The authors discuss high-voltage power conversion. Conventional series connection and three-level voltage source inverter techniques are reviewed and compared. A novel versatile multilevel commutation cell is introduced: it is shown that this topology is safer and more simple to control, and delivers purer output waveforms. The authors show how this technique can be applied to either choppers or voltage-source inverters and generalized to any number of switches.<<ETX>>

Multi-level conversion : high voltage choppers and voltage-source inverters

This paper proposes a new nine-level inverter for medium- and high-power applications. The proposed topology comprises of a three-level (3L) active neutral-point-clamped (ANPC) inverter connected in series with a floating capacitor (FC) fed H-bridge. Besides, two additional switches operating at line frequency are appended across the dc link of the 3L ANPC structure. Compared with conventional hybrid cascaded inverters, the primary advantage of this addition is doubling of the resulting root mean square output voltage. This amelioration is achieved while preserving the standard 3L ANPC and H-bridge structures with minimum topological modification. A simple logic-gate-based voltage balancing scheme is developed to regulate the FC voltage. The proposed voltage balancing method is independent of load power factor, inverter modulation index, and can balance the voltage across FC instantaneously. The step-by-step formulation of logical expressions for the generation of gating pulses is deliberated in detail and can be generalized for any $n$ -level inverter. Further, simulation results as well as the experimental measurements obtained from the laboratory prototype are presented to validate the effectiveness and practicability of the proposed configuration. Finally, the notable merits of the proposed inverter over the prior art topologies is established through a comprehensive comparative study.

Operation and Control of an Improved Hybrid Nine-Level Inverter

The technology development in wireless sensor network (WSN) offers a sustainable solution towards precision agriculture (PA) in greenhouses. It helps to effectively use the agricultural resources and management tools and monitors different parameters to attain better quality yield and production. WSN makes use of Low-Power Wide-Area Networks (LPWANs), a wireless technology to transmit data over long distances with minimal power consumption. LoRaWAN is one of the most successful LPWAN technologies despite its low data rate and because of its low deployment and management costs. Greenhouses are susceptible to different types of interference and diversification, demanding an improved WSN design scheme. In this paper, we contemplate the viable challenges for PA in greenhouses and propose the successive steps essential for effectual WSN deployment and facilitation. We performed a real-time, end-to-end deployment of a LoRaWAN-based sensor network in a greenhouse of the 'Proefcentrum Hoogstraten' research center in Belgium. We have designed a dashboard for better visualization and analysis of the data, analyzed the power consumption for the LoRaWAN communication, and tried three different enclosure types (commercial, simple box and airflow box, respectively). We validated the implications of real-word challenges on the end-to-end deployment and air circulation for the correct sensor readings. We found that temperature and humidity have a larger impact on the sensor readings inside the greenhouse than we initially thought, which we successfully solved through the airflow box design.

Leveraging LoRaWAN Technology for Precision Agriculture in Greenhouses.

Wireless sensor networks (WSNs) is one of the most effective tools in collecting data autonomously going as recently as 5–10 years ago. A low deployment and maintenance cost WSN is highly recognized as one of the more advanced Internet of Things networks that can be deployed for a series of purposes namely environmental and industrial monitoring due to the majority of such systems run on expendable power source that offers WSN with a limited service lifetime. The aim of this paper is to review existing renewable energy and prospective approaches in energy harvesting strategy as a means of having a sustainable and low maintenance operation of WSN. Additionally, recent maximum power point tracking (MPPT) of solar energy harvesting is thoroughly discussed in a new perspective of the WSN framework. Semi-pilot cell fractional open-circuit voltage (SPC-FOCV) MPPT is a fairly new concept in WSN application that features less complicated configuration with reduced hardware requirements and lower cost. Recent research findings are evaluated throughout this paper leading to the SPC-FOCV MPPT materialization. A holistic discussion is made encompassing the advantages and disadvantages of the concept, its performance compared to conventional MPPT approaches and the future insight of the technology in WSN.

Power Harvesting in Wireless Sensor Networks and Its Adaptation With Maximum Power Point Tracking: Current Technology and Future Directions

Irrigation is one of the most water-intensive agricultural activities in the world, which has been increasing over time. Choosing an optimal irrigation management plan depends on having available data in the monitoring field. A smart agriculture system gathers data from several sources; however, the data are not guaranteed to be free of discrepant values (i.e., outliers), which can damage the precision of irrigation management. Furthermore, data from different sources must fit into the same temporal window required for irrigation management and the data preprocessing must be dynamic and automatic to benefit users of the irrigation management plan. In this paper, we propose the Smart&Green framework to offer services for smart irrigation, such as data monitoring, preprocessing, fusion, synchronization, storage, and irrigation management enriched by the prediction of soil moisture. Outlier removal techniques allow for more precise irrigation management. For fields without soil moisture sensors, the prediction model estimates the matric potential using weather, crop, and irrigation information. We apply the predicted matric potential approach to the Van Genutchen model to determine the moisture used in an irrigation management scheme. We can save, on average, between 56.4% and 90% of the irrigation water needed by applying the Zscore, MZscore and Chauvenet outlier removal techniques to the predicted data.

