A thesis submitted to the Department of Electrical and Computer Engineering In conformity with the requirements for the degree of Master of Applied Sciences Queen’s University Kingston, Ontario, Canada 

 Abstract This thesis concentrates on the design and control of a single stage inverter for photovoltaic (PV) micro-inverters. The PV micro-inverters have become an attractive solution for distributed power generation systems due to their modular approach and independent Maximum Power Point Tracking (MPPT). Since each micro-inverter has an individual inverter section, it is essential to have small-sized power conversion units. Moreover, these inverters should provide large voltage amplification in order to connect to the utility grid because of the low voltages of the PV panels. In order to operate these inverters at high frequencies, the soft-switching of the power MOSFETs is an important criterion to minimize the switching losses during the power transfer. A novel Zero Voltage Switching (ZVS) scheme to improve the efficiency of a single stage grid-connected flyback inverter is proposed in this thesis. The proposed scheme eliminates the need for auxiliary circuits to achieve soft-switching for the primary switch. ZVS is realized by allowing the Current from the grid-side to flow in a direction opposite to the actual power transfer with the help of bi-directional switches placed on the secondary side of the transformer. The negative current discharges the output capacitor of the primary MOSFETs thereby allowing turn-on of the switch under zero voltage. In order to optimize the amount of reactive current required to achieve ZVS a variable frequency control scheme is implemented over the line cycle. Thus the amount of negative current in each switching cycle is dependent on the line cycle. Since the proposed topology operates with variable frequency, the conventional methods of modeling would not provide accurate small signal models for the inverter. A modified state-space approach taking into account the constraints associated with variable switching frequency as well as the negative current is used to obtain an accurate small signal model. Based on the linearized inverter model, a stable closed loop control scheme with peak current mode control is implemented for a wide range of operation. The system incorporates the controllers for both the positive as well as negative peak of inductor current. Simulation and the experimental results presented in the thesis confirm the viability of the proposed topology.