Secondary Winding Of Transformer Research Articles

Study of the influence of the current distortion power of the secondary winding of a transformer on the level of losses in it using the method of experiment planning

Purpose. Detection the relationship between the level of losses of a three-phase transformer and the power of distortion caused by current harmonics.. Methodology. During the research, the methods of determining power losses and additional losses in the elements of the electrical system from higher current and voltage harmonics, the visual programming method, the experiment planning method, and the orthogonal central composite plan method were used. Findings. An analysis of the indicators characterizing voltage and current distortions was carried out, and it was found that these distortions are most fully characterized by the current distortion power and voltage distortion power. These indicators are used to analyze the transmission of electric energy by a transformer of a traction substation. It is noted that the order of harmonics in the distortion power is not eliminated, and higher harmonics are taken into account by the corresponding effective current of higher harmonics. The specifics of the transformer secondary winding connections to the consumer, namely the grounding of one of the secondary winding phases, were taken into account. A number of combinations of current harmonics were used to simulate current distortions. The experiment was carried out using the planning method. The coefficients of the quadratic regression equation that relates power losses to the level of load current harmonics of the third, fifth, and seventh orders are obtaine To determine the significance of the obtained coefficients of the regression equation, the variances and the corresponding values of the Student's criterion were calculated, as a result, factors that do not affect the process and can be excluded from the regression equation were identified. The adequacy of the obtained regression equation was checked by Fisher's criterion. The analysis of the effects and their interaction showed that the standard error of the sample does not exceed 1.66%. As a result of analyzing the combinations of current harmonics that were set during the experiment, it was noted that some of them lead to the same effective phase current, while the power of current distortion is different. The greatest significance of the level of the third harmonic of the current is determined. The constant level of active power on the high voltage side of the transformer is noted, which is due to the absence of voltage distortions on it. Originality. Cases of combinations of current harmonic levels at which the current distortion power index remains unchanged, while the level of transformer power losses caused by current harmonics changes, have been identified. Practical value. This research can be used to assess and reduce the level of power losses in a transformer by filtering certain current harmonics.

An Improved Grouping Transformer's Secondary Windings Current-Sharing Method for Multiphase LLC Converter

Current balancing performance of the existing grouping transformer's secondary windings (GTSW) method is determined by leakage inductance mismatches. Nevertheless, the transformer's leakage inductance parasitic parameters in practice are difficult to accurately design, especially in high-frequency occasions, causing a large current-sharing error between phases. To solve this problem, this paper proposes an improved GTSW (IGTSW) current-sharing method. By ingeniously changing the connection mode of transformer's secondary windings, the influence of secondary leakage inductance mismatch on current sharing performance is eliminated, and the current sharing performance of secondary side is significantly improved. The first harmonic approximation (FHA) analysis method is used to establish the current sharing error model of the primary side and secondary side of the system. Furthermore, the current sharing performance of the existing GTSW method and the proposed method is quantitatively compared. Then, the effectiveness of the proposed method is verified by simulation and the two-phase 480W experiment results. Finally, some great performances of the proposed method are discussed, such as advantages in high-frequency applications, no effect of parasitic capacitance on the current sharing performance, the potential scalability in the case of other DC-DC topology and high current scenarios, and modular expansion capabilities, etc.

A DRM technique for OLTC testing by the transformer secondary winding DC voltage curve

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A Novel Isolated Resonant Gate Driver With Adjustable Duty Ratio for SiC MOSFET

Resonant gate driver is a promising technique to save gate driver loss at high switching frequencies to further promote the integration level of gate driver with power modules. State-of-the-art isolated resonant gate drivers (RGDs) have to keep duty ratio fixed at 0.5 to avoid transformer saturation, which significantly limits the practical applications. A new isolated RGD (IRGD) with adjustable duty ratio to drive silicon carbide (SiC) MOSFET is proposed in this article by employing switching period expansion technique with a dual-secondary transformer. Transformer secondary windings are involved in the turn-on and turn-off processes alternatively and are switched at the falling edge of each input driving cycle. The effective switching frequency at gate driver transformer is reduced to 1/2 to further save power losses at high switching frequencies. This article further discusses the optimal damping approach to suppress <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$v_{\mathrm {gs}}$ </tex-math></inline-formula> overshoot and oscillation due to an adjacent second driving stage brought by parasitic gate resistor for IRGDs. The proposed IRGD is built with printed circuit board (PCB) integrated planar transformers, designed at leakage inductance of 303 nH with primary-side silicon (Si) devices and secondary bidirectional gallium nitride (GaN) devices. The duty ratio is proven to be adjusted from 0.15 to 0.9. The power consumption of the prototype is 0.883 W at 500 kHz and 1.473 W at 1 MHz driving a 900-V SiC device with 87-nC gate charge, which is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$6\times $ </tex-math></inline-formula> less power consumed than a conventional gate driver (CGD). The adopted SiC power device achieves dv/dt on of 18 V/ns and dv/dt off of 35 V/ns with the proposed IRGD.

