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This paper presents the design and the experimental evaluation of a power converter for energy storage applications suitable for household installation or to facilitate distributed energy storage capability within a local/community low-voltage grid. The technology to build the power converter is a common / low cost one in order to make it affordable which was expected to limit the overall efficiency...
Power losses in transmission systems are proportional with square the current, where current is proportional with power transferred. For that reason, in cases where the power transfer contains a high degree of fluctuation such produced by a wind farm, power losses will be much higher than with same average power transferred smoothly. For this reason, the use of energy storage in power systems reduces...
This paper proposes a new hybrid inverter solution for medium/high voltage applications that consists of a slow switching inverter using high voltage or series connected switching devices, fitted with a low kVA rated auxiliary current source inverter to cancel the switching ripple produced by the main inverter. The reduction in CSI voltage stress is obtained by connecting it to the MV grid via a series...
This paper investigates the advantages of using interleaved based direct sinusoidal current shaping techniques as alternative to 5-level Pulse Width Modulation (PWM) when used in conjunction to a two stage Current Source Inverter (CSI) in PV applications. By using simulation based modelling it is proven that; in combination with switching harmonic cancellation techniques; for a given output power,...
This paper presents a cost effective winding design and evaluation of a medium frequency isolation transformer typically used in bidirectional isolated DC/DC converters. Since leakage inductance and winding resistance of a high frequency transformer are interdependent, any attempt to increase the leakage inductance by adjusting the winding arrangement increases the resistance as well and impacts the...
Newly developed electrochemical energy storage devices are typically produced as single/small quantity and small size devices. This makes their evaluation very difficult in high power applications that would require production of much larger size devices and higher quantities. Also, doing practical work in an electrical engineering labs with chemical devices not fully certified from safety point of...
In this paper, a few known characterization techniques for supercapacitors have been evaluated with the purpose of being able to predict the roundtrip efficiency of an energy storage system under constant power application. It is found that the user cannot rely on a single characterization method since the methods based on small signal disturbance are not very precise when the model is subjected to...
This paper proposes a high performance hybrid cascaded H-Bridge (HB) Multilevel Converter (MLC) with integrated Series Active Power Filter SAPF for interfacing energy storage systems with medium voltage grids. Isolated DC sources comprised of modular dual DC/DC converters and Medium Frequency Transformers MFT are used to energise the MLC HBs. The primary sides of the DC/DC converters are connected...
The paper presents a nine-level selective harmonic elimination pulse width modulation (SHE-PWM) cascaded voltage source converter based STATCOM system. The structure allows direct connection to the grid without the need of any step-up transformers. The converter is controlled with the SHE-PWM technique which provides an elimination to lower order harmonics to improve output waveforms and furthermore,...
The paper addresses a novel scheme for the control of variable wind energy and energy storage plant such that the generation and energy storage can deliver a smooth and constant power as demanded by the grid load. In addition, the wind energy generators are assumed large compared to the local grid rating and will contribute to the voltage and frequency regulation of a grid using adaptive frequency...
Permanent magnet synchronous generators (PMSG) are at the core of small scale wind power generators manufactured by a wide range of manufacturers in different configurations: vertical or horizontal axis blades, with various geometries and aerodynamics of the blades; by installing these small scale wind turbines in very large numbers at household levels, it is expected that these will make a positive...
Renewable energy sources such as Photovoltaics (PVs) and Fuel Cells (FCs) generate DC voltage/current and have a high internal resistance/nonlinear V/I dependence, which is why a digitally controlled power electronic interface is always needed to facilitate connection to an AC grid and maximum power extraction. This paper evaluates four single-stage power electronic converters for PVs: the traditional...
Nowadays, energy storage devices such as supercapacitors or ultracapacitors are available to address the high specific energy (compared to electrolytic capacitors) and high specific power (compared to batteries) applications, and most of them would consist of constant power operation which means that the current handled by the device needs to compensate the variation of the voltage. Also, for most...
A matrix converter is an ac-ac power converter topology that has received extensive research attention as an alternative to traditional ac-dc-ac converter. A matrix converter is able to convert energy from an ac source to an ac load without the need of a bulky and limited-lifetime energy-storage elements. The indirect three-level sparse matrix converter (I3SMC) is a new topology from this family that...
The current source inverter (CSI) is preferred to interface a renewable source such photovoltaics (PV) to the AC power grid because it can provide smooth current source in the DC side, which fits to the PV behaviour and also steps-up the voltage from DC side to AC side, which allows smaller and safer DC voltage levels to be used. However, the CSI has the problem that during an AC grid fault, it cannot...
This paper presents the initial investigations in selecting the topology of the power electronic interface for an energy storage system for power levelling applications based on a novel storage device, the supercapattery. The particularities of the supercapattery device are summarized leading to a multistage power converter structure. A review of the two stage DC/DC converter structure to interface...
Power converters consisting of naturally commutated thyristors such as cycloconverters and current source inverters were the first used in driving electrical motors with variable speed but now due to their inferior performance compared to forced commutated converters, their use is restricted in the high voltage/high power range where the performance and cost of forced commutated switching devices...
Multilevel inverters are traditionally seen as a step forward in DC/AC conversion, providing more output voltage levels, better quality of the generated waveform and lower switching losses than the two-level and can process higher voltages with a given forced commutated switch technology. There are also drawbacks associated with this technology: more switching devices and associated gate driver circuitry,...
This paper investigates embedding Energy Storage (ES) with multiple wind turbines in order to deliver to the grid a smooth and constant power as demanded by the system operator. The demand power is shared by DFIGs proportional to their ratings utilizing classical voltage and frequency droop characteristics. The paper addresses the system control methodologies for delivering constant power to the grid...
Selective harmonic elimination (SHE) is usually the preferred modulation technique for high power converters. When such modulation is used with current source rectifiers (CSR), control of the DC-link current and of the input displacement power factor is typically achieved by adjusting the amplitude and phase of the CSR modulation index. In this paper control of an SHE modulated CSR is achieved by...
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