Variable DC Voltage Research Articles

Design and Modelling of MEMS Vibrating Internal Ring Gyroscopes for Harsh Environments.

This paper presents a design, model, and comparative analysis of two internal MEMS vibrating ring gyroscopes for harsh environmental conditions. The proposed design investigates the symmetric structure of the vibrating ring gyroscopes that operate at the identical shape of wine glass mode resonance frequencies for both driving and sensing purposes. This approach improves the gyroscope's sensitivity and precision in rotational motion. The analysis starts with an investigation of the dynamic behaviour of the vibrating ring gyroscope with the detailed derivation of motion equations. The design geometry, meshing technology, and simulation results were comprehensively evaluated on two internal vibrating ring gyroscopes. The two designs are distinguished by their support spring configurations and internal ring structures. Design I consists of eight semicircular support springs and Design II consists of sixteen semicircular support springs. These designs were modelled and analyzed using finite element analysis (FEA) in Ansys 2023 R1 software. This paper further evaluates static and dynamic performance, emphasizing mode matching and temperature stability. The results reveal that Design II, with additional support springs, offers better mode matching, higher resonance frequencies, and better thermal stability compared to Design I. Additionally, electrostatic, modal, and harmonic analyses highlight the gyroscope's behaviour under varying DC voltages and environmental conditions. Furthermore, this study investigates the impact of temperature fluctuations on performance, demonstrating the robustness of the designs within a temperature range from -100 °C to 100 °C. These research findings suggest that the internal vibrating ring gyroscopes are highly suitable for harsh conditions such as high temperature and space applications.

Selective Harmonic Elimination Technique Improvement for Cascaded H-Bridge Multilevel Converters Under DC Sources Uncertainty

The performance of multilevel converters (MLCs) is at the risk of uncertainty of DC sources. This issue has a more negative effect on three-phase cascaded H-bridge MLCs (CHB-MLCs) due to more isolated DC sources. DC voltage variation can take place in all phases, but in this paper, the effect of DC voltage variation of one phase on line voltages is considered. This problem can lead to unbalanced line voltages and a lack of third harmonic elimination in a spontaneous way. Therefore, these problems cause to modify the formulation of quarter-wave symmetrical selective harmonic elimination (SHE) for three-phase CHB-MLCs so that the line voltages become resistant to DC voltage variations as well as mitigating third harmonic. To keep line voltages amplitude fixed under variation of DC voltages, it is necessary to take advantage of non-identical modulation indices to exploit the maximum capacity of DC voltages. Furthermore, regarding unequal DC voltages that can appear in numerous states in a phase, a new method based on the average of DC voltages (ADCV) per phase is employed in the formulation of SHE to reduce these states. Finally, both simulation and experimental results are presented to validate the performance of the proposed method.

Improving Wave-to-Wire Efficiency of Direct-Drive Wave Energy Converters With Loss-Aware Model Predictive Control and Variable DC Voltage Control

Improving Wave-to-Wire Efficiency of Direct-Drive Wave Energy Converters With Loss-Aware Model Predictive Control and Variable DC Voltage Control

A double T‐type H‐bridge reduced switch multilevel inverter for a wide range of DC voltage variations

AbstractRenewable energy sources are subject to input source uncertainties, which can negatively impact output voltage THD. Having a high number of voltage levels in multilevel inverters (MLIs) with minimum components is cost‐effective. This paper proposes a new structure, Double T‐type H‐bridge (DTH) module, that can produce 9, 13, 17, 19, 21, and 25 levels using reduced components. Switching patterns in MLIs refer to the way in which the power switches are controlled to generate the desired output voltage waveform. As a result, having more switching patterns make the converter flexible to produce voltage levels in the face of input source uncertainties. The DTH structure provides new switching patterns, making it possible to produce levels when the difference of capacitor voltage is negative in a positive cycle or vice versa. This paper presents a new algorithm based on nearest level control to order voltage levels in ascending order, which improves output THD significantly. This topology brings a lower switching state that is linked to switching losses directly compared to the topologies with the same number of power switches. The DTH module's performance is evaluated through graphical analysis, simulations, and experimental results in symmetrical, asymmetrical, and load change conditions.

