The Study of 3-Phase DC-AC Inverter for a Bi-Modal Photovoltaic Power Conditioning System Seungdae Yang Department of Embedded Software Graduate School, Kwangwoon University Seoul, Korea

ABSTRACT
The Study of 3-Phase DC-AC Inverter for a Bi-Modal Photovoltaic Power Conditioning System Seungdae Yang
 Department of Embedded Software Graduate School, Kwangwoon University Seoul, Korea Supervised by professor Juyeop Choi

 This paper designs the 3-phase DC-AC inverter controller for a bi-modal PV PCS which transmit a power bi-directionally. Also it proposes a new compensation algorithm for a distorted grid current caused by a distorted grid voltage. Simulation and experiment are used to validate the proposed bi-directional inverter controller design and compensation algorithm. Furthermore, it analyzes the Euro efficiency of the inverter by calculating the sum of each weighted loss for an inductor and PWM circuit. At first, in order to run inverter bi-directionally, inverter must control both DC link voltage and also inverter output current. Therefore, the control block has a voltage controller to control DC link voltage at outer loop and a current controller to control inverter output current at inner loop. For calculating phase of AC current, this paper provides the optimum gain of PLL(Phase Locked Loop) for voltage controller and current controller. Simulation and experiment are also used to validate the proposed bi-directional inverter controller design. Because of connected nonlinear or single phase load at PCC(Point of Common Coupling), grid voltage usually has small distortion and unbalance. Distorted current by nonlinear load caused voltage distortion at PCC. Also unbalanced current by single phase load caused voltage unbalance at PCC. Finally, unbalanced and distorted voltage of grid voltage makes oscillated DC link voltage causing grid current distortion and also worsening grid voltage distortion. So this paper proposes simple compensation algorithm for distorted grid current in unbalanced and distorted grid voltage environment. The proposed compensation algorithm provides robust PLL using positive sequence for calculating grid voltage and feedforward calculated distortion voltage to inverter output reference. It is validated PSIM simulation and experiment with inverter stack and DSP control circuits, NF 3-phase power supply and My Way PV simulator.