Parallel Rectifiers Research Articles

A WPT System With DC-Link Series/Parallel AC-Link Parallel Rectifiers for AUVs With Multiple Charging Voltages and Currents

A WPT System With DC-Link Series/Parallel AC-Link Parallel Rectifiers for AUVs With Multiple Charging Voltages and Currents

Energy management in gyms microgrid: Nonlinear control of stationary bikes and treadmills with parallel rectifiers and AC/DC conversion

This article presents the complete design of a nonlinear control system for multiple stationary bikes connected to a mechanical energy conversion system equipped with squirrel cage induction generators (SIGs) linked to AC/DC converters. The primary objective of this study is to investigate the feasibility of powering multiple treadmills using the DC bus via DC/AC converters. The novelty of our approach lies in the integration of a new strategy of control system to achieve multiple control objectives within a gym microgrid environment, and an energy management algorithm to ensure the energy flow between intermittent generation and the considered, somewhat random, demand. The system is composed of several subsystems: i) stationary bikes connected to the DC bus via inverters acting as intermittent power sources; ii) a Li-ion battery-based energy storage system interfaced through a Buck-Boost converter; iii) electromechanical loads, including treadmills, powered by DC/AC converters, in addition to other DC loads. The main control objectives are as follows: a) each stationary bike extracts energy from the DC network by regulating the torque applied by the athlete, ensuring that the torque follows the reference torque; b) the treadmill’s speed must follow the reference generated based on the athlete’s condition; c) ensuring the protection of the energy storage system by monitoring its current and voltage; d) all mentioned objectives are achieved while maintaining the DC bus voltage at a reference value. To achieve these objectives, a nonlinear control approach based on Lyapunov theory is used to design the controllers. A formal analysis is conducted to assess the performance of the studied system. The system’s performance is demonstrated using the MATLAB/Simulink environment. Numerous simulations demonstrate that every control objective is achieved. Specifically, the system maintained the DC bus voltage at 500 V with a maximum deviation of 1 V, and the treadmill speed followed the reference within a margin of 0.1 m/s.

Voltage Compensation Method for Multi-feeder Distribution Networks Based on a UPQC with PV Injection

Abstract In response to the problem of prolonged low voltage at the end of distribution grids, a voltage compensation method for multi-feeder distribution networks based on a unified power quality controller (UPQC) with PV injection is proposed in this paper. In the proposed scheme, two series inverters, a single parallel rectifier and photovoltaic (PV) system are flexibly interconnected via DC bus. The voltage attenuation can be compensated by the two series inverter, and the parallel rectifier is capable of supplying energy to the DC side of the two series inverters on adjacent AC feeders. Meanwhile, active power can also be supplied by the PV panel through a DC/DC converter. The operation modes and control strategies of the proposed method are analyzed in-depth. Finally, a MATLAB/Simulink model is shown to verify the effectiveness of the method proposed in this paper.

Predictive Control for a Single-Phase to Three-Phase Converter with Two-Parallel Single-Phase Rectifiers


 This paper presents a parallel single-phase to three-phase drive system, using two single-phase rectifiers. The rectifiers are not isolated from the grid by low-frequency transformers, so the reduction of the circulation current is an important objective for the control strategy. Modulated Model Predictive Control regulates the grid current and minimizes the circulation current between the parallel rectifiers. Furthermore, the analyzed predictive control consists of two strategies, where the first has the application of two vectors in a sampling period while the second has three vectors. The addition of a vector allows the reduction of the computational cost due to the reduction of tests performed in the predictive control and reduces the harmonic distortion in the electrical grid due to the greater application of vectors in a sampling period. Simulation and experimental results are presented in order to validate the control strategy.
 

