Inverter Unit Research Articles

Research on Underwater Constant High-Voltage DC Switching Technology for MCSEM.

The marine controlled source electromagnetic (MCSEM) transmitter can transmit high currents near the seabed to detect the electrical structure of the seafloor. The use of three-phase alternating current (AC) transmission can lead to three-phase imbalance, which results in an excessive current in one phase's power line and affects the safety of the tow cable. This paper proposes an MCSEM underwater constant high-voltage direct-current (DC) switching scheme that replaces AC transmission with DC transmission. This scheme can fundamentally avoid three-phase imbalance and the AC loss caused by inductance. After establishing a simulation model to analyze the effect of the scheme, the relevant hardware units were designed. The hardware unit mainly consists of three parts: a DC switching inverter unit, a filter unit, and a step-down rectification unit. The DC inverter unit controls six insulated gate bipolar transistor (IGBT) modules with sinusoidal pulse width modulation (SPWM) signals to convert DC to three-phase AC power; the filter unit filters out extra harmonic components; and the step-down rectification unit converts high-voltage three-phase AC to low-voltage DC. The scheme ultimately achieved an adjustable DC output of 48.3-73.4 V under a constant DC input voltage of 3000 V and effectively reduced the current on the cable. This scheme has the potential to replace the previous AC transmission, reducing the risk of tow cable burnout and enhancing the safety of MCSEM operations.

PERANCANGAN PEMBANGKIT LISTRIK TENAGA SURYA (PLTS) PADA ATAP GEDUNG PARKIR BANDAR UDARA INTERNASIONAL I GUSTI NGURAH RAI

Using sustainable energy as a source of electrical energy is a safe way to increase ecosystem energy. One of them is the utilization of photovoltaic directed energy by upgrading the PLTS on top of the structure as a mechanism for introducing photovoltaic modules. The study finalized the plan to install PLTS on the roof of the I Gusti Ngurah Rai Airport parking lot as a source of electrical energy to reduce PLN electricity bills. The I Gusti Ngurah Rai Airport Parking Roof Solar Power Plant uses a battery-free on gridsystem with 600 units of 555Wp monocrystalline solar-based modules and four 100kW inverter units. The solar power plant to be built on the car park of Terminal I Gusti Ngurah Rai will have a capacity of 333kWp and will produce 604.929kWh of energy annually. The required speculation cost is Rp 3.004.620.000 and payback period for 6 years.

Enhancing the Concentration Capability of Nonsupported Electrically Driven Liquid-Phase Microextraction through Programmable Flow Using an All-In-One 3D-Printed Optosensor: A Proof of Concept.

A versatile millifluidic 3D-printed inverted Y-shaped unit (3D-YSU) was prototyped to ameliorate the concentration capability of nonsupported microelectromembrane extraction (μ-EME), exploiting optosensing detection for real-time monitoring of the enriched acceptor phase (AP). Continuous forward-flow and stop-and-go flow modes of the donor phase (DP) were implemented via an automatic programmable-flow system to disrupt the electrical double layer generated at the DP/organic phase (OP) interface while replenishing the potentially depleted layers of analyte in DP. To further improve the enrichment factor (EF), the organic holding section of the OP/AP channel was bifurcated to increase the interfacial contact area between the DP and the OP. Exploiting the synergistic assets of (i) the continuous forward-flow of DP (1050 μL), (ii) the unique 3D-printed cone-shaped pentagon cross-sectional geometry of the OP/AP channel, (iii) the bifurcation of the OP that creates an inverted Y-shape configuration, and (iv) the in situ optosensing of the AP, a ca. 24 EF was obtained for a 20 min extraction using methylene blue (MB) as a model analyte. The 3D-YSU was leveraged for the unsupervised μ-EME and the determination of MB in textile dye and urban wastewater samples, with relative recoveries ≥88%. This is the first work toward analyte preconcentration in μ-EME with in situ optosensing of the resulting extracts using 3D-printed millifluidic platforms.

