Active Front-end Rectifier Research Articles

Improved Dynamic Performance of Average-Value Modelled Active Front-End Rectifiers

Active front-end (AFE) rectifiers have become widely employed in power systems to achieve unity power factor and harmonic mitigations. The typical modeling approaches applied for AFE rectifiers in the literature mostly relied on two baselines: the detailed model and the time-average model. The former approach deals with the switching element model (SEM), which leads to significant harmonics in currents with distorted waveforms. The latter approach uses the average-value model (AVM) to overcome the currents’ harmonics as well as provide fast responses. However, even the AVM baseline has shown problems during the starting stage (lack of control signals) and over the dead-time periods, which causes serious issues in the implementation process. This paper presents an improved dynamic AVM for AFE rectifiers by precisely considering the issues mentioned above, along with the practical starting procedure and desirable initialization. The studied AFE rectifier is developed using the voltage-oriented control (VOC) technique based on the different modeling methodologies, including SEM, Conventional AVM, and the proposed AVM. The performance of all models is analyzed and compared using simulation results with MATLAB/Simulink R2023a Function blocks for all the algorithm parts and SimScape elements for the electrical circuit model. The simulation results illustrate that the performance of the proposed AVM approach can closely resemble the behavior of the SEM baseline with low harmonic distortion. To evaluate the performance of the proposed model, several case studies are investigated to verify the AFE rectifier operation, regarding mostly the total harmonic distortion (THD) wherein the THD percentages are improved to 4.78 and 2.5 from 5.14 and 2.78 for low- and high-power loads, respectively.

Voltage Injection Based MPDPC Technique for Individual Phase Loss Reduction in Active Front-End Rectifier

Voltage Injection Based MPDPC Technique for Individual Phase Loss Reduction in Active Front-End Rectifier

Разработка и исследование усовершенствованных алгоритмов ШИМ активных выпрямителей с целью улучшения качества электроэнергии во внутризаводских электрических сетях 6–35 кВ

Currently, application of frequency converters with active front end rectifiers (FC-AFE) has become a standard solution for powerful adjustable AC drives with frequent dynamic modes. The advantages of these converters include the possibility of recuperation of braking energy to the supply network, as well as the best electromagnetic compatibility of electromagnetic capability (EMC) with the supply network as stated by the manufacturers of converter technology. This statement is only partly true, since FC-AFE manufacturers do not consider possible resonant phenomena in the 6–35 kV intra-factory distribution network caused by the interaction of reactive elements of the power supply system. When significant harmonics of the FC-AFE current are superimposed on the resonant region, dangerous voltage distortions of 6–35 kV may occur. Traditional methods of providing electromagnetic capability of FC-AFE in this case may not have the desired effect. Therefore, it is relevant to develop alternative technical solutions to ensure an acceptable level of electromagnetic capability of FC-AFE. One such solution is the use of advanced PWM algorithms in the FC-AFE adapting to resonant phenomena in the 6–35 kV intra-factory network. The materials for the study are the oscillograms of the currents and voltages at the input of the FC-AFE obtained experimentally and using mathematical modeling. Experimental data have been obtained on operating equipment with FC-AFE and on a special laboratory setup. When developing improved PWM algorithm of AFE, a well-known mathematical apparatus is used. It describes the dependence of individual harmonics on the number of switching and switching angles. The results obtained show the effectiveness of improved PWM algorithms in terms of reducing the effect of FC-AFE on the supply network and improving the quality of electricity in intra-factory networks of 6–35 kV. The results of the study are implemented at a number of metallurgical enterprises, thanks to which it is possible to reduce voltage distortions of 6–35 kV and increase the stability of the operation of sensitive electrical receivers. The developed improved PWM algorithm of FC-AFE can significantly improve the quality of electricity in the in-house electrical networks of 6–35 kV without additional capital costs and installation of additional equipment. Based on the results obtained, it is recommended to use the developed PWM algorithms on the operating equipment with FC-AFE of industrial enterprises.

