Multilevel inverters (MLIs) have gained increasing interest for advanced energy-conversion systems due to their features of high-quality produced waveforms, modularity, transformerless operation, voltage, and current scalability, and fault-tolerant operation. However, these merits usually come with the cost of a high number of components. Over the past few years, proposing new MLIs with a lower component count has been one of the most active topics in power electronics. The first aim of this article is to update and summarize the recently developed multilevel topologies with a reduced component count, based on their advantages, disadvantages, construction, and specific applications. Within the framework, both single-phase and three-phase topologies with symmetrical and asymmetrical operations are taken into consideration via a detailed comparison in terms of the used component count and type. The second objective is to propose a comparative method with novel factors to take component ratings into account. The effectiveness of the proposed method is verified by a comparative study.

Voltage Source Multilevel Inverters With Reduced Device Count: Topological Review and Novel Comparative Factors

Pumped storage power plant has gained a high level of attention in recent years, mainly because of its ability to act as a large-scale energy storage option and to improve power system flexibility Doubly fed asynchronous machine with the partially rated power electronic converter is adopted in pumped storage plants to provide variable speed operation and improve energy efficiency This paper summarizes the power converter topologies in large rated variable speed pumped storage plant (VSPSP), also covers the suitability of each converter topology, modulation techniques, and parallel converter schemes Also, it presents operational issues of the parallel converter system in VSPSP such as the shutdown of the plant due to insufficient converter redundancy and lack of fault-tolerant control schemes, a power outage due to the inadequacy of converter protection system, and unbalanced power sharing due to circulating current Furthermore, the reliable mitigating/additional techniques are discussed for future research It concludes that the refinement of these aforementioned issues will provide continuous operation of the plant

A Review of Power Electronic Converters for Variable Speed Pumped Storage Plants: Configurations, Operational Challenges, and Future Scopes

Hydropower is a major energy source among the renewable energy sources. According to “BP Statistical Review of World Energy, June 2013”, 16.34 percentage of global power generation acquire from hydropower. To attain efficient generation in hydro plant, extensive design with the up to date technology is mandatory. To make the generation more effective various technologies are adopted, among these the very effective one is power electronics (PE) technology. The paper has reviewed the challenges in how PE technology fits in as the solution for various hydroelectric energy systems (HEES). The PE technology is adapted efficiently in various parts of HEES like, grid integration, machine control, switching (pumping mode to generating mode and vice versa), power control, voltage and frequency control, power factor correction, etc., The advancement of PE technology diminishes the cost and space of the plant and enhances the power handling capability. The paper emergence the outstanding features of power electronics in various aspects that will extensively contribute to the development of HEES around the world. In addition, PE contribution satisfies the need of reliability, dynamic response, efficiency, protection, etc., in HEES.

Power electronics in hydro electric energy systems – A review

A 300MW drive system consisting ofacyclo-converter driven doubly-fed induction machine for pump-storage stations operating inGoldisthal, Germany, ispresented. Thecyclo-converter supplied by ALSTOMisoneofthelargest intheworld. Major benefits ofthis innovative concept aretheincrease oftheturbine efficiency bymeansofspeed variation andthehigh dynamic powercontrol forthe stabilisation ofthegrid. Major benefits compared toclassical approaches areidentified. Emphasis is placed onthebehaviour ofthedrive atgrid failures. A newmodified topology isproposed tomeetthe grid code requirements atvarious grid failures.

http://ieeexplore.ieee.org/iel5/11048/34861/01665624.pdf

Analysis ofa300MW Variable Speed Drive forPump-Storage Plant Applications

The increasing share of renewables in the power generation mix makes the power system volatile to uncertain meteorological conditions. The stochastic nature of renewables demands energy storage systems (ESS) to maintain the stability of the grid. Among various ESS, pumped hydro storage (PHS) is a technically matured and economically viable option for large scale energy storage. However, it has not gained much attention from researchers due to its technical maturity and site-specific nature. Lately, the focus is shifting towards the development of variable speed PHS and different reservoir schemes to realize PHS with the existing infrastructure. Nevertheless, the development of variable speed PHS necessitates a proper selection of power converter topology with a suitable control technique. Thus, the principal objective of this paper is to present a critical review of different levels of control of the variable speed PHS. Firstly, a state of the art comparison between PHS and other ESS is presented through critical data analysis using Tableau software. Secondly, the control strategies are categorized into a hierarchical structure and reviewed based on a bottom-up approach. Towards the end, a synoptic review is presented to elucidate the dominating strategy at each level of the control hierarchy. Finally, the domains which require further attention are distinctively reported to leverage the future research of PHS.