Technical and Enviro-economic Analysis of a 0.78 kWp PV System

Aim: To determine the technical, economic and environmental performance analysis of an installed PV backup system. Study Design: To attain this goal, analysis were performed using a freely available PVSyst 6.7.0 software tool. Economic evaluation was performed using respective present worth of individual component prices. Environmental performance comparison is made between the PV system and diesel generator when each is used as an independent backup system. Input in-situ measured data were determined, measured and keyed into the tool. Place and Duration of Study: The system is installed in an institutional building in a tropical climatic zone with coordinates 0.42 N and 35.03 E. The system was studied for a period of one year where data was collected and recorded for techno-enviroeconomic analysis. Methodology: The system consists of four PV modules rated at 0.78 KWp, charge controller and an inverter unit and battery bank, and is utilized as a power backup system to supply electricity whenever power failure occurs, which is frequent and real in Kenya. The techno-enviroeconomic performances analysis of the system were evaluated using the PVSyst software, a freely available design and analytical tool, where input data were measured and recorded at the site. Results: The performance analysis of the system showed that PV array efficiency of 13.24%, FF of 0.68, CF of 21.23%, and PR of 73.63% and generated electrical energy of 1092 kWh/year. The LCOE of PV electricity was 0.059 $/kWh, while total saving of CO2 emission in tons of CO2 was 9.0 tCO2 with LCE value of 331 gCO2/ kWh. Conclusion: Techno- enviroeconomic performance results of the studied PV system show that the system can contribute significantly to the mitigation of CO2 emission. This work also could be helpful for consumers and policy makers in the choice of renewable based or fossil based backup generation systems.

Improving the operational characteristics of electrical power systems of marine vessels

THE PURPOSE. Consider the experience of use and conduct a study of the electrical power systems of sea vessels to determine the possibility of improving their operational characteristics. Obtain data on noise and vibration levels of electrical power systems elements.METHODS. The article analyzes the electrical power systems of the Azipod type steering columns of the Baltika icebreaker. The issue of regulating the rotation speed of propulsion electric motors using frequency control based on a DC link and parallel-connected inverter units on IGBT transistors is considered. Motor control on the frequency converter side can be based on direct torque control, scalar and vector control. There are control modes for reducing and increasing voltage.RESULTS. Typical dependences of structure-borne noise levels of main engines and generators are given. Measurements were taken at various frequencies of engine sound power levels, exhaust gases and vibration of generator sets. Experimental oscillograms of studies of the parallel operation of diesel generator sets were obtained, on which power exchange and common-mode oscillations were recorded.CONCLUSION. It is proposed to use multiphase AC electric motors to improve performance characteristics, including reducing noise and vibration. The existing experience in using frequency converters based on a rectifier section and inverter units in electric rowing installations with Azipod propellers makes it possible to implement such a change. To do this, it is necessary to parallelize the inverters that supply each of the three phases and provide the appropriate phase shifts.

A Decentralized Control Strategy for Series-Connected Single-Phase Two-Stage Photovoltaic Grid-Connected Inverters

Currently, most of the series inverter control methods rely on communication, which greatly reduces the reliability of the system and increases the cost. To address the above problems, this paper proposes a decentralized control strategy for series-connected single-phase two-stage grid-connected photovoltaic (PV) inverters. By improving the traditional droop control, the frequency and phase of the output voltage of each inverter unit are consistent and self-synchronized with the power grid while relying only on local independent control, and each unit realizes maximum power point tracking (MPPT). At different light intensities, each series-connected unit can quickly track the new maximum power point while still maintaining self-synchronization between the units. The system stability is analyzed via the small signal method, and sufficient conditions for system stability are obtained. Finally, the simulation results verify the correctness and effectiveness of the proposed control strategy.

