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AC/DC converters, controlled by pulse width modulation (PWM) and used as power factor correction (PFC), is considered one of the main contributors to emissions in the range 2 kHz–150 kHz, recently known as the supraharmonic (SH) range. This study looks at the impact of SH grid distortion on the LF (<2 kHz) and HF (>2 kHz) emission of an AC/DC converter. The PFC boost converter is used as a particular case for validation of the results. It is observed that the AC/DC converters emit additional LF interharmonics and subharmonics when the grid voltage contains interharmonic components in the SH range. A mathematical analysis is provided to study and assess the interference between the SH in the background distortion and the AC/DC converters. Experimental studies are then performed for a PFC boost setup based on dSPACE MicroLabBox for the purposes of validating the mathematical analysis. [ABSTRACT FROM AUTHOR]

Against the background of 'Emission Peak, Carbon Neutrality', there is a significant integration of new energy into the power grid. The characteristics of ‘double high’ and ‘double peak’ in power systems become more pronounced, posing a substantial challenge to the stability and energy coordination of the power grid. To address this, we propose a flexible interconnection scheme based on an AC-DC bidirectional converter. It can solve the problem of high-load caused by new energy generation. Firstly, high-load and adjacent substations are flexibly interconnected through the DC bus on the low-voltage side, enabling load management within a small range. Secondly, AC-DC power transfers the excess new energy generation to other substations. It can promote the absorption of new energy. This method can improve the utilization efficiency of distribution transformers, realize capacity sharing between different transformers, and improve the reliability of power systems in low-voltage distribution networks. Finally, based on a DC interconnection project in Shandong Province (China), the effectiveness of the proposed flexible interconnection scheme is verified. The new energy consumption increases from 5% to 24.4%, and the load rate of high-load transforms drops below 70%.

Against the background of 'Emission Peak, Carbon Neutrality', there is a significant integration of new energy into the power grid. The characteristics of 'double high' and 'double peak' in power systems become more pronounced, posing a substantial challenge to the stability and energy coordination of the power grid. To address this, we propose a flexible interconnection scheme based on an AC-DC bidirectional converter. It can solve the problem of high-load caused by new energy generation. Firstly, high-load and adjacent substations are flexibly interconnected through the DC bus on the low-voltage side, enabling load management within a small range. Secondly, AC-DC power transfers the excess new energy generation to other substations. It can promote the absorption of new energy. This method can improve the utilization efficiency of distribution transformers, realize capacity sharing between different transformers, and improve the reliability of power systems in low-voltage distribution networks. Finally, based on a DC interconnection project in Shandong Province (China), the effectiveness of the proposed flexible interconnection scheme is verified. The new energy consumption increases from 5% to 24.4%, and the load rate of high-load transforms drops below 70%. [ABSTRACT FROM AUTHOR]

Abstract Cascaded H‐bridge rectifier (CHBR) is widely used in high‐power fields such as STATCOM and power electric traction transformer (PETT) due to its high efficiency and easy expandability. With the high‐reliability operation requirements of power equipment, the fault‐tolerance capability has gradually become a research hotspot nowadays. In order to improve the reliability of the power supply, cascaded H‐bridge rectifier should restore as soon as possible after a fault. However, the traditional fault‐tolerant strategies have a great effect on the grid side and a long recovery time. This paper proposed a quasi‐hot standby fault‐tolerant control strategy. Compared with the traditional strategies, the quasi‐hot standby fault‐tolerant control strategy has a faster recovery speed after the malfunction, and its transient recovery process has less impact on the power grid. Simulation and experiment results show the effectiveness and good recovery performance of the proposed fault‐tolerant control strategy.

