Interphase Transformer Research Articles

A Simple 18‐Pulse Uncontrolled Star Rectifier by Adopting Dual Passive Injection Circuits at DC Side

ABSTRACTThis research introduces a simple 18‐pulse star rectifier, which is a combination of a conventional double‐star rectifier and two new passive injection circuits. The proposed passive injection circuits are constituted with a specially tapped interphase transformer (STIPT) and four diodes. The proposed passive injection circuits can simultaneously increase the step number of the input line current and the pulse number of the load voltage. The first passive injection circuit (FPIC) doubles the pulse number of the traditional double‐star rectifier converting it into an asymmetrical 12‐pulse star rectifier while the second passive injection circuit (SPIC) further converts the 12‐pulse star rectifier into 18‐pulse star rectifier. For tripling the pulse number of the double‐star rectifier, the STIPT requires to be designed optimally. For designing purpose, the proper tap ratios of the STIPT are determined depending on the minimum total harmonic distortion (THD) of the input line current. When designed optimally, the proposed rectifier simultaneously reduces the THD of the input line current and ripple of the output voltage with increasing pulses. In order to provide experimental validation for the theoretical evaluation, a laboratory prototype is constructed. The theoretical THD of the input line current is about 10.1%, whereas the experimental THD is about 5.42%.

Active Current Balancing for Paralleled SiC Semiconductors in Time-Staggered Switching Mode

The steep voltage slopes of today's wide-bandgap, fast-switching power semiconductors — like SiC and GaN — lead, among other challenges, to reflection on long cables and thereby overvoltage at inductive loads. To apply this technology to motor drives without specially reinforced insulation the voltage slopes need to be reduced. This article presents a new low-loss countermeasure, which involves the parallel connection of two half-bridges via an interphase transformer. Undesired components in the cross-current of the interphase transformer occur due to non-idealities in the voltage symmetry. The resulting additional magnetization can cause the core to saturate. Influences on the converter voltage due to various parasitic influences are described. Especially aspects relevant for dimensioning the magnetic core of the interphase transformer are emphasized. Also, this article describes an approach to deal with the undesired cross-current components using two different closed-loop control concepts. The control uses a special differential-mode shunt for a dedicated measurement of the cross-current mean value. Both control concepts are verified and compared on a 500-kVA SiC inverter test bench, using measurements of the controlled current.

High power four-phase interleaved DC-DC converter using interphase transformers

This paper explores the design and practical implementation of a high power, 100kW, four-phase, interleaved DC-DC converter using SiC power modules and a novel interphase transformer arrangement. The interleaving of the four phases of the converter increases the ripple current frequency at the input and output of the DC-DC converter. This reduces the capacitor size but does not reduce the current ripple in the individual phases. When using interphase transformers (IPTs) some of the components see a frequency multiplication and so can be reduced in size, increasing the power density of the converter. Using the leakage inductance of one of the IPTs, as discussed in this paper, also removes the necessity for a separate filter inductor, reducing weight and cost and further increasing power density. When combined with a stationary battery which can be trickle charged from a low power grid connection, the converter can provide rapid vehicle charging in areas where only a low power connection to the grid is possible.

Project and Performance Evaluation on an Optimized 18-Pulse Rectifier With Delta-Differential Connection ATRU and Cascaded Boost Converters for More Electric Aircraft

This paper presents the design and analysis of a special Rectifier Unit (RU) composed of a Delta-Differential Symmetric 18-pulse Autotransformer and cascade Boost converters for applications in More Electric Aircraft (MEA), which is denominated as RU-DDS18PATR+Boost. The cascaded Boost converters provide dc-link regulation, while eliminating the need to use interphase transformers (IPTs), interphase rectors (IPRs), and zero-sequence blocking transformers (ZSBTs), thus contributing toward decreasing the complexity and at the same time increasing reliability. The proposed RU-DDS18PATR+Boost operates with an active current shaping strategy in order to meet the harmonic content restrictions imposed by the DO-160F standard, while allowing for the design of a DDS18PATR with a notable kVA rating of 21.03%. The performance of the RU-DDS18PATR+Boost was analyzed operating in a system with a supply voltage of 115VAC and variable frequency in the range of 360Hz to 800Hz, which is converted to 540VDC. Experimental results are presented corroborating the theory put forward herein, especially with regard to meeting the limits imposed by the DO-160F standard.

