A high efficiency transformerless PV grid- Connected inverter with leakage current suppression

© 2016 IEEE. This paper presents a new diode free freewheeling and common-mode voltage (CMV) clamping branches for single phase transformerless grid connected photovoltaic (PV) inverter for complete leakage current elimination and low conduction losses. In the past, various isolation techniques have been proposed for leakage current elimination in transformerless PV inverters. However, galvanic isolation only cannot completely eliminate leakage current due to that a resonant path is created by the switch junction capacitors, which also generate leakage current. The proposed freewheeling branch consists of four MOSFETs along with a clamping branch, which consists of two MOSFETs and a capacitor divider. The divider is connected to the DC side of the converter to keep constant CMV in the freewheeling path. As a result, the improved CMV clamping has been achieved for complete leakage current elimination. The unipolar sinusoidal pulse width modulation (SPWM) technique and modified HERIC topology with AC-decoupling for galvanic isolation is adopted for lower conduction losses. The proposed topology consists of only MOSFET in the freewheeling and clamping path which provides lower conduction losses compared with diode based topologies. The performances of the proposed topology in terms of common mode characteristics, leakage current, total harmonic distortion and conversion efficiency are analyzed and compared with H5, H6, HERIC and HBZBR topologies. The detail analyses are performed using MATLAB/Simulink and PSIM

CAPACITANCE REDUCTION USING RIPPLE SUPPRESSION CONTROL OF SINGLE PHASE ENERGY STORED QUASI-Z-SOURCE INVERTER

The energy stored Quasi-Z-source Inverter (qZSI) allows integrate energy storage in addition to the other energy source mainly for output power smoothening. Single phase inverter suffers from double-frequency power ripple in the input side and also in the energy storage that is transferred there from the ac-side. In qZSI must be used large electrolytic dc capacitors in the impedance network to suppress this 100 Hz ripple. Also to suppress this ripple can be applied two types of power decoupling: passive power decoupling and active power decoupling. In this paper is analyzed passive power decoupling that is realized by means of the modified control strategy that produces the time-varying shoot-though duty cycle to mitigate power ripple without deteriorating of the output power quality. The validity of proposed control strategy was confirmed by simulation results that were obtained in PSIM software

DESARROLLO DE UNA ESTRATEGIA DE MODULACION BASADO EN CONTROL PREDICTIVO APLICADO EN SISTEMAS CONECTADOS A LA RED ELÉCTRICA (DEVELOPMENT OF A MODULATION STRATEGY BASED ON PREDICTIVE CONTROL APPLIED TO GRID-CONNECTED SYSTEM)

Resumen Se presenta una estrategia de modulación basada en técnicas de control predictivo, la cual es implementada en un inversor monofásico sin transformador en modo común conectado a la red eléctrica; dicha estrategia, se conforma de un algoritmo que actúa de acuerdo con la toma de decisiones basadas en la comparación de las señales de referencia y la respuesta completa del sistema. Se pretende obtener una intensidad de corriente de salida que se encuentre con el mismo ángulo de fase con la tensión de la red ante cambios de carga resistiva y de valores de referencia. Por otra parte, se desea que esta modulación sea igualmente efectiva ante cargas reactivas no lineales. Palabras Clave: Carga resistiva, Control predictivo, Inversor monofásico sin transformador, Respuesta completa. Abstract A modulation strategy based in predictive control techniques is presented, which is implemented in a Transformerless Common-Mode Current-Source Inverter Grid-Connected. The strategy is conformed by an algorithm that responds according to the decision making between reference signals and the complete response of the system. This work seeks to obtain an output signal of current in the same phase than the voltage grid which responds on resistive loads and reference values changes. Finally, it is desired to obtain same performance. Even with non-lineal reactive loads. Keywords: Complete response, Predictive control, resistive load, Transformerless Single Phase Inverter

Análisis de un inversor sin transformador en micro redes eléctricas

Energy efficiency is a key factor when working with non-conventional energy sources, for this reason, interconnected grid photovoltaic systems use transformer less inverters to obtain efficiencies close to 98%. This idea can be adapted to microgrids, in order to increase its efficiency. In this paper is presented the transformer less half bridge topology working in an electric microgrid. The operation of the topology and the bidirectional power flow are simulated in the PSIM software with the system connected to the grid. Additionally, the operation of the converter in island mode also is simulated. Finally, the conclusions are presented.La eficiencia energética es un factor clave a la hora de trabajar con fuentes no convencionales de energía, es por eso que los sistemas fotovoltaicos interconectados a red utilizan inversores sin transformador con el fin de obtener eficiencias cercanas al 98%. Dicha idea puede ser adaptada a las micro redes eléctricas, con el fin de aumentar la eficiencia de esta. En este artículo se presenta la topología medio puente sin transformador operando en una micro red eléctrica.  Se analiza el principio de funcionamiento de la topología y se simula, con el software PSIM, el flujo de potencia bidireccional cuando el sistema se encuentra conectado a red, así como la entrega de energía a una carga en modo isla. Finalmente, se presentan las conclusiones

Hybrid bypass technique to mitigate leakage current in the grid-tied inverter

The extensive use of fossil fuel is destroying the balance of nature that could lead to many problems in the forthcoming era. Renewable energy resources are a ray of hope to avoid possible destruction. Smart grid and distributed power generation systems are now mainly built with the help of renewable energy resources. The integration of renewable energy production system with the smart grid and distributed power generation is facing many challenges that include addressing the issue of isolation and power quality. This paper presents a new approach to address the aforementioned issues by proposing a hybrid bypass technique concept to improve the overall performance of the grid-tied inverter in solar power generation. The topology with the proposed technique is presented using traditional H5, oH5 and H6 inverter. Comparison of topologies with literature is carried out to check the feasibility of the method proposed. It is found that the leakage current of all the proposed inverters is 9 mA and total harmonic distortion is almost about 2%. The proposed topology has good efficiency, common mode and differential mode characteristics