Cascaded H‐bridge rectifier (CHBR) is widely used in high‐power fields such as STATCOM and power electric traction transformer (PETT) due to its high efficiency and easy expandability. With the high‐reliability operation requirements of power equipment, the fault‐tolerance capability has gradually become a research hotspot nowadays. In order to improve the reliability of the power supply, cascaded H‐bridge rectifier should restore as soon as possible after a fault. However, the traditional fault‐tolerant strategies have a great effect on the grid side and a long recovery time. This paper proposed a quasi‐hot standby fault‐tolerant control strategy. Compared with the traditional strategies, the quasi‐hot standby fault‐tolerant control strategy has a faster recovery speed after the malfunction, and its transient recovery process has less impact on the power grid. Simulation and experiment results show the effectiveness and good recovery performance of the proposed fault‐tolerant control strategy. [ABSTRACT FROM AUTHOR]

A modified forward power factor correction (PFC) converter for light-emitting-diode (LED) lighting applications is proposed in this paper. The proposed circuit topology is an integration of a forward converter and a flyback converter with a multi-windings transformer. The flyback converter is operated as an auxiliary voltage source (AVS) connected in series with the rectified ac grid voltage to achieve low harmonic current distortion and high power factor. The magnetizing inductance energy is recycled to charge the capacitor in the AVS. The commonly used constant on-time control and primary side regulation can be easily adopted to control the proposed LED driver. The operation principle of the proposed converter is presented followed by the mathematical derivation of the parameter design. An 80 W prototype converter was built and tested to verify the performance of the proposed PFC converter. Experimental results show that the proposed PFC converter can comply with the IEC 61000-3-2 standard with high efficiency, low current harmonics, and a nearly unity power factor under universal input voltage range.

Optimization of supply current total harmonic distortion (THD) of multi-pulse AC-DC power converter fed induction motor drive (IMD) is always a challenging issue. Higher amount of supply current THD degrades the input power quality of IMD. The supply current THD should be controlled in such a way so that it adheres the power quality standard of IEEE-519. With the increase of the pulse number of multi-pulse AC-DC converter, supply current THD increases. In this work, an investigation has been carried out on 6-pulse, 12-pulse, 18-pulse, and 24-pulse AC-DC power converters based IMD. A thorough analysis of input current profile, THD, dynamic responses including stator current, speed, torque profile of the induction motor are highlighted in this work with the various load perturbation conditions. This work will provide a message to the industrial community about the proper selection of AC-DC power converter for IMD application considering power quality and circuit configuration issues. All the investigating works are conducted in MATLAB/Simulink platform.

This article introduces a new transformerless ac–dc–ac converter topology suitable for a high-power-density high-frequency single-phase online uninterruptible power supply (UPS) with a common neutral between the input and output ac ports. The proposed converter comprises an input power factor correction rectification (ac–dc) stage which is followed by an inversion (dc–ac) stage. The rectification stage operates in boost mode during the input positive half line cycle and buck–boost mode during the input negative half line cycle, while the inversion stage operates in buck and buck–boost modes in the output positive and negative half line cycles, respectively. The rectification stage utilizes boundary conduction mode control enabling soft-switching and allowing high-frequency operation. The inversion stage is operated in continuous conduction mode, wherein a digital controller regulates the output voltage of the converter across both resistive and reactive loads. The proposed online UPS utilizes a single (nonsplit) dc-bus between the rectification and inversion stages, resulting in a 50% reduction in dc-bus capacitance requirement compared to conventional split-bus online UPS topologies. Additionally, two battery interface solutions are also investigated which provide a trade-off between passive volume and additional switch-count. To verify the performance and control of the proposed online UPS, a GaN-based electrolytic-free 1-kVA prototype online UPS is designed, built, and tested. The prototype ac–dc–ac converter achieves a peak efficiency of 95.2% and maintains a high efficiency of above 92.3% across the full output power range. The electrolytic-free prototype ac–dc–ac converter for the online UPS achieves a power density of 26.4 W/in3. [ABSTRACT FROM AUTHOR]

A multiport ac–dc converter topology is proposed that offers bidirectional power transfer capability between the two dc ports and the ac port. The decoupling of power flows can be exploited as a pole voltage balancing mechanism to accommodate unbalanced dc side loads in bipolar dc distribution systems. The proposed topology gains bipolar operation by using two three-phase two-level voltage-sourced converters connected in a differential fashion with a center-tapped transformer. The analysis shows that no penalties are incurred in terms of increased power ratings for either the grid interface transformer or the semiconductors; only access to the center point of the converter side winding is required. A control scheme for the topology is proposed with the ability to independently control power flows between the different ports. Both the topology and control scheme are validated by extensive simulations and experiments. [ABSTRACT FROM AUTHOR]

