Number Of Power Electronic Devices Research Articles

Research on harmonic power flow calculation of novel urban distribution network considering the switching power supply harmonic and the correlation of impedance-frequency

Harmonic power flow calculation is the basis of harmonic analysis, tracing, and treatment. This paper focuses on the harmonic issues associated with the implementation of the “dual-carbon” plan in novel urban distribution networks. Due to the widespread integration of renewable energy generation into urban electrical grids, an increasing number of power electronic devices are being connected to the grid, which has a certain impact on harmonic power flow. Firstly, the harmonic components of 6-pulse and 12-pulse rectifiers are analyzed for the switching power supply model widely used in the distribution network. Secondly, the equivalent parameter models of the generator, the transformer, and the lines are reviewed. Finally, from the perspective of power balance, a harmonic power flow model considering the terminal switching power supplies and the correlation between impedance and frequency is proposed. Simulation verification is conducted to demonstrate the feasibility and accuracy of the proposed method.

A new submodule‐based generalized multilevel inverter topology with reduced switches and DC sources

SummaryMultilevel inverters are known as essential converters in renewable sources. First, in this paper, a new submodule is presented, and based on it, a new sub‐multilevel inverter is presented. The proposed sub‐multilevel inverter consists of several unidirectional and bidirectional switches and DC voltage sources. Then, the generalized topology, developed in two modular and cascaded modes, is presented to increase production levels. The proposed submodules are connected in series in the modular topology, increasing production levels. The proposed topology to produce the maximum output levels has the minimum number of IGBTs, drivers, DC voltage sources, etc. Mathematical analyses for conduction and switching losses are provided, and mathematical analyses for the number of devices and voltage across the switches are also presented. In addition to the mathematical analysis of losses, the simulation results are also presented. A general comparison of proposed topology components is presented to demonstrate their advantages. This comparison shows that the proposed topology has the minimum number of power electronic devices. In this paper, nearest level modulation is used to control the proposed topology. The simulation and experimental results of the proposed sub‐multilevel verify the performance of the proposed topology.

A Two-Level Coordination Strategy for Distribution Network Balancing

Uncertain distributed energy resources and uneven load allocation cause the three-phase unbalance in distribution networks (DNs), which may harm the health of power equipment and increase the operational cost. There are emerging opportunities to balance three-phase DNs with a number of power electronic devices installed in the system. In this paper, we propose a novel two-level coordination strategy to improve the network balancing performance, where soft open points (SOPs) and phase switch devices (PSDs) are hierarchically coordinated in the network. At the upper level, a new type of SOPs with the function of phase switching is designed to explore the cross-phase power transfer ability; at the lower level, PSDs are utilized to flexibly allocate individual loads to specific phases. The two-level coordination strategy is typically formulated as a mixed-integer nonlinear programming (MINLP) problem. To solve the model accurately and efficiently, we develop a successive linearization algorithm to approximate it to a mixed-integer linear programming (MILP) problem at each iteration. On this basis, we propose a heuristic time-independent fixing algorithm to further ease the computational burden by eliminating a large number of integer variables in the MILP problem. Numerical simulations are conducted to validate the effectiveness, accuracy, and efficiency of the proposed method.

Novel Gramian-Based Structure-Preserving Model Order Reduction for Power Systems With High Penetration of Power Converters

Renewable energy and high voltage direct current connections increase the number of power electronic devices in the grid, changing how power systems operate and introducing new dynamic behavior. For this reason, it is fundamental to understand what modeling details are needed to represent the system in this new context. This paper proposes a novel model reduction approach using frequency-limited controllability and observability Gramians that preserves the link between the physical structure of the system and the state variables. This method allows understanding and analytically determining how vital each state is to the input-output behavior in different frequency ranges. The primary contribution of this paper is an algorithm that can provide intuitive results to help power system experts understand the simulation tools and minimum modeling details needed to perform different stability studies. Two case studies supported the applicability of the developed method, and a tool for MATLAB/Simulink was developed based on the findings, allowing visualization and immediate identification of the model components that are most relevant for the system dynamics under study. This tool can analyze dynamic behaviors where the cause is poorly understood and provide clarity around modeling detail requirements in converter-rich power systems.

