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Today's three-phase Adjustable Speed Drive (ASD) systems still employ Diode Rectifiers (DRs) and Silicon-Controlled Rectifiers (SCRs) as the front-end converters due to structural and control simplicity, small volume, low cost, and high reliability. However, the uncontrollable DRs and phase-controllable SCRs bring side-effects by injecting high harmonics to the grid, which will degrade the system...
Static Synchronous Compensators (STATCOMs) are being applied for offshore wind power plants to satisfy the grid codes under both normal operation and grid fault conditions. This paper investigates the performances of Modular Multilevel Cascade Converters (MMCC) for the STATCOM application, with special focus is on asymmetrical Low-Voltage-Ride-Through (LVRT) operation under grid faults. The design...
Single-phase grid-connected inverters with LCL filter are widely used to connect photovoltaic systems to the utility grid. Among the existing control schemes, predictive control methods are faster and more accurate but also more complicated to implement. Recently, the Model Predictive Control (MPC) algorithm for single-phase inverter has been presented, where the algorithm implementation is straightforward...
Nowadays capacity of the photovoltaic systems in the grid is remarkable and provides a major part of energy in the grid. Therefore, an abruption of these systems from the grid can create a damage to the grid. Unlike in the past that PV systems disconnected from the grid when a voltage drop occurred, nowadays these systems should have Low Voltage Ride-Through (LVRT) capability. The PV system should...
In order to reduce the Common-Mode Voltage (CMV) in three-to-five phase indirect matrix converters, three improved Space Vector Pulse Width Modulation (SVPWM) methods are proposed and discussed. The improved modulation schemes are achieved by reorganizing zero vectors from the inversion stage to the rectification stage. The proposed methods can not only theoretically reduce the CMV peak value by up...
A novel switching power loss estimation method for modular multilevel converters (MMCs) with the nearest level modulation (NLM) is introduced in this paper. It focuses on the switching actions caused only by change of the inserted submodule (SM) number per arm, named as the essential switching transitions. Every essential switching action can be identified under the assumption of ideal sinusoidal...
The following paper presents a modular system for active power support in wind generators. It works on the base of a Flywheel Energy Storage System (FESS) coupled to the DC link of a medium voltage back-to-back multilevel converter. Two ANPC-5L compose a full-scale converter interface and a third converter tied to the DC link drives a flywheel through an induction machine. All converters have predictive...
Static Synchronous Compensators (STATCOMs) have been applied for offshore wind power plants to satisfy the grid codes under both normal operation and grid fault conditions. This paper investigates the performances of two types of Modular Multilevel Cascade Converters (MMCC) for STATCOM applications, with the special focus on asymmetrical Low-Voltage-Ride-Through (LVRT) operation under grid faults...
In this paper, a Selective Harmonic Elimination Pulse Width Modulation (SHE-PWM) method, which utilizes adjustable dc links, is presented for a Static Synchronous Compensator (STATCOM) based on Cascaded H-Bridge (CHB) multilevel converter. The proposed switching algorithm is able to fix the capacitors voltages at optimum and unequal values, while injecting the desired reactive power, in order to eliminate...
As an almost standardized configuration, Diode Rectifiers (DRs) and Silicon-Controlled Rectifiers (SCRs) are commonly employed as the front-end topology in three-phase Adjustable Speed Drive (ASD) systems. Features of this ASD configuration include: structural and control simplicity, small volume, low cost, and high reliability during operation. Yet, DRs and SCRs bring harmonic distortions in the...
The paper proposes a distributed optimal control strategy for islanded microgrids, which allows to perform reactive power sharing and voltage regulation without communication system. To realize the twofold objective, an improved small signal model is developed first to reconstruct the system input-output relationship, where the relationship is evaluated with sensitivity analysis. A state estimator...
The widespread adoption of mixed renewables urgently require reactive power exchange at various feed-in points of the utility grid. Photovoltaic (PV) inverters are able to provide reactive power in a decentralized manner at the grid-connection points even outside active power feed-in operation, especially at night when there is no solar irradiance. This serves as a motivation for utilizing the PV...
Droop based autonomous control offers several advantages such as communication independence, plug-n-play capability and enhanced reliability of the system. Despite these advantages, frequency and voltage of droop controlled microgrid varies with the load change which is one of the major drawback of the droop control. Presently, the frequency and voltage restoration in microgrid is achieved through...
The Smart Transformer (ST), which is a power electronics-based transformer, represents an enabling technology for providing new services to the Low Voltage (LV) and Medium Voltage (MV) grid. The 3-stage configuration, with a high frequency transformer and 2 DC links, allows the electrical separation of the LV and MV grids. This leads to the independence of the two grids: any disturbance downstream...
Current energy paradigm of mixed renewables seems to urgently require reactive power provision at various feed-in points of the utility grid. Photovoltaic (PV) inverters are able to provide reactive power in a decentralized manner at the grid-connection point even outside active power feed-in operation, especially at night. This serves as a motivation for utilizing the PV inverters at night for reactive...
The dc-link capacitor is one of the critical components, which influences the lifetime of the whole voltage source converter unit. For reliable design, the operating temperature of the dc-link capacitor should be known, which is primarily determined by the ambient temperature and the rms value of the current flowing through the dc-link capacitor. A simple analytical method to calculate the rms value...
The power handling capability of the state-of-the-art semiconductor devices is limited. Therefore, the Voltage Source Converters (VSCs) are often connected in parallel to realize high power converter. The switching frequency semiconductor devices, used in the high power VSCs, is also limited. Therefore, large filter components are often required in order to meet the stringent grid code requirements...
With the increasing penetration of the wind power, reliable operation and cost-effective wind energy production are of more and more importance. As one of the promising configurations, the cost on reliability and production losses of permanent-magnet synchronous generator based full-scale wind power converter is studied considering the grid code with reactive power production as well as the annual...
The modern grid requirement has caused that the wind power system behaves more like conventional rotating generators and it is able to support certain amount of the reactive power. For a typical doubly-fed induction generator wind turbine system, the reactive power can be supported either through the rotor-side converter or the grid-side converter. This paper firstly compares the current ripples and...
A new method to selectively control the amount of dc-link voltage ripple by processing the desired reactive power by a DC/DC converter in an isolated AC/DC or AC/DC/AC system is proposed. The concept can reduce the dc-link capacitors used for balancing the input and output power and thereby limiting the voltage ripple. It allows the use of a smaller dc-link capacitor and hence a longer lifetime and...
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