Parametric transformers are magnetic components which employ a variable inductance to generate parametric oscillations in a secondary resonant tank. Power conversion with parametric transformer can provide constant output voltage regulation, short‐circuit protection, input over‐voltage and under‐voltage protection, and bidirectional filtering. In spite of these benefits, parametric transformers did only experience small scientific attention during the 1970s. Due to the low energy density and low efficiency of the topologies developed at the time, parametric transformers were discarded in favour of the more common power converters based on the magnetic amplifier. In spite of the great developments in power semiconductors, magnetic amplifier control still remains a competitive option in present‐day power electronic applications benefiting from its high robustness. This publication presents a new topology of parametric transformer based on permanent magnet (PM)‐inductors, presenting higher efficiency and higher energy density. Finite element method magnetics simulations are used to analyse the variable inductance mechanisms. A physical prototype is developed and tested empirically in an AC/DC power converter. The prototype verifies all the mentioned benefits of parametric power conversion, and presents an efficiency and energy density equivalent to presently employed solutions for voltage regulation, using power semiconductor magnetic amplifiers. [ABSTRACT FROM AUTHOR]

The principle of operation of a modular AC-DC converter for Plug in Electric Vehicles (PEV's) battery charger applications is presented. The topology is a split version of a conventional active rectifier in a three-phase matrix converter and an H bridge. A Space Vector Pulse Width Modulation (SVPWM) scheme is used together with a Zero Voltage Switching (ZVS) strategy to reduce the switching loses, output voltage regulation, and a low Total Harmonic Distortion (THD). Simulation results are presented to verify the principle of operation of the AC-DC topology with a 5 kW converter. [ABSTRACT FROM AUTHOR]

In this paper, a new class of bidirectional partial-resonance power converters is presented. The proposed family can be configured to interface single- or multi-port dc, single- or multi-phase ac systems at input-side and/or output-side. The proposed family offers a very modular structure, which can lead to cost reduction from a common designed module. In this converter, which accomplishes power conversion in a single stage, a small inductor placed in series with the input and output switch-bridges forms the link. This small link inductor is responsible for transferring power between different ports of the system. The proposed topologies can operate in buck, boost, and buck–boost modes of operation to step up and/or step down the voltage. In buck–boost mode of operation, the converter is controlled such that the power is entirely transferred through the link inductor; whereas, in buck or boost modes of operation only a fraction of the power is transferred through the link inductor, and the remaining power is directly transferred from input phases to the output phases. Galvanic isolation, which is typically a prominent factor contributing to power density of a converter, can be provided by means of a compact and lightweight single-phase high-frequency transformer added to the link. In comparison with earlier generations of partial-resonance inductive-link power converters, in the proposed converter, the level of link peak current and consequently power-loss, as well as voltage and current stress of switches are dramatically decreased. A very small film capacitor can be placed in parallel with the link inductor to facilitate zero-voltage-switching (ZVS) operation for all the switches/diodes. Apart from increasing the overall efficiency, minimized dv/dt stress and improvement in power density are achieved by adding the link capacitor. The proposed converter employs four-quadrant switches, i.e., bidirectional-conducting bidirectional-blocking switches, and charges the link inductor in both positive and negative directions in each cycle. In view of this, better utilization of the link inductor and lower total harmonic distortion (THD) are offered. Furthermore, two distinct switching algorithms are developed for the proposed family of converters. In this paper, the detailed behavior of the proposed family is investigated analytically, and simulation and experimental results are presented to evaluate the performance and effectiveness of the proposed converter. A low-power proof-of-concept prototype with input voltage of 59 V/161 V, load voltage of 178 V/73.5 V, maximum switching frequency of 4.9 kHz/3.65 kHz at 215 W/450 W in a step-up/step-down operation is considered for the experimental verification. [ABSTRACT FROM AUTHOR]