Variable speed pumped hydro storage: A review of converters, controls and energy management strategies

The paper presents the modeling and simulation study of a variable speed pump-storage power plant composed of a reversible turbine, a doubly fed induction machine (DFIM), and a multistage-multilevel frequency converter. The DFIM rotor circuit is fed by a 5-level NPC VSI. The inverter DC-link capacitor voltages are kept in balance by means of four multistage PWM rectifiers. The paper considers start-up responses and performance characteristics of the drive system along with its behavior under the stator short-circuit fault conditions. An emphasis is placed upon modifying the PD PWM modulation waveforms in order to level RMS values of currents flowing in PWM rectifiers and related secondary windings of a step-down transformer.

Features of a drive system for pump-storage plant applications based on the use of double-fed induction machine with a multistage-multilevel frequency converter

The paper presents a variable speed drive for pump-storage plant applications. A reversible turbine is energized by a double-fed induction machine (DFIM) exited on the rotor side with a cascaded frequency converter made up of M single-phase cells. The DFIM is started up as a synchronous machine by means of a CSI on the stator side and a VSI on the rotor side. An emphasis is placed on the control system aimed at the plant active and reactive power regulation. In order to balance out currents of the transformer secondary windings feeding single-phase active rectifiers, a phase disposition PWM strategy has been modified by introducing a consecutive cycling step-wise displacement of triangular wave offsets within a saw tooth period consisting of M triangle wave periods. The paper concludes by analyzing start-up responses and performance characteristics of the system in sub- and over-synchronous modes of operation.

http://ieeexplore.ieee.org/iel5/6014782/6020091/06020328.pdf

A pumped storage power plant with double-fed induction machine and cascaded frequency converter

The paper presents the modeling and simulation study of a variable speed drive for the pump-storage station composed of a reversible turbine and a doubly fed induction machine (DFIM) exited with a multistage-multilevel frequency converter The DFIM is started up as a synchronous machine by means of a CSI on the stator side and a VSI on the rotor side An emphasis is placed on the control system structure aimed at the active and reactive power regulation via a mechanical governor and a slip controller The paper concludes by analyzing start-up responses and performance characteristics of the system in sub- and over-synchronous modes of operation

A double-fed induction machine with a multistage-multilevel frequency converter for pumped storage power plant applications

The power supply system and HPS (PSHPS) model is developed in which the electric power system is presented by a powerful adjustable synchronous machine, the HPS (PSHPS) hydroelectric power plant - by the adjustable turbine and electric machine of smaller power and sluggishness and the HPS (PSHPS) hydraulic part is described. Modifications of synchronous and asynchronous machine systems are considered and the operation of regulators is taken into account. The analysis of power and hydraulic subsystem processes at power changes hydroblow is presented.

Electric and hydraulic process connection in hydraulic and pumped storage hydroelectric power stations

The paper presents a model of a poly-phase permanent magnet motor of the marine propulsion drive energized by multistage VSI. The model defines more precisely the non-sinusoidal waveform of back-EMF and its impact on the current distortion and electromagnetic torque ripples. The paper concludes by analyzing simulation results that have shown significant suppression of high order current harmonics and corresponding decrease in torque ripples due to the proposed control algorithm realized in a phase reference frame.

http://ieeexplore.ieee.org/iel5/5254890/5278662/05279345.pdf

MODELING a transistor converter-fed permanent magnet poly-phase machine and a variable-frequency drive controller under non-sinusoidal back-EMF conditions

G. Gogolev

Papers

Features of a drive system for pump-storage plant applications based on the use of double-fed induction machine with a multistage-multilevel frequency converter

A pumped storage power plant with double-fed induction machine and cascaded frequency converter

A double-fed induction machine with a multistage-multilevel frequency converter for pumped storage power plant applications

Electric and hydraulic process connection in hydraulic and pumped storage hydroelectric power stations

MODELING a transistor converter-fed permanent magnet poly-phase machine and a variable-frequency drive controller under non-sinusoidal back-EMF conditions