An efficient iterative optimization-based algorithm for the real-time estimation of harmonics under power system frequency deviations

In current electrical power industry, a great number of power electronic devices produce harmonics. Moreover, the fundamental system frequency of a power line can deviate in the cases of fluctuating and periodically varying loads and transients. This frequency deviation introduces further undesirable frequency components in the spectrum. Correct measurement of harmonics under such system frequency deviations has prominent importance for the protection of power electronics devices. For this goal, this paper proposes a new iterative optimization-based algorithm for the estimation of harmonics in these circumstances. The method is based on time-domain Gauss-Newton optimization of distorted power line signal which attains its parameters directly from the spectrum of the signal by employing local extrema of the corresponding spectrum. In the first phase of the algorithm, the deviated system frequency is estimated. In the second phase, the harmonic components are estimated and fine-tuned correspondingly. Case studies show that the proposed method is robust and precisely estimates deviations in the system’s fundamental frequency and measure the amplitudes of harmonic components very accurately. It requires just a stoppage criterion. The computational assessment of the method also shows its time efficiency in identifying harmonics. Thus, it is a very good candidate for real-time harmonic measurements.

Multi-Port Hybrid DC Circuit Breaker Based on Bridge Commutation Branch

Flexible DC grids have become an important means to support large-scale new energy integration utilization due to their advantages of flexible power control and high efficiency. Flexible DC grids generally consist of multiple converter stations and DC lines. Therefore, there are multiple line intersection points, and DC circuit breakers (DCCBs) need to be installed at the intersection to isolate faults. Multi-port hybrid DCCBs (MPHCBs) based on topology optimization can greatly reduce the cost by replacing multiple two-port DCCBs with one multi-port DCCB at the intersection. However, currently researched multi-port DCCBs still have a high cost and large volume while lacking engineering verification. This paper proposes a hybrid multi-port DCCB based on a bridge commutation branch that greatly reduces the number of power electronic devices used and the cost and volume of the DCCB. First, the topology and control method of the proposed MPHCB are studied, and its cost and reliability are analyzed. Then, the breaking test of the proposed MPHCB based on the bridge commutation branch is carried out at a 15 kV voltage level. The results show that the proposed MPHCB can interrupt a 15 kA current in 3 ms, which verifies the feasibility of the scheme.

Research on active power filter technology

A large number of power electronic devices used and transformed for the electrical energy in the grid has improved the characteristics and economic efficiency of the utility grid of the power system, but the nonlinear load components make the harmonic pollution in the grid more and more serious, which reduces the power quality of the power supply network. An active filter model based on ip-iq algorithm and PI control strategy is proposed and simulated to show that the filter can compensate for reactive power factor and harmonics and effectively suppress harmonics.

Research on control strategy of photovoltaic hydrogen generation system based on Fuzzy PI control

Under the goal of carbon peak and neutrality, the search for efficient and clean green energy has attracted widespread attention. Photovoltaic (PV) hydrogen production has become a research hotspot because of its clean and near-zero carbon emissions. However, due to the influence of natural light, PV power generation is volatile and intermittent, reducing the system’s stability. In order to improve the stability of the system, a large number of power electronic devices and control strategies are applied to the PV hydrogen production system. Among them, the Buck circuit using proportional–integral (PI) control is the most widely used. However, the PI control has a long response time and large ripple, which affects the energy efficiency of PV hydrogen production. This paper proposes a PV hydrogen production system control strategy based on Fuzzy PI control. In the Matlab/Simulink environment, a simulation model of a PV hydrogen production system composed of PV cells, proton exchange membrane electrolyzers, and DC/DC units is built. The DC/DC unit uses a Buck circuit. Simulation analysis compares the output voltage and current ripple of the PV hydrogen production system model under different working conditions using the Fuzzy PI control and classical PI control strategies. Finally, the simulation results verify that the proposed control strategy reduces the system output voltage and current ripple.

