Operation Of Power Converter Research Articles

A Simple and Effective Open-Circuit-Fault Diagnosis Method for Grid-Tied Power Converters—A New Technique Based on Tellegen’s Theorem

Grid-tied power converters are widely adopted in renewable energy integration systems. Reliable operation of such power converters is highly desirable, which relies on effective fault diagnosis and ride-through techniques. In this work, we propose a new open-circuit fault diagnosis method for grid-tied power converters based on Tellegen’s theorem, which is fast in fault detection and accurate in faulty component location. We first developed a “quasi-power” concept to define the relationship between current and voltage magnitudes for the underlying power converter. The value of the afore-developed quasi-power in this proposal depends solely on the connection state (i.e., the switch position and status) of a power converter, resulting in its good features of robustness to parameter variations and immunity to operation changes. Thereafter, we propose a fault diagnosis method based on the quasi-power of a converter, which is able to identify any faulty component among all the semiconductor switches (i.e., the insulated gate bipolar translators (IGBTs) and freewheeling diodes) at a time-scale of only one sampling period. As a case study, the proposed technique is incorporated into a well-known model predictive control (MPC) framework of a grid-tied two-level (2L) power converter and tested at a lab-constructed test bench. Experimental results confirm its effectiveness.

Simple Loss Model of Battery Cables for Fast Transient Thermal Simulation

In electric vehicles, currents with high-frequency ripples flow in the power cabling system due to the switching operation of power converters. Inside the cables, a strong coupling between the thermal and electromagnetic phenomena exists, since the temperature and Alternating Current (AC) density distributions in the strands affect each other. Due to the different time scales of magnetic and heat flow problems, the computational cost of Finite Element Method (FEM) numeric solvers can be excessive. This paper derives a simple analytical model to calculate the total losses of a multi-stranded cable carrying a Direct Current (DC) affected by a high-frequency ripple. The expression of the equivalent AC cable resistance at a generic frequency and temperature is derived from the general treatment of multi-stranded multi-layer windings. When employed to predict the temperature evolution in the cable, the analytical model prevents the use of complex FEM models in which multiple heat flow and magnetic simulations have to be run iteratively. The results obtained for the heating curve of a 35 mm2 stranded cable show that the derived model matches the output of the coupled FEM simulation with an error below 1%, whereas the simple DC loss model of the cable gives an error of 2.4%. While yielding high accuracy, the proposed model significantly reduces the computational burden of the thermal simulation by a factor of four with respect to the complete FEM routine.

GaN-based step-down power converter and control strategy for hydrogen energy systems

The conventional Si-based semiconductors suffer from low switching frequency, high conduction loss and low efficiency. These shortcomings hinder the improvement of power electronic power converter performance. An attractive solution is to replace Si-based semiconductor devices with the wide-bandgap semiconductors based on gallium-nitride material. In terms of the step-down converters which are used for hydrogen energy systems, it is difficult for the traditional buck circuit to eliminate the output current ripple and achieve fault-tolerant operation. Therefore, topologies of the step-down power converter also need improvement. In this paper, a GaN-based step-down power converter and control strategy for hydrogen energy systems is presented. Firstly, the mathematical analysis of the conventional buck converter is done to clarify why it has limitations regarding the reliability and current ripple. Another alternative solution is discussed but still suffers from ripples. In order to eliminate the current ripple and enhance the fault-tolerant ability, a novel GaN-based solution is given and both analysis and design are provided. The current ripple can be perfectly cancelled and fault-tolerant operation can be fully achieved. The comparison is carried out with the existing solutions. The time-domain simulation tests are carried out. And the experimental prototype is established based on the enhancement mode GaN transistor. The experimental results verify the effectiveness of proposed design regarding the current ripple cancellation and dynamic performance.