Grid Harmonics Suppression for Three Phase Dual-Frequency Grid-Connected Inverter Based on Feedforward Compensation

Using a low pulse ratio, the electromagnetic interference and switching loss of an inverter can be effectively reduced, particularly in high-power applications. However, due to variations in grid impedance, it is a challenging task to achieve stable operation of an LCL-type grid-connected inverter (GCI) using the active damping method with low pulse ratio. Thus, a novel three-phase dual-frequency GCI is presented to ensure the symmetry of the output power and the stable operation of the system address stability issues. The proposed inverter topology in this article is composed of two inverters in parallel, which are, respectively, a power inverter unit (PIU) and an auxiliary harmonic elimination unit (AHEU). To reduce the switching loss and improve the inverter efficiency, the switching frequency of the PIU is relatively low, injecting current into the grid. Moreover, the feedforward compensation method is used in AHEU. AHEU operates at high switching frequency to generate a current component that is symmetrical with the ripple com-ponent, improving the power quality, without extracting the current harmonic as the current reference. The operating principle of feedforward compensation is explained, and a proper parameter design procedure is presented in this paper. Since L filters are used for the proposed inverter, the system can operate stably where the ratio of switching frequency to fundamental frequency is low. A 10 kW laboratory prototype was built. The experimental results showed that the grid current ripple could be effectively eliminated and the THD of the grid current was 3.01%. The proposed inverter has good stability in a weak grid, and the efficiency of the proposed inverter is 95.98% at rated current, which is 0.81% higher than the traditional GCI, effectively increasing the efficiency of the system.

Control Strategy for Multiple Residential Solar PV System in Distribution Network With Improved Power Quality

This paper presents a modified power control (MPC) for a grid-interfaced autonomous microgrid connecting multiple solar photovoltaic inverter (SPI) units. An MPC provides the automatic transition capability between grid-tied mode (GTM) and an islanding mode (IAM) for a microgrid consisting of multiple parallel-operated SPIs. In GTM, SPIs extract PV power to fulfil the load demand, and the rest power is fed to the grid at the unity power factor (UPF) by working in the current control mode (CCM). Upon grid failure, the main SPI unit inherently changes from CCM in GTM to voltage control mode (VCM) in the IAM state to achieve an uninterruptable power supply to loads. When the grid restores, the main SPI unit near the point of common coupling (PCC) re-synchronizes the PCC voltage with grid voltage in the microgrid and control shifts back to GTM. A seamless mode transition in the microgrid is achieved without rearrangement of control formation, and power distribution between the parallel SPI units is achieved without communication setup. This reduces the cost of remote communication setup for resynchronization and saves the complexity. Moreover, MPC accurately regulates the reference grid current of SPIs when the load demand fluctuates. The MPC method combines the adaptive integrator filter (AIF), which attenuates the harmonics from the input signal to strictly control the power factor at PCC and maintains the total harmonics distortion (THD) of grid current and PCC voltage according to the IEEE stand. 519. The performance of the presented MPC method is evaluated via a simulation and test results.

Control of Multiple SPV Integrated Parallel Inverters for Microgrid Applications

<bold xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">This work presents a hybrid control method (HCM) for inverters in a single-phase AC grid-interactive photovoltaic (PV) microgrid connecting multiple PV inverter (PVI) units. The HCM is incorporated into a single control method employing three cascaded loops -grid current loop, voltage control loop and improved third order adaptive integrator-quadrature signal generator (ITOAI-QSG). The HCM is used for mode transitions between the grid integrated mode (GIM) to islanding mode (IAM) and vice-versa, and this confirms the seamless transfer between the modes without rearranging the control structure. In GIM, the presented controller regulates the grid current and provides dynamic grid support by the reactive power compensation. In IAM, the controller changes from the grid current control to the voltage control to adjust the PV inverter's output voltage. The control method is presented for a parallel-operated single-stage where PV panels are interfaced with the inverters with independent maximum power point tracking (MPPT) to harvest maximum power. The battery energy storage (BES) is interfaced with the main PVI unit to support the load demand in peak demand periods and maintains the power balance in IAM. The charging and discharging profiles of BES are achieved by a DC-DC bidirectional converter (DBC). Test results verify the performance of the developed control.</b>

Improved current droop control strategy of parallel inverters for microgrid based on negative feedback of current

In order to increase the current distribution accuracy of the system and restrain the system frequency fluctuation on the basis of reducing the control operation complexity, this paper proposes an improved current droop control strategy. The strategy can be described as follows: Firstly, a virtual negative inductance and a virtual resistance are introduced into the voltage and current double closed loop control to balance the output impedance of the inverter unit. Then an impedance ratio is introduced to solve the contradiction between the virtual complex impedance and potential drop. Finally, by introducing new current variables and using these current variables to form the negative feedback to the droop coefficient in the voltage equation in the droop control, the allocation of the active current and reactive current is implemented in terms of the inverter capacity, and the plug and play function of the inverter unit is realized in the low-voltage microgrid. A great number of simulation results show that by the strategy, the active and reactive currents output can be distributed in terms of the own capacities of the inverters in the system, the smooth operation of parallel inverters with the same or different capacities is ensured and the computational complexity is simplified.

