Emerging Converter Topologies and Control for Grid Connected Photovoltaic Systems

Continuous cost reduction of photovoltaic (PV) systems and the rise of power auctions resulted in the establishment of PV power not only as a green energy source but also as a cost-effective solution to the electricity generation market. Various commercial solutions for grid-connected PV systems are available at any power level, ranging from multi-megawatt utility-scale solar farms to sub-kilowatt residential PV installations. Compared to utility-scale systems, the feasibility of small-scale residential PV installations is still limited by existing technologies that have not yet properly address issues like operation in weak grids, opaque and partial shading, etc. New market drivers such as warranty improvement to match the PV module lifespan, operation voltage range extension for application flexibility, and embedded energy storage for load shifting have again put small-scale PV systems in the spotlight. This Special Issue collects the latest developments in the field of power electronic converter topologies, control, design, and optimization for better energy yield, power conversion efficiency, reliability, and longer lifetime of the small-scale PV systems. This Special Issue will serve as a reference and update for academics, researchers, and practicing engineers to inspire new research and developments that pave the way for next-generation PV systems for residential and small commercial applications

Investigation of a Cascaded H-bridge Photovoltaic Inverter under non-Uniform Insolation Conditions by Hardware-in-the-Loop Test

Abstract- In this paper, the cascaded H-bridge (CHB) multilevel inverter is employed as a grid connected inverter. This kind of inverter has interesting features compared to conventional inverters, including better efficiency, lower THD, lower common mode current injection, and better waveform quality. Using a series connection of H-bridge cells in this topology, a high modularity is achieved and a stepwise voltage waveform is synthesized at the ac side, leading to lower filter size and complexity. This topology processes the electric power in one stage and does not need any step-up voltage transformer for grid connection. The dynamic performance of control system is studied through simulations and is compared with the conventional approach. In addition, a new voltage estimation approach is proposed to reduce the number of voltage sensors compared to existing methods. The simulation results are presented for a 1.5 kW grid connected 7-level CHB inverter and then the hardware-in-the-loop implementation of the CHB inverter is presented to verify the performance of control system. Keywords- Cascaded H-bridge Inverter, Grid Connection, Hardware-in-the-loop implementation, Photovoltaics, and Real-time simulation

New Three Phase Photovoltaic Energy Harvesting System for Generation of Balanced Voltages in Presence of Partial Shading, Module Mismatch, and Unequal Maximum Power Points

The worldwide energy demand is growing quickly, with an anticipated growth rate of 48% from 2012 to 2040. Consequently, investments in all forms of renewable energy generation systems have been growing rapidly due to growth rate and climate concerns. Increased use of clean renewable energy resources such as hydropower, wind, solar, geothermal, and biomass is expected to noticeably alleviate many present environmental concerns associated with fossil fuel-based energy generation. In recent years, wind and solar energies have gained the most attention among all other renewable resources. As a result, both have become the target of extensive research and development for dynamic performance optimization, cost reduction, and power reliability assurance. The performance of Photovoltaic (PV) systems is highly affected by environmental and ambient conditions such as irradiance fluctuations and temperature swings. Furthermore, the initial capital cost for establishing the PV infrastructure is very high. Therefore, it is essential that the PV systems always harvest the maximum energy possible by operating at the most efficient operating point, i.e. Maximum Power Point (MPP), to increase conversion efficiency to reach 100% and thus result in lowest cost of captured energy. The dissertation is an effort to develop a new PV conversion system for large scale PV grid-connected systems which provides 99.8% efficacy enhancements compared to conventional systems by balancing voltage mismatches between the PV modules. Hence, it analyzes the theoretical models for three selected DC/DC converters. To accomplish this goal, this work first introduces a new adaptive maximum PV energy extraction technique for PV grid-tied systems. Then, it supplements the proposed technique with a global search approach to distinguish absolute maximum power peaks within multi-local peaks in case of partially shaded PV module conditions. Next, it proposes an adaptive MPP tracking (MPPT) strategy based on the concept of model predictive control (MPC) in conjunction with a new current sensor-less approach to reduce the number of required sensors in the system. Finally, this work proposes a power balancing technique for injection of balanced three-phase power into the grid using a Cascaded H-Bridge (CHB) converter topology which brings together the entire system and results in the final proposed PV power system. The developed grid connected PV solar system is evaluated using simulations under realistic dynamic ambient conditions, partial shading, and fully shading conditions and the obtained results confirm its effectiveness and merits comparted to conventional systems. The resulting PV system offers enhanced reliability by guaranteeing effective system operation under unbalanced phase voltages caused by severe partial shading

