Operation Of Power Converter Research Articles

A Novel Mathematical Approach to Model Multi-Agent-Based Main Grid and Microgrid Networks for Complete System Analysis

Penetration of renewable energy resources in modern power systems has increased rapidly. The integration of different renewable and nonrenewable resources for the purpose of electricity generation is referred to as Distributed Generation (DG) units. The penetration of DG units gave birth to the concept of power microgrid. Power inverters play a major role in the integration of DGs in the power system. Control and stability analysis of microgrids in power systems is a challenging task for the control community. Dynamic microgrid modeling demands knowledge of fundamental engineering laws to detailed theoretical analysis. To model the dynamic behavior of the power microgrid, a basic understanding of the power converter operation modes and their control schemes is necessary. The main microgrid modeling components are power converters, power lines, transformers, protection systems, load, and faults. In this paper, preliminary concepts of power systems along with graph theoretic approach are used to develop the model of the microgrid and main grid networks. A mathematical model of a power microgrid in islanded mode, as well as the grid-connected mode, is developed and comprises of generation sources, power inverter interface, protection mechanism, load, faults, and transmission lines. The developed mathematical model can be used to address the stability issues as well as resilience in the power networks for complete system analysis. To validate the mathematical model, a renewable energy-based main grid and microgrid model is simulated. The graphical result of simulated model presents the generation and load curves.

Numerical simulation of the effect of laser intensity and temperature on the performance of laser power converters

To study the influence of laser intensity and temperature on the performance of laser power converters (LPCs), a two-dimensional model of an In0.3Ga0.7As LPC by the finite element method was established. The validity of the model was verified by comparing the theoretical value with the experimental results. The factors that influence the performance of LPCs were analyzed from the perspective of recombination. Results indicate that the existence of grids at the front surface improves the collection of carriers efficiently, and the influence of temperature and laser intensity on carriers recombination is quite different at 0 and Vm (voltage at maximum power point) bias voltages. The research of this paper provides a reference for the optimization of LPCs.

A robust nonlinear PI-type controller for the DC–DC buck–boost power converter

In this study, a novel Lyapunov function-based robust nonlinear proportional–integral (PI)-type controller for regulating the output voltage of the direct current to direct current (DC–DC) inverting buck–boost power converter operating in continuous conduction mode (CCM) is presented. The control scheme guarantees global asymptotic stability of the closed-loop system even in case of parameter uncertainty. The analysis of the closed-loop trajectories is carried out using Lyapunov method and LaSalle’s invariance principle. Robustness to additive disturbances is shown and simple gain tuning guidelines are given. Real-time experiments support the theoretical results. Experimental tests are presented where the proposed PI-type control design is compared with other PI-type schemes found in the literature. The proposed scheme presents very good consistent performance under line and load disturbance.

A digital‐controlled gate charge detection circuit for short‐circuit protection and condition monitoring of SiC MOSFET

The safe and reliable operation of power converter requires a protection circuit with fast response when the power device is subjected to the short-circuit (SC) fault. In addition, the on-line condition monitoring circuit is beneficial to provide a suggestion for the replacement of aged device. The silicon carbide (SiC) power devices promise the higher power density in the system performance, but is still limited by the poor SC reliability issue. Thus, it is crucial to improve the robustness of SiC-based power converter from the circuit design. This work proposes a novel gate charge detection circuit for SiC devices. It achieves a high-speed SC protection against hard switching fault (HSF) based on the difference of Miller capacitance between normal condition and SC fault. Meanwhile, the condition monitoring is achieved based on the high gate leakage current of aged device. A high-precision analog amplifier circuit is designed to acquire the gate signal. The normal/fault signal is distinguished and the protection is triggered using a digital-controlled method to reduce the hardware cost. A 600-ns SC response time is achieved, and the monitoring circuit can differentiate the aged device from the healthy one.

The Influence Factor Analysis of Symmetrical Half-Bridge Power Converter through Regression, Rough Set and GM(1,N) Model

Analysis of power converter performance has tended to be engineering-oriented, focusing mainly on voltage stability, output power and efficiency improvement. However, there has been little discussion about the weight relations between these factors. In view of the previous inadequacy, this study employs regression, rough set and GM(1,N) to analyze the relations among the factors that affect the converter, with a symmetrical half-bridge power converter serving as an example. The four related affecting factors, including the current conversion ratio, voltage conversion ratio, power conversion ratio and output efficiency, are firstly analyzed and calculated. The respective relative relations between output efficiency and the other three factors are obtained. This research can be referred to by engineers in their design of symmetrical half-bridge power converters.