Improved Square Wave Injection Strategy for the Voltage Balance Control of Cascaded H-Bridge Rectifier

The modular cascaded H-bridge (CHB) adopted as the active front-end rectifier in the power electronic traction transformer tends to suffer from dc voltage imbalance issues when the load powers of each module are severely unbalanced. The existing square wave injection strategy (SWIS) can improve the capacitor voltage balancing performance, but the maximum amount of the injected square wave in the high-power modules is only 1– <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> is the average modulation index). In order to extend the load imbalance operation range of the CHB, the improved SWIS (ISWIS) proposed in this paper not only increases the square wave content in the high-power module to 1 (the modulation index is increased to 1.27), but also reduces the phase between the ac voltage and ac current of the high-power module to 0 when the load imbalance becomes severer. These two important changes allow the high-power H-bridge modules to transmit the maximum active power. Moreover, the over-modulation problem caused by the superposition of the opposite compensation signal in the low-power modules is analyzed and an effective solution is then proposed to avoid the current distortion issue. Both simulation and experimental results prove the correctness and validity of the proposed strategy.

Control over Grid Reactive Power by Using a Powerful Regenerative Controlled-Speed Synchronous Motor Drive

The authors propose a technique for reactive power compensation using a powerful regenerative controlled-speed synchronous motor drive (SMD) based on a three-level (3L) neutral point clamped (NPC) active front-end rectifier (AFE) and a voltage source inverter (VSI). The review of technical solutions for reactive power compensation showed that the limitations on the transmitted reactive power in the system under consideration still have not been studied. The paper provides a mathematical description and proposes synthesis-friendly block diagrams of the mathematical 3L-NPC-AFE-VSI and SMD models. The developed models allow defining the instantaneous values of the total 3L-NPC-AFE power consumed from the grid depending on the SMD load diagram. It is noted that the 3L-NPC-AFE-VSI-SMD system is designed without considering the opportunities for reactive power generation. It was determined that the limit value of reactive power generated by a 3L-NPC-AFE depends on the DC link voltage, the grid current consumption and the modulation index. The possibility of reactive power compensation by the SMD system through a 3L-NPC-AFE was experimentally tested on the main drive of a metal plate hot rolling mill. The analysis of the results obtained showed that during the breakdown, an SMD can generate reactive power equal to 16% of the total rated power using a 3L-NPC-AFE at a rated DC link voltage and without overcurrent. It was shown that generating reactive power is expedient in low-load SMD operation modes or at idle. Research in this area is promising due to the widespread use of high-power SMD based on a 3L-NPC-AFE-VSI and the tightening of requirements for energy saving and efficiency and supply voltage quality. The proposed reactive power control technique can be used as part of an industrial smart grid.

Stability Analysis of Active Front End and Permanent Magnet Synchronous Generator With Back EMF-Based Sensorless Control for DC Marine Vessels

This article studies the influence of sensorless control on the permanent magnet synchronous generator (PMSG) and pulsewidth modulation (PWM) converter (active front end rectifier, AFE) system for dc marine vessels. Back EMF-based sensorless control is adopted in this article because the minimum speed of PMSG in a dc marine vessel is enough for obtaining a sufficient back EMF signal. First, the output impedance of “PMSG+AFE” system with a typical topology and controller is deduced by small-signal analysis. The stability analysis with constant power load (CPL) is analyzed, including the influence of sensorless control bandwidth on PMSG with a significant per-unit impedance value. Since the inductance parameter affects both the current control and sensorless control, the influence of error in the estimated inductance parameter on the stability of “PMSG+AFE” system is analyzed. To verify the proposed impedance model, output impedance is measured in the simulation and experiment. The stability analysis with the proposed impedance model and load impedance of CPL is provided in MATLAB, and simulation results and experimental measurements are given to verify the analysis.

