Three-level inverter configuration with common mode voltage elimination for induction motor drive (To continue)

The multiplicity of vector combinations for vectors of combined three-level inverters plays an important role, when deciding on the modulation scheme, to obtain minimum switching per inverter vector change, as described in the next Section. This is not possible with reduced common-mode three-level inverter structure, obtained with a five-level cascaded H-bridge configuration, as the space vectors locations do not exhibit multiplicity. Moreover, the proposed configuration requires only two power supplies, whereas the scheme with the five-level H-bridge configuration requires six isolated power supplies.

Three-level inverter configuration with common mode voltage elimination for induction motor drive

The multiplicity of vector combinations for vectors of combined three-level inverters plays an important role, when deciding on the modulation scheme, to obtain minimum switching per inverter vector change, as described in the next Section. This is not possible with reduced common-mode three-level inverter structure, obtained with a five-level cascaded H-bridge configuration, as the space vectors locations do not exhibit multiplicity. Moreover, the proposed configuration requires only two power supplies, whereas the scheme with the five-level H-bridge configuration requires six isolated power supplies.

Control of Distributed Generation Using Non-Sinusoidal Pulse Width Modulation

The islanded mode is one of the connection modes of the grid distributed generation resources.In this study,a distributed generation resource is connected to linear and nonlinear loads via a three-phase inverter where a control method needing no current sensors or compensator elements is applied to the distribute generation system in the islanded mode.This control method has two main loops in each phase.The first loop controls the voltage control loops that adjust the three-phase point of common coupling,the amplitude of the non-sinusoidal reference waveform and the near-state pulse width modulation(NSPWM)method.The next loop compensates the harmonic compensator loop that calculates the voltage harmonics of the point of common coupling in each phase,and injects them to compensate the non-sinusoidal reference waveforms of each phase.The simulation results in MATLAB/SIMULINK show that this method can generate balanced threephase sinusoidal voltage with an acceptable total harmonic distortion(THD)at the joint connection point.

Ride through Strategy for a Three-Level Dual Z-Source Inverter Using TRIAC

A new ride through strategy is introduced in a three-level dual Z-source inverter, for isolation under semiconductor switching failure condition. Here the output will have no significant decrease in the amplitude and quality. Instead of diodes, the triacs are added to the inverter source ends, as it can perform a bidirectional power transfer also it can operate well in both low and high voltage operating conditions. The faulted part can be isolated by simply altering the firing pulses for turning on/off the triacs using the carrier based SPWM technique and resulting in a boosting output with zero common mode voltage. Consequently, it forms a common floating point or null point with a zero common mode voltage. It is experimentally verified by using MATLAB, and digital oscilloscope.

Single-stage Five-level Common Ground Transformerless Inverter with Extendable Structure for Centralized Photovoltaics

The paper presents a five-level common ground type(5L-CGT),transformer-less inverter topology with double voltage boosting.The proposed inverter uses eight switches and two capacitors,charged at input voltage level.The inverter in its basic form acts as a string inverter for low-power PV applications.However,it can be extended to work as a scalable multi-level inverter with higher power handling capability to act as a centralized inverter.The working of the inverter with the sizing of the components is presented with mathematical analysis.The efficiency of the proposed PV inverter is found using thermal losses associated with switches using PLECS software.A prototype of 1 kW has been designed,and experimentation has been carried out.Various loads with a lagging power factor up to 0.6 have been tested with the inverter to establish the usability of the proposed inverter in a worst-case emulated homeuse scenario.The total harmonic distortion(THD)at the output has been recorded using a power quality analyzer with voltage and current THD values of 4.5%and 2.5%,respectively,which lies within the limits of IEEE 519 standards.The highest power conversion efficiency of the inverter has been recorded to be 96.20%.

Study of Improved Load Sharing Methodologies for Distributed Generation Units Connected in a Microgrid

In this paper,an improved load sharing strategy is proposed for distributed generation units(DGs)connected in a microgrid.Conventional frequency and voltage droop control result in unacceptable active and reactive power sharing.The proposed method formulates a suitable algorithm for load sharing in the islanded microgrid.The feeder power loss and the line impedance voltage drops are minimized so as to regulate the voltage at the point of common coupling(PCC)at its nominal value.The desired DG output voltages are calculated and a linear relationship is obtained between the shared active and reactive powers and the DG output voltages.A master DG controller sets the frequency which is followed by other DG units.The reference powers for the DG units are adjusted so as to maintain the rated PCC voltage.The proposed strategy is verified taking into account the DG ratings,unequal line impedance drops,feeder losses,change in system impedance and effect of DG local loads and formulates an improved power sharing strategy that also facilitates PCC voltage regulation under variable loading conditions.Simulation and experimental results are presented to verify the effectiveness of the proposed method.

A new five-level inverter with reduced leakage current for photovoltaic system applications

A general growth is being seen in the use of renewable energy resources,and photovoltaic cells are becoming increasingly popular for converting green renewable solar energy into electricity.Since the voltage produced by pho-tovoltaic cells is DC,an inverter is required to connect them to the grid with or without transformers.Transformerless inverters are often used for their low cost and low power loss,and light weight.However,these inverters suffer from leakage current in the system,a challenge that needs to be addressed.In this paper,a topology with two alternative connection models is presented to stabilize the common mode voltage and reduce the leakage current.The output voltage characteristic of the proposed inverter is five-level,which reduces the harmonic distortion in the output cur-rent compared to the two-and three-level inverters.The operation modes and output of the proposed topology are described and analyzed.The structures of the proposed inverter are simulated in MATLAB/Simulink and are compared with some well-known structures.Results show that the proposed structure with both connection models effectively reduces leakage current and improves grid current THD.