Ideal DC Research Articles

Machine Learning Algorithms for Performance Enhancement in DCO-OFDM-Based LiFi Systems

This study describes how machine learning methods can be used to enhance the performance of LiFi (light fidelity) systems that are based on DCO-OFDM (direct current bias optical orthogonal frequency division multiplexing). LiFi, a rapidly developing technology that uses light for wireless communication, has to contend with issues like channel impairments and signal interference. This work investigates several machine learning strategies to address these problems and improve the DCO-OFDM LiFi systems' overall performance. It is determined how well various machine learning techniques perform in terms of improving system parameters, decreasing latency, and raising throughput by analyzing real-world data and simulation studies. Various sorts of symmetrical recurrence division multiplexing (OFDM, for example, DC one-sided optical OFDM (DCO-OFDM), are utilized in light devotion (LiFi). A critical DC predisposition in DCO-OFDM brings about optical power failure, while a minor inclination increment cutting commotion. In this manner, it's essential to decide the appropriate DC predisposition level for DCO-OFDM. This examination finds the ideal DC-predisposition an incentive for DCO-OFDM based LiFi frameworks utilizing machine learning (ML) algorithms. To do this, a MATLAB device is utilized to create a dataset for DCO-OFDM. Thusly, Python writing computer programs is utilized to apply machine learning methods. ML is used to recognize the basic DCO-OFDM qualities that influence the ideal DC predisposition. Here, it is exhibited that the base, greatest, and standard deviation of the bipolar OFDM signal, as well as the size of the heavenly body, decide the ideal DC inclination.

DC‐side stability analysis of grid‐tied converter with different control modes based on electrical torque analysis

AbstractThe DC‐side stability of the grid‐tied converter under different control modes is fully investigated using electrical torque analysis. The small‐signal model of a single converter connected to an ideal DC bus under various control modes is formulated. Accordingly, the damping and synchronising coefficient contributed by the DC network and controllers of grid‐tied converter are separately accessed using the electrical torque analysis method and the stabilising conditions of the grid‐tied converter operating under different control modes are further derived. The system stability mainly corresponds with DC network dynamics under constant active power control mode. On the contrary, the grid‐tied converter under constant DC‐link voltage control mode has no stability problem. Generally, elevating the DC‐link capacitance or decreasing the droop gain can greatly improve the stability margin reserve of the VSC‐HVDC links. In addition, the control gains of the classical PQ controller are proven to have limited impacts on DC‐side system stability. Finally, the results of numerical simulation prove the validity of the proposed stability analysis method and the stable boundary for the grid‐tied converter with different control modes.

Interconnection of Lagrange–Dirac systems through nonstandard interaction structures

The Lagrange–Dirac interconnection theory has been developed for primitive subsystems coupled by a standard interaction Dirac structure, i.e. a structure of the form [Formula: see text], where [Formula: see text] is a regular distribution, [Formula: see text] is its annihilator and [Formula: see text] is the configuration manifold of the theory. In this work, we extend this theory to allow for parameter-dependent subsystems coupled by nonstandard interaction Dirac structures. This is done, first, by using the Dirac tensor product and, then, by using interaction forces. Both approaches are shown to be equivalent, and also equivalent to a variational principle. After that, we demonstrate the relevance of this generalization by investigating three applications. First, an electromechanical system is modeled; namely, a piston driven by an ideal DC motor through a scotch-yoke mechanism. Second, we relate the interconnection theory to the Euler–Poincaré–Suslov reduction. More specifically, we show that the reduced system may be regarded as an interconnected Lagrange–Dirac system with parameters. The nonholonomic Euler top is presented as a particular instance of this situation. Lastly, control interconnected systems are defined and a control for a planar rigid body with wheels is designed.

On-Chip Power Integrity Simulation Using LSI-Core Macromodels Considering Voltage Fluctuations Caused by Inter-Function-Block Interference

When designing on-chip power distribution networks (PDNs) of a large-scale integrated circuit (LSI), power integrity (PI) must be ensured not to cause malfunctions. LSI-core macromodels are expected to be used for fast PI simulation. When building LSI-core macromodels from design information, the impedance and equivalent current sources are often extracted for each function block or smaller operating block. In the stage of modeling function blocks, the layout and operation of the surrounding function blocks are not fixed, so equivalent current sources of the macromodel of each function block are extracted under ideal power supply conditions. However, in an actual LSI, the on-chip PDNs have a certain impedance and the power supply voltage of each function block is not ideal dc voltage because of its own operation and the interference from the operation of surrounding function blocks in the same power domain. Since operating currents of transistors are affected by on-chip supply voltage fluctuations, this effect must be taken into account when simulating the PI of the entire LSI or the simulation accuracy will degrade. This article proposes a PI simulation method using LSI-core macromodels that takes into account on-chip supply voltage fluctuations due to the interference between function blocks in the same power domain. To verify the proposed method, a test chip with several function blocks was built, and it was confirmed that the proposed method can simulate PI with high accuracy.

