Control of Power Converters for
Distributed Generation Applications
Min Dai, Ph.D.
Ali Keyhani, Professor of Electrical Engineering
The Ohio State University
Electrical and Computer Engineering Department
Columbus Ohio 43210
Tel: 614-292-4430
Fax: 614-292-7596
Keyhani.1@osu.edu
2005
ABSTRACT: The contributions
of this research include the application of a modified space vector pulse width
modulation (MSVPWM) scheme combined with robust servomechanism control in a
three-phase four-wire split dc bus inverter and real-time implementation of
Newton-Raphson Method on digital signal processors for on-line power system
identification and power flow control of a distributed generation (DG) unit.
This report addresses digital control strategies of solid-state electric power
converters for distributed generation applications in both island and
grid-connected modes. Three major issues of DG, island operation, grid-connected
operation, and front-end converter control, are discussed with proposed
solutions and related analysis. In island mode, a control approach is developed
for a three-phase four-wire transformerless inverter system to achieve voltage
regulation with low steady state error and low total harmonic distortion (THD)
and fast transient response under various load disturbances. The control
algorithm combines robust servomechanism and discrete-time sliding mode control
techniques. An MSVPWM scheme is proposed to implement the control under Clarke's
reference frame. The robust stability of the closed-loop system is analyzed. In
grid-connected mode, a real and reactive power control solution is proposed
based on the proposed voltage control strategy for island operation. The power
control solution takes advantage of a system parameter identification method and
a nonlinear feedforward algorithm, both of which are based on Newton-Raphson
iteration method. The proposed technique also performs gridline current
conditioning and yields harmonic free grid-line current. A phase locked loop (PLL)
based algorithm is developed as a part of the solution to handle possible
harmonic distorted grid-line voltage. In a DG unit with three-phase three-wire
ac-dc-ac double conversion topology including a controlled power factor
correction (PFC) front-end rectifier, unbalanced inverter load could cause
current and voltage fluctuation on the dc bus. Mathematical analysis is
conducted to disclose the mechanism of the dc bus voltage ripple and a notch
filter based rectifier control strategy is proposed to eliminate the impact of
the ripple and yield balanced input current. The effectiveness of the techniques
proposed in this report is demonstrated by both simulation and experimental
results. The implementation related technical details are included in the
specific chapters and attached electronic files.
Technical details are provided in descriptions, illustrations, schematics, and
Matlab code about the frequency domain analysis and robust stability analysis
for the four-wire inverter study, the experimental setup power stage
configuration, the grid-connecting contactor design, and the dc bus overvoltage
protection board design. Simulink models and DSP code are given as electronic
files.
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If your company is a member of the Mechatronic Laboratory, please send the
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please send a request to Ali Keyhani, Department of
Electrical Engineering, Mechatronics Program at the following address: Ali
Keyhani, Ohio State University, Electrical Engineering Department, Mechatronics
Systems Laboratory, 2015 Neil Ave., 205 Dereese Lab., Columbus, OH 43210.