In this article, a new DC hybrid power filter is proposed to attenuate the low–frequency ripple of AC-DC power converter. The proposed DC hybrid power filter is connected between the DC bus of AC-DC power converter and the load, and it composes of a passive power filter and a single-arm power converter. The passive power filter can reduce the voltage rating of single-arm power converter, and the operation of single-arm power converter generates a virtual harmonic resistor connected to the load in series. The DC hybrid power filter can suppress the twice-utility-frequency ripple for eliminating the use of electrolytic capacitor. The salient feature is that the control circuit of the proposed DC hybrid power filter is simplified because only a feedforward control is used. A hardware prototype is developed to validate the performance of the proposed DC hybrid power filter. The experimental results are as expected. [ABSTRACT FROM AUTHOR]

In AC-multi-terminal DC (MTDC) systems, if converter controllers are designed individually, the interactive system modes stemming from the dynamic couplings among the converters and the DC system components may result in the instability of the interconnected system (INTSYS). This paper presents a comparative system-level study to determine the suitable models for an individual design of converter controllers to prevent INTSYS instability. The goal is to identify suitable individual system (INDSYS) models that do not contain the internal dynamics of adjacent converters and only include the coupling dynamics corresponding to the interactive system modes among the converters. The use of these models for control design will result in the dynamic response of the INTSYS being close to that of the INDSYS models. Furthermore, such models can ensure INTSYS stability when converter controllers are designed individually without requiring the complete model of the INTSYS or internal dynamics of the adjacent converters. Both the master–slave and the droop control modes of operation are analyzed, and specific INDSYS models among those available in the literature are recommended for each operation mode. Time-domain simulations in PSCAD validate the accuracy of the INDSYS models. Furthermore, eigenvalue analysis along with the participation factor and sensitivity analyses for a large set of control parameters are employed to evaluate the efficacy of the recommended models. • A comparative system-level study has been done in AC-MTDC systems, and suitable individual system models (INDSYS) are selected to enable designing converter controllers independent of those of the adjacent converters. • Both the master–slave and the droop control modes of operation are analyzed, and specific INDSYS models among those available in the literature are recommended for each operation mode. • Eigenvalue analysis along with the participation factor and sensitivity analyses for a large set of control parameters are employed to evaluate the efficacy of the recommended models. [ABSTRACT FROM AUTHOR]

A novel topology of the ac–dc power converter to supply neutral-point-clamped inverters used in ac motor drives and wind offshore power grids is proposed. It is based on the T-type multi-state switching cell, which allows obtaining a five-level voltage waveform downstream of the input filter inductor. The converter presents a high voltage gain due to the transformer secondary windings associated with series-connected diode rectifiers. Prominent main characteristics of this topology include power factor correction, operation of the filter inductor at twice the switching frequency, reduced conduction losses in the semiconductors, and voltage balance across the output capacitors. To verify the operating principle of the converter a design example is described, considering that the converter specifications are: output power of 3 kW; rms input voltage of 110 V; total output voltage of 1 kV, which is equally divided among four capacitors and switching frequency of 20 kHz. Simulation results are shown to validate the theoretical assumptions and verify the behaviour of the rectifier in terms of dynamic response while also supplying unbalanced loads. [ABSTRACT FROM AUTHOR]

In this work, a feedback linearization controller together with a gain scheduling function is proposed in order to control a high-voltage direct-current transmission system (VSC-HVDC), composed by two three-phase three-level neutral point clamped converters. The described dq0 model has the advantage of simplifying the mathematical analysis and does not disregard the zero-dynamics, against other reported solutions. In addition, based on the input-output linearization a direct current control (DCC) for the whole VSC-HVDC system is presented, where the control tasks are distributed between both converters. Moreover, a control loop to balance, in an independent way the voltage between capacitors at each converter is designed. Additionally, to the unbalance compensator, a gain scheduling scheme is proposed to assigning new tuning parameters for the PI controller, considering the system states as scheduling variables. The real-time simulator OPAL-RT ® is employed as rapid prototyping and test the performance of the proposed DCC scheme. [ABSTRACT FROM AUTHOR]