Design and Optimization Approach for the Magnetic Components of a Five-Level Current Source Rectifier

This work presents a design and optimization method of the five-level current source converter magnetics components, this is a contribution of this work, since the magnetics volume information of this topology lacks in the literature. The magnetics components are: the interphase transformers, the input and the output filter inductors. The converter volume is minimized when the magnetic components multi-domain optimization is done. The inductance values are defined with given constraints such as Electromagnetic Compatibility standards for differential mode filters, conduction and switching losses of the semiconductors and maximum current variation. This optimization is shown for two different converter switching frequencies: 45 kHz and 150 kHz. The copper losses, iron losses and temperature rise are calculated and used for selecting the smallest volume of each magnetic component with given specifications. A 6-kW prototype with the optimized magnetics was constructed

An improved 24‐pulse rectifier for harmonic mitigation in more electric aircraft

AbstractTo increase the power rating and reduce the cost and complexity of a multi‐pulse rectifier (MPR), it is well known that the pulse number must be increased. In some practical cases, a 12‐pulse rectifier (12PR) is suggested as a good solution considering its relatively simple structure and low weight. However, 12‐pulse rectifiers cannot technically meet the standards of harmonic distortion requirements for some industrial applications, and therefore they must be used along with output filters. Two cost‐effective 24‐pulse rectifiers (24PRs) are suggested in the article, which consist of a polygon autotransformer 12PR and two pulse doubling circuits (PDCs) at dc link. The first PDC (PDC1) is based on an inter‐phase transformer (IPT) with a step‐up secondary winding, and the second one (PDC2) is based on an IPT with a step‐down secondary winding. To show the advantages of the proposed combinations compared with other solutions, simulation results are used, and also a prototype is implemented to evaluate and verify the simulation results. The simulation and experimental test results show that the total harmonic distortion (%THD) of the input current for the 12PR with PDC1 is less than 3.67%, and the 12PR with PDC2 is less than 1.45%, which meets the IEEE 519 and DO‐160G requirements. Also, it is shown that in comparison with other solutions, the proposed two configurations are cost‐effective, power factor is near unity, rating is almost 29% of the load rating, and the efficiency is almost 97.5%, which makes them a practical solution for more electric aircraft.

Performance evaluation of interphase transformers based on a new 48-pulse AC–DC converter for industrial applications

Performance evaluation of interphase transformers based on a new 48-pulse AC–DC converter for industrial applications

Harmonic Analysis of a Third Rail Systems: A Case Study in Malaysia

Harmonic distortion is one of the most important power quality issues in third rail electrification systems. The use of rectifiers and inverters in the third rail system can inject a significant amount of harmonic distortion to the electrical network. This paper aims to investigate the harmonic distortions for a DC urban third rail system at various operating conditions. The electrical network of Mass Rapid Transit Line 2 (MRT 2) Malaysia is modelled using ETAP software. The model had considered the effect of the inter-phase transformer in the 12-pulse rectifier. The current injection method is used to measure harmonic distortion at Point of Common Coupling (PCC) at the 132 kV and 33 kV buses. A normal and degraded operating conditions of power supply are investigated. From the simulation results, it is found that the 11th and 13th order harmonics have exceeded the statutory limit at 33 kV network for the normal operating condition. For the degraded operating condition, only the 11th harmonic order has exceeded the statutory limit. Keywords: Harmonic Distortion; DC Urban Rail; Various Operating Conditions

A 12-pulse rectifier with passive harmonic reduction based on UIPT in more electric aircrafts