Impartial Sequential Model Predictive Control of Parallel T-Type Rectifiers for Power Sharing and Circulating Current Elimination

A parallel T-type rectifier connection is often required to improve the system capacity and stability in high-power applications. However, the parallel rectifier faces the challenges of zero-sequence circulating current (ZSCC) elimination, neutral point (NP) voltage balance, DC voltage stability and power sharing. First, to solve the multi-objective optimization problem of two parallel three-level T-type rectifiers with LCL filters (LCL-3LT <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> Rs), a double closed-loop control scheme is adopted. In this scheme, an impartial sequential model predictive control (ISMPC) is proposed as the inner-loop controller for ZSCC elimination and NP voltage balance, and an adaptive droop control with voltage feedforward is designed as the outer-loop controller to achieve DC voltage stability and power sharing for each rectifier based on its capacity. Second, the main influencing factors of ZSCC in LCL-3LT <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> Rs are analyzed, and ZSCC elimination is considered as one control objective in ISMPC. Finally, ISMPC is proposed to solve the problem that sequential model predictive control (SMPC) could not select the optimal solution due to the fixed priority and the excessive process only controlled a single objective. The proposed method is tested on a prototype hardware platform of a 10-kW and a 5-kW parallel rectifier. Experiment results demonstrate the superiority of this method over existing methods under several typical scenarios.

Two-Port Five-Band Rectenna for Ultralow Ambient RF Energy Harvesting

A two-port rectenna is proposed to harvest the ambient RF power from five commercial bands, including 1.8 GHz, 2.1 GHz, 2.4 GHz, 2.65 and 3.5 GHz for GSM, LTE, WLAN and 5G, respectively. The novel rectenna comprises a hybrid half-wave rectifier and two back-to-back slot antennas. The rectifier consists of a series rectifier branch and a parallel rectifier branch to extend its multi-band coverage, only sharing one diode. With this design strategy, its RF-DC power conversion efficiency (PCE) can reach 23.1% at 1.8 GHz, 26.4% at 2.1 GHz, 27.2% at 2.4 GHz, 20.7% at 2.66 GHz and 19.1% at 3.47 GHz with -20 dBm input power level. Notably, once a five-tone signal is input simultaneously with the identical power level of -20 dBm, the PCE of rectifying circuit can be improved to 43.7%, breaking the existing record to our best knowledge. The designed slot antennas can also receive omnidirectional RF power at five corresponding frequencies. The experimental results demonstrate that our proposed rectenna is competitive in band coverage and PCE with ultra-low input power, indicating enormous potential for RF energy harvesting and powering sensors, wearables, and other low-power scenarios.

A Comprehensive Steady-State Analysis for Modular Multi-Parallel Rectifiers (MMR) With Shared DC-Link

This article proposes a comprehensive steady-state analysis for a front-end Modular Multi-Parallel Rectifiers (MMR) system with a shared DC-link. A generalised mathematical representation for an n-number of parallel rectifiers is proposed. The MMR is analysed for both Continuous Conduction Mode (CCM) and Discontinuous Conduction Mode (DCM). In addition, the CCM and DCM boundary of the MMR is identified mathematically. The impact of parasitic elements on the mode of operations is studied. In addition, the impact of different ASD scenarios on the mode of operation is studied. A 200 W Simulink model for the MMR is utilised to confirm the proposed steady-state mathematical modelling equations. A 200 W practical setup is implemented in a laboratory to validate the proposed mathematical equations.

An Improved Modulation Method for Parallel Three-Level Rectifiers With Circulating Current Mitigation

An improved modulation method is proposed for two parallel three-level interleaved rectifiers to reduce current harmonics and high-frequency zero-sequence circulating current, which uses sinusoidal pulse width modulation. First, a model of the two parallel rectifiers is constructed, and the main factor affecting the line current performance and zero-sequence circulating current is discussed. Second, the current harmonics are the priority optimization target to guarantee better line current performance. Finally, an exchange of the large common-mode voltage between two converters is made to reduce the high frequency zero-sequence circulating current based on the low current harmonics. Performance comparisons between the proposed method and existing methods in terms of total current harmonics, zero-sequence circulating current value and switching loss are made in the experiment, which confirm the effectiveness of the proposed method.

