This paper presents a transformerless single-phase inverter topology based on a modified H-bridge-based multilevel converter. The topology comprises two legs, namely, a usual two-level leg and a T-type leg. The latter is based on a usual two-level leg, which has been modified to gain access to the midpoint of the split dc-link by means of a bidirectional switch. The topology is referred as an asymmetrical T-type five-level (5L-T-AHB) inverter. An ad hoc modulation strategy based on sinusoidal pulsewidth modulation is also presented to control the 5L-T-AHB inverter, where the two-level leg is commuted at fundamental frequency. Numerical and experimental results show that the proposed 5L-T-AHB inverter achieves high efficiency, exhibits reduced leakage currents, and complies with the transformerless norms and regulations, which makes it suitable for the transformerless PV inverters market. 1 1 This updated version includes experimental evidence, considerations for practical implementation, efficiency studies, visualization of semiconductor losses distribution, a deeper and corrected common mode analysis, and an improved notation among other modifications.

A Single-Phase Asymmetrical T-Type Five-Level Transformerless PV Inverter

Recently, solar energy has been intensively employed in power systems, especially using the photovoltaic (PV) generation units In this regard, this paper proposes a novel design of a fuzzy logic based algorithm for varying the step size of the incremental conductance (INC) maximum power point tracking (MPPT) method for PV In the proposed method, a variable voltage step size is estimated according to the degree of ascent or descent of the power-voltage relation For this purpose, a novel unique treatment is proposed based on introducing five effective regions around the point of maximum PV power To vary the step size of the duty cycle, a fuzzy logic system is developed according to the locations of the fuzzy inputs regarding the five regions The developed fuzzy inputs are inspired from the slope of the power-voltage relation, namely the current-voltage ratio and its derivatives whereas appropriate membership functions and fuzzy rules are designed The benefit of the proposed method is that the MPPT efficiency is improved for varying the step size of the incremental conductance method, thanks to the effective coordination between the proposed fuzzy logic based algorithm and the INC method The output DC power of the PV array and the tracking speed are presented as indices for illustrating the improvement achieved in MPPT The proposed method is verified and tested through the simulation of a grid-connected PV system model The simulation results reveal a valuable improvement in static and dynamic responses over that of the traditional INC method with the variation of the environmental conditions Further, it enhances the output dc power and reduce the convergence time to reach the steady state condition with intermittent environmental conditions

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An Efficient Fuzzy-Logic Based Variable-Step Incremental Conductance MPPT Method for Grid-Connected PV Systems

This research work deals with the modeling and control of a hybrid photovoltaic (PV)-Wind micro-grid using Quasi Z-source inverter (QZsi). This inverter has major benefits as it provides better buck/boost characteristics, can regulate the phase angle output, has less harmonic contents, does not require the filter and has high power performance characteristics over the conventional inverter. A single ended primary inductance converter (SEPIC) module used as DC-DC switched power apparatus is employed for maximum power point tracking (MPPT) functions which provide high voltage gain throughout the process. Moreover, a modified power ratio variable step (MPRVS) based perturb & observe (P&O) method has been proposed, as part of the PV MPPT action, which forces the operating point close to the maximum power point (MPP). The proposed controller effectively correlates with the hybrid PV, Wind and battery system and provides integration of distributed generation (DG) with loads under varying operating conditions. The proposed standalone micro grid system is applicable specifically in rural places. The dSPACE real-time hardware platform has been employed to test the proposed micro grid system under varying wind speed, solar irradiation, load cutting and removing conditions etc. The experimental results based on a real-time digital platform, under dynamic conditions, justify the performance of a hybrid PV-Wind micro-grid with Quasi Z-Source inverter topology.

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Hybrid PV-Wind Micro-Grid Development Using Quasi-Z-Source Inverter Modeling and Control –Experimental Investigation

In this research paper, a hybrid Artificial Neural Network (ANN)-Fuzzy Logic Control (FLC) tuned Flower Pollination Algorithm (FPA) as a Maximum Power Point Tracker (MPPT) is employed to amend root mean square error (RMSE) of photovoltaic (PV) modeling. Moreover, Gaussian membership functions have been considered for fuzzy controller design. This paper interprets the Luo converter occupied brushless DC motor (BLDC)-directed PV water pump application. Experimental responses certify the effectiveness of the suggested motor-pump system supporting diverse operating states. The Luo converter, a newly developed DC-DC converter, has high power density, better voltage gain transfer and superior output waveform and can track optimal power from PV modules. For BLDC speed control there is no extra circuitry, and phase current sensors are enforced for this scheme. The most recent attempt using adaptive neuro-fuzzy inference system (ANFIS)-FPA-operated BLDC directed PV pump with advanced Luo converter, has not been formerly conferred.

