Overview of current development in electrical energy storage technologies and the application potential in power system operation

This paper gives an overview of medium-voltage (MV) multilevel converters with a focus on achieving minimum harmonic distortion and high efficiency at low switching frequency operation. Increasing the power rating by minimizing switching frequency while still maintaining reasonable power quality is an important requirement and a persistent challenge for the industry. Existing solutions are discussed and analyzed based on their topologies, limitations, and control techniques. As a preferred option for future research and application, an inverter configuration based on three-level building blocks to generate five-level voltage waveforms is suggested. This paper shows that such an inverter may be operated at a very low switching frequency to achieve minimum on-state and dynamic device losses for highly efficient MV drive applications while maintaining low harmonic distortion.

Medium-Voltage Multilevel Converters—State of the Art, Challenges, and Requirements in Industrial Applications

DC microgrids and distribution systems: An overview

The photovoltaic (PV) system is one of the renewable energies that attract the attention of researchers in the recent decades. The PV generators exhibit nonlinear I–V and P–V characteristics. The maximum power produced varies with both irradiance and temperature. Since the conversion efficiency of PV arrays is very low, it requires maximum power point tracking (MPPT) control techniques. The maximum power point tracking (MPPT) is the automatic control algorithm to adjust the power interfaces and achieve the greatest possible power harvest, during moment to moment variations of light level, shading, temperature, and photovoltaic module characteristics. The purpose of the MPPT is to adjust the solar operating voltage close to the MPP under changing atmospheric conditions. It has become an essential component to evaluate the design performance of PV power systems. This investigation aims to assess different MPPT techniques, provide background knowledge, implementation topology, grid interconnection of PV and solar microinverter requirements presented in the literature, doing depth comparisons between them with a brief discussion. The MPPT merits, demerits and classification, which can be used as a reference for future research related to optimizing the solar power generation, are also discussed. Conventional methods are easy to implement but they suffer from oscillations at MPP and tracking speed is less due to fixed perturb step. Intelligent methods are efficient; oscillations are lesser at MPP in steady state and tracked quickly in comparison to conventional methods.

MPPT techniques for photovoltaic applications

A comprehensive comparison of different MPPT techniques for photovoltaic systems

Maximum power point tracking (MPPT) techniques are employed in photovoltaic (PV) systems to maximize the PV array output power which depends on solar irradiance and temperature. Among all the MPPT strategies, The P&O Maximum Power Point Tracking algorithm is mostly used, due to its ease of implementation. On the other hand, its main drawbacks are the waste of energy in steady state conditions, when the working point moves across the MPP and the poor dynamic performances exhibited when a step change in solar irradiance or in temperature occurs. In this paper, a modified variable step size P&O MPPT algorithm is proposed, the step size is automatically tuned according to the operating point. Compared with the conventional fixed step size method, the proposed approach can effectively improve the MPPT speed and efficiency simultaneously. A theoretical analysis and the design principle of the proposed algorithm are provided and its feasibility is also verified by simulation results.

Variable step size P&O MPPT algorithm for PV systems

As the capacity of wind power continues to increase globally, stricter requirements regarding grid connection of wind generators are introduced by system operators The development of wind turbine technology is inevitably affected by the new grid codes, and wind power plants are expected to support the grid and provide ancillary services much like conventional power plants The most demanding regulations are found in Europe where wind penetration levels are higher This paper presents the main aspects of current grid code requirements for the integration of wind power in European countries and suggests performance characteristics in order to satisfy the most demanding requirements The dynamic behavior of wind turbines with doubly fed induction generators is investigated and a solution for low voltage ride through compliance is presented

https://downloads.hindawi.com/archive/2013/437674.pdf

Grid Code Requirements for Wind Power Integration in Europe

With worldwide increasing shares of electricity generated by wind energy converters (WECs), their influence on the mains stability and contribution to reliable energy supply becomes more and more relevant. The system management of WECs has great influence on the power yield and the damping/amplification of wind-caused power fluctuations. This paper compares the performance of different control methods for WECs, regarding their energy yield and electrical power-output fluctuation at different wind conditions. The results show that the stochastic dynamic optimization control combines very high energy yield with the highest damping of fluctuations.

Energy Yield and Power Fluctuation of Different Control Methods for Wind Energy Converters

As the penetration of wind power and other distributed generation sources increases, more demanding grid code requirements are introduced by the network operators in order to ensure the stability of the evolving electrical networks. The most challenging requirement for wind energy converter systems is the low voltage ride through capability that expects generators to remain connected during symmetrical and asymmetrical grid faults and to contribute to the system recovery. Asymmetrical voltage conditions and dips in the grid can have significant negative effects on the performance of doubly-fed induction generators. These effects can decrease the lifetime of sensitive components in the wind energy converter in the long term and in extreme cases they can cause damages and tripping of the system, leading to violation of the grid code requirements. Protective measures must be taken so that the wind energy converters remain connected and support the grid without putting the reliability of the system at risk. Various control solutions have been developed to deal with these challenges. Although the most common voltage dips caused by grid faults are asymmetrical, the majority of the control solutions developed so far consider only symmetrical faults and they cannot mitigate the problems faced under asymmetrical conditions. This paper provides a comprehensive overview of different linear vector control methods for wind energy converter systems with doubly-fed induction generators which have been proposed in the literature to deal with the challenge of operating during voltage asymmetry and `riding-through' all types of voltage dips, symmetrical and asymmetrical.

Review of control strategies for DFIG-based wind turbines under unsymmetrical grid faults

A drive train system (DTS) powered by an ideal voltage source and driving a permanent-magnet synchronous motor (PMSM) is discussed in this paper. A two-level three-phase voltage source inverter is used as a means of power conditioning. This converter is not equipped with any harmonic filters on neither the ac nor the dc side. The mechanical part of the DTS is modeled as a double oscillator according to a drive train in an electric vehicle (EV). Various inverter modulation schemes are applied, namely, a single-phase hysteresis scheme, two-space vector-based hysteresis control schemes, for one, a stator aligned hysteresis and for another, a rotor aligned hysteresis, a modulation scheme based on pulsewidth modulation (PWM), such as sinusoidal modulation (including zero-sequence components) and space-vector pulsewidth modulation (SVPWM). The hysteresis-based pulsing methods are nondeterministic and build a current controller in their structure by nature. The other pulsing methods are deterministic due to their underlying PWM and require a separate control unit. The influence of these modulation schemes on the performance of the DTS is determined by assessing the level of inverter generated harmonics flowing to the PMSM and to the tires [downforce, (mechanical part)] as well as the resulting switching frequency (electrical part). The simulated results presented in the paper indicate that the pulsing frequency can be reduced by means of the hysteresis controller. In addition, the dispersion of the harmonic energy of the inverter generated spectrum partly compensate the absence of filters.

Constantinos Sourkounis

Papers

Variable step size P&O MPPT algorithm for PV systems

Grid Code Requirements for Wind Power Integration in Europe

Energy Yield and Power Fluctuation of Different Control Methods for Wind Energy Converters

Review of control strategies for DFIG-based wind turbines under unsymmetrical grid faults

On Influence of Non Deterministic Modulation Schemes on a Drive Train System With a PMSM Within an Electric Vehicle