Power quality improvement in wind-solar hybrid system using solid state transformer

A Solid-State Transformer as Enabling Technology for Microgrids for Integration into the Power Distribution System: An Overview

Solid State Transformer (SST) is a new type of power transformer based on power electronic converters and high frequency transformers. The SST realizes voltage transformation, galvanic isolation, and power quality improvements in a single device. In the literature, a number of topologies have been introduced for the SST. In this work, employing a modular multilevel converter, a new SST topology is introduced which provides not only high-voltage AC (HVAC), low-voltage AC (LVAC) and low-voltage DC (LVDC) ports, but also high-voltage DC (HVDC) port. Besides, the proposed topology is easily scalable to higher voltage levels.

This paper focuses on the development of a protection scheme for a smart distribution system containing DERs (Distributed Energy Resources) and Solid State Transformers (SSTs). First, the paper describes the fault analysis that needs to be conducted on such systems. Then, a communication assisted protection scheme is proposed, in order to overcome the shortcomings observed in the conventional protection schemes.

Distributed Energy Resources (DERs) installed on low-voltage distribution systems, both utility-owned and nonutility owned may be employed to make improvements to system resiliency and power quality, in addition to simply serving load demand. By selectively dispatching active and reactive power from these existing DERs, improvements in voltage profiles and service availability during adverse events may be achieved. Further benefits can be gained by optimally choosing which DERs to dispatch power from, and the distribution of power from those DERs. For a given operating condition, using Linear Programming methods, optimal power dispatch values for individual DERs can be determined, while considering variables such as voltage gains, losses in the lines and the DERs, and DER reserve capacities. One such optimization technique is developed in this paper, and results from a real-time simulation study on a modified IEEE 13-bus distribution system with three DERs, are being presented. The operation of the optimized DER selection and dispatch algorithm is shown during normal operation of the transmission system when the DERs operate in grid-connected mode. Similar analyses can drive decision making during transmission system failure when the DERs operate in grid-forming or islanded mode.

This paper represents a review of the dynamic voltage restorer for power quality improvement in the electrical distribution system. Over the past 50 years, issues concerning power quality have steadily increased, to prevent the effect of the voltage disturbances, some of the devices are put as a solution to these problems such as distribution static compensator (D- STATCOM), solid-state transformer (SST), uninterruptible power supply (UPS), dynamic voltage restorer (DVR). The DVR is one of the economic solutions to overcome the voltage disturbances like voltage sag/swell and harmonics. It is widely used to mitigate the voltage disturbances in the power distribution system, especially in the medium and low distribution networks. This paper aims to review the implementation of the DVR in the system integrated with renewable energy resources. This is important because the future of electricity business is moving towards renewable energy and also provides a thorough discussion of the typical components, controllers, compensation methods, and the application of DVR. The extensive review of the technology aims to ease and speed up the development and the advancement of the DVR in the near future.

Solid state transformers (SSTs) have found widespread power applications in traction locomotives, distribution systems, smart grids, etc., where they are going to replace conventional transformers and associated power enhancement equipments to provide better power quality features and functionalities. An eminent structure of SST comprises of three power conversion stages: input (AC-DC), isolation (DC-DC), and output (DC-AC). Multilevel converters are incorporated in several SSTs for operating at high voltage levels. This paper presents a three phase multilevel converter based SST (MCSST) which contains Cascaded H Bridge (CHB) multilevel converters in its input stage. Most of the reported topologies of MCSST have a common low voltage DC (LVDC) bus and a common control block for the entire SST structure. The presented MCSST consists of three independent phase modules and each phase module is controlled separately. Therefore, the outputs of these modules can be applied to both three phase loads as well as three independent single phase loads. Such a configuration can also be used to operate effectively under unbalanced load conditions. The discussed analysis of the reported work is verified using PSCAD/EMTDC simulation results.