Design of Inductive Power Taking System for Smart Grid Monitoring Equipment

Due to the continuous growth of urban electricity load and the increasing development of high-voltage transmission technology, the effective operation of the online monitoring equipment of the transmission line is particularly important, which is also a necessary condition for the development of the smart grid. However, the power supply conditions for the usage scenarios of smart grid monitoring equipment are limited. Conventional power supply methods such as battery power supply and new energy power generation have disadvantages such as cumbersome battery replacement, and the power supply stability is greatly affected by the environment, so they are difficult to meet the development trend of a rapid capacity increase of power grid and stable power supply of power equipment. Aiming at the technical bottleneck of smart grid monitoring equipment in power supply, this paper proposes a current transformer inductive power taking method based on capacitive reactance matching shunt, using the open air gap current transformer secondary winding set on the bus to connect the capacitor and its excitation inductance in series carry out capacitive impedance matching, and then shunt through another branch with load and connect it at both ends of the open air-gap current transformer to obtain electric energy. Through the circuit model experiment of the inductive power-taking system, it is verified that the current transformer inductive power-taking method based on capacitive reactance matching shunt can obtain more power.

Grid Connection Circuits for Powerful Regenerative Electric Drives of Rolling Mills: Review

AC regenerative electric drives (AC REDs) are widely used in metallurgical rolling due to their reliability, efficiency, and power sufficient to maintain the process. This paper reviews the latest achievements in building the grid connection circuits for the main AC REDs of rolling mills. The paper discusses multipulse connection circuits formed by various transformer types and algorithms for preprogrammed pulse-width modulation with selective harmonic elimination technique (PPWM with SHE) of three-level active front ends (AFE), provides the theoretical and practical measurement results, and gives recommendations for improving existing systems. For 6-, 12-, and 18-pulse grid connection circuits, switching patterns of AFE semiconductor modules with a smooth downward trend within the modulation index range from 0.7 to 1.15 are provided. A simulation was performed under comparable conditions on simulation models in the Matlab/Simulink to objectively evaluate the performance and opportunities of 6-, 12-, and 18-pulse grid connection circuits, including the three-level AFE and transformer specifications. The waveforms and spectra of the grid currents and transformer secondary winding phase currents are shown; total harmonic distortion (THD) factors have been calculated up to the 60th harmonic for various PPWM with SHE patterns. The results of simulation and experimental measurement on operating equipment have been compared. The paper is expected to provide a broad overview of multipulse connection circuits of the rolling mill’s main AC REDs, in particular, identify the latest solutions capable of significantly improving their electromagnetic compatibility with the grid. The results obtained are of high genericity and can be used by researchers and engineers to provide the electromagnetic compatibility of non-linear consumers in similar circuits, as well as design them.

Finding the Best Programmable PWM Pattern for Three-Level Active Front-Ends at 18-Pulse Connection