A unified decentralized framework for isolated interlinking converters of hybrid DC/AC microgrids

Due to the advantages of effectively integrating diversified loads and renewable sources, hybrid DC/AC microgrids have attracted the common attention of industry and academia. Meanwhile, with the increasing number of power electronic devices connected to the system, the complexity of the system increases, which puts forward higher requirements for galvanic isolation and intelligent control methods. This study proposes a unified decentralized framework for isolated interlinking converters (IICs) in hybrid DC/AC microgrids, which include topology and a control strategy to solve the aforementioned problems. Firstly, in terms of topology, a dual active bridge (DAB) converter is adopted to realize galvanic isolation and DC voltage conversion, which can facilitate the interconnection of DC microgrids or be combined with VSC for the interconnection of DC and AC microgrids. Secondly, in terms of the control strategy, a bidirectional voltage–supporting control strategy is proposed for IICs, in which the frequency and voltage are adopted as the indications to balance the power and strengthen the inertia interaction of microgrids. Furthermore, with the proposed control strategy, the voltage sources of different microgrids can share the power fluctuation, cooperatively. The stability of the proposed strategy is analyzed, and the effectiveness is verified by several HIL experiments.

An Improved Quantitative Analysis Method of Oscillation Mode for DFIG-Based Wind Power Base With LCC-HVDC Transmission Considering Frequency Coupling Characteristic

The line-commutated converter-based high-voltage direct-current (LCC-HVDC) transmission has become one of the main forms to deliver wind power in China. However, due to the connections of a large number of power electronic devices (PEDs), there emerges a risk of sub/super-synchronous oscillations in the DFIG-based wind power base with LCC-HVDC transmission. The existing multi-node system analysis methods have ignored the frequency coupling characteristic (FCC) of PEDs, unable to obtain accurate oscillation characteristics. Besides, the relationship between the oscillation and multi-level factors has not been revealed yet. Therefore, this paper proposes an improved quantitative analysis method of oscillation mode which considers the FCC on the basis of the system admittance network model. Firstly, the impedance model of the system considering the FCC is established. Then, the improved quantitative analysis method of the oscillation mode considering the FCC is proposed and its steps are as follows. 1) To establish the system transfer function matrix considering the FCC, and determine the system stability accurately by the dominant oscillation mode; 2) To define the node oscillation participation factor, considering the effect of the coupling frequency, and quantify the participation degree of each node and identify the origin and weak point of oscillation; 3) To carry out multi-level oscillation mode sensitivity analysis. Finally, the oscillation characteristics and laws of the DFIG-based wind power base with LCC-HVDC transmission are studied, and the time-domain simulations in MATLAB/Simulink validate the analytical results.

Study on Quantitative Evaluation Index of Power System Frequency Response Capability

Frequency stability is an important factor for the safety and stability of the power system operation. In a traditional power system, the operation stability is ensured by the inertia response, primary frequency modulation, and secondary frequency modulation. In recent years, in order to achieve the goal of carbon neutralization and carbon peaking, China has made great efforts in new energy development. With large-scale new energy connected to the power grid, the proportion of traditional conventional synchronous units has gradually declined. At the same time, a large number of power electronic devices have been used in the power grid, which led to the capability decline of the inertia response and primary frequency modulation. For example, the East China Power Grid has experienced a sharp frequency drop in such an environment. In order to solve the above problems, the operation principle and control mode of various new energy resources are analyzed in this paper. Moreover, the process and principle of power grid frequency response are studied and the evaluation index of frequency response capability is proposed. The research results can quantitatively evaluate the system inertia response and primary frequency modulation level and provides a judgment tool for dispatching operators and system planners.

Half‐bridge Z‐source inverter based on T‐source configuration with continuous input current and a high boost factor

SummaryThis paper proposes a new half‐bridge‐based impedance source inverter with coupled T‐shaped inductors. The proposed inverter has a continuous input current and a high boost factor. The proposed topology is thoroughly investigated, along with its operating modes and control system, and the boost factor equation is derived. Additionally, the operating modes' results are incorporated into the design of used components, such as capacitors and inductors. To determine the suggested topology's advantages and disadvantages, a comparison with similar topologies is made based on the number of power electronic devices employed, the boost factor, and the voltage stresses experienced by the components. On the base of these comparisons, it is concluded that the proposed half‐bridge‐based Z‐source inverter has a high boost factor, fewer power electronic components, and reduced voltage stresses. Following that, a power loss study is performed to ascertain the system's power losses and overall efficiency. The prototype's experimental results are considered to evaluate the proposed topology's correct performance.