Autonomous Restoration of Networked Microgrids Using Communication-Free Smart Sensing and Protection Units

This paper presents autonomous restoration of networked microgrids using distributed energy resources (DERs), inverter-based resources (IBRs) in general, and controllable assets of intelligence without communication to achieve a extremely resilient power system restoration. The main innovation of this work lies in use of real-time smart sensing and decision making that enable autonomous recombination of islanded microgrids, which are individually black-started by local grid-forming (GFM) inverter units. The smart circuit breakers (SCBs) designed and demonstrated here play critical roles in the restoration process to achieve autonomy; the autonomous restoration scheme is not pre-engineered and may be subject to encounter overloading, live or downed segments as the boundary of the microgrids dynamically expands without prior knowledge and only with local measurement. We demonstrate autonomous microgrid restoration both in simulation of a modified IEEE 13-bus system, and in a hardware testbed comprising 24 GFM-IBRs and 6-SCBs, depicting several scenarios to evaluate their functionalities and interoperability. This work validates high potential of extremely resilient microgrid using novel approaches for inverter-based bottom-up system restoration in a communication-free paradigm.

Large-capacity AC superimposed DC power supply for the degradation evaluation of DC-link capacitors

The DC-link capacitor, whose operating voltage is a periodic irregular waveform, is a key device in the converter. A large-capacity DC/AC superimposed experimental power supply above 100 kVA is an important piece of equipment that must be used in the aging research of DC-link capacitors. The irregular periodic operating voltage of the DC support capacitor is equivalent in the form of DC voltage superimposed with multiple harmonics based on the Fast Fourier transform analysis. The power supply is mainly divided into four parts: an AC module, a DC module, a protection module, and an isolation component. The composited harmonics are output by the IGBT (Insulated Gate Bipolar Transistor) inverter of the AC module. The soft start method is applied to the AC module in order to ensure the long-term reliable operation of the power supply. The kV-level high-voltage is output by four inverter units connected in series. The amplitude and phase control of harmonic decomposition is adopted, and the inverter is controlled by Sinusoidal Pulse Width Modulation. The output voltage of the power supply is close to the operating voltage of the capacitor. Based on the designed power supply, the degradation experiment was carried out. The temperature rise and aging characteristics of DC-link capacitors under different AC/DC ratios were studied.

An 800V End to End SiC Powertrain to Accommodate Extremely Fast Charging

Widespread adoption of electric vehicles has presented the challenges of short range and prolonged charging time. Going forward, extremely fast charging is the only solution to these problems. However, the typical Silicon power electronics supported 400 V electric vehicle powertrain cannot live up to this challenge. Limitations include the huge cable size, heating of equipment due to high current and user safety, to name a few. In this paper, we have analyzed an 800 V EV powertrain using power electronics based on silicon carbide. In order to implement 800 V powertrain, the complete reconsideration of the electrical system is imperative. In this paper we have presented the implementation of Silicon Carbide based Power electronics to operate an 800 V powertrain and evaluate it against the 800 V Si powertrain. Details of drivetrain, inverter, and auxiliary power units in high voltage charging (Megawatt Level) system are presented in this research.