Power Converters in Power Electronics

In recent years, power converters have played an important role in power electronics technology for different applications, such as renewable energy systems, electric vehicles, pulsed power generation, and biomedical sciences. Power converters, in the realm of power electronics, are becoming essential for generating electrical power energy in various ways. This Special Issue focuses on the development of novel power converter topologies in power electronics. The topics of interest include, but are not limited to: Z-source converters; multilevel power converter topologies; switched-capacitor-based power converters; power converters for battery management systems; power converters in wireless power transfer techniques; the reliability of power conversion systems; and modulation techniques for advanced power converters

Design and Control of Power Converters 2019

In this book, 20 papers focused on different fields of power electronics are gathered. Approximately half of the papers are focused on different control issues and techniques, ranging from the computer-aided design of digital compensators to more specific approaches such as fuzzy or sliding control techniques. The rest of the papers are focused on the design of novel topologies. The fields in which these controls and topologies are applied are varied: MMCs, photovoltaic systems, supercapacitors and traction systems, LEDs, wireless power transfer, etc

Delta STATCOM with partially rated energy storage for intended provision of ancillary services

This thesis presents research on two distinct areas, where the work carried out in the first half highlights the challenges posed by the declining system inertia in the future power systems and the potential capability of the energy storage systems in bridging the gap, supporting a safe and reliable operation. A comparison of various energy storage technologies based on their specific energy, specific power, response time, life-cycle, efficiency, cost and further correlating these characteristics to the timescale requirements of frequency and RoCoF services showed that supercapacitors (SC) and Li-ion batteries present the most suitable candidates. Results of a network stability study showed that for a power system rated at 2940 MVA with a high RES contribution of 1688 MVA, equating to 57% of the energy mix, during a power imbalance of 200 MW, an ESS designed to provide emulated inertia response (EIR) in isolation required a power and energy rating of 39.54 MW and 0.0365 MWh respectively. Similarly, providing primary frequency response (PFR) on its own required a power and energy rating of 114.52 MW and 2.14 MWh respectively. ESS providing these services in isolation was not able to maintain all the frequency operating limits and similar results were also seen in the case of the recently introduced Dynamic Containment service. However, with the introduction of a combined response capability, a significantly improved performance, comparable to that of the synchronous generators was observed. In order to maintain the RoCoF and the statutory frequency limit of 0.5 Hz/s and ±0.5 Hz respectively, an ESS must be able to respond with a delay time of no more than 0.2 seconds and be able to ramp up to full response within 0.3 seconds (0.5 seconds from the start of contingency) for a frequency deviation of ±0.5 Hz. The second half of the thesis focused on investigating the current state-of-the-art power conversion system topologies, with the objective of identifying a suitable topology for interfacing ESSs to the grid at MV level. A delta-connected Modular Multilevel STATCOM with partially rated storage (PRS-STATCOM) is proposed, capable of providing both reactive and active power support. The purpose is to provide short-term energy storage enabled grid support services such as inertial and frequency response, either alongside or temporarily instead of standard STATCOM voltage support. The topology proposed here contains two types of sub-modules (SM) in each phase-leg: standard sub-modules (STD-SMs) and energy storage element sub-modules (ESE-SMs) with a DC-DC interface converter between the SM capacitor and the ESE. A control structure has been developed that allows energy transfer between the SM capacitor and the ESE, resulting in an active power exchange between the converter and the grid. A 3rd harmonic current injection into the converter waveforms was used to increase the amount of power that can be extracted from the ESE-SMs and so reduce the required ESE-SMs fraction in each phase-leg. Simulation results demonstrate that for three selected active power ratings, 1 pu, 2/3 pu, & 1/3 pu, the fraction of SMs that need to be converted to ESE-SMs are only 69%, 59% & 38%. Thus, the proposed topology is effective in adding real power capability to a STATCOM without a large increase in equipment cost. Furthermore, modifying the initially proposed topology with the use of Silicon Carbide (SiC) switching devices and interleaved DC-DC interface converter with inverse coupled inductors resulted in similar efficiencies when operated in STATCOM mode.Open Acces

Power Converter of Electric Machines, Renewable Energy Systems, and Transportation

Power converters and electric machines represent essential components in all fields of electrical engineering. In fact, we are heading towards a future where energy will be more and more electrical: electrical vehicles, electrical motors, renewables, storage systems are now widespread. The ongoing energy transition poses new challenges for interfacing and integrating different power systems. The constraints of space, weight, reliability, performance, and autonomy for the electric system have increased the attention of scientific research in order to find more and more appropriate technological solutions. In this context, power converters and electric machines assume a key role in enabling higher performance of electrical power conversion. Consequently, the design and control of power converters and electric machines shall be developed accordingly to the requirements of the specific application, thus leading to more specialized solutions, with the aim of enhancing the reliability, fault tolerance, and flexibility of the next generation power systems