Ant Colony Optimized Controller for Fast Direct Torque Control of Induction Motor

Induction motor (IM) drives have tremendous applications as high-performance drives in things such as mine winders, machine tools, electric vehicles, and elevators. Usually, IM drives controlled by direct torque control are preferred for these applications due to their fast torque control and simplicity compared with IM drives with field-oriented control. Proportional–integral–derivative (PID) controllers are commonly used to control IM drives using DTC. Though these controllers are simple and provide excellent response for linear systems with constant set points, they perform poorly with variable set points and IM motor parameter uncertainties. Hence, many control techniques and optimization algorithms have been applied to improve IM drive performance. This paper proposes an IM drive controlled using direct torque control principles, but with the power converter operation optimized to give fast torque performance. The IM drive speed response is improved using an optimized fuzzy PID (FPID). The FPID optimization is accomplished by the ant colony optimization (ACO) algorithm. All components of the IM drive with the optimized control system were simulated using the MATLAB/Simulink platform. The responses of the introduced drive using three different controllers—conventional PID, FPID, and optimized FPID—were compared. The simulation results indicate that the optimized FPID controller provided the best performance in terms of speed and torque. Additionally, the performance of the IM with the proposed optimized FPID under parameter uncertainties was studied. The simulation results indicated the robustness of the optimized FPID controller against parameter uncertainties.

Grid code analysis considering converter-based grid voltage support during faults

Modern power systems are increasingly integrated with power electronic converters, which allow precise control of active and reactive current injections within a certain range of operation. Power converters are usually required to provide grid voltage support service in case of fault. This poses the challenge to determine the current injection from a converter that maintains the grid voltage while not surpassing the converter’s current limitation. Conventional grid codes simply set the linear relationship between the voltage droop and the grid-support current, consequently not providing the optimized voltage support. In this paper, the grid voltage support operation of power converters is analysed from an optimization perspective. A formulation for the analysis of faults in a generic system is presented. Numerical cases have been studied with different fault scenarios. The optimized solutions show the traditional grid code can be potentially improved in order to maintain the grid voltage closer to the nominal value during the fault. In this line, two improved adaptations of this grid code have been proposed. These two alternative grid codes have been found to be near-optimal as they just differ slightly from the optimized results despite only injecting reactive power.

A High-Efficiency Low-Wearing Hybrid Voltage Regulator for Utility Applications

Step voltage regulator (SVR) has been utilized in power distribution systems for decades as the voltage regulation device. Due to the increasing integration of distributed energy resources, the conventional SVR is severely challenged by the modern power distribution pattern with high renewable energy penetration. The induced arc from the conventional SVR tap change and more frequent tap changes due to voltage instability from the renewable energy impose constraints on the conventional SVRs lifetime. Meanwhile, the conventional SVR device cannot regulate the voltage accurately since the SVR regulates the voltage step-by-step. This article proposed a hybrid voltage regulator with high-efficiency and low contact wearing, which can achieve arcless tap change and stepless voltage regulation by using a fractionally rated back-to-back power converter. The accurate load voltage regulation is guaranteed, while the tap changer mechanism remains in the system, which helps to promote the upgrade to the existing power distribution systems. The power converter capacity in the proposed topology is only 0.31% of the distribution transformer rating to achieve a stepless voltage regulation range of ±10%, significantly reducing the system cost compared with the full power electronics solutions and projects high total system efficiency. The proposed hybrid voltage regulator was simulated and experimentally validated. The experimental results demonstrate arcless tap change operation and stepless voltage regulation. Collaborative operation between the conventional mechanical tap change and the power converter operation is also demonstrated to acquire large voltage regulation with fast-acting voltage control.

Photogeneration and Performance Optimization (PhPO): A New Algorithm to Improve the Performance of Vertical Epitaxial Hetero-Structure Architecture Laser Power Converters

Photogeneration and Performance Optimization (PhPO): A New Algorithm to Improve the Performance of Vertical Epitaxial Hetero-Structure Architecture Laser Power Converters

스위칭 소자 노화에 의한 모듈러 멀티레벨 컨버터 성능 변화 분석 연구

Industrial, electronics goods, and transportation sectors employ power converters for a variety of power conversion applications. Among various reliability challenges in a power converter, capacitor and semiconductor switching devices degradation, caused by aging, are the most notable. The long-term device degradations in capacitors and semiconductor devices may exert negtive impacts on the output performance of power converters. In this study, the impact of an aging capacitor and aging semiconductor switch on a modular multilevel converter (MMC) is presented in detail. Various performances of MMC are measured and quantified through simulation to evaluate the effect of aging devices on converter performance.

