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A Novel Single-Phase Grid-connected PV Inverter System
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Renewable energy sources, especially solar energy, continue to gain popularity and are ready to become a significant part of global energy portfolio. Grid-connected inverter based distributed generator is becoming increasingly popular due to its advanced control flexibility. Power quality and reliability are attracting much attention in such systems. In order to meet requirements of future applications and maximize the value of inverter system, advanced inverter functions are expected to provide more functionalities. This dissertation proposes a novel single phase inverter system combining proposed advanced control schemes and active power decoupling technique. This dissertation firstly investigates the existing power control schemes for single phase grid-connected inverter and then proposed an independent power control scheme, which is implemented in stationary reference frame. The synchronization function is combined in power loop directly to eliminate the use of conventional phase locked loop. The proposed controller with double-loop current controller based on proportional resonant compensator is proved to achieve good power tracking performance even under distorted grid conditions. Active damping function for resonant peak problem is also implemented in controller. Inverter based distributed generators may operate in different conditions and transition between different operating conditions may result into voltage spikes across the local loads and inrush currents into the grid due to the failure of synchronization on point of common coupling voltage. In this dissertation, a novel control scheme based on model predictive control is proposed for grid connected inverter to enable the capability to operate in both grid-connected and island conditions and the capability to seamless transfer between different conditions through proposed synchronization and phase adjustment algorithm. The auto-tuning strategy of weight factor is presented as well as the stability analysis on the system. Compared with the conventional methods, the proposed seamless transfer control strategy has simpler structure and exhibits good transient performance. Double line frequency ripple power is inherent in single phase rectifiers and inverters and can be adverse to system performance. Therefore, numerous active power decoupling techniques have been introduced to decouple that. All existing active topologies are investigated. Comprehensive comparison is conducted on the minimum required capacitance for power decoupling, the dc voltage utilizations, the current stresses, the modulation complexity and even application evaluations except for power rating and component counts. Based on the investigations and generalized comparison results, a new active power decoupling circuit composed of dual buck converters is proposed together with its control and modulation strategy. The ripple power is stored in split dc link capacitors with high energy utilization. The proposed power decoupling circuit could reduce the storage capacitance needed. The proposed power decoupling circuit does not have shoot-through concern, thus it could enhance the overall system reliability and decoupling performance.
Li, Xiao (2017). A Novel Single-Phase Grid-connected PV Inverter System. Doctoral dissertation, Texas A & M University. Available electronically from