Development Of Power Electronic Devices Research Articles

Robust Operation of Flexible Distribution Network With Large-Scale EV Charging Loads

The increasing integration of electric vehicles (EVs) significantly challenges the efficient operation of distribution networks. With the rapid development of power electronic devices represented by soft open point (SOP), flexible distribution networks (FDNs) provide a promising opportunity for integrating large-scale EVs. In this paper, a robust operation method is proposed to improve the economy of EVs and ensure the flexible operation of FDN. First, an EVs-aggregator (EVs-AGG) model is formulated to incorporate diverse charging behaviors. The EVs-AGG is efficiently integrated into FDN through the DC link of multi-terminal SOP. Then, optimal operation strategies are obtained by coordinating EVs charging/discharging power with the regulation of multi-terminal SOP. Furthermore, considering the uncertainties of EVs and photovoltaics, a robust operation framework is established to deal with uncertainties. Finally, case studies based on a practical distribution network indicate that through the interactive power regulation between multi-terminal SOP and EVs-AGG, the proposed method alleviates the negative impacts caused by large-scale EVs integration and improves the operational flexibility of FDN.

Time-Varying Cumulative Damage Recursive Method for Power Semiconductor Devices

Accurate simulation of power semiconductor devices failure process is one of the most important means to clarify the failure mechanism and evaluate the device reliability, which is induced by the associated internal temperature gradient acting on the mismatch of coefficients of thermal expansion between adjacent layers and internal temperature gradients. This paper investigates the microstructure change of the new and replaced modules using the CT scanner, which represents that the void distribution of the die-attach solder layer is an important factor to indicate the reliability status of the power semiconductor devices. A multiple physical field model combining time-varying cumulative damage recursive method is proposed to simulate the damage accumulation and the physical failure process based on mesh automatic updated method and material failure formula. The number of cycles to failure, thermal resistance, and junction temperature extracted from power cycling test results are used to validate the accuracy of the parameter variation. The physical outline of the voids is extracted to prove the consistency of the microstructure change. This method is intended for operational management and also provided the foundation for the design and development of power electronic devices with high power and high reliability.

Reliability issues of GaN HEMT: Current status and challenges

With the development of power electronic devices, there is an increasing demand for energy-saving, emission reduction, and environmental protection. Thus, higher energy conversion efficiency of power electronic devices is required. While traditional Si-based power electronic devices have the disadvantage of low energy utilization efficiency and high thermal losses, GaN-based HEMT has significant advantages, making it a frontier and hotspot in global semiconductor research. However, the failure mechanisms that affect the reliability of GaN HEMTs are not completely comprehended. Many reliability issues affect devices performance, among which electrical reliability and thermal reliability are widely studied concerns. Electrical reliability issues contain inverse piezoelectric effect, hot electron effect, trapping effect, and mental instability. Thermal reliability issues contain self-heating effects, which are caused by the materials unsatisfying thermal conductivity, and improper structure design. This paper is focused on the current research results of the GaN HEMTs electrical reliability and thermal reliability. The first part of this paper gives a review of GaN HEMT reliability issues at their current status, and the second part outlines the challenges of GaN HEMTs in future development. This review will help researchers to better understand factors that affect GaN HEMTs reliability and help with their device design for further research.

A Comparative Study of Flow Boiling Heat Transfer and Pressure Drop Characteristics in a Pin-Finned Heat Sink at Horizontal/Vertical Upward Flow Orientations