The existing publications on the analysis of power quality indicators in modern electric power supply systems are void of a comprehensive approach to improving these indicators in power systems by implementing multipulse connections. To the authors’ knowledge, this paper is the first to analyze current harmonic distortions in an 18-pulse connection of three-level active front-ends (AFE) featuring a programmed PWM. Raw data were obtained from, and current quality was analyzed for the power circuit of the main electric drive actuating the rolls in the rolling stand of a plate mill. The key feature of such circuitry is that the synchronous motor of each work roll is connected to the grid with an 18-pulse connection that uses three phase-shift transformers, where the phase shifts are 0° (delta/delta), 20° (delta/polygon) and −20° (delta/polygon). The circuitry connects three frequency converters (FC) with the AFEs in parallel. Phase-shift transformers were found to periodically overheat in the process. When overheating occurred, a programmed PWM voltage waveform was applied where harmonics 17 and 19 were eliminated. The goal and objectives were to analyze why the transformer would overheat and to find out how the issue could be addressed. The authors developed a simulation model of the research object in order to assess power quality parameters. Simulation results obtained in Matlab/Simulink were used to estimate the total harmonic distortions (THD) and individual harmonic factors for up to the 50th secondary transformer winding and grid harmonic with four different programmed AFE PWM voltage waveforms. The results helped find the best such waveform to prevent phase-shift transformers from overheating; one with harmonics 5, 7, 17 and 19 eliminated. The experimental and mathematical modeling results in the paper were confirmed by positive effects after industrial implementation of the system. Research performed directly on the operating equipment has been classified by the company and is not publicly available. These results are highly versatile and could be used in similar research on other circuitries to ensure the electromagnetic compatibility of nonlinear power-consuming devices.

Analysis of the Resistances of the Equivalent Circuit of TM Series Transformers

An assessment of the ratio of active and reactive components of the resistances of the primary and secondary windings of transformers included in the simplified equivalent circuit is made. It is shown that the reactances of the primary and reduced secondary windings are the same. Based on the reference data of the TM series transformers, it has been established that the active resistance of the primary winding exceeds the reduced secondary resistance. The ratios of the resistances of the primary and reduced secondary windings of transformers with a capacity of 20 to 1000 kVA are obtained, taking into account the electrical skin effect and thermal change in the resistances of copper and aluminum windings

A Single-Stage Dynamically Compensated IPT Converter With Unity Power Factor and Constant Output Voltage Under Varying Coupling Condition

Leakage and magnetizing inductances of a loosely coupled transformer are constantly changing due to the relative positions of the primary and secondary transformer windings in inductive power transfer systems. In order to counteract the nonnegligible inductances and extract desirable characteristics from the system, various compensation networks have been proposed to obtain unity input power factor and constant output voltage for minimum reactive power and ease of control for battery charging or other power electronic applications. However, most of the existing control methods with fixed compensation networks, which are usually designed for a specific coupling coefficient, have failed to fulfill both requirements simultaneously due to the mismatch between the resonant frequencies of the networks after the deviation of the designed coupling condition. In this article, a dynamic series/series–parallel compensation network based on a switch-controlled capacitor is proposed to rematch the series- and parallel-resonant frequencies of the network such that the magnetizing inductance can be adaptively compensated for different sizes of air gap/misalignment. By doing so, the requirements of load-independent output voltage and unity input power factor can be simultaneously fulfilled, while zero-voltage switching on the primary bridge is still maintained under different coupling conditions by a single-stage converter. An experimental prototype with the air gap ranging from 10–16 cm is built to verify the idea.

Harmonic distortion assessment in power distribution networks considering DC component injection from PV inverters

The large-scale connection of distributed generation (DG) units imposes on utilities a series of technical, economic, and regulatory challenges required to ensure the reliability and the power quality in the distribution networks. One of the technical problems refers to the harmonic current levels caused by inverters employed in photovoltaic distributed generation (PV), increasing the possibility of resonance in systems with capacitors. In addition, inverters without isolation transformer can also inject a certain amount of DC current which, being present in power transformer secondary windings, favor the generation and propagation of additional harmonics in the primary side. Thus, this paper shows that DC currents injected by PV inverters create one more condition that may cause system-capacitor resonance. For this, laboratory analyses are presented showing the conditions under which different models of PV inverters inject a higher DC current level. As a result, it is verified that higher DC current level is injected in conditions different from those in which there is higher harmonic current injection, concluding that the inverter may affect the power quality for whatever the power injected by the PV system.

AC–DC boost converter based on T-type multi-state switching cell and output voltage balancing

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.

Duty Cycle Loss Compensation Method Based on Magnetic Flux Cancelation in High-Current High-Frequency Synchronous Rectifier of LCLC Converter

With uncertainty of the parasitic parameter in different practical layout, two synchronous rectifiers (SR) with same topology and identical components may exhibit significant difference in driving timing and each SR FET may suffers from the duty cycle loss. In this article, the mutual induction between the voltage detection network of SR controller and the transformer secondary windings is first investigated. Then, a compensation method based on magnetic flux cancellation is proposed to solve the duty cycle loss issue caused by the parasitic inductive coupling, which enables further increase of switching mode power supply efficiency. With the proposed compensation method, only an additional wire turn is required with no need to change the layout, resulting in reducing the difficulty for implementation in practical prototypes. Where, a most compatible method is employed after multiparameter extraction methods comparison and the parasitic parameters are given out. Then, the design process of a specific compensator is proposed. Finally, a prototype of 400 to 14 V, 1.5 kW LCLC resonant converter was employed to verify the advantages of the proposed method. An efficiency improvement of 0.8% is achieved. The method can be generally applied to different kinds of SR controllers. This article is accompanied by a video demonstrating operation waveforms.