PurposeThe purpose of this paper is to provide a T autotransformer based 12-pulse rectifier with passive harmonic reduction in more electric aircraft applications. The T autotransformer uses only two main windings which result in volume, space, size, weight and cost savings. Also, the proposed unconventional inter-phase transformer (UIPT) with a lower kVA rating (about 2.6% of the load power) compared to the conventional inter-phase transformer results in a more harmonic reduction.Design/methodology/approachTo increase rating and reduce the cost and complexity of a multi-pulse rectifier, it is well known that the pulse number must be increased. In some practical cases, a 12-pulse rectifier (12PR) is suggested as a good solution considering its simple structure and low weight. But the 12PR cannot technically meet the standards of harmonic distortion requirements for some industrial applications, and therefore, they must be used with output filters. In this paper, a 12PR is suggested, which consists of a T autotransformer 12PR and a passive harmonic reduction (PHR) based on the UIPT at direct current (DC) link.FindingsTo show the advantage of this new combination over other solutions, simulation results are used, and then, a prototype is implemented to evaluate and verify the simulation results. The simulation and experimental test results show that the input current total harmonic distortion (THD) of the suggested 12PR with a PHR based on UIPT is less than 5%, which meets the IEEE 519 requirements. Also, it is shown that in comparison with other solutions, it is cost effective, and at the same time, its power factor is near unity, and its rating is 29.92% of the load rating. Therefore, it is obvious that the proposed rectifier is a practical solution for more electric aircrafts.Originality/valueThe contributions of this paper are summarized as follows. The suggested design uses a retrofit T autotransformer, which meets all technical constraints, and in comparison, with other options, has less rating, weight, volume and cost. In the suggested rectifier, a PHR based on UIPT at its dc link of 12PR is used, which has good technical capabilities and lower ratings. In the PHR based on UIPT, an IPT is used, which has an additional secondary winding and four diodes. This solution leads to a reduction in input current THD and conduction losses of diodes. In full load conditions, the input line current THD and power factor are 4% and 0.99, respectively. The THD is less than 5%, which satisfies IEEE-519 and DO-160G requirements.

Single-Phase Hybrid Switched-Capacitor Interleaved AC-DC Boost Converter

In this paper a single-phase boost PFC multilevel interleaved high-voltage gain based on the hybrid switched-capacitor concept is presented. The proposed converter merges interphase transformers and switched-capacitor cells to obtain current sharing and high voltage gain. These features allow for both the reduction of voltage and current stresses on the semiconductors. Furthermore, the interleaving method allows for obtaining multilevel voltages at AC terminals, thereby reducing the weight and bulk of the input inductor. PFC operation is guaranteed through both input current control and output voltage control. Both steady-state and dynamic analyses were conducted. Experimental results for a 1.25 kW, 127 V to 800 V laboratory prototype are presented and discussed.

Instability in Active Balancing Control of DC Bus Voltages in STATCOM Converters Paralleled via Interphase Transformers

In high power applications, 3-phase ac/dc Voltage Source Converters (VSCs) are paralleled to increase the overall aggregated converter power rating, effective switching frequency and control bandwidth. For this, interleaved Pulse Width Modulation (PWM) and current limiting paralleling inductors are required. Interphase Transformers (ITRs) are often used for the converter paralleling because they provide large magnetizing inductances for the currents flowing between the converters while introducing negligible leakage inductances for the currents flowing from the converters to the ac grid. This large asymmetry in the inductance values makes it difficult to independently control active power flows in the individual converters. Thus, if the converters dc buses are not mutually interconnected, instabilities in active control of balance of converter dc bus voltages can occur in certain operational conditions. This paper presents a theoretical analysis of the active power flows produced by the currents flowing among the converters and explains origins of potential instability in the active control of balance of dc bus voltages in multi-converter systems with floating dc buses, paralleled using the ITRs.

