Value Of DC Voltage Research Articles

A fault ride-through strategy for accurate energy optimization of offshore wind VSC[sbnd]HVDC system without improved fault ride-through strategy of wind turbines

The transmission of offshore wind power through High Voltage Direct Current (HVDC) systems is an important way to utilization of offshore renewable energy. However, onshore AC grid faults can make it difficult to transmit the energy from offshore wind farms, resulting in HVDC system overvoltages. Existing solutions to this problem mainly include adding DC or AC energy-dissipation devices, adding communication systems, and improving the fault ride-through(FRT) strategy of wind turbines, which have issues with economics or reliability. Based on this, this paper proposes a device-free, communication-free FRT strategy, and the fault ride-through strategy of wind turbines does not need improvement. The exchange of active power between the AC side and DC side of the onshore MMC is calculated under grid-following and grid-forming control strategy. The reference value of DC voltage and offshore MMC capacitance energy are proposed at different control stages. Especially, the dynamically calculated offshore AC voltage reference values have been theoretically provided. This approach ensures that the HVDC system avoids over-voltage and effectively stores more energy. The effectiveness and correctness of the proposed scheme were verified through simulation on the RTDS platFform. This paper is of great significance to promote the development of offshore renewable energy and ensure the safe operation of offshore wind HVDC systems.

Improved coordinated control strategy for VSC-MTDC system with DC voltage secondary regulation

Droop control is widely used in multi-terminal flexible DC (VSC-MTDC) transmission systems by virtue of the advantage of multi-station cooperative unbalanced power dissipation, however, the essence of the droop control strategy is to change the DC current to realize the unbalanced power dissipation, and the resulting DC voltage deviation will affect the normal operation of the system. Firstly, this paper theoretically analyses the working characteristics of the conventional droop control and proposes a control method to realize the quasi-differential-free regulation of DC voltage by translating the droop curve. Second, according to the power margin of the converter station, the feedforward compensation amount of each converter station is reasonably set to avoid the power impact on the converter station. Finally, for the problem that the actual value of DC voltage still deviates from the rated value, a control strategy containing secondary regulation of DC voltage is proposed to further restore the DC voltage to the initial value on the basis of ensuring the effect of power regulation, which improves the stability of the operation of the VSC-MTDC system. The final simulation results verify the effectiveness of the proposed method.

Efficient DC Voltage Balancing of Cascaded Photovoltaic System Based on Predictive Modulation Strategy

This paper presents a predictive modulation strategy for dc voltage balancing of cascaded H-bridge-based photovoltaic generation systems (CHB-PV). It is intended for improving the efficiency of CHB-PV by reducing the number of switching events. The strategy enables the charge/ voltage estimation and the design of a real-time discharge-order exchange, ensuring discrete dc voltage balancing. The conventional loss-reduced level-shifted-pulse-width-modulation (LS-PWM) is embedded and used to predict the discharge values and the target dc voltage value. The real-time discharge-order exchange is used to make the individual voltages converge to the target value at intervals of maximum 1/4 fundamental cycle. The voltage spread range introduced by the discrete voltage balancing is also considered and well suppressed by a simple adaptive method. Balancing of the dc voltages is finally achieved in a more discrete way, which makes reduced switching events compared with only using the loss-reduced LS-PWM. Experiment results based on a 2.1 kW/311 V setup are presented to demonstrate the effectiveness of the proposed technologies.

Design of Short Circuit Detection and Destruction Equipment for Electronic Components and Circuits

This research aims to design and understand the working principles of short circuit detection and destruction devices in electronic circuits and components. The short circuit detector and destroyer uses a voltage injection method which is applied to the electronic circuit path and detects short components. Changes in temperature, voltage and current values produced by the DC Buck Converter were observed using supporting fluids, namely rosin and wax. The results obtained on electronic components and circuits are more efficient using liquid wax compared to liquid rosin (Flux). This tool is designed to use a DC Buck Converter as the main circuit and a Volt Meter as a voltage display and can be used effectively to detect short circuits, check DC voltage values, source DC voltage input and increase the voltage value on the battery (1.3-12 VDC).

