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.