Challenges and potential solutions of grid-forming converters applied to wind power generation system—An overview

As the capacity of wind power generation increases, grid-forming (GFM) wind turbine generators are deemed as promising solutions to support the system frequency for future low inertia power grids. So far, the GFM converter with a nearly ideal dc voltage source has been studied thoroughly. However, when the GFM converter is applied to wind power applications, there are some realistic problems and challenges, such as coordinating wind turbine control and GFM control, limited energy to support the grid, variable wind speed, etc. These problems still need more discussion. In this paper, an overview of challenges and potential solutions of GFM converters applied to wind power generation systems are provided, where different energy reserving schemes, GFM control schemes, and overcurrent protection schemes are compared and discussed. Finally, a few perspectives on future trends are shared according to the authors’ knowledge.

Influence of rotor excitation source model in electromagnetic field–circuit coupling analysis model of tubular hydro‐generator on no‐load voltage waveform and damper winding loss calculation results

AbstractIn this study, a 34‐MW tubular hydro‐generator was selected as the study example. For the electromagnetic field–circuit coupling analysis model, the effects of the ideal DC voltage and current sources (i.e. two models of the rotor excitation power supply) on the no‐load voltage waveform quality and the damper winding loss calculation results were studied by considering the influence of the electromagnetic induction of the rotor excitation winding. The obtained results provide direct and effective theoretical support and technical reference for improving the accuracy and rationality of the calculation results of the electromagnetic performance parameters and the analysis, design, manufacturing and operating level of such generators.

The Simulation of a Pid Controlled Robotic Drive Based on Bond Graph Modelling

AbstractDuring the study, the simulation of a robotic drive was realised using the 20-sim simulation software. The assumed robotic drive consists of an ideal permanent magnetic DC motor, a gear pair to realise the speed reduction, a torque transfer torsion shaft and a differential gear pair to change the direction and inertia. The drive is controlled by a speed control loop using a PID controller. In line with the purpose and result of the study, the simulation proved the effectiveness of Bond Graph-based modelling.

Measurements and Analysis of Partial Discharges at HVDC Voltage with AC Components

This paper presents the methodology for phase-resolved partial discharge measurements in HVDC systems with a DC voltage containing trace AC harmonics or a DC voltage ripple. The measurement result of partial discharges is an indicator of the current condition of the high-voltage power devices’ insulation system. The voltage waveforms in HVDC systems are not ideal DC, because different disturbances occurring naturally in these systems can affect the DC voltage. The AC harmonics related to the AC source voltage, and the voltage ripples provided by the power converter topology, can be found in the HVDC voltage. This paper proposes a novel approach to partial discharge measurement in DC networks. The synchronization to the particular AC harmonics appearing in DC voltage was applied to the PD measurements. The analyses were performed on the model sample containing a void inclusion, which was placed between electrodes fed by the DC voltages with the imposed chosen AC harmonics. Two scenarios were analyzed at a constant DC level: one with a variable AC magnitude and the second with a variable frequency of an AC source adjusted to the harmonics: 50, 150, 300, and 350 Hz. It was observed that the superimposed AC voltage component resulted in an intensification of PDs.

A Closed-Form Mathematical Model and Method for Fast Fault Location on a Low Voltage DC Feeder Using Single-Ended Measurements

Fault location on a dc microgrid feeder needs to be extremely fast to protect the circuit breaker and converter-source components. This paper develops a seminal theoretical foundation for fast fault location on a dc feeder that uses only single-ended local measurements in time domain. The theory provides a closed-form deterministic solution for fault location, making the resulting fault location method agnostic to system-topology and immune to fault resistance. The theory is developed with ideal dc voltage sources, and extended to practical converter-sources. The performance of the resulting method is demonstrated by simulating a dc feeder with converters connected at both ends, modeled in PSCAD.