Efficiency Enhanced Seven-Band Omnidirectional Rectenna for RF Energy Harvesting

In this article, a seven-band omnidirectional rectenna is proposed for the first time to harvest RF energy. The designed rectenna operates in the following practical and up-to-date frequency bands: GSM1800 (1.8 GHz), LTE (2.1 GHz), WLAN/Wi-Fi (2.4 and 5.8 GHz), and 5G bands (2.6, 3.5, and 4.9 GHz). To obtain the multiband rectenna, a novel seven-band rectifier is introduced and composed of three optimized single shunt diode rectifiers in parallel. Overall RF-to- dc conversion efficiencies as high as 44.4% @ 1.84 GHz, 43.9% @ 2.04 GHz, 45.4% @ 2.36 GHz, 43.4% @ 2.54 GHz, 36.1% @ 3.3 GHz, 32.4% @ 4.76 GHz, and 28.3% @ 5.8 GHz are achieved at an input power level of −10 dBm. Moreover, a broadband omnidirectional monopole antenna is further codesigned with elaborate impedance matching to the rectifier. The antenna can harvest RF energy in the bandwidth of 1.67–5.92 GHz ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{S}_{\mathbf {11}}$ </tex-math></inline-formula> no more than −10 dB) with stable omnidirectional radiation patterns. By integrating the rectifier and the monopole antenna in a low profile, a prototype of the rectenna was manufactured and tested. The experimental results demonstrate that the proposed rectenna has competitive performance in terms of RF-to- dc conversion efficiency and band coverage, indicating enormous potential for numerous battery-free or low-power-needed applications in the real world.

Subway Traction Power Supply System Based on PWM Rectifier

At present, PWM rectifier is widely used in various high power and high voltage situations because of its high energy, low harmonic content, constant voltage and bidirectional energy. The energy supply system of subway traction power supply system based on PWM rectifier shows the topology of a dual transformer with three winding transformers and four PWM rectifiers in parallel, which is superior to the modular model. Finally, the correctness of the control strategy is verified by Matlab/Initial simulation.

Zero-sequence current injection based power flow control strategy for grid inverter interfaced renewable energy systems

ABSTRACT This paper deals with an energy management issue for the grid-connected renewable energy sources connected with unbalanced loads. In the grid-connected energy systems, conventional energy management methods are used to manage balanced active power supplied from energy units to grids/loads. However, unbalanced load groups, like single-phase loads, parallel rectifiers, and three-winding transformers tied to the electric networks, cause zero-sequence currents and impair the power stability at the grid-side. For this purpose, in this study, an improved power flow controller method with zero-sequence current injection is proposed in order to compensate zero-sequence currents and ensure phase equilibrium at grid-side. Therefore, it is tested in a photovoltaic/fuel cell-based hybrid energy system with unbalanced loads, including zero-sequence. Instead of the conventional abc/dq frame used in energy management control, the proposed method makes use of triple αβ transforms and implemented in each phase to be controlled separately under designed unbalanced load groups. Hence, it abolishes the weakness of the conventional abc/dq frame method that generates the undesirable mean reference for zero-sequence situations. In addition, the designed system cannot only mitigate the grid-side zero-sequence currents but also supply active powers to three-phase loads/grids. The optimization of energy systems is also provided through a maximum power point tracking algorithm. In the performance testing, the energy generation units are performed under three states, which produce different supplied currents at the output. In the performance section, it is obvious that zero-sequence components at grid-side currents are significantly reduced via the proposed power flow controller-based system. Also, the results are compared to the conventional method in order to verify the validity of the proposed approach under the designed load groups.

