DC Voltage Level Research Articles

Topology and Control Strategy of Multi-Port DC Power Electronic Transformer Based on Soft Switching

Multi-port DC power electronic transformer (PET) is a core equipment for achieving transformation of different voltage levels and flexible interconnection of different DC buses in a DC distribution system. It is capable of bidirectional energy flow, flexible regulation of power flow, port fault isolation, and other functions. A new five-port DC transformer topology based on soft switching technology is proposed in this paper. In this topology, different DC voltage levels can be interconnected efficiently, such as 20 kV, 750 V, ±375 V, and 300 to 500 V adjustable. The control of each port is simple and flexible. The output voltage is stable, and they are independent of each other, which can improve the system reliability. The topology of the proposed multi-port DC transformer is introduced in detail. The working principle, control strategy, and parameter design method of the transformer are analyzed. Simulations and experimental results are provided to validate the theoretical analysis.

Advanced Beam Estimation for Antennas Via Patterned Coupling-Line Detection Board in Ka-Band

In this research, we present an innovative method for estimating the beams of array antennas. Traditional beam analysis methods rely on placing receiving antennas in the far-field region, which requires moving or rotating the Tx or Rx, and using radiation pattern measurements. However, such methods often demand vast spatial requirements and the use of high-cost network analyzers. In contrast, the technique proposed in this study utilizes a board patterned with coupling lines strategically placed in the antenna's near-field zone. Signals intercepted by these coupling lines undergo conversion into DC voltage via a power detector situated at the line terminus. Interestingly, this method enables beam estimation solely based on the DC voltage level output of the power detector, thus offering a cost-effective and space-efficient solution that represents a significant advancement from traditional beam estimation methods.

Small signal analysis of DC voltage control based on a virtual resistance of DC/DC converter integrated in a multiterminal DC grid

AbstractThe future multi‐terminal direct‐current (MTDC) grid will require the interconnection of point‐to‐point high‐voltage (HV) DC links with different specifications such as DC voltage level, system grounding configuration and HVDC technology. To adapt these differences, it is obligatory for DC/DC converters to interconnect HVDC links. Additionally, they are capable of providing supplementary functionalities as they are highly controllable devices. In this article, a primary virtual resistance DC voltage controller associated with DC/DC converter is proposed for managing DC grid voltages of the interconnected HVDC grids, increasing the reliability of the system. The commonly known topology, Front‐to‐Front Modular Multilevel Converter (F2F‐MMC) is adopted for DC/DC converter. Time‐domain simulations are performed using EMTP software for validating the controller behaviour under power disturbances and large events of loss of one converter in a MMC‐based MTDC system. The converters are modelled using reduced order modelling (ROM) methodology. Apart from this, dynamic studies have been carried out using a linear state space model for small‐signal stability analysis of a HVDC system integrating DC/DC converter with a virtual resistance DC voltage controller. The results are examined through parametric sensitivity analysis.

In-Depth Exploration of Design and Analysis for PM-Assisted Synchronous Reluctance Machines: Implications for Light Electric Vehicles

In electric or hybrid vehicles’ propulsion systems, Permanent Magnet-Assisted Synchronous Reluctance Machines represent a viable alternative to Permanent Magnet Synchronous Machines. Based on previous research work, the present paper proposes, designs, and optimizes two ferrite PMaSynRM topologies, analyzed against a reference machine (also PMaSynRM) with improved torque ripple content, based on similar specifications and dimensional constraints. Considering the trend of increasing the DC voltage level in electric and hybrid vehicles, the optimal topology is included in an analysis of the DC voltage level impact on the design and performances of PMSynRM.

An Optimization Algorithm for Embedded Raspberry Pi Pico Controllers for Solar Tree Systems