Analysis of exact and approximating dependences of active resistance of a conductor on the current frequency based on the influence of skin effect

The operation of semiconductor power converters, which are part of tractionsubstations, frequency-controlled electric drives and other powerful nonlinear loads, cause asignificant emission of higher harmonics of currents to electrical networks. Higher harmonics ofcurrents in electrical networks cause a complex negative effect on the energy efficiency of thenetwork. The increase in power losses in the active resistance under the action of higher harmonicsis due to the increase in the root mean square value of the current and the action of the skin effect.Analytical expressions describing the dependence of the active and impedance of the electricnetwork on the current frequency are determined. Based on them, analytical expressions are obtainedfor the calculation of additional power losses under the action of higher harmonics of currents, whichare due to the skin effect. The dependences of the active resistance of the electric network on thefrequency of higher harmonics are determined on the basis of Bessel equations. The analysis of convergence of the received equations with the data of the international standard IEC 60287-1-1 iscarried out. For the high-frequency zone, simplified approximating dependences are given, whichdetermine the parabolic dependence of the active resistance on the frequency. Simplifiedapproximating dependences of active resistance on the frequency of higher harmonics are obtainedfor engineering calculations. The obtained equations can be used to determine additional powerlosses in the active supports of electrical networks, windings of electric machines, high-frequencytransformers from higher harmonics of currents at different nonlinear loads. In addition, the obtainedexpressions can be used to justify the use of filter-compensating devices.

Online Monitoring of Power Converter Degradation Using Deep Neural Network

Power semiconductor devices in the power converters used for motor drives are susceptible to wear-out and failure, especially when operated in harsh environments. Therefore, detection of degradation of power devices is crucial for ensuring the reliable performance of power converters. In this paper, a deep learning approach for online classification of the health states of the snubber resistors in the Insulated Gate Bipolar Transistors (IGBTs) in a three-phase Brushless DC (BLDC) motor drive is proposed. The method can locate one out of the six IGBTs experiencing a snubber resistor degradation problem by measuring the voltage waveforms of the three shunt resistors using voltage sensors. The range of the degradation of the snubber resistors for successful classification is also investigated. The off-the-shelf deep Convolutional Neural Network (CNN) architecture ResNet50 is used for transfer learning to determine which snubber resistor has degraded. The dataset for evaluating the above classification scheme of IGBT degradation is obtained by measuring the shunt voltage waveforms with varying snubber resistance and reference current. Then, the three-phase voltage waveforms are converted into greyscale images and RGB spectrogram images, which are later fed into the deep CNN. Experiments are carried out on the greyscale image dataset and the spectrogram image dataset using four-fold cross-validation. The results show that the proposed scheme can classify seven classes (one class for normal condition and six classes for abnormal condition in one of the six IGBTs in a three-phase BLDC drive) with over 95% average accuracy within a specific range of snubber resistance. Using grayscale images and using spectrogram-based RGB images yields similar accuracy.

Noncontact Monitoring of IGBT Turn-OFF Time Using PWM Switching Ringing for Inverter-Fed Machine Systems

Turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> time is an important condition parameter for insulated gate bipolar transistor (IGBT), which could provide useful information on the device junction temperature and its state of health. Currently, it is measured directly from the IGBT collector-emitter voltage <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ce</sub> or indirectly from the gate side, which may cause problems of safety and complexity for a power converter operating in a harsh electromagnetic environment. To address the challenges, this article proposes a noncontact method to monitor the IGBT turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> time from the PWM switching ringing in the converter output current. First, a phenomenon is observed that there are two switch-over points in the switching ringing current corresponding to the transition of IGBT turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> voltage. Analytical analysis is performed with a high-frequency (HF) equivalent circuit to investigate the mechanism of the one-to-one temporal relationship. Then, the noncontact condition monitoring (CM) scheme including the HF switching ringing current sensor and the framework of CM system is devised. Finally, experimental work is carried out to validate the theoretical analysis and the effectiveness of the method. Research results show that the turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> time of multi-IGBTs can be effectively extracted at the terminal of converter during system normal operation with electrically isolated safety.

