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This paper presents a PWM strategy for the reduction of common-mode (CM) voltage generated by variable-speed motor drives composed of two-level, three-phase active-front-end rectifier and three-phase inverter. This method theoretically provides complete elimination of the CM voltage by synchronizing all inverter commutations with rectifier commutations, so that the resulting CM voltage does not vary...
This paper presents a controller for three-phase DC/AC converters that is able to operate the converter in grid-connected and stand-alone modes and ensure seamless transition between these modes without reconfiguration of the control structure. The proposed controller provides control over real and reactive powers in grid-connected mode and it performs voltage support in the islanded mode. It integrates...
The Microgrid voltage may deviate from the grid voltage when it operates in islanded mode, which will result in unexpected large inrush currents during the re-connection process. This paper proposed a new self-synchronization control strategy for synchronverter with local loads which utilizes the reference phase angle of synchronverter as the reference angle in the rotating frame. A compensation quantity...
This paper shows a current measurement technique, which combines approaches for synchronized inverter current measurement with an advanced system of digital transmission and filtering of current measurement values. The measurement technique gives a significant increase in performance, accuracy and robustness compared to classical measuring with sampled A/D conversion or not synchronized techniques...
In this paper, we propose the use of sliding mode (SM) control to improve the maximum power point tracking (MPPT) performance of a two-stage single-phase inverter (comprising a first-stage DC/DC boost converter and a second-stage full-bridge inverter) in photovoltaic (PV) systems. To underscore the benefits of SM control, the MPPT performance of the PV system under the SM control is compared to that...
Owing to the growth in penetration of DGs (distributed generators), inverters installed together with the DGs have been increasing rapidly. In general, these grid-connected inverters need a dedicated synchronization unit such as a phaselocked loop (PLL), which receives voltage phase, frequency, and amplitude of the grid voltage as reference from power grids. As the installation of inverters keeps...
In this paper, modulation processes have been analyzed in six-phase asymmetrical motor drive on the base of four inverters with discontinuous synchronous modulation. It has been shown, that flexible PWM strategy based on control of switching frequencies of inverters as function of dc voltages allows to improve system performance and to insure voltage waveform symmetries during adjustment range. Simulations...
In general, residential solar inverters can operate in either island or grid-tied mode. In grid-tied mode, the inverter can be operated based on either voltage control or current control. In this paper, a grid-connected current controlled inverter is presented. A stationary frame nonideal proportional resonant (PR) controller, in lieu of a conventional PI based controller, is applied to the outer...
Clock drift in digital controllers is of great relevance in many applications. Since almost all real clocks exhibit drifts, this applies in particular to networks composed of several individual units, each of which being operated with its individual clock. In the present work, we investigate the effect of clock drifts in inverter-based microgrids. Via a suitable model that incorporates this phenomenon,...
Grid-connected renewables are increasingly developed in recent years, e.g. wind turbine systems and photovoltaic systems. Synchronization of the injected current with the grid is mandatory. However, grid disturbances like voltage sags, harmonics, and frequency deviations may occur during operation, becoming inevitable challenges to the synchronization of the grid-connected renewable energy systems...
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...
Distributed secondary control strategies have been recently studied for frequency regulation in droop-based AC Microgrids. Unlike centralized secondary control, the distributed one might fail to provide frequency synchronization and proportional active power sharing simultaneously, due to having different control parameters. This paper introduces a cooperative algorithm that regulates the system frequency...
Microgrid is intended and featured to be able to operate in both grid-connected and islanded mode to ensure high quality and reliable power supply. In order to achieve stable operation of the microgrid-connected voltage source inverter (MVSI) units under paralleled or grid-connected mode, a novel synchronization method based on droop control is proposed in this paper. The difference of phase and amplitude...
With increasing penetration of grid-connected photovoltaic (PV) power generation, the grid codes about low-voltage ride-through (LVRT) of PV plants and their interface inverters have been established. Under a grid voltage sag, the underlying reasons may cause overcurrent of the grid-connected inverter and failure in ride-through. In this paper, a positive-sequence current injection with feedforward...
A rapid grid synchronization technique is proposed for enhanced low voltage ride-through (LVRT) operation of voltage source inverter based distributed energy resource (DER). The proposed synchronization method aims at enhancing the LVRT capability by providing fast information of the fundamental positive and negative sequence components of the grid voltage vector. This is achieved by a novel pre-filter,...
For a grid connected solar photovoltaic power system, synchronization in between generated voltage and grid voltage plays a pivotal role. This paper deals with modeling and synchronization in high voltage grid connected photovoltaic (PV) generation system. The proposed configuration not only can generate and boost up the DC voltage, but can also convert the solar DC power into high quality AC power...
Dual-edge-triggered (DET) synchronous operation is a very attractive option for low-power, high-performance designs. Compared to conventional single-edge synchronous systems, DET operation is capable of providing the same throughput at half the clock frequency. This can lead to significant power savings on the clock network that is often one of the major contributors to total system power. However,...
We present in this work the study and the realization of a photovoltaic system connected to the network. This system was simulated in the Matlab/Simulink environment and a laboratory prototype was manufactured for various tests and measures. Results of MPPT control, PWM control of a DC/AC single-phase converter, signal filtering of harmonic of the inverter as well as synchronization with the network...
The significant PVT variations seen with modern technologies make synchronous design inefficient. Asynchronous design with its flexible timing is a promising alternative, but prototyping is difficult on the available FPGA platforms which are clock centric and do not provide the required functional primitives like mutual exclusion or Muller C-elements. The solutions proposed in the literature work...
This paper presents the results of a proof-of-concept implementation of a platform for distributed, real-time fault-tolerant control of parallel single-phase inverters, integrated in modular uninterruptible power supplies (UPS) or Battery Energy Storage Systems (BESS). Each inverter controller runs a basic clock which schedules all the real-time control tasks, according to the time-triggered paradigm...
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