AC-DC Voltage Research Articles

Cascaded AC–DC Voltage Control to Provide Reactive Power Support for the PV‐Driven Grid‐Tied Synchronverter

ABSTRACTThe objective of this submission is to provide flexible reactive power regulation of a photovoltaic (PV)‐driven grid‐connected inverter. Here, inverter is realized as a synchronverter by employing frequency regulation using well‐established swing equation. However, reactive power regulation is accomplished by employing combined AC–DC voltage control in addition to traditional synchronverter control for ensuring smooth tracking of reactive power. Thus, the PV‐driven voltage source converter (VSC) will be injecting available active power as per the prevailing irradiation, temperature, and operator defined reactive power by employing proposed control. The performance of suggested control is evaluated and compared against existing control by considering realistic operational scenarios through a case study.

Bifurcation and dynamics of periodic solutions of MEMS model with squeeze film damping

In this paper, we study the oscillations of an idealized mass–spring model of micro-electro-mechanical system (MEMS) with squeeze film damping. The model consists of two parallel electrodes separated by a gap d: one of them is fixed, and another one is movable and attached to a linear spring with stiffness coefficient k>0. The oscillation, under the influence of AC–DC voltage V(t)=vdc+vaccos2πTt, is ruled by the following singular differential equation my′′+[A(d−y)3+Ad−y]y′+ky=θ0A2V2(t)(d−y)2.Here, y is the vertical displacement of the moving plate (y is always assumed to be less than d), m>0 is its mass, A>0 is the electrode area, and θ0>0 is the absolute dielectric constant of vacuum. Taking d as the parameter, we show the existence of saddle–node bifurcation of T-periodic solutions to the equation in the parameter space. This answers, from certain point of view, the open problem proposed by Torres in his monograph, see Torres (2015, Open Problem 2.1, p. 18). Further, we prove that the equation has exactly two classes of T-periodic solutions: as d tends to +∞, one of them uniformly tends to +∞ at the rate of d, while the minimum values of the second class tend to, or cross, 0.

Analysis, design, and control of standalone PV based boost DC-AC converter

This paper presents a new control scheme for a boost DC–AC converter which is used for solar power applications. The proposed DC-AC converter configuration can produce an AC voltage level across the output or load side greater than input DC voltage based on the operating duty cycle. Generally, the conventional DC-AC converter or voltage source inverter (VSI) generates AC voltage which is less than input DC voltage. Maintaining a constant voltage across the load with improved dynamic performance is challenging for anyone for the solar photovoltaic (PV) system. A dual-loop sliding mode control is proposed for the boost VSI to address the above issues. The proposed controller has robust in nature against the wide fluctuation in the plant or load parameters. The design, analysis and control of the boost DC-AC converter are briefly discussed in this paper. This topology can be broadly used in solar powered uninterruptible power supply (UPS) where boosting operation is essential for low voltage solar PV system. This topology eliminates the DC boosting power processing stage which leads an improved efficiency of the overall system. The MATLAB/Simulink results are presented to highlight the above issues.

Influence of PD Between Needle and Plate Electrodes on Oil-Pressboard Aging Under Combined AC–DC Voltage

Influence of PD Between Needle and Plate Electrodes on Oil-Pressboard Aging Under Combined AC–DC Voltage

Performance improvement of predictive voltage control for interlinking converters of integrated microgrid

Voltage quality in Renewable Energy System may be harmed by varying power demand and fluctuating energy source outputs. The model predictive voltage (MPV) control approach is suggested in this study. The proposed control strategy enables appropriate power interactions between the AC and DC subgrids while sharing power fluctuations in a coordinated way. Both the AC and DC subgrids support each other in accordance with their normalized relative changes in AC frequency and DC voltage, respectively. A typical photovoltaic (PV) wind-battery-based hybrid AC/DC microgrid is modelled and investigated, and the usefulness of the proposed scheme is validated under the renewable energy variations and load perturbations. MATLAB/Simulink has validated the efficacy of the suggested strategy. A set of comparative tests was conducted between conventional Proportional-Integral (PI) control, Sliding Mode Control (SMC) strategies, and a novel Model Predictive Voltage Control (MPV) approach under diverse conditions. The aim was to comprehensively assess the advantages of the proposed MPV method. Results demonstrate that, in contrast to traditional PI and SMC control strategies, the MPV technique exhibits distinct benefits in terms of superior control performance and achieves exceptionally low Total Harmonic Distortion (THD) values. Ultimately, the proposed solution not only raises the performance standard but also ensures the stable operation of the Renewable Energy System (RES).