Design and Analysis of Front Side Modular Multilevel Converter for Smart Transformer in 15 kV Arba Minch Distribution Network Using Diverse Controllers and Multicarrier Modulation

This paper presents design and analysis of a bidirectional medium voltage (MV) front-side converter of smart transformer (ST) for Arba Minch Town distribution system. A modular multilevel converter (MMC) configuration is used in the MV side of the ST. The grid side MV is 15 kV RMS line value and the desired MVDC voltage is 24.5 kV for ensuring bidirectional operation of the converter in the time of grid outage. A half bridge semiconductor power module is used to model the front-side MMC. Based on the MV DC voltage requirement, the number of submodules per phase leg is designed to be four (four in the upper arm and four in the lower arm). Multicarrier modulation techniques such as phase-shifted PWM and level-shifted PWM are used to generate gate signals. The model is developed in MATLAB/Simulink, and its performance with respect to input side voltage harmonics, current harmonics, and output DC voltage value has been tested by carrying out several case studies under different controllers such as proportional integrator(PI), fuzzy inference system (FIS), and adaptive neuro fuzzy inference system (ANFIS) for obtaining reference signal for modulation. Level-shifted PWM is used with PI, FIS, and ANFIS, whereas phase-shifted PWM with a technique of introducing DC bias is used with PI controller alone. From the simulation results, it has been observed that better power system current quality of FS-MMC is obtained for PS-PWM (2.16%) than level-shifted PWM (5.22%). Use of FIS and ANFIS with level shift PWM method slightly brings down the current THD values to 2.98% and 2.72%, respectively (decrease by 2.5%). Also, a maximum output DC voltage of 24650 V is obtained for ANFIS with level shift PWM as compared to values obtained by PI with level shift PWM and PI with phase shift PWM.

A single source based multilevel boost inverter with reduced peak standing voltage for renewable energy and EV applications

This paper introduces a nine-level (9L) boost inverter topology with reduced peak standing voltage (PSV) across the switches. The topology consists of a single DC source, two capacitors, a switched-capacitor (SC) and a floating capacitor (FC), and eleven power electronics switches. Due to the inherent voltage boosting capability, the proposed inverter is suitable for low-scale voltage applications such as photovoltaic (PV), fuel cell, and single battery-operated electric vehicles (EVs). A sensorless approach is introduced to stabilize the requisite voltage across the FC for any changes in input voltage. A generalized topology is also presented to obtain n-times voltage gain along with a high number of intermediate voltage levels. The PSV of the switches does not exceed the value of the input DC voltage, irrespective of increase in voltage gain. The results show that the voltage across the FC is unaffected by stepped variations in the modulation indices, power factor of load, pulse width modulation (PWM) techniques, and the operating frequency. Furthermore, when the input voltage changes, the voltage across the FC is automatically adjusted to a new requisite value within 0.6s. The topology works for a wide range of modulation indices (0–1) and loads. A thorough analysis is done to show that the proposed topology is superior to recent topologies.

Electrical activating of the “nonradiative” terahertz plasmon modes in a periodic grating-gate graphene structure with asymmetrical gating

Electrical tuning the radiative damping of “nonradiative” (weak) terahertz plasmon mode in a periodic dual-grating-gate graphene structure is studied theoretically. Tuning the dc voltage value applied to one of the gate subgratings can change the radiative damping of the weak plasmon mode from zero to the dissipative damping of the plasmons in high-quality graphene allowing for maximum energy conversion from the incident wave to “nonradiative” plasmon mode. Radiative damping increases due to the increase of the dipole moment of this mode by virtue of its asymmetrical gating. Using the weak plasmon modes is important for effective excitation of the plasmon resonances in high-quality graphene as well as for realizing the concept of low-threshold terahertz lasers based on graphene plasmonic structures. Data availabilityData underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.

