Power Electronic Equipment Research Articles

Classification and Identification of Power Quality Disturbances Based on Stochastic Forest Model

With the emergence and use of a large number of new power electronic equipment, the power supply department has begun to pay extensive attention to the problem of power quality, and the majority of users have put forward higher requirements for the quality of power supply. This paper studies the classification and identification method of power quality disturbances based on random forest model. In this paper, according to IEEE power quality standard, the normal waveform and 16 common power quality disturbance waveforms are mathematically modeled, and the power quality disturbance signal is analyzed by S-transform. In this paper, the power quality disturbance identification algorithm based on random forest is optimized. Experimental data show that the optimized method has higher disturbance recognition accuracy and better anti noise ability. Therefore, using the power quality disturbance identification method proposed in this paper to monitor the power quality of power grid is of great significance to ensure the safe and stable operation of power grid and improve economic benefits.

Evaluation of Modular Power Converter Integrated with 5G Network

This paper focuses on two key technical concepts, which may have a tremendous impact on future generations of power electronic converters: the Power Electronic Building Block (PEBB) concept, and the 5G/6G wireless data transfer. It is expected that these two trends may induce development of new cognitive of power electronic converters: Power Electronics 4.0. To investigate this concept, a Proof of Concept (PoC) of PEBB-based power converter integrated with a 5G network, was designed and tested. Study confirmed that power converter assembled from PEBB modules can compete with state-of-the-art devices. Moreover, test results indicates that several challenges related to PEBB and integration of power electronic equipment with 5G network has to be resolved, to enable growth of augmented power electronic converters, especially if wireless data transfer is meant for communication between PEBB modules.

A Current Amplifier Circuit and Control Strategy Based on FPGA

With the extensive application of electric vehicles, energy storage systems and other power electronic equipment, the research on large capacity controllable current source will be an important direction in the future. This paper proposes controllable current source controlled by a full digitally hysteresis current based on field programmable gate array(FPGA), in which the single phase full bridge topology is adopted as the main circuit of current source. The two levels and three levels hysteresis current control strategies are analyzed and compared with the platform of PSCAD/EMTDC. The user defined component was adopted to realize the two difference control strategies with fortran language program. The simulation results verified that the two levels hysteresis current control strategy is much more fit for the controllable current source. Finally, a prototype is designed and fulfilled and it is controlled by the digitally controller with FPGA. The hysteresis current control is realized by FPGA controller with VHDL programming. The experimental results show that the researched hysteresis current control technology is effective for the current amplifier

A Novel Fast Hybrid Frequency Domain Approach for Evaluating Harmonic Power Flow in Electricity Networks

Ideally, an AC power supply should constantly provide a perfectly sinusoidal voltage signal at every customer location. Nowadays, many power electronic equipment’s are used in industry in seeking higher system reliability and efficiency and more electronic or microprocessor controllers are used in power system to control AC/DC transmission lines or loads. Moreover, the importance of green energy such as wind and solar is continually growing in our societies not only due to environmental concerns but also to resolve the problem of access to electricity in rural areas. As a result of these issues, power quality problems especially generation of harmonics are on the rise in the distribution network. In electrical power system, harmonics have a number of undesirable effects on power system devices as well as on their operation. It therefore becomes imperative for power system engineers to analyse the penetration of harmonics from the various sources into the network which commonly is known as harmonic power flow evaluation. This paper proposed a novel fast hybrid frequency domain approach (FHA) to evaluate the steady state harmonic power flow with discrete harmonic frequency. The proposed method is applied to IEEE – 14 bus, IEEE New England 39 - bus, IEEE – 57 bus and IEEE 118 - bus power system respectively and compared with Newton – Raphson (NR) load flow method and Fast decoupled load flow method (FDLF) and the results validate the accuracy, robustness and authenticity of the proposed method.

