The contributions of this Ph.D. 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 dissertation 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 grid-line 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 dissertation is demonstrated by both simulation and experimental results.
|School:||The Ohio State University|
|School Location:||United States -- Ohio|
|Source:||DAI-B 79/09(E), Dissertation Abstracts International|
|Keywords:||Distributed generation, Inverter control, Island mode, Power converters, Three-phase four-wire, Transformerless|
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