Two-Phase, Dual Interleaved Buck–Boost DC–DC Converter for Automotive Applications

A two-phase buck-boost converter utilizing dual interleaving is presented in this article. The dual interleaving consists of an interphase transformer (IPT) that doubles the ripple frequency together with two conventional buck-boost switching arms, mitigating the inductor ripple current and aiding to increase the power density of the converter. A description of the design and selection of the power devices is presented for a 32-kW, 75-kHz dual interleaved SiC prototype with an IPT, such that a power density of 7.4 kW/kg is achieved. The operation of the circuit is verified experimentally using a prototype with 315-385 V supply range and 350-V output voltage, achieving 97.1% peak efficiency at 32 kW. The experiments reveal that the interleaved coupled currents are equalized without an active balancer.

Power-Dense Bi-Directional DC–DC Converters With High-Performance Inductors

An investigation is described into the optimization of multi-phase, high power, bi-directional DC-DC interleaved converters suitable for Electric Vehicle (EV) applications. Two dual-interleaved topologies were considered initially for the optimization, the main difference being the magnetic devices: either discrete inductors (DI) or an Interphase Transformer (IPT). The comparison used a comprehensive multi-objective design optimization procedure for an 80 kW case study. High performance inductors comprising a split-core structure and dual-foil windings to reduce losses, and a 180 °C core, enabled the DI to be competitive with IPT in terms of power density and efficiency. The optimized designs are validated experimentally with an 80 kW bi-directional SiC DC-DC converter, achieving a power density of 31.4 kW/L and specific power of 15.7 kW/kg. The study is then extended to 100-kW three and four-phase interleaved topologies.

Modeling Phase Interactions in the Dual-Interleaved Buck Converter Using Sampler Decomposition

In this paper, the averaged small-signal model of the dual-interleaved buck converter is extended to include the phase interaction effects that arise from the interleaved sampling of the phase currents. Sampler decomposition techniques are used to extend the averaged model, revealing a slow-scale instability that can place significant restrictions on the choice of controller parameters. The model is confirmed by simulations and measurements using a 60-kW dual-interleaved prototype with an interphase transformer; however, the analysis is equally applicable to interleaved converters without magnetic coupling.

Six‐phase dual‐interleaved buck‐boost converter for high power‐density automotive applications

This study presents a 30 kW, six-phase dual-interleaved buck-boost converter which uses an interphase transformer together with six buck-boost switching arms hard switched at 75 kHz for electric/hybrid vehicle applications. Parameters and construction details of the interphase transformer and common inductors are provided together with a description of the selection of semiconductor devices. Weight, power losses, and temperature rise are evaluated at rated power conditions showing experimental results with a 7 kW/kg gravimetric power density achieved with the converter prototype.

Cost‐effective multi‐pulse AC‐DC converter with lower than 3% current THD

SummaryIn this paper, a new multi‐pulse clean power converter topology is presented with lower than 3% input current total harmonic distortion (THD). The topology is based on the combination of a 36‐pulse converter and a pulse doubling circuit. The 36‐pulse converter consists of a “polygon” autotransformer and two 18‐pulse diode bridge rectifiers. Pulse doubling circuit consists of zero‐sequence‐blocking transformer (ZSBT) and tapped interphase transformer (IPT). The important advantage of the proposed AC‐DC converter is considerable reduction in burdens of the magnetic parts with respect to the nominal load rating. It provides more economical solution to achieve harmonic mitigation in electric power systems as compared with other 72‐pulse AC‐DC converters. The simulation and experimental results show that the input current THD is less than 3% using the proposed topology. The results indicate a significant reduction in the total cost and volume of the proposed 72‐pulse configuration in comparison with similar configurations. Also, it is shown that the proposed converter rating is about 44% of the DC load power.