The Effects of the Model Predictive Controller Compared to the LQR Controller on the Optimal Distribution of the Suitable Load and the Creation of Balance in Microgrids

Background and Objectives: Distributed generation (DG) sources are modeled using an ideal DC voltage source connected to the microgrid via voltage source converters (VSCs). Model predictive control presents a distinct method for energy processing.Methods: In this method, the electric power converter is considered a power amplifier with a discrete and nonlinear structure. Therefore, unlike linear control methods, the discrete and nonlinear nature of the converter is considered in this method. In this paper, the distributed model predictive controller was selected from among different methods of load allocation among DG sources due to its more advantages compared to the linear quadratic regulator (LQR) controller.Results: It has been Proposed that we could obtain better results in predictive control, utilizing similarity transform in the state matrix and its modification. In this research, all the simulations have been performed in the MATLABSimpower environment of MATLAB software.Conclusion: Moreover, to demonstrate the superior performance of the model predictive controller compared to the LQR controller, both performance modes of the microgrid, namely the grid-connected and islanding modes, have been considered.

Variable DC-Link Voltage Regulation of Single-Phase MMC Battery Energy-Storage System for Reducing Additional Charge Throughput

Battery energy-storage system (BESS) based on the modular multilevel converter (MMC) can flexibly manage the battery packs integrated into submodules, where the battery pack can directly or through a small capacitor connect to the rear-end half-bridge circuit for reducing cost and volume caused by an additional dc-dc converter. But the alternating current ripples will cause substantial additional charge throughput for battery packs and, consequently, reduce the battery lifetime in theory. Therefore, this article proposes a variable dc-link voltage regulation method for a single-phase MMC-BESS. In specific, the phase disposition (PD) modulation scheme is improved to properly bypass the gating signals with unnecessary conduction during operation and the modified gating signals will be rearranged for balancing the states-of-charge and states-of-health. Doing so, the additional charge throughput could be significantly reduced compared with the traditional phase-shift modulation and PD modulation. Even comparing with the ideal dc current charging/discharging, the proposed method will only increase slight additional charge throughput and nearly negligible capacity loss. The experimental results of a 6.6 kW/6.6 kWh single-phase MMC-BESS prototype verified the performance of the proposed method.

Seamless switching power sharing control method in a hybrid DC‐AC microgrid by the isolated two‐stage converter based on SST

To facilitate the application of various renewable generations as well as diversified loads, hybrid DC/AC microgrids have aroused widespread interest; however, direct access of different types of sources and loads to the utility through multiple converters may be inefficient. In addition, with the complexity growth of the system, the stable and efficient operation puts forward new requirements for the isolation protection and more intelligent control. Facing these problems, the isolated two-stage converter topology based on solid state transformer (SST) is designed and the automatic seamless switching power sharing control strategy is proposed. The proposed topology replaces the conventional passive transformer with dual-active-bridge converter (DABC) to realize voltage matching and galvanic isolation for higher controllability and less volume occupation. Constant ratio control method is adopted for DABC to operate as an ideal DC transformer. Further, AC frequency and DC voltage are measured as characterizations of power level to adjust the transferred power of the converter. Through the non-directional strategy, bidirectional power support and decentralized cooperation are realized, and the capacity and sensitivity of microgrids are considered. The stability of the proposed control strategy is analyzed and the feasibility is verified by several real-time hardware-in-loop experiments.

A novel five-level neutral-point-clamped inverter with an auxiliary DC source

Multi-level inverters have drawn much intention from researchers and industry, in which 3-level inverters have been widely used in practice. One of the most interesting issues is to increase the number of levels to achieve higher performances such as large power, high voltage and low harmonic distortion. Basic multilevel inverter configurations such as neutral point clamping diodes, flying capacitor clamping, and cascaded inverters have their own disadvantages when increasing the number of levels. To overcome these problems, different hybrid multilevel inverters have been proposed. As results, there are a lot of five-level hybrid inverters designed for practical applications. This paper proposes a new hybrid 5-level neutral point clamped inverter by adding auxiliary DC source. The novel hybrid inverter shows its performances comparable to the ideal NPC inverter fed by 4 ideal DC sources, and requires hardware simpler than cascaded and flying multilevel inverters. It has a good ability of self-balancing of the voltages across the DC capacitors. Consequently, simple and effective PWM control strategies can be utilized that enables achieving high working performances. The paper content consists of analyzing of the proposed hybrid inverter configuration, investigating the voltage balance on the DC capacitors, validating control characteristics and studying output performance when applying the carrier based pulse width modulation control. The analysis and characteristics of the proposed configuration are verified through simulation results using MATLAB/SIMULINK.

