Model predictive control of VSC-HVDC transmission system for power supply to passive networks

In the traditional double closed-loop control strategy for VSC-HVDC transmission system that supply power to passive networks, the control structure is complex, the PI parameters are more difficult, the tuning is slow, and the response speed is slow. Rectifier-side direct power control based on model prediction and direct AC voltage control strategy on inverter side are proposed. Based on the discrete mathematical model of the converter, the system output under all switching function combinations is calculated by the ergodic method, and the switching function that minimizes the objective function is selected to act on the inverter. The utility model has the advantages of simple structure, no complicated PI parameter setting, fast dynamic response, high voltage quality electric energy to the passive network, good steady state performance and dynamic performance. The simulation results verify the feasibility and effectiveness of the proposed control strategy

Effects of environmental factors on growth, survival, and metamorphosis of geoduck clam (Panopea japonica A. Adams, 1850) larvae

A series of experiments were conducted to evaluate the effects of temperature, salinity, diet, and stocking density on the growth, survival, and metamorphosis of geoduck clam Panopea japonica larvae. The larvae all died at a temperature of 22 °C after day 12, suggesting that the larvae of P. japonica could not survive when the temperature was higher than 22 °C. P. japonica could be incubated at 19 °C for the fast growth, high survival and metamorphosis of larvae. The embryos all died when the salinity was below 25 ppt. The larvae showed poor survival when the salinity was below 25 ppt, with all larvae dying before day 12, suggesting that larvae are sensitive to low salinity. The optimum salinity for the growth, survival and metamorphosis of larvae was 32 ppt. The use of a mixture of Isochrysis galbana and Nitzschia closterium (1:1) as a food source for the P. japonica larvae improved their growth, survival, and metamorphosis. A density of 20 individuals/ml appeared to be optimal for normal D-larvae of Panopea japonica, and 3–9 larvae/ml was optimal for the growth and survival of the P. japonica larvae raised in the hatchery