Inverter Unit Research Articles

Small Signal Stability Analysis of Microgrid with Multiple Parallel Inverters

Microgrids are introduced into power grid for managing the high penetration of renewable energy sources(RESs). Based on the resistive characteristics of the microgrid line, this paper proposes an inverter control mode combining the outer power loop controller with anti-droop control and the inner voltage-current dual-loop controller. Meanwhile, a complete small signal model of single inverter including anti-droop control, dual-loop control, filter and branch is established. Then considering the coupling relationship of the output voltage phase angles of each inverter, the small-signal model of the microgrid with multiple parallel inverters is established under the global coordinate system. The static stability analysis of the complete microgrid is carried out by the root locus method. Results show that the anti-droop control is more conducive to the accurate distribution and fast response of the active power output by inverter units than the traditional droop control.

Emproved Z-Source Dynamic Voltage Restorer Based on the Minimum Energy

Dynamic voltage restorer (DVR) is a good choice to solve voltage sag problem. Aiming at the shortcomings of traditional DVR, an improved DVR model is proposed. The improved DVR took H-bridge inverter as the main frame, and the energy storage unit was based on the battery. The coupling unit directly connected the capacitor in LC filter to the power grid instead of the transformer, and connected a Z-source network between the energy storage unit and the inverter unit to improve the voltage compensation range and eliminate the impact of the series transformer. Finally, by connecting a current compensation device in parallel on the load side, combined with the minimum energy compensation control strategy, the amplitude and phase of the load voltage compensated by the improved DVR device were consistent with that before the drop. A MATLAB / Simulink simulation model is built to verify the effectiveness of the proposed improved DVR. The simulation results verify the effectiveness of the proposed improved DVR.

Modular Stator Flux and Torque Control of Multi-Three-Phase Induction Motor Drives

The recent advancements of power electronics are encouraging the development of the multiphase drives in both transport electrification and energy production applications. Among the multiphase solutions, the “multi-three-phase” drives are gaining impressive attention from the industry since they can be configured as multiple three-phase units operating in parallel. In this way, the three-phase technologies can be used, leading to a significant reduction in the costs and design time. Although the multi-three-phase drives possess natural modularity in terms of both machine winding and power converter, few control solutions able to implement a modular regulation of the torque are available in the literature. Therefore, this article proposes a control scheme implementing an independent regulation of the stator flux amplitude and torque contribution belonging to each winding set of a multi-three-phase induction machine. The proposed control solution can manage the voltage and current constraints introduced by each inverter unit. Besides, torque-sharing strategies among the three-phase sets of the machine can be implemented. Experimental results are provided for a modular power converter feeding a 12-phase induction machine with a quadruple-three-phase configuration, thus demonstrating the effectiveness of the proposed solution.

Research on Harmonic Power Sharing Method Based on Intelligent Matching Virtual Harmonic Impedance

The mismatch between the feeder impedance of each parallel inverter connected to the public AC bus in the microgrid and its rated capacity will cause harmonic circulation in the system. In order to effectively suppress the harmonic circulating current and balance the power distribution among the inverter units, this paper introduces an adaptive virtual harmonic impedance controller in the harmonic domain to reshape the impedance of the system to match the feeder impedance, Dynamically adjust the harmonic current distribution, obtain the modulated wave through the measuring current and voltage double-loop control, and then drive the inverter to operate through the SPWM modulation circuit. MATLAB/Simulink simulation, the results show that the harmonic power distribution method based on virtual intelligent matching harmonic impedance raised in this paper can significantly suppress the harmonic circulating current between parallel inverter systems, and improve the quality of output voltage of parallel inverter systems. The accurate power distribution of the inverter is realized, and performance of inverter in parallel system with a nonlinear load is improved.

Three‐phase quasi‐Z source inverters with regulated multiple AC outputs for microgrid applications and three‐phase residential load

In this study, two 3- φ quasi-Z source inverters (qZSIs) with multiple ac outputs are proposed. The proposed topologies are developed from qZSI to obtain parallel mode and series mode 3- φ multi-output inverters. In parallel mode, the topology yields n -number of parallel ac outputs with different voltages and currents for different load conditions. For series mode, topology yields n -number of series ac outputs with same voltages and same load currents. Unlike voltage source derived multi-output inverters, the proposed inverters have all inherent properties of qZSI, like shoot-through protection and both buck–boost operations. For generating switching signals in these inverters, sinusoidal pulse width modulation with constant frequency shoot-through scheme is used. The proposed topologies fulfil more than one load demand at a time without any extra adaptor or regulator. The proposed inverters can be used for simultaneous multiple dc/ac power conversion for three-phase microgrid applications and three-phase residential loads. In this work, the proposed topologies with closed-loop control have been implemented for two inverter units, which is capable of supplying two ac outputs simultaneously. The mathematical modelling of the proposed topologies is carried out for performance analysis. The experimental results of 240 W lab prototypes have been presented to validate the proposed three-phase multi-output qZSIs.