Communication-Free Equivalent Grid Impedance Estimation Technique for Multi-Inverter Systems

Interactions between grid-connected inverters bring major problems, such as increased harmonic distortion and instability. Furthermore, as the existing literature on inverter-based online grid impedance estimation mainly focuses on one inverter unit, the effects of the interactions on the estimation accuracy have been neglected. This article initially investigates how the interactions among the grid-connected inverters impact the accuracy of the estimated fundamental and wideband grid impedances. Afterward, a communication-free approach for multi-inverter systems is proposed to avoid the possible interactions between the inverters while estimating the equivalent grid impedance. Hence, accurate estimation results are ensured. The presented method is implemented in the local controller of each inverter, relying only on local measurements. Thus, it is more practical as coordinating different communication protocols between inverters is challenging. Furthermore, it is a generic approach as it can be used for single-/three-phase inverters and for implementing fundamental/wideband impedance estimation algorithms. The proposed strategy also minimizes the power quality issues as it is a trigger-based approach. The simulation and experimental results validate the effectiveness of the proposed communication-free strategy to accurately coordinate impedance estimation in multiple grid-connected inverter systems.

DEVELOPMENT AND IMPLEMENTATION OF AN AUTOMATIC SOLAR/AC POWER SUPPLY UNIT FOR A REFRIGERATOR

This work focuses on a solar and AC power supply unit for a refrigerator. The two sources of power supply, an alternating current power supply and solar power supply, each connected to an automatic changeover used to switch power supply to the refrigerator unit. The alternating current power supply and solar power supply both charge the battery interchangeably through the inverter depending on the power source in use. The inverter unit consists of a battery used to store the solar energy needed to keep a constant supply of refrigeration to the refrigerator unit even when there is no alternating current power supply; a transformer which is used to step up the voltage supplied by the battery to match the voltage needed by the refrigerator unit to work properly and also an oscillator which is used to convert the direct current voltage supplied by the battery into alternating current voltage. This aims at maintaining constant operation of the refrigerator unit.

A Symmetric Switched-Capacitor-Based Basic Inverter Unit for Grid-Connected PV Systems

In this article, a new inverter unit is proposed. It is a compact switched-capacitor-based inverter, which is combined of four switches, two diodes, and four capacitors. Since this inverter unit is a mid-point-clamped inverter, it can mitigate the capacitive leakage current in many applications. One of the main applications of the proposed inverter is in grid-tied photovoltaic systems, where the common-mode current brings many challenges. Other than the mentioned feature, the proposed inverter includes the following advantages: 1) spontaneous balancing of the voltage across the capacitors without needing any control system or auxiliary circuits; 2) capability of full reactive power transfer; 3) low voltage stress on the capacitors compared to common three-level inverter topologies (NPC, T-type-NPC, FC, etc.); and 4) symmetric switching sequence, which causes a continuous input current. The feasibility and versatility of the proposed inverter unit is validated by experimental tests, which are conducted by using a lab-scale prototype.

Grid integration of multiple PV inverters with reduced number of interfacing transformers— A dedicated controller for elimination of DC current injection

The injection of dc current offset into ac networks may impacted the lifespan of the distribution system equipment including isolation transformers and measurement devices and in serious event may cause equipment’s malfunction. This paper intents to eliminate dc current offsets in the output currents using a combinational of proportional-integral (PI) and proportional resonance (PR) controls embedded in one inverter unit. Resultant output currents of this method are sinusoidal and clean from dc offset before entering the point of common coupling. This method gives advantages for transformerless option for group of interfacing inverters in the medium-scale solar farm or in arrangement of inverters restricted in a small locale. Moreover, the use of expensive and high-accuracy measurement sensor nor complex transformer can be omitted, whilst indirectly give positive impact to the operational cost of the farm. The simulation verifications proved the usefulness of the proposed method by introducing varying unknown dc offset levels in the phase currents, and a dedicated dc offset suppressor inverter able to successfully eliminate the dc offset to zero. The validity of the proposed method is demonstrated in simulation using MATLAB/Simulink.

