Three-phase Power Electronics Research Articles

A real-time digital twin approach on three-phase power converters applied to condition monitoring

This paper describes a methodology based on the digital-twin concept applied to the condition monitoring of three-phase power electronics converters. The proposed solution does not need additional hardware circuits or sensor calibration. The digital replica acts as a permanent watchdog, working in parallel with the converter control system and providing in real-time the signals to be monitored. An application for a Three Leg Neutral Point Clamped (3L-NPC) converter is demonstrated including theoretical analysis for the digital model, practical considerations about the real-time execution of the virtual representation, and experimental verification. The combination of two optimization algorithms (Particle Swarm Optimization (PSO) and a genetic algorithm (GA)) working in series is employed to estimate the circuit parameters of interest, specifically the degradation of the output LC filter. The results shown in this paper serve as a first step for attaining a low-cost and robust parallel digital-twin model as a basis for its application to the concepts of monitoring and reliability.

A Novel Decoupling Control Scheme for Non-Salient Multi-Three-Phase Synchronous Machines Based on Multi-Stator Model

As competitive alternatives to conventional three-phase synchronous machines, synchronous multi-three-phase machines (MTPMs) are gaining increasing interests in various fields such as electrified transportation and power generation. The modular configuration is preferred for multi-three-phase drives in specific applications regarding the availability of advanced three-phase power electronics techniques and the superior capability of fault tolerance. The multi-stator (MS) modelling would be an ideal solution for the control of such modular drives as it facilitates power sharing among winding sets in a straightforward way and enables simple post fault strategies compared with the well-known vector space decomposition (VSD) modelling approach. Nevertheless, the strong magnetic coupling existing in MS model has hindered its use due to the instability and the performance deterioration issue. To solve the problem, a new decoupling control scheme directly applied in MS frame is proposed in this paper. The proposed method can deal with non-salient multi-three-phase machines whose three-phase winding sets can be identical or different, under the assumption of the sinusoidal airgap flux. Furthermore, it is shown by analysis the proposed method is characterized by significant simplicity and flexibility compared with the existing decoupling methods. The effectiveness of the proposed method has been verified through experiments including a single-side operation, a power-sharing test, and a post fault tolerant operation on a non-salient dual three-phase permanent magnet synchronous machine with quasi sinusoidal air gap flux.

Universal System for Detection and Compensation of Current Sensor Faults in Three-Phase Power Electronic Systems

Abstract The article discusses the universal current sensor fault detection and compensation mechanism, which can be applied in three-phase power electronics (PE) symmetrical system. The mechanism is based on the assumption that a symmetrical system can be described using different components in the stationary reference frame. The solution given in article as a Cri-base detector was tested in electrical drives with induction motors (IMs) and permanent magnet synchronous motors (PMSMs). This study also proves that the same algorithm can work stable in active rectifier systems. Such an application of this detector has not been previously reported in the literature. The article describes the detection of various types of faults in different phases. The fault-tolerant voltage-oriented control (FTVOC) of an active rectifier is compared with previously described solutions for IMs and PMSMs. By analysing in various types of systems, the work proves the universality of the detector based on Cri markers.

Exact Force Vector Regulation of the Three-Pole Magnetic Bearing

The three-pole magnetic bearing is an attractive alternative to the conventional four- and eight-pole magnetic bearings because of its simple structure and ability to be operated with three-phase power electronics. However, accurately controlling the three-pole bearing is significantly more complicated. The conventional control implementations are prone to large force vector errors that can lead to instability in the magnetic suspension system. This article proposes a new control implementation for externally biased three-pole bearings that eliminates force vector error. This control implementation is based on solving a fourth-order polynomial in the form of a depressed quartic to determine coil current commands. An analytic framework and graphic techniques are developed to study the solution space for the bearing's coil currents and explain discontinuities that can arise in certain bearing designs. It is shown that bearings with either no bias or a normalized bias field in excess of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\frac{1}{3}$</tex-math></inline-formula> are preferred for suspension stability. The exact force vector regulator is experimentally demonstrated in a bearing prototype and shown to be advantageous over the conventional regulation approach.

Harmonic mitigation technique using active three‐phase converters utilised in commercial or industrial distribution networks

Current harmonics generated by adjustable-speed drives (ASDs) are one of the main power quality concerns in commercial and industrial distribution networks due to a high number of ASDs. These harmonics affect the grid power quality, instability, resonances, and power losses. Therefore, different harmonic mitigation strategies using active front end have been proposed to tackle this issue. However, due to the cost-effectiveness, conventional front end such as diode rectifier is still recommended in industries for a broad range of three-phase power electronics systems. Thus, in this study, a new DC modulation method is proposed using three-phase diode rectifier with controlled DC-link current (boost converter) for grid harmonic elimination approach. Simulations and experiments have been carried out to validate the proposed concept that a selective harmonic can be eliminated from the grid using the developed strategy.

Effective and Simple Control of Grid-Connected Three-Phase Converter Operating at a Strongly Distorted Voltage

Three-phase power electronics converters (PECs) are commonly used as an interconnection of DC loads/sources with the electrical AC power system. Their important goal is to ensure three-phase symmetrical and pure sinusoidal grid current waveforms. Unfortunately, frequent adverse of grid voltage conditions like the occurrence of higher order harmonics and dips/sags leads to problems in maintaining high-quality parameters of current and stable operation of PEC. Therefore, a more complex control algorithms are usually used to solve those problems. In this paper, effective and simple control is proposed to mitigate grid current distortions caused by grid-voltage harmonics. This improvement of current quality can be easily obtained in control of grid-connected PEC using only band notch filtered grid voltage as a feedforward without any additional control loops parallel connected to linear current controllers (tuned to fundamental frequency). Theoretical analysis with simulation and experimental investigations are presented, which prove very good properties and advantages of the proposed control idea.