An improved differential evolution (IDE) algorithm‐based Elman neural network (ENN) controller is proposed to control a squirrel‐cage induction generator (SCIG) system for grid‐connected wind power applications. First, the control characteristics of a wind turbine emulator are introduced. Then, an AC/DC converter and a DC/AC inverter are developed to convert the electric power generated by a three‐phase SCIG to the grid. Moreover, the dynamic model of the SCIG system is derived for the control of the square of DC‐link voltage according to the principle of power balance. Furthermore, in order to improve the transient and steady‐state responses of the square of DC‐link voltage of the SCIG system, an IDE‐based ENN controller is proposed for the control of the SCIG system. In addition, the network structure and the online learning algorithm of the ENN are described in detail. Additionally, according to the different wind speed variations, a lookup table built offline by the dynamic model of the SCIG system using the IDE is provided for the optimisation of the learning rates of ENN. Finally, to verify the control performance, some experimental results are provided to verify the feasibility and the effectiveness of the proposed SCIG system for grid‐connected wind power applications. [ABSTRACT FROM AUTHOR]

Thyristor‐based line‐commutated converters (LCCs) are widely used to achieve AC/DC and DC/AC power conversions in UHVDCs (ultrahigh‐voltage direct currents) transmission. Valve saturable reactors are used to protect power thyristors. To improve the efficiency of bulk electricity transmission over long distance, the operating voltage and current of UHVDCs and therefore the thermal stresses applied to the valve saturable reactors have steadily increased over the last decades. Valve saturable reactor iron losses were studied by accounting for the reverse recovery characteristics of the valve thyristors and the non‐linear characteristics of the saturable reactors. The impact of UHVDC current on valve saturable reactor iron losses was quantified and verified. The valve saturable reactor iron losses of an LCC are generated not only at the turn‐on and turn‐off periods of the valve, but also at the off‐state of the valve. The amount of the losses are affected by the AC busbar stray capacitances of the converter, the valve firing and extinction voltages, the rates of change of valve commutation current, and the reverse recovery current of the valve thyristors. The conclusion obtained will help to understand better the forming mechanism of valve saturable reactor iron losses and optimise the valve saturable reactor design. [ABSTRACT FROM AUTHOR]

Optimization of supply current total harmonic distortion (THD) of multi-pulse AC-DC power converter fed induction motor drive (IMD) is always a challenging issue. Higher amount of supply current THD degrades the input power quality of IMD. The supply current THD should be controlled in such a way so that it adheres the power quality standard of IEEE-519. With the increase of the pulse number of multi-pulse AC-DC converter, supply current THD increases. In this work, an investigation has been carried out on 6-pulse, 12-pulse, 18-pulse, and 24-pulse AC-DC power converters based IMD. A thorough analysis of input current profile, THD, dynamic responses including stator current, speed, torque profile of the induction motor are highlighted in this work with the various load perturbation conditions. This work will provide a message to the industrial community about the proper selection of AC-DC power converter for IMD application considering power quality and circuit configuration issues. All the investigating works are conducted in MATLAB/Simulink platform., Competing Interests: The authors declare no conflict of interest., (© 2022 The Author(s).)

An intelligent controlled three‐phase squirrel‐cage induction generator (SCIG) system for grid‐connected wind power application using wavelet fuzzy neural network (WFNN) is proposed in this study. First, the indirect field‐oriented mechanism is implemented for the control of the SCIG system. Then, an AC/DC power converter and a DC/AC power inverter are developed to convert the electric power generated by a three‐phase SCIG from variable‐voltage and variable‐frequency to constant‐voltage and constant‐frequency. Moreover, the intelligent WFNN controller is proposed for both the AC/DC power converter and DC/AC power inverter to improve the transient and steady‐state responses of the SCIG system at different operating conditions. Three online trained WFNNs using backpropagation learning algorithm are implemented as the tracking controllers for the DC‐link voltage of the AC/DC power converter and the active power and reactive power outputs of the DC/AC power inverter. Furthermore, the network structure and the online learning algorithm of the WFNN are introduced in detail. Finally, some experimental results are provided to demonstrate the effectiveness of the proposed SCIG system for wind power. [ABSTRACT FROM AUTHOR]

