19,014 research outputs found
Double-Frame Current Control with a Multivariable PI Controller and Power Compensation forWeak Unbalanced Networks
The handling of weak networks with asymmetric loads and disturbances implies
the accurate handling of the second-harmonic component that appears in an
unbalanced network. This paper proposes a classic vector control approach using
a PI-based controller with superior decoupling capabilities for operation in
weak networks with unbalanced phase voltages. A synchronization method for weak
unbalanced networks is detailed, with dedicated dimensioning rules. The use of
a double-frame controller allows a current symmetry or controlled imbalance to
be forced for compensation of power oscillations by controlling the negative
current sequence. This paper also serves as a useful reminder of the proper way
to cancel the inherent coupling effect due to the transformation to the
synchronous rotating reference frame, and of basic considerations of the
relationship between switching frequency and control bandwidth.Comment: 17 pages, contribution to the 2014 CAS - CERN Accelerator School:
Power Converters, Baden, Switzerland, 7-14 May 201
Performance Evaluation of Fuel Cell and Microturbine as Distributed Generators in a Microgrid
This paper presents dynamic models of distributed generators (DG) and investigates
dynamic behaviour of the DG units within a microgrid system. The DG units include micro
turbine, fuel cell and the electronically interfaced sources. The voltage source converter is
adopted as the electronic interface which is equipped with its controller to maintain
stability of the microgrid during small signal dynamics. This paper also introduces power
management strategies and implements the DG load sharing concept to maintain the
microgrid operation in standalone, grid-connected and islanding modes of operation. The
results demonstrate the operation and performance of the microturbine and SOFC as
distributed generators in a microgrid.
Keywords: Microgrid, Distributed Generation, Microturbine, Fuel Cel
Realization of a 10 kW MES power to methane plant based on unified AC/DC converter
This paper presents a galvanic isolated multi output AC/DC topology that is suitable for Microbial electrosynthesis (MES) based Power to Methane energy storage systems. The presented scheme utilizes a three phase back to back converters, a single-input and multiple-output three phase transformer, single diode rectifiers and buck converters that employ a proper interconnection between MES cells and the mains. The proposed topology merges all the required single phase AC/DC converters as a unified converter which reduces the overall system size and provides system integrity and overall controllability. The proposed control scheme allows to achieve the following desired goals:1) Simultaneous control of all cells; 2) Absorbing power from the grid and covert to methane when the electricity price goes down; 3) the power factor and the quality of grid current is under control; 4) Supplying MES cells at the optimal operating point. For verification of system performance, Real time simulation results that are obtained from a 10-kW MES energy storage are presented.Postprint (author's final draft
Impedance-compensated grid synchronisation for extending the stability range of weak grids with voltage source converters
This paper demonstrates how the range of stable power transfer in weak grids with voltage source converters (VSCs) can be extended by modifying the grid synchronisation mechanism of a conventional synchronous reference frame phase locked loop (PLL). By introducing an impedance-conditioning term in the PLL, the VSC control system can be virtually synchronised to a stronger point in the grid to counteract the instability effects caused by high grid impedance. To verify the effectiveness of the proposed approach, the maximum static power transfer capability and the small-signal stability range of a system with a VSC HVDC terminal connected to a weak grid are calculated from an analytical model with different levels of impedance-conditioning in the PLL. Such calculations are presented for two different configurations of the VSC control system, showing how both the static power transfer capability and the small-signal stability range can be significantly improved. The validity of the stability assessment is verified by time-domain simulations in the Matlab/Simulink environment.Peer ReviewedPostprint (published version
Distributed control of a fault tolerant modular multilevel inverter for direct-drive wind turbine grid interfacing
Modular generator and converter topologies are being pursued for large offshore wind turbines to achieve fault tolerance and high reliability. A centralized controller presents a single critical point of failure which has prevented a truly modular and fault tolerant system from being obtained. This study analyses the inverter circuit control requirements during normal operation and grid fault ride-through, and proposes a distributed controller design to allow inverter modules to operate independently of each other. All the modules independently estimate the grid voltage magnitude and position, and the modules are synchronised together over a CAN bus. The CAN bus is also used to interleave the PWM switching of the modules and synchronise the ADC sampling. The controller structure and algorithms are tested by laboratory experiments with respect to normal operation, initial synchronization to the grid, module fault tolerance and grid fault ride-through
Remote power control strategy based on virtual flux approach for the grid tied power converters
The control of active and reactive power for the Renewable Energy Sources (RES) based power plants are very important. The injection of active and reactive power to the grid is normally controlled at the Point of Common Connection (PCC) where this point is typically far away from the power converter station. This paper proposed a controlling principle which is based on virtual flux approach that permits to control remotely the power injected at the PCC. The results will show that the Virtual Flux (VF) estimation is capable to estimate the grid voltage in any point of the network as well as the capability of the control principle to inject the specific amount of active and reactive power at a point that can be some kilometers away. In this paper, the basic principle for the remote power control is presented and the effectiveness of the proposed system has been validated by experimental studies.Postprint (published version
Power Quality Enhancement in Electricity Grids with Wind Energy Using Multicell Converters and Energy Storage
In recent years, the wind power industry is experiencing a rapid growth and more wind farms with larger size wind turbines are being connected to the power system. While this contributes to the overall security of electricity supply, large-scale deployment of wind energy into the grid also presents many technical challenges. Most of these challenges are one way or another, related to the variability and intermittent nature of wind and affect the power quality of the distribution grid. Power quality relates to factors that cause variations in the voltage level and frequency as well as distortion in the voltage and current waveforms due to wind variability which produces both harmonics and inter-harmonics. The main motivation behind work is to propose a new topology of the static AC/DC/AC multicell converter to improve the power quality in grid-connected wind energy conversion systems. Serial switching cells have the ability to achieve a high power with lower-size components and improve the voltage waveforms at the input and output of the converter by increasing the number of cells. Furthermore, a battery energy storage system is included and a power management strategy is designed to ensure the continuity of power supply and consequently the autonomy of the proposed system. The simulation results are presented for a 149.2 kW wind turbine induction generator system and the results obtained demonstrate the reduced harmonics, improved transient response, and reference tracking of the voltage output of the wind energy conversion system.Peer reviewedFinal Accepted Versio
Full- & Reduced-Order State-Space Modeling of Wind Turbine Systems with Permanent-Magnet Synchronous Generator
Wind energy is an integral part of nowadays energy supply and one of the
fastest growing sources of electricity in the world today. Accurate models for
wind energy conversion systems (WECSs) are of key interest for the analysis and
control design of present and future energy systems. Existing control-oriented
WECSs models are subject to unstructured simplifications, which have not been
discussed in literature so far. Thus, this technical note presents are thorough
derivation of a physical state-space model for permanent magnet synchronous
generator WECSs. The physical model considers all dynamic effects that
significantly influence the system's power output, including the switching of
the power electronics. Alternatively, the model is formulated in the -
and -reference frame. Secondly, a complete control and operation
management system for the wind regimes II and III and the transition between
the regimes is presented. The control takes practical effects such as input
saturation and integral windup into account. Thirdly, by a structured model
reduction procedure, two state-space models of WECS with reduced complexity are
derived: a non-switching model and a non-switching reduced-order model. The
validity of the models is illustrated and compared through a numerical
simulation study.Comment: 23 pages, 11 figure
Improving long line stability by integrating renewables using static synchronous generators
Postprint (author's final draft
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