Review of Active Front-End Rectifiers in EV DC Charging Applications

Active Front-End (AFE) rectifiers have regained momentum as the demand for highpower Electric Vehicle (EV) charging infrastructure increases exponentially. AFE rectifiers have high efficiency and reliability, and they minimize the disturbances that could be generated due to the operation of the EV charging systems by reducing harmonic distortion and operating close to the Unity Power Factor (UPF). The purpose of this review is to present the current state-of-the-art AFE rectifiers used in fast chargers, focusing on the comparison between different AFE topologies and their components, as well as modular AFE solutions. Furthermore, different control strategies of AFE converters are presented and compared. Some of their more widely used control techniques, namely Voltage Oriented Control (VOC), Direct Power Control (DPC), Hysteresis Current Control (HCC), and Model Predictive Control (MPC), have been implemented, and their performance compared. Centralized and distributed control systems are compared for operating parallel AFE rectifiers for modular, fast charging systems. An overview of cooling systems and reliability evaluation tools is also presented. Finally, trends and future outlooks are analyzed.

Floating, Production, Storage, and Offloading Unit: A Case Study Using Variable Frequency Drives

The use of variable frequency drives (VFD) in floating, production, storage, and offloading (FPSO) units provides well-known benefits to the power system, such as: soft-starting of motors, increase of energy-efficiency, reduction of short-circuit currents, and enhancement of the load shedding capability. The VFDs with passive front-end rectifiers are the most commonly used for these applications due to their wider commercial availability and lower cost compared to VFDs with active front-end rectifiers. However, the latter can control the exchange of reactive power with the grid, which may contribute to voltage support and power factor regulation at the electrical system. This paper presents a case study considering the Production operating mode of an FPSO unit with two VFDs connected to the largest motors (i.e., water injection pumps). Simulations of the FPSO power system are evaluated using both active and passive VFDs, considering scenarios with analysis of steady-state, start of largest motors and symmetrical three-phase short-circuit.

Исследование спектров тока 18-пульсной схемы подключения трёхуровневых активных выпрямителей

Исследование спектров тока 18-пульсной схемы подключения трёхуровневых активных выпрямителей

Current Electromagnetic Compatibility Problems of High-Power Industrial Electric Drives with Active Front-End Rectifiers Connected to a 6–35 kV Power Grid: A Comprehensive Overview

Today, electric drive systems based on frequency converters with active front-end rectifiers (FC-AFEs) are widespread across industries. In the course of the upgrade of production facilities, such systems replace the conventional converters with thyristor- and diode-based rectifiers. FC-AFEs have the following advantages: the capacity to regenerate the power to the grid and the capacity to operate at the set power factor. The manufacturers of FC-AFEs also claim that their products have the best electromagnetic compatibility (EMC) with the power grid. The best EMC shall be achieved via a multilevel FC-AFE topology and specialized pulse-width modulation (PWM) algorithms for AFE rectifiers. However, the experience of operating mid-voltage high-power electric drives with an FC-AFE in 6–35 kV factory distribution grids with non-linear frequency response due to resonant phenomena refutes the claims of the FC-AFE manufacturers. Resonant phenomena in 6–35 kV grids are caused by the interaction of the inductance of grid components (transformers, reactors) and the capacitance of output cable lines. If the resonance frequency at a sufficient amplitude corresponds to the harmonic frequency of the current consumed by the FC-AFE, the distribution grid will feature high-frequency voltage distortions. This may lead to failures in voltage quality-sensitive electrical consumers. This problem recurred at various metallurgical companies. The purpose of this research is to make a comprehensive overview of the EMC problems during the operation of FC-AFEs at active production facilities, as well as the analysis of the technical solutions aimed at the improvement of the EMC of high-power FC-AFEs with the power grid.