Low system voltage in traction networks, mainly caused by active power absorption of locomotives, adversely affects the performance of the locomotives and also the power transmission capability of the catenary line. This paper introduces a voltage support scheme to compensate for the adverse effects of low system voltage. The proposed method is based on the injection of reactive power through the current-controlled line-side converter of locomotives. Comparing the catenary voltage with its reference value, the error is fed to a high-order controller. The controller generates the quadrature (q)-axis reference value of a current control strategy, which is responsible for the reactive power injection. To design the high-order controller, adopting the nonparametric models of the system at various locations, an optimization-based loop-shaping approach is used. The loop shaping guarantees the stability and the acceptable performance of the closed-loop system for various locomotive positions in the network. The performance of the proposed control strategy is evaluated based on simulation results in MATLAB/PLECS environment. Moreover, implementing a scaled-down laboratory setup, the performance of the proposed scheme is experimentally evaluated. [ABSTRACT FROM AUTHOR]

In this paper, the H∞ control approach is used to design and apply a robust controller to a DC drive supplied by an A C-DC power converter. The H∞, mixed sensitivity design based on three-block criterion is adopted to improve performance and robustness specifications in term of tracking, control signal moderation and robust stability. Based on a PCI-1710 multi-function data acquisition board, the proposed H∞ controller algorithm is successfully implemented Both hardware and software control developments are presented. [ABSTRACT FROM AUTHOR]

A frequency controlled three-phase induction generator (IG) system using ac-dc power converter is developed in this study. The electric frequency of the IG is controlled using the indirect field-oriented control mechanism. Moreover, an ac-dc power converter is adopted to convert the electric power generated by a three-phase IG from variable-frequency and variable-voltage to constant dc voltage. The rotor speed of the IG, the dc-link voltage and current of the power converter are detected simultaneously to yield maximum power output of the IG through dc-link power control. In this study, first, the indirect field-oriented mechanism is designed for the control of the IG. Then, a novel fuzzy modeling is developed to determine the flux control current and the maximum output power of the IG according to the rotor speed and the desired terminal voltage of the IG. Moreover, an online training recurrent fuzzy neural network (RFNN) with backpropagation algorithm is introduced as the tracking controller of dc-link power. Furthermore, some experimental results are provided to show the effectiveness of the proposed IG system using the RFNN controller for the dc-link power control. Finally, the control performance of the dc-link voltage control using the RFNN is also discussed by some experimental results. [ABSTRACT FROM AUTHOR]

A voltage multiplier rectenna is a combination of a voltage multiplier rectifier and an antenna used for the conversion of AC to DC. It is an essential part of the system of RF energy harvesting. Conventional rectennas are characterized by low conversion efficiency. This study presents an analytical novel mode designed for RF energy harvesting systems to study the voltage and current output of rectifier stages for efficiency optimization. The design contains a voltage multiplier rectification circuit with seven stages. The Schottky diode HSMS 285-C was selected for the circuit modeling voltage multiplier circuit. Advanced Design System (ADS) simulation was used to validate the equations of the theoretical model solved with MATLAB code. The fabricated system was tested for an input power range of 10 μW to 100 mW; the maximum output power is 0.2577 mW with maximum efficiency of 29.85%. [ABSTRACT FROM AUTHOR]

In recent years, hundreds of technical papers have been published which describe the use of sliding mode control (SMC) techniques for power electronic equipment and electrical drives. SMC with discontinuous control actions has the potential to circumvent parameter variation effects with low implementation complexity. The problem of controlling time-varying DC loads has been studied in literature if three-phase input voltage sources are available. The conventional approach implies the design of a three-phase AC/DC converter with a constant output voltage. Then, an additional DC/DC converter is utilized as an additional stage in the output of the converter to generate the required voltage for the load. A controllable AC/DC converter is always used to have a high quality of the consumed power. The aim of this study is to design a controlled continuous signal generator based on the sliding mode control of a three-phase AC-DC power converter, which yields the production of continuous variations of the output DC voltage. A sliding mode current tracking system is designed with reference phase currents proportional to the source voltage. The proportionality time-varying gain is selected such that the output voltage is equal to the desired time function. The proposed new topology also offers the capability to get rid of the additional DC/DC power converter and produces the desired time-varying control function in the output of AC/DC power converter. The effectiveness of the proposed control design is demonstrated through a wide range of MATLAB/Simulink simulations. [ABSTRACT FROM AUTHOR]