Influence of capacitor-buffered hybrid DC circuit breaker on bipolar short circuit fault of three-terminal MMC-HVDC transmission system

The flexible DC transmission system needs a DC circuit breaker to remove and isolate the bipolar short-circuit fault to prevent the excessive short-circuit current from damaging the DC transmission system. In this paper, a comprehensive model of DC circuit breaker and transmission system is established by using PSCAD based on capacitive buffered hybrid DC circuit breaker. The short-circuit current waveform and DC port voltage waveform of the three-terminal ±350 kV flexible DC transmission system under the condition of double-pole short-circuit fault at the DC side of rectifier station are simulated and calculated. The simulation results show that the maximum current and voltage of the capacitor-buffering hybrid DC circuit breaker model is lower than that of the ideal DC circuit breaker model under the condition of bipolar short-circuit fault at the DC side of the rectifier station. The system fault waveform under different parameters of capacitor-buffered hybrid DC circuit breaker is compared and analyzed through simulation, so as to optimize the parameters of circuit breaker. It can be seen that the actual results more in line with the switching process can be obtained by using the capacitor buffer type hybrid DC circuit breaker.

Simplified hybrid reliability simulation approach of a VSC DC grid with integration of an improved DC current flow controller

In this paper, different reliability simulation approaches of an improved DC current flow controller (CFC) integrated voltage-sourced converter (VSC) based DC grids are investigated with the following contributions: (1) In order to achieve bidirectional power flow control and fault current blocking capability, an improved DC CFC topology with a set of reversed switches is analysed to enhance the controllable path and control margins; (2) Two different reliability simulation approaches of the improved DC CFC integrated meshed multi-terminal DC (M2TDC) grid are analysed. In Approach 1, the VSCs and their AC sides are modelled without simplification. In Approach 2, the VSCs and their AC sides are represented by ideal DC voltage/current sources to simplify the system modelling; (3) Synthesizing the merits of both approaches while avoiding the deficiencies, a hybrid reliability simulation approach is proposed with high efficiency of simulation while maintaining the accuracy; (4) In order to further enhance the simulation efficiency, a different reliability simulation approach of the ideal DC current source, namely improved ideal DC current source, is proposed. Simulation systems are established in PSCAD/EMTDC for verification.

Effect of power quality on the design of proton exchange membrane water electrolysis systems

Water electrolyzer technologies may play a key role in the decarbonization of the fossil-fueled world economy. Electrolytic hydrogen production could bridge emission-free power generation and various energy end-use sectors to drive the energy system towards a net zero-emission level. In order to reduce the economic cost of the required energy transition, both the overall system efficiency in converting electrical energy into the chemical energy carried by hydrogen, and the material used to build electrolytic cell stacks, should be optimal. The effect of power quality on the specific energy consumption of proton exchange membrane (PEM) water electrolyzers is investigated with a semi-empirical cell model. An experimentally-defined polarization curve is applied to analyze cell-specific energy consumption as a function of time in the case of sinusoidal current ripples and ripples excited by an industrial 12-pulse thyristor bridge. The results show that the effective electrolyzer cell area should be up to five times as high as an ideal DC power supply when powered by the 12-pulse thyristor rectifier supply to match the specific energy consumption between the two power supply configurations. Therefore, the improvement of power quality is crucial for industrial PEM water electrolyzer systems. The presented approach is applicable to simulate the effect of power quality for different proton exchange membrane electolyzers.

Classification and dynamic assessment of droop-based grid-forming control schemes: Application in HVDC systems

This paper introduces a novel classification for droop-based control strategies towards emerging interest of utilizing grid-forming control schemes in high voltage direct current (HVDC) systems. Classical droop control for grid-forming operation does not conventionally depend on a phase-locked loop (PLL). It is demonstrated that by including a PLL in droop control, it is possible to define two other droop-based control variants with different capabilities and functionalities. To highlight the differences in performance of each control scheme, the active power response of the power converter is evaluated in case of variation in grid short circuit ratio (SCR) as well as the PLL response time by considering an ideal DC bus. Accuracy in active power regulation, frequency support capability and virtual inertia emulation are the functionalities that have been addressed for the proposed three different control schemes. In a next step, the introduced droop-based grid-forming schemes are assessed by considering the dynamics of both AC and DC side of the power converter at one terminal of an HVDC link. Finally, based on the simulation results, a summary of features for all introduced grid-forming control schemes is presented11This work is supported by the project “HVDC Inertia Provision” (HVDC Pro), financed by the ENERGIX program of the Research Council of Norway (RCN) with project number 268053/E2, and the industry partners; Statnett, Statoil, RTE and ELIA..