Abstract With the continuous development of power electronic devices toward miniaturization and compactness, it is necessary to develop more efficient flow boiling heat transfer technologies. In this work, the flow boiling heat transfer and pressure drop characteristics of Novec649 in a pin finned channel under two kinds of flow orientations (horizontal and vertical upward) are experimentally investigated. Heat flux, inlet flow velocity, and inlet subcooling are considered as the variable parameters. The results show that among all boiling operating conditions, the heat transfer performances between two orientations are basically consistent, while the pressure drop of vertical upward pin finned channel is relatively lower, indicating that the comprehensive flow boiling heat transfer performance of vertical oriented channel is better. Subsequently, a series of flow visualization experiments are performed in vertical upward pin finned channel. With the increase of heat flux, four kinds of flow pattern are discovered in the order of dispersed bubble flow, bubble flow, homogeneous flow, and annular flow. In the region of annular flow, although a vapor flow has already formed in the channel, there is still a large amount of liquid phase surrounding the wall and pin fins. Therefore, no obvious heat transfer deterioration was observed in the pin finned channel. Along the flow direction, the diameter of bubbles will increase first, and then present obvious oscillation. As the heat flux increases, both the average bubble detachment diameter and the frequency increase correspondingly. As the fluid velocity increases, the average bubble detachment diameter presents a downward trend, while the average bubble detachment frequency presents an upward trend.

Orthotropic viscoelastic characterization of thin woven composites by a combination of experimental and numerical methods

Electric mobility is the driving force for the development of power electronic devices embedded in printed circuit boards (PCBs). Fast charge of batteries generates large increase of temperature in PCBs. Therefore, the characterization of the thermo-viscoelastic behavior of laminates is a necessity. Tests have been conducted at elevated temperature, with a specific attention to minimize the oxidation of the material. To model precisely the viscoelastic response of the laminate, since pure resin samples are usually not available, an inverse method based on the comparison of experimental results and finite elements simulations is proposed. Periodic boundary conditions allowing to apply uniaxial tension with an arbitrary orientation are developed. In order to validate this method, resin samples are extracted from pre-impregnated material and tested under the same temperature conditions. In a last step, the cyclic response of a buried hole in a PCB is simulated by finite element calculations, using the identified material data. For large maximum temperature, substantial differences are highlighted between thermo-elastic and thermo-viscoelastic approaches in terms of accumulated plastic strain in the copper barrel. The present work opens new possibilities to model the lifetime of electronic devices facing temperature excursions ranging over the glass transition temperature.

Research on High Harmonic Amplification of 10kV Series Static Var Generator

With the continuous development of power electronic devices and science and technology, cables and rectifiers, inverters, DC transmission equipment, and other nonlinear loads have been widely used in power systems. However, this causes harmonic pollution and large capacitive reactive power, which can affect the safe and stable operation of the power system. Based on the analysis of the reasons for the use of static var generator in the power grid and the existing conditions of even harmonic, the impedance analysis method was used to analyze the abnormal noise event of a transformer in a substation. Firstly, the equivalent impedance model diagram is drawn by the equivalent circuit method, and the equivalent impedance value of the system is calculated. A number of harmonic amplifications and the positions of the resonance point are calculated by MATLAB software. Secondly, the correctness of the above theoretical analysis is verified by field test and simulation model built in ETAP software. Finally, because of the abnormal noise of the transformer in a substation caused by harmonic amplification, three harmonic suppression measures are given.

Space charge characteristics of silicone elastomer for device packaging under positive square wave voltage

AbstractWith the rapid development of power electronic devices towards high voltage and power, the insulation challenges faced by devices have attracted widespread attention. Silicone elastomer is widely used in device packaging as one insulating material, and the study of its insulating properties is helpful to the reliable operation of devices. To this end we obtained the space charge characteristics of silicone elastomer under positive square wave voltage by using the pulse‐electroacoustic (PEA) method. Firstly based on the existing research and IEC standards, the selection criteria of the resistance and capacitance parameters of a PEA system for space charge measurement under square wave voltage are given. Through this experimental system, the space charge distribution under the positive square wave voltage with different waveform parameters is obtained, and the influences of the waveform parameters on the space charge accumulation are analysed. The amounts of charges under the action of square wave voltage with different waveform parameters are calculated, and the influences of waveform parameters on the amounts of charges are analysed. In addition, the reasons for the difference in the accumulation of positive and negative charges are explained through Schottky injection model, the synthesis reaction and the infrared spectrum of the silicone elastomer.