Power Quality Measurement Results for a Configurable Urban Low-Voltage DC Microgrid

The growing use of renewable energy sources and sustainable technologies has increased the attractiveness of low-voltage DC distribution grids. Despite initial research and standardization work, the definition of power quality (PQ) issues and their related compatibility levels in DC grids and the related measurement techniques remain in their infancy. The lack of available measurement results obtained in real-world situations is a major shortcoming. In this paper, the results of a measurement campaign obtained in a configurable bipolar 350 V/700 V DC microgrid in an urban environment are presented. Voltage and current signals were registered continuously at different positions in the microgrid with a sampling rate of 500 kSa/s while changing the configuration of the microgrid; the resulting data were analyzed afterwards, with a focus on DC voltage and current variation, ripple, and spectral analysis. The measurements were taken with custom-designed metrology-sound measurement equipment. The measurement results provide input to the development of DC PQ analysis tools and the standardization of DC PQ measurement methods. Furthermore, the experience obtained will be beneficial for utility companies and regulatory authorities for reliable planning-level and compatibility-level surveys.

Reduction in Submodule Capacitance in FB- and HYB-MMCs With Variable DC Voltages

Full-bridge submodule (FBSM)-based modular multilevel converter (FB-MMC) or hybrid MMC (HYB-MMC) composed of FBSMs and half-bridge submodules are necessary in many applications. However, the arm energy fluctuation during reactive power exchange is very high, causing large sizes and high costs of submodule capacitors. Using the negative states of the FBSMs, the FB-, and HYB-MMCs can dynamically adjust the dc voltage, and this technique has been used in many commissioned projects. This study treats the dc voltage as a new dimension and proposes a new operation mode based on variable dc voltage for FB- or HYB-MMCs to reduce the arm energy fluctuations and submodule capacitance. The basic idea is to reduce the dc voltage in high reactive power and low active power conditions, thereby suppressing the arm energy fluctuations. Theoretical analysis shows that the energy fluctuation and submodule capacitance can be reduced by 30%–40%, and the valve cost can be reduced by 13%. Economic and technical comparison results show that the proposed approach can have similar reduction effects on the capacitance and valve cost, but has fewer technical limits. Simulation and experimental results verify the analysis.

Optical Orbital Angular Momentum Processors with Electrically Tailored Working Bands

AbstractNovel options for multiplexing, such as orbital angular momentum (OAM), are sought to satisfy the explosive growth of information capacity. Consequently, spatial phase modulation with on‐demand tailoring of working bands is increasingly investigated. In this study, a polymer‐stabilized cholesteric liquid crystal is used to address this requirement. A varying DC voltage is applied, and the working band is increased over eightfold owing to the electric‐induced gradient pitch of the polymer network. Thus, the working band of an OAM processor is reversibly switched between narrowband and broadband states. An OAM‐multiplexing hologram is designed for parallel OAM encoding and decoding, enabling a wavelength‐division‐multiplexing compatible approach for in situ and non‐destructive OAM processing. The proposed design offers a promising solution for the on‐demand tailoring of working bands in liquid crystal planar optics and can promote advancements in massive information transmission and large‐capacity data processing.

Design and Analysis of Solid State DC-AC Transformer

Multimodal single/dual stage conversion (BSDC) based on a new solid-state DC-AC transformer (SDAT) is proposed. The suggested conversion can perform variable or constant DC voltage operation. A variable DC voltage is controlled dynamically in response to changes in DC input side voltage, allowing the DC-DC conversion stage to always operate at its best. New DC-AC power conversion of 2 port two-way choppers (TBDC) and two-way rectifier/inverter conversion (BRIC) was planned for the implementation of the proposed SDAT. SDAT, consisting of a bi-directional step-down-step-up converter and a bi-directional step-up-step-down converter, has been used as a prototype model to check the suggestion system. Functional concepts of this BSDC converter with TBDC are designed and simulated on the MATLAB/simulink environment network. PWM and control methods have been applied for SDAT to accomplish a wide variety of voltage and power loss reduction in the proposed device. Test bench model hardware is designed and tested to validate the effectiveness and benefits of the proposed approach.

