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This paper investigates the problem of accurate active power sharing in virtual flux droop where flux angle droop control is used for DG controllers instead of traditional frequency droop control. Firstly, the virtual flux droop control method is introduced. Then, the reasons for inaccurate active power sharing in flux angle droop are analysed. Further, to solve this problem, an active power compensation...
This paper presents the small signal model of a multi Photovoltaic (PV) inverter system to study the effect of controller and system parameters on the frequency modes of a microgrid. The paper describes the state space model of a system having two PV inverters connected by a line and working under droop control mode for active power sharing. The PV sources are working under load following mode and...
Distributed generation (DG) is connected through three-phase inverter to the microgrid. The virtual power based droop control can guarantee the pure decoupling between active and reactive power irrespective of low-voltage or high-voltage microgrid application if the line-impedance information is known in advance. However, unbalances are commonly existent in practice so that this conventional control...
In this work is present the comparison of two methods of controllers design and the model of a single phase inverter for island mode operation in a microgrid. These methods are: direct current conventional method based on frequency analysis that allows the design of a proportional-integral controller and a second method based on dc-ac coordinate transformation, that allows the design of a proportional...
The increasing penetration of renewable energy systems force the grid-connected power converters to use advanced active power controls, which needs to add more functionalities to their control strategies. A power reserve control is being required for grid support capabilities on Renewable Energy Sources (RES). Classical algorithms as the Maximum Power Point Tracking (MPPT) cannot withstand power reserve...
It is well-know that in systems composed of several digital processors, clock signals of individual units differ from each other due to clock drifts. This paper investigates the effect of clock drifts from voltage source inverters (VSI) in industrial microgrids. Particularly, a primary/secondary droop-free distributed control scheme is considered in order to evaluate its robustness against clock drifts...
In order to test the renewable energy grid-connect converters, a grid simulator is in need which is able to simulate grid transition such as voltage sags, unbalanced voltages, flicker and low-order harmonics. The main concern of this paper is on the harmonics generation. A compound control strategy is proposed on the basis of three-phase inverter to generate precise controllable required voltage harmonics...
This paper presents a wind-driven DC power generation and control system modified by a doubly fed induction generator (DFIG), which stator is connected with a full-power diode rectifier to supply DC power to a stand-alone load and rotor is connected to the DC link with a PWM converter in charge of regulation of frequency and voltage on stator side. The transient character and behavior of current,...
This paper presents a decentralized control for grid-connected cascaded PV inverter system. The system is composed of a number of PV units in series and then connected to utility grid. The topology of this type is meaningful for low voltage (LV) devices to integrate into medium voltage (MV) or high voltage (HV) grid. The proposed decentralized control ensures independent control of each PV unit without...
Communication bandwidth inconsistency between traditional secondary control and tertiary control may decrease the economic efficiency of a microgrid. To solve the problem, this study proposes a fully distributed cooperative strategy in secondary level to minimize the operation cost in an AC microgrid and achieve the synchronization of the voltage and frequency. The proposed strategy is based on the...
The situation of automatic generation control(AGC) in ultra-high voltage(UHV) receiving-end grid has changed greatly, and it is necessary to develop on-line monitoring and remote diagnosis technology to solve new AGC control problems. Through the construction of generation-grid integrated data platform of Shandong power system, online running data of sixteen typical thermal power units are accessed...
This paper is introducing a new method of operation for a series resonant converter, with intended application in megawatt high voltage DC wind turbines. Compared to a frequency-controlled series resonant converter operated in sub-resonant mode, the new method (entitled pulse removal technique) allows the transformer design to be determined by peak load and maximum switching frequency, while still...
Power system restoration takes place where power systems experience a blackout and might be splitted into several islands with limited number of black start units. The main challenge of the restoration process is to keep both frequency and voltage within allowable limits while restoring the network through energizing lines and transformers as well as load pickup. The load pickup scheme is determined...
This paper describes a method of deriving frequency characteristics of PMSM current control system based on Model Predictive Control (MPC). MPC controller predicts the current behavior using the mathematical model of PMSM and directly selects the optimal switch state based on evaluation of these predicted results. So, we have focused the possibility of MPC, which makes it possible to drive machines...
A circulating current is a major problem introduced by directly connecting voltage source inverter (VSI) in parallel. This circulating current occurs as a zero-sequence current between the inverters by specic switch states. Its alternatives were presented by hardware and software methods in many papers. When coupled inductor (CI) are employed for the high frequency circulating current, a circulating...
One of the main revenue streams of the power system industries is provide a stable frequency all the time. Energy storage systems are well suited for the purpose because of their bidirectional capabilities. Recently converter based energy storage system has been gaining interests for providing frequency response replacing traditional generator based solutions due to the speed of the power electronic...
This paper addresses the proposal and simulation of a direct voltage and frequency control (DVFC) of an offshore wind farm (OWF) with LCC-HVDC connection. The proposed control system allows the connection of the OWF to the LCC rectifier by generating a controlled voltage and frequency in a capacitor bank. The decoupled control of the d-q component of the voltage at the capacitor bank, connected to...
The distributed control of islanded AC microgrids is based on the local measurements of the electrical variables at some nodes of the system to perform the secondary control. The Phasor Measurement Units (PMUs) guarantee accurate synchronized measurements that can be used as input signals for such distributed controllers. This paper analyzes the effect of one of the characteristic parameters of the...
Formation of microgrids have been proposed as a solution to improve grid reliability, and enable smoother integration of renewables into the grid. Microgrids are sections of the grid that can operate in isolation from the main power system. Maintaining power balance within an islanded microgrid is a challenging task, due to the low system inertia, which requires complex control to maintain stable...
This paper proposes improved multi-loop control strategies for three-phase four-leg virtual synchronous generator with unbalanced loads. Through the decoupling control of active and reactive power, inverter can simulate the characteristics of synchronous generator, including primary frequency modulation, primary voltage modulation, inertia and excitation characteristics. To improve the dynamic performance...
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