Solid-state transformers (SSTs) operate within the overvoltage and undervoltage limits to ensure safety and power quality (prevent overmodulation). This constrained region of operation creates a reserve of available energy in the system, which is primarily stored in the multiple dc-link capacitors. The energy reserves in the system are essential during load transients as the initial energy demand is compensated by the dc-link capacitors. This article presents a detailed analysis of the energy distribution during load transients for different SST control strategies and the impact of control gains. Subsequently, a reserved-energy-aided control parameter design approach is proposed that effectively distributes the stored energy of the capacitors within prescribed operating limits for a safe and controllable operation. The proposed design approach expands the operational range of SSTs, allowing them to handle larger variations in load power compared to conventional control design strategies. The results are validated on a single-phase, two-stage, two-string 230-V/250-V 1-kVA 50-kHz SST system.

Power Quality Improvements in Wind Based DG Systems using Solid State Transformer

The use of nonconventional power supplies featuring unstable quality of the electricity produced and fluctuations in the output power, on the one hand, and the availability of various consumers connected to power supply grids, on the other hand, are factors that give rise to phase unbalances in the grids. These circumstances complicate the operation of smart grids, especially in microgrids. One of possible ways to improve the quality of smart power supply grids is to use a three-stage solid-state transformer with galvanic isolation and two DC links, an arrangement that makes it possible to connect power supply sources and consumers, and to arrange backup storage of electricity in storage batteries. The aim of the study is to analyze the electric power quality at the output of a three-stage solid-state transformer powered by an unbalanced three-phase voltage source. The study was carried out by numerical modeling using the Matlab/Simulink software package. The modeling parameters are given, and the current and voltage waveforms at the solid-state transformer output are obtained. Phasors of the input and output voltages are constructed with expanding them into zero-, positive-, and negative sequence harmonic components. The harmonic distortion coefficients for current and voltage in each phase, and the voltage unbalance coefficients for the zero and negative sequences at the solid-state transformer input and output are determined using the method of symmetric components. It has been shown that by using solid-state transformers it becomes possible to obtain noticeably better quality of electric energy and eliminate the unbalance to the levels stipulated by the relevant state standard. It is shown that solid-state transformers are a promising technology as part of smart power supply grids, which opens the possibility to control and adjust power supply parameters, improve the power supply quality, distribute power flows between the sources and consumers, and integrate DC and AC grids of various voltage and power levels.

Conventional voltage regulation strategies that use reactive or active power injection are ineffective in active distribution networks (ADNs) used as conventional power systems. This paper proposes a new way to operate solid-state transformers (SSTs) to improve voltage quality in active distribution networks (ADNs). The proposed control method uses the unused capacity of SSTs to regulate voltage in ADNs without adding any new hardware or overloading the SST. Since SSTs can participate in voltage regulation via reactive and active power control with the proposed method, they can be operated as “enhanced smart inverters” rather than smart inverters that provide voltage regulation service by reactive power regulation. In this paper, the fundamentals of the proposed method are explained and its effectiveness is confirmed with simulation results obtained from an IEEE 13 node test feeder modeled in MATLAB/SIMULINK.

A major portion of a power system's total performance and energy loss is attributable to voltage profiles and power losses in electrical distribution networks (DNs). Enhancing voltage profiles and lowering network losses can result in a more efficient power grid. In the literature, reactive power support has been used with a number of devices to improve DN performance. Some examples are shunt capacitor banks, distribution static compensators (DSTATCOM), and universal power quality condensers (UPQC). A solid-state transformer (SST) that can be built to support the grid has recently attracted a lot of attention. In particular, the SST is being looked at as a possible replacement for the more common fundamental frequency transformer. This paper suggests using the SST's stage-I reactive power support (SI-RPS) function to reduce radial DN losses and improve the voltage profile of the network. With the competing goals of reducing network losses and improving the voltage profile, a planning strategy is given for putting SST installations in the right places and at the right sizes. The simulation results verified the viability and rationale of the suggested model and algorithm for the 69-bus RDN. The outcomes of a number of different situations are detailed in this work. The code for solving the mixed-integer non-linear programming model was developed in MATLAB R2020a. Increasing SST deployment demonstrated an improvement in the voltage profile of the network, along with cutting down on losses significantly.