Fuzzy Sliding-Mode Control for Three-Level NPC AFE Rectifiers: A Chattering Alleviation Approach

Due to the high-performance requirements of power converters in industrial applications, sliding-mode control has drawn extensive research attention for its insensitivity against external disturbances. In order to ensure this advantage while suppressing the chattering problem caused by discontinuous switching functions, in this article, a fuzzy sliding-mode control (FSMC) strategy consisting of three control loops is proposed for three-phase three-level neutral-point-clamped active front-end rectifiers. In the power tracking loop, an improved super-twisting algorithm is proposed to enforce the tracking errors of active power and reactive power to bounded regions in finite time and guarantee the transient performance. Next, in the dc-link voltage regulation loop, the regulation error of dc-link voltage converges to a bounded region with a super-twisting extended state observer-based FSMC strategy. A simple but efficient proportional-integral controller is employed in dc-link voltage balancing loop to reduce the voltage difference between two dc-link capacitors. The proposed controller is characterized by attenuated chattering phenomenon and improved the dc-link voltage regulation performance, disturbance rejection ability, and power tracking performance. Experimental results are provided to verify the effectiveness and superiority of the proposed strategy.

Analysis, Limitations, and Opportunities of Modular Multilevel Converter-Based Architectures in Fast Charging Stations Infrastructures

As fast and ultrafast charging stations (FCS/UFCS) increase their degree of penetration in the grid, it becomes beneficial to connect them directly at the medium-voltage (MV) level, as this reduces volume, losses, and cost. Recent solutions propose the replacement of the typical combination of the low-frequency transformer plus low-voltage rectifier by a solid-state transformer (SST), which can be composed, among other topologies, by a modular multilevel converter. This article proposes and discusses the application of the modular multilevel converter (MMC) in FCS infrastructures, utilized as an active front-end rectifier, either as part of an SST or for direct connection to the second stage, comprised of isolated dc/dc converters. Focus is given on the advantages and limitations of the converter operating as a step-down rectifier, where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$U_\text{DC}&lt; \hat{U}_\text{AC}$</tex-math></inline-formula> . As different architectures are presented, first the MMC step-down constraints and optimum operation points are explored and discussed, then the architectures are evaluated in terms of key performance indicators, such as size, efficiency, and reliability. At the end, experimental results for a full-scale MV MMC are presented, validating the analysis carried throughout this article.

Comparative Analysis on AC and DC Distribution Systems for Electric Propulsion Ship

Decarbonization is an ongoing issue in the shipping industry, and electric propulsion systems are being proposed as alternative solutions to satisfy this requirement. To answer the fundamental questions of “Are electric propulsion systems the green solution?” and “Can DC distribution systems contribute to the decarbonization in shipping?”, this paper analyzed DC distribution system electrical characteristics, economic feasibility, and environmental evaluation for a full-scale AC-DC hybrid distribution electric propulsion system facility. By applying the actual ship’s operating profile as inputs, a DC distribution system with an active front end rectifier and a variable speed generator engine was proven to guarantee the same electric stability as the conventional AC distribution system. The life cycle assessment results achieved economic and life cycle environmental benefits of about 10% (8.9% for Case 1 and 12.4% for Case 2). These research findings offer meaningful insights into the DC distribution system to minimize fuel consumption and emissions toward cleaner shipping.

Design and Real-Time Implementation of a Control System for SiC Off-Board Chargers of Battery Electric Buses

Emerging wide bandgap (WBG) semiconductors, such as silicon carbide (SiC), will enable chargers to operate at higher switching frequencies, which grants the ability to deliver high power and enhances efficiency. This paper addresses the modeling of a double-sided cooling (DSC) SiC technology-based off-board charger for battery electric buses (BEBs) and the design of its control and real-time (RT) implementation. A three-phase active front-end (AFE) rectifier topology is considered in the modeling and control system design for the active part of the DC off-board charger. The control system consists of a dual-loop voltage–current controller and is used to ensure AC to DC power conversion for charging and to achieve the targeted grid current total harmonic distortion (THD) and unity power factor (PF). Linear and nonlinear simulation models are developed in MATLAB/Simulink for optimum control design and to validate the voltage and current control performances. Four types of controllers (i.e., proportional–integral (PI), lead–lag, proportional–resonant (PR), and modified proportional–resonant (MPR)) are designed as current controllers, and a comparative analysis is conducted on the simulation model. In addition, the final design of the dual-loop controller is implemented on the RT–FPGA platform of dSpace MicroLabBox. It is then tested with the charger to validate the control performance with experimental data. The simulation and experimental results demonstrate the correct operation of the converter control performance by tracking the reference commands.

