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The capacitive-coupling grid-connected inverter (CGCI) is coupled to the point of common coupling via a second-order LC branch. Its operational voltage is much lower than that of a conventional inductive-coupling grid-connected inverter (IGCI) when it serves as a multifunctional inverter to compensate reactive power and transfer active power simultaneously. It is a promising solution for microgrid and building-integrated distributed generator systems. A quasi-proportional-resonant (quasi-PR) controller is applied to reduce the steady-state current tracking errors of the CGCI in this paper. The quasi-PR controller generates the voltage reference for use of carrier-based pulse-width modulation, which can effectively reduce output current ripples. The second-order coupling impedance of the CGCI causes its modeling and controller design to differ from that of the conventional IGCI. A comprehensive design method for the quasi-PR controller in a CGCI is developed. The quasi-PR controller is also compared with a proportional-integration current controller. Simulation results are provided to verify the effectiveness of the quasi-PR controller and its design method in a CGCI. The current tracking errors are greatly reduced when the quasi-PR controller rather than the proportional-integration controller is applied. Experimental results are also provided to validate the CGCI as a multifunctional grid-connected inverter. [ABSTRACT FROM PUBLISHER]

Single-phase traction transformers are widely used in traction power supply systems due to their characteristics such as a low cost and a simple structure. Railway power conditioners (RPCs) could increase the loading capacity of substations and improve the supply quality. In this paper, a hybrid RPC (HRPC) is applied to reduce reactive power, relieve system unbalance, and suppress harmonics. The operational voltage of the HRPC is much lower than that of a conventional RPC. A method named partial compensation was used to reduce the current rating of the RPC, in which the compensating currents are expressed as a function of the power factor target at the grid side. When this method is used in the HPRC, the operational voltage varies with the compensating currents over a wide range. A comprehensive design procedure is proposed so that both the current and voltage ratings of the HRPC are reduced with partial compensation. A reduction of more than 50% is achieved by compensating the power factor at the grid side to 0.95 instead of to unity. The control block diagram for the HRPC with partial compensation is presented. The design and control of the HRPC are validated by simulation and experimental results. [ABSTRACT FROM PUBLISHER]