Research and design of high-performance DSP control system based on frequency control

With the rapid development of power electronic devices and microprocessors, AC variable frequency and speed regulating system has also made a breakthrough. The thesis introduces the hardware circuit design based on TMS320F28335, and the result of the experiment proves the SVPWM algorithm is correct. It also does some research on VF control system of the inverter and the result of the experiments proves that the control system achieves the purpose, and has a quick dynamic response.

Modeling of Efficient Control Strategies for LCC-HVDC Systems: A Case Study of Matiari-Lahore HVDC Power Transmission Line.

With the recent development in power electronic devices, HVDC (High Voltage Direct Current) systems have been recognized as the most prominent solution to transmit electric power economically. Today, several HVDC projects have been implemented physically. The conventional HVDC systems use grid commutation converters, and its commutation relies on an AC system for the provision of voltage. Due to this reason, there are possibilities of commutation failure during fault. Furthermore, once the DC (Direct Current) system power is interrupted momentarily, the reversal of work power is likely to cause transient over-voltage, which will endanger the safety of power grid operation. Hence, it is necessary to study the commutation failure and transient over-voltage issues. To tackle the above issues, in this paper, the dynamic and transient characteristics of Pakistan’s first HVDC project, i.e., the Matiari–Lahore ±660 kV transmission line has been analyzed in an electromagnetic transient model of PSCAD/EMTDC. Based on the characteristics of the DC and the off-angle after the failure, a new control strategy has been proposed. The HVDC system along with its proposed control strategy has been tested under various operating conditions. The proposed controller increases the speed of fault detection, reduces the drop of AC voltage and DC and suppresses the commutation failure probability of LCC-HVDC (line commutated converter- high voltage direct current).

High-Performance Five-Phase Axial Flux Permanent Magnet Generator for Small-Scale Vertical Axis Wind Turbine

Commonly, electrical energy is generated by using non-renewable energy such as natural gas, coal, and oil. As electrical energy is a basic asset for the development of a region, its utilization is increasing every year, which causes the existence of non-renewable energy to decrease every year. This issue is becoming a serious concern all over the world, which encourages every country to harness energy from renewable energy. Wind energy is a promising candidate for generating electricity today. In wind turbine generation, a three-phase generator is usually used. Along with the rapid development of power electronic devices and efforts to improve generator performances, the use of a multiphase system is considered important for harnessing energy from the wind more efficiently. In this study, a five-phase system is proposed to upgrade the output power and power density of the most qualified AFPMG in the previous study. The Taguchi optimization method is employed to obtain the lowest total harmonic distortion (THD) of the on-load voltage waveform. In addition to the Taguchi method, an Artificial Neural Network (ANN) is also employed to compare the results from the Taguchi method and the results are proven to have an excellent relationship. The data processed for Taguchi and ANN methods are strongly helped by using the finite element method from the Ansys Maxwell software. The performances of the proposed five-phase axial flux permanent magnet generator (FP-AFPMG) show good improvement, especially in THD, ripple torque, and ripple in the rectified voltage.

A Fast and Accurate Double-Precision Floating Point Format Paralleled Transient Emulator of AC/DC Grids on Heterogeneous CPU-FPGAs

The rapid development of power electronic devices and the complexity of large-scale power systems call for high fidelity real-time electromagnetic transient (EMT) emulators, which can achieve high precision, high accuracy, and real-time realization simultaneously. Compared with traditional emulators, the emulator that adopted high precision and accuracy brings huge amount of extra hardware resource consumption. Therefore, hardly any traditional field-programmable gate array (FPGA) based real-time emulators can achieve the real-time simulation of large-scale systems with restricted hardware resources. To resolve these issues, this article proposed a novel heterogeneous CPU-FPGA hybrid multirate EMT real-time emulator which supports double-precision floating-point format. Several efforts are made to enhance the simulation scale and accuracy of the emulator: 1) a multiple floating-point sets reduction module is proposed on hardware design to achieve small and real-time simulation step such as 2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> s; and 2) time division multiplexing strategy is conducted throughout the calculation to improve the supported simulation scale by 31%. Simulation results have validated that the one Xilinx VC709 FPGA board can achieve a small time-step of 2- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> s real-time realization and the supported scale can be expanded to more than 600 node buses.