Parallel Battery Management System for Electric Vehicles

Battery bank comprises of ‘N’ No. of. Battery pack where the required cells are connected in parallel and each pack will be made to connect both in series and parallel combination to attain a required voltage. Multi Secondary Coaxial Winding Transformer is used to maintain the battery in balanced condition. During charging and discharging of battery, each battery pack is connected to the secondary winding of transformer including Electronic Switches, Temperature Sensor, Voltage &amp; Current Sensor. The voltage, current and temperature sensor is used to measure the parameters of each pack, from which the state of the health, state of the charge and temperature of the battery can be calculated. The voltage induced in the primary side is based on the switching frequency &amp; duty cycle of the MOSFET. To compensate the required voltage needed by the load, a boost converter is connected to the system on the primary side of the system where the transformer will be coupled. The output is connected to the inverter that produces power to drive a BLDC motor.

GEARLESS WIND POWER PLANTS

The use of wind farms has great long-term potential as a highly efficient alternative source of cheap energy. The article is devoted to the development of new designs of wind power plants with the participation of the authors, which increase their energy, economic and operational efficiency. The developments concern designs that allow the use of a gearbox to be disconnected to connect a generator included in a wind farm. The principle of operation according to which depending on the magnitude of the voltage of the generator, ie the magnitude of the wind turbine speed, is connected to the thyristor rectifier one of the secondary windings of the transformer by means of switching on the corresponding pair of triacs by the device of selecting the working secondary winding. It is substantiated that any hardware logic or software-logic device, including a generator voltage sensor and threshold elements, will be used as a device for selecting the secondary transformer winding of the transformer, which will activate the corresponding pair of triacs depending on the voltage value of the generator. It is substantiated that the above-mentioned developments can be widely used in the creation of wind turbines with wind turbines of various design and purpose - with a horizontal or vertical axis of rotation, which includes generators for converting the energy of VP into electrical. It has been proved that the creation of an industrial or domestic wind turbine is one of the main tasks of ensuring an acceptable level of economic efficiency, realized by solving a number of technical problems.

THE EFFECT OF THE ACTIVE RESISTANCE OF THE PULSE TRANSFORMER WINDINGS ON THE PARAMETERS OF VOLTAGE PULSES GENERATED ON A CAPACITIVE LOAD

Goal. Analysis of the influence of the active resistance of the primary and secondary windings of a pulse transformer on the voltage at the load capacitance based on the developed methodology for the analysis of transients caused by the discharge of the storage capacitance in the primary winding. Methodology. A model for calculating transients is developed using the Laplace transform. Transient modeling is carried out in the MATLAB software package. The results of transient calculations are compared with experimental results. Results. A method for calculating transients in test installations with pulse transformers has been developed, which allows taking into account the effect of power losses in the primary and secondary windings on the voltage at the load capacitance. The calculated relations are obtained, allowing to take into account the influence of the active resistance of the primary and secondary windings of the transformer on the voltage at the load capacitance, the currents in the primary and secondary windings of the transformer, as well as on the voltage drop on the inductance of the primary winding of the transformer. Scientific novelty. A mathematical model is developed for calculating transients in the primary and secondary windings of a pulse transformer, taking into account the influence of the active resistance of the windings when it changes over a wide range of possible values. Practical value. Using the proposed technique, it is possible to determine the parameters of the discharge circuit at which test voltage pulses are formed on the load capacitance without distorting the shape of the pulse front.

A Novel Current Sharing Method by Grouping Transformer's Secondary Windings for a Multiphase LLC Resonant Converter

A novel current sharing method for a multiphase LLC resonant converter is proposed in this article. Without additional components or control strategies, the proposed method can achieve good current sharing performance even with 10% tolerance of the resonant parameters. Besides, the proposed method is very simple; only the secondary windings of the transformers need to be grouped. This method does not affect the efficiency and load transient characteristics of the LLC resonant converter. The excellent current sharing capability of the proposed method is demonstrated via theoretical analysis under first harmonic approximation assumption and powersim simulation. The experimental results of a 960-W two-phase LLC resonant converter prototype are provided to verify the effectiveness of the proposed method.