A Hierarchical Identification Method of Commutation Failure Risk Areas in Multi-Infeed LCC-HVDC Systems

In the multi-infeed LCC-HVDC system, the concurrent commutation failure (CCF) caused by the AC fault of the receiving-end system may lead to the blocking of multiple converter stations, which challenges power grid security and stability. This paper proposes a novel method to quickly and accurately identify the CF risk areas, considering the CF probability (CFP) during the single-line-to-ground (SLG) fault. First, an AC-DC voltage asymmetry factor (ADVAF) and its theoretical derivation are proposed to quantify the influence of the fault position on the CF. Second, the critical ADVAF (CADVAF) is derived based on the equivalent method. By comparing ADVAF and CADVAF, the CF risk areas can be quickly divided into non-, possible- and inevitable-concurrent CF risk areas. Third, the relationship between local CFP (LCFP) and fault position is established, and the concurrent CFP (CCFP) is calculated. The proposed method has improved the accuracy and computational efficiency of theoretical analysis than earlier methods. Finally, the validity and accuracy of the proposed method are verified in dual-infeed and five-infeed LCC-HVDC systems built based on the IEEE 39-bus and IEEE 118-bus models, respectively.

The Nonlinear Dynamics of a MEMS Resonator with a Triangular Tuning Comb.

The nonlinear dynamic response of a MEMS resonator with a triangular tuning comb is studied. The motion equation with dis-smooth tuning electrostatic force is derived according to Newton's second law. The analytical solution of the periodic response is obtained using the harmonic balance method and section integral method. The singularity theory is then applied to investigate the bifurcation of the periodic response of the untuned system. The transition sets on the DC-AC voltage plane dividing the planes into several persistent regions are obtained. The bifurcation diagrams' topological structures and jump phenomena corresponding to different parameter regions are analyzed. We explore the effects of tuning voltage on the response. This demonstrates that the amplitude-frequency curves present more hardening characteristics with increased tuning voltage. Many twists, bifurcation points, and unstable solutions appear, leading to complicated jump phenomena. Two bifurcation points exist on the response curves: the smooth and dis-smooth bifurcation points, with the latter occurring on the switching plane of non-uniform fingers.

Improved vµ-LMS-Controlled Single-Phase Grid Tied PV Powered Electric Vehicle Battery System with High Gain DC-DC Converter and Power Management

The increasing solar photovoltaic (PV) and EV charging applications create power quality issues at utility grid. It requires efficient control thus, in this paper, single-phase grid-tied PV powered electric vehicle battery (EVB) system is proposed with reliable control and power management. The presented work offers efficient EVB charging either from PV power or utility to handle PV impacts on the utility. During peak power demand, the proposed power management offers less burden on utility and allows EVB to feed increased load along with changing PV power. In work, a recent high-gain DC-DC boost converter topology is utilized thereby making smaller household PV arrays in grid-tied mode with DC-AC voltage source converter (VSC). Moreover, a new improved variable step-parameter ‘µ’ least mean square (IvµLMS) adaptive control is proposed and compared for efficient control of VSC with various nonlinear load and PV irradiance variations. The IvµLMS offers good convergence, less burden on controller and improved dynamic responses under various conditions. As per IEEE-519 standard, the PV power is fetched to grid at unity power factor (UPF) with low total harmonic distortion (THD). The proposed grid tied EVB system, and its controls are modelled in MATLAB/Simulink environment and test results are analyzed and validated on a laboratory prototype.

A Novel Modulation Scheme for Simultaneous Common-Mode Voltage Reduction and Neutral-Point Voltage Balance in the Reduced Switch Count Quasi-Z-Source Three-Level Inverter