Comprehensive Review of Power Electronic Converters in Electric Vehicle Applications

Emerging electric vehicle (EV) technology requires high-voltage energy storage systems, efficient electric motors, electrified power trains, and power converters. If we consider forecasts for EV demand and driving applications, this article comprehensively reviewed power converter topologies, control schemes, output power, reliability, losses, switching frequency, operations, charging systems, advantages, and disadvantages. This article is intended to help engineers and researchers forecast typical recharging/discharging durations, the lifetime of energy storage with the help of control systems and machine learning, and the performance probability of using AlGaN/GaN heterojunction-based high-electron-mobility transistors (HEMTs) in EV systems. The analysis of this extensive review paper suggests that the Vienna rectifier provides significant performance among all AC–DC rectifier converters. Moreover, the multi-device interleaved DC–DC boost converter is best suited for the DC–DC conversion stage. Among DC–AC converters, the third harmonic injected seven-level inverter is found to be one of the best in EV driving. Furthermore, the utilization of multi-level inverters can terminate the requirement of the intermediate DC–DC converter. In addition, the current status, opportunities, challenges, and applications of wireless power transfer in hybrid and all-electric vehicles were also discussed in this paper. Moreover, the adoption of wide bandgap semiconductors was considered. Because of their higher power density, breakdown voltage, and switching frequency characteristics, a light yet efficient power converter design can be achieved for EVs. Finally, the article’s intent was to provide a reference for engineers and researchers in the automobile industry for forecasting calculations.

DC BOOST CONVERTER USING A FUZZY CONTROL SYSTEM, SIMULATED IN SIMULINK

Decisive for the operation of voltage, current and power converters is the choice of control method. Control of complex dynamic systems in conditions of insufficient or fuzzy information requires the involvement of non-standard approaches during the construction of the control system. There are two possible ways out of the traditional framework of linear control. The first, is to develop more accurate nonlinear models on which high-performance controller design can be based. However, when choosing this way, one has to develop very complex control algorithms, and, consequently, the controller will perform complex mathematical calculations, which can have a negative impact on the control speed and response. Another way is to use a neural network controller based on fuzzy logic. Fuzzy logic is a generalization of mathematical logic and set theory, which is a function of the object belonging to a set and can take any value in the range [0; 1], not only 0 or 1. In the case of fuzzy logic we don't need simulation, because the whole work on designing of the controller is reduced to the transformation of the rules included in the fuzzy logic into the algorithm of automatic control.

Design and control of Takagi-Sugeno-Kang fuzzy based inverter for power quality improvement in grid-tied PV systems

The addition of solar photovoltaic energy penetration to the electric grid is widely increasing across the world due to the many advantages such as clean energy source, easy to install and improved performance of power converters for the grid synchronization, and so on. Instead of many stages taking place for the grid-tied, a single stage is preferable to avoid the greater number of power electronic converters connected in the system which in turn reduce the cost of the overall system. In general, the DC-to-DC converters are used in the PV systems to track the maximum power point. However, an inverter circuit is needed to synchronize the source to grid and it can be utilized to extract maximum power from PV systems through proper controlling techniques. The proper control of inverter avoids the DC-to-DC power converter usage for the maximum power point tracking purpose. On the other hand, this technology can be used for small scale solar power plants. An irregular irradiance of solar is a bottleneck for the solar systems and to overcome it, a Takagi-Sugeno-Kang Fuzzy (TSKF) controller is designed for controlling the inverter operation in this paper. The TSKF controller responds very quickly to the input rapid changes of solar irradiance than the conventional proportional integral controllers. In this paper, a single stage 1 MW rating solar PV grid system is designed and verified the performance of the proposed controller under different loading conditions. Further, the proposed system is loaded with local loads and their reactive compensation is evaluated through hardware-in-loop on the platform of OPAL-RT software.

Mitigation of power oscillations for energy harvesting capability improvement of grid-connected renewable energy systems

The increasing penetration of renewable energy sources in the power system raises several challenges from the power quality and output power fluctuations point of view. However, the output power oscillations and power quality problems caused by the low order harmonic oscillations at the second-order frequency of the utility grid on the dc-link capacitor are emerging as major issues for the efficient operation of power converters. In this manner, a novel method based on modification in the control algorithm to alleviate the output power oscillation and reduce the output current total harmonic distortion is proposed. The proposed control approach seems as a promising solution for the satisfactory grid operation of renewable energy sources regarding not requiring any additional circuit and increment in the capacity of the dc-link capacitor. Moreover, mitigation of oscillations enhances the active power reference tracking capability of the controller that enables the overall efficiency improvement of the system. The performed case studies reveal that the overall efficiency rate of the system is increased by 1.3%. On the other hand, the output current harmonic distortion is decreased below 3% even under low power operating conditions. Also, the complexity level of the control algorithm is quite low for real-time implementation.