Hybrid Input Power Balancing Method of Modular Power Converters for High Efficiency, High Reliability, and Enhanced Dynamic Performance

Input parallel output parallel (IPOP) modular power converters have been used to supply high power and high current in various applications. In general, the IPOP modular power converter uses an output power balancing method to equally distribute the amount of output power to each converter. In this article, a hybrid input power balancing method is proposed to obtain high power conversion efficiency, high reliability, and enhanced dynamic performance of the IPOP modular power converters. In the steady state, the proposed method controls input power to be balanced in each converter. A power loss distribution capability of the input power balancing method can improve the entire power conversion efficiency and can reduce the overall operating temperature of the IPOP converters, which can increase lifetime and can improve reliability. During the transient operation, the proposed method makes the IPOP converters under an interleaving mode to tightly regulate the output voltage and to obtain fast dynamic performance. Experimental results with 200-W prototype modular synchronous buck converters verify the performance improvements of the proposed method such as high power conversion efficiency, the power loss distribution capability in the steady-state operation, and the enhanced dynamic performance in the transient operation.

Model-Free Neural Network-Based Predictive Control for Robust Operation of Power Converters

An accurate definition of a system model significantly affects the performance of model-based control strategies, for example, model predictive control (MPC). In this paper, a model-free predictive control strategy is presented to mitigate all ramifications of the model’s uncertainties and parameter mismatch between the plant and controller for the control of power electronic converters in applications such as microgrids. A specific recurrent neural network structure called state-space neural network (ssNN) is proposed as a model-free current predictive control for a three-phase power converter. In this approach, NN weights are updated through particle swarm optimization (PSO) for faster convergence. After the training process, the proposed ssNN-PSO combined with the predictive controller using a performance criterion overcomes parameter variations in the physical system. A comparison has been carried out between the conventional MPC and the proposed model-free predictive control in different scenarios. The simulation results of the proposed control scheme exhibit more robustness compared to the conventional finite-control-set MPC.

A GaN-HEMT Compact Model Including Dynamic RDSon Effect for Power Electronics Converters

In order to model GaN-HEMT switching transients and determine power losses, a compact model including dynamic RDSon effect is proposed herein. The model includes mathematical equations to represent device static and capacitance-voltage characteristics, and a behavioural voltage source, which includes multiple RC units to represent different time constants for trapping and detrapping effect from 100 ns to 100 s range. All the required parameters in the model can be obtained by fitting method using a datasheet or experimental characterisation results. The model is then implemented into our developed virtual prototyping software, where the device compact model is co-simulated with a parasitic inductance physical model to obtain the switching waveform. As model order reduction is applied in our software to resolve physical model, the device switching current and voltage waveform can be obtained in the range of minutes. By comparison with experimental measurements, the model is validated to accurately represent device switching transients as well as their spectrum in frequency domain until 100 MHz. In terms of dynamic RDSon value, the mismatch between the model and experimental results is within 10% under different power converter operation conditions in terms of switching frequencies and duty cycles, so designers can use this model to accurately obtain GaN-HEMT power losses due to trapping and detrapping effects for power electronics converters.

Web-based Monitoring System for Power Electronics Devices on Off-grid Solar Power Generator

Power electronic devices are the main component of the solar power generation system. This study proposes a web-based monitoring system which presents power electronic performance parameter in a real-time across an internet connection. The investigation takes ACS712 and PZEM-004T for the power converter performance measuring and Arduino Mega 2560 with an ethernet shield for data acquisition and transmission. This paper describes the schematic design of the hardware and also explains the software work-flow and structure. The test and calibration on the sensor's voltage and current to standard digital multi-meter Tektronix DMM4050 show the sensor able to accurately read the converter performance parameter and meet the standard IEC-61724. The functionality test on the web-based information system indicates the designed user interface to present the power electronic performance parameter of the solar power generator.Keywords: Monitoring System, Power Electronics and Solar Power

Novel control approach for enhancing multi-performance of two-stage converter during power transfer from solar photo-voltaic array to AC grid