Smart & Green: An Internet-of-Things Framework for Smart Irrigation.

The agriculture sector is changing rapidly pointing to the future of automated and embedded systems with an array of sensors to monitor and control the growing plants in a way to protect workers, the environment and profits associated with it. The continuous monitoring and controlling of distantly located plants is labour intensive and technically challenging business. In modern precision agriculture, a Wireless Sensor Network (WSN) provides a simple cost effective solution to monitor and control. The basic parameters to be monitored are temperature and humidity (moisture content in the soil). A smart low cost WSN system for precision agriculture is proposed for monitoring and control using open software and electronic prototype - ARDUINO.

Development of WSN system for precision agriculture

This paper proposes a novel flying capacitor (FC) based inverter for a grid-connected photovoltaic (PV) system. It is possible to connect the grid neutral directly with the PV negative bus; thereby, the topology exhibits an inherent zero leakage current. The devised topological structure is such that it can be implemented using industry-standard half-bridge modules, making it an industry-ready solution. A simple unipolar pulsewidth modulation is applied with the aid of a simple logic gate based gating pulse generation scheme. Further, the capacitance value of the FC is low owing to the cyclic charging of FC in every switching period. The operating principle with the proposed modulation scheme is detailed, and simulation results validating the operability are presented. Finally, through a comprehensive comparative study, the key advantages of the proposed topology are highlighted.

Six-Switch Inverter for Grid-Connected PV Application with Zero Leakage Current

Multilevel inverter enables to completely remove the passive filtering requirement at the grid interfacing end, resulting in improved efficiency and reduced cost. These features have led to increasing attention towards their application to medium and high-power arena. In this paper, investigation of a hybrid 9-level inverter topology for grid integration of renewable energy sources is presented. The structural details, operating principle, capacitor voltage balancing control and the main features of the proposed inverter are presented. The proposed topology is compared with other similar 9-level converters to emphasize its superior characteristics and performance. Simulation results demonstrating the grid connected operation of the converter for two test cases are presented. The results affirm the effectiveness of the capacitor voltage balancing control in maintaining capacitor voltages at set values, under steady state and transient operation of the converter.

A new nine-level single-DC source-based inverter topology for distributed generation

This paper presents a control scheme for single-phase grid-connected modular five-level inverter applied to photovoltaic (PV) system. The five-level topology considered consists of two series connected H-bridge cells popularly known as cascaded H-bridge inverter. The reason that it requires an isolated dc sources makes it very attractive and its inherent modularity, easy scalability makes the system more reliable. One of the main challenges associated with multilevel converter is to control the drift in dc-link voltage caused by the power imbalance of the cells. A two loop control scheme is proposed to combat this issue; it consists of an asynchronous frame or proportional resonant (PR) for regulating the grid current and a proportional integral (PI) controller for regulating dc-link voltage. The proposed scheme regulates the dc-link voltage independently, in accordance with the reference value generated by the maximum power point tracking (MPPT) algorithm enabling the extraction of maximum power from each module. The inverter injects current which is in phase with the grid voltage ensures the unitary power factor operation with zero reactive power and less total harmonic distortion. The proposed control scheme can be extended to any number of cells connected in series for increasing the number of level in output voltage. Simulation results are presented to validate the analytical expectations and the control scheme developed.

Single-phase modular multilevel inverter based grid-connected photovoltaic system

In this paper, a current fed DC-DC converter topology is proposed for electrical vehicle battery charging of a wireless power transfer system. The proposed configuration is composed of a conventional current source inverter (CSI) interfaced to a diode bridge rectifier through a suitably modified tank circuit. It will be shown that an addition of a capacitor in the primary side transmitter loop results in the relieving of the CSI from supplying the reactive power demand while catering only to the active power demand of the load. Furthermore, this reduces the voltage stress of the CSI switches and thereby leads to reduced switching power losses, which further enhances the overall power conversion efficiency. The operating principle, mathematical analysis and design guidelines of the proposed converter are presented. An experimental verification using the laboratory developed prototype rated for 260 W is carried out and the resultes are presented. The obtained efficiency from the laboratory prototype is approximately 86.22% with a coupling coefficient of 17.88%.

Udaykumar R Y

Papers

Development of WSN system for precision agriculture

Six-Switch Inverter for Grid-Connected PV Application with Zero Leakage Current

A new nine-level single-DC source-based inverter topology for distributed generation

Single-phase modular multilevel inverter based grid-connected photovoltaic system

An Efficient Topology for Inductive Wireless Power Transfer in Vehicular Application