Design and Control Method to Suppress Resonance Circulating Current for Parallel Three-Level Rectifiers With Modified LCL Filter

The high-frequency zero-sequence circulating current (HFZSCC) is generated when the carrier phases are different in a parallel rectifiers system. Therefore, a modified <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> filter is adopted to suppress the HFZSCC. Nevertheless, the internal common mode resonance current (ICMRC) and external zero-sequence resonance circulating current (EZSRCC) are produced, which causes system instability unavoidably. Since these two issues are coupled with each other, the conventional resonance currents control methods reported so far cannot address them properly simultaneously. To suppress ICMRC and EZSRCC, a detailed model analysis of internal common mode current and zero-sequence circulating current (ZSCC) are presented, which reveal the ICMRC and EZSRCC are related to capacitor-side ZSCC (CSZSCC). Then, based on the model, in this article, the controller of CSZSCC is presented to suppress ICMRC and EZSRCC. Additionally, a closed-loop controller is designed to reject disturbances of low-frequency zero-sequence circulating current (LFZSCC). It is realized by adjusting the duty cycle of the small vectors in each pulsewidth modulation sampling period. As a result, HFZSCC, ICMRC, EZSRCC, and LFZSCC are mitigated with the proposed scheme, thus, improving the quality of the input currents. Simulation and experimental results verify the effectiveness of proposed method.

Polarization-Insensitive Rectenna Arrays With Different Power Combining Strategies

This letter presents two 2 × 2 polarization-insensitive dual-polarized rectenna arrays with different power combining strategies for wireless power transmission applications. With a dual-polarized antenna array, the incident wave can be received and decomposed into the horizontally and vertically polarized components, which are equally redistributed by a hybrid coupler. By this means, the efficiency of the rectenna, in which the power is equally input to the two rectifiers in parallel, is independent of the incident wave's polarization. Based on the equal power routing mechanism, two rectenna arrays using the RF and dc combining strategies are designed and analyzed. Measurement results show that both rectenna arrays are insensitive to the incident wave's polarization, and have their own advantages and disadvantages.

Voltage Control of Rectification-type Three-Phase Squirrel-Cage Induction Motor

The VSCF squirrel-cage generation system mostly adopt full power double pulse width AC/DC/AC modulation. In order to reduce the capacity of the rectifier, a rectification system and its voltage control strategy is proposed. The rectifier and capacitor in parallel with the generator are used to compensate the excitation current and to adjust the generator voltage. Uncontrolled rectifier bridge and inverter are connected to the generator to supply electricity for the AC loads. The selection of build-up voltage capacitor is analyzed and system voltage control method is simulated and experimented. The rectification voltage can be kept basically a constant when the rotor speed and load change in a certain range. The rectifier compensating current is small which proves that the system structure is feasible and control method is effective.

Current Shaping in a Hybrid 12-Pulse Rectifier Using a Vienna Rectifier

This paper presents a hybrid rectifier consisting of a 12-pulse rectifier in parallel with a Vienna rectifier. In the proposed structure, the 12-pulse rectifier supplies the bulk power to the load, whereas the Vienna rectifier shapes the input current to reduce its harmonic distortion. The unidirectional power flow of the Vienna rectifier results in undesirable distortion around the current zero crossing, which deteriorates current shaping in this region. To overcome this problem, besides current shaping, the Vienna rectifier is forced to participate in the active power. In this regard, the share of output power in each rectifier module must be calculated. To shape the input current, the reference current for the Vienna rectifier is generated using instantaneous power theory, and current tracking is carried out using the finite control set model predictive control. A detailed analysis of how to select the output power sharing ratio based on system losses and input current distortion is presented. The theoretical analysis is verified by using simulation and experimental results obtained from a 1 kW laboratory setup.

