Number Of Power Converters Research Articles

Review of Grid Stability Assessment Based on AI and a New Concept of Converter-Dominated Power System State of Stability Assessment

Artificial intelligence (AI) has been increasingly used for power system stability assessment due to its fast evaluation speed compared to conventional time-domain methods. This paper reviews four types of classic grid stability assessment (GSA) methods based on AI in the recent literature firstly where different AI algorithms from the literature are summarized and compared. Moreover, as the number of power converters using grid forming control intensively increases in the modern system, the influence of the converter parameters on grid stability needs to be investigated. In this context, the concept of the converter-dominated power system state of stability (CDPS-SOS) assessment based on AI is qualitatively discussed. The CDPS-SOS assessment can reveal the system stability margin by considering the converter control parameters and grid bus voltages. Overall, this paper aims to give an overview of AI-based stability assessment for the traditional grid and to provide a new stability assessment concept and inspiration for solving the challenges of future converter-dominated grids.

A Unified Power Converter for Solar PV and Energy Storage in dc Microgrids

This paper deals with the development and experimental validation of a unified power converter for application in dc microgrids, contemplating the inclusion of solar photovoltaic (PV) panels and energy storage systems (ESS), namely batteries. Considering the limitations presented by the current structure of the power grid, mostly highlighted by the accentuated integration of emerging technologies (ESS, renewables, electric vehicles, and electrical appliances that natively operate in dc), it is extremely pertinent to adopt new topologies, architectures, and paradigms. In particular, decentralized power systems, unified topologies, and correspondent control algorithms are representative of a new trend towards a reduction in the number of power converters. Thus, the developed solution is designed to operaSAVE-15te at a nominal power of 3.6 kW, with a switching frequency of 100 kHz, and in four operation modes concerning power flow: (i) solar PV panels to batteries (PV2B); (ii) solar PV panels to dc grid (PV2G); (iii) batteries to dc grid (B2G); (iv) dc grid to batteries (G2B). Moreover, a dual active bridge converter guarantees galvanic isolation, while two back-end dc–dc converters are responsible for interfacing solar PV panels and batteries. The experimental validation of the proposed unified power converter proves its application value to self-consumption production units.

The performances of partial shading adjuster for improving photovoltaic emulator

A photovoltaic (PV) emulator (PVE) is essential equipment for the research and diagnostic of PV generation. It is a convenient, highly efficient, and low-cost approach when compared to controllable light sources. Nonetheless, the implementation of the partial shading capability in a PVE is highly limited in terms of efficiency, computation burned, number of power converters, and flexibility to change in the ambient condition. This paper proposes a partial shading adjuster for a PVE that can overcome the aforementioned limitations. The adjuster is applicable to the conventional PVE since it is based on an algorithm that can be added to the controller of the PVE. By adding the adjuster, the conventional PVE can emulate partial shading. The partial shading adjuster is added into a PVE that uses the direct referencing control strategy with the buck controller regulated by the proportional-integral controller. The results show that the PVE maintains its accuracy and produces a stable output voltage and current during the load changes when the adjuster is added. In conclusion, the proposed partial shading adjuster able to improve th

Economic Evaluation of DC Smart House Groups Considering Electric Vehicle Operation Patterns

Smart houses, which have installed on-site distributed generators such as photovoltaics and batteries and manage their own energy usage using information technology, are being studied and developed around the world. Most of the facilities in a smart house are operated as DC systems; however, conventional supply systems are AC. Moreover, the number of electric vehicles (EV), which also need DC power, have been increasing on the residential side. Therefore, a DC power supply system for smart houses can reduce the number of power converters, conversion losses, and electric charges. The initial and running costs of DC- and AC-based smart houses were calculated under various conditions in this paper. It was concluded that DC-based smart houses have lower costs than AC-based ones regardless of the AC/DC ratio in the load and in the use of EV.

Power flow control of hybrid micro-grids using modified UIPC

This work introduces a replacement advent for power flow control of interconnected AC-DC micro-grids in hybrid micro-grids connected to grids. It also supports implementing an Adaptive Neuro Fuzzy Inference System (ANFIS) controlled modified Unified Inter-Phase Power Controller (UIPC). For study, a classic hybrid micro-grid connected to grid comprising of a AC micro-grid and a DC micro-grid is taken into account. These micro-grids are interconnected employing a modified UIPC, rather than using the power converters connected in parallel. As the first input of this paper is the standard structure of UIPC, which used three power converters in every phase. It was then modified such as number of power converters is used less and implemented for the control of the exchange of power between AC-DC micro-grids. In every phase there is one power electronic converter in the improved structure. It is called as Line Power Converter (LPC). Also there is Bus Power Converter (BPC) to regulate the voltage of the DC bus. The Line Power Converters links the AC micro-grid to the main grid. The DC buses are also linked with them. It can be operated in Inductance Mode (IM) as well as Capacitance Mode (CM). The control structure of LPCs has an Adaptive Fuzzy Logic Controller in it. For hybrid micro-grids, the capability of the suggested power flow control strategy is confirmed by the MATLAB simulation results.