Techno-environmental Simulations for Solar Energy-Powered Seawater Reverse Osmosis Desalination for a Hyper Arid Coastal Region

This study investigates the efficiency of a solar-powered seawater desalination plant (DP) using reverse osmosis for an arid coastal region. The solar models are investigated using local meteorological data, including direct, diffused and global irradiance. The meteorological data are obtained using local typical meteorological data set collected from a ground weather station. The PVsyst simulation tool is used to model a grid-connected solar PV system utilizing three photovoltaic (PV) technologies: thin-film, monocrystalline, and polycrystalline. Three scenarios were considered: restricted area, daily water production and design capacity. The optimum configuration for the restricted area scenario at the seawater DP location considered is an on-grid thin-film module (170 W) with a tilt angle of 20° and an inverter unit of 2000 kW. The solution module area is 15,248 m2. The annual electricity production will be approximately 4251.1 MWh/y, which represents only 3.1% of the DP demand. Thin-films produce higher annual electricity than monocrystalline and polycrystalline silicon by 8.3% and 5.9%, respectively, but require 15.9% and 5.7% more space than monocrystalline and polycrystalline silicon, respectively. For Shuwaikh DP, a 30 MIGD DP will require a PV system with a capacity of 120 MWp at 30° tilt angles and 60 inverters. The design environmental impact was assessed using life cycle assessment (LCA). The carbon footprint will decrease from 7.3 x10-5 to 1.8 x10-5 (kg CO2 equivalent), for the 30 MIGD production. The fossil fuel depletion will decrease by approximately 80%. However, the large number of solar panels and the significant total ground area required for the 30 MIGD. The solar array of 1,531,054 m2 will adversely affect the urban land occupation impact category by 84% and will increase metal depletion by 37%.The response surface optimization indicates that the optimal performance in the coastal region for power desalination plants is achieved when using a thin-film at a tilt angle of 20 o.

Performance Evaluation of Solar PV-Based Z-Source Cascaded Multilevel Inverter with Optimized Switching Scheme

AC loads may demand a fixed or variable voltage at their input terminals. When using inverters to power such loads, the response of the inverter must be precisely controlled to suit the demands of the AC loads. Inverters with higher efficiency and sensitivity will play an increasingly essential role as the need for solar PV applications in prospective green technology grows. To increase power quality and provide a reliable power source, an inverter architecture with harmonic reduction approaches is proposed. The multilevel inverter (MLI), unlike conventional inverters, is developed by cascaded single inverter units and is often used to connect renewable energy sources. As a result, they can be utilized to efficiently reduce harmonics. Among the three topologies, the most widely used in industries is the neutral-point clamped MLI. When the levels are raised, however, they demand a larger number of diodes. When the level of the flying capacitor exceeds three, several capacitors are necessary. As a result, the optimum option for synthesizing the right output voltage from several DC sources is a cascaded multilevel inverter (CMLI). Each link in a CMLI is connected by a single DC source; therefore, there is no voltage imbalance. However, getting equal DC voltages at the input of each unit is once again a limitation. In this work, various existing multilevel inverter topologies including hybrid topologies with different switching strategies are investigated and reported. The performance of a solar PV-based seven-level quasi-Z-source cascaded H-Bridge MLI (qZS-CHBMLI) has been thoroughly examined with the best switching scheme and best topology of multilevel inverters using MATLAB/Simulink.

Self-organized quantum dots in marginally twisted MoSe2/WSe2 and MoS2/WS2 bilayers

Moiré superlattices in twistronic heterostructures are a powerful tool for materials engineering. In marginally twisted (small misalignment angle, θ) bilayers of nearly lattice-matched two-dimensional (2D) crystals moiré patterns take the form of domains of commensurate stacking, separated by a network of domain walls (NoDW) with strain hot spots at the NoDW nodes. Here, we show that, for type-II transition metal dichalcogenide bilayers MoX2/WX2 (X=S, Se), the hydrostatic strain component in these hot spots creates quantum dots for electrons and holes. We investigate the electron/hole states bound by such objects, discussing their manifestations via the intralayer intraband infrared transitions. The electron/hole confinement, which is strongest for θ < 0.5°, leads to a red-shift of their recombination line producing single-photon emitters (SPE) broadly tuneable around 1 eV by misalignment angle. These self-organized dots can form in bilayers with both aligned and inverted MoX2 and WX2 unit cells, emitting photons with different polarizations. We also find that the hot spots of strain reduce the intralayer MoX2 A-exciton energy, enabling selective population of the quantum dot states.