A Modular Multilevel Converter With Integrated Energy Dissipation Equipment for Offshore Wind VSC-HVDC System

VSC-HVDC technology has great application prospects in the field of offshore wind system. In order to realize the capability of fault ride through of offshore wind VSC-HVDC system, this paper proposes a modular multilevel converter with integrated energy dissipation equipment (IEDE-MMC), which combines the complementary advantages of MMC and DC chopper. The working process of the short-time pulse of the energy dissipation equipment provides an opportunity for the use of low current switch devices, and it shares the water-cooling system, control-protection system and energy-supply system with the MMC submodule, which eliminates the independent systems required by the traditional DC chopper, providing an economic and reliable solution for the problem of fault ride through. The simulation results of 400 MW/±150 kV VSC-HVDC system verify the fault ride through capability of IEDE-MMC, and the peak value of DC voltage is less than 1.1 p.u., which meets the requirements of the system. Finally, the manufacturing cost and floor area of IEDE-MMC are analyzed. Compared with the scheme of adding DC chopper outside MMC, the IEDE-MMC cost is reduced by 22%, and the total floor area is reduced by 35%.

Analyses and Comparisons of Generic and User Writing Models of HVDC System Considering Transient DC Current and Voltages

Analyses and comparisons of generic models and a novel modeling method of line-commutated converter (LCC)-based high voltage direct current (HVDC) systems are presented for the power system simulator for engineering (PSS/E) simulation tool. The main purposes are to describe the dynamics of the DC voltage and current of HVDC system and to improve estimation of the maximum values using the generic and proposed HVDC models when AC line-to-ground faults are occurred. For the generic HVDC models, the characteristics and limitations as well as parameter investigations are conducted. Three modules are also are developed for the proposed HVDC model, which are composed of (a) AC/DC conversion; (b) controller selection; and (c) DC line model. Case studies were conducted considering the real-operated HVDC system in Korea under the PSS/E and power systems computer aided design (PSCAD) simulation environments. The simulation results were compared with measured data from the real-operated HVDC system and the results from the PSCAD HVDC models considering single- and three-phase line-to-ground faults. The case study results show that a specific generic HVDC model in PSS/E can simulate the dynamics of the DC voltage and current after the AC line-to-ground faults. The case studies also showed that the proposed modeling method is effectively improves the estimation of the maximum DC voltage and current values for the AC line-to-ground faults.

MODELING AND SIMULATION OF 1.8 KW GRID-CONNECTED PHOTOVOLTAIC SYSTEM USING MATLAB

A maximum power point tracking (MPPT) DC/DC converter for a photovoltaic (PV) system is an important component in a PV system. The converter is used to convert the value of DC voltage produced by PV panels to a value accepted by the inverter for on-grid, or battery for off-grid system. In addition, the MPPT is used to extract and maintain the solar PV to its maximum power in all conditions. However, the values of components used in literature of MPPT DC/DC converter for a specific PV module cannot be applied for different capacity. Although sets of equations are given in literature to determine the values of inductor and capacitor used in the circuit, the calculated values do not produce the desired output in most cases because of unclear explanation. The validation of input parameters of the converter is also not properly presented for different solar irradiance and temperature. The efficiency of the converter is still low. Hence, this paper presents step-by-step process on how to design a MPPT DC/DC boost converter in MATLAB/Simulink environment. The incremental conductance method is used as MPPT algorithm to control the duty cycle of the converter. Then, a thorough analysis is done by simulating the developed model under different solar irradiance and temperature. Simulation results are then compared with the theoretical values from I-V and P-V curves of the selected PV modules. The results show that the proposed MPPT DC/DC converter is able to extract maximum power from PV modules and the output power produced by the converter also indicates that the converter has a high efficiency at 99.7% in all selected values of solar irradiance and temperature.

A Compact Rectenna With Flat-Top Angular Coverage for RF Energy Harvesting

The efficiency of rectifying antennas (rectennas) always suffers when the energy sources change with space and time and have low incident power density in the harvesting of radio frequency (RF) energy. This letter presents a novel rectenna design which consists of a receiving antenna array insensitive to the location of the energy source and a rectifier suitable for the low incident power conditions. The design of the receiving array is based on the method of maximum power transmission efficiency expressed in the form of quadratically constrained quadratic programing. The receiving antenna features a flat-top beam collection range whose angular coverage is adjustable depending on the applications. The SMS 7630 diode is selected and mounted on the rectifier for the enhancement of rectification efficiency when the incident power is low. To validate the design method, a six-element patch receiving array with less than half-wavelength interelement spacing and a rectifier operating at 5.8 GHz industrial, scientific, and medical (ISM) band are fabricated, and the overall rectification performance is tested. The measurement results indicate that the value of output dc voltage remains almost unchanged when the energy source moves within the range from –45° to +45° in the H -plane under the identical distance.

