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

There has been a lot of progress going on in field of solar inverters. transformerless inverters has ben the most research area in recent time. For the operation of inverter in stand alone condition it is necessary to make sure that the control of the inverter is taken in account for maintaining the different operation parameters and making the system more safe and stable. This paper presents a comparative analysis of Highly Efficient and Reliable Inverter Concept (HERIC) inverter which is being controlled by hybrid controller. Stability testing of the HERIC inverter is performed based on load varying condition using Fuzzy-Proportional Integral Derivative (PID) and ANFIS-PID controller. Numerous different requirement is taken into consideration and analysis is carried out on basic of settling time and harmonic distortion present. At the end the experimental result conclude that system is running accurately with low settling time and harmonics distortion of less then 3.7%.

Hybrid Voltage Control for Stand Alone Transformerless Inverter

Transformer-less inverter is popular for grid-tied photovoltaic (PV) system due to low cost, smaller size and higher efficiency. However, one of the technical challenges, which need to be handled carefully, is the issue of leakage current. Moreover, an inverter must be capable of controlling the reactive power to a certain extend to maintain the power factor (PF) close to unity. Therefore, many inverter topologies have been proposed. In this paper, a new four diodes and two IGBT switch based H2D4-type highly efficient transformer-less inverter is proposed that can handle the issue of leakage current maintaining low total harmonic distortion (THD) and higher PF where the common mode (CM) voltage is maintained constant. As a result, the leakage current deceases and the conduction loss as well as size of the system is decreased due to minimum number of IGBT switches. Furthermore, two control systems are proposed to control the reactive power with desire PF. The comparison among proposed H2D4 topology and conventional neutral point clamped (NPC) and H6 topology have been analyzed in this paper. To validate the accuracy of the theoretical analysis, the compared topologies are simulated in MATLAB/Simulink software. It is found that the PLL and PI closed loop control based H2D4 inverter topology controls the reactive power maintaining a low current THD with higher efficiency and high PF as compared to the system with only PI control based topology.

H2D4-Type Single Phase Transformer-Less Inverter with Reactive Power Control for Grid-tied PV System

Although PV systems are one of the most widely used alternatives as a renewable energy source due to their well-known advantages, there are significant challenges to address related to voltage fluctuations and reverse power flow caused by high PV penetration scenarios. As a potential solution to this problem, an active power management strategy is proposed in this work using a residential cluster as a benchmark. The proposed strategy is analyzed and experimentally verified, offering a simple way to reduce the voltage fluctuations by regulating the active power delivered by the PV system, achieving also relevant functionalities for the system, such as the regulation of the DC bus voltage, maximum power point tracking (MPPT), synchronization with the grid voltage, detection of high penetration conditions, and a simple strategy for the main controller with an effective performance. The proposal system shows satisfactory results being able to maintain grid voltage fluctuations within the voltage standard specifications.

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Active Power Management for PV Systems under High Penetration Scenario

Characteristics of large photovoltaic (PV) panels under partially shaded conditions are characterized by multiple peaks and steps. This makes the tracking of the actual maximum power point (MPP) a difficult task. Moreover, most of the existing maximum power point tracking (MPPT) is unable to extract maximum power from the PV array under partial shading conditions. In this paper, a novel FLC method has been presented to track the global maximum power point (GMPP) of PV. The proposed technique is based on the output current of the photovoltaic system (PVS). Compared with the P&O method, The proposed FLC method can quickly find GMPP and avoid much energy loss due to blind scan. The Simulation results demonstrate an average 13% improvement in efficiency when compared with the P&O method.

Maximum power point tracking applied to PV systems under partial shading conditions

In a grid connected photovoltaic system, the main aim is to design an efficient solar inverter with higher efficiency and which also controls the power that the inverter injects into the grid. The effectiveness of the general PV system anticipate on the productivity by which the direct current of the solar module is changed over into alternating current. The fundamental requirement to interface the solar module to the grid with increased productivity includes: Low THD of current injected to the grid, maximum power point, and high power factor. In this paper, a two stage topology without galvanic isolation is been carried out for a single phase grid connected photovoltaic inverter. The output from the PV panel is given to the DC/DC boost converter, maximum power point tracking (MPPT) control technique is being used to control the gate pulse of the IGBT of boost converter. The boosted output is fed to the highly efficient and reliable inverter concept (HERIC) inverter in order to convert DC into AC with higher efficiency.

Payal Somani

Papers

Design of HERIC configuration based grid connected single phase transformer less photovoltaic inverter