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This paper presents an improved cascaded DC-DC resonant converter for offshore windfarms. The improvements are reduced losses and the number of components. The topology is based on the Marx principle where charged capacitors are charged in parallel and discharged in series to achieve the voltage transformation. The four inductors of the converter are designed to resonate with the capacitors to create...
An investigation of the voltage imbalance of the two capacitors of the semi-full-bridge submodule is performed. Since the capacitances are not exactly the same, there may be a difference between the capacitor voltages. The resulting current-spike when they are connected in parallel has been analyzed in a full-scale laboratory experiment.
This paper extensively analyzes the operation limits, system stability and disturbance rejection capability of the voltage control loops used in master-slave AC and DC Microgrids (MGs). Two different control schemes are studied analytically, simulated and experimentally tested, focusing on Constant Power Loads (CPL). Additionally, the use of the virtual capacitance (VC) as a tool for response enhancement...
The transient performance of a DC power supply strongly depends on the loop design and output filter sizing. Most of the time, the finite loop bandwidth imposes the need of a large output filter capacitor in order to comply with the required regulation performance and stability margins. In space applications the linear conductance control principle has been used for a long time. It reduces the voltage...
Input-series-output-series (ISOS) inverter system is very suitable for high input voltage and high output voltage power conversion applications. If the inverter system topology is applied to the grid-connected application, a large-capacity inverter system can be built with multiple small-capacity standardized inverter modules, which will improve system reliability and simplify system design. For the...
The very high voltage ratio has been achieved by introducing the switched-coupled-inductor to the quadratic boost converter and combining it with the diode-capacitor Dickson multiplier. The operating principles and steady-state analyses of continuous conduction mode are performed. The formulas to calculate the maximal voltage stresses on the transistor and on the diodes are provided. Simulation and...
A single-phase quasi-impedance source inverter (qZSI) has become an attractive solution for residential PV applications. However, due to the nature of this inverter topology, double-frequency (2ω) power ripple issue should be considered since this issue has a negative impact on the system performance. This paper presents model predictive control (MPC) based current ripple damping control technique...
Contactless power transfer (CPT) is an emerging topic which relies in high frequency resonant inverters to transfer power from a transmitter to a physically separated receiver inductively. Capacitive compensations on both the primary and secondary sides of a loosely coupled transformer are usually employed in recent researches in order to enhance the power transfer capability and the system efficiency...
The AC/AC single-phase/single-phase Modular Multilevel Converter (MMC) presents very interesting features for the realization of a Medium Frequency Power Electronic Transformer for traction applications, in AC-fed or multisystem railway rolling stock, like locomotives, Electric Multiple Units (EMU), high-speed units, and so on. Aiming to maximize the output frequency of the converter, i.e. the operating...
A MIMO1 current-control approach for 3-phase grid connected inverter systems in the abc-frame is proposed. Redundant states are eliminated and the system is controlled via an explicit MPC2-approach. To achieve steady-state accuracy, the system-model is augmented by a simplified grid-model to obtain a high dynamic control structure, which supersedes the use of resonant controllers and coordinate transformations...
A grid-connected inverter with energy storage and active DC-link voltage balancer circuit is presented. The system is implemented with two identical 100kW three-phase converters. The operating limits of the system under asymmetric grid currents with the given hardware architecture are considered and solutions for symmetrisation of the DC-link are proposed.
This paper presents an interleaved multiphase hybrid buck-boost DC/DC converter. This converter type provides high efficiency and can be used for applications with wide voltage conversion ratio. At the beginning, the circuit function and the design of a single-phase converter is described. With a multiphase design, the filter circuit effort can be significantly reduced. In these circuits the different...
The paper presents a technique of parameter stabilization of a wireless, resonance based energy transfer system for maximizing its power. The technique combines tuning of resonant frequency by means of variable capacitance and adjustment of magnetic coupling to maximize power. The paper presents experimental test results on a laboratory prototype of the system.
The multilevel converters have advantages of low voltage stresses of the switches and possible reduction of size of the passive components. Input-series output-series (ISOS) configuration of the converter enable the utilization of low voltage rating switches in converters with high input voltage and high output voltage in applications that requires galvanic isolation. While multilevel topology offers...
The increasing number of renewable energy sources and their integration into the medium voltage grid leads to an increasing interest in multilevel structures for the interfacing power electronic converters. A feasible topology for MV applications is the Stacked Multicell Converter (SMC) offering a modular structure and several voltage levels. A robust control, current limiting strategies under grid...
Fault-tolerant multilevel inverters outperform known fault-tolerant 2-level inverters regarding efficiency and power density. The most promising fault-tolerant multilevel inverters for system voltages below 2 kV are the flying capacitor and the active neutral point clamped type. They differ regarding required voltage overrating of semiconductors, tolerance for open and short-on failure types and maximum...
This paper presents a comparison between two DC-voltage balancing strategies for cascaded star-connected multilevel STATCOM: zero-sequence voltage, and negative-sequence current control. Different levels of unbalance and grid strengths are considered. The impact of the control strategies on the convert ratings in terms of voltage and current requirements are compared and the operating range of the...
The impact of capacitor voltage changes during the modulation period is examined in order to improve the arm voltage of a modular multilevel converter. Different methods are used to predict and compensate for the capacitor voltage change and the resulting arm voltage error, whereby two of the improvements provide a possibility to easily upgrade existing modulation algorithms. Simulation and measurement...
The series resonant DC/DC converter with an isolation transformer and bridge mode inverter input junction, at its operation in the Buck case, is investigated, at that input DC supply circuit comprises the qZ (quasi-Z) link as impedance source. Operation at such Buck case can be provided under different inverter bridge control methods. Recommended by the literature sources, is the method of control...
This work develops the synchronous reference frame control of an interlinking converter between the DC and the AC bus of hybrid microgrids. The interlinking converter is based on two parallel connected inverters. A 3D Space Vector Modulator is proposed to avoid the presence of circulating currents between inverters.
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