This paper presents a nonconventional control approach for augmenting various performances of two-stage power converter (DC-side boost converter and three-phase voltage source inverter (VSI)) during power transfer from solar photo-voltaic array to AC grid. In the application, intermediate DC link voltage is traditionally regulated to settle at a constant and high value. This fixed value is not optimum in respect of various performances of the converters under variable power transfer scenarios. In this respect, variable values of DC link voltage under different power transfer conditions are necessary, which is absent in conventional scheme. For achieving the control flexibility, two modifications of traditional control scheme are proposed as, omission of intermediate DC link voltage regulating loop and controlling of modulation index of current loop between 0.98 and 1 for VSI. In effect, significant multi-benefits are obtained as, (i) reduction of voltage stress on power switches to enhance their life span, (ii) reduction of size, cost and enhanced lifetime of DC link capacitor, (iii) improved efficiency of conversion system and (iv) reduction of total harmonic distortion (THD) during maximum power injection from solar photo-voltaic (PV) array to connected AC system. First three benefits are produced due to reduction of DC link voltage for achieving required power transfer and fourth benefit is achieved due to high valued modulation index (between 0.98 and 1). Both simulation and experimental studies verify superior performances of two-stage converter with the help of proposed logic under variable solar power conditions. Derived mathematical condition on interplay between DC link voltage value and power transfer amount at different power factors (unity and leading) provides insight of proposed control approach.

Improved Analysis Model of SiC Power MOSFET with Staged Critical Parameters

Silicon carbide (SiC) metal-oxide-semiconductor field-effect transistors (MOSFETs) have great advantages in improving the power density and performance of power converters due to the high switching frequency, high operating voltage. However, the increase in switching frequency is also increasingly inflicted the voltage and current stresses to the parasitic elements of the SiC MOSFET, which restricts the device’s optimal performance. In addition, many parasitic elements of SiC MOSFET are coupled with each other during the switching process, which makes the analysis complicated and calculation cumbersome. This paper presents an analytical model for SiC MOSFETs, which identifies and selectes the dominant elements and key variations of each stage separately according to the change stages of major variables. The complexity of the model is reduced while the accuracy is guaranteed. Using this model, the voltage and current switching rate of SiC MOSFET can be quickly solved, and the impact mechanism of each critical parameter can also be revealed clearly. A double pulse test circuit composed of a 600V/20A SiC MOSFET is set up and experimental results are obtained to verify the accuracy of the proposed analytical model.

Design Implementation and Operation of an Education Laboratory-Scale Microgrid

To enable more wide-scale exploitation of renewable energy sources (RESs), distributed generations (DGs) as in microgrids have gained prominence recently. This study describes the design, modeling, implementation, and operation of a microgrid, in which a standalone hybrid power system has been installed for an education and research laboratory. The unstable nature of RESs results in power compatibility issues on DGs. Therefore, providing a decent power flow from renewables to loads is the scope of this paper. To satisfy defined load profiles and sustain the power with the desired level, the design and operation of power converters are a remarkable part of performing microgrids as well. For a robust microgrid structure, the presented control algorithm includes an energy management system (EMS) between renewables, batteries, and loads. Primarily, modeling of the system has been developed in MATLAB/Simulink environment. Additionally, case studies have been exemplified to further demonstrate the simulated system. Within this scope, certain load profiles not only have been fed but also power flow has been managed and analyzed to ensure effective and flexible operation with two different EMS cases. The real-time operation has been also provided to validate the system under various input and output conditions during a lab course.

Impacts of Grid Voltage Harmonics Amplitude and Phase Angle Values on Power Converters in Distribution Networks

Motor drive systems based on diode-rectifier are utilised in many industrial and commercial applications due to their cost-effectiveness and simple topology. However, these diode rectifier-based systems can be affected by power quality and harmonics in distribution networks. Thus, this paper investigates the impact of grid voltage harmonics on the operation of power converters with three-phase diode rectifier using mathematical formulation of the drive voltage and current harmonics based on grid voltage harmonics. Simulation analysis and practical tests have been then carried out to validate the mathematical equations and the impact of grid voltage harmonics on the power converter harmonics. The results illustrate that even a small amount of grid voltage harmonics (around 4%) could significantly impact the input current harmonic contents of the three-phase diode rectifier. It is also shown that the phase-angle of grid voltage harmonics plays a crucial role to improve or deteriorate the input current harmonics of the power converters. In the next step, the optimum condition of grid voltage harmonics to minimise the input current harmonics has been evaluated and verified based on different grid codes. Finally, a harmonic mitigation technique in multi-drive systems using Electronic Inductor is proposed to mitigate the current harmonics at the PCC.

