Parameter Design of DC Transformer based on LC Resonance Principle

HVDC is suitable for bulk-power and long-distance transmission. Most of the existing HVDC systems are point-to-point LCC-HVDCs. By interconnecting existing LCC links can achieve more economical benefits and higher flexibility of power transfer. However, due to different voltage levels and control modes of these links, it is impossible to interconnect them together directly through dc cables. The side-by-side connection of LCC links using DC transformers at a geographic crossing point or close proximity between the LCC links is proposed. Such connection is to achieve the benefits of dc grid operation without incurring vast amount of costs by constructing new DC transmission lines but making full use of existing LCC lines. Two LCC links tied by a DC transformer are tested as a case study. The DC transformer based on full-bridge sub-module is designed for coping with power reversal, temporary DC and AC faults and reduced voltage operation. And its control system is designed to match the operation of LCC links.

A SOGI-based adaptive controller design for second-harmonic currents suppression of variable frequency loads in DC buildings

This paper proposes a new wideband phase shifter, aligning phase slope between the reference line and main line to reduce the slope deviation using 3 types of LC resonance circuits (series, parallel and composite type). Compared to the conventional ones, the proposed phase shifters have several advantages such as a simple structure with single layer, accurate LC values from the derived formulas that are not optimization values. In addition, any phase shift value is applicable to the proposed theory, since the phase shift range of the proposed phase shifter can be implemented from 0 to 360 degree. The design theory of the proposed phase shifter is derived by taking a differential of difference between reference line and LC resonant circuit with respect to angular frequency, then calculate the value of each element of L and C at the center frequency. Although the proposed phase shifter is designed with only one or three resonant circuits in this paper, the number of resonant circuits constituting the main line can be three or more. By the design theory, the total sum of the phase values allocated to each resonant circuit may be a phase shift value to indicate a desired phase difference between the reference line and the main line. To validate the design theory, 180○ wideband phase shifters with singles (series and parallel) and composite resonant circuits are designed, fabricated, and measured. The fractional bandwidth of the proposed circuits for a parallel and a composite resonant circuit are both greater than 64%. Therefore, the measurement results agree well with the design theory within 0.5 dB insertion loss ±10° and phase deviation, except fabrication error.

The symmetrical CLLC-type DC transformerDC transformer (DCT), with its high power density and exceptional capability for bidirectional power transfer, has been widely used in DC microgrids. It presents some difficulties for the parameter design of the CLLC-type DCT to meet the following two design requirements since the actual values of the inductors and capacitors in the circuit may change due to fluctuations in temperature and power. First of all, it is anticipated that the CLLC-type DCT will remain stable when it is cascaded with a constant power load (CPL), even though the output impedance is impacted by changing inductor and capacitor values. Second, even if the inductors or capacitors fluctuate, the CLLC-type DCTDC transformer is anticipated to retain an acceptable power efficiencyPower efficiency. This work proposes a four-stage PSOPSO-aided parameter design approach for the CLLC-type DCT that completely accounts for the unpredictable fluctuations of real-world inductors and capacitors to satisfy both design requirements, cascaded system stabilityCascaded system stability, and adequate power efficiency. With this proposed method, the CLLC-type DCT can operate steadily when it is cascaded with CPL and achieve the power efficiencyPower efficiency criterion even if the values of inductors or capacitors change. Finally, experimental evidence has been presented to support the efficacy of the proposed four-stage PSO-aided parameter design approach.

The symmetrical CLLCCLLC resonant DC transformerDC transformer has gained popularity in DC microgrids due to its strong galvanic isolation and capability for bidirectional power transfer. However, there are certain issues with the CLLC resonant DCT’s design that could affect its overall performance. Firstly, when it operates alone, its voltage transfer ratioVoltage transfer ratio (VTR) is challenging to keep within a tolerable range when inductance or capacitance fluctuations are present in reality. Secondly, impedance interactions may cause instability phenomena when the CLLC resonant DCTDC transformer works in a cascaded system with a constant power load (CPL). The stability of this cascaded system will also be impacted by variations in inductance or capacitance. This work proposes a parameter design strategy for the CLLCCLLC resonant DCT to address these issues. A particular application of the Particle Swarm Optimization (PSO)Particle Swarm Optimization (PSO) technique is made to achieve extensive assessments of erratic parameter variations. Thus, even in the presence of circuit parameter variations, the developed CLLC resonant DCT can maintain a stable system and a strong VTR. A 1 kW prototype has demonstrated the viability of this paper’s proposed design strategy.

The modular multi-active bridge (MMAB) converter—characterized by electrical isolation, modular design, high power density, and high efficiency—can be readily scaled to multiple DC ports through an internal shared high-frequency bus (HFB), establishing it as a viable topology for DC transformer (DCT) applications. However, its interconnection to a DC grid via low-damping inductors may provoke low-frequency oscillations and instability. To mitigate this issue, this paper employs a pole-zero cancellation approach to model the conventional constant-power control (CPC) loop as a second-order system, thereby elucidating the relationship between equivalent line impedance and stability. An active damping control strategy based on virtual impedance is then introduced, supported by systematic design guidelines for the damping compensation stage. Simulation and experimental results confirm that under weak damping conditions, the proposed method raises the damping coefficient to 0.707 and effectively suppresses low-frequency oscillations—all without altering physical line impedance, introducing additional power losses or requiring extra sensing devices—thereby markedly improving grid-connected stability.

