Abstract: The present disclosure relates to the field of electric power system, and more particularly to a topology of a series-connected MMC with a small number of modules, where the topology is composed of a three-phase bridge circuit, half-bridge valve strings, a three-phase filter inductor, and a three-phase grid frequency transformer. The topology of a series-connected MMC with a small number of modules in the present disclosure needs only two half-bridge valve strings, thus greatly reducing the number of the submodules as compared with the conventional MMC structure. When achieving the same high DC voltage output, the present disclosure can improve the power density of the MMC, realize stable three-phase AC output voltage, and further achieve balance of capacitor voltages in the two half-bridge valve strings.

Abstract: The present disclosure relates to the field of electric power system, and more particularly to a topology of a series-connected MMC with a small number of modules, where the topology is composed of a three-phase bridge circuit, half-bridge valve strings, a three-phase filter inductor, and a three-phase grid frequency transformer. The topology of a series-connected MMC with a small number of modules in the present disclosure needs only two half-bridge valve strings, thus greatly reducing the number of the submodules as compared with the conventional MMC structure. When achieving the same high DC voltage output, the present disclosure can improve the power density of the MMC, realize stable three-phase AC output voltage, and further achieve balance of capacitor voltages in the two half-bridge valve strings.

Abstract: A water injection method for a PID control-based adaptive intelligent water injection system is provided. The system includes a water injection portion, a power portion, a control portion, and a measurement and transmission portion. The water injection portion includes a hydrogenation reactor, heat exchangers, air coolers, and a separation tank. The power portion includes a motor and a water pump. The control portion includes a console and a bus. Temperature, pressure and flow velocity transmitters are additionally arranged at each of inlet and outlet pipes of various heat exchangers, and water injection points are disposed. Temperature, pressure and flow velocity signals of the inlet and outlet pipes of heat exchange devices are monitored, and the console performs error analysis on the three signals and uses a PID control algorithm to control the adjustment valve to alter the valve opening degree to adjust the water injection amount in real time.