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Unpredictable power quality (PQ) events such as, balanced and unbalanced voltage sag/swell, frequency shift, phase jump and harmonic distortions in the utility grid voltage drastically affects the performance of a grid interfaced distributed generation (DG) systems due to unreliable synchronization. This paper presents adaptive synchronization based dq-current control technique for three-level NPC...
In this paper, an improved control strategy for three-phase inverter is proposed, which ensures three-phase output voltage symmetry under unbalanced grid voltage. Firstly, the positive and negative sequence separation module is used to obtain unbalance output voltage and current during the grid faults. By calculating output power of the inverter, an improved P-ƒ, Q-U and Q-G droop control strategy...
This paper proposes a single-phase UPFC topology using an autotransformer structure. The proposed topology uses a N:1 transformer, which is connected as an autotransformer and a power converter module which consists of a single-phase half-bridge converter and an inverter. Also, the three-phase system can be comprised of three single-phase UPFCs. In three-phase system, while the conventional UPFC topology...
This paper proposed the repetitive controller (RC) controlled single-phase micro-grid power converter system with nonlinear load. Conventional RC (CRC) and 4k±1-order harmonic RC (4ı1 RC) added into a propositional controller are chosen as the controllers to achieve micro-grid power balance between dc-side and load, unit power factor, and zero-error grid current tracking its reference. Moreover,...
The goal of this paper is to test a decentralized power flow controller using a Hardware-In-the-Loop (HIL) approach. The HIL set-up include real-time simulation of the distribution grid and real-time emulation of the communication network. Reactive power is iteratively cancelled between pairs of inverters in a way that eliminates reactive flow between inverters while minimizing network resource consumption...
Electric spring (ES) is a novel smart grid technology, which is based on power electronic components. It has multitude of benefits associated with its widespread use at distribution level, which includes voltage profile enhancement, power imbalance mitigation, and power quality improvement. With the ever increasing need of incorporating intermittent renewable energy sources (RES), electric spring...
The Smart Grid (SG) implementation requires a constant monitoring and control of the power network. An Advanced Metering Infrastructure (AMI) allows the Distribution System Operator (DSO) to know what is happening on the power network. However, existing smart meters are not prepared for an emerging energy market nor to be integrated with LV/MV dispatch centres. The Unbundle Smart Meter (USM) concept...
This paper considers a three-phase grid-connected photovoltaic (GCPV) system, which comprises a 120kW PV farm connected to the grid through a step-up transformer. GCPV is considered as a distributed generation (DG) serving a variable local load (LL) connected to the low voltage side of the transformer. A power conditioning unit (PCU) consisting of a two-stage energy conversion device is used to (i)...
Loads have an important impact on the behavior of an islanded grid, yet they remain the main unknowns of the system. Electronic-based loads — like rectifiers in particular — are rarely studied in the context of unintentional islanding studies, in spite of the fact that the rate of electronic loads has strongly increased in the last decades. In this paper, the impact of electronic loads on islanding...
The increasingly introduction of Photovoltaic (PV) systems into residential power system because of customers' desire to reduce electricity supply cost causes detrimental impacts, e.g. voltage operation and voltage unbalance (VU) issues. In order to cope with these problems, the control strategy of PV units where both reactive power control and active power curtailment are allowed has been proposed...
Challenges in active distribution networks increase as the penetration of DERs grows, causing difficulties for distribution system operators to efficiently manage and plan their networks. One of the main concerns is controlling the limits in voltage profiles that otherwise may lead to load or renewable generation curtailment. One of the promising methods to solve this challenge is through PV inverter...
The massive penetration of renewable energy sources in grid-tied systems has boosted the improvement of conventional control solutions to fulfill the requirements demanded during grid faults. In this paper, balanced positive-sequence reference extraction method (BPSC) is proposed with the predictive technique to control the 3L-NPC inverter under grid sags. Only positive sequence extraction is needed...
For high PV penetration, grid ancillary services such as dynamic voltage support and low-voltage ride-through (LVRT) operation are recommended by network operators. This paper proposes an integrated controller for LVRT capability of a three-phase grid-tied PV system connected to a LV grid. Generally X/R ratio is low for LV grids, therefore the active power injection is given higher priority than the...
Inverters in voltage control mode including droop control and virtual synchronous generator (VSG) are promising for interconnecting the renewable energy to the grid, which are both emulating the frequency and voltage regulating functions of synchronous generators through droop method. However, improper transient impact current and reactive power output are observed for inverters in voltage control...
In this paper, Lyapunov law based model predictive control scheme is proposed for the grid integration of 3L-neutral point clamped (NPC) inverter. Lyapunov law based cost function, which aims to select the optimal voltage vector using system discrete model equations just once in each control cycle is able to reduce the current tracking error. Thus, low THD symmetrical current is injected to the utility...
The inverter with critical loads should be able to provide critical loads with a stable and seamless voltage during control mode change as well as clearing time. The indirect current control has been proposed for providing stable voltage with critical load during clearing time and seamless control mode transfer of inverters. However, the islanding detection is difficult since with the indirect current...
This paper describe and present the study on online tap change (OLTC) operation in distribution network in the case of utilizing reactive power capability of PV inverter. The conventional voltage control scheme and the effect of solar PV variation on the voltage profile in distribution network are discussed. Solar resources in the state of Qatar for different seasons and weather condition are presented...
High inertial loads are abundant in the industry and most of them are direct on line starter type induction machines with double cage rotors. Due to their higher starting time higher power dissipation in the rotor makes the rotor wear out and eventually gets destroyed. A new starting method proposed herein makes the motor start quickly and smoothly by using an inverter. After reaching it's steady...
There is a general increase in global electricity consumption. As at February 2014, South Africa had a 2.2% electricity consumption increase per annum. Distributed generation with interconnection of renewable energy generation to the electrical grid at the load end of the network is the favored solution to match this demand increase. One of the most abundant forms of renewable energy in Africa is...
This paper describes a concept for the coordination of active applications in LV networks to avoid unacceptable voltages and to ensure a stable control operation. The concept has been kept simple, without using an extensive algorithm. This ensures an uncomplicated implementation and operation. The focus of the paper lies on the explanation of the algorithm and the practical implementation. Furthermore,...
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