Solar photovoltaic (PV) systems stand out as a promising solution for generating clean, carbon-free energy. However, traditional solar panel installations often require extensive land resources, which could become scarce as the population grows. To address this challenge, innovative approaches are needed to maximize solar power generation within limited spaces. One promising concept involves the development of biological tree-like structures housing solar panels. These “solar trees” mimic the arrangement of branches and leaves found in natural trees, following patterns akin to phyllotaxy, which correlates with the Fibonacci sequence and golden ratio. By adopting an alternative 1:3 phyllotaxy pattern, three solar panels can be efficiently arranged along the stem of the solar tree structure, each rotated at a 120-degree displacement. Optimizing the performance of solar trees requires effective maximum power point tracking (MPPT), a crucial process for extracting the maximum available power from solar panels to enhance the overall efficiency. In this study, a novel metaheuristic algorithm called horse herd optimization (HHO) is employed for MPPT in solar tree applications. Moreover, to efficiently manage the generated power, a cascaded buck–boost converter is utilized. This converter is capable of adjusting the DC voltage levels to match the system requirements within a single topology. The algorithm is implemented using MATLAB and embedded within a Raspberry Pi Pico controller, which facilitates the generation of pulse-width modulation (PWM) signals to control the cascaded buck–boost converter. Through extensive validation, this study confirms the effectiveness of the proposed HHO algorithm integrated into the Raspberry Pi Pico controller for optimizing solar trees under various shading conditions. In essence, this research highlights the potential of solar tree structures coupled with advanced MPPT algorithms and power management systems to maximize solar energy utilization, offering a sustainable solution for clean energy generation within limited land resources.

Interruption characteristics of self-powered hybrid DC circuit breaker with synergistic effect of step-down and divided current

The DC voltage level of photovoltaic and PEDF applications have continuously advanced, reaching up to DC3000V. This presents new requirements for DC circuit breakers operating at higher voltages (>DC1500V) to ensure effective fault protection in the DC side. Based on this, a self-powered hybrid DC circuit breaker with synergistic effect of step-down and divided current is proposed. This innovative design utilizes the voltage of main branch to trigger IGBT conduction, eliminating the need for an additional trigger circuit. The interruption characteristics is analyzed by simulation. The reactor and shunt resistance effectively reduce the peak currents of both main and transfer branches. This approach significantly mitigates the voltage stress on the mechanical switch, reduces the risk of post-arc reignition, and shortens the interruption time. The circuit breaker topology proposed enables the DC arc interruption at larger current and higher voltage, serving as the valuable guide for the implementation of hybrid DC circuit breakers in renewable energy power systems.

New analysis of VSC-based modular multilevel DC-DC converter with low interfacing inductor for hybrid LCC/VSC HVDC network interconnections

The integration of multiterminal hybrid HVDC grids connecting LCC- and VSC-based networks faces several technical challenges such as DC fault isolation, ensuring multi-vendor interoperability, managing high DC voltage levels, and facilitating high-speed power reversal without interruptions. The two-stage DC-DC converter emerges as a key solution to address these challenges. By implementing the modular multilevel converter (MMC) structure, the converter's basic topology includes half-bridge sub-modules on the VSC side and full-bridge sub-modules on the LCC side. However, while this topology has been discussed in the literature, its connection to an LCC-based network with controlled current magnitude lacks detailed analysis regarding operational challenges, control strategies under various scenarios, and design considerations. This paper fills this gap by providing comprehensive mathematical analysis, design insights, and control strategies for the modular DC-DC converter to regulate DC voltage on the LCC-HVDC side. Additionally, the proposed control scheme minimizes the interfacing inductor between the two bridges, ensuring uninterrupted power flow during reversal and effective handling of DC faults. Validation through Control-Hardware-in-the-Loop testing across diverse operational and fault scenarios, along with a comparative analysis of different converters, further strengthens the findings.© 2017 Elsevier Inc. All rights reserved.

Design and testing of a high-precision generating voltmeter for metal-enclosed megavolt level DC voltage source.

An extremely stable megavolt (MV) level DC voltage source is the key foundation for many scientific instruments, and the need for accurate measurement and long-term real-time monitoring of its output voltage is increasingly urgent. The utilization of conventional resistive voltage dividers for measurements introduces leakage currents, resulting in considerable measurement errors. The non-contact generating voltmeter (GVM) sensor based on electric field measurement has a simple structure and a low cost, making it expected to be an effective solution. Currently, most research on GVM sensors focuses on the measurement of weak electric fields at kV/m levels with significant interference. In this paper, an improved high-precision non-contact GVM sensor was designed. A DC voltage test platform was built, and the effects of the sampling resistor and motor rotation speed on the measurement results were discussed. The relative combined uncertainty of the improved GVM sensor reached 0.042%, which satisfied the urgent need for MV level DC voltage source measurement. The improved GVM sensor can provide an effective reference for measuring the output voltage of a metal-enclosed MV level DC voltage source or the potential of a suspended electrode.

