A 4-Switch Single-Stage Single-Phase Buck-Boost Inverter

 

Abstract

This paper proposes a single-phase, single-stage buck-boost inverter for photovoltaic (PV) systems. The presented topology has one common terminal in input and output ports which eliminates common mode leakage current problem in grid connected PV applications. Although it uses four switches, its operation is bi-modal and only two switches receive high frequency PWM signals in each mode. Its principle of operation is described in detail with the help of equivalent circuits. Its dynamic model is presented, based on which a bi-modal controller is designed. Experimental results, in standalone and grid connected mode, obtained with a 300 W laboratory prototype are presented to validate its performance.

EXISTING  SYSTEM:

A class of reported topologies share one common terminal between PV and grid, which ensures zero CMLC. one such topology is proposed with buck boost capability. But since it uses two input voltage sources for positive and negative halves of output voltage, this leads to underutilization of PV panel. In differential connection of two buck- boost and boost converters were proposed. These converters have simple configuration with four active switches suitable for renewable energy application. However, hard switching of all the devices at high frequency reduces the efficiency and increases its affinity towards EMI problems. The inductors in [8] are replaced by coupled inductor pairs. This provides high voltage gain capability but the problems of its parent topology persist. Topologies like which operate only in buck mode, require high input voltage for grid connected applications. Solutions propose a buck boost inverter where an ac-ac unit is used to perform the boost function. However, this unit comprises four active switches which increase the overall switch count, which greatly reduces power density and efficiency. Proposed doubly grounded buck boost inverters. However, active switch count of all these are greater than or equal to five, which makes them no better than traditional two stage configuration. Single stage inverter proposed in uses a pair of coupled inductors which allows it to attain high voltage gain and reduces the size of power decoupling filter size. However, the use of seven semiconductor devices impair system efficiency

PROPOSED SYSTEM:

This paper proposes a buck-boost single-phase inverter with only four switches, two inductors and two capacitors. It also shares a common terminal between the input and output ports, which practically eliminates CMLC problems and reduces possibilities of consequent panel degradation. It is basically a combination of two dc-dc buck-boost converters operating sequentially to generate an ac voltage output. Principle of operation and AC voltage generation is explained with the assistance of modal equivalents for both polarities of the ac voltage. Current programmed mode (CPM) based controller is designed to achieve the desired control constraints. Finally, experimental results under different load conditions and in grid connected mode are showcased to validate the performance of the inverter.

CONCLUSION

This paper presents a new single-stage, single-phase, buckboost inverter, with both input and output ports sharing a common terminal. This eliminates the problem of common mode voltage in grid connected PV applications, which helps  to increase productive life of PV systems. It uses four switches and two inductors, which ensures minimum part count a reported topologies of comparable rating. Its bi-modal operation principle is explained in detail through steady-state and dynamic analyses. A two-loop controller structure is used, with the inner current loop realized by CPM. Outer loop design is based on a minimal constraint on phase-margin, applied to the set of small-signal plants derived from the large-signal inverter model. All controller design aspects are presented in detail. Power decoupling at low input voltage side requires a large capacitor, which adds to the overall size and slightly increases cost. Design of the energy storage elements, loss and efficiency calculations have been presented. A 300 W, 110 V, 50 Hz prototype was developed based on the developed design and experimental results, in standalone and grid-connected mode, show excellent steady-state and transient performance.

REFERENCES

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