Open switch fault diagnosis of cascade H-bridge multi-level inverter in distributed power generators by machine learning algorithms

In recent years, multi-level inverters have had remarkable applications in renewable energy sources, high voltage, and other high-power applications. The multi-level inverter has advantages like minimum harmonic distortion and can operate on several voltage levels. A multi-level inverter is being utilized for multipurpose applications such as transportation, communication, industrial manufacturing, aerospace active power filter, Static Var Compensator, and machine drive. Power electronics equipment reliability is very important, and to ensure a multi-level inverter system’s stable operation; it is important to detect and locate faults as quickly as possible. It is difficult to diagnose a fault in a multi-level inverter using a mathematical model because it consists of many switching devices, in this context and to improve fault diagnosis accuracy and efficiency of a cascaded multi-level inverter (CHMLI), a fault diagnosis strategy based on the probability principal component analysis (PPCA) might be utilized. Different machine learning algorithms are used to classify and diagnose the faults under different conditions in a cascaded H-bridge multi-level inverter (CHMLI). This paper presents the comparison of two different machine learning algorithms, such as support vector machine (SVM) and k-Nearest neighbors algorithm (k-NN), based on probabilistic principal component analysis (PPCA) for the effective open switch fault diagnosis in CHMLI employed in distributed generator units. PPCA is a useful technique used for optimizing and data processing without changing the input data’s original properties and characteristics. Using the phase shift pulse width modulation technique, the output voltage signals under different switching fault conditions if the CHMLI are taken as fault features. Both algorithms are used to identify and locate the fault under different modes in CHMLI of distributed generator units. The proposed fault diagnosis methods are compared using simulations and experimental results employing a field-programmable gate array (FPGA) controller. The developed system’s simulation and experimental results perform satisfactorily to detect the fault type, fault location, and reconfiguration. The fault diagnosis time using PPCA-SVM as a fault diagnosis tool for the simulation and experimental case is 0.065 ms and 2.12 ms, respectively. On the other hand, 347 ms and 415 ms fault diagnosis time for simulation and experimental case, respectively, are recorded for the PPCA-kNN based fault diagnosis technique. Therefore, the SVM-based fault diagnosis method is much more efficient and accurate than the k-NN based fault diagnosis method. Moreover, the proposed SVM-based fault diagnosis guaranteed high reliability for CHMLI.

A method to improve the accuracy and efficiency for metallized-film capacitor's reliability assessment using joint simulation

Metallized-film capacitors are widely used in large capacity power electronic equipment to filter the harmonics, buffer the pulsation power and support an operating voltage. However, with the reliability design standard becoming more stringent, the demand to estimate the lifetime more precisely for capacitors surges out. Extracting the hot-spot temperature is the core step, but conventional methods could not fully consider the influence brought by internal and external stresses. Finite element method is more precise but the modification of parameters needs to be done manually, which could be time-consuming. A joint simulation method is then proposed by means of interface between different computer software. This method keeps the advantage of finite element method, taking both the aging of capacitor and the time-varying equivalent resistance into consideration, with the operations being automatically done. Hence the accuracy of hot-spot temperature estimation is improved compared to traditional ways and in the meantime, a more time-efficient reliability evaluation is fulfilled.

Design and Simulated Analysis of Low Heat Flux Cold Plate for High-power Power Electronics Equipment

The thesis has carried out design and simulated analysis of low flux cold plate for high-power power electronics equipment. First, according to heat distribution and design requirements, two kinds of flow passage for low flux cold plate is designed. Then performance characteristics simulation of different flow passage for cold plate is performed. And the heat dissipation characteristics of two kinds of flow passage can both meet the design requirements. Finally, from the perspective of high temperature, temperature difference, pressure drop and so on, the simulated results are comparative analysis. And it is helpful to the design and optimizing of cold plate for high-power power electronics equipment.

Research on Design, Detection and Realization of Monitoring System Based on Ship Power Grid Parameter

The power system of the ship is closely related to the it’s shipping, production and operation, navigation and communication, daily life and other subsystems, and has a very important impact on the operation of the ship. Due to the characteristics of the micro-grid of the ship and the use of a large number of power electronic equipment, the reliability of the power system of the ship is reduced, and the power quality of the power grid continues to decline. This paper studies the power parameter monitoring of the ship’s power grid, and designs a power parameter monitoring system for the ship’s power grid, which can monitor the power parameters of the ship’s power grid in real time. It is helpful to master the operation of the ship power system, and plays a positive role in improving the power quality of the ship power grid, and ensuring the safety and economic operation of the ship power system.