The reduced switch count quasi-Z-source three-level inverter (RSC-QZS-TLI) not only maintains the advantages of continuous input current in the conventional quasi-Z-source three-level inverter (C-QZS-TLI), but also reduces the number of power switches and system cost. However, it inevitably faces the challenges of high common-mode voltage (CMV) and neutral-point voltage (NPV) imbalance, which threaten system safety and reliability. Moreover, due to the inherent features of this topology, the medium vectors cannot be generated, which means that the traditional modulation method is not applicable any more. To address the above challenges, a novel modulation method is proposed. The pre-selected basic vectors are optimized primarily, which restrict the CMV magnitude within one-sixth of dc-link voltage. Then, for the particularity of RSC-QZS-TLI, the distribution factor of small vector and its limitation range are introduced for the first time, and an indirect calculating approach is developed to obtain the duty cycles of the pre-selected four vectors, which maintains the correct ac output voltage and dc voltage boosting ability. Meanwhile, according to sector number and output of NPV controller, the distribution factor is modified to control the NPV balance. Compared with the traditional modulation method, the CMV magnitude of the proposed method is reduced by 50 %, and the balanced NPV is controlled actively. Simulated and experimental results verify the feasibility of the proposed scheme.

Design Water Turbine as Pump Drive for Irrigating Paddy Fields in the Highlands in the Panjalu Ciamis Region

In electrical systems, safety is the main factor, but it is often overlooked because it is quite expensive. The current conventional outlet, although it has been standardized by the Indonesian national standard, is a fact in the field that there are still many incidents of electric shock, because the voltage continues to flow through the copper terminals inside the plastic frame protector. This incident can occur because the terminal is plugged into a conducting object such as a fork, spoon, iron rod, or held directly with a finger. For this reason, in this study, a safety system is made that uses the main component of the Relay as an intermediary for DC voltage and AC voltage. Trials carried out 50 times on each socket box resulted in solving the problem by conditioning the plug that had not been plugged into the terminal so that there was no voltage flowing into the outlet, this certainly distinguishes safety from using an ELCB which must have contact with the human body first.

Multistage Cascaded H-Bridge Inverter Based Booster Circuit for Hybrid Power Applications

The H-bridge MLI has cascaded to addicted cascaded the diode with switches of lower rated power, consumption of power reactive and active. A new system is being developed to increase effectiveness of MLI (multilevel inverter). within the electricity system, to inverter is critical for DC-AC voltage conversion. MLI focuses more on Industry Needs. MLI is typically used to provide high power at high voltage applications. In comparison to inverters flying capacitors and the diode-clamped, it has the fewest components and the voltage level it same number to achieve the voltage balancing capacitors or diodes any voltage clamping. This design incorporates a multilayer inverter with a cascaded H Bridge based on a Boost circuit (BCCHB). The job of the voltage to increase the boost circuit of the multilevel inverter. Boost circuits are essential in an application of wide range, including photovoltaic and the use of fuel cells. ML Inverter with Cascaded H Bridge is a Voltage Controlled Source Inverter with the advantages of being small in size and having an output waveform that is independent of load type. A cascaded H Bridge prototype model based on a boost circuit is validated, and the results simulation has been compared with the result.

Analysis of Asymmetric Fault Commutation Failure in HVDC System Considering Instantaneous Variation of DC Current

HVDC is an important part of reducing energy transmission losses and maintaining energy sustainability. Commutation failure is the most common fault in HVDC systems, but existing commutation failure analysis approaches for HVDC systems do not consider the effects of instantly increasing direct current on the turn-off angle after an asymmetric fault in the AC system. To address this problem, we developed a commutation failure analysis approach that considers instantaneous variation of the DC current and AC voltage after asymmetrical faults. Firstly, the effects of the AC voltage and the DC current on the turn-off angle and the coupling relationship between the two are analyzed. Secondly, an equivalent mathematical model of the DC line, which covers the reactance, is built in Laplace space. Combined with the phase angle offset generated by the voltage after an asymmetric fault, a single relation expression containing only the AC voltage and turn-off angle is obtained by decoupling the DC current and AC voltage. The critical instantaneous AC voltage leading to system commutation failure is then derived based on the critical turn-off angle. Lastly, based on the CIGRE HVDC model built in the PSCAD electromagnetic transient simulation software (PSCAD v46), the accuracy of the proposed commutation failure analysis method compared with the other two methods is verified via simulation experiments under different grounding impedance values, and the applicability of the proposed method is further verified using simulation experiments with different smoothing reactor parameters.