Source-load-variable voltage regulated cascaded DC/DC converter for a DC microgrid system

<span lang="EN-US">Solar energy is available abundantly, the utilization of solar energy is developing rapidly and the photovoltaic based direct current (</span><span lang="EN-US">DC) microgrid system design is under demand but the stability of the DC voltage is of most important issue, as the variation of the output DC voltage is a common problem when the load or source voltage varies, hence a regulated DC output voltage converter is proposed. This paper presents source-load-variable (SLV) voltage regulated cascaded DC/DC converter which is used to obtain regulated output voltage of 203.1 V DC at 0.4 duty ratio with ±2% voltage fluctuations for the variation in the input source voltage and ±1.5% voltage fluctuations for the variation in load resistance of the nominal value with lower output voltage ripple and without use of sub circuits. A simulation model of SLV voltage regulated cascaded DC/DC converter in LTspice XVII software environment for the assessment of converter performance at different input source voltages and load resistances are verified.</span>

A Novel State-of-Charge-Based Droop Control for Battery Energy Storage Systems to Support Coordinated Operation of DC Microgrids

A modern dc microgrid often comprises renewable energy sources (RESs), such as photovoltaic (PV) generation units, battery energy storage systems (BESSs), and local load, and it is also connected to the utility grid through a point of common coupling (PCC). While most existing approaches have to rely on communication links to achieve the desired control performance, this article proposes a novel control strategy without resorting to the communication links. This is achieved by assigning BESSs as master units and regulating the dc bus voltage with a novel state-of-charge (SoC)-based droop control, where the BESSs coordinate the slave units (e.g., RES and utility grid) with the aid of the dc bus signaling (DBS) technique to avoid overcharging and overdischarging of these BESSs. In the proposed droop control, the reference voltage for these BESSs is designed for coordinated operation between BESSs and utility grid, and it is maintained constant in the normal SoC range, which can reduce dc voltage variation. Droop coefficients designed for SoC balance of BESSs are dynamically adjusted based on their own SoC values. Furthermore, the preset maximum deviation between the reference voltage and the dc bus voltage ensures the reliable coordinated operation. Real-time hardware-in-loop (HIL) tests considering three different scenarios are conducted to validate the effectiveness of the proposed method.

Interoperability of classical and advanced controllers in MMC based MTDC power system

This paper presents the modular-multilevel-converter (MMC) control interoperability (IOP) and interaction within the High Voltage Direct Current (HVDC)-based power system. IOP is a crucial issue in the large-scale HVDC grid with different suppliers. To accommodate future multi-vendor HVDC grids developments, this article comprehensively investigates the MMC control IOP issue. Firstly, the most commonly adopted proportional-integral (PI) control and other non-linear controllers, e.g., model predictive control (MPC), back-stepping control (BSC), and sliding mode control (SMC), are constructed for MMC. Then, the IOP simulations are carried out in a multi-terminal direct current (MTDC) system in real-time digital simulator (RTDS) environment. The most frequent transients of the practical projects, e.g., power flow changing, wind speed changing, and DC/AC grid faults, are simulated with eight different scenarios. Each scenario presents different control capabilities in maintaining system stability, more precisely, the scenarios with non-linear controllers show faster settling time and fewer DC voltage and power variations. Controller switchings are also achieved without bringing large system oscillations. This paper provides the optimal allocation strategy of controllers to cope with system transients.

Online Identification of Inductance and Flux Linkage for Inverter-Fed SPMSMs Using Switching State Functions

This article presents an online method to acquire the stator inductance and flux linkage for inverter-fed surface-mounted permanent magnet synchronous motors (SPMSMs) using switching state functions instead of average models. Given the switching state functions when different voltage vectors are applied to the motors, the information of inductance and flux linkage is revealed. Based on the dc bus voltage and current derivatives obtained from either hardware methods like Rogowski coil and differential circuit, or software methods such as tracking differentiator, stator inductance, and flux linkage are able to be figured out directly using the redundant or more practical methods with the help of recursive least square (RLS). Simulations and experiments are carried out to prove the effectiveness of the proposed methods, besides, dc voltage and operating speed variation as well as the impact of resistance are taken into account. Finally, compared with the conventional parameter identification based on the average models either in <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">α</i> – <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">β</i> or <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> – <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> coordinate, the proposed methods with switching state functions have remarkable advantages especially when the rotor position error exists. What needs further effort is the challenging case at very low speed, e.g., it is hard to identify flux linkage due to the small back electromotive force (EMF).