Stability of Electronic Circuits Based on Complex Neural Network Theory

In recent years, with the widespread application of power electronic equipment in various fields of the national economy, the problem of insufficient stability of power electronic equipment has brought a greater negative impact on the application and promotion of new technologies and the development of the national economy. Therefore, to carry out the stability research of power electronic circuits and find suitable methods to reduce the failure rate of power electronic circuits is of great significance for improving the stability of power electronic circuits and promoting the development of power electronic technology and social progress. The purpose of this article is to study the stability of electronic circuits based on the theory of complex neural networks. In this paper, in order to realize the effective use of power grid electricity, during the low period of power consumption, the energy storage battery is operated in the charging state to store the excess energy in the grid; during the peak period of power consumption, the energy storage battery is operated in the discharged state to the load side of the grid powered by. This paper adds a multi-agent system to the power system and uses the linear time-invariant consistency protocol of the multi-agent system to obtain the net active power of the grid. Then, according to the size of the net active power and the working state of the energy storage battery, it is determined whether switch the working status of the energy storage battery. By calculating the changes in the network efficiency value of the circuit weighted network model when the failure rate of each component in the power electronic circuit changes, find the weak points in the power electronic circuit, and prove that the component’s stability to the power electronic circuit is not only related to the failure of the component itself the rate is related to the position of the component in the circuit. Experimental studies have shown that the resistance of current or control signal transmission becomes smaller, especially when the component D1 or D4 is short-circuited, the circuit network efficiency value increases by about 15%.

Simultaneously Enhanced Thermal Conductivity and Dielectric Breakdown Strength in Sandwich AlN/Epoxy Composites.

Polymer-based composites with high thermal conductivity and dielectric breakdown strength have gained increasing attention due to their significant application potential in both power electronic devices and power equipment. In this study, we successfully prepared novel sandwich AlN/epoxy composites with various layer thicknesses, showing simultaneously and remarkably enhanced dielectric breakdown strength and thermal conductivity. The most optimized sandwich composite, with an outer layer thickness of 120 μm and an inner layer thickness of 60 μm (abbreviated as 120-60) exhibits a high through-plane thermal conductivity of 0.754 W/(m·K) (4.1 times of epoxy) and has a dielectric breakdown strength of 69.7 kV/mm, 8.1% higher compared to that of epoxy. The sandwich composites also have higher in-plane thermal conductivity (1.88 W/(m·K) for 120-60) based on the novel parallel models. The sandwich composites with desirable thermal and electrical properties are very promising for application in power electronic devices and power equipment.

Design of thermoelectric battery based on BN aerogels and Bi2Te3 composites

The Seebeck coefficient, electrical conductivity and thermal conductivity of thermoelectric materials are related but not independent, so it is difficult to improve the figure of merit value of thermoelectric materials. In the compound with nanometer grain size, a large number of surface interfaces and various defects in the material will increase the phonon scattering, resulting in the decrease of lattice thermal conductivity. Therefore, the nano-structure of the material is expected to increase its thermoelectric performance parameters. This work presents is based on the self-synthesized BN nano-materials, different structure of the thermoelectric cell composed of nanomaterial BN and thermoelectric material bismuth telluride are designed and analyzed, and its output voltage and power are simulated. Low dimensional BN nanomaterials with low thermal conductivity may contribute to reduce the overall thermal conductivity of the battery and improve the output efficiency. The thermoelectric coefficient of the thermoelectric battery is approximately calculated to be 1.22, which will satisfy the power supply requirements of some small power electronic equipment in practical application.

Multi-objective NSGA-II based shape optimisation of the cross-sectional shape of passively cooled heat sinks

PurposeThe purpose of the study is to optimise the cross-sectional shape of passively cooled horizontally mounted pin-fin heat sink for higher cooling performance and lower material usage.Design/methodology/approachMulti-objective shape optimisation technique is used to design the heat sink fins. Non-dominated sorting genetic algorithm (NSGA-II) is combined with a geometric module to develop the shape optimiser. High-fidelity computational fluid dynamics (CFD) is used to evaluate the design objectives. Separate optimisations are carried out to design the shape of bottom row fins and middle row fins of a pin-fin heat sink. Finally, a computational validation was conducted by generating a three-dimensional pin-fin heat sink using optimised fin cross sections and comparing its performance against the circular pin-fin heat sink with the same inter-fin spacing value.FindingsHeat sink with optimised fin cross sections has 1.6% higher cooling effectiveness than circular pin-fin heat sink of same material volume, and has 10.3% higher cooling effectiveness than the pin-fin heat sink of same characteristics fin dimension. The special geometric features of optimised fins that resulted in superior performance are highlighted. Further, Pareto-optimal fronts for this multi-objective optimisation problem are obtained for different fin design scenarios.Originality/valueFor the first time, passively cooled heat sink’s cross-sectional shapes are optimised for different spatial arrangements, using NSGA-II-based shape optimiser, which makes use of CFD solver to evaluate the design objectives. The optimised, high-performance shapes will find direct application to cool power electronic equipment.