The Enhancement of Solar Power System Implementation in LAS Building

In Malaysia, the installation of PV panels in residential, industrial and commercial buildings has been imposed since 2001. This is due to the 8th Malaysia Plan (2001-2005) when Government introduced Malaysia Building Integrated Photovoltaic Technology Application (MBIPV) plan to encourage the application of renewable energy source in Malaysia. One of the alternatives that have been done by the Ministry of Energy, Green Technology and Water (KeTTHA) was installing PV panels in government buildings in Putrajaya. Mostly, the installed PV panels only cover up to 30% of the energy demand in one level of a building. However, after operating for some years, the performance of the PV panels was degrading. Since the maintenance cost for PV system is quite high, and due to the factor of lack of knowledge on how to maintain the system, the installed PV systems are mostly abandoned now. The project was discontinued after the warranty period and the contract with the contractor end. Therefore, the aim of this study is to re-improvise the abandoned PV system in one of them which is Building of Section of Legal Affairs (BHEUU). Through this study, three new models of the BIPV system were proposed, namely Model 1 (4IWOB), Model 2 (4IWB), Model 3 (1IWOB), and Model 4 (1IWB). In this study, the technical and economic assessment has been performed. From the findings, results show that Model 3 (1IWOB) provides the best choice to replace the existing BIPV system where this model only use 1 unit of inverter and no battery storage is used. Saving can be saved up to 37.5% if Model 3 (1IWOB) is chosen to replace the existing PV system at BHEUU building, where the existing system is represented by Model 1 (4IWOB), which used 4 inverters, and no battery was installed.

A Nonlinear Controller Design for Power Conversion Units in Islanded Micro-grids using Interconnection and Damping Assignment Tracking Control

Conventional controllers for electronically interfaced distributed generators (EI-DGs) that utilize droop controllers along with voltage/current proportional-Integral (PI) controllers illustrate undesirable transient responses in facing large disturbances generated following the changes in the system operating point. This article presents a nonlinear tracking controller for multisource EI-DGs operating in islanded micro-grids (MGs). The proposed controller is designed based on interconnection and damping assignment passivity-based controller (IDA-PBC) in the synchronous reference frame (SRF). The controller accounts for the complete dynamics of power conversion units (PCU) components that include DC/DC boost converters coupled with DC/AC inverter units through the interlinking capacitor and are connected to the grid through LC filters. The proposed controller enables PCUs to smoothly suppress the voltage/current and active/reactive power transitions during system operating point changes while precisely track the reference commands generated by the droop controllers. A set of time-domain simulations using realistic modeling of components of PCUs are carried out on a multi-resource islanded MG to validate the results. The performance of the proposed method is compared with that of PI controllers and existing nonlinear control strategies.

Utilization photovoltaic for electrical energy needs in Kelapan island, Indonesia

Kelapan Island is one of the outermost islands in the Bangka Belitung Province. With a total of 30 households consisting of 120 people, electricity is currently from diesel generators. The dominant electrical equipment used on Kelapan Island are lights, televisions, fans, irons also several units of refrigerators and washing machines. For reducing the use of fossil energy, electrical energy sources are modeled for supply using a photovoltaic system. The average amount of electricity needed per house is 290.9 W, so the amount of power required for 4 hours at night is 34.908 kWh. The photovoltaic system will be modeled in 2 stages, centralized photovoltaic and photovoltaic at each resident’s house. The photovoltaic system that is installing in each residential house requires four units of 100 Wp solar panels, six units of 100 Ah batteries, 1 unit of a 400-watt inverter, and four units of solar charger controllers. Whereas for the centralized photovoltaic system model requires 97 units of 100 Wp solar panels, 160 units of 100 Ah batteries, 25 units of 400-watt inverters and 108 units of solar charger controllers.