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Maximum Power Point Tracking for Brushless DC Motor-Driven Photovoltaic Pumping Systems Using a Hybrid ANFIS-FLOWER Pollination Optimization Algorithm

This paper proposes a circuit analysis and system modeling of an ozone generator using a phase-shifted pulsewidth modulation full-bridge inverter connected to two electrodes via a step-up transformer. The circuit operation of the inverter is fully described. Approximate models of the high-frequency transformer and the ozone-generating tube are given. Model parameter values are obtained from electrical characteristic measurement in conjunction with physical dimension calculation. In order to ensure that a zero-voltage soft-switching mode always operates over a certain range of a frequency variation, a series compensated resonant inductor is included. The advantage of the proposed system is a capability of varying ozone gas production quantity by varying the frequency of the inverter while the applied electrode voltage is kept constant, in order to overcome a high-frequency effect on the transformer voltage regulation. As a consequence, the absolute ozone production affected by the frequency is possibly achieved. The correctness and validity of the proposed system are verified by both simulation and experimental results.

Circuit Analysis and Modeling of a Phase-Shifted Pulsewidth modulation Full-Bridge-Inverter-Fed Ozone Generator With Constant Applied Electrode Voltage

Transformerless photovoltaic systems are one of the best options to connect a photovoltaic system to the electrical grid given their high efficiency, low cost, small size and low weight regarding their counterparts based on a transformer. In this paper a multilevel single-phase inverter is aimed to link a photovoltaic generator with the electrical grid with reduced common mode current. A sinusoidal based modulation strategy is also presented which focus not only in the reduction of the common mode current but also in the reduction of the switching and conduction losses. Five voltage levels are obtained at the inverter output, therefore, a good behavior is achieved regarding harmonic distortion. Numerical results show that the proposed inverter and modulation strategy give a reduced common mode current and low harmonic distortion which is suitable for transformerless photovoltaic systems.

H5-HERIC based transformerless multilevel inverter for single-phase grid connected PV systems

This paper describes a nonlinear model of high-intensity discharge (HID) lamps based on electrical variables. The proposal, oriented to the engineering area, has a special application for the design of electronic ballast. Parameters are obtained from straightforward measurement of electrical variables as power, current, and voltage in the lamp. The lamp resistance is obtained as a function of electrical power; which is estimated from the Saha equation. This model, which can be simulated using software such as ?Simulink? or ?Pspice,? takes into account some important dynamic behaviors of HID lamps, which are normally omitted in some other models suggested in literature nowadays. Experimental and simulation results are shown.

Electric Dynamic Modeling of HID Lamps for Electronic Ballast Design

Single-phase transformerless photovoltaic (PV) inverters have become more widespread in the solar energy market. This is due to the higher efficiencies they achieve together with the very low ground currents, which are their main advantages. In this paper a multilevel transformerless single-phase topology, based on the H-bridge with an active clamping, is proposed. Multilevel output voltage is achieved by using a split DC link and an active bidirectional switch to clamp the first leg in the H-bridge circuit. Therefore, a good behavior is achieved regarding total harmonic distortion (THD). A sinusoidal based pulse width modulation (PWM) strategy is also proposed to control the power converter. Numerical results show that the proposed PV inverter complies with the transformerless norms and regulations, operating with high efficiency, and being suitable for the transformerless PV inverters market.

Transformerless single-phase multilevel inverter for grid tied photovoltaic systems

This paper presents a comparison between two different passive filters for power converters tied to the grid with the application of active power injection. It addresses the L (inductive) filter and the LCL (inductive-capacitive-inductive) filter in single-phase power converters for which are presented the parameter design and modeling. These filters provide coupling of the power converter to the electrical grid and mitigation of high frequency harmonics which are inherent to switching power converters. It is obtained the state-space model and the transfer function of both type of filters and some design considerations for active power injection are presented. An evaluation, by means of numerical simulations, is presented for a single-phase H-bridge inverter with unipolar pulse width modulation for active power injection.

Comparative evaluation of L and LCL filters in transformerless grid tied converters for active power injection

This paper studies a modified DC-DC boost converter where the input inductance has been replaced by an LCL filter. The voltage conversion ratio of the proposed converter is equivalent to the conversion ratio of a conventional boost converter, and it has only one active switching device. A controller is proposed to regulate the output voltage to a given reference with guaranteed reduced input current ripple, i.e., high-frequency current components are minimized at the input current source. Low current ripple is required when dealing with sensitive electric power sources such as fuel cells, batteries and electrolytic capacitors used at DC-links in power electronics applications. The controller design follows a Lyapunov approach, and provides active damping to the input LCL filter. Numerical simulations are presented to evaluate the closed-loop performance.

Mario A. Juarez

Papers

H5-HERIC based transformerless multilevel inverter for single-phase grid connected PV systems

Electric Dynamic Modeling of HID Lamps for Electronic Ballast Design

Transformerless single-phase multilevel inverter for grid tied photovoltaic systems

Comparative evaluation of L and LCL filters in transformerless grid tied converters for active power injection

A model-based controller for a DC-DC boost converter with an LCL input filter