Purpose: This paper aims to enhance the design of Solid-State Transformers (SSTs) operating at medium and high frequencies (MF/HF) by optimizing key performance attributes such as efficiency, power density, and thermal management through the use of advanced nanocrystalline materials. Design/Methodology/Approach: An interactive MATLAB-based magnetic characterization tool was utilized to evaluate transformer core losses and efficiencies with various core materials. A hybrid optimization methodology integrating L9 Taguchi design and Response Surface Methodology (RSM) was employed to design a 2 kVA, 20 kHz, 600/60 V shell-type SST. Design parameters such as duty cycle, window utilization factor, insulation material, and core series were optimized across three levels to achieve minimal losses and maximum efficiency. Research Limitations/ Implications: While the study demonstrates promising results, the research is limited to a specific transformer rating and operating frequency, indicating a need for further exploration across varying ratings and frequencies. Practical Implications: The findings contribute to the development of efficient and compact SSTs, benefiting renewable energy systems, electric vehicle charging, grid-connected converters, and compact power supplies by ensuring reduced thermal stress and enhanced durability. Originality/Value: This research highlights the efficacy of integrating advanced nanocrystalline materials and hybrid optimization methodologies in SST design, offering substantial improvements in energy efficiency and operational reliability, thus contributing valuable insights to transformer design and application fields. Major Findings: The optimized Solid-State Transformer (SST) design achieved an impressive efficiency of 99.5832% with core and winding losses of 6.2391 W and 2.2457 W, respectively. The temperature rise was minimized to 11.4541°C, confirming the effectiveness of the hybrid optimization approach. Validation through fuzzy inference systems demonstrated robust alignment with both theoretical and experimental results.

The escalating global energy requirement, driven by population expansion and industrial development, has been met through traditional energy resources till now, many of which are now impending depletion. Renewable energy sources, specifically photovoltaic (PV) and wind power, have emerged as viable and sustainable options to fossil fuels. These systems are praised for their reliability, scalability, and cost-effectiveness, making them integral to modern energy frameworks. However, the integration of PV and wind power systems and power electronics-based loads introduces harmonic distortions, posing critical challenges to power quality and system stability. Addressing these concerns is imperative for realizing the full potential of renewable energy systems in sustainable energy development. To meet these concerns, this research proposes an ANN based DSTATCOM to mitigate power quality concerns in PV-wind power systems. Traditional DSTATCOM control appraches like “synchronous reference frame and instantaneous reactive power” often create challenges in parameter valuation and eficacy under uneven load scenarios. The model designed using XANN approach mitigates harmonics perfectly and showcase better performance even while operating under uneven non-linear loading scenarios. The model simulated using MATLAB and the results are validated using the realtime setup. The outcomes reflects the satisfactory performance interms of enhancing the power quality of the solar-wind systems.

As an important form of receiving renewable energy, microgrids can be a useful supplement to large grids, which can solve the power supply problem of residents in remote mountainous areas, pastoral areas, and islands. Modeling and simulation of energy management for microgrid operation characteristics with wind and solar storage have important practical significance. In this paper, mathematical models of photovoltaic cells and wind power systems are established, simulation models are constructed, and their respective characteristics are simulated and analyzed to verify the correctness of the mathematical models. A simulation model of maximum power point tracking for wind and solar power systems was established based on the respective shortcomings and limitations of independent operation of wind power systems and photovoltaic systems. According to the simulation results, it can be seen that the maximum power control technology used in this system can achieve maximum power tracking for wind power generation systems and photovoltaic power generation systems. The simulation results verify the correctness of the system and the feasibility of the control strategy.

Hybrid renewable energy systems are one among the key areas of research in the fields of sustainable energy in recent times. With the ever-increasing demand in need for energy, renewable sources of energy are much sought after as they are also environment friendly in nature when compared with their non-renewable energy system counterparts. A solar–wind turbine hybrid system is proposed in this research paper, and a generalized predictive controller has been implemented to improve the stability and power quality of the proposed hybrid system. Survey of related works indicates certain limitations in implementing renewable energy systems with respect to stability, reliability and flexibility in fuel which have been effectively addressed in this research article. A three-level inverter has been implemented to fine-tune the power factor which is a combined power factor in the proposed work. A FFT analysis on the power indicates a reduced total harmonic distortion in the proposed work and has been justified over the conventional MPPT-based power generation systems without a properly designed controlling method. The constraints in designing a hybrid system with respect to power quality act as input to the model predictive controller in the proposed work. The work could also be implemented in cascading two or more number of heterogeneous renewable power sources.