Phase synchronization of autonomous AC grid system with passivity‐based control

SummaryThis paper discusses a ring‐coupled buck‐type inverter system to harness energy from direct current (DC) sources of electricity. The DC‐DC buck converter circuit is modified with an H‐bridge to convert the DC input voltage to a usable alternating current (AC) output voltage. Passivity‐based control (PBC) with port‐controlled Hamiltonian modelling (PCHM) is a method where the system is controlled by considering not only the energy properties of the system but also the inherent physical structure. PBC is applied to achieve stabilization of the AC output voltage to a desired amplitude and frequency. Unsynchronized output voltages in terms of phase angle or frequency can cause detrimental effects on the system. Phase‐locked loop (PLL) is employed in the ring structure to maintain synchronization of the AC output voltage of all inverter units in the ring‐coupled system.

Novel High-Frequency Isolated Cascade PV Inverter Topology Based on Multibus DC Collection

This article proposes a novel single-stage isolated cascade photovoltaic (PV) inverter topology based on a multibus dc collection. The PV power plant can be divided into many arrays, each of which supplies power to three cascaded isolated inverter units through a dc bus. This isolated inverter unit is composed of cascade isolated bridge cells (I-BCs) connected in input-parallel output-series (IPOS). Compared with a conventional two-stage isolated cascade PV converter, the proposed PV topology can totally eliminate the individual dc-link capacitors at the high-voltage (HV) side, which leads to extremely reduced system volume and eliminated the voltage-balancing control between the dc-link capacitors. This article, first, describes the basic principle and the carrier phase shift pulse-width modulation (CPS-PWM) applied to this topology and, then, analyzes the power balance constraints between the cascade three-phase units for the PV grid-connected system. Finally, the effectiveness of the novel topology is verified by the simulation and experimental results.

Three-Loop-Based Universal Control Architecture for Decentralized Operation of Multiple Inverters in an Autonomous Grid-Interactive Microgrid

This article presents a decentralized control architecture for inverters in a utility-interactive autonomous microgrid involving multiple inverter units. The architecture is novel as all the system requirements, viz., automatic/seamless-mode transitions between grid-tied to standalone mode of operation and vice versa, islanding/anti-islanding detection, low-voltage ride-through, and dynamic grid support by reactive-power injection, are organized into three cascaded control loops-voltage control, frequency control, and a PLL. The control loops are designed to operate in the synchronous reference frame so that the control structure becomes compact and free from any computational complexities and associated delays. An equivalent droop combining virtual resistance with the active (P) and reactive (Q) power-based droops is used to achieve proportional load-sharing among the inverters in the standalone mode. The references to these loops are self-modified by the controller according to the operational mode. The architecture is autonomous but straightforward, where each inverter operates on its terminal information eliminating the requirement of any centralized controller or intercommunication network. The performance of the proposed control strategy is validated through comprehensive experimental results on a laboratory prototype that tests all the functions of an autonomous microgrid.

All-solution-processed colour-tuneable tandem quantum-dot light-emitting diode driven by AC signal.

We demonstrate a novel structure for a quantum-dot light-emitting diode (QD-LED) with wide-range colour-tuneable pixels, fabricated via full solution processing. The proposed device has a symmetrical structure produced via stacking of an inverted-structure diode with a green QD emission layer (EML) and normal-structure diode with a red QD EML. It is an electron-only device; however, a charge generation layer in the middle of the device generates holes for the formation of excitons. Depending on the polarity of the applied voltage, either the bottom inverted unit or the top normal unit is operated, thereby emitting green or red light, respectively. The working mechanism of the device is investigated via analysis of the charge generation mechanism and carrier transport path. In addition, the colour tunability is verified using a simple alternating current (AC) driving scheme; the duty cycle modulation of the AC signal enables fine colour adjustment over a broad range, from pure green to pure red. Thus, our colour-tuneable QD-LED with vertically stacked independently operated sub-pixels can open a promising pathway towards cost-effective ultra-high-resolution displays.

Adoption of Multilevel Inverter based Dynamic Voltage Restorer for Power Quality Improvement with Adjustable DC-Link

Dynamic Voltage Restorer (DVR) is a method of overcoming voltage sag and swell in electrical power distribution. To boost up voltage levels on load side on power disturbances DVR can be used so as the equipment connected will have good voltage profile In this Pulse Width Modulation inverter is in solid-state electronic switching device were employed along with Integrated Gate Bipolar Transistor by the DVR, the alternating current voltage is controllable at real and reactive powers which are made independently. The MLI; is organized as the cascaded H-bridge inverter units. The function of Multilevel Inverter; is to arrange the voltages from a significant direct current source. Here in the DVR, there is no need for external output filters. In the planned DVR, a dc-dc converter is combined with an MLI. By considering the voltage sag magnitude of a dc-dc converter can regulate the dc-link voltage. Hence the output voltage of the multilevel inverter; always has a last number of levels. Instead of using the PWM based technique, the fundamental frequency method can be used in the multilevel inverter. The proposed DVR operation range of mathematical analysis is specified in detail. The simulation results are prepared by using Simulink/MATLAB.