An Intelligent Fault Diagnosis Method for Open-Circuit Faults in Power-Electronics Energy Conversion System

Applying the fault diagnosis techniques to power electronic equipments is beneficial to improve the stability and reliability of renewable energy system, because power electronic equipments are a key component of renewable energy system that largely defines their performance. This paper presents a novel intelligent fault diagnosis method for a three-phase power-electronics energy conversion system based on knowledge-based and data-driven methods. Firstly, the three-phase AC currents of the power-electronics energy conversion system are collected and used to analyze. Secondly, the feature transformation, a knowledge-based method, is utilized to preprocess the fault data. After feature transformation, the slopes of current trajectories (transformed features) are not affected by different loads. And then random forests algorithms (RFs), a data-driven method, are adopted to train the fault diagnosis classifier with the processed fault data. Finally, the proposed method is implemented online on an actual three-phase PWM rectifier platform. The results show that the proposed fault diagnosis method can successfully detect and locate the open-circuit faults in IGBTs of the three-phase PWM rectifier. In addition, the proposed method is suitable for most of three-phase power-electronics energy conversion systems.

A Three-Phase Integrated Onboard Charger for Plug-In Electric Vehicles

A three-phase onboard charger, integrated with the propulsion system of a plug-in electric vehicle, is presented. It is constructed by connecting an add-on three-phase power electronics interface to the propulsion system. The propulsion motor is utilized as a coupled DC inductor for the charger. The charging power level of the proposed charger could be as high as that of the propulsion system. The charger topology is capable of three-phase power factor (PF) correction and battery voltage/current regulation. Detailed analyses of the circuit operation and modeling of the circuit are presented. Experimental results of a 3.3-kW three-phase integrated charger, using a permanent magnet synchronous machine (PMSM), are provided. A nearly unity PF and 4.77% total harmonic distortion are obtained with a maximum efficiency of 92.6%.

Synchronous Generator Emulator Prototype as a Testbed for Electric Equipment

The aim of this study is to describe a synchronous generator emulator prototype based on a three-phase power electronics converter. The physical structure of the emulator and its relation with the generator mathematical model is described. A voltage-behind-reactance model is used to reproduce the behavior of the generator. Comparison of experimental results against simulations confirms the validity of the proposal.

Control Strategies of Three-Phase Distributed Generation Inverters for Grid Unbalanced Voltage Compensation

The high penetration level of power electronics interfaced distributed generation (DG) systems creates great ancillary services potential through the DG interfacing converters, such as the grid unbalanced voltage compensation. However, the unbalanced voltage compensation may cause adverse effects on the DGs' operation, such as output active power oscillation and dc-link voltage variations. Moreover, since the compensation is realized through the available rating of DGs' interfacing converters, it is equally important to consider the effectiveness of control strategy for unbalanced voltage compensation. Considering these challenging issues, two grid unbalanced voltage compensation strategies for three-phase power electronics interfaced DG systems are proposed in this paper. Especially, the first control strategy aims at minimizing the DG's active power oscillation and reducing the adverse effects of unbalanced voltage compensation on DG's operation. The second control strategy focuses on the effectiveness of unbalanced voltage compensation by controlling DG's negative sequence current to be inphase with the grid negative sequence current. Performances of the two proposed control strategies under different grid conditions and DG operating conditions are studied, and recommendations for appropriate control strategy utilization under various conditions are provided. Finally, validity of the proposed strategies is verified by both simulations and experimental results.

A Unifying Approach to Single-Phase Synchronous Reference Frame PLLs

The three-phase synchronous reference frame phase-locked loop (3-SRF-PLL) is widely used in three-phase power electronics and power system applications thanks to its desirable performance and its simple yet robust structure. Inspired from the 3-SRF-PLL and due to the increasing interest in single-phase applications, multiple single-phase SRF-PLL (1-SRF-PLL) versions have also been proposed in the recent years. This paper presents a unifying approach to the understanding and analysis of the 1 -SRF-PLLs. This paper integrates several 1 -SRF-PLLs having apparently different structures into a single structure. The approach is much useful in understanding various PLLs and also in facilitating further developments in this field.

Fault Detection and Isolation Filters for Three-Phase AC-DC Power Electronics Systems

This paper develops and experimentally demonstrates a new class of high-fidelity model-based fault detection and isolation filters for three-phase AC-DC power electronics systems. The structure of these filters is similar to that of a piecewise linear observer and in the absence of faults the filter residual converges to zero. On the other hand, whenever a fault occurs, by appropriately choosing the filter gain, the filter residual will exhibit certain geometric characteristics that allow the fault to be detected and, in certain cases, also isolated. Key advantages of these filters include fast detection of all possible component faults and the ability to capture slow degradation in individual components. In order to experimentally demonstrate their feasibility, the filters are implemented on an ultra-fast application-specific real-time processor. While the theoretical framework developed is general, the analysis, simulations, and experiments are focused on widely used power electronics systems implementing three-phase AC-DC converters that are used in, e.g., motor drive applications and distributed static compensators.

Characterization and Design of Three-Phase EMI Noise Separators for Three-Phase Power Electronics Systems

In this paper, three-phase noise is first analyzed using symmetrical component theory. Three-phase noise separators are modeled and characterized using symmetrical component theory and S-parameters. The critical formulas used to evaluate a three-phase noise separator are derived. A function scheme and a circuit structure for three-phase noise separators are proposed based on the theory developed. The technique to design a high-performance three-phase noise separator is explored. A three-phase noise separator prototype is finally built, measured, and evaluated using the theory developed in this paper. The prototype is used in a practical three-phase power electronics system for electromagnetic interference measurement.