Bidirectional AC–DC Modular Multilevel Converter With Electric Spring Functions for Stabilizing Renewable AC Power Grid at the Distribution Voltage Level

Bidirectional ac–dc power converters are essential in emerging smart grids with increasing renewable energy penetration. This article presents a bidirectional ac–dc power converter system comprising modular multilevel converters (MMCs) and dual active bridges (DABs) with medium-frequency transformer isolation designed for linking an ac distribution voltage of 6.6 kV to a dc grid of 800 V for future electric vehicle (EV) charging infrastructure. The novel contributions include: 1) a modular method to power EV charging infrastructures in multistorey carparks without mains-frequency transformers and 2) the incorporation of a front-end control with electric spring (ES) functions that enable the dc power grid with battery energy storage to interact dynamically with the ac power grid at the distribution voltage level to achieve instantaneous power balance and hence system stability. The long-term aim is to use large EV charging infrastructures to stabilize increasing intermittent renewable energy via the proposed ac–dc converter, consequently accelerating the adoption of large-scale renewable energy and EV as a complementary solution to combat climate change. This article focuses on the bidirectional ac–dc converter of this overall idea based on the MMC and DAB technologies as an example. Results on the power converter operation level and ac microgrid level are included.

Artificial-Intelligence-Based Design for Circuit Parameters of Power Converters

Parameter design is significant in ensuring a satisfactory holistic performance of power converters. Generally, circuit parameter design for power converters consists of two processes: analysis and deduction process and optimization process. The existing approaches for parameter design consist of two types: traditional approach and computer-aided optimization (CAO) approach. In the traditional approaches, heavy human-dependence is required. Even though the emerging CAO approaches automate the optimization process, they still require manual analysis and deduction process. To mitigate human-dependence for the sake of high accuracy and easy implementation, an artificial-intelligence-based design (AI-D) approach is proposed in this article for the parameter design of power converters. In the proposed AI-D approach, to achieve automation in the analysis and deduction process, simulation tools and batch-normalization neural network (BN-NN) are adopted to build data-driven models for the optimization objectives and design constraints. Besides, to achieve automation in the optimization process, genetic algorithm is used to search for optimal design results. The proposed AI-D approach is validated in the circuit parameter design of the synchronous buck converter in the 48 to 12 V accessory-load power supply system in electric vehicle. The design case of an efficiency-optimal synchronous buck converter with constraints in volume, voltage ripple, and current ripple is provided. In the end of this article, feasibility and accuracy of the proposed AI-D approach have been validated by hardware experiments.

Short-Circuit Analysis of AC Distribution Systems Dominated by Voltage Source Converters Considering Converter Limitations

This paper deals with the short-circuit analysis of distribution systems dominated by Voltage Source Converters (VSCs). A novel methodology has been proposed in this paper for short-circuit calculation of power systems populated with VSCs where the control modes and potential current-saturated operation of power converters are considered. The studied distribution system has been modeled using an element-based steady-state formulation that includes the converter equations in both normal operation and fault scenarios. Then, equilibrium points of the studied distribution system are identified by solving the established systems of equations for different potential current-saturation states of the VSCs. The methodology identifies possible solutions involving different saturation states of different converters. The proposed methodology is applied to a specific case study of a distribution system penetrated with VSCs in both grid-forming and grid-following control. The short-circuit analysis results indicate that VSCs operation shows a significant impact on the short-circuit equilibrium points of the studied system. In addition, multiple equilibrium points may exist depending on whether the grid-forming converter is saturated or not. The existence of multiple equilibrium points is validated through dynamic simulations.

A State Observer for Sensorless Control of Power Converters With Unknown Load Conductance

In this article, the sensorless control problem of a large class of power converters with unknown load conductance is investigated. A reduced-order generalized parameter estimation-based observer (GPEBO) is presented to reconstruct the unmeasurable states and estimate the unknown load conductance of the system. Three nice features of this observer are as follows: finite-time convergence (FTC) is guaranteed, an alertness preservation is imposed to be able to estimate a possibly time-varying load, and the required excitation condition is very weak and can be satisfied in normal operation of power converters. Then, replacing the estimated states and parameter, in a certainty equivalent manner, in a PI passivity-based controller, a sensorless control scheme is proposed to stabilize the systems with exponential convergence. By virtue of the FTC property of the GPEBO, the global exponential stability of the overall closed-loop system is established. Simulation and experimental results of the proposed controller with application to the boost and Ćuk converters are given to assess its effectiveness.