Research on Flexible Virtual Inertia Control Method Based on the Small Signal Model of DC Microgrid

Renewable energy is usually connected to the DC micro-grid by a large number of power electronic devices, which have the advantages of a fast system response, but the disadvantage to reduce the inertia of the system, which makes the stability of the system worse. It is necessary to increase the inertia of DC micro-grid so that it can recover and stabilize well when it receives a disturbance. In this paper, a small-signal model of DC micro-grid with constant power load (CPL) is established, and a flexible virtual inertial (FVI) control method based on DC bus voltage real-time variation is proposed, by controlling the DC/DC converter of the energy storage system, the problem of system oscillation caused by introducing voltage differential link to the system is solved. Compared with the droop control method, the FVI control method can increase the inertia of DC micro-grid system, reduce the influence of small disturbances, and improve the stability of the system. Finally, the validity of the FVI control method based on small signal model is verified in dSPACE.

Bidirectional Converter for Plug-In Hybrid Electric Vehicle On-Board Battery Chargers with Hybrid Technique

Recently, Plug-in Hybrid Electric Vehicles (PHEVs) have gathered a lot of attention by integrating an electric motor with an Internal Combustion Engine (ICE) to minimize fuel consumption and greenhouse gas emissions. The On-Board Chargers (OBCs) are selected in this research because they are limited by dimensions and mass, and also consume low amounts of power. The Equivalent Series Resistance (ESR) of a filter capacitor is minor, so the zero produced by the ESR is positioned at a high frequency. In this state, the system magnitude gradually drops, causing a ripple in the circuit that generates a harmful impact on the battery’s stability. To improve the stability of the system, a Neural Network with an Improved Particle Swarm Optimization (NN–IPSO) control algorithm was developed. This study establishes an isolated converter topology for PHEVs to preserve battery-charging functions through a lesser number of power electronic devices over the existing topology. This isolated converter topology is controlled by NN–IPSO for the PHEV, which interfaces with the battery. The simulation results were validated in MATLAB, indicating that the proposed NN–IPSO-based isolated converter topology minimizes the Total Harmonic Distortion (THD) to 3.69% and the power losses to 0.047 KW, and increases the efficiency to 99.823%, which is much better than that of the existing Switched Reluctance Motor (SRM) power train topology.

Design and fabrication of an interleaved high step‐up DC–DC converter with soft‐switching capability to implement in renewable energy systems

AbstractThis paper presents a soft‐switching non‐isolated interleaved high step‐up topology to implement in renewable energy systems. By using low number of power electronic devices and incorporation with the coupled inductors (CIs) and built‐in transformer (BIT), simultaneously, mixed with a voltage multiplier cell (VMC), an ultra‐large gain can be obtained. In addition, the interlevead structure in the input side causes to diminish the input current ripple. Moreover, the automatic current sharing is another characteristic of the proposed converter. The voltage stresses across power semiconductors are decreased by increasing the turns ratio of the implemented CIs and BIT and also reverse recovery losses are attenuated which improves the efficiency. Furthermore, zero‐current‐switching (ZCS) condition for diodes is achieved at turn off instant, due to the leakage inductances of the magnetic means. Also, power MOSFETs are switched with zero‐voltage‐switching (ZVS) performance by adding active clamp. A 600‐W experimental prototype with 24‐V input to 400‐V output voltage at a switching frequency of 100 kHz is built and tested to examine the merits of the proposed topology

A data-driven probabilistic harmonic power flow approach in power distribution systems with PV generations

Large-scale electrification in the end-user and renewable energy fields is one of the key pathways to achieving carbon neutrality by 2050. Meanwhile, a large number of power electronic devices are used in residential, commercial, and office loads and photovoltaic (PV), which leads to the power quality harmonics in the power distribution system (PDS) becoming more prominent than ever before. Due to the nature of the random behavior of users and random changes in external factors, e.g., illumination and temperature, the harmonics in the PDS are strongly random and time-varying, which makes it hard to evaluate and mitigate the harmonics using the individual deterministic harmonic power flow (HPF) approach. This paper proposes a data-driven piecewise probabilistic HPF method for the PDS with PVs. First, a data-driven piecewise probabilistic harmonic cross coupling model is proposed for analyzing the harmonics generated by different harmonic sources, and the probabilistic and time-varying features can be manifested via this model. Moreover, this proposed harmonic model has a certain predictive capability. Then, the decoupled method based on graph theory and injection current is developed for computing the HPF. Finally, a field theory-based piecewise probabilistic HPF is applied for assessing the probabilistic harmonics of the PDS with PVs. Actual measurements for various harmonic sources and simulations in three different sizes of IEEE systems validate the precision, effectiveness, and efficiency of the proposed models and methods.