Сравнительный анализ спектров тока в многопульсных схемах подключения к питающей сети трёхуровневых активных выпрямителей напряжения с предварительно запрограммированной широтно-импульсной модуляцией

Проанализированы спектры тока в 6-, 12- и 18-пульсных схемах подключения трёхфазных трёхуровневых активных выпрямителей напряжения (АВН) с предварительно запрограммированной широтно-импульсной модуляцией (ПЗШИМ) при удалении выделенных гармоник. Представлены значения суммарного коэффициента гармонических составляющих тока в рассматриваемых схемах подключения АВН с ПЗШИМ на частотах 150 – 350 Гц с удалением только наиболее значимых гармоник при одинаковой потребляемой мощности и параметрах питающей сети. Результаты сравнительного анализа могут быть использованы для проектирования или поиска проблем обеспечения электромагнитной совместимости мощных АВН с питающей сетью в многопульсных схемах

ВОЗМОЖНОСТИ КОМПЕНСАЦИИ РЕАКТИВНОЙ МОЩНОСТИ В СЕТИ ПОСРЕДСТВОМ ВЫСОКОМОЩНОГО РЕКУПЕРАТИВНОГО ЭЛЕКТРОПРИВОДА ПЕРЕМЕННОГО ТОКА

Relevance At present, there is no complete understanding of the possibilities of reactive power compensation by means of high-power regenerative AC drives (RACD) with active frondend rectifiers (AFE), given the limitations and associated problems with electromagnetic compatibility. Aim of research The article is devoted to the issues of reactive power compensation and improvement of the voltage quality in the grid by high-power RACD with AFE. Research methods Methods of theoretical and experimental researches are applied in the work. Results It was noted that the smooth component of the first harmonic of the AFE output voltage is limited by the voltage in the DC link and the maximum allowable AFE current, and this affects the range of transmitted reactive power in the system «RACD with AFE – grid». Thus, there are restrictions for the generation of reactive power in the system «RACD with AFE – grid», which requires their special calculation in the synthesis of the control system. Power quality improving by powerful RACD with AFE is possible only with the correct choice of the grid connection, the switching frequency of semiconductor modules, resonance analysis, AFE control system parameters and thermal control of the power modules. The experimental curves of current consumption from the grid presented in the paper with two different PWM algorithms for the AFE demonstrates a decreasing of current total harmonic distortion. Keywords: active front-end rectifier, pre-programmed PWM, selective harmonic elimination, electromagnetic compatibility, power quality Acknowledgments: The work was supported by the Grant of the President of the Russian Federation for young scientists — candidates of sciences MK-3803.2022.4.

A Predictive Shortest-Horizon Voltage Control Algorithm for Non-Minimum Phase Three-Phase Rectifiers