The relevance The methods of functional integration of discrete electrical and electromagnetic components allow increasing the reliability and efficiency of electrical energy conversion systems, reducing their weight and dimensions. The authors proposed a circuit solution based on the replacement of some individual discrete components of a DC boost converter with a multifunctional integrated electromagnetic component (MIEС). The component performs the functions of an inductor and a filter capacitor. Aim of research This article discusses the investigation of a DC voltage booster converter based on a multifunctional integrated electromagnetic component. The main task is to investigate a DC voltage booster converter based on a multifunctional integrated electromagnetic component. Research methods In this study, the following methods were used: the study of scientific literature and computer simulation in the Matlab environment. Results A computer model of a step-up DC voltage converter based on MIEС in the Circuit Simulator software package has been developed. Graphs of the output voltage are obtained. The circuits of step-up DC voltage converters are analyzed. A circuit of a DC voltage boost converter based on MIEС has been assembled. Output voltage waveforms were taken. An analysis of the computer model and laboratory test sample was carried out. A set of works has been completed to improve the output characteristics of a step-up converter based on MIEС. The optimal scheme has been chosen to implement the replacement of the inductor and filter capacitor with a multifunctional integrated electromagnetic component. Conducted laboratory studies confirmed the operability of MIEС as a replacement for individual discrete components of the DC voltage boost converter circuit. The optimal mode of operation of the boost converter based on MIEС is determined, which makes it possible to expand the output voltage range and reduce ripples. Expansion of the output voltage range is feasible due to the near-resonant or resonant mode of operation of the converter, which is feasible due to the MIEС structure, which is a resonant LC circuit.

A practical study of a hybrid series active power filter (HSAPF) for current harmonic compensation is presented in this paper. Part 1 emphasizes on the dimensioning and the designing of the passive components of the HSAPF namely the source impedance, passive filters (based on resonant LC circuits), and the current transformers. The needed electric coils were handily manufactured in the workshop using a separately excited DC machine. With the proposed winding method, it is possible to design all desired coils just by the knowledge of their geometric dimensions. To verify the validity of the proposed approach (applied to two different power scales) simulation and practical results are provided and discussed. The obtained results demonstrate the effectiveness of the adopted passive filtering technique in removing the harmonic distortion of the source current, and to compensate the power factor without adding further disturbance such as unbalance, which results in an improved power quality.

The recent trend in electric power consumption shows a steady increase and concentration in large cities and industrial districts. This indicates a strong need for a long-distance and enclosed-type power transmission line with large capacity and high reliability. A hybrid gas-insulated transmission line (H-GIL), which has the combined features of an XLPE cable and a conventional gas-insulated transmission line (GIL), has the potential to be applicable to such use. In the present work, we analyze the required dimension and the current capacity of H-GIL on the basis of insulation and thermal design for various parameters determining the structure. We also report an experimental study on flashover characteristics for a simple electrode model of H-GIL. The results show that the H-GIL can be realized with almost the same sheath diameter and current capacity as a conventional GIL. The experiment has also clarified that the insulation reliability of the H-GIL is much higher than that of a GIL. These properties show that the H-GIL has enough feasibility applicable as a long-distance and reliable transmission line with large capacity especially in urban areas. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 119(3): 27–39, 1997

Tapping on HVDC lines using DC transformers

A scientifically designed Design based courses namely, Electrical Machine Design has remained challenging to the learners. Additionally, limited critical thinking, inappropriate strategies to identifying the technical attributes of a problem make the task difficult. Students face limitations in understanding the inter-relationships of design variables and their influence on design parameters using theoretical approach of teaching. For teachers, imparting such higher order learning attributes are difficult using conventional pedagogy. Use of one of the modern pedagogies namely “Collaborative Learning Approach” (CLA) may be one of the solutions. CLA is well accepted method for catering the learners’ diversified cognitive requirements. However, for the design-based courses it is seldom practiced and requires detailed study and customization. This paper represents the outcomes of a case study. The learners of electrical engineering undergraduate program were taught with the design solutions in Design of DC Machine and Transformers in semester 6 and Design of AC Machine course in semester 7 using modified CLA model. The CLA model was modified by scaffolding the values of design parameters, use of spreadsheet as a teaching aid, and unique data set for each group. The objective was to demonstrate that using CLA as a pedagogical tool, the learners can develop skills to modify the design under the real time conditions. The study showed excellent cognitive improvement in leaners ensuring the success of modified CLA model. The results revealed that CLA may customized to cater diversified learners namely premier, average and challenged students. The study revealed that with a few innovative changes, CLA can effectively provide a better learning experience for students for design-based courses.

Coupled circuit based representation of piezoelectric structures modeled using the finite volume method

The equivalent impedance curve of a 40W electrodeless fluorescent lamp is measured. A simulation circuit is used in the circuit simulation software (orCAD). The simulated results are compared with the experiments. With the operation frequency increase, the error between the simulation and experiment is increase from 3.3% (198KHz) to 20.1% (233KHz). The analysis of the increase of error has also been discussed

Experimental observation of chaotic properties in a system of two coupled Wien-Bridge oscillators

Thermocouples are widely used as temperature sensors in industrial as well as laboratory settings owing to their low cost, usability and stability over a wide range of temperatures. However limitations arise in the form of cold junction compensation and non-linearity of the thermocouple emf. The present paper proposes an analog signal conditioning circuit that performs the dual task of cold junction compensation and linearization. Cold junction compensation is done using a thermistor based circuit to emulate the output voltages of the thermocouple at different ambient temperatures with respect to 0°C, and linearization is performed by employing a temperature-compensated dual-input logarithmic amplifier. Optimum circuit parameters have been found by standard optimizations methods, and simulations have been performed using a circuit simulation software `PSpice' by considering the characteristics of a 5kΩ thermistor and a T-type Copper Constantan Thermocouple. Nonlinearity errors and variation of output voltage of the signal conditioning circuit with ambient temperature are investigated from the simulation results.