Design of fuzzy logic controlled zero voltage switching based interleaved high gain converter

The conversion of low level DC voltage to high level DC voltage at lower duty ratios with less ripple current at source side is a challenging task in the distributed generation systems. Active switched inductor (ASL) converter is a high gain converter and has a large amount of input ripple current due to the parallel charging of the inductors during on time of the switches and series discharge of the inductors during off time of the switches. This large input ripple current in the converter when used in distributed generation (DG) affects the life time of low voltage batteries and fuel cells, the efficiency of photovoltaic source, increases the size and losses in the filtering stages and decreases the power density of the converters. In this paper, soft switching of interleaved active switched inductor (IASL) through Zero Voltage Switching (ZVS) is designed to overcome the limitations of ASL. The performance is analyzed in terms of its gain, input current ripple, switching loss and efficiency. An M-type resonant switch is used to achieve soft switching through ZVS technique.A proper value of resonant elements (inductor and Capacitor) is designed to achieve ZVS to improve the efficiency. Regulated voltage of proposed converter is required in DG systems and is possible with closed loop control. Fuzzy Logic controller (FLC) is designed to regulate the voltage and its dynamic performance is analyzed for different load values and also for sudden changes in load. Hardware model of the proposed ZVS based IASL converter with FLC is implemented and the results are verified with simulation results obtained from MATLAB Simulink.

Single-Phase Shift Modulation of DAB Converter in Typhoon HIL Simulation

Solid-state transformer (SST) could be a solution for a future distribution system, in which many renewable energy sources (RES) are integrated. The SST consists of a single-phase dual-active bridge (DAB) converter, which is scale-down the dc voltage level. The control objective of the DAB converter used in the SST is to control its output voltage. This control strategy consists of a proportional-integral (PI) controller and a single-phase shift (SPS) modulation. Numerous literatures have mentioned about the SPS modulation for the DAB converter. However, they do not provide procedures in implementing the SPS modulation in the real controller. This paper aims to develop the SPS modulation in the real controller of the STM32F446RE microcontroller. The proposed SPS modulation is based on a master-slave timer feature, which is available in the STM32 microcontroller. The development process and testing of the complete control strategy of the DAB converter were carried out in the hardware-in-the-loop (HIL) simulation using Typhoon HIL. This scheme speeds up the development of process and reduces the costs. The experiment in the HIL environment shows that proposed control strategy of the DAB converter consisting of the PI controller and the SPS modulation is successfully implemented in the real microcontroller of the STM32F446RE. The proposed control strategy of the DAB converter is capable of bidirectional power flow, which is useful for integrating distributed generators in the load side. Moreover, this control strategy can reject the disturbance caused by loads.

Coupled dynamic instability of graphene platelet-reinforced dielectric porous arches under electromechanical loading

Graphene platelet-reinforced dielectric porous (GPLRDP) arches are a kind of multifunctional structures, which can be used to design various dielectric resonators and soft robotic components. This work studies the coupled dynamic instability of GPLRDP arches under electromechanical loading. It is assumed that the presence of voids is uniformly distributed in the arch structure, while graphene platelets (GPLs) are uniformly dispersed inside the skeleton of such voids. The effective medium theory (EMT) is used to determine the effective dielectric permittivity and Young's modulus of such structures. Based on the Hamilton principle, the governing equations of this problem are formulated. The differential quadrature method (DQM) and the Bolotin method are then used for solving the arch system to identify the coupled dynamic instability region. In this study, we observe the coupling effect of parametric and forced resonance phenomena. A series of numerical experiments are also carried out to examine the influence of porosities, GPL weight fractions, boundary conditions, and electrical voltage levels on the critical excitation frequency and coupled dynamic instability behavior of GPLRDP arches. It is found that the coupled dynamic instability region becomes wider and shifts to low frequency as the effect of porosity increases. When the signal amplitude of AC frequency is within a certain range, there is an abrupt increase of the critical excitation frequency under a high level of DC voltage. The numerical results of this work demonstrate that the location and size of the coupled dynamic instability region can be actively controlled by adjusting the material and structural parameters.

Ferroelectric Transformer Using High Frequency Electric Field for Switching Polarization to Get Multiple Levels of DC Voltage and for Fault Protection

Abstract: The fundamental understanding of negative capacitance is not fully complete. Ferroelectrics are like ferromagnetics in that the different areas of ferroelectrics get polarized in different directions based on the charge density and finally the net charge of the material, as a whole gives the resultant polarization in a particular direction. The negative permitivity results in opposite polarization and it can be further explained in multidomain ferroelectrics. The application model as a static DC transformer based on magnetic capacitor model is discussed here.