Modelling and design of parameters for fast simulation of electromagnetic transient in AC / DC hybrid microgrid

AC/DC microgrids contain a large number of power electronic devices, and their frequent switching process will bring a huge amount of calculation to the electromagnetic transient simulation, thus reducing the simulation efficiency. The research on the external characteristics of the microgrid does not need to pay attention to the dynamic process inside the converter. Therefore, the equivalent simplification of mathematical model is used in this paper to reduce the amount of simulation calculation data of the electromagnetic transient model to achieve the purpose of improving simulation efficiency. This method is concise and efficient, which does not relay on the performance of computer or change the program algorithm of software. By simplifying the current loop with fast dynamic response in the control system, he time response capability of the model is improved, and the converter is replaced by a controlled voltage source, which reduces the dynamic process of frequent changes in the converter. Based on the mathematical equivalent simplified model of microgrid, an electromagnetic transient simulation model was established. Through simulation verification, the simulation efficiency can be significantly improved while the accuracy of the simulation results is guaranteed.

Analysis for magnetic field disturbance of hybrid DC circuit breaker during breaking

The high current of hybrid DC circuit breaker (HCB) in the process of breaking generates strong transient magnetic field (MF), which may interfere with the normal operation of driver control units (DCUs). Therefore, the analysis for transient MF disturbance is of great significance. Due to the large space scale of HCB, with the large number of power electronic devices, the numerical calculation method has the disadvantages of large consumption of resources and slow calculation speed in solving the transient MF inside the HCB. In this study, the current generation mechanism of a 500 kV HCB is analysed, and the equivalent current path is obtained by considering the skin effect. Combined with the temporal and spatial distribution of transient current, the multi-process transient equivalent model of transient MF calculation is established, and the model has the advantages of high precision and high speed. Then, the breaking experiment of HCB is carried out, and the transient MF near the DCU is measured. The experiment results verify the validity of the model. Furthermore, the disturbance of transient MF at the DCU of the transfer branch during breaking 25 kA current is analysed.

Estimation of Power Losses Caused by Supraharmonics

Nowadays increases the number of power electronic devices in distribution electrical networks rapidly. Modern generation and consumption units use high switching frequency power converters for the network connection and therefore cause the voltage and current distortion in the frequency range over 2 kHz (so-called “supraharmonics”) in addition to conventional harmonics. Supraharmonics cause additional power losses in electrical equipment. The goal of the offered paper is the estimation of power losses caused by supraharmonics. The method of the supraharmonic power losses estimation combining the analytic determination of AC cable resistances at the supraharmonic frequencies with the use of measurement results of supraharmonic currents in a real MV/LV cable network is considered in the paper. In the paper is shown that supraharmonic power losses in a MV cable under study can reach the values of several percent with respect to the power losses at the fundamental frequency and can exceed 10% regarding the power losses caused by conventional current harmonics. &nbsp

Architecture Design of Digital Twin Platform for AC&DC Hybrid Transmission System with MMC-HVDC

With the development of power electronic devices, more and more high-power power electronic devices were used in high-voltage DC transmission. The purpose is to improve the stability of grid and the acceptance ability of new energy. The Yu-E flexible DC back-to-back interconnection project is a typical example of this technology. However, due to the large number of power electronic devices and sub modules, it brings many difficulties to the analysis of AC&DC hybrid power system, Especially when there is a lot of new energy penetration. This paper is based on the concept of digital twin, equivalent to the MMC sub-module as a series connection of the power supply and its on-resistance, then based on actual operating parameters and grid planning, a set of digital twin platforms for AC&DC transmission systems with large-scale new energy integration has been established. Comparing the running results of the digital twin model with the actual running state, the method and architecture described in this paper have certain practicability and effectiveness.