Wide-Bandgap Device Enabled Multilevel Converters With Simplified Structures and Capacitor Voltage Balancing Capability

This paper aims to point out and demonstrate the opportunities enabled by wide-bandgap (WBG) devices for multilevel converters, contributing to the international technology roadmap for WBG power semiconductors (ITRW). The emergence of silicon carbide (SiC) and gallium nitride (GaN) devices offers new opportunities to push the boundaries of power converter performances. Featuring high single-device blocking voltage and ultra-low switching loss, WBG devices can enable a group of multilevel converters with simplified structures and a higher number of levels to be practically implemented in applications with various power levels. This paper highlights how the use of WBG devices can reduce the number of required devices in the simplified multilevel topologies, how the capacitor voltage balance can be achieved with the newly proposed redundant level modulation (RLM) enabled by the ultra-low switching loss of WBG devices and how the switching frequency and efficiency can be improved with WBG multilevel converters. A 1.2 kV/100 kW, three-phase demonstrator implemented with a simplified four-level active neutral point clamped (ANPC) structure and commercial SiC power modules is studied to show the opportunities brought by WBG devices for multilevel converters. A voltage balancing scheme based on the RLM and a power loss analysis are presented for this configuration.

Thermal Performance Improvement in Multi-Megawatt Power Converters Serving to Asynchronous Hydro Generators Operating Around Synchronous Speed

In multi-MW three-level neutral point clamped back-to-back (3L-NPC) power converters, power semiconductor devices are considered as most vulnerable components due to its thermo-mechanical fatigue stress. Particularly, rotor side converter (RSC) in doubly fed induction machine (DFIM) experiences high thermal stress during its operation around synchronous speed. It degrades the performance of power converter and reduces the lifetime availability of the drive. In practice, stabilization of temperature fluctuation across each power semiconductor device improves the efficiency and reliability of power converter. With respect to this prime aim, this paper proposes a carrier-based active thermal control method to regulate temperature fluctuation across power semiconductor devices in a multi-MW (5 x 5 MW) 3L-NPC power converters serving to a 250 MW asynchronous hydro-generating unit. To test the proposed active thermal control method, different operating conditions of a 250 MW DFIM hydro-generating unit (to be commissioned in Tehri pumped storage plant, India) are examined in MATLAB/PLECS environment. The designed active thermal control method effectively regulates mean junction temperature and temperature fluctuation of power semiconductor devices within a safe operating limit. The practical feasibility and adoptability of proposed active thermal control is examined through a 2.2-kW DFIM laboratory prototype.

Diamond semiconductor performances in power electronics applications

This paper proposes a system-level comparison between diamond and silicon carbide (SiC) power devices. It highlights the benefits of diamond semiconductors for power electronics applications. Actual diamond power devices were fabricated and characterised (DC, AC small-signal, large-signal power switching in a buck converter). Models of the diamond devices are discussed based on the experimental data, and the expected performances of the future diamond semiconductors in power converters are presented. These performances are compared to the commercialised SiC Schottky diodes for a given application. Our analysis shows that diamond devices can be used to increase the performance of power converters, especially at high temperatures. We demonstrate that for a junction temperature of 450 K, diamond semiconductors can divide the semiconductor losses and heatsink volume by three, in comparison with SiC devices. We also demonstrate that the switching frequency with diamond devices can be five times higher than with SiC devices, with lower total semiconductor losses and smaller heatsink in diamond-based power converters. This system-level analysis clearly shows the future improvements in the efficiency and power densities of power converters thanks to diamond power devices. The need for management of the specific junction temperature, which is required in order to exploit all of the properties of diamonds, is demonstrated and discussed.

Dual-Mode Stable Performance Phase-Shifted Full-Bridge Converter for Wide-Input and Medium-Power Applications

Power converters with an extended range of line voltage are the main requirement in today's industrial applications such as photovoltaics- and supercapacitors-based energy systems. The variation in the line voltage severely degrades the performance of power converters, because of the extended freewheeling interval, more circulation current, narrow range of zero voltage switching, and increased EMI. This article suggests a modified phase-shifted full-bridge converter that cuts the freewheeling interval and minimizes these problems. It extends the input voltage range by keeping the operational duty cycle of the converter high over the wide range of input voltage while maintaining the performance stable. The proposed converter consists of four low-profile transformers having reconfigurable interconnection structure. There are two distinct reconfigurable modes, a series mode and a parallel mode, which can be configured with changes in the operational conditions. The operation of the proposed converter with high switching frequency improves the power density. Additionally, the use of multiple transformers minimizes the heat management efforts and reduces the overall volume of the converter. The proposed work, in this article, is validated in hardware characterization for a wide range of input voltage 100-400 Vdc and up to the load power of 1 kW. The measured energy efficiency of the proposed converter remains stable over the complete range input voltage 100-400 Vdc.