Three-phase active front end rectifiers are a widely used power topology in applications such as renewable energy interfaces and motor drives, among many others. Its control is usually performed by a cascade combination of linear controllers which must be properly tuned for correct operation, and which depend on the operating point and system parameters. These family of controllers place inherent limits on the system dynamic response. On the other hand, the predictive control approach has been proposed as an alternative technique for these converters due to its fast dynamic response, simple concept, flexibility, multiple objective capability, among other desirable properties. In the case of power converter applications, short prediction horizons are usually used due to computational limitations. However, when short horizons are considered, the non-minimum phase characteristic of the rectifier voltage response can introduce stability issues, as its direct inversion is not possible without jeopardizing it. Indeed, this may lead to voltage regulation loss, and in the worst case, overcurrents that could damage the converter. To overcome such problem, this paper proposes a new concept for a predictive horizon one voltage controller for grid-connected three-phase active front end rectifiers. The proposal is based on the minimum and non-minimum phase plant factorization concept and the use of different sampling periods, to prevent the direct inversion of the non-minimum phase voltage dynamic. Simulated and experimental results are included and show its correct operation, even with a horizon one predictive voltage controller, thus ensuring the fastest response of the system for a given sampling time.

A fast charging of Li‐ion battery based on Lyapunov function for electrical vehicle

This paper focuses on design of a control system for full bridge DC-DC converter based on Lyapunov stability theorem which guarantees system stability. To achieve this goal, a full bridge DC-DC converter is used as a Li-ion battery charger and sinusoidal ripple current (SRC) is implemented as the charging algorithm. In initial step, state space equation of the system including DC-DC converter and battery are obtained. After that, switching function is extracted by applying Lyapunov stability theorem to state space equation. Also in order to achieve unity power factor and allowable current Total Harmonic Distortion (THD) range based on standards, an Active Front End (AFE) PWM Rectifier is used. To evaluate the effectiveness of the proposed controller scheme, a laboratory prototype is implemented. Experimental result shows appropriate performance of proposed controller in tracking of reference values in comparison with fixed PI controller. In addition, results of AFE rectifier performance is evaluated by showing the unity power factor and low THD value.

Concept design of the control method for the NBI acceleration grid power supply-conversion system of CFETR

The China Fusion Engineering Test Reactor (CFETR) uses a negative-ion neutral beam injection (N-NBI) system that requires a powerful acceleration grid power supply (AGPS). The AGPS is rated at -1000 kV/80 A and feeds one injector. AGPS-conversion system, which uses a three-level neutral-point-clamped active front-end rectifier as well as a five-level neutral-point-clamped / cascaded H-bridge inverter, was investigated in the reference design. Because the control problem of the conversion system is crucial for the AGPS, a well-designed control method can improve the steady-state performance during operation substantially. To achieve the full potential of the proposed design and meet the challenging demands of the CFETR N-NBI system, a new control method is proposed and investigated in this paper. Considering the requirement to provide a wide range output voltage, the new control method provides an adjustable DC-link voltage for the rectifier with unity power factor and a suitable modulation factor for the inverter, while maintaining a low ripple voltage of output voltage. The steady performance of the AGPS is successfully improved using phase-shifted carrier-pulse-width modulation. Simulation results are performed that validate the new control method.

Multicell AFE Rectifier Managed by Finite Control Set–Model Predictive Control

Multicell converters, based on power cells that use low-voltage semiconductors, implement AC motor drives for medium-and high-voltage applications. These converters feature an input multipulse transformer, which performs low-frequency harmonics cancelation generated by three-phase diode rectifiers in the power cells. Despite this advantage, the multipulse transformer is bulky, heavy, expensive, and must be designed according to the number of power cells required by a specific case, limiting the modularity of the topology. This work proposes a multicell converter based on power cells that requires a standard input transformer and uses active front-end rectifiers controlled by employing a finite control set-model predictive control algorithm. The proposed approach emulates the multipulse transformer harmonic cancelation owing to the predictive algorithm operation combined with input current references that are phase-shifted for each active front-end rectifier. Simultaneously, the DC voltages of the power cells are regulated and equalized among the cells using PI regulators. Experimental results confirm the feasibility of the proposed system as input currents in each Multicell AFE rectifier with a unitary displacement factor, and a low THD of 1.87% was obtained. It is then possible to replace the input multipulse transformer with standard ones while reducing the copper losses, reducing the K factor, and extending the modularity of the power cell to the input transformer.