A Model-Based Design Approach for Stability Assessment, Control Tuning and Verification in Off-Grid Hybrid Power Plants

This paper proposes detailed and practical guidance on applying model-based design (MBD) for voltage and frequency stability assessments, control tuning and verification of off-grid hybrid power plants (HPPs) comprising both grid-forming and grid-feeding inverter units and synchronous generation. First, the requirement specifications are defined by means of system, functional and model requirements. Secondly, a modular approach for state-space modelling of the distributed energy resources (DERs) is presented. Flexible merging of subsystems by properly defining input and output vectors is highlighted to describe the dynamics of the HPP during various operating states. Eigenvalue (EV) and participation factor (PF) analyses demonstrate the necessity of assessing small-signal stability over a wide range of operational scenarios. A sensitivity analysis shows the impact of relevant system parameters on critical EVs and enables one to finally design and tune the central HPP controller (HPPC). The rapid control prototyping and control verification stages are accomplished by means of discrete-time domain models being used in both off-line simulation studies and real-time hardware-in-the-loop (RT-HIL) testing. The outcome of this paper is targeted at off-grid HPP operators seeking to achieve a proof-of-concept on stable voltage and frequency regulation. Nonetheless, the overall methodology is applicable to on-grid HPPs, too.

Optimasi Perbaikan Faktor Daya Dengan Pemasangan DC Reaktor Akan Mereduksi Harmonisa Di Inverter Motor Pendingin Air Industri

Three phase induction motor is widely used in the manufacturing industry because it has many advantages including easy maintenance, efficient use in various fields, durability and easy construction. This is behind the massive use of motorcycles. but the 3 phase induction motor also has disadvantages such as high starting currents and difficult to regulate speed. After emerging innovations regarding inverters as induction motor starters, the application of the device expanded because of its principle which regulates the number of motor frequencies slowly so as to make the 3-phase induction motor more efficient.The use of an inverter is indeed a solution to the problem of starting a 3-phase induction motor and regulating the motor speed, but behind the advantages there are disadvantages that the inverter produces a low power factor when operating the motor. The highest power factor when the inverter is working is 0.748, the lowest value is 0.478 and the average is 0.634. Based on this, it is necessary to optimize the improvement of the power factor to restore the condition of the motor to a standard power factor rating of 0.85.This research discusses the optimization of the improvement of the power factor by installing the DC reactor on the inverter unit and the results of an increase in the value of the highest power factor of 0.942, for the lowest value of 0.908 and an average of 0.927. the value of harmonics in the THD I1 (R) phase for the highest value of 184,230%, then the lowest value of 83,764% and for an average value of 119,329%

Sizing an Off-Grid Photovoltaic System and Economic Comparison with Petrol Generator Using Life Cycle Cost (LCC) Approach for a Typical Rural Primary Healthcare Center in Nigeria

It is needless to re-emphasize that modern day healthcare systems require uninterruptible power supply, relying on the national grid for power supply most especially in remote areas in Nigeria is a deliberate attempt to paralysis and underutilize both the human and non-human resources. This paper presents the sizing of a stand-alone photovoltaic system and economic comparison with petrol generator in powering a rural Primary Health Care Center (PHC) in Agbado, Ado-Odo, Ota Local Government, Ogun State, Nigeria. Load survey of the PHC was done in order to know the daily energy demand. The average annual solar radiation and the estimated load for the PHC used as case study are 4.89kWh/m2/day and 14.40kWh/day respectively. The result obtained from sizing the photovoltaic system reveals that the estimated load will require 5.25kW photovoltaic array capacity, 21 modules (24V, 250W each), 10 batteries (12V, 200Ah each), 3 solar charge controllers (24V, 80A each), 1 unit of 4kW inverter (24Vdc/220Vac, 50Hz), 3x70mm2 insulated flexible copper cable and 3x2.5mm2 insulated flexible copper cable. Life Cycle Cost (LCC) technique was used to assess the most economically viable option in powering the PHC. The study also reveals a savings of 64.4% in LCC using PV system as against petrol generators in powering the PHC. The replacement cost constitutes the higher factor affecting the LCC of the PV system constituting about 47.7%, while the operation and maintenance cost forms the least factor with about 28.9%. Also, for that of petrol generator, the fuel cost constitutes the highest factor affecting the LCC, constituting about 87.6%, while the initial capital cost forms the least factor which is about 0.24%. The insights from this study can be reciprocated to other rural PHCs in Nigeria.

