unit (GPU) applications. In such mode of operation, a dedicated controller has to regulate the inverter output voltages, which are measured at the output of the power filter. The proposed Repetitive Control can provide the required harmonic compensation capabilities that...
This paper presents an ac ripple repression method for neutral-point voltage of three-level inverter system with electrolytic capacitor less. To reduce the volume of three-level inverter system, electrolytic capacitor with huge capacitance is must eliminated from dc-link. In the inverter system applying film capacitors, however, the ac ripple component in neutral-point voltage of dc-link is increased...
This paper presents the analytical design procedure to select the inductance and the capacitance values of both the input and output filters for the 5-Level three-phase Back to Back E-Type Converter (5L3Φ BTB E-Type Converter). The 5L3Φ BTB E-Type Converter is used to accomplish the double conversion AC-DC/DC-AC in applications which include variable speed industrial electric drives and the interfacing...
The three-level T type inverter has been extensively used in photovoltaic (PV) generation. Various PV panels in cascaded connection normally require unequal dc voltage to accomplish separate maximum power point tracking (MPPT). This paper proposes a DPWM-controlled three-level T type inverter for two strings of PV panels in cascaded connection. The proposed modulation is developed based on the so-called...
The resonance problems may arise among multi-connected LCL-filtered inverters and make the system instable. The recently proposed GSPWM can reduce the filter order without reducing other performance in large-scale application, which has potential to avoid the resonance. But GSPWM will introduce specific phase delay to PWM sequences and it may influence the response character in different grid conditions...
The control of the grid side current in an LCL filter based grid connected converter is generally complex and involve multi loop structure. This paper presents a method to control the grid current indirectly by controlling the converter side current with compensation of the filter capacitor current. The proposed control algorithm uses only one current sensor to measure the converter side current....
Power quality of ac bus voltage is a key issue for microgrids. A model-predictive-control (MPC)-based distributed bus voltage compensation methods using inverter-interfaced distributed generators (DGs) connected to the concerned bus is proposed. The presented method can compensate bus voltage unbalance and harmonics and share the compensated current between inverters autonomously, with neither communication...
Current-controlled LCL-filtered inverters are usually paralleled together for interconnecting the renewable energy resources into the grid. When the inverter output impedance is not well designed, the harmonic circulating currents out of the control bandwidth may be easily aroused. To reveal this resonant phenomenon and to enhance the stability of the parallel system, this paper builds the parallel...
The hybrid active harmonic filters use a series capacitor in order to reduce the voltage rating of the inverter compared to regular inductive-coupled active filters. Different control strategies are applied on this topology in the literature. The main contribution of this paper is to apply a H-infinity controller in order to achieve current tracking in voltage source inverters connected to the grid...
The LCL-type grid connected inverter has been widely used as the intelligent power interface between the distributed generation unit and the power grid. To reduce the cost and volume of the filter, it is desirable to design the LCL filter with higher resonance frequency provided that the quality of injected grid current is not compromised. Actually, it is the typical case for the T-type or NPC three-level...
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