Damping forced oscillations in power system via interline power flow controller with additional repetitive control

With the continuous expansion of power systems and the application of power electronic equipment, forced oscillation has become one of the key problems in terms of system safety and stability. In this paper, an interline power flow controller (IPFC) is used as a power suppression carrier and its mechanism is analyzed using the linearized state-space method to improve the system damping ratio. It is shown that although the IPFC can suppress forced oscillation with well-designed parameters, its capability of improving the system damping ratio is limited. Thus, combined with the repetitive control method, an additional repetitive controller (ARC) is proposed to further dampen the forced power oscillation. The ARC control scheme is characterized by outstanding tracking performance to a system steady reference value, and the main IPFC controller with the ARC can provide higher damping, and further reduce the amplitude of oscillations to zero compared with a supplementary damping controller (SDC). Simulation results show that the IPFC with an ARC can not only greatly reduce the oscillation amplitude, but also actively output the compensation power according to the reference value of the ARC tracking system.

Linearization threshold condition and stability analysis of a stochastic dynamic model of one-machine infinite-bus (OMIB) power systems

With the increase in the proportion of multiple renewable energy sources, power electronics equipment and new loads, power systems are gradually evolving towards the integration of multi-energy, multi-network and multi-subject affected by more stochastic excitation with greater intensity. There is a problem of establishing an effective stochastic dynamic model and algorithm under different stochastic excitation intensities. A Milstein-Euler predictor-corrector method for a nonlinear and linearized stochastic dynamic model of a power system is constructed to numerically discretize the models. The optimal threshold model of stochastic excitation intensity for linearizing the nonlinear stochastic dynamic model is proposed to obtain the corresponding linearization threshold condition. The simulation results of one-machine infinite-bus (OMIB) systems show the correctness and rationality of the predictor-corrector method and the linearization threshold condition for the power system stochastic dynamic model. This study provides a reference for stochastic modelling and efficient simulation of power systems with multiple stochastic excitations and has important application value for stability judgment and security evaluation.

Thermal Analyses of Reactor under High-Power and High-Frequency Square Wave Voltage Based on Improved Thermal Network Model

In order to quickly calculate the stable temperature of a reactor driven by high-frequency and high-power pulse voltage, an improved thermal network model suitable for a reactor under this condition is established in this paper. In power electronic equipment, the maximum temperature of the reactor is usually concentrated in its internal core. Moreover, with the increasing demand of high-power density in power electronic devices, the structure design of the reactor is more compact, and the internal magnetic field will affect the accuracy of the temperature-measuring device. Therefore, it is difficult to measure the internal temperature rise of the reactor directly. However, its stable operating temperature could be analyzed by the thermal network modeling methods and heat transfer analysis tool. Therefore, a convenient and accurate thermal network model of the reactor under high-frequency and high-power square wave voltage is established by considering the equivalent thermal resistance of the winding, the three-dimensional geometrical effect of the core and the effect of the high-frequency repeated pulse stress on the thermal penetration depth. Additionally, the internal temperature of the reactor can be obtained through the external temperature in terms of the presented model. To verify the feasibility of the thermal network model, the corresponding multiphysical field finite element simulation and the reactor temperature measurement platform is built. The simulation and experimental results show that the proposed thermal network model has a high precision and fast calculation speed, and it is an effective tool for thermal analysis of the reactor.

Switching transient analysis of the cascade STATCOM by the equivalent model with redundant H-bridge submodules

Cascade Static Synchronous Compensator (STATCOM) is a multilevel power electronic device, and its safety, reliability, and operation life are directly affected by switching transient processes. The work presented a switching transient analysis of the redundancy fault-tolerant control for the Cascaded STATCOM by the proposed contactor equivalent model. It was more accurate, ignoring fast dynamic changes and replacing the instantaneous speed with the average speed. Redundancy fault-tolerant control of submodules was crucial to the reliability of Cascade STATCOM. The closing and opening process of the AC contactor generally lasted for several milliseconds. When failure occurred in H-bridge, many factors such as the change of excitation circuit, the resistance, and the capacitance affected the electromagnetic transient process during the closing of the AC contactor. Arc discharge occurred when the H-bridge submodule was re-entered, and the AC contactor was turned off. Based on this, an equivalent model of ac contactor suitable for h-bridge was proposed, considering the influences of excitation circuit, arc discharge, and distribution parameters on switching transient. Simulation and experiments were used to analyze the electromagnetic transient waveform of a single H-bridge sub-module in the contactor closure and disconnection process, and the electromagnetic transient waveform of cascade STATCOM in the redundant sub-module contactor closure and disconnection process. The results showed that the transient change of the proposed model during sub module’s bypass and re-entry process was closer to the physical process. The equivalent model obtained in the work provides the theoretical and numerical basis for the design and operation of high-power power electronic equipment.