Fault Location with High Precision of Flexible DC Distribution System Using Wavelet Transform and Convolution Neural Network

Though flexible DC distribution system (FDCDS) is becoming a new hotspot in power systems lately because of the rapid development of power electronic devices and massive use of renewable energy, the failure to realize accurate fault location with high precision restricts its further application. Thus, a novel precise pole-to-ground fault location method of FDCDS based on wavelet transform (WT) and convolution neural network (CNN) is proposed in this paper for the limitation on the number of measuring points and high difficulty in extracting characteristics of FDCDS. The fault voltage signal is decomposed with multi-resolution by discrete wavelet transform (DWT), and then the transient energy function is constructed to select the frequency bands containing rich fault characteristics for signal reconstruction. The reconstructed signal forms two-dimensional time-frequency images through continuous wavelet transform (CWT), which are used as the input of CNN classifier after image enhancement to form the mapping relation between the fault feature and fault position using the powerful generalization ability of CNN, so as to complete fault location with high precision. The sample data on PSCAD/EMTDC verifies the accuracy and reliability of the proposed method, which can achieve fault location with positioning precision of 30 m. The proposed method overcomes the influence of the control strategy of the converter and the number of input capacitors of the bridge arm in the time-domain analysis, and still has strong robustness in the case that FDCDS is connected with many distributed generations (DGs) with output fluctuation. Furthermore, four other methods for fault location as comparisons are given to reflect the validity and anti-interference ability of proposed methods in various noises.

Design and optimization of a liquid cooled heat sink for a motor inverter in electric vehicles

The rapid development of power electronic devices has made them have higher power density, which puts forward higher requirements for cooling technology. The contribution of this paper is the integrated design of the liquid cooled heat sink for a 30 kW motor inverter considering the distribution of power devices. In order to find an optimal heat sink configuration, the cooling performance of three different configurations of heat sinks was investigated. And the distribution characteristics of the temperature and fluid velocity field were compared and analyzed. The heat sink with serpentine channel configuration was selected due to its best temperature uniformity and cooling characteristic. In addition, the effects of geometric parameters (fin thickness) and flow parameters (flow rate) on cooling performance were further studied. On this basis, the geometrical configuration of the heat sink was optimized. The experimental results of the optimized heat sink are in good agreement with the numerical simulation results. The motor inverter achieves high power density of 9.677 kW/kg.

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.

Control strategy for DC soft open point in large scale distribution networks with distributed generators

Development of power electronic devices and their implementation in power distribution networks significantly improve not only the easier integration of distributed generation into distribution networks but also the further refinement of control algorithms specialized in the application of power management procedures in distribution systems. Implementation of DC Soft Open Points (DCSOP) for closing loops in distribution networks could serve as one of the most representative examples of the use of power electronics devices as a management resources in modern distribution networks. The paper describes the possibilities of application of DCSOP used for loops closure and power flow control in medium voltage distribution networks with integrated distributed generators. Considering all benefits of loops closure and the controllability of the DCSOP, DCSOP has been considered as a management resource capable of achieving the desired/optimal state in the distribution network. The management strategy proposed in this paper covers two cases: the first case where adequate communication infrastructure is available when all DCSOP operation is based on Optimal Power Flow (OPF) calculations, and the second case when OPF results are unavailable for some reason (most often due to communication interruptions) and DCSOP operation is based on processing available data using neural network based algorithm. The proposed management strategy has been implemented and tested on the IEEE 33 distribution test network with integrated distributed generators. The simulation results, described in this paper, can serve not only as a basis for further scientific research but also as a basis for the practical implementation of real controllers based on the proposed algorithm and its application in practice, in real distribution networks.