Onset of chaos in nano-resonators based on strain gradient theory: Numerical analysis

In recent years, experimental and theoretical studies have shown that size effect is non-negligible in mechanical micro- and nano-structures. As a result, classical continuum theory cannot model these structures. To accurately predict the behavior of micro- and nano-structures, non-classical continuum theories should be used. In this paper, the effect of size on the chaotic region of resonators is studied by comparing the results of classical and strain gradient theories. A bifurcation diagram and Lyapunov exponent are used for detecting chaos in nano-resonators.It is shown that the effect of size on the chaotic region in bifurcation diagram varies significantly depending on the bias voltage. Lyapunov exponent is utilized to validate the chaotic region and it is in best agreement with bifurcation diagram. For some DC voltage values, size effect can eliminate chaotic vibrations while in higher DC voltages, it can result in chaos at much lower amplitudes than those predicted by classical theories. Dynamic behaviors of nano-resonators are categorized based on their bias voltages and their chaotic behaviors are analyzed based on classical and non-classical theories in detail. The obtained numerical results are compared with Melnikov and Maximum Velocity methods and it is shown that all methods predict the lower critical actuation amplitude for strain gradient theory.

DC Fault Ride-Through Strategy Based on Overmodulation

The hybrid modular multilevel converter (hybrid MMC) can realize DC fault ride-through based on the capability of overmodulation and can continue to output reactive power to AC side during the fault, which can speed up the recovery of DC grid power after the fault is cleared. This paper improves the control strategy of DC fault ride-through. During the bipolar short circuit on the DC side, hybrid MMC blocks the short-circuit current of the DC side by adjusting the reference value of DC voltage dynamically. Moreover, the average value of the sub-modules is introduced into the active current controller to maintain the balance of the sub-module voltage. Then, the performance of the improved strategy is verified by MATLAB/Simulink simulation model.

Design of 1 kW Buck-Boost Chopper with PI Control for Photovoltaic Power Conversion

The design of a 1 kW buck-boost chopper with proportional-integral (PI) control is presented and discussed in this paper. The buck-boost chopper was proposed as a photovoltaic power converter to achieve a stable dc output voltage. In the design, the circuits employed IGBT power switch to function the PWM control signals to adjust the chopper’s output voltage. The circuits were tested to investigate the output waveform set at 24 V from various dc input voltage values. The chopper circuits were connected to ten solar PV modules with a total capacity of 1 kW. Simulation test results confirmed that the system was able to output 24 dc voltage with output current about 41 A. Furthermore, a prototype of the buck-boost chopper was set up and tested. The circuits worked well to output a stable 24 V DC voltage from PV output voltage varied 15 V-32 V.

Yarı Empedans Kaynaklı İnverter Devresinin Performans Analizi

Today, new topology studies have been introduced for current and voltage source inverters that are widely used in power electronics applications in order to convert direct current to alternating current. In recent years, Z-source inverters (ZSIs) have become very popular by eliminating the conceptual and theoretical limitations of traditional inverters. ZSIs have the advantages like the shoot-through operation in the same phase leg of the inverter without using of DC-DC converters or transformers, the ability to operate as a buck or boost inverter depending on the applied modulation index and having a flexible-reliable circuit structure. In this study, performance analysis of a quasi Z-source inverter circuit (qZSI) under different operation conditions is comparatively examined. Among the most used control methods for the switching devices, the simple boost control technique has the largest voltage stress for a given voltage gain and the maximum boost control technique produces variable shoot-through signals resulting of low-frequency ripples on the passive components in the impedance network. Therefore constant boost control technique has been applied to the switches to generate the gate signals. The operating principle of the constant boost control technique with low voltage stress and stable shoot-through signals is explained. Boost factor, voltage gain, voltage stress and AC output voltage for different modulation indexes and DC voltage values of the qZSI are calculated with the related equations. Theoretical results have been verified with simulation studies by using Matlab/Simulink environment. According to the findings, stable shoot-through duty ratios are generated, and the qZSI circuit has been able to operate as a buck-boost converter to obtain the desired output voltage for different cases.