New research progress of large capacity new synchronous condenser

With the increase of HVDC(high voltage direct current) transmission system, the new large-capacity synchronous condenser is the most suitable device to meet the dynamic reactive power demand of the power grid system. Therefore, it has gradually become one of the research hot topics. Based on this, the paper systematically summarizes the research status of the new synchronous condenser. Firstly, the operation principle of the synchronous condenser is introduced from four aspects: its reactive power characteristics, operation state and the typical type and control strategy. Secondly, by comparing it with power electronic reactive power compensation equipment, the superior dynamic reactive power output characteristics of the new synchronous condenser are expounded, and the influence factors are analysed, the example that stable grid voltage is given. Finally, the latest development of the state monitoring technology of the synchronous condenser is summarized from both the existing fault diagnosis technology and parameter identification technology. In this paper, the basic theory, control strategy and operation state monitoring of the new synchronous condenser are summarized, which could provide reference for the further research.

Low Frequency Damping Control for Power Electronics-Based AC Grid Using Inverters with Built-In PSS

Low frequency oscillations are the most easily occurring dynamic stability problem in the power system. With the increasing capacity of power electronic equipment, the coupling coordination of a synchronous generator and inverter in a low frequency range is worth to be studied further. This paper analyzes the mechanism of the interaction between a normal active/reactive power control grid-connected inverters and power regulation of a synchronous generator. Based on the mechanism, the power system stabilizer built in the inverter is used to increase damping in low frequency range. The small-signal model for electromagnetic torque interaction between the grid-connected inverters and the generator is analyzed first. The small-signal model is the basis for the inverters to provide damping with specific amplitude and phase. The additional damping torque control of the inverters is realized through a built-in power system stabilizer. The fundamentals and the structure of a built-in power system stabilizer are illustrated. The built-in power system stabilizer can be realized through the active or reactive power control loop. The parameter design method is also proposed. With the proposed model and suppression method, the inverters can provide a certain damping torque to improve system stability. Finally, detailed system damping simulation results of the universal step test verify that the analysis is valid and effective.

Research Progress of All Organic Polymer Dielectrics for Energy Storage from the Classification of Organic Structures

AbstractDielectric films are the foundation of power electronic equipment for energy storage in capacitors. However, typical dielectric films exhibit undesirable energy storage density and thermal stability, limiting its further application in the advanced field. For both pure polymers and composites‐based dielectrics, the macromolecular matrix greatly determines the performances. This paper summarizes the research progress of all‐organic polymer materials for the dielectric application from the perspective of molecular structure design. Systematic comparisons on properties, including dielectric constant and dielectric loss, glass transition temperature, and energy density are given, expecting to inspire researchers to devote further efforts in this area. An outlook for the future of all‐polymer dielectrics is also presented.

Energy storage performance of BaTiO3-based relaxor ferroelectric ceramics prepared through a two-step process

As the industrial pillar of electronic ceramics, BaTiO3 ceramic is difficult to achieve large energy storing performance due to its high Pr and low dielectric breakdown field strength, making it difficult to satisfy their development requirements of miniaturization and lightweight of power electronic equipment. Therefore, a two-step strategy including adjusting the ratio of chemical elements to modify the microstructures and optimizing the preparation process to enhance electric breakdown strength has been proposed to greatly enhance the energy storing performance of lead-free ferroelectric ceramics, whose effectiveness has been proved within this investigation. Especially, the (Ba0.65Sr0.245Bi0.07)0.99Nd0.01TiO3 (BT-SBT-NdVPP) ceramic prepared by this strategy obtains a superhigh energy storage density of 4.2 J/cm3 under 460 kV/cm, and its temperature (30 ~ 100 °C) and frequency (10 ~ 400 Hz) stabilities under 300 kV/cm are pretty good. In addition, this ceramic has excellent pulse performance under 350 kV/cm between 30 and 150 °C. Therefore, this two-step strategy put forward within this investigation not only significantly improves the energy storage performance of BT-based ceramics but also provides a reference for the preparation of dielectric ceramics with high quality, which could has great potential for the practical industrial application.