Capacitor Size Reduction of Multilevel Inverters by Utilizing Neutral Shifting

Reduction of size of capacitor is an active area of research as it greatly reduces cost and footprint of the system. A level doubling network (LDN) is a half-bridge with floating capacitor in its dc bus, which doubles the number of ac output voltage levels when connected to a multilevel inverter unit. LDN automatically gets settled at a desired voltage level without closed-loop control. Capacitor of the LDN gets charged for a complete half cycle and discharges for the next half-cycle and therefore results in a higher ripple voltage demanding a higher capacitance. This paper presents a new method to reduce the size of LDN capacitor keeping the voltage ripple within limits. This is achieved by shifting the Neutral point of inverter between positive and negative dc busses of the LDN, which enables the capacitor to charge or discharge more frequently, irrespective of the modulation index and load power factor. In addition, controlling is done in such a way that uniform power distribution ratio among the cells of a single phase leg of the inverter is achieved. Working principle of the proposed method is verified through simulation in MATLAB/Simulink and experimentation on a laboratory prototype.

P-Q capability chart analysis of multi-inverter photovoltaic power plant connected to medium voltage grid

This paper presents the proposal of the methodology for the development of realistic P-Q capability chart at point of common coupling of photovoltaic power plant, comprised of multiple inverter units and connected to medium voltage grid. Theoretical equations for the contribution to the total active and reactive power of the plant are derived for all plant components: inverters, low voltage cables, transformers, medium voltage cables and auxiliary consumption. It is concluded that equations for total active and reactive power are dependable on only two changing variables: voltage and momentary generation power of inverters. Equations for maximum and minimum values for total active and reactive power are further derived when known maximum and minimum values of changing variables are entered to equations, and these are presented on graph diagram as curves. Area in P-Q diagram within such calculated border curves is area of possible power plant operation points at the point of common coupling. Such representation model of this type of plant has not been proposed before. The proposed methodology has been applied to the case study plant and its operation P-Q diagram is constructed Measurements conducted on this case study plant are compared with calculated values for necessary corrections to the model.

Electrical Coupling and Simulation of Monolithic 3D Logic Circuits and Static Random Access Memory.

In order to simulate a circuit by applying various logic circuits and full chip using the HSPICE model, which can consider electrical coupling proposed in the previous research, it is investigated whether additional electrical coupling other than electrical coupling by top and bottom layer exists. Additional electrical coupling were verified through device simulation and confirmed to be blocked by heavily doped source/drain. Comparing the HSPICE circuit simulation results using the newly proposed monolithic 3D NAND (M3DNAND) structure in the technology computer-aided design (TCAD) mixed-mode and monolithic 3D inverter (M3DINV) unit cell model was once more verified. It is possible to simulate various logic circuits using the previously proposed M3DINV unit cell model. We simulated the operation and performances of M3DNAND, M3DNOR, 2 × 1 multiplexer (MUX), D flip-flop (D-FF), and static random access memry (SRAM).

Main Trends of Technical Development of a Direct-Current Traction Power Supply System and Its Adaptation to High Speed Motion

The main trends of technical development and improvement of dc traction power supply systems are considered. Methods and programs are developed that make it possible to study the electromagnetic processes in rectifier–inverter units of traction substations and the self-excited source voltage inverter of induction traction drive and determine and predict the levels of harmonic components of the current in both dc–ac converters themselves and that in the traction network. This makes it possible to determine the electromagnetic effect of various power semiconductor converters on communication devices and railway automation and ground the choice of circuits and protection parameters ensuring electromagnetic compatibility. Analysis and synthesis of electromagnetic processes and the main characteristics of multipulse converters reveals that 24-pulse rectification circuits with serial connection of three-phase bridges are the most effective for a dc traction power supply system with a 24-kV voltage traction network. The introduction of 24-pulse rectifiers makes it possible to decrease power loss in the traction network and reduce the consumption of reactive energy from the primary power supply system. These rectifiers provide not only an increase the traction substation efficiency, but also refinement of electric energy in the primary power supply system and traction network. The latter makes it possible to use simpler and more economical smoothing filters that ensure electromagnetic compatibility of the new dc traction power supply system with communication devices, railway automation, and other infrastructure.