Regulating Сharacteristics of the Pulse Regulator Taking into Account the Nonlinearity of the Internal Resistance of the Power Source

Switching DC voltage regulators are widely used to regulate the average value of DC voltage at a load. The most important characteristic of any regulator is its regulating characteristic. In the case of power from traditional sources of electricity, it is often assumed that the load resistance is much greater than the internal resistance of the source. Therefore, it is not taken into account in the calculations, assuming that the resistance is zero. In the case of the use of non-traditional and renewable energy sources, which have limited power, the internal resistance of the source and the load resistance are values of the same order. In such cases, the internal resistance of the source significantly affects the type of regulatory characteristic and must be taken into account. In the literature, the regulatory characteristics of various types of pulse regulators are analyzed in detail for the case when the resistance is zero. There are works in which the regulatory characteristics of individual types of pulse regulators are analyzed taking into account the internal resistance of the power source for the case when this resistance is linear. However, the internal resistance of alternative and renewable sources of electricity is often substantially non-linear. The aim of the work is to develop a methodology for determining the regulatory characteristics of pulse regulators taking into account the nonlinearity of the internal resistance of its power sources and analysis of the obtained characteristics. The paper considers approaches to determining the regulatory characteristics of pulse regulators, taking into account the internal resistance of their power sources. It is proposed that the nonlinearity of the internal resistance of the source be taken into account using its output characteristic. The operating point on this characteristic is determined by the load resistance. If a pulse regulator is connected to the power source, the load of the source will be the input resistance of the regulation, which depends on the load resistance, as well as the relative time of the closed (open) state of the switch. A pulse regulator can be considered as a transformer of constant voltage and current. Therefore, the load resistance can be assigned to the input of the pulse regulator, and its value will depend on the duty cycle of the pulses. Based on this, a methodology for determining the regulatory characteristics of pulse regulators is proposed taking into account the nonlinearity of the internal resistance of their power source. Using az example of a step-down voltage regulator, using the developed methodology, we determined and analyzed a family of regulating characteristics for various values of the regulator load resistance. The conditions for ensuring the transfer of maximum power from the power source to the load are analyzed. The obtained characteristics are valid for the continuous current mode in the inductance of the regulation. A method for determining the inductance of the reactor of the regulator, in which it provides a continuous current mode in the entire control range is considered.

Electronic beam switching using graphene artificial magnetic conductor surfaces

This paper presents an electronic reconfigurable pattern control using artificial magnetic conductor (AMC) graphene surfaces for terahertz (THz) applications. The proposed graphene AMC surface consists of modified star-shaped slotted graphene sheets printed on the top and bottom sides of dielectric substrate. Square graphene ring with 1 µm width is used to control the ground plane size of the AMC-surface. The AMC-cell operates at 1.4 THz with wide frequency varying range from 1.05 to 2.2 THz for µc changed from 0.1 to 2 eV. The radiated waves from a rectangular dipole antenna backed by graphene AMC surface is deflected from the broadside direction to the end-fire direction. According to the number of unbiased graphene ring rows Nun the beam direction is controlled. The effective area of the proposed graphene-based AMC reflector is increased or decreased through operating these rings, respectively. Biasing graphene means applying a DC voltage value across it corresponding to µc = 2 eV, while corresponding to µc = 0 eV. Different AMC surfaces arrangements are investigated. For 17 × 17 AMC unit-cell, the peak gain direction in the y–z plane is θ = 0° for Nun= 0, θ = ± 16° for Nun= 4 rows, θ = ± 65° for Nun= 6 rows, and θ = ± 90° for Nun= 8 rows. The HPBW is 232°, 236°, and 239° for Nun= 4, 6, and 8 unbiased rows, respectively.