Distributed Unified Control for Global Economic Operation and Resilience Reinforcement of Hybrid AC–DC Microgrids

The paralleled bidirectional interlinking converters (BILCs) of the hybrid AC/DC microgrid (HMG) provide a flexible and reliable power interaction way between AC and DC subgrids with high power density. A distributed unified control (DUC) is proposed for BILCs to achieve both resilience reinforcement and global economic operation of the HMG. For distributed generators (DGs), the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$f_{ac}-\lambda _{ac}$</tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$v_{dc}-\lambda _{dc}$</tex-math></inline-formula> economic droop controls are employed for AC DGs and DC DGs to decrease the individual subgrid's generation expense by equaling DGs' incremental expenses (IEs). For BILCs, the normalized AC subgrid's frequency and DC subgrid's voltage are coordinated to achieve the economic power interaction (EPI), which further decreases the total generation expense (TGE). Besides economic operation, the proposed DUC is capable of adopting different MG operation modes into a unified control structure without any mode switching. Paralleled BILCs are managed to reinforce the system resilience by supporting the DC voltage or AC voltage once all DC or AC DGs fail. In addition, the proposed DUC enables BILCs with plug-and-play characteristics, resistance to the maximum acceptable communication delay, and the communication disruption robustness. The corresponding hardware-in-the-loop (HIL) results verify the effectiveness of the proposed control strategy.

Voltage and frequency instability in large PV systems connected to weak power grid

The voltage and frequency control of photovoltaic (PV) systems are influenced by coupled nonlinear factors. It has been discovered that frequency control stability is threatened by voltage regulation methods in PV systems. However, the frequency instability caused by voltage regulation methods has not been fully investigated. This paper investigates the voltage and frequency stability problems in PV systems connected with weak power grids. The voltage problems caused by grid impedance, comprising inverter AC voltage and DC voltage, are first analyzed. Then, methods for improving voltage stability, such as reactive power compensation, and the benefits and drawbacks of various compensation methods are investigated. Finally, the effect of reactive power compensation on frequency control stability is investigated and resolved. Simulations and experiments are used to validate the theory’s correctness.

Adaptive Droop Control of VSC-MTDC System Based on Virtual Inertia

In order to solve the problem that the voltage source converter based multi-terminal direct current (VSC-MTDC) system cannot provide inertia and participate in frequency modulation after connecting to the AC power grid under the traditional control strategy, an adaptive control strategy based on virtual inertia is proposed. First, the relationship between AC frequency and DC voltage was established by a virtual inertia control, allowing the VSC-MTDC system to provide inertia to the AC side. Second, to address the limited inertia coefficient selection due to DC voltage deviation, an adaptive control was adopted. When the DC voltage deviation is small, the inertia coefficient is increased to obtain a better inertial response; on the contrary, the inertia coefficient is reduced to prevent the DC voltage from exceeding the limit. Finally, to solve the problem of insufficient flexibility of the fixed droop coefficient, this paper introduces the power margin of a VSC-station into the droop coefficient to dynamically adjust the distribution ratio of unbalanced power and reduce the DC voltage deviation. The three-terminal VSC-MTDC system was modelled on the PSCAD/EMTDC simulation platform, and the superiority of the control strategy was highlighted in this paper by comparing it with conventional droop control and a fixed virtual inertia coefficient.

Model Predictive Torque Control-Based Induction Motor Drive with Remote Control and Monitoring Interface for Electric Vehicles

While the increased use of internal combustion engine vehicles raises carbon emissions, electric vehicles (EVs) are becoming more important for reducing air pollution. EV production costs are decreasing as technology advances since they are typically powered by alternating current induction machines (ACIM). In EV configurations that are propelled with ACIM, an inverter is required to obtain appropriate voltage levels to drive the IM. Multilevel inverters are widely preferred in the industry for DC–AC voltage conversion due to their high-power quality. In this study, the ACIM is supplied with the appropriate voltage using an active neutral point clamped (ANPC) inverter. The ANPC inverter acting as ACIM driver is controlled with model predictive torque control. The simulation of the proposed ACIM drive has been performed with torque and speed control features to determine the operational features of the experimental test bench. Furthermore, the designed ACIM drive includes remote control and monitoring functions via an Internet of Things-based module. This allows for instant monitoring of the input, output, and current values of the ANPC inverter. The graphical monitoring function is used to track the speed and torque values of ACIM while the speed can be changed remotely via the web interface.