Increasing Copper Production in Electrochemical Plants Using New Small Transformer–Rectifiers in Parallel With Existing Power Rectifiers

The production of copper in electrochemical plants requires a large amount of dc current to obtain the desired copper product output. The dc current is supplied by high-current thyristor-based controlled rectifiers. Many copper plants use rectifier systems designed with two or more similar transformer-rectifiers connected in parallel to obtain the desired dc current output. Parallel rectifier systems may use 12 or 24 pulses depending on rated values of dc current. To maximize copper production when higher quality mineral is being processed, the dc current needs to be increased to values that exceed the designed rated output value of the transformer-rectifier. To solve this problem, a smaller supplementary low-current rectifier can be connected in parallel with the existing rectifiers to achieve the desired dc current output. This solution proves to be economical compared with other alternatives such as increasing the number of cells in the process or replacing the existing transformer-rectifiers with larger ones. This solution has been implemented in several copper plants with satisfactory results. As an example, a 2 x 25 kA 12-pulse rectifier installation was modified to a 60-kA 18-pulse rectifier installation by adding a 10-kA auxiliary transformer-rectifier in parallel with the existing rectifiers. This modified design has continuously and successfully operated for the past five years. This paper will describe the requirements for determining if an auxiliary transformer-rectifier is the best solution for increasing the total dc current capacity.

Control and Operation Mode of ITER High-Power DC Testing Platform

This paper introduces a high power dc testing platform for components test of ITER poloidal field converter prototype. The platform is composed of four phase-controlled rectifiers in parallel with the same direction and output up to rated 120 kA long pulse and 400 kA maximum impulse dc current. In this paper, the circuit model is built and circuit analysis is performed to observe the dynamic behaviors. Due to the feature of strong coupling among paralleled branches, two different control strategies are compared, which respectively are decoupling control and dual closed-loop control. Two operation modes, long pulse model and impulse model adopt their own strategy. Experiments results are performed and the operation modes make an agreement with the theoretical analysis.

Field-circuit modelling of an advanced welding transformer with two parallel rectifiers

Abstract The new topology of three-winding welding transformer is proposed. Each secondary winding is connected in parallel through the separate bridge rectifier to the welding arc. The main feature of the proposed device is parallel working of two secondary windings with different rated voltage. The advantage is nonlinear transformation ratio of current that provides unprecedented power efficiency. The self- and mutual leakage inductances, which are important in power conversion, are calculated by 2D FEA model. The operational current of the device is modelled numerically via P-Spice simulator. The proposed topology is up to 30% more power effective than conventional welding transformer provided that the leakage inductances of primary and secondary windings are correctly fitted. This transformer is used for manual arc welding

The Development of High-Current Power Supply System for Electrolytic Copper Foil

A 6.5 V/50 kA high-frequency switching power supply (HSPS) system composed of 10 power modules is developed to meet the requirements of copper-foil electrolysis. The power module is composed of a two-leg pulse width modulation (PWM) rectifier and a DC/DC converter. The DC/DC converter adopts two full-wave rectifiers in parallel to enhance the output. For the two-leg PWM rectifier, the ripple of the DC-link voltage is derived. A composite control method with a ripple filter is then proposed to effectively improve the performance of the rectifier. To meet the process demand of copper-foil electrolysis, the virtual impedance-based current-sharing control method with load current full feedforward is proposed for n-parallel DC/DC converters. The roles of load current feedforward and virtual impedance are analyzed, and the current-sharing control model of the HSPS system is derived. Virtual impedance is used to adjust the current-sharing impedance without changing the equivalent output impedance, which can effectively reduce current-sharing errors. Finally, simulation and experimental results verify the structure and control method.

Efficiency Enhancement of DC to DC Multilevel Boost Converter and Its Applications

The aim of this study is to propose a experimental verification for single-phase to three phase drive system composed of two parallel single-phase rectifiers, a three-phase inverter and an induction motor. Apart from traditional application in dc motor drives, new applications of BDC include energy storage in renewable energy systems, fuel cell energy systems, Hybrid Electric Vehicles (HEV) and Uninterruptible Power Supplies (UPS). A dc-dc converter is always required to allow energy exchange between storage device and the rest of system. In HEV applications, BDCs are required to link different dc voltage buses and transfer energy between them. A non-isolated bi-directional dc-dc converters is used in our project to achieve better efficiency.