FOUR SWITCH THREE PHASE SEPIC INVERTER WITH FRONT END BOOST CONVERTER

In this paper, four switch sepic inverter with front end boost converter capable of producing quality three phase ac output is explained. Proposed topology is an advanced one when comparing with conventional topologies .Converter offer a design for the inverter with the combination of single-ended primary-inductance , which can obtain higher phase voltages compared to conventional four switch and six switch three phase inverters. A differential arrangement of SEPIC enables to obtained three phase balanced output voltage with only four switches. The output voltage is pure sinusoidal without the help of external filter. This proposed inverter is designed to reduce the cost, complexity and switching losses .It also improves the efficiency and reduces the harmonic distortion. Here the output of the inverters are connected deferentially across the load. The line voltage can not exceed the full value of the input dc voltage, for avoiding this a dc - dc boost converter is placed in the front end of the four switch sepic inverter, thus producing the required output voltage along with the sinusoidal nature. Due to this features, the inverter can be used for the grid integration and pv based power extraction. Proposed topology is operated in both current control algorithm and a modified sine pwm control technique. In this paper it is based on the novel sine pwm control technique. The topology is analysed, simulated using MATLAB/SIMULINK and also a prototype is accomplished to verify the feasibility of the proposed topology. Index Terms—Three-phase inverter, Bi directionl sinlge ended primary inductance converter, Novel sin pwm control, DC-DC boost converter,

Cross Connected Compact Switched-Capacitor Multilevel Inverter (C3-SCMLI) Topology With Reduced Switch Count

In this brief, a new cross-connected compact switched capacitor (C3SC) cell is introduced for multilevel inverter applications. The proposed CCS cell uses four switches and two diodes for interconnecting the input dc source and floating capacitors (FCs). A nine-level inverter is derived with the proposed C2SC cell requiring only ten switches and two FCs. The proposed C3SC cell-based MLI is self-balancing and has a voltage gain of two. All the switches of the proposed topology have a maximum blocking voltage within the input dc voltage ( v $_{in}$ ) value. The operating principle is detailed, and a simple logic gate based gate pulse generation scheme is presented. Detailed simulations and experimental results obtained from an 850 W prototype with several test cases are presented to validate the operation of the proposed topology. Finally, a detailed comparative assessment is performed with other recent SCMLIs to demonstrate the merits and superiority of the proposed topology.

Параметричний ємнісний вимірювальний перетворювач повітряного зазору між ротором і статором обертових електричних машин

The paper substantiates that based on the considerations of ensuring the versatility and reducing the cost of construction of measuring the air gap between the rotor and stator of rotating electric machines, it is advisable to use measuring transducers of air gap in the value of the output DC voltage. Such a measuring transducer will allow you to implement a measuring instrument based on serial microcontrollers with built-in ADC. It is shown that the most suitable for use in conjunction with electric machines in the process of their industrial operation are capacitive air gap sensors. However, due to the relatively low sensitivity of this class of primary measuring transducers, their use in conjunction with serial secondary transducers such as capacitance - voltage has serious limitations, exacerbated by the need to adapt the measuring instrument to a wide class of rotating electric machines with different nominal air values the clearance between the rotor and the stator. Given these circumstances, it was proposed to design a secondary measuring transducer type capacitance-voltage, characterized by variable gain, relatively simple design and low value of additional error, which will solve the existing problem of matching the measuring signal between the sensor and the sensor existing analog-to-digital converters, which are usually equipped with modern microcontrollers. A mathematical model of the proposed secondary measuring instrument obtained by further development of the Terentyev rectifier calculation method (monogram method) was developed, which allowed adapting it for calculation of rectifiers with low value of input supply and small value of load currents. A mathematical model of the air gap measuring transducer between the rotor and the stator of rotating electric machines into is obtained, which is a series connection of the capacitive air gap sensor and the proposed secondary measuring transducer of the capacitance-voltage type. The adequacy of the mathematical model was confirmed experimentally.