High-Efficiency and High-Power Multijunction InGaAs/InP Photovoltaic Laser Power Converters for 1470 nm

The high-efficiency capabilities of multijunction laser power converters are demonstrated for high-power applications with an optical input of around 1470 nm. The InP-based photovoltaic power converting III-V semiconductor devices are designed here, with 10 lattice-matched subcells (PT10-InGaAs/InP), using thin InGaAs absorbing layers connected by transparent tunnel junctions. The results confirm that such long-wavelength power converter devices are capable of producing electrical output voltages greater than 4–5 V. The characteristics are compatible with common electronics requirements, and the optical input is well suited for propagation over long distances through fiber-based optical links. Conversion efficiencies of ~49% are measured at electrical outputs exceeding 7 W for an input wavelength of 1466 nm at 21 °C. The Power Converter Performance Chart has been updated with these PT10-InGaAs/InP results.

Electrical characterization of a 1200V GaN HEMT at cryogenic temperatures

The cryogenic operation of power converters integrated with the superconducting electric machines can leverage the lower parasitic, lower core material, and insulation requirement to reduce weight and increase power density in aerospace applications. To that end, Gallium Nitride High Electron Mobility Transistor (GaN HEMT) has recently proven to be the most viable option for the cryogenic converter operation. However, the topology selection and optimization are greatly influenced by the current/voltage rating of the power devices. Although series connected HEMTs can increase the blocking voltage, the dynamic voltage imbalance issue stemming from device parameter fluctuations, the larger number of required isolated gate driver makes the need for single high blocking voltage devices more compelling. This is even more pronounced in GaN due to its higher operating frequency which stems from the lower input capacitance. Although 900V cascode GaN HEMTs are now commercially available, single-chip high voltage HEMTs are attractive due to their zero reverse recovery charge, and lower package bonding parasitics. In this paper, a 1200V enhancement-mode GaN HEMT from GaNPower International has been characterized at cryogenic temperature. A 63% decrease has been demonstrated in the on-resistance, Rds(on) from room temperature to -150°C. The threshold voltage shows a 1.2x increase from room temperature to cryogenic temperature (-178°C). The transconductance (Gfs) shows a 1.34x increase for a temperature difference of 175°C. The results translate to a lower conduction loss and a faster switching speed and unfold further possibility of GaN in cryogenic converter applications.

A Fully Integrated Power Converter for Thermoelectric Energy Harvesting With 81% Peak Efficiency and 6.4-mV Minimum Input Voltage

This letter introduces a fully integrated inductive power converter for thermal energy harvesting using the thermoelectric generator (TEG). With a three-step self-start block, the power converter can cold-start from 83 mV. After self-start, the minimum input voltage to sustain the power converter operation is only 6.4 mV. An integrated maximum power point tracking block keeps impedance matching at the TEG output. A novel low-power zero-current switching block realizes accurate switching with little overhead. The proposed power converter is implemented in a 55-nm CMOS process and achieves 81% peak end-to-end efficiency.

Circuit Dynamics Analysis and Control of the Full-Bridge Five-Branch Modular Multilevel Converter for Comprehensive Power Quality Management of Cophase Railway Power System

This article presents an in-depth study on the circuit dynamics and control strategy of the recently proposed full-bridge five-branch modular multilevel converter (FB5B-MMC) to qualify its application potential for comprehensive power quality management of cophase railway power system (RPS) with detailed consideration of nonideal operating conditions. In particular, the circuit dynamics coupling induced by branch inductor parameter discrepancy, and the effects on branch voltages, branch currents, capacitor voltage stability, and fluctuations brought by compensating nonlinear traction loads are thoroughly investigated. With the presence of nonlinear traction loads and branch inductance discrepancy, current controllers based on the repetitive control theory are proposed to achieve high-performance suppression of the grid-side rich-content harmonic currents along with other power quality management goals. In addition, branch energy controllers are well designed to ensure capacitor voltage stability against disturbances. Therefore, the power quality management performance and converter operating stability can be effectively enhanced. The effectiveness of the FB5B-MMC and the proposed control strategy for cophase RPS power quality management are verified by means of simulations and experiments.