Novel Energy Management Scheme for a Permanent Magnet Electric Drive-Based Hybrid Vehicle Using Model Predictive Control

The present work deals with the design of a traction system for a hybrid vehicle using a PMSM-type motor, including an energy regeneration stage, using a Neutral Point Piloted (NPP) inverter. Optimal operation allows the motor to be supplied in the traction stage with the correct energy in such a way that it operates properly; on the other hand, during braking, it facilitates the transfer of energy in regenerative mode to the DC bus, storing the greatest amount of energy in the storage elements, which, in this case, refers to a battery bank. It also includes a DC-DC bidirectional boost interleaved converter to regulate the DC voltage levels both in traction and in braking. Its fundamental characteristic is that with a reduced number of switching devices, it allows for the reduction in DC voltage of the DC bus with adequate characteristics, constant and stable, regardless of abrupt changes in the output voltage reference value. Also, other features include oscillation control, that is, reducing or increasing oscillations according to operating conditions. Its transient operation is excellent, since the settling time is considerably reduced, which implies that the voltage of the DC bus does not cause mishaps in the operation of the motor. In its operation as a boost converter, in the event of any voltage value of the DC bus, the converter raises the voltage value according to the reference conditions. Similarly, control allows the voltage to be held at a stable value regardless of changes in the set point. This work presents a novel energy management scheme for permanent magnet electric drive based on a Model Predictive Control strategy, thus contributing to the effective energy management of a standard hybrid electric vehicle driving cycle. Results obtained using a real-time Hardware-in-the-Loop (HIL) platform showed the effectiveness of Model Predictive Control in dealing with power flow management while ensuring control of electric drive in all the required speed–torque profiles.

Analysis of the Performance of a 5-Level Modular Multilevel Inverter for a Solar Grid-Connected System

The main purpose of a multilevel inverter is to combine numerous levels of dc voltage to create a nearly sinusoidal voltage. The synthesized output waveform has more stages as the number of levels rises, creating a staircase ripple which resembles the preferred waveform. As the number of voltage levels rises, the output wave's harmonic distortion diminishes and eventually approaches zero. In particular, the performance analysis of a five-level inverter with variable loads is highlighted in this paper. This topology has fewer devices than traditional multilevel inverters for the same five output levels, which makes it more affordable due to lesser driver circuits. The proposed modular five level topology is simulated using both high frequencies switching pulse width modulation and basic frequency switching modulation techniques. The output voltage, current waveform, and THD are examined and compared using Simulink to confirm the viability of the modular multilevel inverter topology.

Direct current power system stabilizers for HVDC grids: Current status

AbstractA power system stabilizer (PSS) is a control system integrated into the control structure of specific generation units within AC grids. It monitors current, voltage, and machine shaft speed. Analysing these variables, the PSS generates appropriate control signals to the voltage regulator unit, aiming to damp system oscillations. With the advancement of high‐voltage direct current (HVDC) overlaid high‐voltage alternative current (HVAC) grids, it is anticipated that direct current power system stabilizers (DC‐PSS) will be developed to perform a similar role as their AC counterparts. DC‐PSS will be responsible for monitoring and controlling DC voltage levels, ensuring stable operations. This paper focuses on DC‐PSS in HVDC grids, designed to ensure stable operation and mitigate voltage fluctuations. Unlike conventional AC power systems, HVDC includes only DC voltage and power. The input signal for DC‐PSS is the variations in DC voltage, and the output signal is proportional to the power changes at the specific bus where the DC‐PSS is installed, aiming to minimize DC voltage oscillations. These characteristics pose significant challenges in DC‐PSS. The paper addresses the challenges and highlights issues such as inertia and low‐frequency oscillations associated with DC‐PSS. Various control methods are presented and a comparison is made among these methods.

Performance investigations of five-level reduced switches count Η-bridge multilevel inverter

Introduction. This research paper describes a simple five-level single-phase pulse-width modulated inverter topology for photovoltaic grid applications. Multilevel inverters, as opposed to conventional two-level inverters, include more than two levels of voltage while using multiple power switches and lower-level DC voltage levels as input to produce high power, easier, and less modified oscillating voltage. The H-bridge multilevel inverter seems to have a relatively simple circuit design, needs minimal power switching elements, and provides higher efficiency among various types of topologies for multi-level inverters that are presently accessible. Nevertheless, using more than one DC source for more than three voltage levels and switching and conduction losses, which primarily arise in major power switches, continue to be a barrier. The novelty of the proposed work consists of compact modular inverter configuration to connect a photovoltaic system to the grid with fewer switches. Purpose. The proposed system aims to decrease the number of switches, overall harmonic distortions, and power loss. By producing distortion-free sinusoidal output voltage as the level count rises while lowering power losses, the constituted optimizes power quality without the need for passive filters. Methods. The proposed topology is implemented in MATLAB/Simulink with gating pulses and various pulse width modulation technique. Results. With conventional topology, total harmonic distortion, power switches, output voltage, current, power losses, and the number of DC sources are investigated. Practical value. The proposed topology has proven to be extremely useful for deploying photovoltaic-based stand-alone multilevel inverters in grid applications.