A Survey on HVDC Power Transmission Systems

Electric power is generated and transported globally by the means of an “Alternating Current” (AC) process. However, there are some applications in which “Direct Current” (DC) power transmission is superior to AC. Problems due to the lack of technology that provides good control and regulation for conversions of DC-to-AC and AC-to-DC hampered deployment of DC power transmission technology. The development of power electronic devices has removed a large portion of restrictions on “High Voltage Direct Current” (HVDC) power transportation. HVDC use has become part of daily use for a long time due to its economic benefits and technical advantages over the “High Voltage Alternating Current” (HVAC) power transmission. The advantages of HVDC make it suitable for power transmission over long distances and for connecting power systems of countries operating at different frequencies. This paper introduces the principles of HVDC, compares the applications of HVDC in the world, and discusses the future improvements needed within this technology.

Robust control of a multi-bus DC microgrid based on adaptive Lyapunov function method

Due to the development of power electronic devices, the DC microgrids are competing AC microgrids, and even in some areas, such as efficiency, reliability, stability, DC microgrids are superior. In spite of mentioned advantages, the main technical challenge related to operation of the DC microgrids is to provide a fast and stable voltage regulation. In this paper, a robust control structure is proposed for multi-bus DC microgrids. Adopting master–slave control strategy, an adaptive voltage control scheme is proposed to robustly maintain the master unit voltage at the nominal value. In addition, an adaptive current controller is designed to robustly regulate the current of all the DG units in the grid-connected mode, as well as the slave units in the islanded mode of operation. All of the controllers are designed based on local measurements and are independent with respect to parameters, dynamic, and topology of the DCMG loads. The control scheme is shown to be stable and robust subject to parametric uncertainties and various types of disturbances. The consistent and effectiveness of the proposed control scheme is demonstrated through simulation studies in MATLAB® software environment.

Engineering practices for the integration of large-scale renewable energy VSC-HVDC systems

With the continuous development of power electronic devices, intelligent control systems, and other technologies, the voltage level and transmission capacity of voltage source converter (VSC)-high-voltage direct current (HVDC) technology will continue to increase, while the system losses and costs will gradually decrease. Therefore, it can be foreseen that VSC-HVDC transmission technology will be more widely applied in future large-scale renewable energy development projects. Adopting VSC-HVDC transmission technology can be used to overcome issues encountered by large-scale renewable energy transmission and integration projects, such as a weak local power grid, lack of support for synchronous power supply, and insufficient accommodation capacity. However, this solution also faces many technical challenges because of the differences between renewable energy and traditional synchronous power generation systems. Based on actual engineering practices that are used worldwide, this article analyzes the technical challenges encountered by integrating large-scale renewable energy systems that adopt the use of VSC-HVDC technology, while aiming to provide support for future research and engineering projects related to VSC-HVDC-based large-scale renewable energy integration projects.

Enhanced Z-source inverter-based voltage frequency generator to conduct induced over voltage test on power transformers

Transformer is said to be the heart of an electrical power system. Testing of transformer is required, as it is an indication of the extent to which a transformer is able to comply with the customer's specified requirements and the respective standards. Before the development of power electronic devices, motor generator set was used to generate the required voltage and frequency to conduct the induced over voltage test on power transformers. In this paper, induced over voltage testing on power transformers using enhanced Z-source inverter is discussed. First, the power transformer was fed with the required voltage and frequency using a conventional Z-source inverter, and then with an enhanced Z-source inverter using MATLAB platform and the performance is analysed. Field testing was done with an enhanced Z-source inverter circuit on a power transformer based on the simulation results.

Enhanced Z- Source inverter based voltage frequency generator to conduct Induced over voltage test on Power transformers

Transformer is said to be the heart of an electrical power system. Testing of transformer is required, as it is an indication of the extent to which a transformer is able to comply with the customer's specified requirements and the respective standards. Before the development of power electronic devices, motor generator set was used to generate the required voltage and frequency to conduct the induced over voltage test on power transformers. In this paper, induced over voltage testing on power transformers using enhanced Z-source inverter is discussed. First, the power transformer was fed with the required voltage and frequency using a conventional Z-source inverter, and then with an enhanced Z-source inverter using MATLAB platform and the performance is analysed. Field testing was done with an enhanced Z-source inverter circuit on a power transformer based on the simulation results.