A Single Stage CCM Zeta Micro inverter for Solar Photovoltaic AC Module. Abstract

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1 Page number 1 A Single Stage CCM Zeta Micro inverter for Solar Photovoltaic AC Module Introduction: Abstract Among various microinverters reported in literature, the most generic are two stage inverters where a dc/dc converter is used in the front-end to track MPPT and to boost the voltage while second stage pulse width modulated (PWM) inverter convert dc to ac. The major drawback of this type of inverters is the components count and cost. Non-isolated microinverters are simple and compact, but boosting the voltage to the grid level without transformer is a major concern. Third kind is singlestage microinverters where all three tasks i.e. MPPT, voltage boosting and dc to ac conversion are done in one stage. Such microinverters are very promising due to reduced switch count and high power density. Other type of microinverters utilize active power decoupling that enables the use of thin film capacitors instead of electrolytic capacitors to increase the life span of the microinverter. However, this comes with an additional cost and relatively low efficiency.

2 Page number 2 Existing system: The flyback converter is used in both AC/DC and DC/DC conversion with galvanic isolation between the input and many outputs. The flyback converter is a buck-boost converter with the inductor split to form a transformer, so that the voltage ratios are multiplied with an additional advantage of isolation. The flyback converter is an isolated power converter. The two prevailing control schemes are voltage mode control and current mode control (in the majority of cases current mode control needs to be dominant for stability during operation). Both require a signal related to the output voltage. There are three common ways to generate this voltage. The first is to use an optocoupler on the secondary ry to send a signal to the controller. The second is to wind a separate winding on the coil and rely on the cross regulation of the design. The third consists on sampling the voltage amplitude on the primary side, during the discharge, referenced to the standing primary DC voltage. Proposed system: Operation of zeta microinverter is explained for the positive half cycle of load current at switching frequency. The main switch Sm is modulated at high frequency (HF) with a variable

3 Page number 3 duty cycle to generate rectified ac output and secondary switches S1 - S4 are operated at line frequency to produce ac output at line frequency. On the secondary side, during positive half cycle of load current switches S1, S3 are gated to conduct and during negative half cycle of load current, switches S2, S4 are gated to conduct. Steady-state operation of the proposed microinverter in DCM and CCM mode of operation is analyzed. Advantages: Reduced conduction losses, switch ratings and current stress.

4 5 V DC LeMeniz Infotech Page number 4 Applications: PV applications. Block diagram: INPUT DC supply Isolated Zeta converter Single Phase Inverter Load 12 V DC OPTO coupler Gate driver 12 V DC BUFFER PIC controller

5 Page number 5 Tools and software used: MPLAB microcontroller programming. ORCAD layout. MATLAB/Simulink Simulation.