A kilo-ampere level HTS flux pump

This paper reports a newly developed high current transformer–rectifier high-Tc superconducting (HTS) flux pump switched by dynamic resistance. A quasi-persistent current of over 1.1 kA has been achieved at 77 K using the device, which is the highest reported operating current by any HTS flux pumps to date. The size of the device is much smaller than traditional current leads and power supplies at the same current level. Parallel YBCO coated conductors are used in the transformer secondary winding as well as in the superconducting load coil to achieve high current. The output current is limited by the critical current of the load rather than the flux pump itself. Moreover, at over 1 kA current level, the device can maintain high flux injection accuracy, and the overall flux ripple is less than 0.2 milli-Weber. The work has shown the potential of using the device to operate high field HTS magnets in ultra-high quasi-persistent current mode, thus substantially reducing the inductance, size, weight, and cost of high field magnets, making them more accessible. It also indicates that the device is promising for powering HTS NMR/MRI magnets, in which the requirement for magnetic field stability is demanding.

Forward Converter Current Fed Equalizer for Lithium Based Batteries in Ultralight Electrical Vehicles

In this paper, the concept of a forward balancing technique fed by a buck converter for lithium-based batteries in Electrical Vehicle (EV) applications is investigated. The proposed active topology equalizes eight cells in a series in a battery pack, by using a forward converter for each battery pack and the whole battery packs, using a buck converter. The battery bank consists of four battery packs, which are in series. Therefore, the proposed system will equalize 32 cells in series. In this paper, the proposed circuit employs a single transistor used in a Zero Voltage Switch (ZVS) for the forward converter. In practice, this means a capacitor in parallel with the switch at the same time a demagnetizing of the transformer is obtained. The circuit realizes a low Electromagnetic Interference (EMI) and reduces ringing. To overcome the problem of many pins on a coil former, the transformer secondary windings are made by using hairpin winding, on a ring core. It permits, e.g., having eight secondaries and uniform output voltages. Each secondary winding is made by two hairpin turns using two zero-Ohm resistors in series. The proposed topology has less components and circuitry, and it can equalize multiple battery packs by using a single buck converter and several forward converters for each battery pack. Experimental and simulation results are performed to verify the viability of the proposed topology.

Analysis, Design, and Implementation of Improved LLC Resonant Transformer for Efficiency Enhancement

In battery charging applications, the charger changes its output voltage in a wide range during the charging process. This makes the design of LLC converters difficult to be optimized between the efficiency and the gain range. In this paper, an improved resonant transformer is presented for LLC resonant converter charger to improve the gain adjustment and charger efficiency. The resonant inductance and magnetizing inductance are integrated in the designed LLC transformer, and the magnetizing inductance can be adjusted dynamically with the change of output voltage and load, which is realized by a switch-controlled inductor (SCI) parallel to the secondary winding of transformer. The proposed transformer has 22.4% reduction in losses under full load conditions compared to conventional solutions. Moreover, the conduction loss and switching loss of LLC resonant tank are reduced by dynamically adjusting the magnetizing inductance, which improves the comprehensive efficiency of the whole charging process. The proposed transformer design is verified on a 720 W prototype.

Novel ZVS DC-DC converter with low current ripple for light rail transit

ABSTRACTThis paper develops and studies a three-level zero-voltage turn-on converter for providing auxiliary power system in a DC light rail vehicle. The proposed converter includes a three-level circuit and a half-bridge circuit sharing the same power switches on the high voltage side in order to reduce switch counts and distribute total power into two circuits. The Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs) with a low voltage rating and a turn-on resistance are adopted in the developed converter in order to decrease conduction losses on power switches. On the secondary side, two inductors and four rectifier diodes are employed to reduce output ripple current and transformer secondary winding turns. A duty cycle control based on the phase-shift pulse-width modulation is used to regulate the output voltage and achieve the wide range of zero-voltage turn-on. Experimental results with a prototype with a 760 V input and a 48V/30A output are provided to verify the feasibility and effectiveness of the developed converter.