Grid-Connected Resonance Suppression Of Group-Series Photovoltaic Cluster Inverters Based On Hybrid Damping

Grid-connected group-series photovoltaic cluster inverter system will cause resonance, which will adversely affect the system. To suppress grid-connected resonance, the mathematical model, resonance mechanism and resonance characteristics of the cluster inverters are analyzed, and a global resonance suppression strategy based on hybrid damping is proposed. In the current loop of the inverter, capacitive current feedback and parallel voltage proportional feed-forward are introduced as active dampers to reduce the harmonics of the parallel current. On this basis, RLC type second-order resonance suppression circuit is added as passive damping to suppress system resonance, so that the output current of the inverters can meet the grid-connected conditions when the cluster is connected to the grid. The simulation and experimental results show that the total harmonic distortion of the grid-connected current decreases from 10.54% to 1.97% after three series photovoltaic cluster inverters adopt this strategy, which effectively suppresses the grid-connected resonance.

Five-level parallel current source converter for high power drives with DC current balance control and superior harmonic performance

In this thesis, space vector modulation is developed for a 5-level parallel current source converter for high power drives. The modulation scheme is designed to bring superior harmonic performance to the currents on the AC sides. This method synthesizes the rotating reference current vector in the converter's space vector's plane with three adjacent switching vectors. Unbalanced currents of DC links become a practical challenge when two converters are connected in parallel. To balance the DC currents, the proper switching state for every Small and Medium switching vector is chosen from redundant switching states corresponding to the vector based on circuit circumstances and the designed switching sequence. Simulated results verify the effectiveness of the method. In addition, the switching sequence is designed to lower the switching frequency and minimize the switching loss. Finally, the proposed converter and switching scheme are simulated and steady state and dynamic performance are investigated in detail.

Five-level parallel current source converter for high power drives with DC current balance control and superior harmonic performance

In this thesis, space vector modulation is developed for a 5-level parallel current source converter for high power drives. The modulation scheme is designed to bring superior harmonic performance to the currents on the AC sides. This method synthesizes the rotating reference current vector in the converter's space vector's plane with three adjacent switching vectors. Unbalanced currents of DC links become a practical challenge when two converters are connected in parallel. To balance the DC currents, the proper switching state for every Small and Medium switching vector is chosen from redundant switching states corresponding to the vector based on circuit circumstances and the designed switching sequence. Simulated results verify the effectiveness of the method. In addition, the switching sequence is designed to lower the switching frequency and minimize the switching loss. Finally, the proposed converter and switching scheme are simulated and steady state and dynamic performance are investigated in detail.

A Multi-Functional De-Icing Equipment Using Hybrid Type Parallel Current Source Converters

This paper has proposed a phase controlled and PWM controlled power current source converter (CSC) for transmission line de-icing. The proposed system consists of a high-power thyristor-based line commutated converter to contribute a majority of the dc de-icing current and a low power PWM CSC to provide a part of the dc de-icing current and to compensate the low order harmonic ac current from the TCR. Thus, the grid current can be highly sinusoidal. In order to avoid the resonance caused by the interaction between TCR and PWM CSC, a virtual impedance control is implemented in the PWM CSC without using any additional sensors. Comprehensive verification results have been obtained to validate the correctness of the proposed approach.

CATS-CAE Reflective Middleware Framework for Adapting Context-Aware Transactional Services

Pervasive environments are characterized by limited computing resources and wireless connectivity. In parallel, current application domains have variable transactional requirements that do not fit the traditional ACID model. As a result, the pervasive environment characteristics are compelling and cannot be supported by conventional solutions that are typically dedicated to a specific application domain and support a limited set of context parameters. This article aims at providing a complete solution that addresses the challenges of the adaptability of context-aware transactional services “CATS” in pervasive environments. Thus, a new framework CATS-CAE was designed, which offers a comprehensive structure of multiple component chains. The adaptation strategy in CATS-CAE is based on a hybrid approach combining the use of adaptation policies, alternative strategy and behavioral adaptation of composite services through the “Profiled Task Class” concept. A probabilistic model is also presented to support the efficiency of the proposed approach.

Critical frequency of autonomous current inverter when operating on active-inductive load

The article presents the results of a study of a circuit of an autonomous current inverter with shut-off valves when operating on an active-inductive load in terms of identifying its properties, energy characteristics and comparing the circuit with a traditional parallel current inverter with capacitive switching without additional valves.