A Study on the Improvement of Parallel Operation Characteristics of DC/DC Converter Using Improved Full-Duplex Communication Hardware

Recently, as dependence and demand for electricity are rapidly increasing in all areas, including industry, methods for increasing capacity and reliability through parallel operations have been studied. In general, Modbus communication method with RS485 is used as a method of parallel operation for capacity increase. However, this method has a disadvantage in that it is a half-duplex communication system that cannot transmit and receive at the same time. However, the Modbus communication method is a half-duplex communication system where physical transmission and reception cannot be performed simultaneously. Therefore, as the number of power converters performing parallel operation increases, the communication period increases, which affects the power quality due to the decrease in control speed. Therefore, in this paper, we propose a hardware that can achieve a full-duplex communication method by a communication signal level to improve power quality. The characteristic of the proposed communication hardware is that the transmitter generates two-level signals for data transmission, but the receiver generates three-level electrical signals according to the state of the transmission data generated by the receiver. The generated three-level electrical signal is characterized in that the data transmission signal information of the transmitter and the data transmission signal information of the receiver occur at the same time. As a result, the communication speed is reduced by more than twice, which improves the power quality by improving the control characteristics when performing parallel operation.

Cyber Security in Control of Grid-Tied Power Electronic Converters—Challenges and Vulnerabilities

Grid-tied power electronic converters are key enabling technologies for interfacing renewable energy sources, energy storage, electrical vehicles, microgrids, and high-voltage dc transmission lines with the electrical power grid. As the number of power converters in modern grids continually increases, their monitoring and coordinated control in a way to support the grid have become topics of increased practical and research interest. In connection with this, latest standards have also defined a mandatory set of control parameters for grid-tied converters, which should be adjustable by a remote entity that sends commands through a communication network. While such a remote control capability allows many new control functions in grid-tied converters, it also renders them vulnerable to cyber-attacks. The aim of this article is first to shed light on the portions of the power converter control systems that are vulnerable to cyber-attacks. Next, typical cyber-attacks are overviewed by considering different applications of the grid-tied converters. Further, the impact of different types of cyber-attacks on grid support functions is studied. Finally, this article is concluded with summary and recommendation for further research.

Single-Phase Bidirectional On-Board Charger Using Starter Generator System in Hybrid Electric Vehicles

This paper presents the design and control methods of a single-phase bidirectional on-board charger (OBC) using a hybrid starter generator (HSG) and an inverter in a hybrid electric vehicle (HEV). In an HEV, there are a number of components, including the combustion engine, transmission, traction motor, motor controller, OBC, and HSG system. The proposed design reconfigures the HSG system to provide battery-charging capability instead of a conventional OBC based on the use of additional power relays. As a result, the number of power converters is effectively reduced through the replacement of the conventional OBC, and, thus, the power density is increased. This paper also proposes a control method for enabling not only battery charging but also a reactive power support depending on the grid command. Compared with a conventional reactive power compensation method, the proposed method has an advantage because it is located near the principal reactive power source. The simulation and experimental results verify the validity and feasibility of the proposed bidirectional OBC design and its control methods.

Complex non‐linear phenomena and stability analysis of interconnected power converters used in distributed power systems

Distributed power systems are considered to be a key element of future power grids. Their main characteristic is the local production and consumption of energy that is accomplished using a number of power converters that interconnect local sources and loads. In this paper, a current mode controlled dc-dc converter which feeds another current mode controlled dc-dc converter is considered to meet the demands of the load. It shows that the existence of the second converter at the output has destabilising effect on the overall system. Such a system may also exhibit interactions of various types of instability that conventional modeling methods cannot predict. Slow-timescale oscillation in standalone switching converters is usually attributed to the occurrence of a Neimark-Sacker bifurcation of the fundamental periodic orbit of the discrete-time model of the system. But in the studied cascaded system, the underlying mechanism is quite different. This paper fully explains the mechanisms as well as the conditions of the occurrence of such instabilities by employing the analytical and numerical tools of the exact switched model of the system. These results can be useful for developing design guidelines to avoid such problems. Finally, the results have been validated experimentally.

Analysis of Turbine Generator Shaft Torsional Vibration Caused by Self‐Commutated Converters

SUMMARYThis paper presents a simple analysis tool for torsional vibration of the rotor shaft of a turbine generator which is interconnected with a power system with self‐commutated converters. The evaluation is based on analysis of measurement data in the field and instantaneous value‐based power system simulation. A number of power converters with large capacity are installed in industrial power systems. Especially, interharmonics originating from self‐commutated converters cause torsional vibration at the rotor shaft of rotating machines. The interaction between rotating machines and converters is known as sub‐synchronous torsional interaction. The resonance between interharmonics from converters and the natural frequency of the rotor shaft causes large torsional vibrations, leading to shaft damage. In this paper, the influence of interharmonics on turbine generators is investigated. If there were air gap torque fluctuations with a frequency near the natural frequency caused by interharmonics, which have frequencies below 100 Hz of the sideband wave caused by asynchronous pulse width modulation, the rotor shaft may be damaged by the torsional vibration. In this paper, the emerging condition of the torsional vibration and the impact on the generator are investigated.