Application of voltage multiplier in 12‐pulse rectifier for sinusoidal input current

A DC current injection circuit of a trifurcated autotransformer (TAT)-based 12-pulse diode bridge rectifier (DBR) is proposed which can help reduction of harmonics in the AC mains. The circuit at the DC side employs a voltage multiplier (VM) circuits namely voltage doubler, voltage tripler and voltage quadrupler and an interphase transformer which provides the required circulating current. This induced circulating current shapes the input AC line current near to a sine wave. The output of VM circuits is connected across the load and thereby reuses the harmonic energy absorbed by the system. Thus, improves the energy conversion efficiency of the proposed system. The TAT-based 12-pulse DBR has the implicit ability to prevent the zero sequence components thus expels the necessity of zero sequence blocking transformer. The proposed configuration is analysed, simulated in MATLAB Simulink and the simulation results are presented, which confirms the improvement in power quality parameters in the input AC line current. Further, the viability of the proposed configuration is verified by experimental results which confirm the suitability of the proposed configuration in AC–DC applications.

A Simple Harmonic Reduction Method in 20-Pulse AC–DC Converter

This paper proposes a simple and passive harmonic reduction method at dc link of 20-pulse rectifier. The 20-pulse topology is obtained via two paralleled 10-pulse ac–dc converters, each of them consisting of a five-phase (five-leg) diode bridge rectifier. For independent operation of the paralleled diode-bridge rectifiers, a zero sequence blocking transformer (ZSBT) is designed and implemented. Connection of a tapped inter-phase transformer (IPT) at the output of the ZSBT results in doubling the number of the output voltage pulses. The application of the pulse doubling technique with a low power rating (2% of the load power rating) results in a simpler and more economical configuration of the whole system and increased number of pulses. The design is suitable for retrofit applications where a six-pulse diode bridge rectifier is being utilized. The proposed structure is simulated using Matlab/Simulink software under different loading conditions. The simulation results confirm the significant improvement of the power quality indices (IEEE-519 standard requirements) at the point of common coupling (PCC). Experimental results are obtained using the designed and constructed laboratory prototype of the proposed converter to validate the design procedure and the simulation results. The VA rating of the magnetic circuit is calculated to confirm the savings in space, volume, weight and cost of the proposed configuration.

Power Quality Enhancement Using Current Injection Technique in a Zigzag Configured Autotransformer-Based 12-Pulse Rectifier

This paper proposes a DC-side circuit configuration that improves the harmonic suppression ability of a 12-pulse diode bridge rectifier (DBR) using a zigzag configured autotransformer. The DC-side circuit uses a single-phase DBR along with interphase transformer which generates the required circulating current thereby modifies the DC currents at the DBR output, in turn shapes the input line current near to a sine wave. The proposed single-phase DBR is connected in parallel with the load which enables to reuse the harmonic energy thus improving the energy conversion efficiency. The zigzag configured autotransformer used for 12-pulse DBR possesses the inbuilt ability to hinder the zero-sequence components, which expel the need of zero sequence blocking transformer. The proposed configuration is analyzed, simulated in MATLAB Simulink and the simulation results are presented, which confirm the reduction of total harmonic distortion (THD) in the input line current thereby improving the power quality under large load variations. Furthermore, the viability of the proposed configuration is verified by experimental results, which confirm the suitability of the proposed configuration in industrial applications.

High-Frequency Isolated AC–DC–AC Interleaved Converter for Power Quality Applications

This paper presents a single-phase ac-dc-ac converter with high-frequency isolation, which employs the interleaved technique. The proposed converter is suitable for power quality applications, such as dynamic voltage restorers, uninterruptable power supplies, and voltage regulators. The modeling of power flow is presented, focusing on the minimization of the transformer current. This analysis is improved by the introduction of the actuators type concept, which ensures reduced current through the transformer. Moreover, the effective longitudinal inductance of the series association of the boost inductor and two interphase transformers is determined. The soft-switching regions are also obtained as well as their dependency on the phase-shift angle. The proposed converter is compared with one indirect ac-dc-ac topology, which uses the dual active bridge converter as the isolation stage. Experimental results are obtained to show that the proposed converter is able to provide power factor correction, mitigate voltage sags, and regulate the output voltage.