Optimization Design of Voltage Level of Flexible DC Transmission with Offshore Wind Power Based on Genetic Algorithm

Voltage level selection is the foundation of planning and designing for flexible DC transmission with offshore wind power. Traditional voltage level selection method is largely dependent on the manufacturing level of DC cable and converter with having standardization or project experience. For flexible DC transmission with large-scale offshore wind power, the voltage level using the traditional selection method may be not the best. By studying calculation methods of main devices and system cost, under the condition of system capacity and length of DC cable known, system cost function with DC voltage and sub-module capacitor voltage as variables was built. Taking the lowest cost as a target, aiming at the low stability of the optimization results of the traditional genetic algorithm, an optimization design method of DC voltage level based on subsection searching genetic algorithm was proposed. The simulation model of flexible DC transmission with offshore wind power was built based on PSCAD/EMTDC. The AC fault ride-through of the converter station and the safety of the main equipment under the optimal DC voltage level was verified.

A Review of Single-Stage Multiport Inverters for Multisource Applications

Conventional power electronic interfaces for multisource applications always need multiple conversion stages as intermediate dc-dc power conversion stages are inevitably installed for matching the different dc voltage levels and regulating the power distribution among dc sources. Dually, single-stage multiport inverter for multisource applications enables direct connection from the dc source to ac side without an extra conversion stage and has witnessed an upward trend in recent years. The salient advantages of single-stage multiport inverters comprise fewer power losses, fewer passive filters, and higher system efficiency. To capture the advancement in the field, the article reviews various single-stage multiport inverters for multisource applications, offers a comprehensive understanding of the current development of this configuration, and provides an insightful forward look at potential research issues of single-stage multiport inverters. This article presents various state-of-art single-stage multiport topologies as well as their applications and comparisons. In addition, systemic topology derivation methods of single-stage multiport inverters are discussed to provide inspiration for exploring new topologies. Moreover, the main challenging issues of this topology such as modulation, control, and energy management strategies are analyzed and summarized. Finally, some open questions and future trends of single-stage multiport inverters are also discussed to motivate future research and explore new alternatives.

GRID-CONNECTED PHOTOVOLTAIC SYSTEMS WITH MULTILEVEL CONVERTERS – MODELING AND ANALYSIS

In this paper, a comparison between three double-stage grid-connection systems in central inverter configuration is presented. This configuration can be used to obtain a wide power range and is suitable for the connection to three-phase grids. In this case, the photovoltaic (PV) panels are connected to the inverter via a dc-dc converter to ensure an optimal dc voltage level. The focus is on the characteristics and properties of the used converter’s structures. All the design steps of a grid connection system are also presented. Both two-level (2L) and three-level (3L) voltage structures are implemented. At the end of the paper, a detailed analysis highlights the advantages and disadvantages of the three photovoltaic systems connected to the grid.

A New Communication-Free Grid Frequency and AC Voltage Control of Hybrid LCC-VSC-HVDC Systems for Offshore Wind Farm Integration

We propose frequency and voltage control method for a hybrid high-voltage direct current (HVDC) system for integrating an offshore wind farm into transmission networks. Conventionally, DC voltage level is maintained as constant regardless of the wind velocity and the grid frequency, so AC voltage fluctuates with active power variation in a hybrid HVDC system due to the innate reactive power absorption of inverter side line-commutated converter (LCC). However, in the proposed method, the DC voltage changes according to the wind velocity. Furthermore, DC voltage is simultaneously regulated to participate in frequency control in a communication-free manner. These two characteristics can be achieved by using five droop control methods proposed here. Additionally, by determining droop constants using the proposed determination methods, AC voltage can be maintained as constant during active power fluctuations. Therefore, using the proposed method, an offshore wind farm can be stably connected to mainland transmission networks and successfully used as frequency supporting resources, because voltage characteristics of the AC network are not destabilized. A small-signal state-space (SS) model of the target system was also developed to investigate stability of the proposed control. The utility of the proposed method is demonstrated by case studies using PSCAD and SS models.