Approaching the Ideal BLDC Motor: A Novel Electronic Speed Controller System for a Generator-Converted BLDC Motor with Field Weakening Feature

The concept of an ideal Brushless DC (BLDC) motor which has adjustable rotor magnetic field offers an opportunity for wider BLDC area of implementation as a very versatile electric powerhouse especially in variable load areas such as on electric vehicle or other people movers. Characterized by its high-efficiency level, low maintenance and long service duration, the lack of physical commutation brush like in regular DC motor dictates the requirement of an electronic control system to regulates its commutation.
 
 An electronic control system equipped with rotor field control capability in a collaboration with an ideal BLDC motor, is believed to offers wider implementation opportunity. Unlike a normal BLDC motor which has a standard power curved characterized with maximum power is only achievable in one specific speed, if properly controlled will have an adjustable maximum power in a wide range of rotational speed. 
 
 This study proposes a novel approach to an ideal BLDC implementation through novel electronic speed controller with rotor field control in addition to normal standard motor power control. As there is no such thing as an ideal BLDC motor at the current moment, an automotive generator which has an electromagnetic rotor is converted to become a BLDC motor as an effort to approach the ideal BLDC motor concept. Field weakening, the term used for adjusting rotor magnetic field in induction motor control, is adopted as the term for adjusting the BLDC rotor field in operation. Further, a novel an electronic control system is developed which special features to also control the rotor magnetic field.
 
 The converted generator has been found to able to function like an ideal BLDC motor, by adjusting the electromagnetic rotor in its operation. It has been found to be able to provides maximum motor power within a wide range of rotational speed. Through rotor field adjustment, the converted generator provides a real-time versatile capability of allocating its power to either the high torque at low motor speed or to a very high speed at minimum torque. 39% to 81% operational efficiency levels have been achieved during the experiment, rendering the performance level of the converted generator and controller way above brushed DC motor and in par with most of standard BLDC motor.
 
 The Field Weakening control has also been found to be useable for speed control. Further, a Proportional – Integral close-loop speed regulation has also been developed for both motor and rotor control and was found to be able to works subsequently with seamless transition between each other.

PV control systems using iterated local search MPPT with an improved switched capacitor DC-DC converter

An optimisation to the steady state performance of wide range of switched capacitor (SC) converters made use in control of photo voltaic (PV) systems that aims to enhance its efficiency and output regulation performed by a switched capacitor direct current (SCDC) converter is proposed. This uses many power converters to effectively transmit power via a large cable with greater electro-magnetic interference (EMI). Under no-load conditions, this explained model shows that an ideal DC voltage transformation is achieved by the converter and the loss during the conversion are altered because the drop in voltage due to the non-zero load current measured at the impedance at load side has lesser electro-magnetic interference (EMI). The charging of capacitor and loss during discharging and the conduction loss at resistance is mainly due to the impedance of output resistance. Followed by this, our DC to DC converter is extended to a smart control technique to track maximum power point (MPP) of a PV system with constraints of varying temperature and irradiance along with iterated local search (ILS).

Effect of Converter Topology on the Specific Energy Consumption of Alkaline Water Electrolyzers

Water electrolysis will be used to produce renewable hydrogen for energy storage and Power-to-X applications in the future renewable-energy-based energy systems. Therefore, the energy efficiency of hydrogen production will probably become a major issue. In this study, the effect of practical supply power converters on the specific energy consumption of megawatt (MW)-scale alkaline electrolyzers is studied and compared with an ideal dc power supply. The current quality and the stack specific energy consumption are studied in the case of traditional thyristor rectifiers and a transistor-based converter. The stack specific energy consumption is analyzed based on the simulated current waveforms and the electrical equivalent circuit of the electrolyzer stack. It is found that the transistor-based converter offers up to 14% lower electrolyzer stack specific energy consumption than the 6-pulse thyristor rectifier and up to 9.2% lower electrolyzer stack specific energy consumption than the 12-pulse thyristor rectifier as the current varies between 5000 and 1000 A. The simulated change in the stack specific energy consumption of the MW-scale alkaline water electrolyzer outweighs the losses occurring in the rectifiers. Further, selection of the ac voltage level may have a more adverse effect on the stack specific energy consumption with the thyristor rectifier topologies compared with the transistor-based topologies.