Single Phase VSI Behavior Improvement using Combined Feedback and Feedforward Controllers

Nowadays, the demand for power electronics technology has increased due to the importance of its applications such as power inverters. The power inverter is required to modify the DC power from PV cells to AC power. One of the most common issues of on-grid PV systems is the high variations of the generated DC voltage. This will affect the stability of the generated AC voltage at the Point of Common Coupling (PCC) with the grid. This paper combines the Feed-Forward and Feedback (FFFB) controller in a novel way to reduce the variation of the PV cells DC voltage. This paper presents both mathematical and Simulink models of single-phase voltage source inverters VSI. Then, a case study of 15% disturbance of DC-generated voltage is considered. The static and dynamic behaviour of the single-phase H-bridge inverter is analysed under different loads. The new combination is used to reduce the effect of the disturbance on the performance of the system. Also, the proposed closed-loop controller (FFFB) can reduce the overshoot by 50% less than the feedback controller only. The settling time has been improved by 41%, 61% for RL and induction motor.

Voltage-modulated surface plasmon resonance biosensors integrated with gold nanohole arrays.

Surface plasmon resonance (SPR) has emerged as one of the most efficient and attractive techniques for optical sensors in biological applications. The traditional approach of an EC (electrochemical)-SPR biosensor to generate SPR is by adopting a prism underneath the sensing substrate, and an angular scan is performed to characterize the reflectivity of target analytes. In this paper, we designed and investigated a novel optical biosensor based on a hybrid plasmonic and electrochemical phenomenon. The SPR was generated from a thin layer of gold nanohole array on a glass substrate. Using C-Reactive Protein (CRP) as the target analyte, we tested our device for different concentrations and observed the optical response under various voltage bias conditions. We observed that SPR response is concentration-dependent and can be modulated by varying DC voltages or AC bias frequencies. For CRP concentrations ranging from 1 to 1000 µg/mL, at the applied voltage of -600 mV, we obtained a limit of detection for this device of 16.5 ng/mL at the resonance peak wavelength of 690 nm. The phenomenon is due to spatial re-distribution of electron concentration at the metal-solution interface. The results suggest that CRP concentration can be determined from the SPR peak wavelength shift by scanning the voltages. The proposed new sensor structure is permissible for various future optoelectronic integration for plasmonic and electrochemical sensing.

Active Power Control of DPC Based Operation of Three Phase Inverter Under Stand-Alone Mode

This paper presents the successful application of direct power control (DPC) based algorithm in the DC–AC conversion of a standalone system. This algorithm is successful at the smooth variation of active power in the standalone mode of operation of renewable power generating system. Thus, it can supply the variable nature of power demand. The algorithm also successfully rejects the variation of DC voltage at the input of the inverter. The power output of the inverter in this standalone mode is successfully maintained during this condition. So, it can be said that the DPC in the standalone mode, is flexible enough to adopt the fluctuation of the DC voltage. It has also been seen that the inverter operating with DPC-based control can deliver constant power at the load end even under fluctuating load impedance. The claims stated, in theory, are successfully justified in both simulation and real-time environment.

Analysis and Optimization of Energy Variations in MMCs With Variable DC Voltages

The modular multilevel converter (MMC) containing full-bridge submodules (FBSMs) can increase the modulation index to reduce the energy storage requirement. The MMCs containing FBSMs can also adjust the dc voltage to fit special applications. However, limited research explores the energy storage characteristics of MMCs with variable dc voltages, and few effective approaches can ensure low-energy storage requirements. This study proposes an approximate analysis method for the energy storage requirement in MMC with variable dc voltages. Results reveal that the energy variation under low dc voltages restricts the reduction effects of the increased modulation index on the energy storage requirement. Then, on the basis of the fact that the low ac component of the arm current under low dc voltages provides a large current margin, an optimal circulating current (OCC) is proposed to optimize the energy variation under low dc voltages. In addition, a practical curve-fitting approach is proposed to facilitate the calculation of OCC in real-time controllers. With these approaches, the energy storage requirement with variable dc voltage becomes similar to that with constant rated dc voltage. Simulation and experimental results verify the analysis.

Application of Deep Learning Gated Recurrent Unit in Hybrid Shunt Active Power Filter for Power Quality Enhancement

This research work aims at providing power quality improvement for the nonlinear load to improve the system performance indices by eliminating maximum total harmonic distortion (THD) and reducing neutral wire current. The idea is to integrate a shunt hybrid active power filter (SHAPF) with the system using machine learning control techniques. The system proposed has been evaluated under an artificial neural network (ANN), gated recurrent unit, and long short-term memory for the optimization of the SHAPF. The method is based on the detection of harmonic presence in the power system by testing and comparison of traditional pq0 theory and deep learning neural networks. The results obtained through the proposed methodology meet all the suggested international standards of THD. The results also satisfy the current removal from the neutral wire and deal efficiently with minor DC voltage variations occurring in the voltage-regulating current. The proposed algorithms have been evaluated on the performance indices of accuracy and computational complexities, which show effective results in terms of 99% accuracy and computational complexities. deep learning-based findings are compared based on their root-mean-square error (RMSE) and loss function. The proposed system can be applied for domestic and industrial load conditions in a four-wire three-phase power distribution system for harmonic mitigation.