An Improved Power Electronic Controller with Unity Power Factor for a Single-Stage Grid-Tied PV System

A single-stage PV system using Z-source inverter (ZSI) capable of operating in grid-connected mode or stand-alone mode has been developed for extracting power from PV array. For feeding the extracted power to the grid, an analog current controller adjusting the modulation index of ZSI combined with the shoot-through duty ratio has been designed and developed. The proposed system has the advantage of using less number of power converters and can be built with simple controllers. Experiments have been conducted on a PV array consisting of seven PV panels (each rated for 21.2V, 5.17A) connected in series, feeding a 110V single-phase utility grid through ZSI. A hysteresis current controller for varying the modulation index of ZSI has been built using analog ICs. Using MATLAB/Simulink, the complete system has been simulated and the simulation results closely correlate with experimental ones. The efficacy of the proposed scheme with the power being fed to the grid at unity power factor is indicated by the results. It is also proved that the total harmonic distortion of both voltage and current waveforms fed to the grid terminals is less than 5%.

Analysis of Turbine Generator Shaft Torsional Vibration Caused by Self-commutated Converters

SUMMARY This paper presents a simple analysis tool for torsional vibration of the rotor shaft of a turbine generator which is interconnected with a power system with self-commutated converters. The evaluation is based on analysis of measurement data in the field and instantaneous value-based power system simulation. A number of power converters with large capacity are installed in industrial power systems. Especially, interharmonics originating from self-commutated converters cause torsional vibration at the rotor shaft of rotating machines. The interaction between rotating machines and converters is known as sub-synchronous torsional interaction. The resonance between interharmonics from converters and the natural frequency of the rotor shaft causes large torsional vibrations, leading to shaft damage. In this paper, the influence of interharmonics on turbine generators is investigated. If there were air gap torque fluctuations with a frequency near the natural frequency caused by interharmonics, which have frequencies below 100 Hz of the sideband wave caused by asynchronous pulse width modulation, the rotor shaft may be damaged by the torsional vibration. In this paper, the emerging condition of the torsional vibration and the impact on the generator are investigated.

A carrier phase control suitable for conducted EMI noise reduction in a multiple‐converter system

AbstractThe conducted EMI noise flowing from power converters to an AC utility line is regulated by international commissions such as the International Electrotechnical Commission (IEC). Adherence to the IEC regulations requires that EMI filters should be used in power electronics equipment. This paper proposes a method for analyzing conducted EMI noise in multiple power converters connected to the same power line. In this method, the phase difference between subharmonic modulated carrier signals at each power converter is taken into account. The phase difference among the power converters determines the EMI noise level in a multiple converter system, as is evident from the analysis of the waveform of the common mode current. In addition, EMI noise suppression using carrier phase control is proposed. In order to reduce the size of the EMI filter effectively, the phase difference θ should be set to 360/nN°, where n is a high‐order harmonic component near 150 kHz and N is the number of power converters. Therefore, the conducted EMI noise can be reduced effectively with the help of the proposed phase control. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 183(3): 56–66, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21305

Direct Connection of Supercapacitors to Photovoltaic Panels With On–Off Maximum Power Point Tracking

A system dedicated to energy storage is presented. It allows energy storage from photovoltaic panels to a compressed air accumulator. This accumulator is controlled to enable compression and expansion modes under Maximum Efficiency Point Tracking (MEPT). A Maximum Power Point Tracking (MPPT) power converter is as usual connected to the solar cells. An intermediary storage tank consisting of supercapacitors and its associated power converter are inserted as a buffer. They adapt the power extracted from the solar cells under the MPPT condition to the power injected into the hydro-pneumatic system under the MEPT condition. Energy transfer from the solar cells to the hydro-pneumatic system is sequentially operated. The number of cascaded power converters decreases the global efficiency of this hybrid accumulator. This paper introduces a solution that consists of the reduction of the number of power converters. It is obtained by a direct connection of the supercapacitors on the solar panels to lower losses. Taking advantage of the sequential energy transfer, the MPPT mode is kept for the solar panels, as well as the MEPT mode for the hydro-pneumatic accumulator. The general topologies, sizing criteria, and control are presented, as well as considerations on efficiency.

複数の電力変換装置から構成されるシステムにおける雑音端子電圧低減に適したキャリア位相制御法

The conducted EMI noise flowing from power converters to an AC utility line is regulated by international commissions such as the International Electrotechnical Commission (IEC). Adherence to the IEC regulations requires that EMI filters should be used in power electronics equipment. This paper proposes a method for analyzing conducted EMI noise in multiple power converters connected to the same power line. In this method, the phase difference between subharmonic modulated carrier signals at each power converter is taken into account. The phase difference among the power converters determines the EMI noise level in a multiple converter system, as is evident from the analysis of the waveform of the common mode current. In addition, EMI noise suppression using carrier phase control is proposed. In order to reduce the size of the EMI filter effectively, the phase difference θ should be set to 360/nN°, where n is a high-order harmonic component near 150 kHz and N is the number of power converters. Therefore, the conducted EMI noise can be reduced effectively with the help of the proposed phase control. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 183(3): 56–66, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21305