An Active Power Decoupling-Integrated Reduced-Switch Current-Fed Switched Inverter

In recent literature, high-gain dc–ac inverters are employed in grid-connected photovoltaic (PV) systems. These inverters can have several features, such as shoot-through immunization and buck/boost capabilities achieving a wide range of operations with reliability and minimum distortion. One such example is the single-phase reduced-switch current-fed switched inverter (RSCFSI). This article proposes the enhanced boost control-based pulsewidth modulation (EBC-PWM) strategy for RSCFSI to improve the inverter’s dc–ac gain. Being a single-phase inverter, RSCFSI suffers from the double-line frequency ripple problem. However, a low-frequency (LF) ripple analysis reveals that the RSCFSI is also plagued with fundamental frequency ripple, which poses additional challenges for the active power decoupling (APD) integration and corresponding closed-loop controllers. Although both LF ripples can be alleviated using markedly large passive elements, the power density and reliability of the inverter worsen. In this article, an APD-integrated RSCFSI (APDRSCFSI) is introduced as a solution that deflects the aforementioned LF ripple energy to an auxiliary capacitor without adding more active switches. As a result, the inverter can employ smaller passive elements. In addition, the EBC-PWM strategy is also extended for APDRSCFSI, improving its dc–ac voltage gain and voltage stress. A closed-loop control technique that combines output voltage control and APD functionality is also illustrated. A hardware prototype is used to corroborate the advantages of APDRSCFSI.

Suppression to concurrent commutation failure of UHVDC with hierarchical connection mode based on improved dc current prediction

AbstractFor the ultra high‐voltage dc (UHVDC) transmission with hierarchical connection mode (HCM) at the inverter side, local commutation failure (LCF) at one layer after the ac fault may cause concurrent commutation failure (CCF) at the non‐fault layer. The inter‐layer couplings at the ac and dc sides add the difficulty to suppress the CCF. The fault instant may decide the dc current variation during the commutation, which affects the suppression effect. This paper shows the mechanism of the CCF including the inter‐layer ac and dc coupling, and proposes a control method for the inverter at the fault and non‐fault layers. First, an analytical expression among the dc current, ac voltage, and extinction angle of both layers is newly derived to find the dominant factors to the CCF. Second, to improve the calculation accuracy, a three‐point sampling function using Newton interpolation is newly proposed to predict the dc current. Finally, a coordinated control strategy based on the constant extinction area, the overlap‐arc area, and the dominant factor of the CCF is proposed to adjust the firing angle and suppress the CCF. The simulation results using the PSCAD/EMTDC software are given to verify the control effect of the proposed method against the CCF.

Inter-connected AC/DC HMGS power management with 3-phase and 1-phase ILC

In AC/DC hybrid micro grid system (HMGS) power converters are always tested for is performance in distribution, its ability to provide accurate power sharing, transient stability and load dynamics. The existing control methods either complex or limited to achieve optimal power flow. This paper proposes a modified decentralized droop control scheme for interlinking converter (ILC) connected to interconnected AC and DC grids. A three coordinated model is proposed where AC frequency, ILC power and DC voltage are corresponding axis. The power sharing through the ILC is dependent on the AC frequency droop and DC voltage droop which occurs due to overloading. The control scheme is designed for single and three phases ILC. The obtained results are compared with double loop control method which shows less frequency deviations, accurate power sharing. The ILC performs autonomously and transfer power bidirectional under islanded mode. The simulation is carried in MATLAB/Simulink.

Modelling and nonlinear dynamics of dielectric elastomer sandwich cantilever-plate actuators

Inspired from the bimorph actuators for flapping and propelling swimming vehicles, a soft actuator made of two dielectric elastomer layers and a hyperelastic material core is presented. This actuator is also termed as a sandwich cantilever rectangular plate, which is stimulated by alternating voltages with a phase difference. Based on the classical plate theory and the variational method, the governing equation describing the nonlinear vibration of the sandwich cantilever plate is formulated. Employing the harmonic balance method and the arc-length continuation method, periodic solutions are obtained, then the convergence analyses of the numbers of discrete modes and harmonics are conducted. In order to illustrate the frequency features more clearly, a modified mode numbering scheme is developed. The numerical results manifest that, the combined DC-AC voltage excitation and the AC voltage excitation can excite abundant nonlinear behaviors of the soft actuator, including the local peak and the isolated bubble aroused by the nonlinear coupling. Additionally, the fundamental mode response keeps dominating the dynamic behaviors of the cantilever-plate actuator. The nonlinear dynamics broaden the resonant domain significantly, which can be potentially applied to the design and manufacture of high-performance soft actuators through the vibration enhancement strategy.