A Proposed Three-Phase Induction Motor Drive System Suitable for Golf Cars

In this paper, a proposed electric drive system for a three-phase induction motor is presented. The proposed drive system is suggested for a golf car as one type of electric vehicle. The suggested system consists of three similar single-phase buck–boost converters. Hence, each single-phase buck–boost converter is used as a buck–boost inverter and is used to energize only one phase of the induction motor. The suggested system has the advantage of high reliability, as it can deal with different fault conditions such as battery and motor winding faults. The suggested electric drive system depends on a buck–boost converter which gives variable voltages as well as variable frequencies. Thus, variable speeds of the electric vehicles can be easily achieved. A variable DC voltage (positive or negative) can be achieved at the output of the adopted buck–boost converter, which is considered another advantage of the proposed drive system. This DC voltage can be used to achieve braking of the induction motor used to drive the electric vehicle. Therefore, this advantage can be used instead of ordinary mechanical braking to increase vehicle reliability. To demonstrate our proposed idea, a simulation study is presented. The simulation is carried out using Power Simulation Program (PSIM) software. The simulation study takes into consideration the performance of the adopted buck–boost converter under different conditions to present its advantages. Furthermore, a performance study of the suggested induction motor drive system is carried out under different conditions ranging from healthy to faulty conditions to test system reliability. For more illustration, an experimental prototype of the adopted buck–boost converter is built, and its performance is studied. From all the obtained results, the efficacy of the proposed system is demonstrated.

A Combined Hierarchical and Autonomous DC Grid Control for Proportional Power Sharing With Minimized Voltage Variation and Transmission Loss

This paper presents a combined control scheme that consists of two complementary control strategies, namely hierarchical control and autonomous control to handle contingencies in a multi-terminal high voltage direct current (MTDC) system. The proposed hierarchical control considers three optimal targets, i.e., equal or proportional power sharing, minimizations of transmission loss and total DC voltage variation. The primary control layer implements the droop control for voltage source converters (VSCs). While in the secondary control layer, voltage reference setpoints of the VSCs in droop control scheme are calculated by the proposed optimal power flow method with the equal or proportional power sharing as equality constraints. As the hierarchical control relies on communication system, the autonomous control for power sharing can be activated during communication system malfunctioning or rapid power variation caused by renewable energy sources. The combined control strategy can greatly increase the reliability of the MTDC system. The simulation results of a five-terminal MTDC network conducted in the MATLAB/Simulink software verify the performance of the proposed combined control strategy.

AC unbalanced and DC load management in multi-bus residential microgrid integrated with hybrid capacity resources

This paper presents a control scheme including resources and load management in the residential DC microgrid. The DC microgrid is supported by fuel-cell, solar-cell and battery. The DC, AC single-phase and AC three-phase loads with 50 Hz frequency are integrated. The DC microgrid is connected to the external 60 Hz AC three-phase network. An efficient multi-bus topology is proposed for the microgrid and it is formed by various AC/DC buses to supply the loads and managing the resources. The main bus of system is a 470 V DC bus and it is connected to the external 440 V/60 Hz AC grid. The main DC bus supplies three LV, MV and HV DC buses with 100, 220, and 110–380 V, respectively. The HV DC bus produces a variable output DC voltage between 110 and 380 V in order to regulate the load power (i.e., motor speed). The MV DC bus is connected to 220 V/50 Hz AC single-phase loads. The connections between DC microgrid with AC loads and AC external gird are made by single-phase or three-phase inverters. The interface inverters between DC bus and AC loads are operated to control power, torque, speed, frequency and voltage of loads. The unbalanced AC loads are appropriately balanced by proper control of interface inverters. The resources and inverters are efficiently controlled to enable operation of residential building under both off-grid or grid-tied conditions. The coordination of fuel-cell, solar-cell and battery can supply a fixed 8 kW power to external grid and supply the internal loads under all outages and off-grid conditions. The simulations demonstrate that the proposed control realizes all the objectives including AC/DC load management, unbalanced load amendment, frequency adaptation, and off-grid operation.